Power Converter Controller for DC Capacitor Voltage Balance
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Solution Overview
Problem
In modular multilevel converters, voltage imbalances among DC capacitors in series-connected unit converters can be exacerbated by gate block states, leading to potential component breakdown and insufficient power supply to control circuits.
Innovation Solution
A power conversion device with a controller that adjusts the resistance value of the current-limiting resistance circuit based on the voltage magnitude and gate block state, ensuring balanced voltage across DC capacitors by dynamically changing the resistance value in response to these conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gate block is applied to fix switching elements in non-conductive states, then control of the power converter is simplified, but voltage imbalance among DC capacitors increases
Solution Approach 1:
The patent applies dynamics by making the resistance value of the current-limiting resistance circuit variable rather than fixed. The control unit dynamically adjusts the resistance value based on real-time voltage detection from each unit converter, allowing the system to adapt to changing conditions during gate block and prevent voltage imbalance among DC capacitors.
Solution Approach 2:
The patent changes the parameter of resistance value in the current-limiting resistance circuit from a constant value to a variable value. By detecting voltage levels across DC capacitors and adjusting the resistance accordingly, the system maintains voltage balance among unit converters even when switching elements are in gate block state.
2Reliability
If current-limiting resistance circuit has high resistance value, then overcharge of second capacitor is suppressed, but power supply to control circuit becomes insufficient
Solution Approach 1:
The resistance value in the current-limiting resistance circuit is dynamically adjusted based on the operational state of the power converter. During normal operation, a lower resistance value ensures sufficient power supply to the control circuit. During gate block or overcharge conditions, the resistance value increases to suppress overcharge of the second capacitor, thus adapting to different operational requirements.
Solution Approach 2:
The patent changes the resistance parameter of the current-limiting resistance circuit based on detected voltage levels and operational states. This parameter change allows the system to optimize between two conflicting requirements: suppressing overcharge of the second capacitor while ensuring adequate power supply to the control circuit under different operating conditions.
3Power
If DC voltage is lowered by current-limiting resistance, then power supply to control circuit is enabled, but voltage imbalance among unit converters increases
Solution Approach 1:
The patent applies parameter changes by adjusting the resistance value of the current-limiting resistance circuit based on the specific operational state of each unit converter. Rather than using a fixed resistance value that causes voltage imbalance, the control unit detects voltage levels and dynamically changes the resistance parameter to maintain voltage balance while still enabling power supply to control circuits.
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 effectively prevents the increase of voltage imbalances among DC capacitors during gate block states, ensuring stable operation and adequate power supply to control circuits, thereby enhancing the reliability and efficiency of the power conversion device.
Implementation Method 1
the DC voltage across the DC capacitor in the main circuit is lowered by a current-limiting resistance, thereby generating an input voltage to a power supply
Implementation Method 2
The electric power appropriate to this input voltage is temporarily stored in a capacitor provided inside the power supply. The power supply supplies a power supply voltage, which is obtained by further lowering this input voltage, to a control circuit.
Data Source
AI summary
A power supply includes a second capacitor, an overcharge suppression circuit, a power supply circuit, and a controller. The controller includes: an overcharge suppression control circuit that controls the overcharge suppression circuit in accordance with a magnitude of a voltage of the second capacitor; and a resistance switching circuit that changes a resistance value of the current-limiting resistance circuit depending on whether a gate block state occurs or not and in accordance with a magnitude of the voltage of the first capacitor. In the gate block state, each of the switching elements is fixed in a non-conductive state.