Virtual Synchronous Generator Power Converter Control
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Solution Overview
Problem
Power converters used in distributed power supply systems face complexity in control circuits due to differential equations like Park's equation, and PLL circuits are susceptible to time lag and voltage variations, leading to potential system instability and operational disruptions.
Innovation Solution
A power converter design that operates as a virtual synchronous generator, using an AVR model, governor and driving source model, and algebraic expressions to control power conversion units without a PLL circuit, allowing continuous operation through arithmetic operations that stabilize the system and maintain synchronization with the power grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a PLL circuit is used to detect system frequency, then frequency detection capability is provided, but control time lag and susceptibility to voltage variations occur leading to system instability
Solution Approach 1:
The patent removes the PLL circuit from the control system entirely. Instead of using PLL for frequency detection, the invention uses a virtual synchronous generator model that inherently maintains synchronization through its control architecture, eliminating the source of instability while preserving frequency detection capability through alternative means.
Solution Approach 2:
The patent creates a virtual copy of synchronous generator characteristics through control algorithms. By modeling the dynamic behavior of a synchronous generator in software (virtual synchronous generator), the system achieves genuine synchronization capability without requiring physical PLL hardware, thereby eliminating PLL-related instability issues.
2Reliability
If Park's equation is used in the generator model, then accurate power generator dynamics are simulated, but control circuit complexity increases
Solution Approach 1:
The patent uses algebraic expressions to create a simplified mathematical model that copies the essential characteristics of synchronous generator operation. This virtual model achieves adequate simulation accuracy for control purposes without requiring the complex differential equations of Park's transformation, thereby reducing control circuit complexity while maintaining functional equivalence.
3Device complexity
If a simplified generator model using phasor diagram is used, then control system complexity is reduced, but response time adjustment and expertise requirements increase
Solution Approach 1:
The virtual synchronous generator model incorporates self-adjusting characteristics that automatically adapt to system conditions. The control algorithm inherently manages response time parameters without requiring manual adjustment or expert intervention, as the virtual model naturally responds to frequency and voltage variations through its designed control logic.
Data Source
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AI summary
Provided is a power converter not using a PLL circuit for use in detecting a system frequency and capable of continuous operation regardless of a variation in system voltage or frequency. The power converter includes: a power conversion unit (3) configured to convert DC power inputted thereto into AC power; and a control unit (12) configured to control the power conversion unit 3 such that the power conversion unit (3) operates as a virtual synchronous generator. The control unit (12) includes: an AVR model unit (70) configured to perform arithmetic operation to obtain an induced voltage of the virtual synchronous generator; a governor and driving source model unit (80) configured to perform arithmetic operation to obtain a driving torque driving the virtual synchronous generator; a power generation torque arithmetic operation unit (40) configured to perform arithmetic operation to obtain a power generation torque of the virtual synchronous generator; a rotation angle arithmetic operation unit (50) configured to perform arithmetic operation based on at least an acceleration torque and inertia of a rotor of the virtual synchronous generator to obtain a rotation angle of the rotor; a voltage d-q conversion unit (60) configured to perform arithmetic operation with use of the rotation angle of the rotor to obtain a d-axis component and a q-axis component of an output voltage; and a generator model unit (30) configured to perform arithmetic operation, with use of an algebraic expression that is specified by a phasor diagram representing a relationship among an induced voltage, a phase voltage, and a line current of a synchronous generator, to obtain a d-axis current command value and the q-axis current command value corresponding to a d-axis component and a q-axis component of an armature current of the virtual synchronous generator.