Abstract
Hierarchical linear control scheme is widely used in ac microgrids. However, its transient response is slow and parameter tuning is time-consuming. Finite Control Set-Model Predictive Control (FCS-MPC) strategy has desired dynamic performance. Nevertheless, it requires an additional sensor to measure the inductor current. This article aims to mitigate these problems by introducing an improved FCS-MPC strategy for paralleled Voltage Source Inverters (VSIs). A capacitor current estimator is employed to reduce the extra current sensor in each VSI. The proposed control scheme consists of two loops: voltage reference generation loop and voltage tracking loop. The voltage reference generation loop achieves accurate load power sharing using virtual impedance-based droop control. Thus, communication is unnecessary among parallel VSIs. The voltage tracking loop utilizes a modified FCS-MPC block with capacitor current estimator to regulate the VSI output voltage. In order to verify the concept of the proposed control strategy, an ac microgrid consisting of two paralleled VSIs is implemented in dSPACE DS1202 hardware-in-the-loop platform. Then a single VSI hardware prototype is implemented and tested experimentally. The proposed method has the merits of good extensibility, low system cost and compact structure. Its steady-state performance is competitive with hierarchical linear control, while the transient response is significantly improved.
Highlights
Microgrid is an emerging technology for energy distribution systems due to its compatibility with renewable energies [1]–[3]
To validate the concept of the proposed control scheme, HIL simulations for an ac microgrid consisting of two parallel Voltage Source Inverters (VSIs) and experiments for one VSI system are carried out
The average switching frequencies of the converters are equal for hierarchical linear method and the Finite Control Set-Model Predictive Control (FCS-model predictive control (MPC)) method
Summary
Microgrid is an emerging technology for energy distribution systems due to its compatibility with renewable energies [1]–[3]. The ac microgrid can operate in both grid-connected and islanded modes. In order to ensure stable and economic operation of the microgrid, the real and reactive powers of DGs should be split in proportion to their power rating [7]. Droop control can realize the power sharing control without external communications among different voltage source. In [9], a power derivative term is added into conventional droop. It helps to improve the transient response in power sharing between inverters. In [10], [11], adaptive virtual impedance is proposed to improve the accuracy of reactive power sharing with nonlinear loads. In [12], by combining the virtual impedance and conventional droop control, the load powers can be shared with mismatched line impedances.
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