Issues for reactive power and voltage control pricing in a deregulated environment

This paper addresses issues related to reactive power, voltage support and transmission losses as dictated from a certain class of electric loads. Specifically, it addresses the impact of predominantly induction motor loads on voltage support, reactive power requirements, and transmission losses. These issues are examined with a model which explicitly models the induction motor mechanical load. Simulation results on a simplified electric power system are presented. The results are utilized to propose a pricing structure for voltage and reactive power support. The basic assumption of the paper is that, in a deregulated environment, the expense of the incremental requirements for voltage control should be charged to the member causing the additional requirements. Alternatively, the results can be used to justify long term pricing agreements between suppliers and customers.

With the rapid growth of new energy and flexible load, the random fluctuation of power system operation is enhanced, and the traditional voltage control scheme is limited. In view of the shortcomings of traditional reactive voltage control in matching the dual characteristics of the source and load in new power system, a multi-time scale coordinative strategy of reactive power and voltage control for frequent power flow fluctuation in new power system is proposed, and the reactive power and voltage control is carried out according to the normal and the unexpected large fluctuation of the power flow. The reactive power and voltage coordinated control mode of hour-minute level is used in the normal fluctuation of power flow. The timely adjustment of voltage deviation and the rapid suppression of voltage fluctuation are realized by MPC rolling optimization and dynamic-static reactive power resource substitution, and sufficient dynamic reactive power reserve is reserved for the system. The reactive power and voltage coordinated control mode of second level is used in the case of non-expected large fluctuation of power flow, and the fast decision-making ability of deep reinforcement learning realizes the rapid recovery of over-limit voltage. An example of a regional power grid in eastern China verifies the effectiveness of the proposed method.

Traditional grid-following wind turbines lack active voltage support capabilities, while grid-forming units, adopting voltage source self-synchronizing control methods, possess the ability to autonomously establish voltage and frequency. Hybrid grid-following/grid-forming wind power stations can achieve both voltage stability and efficient power generation in wind farm aggregation areas, representing a key paradigm for constructing new-type power systems. However, significant differences exist between grid-following and grid-forming wind turbines in terms of response mechanisms, control modes, and support characteristics. The response coupling during dynamic regulation processes makes balanced reactive power and voltage control in hybrid wind farms particularly challenging. To address these challenges, this paper first analyzes the control structures and regulation characteristics of grid-following/grid-forming units, clarifying applicable scenarios for different device types. Subsequently, it investigates the reactive power-voltage distribution characteristics and voltage support requirements in wind farms, proposing a reactive power allocation strategy for hybrid wind farms that coordinates turbine terminal voltage control with smooth system-wide voltage regulation. This strategy achieves balanced voltage control across the wind farm. Finally, a simulation test platform for hybrid grid-following/grid-forming wind farms is established, validating the effectiveness of the proposed strategy.

Comprehensive review of the requirements of AC transmission grid codes and the role of FACTS devices in integrating renewable power plants

Abstract— The concept of Var compensation embraces a wide and diverse field of both system and customer problems, especially related with power quality issues, since most power quality problems can be attenuated or solved with an adequate control of reactive power. In general, the problem of reactive power compensation is viewed from two aspects: load compensation and voltage support. Static voltage instability is mainly associated with reactive power imbalance. Thus, the load ability of a bus in a system depends on the reactive power support that the bus can receive from the system. As the system approaches the maximum loading point or voltage collapse point, both real and reactive power losses increase rapidly, therefore the reactive power supports have to be locally adequate. With static voltage stability, slowly developing changes in the power system occur that eventually lead to a shortage of reactive power and declining voltage. The Flexible AC Transmission System (FACTS) technology is a promising technology to achieve complete deregulation of power system based on power electronic devices, used to enhance the existing transmission capabilities in order to make the system flexible and independent in operation then the system will be kept within limits without affecting the stability. Increased transmission demand is met where possible by increasing the existing transmission capacity. When trying to improve the transmission capacity, a key assumption is made that if the overall system reliability is not improved, at least the existing system reliability is maintained. The research work in this work is focused on FACT’S Controllers. Keywords: Flexible AC Transmission System, variable-speed wind turbine, rotor-side converter, grid-side converter, doubly fed induction generator, Static Synchronous Compensator, phase-locked loop.

The large-scale integration of distributed renewable generation (DRG) reduces carbon emissions in power systems, but its intermittency and volatility introduce new challenges for voltage and frequency control. This paper proposes a multi-time-scale reactive power optimization approach that incorporates demand-side response. Firstly, based on the interaction characteristics between sources and loads in the distribution network, a demand-side response mechanism using dynamic time-of-use pricing is designed to explore the source-load matching and tracking capabilities. Secondly, a multi-scale day-ahead reactive power optimization control model is constructed, which comprehensively considers the dynamic response mechanism on the demand side. The objective function of this model aims to minimize network losses and voltage deviations while accounting for the day-ahead price response characteristics of loads. The multi-scale reactive power optimization model is then transformed into a Markov decision process and solved via a locally-observed multi-agent deep deterministic policy gradient algorithm to obtain real-time intraday reactive power and voltage control strategies. Finally, the effectiveness of the proposed method is verified through experiments on the IEEE 33-bus system and an actual power grid. Experimental results show that this method can effectively coordinate various reactive power compensation devices and flexible resources, and improve the efficiency and real-time performance of reactive power and voltage control.

As power generation from variable distributed energy resources (DER) grows, energy flows in the network are changing, increasing the requirements for ancillary services, including voltage support. With the appropriate power converter, DER can provide ancillary services such as frequency control and voltage support. This paper outlines the economic potential of DERs coordinated in a microgrid to provide reactive power and voltage support at its point of common coupling. The DER Customer Adoption Model assesses the costs of providing reactive power, given local utility rules. Depending on the installed DER, the cost minimizing solution for supplying reactive power locally is chosen. Costs include the variable cost of the additional losses and the investment cost of appropriately over-sizing converters or purchasing capacitors. A case study of a large health care building in San Francisco is used to evaluate different revenue possibilities of creating an incentive for microgrids to provide reactive power.

The wind power generation system driven by a variable speed wind turbine is extensively studied for its ability of varying rotating speed to track the optimal TSR and the maximal energy capture when the wind speed is changed. Another advantage of the variable speed wind power generation system than a fixed-speed one is its capability of reactive power and voltage control. Doubly-fed induction generators are widely used in variable speed wind power generation systems, with a frequency converter connected between the grid and the rotor winding, which is used for match of variable speed and constant frequency. Additionally, the converter can act for reactive power and voltage control by feeding particular voltages on the rotor winding. Naturally, the rotor voltage may have simultaneous influence on both speed and reactive power of the generator, but the rotor voltage indeed has two freedoms. So, a decoupled control of speed and reactive power is developed in this paper, based on the nonlinear inverse system method, and simulation results show the validity of the proposed control law.

The low voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG) significantly impacts upon the integration of wind power into the power grid. This paper develops a novel comprehensive control strategy to enhance the LVRT and reactive power support capacities of the DFIG by installing the energy storage system (ESS). The ESS is connected to the DC-link capacitor of the DFIG and used to regulate the DC-link voltage during normal or fault operations. The unbalanced power between the captured wind power and the power injected to the grid during the transient process is absorbed or compensated by the ESS. The rotor-side converter (RSC) is used to control the maximum power production and the grid-side converter (GSC) is used to control the reactive power before participating in the voltage support. When the supply voltage continues to drop, the rotor speed is increased by controlling the RSC to realize the LVRT capability and help the GSC further enhance the reactive power support capability. The capacity of the GSC is dedicated to injecting the reactive power to the grid. An auxiliary transient pitch angle controller is proposed to protect the generator’s over speed. Both RSC and GSC act as reactive power sources to further enhance the voltage support capability with serious voltage sags. Simulations based on a single-machine infinite-bus power system verify the effectiveness of the developed comprehensive control strategy.

Verification of Dependability on Parallel Particle Swarm Optimization Based Voltage and Reactive Power Control

In order to meet the high permeability and the access of large scale distributed generation, at present and in the future, active distribution network becomes the trend of smart grid research. This paper introduces the influence of distribution network voltage distribution and stability of distributed energy access based on active distribution network; The reactive power and voltage optimization control method of active power distribution network is summarized from the aspects of optimal voltage regulation measure, voltage regulation measure of power network equipment, reactive power optimal dispatch of power system, and so on. Analysis of the current status of the research, and summarized the existing active distribution network with a distributed power pickup distribution network reactive power and voltage control of the existence of some problems and the insufficiency still some problems that must be solved in the study of reactive power and voltage optimization control of active distribution network are pointed out.

This paper presents a situational-aware, data-driven, and agnostic-coordinated control methodology for voltage regulation in the active distribution systems (DS) considering voltage source converters (VSCs) as reactive power sources that work in conjunction with the existing legacy controllers. The approach uses time-scale coordination based on regulator warnings such that the voltage support from regulators is time separated from the reactive power support using VSCs. Two type of voltage changes are considered; a slow changing one based on the feeder load and a fast-changing one based on sudden changes in load or PV output. The reactive support for both these changes is then designed based on the voltage to reactive power sensitivities. The combined reactive support is then used as a set-point to dispatch reactive power from the VSCs. The proposed control technique has been tested in the field verified model of a real feeder and the scalability is verified on an 8500-node real feeder. Results show that the proposed coordination approach has major economic as well and power quality benefits in the operation of DS. It has also been shown that this can be achieved without major changes in the communication framework currently utilized by the utility.

Voltage control and reactive power support have been deeply investigated by the technical point of view. System operators and planners have developed complex control schemes, in order to achieve a secure and efficient operation. After the enforcement of market structures, new issues have appeared. Nowadays, the main subjects related with the reactive power management are: maintaining an adequate security level, defining correct economic signals, providing a simple and transparent structure, ensuring market equity, and avoiding additional charges on the final energy price. The economic issues related to the transmission network (and to the system control) have to be managed separately from the real power generation and this results in the need for defining fair payments for participating to the voltage regulation. The evaluation of the costs of the reactive power demand and the benefits of the reactive power production can be performed by means of different methods: a brief summary of the approaches proposed in literature is reported, together with some results obtained by the use of a suitable optimal reactive power flow (ORPF), which embeds the hierarchical voltage control (HVC) scheme designed for the Italian EHV transmission system. The results can be used for setting the presented proposal for the reactive power pricing.

This paper presents a particle swarm optimization (PSO) for reactive power and voltage control (volt/VAr control: VVC) considering voltage security assessment (VSA). VVC can be formulated as a mixed-integer nonlinear optimization problem (MINLP). The proposed method expands the original PSO to handle a MINLP and determines an online VVC strategy with continuous and discrete control variables such as automatic voltage regulator (AVR) operating values of generators, tap positions of on-load tap changer (OLTC) of transformers, and the number of reactive power compensation equipment. The method considers voltage security using a continuation power flow and a contingency analysis technique. The feasibility of the proposed method is demonstrated and compared with reactive tabu search (RTS) and the enumeration method on practical power system models with promising results.

This paper studies the participation of doubly-fed induction wind generator (DFIG), as a continuous variable, in dynamic optimization of reactive power and voltage control in the distribution network by obtaining the reactive power capability through controlling the power electronic interfaces and taking DFIG rated parameters into accounts. Given the fluctuation in the DFIG output active power, a time partition method based on the variance of the DFIG output active power has been proposed. According to the results of the time partition method, the operational requirements and the characteristics of the control variables in the distribution network, different dynamic optimization algorithms have been applied in different optimization time. The simulation based on the improved IEEE 33-bus system has been conducted to validate the effectiveness of the proposed optimization strategy.