Abstract
There are contradictions between the steady-index and dynamic characteristics of active power responses, when virtual synchronous generator (VSG) is connected to grid as a PQ source. The concept of virtual power was proposed for explaining the physical meaning of the control parameters in this paper. Furthermore, the amplitude-frequency characteristics of virtual power were analyzed and corrected to improve system characteristics, and a general expression of improved VSG control scheme is demonstrated. Afterward, the related control parameters were analyzed and designed for a specific case, and the implement steps were conducted. Finally, the effectiveness of the proposed control method was verified.
Highlights
As the penetration rate of renewable energy increases, the inertia of the power grid decreases
The primary frequency and voltage regulation function are realized by droop control, and the rotor inertia is simulated through virtual inertia link
When virtual synchronous generator (VSG) is connected to the power grid in PQ mode, the requirements of dynamic and steady characteristics of active power responses are not met at the same time
Summary
As the penetration rate of renewable energy increases, the inertia of the power grid decreases. Derived from (19), the closed-loop small signal transfer function of active power can be expressed as It can be seen from formula (21) that the improved VSG control strategy adds a pair of closed-loop poles and two zeros generated by the modification of damping power and inertia support power, respectively. It can be seen from the bode-plot, the improved VSG eliminates the resonance peak, and obtains a higher system gain in transient band. Step5) repeat Step 3 and Step 4 to meet the demand of system (n ≥ m) [28]
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