Three-Level Inverter Control for Common Mode Noise Reduction
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Solution Overview
Problem
Power conversion devices that convert DC to AC for loads face challenges with common mode noise, which can cause zero-phase currents and degrade motor performance, requiring large EMI filters that increase device size.
Innovation Solution
A power conversion device with a three-phase three-level inverter and three single-phase inverters, controlled by a controller that generates gate signals based on sinusoidal phase voltage commands, superimposing a common voltage component to reduce common mode noise without increasing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large-sized heavy EMI filter is used to reduce common mode noise, then common mode noise is reduced, but the device size increases
Solution Approach 1:
The patent extracts the common mode voltage component from the three-phase voltage commands and processes it separately through a common mode voltage elimination unit. By isolating and specifically addressing the common mode component rather than treating all voltage commands uniformly, the system can reduce common mode noise without requiring large EMI filters that would increase device size.
Solution Approach 2:
The patent changes the voltage command parameters by superimposing a common voltage component on the mean voltage commands based on the sum of three-phase instantaneous voltage commands. This parameter adjustment actively controls the common mode voltage to prevent zero-phase current flow, thereby reducing common mode noise without adding physical filtering components that would increase device size.
2Object-affected harmful factors
If common mode noise is reduced using traditional EMI filters, then common mode noise is reduced, but the device becomes larger and more complex
Solution Approach 1:
The patent replaces the mechanical/physical EMI filter system with an electronic control system. Instead of using passive filtering components (inductors, capacitors) that physically block common mode noise, the system uses active voltage command modification through the common mode voltage elimination unit to prevent common mode noise generation at the source, thereby reducing device complexity.
Solution Approach 2:
The patent introduces a common mode voltage elimination unit as an intermediary between the voltage command generation and the inverter operation. This intermediary process analyzes the sum of three-phase instantaneous voltage commands and adjusts the mean voltage commands accordingly, acting as a mediator that eliminates common mode effects without requiring additional physical filtering hardware.
3Object-affected harmful factors
If the sum of three-phase instantaneous voltage commands is positive, then a common voltage component is superimposed to make the sum of mean voltage commands non-positive, reducing common mode noise
Solution Approach 1:
The patent implements dynamic control by continuously monitoring the sum of three-phase instantaneous voltage commands and adjusting the common voltage component superimposition in real-time. The control strategy changes dynamically based on whether the sum is positive or negative, making the common mode voltage elimination adaptive rather than static, which maintains ease of operation while effectively reducing common mode noise.
Solution Approach 2:
The patent performs preliminary action by calculating and superimposing the common voltage component on the mean voltage commands before they are applied to the inverter. This proactive adjustment prevents common mode voltage generation at the source rather than reacting to it afterward, simplifying the overall control process by addressing the common mode issue in the voltage command stage rather than requiring additional correction mechanisms.
Data Source
AI summary
A power conversion device includes a power conversion controller that generates gate signals for controlling operation of a three-phase three-level inverter and of three single-phase inverters, based on sinusoidal phase voltage commands. In the power conversion controller, the sinusoidal phase voltage commands are divided into three-phase instantaneous voltage commands to be indicated to the three-phase three-level inverter, and mean voltage commands to be indicated to the respective three single-phase inverters. When the sum of the three-phase instantaneous voltage commands is a positive value, a common voltage component is superimposed on each of the three mean voltage commands to make the sum of the three mean voltage commands a non-positive value, and when the sum of the three-phase instantaneous voltage commands is a negative value, the common voltage component is superimposed on each of the three mean voltage commands, making the sum of the three mean voltage commands non-negative.