Power Conversion Device Carrier Wave Frequency Control
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Solution Overview
Problem
Conventional methods for suppressing harmonic current in AC electric vehicles are insufficient when the connection status of main transformers and power conversion devices changes, particularly when one power conversion device stops operating, leading to inadequate electromagnetic coupling interference cancellation.
Innovation Solution
A power conversion device with a control unit that generates a PWM signal using a carrier wave with specific characteristics, including periodic changes in time ratio, to accurately suppress harmonic currents regardless of the connection status, by maintaining constant carrier wave frequency and deforming the switching symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional phase shift method is used for harmonic current suppression, then suppression is effective under identical transformer conditions, but suppression becomes insufficient when connection status changes
Solution Approach 1:
The patent applies dynamics by making the carrier wave frequency variable rather than fixed. The control unit dynamically adjusts the carrier wave frequency based on the connection status of power conversion devices and main transformers. When connection status changes (e.g., one device stops operating), the system changes the carrier wave frequency to maintain optimal harmonic current suppression, thereby resolving the contradiction between suppression effectiveness and adaptability.
2Measurement precision
If fixed carrier wave frequency is used, then control is simple, but harmonic current suppression accuracy decreases when electromagnetic conditions change
Solution Approach 1:
The patent implements feedback by having the control unit monitor the connection status of power conversion devices and main transformers, then adjust the carrier wave frequency accordingly. The control unit receives information about which devices are operating and uses this feedback to optimize the carrier wave frequency for harmonic current suppression, achieving high suppression accuracy while maintaining manageable control complexity through automated status detection.
3Power
If multiple power conversion devices are connected to main transformers, then power conversion capacity is increased, but electromagnetic coupling interference affects current generation
Solution Approach 1:
The patent applies parameter changes by adjusting the carrier wave frequency parameter based on the number and connection status of power conversion devices. When multiple devices are connected to main transformers with electromagnetic coupling, the system optimizes the carrier wave frequency to minimize the harmful electromagnetic coupling effects while maintaining high power conversion capacity. This dynamic parameter adjustment resolves the contradiction between maximizing power capacity and minimizing interference.
Data Source
AI summary
To generate a PWM signal, as an on/off signal of a semiconductor switch that constitutes a power conversion main circuit, by comparing a modulation wave command based on an input voltage waveform command of the power conversion main circuit with a carrier wave having changes from a lower limit to an upper limit and from the upper limit to the lower limit for an integral number of times per one cycle of an AC power supply, where the carrier wave has characteristics such that one change time from the lower limit to the upper limit and then returning to the lower limit is constant, and a time ratio between a change time from the lower limit to the upper limit and a change time from the upper limit to the lower limit changes periodically.