With the increasing proportion of wind turbines connected to grid, the security and stability problem caused by wind farm separated from power grid are becoming more and more serious. So it is particularly important to improve DFIG fault ride through capacity and reduce the occurrence of offgrid events. In view of the problems, existing DFIG fault ride through control schemes are introduces first. Considering that frequently switched of DC chopper circuit is easy to cause voltage waveform distortion and supercapacitor control scheme has high economic cost, the DFIG fault ride through control scheme based on smart chopper circuit is further proposed. The proposed method is upgraded based on DC chopper circuit. It connects the unloading resistance with the DC bus through DC/DC converter and introduces active powerDC voltage droop control link to adjust the circuit resistance power dynamically during fault period. Besides it sets two modes of high and low voltage crossing, which can be started automatically according to grid connected voltage. Finally, the smart chopper circuit control scheme is verified in Matlab/Simulink. The simulation results show that considering the DC bus voltage suppression effect, the regulation time for voltage recovery, the distortion degree of rotor current and the economic cost of schemes, fault ridethrough control of DFIG based on smart chopper circuit has the most advantages.

The boost capability of conventional Buck/Boost converter is weak and the power switches suffer from high voltage stress (equals the voltage at the highvoltage side (HVS)), reducing the conversion efficiency. Further, since the HVS current pulsates greatly, large capacity capacitors are required to meet the requirements of current ripple, decreasing the system reliability. Therefore, this paper proposes an improved Buck/Boost converter. By introducing one switch, one inductor and two capacitors into the conventional topology, the proposed converter has continuous input and output current, which greatly reduces the current stress of HVS filter capacitor. The voltage gain in Boost mode is increased to (2D₁)/(1D₁), and all switches have the same low voltage stress, which equals the difference between the voltages at lowvoltage side (LVS) and HVS, so it has higher conversion efficiency. The operation principle, steadystate characteristics, dynamic model and control strategy are analyzed in detail. Its feasibility is verified on a 100 W/120 kHz prototype. The experimental results demonstrate an enhanced efficiency performance over wide operating operations with a maximum efficiency of 95.6%.

With the marketoriented reform of power grid companies, the power market will gradually attract the investment of various social capital. The transformer districts (TDs) subordinated to the distribution network and the distribution network itself provided a platform for the multiagent competition, forming a competitive game pattern. At the same time, the high proportion of DRE access improves the cleanliness of the distribution network, but the uncertainty of DREs' output also leads to the further increase of the distribution network dispatching operation risk.To mitigate the uncertainty, the distributed renewable energy, distributed thermal power generation, energy storage and flexible load within the same TD is treated as a whole and regulated by the distribution grid operator with the objectives of safety and economy. Firstly, a leader follower game model consists of the distribution grid operator and multiple transformer districts is established to coordinate the interests between the distribution grid operator and its subordinate TDs. Conditional valueatrisk theory is used to quantify the uncertainty risk caused by renewable energy represented by wind and solar power. Next, the profit of each TD in the carbon market is incorporated into the optimization scheduling model to further consider the carbon emission costs of distributed thermal power generation achieving flexible complementary regulation between distributed renewable energy and thermal power. The BP neural network is used to fit the model, simplifying the leaderfollower game model into a singlelevel model, which is then solved using a particle swarm algorithm. Finally, the variations in distributed power generation within each TD under different renewable energy output risks and carbon prices are discussed to further validate the effectiveness of the model.

The photovoltaic (PV) array fault detection method based on Spread Spectral Time Domain Reflectometry (SSTDR) has detection blind spots and attenuation characteristics. It is necessary to study the property of the detection signal to improve the fault detection performance. Firstly, the transmission behavior of the detection signal in the PV array is studied to explore the influence of different signal parameters on the detection range and accuracy. Secondly, based on the dynamic model and layout pattern of the PV cells, a simulation platform for PV array fault detection is established. The simulation results are validated through a simulated experiment of an opencircuit fault. The results show that improving the signal can effectively enhance the ability to identify correlation peaks, increasing the number of PV components detected by four units. Finally, the influence of blind area and attenuation characteristics is comprehensively analyzed. A signal selection strategy of PV array based on SSTDR is proposed to determine the fault detection distance and the optimal parameters of test signal.

In view of the insufficient research on the influence of wind shear on wake at present, two lidars were used to carry out wind field experiments in a wind farm, analyzed the phenomenon of wind shear under different wind speeds and the characteristics of wake change under different incoming flow conditions, and used a threedimensional wake model to verify the vertical wake profiles. The results show that the wind speed has an obvious effect on wind shear, and the wind shear effect increases with the increase of wind speed, and the wind shear index increases about 0.05 for every 1 m/s increase of the wind speed. The wind shear effect has a great influence on the distribution characteristics of the wake. The stronger the wind shear effect is, the greater the gradient of the wake velocity along the height direction, and the greater the width and length of the wake. The predicted curve of the model near the hub center line of the wind turbine and the measured wake data fit well, and the relative errors are basically within 10%, while the relative errors of the prediction near the ground side are large due to the influence of the terrain.

Biomass is a rich and renewable carbon source. The efficient production of fuel ethanol with sugar, starch, straw cellulose or other biomass feedstocks can reduce the demand for fossil energy, among which the second generation fuel ethanol with lignocellulose as feedstock has broad prospects for development. Compared with fossil energy, fuel ethanol has the advantages of environmental protection, economy and renewable energy, but its production technology, economic benefits and environmental impact still need to be further studied. In recent years, through the optimization of fuel ethanol refining system and the study of the whole life cycle analysis, the progress of fuel ethanol technology has been effectively promoted, and the related research on carbon emission reduction of fuel ethanol has been promoted. This paper mainly discussed the development of fuel ethanol production technology in recent years, focused on the research progress of simulation optimization and carbon emission reduction of fuel ethanol system, and looked forward to the development trend of fuel ethanol, in order to provide reference for the sustainable development of fuel ethanol.

A solar thermochemical reactor was designed based on a 5 kW non coaxial concentrator simulator, and a mathematical model of the thermal performance of the reactor under concentrated irradiation was established. The model was used to calculate the influence of solar simulator power, material emissivity of reactor inner wall, working pressure and inlet velocity on the temperature distribution in the reactor. The results show that increasing the power of the solar simulator and the emissivity of the inner wall of the reactor will increase the temperature distribution of the reactor centerline. At the same inlet velocity, the temperature distribution of reactor centerline increases with the increase of working pressure. Under the same working pressure, the temperature distribution of reactor centerline increases with the increase of inlet velocity. The research results have certain reference significance for reactor parameter optimization and thermal stress analysis.

This paper presents an integrated energy system (IES) multiagent game cooperative optimal scheduling strategy considering carbon quota and integrated demand response. Firstly, based on Stackelberg game theory and considering the initiative of demand side and energy storage side, a multiagent game interaction framework of source – load – storage is established. Secondly, with IES operators as leaders and energy storage operators and users as followers, the decisionmaking model of each stakeholder is established. In order to guide users to use energy scientifically and reduce system carbon emissions, a dual incentive policy based on carbon quota and realtime price guidance is introduced into IES operator model, and energy selling price and internal unit output plan are formulated with the goal of maximum net profit. Finally, genetic algorithm combined with CPLEX twostage algorithm is used to solve the proposed multiagent game model. The simulation results show that the proposed dual incentive strategy and game model can effectively take into account the interests of all parties, reduce the carbon emissions of the system without harming the interests of all parties, and realize the multiagent lowcarbon collaborative operation of IES.

This paper analyzes the working mechanism of each components of the proton exchange membrane fuel cell (PEMFC) system, and the mathematical mechanism models of stack, anode, cathode, proton exchange membrane, and temperature of the PEMFC are established using MATLAB/Simulink software, furthermore, the physical model of thermal management system is built in the Simulink/Simscape environment, and the mathematical and physical models are integrated into a complete PEMFC system simulation model. Typical malfunctions, including the radiator fan failure and insufficient coolant flow failure, are injected into the PEMFC system simulation model to analyze the influence of malfunctions on the performance of PEMFC. The simulation results are basically consistent with the experimental results, which indicates that the proposed model is reasonable and accurate. Moreover, the generation mechanism of malfunctions is figured out through malfunction simulation of the thermal management system, which provides a reference for malfunction diagnosis.

Considering the influence of the tower shadow effect of wind turbines, and aiming at the problem that the elevation angle of wind turbines makes the aerodynamic characteristics of wind turbines more complicated, the flow field of horizontal axis wind turbines with different elevation angles was numerically simulated in this paper, and the pressure distribution of wind turbine blade cross section, vorticity and the change law of the tower cylinder surface pressure with phase angle were analyzed, so as to explore the influence of the elevation angle of wind turbines on the output power of wind turbines. The results show that increasing the rotor elevation angle can reduce the blade surface pressure, decrease the pressure difference at the tip part, and reduce the high vorticity area on the blade surface. Adding elevation angle to the wind turbine reduces the influence of the blade on the tower barrel, and the high vorticity area on the tower barrel surface gradually decreases with the increase of the wind turbine elevation angle, thus reducing the pressure fluctuation on the tower barrel surface. When the blade passes through the tower, the tower shadow effect has a great influence on the wind turbine, and the output power of the wind turbine decreases. When the blade is upright, the wind turbine output power reaches its maximum. After the elevation angle is added to the wind turbine, both the output power of the wind turbine and the elevation angle of the wind turbine wheel increase first and then decrease. The output power of wind turbine increases when the elevation angle of wind turbine is 3°, and the fluctuation decreases when the elevation angle is 6 °. The relevant conclusions can provide data support for the operation of wind turbine.