Design and Implementation of Power Plant High-Side Voltage Controller for Coordinated Voltage Control

Effective and efficient management of voltage and reactive power devices is one of the most challenging tasks in power grid operation especially in a large power grid. A Coordinated Voltage Control (CVC) approach that consists of primary voltage control (PVR), secondary voltage control (SVR) and tertiary voltage control (TVR) is the most effective solutions for reactive power and voltage control. CVC refers to an approach in which secondary voltage control or regulations (SVR) is carried out automatically using a control system that would coordinate the various voltage control equipment to achieve a desired voltage at a pilot node in the system. There are various SVR model has been deployed by power utility for their CVC implementation. In Tenaga Nasional Berhad (TNB) power system, coordinated voltage control system is yet to be implemented, but improvement in the approach and methods to performing secondary voltage control are desirable since it could enhance system performance in terms of reliability and security as well as system losses. To demonstrate the capabilities of SVR within TNB grid system, a preliminary studies has been carried out, where new SVR dynamic model has been developed suitable for TNB CVC system implementation. Since voltage control is a real time activity that repeats itself on a daily basis, it was agreed that a more effective approach to study the process of SVR would be to perform simulations on a 24-hour basis where at defined times during the day the SVR would be applied. Two simulations approach has been carried: 24-hour load flow and 24-hour dynamic simulation, both implemented using PSS/E simulation software. From studies conducted, it is clear that implementation of SVR system can bring great potential and benefits to TNB in-term of system loss reduction, better voltage profile, and control and effective utilization of reactive power resources.

Effective and efficient management of voltage control devices and reactive power resources is one of the most challenging tasks in power system operation. The need for proper voltage control is mainly to fulfill the following requirements: system security, economic operation and voltage quality. In Malaysian Transmission System (MTS), most of the voltage control devices and reactive power resources are manually control. Since the guidelines for controlling the primary and secondary voltage control are broad in nature, control actions could vary from one operator to another depending on experience, system information and knowledge. Tenaga Nasional Berhad (TNB) as system operator for MTS System believes that improvement in the approach and methods for voltage controls are desirable. This paper presents the newly developed hierarchical voltage control system called Adaptive and Automatic Closed-Loop Coordinated Voltage Control (A2CLCVC) based system model as a possible solution for better voltage control within Malaysia Transmission System. The A2CLCVC system model is basically a hierarchical voltage control approach that operates at three different voltage control levels which consists of Tertiary, Secondary and Primary voltage control modules. The A2CLCVC based system model will be used to coordinate and optimize the voltage control operation in order to improve security, quality and economic of Malaysian Transmission System. To verify the A2CLCVC model system performance, two new simulation methodologies based on PSS/E simulation software has been developed: 24-hours Load Flow Python-programming (24LFP-PSS/EM) and 24-hours dynamic simulation based method (24DS-PSS/EM). The two simulation methodologies results has shown that the proposed A2CLCVC system can provide great benefits to TNB especially for better voltage control and power system operational. The comparative studies with the commercial automatic voltage control system have shown that the performance of A2CLCVC system is much similar.

In Malaysian Transmission System (TNB), most of the voltage control and reactive power resources are manually controlled. For better and optimal voltage control of the TNB power system network, new secondary voltage control (SVC) system that coordinates the voltage and reactive power control of continuous and discrete control devices has been developed. The primary goal of new SVC system based control strategy is to control the bus voltage at the selected pilot buses to follow the optimal reference values as updated by TVC system, and the secondary goal is to provide a high-side voltage set-point for power plant control to equilibrate the reactive power distribution among all control generators in each control zone to enhance the security of the power system. In this approach, the coordinated SVC system is designed to control not only the generating units, but also the reactive power devices including transformer tap-changers as well as switched shunt capacitors and reactors. The selection of reactive power devices for control is implemented through substation voltage control (SSVC) system, which then will be the input to the SVC system. If the target voltage of the pilot buses is followed, the power plant voltage controller (PPVC) will be able to equilibrate VAR among the participating power generations to enhance the power system security by increasing the MVAr reserve for dynamic control. Simulation studies based on PSS/E load flow and closed-loop real-time power system simulator using TNB snapshots shows that the new coordinated SVC system approach is able to provide more consistent voltage control actions and has produced great control actions for flatter voltage profile, reducing transmission system loss and increasing VAr reserve margin as compared to the existing SVC approach that is only focused on generator control as the main source for the voltage control.

The voltage and reactive power (VAR) management in the power system operation has becoming more challenging than ever. This is mainly due to long distance of power generations to the load centers and mesh interconnection of power grids. Coordinated Voltage Control (CVC) is found to be the most effective solutions for voltage and VAR control. This can be achieved by coordinating reactive power resources at transmission system to achieve a better voltage profiles and to minimize active power losses. This paper presents a systematic study of a hierarchical structure of system-wide automatic Coordinated Voltage Control for TNB system. Through a collaboration between TNB Research and Tsinghua University, a comprehensive simulation study of CVC system based on the approach developed by Tsinghua University has been carried out. The simulations are based on the recursive power flow solutions of the real-time snapshots which are obtained from TNB Energy Management System (EMS). The simulation results on Adaptive Zone Division (AZD), Tertiary Voltage Control (TVC) and Secondary Voltage Control (SVC) are presented in this paper. Furthermore, voltage profiles, system losses and VAR reserves before and after CVC are being analyzed. The results are encouraging. Therefore, the implementation of an automatic CVC system in TNB power grid is being realized.

This paper presents techniques for the application of tertiary and secondary voltage control through the use of intelligent proportional integral derivative (PID) controllers and the wide area measurement system (WAMS) in the IEEE 39 bus system (New England system). The paper includes power system partitioning, pilot bus selection, phasor measurement unit (PMU) placement, and optimal secondary voltage control parameter calculations to enable the application of the proposed voltage control. The power system simulation and analyses were performed using the DIgSILENT and MATLAB software applications. The optimal PMU placement was performed in order to apply secondary voltage control. The tertiary voltage control was performed through an optimal power flow optimization process in order to minimize the active power losses. Two different methods were used to design the PID secondary voltage control, namely, genetic algorithm (GA) and neural network based on genetic algorithm (NNGA). A comparison of system performances using these two methods under different operating conditions is presented. The results show that NNGA secondary PID controllers are more robust than GA ones. The paper also presents a comparison between system performance with and without secondary voltage control, in terms of voltage deviation index and total active power losses. The graph theory is used in system partitioning, and sensitivity analysis is used in pilot bus selection, the results of which proved their effectiveness.

This paper addresses a detailed design of a wind power plant and turbine slope voltage control in the presence of communication delays for a wide short-circuit ratio range operation. The implemented voltage control scheme is based upon the secondary voltage control concept, which offers fast response to grid disturbances, despite the communication delays, i.e., this concept is based on a primary voltage control, located in the wind turbine, which follows an external voltage reference sent by a central controller, called secondary voltage control, which is controlling the voltage at the point of connection with the grid. The performance has been tested using PSCAD/EMTDC program. The plant layout used in the simulations is based on an installed wind power plant, composed of 23 doubly fed generator wind turbines. The resulting performance is evaluated using a compilation of grid code voltage control requirements. The results show that fast response to grid disturbances can be achieved using the secondary voltage control scheme, and the fulfillment of the design requirements can be extended for a wide range of short-circuit ratios.

A multi-time scale coordinated voltage control strategy in an islanded microgrid (MG) is proposed in this paper. The strategy is comprised of local voltage control of distributed generators (DGs), secondary voltage control (SVC) based on PI regulators and a proposed tertiary voltage control (TVC) strategy. A multi-objective function of the TVC is designed to achieve a compromise among three objectives: 1) minimized multi-bus voltage deviations, 2) accurate reactive power distribution among droop-controlled DGs after taking full advantage of surplus capacity of renewable energy DGs, and 3) minimized line losses. Power flow equations with SFC and SVC which are regulated by multi-inverters at different buses are proposed as the equality constraints of the TVC. Limitation constraints including bus voltage limitations, frequency limitation, and capacity limitations of DGs and lines are addressed as inequality constraints of the TVC. Simulation results verify the effectiveness of the proposed method.

Traditionally voltage control is done in a decentralized way at the power plant or substation level in China. Such a traditional mode, lacking of automatic coordination in a system level, is no longer fit for the higher requirements of security and economy of modern large power system operation. In recent years, development and field site applications of close-looped system-wide automatic voltage control (AVC) technique were actively done in China. In the paper, a novel control architecture based on online adaptive network zone division is proposed. Logically such a system is in a three level hierarchical structure, however, both secondary voltage control and tertiary voltage control here are implemented with software in a control center, and the control zones are no longer fixed according to variation in power systems, which is more suitable for the fast developing Chinese power grids. Some key techniques implemented in the AVC system are introduced, such as adaptive zone division, strategies of Tertiary Voltage Control (TVC), strategies of secondary voltage control (SVC), etc. Finally some field experiences, especially some results not from simulation tool but from field site applications, are reported. The excellent performance of the AVC system and significant improvements on power system security and economy are validated. The developed AVC system has been applied to more than a dozen control centers in China, such as the North China Power Grid with generating capacity of 119GW. Evaluation of the potential profits of the proposed AVC system on PJM system in USA is ongoing.

ABSTRACTSolid oxide fuel cell (SOFC) systems have become a research focus because of their clean and high‐efficiency properties. Control of output voltage and fuel utilization is critical to the energy management for multi‐energy systems incorporating SOFC energy supply. However, maintaining precise control of the system's voltage in the presence of perturbations can be challenging. Moreover, the system's voltage control process can lead to fuel utilization fluctuations, which may affect the economy and safety. The design of the controller must meet both of these requirements. The stringent control requirements lead to poor parameter adaptability of existing controllers. This paper designs a nonlinear function and adopts a nonlinear/linear active disturbance rejection controller (ADRC) based on state switching to solve the output voltage tracking control problem of SOFC and maintain the fuel utilization rate in the ideal range. The simulation experimental results show that the proposed method has the advantages of strong and superior parameter adaptability with less control effort, which provides theoretical guidance for the design of the output voltage controller of the actual SOFC system.

Secondary voltage controls, as a non-cost voltage control, are often conducted by utilities as the first option to solve voltage violations. Utilities like PJM and MISO manually coordinate secondary voltage controls aiming at regulating voltage profile and avoiding the use of potentially costly controls, such as transmission loading relief or load shedding. The speed of secondary voltage control devices ranges from three up to 15 minutes, depending on the control mode (either automatic or manual). Increasing voltage stability has not (in the past) been considered as a control objective. In this paper, a novel decentralized secondary voltage control system is designed to automatically generate optimal control decisions meeting different control objectives (such as maximum stability margin, minimum controls and losses). The proposed system aims at providing fast and coordinated secondary voltage control decisions in the time range from several seconds to a few minutes. Comparative studies are performed between the proposed system and existing secondary voltage control approaches applied in utilities.

This paper describes technology required for advanced intelligent voltage and reactive secondary control systems enabling co-ordination of voltage control between main and local power systems. Firstly, the paper comments on the inadequate behavior of voltage and reactive power control systems, such as up-and-down fluctuations, which sometimes occur during off-peak load times, and explains the reasons for voltage fluctuations. It then explains that the true nature of the EMS of power system control is based on an autonomous distributed control system. Based on such recognition, the paper proposes the concept of advanced EMS systems for co-ordination of voltage and reactive power control. As background, the paper briefly describes two previously developed intelligent component functions, namely, flexible fuzzy zones and feed foreword control to prevent voltage fluctuation, and on-line acquisition of voltage characteristics by neural network technology. The paper describes local demand forecasting one hour in advance by the NN method. This method is also applicable to the forecast of the total demand of a power system.

In this paper the basic role of a secondary (regional level) voltage control in a multi-regional electric power system is reviewed. Specifically, certain limitations of presently implemented control schemes are described. Next an improved secondary voltage control (ISVC) scheme is proposed. In the second part of the paper, possible enhancements of a multi-regional power system operation by means of scheduled, tertiary voltage control (TVC) interactions are proposed. It is shown that the prime role of a TVC is in managing limits on voltage control devices, such as generators. The theoretical developments are illustrated on two regions of the French electric power network.

The paper, discusses the possibility to use coordinated Q-V controller (CQVC) to perform secondary voltage control at the power plant level. The CQVC performs the coordination of the synchronous generators' (SG) reactive power outputs in order to maintain the same total reactive power delivered by the steam power plant (SPP), while at the same time maintaining a constant voltage with programmed reactive droop characteristic at the SPP HV busbar. This busbar is the natural pilot node for secondary voltage control at HV level as the node with maximum power production and maximum power consumption. In addition to voltage control, the CQVC maintains the uniform allocation of reactive power reserves at all SGs in the power plant. This is accomplished by setting the reactive power of each SG at given operating point in accordance to the available reactive power of the same SG at that point. Different limitations imposed by unit's and plant equipment are superimposed on original SG operating chart (provided by the manufacturer) in order to establish realistic limits of SG operation at given operating point. The CQVC facilitates: i) practical implementation of secondary voltage control in power system, as it is capable of ensuring delivery of reactive power as requested by regional/voltage control while maintaining voltage at system pilot node, ii) the full deployment of available reactive power of SGs which in turn contributes to system stability, iii) assessment of the reactive power impact/contribution of each generator in providing voltage control as ancillary service. Furthermore, it is also possible to use CQVC to pricing reactive power production cost at each SG involved and to design reactive power bidding structure for transmission network devices by using recorded data. Practical exploitation experience acquired during CQVC continuous operation for over two years enabled implementation of the optimal setting of reference voltage and droop on daily, monthly and seasonal basis. Finally, the paper suggests and elaborates on studies related to application of several coordinated Q-V controllers in power system to facilitate secondary voltage control. It is shown that the CQVC can be used to maintain desired voltage at assigned pilot node in the power system with predefined reactive droop characteristic, and such maintain the required voltage profile across the transmission network based on commands received from upper hierarchical control level.

The power industry in China has grown significantly over the past decade, spurring the adoption of system-wide automatic voltage control (AVC) technology to meet stricter requirements for security and economical power system operation. To cope with the rapidly developing and frequently changing Chinese power grid, an AVC scheme based on adaptive zone division is introduced in this paper. Logically, this type of system has a three-level hierarchical structure, but here, both secondary voltage control (SVC) and tertiary voltage control (TVC) are implemented via software at the same control center. The control zones are no longer fixed but are reconfigured online and updated in accordance with variations in the grid structure. The technical details of these procedures are presented here. The implementation of TVC (which is based on an online reactive optimal power flow) and SVC are also discussed, together with some technical details on improvements to their reliability and robustness. Some results obtained from field-site applications based on similar-days testing rather than simulations are employed to evaluate the performance and improvements of the AVC system. This system has been installed at over 20 control centers in China.

The hierarchical voltage control has been proved to be an effective method to ensure the security, stability and economy operation in power systems. The secondary voltage control is represented by the multiple objective linear programming with sensitive analysis in this paper. Several control objectives are considered. The first objective is that the pilot node voltage should be close enough to the setting value updated by the tertiary voltage control. The second one is that the reactive power output of the control generators should be adjusted to gain more reactive power margin. And the third one is that the error between the important bus voltage and its setting value should be least. This problem is solved by an extension of the simplex known as goal programming simplex by ranking the priority of the control objectives. Some simulation results of the secondary voltage control of Zouxian power plant zone in Shandong Power System in China demonstrate the feasibility of the proposed method