Power Conversion Device Zero-Phase Voltage Control
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Solution Overview
Problem
Current power conversion devices experience current pulsation and skipping, especially in electric motors with small electrical time constants, due to non-continuous phase voltages during transient periods of two-phase and three-phase switching.
Innovation Solution
A power conversion device that dynamically adjusts and inserts a zero-phase voltage into the voltage command based on frequency or time, using a control circuit to ensure continuous phase voltage and minimize current pulsation and skipping, by generating and adjusting zero-phase voltages in accordance with the voltage command characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If zero-phase voltage is inserted to improve voltage utilization factor, then voltage utilization is improved, but phase voltage becomes non-continuous causing current pulsation and skipping
Solution Approach 1:
The patent dynamically adjusts the zero-phase voltage insertion strategy based on motor operating conditions. The control circuit determines whether to insert zero-phase voltage by evaluating phase voltage commands and motor state, transitioning between two-phase and three-phase switching modes adaptively to maintain current continuity while improving voltage utilization.
Solution Approach 2:
The patent changes the modulation parameters (zero-phase voltage amplitude and insertion timing) based on operating conditions. By adjusting these parameters dynamically, the system optimizes voltage utilization factor while preventing current pulsation and skipping in the motor.
2Loss of energy
If two-phase switching is used to reduce switching losses, then switching loss is reduced, but current pulsation occurs in motors with small electrical time constant
Solution Approach 1:
The system dynamically selects between two-phase and three-phase switching modes based on real-time motor operating conditions. The control circuit transitions between modes adaptively, using two-phase switching when appropriate to reduce losses while switching to three-phase mode when current stability is compromised, especially in motors with small electrical time constants.
Solution Approach 2:
The control circuit uses feedback from phase voltage commands and motor operating state to determine the appropriate switching mode. By continuously monitoring system state and adjusting switching strategy accordingly, the system reduces switching losses while maintaining current stability through adaptive mode selection.
Data Source
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AI summary
During a transition period in which two-phase switching and three-phase switching are mixed in the technology disclosed in document 1, phase voltage is momentarily non-continuous, and consequently, for example, there are cases of current pulsation and current skipping in electric motors having a small electrical time constant. Thus, a power conversion device for controlling an electric motor by converting AC voltage or DC voltage into a desired voltage by operating a switching circuit, the power conversion device being characterized by being equipped with a control circuit for changing a first modulation zero-phase voltage to be inserted into a voltage command for each phase, depending on frequency or voltage or time.