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Sustainability and Energy Harvesting | Volume 15
How to design in SiC MOSFETs to improve EV traction inverter efficiency Design for the energy revolution Achieving high efficiency in telecom power supplies Shifting product design to net-zero sustainability
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How to ensure efficient and stable DC current for green hydrogen
Wide bandgap technology to maximize efficiency and power density in high-voltage LED lighting
How to design in SiC MOSFETs to improve EV traction Inverter Efficiency
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What are the different types of adjustable speed industrial motor drives Special feature: retroelectro From kerosene to kilowatts: The story of rural electrification
BESS: A solution to manage energy proactively
Design for the energy revolution
Achieving high efficiency in Telecom power supplies
Shifting product design to net-zero sustainability
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Editor’s note Welcome to the Sustainability & Energy Harvesting eMag Volume 15 , where we explore the latest advancements in technologies that are driving the transition toward a more sustainable future. This issue covers a diverse range of topics, from optimizing energy systems for green hydrogen production to improving the efficiency of electric vehicle (EV) components, all while harnessing innovative solutions that reduce energy consumption and enhance performance. We begin by addressing a critical aspect of the green hydrogen revolution: ensuring efficient and stable DC current for hydrogen production. This article provides valuable insights into the systems that power this growing industry, emphasizing the importance of reliability and efficiency. Next, we take a deep dive into the role of wide bandgap technology in LED lighting, specifically how it can maximize both efficiency and power density for high-voltage applications. These advancements are paving the way for more sustainable lighting solutions that have the potential to revolutionize industries around the world. For those working in the electric vehicle sector, we explore how SiC MOSFETs (Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors) can improve EV traction inverter efficiency. By enhancing power conversion and thermal management, these components are helping to make EVs more energy-efficient and cost-effective. We also discuss adjustable speed industrial motor drives, a key technology for optimizing energy use in industrial environments. Understanding the various types of these drives can significantly contribute to reducing energy waste and improving overall operational efficiency. Finally, we examine strategies to achieve high efficiency in telecom power supplies, which are fundamental to supporting the infrastructure needed for global communications while minimizing environmental impact. Throughout this issue, we showcase the ingenuity and forward-thinking that are driving the sustainable energy landscape forward. Whether you’re working in energy harvesting, power electronics, or green technologies, we hope the articles inspire new ideas and practical solutions to meet the challenges of our time.
How to ensure efficient and stable DC current for green hydrogen
By Art Pini Contributed By DigiKey's North American Editors
The shift toward green hydrogen promises to reduce the level of greenhouse gases. Energy from renewable sources like hydroelectric, wind, and solar power, whether generated locally or transmitted via the power grid, must be converted efficiently to direct current (DC) to electrolyze water. For system designers, providing high and stable DC levels with low harmonic distortion, high current density, and good power factors (PFs) presents a challenge. This article discusses the principle of green hydrogen. It then introduces power components from Infineon Technologies and shows how they can be used to convert the input from environmentally friendly energy sources into stable electrical power outputs with the characteristics required to generate green hydrogen.
Hydrogen generation by the electrolysis of water Hydrogen can be separated from water by the process of electrolysis. The co-product of this process is oxygen. The electrolysis process requires the application of steady, high levels of DC. This process occurs in an electrolysis cell or electrolyzer that typically contains an anode (positive electrode) and a cathode (negative electrode) where the electrochemical reactions occur. A liquid or solid electrolyte encloses the electrodes and conducts the ions between them. A catalyst may be needed to increase the reaction rate depending on the process being used. The cell is powered by a steady, high-level DC source or power supply (Figure 1).
Figure 1: A basic electrolysis cell separates water’s hydrogen and oxygen elements. (Image source: Art Pini)
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How to ensure efficient and stable DC current for green hydrogen
The cell also includes a separator (not shown in this diagram) to prevent the hydrogen and oxygen produced at the electrodes from mixing. The process requires high levels of DC. Under ideal conditions with no energy loss, a minimum of 32.9 kilowatt hours (kWh) of electrical energy is required to electrolyze
The most established electrolyzers are AEL electrolyzers, which use an alkaline solution such as potassium hydroxide between the metal electrodes. They are less efficient than the other types of electrolyzers. PEM electrolyzers use a solid polymer electrolyte enhanced with precious metal catalysts. They are characterized by higher efficiency, faster response times, and compact designs. Solid oxide electrolyzer cells (SOECs) use a solid ceramic material as the electrolyte. They can be highly efficient, but they require high operating temperatures. Their response times are slower than the PEM electrolyzers.
A comparison of the characteristics of the three techniques is shown in Figure 2. Green hydrogen generation currently costs more to produce than hydrogen from fossil fuels. This can be reversed by improving the efficiency of the discrete components, including the electrolyzers and power systems, and scaling up the conversion plants. Power system configurations for grid and green power sources Currently, most hydrogen-generating plants are operating off the power grid. The power source for an electrolyzer is an AC to DC rectifier fed from a line transformer.
enough water molecules to produce 1 kilogram (kg) of
hydrogen. This will vary depending on the efficiency of the electrolysis process being used. Three different processes are currently in use: alkaline electrolysis (AEL), proton exchange membrane (PEM), and solid oxide electrolysis.
Figure 2: A comparison of the characteristics of the AEL, PEM, and SOEC processes highlights the improving efficiencies of the newer electrolyzers. (Image source: Infineon Technologies)
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Electrolysis plants powered from the grid must meet all grid standards and codes, such as achieving a unity PF and maintaining low harmonic distortion. Different power systems are required as green power sources are incorporated into the hydrogen separation process (Figure 3). Like the power grid, wind-based power sources are AC, and powering electrolysis cells from them requires a rectifier to convert the AC into DC. Solar energy and hybrid sources using batteries rely on DC/DC converters to control the DC levels driving the electrolysis cells. The electrolysis cell may also employ a local DC/ DC converter regardless of the
power source. The electrolysis cell represents a constant DC load. Due to aging considerations within the electrolyzer cell, the applied voltage needs to increase over the cell's lifetime, so the power conversion system (PCS) should be able to accommodate that process. PCSs, whether mated to an AC or a DC source, will have some common specifications. Their output voltage should be in the range of 400 VDC to 1,500 VDC). Alkaline cells have a maximum voltage range of approximately 800 V. PEM cells are not as limited and are moving toward the high end of the voltage range to lower losses and reduce
costs. The output power range can be 20 kilowatts (kW) to 30 megawatts (MW). The current ripple from the PCS should be less than 5%, a specification still being studied for its effect on the cell’s lifetime and efficiency. PCS rectifier designs for power grid sources, especially for higher power loads, must comply with power companies’ large load and PF requirements.
Power conversion for AC sources AC-powered hydrogen plants
require a rectifier that may drive an electrolysis cell directly or may drive a DC grid attached to multiple cells.
Figure 3: Electrolysis plants must convert power from the source into DC for the electrolysis cells. (Image source: Infineon Technologies)
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How to ensure efficient and stable DC current for green hydrogen
A multi-pulse rectifier is a common choice (Figure 4). Thyristor-based, this rectifier design has high efficiency, is reliable, supports high current densities, and uses low- cost semiconductors. Multi-pulse, thyristor-based converters are an established and well-known technology. The 12-pulse thyristor rectifier shown in Figure 4 consists of a wye-delta- wye power frequency transformer with two low-voltage secondary windings. The secondary windings drive two six-pulse thyristor rectifiers with their outputs connected in parallel. If this rectifier drives an electrolyzer directly, the thyristor firing angle
controls the output voltage and the current flowing into it. The firing angle can also be used to maintain the current in the system as the electrolyzer cell ages, and the voltage required for the cell stack increases. The transformer may also include an on-load tap changer (OLTC). The OLTC changes the transformer turns ratio by switching among multiple access points or taps on one of the windings to raise or lower the voltage supplied to the rectifier. Infineon Technologies offers a broad range of semiconductor component choices to PCS designers. Thyristor rectifiers are commonly used for these AC-
source applications. For example, the T3800N18TOFVTXPSA1 is a discrete thyristor in a chassis mount TO-200AE disc package that is rated to handle 1800 V at 5970 amperes root mean square (A rms ) on-state current. The disc package offers increased power density due to its double-sided cooling design. The basic rectifier design can be improved by adding buck converters as post-rectification choppers at the rectifier output. Adding the chopper stage enhances control of the process by adjusting the chopper's duty cycle rather than the thyristor's firing angle (Figure 5). This reduces the dynamic range required for the thyristor, allowing optimization of the process.
Figure 4: A multi-pulse rectifier based on thyristors has high efficiency, is reliable, supports high current densities, and uses low- cost semiconductors. Shown is a 12-pulse implementation. (Image source: Infineon Technologies)
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Figure 5: A post-rectification chopper reduces current distortions and improves the PF. (Image source: Infineon Technologies)
Applying the post-rectification chopper using insulated gate bipolar transistors (IGBTs) eliminates the need for the OLTC transformer, reduces current distortions, and improves the PF. Infineon Technologies’ FD450R12KE4PHOSA1 is an IGBT chopper module intended for these applications. It is rated for a maximum voltage of 1200 V and a maximum collector current of 450 A, and comes in a standard 62 millimeter (mm) C-series module. More advanced rectifier circuits include IGBT-based active rectifiers. Active rectifiers replace diodes or thyristors with IGBTs that a controller switches on and off at appropriate times via a gate driver (Figure 6).
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How to ensure efficient and stable DC current for green hydrogen
Figure 6: An active rectifier replaces the diodes or thyristors in the rectifier circuit with IGBTs, which are switched by a gate driver controller. (Image source: Infineon Technologies)
It is rated to handle 1700 V with a maximum collector current of 1700 A. The circuit shown in Figure 6 would use three such modules. An IGBT gate driver such as the 1ED3124MU12HXUMA1 turns a single IGBT pair on and off. The gate driver is galvanically isolated using coreless transformer technology. It is compatible with IGBTs having voltage ratings from 600 to 2300 V, and has a typical output current of 14 A on separate source and sink pins. The input logic pins operate on a wide input voltage range from 3 to 15 V using CMOS threshold levels to support 3.3 V microcontrollers.
Unlike a traditional rectifier, which produces non-sinusoidal line currents, an active rectifier has an inductor in series with the IGBTs that keeps the line current sinusoidal and reduces harmonics. The impedance of the IGBT when conducting is very low, which reduces conduction losses and improves efficiency compared to a standard rectifier. An active rectifier controller maintains a unity PF, so external power factor correction (PFC) devices are unnecessary. It also operates at higher switching frequencies, resulting in smaller-sized passive components and filters. The FF1700XTR17IE5DBPSA1 combines dual IGBTs in a half-bridge configuration in a PrimePACK 3+ modular package.
Power conversion for DC sources Separating hydrogen using DC power sources such as photovoltaic energy and battery-based hybrid systems requires DC/DC converters. As noted earlier, these converters can improve the performance of diode/thyristor rectifiers. They also permit the optimization of local DC grids for plant flexibility. The interleaved buck converter uses half-bridge chopper modules in parallel to change the DC level from the input to the output (Figure 7). With proper interleave control, this DC/DC converter topology significantly reduces DC ripple without increasing the inductors' size or switching frequency. Each
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corrosion of the tank and electrodes of the electrolyzer cell. Identical full-bridge circuits are driven with complementary square waves. The phasing of the drive signals between the primary side and the secondary determines the direction of power flow. In addition, the DAB converter minimizes switching losses by using zero-volt switching of the IGBTs. The circuit can be fabricated with half- bridge IGBT or silicon carbide (SiC) MOSFET modules. Conclusion As the worldwide demand for clean energy sources continues to increase, green hydrogen separation based on renewable energy sources will grow in importance. Such sources demand efficient, reliable, and highly stable DC power. Designers can turn to Infineon Technologies’ broad high voltage and current semiconductors portfolio for the necessary power conversion components.
Figure 7: An interleaved buck converter reduces the input DC level, V DC1, to the output level V DC2 . (Image source: Infineon Technologies)
phase of the implementation can be realized with an appropriate module. The FF800R12KE7HPSA1 is a half-bridge IGBT 62 mm module suitable for the buck topology DC/DC converter. It is rated for a maximum voltage of 1200 V and supports a maximum collector current of 800 A.
The dual active bridge (DAB) converter is an alternative to the buck converter (Figure 8). The DAB converter uses a high- frequency transformer to couple the input and output full-bridge circuits to provide galvanic isolation. Such isolation is often helpful to minimize
Figure 8: A DAB converter performs voltage step-down and provides galvanic isolation between input and output. (Image source: Infineon Technologies)
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Wide bandgap technology to
maximize efficiency and power density in high-voltage LED lighting
By George Hempt
High-voltage LED lighting has proven to be a viable replacement for previous technologies such as high-intensity discharge (HID) lighting. With the adoption of high-voltage LED lighting, many manufacturers rushed to production and implementation in a variety of applications. While there was a significant increase in light quality and power density, efficiency has become an important aspect to address. Also, early applications saw failure rates that were much higher than expected. The main challenge of high-voltage LED lighting is to continue to increase power density and efficiency as well as making it reliable and more affordable for future applications.
In this article, wide bandgap (GaN) technology will be covered and how it can address the efficiency and power density challenge for high-voltage LED lighting. This discussion will show how wide bandgap technology can be used to maximize the efficiency and power density, with a focus on the buck portion of the LED driver architecture shown in Figure 1. Wide bandgap (GaN) semiconductors can operate at higher switching frequencies compared to conventional semiconductors like silicon. Wide bandgap materials require a higher amount of energy to excite an electron to have it jump from the top of the valence band to the
bottom of the conduction band where it can be used in the circuit. Increasing the bandgap, therefore, has a large impact on a device (and allows a smaller die size to do the same job). Materials like Gallium Nitride (GaN) that have a larger bandgap can withstand stronger electric fields. Critical attributes that wide bandgap materials have are high free-electron velocities and higher electron field density. These key attributes make GaN switches up to 10 times faster and significantly smaller while at the same resistance and breakdown voltage as a similar silicon component. GaN is perfect for high-voltage LED applications, as these key attributes make it ideal for implementation into future lighting applications.
Figure 1: System architecture of a non-isolated high-power LED driver. (Image source: STMicroelectronics)
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Wide bandgap technology to maximize efficiency and power density in high-voltage LED lighting
PFC stage is followed by a non- isolated inverse buck stage with CC/CV control. In the cases where isolation is needed, a resonant power converter (LLC, LCC) or a flyback converter can be used depending on the output power requirements of the application. The PFC boost converter generates a regulated DC bus voltage on its output (higher than the peak of the input AC voltage) and passes this higher DC bus voltage to the inverted buck converter stage. The stepdown operation is quite simple. When the switch in the buck is on, the inductor voltage is the difference between the input and output voltages (V IN – V OUT ). When the switch is off, the catch diode rectifies the current and the inductor voltage is the same as the output voltage. MasterGaN system in package (SiP) for LED drivers Along with power density and efficiency, a key challenge for high-voltage lighting applications is the complexity of the design. With the use of wide bandgap semiconductors like GaN, the power density and efficiency of the circuit can be increased. ST’s MasterGaN family addresses that challenge by combining the high- voltage smart-power BCD-process gate drivers with high-voltage GaN transistors in a single package. MasterGaN allows for an easy
Figure 1 shows a high-level architecture of an LED lighting application that will serve as a baseline example for applying GaN wide bandgap technology. Although wide bandgap materials can be implemented across the application, the high-voltage current generator buck, highlighted in green, will be the focus to leverage wide bandgap technology for maximizing efficiency and power density. Most lighting applications require high power factor and low harmonic distortion across a wide AC input voltage range. In this case, it is preferred to implement a PFC boost to provide a clean 400 VDC input for the LED driver and meet power quality requirements. There are multiple options for a front end PFC boost converter; transition mode (TM), continuous conduction mode (CCM) as well as others. Transition mode is characterized by variable frequency operation and zero current switching at turn on of the power MOSFET. Other advantages are simple design, small inductor size, and no reverse recovery of the boost diode. The
main challenges are high peak and RMS input current, which also results in a larger EMI filter as the power increases. CCM, instead, provides fixed frequency operation. The boost inductor current always has an average component, besides near zero crossing points. The inductor is designed for 20-30% ripple, resulting in a smaller EMI filter compared to TM operation. This also means a larger boost inductor and a smaller EMI filter for the same output power when compared to TM operation. The main challenges are more complex control and the need for an ultrafast soft recovery diode or SiC diode. Consequently, the CCM PFC is generally more expensive than a TM PFC. Ideally, a zero reverse recovery switch can be used in place of the rectifying diode in CCM PFCs. This makes GaN transistors very good candidates for this application. Isolation is optional and can be introduced between the input stage and the second stage of power conversion. In this example, isolation is not used, and the input
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Figure 2: Inverse Buck Topology implemented with MASTERGAN4. (Image source: STMicroelectronics)
implementation of the topology shown in Figure 1. It embeds two 650 V GaN HEMT transistors in Half-Bridge configuration as well as the gate drivers. In this example, the entire buck power stage is integrated into a single QFN 9x9 mm package requiring minimal external component count. Even the bootstrap diode, typically needed to supply the isolated high-voltage section of a dual, high-side/low-side, Half-Bridge gate driver, is embedded into the SiP. Consequently, the power density of an application that
uses a MasterGAN device can be increased dramatically compared to a standard silicon solution while increasing the switching frequency or the power output. More specifically, in this LED driver application, a 30% decrease in PCB area was achieved and no heat sinks where used. For high-power LED lighting applications, CCM is the best operating mode to use. When implementing CCM with GaN devices, there will be the high-level benefits previously
discussed as well as a reduced cost. There would be no need for very low R DSON to serve high power applications due to the reduced switching loss contribution to overall power losses. GaN also mitigates a major drawback of using CCM by eliminating recovery losses and reduced EMI, as GaN experiences no reverse recovery. CCM operation with Fixed Off Time control also makes the compensation of output current ripple dependency on V OUT very
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Wide bandgap technology to maximize efficiency and power density in high-voltage LED lighting
easy. It is clear that GaN switch implementation using CCM is a great combination for high- voltage LED lighting applications, as well as many others. The basic scheme of an Inverse Buck topology is shown in Figure 2 along with an implementation that uses the MASTERGAN4 . MASTERGAN4 embeds two 225 mΩ (typical at 25°C) 650 V GaN transistors in Half-Bridge configuration, a dedicated Half-Bridge gate driver and the bootstrap diode. This high level of integration simplifies the design and minimizes PCB area in a small 9x9 mm QFN package. The evaluation board that is shown in Figure 3, was designed with the MASTERGAN4 in an inverse
buck topology has the following specifications: it accepts up to 450 V input, the output voltage of the LED string can be set between 100 V and 370 V; it operates in Fixed Off Time (FOT) CCM with a switching frequency of 70 kHz; the max output current is 1 A. The controller in this solution, the HVLED002 , is used to generate a single PWM control signal. An external circuit based on simple Schmitt Triggers is then used to generate two complementary signals to drive the low side and high side GaN transistors with a suitable dead time. Two linear regulators are also included to generate the supply voltages needed by the MASTERGAN4. The inverse buck topology
Figure 3: Example of Inverse Buck Demo with MASTERGaN4. (Image source: STMicroelectronics)
Figure 4: Efficiency vs. LED voltage for MasterGaN and Silicon MOSFET. (Image source: STMicroelectronics)
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MOS + SIC DIODE
MASTERGAN4
0.66 cm² Diode DPAK or TO220
Power devices area
0.81 cm²
33 cm² Copper area to have 19°C/W
19.7 cm² Copper area to have 24°C/W
Copper area for thermal management
Power inductor footprint
11.2 cm²
11.2 cm²
Overall Area
45.5 cm²
31.71 cm²
Table 1: Size comparison for GaN and Silicon MOSFET
Table 1 compares the silicon solution with the MASTERGAN4 based solution. As can be seen, more than 30% overall PCB area reduction is shown with the GaN design implementation. The results show one path that can be taken with GaN in this inverse buck topology. Increasing the switching frequency above 70 kHz can decrease the output inductor and capacitor size at the expense of higher driving and switching losses. At a higher frequency and reduced filter size, electrolytic capacitors can be replaced with more reliable and larger ceramic capacitors. The tradeoff between filter capacitor and buck inductor size can be optimized based on the switching frequency required by the target application.
implemented with MASTERGAN4 creates a solution for increased power density and efficiency, but let the results discussed below speak for themselves. Experimental Results: The efficiency plots in Figure 4 show the advantages of the proposed solution vs. a traditional silicon solution as a function of the LED string voltage for output currents of 0.5 A and 1 A. The efficiency of MASTERGAN4 stays at or above 96.8% across the entire LED string voltage range. It is possible to observe that across all power levels the gain in efficiency is maximized thanks to the low conduction losses as well as the minimal driving and switching losses of the GaN solution.
Conclusions This article discussed the implementation of an inverse buck topology for LED lighting applications based on MASTERGAN4. The system in package configuration has 650 V, 225 mΩ GaN transistors in half-bridge configuration and dedicated gate drivers. The GaN solution vs. silicon shows higher efficiency and reduced PCB area. MasterGaN is the ideal solution for a compact, high efficiency and high-power inverse buck implementation for lighting applications.
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Article Name
How to design in SiC MOSFETs to improve EV traction inverter efficiency
By Steven Keeping Contributed By DigiKey's North American Editors
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Engineers face a trade-off between the performance and range of modern electric vehicles (EVs). Faster acceleration and higher cruising speeds require more frequent and time-consuming recharging stops. Alternatively, longer range comes at the cost of more sedate progress. To increase range, while also offering drivers higher performance, engineers need to design drive trains that ensure as much battery energy as
possible gets transferred to the driven wheels. Just as important is the need to keep drive trains small enough to fit within the constraints of the vehicle. These twin demands require both high-efficiency and high-energy-density components. The key component in an EV drive train is the three-phase voltage source inverter (or “traction inverter”) which converts the batteries’ DC voltage into the AC
required for the vehicle’s electric motor(s). Building an efficient traction inverter is critical to lowering the trade-off between performance and range, and one of the key routes to improving efficiency is proper use of wide bandgap (WBG), silicon carbide (SiC) semiconductor devices. This article describes the role of the EV traction inverter. It then explains how designing the unit with SiC
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How to design in SiC MOSFETs to improve EV traction inverter efficiency
power metal oxide semiconductor field-effect transistors (MOSFETs) can yield a more efficient EV drive train than one using insulated-gate bipolar transistors (IGBTs). The article concludes with an example of a SiC MOSFET-based traction inverter, and design tips on how to maximize the unit’s efficiency. What is a traction inverter? An EV’s traction inverter converts the DC-current provided by the vehicle’s high-voltage (HV) batteries into the AC-current required by the electric motor to produce the torque required to move the vehicle. The electrical performance of the traction inverter has a significant impact on the vehicle acceleration and driving range. Contemporary traction inverters are driven by HV battery systems of 400-volts, or more recently, 800-volt designs. With traction inverter currents of 300 amperes (A) or greater, a device powered by an 800-volt battery system is capable of delivering over 200 kilowatts (kW) of power. As the power has climbed, the size of the inverters has shrunk, significantly increasing the power density. EV’s with 400-volt battery systems require traction inverters with power semiconductor devices rated in the 600 to 750-volt range, while 800-
Table 1: Typical 2021 traction inverter requirements; energy density shows a 250% increase, compared to 2009. (Image source: Steven Keeping)
volt vehicles require semiconductor devices rated in the range of 900 to 1200 volts. The power components used in the traction inverters must also be able to handle peak AC currents of over 500 A for 30 seconds (s) and a maximum AC current of 1600 A for 1 millisecond (ms). In addition, the switching transistors and gate drivers used for the device must be capable of handling these large loads while maintaining high traction inverter efficiency (Table 1).
A traction inverter typically comprises three half-bridge elements (high-side plus low- side switches), one for each motor phase, with gate drivers controlling the low-side switching of each transistor. The entire assembly must be galvanically isolated from the low-voltage (LV) circuits powering the rest of the vehicle’s systems (Figure 1).
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Figure 1: An EV requires a three-phase voltage source inverter (traction inverter) to convert high- voltage (HV) DC battery power into the AC power required by the vehicle’s electric motor(s). The HV system, including the traction inverter, is isolated from the vehicle’s conventional 12-volt system. (Image source: ON Semiconductor)
The switches in the example shown in Figure 1 are IGBTs. These have been a popular choice for a traction inverter because they are capable of handling high voltages, switch rapidly, offer good efficiency, and are relatively inexpensive. However, as the cost of SiC power MOSFETs has fallen and they have become more commercially available, engineers are turning to these components because of their notable advantages over IGBTs.
the WBG transistor can withstand much higher breakdown voltages than Si devices, as well as a resultant breakdown field voltage about ten times greater than Si. The high breakdown field voltage allows a reduction in device thickness for a given voltage, lowering the “on” resistance (R DS(ON) ) and thus reducing switching losses and enhancing current-carrying capability.
Advantage of SiC MOSFETs for high- efficiency gate drivers The key performance advantages of SiC power MOSFETs over conventional silicon (Si) MOSFETs and IGBTs derive from the devices’ WBG semiconductor substrate. Si MOSFETs have a bandgap energy of 1.12 electron- volts (eV) compared to SiC MOSFETs’ 3.26 eV. That means
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How to design in SiC MOSFETs to improve EV traction inverter efficiency
Another key advantage of SiC is its thermal conductivity, which is about three times higher than Si. Higher thermal conductivity results in a smaller junction temperature (T j ) rise for a given power dissipation. SiC MOSFETs can also tolerate a higher maximum junction temperature (T j(max) ) than Si. A typical T j(max) value for a Si MOSFET is 150˚C; SiC devices can withstand a T j(max) of up 600˚C, although commercial devices are typically rated at 175 to 200˚C. Table 2 provides a comparison of properties between Si and
4H-SiC (the crystalline form of SiC commonly used to manufacture MOSFETs). The high breakdown voltage, low R DS(ON) , high thermal conductivity, and high T j(max) allow a SiC MOSFET to handle much higher
is looking to maximize energy density, is a restriction on the maximum operating frequency due to their “tailing current” and relatively slow turn-off. In contrast, a SiC MOSFET is able to handle high-frequency switching on par with a Si MOSFET, but with the voltage and current handling capability of an IGBT. Wider availability of SiC MOSFETs Until recently, the relatively high price of SiC MOSFETs has seen their use limited to traction inverters for luxury EVs, but falling prices have seen SiC MOSFETs become an option for a wider variety. Two examples of this new generation of SiC power MOSFETS come from ON Semiconductor : the NTBG020N090SC1 and the NTBG020N120SC1 . The major difference between the devices is that the former has a maximum drain-to-source breakdown voltage (V (BR)DSS ) of 900 volts, with a gate- to-source voltage (V GS ) of 0 volts and a continuous drain current (I D ) of 1 milliamp (mA), while the latter has a maximum V (BR)DSS of 1200 volts (under the same conditions). The maximum T j for both devices is 175˚C. Both devices are single N-channel MOSFETs in a D2PAK- 7L package (Figure 2).
current and voltage than a similarly-sized Si MOSFET.
IGBTs are also capable of handling high voltages and currents and tend to be less expensive than SiC MOSFETs – a key reason for them finding favor in traction inverter designs. The downside of IGBTs, particularly when the developer
Table 2: A SiC MOSFET's breakdown field, thermal conductivity, and maximum junction temperature make it a better choice than Si for high-current and high- voltage switching applications. (Image source: ON Semiconductor)
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The NTBG020N090SC1 has an R DS(ON) of 20 milliohms (mΩ) with a V GS of 15 volts (I D = 60 A, T j = 25˚C), and an R DS(ON ) of 16 mΩ with a V GS of 18 volts (I D = 60 A, T j = 25˚C). Maximum continuous drain- source diode forward current (I SD ) is 148 A (V GS = −5 volts, T j = 25˚C), and maximum pulsed drain− source diode forward current (I SDM ) is 448 A (V GS = −5 volts, T j = 25˚C). The NTBG020N120SC1 has an R DS(ON) of 28 mΩ at a V GS of 20 volts (I D = 60 A, T j = 25˚C). Maximum I SD is 46 A (V GS = −5 volts, T j = 25˚C), and maximum I SDM is 392 A (V GS = −5 volts, T j = 25˚C).
Figure 2: The NTBG020N090SC1 and NTBG020N120SC1 N-channel SiC power MOSFETs both come in a D2PAK-7L package and differ primarily in their V (BR)DSS values of 900 and 1200 volts, respectively. (Image source: Steven Keeping, using material from ON Semiconductor)
Designing with SiC MOSFETs
Despite their advantages, designers looking to incorporate SiC MOSFETs into their traction inverter designs should be aware of a significant complication; the transistors have tricky gate drive requirements. Some of these challenges arise from the fact that compared to Si MOSFETs, SiC MOSFETs exhibit lower transconductance, higher internal gate resistance, and the gate turn− on threshold can be less than 2 volts. As a result, the gate must be pulled below ground (typically to −5 volts) during the off−state to ensure proper switching.
Figure 3: For the NTBG020N090SC1 SiC MOSFET, a high V GS is required to avoid thermal stress from high R DS(ON) . (Image source: ON Semiconductor)
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How to design in SiC MOSFETs to improve EV traction inverter efficiency
However, the key gate drive challenge arises from the fact that a large V GS (up to 20 volts) must be applied to ensure a low R DS(ON) . Operating a SiC MOSFET at a V GS that is too low can result in thermal stress or even failure due to power dissipation (Figure 3). Moreover, because a SiC MOSFET is a low-gain device, the designer must take into account the impact this has on several other important dynamic characteristics when designing a gate drive circuit. These characteristics include the gate charge Miller plateau and the requirement for overcurrent protection. These design complications demand a specialized gate driver with the following attributes: ■ An ability to provide a VGS drive of -5 to 20 volts to take full advantage of the SiC MOSFET performance benefits. To provide adequate overhead to meet this requirement, the gate drive circuit should be able to withstand VDD = 25 volts and VEE = −10 volts. ■ VGS must have fast rise and fall edges, of the order of a few nanoseconds (ns). ■ The gate drive must be able to source high peak gate current on the order of several amperes, across the entire MOSFET Miller plateau region.
■ The sink current rating should exceed that which would be required to just discharge the input capacitance of the SiC MOSFET. A minimum peak sink current rating on the order of 10 A should be considered for high- performance, half−bridge power topologies. ■ Low parasitic inductance for high−speed switching. ■ Small driver package able to be located as close as possible to the SiC MOSFET and to boost energy density. ■ A desaturation (DESAT) function capable of detection, fault reporting, and protection for long- term reliable operation.
■ A VDD undervoltage lockout (UVLO) level that is matched to the requirement that VGS > 16 volts before switching begins. ■ VEE UVLO monitoring capability to assure the negative voltage rail is within an acceptable range. ON Semiconductor has introduced a gate driver designed to meet these requirements in traction inverter designs. The NCP51705MNTXG SiC MOSFET gate driver features a high level of Figure 4: The NCP51705MNTXG’s DESAT function measures V DS for anomalous behavior during periods of maximum I D and implements overcurrent protection. (Image source: ON Semiconductor)
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integration making it compatible with not only their SiC MOSFETs but also those from a wide range of manufacturers. The device includes many basic functions common to general purpose gate drivers, but also features the specialized requirements necessary for designing a reliable SiC MOSFET gate drive circuit using minimal external components. For example, the NCP51705MNTXG incorporates a DESAT function that can be implemented using just two external components. DESAT is a form of overcurrent protection for IGBTs and MOSFETs to monitor a fault whereby V DS can rise at maximum I D . This can affect efficiency and, in a worst-case scenario, possibly damage the MOSFET. Figure 4 shows how the NCP51750MNTXG monitors V DS of the MOSFET (Q1) via the DESAT pin through R1 and D1. The NCP51705MNTXG gate driver also features programmable UVLO. This is an important feature when driving SiC MOSFETs because the switching component’s output should be disabled until VDD is above a known threshold. Allowing the driver to switch the MOSFET at low VDD can damage the device. The NCP51705MNTXG’s programmable UVLO not only protects the load but verifies to the controller that the applied VDD is
Figure 5: The UVLO turn−on threshold for the NCP51705MNTXG SiC MOSFET is set by the UVSET resistor, R UVSET , which is chosen according to a desired UVLO turn−on voltage, V ON . (Image source: ON Semiconductor)
HV gate drivers is on the LV side, any isolation must allow for the passage of digital signals from the microprocessor to the gate drivers. ON Semiconductor also offers a component for this function, the NCID9211R2, a high- speed, dual-channel, bidirectional ceramic digital isolator. The NCID9211R2 is a galvanically isolated, full-duplex digital isolator that allows digital signals to pass between systems without conducting ground loops or hazardous voltages. The device features a maximum working
above the turn−on threshold. The UVLO turn−on threshold is set with a single resistor between UVSET and SGND (Figure 5).
Digital isolation for traction inverters
To complete a traction inverter design, the engineer must ensure that the LV side of the vehicle’s electronics are isolated from the high voltages and currents passing through the inverter (Figure 2 above). However, because the microprocessor controlling the
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How to design in SiC MOSFETs to improve EV traction inverter efficiency
insulation of 2000 volt speak , 100 kilovolts/millisecond (kV/ms) common-mode rejection, and a 50 megabit per second (Mbit/s) data throughput. Off−chip ceramic capacitors form the isolation barrier as shown in Figure 6. The digital signals are transmitted across the isolation barrier using an ON-OFF keying
(OOK) modulation. On the transmitter side, the V IN input logic state is modulated with a high-frequency carrier signal. The resulting signal is amplified and transmitted to the isolation barrier. The receiver side detects the barrier signal and demodulates it using an envelope detection technique (Figure 7). The output signal determines the
V O output logic state when the output enable control EN is high. V O defaults to a high-impedance low state when the transmitter power supply is off, or V IN input is disconnected.
Figure 6: Block diagram illustrating a single channel of the NCID9211R2 digital isolator. Off-chip capacitors form the isolation barrier. (Image source: ON Semiconductor)
Figure 7: The NCID9211 digital isolator uses OOK modulation to transmit digital information across the isolation barrier. (Image source: ON Semiconductor)
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Conclusion SiC power MOSFETs are a good option for high-efficiency and high- power-density traction inverters for EVs, but their electrical characteristics bring unique design challenges with respect to gate drivers and device protection. Adding to the design challenges, engineers must also ensure that their traction inverter design offers high-level isolation from the vehicle’s sensitive LV electronics.
As shown, to ease engineering development, ON Semiconductor offers a range of SiC MOSFETs, specialized gate drivers, and digital isolators to meet the demands of traction inverters, and strike a better balance between long-range and high performance for modern EVs.
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The different types of adjustable speed industrial motors
By Jeff Shepard Contributed By DigiKey's North American Editors
International Electrotechnical Commission (IEC) standard 61800 recognizes two types of adjustable speed electrical power drive systems (PDS) for industrial applications. 61800-1 applies to direct current (DC) PDS, and 61800- 2 applies to alternating current (AC) PDS. The term PDS applies to the entire system of drive plus motor. Other sections of 61800 discuss test methods, safety requirements related to thermal and energy conditions, functional safety, electrical and environmental requirements for encoders, electrical interfaces, and performance measurements. The newest part, IEC 61800-9, covers ecodesign for motor systems, including energy efficiency determination and classification. While IEC 61800 defines adjustable speed AC and DC PDS, there are also general definitions for variable speed drives (VSDs) and variable frequency drives (VFDs) in industrial applications. IEC 61800 applies to mains-powered PDS connected to up to 1.5 kV AC 50 Hz or 60 Hz. It also applies to DC input voltages for battery-powered systems like industrial autonomous mobile robots (AMRs) that use adjustable speed drives. Traction and electric vehicle drives are excluded from IEC 61800.
This article briefly presents the common definitions of VSDs and VFDs and looks at why VFDs are widely used. It then reviews the efficiency classes defined in IEC 61800-9 for AC drives and, considers exemplary mains-powered VFDs from Delta Electronics, Siemens, Schneider Electric, Omron Automation , and closes by looking at the use of VFDs in AMRs and other battery- powered systems using an example system from MEAN WELL . The standard definition of a VFD is a drive that uses changes in frequency to control motor speed, making them useful with AC motors. At the same time, a VSD varies the voltage to control the motor, making it useful for both AC and DC motors. But it’s not quite that simple. Both types of drives can be used to control the speed of motors. As a result, sometimes, the term VSD is applied to VFDs. VFDs can be used with brushless DC motors (BLDCs); strictly speaking, they are not limited to AC motors. VFDs are suitable for use with a variety of motors like: ■ Induction (IM), or asynchronous AC motors, are widely used in industrial applications since they are self-starting, reliable, and economical.
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The different types of adjustable speed industrial motors
■ Permanent magnet synchronous motors (PMSM) are highly efficient AC motors and can enable precise control of torque and speed in high- performance applications that demand high energy efficiency. ■ BLDCs are also used in applications that require high efficiency and precise control and typically have long operating lives. ■ Servo motors can be AC or DC and support rapid, high- precision responses. VFDs with specialized control algorithms can be used with servo motors in robots, computer numerically controlled (CNC) machines, and similar applications. ■ Synchronous AC motors (SMs) are suited for applications that require constant speed and
precise synchronization. While VFDs can control the speed of SMs, other (lower cost) drive options can support constant speed operation. There’s a variety of control algorithms used with VFDs that increase their versatility. For example, there are four primary types of VFD control algorithms just for induction motors: volts-per- Hertz (V/f), V/f with encoder, open- loop vector, and closed-loop vector. All use pulse-width modulation and provide different levels of control over speed and torque. The importance of VFDs in a wide range of industrial applications is evidenced by the development of IEC 61800-9, which is focused on the efficiency and ecodesign of VFDs and related motor drive systems.
BDM, CDM, and PDS There are two sections of IEC 61800-9 related to VFDs. Part 1 delineates the methodology for determining an application's energy efficiency index or reference. Part 2 details methods for evaluating efficiency based on a series of classifications. While the efficiency of VFDs, called basic drive modules (BDMs) in IEC 61800-9, is important, it’s not the primary focus of the standard. The standard is more broadly based and considers complete drive modules (CDMs) that consist of a frequency inverter (the VFD), a feeding section, and input and output auxiliaries (like filters and chokes) and on the power drive system (PDS) that consists of the CDM plus the motor (Figure 1).
Figure 1: IEC 61800-9 efficiency classes apply to the CDM (black section) and PDS (red section) in VFD systems. (Image source: Schneider Electric)
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CDM efficiency classes CDM international efficiency (IE) classes are defined from IE0 to IE2. They are determined by comparing the total loss of the CDM with the performance of a reference CDM (RCDM). IE classes for CDMs are defined relative to the 90, 100 operating point using 90% motor stator frequency and 100% torque current to avoid overmodulation and ensure comparability of the performance measurements of drives from different makers. The performance of the RCDM is defined as IE1. A CDM with greater than 25% lower losses than the RCDM is classified as IE2, and a CDM with greater than 25% higher losses than the RCDM is classified as IE0. The RCDM also enables the comparison of the energy consumption with an average technology CDM at eight pre-defined operating points (0, 25), (0, 50), (0, 100), (50, 25), (50, 50), (50, 100), (90, 50) and (90, 100) (Figure 2). PDS efficiency classes PDS international efficiency system (IES) classes are like the CDM IE classes and are defined as IES0 to IES2. They are based on a reference PDS (RPDS) and reflect the efficiency of the complete drive module plus the motor.
Figure 2: IEC 61800-9 CDM operating points and efficiency classes. (Image source: Siemens)
Matching the combined motor and CDM to the specific application requirements provides greater potential for overall efficiency optimization. That efficiency optimization is reflected in a higher IES classification. Like the RCDM, the RPDS enables the comparison
of energy consumption with an average technology PDS at eight pre-defined operating points. The operating points are based on a percentage of torque and a percentage of speed, and the IES value is calculated based on 100% torque and 100% speed, which is the (100, 100) operating point.
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The different types of adjustable speed industrial motors
Figure 3: IEC 61800-9 PDS operating points and efficiency classes. (Image source: Schneider Electric)
components is beyond the control of VFD makers, and 61800-9 doesn’t apply directly to VFDs. Some VFD makers have adapted the 61800-9 methodology. When IE2 compliance is claimed, the data is reported in various formats, including charts, tables, and Excel files.
Instead of using the 25% changes of the IE classes, IES classes are based on 20% changes. A PDS with an efficiency class IES2 has greater than 20% lower losses, and a class IES0 PDS has greater than 20% higher losses than the RPDS performance defined as IES1 (Figure 3). VFD examples VFD makers don’t always report efficiency based on 61800-9. That’s because the simplest efficiency measurement using IEC 61800-9 is for the CDM, which consists of the VFD (frequency inverter) plus numerous additional components, including the feeding section and input and output auxiliary devices. The use of specific additional
For example, Siemens uses the IEC 61800-9 methodology with its SINAMICS V20 drives and reports them as efficiency class IE2 (Figure 4). These drives are offered in nine frame sizes, ranging from 0.16 to 40 horsepower (hp). These drives have been optimized for basic drive systems in manufacturing
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