Virtual Synchronous Generator Inverter Control for Grid Stability
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Solution Overview
Problem
Existing inverter systems cannot control voltage frequency based on a synchronous generator model, limiting their ability to stabilize systems against load variations when converting DC power to AC power synchronized with a bus frequency.
Innovation Solution
A command generation device that calculates the rotation speed of a virtual generator using a rotor model, determines target active and reactive power values, and generates control commands for the inverter to stabilize the system by simulating the driving of a virtual generator, including a rotation target determination unit, a function update unit, and a drive torque calculation unit to adjust the droop function and drive torque accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the inverter uses a phase lock loop (PLL) circuit to synchronize AC power output with bus voltage frequency, then the inverter can generate AC power in synchronization with the bus, but the voltage frequency cannot be controlled on the basis of the synchronous generator model
Solution Approach 1:
The patent creates a virtual synchronous generator model that copies the dynamic characteristics and control behavior of a real synchronous generator. This virtual model includes simulated rotor dynamics, governor control, and AVR control, allowing the inverter to emulate generator-like frequency and voltage regulation without physically controlling the bus frequency through the PLL circuit.
Solution Approach 2:
The patent changes the control parameters by introducing virtual physical quantities (rotation speed, drive torque, field voltage) that do not physically exist in the inverter system but are calculated based on the synchronous generator model. These parameter changes enable the inverter to control active and reactive power output while maintaining synchronization through PLL, effectively decoupling frequency control from direct bus frequency manipulation.
2Reliability
If the inverter controls active power and reactive power based on the synchronous generator model, then the system stability is improved, but the device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent replaces the need for physical synchronous generator hardware with a virtual model implemented through software control algorithms. The virtual generator model, governor, and AVR are realized through computational calculations of virtual physical quantities, substituting complex mechanical systems with electronic control mechanisms that achieve the same stability functions.
Solution Approach 2:
The patent introduces virtual physical quantities as intermediary variables between the inverter's power output and the grid. These virtual quantities (rotation speed, drive torque, field voltage) serve as mediators that translate power control objectives into generator-like behavior, enabling stable active and reactive power control without direct mechanical connection to a synchronous generator.
3Reliability
If the inverter emulates the governor and AVR functions of a synchronous generator, then the system can be stabilized against load variations, but the ease of operation decreases due to complex control requirements
Solution Approach 1:
The patent makes the inverter multi-functional by enabling it to perform both power conversion (DC to AC) and system stabilization functions simultaneously. The virtual synchronous generator model allows the inverter to provide inertia, frequency regulation, and voltage support typically associated with generators, while maintaining its primary function of power conversion, thereby simplifying overall system operation.
Solution Approach 2:
The inverter with virtual synchronous generator capability becomes self-sufficient in providing system stabilization services. Instead of requiring external generator units or complex coordination with other devices, the inverter independently calculates and adjusts its active and reactive power output based on virtual physical quantities, enabling it to stabilize the system against load variations autonomously.
Data Source
AI summary
A rotation calculation unit calculates a rotation speed of a virtual generator on the basis of a rotor model to simulate driving of the virtual generator and calculates the rotation speed of the virtual generator. A target power determination unit determines target values of active power and reactive power of an inverter on the basis of the calculated rotation speed. A command generation unit generates a control command for the inverter on the basis of the determined target values of the active power and the reactive power.