Power Conversion Device Capacitor Current Reduction
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Solution Overview
Problem
Existing power conversion devices fail to effectively reduce capacitor current when the power factor is low, particularly at high motor speeds, leading to increased capacitor current fluctuations and challenges in downsizing the capacitor.
Innovation Solution
A power conversion device with an inverter and a controller that outputs on/off signals to form the second closest and third closest voltage vectors in phase to the current vector, based on calculated voltage command values, to manage capacitor current reduction across varying power factors and motor speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the phase shift control method is used to reduce capacitor current, then capacitor current is reduced at low motor speeds, but the effect is lost at high motor speeds when power factor decreases
Solution Approach 1:
The patent dynamically adjusts the voltage vector selection strategy based on real-time operating conditions. Instead of using a fixed phase shift control method, the system adaptively changes control parameters according to motor speed and power factor, enabling effective capacitor current reduction across both low-speed and high-speed regions.
Solution Approach 2:
The patent changes the control parameter from fixed phase shift to dynamic voltage vector selection based on power factor and motor speed. By monitoring these parameters and adjusting the voltage vector application strategy accordingly, the system maintains capacitor current reduction effectiveness across varying operating conditions.
2Device complexity
If standard two-phase modulation control is used without phase shift, then control simplicity is maintained, but capacitor current cannot be reduced when power factor is low
Solution Approach 1:
The patent modifies the voltage vector selection parameters in the two-phase modulation control based on power factor detection. When power factor is low, the system adjusts which voltage vectors are applied and for what duration, enabling capacitor current reduction without fundamentally changing the control structure or adding significant complexity.
3Volume of stationary object
If capacitor size is reduced, then device downsizing is achieved, but capacitor current fluctuations become problematic
Solution Approach 1:
The patent applies preliminary action by proactively controlling the inverter switching patterns to minimize capacitor current fluctuations before they can cause problems. By using optimized voltage vector selection based on power factor and motor speed, the system prevents large current fluctuations that would otherwise require larger capacitors to handle.
Data Source
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AI summary
A power conversion device is configured to output on/off signals for switching on and off respective semiconductor switching elements of an inverter configured to invert a DC voltage output from a DC power supply into three-phase AC voltages 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 current vector that is based on currents supplied as a result of output of the three-phase AC voltages from the inverter are formed.