Power Converter Control for Microgrid Mode Switching
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Solution Overview
Problem
Current electric power converters, either current control type or voltage control type, face limitations in performing both self-sustaining and interconnected operations in micro grids and stand-alone power systems, requiring high-capacity prime movers and unstable voltage and frequency control, especially when switching between these modes.
Innovation Solution
An electric power converter with a PWM control unit and measuring units, which calculates and sets a virtual internal impedance to stabilize output current, allowing for both self-sustaining and interconnected operations without changing control methods, using a combination of active and reactive power control loops and phase-locked loop calculations for voltage and frequency management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the control method is changed when switching between self-sustaining and interconnected operations, then the operational requirements are met, but the device complexity increases
Solution Approach 1:
The electric power converter is designed with universal control capabilities that can perform both current control and voltage control functions using a single integrated control unit. This multi-functional control architecture eliminates the need for separate control systems for different operational modes, reducing overall device complexity while maintaining operational flexibility.
Solution Approach 2:
The electric power converter dynamically switches between current control mode (for interconnection operation) and voltage control mode (for self-sustaining operation) based on system conditions. The control unit determines the operational mode and adjusts control parameters accordingly, enabling the converter to adapt its control characteristics to match the required operational state.
2Reliability
If high-capacity prime movers are used to maintain voltage and frequency stability, then the stability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent replaces the traditional mechanical prime mover-based voltage and frequency control system with an electric power converter that uses electronic control (PWM control unit, control unit with processing capabilities) to regulate output voltage and frequency. This substitution eliminates the need for high-capacity mechanical prime movers while achieving the same stability objectives through electronic regulation and control algorithms.
Solution Approach 2:
The converter changes its control parameters (control mode, impedance characteristics) based on operational requirements. In interconnection mode, it operates as a current control type converter with controlled output current; in self-sustaining mode, it operates as a voltage control type converter with regulated output voltage and frequency, thereby achieving both operational capabilities through parameter transformation.
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
Enables stable operation in micro grids and stand-alone systems by maintaining voltage and frequency stability without the need for high-capacity prime movers, allowing seamless switching between self-sustaining and interconnected modes, and improving handleability and responsiveness.
Implementation Method 1
an electric power conversion circuit (6) having a switching element which is turned on and off by a PWM control unit (16)
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present invention provides an electric power converting unit that does not require a change in a control method in, for example, system interconnection by calculating a target value of an output current of an electric power converter from an internal phase angle calculated from an active electric power control loop and an internal electromotive voltage calculated from a reactive electric power control loop. Thus, a stand-alone power supply system that is easy to handle can be configured.