Virtual Synchronous Generator and Harmonic Suppression Control in a Solid-State Transformer

The incorporation of distributed generators (DG) to the electrical power system (EPS) has been increasing worldwide. The expectation is that this growth will continue to be observed in coming years due to the popularization of solar photovoltaic energy, which is the most used renewable source in DG. In a scenario of high DG penetration in the EPS, the total rotational inertia of the system would be reduced given that the DG sources are non-inertial, such as, for example, the large synchronous generators (SG) of hydroelectric plants. An alternative to overcome this lack of inertia is to use a control strategy in the inverters at the interface with the EPS such that the EPS perceives the DG system as a SG. This control strategy is called a virtual synchronous generator (VSG). This work aimed to apply a VSG to a solid state transformer (SST) as well as implement and compare two harmonic suppression methods: a linear active disturbance rejection control (LADRC) and an impedance reshaping method, with the purpose of reducing the total harmonic distortion (THD) of the inverter’s output voltage when a nonlinear load is connect to the SST. Real-time digital simulations (RTDS) were carried out with the hardware Typhoon HIL 402 and it was observed that both harmonic suppression methods succeeded in reducing the THD of the output voltage and the VSG control successfully provided virtual inertia to the system.

I. Introduction

Renewable energy sources (RES) have been widely used to generate electricity, especially in DG systems and, because of that, RES are expected to make up a great portion of the future global energy matrix. Given that, it is necessary further studies on how a massive penetration of RES to the EPS would affect the system and its stability [1]. According to [2], a penetration level of photovoltaic (PV) generation higher than 20% may cause stability problems, so it is important to address this problem and come up with measures to overcome this limitation on the penetration level, thus enabling the continuous integration of DG to the grid.