In this paper, the instability mechanism of a grid-connected dc microgrid is revealed considering the impact of voltage positive feedback of selected frequency(VPFOSF) islanding detection scheme by developing the output impedance model of voltage source converter(VSC) and distributed generators(DGs). Then, the stability region is derived to guide the design method of a damping compensator. On the basis of this, an active-damping stabilization method is further proposed to mitigate instability caused by the VPFOSF loop. Finally, the effectiveness of the proposed control method is verified by detailed time-domain simulation results.

The magnetic coupler plays an important role in wireless power transfer(WPT) system and concerns the transmission efficiency and output characteristic of system. The effects of asymmetric two-coil and three-coil magnetic couplers with a large intermediate coil on lateral misalignment tolerance for WPT system are studied. First, circuit models of two-coil and three-coil magnetic couplers are analyzed and the key parameters affecting the efficiency of two-coil and three-coil coupler are deduced. Then, a 3-D finite element model of the two-coil coupler is established, and the efficiency of WPT systems with two different structures is investigated while misaligning. Finally, the applicable conditions of two coil structures are discussed. The results show that when the maximum misalignment distance is reached, the misalignment tolerance effect of two-coil structures is weakened, and the system efficiency can be higher by using the three coils structure with a large intermediate coil.

Angular misalignment is a key issue in wireless p ower transf er systems f or visual p rosthesis, such like retinal p rostheses. The weakened f lux linkage due to the receiver misalignments in the eyeball would significantly imp air the p ower cap acity and efficiency. To increase the magnetic coup ling strength and imp rove the misalignment tolerance, A novel three-dimensional transmitting structure with three transmitting coils at an angle of 120° to each other is p resented in this p ap er. It shows that the new structure can eff ectively comp ensate the f lux linkage loss caused by the angular misalignment of the receiver, and theref ore maintain a high p ower cap acity and efficiency.

Since the LLC topology is widely used in DC-DC converters, this paper firstly analyzes the sufficient and necessary conditions for LLC converter to be used in AC-DC application. Based on the first harmonic approximation method and time domain analysis method, the key parameters design method of LLC for single-stage PFC application is derived and the theoretical expressions are presented, and the effective parameter range is calculated and analyzed to achieve an optimized design. Finally, a single phase 6.6 KW prototype was built. The experimental results show that the prototype can operate in the full input and output voltage range, and the prototype has high efficiency and low total harmonic distortion.

CLLLC resonant converters can realize bidirectional power flow and global soft switching, and are widely used in electric vehicle charging and DC microgrids. In this paper, static modeling method of CLLLC circuit are improved respectively. Since the state variable of the resonant converter contains high-frequency switching components and the average value of each switching period is 0, the condition of the small ripple assumption in the traditional state space averaging method cannot be satisfied. In this paper, the traditional Extended Describing Function(EDF) method is improved, and the corresponding state variables are represented by the superposition of sine and cosine components, and the weighted average of each mode is taken for each state variable. In the case that the switching frequency is less than the resonant frequency, in order to simplify the calculation process of the steady-state value of the state variable in the modeling and maintain high precision at the same time, this paper proposes a state variable optimization calculation method. Where, the equivalent output load introduces the information of switching frequency and resonant frequency, then the output voltage waveform is simplified and approximated to obtain more accurate output equivalent load. Thereafter, the optimized FHA model is obtained, which has the same simplified structure as the Fundamental Harmonic Approximation(FHA) method, and the problem of low accuracy solution of state quantities when it works under under-resonance is solved. Finally, the theoretical analysis and comparison are verified by simulation and experiments.

Modular multilevel converter(MMC) based on voltage sensor multiplexing is beneficial to reduce equipment cost and communication burden, however, usually leading to the performance degradation due to low estimation accuracy of the submodule capacitor voltage(SM-CV). This paper proposes a compensation method based on voltage sensor multiplexing for SM-CV estimation accuracy to solve this issue. In order to improve the estimation accuracy, the novel compensation methods of switching voltage drop and sampling deviation are proposed. The estimation accuracy of SM-CV is significantly improved by correcting the output voltage of the multiplexing group, and compensating for the sampling deviation of the corresponding submodule by modeling the error of the matrix equation Ax=b. Simulation results verify the feasibility of the proposed methods.

The number of sub-modules in the MMC system is large, and in the operating state, the sub-module floating ground voltage generates high dv/dt along with the sub-module switching, which will cause EMI issues in the sub-module itself such as driver interference due to the existence of circuit parasitic parameters. In this paper, a driver interference model is established, a sub-module interference source model is built and simplified, and the sub-module power device driver loop is modeled and equivalent. the model is verified by simulation, and the influence of different parameters on the interference is analyzed.

Online monitoring of junction temperature for insulated gate bipolar transistors(IGBTs) is an important basis for life prediction and health management of power electronic devices. To this end, an optimized online monitoring method of IGBT junction temperature based on switch overshoot voltage is proposed in this paper. Firstly, the expression of overshoot voltage is analyzed, and the online monitoring model of turning-on overshoot voltage is proposed. Secondly, a sampling circuit of the online monitoring model is analyzed and designed, and the parameters of sampling circuit is calculated. Finally, the experiment is carried out to show that the proposed online monitoring method of IGBT is feasible in practical applications and has high accuracy.

The high-voltage and high-power spacecraft power system is the developing trend for the requirement of the future space exploration tasks. Due to the effects of space radiation, the selection of the high voltage power device is limited in spacecraft power system application. Thus, the multi-level power converter is a good solution for the high-voltage and high-power spacecraft power system. In this paper, the fault tolerant strategy of three-level flying capacitor DC/DC converter is proposed to increase the reliability of the converter. The fault tolerant is achieved by changing software strategy, and no extra hardware is needed to add. The detailed analysis of the proposed strategy is given. Finally, the effectiveness of control strategy is verified.

With the gradual increase of the installed proportion of renewable energy, large-scale centralized development and transmission of renewable energy has become an inevitable trend of the development of power system. China's renewable energy resources and loads show the reverse division characteristics. The long-distance transmission of renewable energy power leads to the insufficient support capacity of a high proportion of power electronic equipment to the voltage of the power grid at the sending end, which limits the transmission and consumption of renewable energy. This paper adopts the technical idea of configuring distributed condenser to improve the stable delivery limit of renewable energy, puts forward the optimization configuration method of condenser based on BPA-SCCP joint optimization, and constructs an analysis model of renewable energy consumption to quantitatively evaluate the impact of condenser access on renewable energy consumption. Finally, taking the actual large-scale renewable energy and thermal power combined transmission system as an example, the effectiveness of the optimization configuration method is verified. The research results show that the technical idea of BPA-SCCP joint optimization can effectively solve the problem of the optimal configuration of the condenser. At the same time, the reasonable configuration of the condenser can effectively improve the sending limit of renewable energy and promote the consumption of renewable energy .