PWM Over-Modulation Compensation for Motor Voltage Mitigation
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Solution Overview
Problem
Existing inverter pulse width modulation techniques fail to effectively mitigate excessive motor voltages during over-modulation conditions, leading to reflected waves and high voltages at motor terminals, especially when transitioning between carrier maximum and minimum values or experiencing simultaneous transitions on multiple phases.
Innovation Solution
The implementation of an over-modulation compensation component that adjusts phase signals or values within specific bands during transitions into or out of the carrier waveform range, ensuring dwell time and polarity reversal times are maintained within acceptable limits, thereby preventing excessive voltage generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If minimum dwell time and polarity reversal time are enforced in PWM switching to limit motor peak voltage, then motor over-voltage is reduced, but during over-modulation transitions the dwell time and polarity reversal time are reduced causing high motor terminal voltages
Solution Approach 1:
The system performs preliminary detection of over-modulation conditions by monitoring whether phase modulating signals exceed the carrier waveform range. Before the harmful voltage spikes occur, the system preemptively adjusts the PWM switching patterns to maintain minimum dwell times and polarity reversal times even during over-modulation transitions, preventing the reduction of these critical timing parameters that would otherwise cause high motor terminal voltages
Solution Approach 2:
The system dynamically changes the PWM control parameters by detecting when phase modulating signals transition into or out of the over-modulation range. When over-modulation is detected, the system modifies the switching patterns to enforce minimum dwell times and polarity reversal times, effectively changing the operational parameters to prevent excessive voltage generation while maintaining normal PWM operation during linear modulation conditions
2Productivity
If phase modulating signals are allowed to exceed carrier waveform range during over-modulation, then power conversion efficiency is improved, but reflected waves cause excessive voltage at motor terminals
Solution Approach 1:
The system implements feedback control by continuously monitoring the phase modulating signals to detect when they exceed the carrier waveform range, indicating over-modulation conditions. Based on this feedback, the system automatically adjusts the PWM switching patterns to maintain minimum dwell times and polarity reversal times, thereby controlling the motor terminal voltage to remain within safe limits while still allowing over-modulation to occur for improved power conversion efficiency
Solution Approach 2:
The system applies preliminary anti-action by detecting over-modulation conditions and preemptively adjusting the PWM switching patterns before excessive voltage can develop at the motor terminals. By enforcing minimum dwell times and polarity reversal times during over-modulation transitions, the system counteracts the tendency toward voltage spikes and reflected waves, allowing efficient power conversion without harmful voltage effects
3Speed
If simultaneous transitions to or from over-modulation occur on multiple phases, then system response speed is improved, but polarity reversals generate very high voltages up to four times DC bus level
Solution Approach 1:
The system performs preliminary detection of simultaneous over-modulation transitions on multiple phases by monitoring phase signal relationships. When such conditions are detected, the system preemptively enforces minimum polarity reversal times between phases, preventing the rapid polarity reversals that would otherwise generate extremely high voltages up to four times the DC bus level, while still maintaining fast system response through coordinated multi-phase control
4Productivity
If dwell time is reduced during transition to over-modulation conditions, then switching frequency is improved, but high voltage is generated at motor terminals
Solution Approach 1:
The system dynamically changes the PWM control parameters by detecting transitions to and from over-modulation conditions. When such transitions are detected, the system modifies the switching patterns to maintain minimum dwell times, preventing the reduction of dwell time that would cause high motor terminal voltages. This parameter adjustment allows the system to operate at optimal switching frequencies during normal conditions while preventing harmful voltage effects during over-modulation transitions
Data Source
AI summary
Power conversion systems and methods are provided for operating a multi-phase inverter to drive a load while mitigating reflected waves, in which one or more PWM modulating signals are selectively adjusted if at least one of the phase signals or values is transitioning into or out of an over-modulation range outside a pulse width modulation carrier waveform range.