A Modified Droop Control for Grid-Connected Inverters With Improved Stability in the Fluctuation of Grid Frequency and Voltage Magnitude

Abstract

The droop controlled grid-connecting inverter (DC-GCI) has been widely used in microgrid (MG). However, the power flow of the droop control is very sensitive to the fluctuation of grid frequency and voltage magnitude, which will result in a very fast inrush current of DC-GCI. Owing to the linear relationship of P-F, current limiters are required to prevent DC-GCI output power from exceeding maximum power. However, the impact of grid frequency fluctuation on DC-GCI cannot be mitigated by the current limiter for the reason that the fluctuation will lead to the current limiter saturation, which will cause the error between the angular frequency of the P-F droop output and the angular frequency of the grid voltage, and the system becomes unstable. It is a challenge to limit the output current, meanwhile ensuring the stable operation of the DC-GCI. To solve these problems, a modified droop control strategy is proposed to mitigate the impacts of the fluctuation of grid frequency and voltage magnitude on the system stability. In addition, the proposed control strategy in this paper realizes the stable operation of the DC-GCI through the cooperation between the modified droop control and the current limiter, and the current limiter saturation is avoided. The current limiter is used to restrain the transient current to compensate for the slow bandwidth of the droop loop, and the modified droop loop is used to stabilize output power and restrain the steady-state output current. The simulation and experimental results from a scaled-down laboratory prototype have been presented to verify the major contribution of this paper.

Flexibility Services Provision by Frequency-Dependent Control of On-Load Tap-Changer and Distributed Energy Resources

“…The benefits of coordinated photovoltaic (PV) inverter control with centralised coordination of PV active power curtailment, when compared to autonomous droop control, were presented in [9], in order to increase PV hosting capacity and reduce network losses. Lastly, in [10] a modified droop control strategy was proposed to mitigate the frequency and voltage oscillation impacts on the power system's stability.…”

Parameter Adjustment for the Droop Control Operating a Discharge PEC in PMG-Based WECSs With Generator-Charged Battery Units

“…In general, grid-connected power electronic converters (PECs) are operated by nested control loops, which are an inner current control loop and an outer voltage control loop. The reference voltage for the outer control loop is generated by a droop controller, while the reference current vector is generated by voltage controller [2]- [4]. The reference current is typically limited based on the power ratings of the PEC, in order to avoid saturation of the current control loop.…”

“…The reference current is typically limited based on the power ratings of the PEC, in order to avoid saturation of the current control loop. The saturation in the current control loop can be a result of grid-side frequency dynamics [4]. A small signal state space model of a gridconnected PEC has been developed, and has been used to design various current/voltage controllers without employing droop FIGURE 1.…”

A unified distributed robust control framework for power sharing of grid‐connected dispatchable distributed generator cluster

“…, and 1 N be an N dimensional column vector with every entry being one. Then (14) and (15) can be rewritten into the following compact forṁ=…”

“…The droop control method was applied for microgrids in grid-connected mode. [13][14][15][16] Note that the key to the success of droop control lies in that there is no dominating frequency or voltage magnitude in the system when the droop characteristics are applied for power sharing. However, for grid-connected mode, the frequency and voltage magnitude of the microgrid at the point of common coupling are clamped by the stiff main grid.…”