Maintain Voltage Regulation Research Articles

Piece-Wise Droop Controller for Enhanced Stability in DC-Microgrid-Based Electric Vehicle Fast Charging Station

The need for public fast electric vehicle charging station (FEVCS) infrastructure is growing to meet the zero-emission goals of the transportation sector. However, the large charging demand of the EV fleet may adversely impact the grid’s stability and reliability. To improve grid stability and reliability, the development of a DC microgrid (MG) leveraging renewable energy sources to supply the energy demands of FEVCSs is the sustainable solution. Balancing the intermittent EV charging demand and fluctuating renewable energy generation with the stable DC bus voltage of a DC MG is a challenging objective. To address this objective, a piece-wise droop control strategy is proposed in this work. The proposed scheme regulates DC bus voltage and power sharing with droop value updating in a region-based load current distribution. Voltage compensation in individual regions is carried out to further improve the degree of freedom. In this paper, the performance of the proposed strategy is evaluated with the consideration of real-time solar PV dynamics and EV load dynamics. Further, to showcase the effectiveness of the proposed strategy, a comparative analysis with a maximum power point tracking (MPPT) controller against various dynamic EV load scenarios is carried out, and the results are validated through a hardware-in-loop experimental setup. Despite the intermittent source and EV load dynamics, the proposed piece-wise droop control can maintain voltage regulation with less than 1% deviation.

Adaptive active and reactive power control strategy for virtual synchronous generator

SummaryWith the increase in the penetration level of renewables into the grid, the virtual synchronous generator (VSG) concept has emerged as an attractive solution for controlling grid‐tied inverters. The variation in reactive power also affects the real power of the system as well. To address the voltage variations and phase angle variations occurring because of the energy storage elements, the control of the reactive power loop (RPL) is important. Also, it is used to maintain voltage regulation and improve the power factor of the VSG system. This paper focuses on the damping of oscillations occurring because of load variation by proper adjustment of the rotational inertia, damping coefficient, droop coefficient, and regulatory coefficient of reactive power with a proposed adaptive control strategy. Small‐signal analysis of the active and reactive power and point of common coupling (PCC) have been derived, and the detailed dynamic performances are analyzed. The influences of parameters perturbation on PCC voltage and reactive power were investigated. Furthermore, adaptive control includes optimizing dynamic indexes such as rise time, delay time, and response settling time. Finally, the performance and improvement in the results of VSG with and without adaptive control are compared.

Hosting Capacity Assessment Strategies and Reinforcement Learning Methods for Coordinated Voltage Control in Electricity Distribution Networks: A Review

Increasing connection rates of rooftop photovoltaic (PV) systems to electricity distribution networks has become a major concern for the distribution network service providers (DNSPs) due to the inability of existing network infrastructure to accommodate high levels of PV penetration while maintaining voltage regulation and other operational requirements. The solution to this dilemma is to undertake a hosting capacity (HC) study to identify the maximum penetration limit of rooftop PV generation and take necessary actions to enhance the HC of the network. This paper presents a comprehensive review of two topics: HC assessment strategies and reinforcement learning (RL)-based coordinated voltage control schemes. In this paper, the RL-based coordinated voltage control schemes are identified as a means to enhance the HC of electricity distribution networks. RL-based algorithms have been widely used in many power system applications in recent years due to their precise, efficient and model-free decision-making capabilities. A large portion of this paper is dedicated to reviewing RL concepts and recently published literature on RL-based coordinated voltage control schemes. A non-exhaustive classification of RL algorithms for voltage control is presented and key RL parameters for the voltage control problem are identified. Furthermore, critical challenges and risk factors of adopting RL-based methods for coordinated voltage control are discussed.

Data-driven model predictive control of community batteries for voltage regulation in power grids subject to EV charging

In this paper, a Model Predictive Control (MPC) for community Battery Energy Storage Systems (BESS) is proposed to mitigate the Electric Vehicle (EV) charging demand while maintaining voltage regulation in residential power grids. With the increased penetration of renewable-based Distributed Energy Resources (DERs) and the EV uptake, distribution grids are highly subject to voltage fluctuations due to back power feed from DERs or significant EV charging demand. Conventionally, Distribution Network Operators (DNOs) have addressed this issue by adjusting the taps of transformers. However, managing the naturally unpredictable renewable generation and the power consumption behaviour of technology owners requires advanced real-time algorithms. In this paper, we apply a real-time control algorithm, based on Model Predictive Control (MPC), to a community BESS in order to reduce voltage fluctuations. The MPC algorithm performs in real-time based on readings from smart meters of households. It predicts the future values of voltages at households based on the current and past readings of smart meters, and calculates the BESS charging or discharging rate such that future voltage deviations are minimised. Simulations on the real-world power consumption data from Victorian residential consumers, in Australia, show that the proposed controller performs significantly better than the fixed charging/discharging BESS schedule in both voltage regulation and BESS degradation.

An optimization framework for voltage stability support from active distribution networks

In recent years the number of controllable converter-interfaced generators connected to the distribution grids is rising fast. This gives rise to the concept of active distribution network (ADN), in which a local controller can maintain voltage regulation constraints, while controlling the active and reactive power exchanged with the transmission grid. This paper demonstrates how ADNs can be used in an optimal manner in order to support long-term voltage stability in a power system. The framework is based on a two-stage optimization including a central controller and a number of ADNs. The proposed method is applied on a variant of the IEEE Nordic Test System which includes a simple configuration of distribution feeders.

Self-tuning Fuzzy PID Controller Design and Energy Management in DC Microgrid: Standalone and Grid Connected Mode

This paper presents a control system and energy management strategy with a standalone and grid-connected mode in the microgrid. The microgrid is energized by distributed generation system of a photovoltaic panel, wind turbine and lithium-ion batteries. In this paper, the controller structure for regulating the voltage regulation in this microgrid consisting of renewable energy sources and battery system is covered. Overshoot, rise time, settling performances of designed self-tuning fuzzy proportional-integral-derivative controller and conventional proportional-integral-derivative controller examined comparatively. In addition, an energy management system has been proposed for loads which fed in the microgrid. Here, the aim is to make maximum use of renewable energy sources as much as possible, to maintaining voltage regulation and to ensure continuity in the feeding of the critical load. The system switches between the standalone and grid-connected modes if necessary. A model of the microgrid's dynamic behavior was constructed and it is simulated in the MATLAB®/Simulink environment. The results show that despite the changes in the production and load side of the grid, voltage and frequency oscillations are stabilized within a short time and allowed tolerance limits.

Harmonic Reduction using Three-Phase IGBT Based Detuned Filter in Grid connected PV System

As the energy consumption is steeply increasing globally, alternate methods must be adopted to meet the demands. Also to preserve the conventional resources, energy production by renewable sources such as solar, wind, geothermal, tidal, etc is the need of the hour. Energy generation through solar cells can be largely used. But, the harmonic content in the power generated from the solar panels are seemingly higher than the maximum allowable limits. Harmonics are the deviation in the output value from the actual value, caused due to various phenomenal factors. We have observed that the harmonics in the output power from the photo-voltaic cells is way to larger than the limited value. So, we have proposed a three-phase shunt connected IGBT based detuned filtering system to limit the harmonic levels within the desired values. To reduce the current THD value below the permissible limits as specified by the IEEE standards and also to maintain voltage regulation and power factor correction, as well as to improve the efficiency of the entire system.

Multiperiod Coordination of Local Voltage Controllers and Energy Storage for Voltage Regulation in Distribution Feeder-Connected Renewable Energy Sources

Connection of renewables to the distribution system is growing very rapidly. The inherent uncertainty of renewable energy sources, however, can potentially introduce operational conflicts, disrupting the typical operation pattern of local voltage regulation devices and causing system voltage rise beyond the acceptable limits. This paper describes a joint platform to maintain voltage regulation in a distribution network incorporating a large share of PV energy sources. With an objective to improve the voltage profile and minimize feeder losses, the operation of local voltage controllers and energy storage is coordinated. An optimization approach, based on the genetic algorithm, is developed to find out the optimal settings of the load tap-changing transformers and switched shunt capacitors, as well as the optimal dispatch of energy storage. The proposed method is applied to the IEEE 123 test feeder, using time series analysis over a daily, 24 h, simulation period. Test results clearly exhibit that the close coordination between the voltage control devices and energy storage scales back system energy losses, minimizes the interaction among local voltage controllers and prevents reverse power flow. It consequently upholds the voltage at the customer terminals within the statutory limits, under high penetration levels of solar-fueled generation.

SVPWM: Torque Level Controlling of Wind Turbine System Using Fuzzy and ABC-DQ Transformation

Wind energy conversion systems employ the doubly fed induction generator (DFIG) for maximum energy capture. Many traditional systems used pulse width modulation (PWM) technique to control the DFIG block by a feedback from the load terminal. PWM schemes generate the control pulses for an inverter switches. An independent activation of the wind turbine generator does not offer optimum result. This paper presents the fuzzy-based PWM controlling of wind turbine system in DFIG to provide an optimum result. According to the torque level and the rotation speed of wind turbine, the speed of the generator is controlled to maintain voltage regulation at load side. The integration of ABC-direct quadrature transformation based on the fuzzy rule generates the necessary control signals for gates. To control the operation of multilevel converters, an enhanced phase differential space vector PWM modulation (EPD-SVPWM) is implemented in this paper. The transfer function for maintenance of the reduced level of ripples in inverter switching circuit included in the modification of SVPWM lead to high-speed switching of the insulated gate bipolar transistor (IGBT). Consequently, it results in a low error rate and regulated power at load side. The experimental results exhibit better performance regarding dynamic voltage variation impact, and output voltage level at load side than the existing methods.

Options for Control of Reactive Power by Distributed Photovoltaic Generators

High-penetration levels of distributed photovoltaic (PV) generation on an electrical distribution circuit present several challenges and opportunities for distribution utilities. Rapidly varying irradiance conditions may cause voltage sags and swells that cannot be compensated by slowly responding utility equipment resulting in a degradation of power quality. Although not permitted under current standards for interconnection of distributed generation, fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions. As side benefit, the control of reactive power injection at each PV inverter provides an opportunity and a new tool for distribution utilities to optimize the performance of distribution circuits, e.g., by minimizing thermal losses. We discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters. An important design decision that weighs on the speed and quality of communication required is whether the control should be centralized or distributed (i.e., local). In general, we find that local control schemes are able to maintain voltage within acceptable bounds. We consider the benefits of choosing different local variables on which to control and how the control system can be continuously tuned between robust voltage control, suitable for daytime operation when circuit conditions can change rapidly, and loss minimization better suited for nighttime operation.