Reduce EV range anxiety and improve safety using integrated FOC motor control and advanced sensors
The information from the missing sensors is still needed to implement FOC and can be extracted from the voltages and currents at the motor terminals from the back electromotive force (BEMF) in the motor windings. While the hardware is simpler, the implementation of sensorless FOC requires more complex control software. A sensorless FOC algorithm can enable the highest efficiency and dynamic response while minimizing acoustic noise. It also provides a robust open-loop startup for when the motor is at a standstill when there is no BEMF information available.
tightly controlled to optimize efficiency. To achieve this, it’s useful to include advanced motor- control algorithms such as FOC on the motor controller gate driver.
performance BLDC motors up to 500 watts. These are typically used in xEV high-voltage (HV) battery cooling fans, as well as heating ventilation and air conditioning (HVAC) blowers, and liquid pumps for HV traction inverter cooling systems (Figure 1). In conventional designs, FOC is implemented with external sensors using a microcontroller. Called direct FOC, these designs can be complex, and they tend to suffer from reduced dynamic response due to their reliance on external sensors to measure the motor’s operating parameters. FOC with improved performance and lower cost is possible by eliminating the external sensors.
Easy FOC for automotive cooling fans and pumps While most FOC BLDC drivers require software developers to write and port the algorithm to a microprocessor or microcontroller, the A89307KETSR-J from Allegro MicroSystems integrates the sensorless FOC algorithm directly into the gate driver. With only five external passive components (four capacitors and one resistor), the
A89307KETSR-J also minimizes the bill of materials (BOM), improves reliability, and reduces design complexity (Figure 2). The A89307KETSR-J gate driver operates from 5.5 to 50 volts DC. The integrated FOC algorithm includes constant torque and constant power, as well as open-loop and constant speed operating modes. The A89307KETSR-J includes inputs
for pulse width modulation (PWM) or clock mode speed control, braking, and direction, and output signals for fault conditions and motor speed (Figure 3). The A89307KETSR-J is optimized to drive external low-on-resistance N-channel power MOSFETs. It can supply the large peak drive currents needed to quickly turn the MOSFETs “on” and “off” in order to minimize power dissipation during switching, improving operating efficiency and reducing thermal management concerns. Multiple gate drive levels are available, enabling designers to optimize the tradeoff between electromagnetic interference (EMI) emissions and efficiency. Fast turn on of the MOSFETs reduces switching losses, but increases EMI, while slower MOSFET turn on reduces EMI, with the tradeoff being increased switching losses and lower efficiency.
High-performance cooling
FOC enables smooth operation of electric motors over their entire speed range, and it can generate full torque at startup. In addition, FOC can deliver fast and smooth motor acceleration and deceleration, a feature that is useful for accurate control in high- performance motion applications. FOC can be used to develop high efficiency, compact and quiet low-voltage (LV) (50 volts DC and lower) drivers for a range of high-
Figure 2: A typical A89307KETSR-J xEV battery pack cooling fan application circuit shows the five external components: four capacitors and one resistor. (Image source: Allegro MicroSystems)
Figure 3: The A89307KETSR-J’s internal block diagram shows the FOC controller (center), the PWM or clock mode speed control (SPD), brake (BRAKE) and direction (DIR) inputs (on the left), and the fault (FAULT) and motor speed (FG) outputs (also on the left). (Image: Allegro MicroSystems)
Figure 1: FOC motor controllers can use LV battery power to cool xEV HV batteries and HV traction inverters. (Image source: Allegro MicroSystems)
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