NPC Converter Control System with Dual Compensation Signals
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Solution Overview
Problem
Neutral point voltage imbalance in neutral point clamped (NPC) converters, particularly in renewable power generation systems, is not effectively addressed by single compensation control signals during PWM modulation, leading to suboptimal performance across varying power conversion conditions.
Innovation Solution
The implementation of two distinct compensation control signals for neutral point voltage balancing, tailored for normal operation and wind-free states, allows for improved voltage balance in NPC converter systems by selectively engaging different control units based on power factor states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single compensation control signal is used during PWM modulation for neutral point voltage balancing, then the control system complexity is kept low, but the voltage balancing performance deteriorates under varying power conversion conditions
Solution Approach 1:
The patent implements dynamic selection between different compensation control signals based on the operating state of the power conversion system. The controller automatically switches between a first compensation control signal and a second compensation control signal according to whether the system is in normal operation state or wind free state, making the control system adaptive to varying conditions rather than using a fixed single signal approach
Solution Approach 2:
The patent changes the compensation control parameters based on operating conditions. By detecting the power factor or active power level, the system adjusts which compensation signal is applied, effectively changing the control parameters to match the current operating state and maintain optimal voltage balancing performance across different scenarios
2Ease of operation
If a single compensation control signal is used for all operating conditions, then the control method remains simple, but the adaptability to different power conversion states deteriorates
Solution Approach 1:
The control method dynamically adapts by automatically selecting different compensation signals based on detected operating conditions. The controller monitors system state (normal operation or wind free) and switches compensation strategies accordingly, providing adaptability without requiring complex manual intervention or reconfiguration
Solution Approach 2:
The patent segments the compensation control into distinct modes: a first compensation control signal for normal operation state and a second compensation control signal for wind free state. This segmentation allows each signal to be optimized for its specific operating condition while maintaining overall system simplicity through automated selection
3Reliability
If different compensation control signals are used for different operating states, then the voltage balancing performance is improved, but the device complexity increases
Solution Approach 1:
The controller is designed with multi-functionality, capable of implementing both the first compensation control signal and the second compensation control signal within a single device. This universal controller can detect operating states and automatically select the appropriate compensation strategy, achieving improved voltage balancing performance without requiring separate control systems for different operating conditions
Data Source
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AI summary
A control system 100 includes a fundamental control unit 130, first and second compensation control units 110, 120, a switch control unit 140, and a switch implementation unit 150. The fundamental control unit 130 generates fundamental commands to implement fundamental power conversion operation for a converter. The first compensation control unit 110 generates a first compensation signal for injection into the fundamental command to balance neutral point voltage when the converter is in operation in a first state. The second compensation control unit 120 generates a second compensation signal for injection into the fundamental command to balance neutral point voltage when the converter is in operation in a second state. The switch control unit 140 detects first and second states of the converter and provides first and second switch signals respectively. The switch implementation unit 150 switches the fundamental control unit to communicate with the first and second compensation control units according to the first and second switch signals respectively.