Virtual Synchronous Generator Impedance Peak Compensation
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Solution Overview
Problem
Virtual synchronous machines exhibit impedance characteristics that deviate from those requested by grid operators, leading to resonance issues and low damping in certain frequency ranges.
Innovation Solution
A method for controlling power generating units, such as wind turbines, involves obtaining capacitor voltage signals, determining virtual synchronous machine rotational speed and synchronous machine angle, and using a compensation filter to reduce the magnitude and shift the impedance peak, thereby eliminating or reducing resonance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a capacitive harmonic filter is used in the virtual synchronous machine, then the power generating unit can effectively filter harmonic currents, but the impedance spectrum exhibits extreme high impedance peaks and low damping at resonance frequencies
Solution Approach 1:
The patent introduces an impedance compensation device as an intermediary component connected in parallel with the capacitive harmonic filter. This device acts as a mediator that counteracts the harmful impedance characteristics of the filter by providing compensating inductance and resistance, thereby reducing impedance peaks and improving damping without eliminating the filter's harmonic filtering capability
Solution Approach 2:
The patent modifies the impedance characteristics by changing the parameters of the compensation device (inductance Lc and resistance Rc) to specifically target and counteract the resonant frequency and impedance peaks of the capacitive filter, transforming the overall impedance spectrum to meet grid requirements
2Device complexity
If the virtual synchronous machine uses conventional impedance characteristics, then the control is simpler, but the impedance spectrum deviates from grid operator requirements
Solution Approach 1:
The impedance compensation device serves as an intermediary that bridges the gap between conventional simple control and grid-compliant impedance characteristics, allowing the use of straightforward control algorithms while achieving the required impedance spectrum through the passive compensation network
Solution Approach 2:
The patent separates the impedance characteristic improvement into a distinct functional module (the compensation device with Lc and Rc components) that can be independently designed and tuned, allowing the main control system to remain simple while the impedance profile is shaped by the dedicated compensation segment
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The invention relates to a method for controlling a power generating unit such as a wind turbine which is configured as a virtual synchronous machine. Capacitor voltage signals obtained from voltage measurements of output capacitors are filtered in order to reduce a magnitude of an impedance peak and/or shift the impedance peak where the impedance peak is present in an impedance characteristic of the output of the power generating unit. Filter compensated voltage signals obtained from the output capacitors are combined with a voltage magnitude reference to obtain filtered capacitor voltage signals used for controlling the line side converter and thereby affect the impedance peak in a desired way.