Power Conversion Device Voltage Vector Selection
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Solution Overview
Problem
Existing power conversion devices with individually provided capacitors for each inverter struggle to effectively reduce capacitor currents, as the control methods used in such configurations are inadequate for minimizing impedance and voltage fluctuations.
Innovation Solution
A power conversion device comprising two inverters with semiconductor switching elements, two capacitors, and a control unit that calculates voltage command values and outputs on/off signals to form the second closest and third closest voltage vectors to the voltage command vector, reducing capacitor currents by optimizing voltage vector selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If capacitors are individually provided for two respective inverters, then the voltage applied to the inverters can be kept constant, but the capacitor currents increase and the capacitors cannot be downsized
Solution Approach 1:
The patent changes the control parameters by selectively outputting the second closest and third closest voltage vectors instead of the conventional closest voltage vector. This parameter change in the voltage vector selection strategy modifies the capacitor current characteristics, enabling current reduction while maintaining voltage stability with individually provided capacitors.
2Measurement precision
If the closest voltage vector is output to the inverter, then the voltage control precision is improved, but the capacitor current increases
Solution Approach 1:
The patent modifies the voltage vector selection parameter by choosing the second closest and third closest voltage vectors instead of the closest one. This parameter change achieves a balance between voltage control precision and capacitor current reduction, proving that optimal control does not always require the closest voltage vector.
Solution Approach 2:
The patent converts the potential disadvantage of selecting a slightly less precise voltage vector into a benefit by significantly reducing capacitor current. The second closest and third closest voltage vectors, while not the absolute closest, provide sufficient voltage control precision while delivering the beneficial effect of current reduction.
3Device complexity
If one common capacitor is provided for two inverters, then the device complexity is reduced, but the voltage stability deteriorates due to wiring inductance and resistance
Solution Approach 1:
The patent adopts a segmented capacitor configuration where two capacitors are individually provided for two inverters instead of one common capacitor. This segmentation improves voltage stability by eliminating the negative effects of wiring inductance and resistance, and the control method further optimizes the system by reducing capacitor currents.
Data Source
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AI summary
A power conversion device is configured to output, to each of two inverters configured to invert a DC voltage output from a DC power supply to three-phase AC voltages, on/off signals for switching on and off respective semiconductor switching elements of each of the inverters so that, out of a plurality of voltage vectors defined so as to correspond to patterns of the on/off signals, the second closest voltage vector and the third closest voltage vector in phase to a voltage command vector that is based on a voltage command value calculated for each of the inverters are formed.