MMC Sub-Module Power Control Apparatus Heat Reduction
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Solution Overview
Problem
Conventional power control apparatuses for Modular Multilevel Converter (MMC) sub-modules connected to HVDC and STATCOM systems experience significant heat generation and loss due to current-limiting resistors and Zener diodes, leading to reliability issues and the need for additional heat dissipation components.
Innovation Solution
A power control apparatus utilizing a half-bridge circuit unit, transformer, DC/DC converter, photocoupler, PWM control unit, and starting circuit with a B contact switch, resistor, voltage-drop diode, and Zener diode to efficiently convert high input voltage to low output voltage, minimizing heat generation and loss by controlling switching and current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If current-limiting resistors and Zener diodes are used in the conventional power control apparatus, then the high voltage is converted to low voltage for sub-module operation, but significant heat generation and loss occur leading to reliability issues
Solution Approach 1:
The patent extracts and removes the problematic current-limiting resistors and Zener diodes from the power control circuit. Instead of using these passive components that generate heat and cause power loss, the invention implements an active switching circuit using MOSFETs (Q1, Q2) controlled by a microcontroller to regulate voltage and current to the sub-module, thereby eliminating the source of heat generation and power loss while improving reliability
Solution Approach 2:
The patent replaces the passive resistive voltage control mechanism with an active electronic switching control system. The microcontroller-based PWM switching circuit substitutes the conventional resistor-Zener diode voltage regulation, enabling precise control of power delivery to sub-modules without the inherent power dissipation of resistive elements
2Ease of operation
If current-limiting resistors are selected for normal operation at 800 V, then control power is normally output, but high current flows through the resistors when input voltage increases to 3 kV, increasing loss and heat generation
Solution Approach 1:
The patent implements a dynamic control system where the MOSFET switching circuit is controlled by a microcontroller to adapt to varying input voltages. When input voltage increases to 3 kV, the control circuit dynamically adjusts the switching duty cycle and timing to maintain appropriate current levels, preventing excessive current flow and power loss in the circuit elements while ensuring normal operation across the full voltage range
3Reliability
If most increased current flows into the Zener diode, then voltage regulation is maintained, but high heat is generated in the Zener diode, deteriorating apparatus reliability
Solution Approach 1:
The patent removes the Zener diode from the circuit entirely, replacing its voltage regulation function with an active MOSFET switching circuit controlled by PWM signals from a microcontroller. This eliminates the heat generation problem in the Zener diode while maintaining precise voltage regulation capability through electronic control
Solution Approach 2:
The patent introduces MOSFETs and a microcontroller as intermediary active components between the high-voltage input and the sub-module load. These intermediaries provide intelligent current management and voltage regulation, preventing excessive current flow and heat generation that would otherwise occur in passive Zener diode-based regulation
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 solution minimizes losses and heat generation in internal elements, eliminating the need for additional heat dissipation components and allowing efficient power control at lower voltages, such as 500 to 700 V, while maintaining higher efficiency compared to conventional systems.
Implementation Method 1
a half-bridge circuit unit for switching multiple switches, converting an input voltage across P and N buses of the MMC into a relatively low voltage
Implementation Method 2
a transformer for transferring the low output voltage (primary side), output through switching of the switches in the half-bridge circuit unit via switching of the switches, to a secondary side of the transformer
Implementation Method 3
a DC/DC converter for converting an output voltage on the secondary side of the transformer
Implementation Method 4
a photocoupler for outputting a reference signal corresponding to a magnitude of the secondary side output voltage of the transformer
Implementation Method 5
the high voltage is converted into the low voltage using the Zener diode Z
Implementation Method 6
current is limited using specific resistors R1 and R2, among multiple resistors R1 to R3 connected in series between the P and N buses
Data Source
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AI summary
The present invention relates to a power control apparatus for sub-modules in a Modular Multilevel Converter (MMC), which controls the supply of power to sub-modules in an MMC connected to an HVDC system and to a STATCOM. The power control apparatus includes a half-bridge circuit unit for switching multiple switches, converting an input voltage across P and N buses of the MMC into a relatively low voltage, and outputting the low voltage; a transformer for transferring the low output voltage (primary side), output through switching of the switches in the half-bridge circuit unit via switching of the switches, to a secondary side of the transformer; a DC/DC converter for converting an output voltage on the secondary side of the transformer; a photocoupler for outputting a reference signal corresponding to a magnitude of the secondary side output voltage of the transformer; a Pulse Width Modulation (PWM) control unit for controlling switching of the switches in the half-bridge circuit unit in response to the reference signal output from the photocoupler; and a starting circuit unit for supplying an initial starting voltage to the PWM control unit, wherein the PWM control unit is started in response to the starting voltage initially supplied from the starting circuit unit, and is configured to control switching of the switches in response to the reference voltage received from the photocoupler, and to receive the secondary side output voltage of the transformer as an operating voltage depending on the switching, thus being operated.