Inverter Control Device for Reducing Motor Overcurrent
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Solution Overview
Problem
Existing inverter control devices for electric motors in hybrid and electric vehicles face issues with overcurrent generation due to 3n-order harmonic currents, especially when their frequency exceeds the controllable frequency, leading to increased losses and potential breakdown.
Innovation Solution
The control device calculates and adjusts dq-axis current command values and zero-phase current command values to ensure their vector sum does not exceed a predetermined current value, preventing overcurrent by using a combination of current command calculation, dq-axis current control, and zero-phase current management, thereby restricting the current output within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a 3n-order harmonic voltage command value is calculated to cancel 3n-order harmonic current, then the harmonic current is reduced and loss is decreased, but there is a risk that overcurrent is generated when the harmonic current frequency exceeds the controllable frequency of the inverter control device
Solution Approach 1:
The control device dynamically adjusts the controllable frequency based on the operating conditions and harmonic current frequency characteristics. By making the frequency adaptive rather than fixed, the system can track and control harmonic currents across a broader frequency range, preventing overcurrent while maintaining harmonic cancellation effectiveness.
Solution Approach 2:
The system changes the parameter of controllable frequency based on the detected harmonic current frequency. When the harmonic frequency exceeds the original controllable frequency range, the system adjusts the frequency parameter to expand the controllable range, thereby maintaining reliable harmonic current cancellation without generating overcurrent.
2Reliability
If the controllable frequency of the inverter control device is increased to handle higher frequency harmonic currents, then overcurrent is prevented, but the device complexity and cost increase
Solution Approach 1:
The control device performs preliminary detection of the harmonic current frequency and proactively adjusts the controllable frequency before overcurrent occurs. By anticipating the need for frequency adjustment based on operating conditions, the system prevents overcurrent without requiring permanently oversized or overly complex control hardware.
Solution Approach 2:
The inverter control device autonomously detects its own controllable frequency limitations and self-adjusts the frequency parameter based on the harmonic current characteristics. This self-service capability eliminates the need for external complex control systems or manual intervention, maintaining reliability while minimizing added complexity.
Data Source
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AI summary
An object of the present invention is to reduce an overcurrent of an inverter and a motor. A control device for an electric motor in which windings of respective phases are independently connected, the control device for the electric motor uses a zero-phase current calculation means for calculating a zero-phase current based on detection values of currents of the respective phases flowing in the electric motor and a position of a rotor of the electric motor to control a current flowing in the electric motor such that a vector sum of a drive current and the zero-phase current is equal to or lower than a predetermined current.