Frequency Droop Research Articles

A Wireless Controller to Enhance Dynamic Performance of Parallel Inverters in Distributed Generation Systems

This paper presents a novel control strategy for parallel inverters of distributed generation units in an AC distribution system. The proposed control technique, based on the droop control method, uses only locally measurable feedback signals. This method is usually applied to achieve good active and reactive power sharing when communication between the inverters is difficult due to its physical location. However, the conventional voltage and frequency droop methods of achieving load sharing have a slow and oscillating transient response. Moreover, there is no possibility to modify the transient response without the loss of power sharing precision or output-voltage and frequency accuracy. In this work, a great improvement in transient response is achieved by introducing power derivative-integral terms into a conventional droop scheme. Hence, better controllability of the system is obtained and, consequently, correct transient performance can be achieved. In addition, an instantaneous current control loop is also included in the novel controller to ensure correct sharing of harmonic components when supplying nonlinear loads. Simulation and experimental results are presented to prove the validity of this approach, which shows excellent performance as opposed to the conventional one.

Análise para pequenos sinais de um sistema ca composto de inversores conectados em paralelo

Este trabalho mostra a análise de estabilidade para pequenos sinais de um sistema CA composto de vários inversores de tensão conectados em paralelo sem a presença de uma barra infinita. O controle de cada unidade inversora é baseado nas curvas características frequência versus potência ativa e tensão versus potência reativa, o qual não depende da comunicação entre as respectivas unidades de controle. Os resultados de simulação e experimentais comprovam a eficácia do modelo para pequenos sinais, facilitando os estudos de estabilidade do sistema.

Small-signal stability for parallel-connected inverters in stand-alone AC supply systems

This paper presents a small-signal analysis for parallel-connected inverters in stand-alone AC supply systems. The control technique of the inverters is based on frequency and voltage droops, which depends on the local variable measurements and does not need control interconnections. Simulation and experimental results show that the system is well represented by the small-signal model. Some root locus plots for the system are provided, which make the stability studies and design easier.

96/1649 Optimal dynamic load shedding using a Newton based dynamic algorithm

Compared with frequency regulation by wind generation system, a battery energy storage system (BESS) is a better alternative for providing frequency regulation and inertial response in a faster, more accurate and flexible manner. So, participation of BESS in an islanded microgrid frequency regulation can assist renewable distributed generators (DGs) in operating at their maximum efficiency without excessive power curtailment. Furthermore, a BESS can mitigate the frequency variation with a faster response when the frequency disturbance occurs in an islanded microgrid. If the energy capacity of the BESS is limited, a wind turbine generator can gradually take over the mid-to-long term frequency regulation tasks through emulated droop response and Automatic Generation Control (AGC) control.In this chapter, we will focus on the coordinated frequency regulation and control of BESSs and wind power in the islanded mode of microgrid or microgrid cluster. The objective of microgrid frequency regulation is to regulate the frequency of an islanded microgrid to the specified nominal value in the event of frequency disturbance, and at the same time to maintain the tie-line power interchange among different microgrids within a microgrid cluster, or between two virtual areas within a single islanded microgrid at the scheduled value by coordinating the outputs of wind power generation and BESS through virtual inertial response, frequency droop control and load frequency control.