Power Converter Control Method for Harmonic Suppression
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Solution Overview
Problem
Direct AC-AC power converters without smoothing capacitors face challenges in reducing harmonic components of the load current, particularly odd-numbered order harmonics, which affect the pulsation of effective power and increase power harmonics, necessitating a method to suppress these harmonics effectively.
Innovation Solution
A power converter control method that includes a rectifier circuit and a voltage source inverter, where the modulation factor and voltage commands incorporate both DC and AC components with specific angular frequencies, allowing for the calculation and adjustment of the ratio and phase differences of the AC component relative to the DC component to reduce specific harmonic orders in the load current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a direct AC-AC power converter without smoothing capacitor is used, then circuit miniaturization and high efficiency are achieved, but harmonic components of load current propagate to power side causing increased power current harmonics
Solution Approach 1:
The invention changes the control parameters of the voltage source inverter by introducing AC components to the modulation factor and voltage commands. Specifically, the modulation factor includes a DC component and AC components with angular frequencies that are 6n multiples of the base fundamental angular frequency, with specific amplitude ratios and phase differences to cancel harmonic components in the load current, thereby reducing power current harmonics while maintaining the capacitor-less efficient design
2Ease of operation
If conventional control without harmonic consideration is used, then control simplicity is maintained, but odd-numbered order harmonic components cause pulsation of effective power
Solution Approach 1:
The invention modifies the control parameters by adding AC components to the modulation factor and voltage commands with specific characteristics. The AC component has an angular frequency that is a 6n multiple of the base fundamental angular frequency, with amplitude ratio and phase difference carefully controlled to cancel the odd-numbered order harmonic components, thereby stabilizing effective power without significantly complicating the control structure
3Object-generated harmful factors
If AC components are added to modulation factor and voltage commands, then harmonic components are reduced, but control calculation complexity increases
Solution Approach 1:
The invention introduces AC components to the modulation factor and voltage commands with specific parameters: the angular frequency is a 6n multiple of the base fundamental angular frequency, the amplitude ratio of AC to DC component follows a specific relationship, and the phase difference is controlled to achieve harmonic cancellation. This structured approach reduces harmonics while keeping the control calculation manageable through defined parameter relationships
Data Source
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AI summary
When an AC voltage is outputted to an inductive load, pulsation of an effective power caused by an odd number-th order harmonic component of a current flowing in this load is reduced. A modulation factor k of an inverter 4 includes a DC component k 0 and an AC component k 6n cos(6n·É L ·t + Õ 6n ). The AC component includes a frequency (6É L /2À) which is a 6n multiple of the fundamental frequency (É L /2À) of AC voltages Vu, Vu and Vw outputted from the inverter 4. Even when there are not only the 5th order harmonic component of load currents iu, iv and iw but also the 7th order harmonic component, it is possible to adequately set the ratio of the magnitude of the AC component and the ratio of the DC component and reduce pulsation of consumption power caused by these harmonic components. Reducing the pulsation contributes to suppression of power harmonics.