Microgrid Power Control Research Articles

Power control in microgrid using improved virtual impedance method

AbstractIn this article, a method is proposed to increase the accuracy of reactive power‐sharing for parallel‐connected inverters in Microgrid, this method is done by automatically adjusting the values of the virtual impedance to adjusting the output voltage of the inverters. The virtual impedances are automatically adjusted to compensate for the difference in the output voltage of the inverters due to the influence of the line impedances. The output voltage of the inverters will be adaptively adjusted according to the change of the load, this method greatly improves the accuracy in the reactive power sharing The correct power sharing for the inverters will ensure the stability of voltage and frequency in the Microgrid. The control method is simple and does not need to know the line impedance parameter. The feasibility and effectiveness of the proposed strategy are proven by simulation and experimental results.

Island microgrid power control system based on adaptive virtual impedance

When the microgrid is in the islanding operation mode, affected by the line impedance difference between the distributed power sources (DGs), the traditional droop control strategy will lead to the fact that the reactive power of the system cannot be reasonably distributed according to the droop gain, which makes the power grid prone to failure. To solve this problem, an improved sag control strategy based on adaptive virtual impedance is proposed in this paper. The central controller calculates the given power according to the capacity of each inverter and the total load capacity of the line, and then sends it to each inverter, and the inverter determines the value range of the virtual impedance according to the given reactive power. A voltage compensation link is added to the control strategy to compensate for the voltage drop difference caused by the line impedance difference, thereby ensuring the stability of the output power and realizing the power control of the microgrid. The MATLAB/Simulink simulation platform was built to establish the microgrid simulation model in island mode. The simulation results show that when the inverters with the same capacity are connected in parallel, the output active power is the most stable, and the reactive power maintains an equalized state; When inverters of different capacities are connected in parallel, the output active power takes the shortest time to stabilize, and the reactive power basically matches the rated capacity ratio. Therefore, it is fully demonstrated that this method has a good control effect on the power control and operation of the islanded microgrid.

Voltage Restoration Control for Microgrid With Recurrent Wavelet Petri Fuzzy Neural Network

This study presents a voltage restoration control (VRC) based on battery energy storage system (BESS), which can be used for both supporting power source and voltage compensation. Voltage restoration is an important task for the power control of microgrid during utility disturbances. One of the disturbances is caused by short circuit on power line of the microgrid, which may lead to voltage sag and even blackout of the microgrid system. To tackle this problem, the recurrent wavelet petri fuzzy neural network (RWPFNN) controller is proposed in this study for the VRC of BESS to provide fast control response to mitigate the transient impact. Moreover, to examine the compliance with the requirements of low voltage ride through (LVRT) of the photovoltaic (PV) plant and investigate the performance of the proposed VRC, the microgrid built in Cimei Island in Penghu Archipelago, Taiwan, is investigated. Furthermore, the PV system, the wind turbine generator (WTG) system and the BESS are connected to the same point of common coupling (PCC) with separated step-up transformers in the microgrid. In addition, the diesel generators provide the main power sources and form the isolated microgrid system. Through the hardware in the loop (HIL) mechanism, which is built using OPAL-RT real-time simulator, with two floating-point digital signal processors (DSPs), the effectiveness of proposed intelligent controllers can be verified and demonstrated.

Fuzzy Logic-Based Direct Power Control Method for PV Inverter of Grid-Tied AC Microgrid without Phase-Locked Loop

A voltage source inverter (VSI) is the key component of grid-tied AC Microgrid (MG) which requires a fast response, and stable, robust controllers to ensure efficient operation. In this paper, a fuzzy logic controller (FLC)-based direct power control (DPC) method for photovoltaic (PV) VSI was proposed, which was modelled by modulating MG’s point of common coupling (PCC) voltage. This paper also introduces a modified grid synchronization method through the direct power calculation of PCC voltage and current, instead of using a conventional phase-locked loop (PLL) system. FLC is used to minimize the errors between the calculated and reference powers to generate the required control signals for the VSI through sinusoidal pulse width modulation (SPWM). The proposed FLC-based DPC (FLDPC) method has shown better tracking performance with less computational time, compared with the conventional MG power control methods, due to the elimination of PLL and the use of a single power control loop. In addition, due to the use of FLC, the proposed FLDPC exhibited negligible steady-state oscillations in the output power of MG’s PV-VSI. The proposed FLDPC method performance was validated by conducting real-time simulations through real time digital simulator (RTDS). The results have demonstrated that the proposed FLDPC method has a better reference power tracking time of 0.03 s along with reduction in power ripples and less current total harmonic distortion (THD) of 1.59%.

Distributed energy grid control method based on collaborative consensus algorithm

In this paper, a distributed energy grid control method based on collaborative consensus algorithm is proposed. Faced with the problem of insufficient control ability of independent power grid, multiple system control objectives are optimized. Moreover, according to the research goal of the consistency algorithm, the Pareto solution of the micro-grid control system is obtained. In addition, the optimized topology includes many categories, corresponding to different optimization goals respectively. Meanwhile, according to the micro-grid power control and voltage recovery studied in this paper, the ring network topology has obvious advantages. Through the simulation results, compared with other topologies, the ring topology has obvious advantages in both convergence and delay robustness, which proves its effectiveness.

Backstepping Predictive Control of Hybrid Microgrids Interconnected by Neutral Point Clamped Converters

In this work, DC and AC parts of hybrid microgrids are interconnected by a neutral point clamped—NPC converter controlled using a new backstepping predictive (BP) method. The NPC converter is controlled to operate in the DC microgrid voltage control mode or in the AC microgrid power control mode. The novel backstepping predictive controller is designed using the dq state space dynamic model of the NPC converter connected to the hybrid microgrid. The designed BP controller regulates the DC voltage or AC injected power, balances the capacitor voltages, controls the AC currents, and enforces the near unity power factor. Simulation (MATLAB/Simulink) and experimental (laboratory prototype) results show that the converter can regulate the DC voltage in the DC microgrid interconnection point, by adjusting the AC power conversion to compensate variations on the loads or on the distributed renewable energy sources in the DC microgrid. AC currents are sinusoidal with low harmonic distortion. The obtained BP controller is faster at balancing capacitor voltages than PWM (pulse width modulation) control with carrier offset. The fast AC power response allows the converter to be used as a primary frequency regulator of the AC microgrid. This research is appropriate for power and voltage control in hybrid microgrids with renewable energy.

Voltage Stabilization Control for Microgrid With Asymmetric Membership Function-Based Wavelet Petri Fuzzy Neural Network

Voltage stabilization is an important task for the microgrid power control. The long transient response of voltage caused by the grid transition from the grid-connected mode to the islanded mode or the power variations would deteriorate the operation of the voltage protective relay. This would lead to the difficulty of integration for the renewable energy and the storage system. To solve this problem, the asymmetric membership function based wavelet petri fuzzy neural network (AMFWPFNN) controller is proposed for the voltage stabilization control of storage system in this paper to provide fast response speed and mitigate the transient impact. To investigate the performance of the proposed microgrid controller and examine the compliance with the settings in IEC Std. 60255, Cimei Island in Taiwan is studied. Through the hardware in the loop (HIL) mechanism built with OPAL-RT real-time simulator, the effectiveness of proposed controller can be verified.

REACTIVE POWER CONTROL IN MICRO-GRID NETWORKS USING ADAPTIVE CONTROL

Purpose. Despite their economic and environmental benefits, distributed products in power systems have caused problems in power systems. One of the most important issues in this regard is voltage fluctuations and frequencies in Micro-grids, which depends on several factors, such as variable consumption load and errors in power systems. One of the main challenges associated with the use of Micro-grids is power management among distributed generation sources. Power management plays a pivotal role in numerous Micro-grids and may ensure the stable and improved performance of Micro-grids in the permanent status of the system. The present study aimed to examine the power control in Micro-grids by proposing an adaptive control method along with the PID controller for power management and coordination in Micro-grids. This coordination system operates between production sources and controlling the voltage and frequency levels against the possible disturbances occurring anywhere in the system loop. The results of the simulation of the proposed algorithm in MATLAB software environment exhibited a high success rate (i.e., proper response to the fluctuations in the Micro-grid) and extremely low error rate (i.e., proper reactive power in the grid).

A Projection-Based Decomposition Algorithm for Distributed Fast Computation of Control in Microgrids

We present a novel algorithm for the computation of optimal predictive storage and reactive power control in microgrids operating in grid-tied mode. This algorithm is based on the dual decomposition method, but local constraints are handled by means of primal projections. The use of projections significantly increases the speed of convergence of the approach with respect to the dual decomposition algorithm, which uses dual variables for the local constraints of the problem. Convergence of the algorithm to an optimizer is shown for a general class of quadratic programs, which includes a storage and reactive power control problem. In addition, a distributed implementation of the algorithm which is based on the Jacobi overrelaxation is presented. Simulations compare the algorithm performance with that of a purely dual decomposition approach over a set of standard distribution feeder test cases acting as grid-connected microgrid proxies.

A game-theoretic method for prediction of microgrid growing trends in China

This paper presents a game-theoretic method to predict microgrid (MG) development tendency in China. As many distribution generators (DGs) are integrated in distribution systems, analysis of MG formation necessity is conducted from the aspect of DGs. In order to maximize the profit brought by DGs and to earn money from arbitrage, it may be necessary for customers to combine their DGs and loads and to construct an MG to obtain maximal control ability. A game model is built to emulate trading between MGs and the distribution system based on MG power control, in which both trading profit and outage cost are considered for each MG. Nash equilibrium (NE) is calculated, and sensitivities of NE to some boundary conditions are studied. The results show that variable MG trading prices with appropriate net generation cost (i.e., DG generation cost minus government subsidy price) may encourage the growth of MGs. Government subsidies, generation costs, and trading prices may also affect DG use, and therefore they may impact customer motivation to build MGs.

Power Control of Microgrid with Rich Small Hydropower Stations

In China, some remote areas with rich small hydropower stations suffer from a tradeoff between water surplus and off-limit voltage in the grid during wet seasons. The microgrid of new energy sources provides a new way of solving this problem. Under the background of the microgrid proposed in somewhere of Jiangxi Province, this paper firstly carries out simplified model on the actual system. Output models of PV and small hydropower stations are established. Then with Minimizing transmission losses of microgrid system and the amount of all small hydropower abandoned waters as the optimization objective, and considering the output constraints of each micro power source, power balance constraints and voltage constraints. A micro-power output optimization model is established and then solved by improved particle swarm optimization algorithm. By comparing the micro-power output and system line loss before and after the optimization, it verifies that the proposed power control method can prevent the off-limit voltage effectively and reduce transmission losses of the system.

Reliability Evaluation of Distribution System with Microgrids Considering Power Control Mode

This paper presents a new method for reliability evaluation of distribution system with microgrids. A reliability-switch-simplification model is proposed to compare the reliability effect of different microgrid power control mode to customers. Microgrid structure and operation characteristics are studied comprehensively in this model. The results of a modified RBTS bus 6 verify the validity of the proposed method and show that microgrid power control mode has a significant impact on improving the reliability of customers in distribution system.