How to prevent overvoltage from damaging the motor drive system
Time:2023-09-08
Views:704
One of the factors most likely to damage motor drive components or systems is accidental induced overvoltage. Due to exceeding the absolute maximum rating of such devices, overvoltage may cause damage to system components. This FAQ will discuss the occurrence and mitigation methods of overvoltage.
Electric motors can be used to transmit power from a power source to mechanical torque, as well as as as generators that obtain mechanical torque and convert it back into electrical energy. Therefore, in some cases, the motor may cause the power supply voltage to "rise". When the motor acts as a generator, it is necessary to properly handle the induced current in the system, otherwise overvoltage events may occur.
How overvoltage occurs in the motor drive system
1. Slow down motor sliding: When the motor is sliding, the mechanical/rotational energy of the motor will be converted back into electrical energy (voltage and current). In sliding mode, the power stage diode will conduct current from the motor back to the power supply, causing the power supply to pump back.
2. Response to fault conditions leading to motor sliding: In most fault situations, the default response is to turn off all MOSFETs to prevent any possible damage to the system. Although this can effectively prevent any cascading fault situation caused by high current or other common effects, turning off all MOSFETs can cause the motor to slide. If the motor was rotating at the time, it would coast down and slow down, returning all energy to the power supply, causing the power supply to pump back.
3. Reverse drive motor: Electric bicycles are a good example in this regard. When an electric bicycle goes downhill, the motor acts as a generator and causes an increase in power supply voltage. Some electric bicycle systems utilize this operating mode to bring regenerative energy to the battery for charging. In any motor drive system, when the motor can be forced to rotate externally, if the energy generated by the motor is not controlled, it may lead to overvoltage events.
4. Insufficient large capacitance: When driving a motor with variable loads, the motor usually causes slight power pumping back when rotating. Although this is a normal phenomenon, it needs to be taken into account when designing the system. If the motor drive circuit does not have sufficient large capacitance, this effect may lead to severe power pumping back.
How to alleviate overvoltage problems in motor drive systems
1. Use more braking and less sliding: Adjust the deceleration method to use both "braking" and "sliding" simultaneously, rather than just using "sliding" to alleviate certain counter electromotive forces. When working in braking mode, the current does not recirculate into the power supply, therefore it does not cause the power supply to pump back. However, some motors may generate excessive current when applying braking.
2. Reduce deceleration rate: In the algorithm, the maximum possible deceleration is limited to not applying a driving signal that is significantly less than the back electromotive force, which can reduce the power generated during motor deceleration.
3. Add more high-capacity capacitors: By adding more high-capacity capacitors to the motor, the voltage rise will slow down during the power pump back period. Therefore, the maximum voltage that the power supply will rise to will decrease with the additional large capacity capacitor. Although this will not eliminate power pumping, it can maintain the amount of power pumping within a manageable level.
4. AVS technology: Some devices that integrate motor control algorithms also integrate voltage surge resistance technology.
5. Add an external clamping circuit: Add an external pull-down resistor (braking circuit). This circuit can be used to ‘short circuit‘ the motor externally and release motor power. The clamping circuit can be automatically activated by an analog feedback circuit or controlled by a microcontroller.
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