Power Converter Control Mode Switching in Microgrids
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Solution Overview
Problem
Current power converting apparatuses in self-supported power supply systems, such as microgrids, face challenges in maintaining stable voltage and frequency when switching between single-sustained and linkage operations, and in handling load fluctuations, due to limitations in current control type and voltage control type systems.
Innovation Solution
A power converting apparatus with a voltage measuring device and frequency obtaining device, along with measuring and control devices for active and reactive power, allows for closed-loop control of electricity storage facilities, enabling them to function as both current and voltage control systems, and compensating for load fluctuations using feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current control type power converting apparatus is used in a self-supported power supply system, then the apparatus can operate independently without commercial power system connection, but the system cannot maintain stable voltage and frequency when switching between single-sustained and linkage operations
Solution Approach 1:
The power converting apparatus dynamically switches between current control mode and voltage control mode based on operational requirements. The controller adapts the control strategy in real-time: using current control during linkage operations with commercial power systems, and switching to voltage control during single-sustained operations to maintain stable voltage and frequency. This dynamic adaptability resolves the contradiction between operational versatility and stability maintenance.
Solution Approach 2:
The control parameters of the power converting apparatus are changed based on the operational mode. When transitioning from linkage operation to single-sustained operation, the controller switches from current control parameters to voltage control parameters, adjusting the control variables to maintain stable voltage and frequency output. This parameter adaptation enables the system to handle different operational conditions while maintaining stability.
2Stability of the object's composition
If a voltage control type power converting apparatus is used to maintain stable voltage and frequency, then the system can operate independently, but the apparatus cannot handle abrupt load fluctuations effectively
Solution Approach 1:
The power converting apparatus incorporates feedback control mechanisms that continuously monitor output voltage, frequency, and load conditions. When load fluctuations occur, the feedback system detects the changes and adjusts the control parameters in real-time to maintain stable voltage and frequency. This feedback loop enables the voltage control type apparatus to handle abrupt load fluctuations effectively while maintaining stability.
Solution Approach 2:
The control system dynamically adjusts its response based on detected load conditions. When abrupt load fluctuations are detected, the controller transitions to a more aggressive control strategy with faster response characteristics. This dynamic adjustment of control behavior enables the apparatus to handle load fluctuations effectively while maintaining voltage and frequency stability during normal operations.
3Reliability
If separate control systems are used for current control and voltage control operations, then each control type can be optimized, but the system complexity increases when switching between operation modes
Solution Approach 1:
The power converting apparatus uses a single unified controller that can perform both current control and voltage control functions. This multi-functional controller integrates both control strategies within one device, eliminating the need for separate control systems. The controller automatically selects and implements the appropriate control mode based on operational requirements, maintaining optimized control performance while reducing overall system complexity.
Solution Approach 2:
The control functions for current control and voltage control are merged into a single integrated control system. This combination allows the apparatus to switch between operation modes without requiring separate control hardware or complex coordination between independent control systems. The unified controller simplifies the system architecture while maintaining the ability to provide optimized control for each operational mode.
Data Source
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AI summary
A power converting apparatus, in which when a single-sustained operation is switched into a linkage operation in a combined power generation system such as a microgrid, a control system does not have to be changed, is provided. The apparatus includes a first internal phase difference angle calculator (60) for integrating a deviation between a first frequency command value and a frequency obtained by a frequency obtaining device (14) so as to calculate a first internal phase difference angle, a first internal electromotive voltage command value calculator (50) for proportioning and calculating a deviation between a first reactive power command value and a reactive power obtained based on the value measured by the first measuring device (3, 4), and adding a reference voltage to the deviation so as to calculate a first internal electromotive voltage command value, and a first current command value calculator (70) for calculating a command value of an output current from a first power converter (6) based on the first internal phase difference angle, the first internal electromotive voltage command value, and a voltage measured by the voltage measuring device (4). The apparatus controls the first power converter (6) based on an output from the first current command value calculator (70).