MMC Sub-Module Power Control Apparatus Heat Reduction
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Solution Overview
Problem
Conventional power control apparatuses for sub-modules in Modular Multilevel Converters (MMC) connected to HVDC systems and STATCOMs 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, especially when handling a wide range of voltages.
Innovation Solution
A power control apparatus that includes a first resistor, a second resistor in series, a switch connected with the second resistor, a third resistor in parallel with the second resistor, a Zener diode in parallel with the third resistor, and a DC/DC converter, where the switch's ON/OFF switching controls the current through the Zener diode, minimizing heat generation and loss by varying the current flow based on voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current-limiting resistors and Zener diodes are used to convert high voltage to low voltage in MMC sub-modules, then voltage conversion and current limiting are achieved, but significant heat generation and power loss occur
Solution Approach 1:
The patent changes the operating parameters by using a switching element to dynamically control the circuit configuration. The switching element alternates between ON and OFF states, changing the effective resistance and current path parameters to minimize power loss while maintaining voltage conversion functionality
Solution Approach 2:
The patent employs periodic switching action where the switching element is turned ON and OFF at specific intervals. This periodic action allows the circuit to operate in different modes (high-side switching, low-side switching) that collectively reduce the average power loss compared to continuous operation with fixed resistors and Zener diodes
2Ease of operation
If current-limiting resistors are used to limit current in high voltage range, then current control is achieved, but heat generation increases requiring additional heat dissipation components
Solution Approach 1:
The patent extracts the heat generation problem by removing the continuous current flow through high-value resistors. Instead, it uses a switching element to create intermittent current paths, effectively taking out the continuous thermal load and replacing it with controlled pulsed operation that achieves current limiting without proportional heat generation
Solution Approach 2:
The patent introduces dynamic control through the switching element that can change state based on operating conditions. This dynamic approach allows the circuit to adapt its current path and resistance characteristics in real-time, optimizing performance across different voltage and current conditions while minimizing thermal generation
3Reliability
If Zener diode is used for voltage conversion, then voltage regulation is achieved, but high current flows through it increasing loss and heat generation
Solution Approach 1:
The patent applies preliminary action by using the switching element to control when current flows through the Zener diode. The switch is turned ON before significant current would flow through the Zener, and OFF when current would become excessive, preventing the high current conditions that cause energy loss while maintaining voltage regulation capability
Solution Approach 2:
The patent implements feedback control through the switching element that responds to circuit conditions. The switching element's operation is controlled based on the state of the Zener diode and overall circuit requirements, creating a feedback mechanism that optimizes current distribution and minimizes energy loss through the Zener diode while maintaining stable voltage 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 in current-limiting resistors and Zener diodes, reduces heat generation, and eliminates the need for additional heat dissipation components, enhancing the reliability and efficiency of the power control apparatus by controlling current flow through the Zener diode based on switching operations.
Implementation Method 1
the high voltage is converted into the low voltage using the Zener diode Z
Implementation Method 2
current is limited using specific resistors R1 and R2, among multiple resistors R1 to R3 connected in series
Implementation Method 3
a switch connected in series with the second resistor
Data Source
Figure 1
Figure 2~3
Figure 4(a)~4(b)
AI summary
Disclosed herein is a power control apparatus for sub-modules in an MMC, which controls stable supply of power to sub-modules in MMC connected to an HVDC system and a STATCOM. The power control apparatus includes at least one first resistor connected between P and N buses of MMC; a second resistor connected in series with the first resistor; a switch connected in series with the second resistor; a third resistor connected in parallel with the second resistor and the switch which are connected in series; a Zener diode connected in parallel with the third resistor; and a DC/DC converter connected between both ends of the Zener diode and configured to convert voltage across both ends of the Zener diode into low voltage, and supply the low voltage to the sub-modules, wherein a magnitude of current flowing through the Zener diode is controlled depending on ON/OFF switching of the switch.