Multi-Phase PWM Converter Control for EMC-Safe Switching
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Solution Overview
Problem
Multi-phase power converters for wind turbine generators face EMC-related issues due to simultaneous or close-to-simultaneous PWM switching operations during current zero crossings in different phases.
Innovation Solution
A method of controlling a multi-phase power converter by modifying voltage reference values for each phase to ensure a minimum time difference between PWM switching operations, thereby preventing simultaneous switching and reducing EMC issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PWM switching operations are performed simultaneously or close-to-simultaneously for different phases during current zero crossings, then the power converter can operate with high efficiency and standard PWM control, but electromagnetic compatibility (EMC) related problems occur
Solution Approach 1:
The controller proactively identifies when voltage reference values are close together and preemptively adjusts them to prevent simultaneous switching. By calculating the difference between voltage reference values and comparing against a threshold before PWM generation, the system performs the corrective action in advance, avoiding the EMC problems that would otherwise occur during current zero crossings
Solution Approach 2:
The invention modifies the voltage reference values (parameters) to ensure they maintain a sufficient difference. When the difference between voltage reference values for different phases falls below a predetermined threshold, the controller adjusts these values to increase the separation, thereby preventing simultaneous PWM switching events that cause electromagnetic compatibility issues
2Object-affected harmful factors
If voltage reference values are modified to prevent simultaneous PWM switching, then electromagnetic compatibility problems are reduced, but the control system complexity increases
Solution Approach 1:
The voltage reference value adjustment is applied locally and selectively only when needed. The controller calculates the difference between voltage reference values for each phase pair and only modifies values when the difference falls below the threshold. This localized approach avoids the need for a completely complex control system while addressing the specific EMC problem
Solution Approach 2:
The system continuously monitors the difference between voltage reference values and provides feedback to the adjustment mechanism. When the difference is insufficient, the controller modifies the values and can track the adjustments made, ensuring that the modification strategy remains simple and rule-based rather than requiring complex adaptive control algorithms
3Loss of time
If voltage reference values are adjusted to maintain minimum difference, then PWM switching operations are separated in time, but waveform accuracy may be affected
Solution Approach 1:
The voltage reference value adjustment is applied partially - only when the difference between values falls below the threshold. The adjustment amount is calculated to provide just enough separation to prevent simultaneous switching, rather than applying excessive modification that would distort the waveform. This partial action maintains waveform accuracy while achieving the time separation goal
Solution Approach 2:
The invention carefully modifies voltage reference value parameters to maintain their relationship to the fundamental AC waveform. By adjusting only the offset between phases and maintaining the sinusoidal relationship, the parameter changes achieve time separation while preserving waveform accuracy and preventing distortion
Data Source
AI summary
A method of controlling a multi-phase power converter is provided including at least one PWM inverter module for each phase. The method includes (a) receiving a voltage reference value for each phase, (b) checking, for each pair of phases, whether a difference between the corresponding pair of voltage reference values is below a predetermined threshold value, (c) generating a modified reference value for each phase by modifying the received voltage reference values in such a way that the difference between each pair of modified voltage reference values is equal to or larger than the predetermined threshold value, and (d) generating PWM switching signals for the PWM inverter modules based on the modified voltage reference values. Furthermore, a controller for a multi-phase power converter, a computer program, and a wind turbine generator utilizing such a power converter are provided.