Power Conversion Device Overvoltage Protection via Control Unit
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Solution Overview
Problem
Existing overvoltage suppression circuits in power conversion devices fail to prevent abnormal voltage application to semiconductor elements and filter capacitors when the overvoltage suppression switch fails, leading to potential component damage.
Innovation Solution
A power conversion device with a transformer, breaker, converter, capacitor, charging resistor, and contactors that form a separate discharge path using existing circuit elements, allowing the control unit to manage voltage across the capacitor and bypass the failed overvoltage suppression switch, thereby preventing overvoltage application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an overvoltage suppression circuit is added to short-circuit the filter capacitor through a resistor, then overvoltage damage to semiconductor elements and filter capacitor is prevented, but the device complexity increases and new failure points are introduced
Solution Approach 1:
The patent introduces a control unit as an intermediary that monitors capacitor voltage and activates alternative discharge paths (through converter elements and charging resistor) when overvoltage is detected, rather than relying on a dedicated suppression circuit with its own switch and resistor. This mediator approach provides protection while using existing circuit components.
Solution Approach 2:
The converter elements and charging resistor, which are already part of the circuit for normal operation, are made to serve the additional function of overvoltage suppression. The system uses its own existing components to protect itself, eliminating the need for separate suppression hardware.
2Reliability
If the gates of inverter and converter elements are turned OFF during overvoltage, then regenerative braking stops and voltage can be lowered, but productivity decreases due to operation interruption
Solution Approach 1:
The control unit dynamically adjusts the state of converter elements based on real-time voltage conditions. Rather than simply turning all elements OFF, the control unit selectively activates specific converter elements to create discharge paths while maintaining others in their normal state, allowing partial continuation of operation during overvoltage events.
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
Prevents overvoltage application to semiconductor elements and filter capacitors even when the overvoltage suppression circuit is not functioning, ensuring component safety and stability.
Implementation Method 1
a converter to convert AC electric power output from the transformer into DC electric power
Implementation Method 2
a capacitor connected to the DC side of the converter
Implementation Method 3
an overvoltage suppression circuit to short-circuit the capacitor through a resistor when a voltage across the capacitor exceeds the predetermined value
Implementation Method 4
a transformer to receive electric power supplied from an external circuit and to output AC electric power
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Even when an overvoltage suppression circuit (14) is not formed due to failure of an overvoltage suppression switch, overvoltage application to semiconductors and a filter capacitor (5) is prevented. A control unit (24) controls the overvoltage suppression circuit (14) to short-circuit the filter capacitor (5) when the voltage thereacross exceeds a predetermined value. Then when non-operation of the overvoltage suppression circuit (14) is detected, the control unit (24) opens an AC breaker (2) and AC switch (8), and closes a charging switch (9). Thereafter, the control unit (24) turns ON the converter element (41) (or converter element 43) connecting to the filter capacitor (5) terminal (51) (or terminal (52)) and a charging resistor (10), and turns ON converter element (44) (or converter element (42)) connecting to terminal (52) (or terminal (51)) of filter capacitor (5) and connecting to the terminal of the transformer (3) not connected to charging resistor (10).