Power Converter Control for VL System Stability
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Solution Overview
Problem
The VL control system in power conversion apparatuses experiences instability due to an excessive gain ratio, particularly when the initial voltage control rate is small, leading to harmonic component issues and resonance problems.
Innovation Solution
A method of controlling the power conversion apparatus involves detecting the reactor voltage, calculating a correction coefficient based on the voltage control rate command, and adjusting the switching signal to reduce the gain ratio, with limitations on the correction amount to prevent instability. This includes using a correction coefficient that decreases as the voltage control rate command becomes smaller and increases as the alternating current amplitude becomes larger, ensuring the correction amount remains within defined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed gain is used in the VL control system, then the control is simple, but the system becomes unstable when the voltage control rate is small
Solution Approach 1:
The patent applies dynamics by making the gain variable instead of fixed. The correction coefficient is dynamically adjusted based on the voltage control rate command value, changing from a large value when the voltage control rate is small to a small value when the voltage control rate is large, thereby maintaining system stability across different operating conditions.
Solution Approach 2:
The patent changes the parameter of the correction coefficient based on the voltage control rate command. When the voltage control rate command is smaller than a threshold, a larger correction coefficient is used; when it is larger than the threshold, a smaller correction coefficient is used. This parameter adaptation resolves the stability issue without excessive complexity.
2Object-generated harmful factors
If a large correction coefficient is used to reduce harmonic components, then the harmonic suppression is effective, but the system becomes unstable due to excessive gain ratio
Solution Approach 1:
The correction coefficient is made dynamic rather than fixed. It automatically adjusts its magnitude based on the voltage control rate command, being large when needed for harmonic suppression (at low voltage control rates) and small when excessive gain would cause instability (at high voltage control rates).
Solution Approach 2:
Different correction coefficients are applied in different operating regions. A first correction coefficient is used when the voltage control rate command is below a threshold, and a second correction coefficient is used when it is above the threshold, optimizing performance for each local operating condition.
Data Source
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AI summary
The present invention provides a method of controlling a power conversion apparatus, which is capable of suppressing an instability of a VL control system caused by an increase of a ratio of a gain to a voltage control rate. A voltage (VL) of a reactor (L1) taking a potential on a side of a capacitor (C1) as a reference is detected. A correction coefficient which is made smaller as a first voltage control rate command (ks**) becomes smaller is calculated, the first voltage control rate being a ratio of an amplitude of an AC voltage, which is outputted by a power converter 2, to an average value of the DC voltage (Vdc). A correction is made to subtract a correction amount (H) obtained by multiplying the voltage (VL) of the reactor (L1) by the correction coefficient from the first voltage control rate command (ks**), so that a second voltage control rate command (ks*) is generated. A switching signal (S) which is generated based on a second voltage control rate command (ks*) is given to the power converter 2.