Three Phase Modulation Controller Common Mode Noise Reduction
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Solution Overview
Problem
Three phase converters using space vector PWM experience significant common mode noise, leading to electromagnetic interference and stability issues, particularly in rectifier applications and motor drives, which can cause bearing damage and circulation currents, and existing filters only attenuate noise rather than resolve the issue.
Innovation Solution
A modulation controller for three phase converters that generates vector control signals and employs a transition modifier to extend the transition period of common mode voltage, using a 'soft' space vector pulse width modulation scheme to manage and reduce the root cause of electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If space vector PWM is used for vector control, then wider AC voltage ranges and reduced switching frequency are achieved, but common mode noise increases significantly
Solution Approach 1:
The patent modifies the PWM switching strategy by extending the transition period of common mode voltage through a shaping function applied to vector control signals. This changes the temporal parameters of voltage transitions, reducing the rate of change (dv/dt) and thereby decreasing common mode noise while preserving the wide AC voltage range capability of SVPWM
2Object-affected harmful factors
If common mode filters are added to reduce noise, then electromagnetic interference is attenuated, but device size and cost increase
Solution Approach 1:
The patent extracts and addresses the root cause of common mode noise at its source by modifying the PWM control signals. By applying a shaping function that extends transition periods, the noise is reduced at generation rather than requiring external filtering components, thereby eliminating or reducing the need for large common mode filters
3Reliability
If common mode filters are added to reduce noise, then bearing damage and circulation currents are reduced, but system cost increases
Solution Approach 1:
The patent addresses bearing protection and circulation current issues by removing the need for expensive common mode filters. Instead, it applies a cost-effective control strategy that modifies vector control signals with a shaping function, reducing common mode voltage transitions at their source and thereby protecting motors and converters without additional hardware cost
4Object-generated harmful factors
If transition period of common mode voltage is extended, then common mode noise is reduced, but switching frequency performance may be affected
Solution Approach 1:
The patent applies periodic shaping functions to the vector control signals during specific transition intervals. By extending transition periods only when necessary (during common mode voltage transitions) and maintaining normal switching frequency during steady-state operation, the solution reduces noise while preserving overall switching frequency performance and dynamic response
Data Source
AI summary
The present invention provides a modulation controller for use with a three phase converter. In one embodiment, the modulation controller includes a three phase modulator configured to provide vector control signals for the three phase converter that generate a common mode voltage. Additionally, the modulation controller also includes a transition modifier coupled to the three phase modulator and configured to provide a shaping function for the vector control signals that extends a transition period of the common mode voltage.