Motor Drive Phase Compensation for Smooth PWM Mode Switching
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Solution Overview
Problem
Existing motor drive systems experience significant switching shock and torque fluctuations due to pulse disappearance in the overmodulation and rectangular wave areas, particularly in asynchronous PWM control, which destabilizes motor control.
Innovation Solution
A motor drive system that includes a rotor position detection unit, current sensor, coordinate conversion unit, and phase compensation units to calculate a phase compensation amount, and a PWM control unit, which calculate and adjust the phase compensation amount to stabilize the motor control by compensating for phase changes during mode switching, reducing switching shock and torque fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the inverter output voltage is increased to expand the motor operating area, then the motor torque in middle and high speed areas is improved, but the PWM pulse disappears in the overmodulation and rectangular wave areas causing switching shock
Solution Approach 1:
The patent applies preliminary action by detecting the zero-crossing point of the inverter output voltage in advance and pre-adjusting the PWM pulse timing. Specifically, the center interval of ON pulses or OFF pulses is changed based on the motor output request before the switching shock occurs, preventing the sudden voltage vector increase that causes instability while maintaining the expanded operating area benefit
2Power
If the control area is switched between sine wave area and overmodulation area or rectangular wave area, then the motor torque output is improved, but the voltage vector increases discontinuously causing switching shock
Solution Approach 1:
The patent implements preliminary action by detecting the zero-crossing point of the inverter output voltage beforehand and adjusting the PWM pulse center interval in advance. This pre-adjustment ensures smooth transition of the voltage vector during control area switching, preventing discontinuous increases that cause switching shock while maintaining improved torque output capability
3Ease of operation
If asynchronous PWM control with constant carrier frequency is used, then the control simplicity is improved, but the positive-side and negative-side voltage integration become unbalanced causing remarkable switching shock
Solution Approach 1:
The patent applies preliminary action by detecting the zero-crossing point of the inverter output voltage and pre-adjusting the PWM pulse timing based on motor output request. This approach maintains the simplicity of asynchronous PWM control with constant carrier frequency while compensating for the unbalanced voltage integration through timely pulse center interval adjustment, reducing remarkable switching shock
Data Source
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Figure 3(a)~3(b)
AI summary
In a motor drive device 120, a phase compensation amount calculation unit 110 calculates a phase compensation amount Δθ for compensating a voltage phase θv* when a control mode is switched in a control selection unit 90. The control selection unit 90 outputs the three-phase voltage command Vuvw* according to any one of the plurality of control modes based on the modulation factor Kh*, the voltage phase θv*, and the phase compensation amount Δθ. A PWM control unit 100 outputs gate signals Gun, Gup, Gvn, Gvp, Gwn, and Gwv based on the three-phase voltage command Vuvw* and a rotor position θd. The inverter 20 has a plurality of switching elements, and controls the plurality of switching elements based on gate signals Gun, Gup, Gvn, Gvp, Gwn, and Gwv to drive the AC motor 10.