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In order to improve the automatic generation control (AGC) performance of thermal generators, this paper presents a stochastic model predictive control (SMPC) approach for a battery/flywheel hybrid energy storage system (HESS) to distribute power. The approach combines an adaptive Markov chain for power demand prediction of HESS, a scenario tree generation and model predictive control strategy. To develop an effective prediction model to deal with the randomness of a thermal generator in response to AGC command, a Markov chain is used to describe the randomness of the HESS power demand, and a posteriori information is used to adapt to the fluctuation of the AGC command. A scenario tree generation approach is proposed to make better use of the Markov probability matrix. Based on these efforts, an SMPC approach is proposed for HESS energy management. Simulation results show that the regulation performance of the proposed approach outperforms conventional approaches, and that its performance is close to the model predictive control strategy with prescient information of the future power demand. In addition, compared with other approaches such as rule-based strategies, it does less damage to the battery and yields higher annual average net benefits in the whole life cycle.

Energy storage systems (ESSs) are promising solutions for the mitigation of power fluctuations and the management of load demands in distribution networks (DNs). However, the uncertainty of load demands and wind generations (WGs) may have a significant impact on the capacity allocation of ESSs. To solve the problem, a novel optimal ESS capacity allocation scheme for ESSs is proposed to reduce the influence of uncertainty of both WG and load demands. First, an optimal capacity allocation model is established to minimize the ESS investment costs and the network power loss under constraints of DN and ESS operating points and power balance. Then, the proposed method reduces the uncertainty of load through a comprehensive demand response system based on time-of-use (TOU) and incentives. To predict the output of WGs, we combined particle swarm optimization (PSO) and backpropagation neural network to create a prediction model of the wind power. An improved simulated annealing PSO algorithm (ISAPSO) is used to solve the optimization problem. Numerical studies are carried out in a modified IEEE 33-node distribution system. Simulation results demonstrate that the proposed model can provide the optimal capacity allocation and investment cost of ESSs with minimal power losses.

With the rapid development of distributed power and new energy vehicles, the traditional distribution network is facing enormous challenges. The development of multi-station integration technology is an effective way to solve the above problems. In this paper, a new multi-station integration topology is proposed. The new multi-station integration topology uses soft open point (SOP) as the key equipment of the system, and adopts the hierarchical power supply mode for data center, electric vehicle charging pile and other function stations. Then, based on the new topology of multi-station integration and smooth switching of converter control mode, a coordinated control strategy is proposed. Through the coordinated control strategy to control the working mode of each function station, and then further optimize the system operation conditions. Based on Matlab/Simulink, the simulation model of multi-station integration is established, and two different application scenarios are analyzed. The simulation results verify that the new topology of multi-station integration and its coordinated control strategy effectively improve the voltage level of the distribution network, improves the reliability of sensitive load power supply, and ensure the safe and reliable operation of multi-station integration system.

In a 100% clean energy town, to meet the energy balance and reduce the impact of power fluctuations on the main grid, in this paper, a hierarchical optimal energy management strategy (EMS) for a hybrid energy storage system (HESS) is proposed. The EMS consists of three layers. To meet the requirement of 100% clean energy, in the upper layer, a HESS economic operation model based on the mixed integer non-linear programming (MINLP) is presented. Then, considering the uncertainty of renewable energy and load, a power prediction model is presented in the middle layer. In addition, to reduce the power disturbance on the main grid caused by the stochastic power, a stochastic model predictive control (SMPC) strategy is implemented to optimize the power allocation of a HESS. In the lower layer, to reduce the power fluctuations of the lithium-ion battery (LiB) when mitigating minute-scale power fluctuations, a HESS optimal power allocation strategy based on Pontryagin's minimum principle (PMP) is proposed. In every control period, each layer is optimized based on the results of the previous layer. Finally, a simulation study is provided to validate the effectiveness of the proposed EMS. The results show that the proposed strategy has good performance in typical scenarios.

A large number of distributed photovoltaic power generations that are connected to the distribution network will have a serious impact on the power quality of the distribution network and load power security. Integrating energy storage and photovoltaic cells into the micro-grid can effectively improve the power quality of distribution network and the reliability of load consumption. This paper is a research on the seamless switching control strategy for micro-grid integrating photovoltaic and energy storage (MIPES). Firstly, it analyzes the boundary conditions of MIPES seamless switching control of grid-connected/islanded modes and studies the output characteristics of photovoltaic cells over a day. The DC bus voltage can be stabilized within a certain range to meet the requirements for MIPES seamless switching of grid-connected/islanded mode. Secondly, this paper analyzes the working characteristics of silicon controlled rectifier (SCR). The results show that when SCR is turned off naturally, the load voltage will rise sharply, affecting the safety of local load. Therefore, a control strategy for SCR switch forced shutdown is proposed to solve the problem of sharp rise of load voltage during grid-connected/islanded conversion of MIPES and to ensure the load security. Finally, relevant simulation studies are carried out to verify the rationality and effectiveness of the proposed control technology.

The widely used flywheel energy storage (FES) system has such advantages as high power density, no environment pollution, a long service life, a wide operating temperature range, and unlimited charging&ndash, discharging times. The flywheel array energy storage system (FAESS), which includes the multiple standardized flywheel energy storage unit (FESU), is an effective solution for obtaining large capacity and high-power energy storage. In this paper, the strategy for coordinating and controlling the charging&ndash, discharging of the FAESS is studied in depth. Firstly, a deep analysis is conducted on the loss generated during the charging&ndash, discharging process of the FESU. The results indicate that the loss is related to the charging&ndash, discharging of power. To solve the problems of over-charging, over-discharging, and overcurrent caused by traditional charging&ndash, discharging control strategies, this paper proposes a charging&ndash, discharging coordination control strategy based on the equal incremental principle (EIP). This strategy aims to minimize the total loss and establish a mathematical model of optimal coordination control with the constraints of total charging&ndash, discharging power, rated power limit, over-charging, over-discharging, and overcurrent. Based on the EIP, the optimal distribution scheme of power charging&ndash, discharging is determined. Secondly, this paper gives the specific implementation scheme of the optimal coordinated control strategy. Lastly, the charging&ndash, discharging coordinated control strategy is verified by examples. The results show that the coordinated control strategy can effectively reduce the loss during the charging&ndash, discharging process and can prevent over-charging, over-discharging, and overcurrent of the system. Overall, it has a better control effect than the existing charging&ndash, discharging control strategies.

In recent years, inspired by the idea from FACTS in ac system, scholars put forward the concept of DC FACTS, and the research and application of DC FACTS equipment for DC distributed network is discussed, such as the DC voltage compensator, DC power flow controller, DC fault current limiter and so on. In order to further improve the cost performance of DC FACTS device, drawing on the research results of AC FACTS multiplex, this paper aims at exploring a new structure for series-parallel multi-function composite controller in dc grid which contains multi-function in power flow control, voltage compensation and fault current limiting. The working principle of series-parallel multi-function composite controller is proposed and the main circuit parameter design method is described. The simulation model is built to show the feasibility of the proposed topology.

Custom power park is an industrial/commercial park that integrates state-of-the-art power quality devices. The power quality devices can be classified into two catalogues: voltage quality enhancement devices and current quality enhancement devices. In order to meet the requirement of large capacity, high reliability, high flexibility in both the voltage and current compensation, several operation modes of multiple DVRs and multiple DSTATCOMs are proposed. Moreover, aiming at the negative interaction which may occur when DVR and DSTATCOM are installed on the same feeder, the paper analyzes the mechanism of the interaction with the harmonic impedance method. The stability problem may occur due to impedance parameter mismatch of two devices. Finally, the analysis results are verified by time domain simulation.

Traditional schemes of UPQC and OPEN UPQC are proposed in literature to solve both the voltage quality problem of the load and the current quality problem of the grid. However, the traditional UPQC is not flexible when configured to compensate an industrial park if not all loads are sensitive. The previously proposed OPEN UPQC scheme has the advantages that communication coordination are required. To solve the above problems, a new topology of OPEN UPQC is proposed in this paper. The advantages of the new topology are analyzed in detail and the control scheme and the corresponding power flows are given. Further application topology is also given to not only achieve the function of conventional UPQC, but also to improve the voltage quality within the supply region. Simulation results are presented to verify the effectiveness and feasibility of the proposed topology.

For some kinds of motor drive systems, such as the variable-pitch wind power system, the back-up power needs to output very high power in a short time to meet the emergency. And the work temperature range and cycle life is required more strictly. Supercapacitors are very suitable to be the energy storage component due to its advantages of high power density, high charging speed and extremely high cycling capability. However, the energy density of supercapacitor is relatively low, so the energy management method of supercapacitors based UPS is very important to increase the energy usage efficiency. In this paper the finite state machines theory is applied as management method for supercapacitors based uninterruptable power supply (UPS). Design procedure is discussed in detail. Finally, the simulation and experimental results are provided to verify the design.

As a new energy storage device, ultracapacitors are able to attain greater energy densities while still maintaining the characteristic high power density of conventional capacitors. As a result, ultracapacitor based power electronics system will become an attractive power solution to an increasing number of applications. But in this situation, the ultracapacitor usually has the shortest span, and then determines the system lifetime. Therefore, a deterioration diagnosis of the ultracapacitor is needed for preventive maintenance of the circuit. In this paper the deterioration characteristics of ultracapacitor is presented and an online deterioration diagnosis method is proposed. Experimenal results are given to verify the analysis.

Supercapacitor is an emerging technology in the field of energy storage systems that can offer higher power density than batteries and higher energy density over traditional capacitors. Supercapacitor will become an attractive power solution to an increasing number of applications, such as renewable energy power generation, transportation, power system and many others, because of its advantages which include high charge/discharge current capability, very high efficiency, wide temperature range, etc. In this paper, the advantages and disadvantages of supercapacitor are discussed and some critical technologies for designing supercapacitor energy storage system are presented in detail. Finally, the role of the supercapacitor in renewable energy power system is discussed and a supercapacitor based uninterrupted power system (UPS) for the wind turbine pitch systems is presented as a design example.

Now pitch systems are widely used in the wind turbine system. To enhance stability, the pitch system is equipped with a ride through system to immediately ensure the reliable functioning of the fast blade pitch system in the event of a total power failure. Supercapacitor, as a new energy storage component, offers excellent performance, high power density, wide temperature range, and long life, particularly suitable for this application. In this paper, compared with other forms of energy storage components, the advantages and disadvantages of supercapacitor used in the ride through system for wind turbine pitch systems are discussed, and the design of supercapacitor based ride through system is presented in detail. Finally, experimental results are reported to verify the design.

As a new technology, supercapacitor can attain greater energy density than those of conventional capacitors and greater power density than those of batteries. As a result, supercapacitors may become an attractive power solution for an increasing number of applications. In this paper, after a brief introduction of supercapacitor components, a supercapacitor based ride-through system for industrial drive applications is presented. The design details are discussed and experimental results are given.