Inverter Beat Compensation for Motor Vehicle Systems
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Solution Overview
Problem
Existing power conversion devices face challenges in suppressing current beat phenomena in AC motors due to factors like sensor signal errors, output voltage errors, and voltage differences between inverter outputs, which can lead to pulsation in motor torque and efficiency deterioration, and require adaptation work and may not effectively handle current beat components across various motor operation states.
Innovation Solution
A power conversion device with a beat compensation unit that includes a beat extraction unit to calculate current beat components and a beat compensation voltage calculation unit to estimate and apply compensation voltages, suppressing current beat components without the need for adaptation work, regardless of motor operation states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HPF and PI compensator are used to extract and suppress current beat components, then current beat suppression is achieved, but adaptation work for cutoff frequency and gain is required, increasing device complexity
Solution Approach 1:
The control device automatically determines the cutoff frequency based on the fundamental frequency of the motor current, eliminating the need for manual adaptation work. The system self-configures the HPF parameters by calculating cutoff frequency as a multiple of the fundamental frequency, making the device self-adapting to different operating conditions.
Solution Approach 2:
The invention dynamically changes the cutoff frequency parameter of the HPF based on the fundamental frequency of the motor current. By making the cutoff frequency a variable parameter rather than a fixed value, the system adapts to different operating states without requiring manual reconfiguration.
2Measurement precision
If HPF is used to extract current beat components, then current beat can be detected, but fundamental wave component may be detected as current beat component in low-rotation range, affecting current control system
Solution Approach 1:
The cutoff frequency of the HPF is dynamically changed based on the fundamental frequency of the motor current. By setting the cutoff frequency as a multiple of the fundamental frequency, the HPF effectively separates current beat components from the fundamental wave, preventing false detection especially in low-rotation ranges where frequencies are closer together.
3Power
If switching frequency of inverter is not sufficiently higher than fundamental frequency, then voltage difference occurs between positive and negative outputs, causing current beat
Solution Approach 1:
Instead of trying to prevent the voltage difference between positive and negative outputs, the invention uses this voltage difference to generate a compensation voltage that counteracts the current beat. The control device calculates the voltage difference and converts it into a useful compensation signal that eliminates the harmful current beat effect.
4Reliability
If overcurrent protection function is mounted on inverter, then protection is provided, but overcurrent protection works by current beat causing inverter to stop
Solution Approach 1:
The invention converts the harmful current beat that triggers false overcurrent protection into a useful compensation signal. By calculating the current beat component and generating a compensation voltage, the system eliminates the false overcurrent conditions, allowing the inverter to continue operating without unnecessary shutdowns while maintaining genuine overcurrent protection.
Data Source
AI summary
Provided is a power conversion device that does not require adaptation work and can suppress a current beat regardless of an operation state of a motor. The power conversion device includes an inverter 1 that converts a DC voltage into an AC voltage and drives an AC motor 2, and beat compensation units 46 and 49 that suppress a current beat component of an output current of the inverter 1. The beat compensation units 46 and 49 include beat extraction units 50, 51, and 52 that calculate beat components of the output current of the inverter 1, and beat compensation voltage calculation units 53 and 54 that estimate beat compensation voltages from the beat components calculated by the beat extraction units 50, 51, and 52. The current beat component of the output current of the inverter 1 is suppressed based on the beat compensation voltages estimated by the beat compensation voltage calculation units 53 and 54.