Comparative Study of Control Strategies for Stabilization and Performance Improvement of DC Microgrids with a CPL Connected

Abstract

The DC microgrid system is composed by converters that operate like feeders and loads. Among these loads, we highlight the constant power loads (CPLs) that may cause instability in the microgrid, observed in the form of undesired oscillations due to its negative impedance behavior. Therefore, this work proposes to use performance indices and stability margins to evaluate state and output feedback control strategies for stabilization of DC microgrids. In particular, it is proposed to evaluate the stability margin of the proposed methodologies by means of the impedance relations in the microgrid based on the Middlebrook criterion. Our simulations and tests showed the relation between the performance and stability degradation and the microgrid impedances variation.

Comparação de técnicas de controle via LMI aplicadas em microrredes CC com CPL

“…Uma micro rede CC pode ser representada pelo uso de dois conversores buck-buck em cascata (Figura 1). O primeiro conversor é responsável por ajustar o nível de tensão da fonte com o barramento, podendo ser visto como um alimentador com uma carga resistiva R conectada ao barramento que ajuda no amortecimento do sistema, já o segundo conversor é visto como uma carga que também compõe o sistema (Bessa et al, 2020)…”

“…Para ajustar o nível de tensão das fontes e cargas ao nível do barramento CC é necessário o uso de diversos conversores. Aqueles usados para adequar o valor de tensão entregue as cargas são estritamente controladas, apresentando a característica de carga de potência constante (CPL), que podem levar o sistema a instabilidade devido seu efeito de impedância negativa (Bessa et al, 2020).…”

Voltage Regulation of an Isolated DC Microgrid with a Constant Power Load: A Passivity-based Control Design

“…Therefore, when only a BES is used in the system, the greatest challenge is to design a controller to improve the desired performance without neglecting the battery interaction during the mode transitions in order to preserve its lifespan [14][15][16]. However, some types of loads connected on the DC link can produce a negativeimpedance effect, generating system instability and loss of regulation on the feeder system [3,17,18]. Moreover, other effects such as high stress and temperature rise in power converter elements may occur, reducing its performance and lifetime [19].…”

“…To solve the aforementioned problems produced by CPLs, different approaches have been proposed in the existing literature. These approaches are based on system modification by adding passive elements to minimize these effects or by a control action designed to damp oscillations [18], such as active damping [23], backstepping [6], and feedback linearization [24], among others.…”