Steady-state Voltage Control Research Articles

Development of Steady-State Voltage Control Techniques Applied to Microgrids

Development of Steady-State Voltage Control Techniques Applied to Microgrids

Efficiency Optimization and Resilience Improvement in Wireless Motor System With Flexible DC-Link Voltage Regulation

This paper proposes a novel dc-link voltage regulation (DCVR) strategy for the series-series compensated wireless motor (SSWM) system. The steady-state voltage control is presented to optimize the system efficiency and the feedforward voltage boost control is proposed to improve system resilience. The rated capacity identification (RCI) scheme is proposed to design proper parameters for the SSWM system. To achieve steady-state voltage control, the system efficiency characteristic is analyzed in detail and the efficiency optimization can be achieved without an auxiliary dc/dc converter. The influence of impedance matching, the power capacity of the system, and overmodulation of the motor drive are all investigated. Then, the dynamic model of the system is established to analyze the stability of dc-link voltage. In the proposed feedforward voltage boost control, the dc-link voltage is boosted according to the motor operation state to increase the instantaneous power capacity. The dc-link voltage stability is improved and the system resilience is enhanced against power disturbance. Besides, at the end of the acceleration process, the dc-link voltage is smoothly adjusted to the optimal dc-link voltage. The effectiveness of the proposed RCI scheme and DCVR strategy is verified by experiments on a three-phase wireless permanent magnet synchronous motor platform.

Fast Coscheduling of Discrete and Continuous Resources in Active Distribution Systems

This article proposes a novel fast method for flexibility scheduling and steady-state voltage control in smart distribution systems enabled with both conventional discrete controllable devices (DCDs), e.g., capacitor banks and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -load tap changers, and continuous and faster control devices, e.g., distributed energy resources, renewable resources, and static voltage regulators. By approximating the active and reactive losses, a linear branch flow model is presented for the optimal power flow (OPF) problem in distribution systems. Accurate models are also proposed for DCDs which suit the proposed OPF formulation and require fewer binary variables compared to those available in the literature. Conservation voltage reduction (CVR) scheme is modeled in the proposed OPF methodology. The CVR effects on energy saving, peak-load reduction, line losses, and transformer losses are analyzed in the case studies. As shown in various case studies, the proposed method is fast enough for quasi-real-time applications and is efficacious in minimizing the system operation cost, holding an acceptable level of power quality based on the available standards and evading the conflict between control actions.

Optimal Steady-State Voltage Control Using Gaussian Process Learning

In this article, an optimal steady-state voltage control framework is developed based on a novel linear voltage-power dependence deducted from Gaussian process (GP) learning. Different from other point-based linearization techniques, this GP-based linear relationship is valid over a subspace of operating points and, thus, suitable for a system with uncertainties such as those in power injections due to renewables. The proposed optimal voltage control algorithms, therefore, perform well over a wide range of operating conditions. Both centralized and distributed optimal control schemes are introduced in this framework. The least-squares estimation is employed to provide analytical forms of the optimal control, which offer great computational benefits. Moreover, unlike many existing voltage control approaches deploying fixed voltage references, the proposed control schemes not only minimize the control efforts but also optimize the voltage reference setpoints that lead to the least voltage deviation errors with respect to such setpoints. The control algorithms are also extended to handle uncertain power injections with robust optimal solutions, which guarantee compliance with the voltage regulation standards. As for the distributed control scheme, a new network partition problem is cast, based on the concept of effective voltage control source (EVCS), as an optimization problem which is further solved using convex relaxation. Various simulations on the IEEE 33-bus and 69-bus test feeders are presented to illustrate the performance of the proposed voltage control algorithms and EVCS-based network partition.

Fast Resource Scheduling for Distribution Systems Enabled With Discrete Control Devices

This article proposes a framework for fast short-term scheduling and steady-state voltage control in distribution systems enabled with both continuous control devices, e.g., inverter interfaced distributed generators (DGs) and discrete control devices (DCDs), e.g., on-load tap changers. The voltage-dependent nature of loads is taken into account to further reduce the operating cost by managing the voltage levels. Branch and cut method is applied to handle the integrality constraints associated with the operation of DCDs. A globally convergent trust region algorithm (TRA) is applied to solve the integer-relaxed problems at each node during the branching process. The TRA subproblems are solved using interior point method. To reduce the branching burden of branch and cut algorithm, before applying TRA at each node, a simplified optimization problem is first solved. Using the convergence status and value of objective function of this problem, a faster decision is made on stopping the regarding branch. Solving the simplified problem obviates the application of TRA at most nodes. It is shown that the method converges to the optimal solution with a considerable saving in computation time according to the numerical studies.

Aspects of ultra-high voltage half-wavelength power transmission technology

The necessity of large-scale and long-distance power transmission in future energy development is analyzed and some application scenarios of ultra-high voltage (UHV) half-wavelength transmission (HWLT) system are presented in the paper. Steady state and transient characteristics of half-wavelength transmission lines are reviewed in detail. The characteristics of UHV HWLT are very different from those of conventional UHV transmission mode, especially the overvoltage problem. To analyze the particularity and key techniques of UHV HWLT, current research results are summarized from simulation method, steady-state voltage control, relay protection, tuning network, secondary arc and overvoltage suppression, economic evaluation and engineering design. Some future research directions are also briefly addressed.

Coordinated Control of a DG and Voltage Control Devices Using a Dynamic Programming Algorithm

This paper presents a new control method, in which a distributed generator (DG) actively participates in steady-state voltage control, together with an under-load tap changer (ULTC) and shunt capacitors (Sh.Cs). In the conventional DG control method, the integration of DGs into a distribution power system increases the number of switching operations of the ULTC and the Sh.Cs. To solve this problem, this paper proposes that the DG output voltage be dispatched cooperatively with the operation of the ULTC and the Sh.Cs, based on load forecasts for one day in advance. The objective of the proposed method is to decrease the number of switching device operations, as well as to reduce the power loss in the distribution lines, while maintaining the grid voltage within the allowed range. The proposed method is designed and implemented with Matlab, using two different dynamic programming algorithms for a dispatchable and a nondispatchable DG, respectively. Simulation studies demonstrate that the objective can be achieved under various grid conditions, determined by factors such as the DG output power characteristics, the location of the DG-connected bus on the feeder, and the load profile of the feeder containing the DG.

Application study of a STATCOM with energy storage

With advances in energy storage technology the application of STATCOMs with energy storage for utility applications, such as active- and reactive-power compensation of loads, network-voltage control and mitigation of power system disturbances, is increasingly feasible. As it is more expensive to produce active power than reactive power, it is important to consider methods which can be adopted to minimise the use of the energy store. An application study of a STATCOM with energy storage giving special emphasis to control strategies which minimise the use of the stored energy is reported. Calculation techniques to determine the current rating of the IGBTs, diodes and connecting transformer as well as the losses associated with the switches when the compensator is operated under space-vector modulation are demonstrated. Application studies of the compensator with energy storage for load compensation, steady-state voltage control, mitigation of voltage sags and elimination of power oscillations are described. The analytical studies of each of these applications are supplemented by simulation results carried out in PSCAD/EMTDC and by experimental results obtained from a laboratory prototype.

Application and Operation of a Static Var System on a Power System-American Electric Power Experience Part I: System Studies

American Electric Power's (AEP) Static Var System (SVS) was placed in service at the Beaver Creek Station in eastern Kentucky in November 1980 and has since maintained an excellent record of operation. The purpose of this SVS installation was to provide both steady-state and dynamic voltage control on the 138 kV transmission system. This paper describes the application and operating experience of this unique installation, which is comprised of two thyristor controlled reactors (TCR) and two thyristor switched capacitors (TSC) with an overall dynamic range of ±125 MVAR. These components are connected to the 138 kV transmission system via a 125 MVA, 138/ 8.3 kV transformer. The +125 MVAR upper limit has been extended to +325 MVAR by installing four 50 MVAR, 138 kV capacitor banks which, in effect, function as a steady-state voltage control to optimize the SVS dynamic range.