The large-scale grid connection of doubly fed induction generator (DFIG) will have an important impact on the safe and stable operation of the power system. Simulating the dynamic behavior of DFIG as accurately as possible is critical for conducting related research. However, due to different development backgrounds and usage purposes, there are certain differences in the DFIG models provided by different simulation software. There may be large deviations in the simulation under different scenarios. And with the continuous improvement of wind power penetration, the simulation bias caused by model differences may be accumulated and amplified. To solve this problem, the difference between the DFIG model in two main power system simulation software DIgSILENT and PSASP is studied. The corresponding simulation scenes are set to compare the dynamic behavior of DFIG in the two simulation software, and the characteristics and applicability of the two softwares are analyzed. The research results show that the differences between the two softwares are mainly reflected in the DFIG control model and the degree of simplification, and their applicable scenes are also different accordingly. The obtained conclusions can provide reference for wind power grid-connected simulation analysis, and have engineering application value and practical significance.

For the power system with a large number of power electronic equipment, it is difficult for the traditional electromagnetic transient real-time simulator to realize the small step length simulation. To solve this problem, a hybrid step length real-time simulation method based on field programmable gate array (FPGA) and CPU is adopted to build a transient real-time simulator for power system. Taking photovoltaic power generation system as an example, the system is divided into large step part and small step part by model segmentation method, and asynchronous communication between FPGA and CPU is realized through Ethernet, forming a large step length and small step length hybrid co-simulation platform. Aiming at the error caused by system data interaction after model segmentation, a pulse equivalent averaging method is proposed to equivalent the output voltage of inverter at AC side, so as to reduce the error and FPGA hardware resource occupancy rate. Finally, the real-time simulation results are compared with the simulation results of Simulink offline model and the model before optimization, and it is verified that the proposed method has certain advantages in reducing the resource occupancy under the premise of ensuring the simulation accuracy.

In order to realize the development and utilization of large-scale wind power, it is necessary and urgent to carry out the corresponding simulation research on large-scale wind farm. Due to the large and complex modeling of wind farm, the existing modeling methods adopt equivalent processing to wind farm with single machine or multi-machine. The equivalent model is small, the order of state space equation is low, and it is easy to simulate. However, there are problems such as low accuracy, poor flexibility and weak applicability of the model. In view of this, this paper proposes a full-topology real-time simulation method for large-scale wind farms. The main principle of this method is the combination of model segmentation method and parallel processing technology. To verify the effectiveness of the proposed method, a self developed real-time simulation platform (UUREP-300) is used to simulate an offshore wind farm in real time. Simulation results show that the proposed method can effectively reduce the computational and storage burden of the simulator, and greatly improve the simulation speed and scale, and can achieve the full topology real-time simulation on large-scale wind farms.

Reasonable wind farm faults transient equivalent modeling is the basis for the analysis of grid connected with wind power. In doubly-fed wind farms, the operating points and fault ride-through modes of each unit are different, so single-machine multiplication cannot accurately characterize the transient characteristics of the whole wind farm. Aiming at consistency of wind farm output short circuit current, analytical formula of output short-circuit current under different fault ride-through models of single doubly-fed induction generator(DFIG) machine is theoretically analyzed. Using the voltage drop that indicates external fault and rotate speed that describes its own operating point as the clustering indicators, adopting different indicators weight at different fault stages, DFIG similarity distance matrix is established. The DFIGs are clustered based on hierarchical clustering algorithm, and the parameters of the same cluster are equalized according to the principle of constant output short-circuit current. Comparison results of the wind farm detailed and equivalent model built in PSCAD indicate that the equivalent model can fully describe the characteristics of wind farm output short-circuit current, and the equivalent method is reasonable and effective.

The power system with high proportion of renewable energy and high proportion of power electronic equipment (namely, “double high” power system) is gradually establishing, and the accurate prediction and safe control of grid frequency response are facing greater challenges. This paper firstly presents the establishment and application methods of grid frequency response model in details, including time-domain simulation method, linear analysis method, single-machine equivalent method and artificial intelligence-based frequency prediction method. Then, the temporal and spatial distribution model of power system dynamic frequency based on wide-area measurement system and inertia assessment characteristics are discussed. In addition, the optimization of renewable energy control and under-frequency load shedding schemes based on frequency model are analyzed. Lastly, the main issues to be solved in frequency response model and prediction of new power system are prospected.

Most of the researches about the wind turbines frequency regulation are based on the real-time simulation therefore fail to evaluate the frequency regulation capability quantitatively. To deal with this, this article derives the system frequency response model with wind turbines (WTs) participating in the frequency regulation under the deloaded and maximum power point tracking (MPPT) status. The frequency nadirs (FN) under the two status are calculated according to the system frequency response model and the WT frequency regulation capability can be evaluated by FN quantitatively.Under the deloaded working status, the FN can be obtained by directly taking the inverse Laplace transformation of the system frequency response model. However under MPPT status it is difficult to calculate the FN by directly taking the inverse Laplace transformation due to the high order of the frequency response model. Therefore an order reduction method by negelecting the non-dominant poles is proposed. The FN is calculated through the reduced model. Then the sensitivities of FN with respect to the frequency controller gain and the WT initial speed can be obtained. The sensitivities indicate that the FN is affected both by the controller gain and the WT initial speed. The FN can be improved by increasing the controller gain while the increase of the initial WT speed results in a lower FN. Finally, the influence on the FN of each factor is demonstrated by simulation.

With the improvement of intermittent energy such as photovoltaic in new energy grid, the disadvantages of low inertia and poor stability of the high proportion of new energy grid become more and more obvious. According to the characteristics that the synchronous motor-generator pair (MGP) can provide a large moment of inertia and is beneficial to the stability of the power grid, also by considering that the intermittent energy is unable to modulate frequency at the maximum power output, this paper proposes to introduce the energy storage system into the photovoltaic grid connected system via MGP, so that the ability of photovoltaic to participate in grid frequency modulation can reach the level of traditional thermal power units. A simulation model including thermal power unit, photovoltaic power generation, energy storage, MGP and load is built. By applying disturbance to the simulation model, the frequency modulation capability of MGP and energy storage participating in the new energy grid is studied. The results show that this method can effectively enhance the frequency support ability of the system and is conducive to the stable operation of the power grid.

The increase of renewable energy permeability impacts on the stable operation of power system, leading to the complexity of power grid frequency regulation (FR) process. Therefore, a control strategy of wind-storage cooperative primary FR based on multi-objective optimization is proposed. Firstly, a primary FR model with the cooperative participation of wind storage is constructed. The pitch control is used to enable the wind turbines to participate in the FR of the power grid, and the wind speed is decomposed to eliminate its uncertainty. According to the characteristics of the state of charge (SOC) of the energy storage, adaptive control based on the change of SOC is adopted for the energy storage, and the variable system parameters to be optimized are used to characterize the output demand of the wind-storage. Then, the main cost of wind-storage cooperative participation in FR is analyzed, and multi-objective optimization problem is designed according to FR effect, wind power and energy storage FR loss. On this basis, the NSGA-Ⅱ genetic algorithm is improved through the time-varying adjustment of the fitness coefficient to obtain the parameter solution set under the optimal state, and a comprehensive evaluation index is designed to select the optimal solution of the Pareto front-end distribution. The simulation results show that the solutions of different Pareto front-end positions can better reflect the considerations of different control objectives and obtain the optimal system parameters to meet the FM requirements in different situations.

In recent years, the rapid development of offshore wind power has been affected by the construction period of the power grid. Sometimes it is necessary to arrange a grid-connected transitional operation plan to increase the utilization rate of offshore wind power. Taking offshore wind power in a certain area of Guangdong as an example, this paper evaluates the oscillation risk of planning schemes and transitional operation schemes, and studies the calculation method of short-circuit ratio under the mode of convergent and grid-connected multiple wind farms and the principle of determining the grid-connected capacity of wind power and the influence of centralized control station static var generator (SVG) on grid-connected capacity. Results show that offshore wind power is connected to the grid via AC submarine cables, and there is a strong interaction between wind turbines and SVGs and the AC grid, which makes the wind power grid-connected system at low wind speeds have a risk of oscillation. Moreover, the capacity of the SVG used to compensate the reactive power of submarine cable charging at the centralized control station limits the grid-connected capacity of wind power. Therefore, the SVG capacity needs to be considered when calculating the wind power grid-connected capacity according to the short-circuit ratio. On this basis, technical measures of increasing the grid-connected capacity of offshore wind power are proposed to meet the operational requirements of the grid-connected transition plan.

After bipolar block in high voltage direct circuit (HVDC) transmission system, a large amount of reactive power flows to the AC bus at the sending end due to the lag exit of the rectifier station filter and compensation devices, which leads to the phenomenon of overvoltage at the sending end. A nonlinear robust control strategy based on state-dependent Riccati equation technique is proposed to ensure safe operation of large-scale DC near-field photovoltaic generation system. Firstly, the transient control goal is set to maximize the absorbed reactive power of the photovoltaic generation system during the transient period, and the appropriate adjustment output is selected based on the control goal and the corresponding nonlinear robust control problem is constructed. Secondly, the state-dependent Riccati equation technique is used to transform the nonlinear robust control problem into the state-dependent linear-like system robust control problem, and the state feedback control law is approximately obtained by the online solution of the algebraic Riccati inequality. Finally, the simulation results of MATLAB/Simulink show that the proposed control strategy has good transient control effect and can effectively suppress the overvoltage at the sending end.

When large-scale conventional HVDC transmit electric power in the high renewable energy penetration area, HVDC transmission system fault can easily cause transient overvoltage problems at sending-end. In this paper, with grid-forming inverter and high-performance control system, a new device based on energy synchronous conversion technology is designed to suppress the transient overvoltage. By properly configuring the device, it can not only improve the stability of the power system, but also suppress the transient overvoltage after HVDC fault and solve the problem of large-scale disconnection of renewable energy caused by HVDC fault. Finally, the simulation analysis of Qingyu HVDC sending-end grid and the performance test of the device verify its accuracy and effectiveness.

Circulating current is caused by the mismatch between bridge arm voltage and output voltage in modular multilevel converter with integrated battery energy storage system (MMC-BESS). To solve this problem, a circulating current suppressing strategy based on virtual impedance and passive backstepping control (VI-PBSC) is proposed. Firstly, the passive control based on Euler Lagrange (E-L) model is used to adjust the energy function, accelerate the dissipation and modify the system control parameters to ensure the global stability of the system. Then, the back-stepping control is used to realize the fast tracking of the actual value to the reference value and the fast response of the circulation frequency doubling component control is realized while maintaining the global stability. Moreover, virtual impedance is used to suppress the high-order harmonic component in the bridge arm and suppress the double frequency circulating current to reduce the system loss; Finally, in the state of power fluctuation and load mutation, five different control models are established and compared by simulation. The results show the effectiveness and superiority of the proposed control strategy.

This paper analyzes the core equipment and charging systems of electric vehicle charging stations, and sets up a charger model with voltage source PWM rectifier, phase shift full bridge ZVS DC converter and other equipment in Matlab/Simulink. The average switching model and the impedance model are proposed to simplify the charging systems. Through dynamic simulation comparison, the average switching model is found effictive to simulate the transient response characteristics of charging stations. On this basis, a control method combining the droop control and voltage support control is proposed for charging stations to participate in voltage regulation. With the single-machine infinite system and the IEEE 33-bus system constructed on MATLAB/Simulink platform, it is demonstrated that the proposed method can support the voltage in both static and transient conditions. When the grid voltage drops, reactive power support could be provided to improve the voltage quality and stability of the system.

heating, ventilation, air conditioning systems (HVACs), as one of the load types with the largest proportion of electricity consumption in urban buildings, have great adjustment potential and can participate in demand response to promote the balance of supply and demand in the power system. Based on the existing modeling foundation of HVACs, this paper analyzes the physical model structure of each subsystem, accurately selects the appropriate features through the physical model structure, and provides guidance for the data-driven method. Combined with the MLP network stucture, a knowledge-driven and data-driven approach is proposed to modelHVACs. Then, based on the established HVACs model, the HVACs energy consumption optimization model is established. And MLP network structure is made explicit, so the HVACs energy consumption optimization model is transformed into a mixed integer linear programming problem by linearizing the activation function. Cases analysis show the it can be seen that the modeling method proposed in this paper can quickly and accurately select features, which is beneficial to improve the modeling efficiency. In addition, this control method greatly reduces the difficulty of solving the control model, and the practical application higher value.

The optimal operation of microgrid (MG) with multiple-energy sources is the key technology to improve system energy efficiency. Based on the multi-energy complementary MG demonstration project in a campus, the double objectives optimization operation model considering daily economic cost and pollution treatment cost is constructed. The operation strategies of different equipment units are formulated respectively, and an improved multi-objective particle swarm optimization (MOPSO) algorithm based solution method is proposed to solve the double objectives optimization conflict of MG. And the particle mutation strategy is added to enhance the performance of the algorithm. Finally, based on the actual operation data of campus MG, two different typical days are used for case analysis to verify the effectiveness of the proposed operation strategy.

Hydrogen production from wind power is an important means to solve wind power consumption and to stabilize volatility and intermittency, which can reduce carbon emissions in the power system and help achieve the dual-carbon goal. In order to increase the wide application of wind power in hydrogen production, permanent magnet direct-drive wind turbines, battery packs, proton exchange membrane electrolyzers, and converters are used to form a wind-hydrogen storage coupled system with a common AC bus, and their respective mathematical models are established. Combined with the self-output characteristics and safety of electrolytic hydrogen production, wind power, and battery packs, an energy management strategy that can reduce wind curtailment, suppress power fluctuations, and achieve friendly grid connection is proposed. The effectiveness of the model and control strategy are verified by PSCAD/EMTDC simulation.The simulation results show that the application of this strategy makes the output of each unit of the system (except wind power) controllable, which can fully absorb wind power and improve the quality of grid-connected power. The proposed strategy can provide reference for the management and development of wind-hydrogen storage coupled system.