Direct Power Conversion Harmonic Shaping for Torque Ripple Peaks
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Solution Overview
Problem
In direct power conversion devices, the peaks of motor torque and motor current are unnecessarily high due to coinciding ripple components from the AC power supply frequency and load torque fluctuations, leading to increased motor current peaks.
Innovation Solution
A direct power conversion device with a control unit that controls switching elements to introduce two or more local maximum points in the motor current waveform by combining second, fourth, and sixth harmonics of the power supply frequency, specifically during periods where the fundamental wave of load torque and power supply voltage peaks coincide, to reduce motor current peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If torque control is applied to reduce compressor vibrations by superimposing ripple components, then compressor vibration is reduced, but motor current peaks become unnecessarily high
Solution Approach 1:
The patent applies periodic action by superimposing ripple components at specific frequencies (power supply frequency and load torque fluctuation frequency) to achieve vibration reduction. The control unit generates torque commands with periodic ripple components that counteract the compressor vibrations while managing current peaks through frequency selection.
Solution Approach 2:
The patent changes the frequency parameters of the superimposed ripple components to resolve the contradiction. By adjusting the frequency of the ripple components and selecting appropriate harmonic frequencies, the system achieves vibration reduction while avoiding excessive current peaks that would occur with other frequency selections.
2Reliability
If ripple components from power supply frequency and load torque fluctuations are superimposed, then torque control effectiveness is improved, but motor current variation increases
Solution Approach 1:
The control unit utilizes periodic action by superimposing ripple components with specific frequencies corresponding to the power supply frequency and load torque fluctuation frequency. This periodic superposition maintains torque control effectiveness while the frequency selection manages current variation stability.
Solution Approach 2:
The patent copies the frequency characteristics of the power supply and load torque fluctuations into the torque command signal. By replicating these frequency patterns in the control signal, the system maintains effectiveness in counteracting vibrations while managing current variation through careful frequency matching.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The sign fdc is a frequency twice as high as a frequency of a single-phase AC power supply(20); fL is a frequency of the periodic load fluctuations; and tb=1/|fdc―n×fL|, where n is a positive integer that maximizes tb, in a half period of power supply during a period of tb, the half period of power supply including a timing at which a peak of a fundamental wave of load torque and a peak of an absolute value of a power supply voltage substantially coincide with each other, the control unit(40) controls the switching elements (Su, Sv, Sw, Sx, Sy, Sz) so that two or more local maximum points appear in the half period of power supply, in a waveform obtained by combining a second harmonic, a fourth harmonic, and a sixth harmonic of a power supply frequency contained in a waveform of an absolute value of a motor current vector.