MMC Power Supply Thyristor Overvoltage Protection Circuit
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Solution Overview
Problem
In power conversion devices with modular multilevel converters, the provision of a separate power supply for each unit converter can lead to destruction of circuit components due to overvoltage input, particularly during abnormal conditions such as overcharge of the DC capacitor.
Innovation Solution
A power conversion device is designed with a power supply circuit that includes a thyristor connected in parallel with the main power supply circuit, a current-limiting resistor in series with the thyristor, and a control unit to fire the thyristor when input voltage exceeds a threshold, preventing reverse current flow with a reverse current blocking diode, and transmitting a signal to the control device to fix the switching element in an off state, thus protecting the unit converters from overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power supply is provided for each unit converter to enable independent control, then the control flexibility and reliability of the MMC system is improved, but the risk of circuit component destruction due to overvoltage input increases
Solution Approach 1:
The patent applies beforehand cushioning by introducing a protection circuit that includes a thyristor, current-limiting resistor, and reverse current blocking diode connected in parallel with the power supply circuit. This protection circuit is pre-configured to activate when overvoltage occurs, cushioning the blow to circuit components before damage can occur. The control unit monitors voltage and fires the thyristor to create a bypass path for excess voltage, protecting the power supply circuit and control circuit from destruction.
Solution Approach 2:
The patent uses an intermediary approach by introducing a thyristor as a mediator between the DC capacitor and the power supply circuit. The thyristor acts as a controlled switch that can be fired by the control unit when overvoltage is detected, creating an alternative current path through the current-limiting resistor that bypasses the vulnerable power supply circuit. This intermediary element protects the system components while allowing normal operation under standard conditions.
2Reliability
If the thyristor is fired to protect against overvoltage, then circuit components are protected from destruction, but reverse current flow from the power supply circuit to the thyristor may occur
Solution Approach 1:
The patent converts the potentially harmful reverse current flow into a beneficial protective mechanism by using a reverse current blocking diode connected in series with the thyristor. This diode is specifically oriented to block reverse current while allowing forward current flow during normal protection operation. The harmful reverse current that could damage the thyristor is converted into a controlled feature where the diode's reverse-blocking characteristic becomes the protective element, ensuring unidirectional current flow and preventing thyristor damage.
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
This configuration effectively protects the unit converters from overvoltage damage, ensuring their integrity even in cases of communication errors between the control device and the unit converters, and preventing destruction of circuit components.
Implementation Method 1
a thyristor connected between the first and second input terminals electrically in parallel with the power supply circuit
Implementation Method 2
a reverse current blocking diode connected between an anode and a cathode of the thyristor electrically in series with the power supply circuit to prevent reverse flow of current from the power supply circuit to the thyristor
Implementation Method 3
The power supply circuit is configured to convert input voltage provided between first and second input terminals from the DC capacitor into the power supply voltage
Data Source
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AI summary
An MMC (110) includes arms (A1 to A6) configured with one unit converter or a plurality of cells (10) connected in series. The main circuit of the cell (10) includes a switching element and a DC capacitor. The power supply of the cell (10) lowers voltage of the DC capacitor to generate power supply voltage to be supplied to the control circuit of the cell (10). The power supply includes a power supply circuit configured to convert input voltage provided between first and second input terminals from the DC capacitor into power supply voltage, a thyristor connected between the first and second input terminals electrically in parallel with the power supply circuit, a current-limiting resistor connected between terminals of the DC capacitor electrically in series with the thyristor, and a control unit configured to fire the thyristor when input voltage applied to the power supply circuit exceeds a threshold voltage.