In this paper, a novel distributed active power control method for interlinking converters (ICs) in an islanded hybrid ac/dc microgrid (IHMG) is proposed. The goal is to implement power sharing among all distributed generators (DGs) in an IHMG and among the ICs in a distributed manner, without the need for additional proportional-integral controllers. A mathematical formula for the active power references of the ICs is derived to achieve these objectives. Then, an estimator providing the data required for the reference calculation is proposed based on the modified dynamic consensus algorithm. In addition, a unified state-space model is derived for the entire IHMG, including the cyber-physical interactions, and a design method is presented for the parameters of the estimator. Finally, the effectiveness of the proposed method is verified by performing small-signal analysis and controller-hardware-in-the-loop verification. Compared to a previous distributed control method, the proposed method significantly improves the robustness in terms of communication delay and variation in the status of DGs while achieving the objectives.

We propose a new local controller to determine the active power reference for an interlinking converter (IC) of an islanded hybrid ac/dc microgrid (IHMG). The main objective of the proposed method is to improve the accuracy of global power sharing (GPS) between distributed generators throughout an IHMG to enhance the reliability and stability. Based on our analysis of the required active power of ICs for GPS, a local IC controller is proposed to enable parallel IC operation and improve GPS. The effects of the proposed controller on the system stability and GPS accuracy are also analyzed using a small-signal model. Furthermore, we provide guidelines on how to determine an appropriate control parameter for the proposed controller based on the desired GPS accuracy and the stability margin. Finally, the proposed method is verified by Simulink/MATLAB and hardware-in-the-loop experimental platform.

In this paper, a new control method for a line-commutated converter-based (LCC) high-voltage direct current (HVDC) system to support the frequency and AC voltage was proposed. For coordinated control of the inverter and rectifier, droop-based controllers are adopted for the outer loop of conventional controllers, and DC voltage is used to transfer the frequency information so that communication is not required. A method to determine the droop constants of the proposed controller is presented to emulate the conventional f/P droop characteristic and suppress the AC voltage fluctuations. Furthermore, a small-signal state-space model of the LCC HVDC system with the proposed scheme is derived, and root locus analysis is carried out to evaluate its stability. The effects of the proposed method are verified based on case studies, using the well-known CIGRE BENCHMARK model. The advantages of the proposed method can be summarized as follows: 1) system reliability is enhanced because there is no risk of communication failure during frequency information transfer and 2) voltage stability at the inverter side is enhanced as AC voltage fluctuation during frequency support is minimized.

We present a new reactive power control method for hybrid high-voltage direct-current (HVDC) systems that features a line-commutated converter-based (LCC) rectifier and a voltage-sourced converter-based (VSC) inverter. Our principal objective is to regulate the reactive power of the LCC rectifier side via co-operative control of the DC voltage and switched shunt devices (SSDs) such as capacitors and reactors. To achieve these objectives, we used three operative modes: reactive power, voltage, and power factor control. For each mode, we show how to determine the DC reference voltage. Also, to maintain the voltage within operational bounds and enhance the range over which reactive power is controllable, our method features the cooperation of SSDs. Furthermore, we show how to determine the required SSD capacities. MATLAB and PSCAD simulations confirmed that our method improves reactive power controllability at the LCC rectifier side of a hybrid HVDC system.