Control Strategy For Power System Research Articles

AC/DC Hybrid Power System Damping Control Based on Estimated Model Predictive Control Considering the Real-Time LCC-HVDC Stability

High Voltage Direct Current (HVDC) can quickly vary its power to stabilize an AC power system when the latter is subject to a disturbance. Typically, linear control is used to design that control strategy. However, due to the uncertainties of the faults and the system model, it is necessary to estimate the linear model of the post-fault power system using real-time measurements. This leads to two main problems: Firstly, after the fault, the HVDC will quickly evolve to steady-state operating conditions and, therefore, result in an unobservable control matrix. Secondly, the HVDC power should not exceed its stable range, which is limited by the post-fault system. To address the above issues, the main novelties are as follows: First, this paper proposes a novel system identification method to handle that case when there is no control input excitation. Second, this paper presents an AC/DC hybrid power system control strategy that fully considers the real-time stability constraints of the HVDC. More specifically, this paper proposes to estimate the system matrix and the control matrix separately. Based on the linearized model of the AC/DC hybrid system, the control matrix is calculated using the sensitivities of the active powers of the generators with respect to those of the HVDC. Then, the system matrix is estimated in real-time using measures of the power angle and frequency. Finally, by processing the local voltage and current measurements, the associated Thevenin equivalent parameters on the system side of the HVDC connecting point are estimated in real-time and the upper bound of the DC power is determined. According to the linearized model and the HVDC power constraints, a control strategy is proposed using the model predictive control method. Simulation results reveal the effectiveness of the proposed strategy.

Construction of intelligent energy measurement system suitable for energy block chain technology

Abstract With the increasing scale and complexity of power systems, it is gradually difficult for the traditional central control system to meet the control and management needs of the new power systems. In this paper, a control strategy based on multi-terminal information fusion is proposed to fuse and integrate the information from different control nodes to form a global new power system control strategy. A hierarchical cluster-based control node organization is also proposed to organize the control nodes according to function and hierarchy to realize the cooperative control and maximum power point tracking of the new power system. Finally, the effectiveness of the effect of the cooperative control strategy is verified by modeling and simulating the cooperative control network of the new power system. The simulation results show that the charge frequency fluctuation range is stable in [46.38Hz, 55.15Hz] for all three scenarios, which is only 0.02Hz away from the lower limit of the set allowable frequency fluctuation range [46.35Hz, 56.38Hz], indicating that the cooperative control strategy stabilizes the charge frequency fluctuation within the effective range. Therefore, this paper achieves further exploration of the optimization and improvement of the new power system cooperative control network, which achieves more efficient, stable, and reliable power system control and management.

Research on Hazard Analysis and Control Strategy of Power System Dispatching Operation Based on Information Fusion Technology

Abstract In this paper, a decision model for grid fault diagnosis based on multi-source information fusion is established, and the probability of component fault is obtained by using the change of switching quantity characteristic information and electrical quantity characteristic information during grid fault, and the static fault degree obtained by switching quantity information and the voltage and current energy distortion degree and fault degree obtained by electrical quantity information is used as independent evidence bodies, which are fused by improved D-S evidence fusion technique, and the fused The results are decided by improved fuzzy C-mean decision model to finally determine the fault components. Then, the optimal control of the grid is studied, and the corresponding self-healing control model is established according to the different operating conditions of the system so as to propose a self-healing control strategy of the microgrid based on the improved particle swarm algorithm. After analysis and verification, the accuracy of the grid fault diagnosis method proposed in this paper reaches 0.9681, and the diagnosis results are consistent with the pre-defined fault elements compared with FCM. The system network loss decreases from 0.146 kW to 0.031 kW, and the maximum power supply capacity increases from 1.574 to 2.468 after using the improved particle swarm algorithm-based microgrid self-healing control strategy. Therefore, the method in this paper can improve the reliability of grid operation and resist the risk of accidents.

A Fully Non-Interactive Automatic Generation Control Strategy for Multi-Area Interconnected Power Systems

Frequency is an important index for the stable and secure operation of the power system. In the conventional methods, an inappropriate value of the frequency bias coefficient will lead to over-biasing or under-biasing of generators, causing unintended cross-regional interaction. This paper proposes a fully non-interactive automatic generation control strategy for power systems. Through the derivation of deviation of frequency and tie-line active power under disturbance, it’s found that the disturbance can be located from the deviation of frequency and active power of tie-line. Based on this, the conventional AGC control model is modified. With the proposed method, only the AGC units in disturbed areas respond to disturbances, and the AGC units in other areas will not act. Thus, the unintended cross-regional interaction in the conventional AGC control method is avoided. The proposed method only needs minor modification to the conventional AGC control model and hence is easy to implement for onsite application. The effectiveness of the proposed strategy is confirmed via simulation on the Kundur four-machine two-area system.

Evaluating the Optimal Electric Vehicle Location for a Hybrid Energy System Controlled with Novel Active Disturbance Rejection Controller

Power system control is an important issue with regard to power system safety, flexibility, and reliability. Over the years, various new power system control strategies have been explored, but the main disadvantage of these control strategies is their complexity in structures with respect to industrially applied PID controller. The present paper introduces a novel control strategy based on modified disturbance rejection control, which is a modification of the PID controller that not only preserves the simplicity of control design but also offers an effective control based on state observer-based control law. The proposed control strategy addresses some basic limitations of a PID controller and implements modified control law to remove these limitations. In order to prove the effective control of the proposed control strategy, a standard IEEE-39 bus power system integrated with renewable energy generations is developed, and a comparative analysis of the proposed controller is performed with respect to its ancestor controllers. The comparison is validated based on the system dynamic responses like frequency and tie-line power deviations when the power system is subjected to different disturbances. Furthermore, the power system is integrated with electric vehices (EVs) in vehicle-to-grid (V2G) mode in order to ascertain the effect of EVs when used in V2G mode. A novel study is carried out in which the optimal location of EVs in the power system is determined based on the enhancement in stability of the power system by EVs. The analyses are carried out in MATLAB Simulink software. Simulation reports reflect the optimal control action of the proposed controller with respect to already established strategies projected in the literature. Moreover, the results illustrate that EVs when connected in Area 1 and Area 3 of the power system, the system deviations and steady-state errors are much less as compared to the other cases.

An adaptive under-frequency optimal control strategy for power system combined pumped storage and under-frequency load shedding.

With the construction and development of ultra-high voltage (UHV) power grids, large-scale, long-distance power transmission has become common. A failure of the connecting line between the sending-end power grid and the receiving-end power grid will cause a large-scale power shortage and a frequency drop in the receiving-end power grid, which can result in the frequency collapse. Presently, under-frequency load shedding (UFLS) is adopted for solving the frequency control problem in emergency under-frequency conditions, which can easily cause large load losses. In this context, a frequency coordination optimal control strategy is proposed, which combines the mode transition of pumped storage units with UFLS to deal with emergency under-frequency problems. First, a mathematical model of the frequency dynamic response is established, which combines the mode transition of pumped storage units with UFLS based on a single-machine equivalent model. Then, an optimal model of the minimal area of the power system’s operation frequency trajectory is introduced, yielding the optimal frequency trajectory, and is used for obtaining the action frequency of the joint control strategy. A simulated annealing algorithm based on the perturbation analysis is proposed for solving the optimal model, and the optimal action frequency is obtained that satisfies the transient frequency offset safety constraint of the power system. Thus, the joint optimal control of the mode transition of the pumped storage units and UFLS is realized. Finally, the EPRI-36 bus system and China’s actual power grid are considered, for demonstrating the efficiency of the proposed strategy.

Research on voltage stability and control strategy of power system considering grid connected charging of electric vehicles

The development of new energy vehicles is an important measure to deal with the growing energy demand and climate change. Especially in recent years, with the support of national policies and the maturity of electric vehicles(EVs) related technologies, the number of EVs has increased explosively, and the situation is very good. However, it also means that a large number of charging loads will be connected to the power grid, which will put great pressure on the safe and stable operation of the power grid. Although there have been many studies on the impact of EVs integration into modern power grid, most of the EVs load models are based on probability function and lack accuracy. Therefore, starting with the actual operation data of EVs charging station, this paper studies the influence of a large number of EVs charging loads on the static voltage stability of power grid. It is found that the charging load of large-scale EVs is added to the power grid, which significantly reduces the stability of power grid voltage, especially at the place connected to the EVs load and far away from the balance node. In addition, when the charging station adopts the time-of-use(TOU) price strategy, it can effectively improve the voltage stability of the whole network.

Research on the frequency synchronization control strategy for power system

Power system interconnection makes the modern power system become a huge and complex network, which brings great challenges to frequency stability. The pinning control strategy can reduce the control cost and has a unique advantage. It is one of the most effective method to solve the problem of complex network synchronization. Thus, based on the principle of pinning control strategy, a frequency synchronization control method is proposed to solve the problem of power grid frequency synchronization in this paper. Firstly, in the controller design phase, the pinning control model of a power system is defined based on mathematical model of hydroelectric generator. And the pinning controller is designed based on dynamic compensation LMI sliding mode control. The correctness of the controller is verified by the simulation of a Lorenz chaotic system. Secondly, to determine the controlled generator nodes, an index for evaluating the importance of the generator nodes is defined based on the node deletion method and fuzzy method. Finally, combined with the reality of power network, the external coupling matrix L is calculated based on the successive extended annular domain method and considering the ability of the nodes to receive signals. The feasibility of this method is verified by simulation of the IEEE30-bus system.

Security Assessment and Coordinated Emergency Control Strategy for Power Systems with Multi-Infeed HVDCs

Short-circuit faults in a receiving-end power system can lead to blocking events of the feed-in high-voltage direct-current (HVDC) systems, which may further result in system instability. However, security assessment methods based on the transient stability (TS) simulation can hardly catch the fault propagation phenomena between AC and DC subsystems. Moreover, effective emergency control strategies are needed to prevent such undesired cascading events. This paper focuses on power systems with multi-infeed HVDCs. An on-line security assessment method based on the electromagnetic transient (EMT)-TS hybrid simulation is proposed. DC and AC subsystems are modeled in EMTDC/PSCAD and PSS/E, respectively. In this way, interactions between AC and DC subsystems can be well reflected. Meanwhile, high computational efficiency is maintained for the on-line application. In addition, an emergency control strategy is developed, which coordinates multiple control resources, including HVDCs, pumped storages, and interruptible loads, to maintain the security and stability of the receiving-end system. The effectiveness of the proposed methods is verified by numerical simulations on two actual power systems in China. The simulation results indicate that the EMT-TS hybrid simulation can accurately reflect the fault propagation phenomena between AC and DC subsystems, and the coordinated emergency control strategy can work effectively to maintain the security and stability of systems.

A coordinated voltage control scheme for power system with wind farm integration based on EID compensation

Rapid increase of wind power installation brings new issues and challenges for grid security operation and one of the most important key issues is reactive power and voltage control capability of wind farms. This paper proposes a coordinated voltage control strategy for power system with wind farm based on equivalent input disturbances (EID) compensation. Firstly, the voltage control model of power system with wind farm based on doubly fed induction generator (DFIG) is established. The power system adopts reactive power compensation device for voltage control, and the wind farm connected to the grid adopts frequency converter of DFIG to adjust reactive power output. They can coordinate each other to realize voltage stability control of the wind farm connected to the grid. Moreover, when the system is subjected to load disturbance or wind speed disturbance, the proposed method based on EID compensation also can keep the voltage stability of power system with wind farm. Finally, the simulation results show the feasibility and effectiveness of the proposed voltage coordinated control method in voltage regulation.

Control strategy of energy saving for power system in hydraulic surface drilling rig

In order to achieve the purposes of better energy saving and lower fuel consumption under the condition in which load changes frequently and fluctuates dramatically, the energy-saving control strategy of power system is put forward in a hydraulic surface drilling rig. The structure of power system and working conditions of hydraulic surface drilling rigs are described. The mathematical models of the external characteristic for engine, variable pump, and air screw compressor in hydraulic surface drilling rig are presented in detail. Then the control strategy of power system and the fuzzy PID control algorithm to implement this strategy are proposed to control the engine speed in various working states. The simulation analysis and experimental investigation are carried out to study the fuel consumption in the typical operating conditions by using energy-saving control strategy. Results show that the energy-saving control strategy can reduce fuel consumption for the hydraulic surface drilling rig while ensuring that the system performance is not sacrificed.

On the steady-state behavior of a nonlinear power system model

In this article, we consider a dynamic model of a three-phase power system including nonlinear generator dynamics, transmission line dynamics, and static nonlinear loads. We define a synchronous steady-state behavior which corresponds to the desired nominal operating point of a power system and obtain necessary and sufficient conditions on the control inputs, load model, and transmission network, under which the power system admits this steady-state behavior. We arrive at a separation between the steady-state conditions of the transmission network and generators, which allows us to recover the steady-state of the entire power system solely from a prescribed operating point of the transmission network. Moreover, we constructively obtain necessary and sufficient steady-state conditions based on network balance equations typically encountered in power flow analysis. Our analysis results in several necessary conditions that any power system control strategy needs to satisfy.

Research on User-Side Distributed Power System Control Strategy

Distributed power system, especially the distributed power and micro-grid system in the mountain villages, islands and remote areas, has many advantages, which can be used as an effective supplement of grid to help solve the problem of electricity supply. The connected-grid inverter needs to be able to work in both grid mode and island operation mode in order to ensure the safety of the local critical load. The paper proposed the seamless switching control strategy for two modes of switching. The experimental results verify the property of the topology structure and control strategy.

Innovative method for energy management: Modelling and optimal operation of energy systems

This paper presents an optimal management control strategy for power systems in industrial plants. A dedicated code has been developed to perform system analysis and simulation. The energy/mass balances existing between building and power plant has been depicted through a mathematical model based on vector equations, taking into account the behaviour of each system component. The main result is the definition of the power plant component set points satisfying the energy load under predefined optimization criterion (i.e. system efficiency, costs, pollutant emissions). Input data are the industrial plant loads, both electric and thermal, the technical characteristic of the installations, and the cost of electricity and fuel. As a general result we show that the optimal management of a power plant is as significant as the efficiency of its components for energy saving purposes. In particular, the correlation between the component set point profiles and the energy/cost/pollution savings is highlighted. Yearly simulations are performed on an existing energy system of an industrial plant varying the frequency of energy load dataset. The considered time steps are month, half a day, 4 h and 1 h. The results demonstrate that the whole power plant management leads to a global reduction of the cost and that the availability of more detailed energy load dataset leads to better operation cost estimation. As expected, considering a large time-step, the variation of energy load is not appreciable. The energy saving potential of this method is demonstrated allowing the best plant management solution under different energy loads.

Decision Tree Assisted Controlled Islanding

Controlled islanding refers to the controlled separation of an interconnected power system into electrically isolated regions. The objective of this paper is to develop adaptive controlled islanding as a component of an emergency power system control strategy. There are two primary aspects of controlled islanding: 1) where to and 2) to island? Assisted by a decision tree (DT) approach, this paper seeks to address the when to island aspect. A decision tree based tool is proposed to recognize conditions existing in the system that warrant controlled islanding. A 29-generator, 179-bus system is employed to demonstrate the tool. Simulation data are used to train DTs, and the online performance of DTs is then evaluated as part of a controlled islanding strategy

Switching control strategy for power systems with losses

Energy functions were developed for assessment of stability of multimachine power systems. This paper develops a switching control strategy for suppression of oscillations of power systems. This strategy is based on energy function using shunt and series compensators for lossy multimachine power systems. The switching control design is on the basis of maximizing the convergence rate of an energy function. Fast multimode damping and the monotonic convergence of the energy is demonstrated on a three machine power system.

Power system analysis using space-vector transformation

In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits.

Power System Analysis Using Space Vector Transformation

The space vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and analyze power sources and loads with different connections (delta and wye). this method can also be applied to analyze steady-state or transient phenomena and unbalanced sources, including harm, onics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits.

A Local Control Strategy For Power Systems in Transient Emergency State Part I: Functional Design

This paper is concerned with the investigation of a systematic corrective control approach for the transient emergency state problem of the power system. The proposed new control framework involves distributing the task of system transient stability margin improvement among several local facilities dedicated to the various subsystems comprising the power system. The functional design of the various local controllers to undertake local information processing and provide appropriate closed-loop stabilizing control action during severe transient disturbance is presented. An illustrative example is included to demonstrate the effectiveness of the proposed local control framework.

A Local Control Strategy for Power Systems in Transient Emergency State. Part II: Implementation and Test Results by Simulation

A Local Control Strategy for Power Systems in Transient Emergency State. Part II: Implementation and Test Results by Simulation