Single-Phase Power Converter Virtual Synchronous Generator Control
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Solution Overview
Problem
Conventional power conversion devices with PLL circuits are not suitable for single-phase systems, as they are designed for three-phase systems and fail to ensure stable self-sustained operation when applied to single-phase systems due to varying system frequencies.
Innovation Solution
A power conversion device with a control system that includes a voltage measurer to estimate angular velocity and phase, a power obtainer to calculate active and reactive power, a governor model to calculate phase differences, an AVR model to calculate induced voltage, and a current controller to generate PWM signals, allowing the device to operate as a virtual synchronous generator and perform self-sustained operation in single-phase systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional PLL circuit designed for three-phase systems is applied to a single-phase system, then the circuit configuration is simplified, but stable self-sustained operation cannot be achieved due to varying system frequencies
Solution Approach 1:
The patent changes the fundamental operating parameters of the frequency detection circuit by replacing the conventional PLL with an estimation operation that uses phase as a parameter. This allows the circuit to properly respond to varying system frequencies in single-phase self-sustained operation, resolving the contradiction between circuit simplicity and operational stability
Solution Approach 2:
The patent applies a frequency detection method originally developed for three-phase virtual synchronous generator control to the single-phase system. By copying and adapting the estimation operation approach from three-phase applications, the invention achieves stable single-phase self-sustained operation without requiring a completely new circuit design
2Device complexity
If a frequency detection circuit assuming constant system frequency is used, then the circuit design is simplified for grid-interconnected operation, but it cannot respond to variations in system frequency during self-sustained operation
Solution Approach 1:
The patent implements a dynamic frequency detection approach where the system continuously estimates angular velocity and phase based on current system conditions rather than assuming a constant frequency. The estimation operation dynamically adjusts to frequency variations, allowing the circuit to adapt to both grid-interconnected and self-sustained operation modes
Solution Approach 2:
The frequency detection circuit is designed with universal applicability by using an estimation operation that works for both constant and varying frequency conditions. This multi-functional approach allows the same circuit to serve both grid-interconnected operation (where frequency is relatively stable) and self-sustained operation (where frequency varies), eliminating the need for separate detection circuits
Data Source
AI summary
A power conversion device includes: a power converter to perform output to an output line connected to a single-phase power system; and a control device to control the power converter so it operates as a virtual synchronous generator. The control device includes: a voltage and current measurer to obtain, from a single-phase system voltage, an angular velocity and a phase of the system voltage by an estimation operation that uses the phase of the system voltage as a parameter; a power obtainer to obtain active power and reactive power; a governor model to calculate a phase difference; an AVR model to calculate an absolute value of an induced voltage of a virtual synchronous generator; a generator model to calculate current command values corresponding to an armature current of the virtual synchronous generator; and a current controller to generate and output a PWM signal to the power converter.