Direct Matrix Converter Voltage Control for Power Ripple Reduction
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Solution Overview
Problem
Direct-type AC power converters with a DC link but without a smoothing capacitor face challenges in suppressing ripple of active power caused by odd-number-order harmonic components in the current flowing to inductive loads, such as motors, leading to inefficiencies and harmonic issues.
Innovation Solution
A power converter control method that adjusts the voltage control rate of a direct-type AC power converter or direct matrix converter by incorporating a DC component and a specific AC component with a frequency six times the fundamental frequency, allowing for effective reduction of fifth- and seventh-order harmonic components in the current, thereby minimizing power ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a direct-type AC power converter is used without a smoothing capacitor, then the converter size is reduced, but active power ripple caused by odd-number-order harmonic components increases
Solution Approach 1:
The invention changes the control parameters of the voltage-source converter by introducing a specific AC component to the voltage control rate. This AC component has a frequency six times the fundamental frequency and is designed to counteract the odd-number-order harmonic components in the load current, thereby reducing active power ripple without requiring a smoothing capacitor
Solution Approach 2:
The invention combines a DC component and an AC component in the voltage control rate to form a composite control signal. The DC component maintains basic voltage control while the AC component specifically targets harmonic reduction, creating a synergistic effect that reduces power ripple while maintaining converter compactness
2Object-generated harmful factors
If a smoothing capacitor is added to the DC link, then active power ripple is reduced, but the converter size and complexity increase
Solution Approach 1:
The invention replaces the mechanical/passive smoothing capacitor with an active control mechanism. By dynamically adjusting the voltage control rate with a specifically designed AC component, the system achieves ripple reduction through control action rather than passive energy storage, eliminating the need for large capacitors
3Loss of energy
If concentrated winding is used in motor armature, then copper loss is reduced, but harmonic components in armature current increase
Solution Approach 1:
The invention converts the harmful effect of odd-number-order harmonic components into a controllable parameter. By designing the AC component of the voltage control rate to specifically counteract these harmonics, the system transforms the harmonic problem into a controlled adjustment mechanism, maintaining the efficiency benefits of concentrated winding while eliminating harmonic issues
Data Source
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Figure 3~4
AI summary
Reduced is a ripple in active power caused by odd-number-order harmonic components of a current which flows in an inductive load when an AC voltage is outputted to the load. A voltage control rate (Ks) of an inverter (4) has a DC component (Ks1) and an AC component (-Ks6·cos(6ωLt)). This AC component has a frequency (6ϕ/2πt) which is six times a fundamental frequency (ϕ/2πt) of an AC voltage (Vu, Vv, Vw) outputted by the inverter (4). Even when there are not only a fifth-order harmonic component but also a seventh-order harmonic component of a load current (iu, iv, iw), a ratio between the magnitude (Ks6) of the AC component and the DC component (Ks1) can be appropriately set, so that a ripple in power consumption caused by these harmonic components can be reduced. A redaction in this ripple contributes to suppression of power-source harmonics.