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When the microgrid operates in island mode, the droop control can be adopted to realize effective power distribution among distributed generations (DGs). Due to the different line impedancesof the various DGs, disproportional power distribution and circulating currents occur in conventional droop control, which make it difficult to maximize the efficiency of DGs and even may cause some DGs overloads. Therefore, an improved droop control strategy with an adjustable droop coefficient is proposed. The relationship between line impedance and reactive power is obtained by analysing conventional droop control. Then a new droop control algorithm is proposed. By introducing the output reactive power information of other DGs into the integral feedback link, the droop coefficient is modified to realize the accurate distribution of reactive power. The model is built on the Matlab/Simulink platform, and the effectiveness of the proposed control strategy is verified by comparing its reactive power distribution resultwith that of the conventional droop control.

In order to reduce the use of power electronic devices, adapt to different loads connected to the DC microgrid, and improve the reliability and safety of power supply, this paper proposes a multi-voltage level DC microgrid control strategy. The basic structure and operation mode of multi-voltage level DC microgrid are introduced. The control strategies of photovoltaic power generation and hybrid energy storage are proposed. The model of bidirectional DC/DC converter is established and the control strategy of hierarchical control of DC bus voltage is proposed. A power balance control strategy is proposed for AC/DC bidirectional power converter to realize smooth AC-DC power transfer. Simulation analysis on Matlab platform verifies the feasibility of the control strategy.

In recent years, with the energy transformation and the continuous innovation of new energy technology, the installed capacity of new energy continues to increase, the high proportion of new energy access increases the peak pressure of the power grid, but also increases the possibility of de-electric power. As a key solution, energy storage and wind power and other new energy in-depth integration, can effectively improve the power grid adjustment capacity, to ensure the benefits of new energy generation. Using the time series production simulation method, aiming at the utilization rate of new energy, this paper calculates the principle of energy storage configuration in different regions of Shanxi Province, and provides theoretical support for the analysis of energy storage configuration in Shanxi Province.

In this paper, a new type of frequency and polarization reconfigurable FSS (Frequency selective surface) is designed. By using liquid crystal material, the frequency of the FSS can be reconfigured. The dipole sub-module is used. The upper and lower dipoles separated by the dielectric substrate are orthogonal to each other. The adjacent short-term dipole passes PIN diodes connected, and the switch of the dipoles controls the polarization selection of FSS in the passband. The experimental results show that the FSS can select the TE and TM waves, and the polarization selection and reconfiguration characteristics are obvious.

Duty cycle correctors (DCCs) are utilized in most high-speed circuits to correct the duty cycle of the output clock at 50% and reduce the phase noise introduced by the duty cycle distortion. An all-analogue feedback duty cycle corrector (DCC) with high precision, wide correction range and configurable crossing is proposed in this paper. The duty cycle adjustor (DCA) calibrates the duty cycle by regulating the common mode level of the differential clock signal complementary with both wide correction range and high speed. The duty cycle detector (DCD) has an excellent performance with a high gain to achieve the high correction accuracy and a narrow bandwidth to restrain the deterministic jitter and other noises. Besides, a configurable clock crossing adjustor (CCA) is employed to alter the clock crossing voltage flexibly. The DCC has been implemented in 65nm SMIC CMOS technology with a power supply of 1.8V. The simulation results prove that the output duty cycle is corrected to 50±0.1% over the input duty cycle range of 20%~80% for 1~5GHz, and the crossing voltage can be adjusted over a span of ±180mV centered about the mid-supply point. The DCC consumes 3.2mW at 3GHz and occupies an area of only 0.005mm2.

The ability of the grid-friendly microgrid responding the system operation demand is analyzed by exploiting potentialities of grid operation from the traditional load side. The volatility of DGs output is balanced by including controlling EVs the charging and discharging. The output of microgrid is scalable through coordinating all kinds of DGs based on which a microgrid economic operation model is built. The simulation result shows the microgrid can absorb internal intermittent power and achieve system dispatching well by coordinating kinds of powers. Its dispatching potentiality is sizable.

In this paper, improved solving method are proposed to calculate the maximum entropy probability distribution of negative sequence current. Negative sequence current is got from the process of the measured data obtained from power quality monitoring system first. Second, curve fitting method is used to calculate probability distribution of negative sequence current based on maximum entropy method. Logarithmic function and the method of deleting small probability value points at ends of probability distribution are proposed to improve the parameters solution method of curve fitting. The probability distribution obtained from the improved solving method is more consistent with the actual distribution of measured data compared with the original parameter solution method. Finally, fitting error parameters are used to evaluate the fitting effect of probability distribution and prove the feasibility of the method.

Repetitive control is commonly known as good steady-state tracking but slow transient response. This paper presents a hybrid control scheme with Lyapunov energy function embedded in conventional repetitive control for the purpose of fast transient response with system disturbance. Convergence of control is guaranteed by Lyapunov energy function. The proposed method is applied for single phase grid-connected inverters, which are commonly used in distributed generation interfacing to utility. Under load disturbance, the proposed method is compared with PI + Repetitive control scheme by computer simulation via MATLAB/Simulink. It is shown that the proposed hybrid control strategy has an improved dynamic response and good capacity of steady-state tracking.

Through analysis of measure data on three 220 kV transformer substation in Shanxi China, the results show that harmonic current produced by electrification railroad injects into power system in a proportion through 110 kV point of common coupling, and the infiltration coefficient is closed to 1 if harmonic current direction is 110 kV to 35 kV, this phenomenon coincides with usual law; but there has strong infiltration in harmonic voltage between 110 kV and 220 kV system, and the infiltration coefficient could be not negligible, it does not coincide with usual law. Therefore, 110 kV harmonic distortion produced by electrification railroad not only infiltrates to 220 kV system thought coupling transformer, but also disseminates even hundreds of kilometres thought electric fence.

The dispatch method which track the trend of load demand by arranging the generation scheme of controllable hydro or thermal units faces great difficulties and challenges. With the increase of renewable energy sources such as wind power and photovoltaic power introduced to grid, system has to arrange much more spinning reserve units to compensate the unbalanced power. How to exploit the peak-shaving potential of flexible load which can be shifted with time or storage energy has become many scholars' research direction. However, the modelling of different kinds of load and control strategy is considerably difficult, this paper choose the Air Conditioner with compressor which can storage energy in fact to study. The equivalent thermal parameters of Air Conditioner has been established. And with the use of "loop control" strategies, we can predict the regulated power of Air Conditioner. Then we established the Gen-Load optimal scheduling model including flexible load based on traditional optimal scheduling model. At last, an improved IEEE-30 case is used to verify. The result of simulation shows that flexible load can fast-track renewable power changes. More than that, with flexible load and reasonable incentive method to consumers, the operating cost of the system can be greatly cut down.