Phase-Shift DPWM for Three-Phase Converter Common-Mode Reduction
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Solution Overview
Problem
Existing three-phase converters using discontinuous pulse-width modulation (DPWM) strategies face issues with high common-mode voltage and current, necessitating additional isolation circuits that increase cost and complexity, while existing solutions struggle to concurrently compensate common-mode current and balance mid-point potential effectively.
Innovation Solution
A phase-shift discontinuous pulse-width modulation method that asynchronously switches upper-leg switching elements of each one-phase leg unit, introducing a phase shift ratio ΔΦ between driving signals, reducing common-mode voltage and current, and allowing the mid-point to serve as a reference ground without isolation circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If discontinuous pulse-width modulation (DPWM) strategy is adopted to reduce switching loss, then converter efficiency is improved, but common-mode voltage with large amplitude occurs requiring isolation circuits that increase device complexity and cost
Solution Approach 1:
The patent changes the modulation parameters by introducing phase shifts between different phase legs and adjusting the discontinuous modulation intervals. This modifies the common-mode voltage waveform characteristics, reducing its amplitude to a level that eliminates the need for isolation circuits while preserving the switching loss reduction benefits of DPWM
Solution Approach 2:
The patent converts the harmful large-amplitude common-mode voltage into a beneficial low-amplitude common-mode voltage through phase-shifted discontinuous modulation. The phase shifts cause destructive interference of common-mode voltage components, transforming what was previously a harmful effect requiring isolation into a beneficial effect that simplifies the circuit
2Object-affected harmful factors
If common-mode suppressor circuit is added to reduce common-mode interference, then AC-side current quality is improved, but common-mode current circulates through the suppressor unit causing additional losses
Solution Approach 1:
The patent applies preliminary action by pre-modulating the phase legs with specific phase shifts before the common-mode interference can be generated. This proactive approach shapes the switching patterns to inherently reduce common-mode voltage amplitude, preventing the generation of large common-mode currents that would otherwise require suppression circuits
3Loss of energy
If existing DPWM modulation strategy is used to optimize efficiency, then switching loss is reduced, but it is difficult to realize DPWM modulation when fluctuation occurs to the modulation loop
Solution Approach 1:
The patent introduces dynamic phase shifts that can adapt to modulation loop conditions. The phase shift parameters are designed to be adjustable, allowing the system to maintain optimal common-mode voltage reduction while responding to fluctuations in the modulation loop, thereby improving reliability without sacrificing efficiency
Data Source
AI summary
The present invention discloses a phase-shift discontinuous pulse-width modulation method and a three-phase converter. The method includes: enabling a switching element of an one-phase leg unit to keep switched on or switched off in any switching cycle, and enabling a phase shift ratio ΔΦ to occur between driving signals of switching elements of the other two one-phase leg units, during operation of a three-phase converter, so that an upper-leg switching element of each one-phase leg unit in a three-phase leg assembly is asynchronously switched on or switched off at any time-point. The present invention optimizes the efficiency of the three-phase converter on the basis of simplifying a design for sampling circuits and optimizing costs.