Electric Power Converter Phase-Shifted Modulation Ripple Reduction
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Solution Overview
Problem
Existing electric power converters for three-phase rotary electric machines face challenges in reducing ripple electric current, leading to noise and heat generation in capacitors, due to limited adjustment range of switching ON-OFF timing of switching elements.
Innovation Solution
An electric power converter with two inverter units and a control unit that modulates voltage instruction signals to prevent overlapping of effective voltage vector generation periods, shifting phases by (30+120×n) degrees and adjusting neutral point voltage within an allowable range, thereby reducing ripple electric current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If phase-shifting PWM reference signals or shifting neutral point voltages is used to reduce ripple electric current, then capacitor noise and heat generation is reduced, but the adjustment range of switching ON-OFF timing remains limited when voltage instruction signal amplitude exceeds 50% of allowable output range
Solution Approach 1:
The patent changes the phase relationship between voltage instruction signals for two inverter systems from the conventional same-phase relationship to a phase difference of (30+120×n) degrees. This parameter change in signal phase enables complete separation of capacitor discharge timings between the two systems, significantly reducing ripple electric current and capacitor noise/heat generation while expanding the effective adjustment range of switching ON-OFF timing beyond the 50% amplitude limitation of conventional methods
Solution Approach 2:
The patent utilizes periodic phase-shifting of voltage instruction signals at specific angular intervals ((30+120×n) degrees) to create non-overlapping discharge periods for capacitors in two inverter systems. This periodic action with specific phase offsets ensures that when one system is discharging its capacitor, the other system is charging, thereby eliminating ripple current peaks and expanding the operational range for ripple reduction
Data Source
AI summary
A control unit of an electric power converter, which is used in a three-phase motor having two winding wire systems, performs for a first duty instruction signal regarding a voltage applied to a first winding wire group a flatbed two-phase modulation process, and performs for a second duty instruction signal regarding a voltage applied to a second winding wire group a flattop two-phase modulation process. By phase-shifting the second duty instruction signal by 30° from the first duty instruction signal, a timing of maximum value of the first duty instruction signal is shifted from a timing of minimum value of the second duty instruction signal. Even when the maximum value is greater than a center output value and the minimum value is smaller than the center output value, overlapping of capacitor discharge is avoided, thereby reducing a ripple electric current.