Rotating Machine PWM Control for Minimum Pulse Width Compensation
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Solution Overview
Problem
Existing PWM control technologies for rotating electrical machines face challenges in accurately outputting fundamental wave voltage while reducing harmonic current, particularly in high voltage utilization scenarios, leading to torque shortages, increased motor and inverter losses, and voltage errors due to minimum pulse width limitations.
Innovation Solution
A drive control apparatus that includes a modulation wave operation unit to add an operation amount to modulation waves of three phases based on their saturation states, stopping switching when absolute values exceed a prescribed value, and correcting modulation wave errors to ensure accurate fundamental wave voltage output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If PWM control is used to reduce harmonic current, then voltage waveform distortion is reduced, but voltage output accuracy deteriorates due to minimum pulse width limitation
Solution Approach 1:
The patent applies preliminary action by predicting which phase will have its pulse width limited to the minimum value before PWM generation, and pre-adjusting the modulation wave command values of the other two phases to compensate for the resulting voltage error. This advance compensation prevents the voltage accuracy deterioration that would otherwise occur due to minimum pulse width limitation.
Solution Approach 2:
The patent implements feedback by calculating the pulse width limitation error based on the minimum pulse width constraint and feeding this error information back to adjust the modulation wave command values of non-limited phases. This closed-loop approach ensures that voltage output accuracy is maintained despite the presence of minimum pulse width limitations in PWM control.
2Power
If modulation rate is increased to improve voltage utilization, then fundamental wave voltage output is improved, but pulse width becomes narrower and more susceptible to minimum pulse width limitation
Solution Approach 1:
The patent uses preliminary action by determining in advance which phases will be affected by minimum pulse width limitation at high modulation rates, and pre-compensating the modulation wave command values of unaffected phases. This allows the system to operate at high modulation rates for improved voltage utilization while maintaining voltage output accuracy through proactive error compensation.
3Object-generated harmful factors
If third harmonic component is added to modulation wave to reduce harmonic current, then voltage utilization rate is improved, but voltage error occurs when pulse width is limited to minimum value
Solution Approach 1:
The patent applies feedback by calculating the voltage error caused by minimum pulse width limitation and compensating for it through adjusted modulation wave command values. This feedback mechanism works in conjunction with third harmonic injection, allowing the system to maintain both low harmonic current and high voltage output accuracy even when third harmonic components are present in the modulation wave.
4Measurement precision
If switching frequency is increased to improve control resolution, then PWM control precision is improved, but pulse width becomes narrower and more likely to hit minimum pulse width limit
Solution Approach 1:
The patent implements feedback by continuously monitoring the pulse width of each phase and calculating compensation amounts based on minimum pulse width constraints. This feedback mechanism allows the system to operate at high switching frequencies for improved control resolution while maintaining voltage output accuracy by compensating for any pulse width limitations that occur.
Data Source
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AI summary
In order to provide a PWM control technology that can output an accurate fundamental wave voltage while reducing harmonic current by adding an operation amount to modulation waves of three phases in accordance with the saturation states of the modulation waves of the three phases, this drive control apparatus for a rotating electrical machine drives the rotating electrical machine by controlling an electric power conversion device by means of a PWM signal that is generated by a PWM control unit from a carrier wave and three-phase modulation wave command values generated on the basis of a voltage command value. When the absolute value of a modulation wave command value of one phase, among the three-phase modulation wave command values, is greater than a prescribed value, a modulation wave operation unit, which is provided to the preceding stage to the PWM control unit, stops switching of the one phase by saturating the modulation wave, to the maximum value of the absolute value of the carrier wave, by adding an operation amount to the modulation wave command value of the one phase, and also adds the operation amount to the modulation wave command values of the remaining two phases. Moreover, when the absolute values of modulation wave command values of two phases, among the three-phase modulation wave command values, are greater than the prescribed value, the modulation wave operation unit stops switching of the two phases by saturating the modulation waves, to the maximum value of the absolute value of the carrier wave, by adding the operation amount to the modulation wave command values of the two phases.