Power Conversion Device Fault Current Interruption
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Solution Overview
Problem
Existing power conversion devices in electric vehicles with permanent-magnet synchronous motors face issues with fault currents containing direct-current components that do not generate continuous current zero points, leading to uninterrupted fault currents and potential damage due to heat.
Innovation Solution
A power conversion device with an inverter, a current detector, and a controller that uses an alternating current disconnecting switching unit to set fault currents to a state generating a current zero point, allowing for effective interruption of fault currents between the inverter and motor, even when direct-current components are present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an alternating current disconnecting contactor is used to interrupt fault current, then the contactor can interrupt normal alternating current at current zero points, but it cannot interrupt fault currents containing direct-current components that do not generate continuous current zero points
Solution Approach 1:
The controller changes the parameter of the fault current by controlling the inverter switching elements to generate a current zero point. When a fault current containing a direct-current component is detected, the controller adjusts the switching states of the inverter to transform the fault current into a state that generates a current zero point, enabling the alternating current disconnecting contactor to interrupt it effectively.
Solution Approach 2:
The controller acts as an intermediary between the fault condition and the contactor. It detects the fault current and mediates by controlling the inverter switching elements to create a current zero point, which then enables the contactor to perform the interruption function that would otherwise be impossible with direct-current component-containing fault currents.
2Duration of action of moving object
If the fault current is left uninterrupted, then the motor can continue running, but the damage of the fault portion expands due to heat from continuous fault current
Solution Approach 1:
The controller converts the harmful direct-current component in the fault current into a beneficial state by controlling the inverter switching elements to generate a current zero point. This transformation allows the fault current to be interrupted safely while maintaining the ability to detect and respond to the fault condition, turning a potentially damaging continuous current into an interruptible alternating current pattern.
3Reliability
If the inverter switching elements are controlled to generate a current zero point in fault current, then the fault current can be interrupted, but additional control complexity is required
Solution Approach 1:
The controller performs multiple functions: it normally controls the inverter for motor operation and additionally detects fault currents and generates appropriate switching patterns to create current zero points. By integrating the fault current management function into the existing controller, the patent avoids adding separate dedicated hardware while maintaining the ability to handle various fault modes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables the interruption of fault currents, preventing the expansion of fault portions in the power conversion device, thereby reducing the risk of damage and ensuring continued operation of the electric vehicle.
Implementation Method 1
a sinusoidal alternating current generates a current zero point at each half cycle of a current wave. Therefore, a current can be interrupted by using the current zero point.
Data Source
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AI summary
An object is to obtain a power conversion device capable of interrupting a fault current and preventing expansion of a fault portion in the power conversion device, even when a fault current flowing between an inverter and a motor contains a direct-current component that does not generate a continuous current zero point, regardless of a mode of a fault occurred in the power conversion device. The power conversion device includes: an inverter that drives an alternating-current motor by converting a direct-current voltage into an alternating-current voltage of an arbitrary frequency; an alternating current disconnecting switching unit connected between the inverter and the alternating-current motor; a current detector that detects an output current of the inverter; and a controller that performs on/off-control of the plural switching elements in the inverter and switching control with respect to the switching unit, based on at least a current detected by the current detector. The controller has a configuration to be able to interrupt a fault current by setting the fault current to a state of generating a current zero point, when the fault current containing a direct-current component is generated between the inverter and the alternating-current motor.