Active Front End Drive Common Voltage Reduction
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Solution Overview
Problem
Power conversion systems face challenges in reducing common mode voltage, which can lead to motor bearing degradation and increased costs due to inefficient control of rectifier and inverter switching frequencies.
Innovation Solution
A power conversion system with a controller that operates in two modes: a NORMAL mode for high modulation index values and a CMR mode for low modulation index values, where the inverter modulation signals are shifted to reduce common mode voltage, using pulse width modulation and discontinuous PWM techniques to manage switching frequencies and zero vectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If inverter switching control signals are generated according to inverter carrier signal and inverter modulation signals in NORMAL mode, then power conversion efficiency is improved, but common mode voltage increases causing motor bearing degradation
Solution Approach 1:
The system dynamically switches between NORMAL mode and CMR mode based on real-time operating conditions. The controller monitors the state of the power conversion system and automatically transitions between the two control modes to optimize performance while minimizing harmful effects. This dynamic adaptation allows the system to maintain high efficiency when possible while activating common mode voltage reduction when needed.
Solution Approach 2:
The invention changes the control parameters by shifting inverter modulation signals in CMR mode. Specifically, the modulation signals are shifted by amounts of ±1/3 or ±2/3 to reduce common mode voltage to ±2/3 VDC. This parameter modification allows the system to maintain power conversion functionality while significantly reducing the harmful common mode voltage that causes motor bearing degradation.
2Productivity
If rectifier and inverter switching frequencies are controlled separately, then power conversion performance is optimized, but system complexity increases due to inefficient control
Solution Approach 1:
The invention merges the control of rectifier and inverter switching frequencies by synchronizing them through a unified control strategy. In CMR mode, the system coordinates the switching operations to reduce common mode voltage while maintaining efficient power conversion. This integrated approach simplifies the control architecture compared to separate independent controls, reducing system complexity while preserving performance optimization.
Solution Approach 2:
The controller is designed with multi-functionality to handle both NORMAL mode operation for high efficiency and CMR mode operation for common mode voltage reduction. The same control system performs multiple functions: generating switching control signals, monitoring system state, determining mode transitions, and adjusting modulation signals. This universal controller reduces overall system complexity by eliminating the need for separate dedicated control circuits for different functions.
Data Source
AI summary
A power conversion system, a non-transitory computer readable medium, and a method of operating a power conversion system, in which inverter switching control signals are generated in a first mode according to an inverter carrier signal having an inverter switching frequency, and according to inverter modulation signals, to operate switches of an inverter to provide an AC output signal, and the inverter modulation signals are shifted in a second mode for low modulation index values to reduce common mode voltage.