Secondary Voltage Control Strategy Research Articles

An advanced secondary voltage control strategy for future power systems

The network voltage control together with the regulation of reactive power, has always been recognized as vital feature of power systems. It is aimed at containing the bus voltage within acceptable limits for guaranteeing system security, first and then assessing power quality. The voltage control is a key field in which several Transmission System Operators are currently investing resources to be well prepared in managing power systems with a high share of renewable energy sources, overcoming the drawbacks of the existing architectures. As is well known the voltage control is realized through a hierarchical structure, which is based on classical primary control, secondary control, and tertiary optimization. The secondary control is concerned with the regional level, implying proper coordination at both the geographical and temporal level. Due to its central role in power system operation, the secondary voltage control cannot be excluded from the effects of the dramatic changes that power systems are experiencing worldwide, even though regulators work by implementing well consolidated methodologies and strategies which show excellent performances. The motivation for this study in fact relies on the observation of some oscillatory phenomena in some areas of the Italian power system characterized by a high number of regulating resources highly coupled each other on the basis of the grid topology: despite these oscillatory phenomena are not so frequent, with the increasing of regulating resources enslaved by secondary regulation (such as renewable-based power plants) could potentially be worsened in the near future. Thus, in this paper, an optimal control strategy is proposed by tailoring a proper linear quadratic integral control which allows guaranteeing the desired profile for pilot buses voltage, ensuring a time response of aperiodic type without any oscillations. The aim of the proposed approach is to preserve the strengths of the existing secondary voltage regulation while enhancing the overall stability so enabling the progressive large penetration of renewable energy sources-based power plants and minimize the occurrence of oscillatory phenomena especially in highly electrically coupled areas. The robustness of the proposed regulation is verified first with respect to the WSCC 9-bus test system and successively on an actual regional area of Italian transmission network.

Distributed robust secondary voltage control for islanded microgrid with nonuniform time delays

This paper proposes a nonuniform delay-dependent robust secondary voltage control strategy with a finite-time voltage reference observer for an islanded microgrid. A discrete-time consensus algorithm is introduced to track the output voltage. By model transformation, a closed-loop microgrid control system is obtained. And then, the corresponding global stability and robust performance analysis theorems are derived. After implementing a series of trial studies, the impacts of secondary voltage control gains, sampling time on energy-to-peak robust performance are obtained. And the feasible optimal voltage control gains can be derived. Besides, a distributed cooperative secondary frequency control is introduced. Simulations of a four inverter-based microgrid test system are presented to verify the control performance. The simulation results indicate that our proposed method can maintain accurate voltage/frequency restoration and active power sharing. In addition, the voltage control gain parameters, arbitrary nonuniform time delays, and especially sampling time effects on the secondary voltage control performance are also verified.

Distributed secondary voltage control for autonomous microgrids under additive measurement noises and time delays

This study addresses the secondary voltage restoration problem of ac autonomous microgrids with additive measurement noises and time delays. Existing distributed control methods commonly assume ideal communication among distributed generators (DG), however, the channels are prone to additive noises (i.e. caused by environmental causes, such as rain etc.) and time delays, then each DG obtains noisy and delayed measurements of the states of its neighbouring DGs. The proposed distributed cooperative control strategy will achieve voltage restoration of DGs through a sparse communication network subject to noisy and delayed measurements. The theoretical concepts and necessary conditions for stability and robust performance of the proposed distributed secondary voltage control strategy are outlined by the graph theory, stochastic theory, and Lyapunov functional approach. Furthermore, the proposed control strategy is fully distributed and therefore the central controller is no longer required bringing about several advantages, e.g. plug-and-play property. Simulation results on an autonomous ac microgrid test system are obtained to evaluate the performance of the proposed control method to achieve voltage restoration in the MATLAB/SimPowerSystems Toolbox.

Novel coordinated secondary voltage control strategy for efficient utilisation of distributed generations

This study presents a novel coordinated secondary voltage control (CSVC) and reactive power management scheme for efficient utilisation of distributed energy resources in a smart distribution network. The proposed controller is developed to achieve efficient voltage regulation and to maximise the dynamic reactive power reserve in a distribution network to react during system contingencies. The simulated distribution system, including an on-load tap changer (OLTC) and distributed energy resources, is implemented using PSCAD/EMTDC. The CSVC is designed to provide slow and medium speed responses, using low-pass filters for OLTC and diesel generators, respectively, and a fast response by utilising inverter-based distributed energy resources. Therefore it applies a control strategy with different bandwidth dedicated by the decentralised voltage controllers and reactive power management scheme. The CSVC is used to enhance the bus voltage control by utilising the reactive power loading capabilities among distributed energy resources and on-load tap changers of the substation transformer. A comprehensive simulation has verified the superior performance of the proposed coordinated secondary voltage control with the reactive power management scheme for enhancing the voltage profile and the fault ride-through capability, ensuring higher dynamic reactive power reserves in a distribution network, and improving the transient stability margin.

A Secondary Voltage Control Strategy for Transmission Level Interconnection of Wind Generation

This paper addresses implementation issues associated with secondary voltage control in a doubly-fed induction generator based wind farm. The effects of different system parameters on the performance of the control are considered, namely the short circuit ratio of the interconnection and the inherent communication delay between the wind park and the remote bus. In addition, a strategy for allocation reactive power requirements to each of the generators within the wind park is proposed. The system is developed and simulated for a wind park consisting of six wind generators connected to a typical transmission system. The paper proposes an optimal tracking secondary voltage control method developed to achieve effective voltage regulation, enhance the network voltage profile and provide optimal reactive power compensation to the interconnected power system. The performance of the controller is compared with secondary voltage control at one selected bus, primary voltage control and the optimal voltage profile obtained from the optimal power flow analysis. The performance of the controllers is tested for steady state operation and in response to system contingencies, taking into account the impact of communication time delays and short circuit ratio (SCRs). Simulation results are presented to demonstrate the capability of the controllers to provide the desired reactive power compensation and voltage support to the electric power grid.

Secondary voltage control based on a robust multivariable PI controller

Based on the use of a robust multivariable proportional-integral (PI) control algorithm, a new secondary voltage and reactive power control strategy is described. It permits the coordination of discrete and continuous type of reactive power sources to regulate the voltage profile of each region or ‘zone’. Through this coordination, it is able to drive the continuous type of reactive power sources to work near the unity power factor. Results are presented that show the good performance behaviour of this secondary voltage control strategy when it is employed to control the desired voltage profile of the EHV network of IBERDROLA S.A.