Autonomous Voltage Regulation for Smart Distribution Network With High-Proportion PVs:A Graph Meta-Reinforcement Learning Approach

This paper presents an autonomous voltage control solution in islanded dc microgrid in a decentralized fashion. The dc bus voltage is regulated cooperatively by multiple renewable energy sources (RES) and energy storage units (ESUs) in different operation modes, automatically without relying on underlying communication. Unlike the existing droop control-based solutions that deal with the trade-off between bus voltage regulation and current sharing, we present a state-of-charge (SoC)-based current sharing method through the incorporation of SoC and capacity information into the double closed-loop control for ESUs. This effectively eliminates the dc bus voltage deviation, and simultaneously guarantees the SoC balance among individual ESUs. In addition, an off-maximum power point tracking algorithm is proposed for RES to manage their output generation for cooperatively maintaining the bus voltage stability in the case that the generation-demand balance cannot be regulated by ESUs alone. The suggested solution is assessed through a set of simulation experiments for a range of operational scenarios and its effectiveness is confirmed by the numerical results.

The reactive power capability of distributed photovoltaic (PV) inverters could be exploited to mitigate voltage violations under high PV penetration in the distribution grid. Coordinating the reactive power dispatch of individual PV inverters to obtain desired voltage regulation performance is a major challenge. In this article, a decentralized method is proposed to enable PV inverters to autonomously regulate terminal node voltages. The proposed method minimizes the effect of a terminal node's reactive power contribution on the voltage profile of its respective parent-to-terminal node. This ensures that the interference between the voltage regulation of terminal nodes by individual PV inverters is minimized. The performance of the proposed decentralized scheme is verified by extensive powerflow simulations on the EPRI Circuit 24 test feeder in open-source distribution system simulation platform OpenDSS.

The reactive power capability of distributed photovoltaic (PV) inverters could be exploited to mitigate voltage violations under high PV penetration in the distribution grid. Coordinating the reactive power dispatch of individual PV inverters to obtain desired voltage regulation performance is a major challenge. In this article, a decentralized method is proposed to enable PV inverters to autonomously regulate terminal node voltages. The proposed method minimizes the effect of a terminal node's reactive power contribution on the voltage profile of its respective parent-to-terminal node. This ensures that the interference between the voltage regulation of terminal nodes by individual PV inverters is minimized. The performance of the proposed decentralized scheme is verified by extensive powerflow simulations on the EPRI Circuit 24 test feeder in open-source distribution system simulation platform OpenDSS.

Coordination of OLTC and smart inverters for optimal voltage regulation of unbalanced distribution networks

Photovoltaic (PV) smart inverters can regulate voltage in distribution systems by modulating reactive power of PV systems. In this paper, an optimization framework for optimal coordination of reactive power injection of smart inverters and tap operations of voltage regulators for multi-phase unbalanced distribution systems is proposed. Optimization objectives are minimization of voltage deviations and tap operations. A novel linearization method convexifies the problem and speeds up the solution. The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced IEEE 37 bus test system. Simulation results show that the proposed method estimates feeder voltage accurately, voltage deviation reductions are significant, over-voltage problems are mitigated, and voltage imbalance is reduced.

The grid connection of large-scale wind power and photovoltaics has changed the frequency and voltage characteristics of the traditional power grid. The renewable energy generation system with new energy as the main body has put forward higher requirements for the performance of new energy grid connection, including the multi-energy complementary system(MECS) of renewable energy and energy storage. There is no unified measurement standard for the performance of access to the grid. Therefore, starting from the performance of MECS connected to the power grid, such as autonomous frequency regulation, autonomous voltage regulation, active/reactive power control, etc., a performance evaluation method of MECS connected to the power grid is given. Referring to the relevant standards for renewable energy and energy storage grid connection, a three-level index system for evaluating the grid-connected operation performance of MECS including target-level, performance-level and detail-level is constructed. The fuzzy evaluation method is used to analyze the grid-connected performance of a multi-energy complementary power station in Qinghai Province. The validity and applicability of the proposed evaluation method are verified.

The global capacity for renewable electricity generation has surged, with distributed photovoltaic generation being the primary driver. The increasing penetration of non-programmable renewable Distributed Energy Resources (DERs) presents challenges for properly managing distribution networks, requiring advanced voltage regulation techniques. This paper proposes an innovative decentralised voltage strategy that considers DERs, particularly inverter-based ones, as autonomous regulators in compliance with the state-of-the-art European technical standards and grid codes. The proposed method uses an optimal reactive power flow that minimises voltage deviations along all the medium voltage nodes; to check the algorithm’s performance, it has been applied to a small-scale test network and on a real Italian medium-voltage distribution network, and compared with a fully centralised ORPF. The results show that the proposed decentralised autonomous strategy effectively improves voltage profiles in both case studies, reducing voltage deviation by a few percentage points; these results are further confirmed through an analysis conducted over several days to observe how seasons affect the results.

This paper presents detailed assessment of the behaviour of STATCOM based on modular multilevel converter during steady-state and transient operation. The steady-state performance of the presented STATCOM is examined when it provides autonomous voltage regulation across number of switch loads. Its transient response is examined by subjecting the test system where STATCOM is connected to symmetrical and asymmetrical ac network faults. In this work, STATCOM power circuit is modelled using detailed switch model of modular converter with 16 cells per arm, including capacitor voltage balancing strategy, and control systems are represented detail (dc and ac voltage regulars, and current controller). Simulations conducted in Matlab-Simulink enlivenment are used to assess the STATCOM performance.

Our group is developing the control and power transmission components required to implement a permanent and fully sealed left ventricular assist system (LVAS). Starting with the percutaneously powered HeartMate II blood pump, our development efforts are focused in the following areas: a complete redesign of the transcutaneous energy transmission system (TETS) to include a rectification network and autonomous voltage regulation within the secondary coil, a hermetically sealed electronics package containing a miniaturized implementation of the existing redundant drive and control electronics with several power-input options, an implanted rechargeable lithium ion battery pack capable of providing up to 1 h of untethered operation, implantable electrical connectors that allow components to be connected after placement in the body or to be replaced if needed, and a radio telemetry subsystem to transmit diagnostic information and to permit remote adjustment of selected parameters.

Photovoltaic (PV) distributed energy resources (DER) have reached approximately 27 GW in the U.S., and the solar penetration rate continues to increase. This growth is expected to continue, causing challenges for grid operators who must maintain grid stability, reliability, and resiliency. To minimize adverse effects on the performance of electrical power system (EPS) with increasing levels of variable renewable generation, photovoltaic inverters must implement grid-support capabilities, allowing the DER to actively participate in grid support operations and remain connected during short-term voltage and frequency anomalies. These functions include voltage and frequency regulation features that adjust DER active and reactive power at the point of common coupling. To evaluate the risk of these functions conflicting with traditional distribution system voltage regulation equipment, researchers used several methods to quantify EPS-support function response times for autonomous voltage regulation functions (volt-var function). Based on this study, no adverse interactions between PV inverters with volt-var functions and load tap changing transformers or capacitor banks were discovered.

This paper proposes an autonomous unified var controller to address the system voltage issues and unintentional islanding problems associated with distributed photovoltaic (PV) generation systems. The proposed controller features the integration of both voltage regulation (VR) and islanding detection (ID) functions in a PV inverter based on reactive power control. Compared with the individual VR or ID methods, the function integration exhibits several advantages in high PV penetration applications: 1) fast VR due to the autonomous control; 2) enhanced system reliability because of the capability to distinguish between temporary grid disturbances and islanding events; 3) negligible nondetection zone (NDZ) and no adverse impact on system power quality for ID; and 4) no interferences among multiple PV systems during ID. As the VR and ID functions are integrated in one controller, the controller is designed to fulfill the requirement of VR dynamic performance and ensure small ID NDZ simultaneously. The interaction among multiple PV systems during VR is also considered in the design procedure. Finally, the feasibility of the proposed controller and the controller design method is validated with simulation using a real-time digital simulator and a power hardware-in-the-loop testbed.

8 - Smart distribution networks, demand side response, and community energy systems: Field trial experiences and smart grid modeling advances in the United Kingdom

Design and field implementation of smart grid-integrated control of PV inverters for autonomous voltage regulation and VAR ancillary services

In this study, optimal allocation and planning of power generation resources as distributed generation with scheduling capability (DGSC) is presented in a smart environment with the objective of reducing losses and considering enhancing the voltage profile is performed using the manta ray foraging optimization (MRFO) algorithm. The DGSC refers to resources that can be scheduled and their generation can be determined based on network requirements. The main purpose of this study is to schedule and intelligent distribution of the DGSCs in the smart and conventional distribution network to enhance its operation. First, allocation of the DGSCs is done based on weighted coefficient method and then the scheduling of the DGSCs is implemented in the 69-bus distribution network. In this study, the effect of smart network by providing real load in minimizing daily energy losses is compared with the network includes conventional load (estimated load as three-level load). The simulation results cleared that optimal allocation and planning of the DGSCs can be improved the distribution network operation with reducing the power losses and also enhancing the voltage profile. The obtained results confirmed superiority of the MRFO compared with well-known particle swarm optimization (PSO) in the DGSCs allocation. The results also showed that increasing the number of DGSCs reduces more losses and improves more the network voltage profile. The achieved results demonstrated that the energy loss in smart network is less than the network with conventional load. In other words, any error in forecasting load demand leads to non-optimal operating point and more energy losses.

In modern power systems and especially in autonomous distributed generation (DG), the frequency and voltage regulation should be continuously controlled. Hence the analysis of such a DG system is essential for the reliable operation of the local grid, with the voltage source inverter to play a key role as a controlled interface between the energy sources and the loads. In this frame, the complete model of a stand-alone DG system is analyzed with the full system dynamic model taken into account. Furthermore, as the standard control used, is in cascaded structure with fast current inner-loops and slower outer-loops that employ the frequency and voltage tasks, in a manner based on the droop-characterictics, the stability analysis of the entire system with the fast inner-loops included, is performed. The analysis is based on advanced Lyapunov methods, the input-to-state (ISS) and passivity notion as well as some convergence properties to a nonzero equilibrium for a class of such systems. The construction of suitable Lyapunov storage functions for the study also results in significant simplifications of the proposed inner-loop control schemes that now become independent from the model parameters. The overall scheme is effectively simulated and the results obtained fully confirm a good performance, superior to that of the conventional design.