Overvoltage Control Research Articles

Adaptive transient overvoltage control strategy for wind farm based on data‐driven

AbstractTo achieve the transient overvoltage suppression of doubly fed induction generator (DFIG) terminals and the point of common coupling (PCC) in the wind farm (WF), an adaptive overvoltage control strategy based on data‐driven approach is proposed. Firstly, the PCC reactive power demand and DFIG overvoltage threshold are derived, respectively. Secondly, three regression models are developed through surface fitting to determine three variables: the maximum overvoltage of each DFIG, the PCC maximum overvoltage, and the reactive power demand of each DFIG. Subsequently, the K‐means clustering method is adopted to group all DFIGs, and then the reactive power requirement of the PCC is proportionally distributed to each group of DFIGs. Lastly, a coordinated control strategy of DFIGs and static var generator (SVG) is designed based on the values of three regression models, which can adaptively adjust the reactive power absorbed by each DFIG and SVG. In particular, the de‐load control is adopted to enlarge the maximum reactive power capacity of DFIG. The simulation results show that the proposed control strategy can timely and effectively restore the transient overvoltage of the wind farm to the normal range during the gird failure, ensuring the stable operation of the wind farm.

An overvoltage adjustment strategy Based on Integrated Voltage Sensitivity in the Active Distribution Network

With the growing proportion of renewable energy resources represented by distributed photovoltaics in the distribution network, the overvoltage problem is becoming more and more serious owing to the photovoltaic reverse power flow in the active distribution network. This paper begins with the quantification and analysis of node voltage sensitivity, and the influence calculation formula of photovoltaic injection on the voltage sensitivity of the target node and other nodes is deduced; next, a general conclusion on the change of voltage sensitivity caused by active and reactive power of Photovoltaic is given. To solve the possible low control efficiency of control strategy simply depends on voltage sensitivity, a definition of so-called Integrated voltage sensitivity is proposed, and an optimized overvoltage control scheme is utilized under the distribution network structure. The effectiveness of the proposed control strategy is validated by a simulation example, namely, on the premise of not affecting the active power output of the photovoltaic as much as possible, the same overvoltage regulation effect can be obtained with smaller adjustments in reactive power output, further, rapid overvoltage regulation is achieved.

Control Strategy for Improving the Voltage Regulation Ability of Low-Carbon Energy Systems with High Proportion of Renewable Energy Integration

In low-carbon energy systems, due to the high proportion of renewable energy access, the voltage regulation capacity of the system will decrease. Therefore, in the event of voltage violation, it is easy to cause large-scale renewable energy off-grid and power outages. In order to improve the voltage regulation ability of low-carbon energy system, this paper proposes a two-stage overvoltage suppression strategy for sending-end power grid. Firstly, the principle of overvoltage phenomenon in the sending end power grid of low-carbon energy system with high proportion of renewable energy access is studied, and an overvoltage control strategy composed of two stages of centralized control of rectifier station and flexible resource control of distributed power grid is proposed. Then, the PSO algorithm and consensus algorithm are used to solve the established control model. Finally, a simulation system is established based on actual operating power grid data to verify the proposed control strategy through simulation. The results indicate that the control strategy proposed in this paper can effectively suppress transient overvoltage of AC buses and improve the operational stability of the high proportion of renewable energy sending-end power grid under various operating conditions. In addition, during the daytime overvoltage regulation process, the potential of flexible regulation equipment can be fully utilized. Shortening the duration of voltage exceeding the limit and reducing the peak voltage exceeding the limit can help reduce the renewable energy waste rate of the power grid.

Analytical Overvoltage and Power-Sharing Control Method for Photovoltaic-Based Low-Voltage Islanded Microgrid

Analytical Overvoltage and Power-Sharing Control Method for Photovoltaic-Based Low-Voltage Islanded Microgrid

Research on VFTO Identification of GIS Based on Wavelet Transform and Singular Value Decomposition

The accurate identification of Very Fast Transient Overvoltage (VFTO) is the key of overvoltage control in modern smart grids. In order to accurately identify VFTO generated by the operation of a disconnector in Gas Insulated Substation (GIS), a VFTO identification method based on Wavelet Transform (WT) and Singular Value Decomposition (SVD) is proposed. The simulation model of VFTO is established in ATP-EMTP software first, and then wavelet decomposition is used in MATLAB software for VFTO simulation of the waveform from the ATP-EMTP software. Then, the feature matrix is composed of the coefficients of each frequency layer of the wavelet. The SVD is used to decompose the feature matrix, and finally the characteristic parameters of the VFTO are obtained. The simulation results in Matlab software indicate that the characteristic parameters of VFTO have an obvious difference compared with those of power frequency AC voltage, especially in the load-side, which verifies the effectiveness of the VFTO identification method based on WT and SVD proposed in this paper.

Integrated Local and Coordinated Overvoltage Control to Increase Energy Feed-In and Expand DER Participation in Low-Voltage Networks

Large amounts of active power injection by inverter-interfaced distributed energy resources (DER) is a common cause of overvoltage in low-voltage networks. Hence, local active and reactive power control (i.e., Volt/Watt and Volt/VAR, respectively) are adopted to limit voltage rise, leading to active power curtailment. This paper proposes an automatic control strategy to steer non-dispatchable (nd-DER) and dispatchable (d-DER) inverters in low-voltage networks, mitigating overvoltage through integrated local and coordinated Volt/Watt and Volt/VAR functionalities. Moreover, active power curtailment is avoided whenever possible. The method does not require <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> ) the implementation of optimization algorithms or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</i> ) knowledge about line impedance parameters or the location of DERs. The control approach exploits the power flow dispatchability of low-voltage networks comprising one point-of-common coupling with the distribution grid, allowing DERs close to the distribution transformer to also contribute to voltage regulation by only using a low-bandwidth communication link. Simulation results show the flexibilities of the proposed approach and demonstrate that active power injection can be increased by up to 25% for the considered scenario in comparison to conventional local Volt/Watt or Volt/VAR schemes. Experimental results based on a laboratory prototype with three inverter-interfaced DERs certify the applicability of the approach to real-life implementations.

Overvoltage Prevention and Curtailment Reduction Using Adaptive Droop-Based Supplementary Control in Smart Inverters

Recent developments in the renewable energy sector have seen an unprecedented growth in residential photovoltaic (PV) installations. However, high PV penetration levels often lead to overvoltage problems in low-voltage (LV) distribution feeders. Smart inverter control such as active power curtailment (APC)-based overvoltage control can be implemented to overcome these challenges. The APC technique utilizes a constant droop-based approach which curtails power rigidly, which can lead to significant energy curtailment in the LV distribution feeders. In this paper, different variations of the APC technique with linear, quadratic, and exponential droops have been analyzed from the point-of-view of energy curtailment for a LV distribution network in North America. Further, a combinatorial approach using various droop-based APC methods in conjunction with adaptive dynamic programming (ADP) as a supplementary control scheme has also been proposed. The proposed approach minimizes energy curtailment in the LV distribution network by adjusting the droop gains. Simulation results depict that ADP in conjunction with exponential droop reduces the energy curtailment to approximately 50% compared to using the standard linear droop.

배전계통에서 태양광발전의 출력 특성을 고려한 분산전원 수용성 증대 방안 연구

This study presents method to increase the hosting capacity considering output characteristics of photovoltaic (PV) generators in power distribution systems. The analysis of hosting capacity is conducted based on PV generators with large output volatility. The method for increasing hosting capacity is proposed in terms of overvoltage control at PCC voltage, thermal capacity of power distribution line, and interconnecting capacity of PV. The overvoltage of the distribution line according to power output of distributed generation can be controlled by applying a smart inverter with active and reactive power control functions. Currently, the thermal capacity standard of distribution lines follows the maximum normal operating capacity, but it is suggested to change it to the maximum emergency operating capacity. Through case studies, it appears that even if the maximum emergency operating capacity is applied to distribution line, the thermal capacity standard is not exceeded in the case of a smart inverter installed. This study reveals that there is no problem in the operation of the distribution systems even if the interconnection capacity of distributed generation changes from 10 [MVA] to 14 [MVA].

A two-level over-voltage control strategy in distribution networks with high PV penetration

Over-voltage in low voltage feeders due to the increasing penetration level of photovoltaic (PV) is a crucial issue to be addressed. There is a need to use more advanced voltage control methods to satisfy the response time of the control system. In this paper, a two-level voltage control strategy is presented. In the first level, based on day-ahead PV production scenario, Both the on-load tap changer (OLTC) and the battery energy storage systems (ESSs) are applied to deal with over-voltage in the peak of PV generation and as well the voltage drop in the peak of demand. In this level, the batteries and the tap position of the feeder transformer are optimally set in order to improve the voltage profile for the entire planning horizon (next day) taking into account the uncertainties in the PV production. In the second level, based on the partitioning of the distribution network, reactive power compensation capability of PV inverters is employed to fine-tune the voltage profile for the next operating hour. To model the uncertainty pertaining to the output power of PV units, the parameters of beta distribution function are estimated for each hour time interval, and then Monte Carlo simulation method is used to generate daily scenarios. In order to reduce the complexities and computational burden, the linearized model of power flow equations and PV inverters have been implemented. A real and practical, 10 kV, 37-bus system is used to test the performance of the proposed method.

Research on Transient Overvoltage Suppression Measures for Photovoltaics Connected to the DC Sending End in the Smart Power System for Industry 4.0

The development of smart power systems in Industry 4.0 will bring people better quality electrical energy. The photovoltaic power generation system in the smart grid for Industry 4.0 is also the focus of development. The rapid development of photovoltaic power generation systems will bring people cleaner and greener energy. However, it will cause the transient overvoltage phenomenon near the DC sending terminal when the large-scale photovoltaic plant is connected to the power grid, further bringing about a profound impact on the power grid and its security and stability. In this paper, it is proposed that the rise of transient overvoltage at the photovoltaic terminal is caused by three main factors including the reactive power surplus of DC commutation failure, the weak power grid at the sending terminal, and the control characteristics of the photovoltaic plant. Then, the coordinated control strategy of transient overvoltage is proposed, and the overvoltage control strategy of the DC transmission terminal and the photovoltaic power plant control strategy are, respectively, optimized. Finally, the influence parameters of overvoltage are analysed and the corresponding photovoltaic strategy is presented. The optimization results of photovoltaic parameters and the proposed strategies of photovoltaic power generation can effectively restrain the voltage or frequency fluctuation and power oscillation caused by HVDC commutation failure. This study promotes the development of the photovoltaic power generation system in the intelligent power system of industry 4.0.

Resonance overvoltage control algorithms in long cable frequency conversion drive based on discrete mathematics

AbstractIn order to solve the problem that the long cable variable voltage and variable frequency (VVVF) system does not adopt an effective capacitor voltage sharing control method, resulting in a poor effect of resonance overvoltage control, the resonance overvoltage control algorithm of the long cable VVVF system based on discrete mathematics is studied. First, the long cable frequency conversion drive system is established. In order to ensure voltage loss in the range of motor requirements, a frequency converter–cable–motor (ICM) system connection mode is used to maintain the system operation. Based on the research of the capacitor voltage balance control strategy of a long cable frequency conversion drive system, the discrete mathematical model of the AC side of the ICM system is established by using this control strategy. The improved constant active power controller is obtained by establishing the mathematical model, and the resonant overvoltage in a long cable frequency conversion drive is realized by using the constant active power controller. The experimental results show that the algorithm can effectively control the resonance overvoltage phenomenon in the long cable frequency control system, and the control accuracy is over 97%. It has good performance and can be applied in practice.

Control of PV systems for distribution network voltage regulation with communication delays

Various approaches including the real power control through photovoltaic (PV) inverters have been proposed to address voltage issues due to high penetration of PV generators (PVs). However, most of the existing methods did not include communication delays in the control loop. Communication delays, short or long, are inevitable in the PV voltage regulation loop and can not only deteriorate the system performance with undesired voltage quality but also cause system instability. In this paper, a novel approach is presented to convert the overvoltage control problem via PV inverters for multiple PVs into a problem of single-input–single-output (SISO) systems. The method can handle multiple PVs and different communication delays. The impact of communication delays is then systematically analyzed and the maximum tolerable delay is rigorously obtained. Different from linear matrix inequality (LMI) techniques that have been extensively studied in handling systems with communication delays, the proposed method gives the necessary and sufficient condition for obtaining a controller and the design procedure is explicitly and constructively given in the paper. The effectiveness of the proposed method is verified by simulation studies on a distribution feeder and the widely-used 33-bus distribution test system.

Fundamentals of Intelligent Automatic Reclosing of Long-Distance Transmission Lines with Shunt Reactors

Abstract—One effective overvoltage control method for the automatic reclosing cycle (ARC) of long-distance high-voltage transmission lines is intelligent automatic reclosing. The method is based on the selection of a reclosing time that is optimal for reducing the intensity of the transient process. The article investigates the basic transient process patterns in the ARC and analyzes various automatic reclosing methods. The principle of superposition is used for the analysis as well as the proposed universal electrical network model, which describes the processes at all ARC stages. It is shown that the intensity of the transient process at the automatic reclosing directly depends on the ratio of the supply voltage and line voltage at the reclosing time. It is shown that the overvoltage level can be reduced by line reclosing at the breaker contacts’ voltage zero-crossing time or at the valley point of this voltage envelope, but the intelligent automatic reclosing is more effective, combining both approaches and performing reclosing at the zero-crossing time near the envelope valley. Computational experiments confirm that the reclosing time has a decisive influence on the overvoltage in the ARC, while the influence of the compensation degree and transmission angle is not so important.

A Master/Slave Approach to Power Flow and Overvoltage Control in Low-Voltage Microgrids

This paper proposes a technique to control distributed energy resources in low-voltage microgrids aiming at (i) allowing power flow control at the point of connection with the upstream grid, (ii) keeping voltage profiles within the operational limits. The first feature is crucial in smart low-voltage power systems. In fact, it enables both demand-responses, which is extremely valuable from the point of view of distribution system operators and for energy trading, and the autonomous operation of the microgrid. The latter can be achieved by regulating to zero the power exchanged with the main grid. The second feature allows to limit voltage increases due to active power injection by distributed energy resources and, thus, to limit stresses on the electrical infrastructure and the served loads, which is a concrete issue as renewables become widely deployed in the low-voltage scenario. The proposed approach is firstly described in detail, then a systematic analysis of its local and global properties is reported. All the obtained results are verified considering the IEEE 37 test feeder in realistic operating conditions.

Simulation and research on over‐voltage suppression for high voltage transmission line

For different types of fault in transmission line, the generation mechanism of tripping and closing over-voltage is analysed. To built the double power supply system of high-voltage transmission line simulation model by PSCAD/EMTDC, finally, for the operation of over-voltage, when the line occurs of different types faults, simulation to study tripping and closing over-voltage's size and the extent of influence, derived its tripping and closing over-voltage suppression measures and control strategies. The results showed that: for the circuit breaker tripping and closing over-voltage, the circuit breaker shunt reactor has better effect on the over-voltage suppression and improves the reliability of operation and the safety of protection of the system.

Environmentally Friendly Compact Air-Insulated High-Voltage Substations

This paper investigates the possible options for achieving a substantial reduction in a substation footprint using air-insulated switchgear as a more environmentally-friendly alternative to gas-insulated substations that use SF6 gas. Adopting a new approach to surge arrester location and numbers, International Electrotechnical Commission (IEC) minimum clearances can be successfully selected instead of the maximum clearances as currently adopted by many utilities, as is the case in the UK. In addition, innovative alternative compact busbar arrangements using vertical and delta configurations have been proposed by the authors. A further opportunity for compaction is offered by the application of compact and integrated technology offered from several manufacturers. The full overvoltage control within the entire substation under any surge condition is a key aspect of the feasibility of this type of substation. This work demonstrates that the new design option can be an attractive alternative for future substation configuration with minimum footprint.

Design of Wind Turbine Dynamic Trip-Off Risk Alarming Mechanism for Large-Scale Wind Farms

The wind power in China is being developed mainly in terms of large scale, long distance, and high clustering. In this scenario, the uncertainty of wind farm operation gradually becomes a significant factor that power grid dispatcher needs to deal with. Among which, trip-off risk of wind turbine results from system disturbance, fault and fault removal of wind farm, etc. Besides, the geographical distribution of wind turbine usually also has the impact on the trip-off risk of wind farm. In view of above factors, existing security analysis methodology is difficult to satisfy the requirement of real-time alarming due to extreme analytical difficulty and huge computing complexity. Therefore, reasonable design of trip-off risk measure index of wind turbine becomes a key issue to implement a dynamic trip-off real-time alarming system. In this paper, a wind turbine trip-off decision tree system is constructed with the discrete characteristics of wind turbine distribution in wind farms taken into account. The decision trees can perform data mining using online information and make fast prediction on wind turbine voltage out-of-limit and trip-off situations under anticipated accident sets. The trip-off risk measure indexes are then output in light of the prediction results, which can provide intuitive risk level information and decision references for operators in wind farms and power systems. The results of case studies show that the proposed method can meet the requirement of prediction accuracy and resolve the contradictions between the amount of modeled nodes, the diversity of anticipated faults and the computation time when performing over-voltage early warning and control strategies.

Electromagnetic transient study on flexible control processes of ferroresonance

Ferroresonance, which is a common phenomenon in power systems, have threatened the security of power systems for a long time. Although several ferroresonance suppression measures have been applied in power systems, ferroresonance still occurs occasionally. In this study, a flexible control strategy to control different ferroresonant modes is proposed. The behavior of a typical ferroresonant circuit acquired from a ferroresonance testing system to obtain the electromagnetic transient and control details of the control method is also investigated. The key parameters in the control module are determined, including the switching frequency and the coefficients of the proportional–integral (PI) controller. Then, six typical ferroresonant overvoltages are selected as control systems using the proposed method. Given the effect of a damping resistor and fully controllable power electronic switches with a gate signal controlled by a proportional–integral (PI) control system, these six typical ferroresonant overvoltages can all be suppressed in 0.12s to the non-ferroresonant state after the controller is activated. The electromagnetic transients, including the essential system state quantity transients in the control process, are also investigated. At last, a laboratory prototype is implemented, and the experimental results show that the proposed method is useful for ferroresonant overvoltage control.

Optimal Cooperative Management of Energy Storage Systems to Deal with Over- and Under-Voltages

This paper presents an optimal cooperative voltage control approach, which coordinates storage units in a distribution network. This technique is developed for storage systems’ active power management with a local strategy to provide robust voltage control and a distributed strategy to deliver optimal storage utilization. Accordingly, three control criteria based on predefined node voltage limits are used for network operation including normal, over-voltage, and under-voltage control modes. The contribution of storage units for voltage support is determined using the control modes and the coordination strategies proposed in this paper. This technique is evaluated in two case studies to assess its capability.

Micro Static Var Compensator for Over-Voltage Control in Distribution Networks with High Penetration of Rooftop Photovoltaic Systems

A micro static var compensator (µSVC) is introduced in this work to prevent the over-voltage problems in radial distribution networks with high number of rooftop photovoltaic (PV) connections. The µSVC is aimed to use in the PV system that has the fixed-power factor inverter, which cannot provide the active voltage controllability. The µSVC is a small shunt compensator installed parallel with the PV system and providing the automatic reactive power support to deal with the dynamic voltage variations at the point of common coupling. Two reactive power control methods, Q(P) and Q(V), can be employed into each µSVC depending on the location of PV systems. Moreover, the coordinated reactive power control among µSVCs, without communication system requirement, is presented for enhancing the Volt-Var controllability to the group of PV systems located in the same feeder. The dynamic voltage control performances are examined on simulation in DIgSILENT PowerFactory software. The results showed that the proposed control method can mitigate the rise of voltage level sufficiently.