The influence of ash deposition on the output characteristics of photovoltaic (PV) modules and the deposition rule of pollution particles on the modules' surface are studied, which are helpful for formulating an ash removal scheme and improving the efficiency of photoelectric conversion. The PV array on the roof of a fan hall in North China Electric Power University is taken as the research object, and an artificial ash distribution experiment was carried out to explore the influence of different ash deposition amounts on the output power, current and voltage of modules. To determine the influence of one single factor on the deposition of pollution particles, a numerical model of particle deposition is established using COMSOL under the same conditions as those in the natural deposition test of PV modules, and the influences of wind speed, humidity, particle size and pollution concentration on the deposition of pollution particles on the surface of PV modules are simulated and analyzed. Test results show that ash deposition has little influence on the working voltage, but a great influence on the output power and working current. When the ash deposition density is 5.07 g/m², the changing rates of output power, current and voltage are 8.71%, 6.48% and 0.40%, respectively. Simulation results show that when other conditions are the same, the deposition amount of particles decreases first and then increases with the growing wind speed and particle size, and the minimum value is reached at the wind speed of 3 m/s and particle size of 15 µm. Under the same conditions, the particle deposition amount increases with the growing humidity and pollution concentration.

The existing power amplifier cannot strike a balance among aspects such as its output efficiency, output power and linearity. To solve this problem, on the basis of a three-level cascade amplification method, a kind of AB class RF power amplifier based on a power synthesizer and a power splitter is proposed. Aimed at the problems of linearity and gain, the band-pass matching and T-network matching techniques are used to optimize the design of the pre-driver circuit. The problem that the output power of the final amplifier is too large is solved by using the power synthesis technique, and the stability and efficiency of the power amplifier are guaranteed. To prevent the temperature of the power amplifier from being too high, the thermal characteristics of the power amplifier cavity are analyzed. The highest temperature is 81°C, which can make the power amplifier get a good cooling. At room temperature, the RF power amplifier has an output power of 47 dBm, an amplification gain of 42 dB and a maximum power added efficiency of more than 45% at a central frequency point of 2.45 GHz. The test results were close to simulation results, indicating that the research in this paper can provide some guidance for the subsequent research and design of amplifiers.

Building a complete spacecraft electrical power and distribution standard system is an important tool for improving the design of spacecraft electrical power and distribution system and ensuring the safety and reliability of satellite energy. In this paper, the electrical power and distribution standard systems published by European Cooperation for Space Standardization (ECSS), National Aeronautics and Space Administration (NASA), Japan Aerospace Exploration Agency (JAXA), International Standard Organization (ISO) and American Institute of Aeronautics and Astronautics (A-IAA) were investigated. The focuses of their respective standard specialties were analyzed, the corresponding content was discussed, and the standard systems of various organizations were summarized. Combined with the actual situation in China, the suggestion and reference for the spacecraft electrical power and distribution standard system are put forward.

The development of the flexible DC fault line selection technology plays an important role for DC distri-bution network. In this paper, a novel algorithm is proposed to solve the problem that there is less available fault infor-mation about the existing flexible DC fault, which makes full use of the advantages of ensemble empirical mode decom-position (EEMD), principal component analysis (PCA) and the correlation coefficient algorithm. First, the transient cur-rent sample signal is extracted, and the data matrix represented by the orthogonal basis function is obtained by EEMD. Then, the feature vector of the matrix element is transformed into the principal component based on PCA, and the sam-ple signal is projected into the principal component space to realize coordinate transformation, so as to obtain the clus-tering and identification results of the sample data. Finally, fault line identification is performed based on the correlation coefficient. The EEMD of the proposed algorithm reveals the internal variation law of the original historical data, while PCA can effectively select the effective fault features. A large num-ber of experiments show that the novel algorithm is accurate and effective. Compared with other existing methods, it has ad-vantages in the cases of unclear fault information and different transition resistances.

Based on the fact that inductance and capacitance are of fractional-order, the nonlinear dynamic characteristics of a fractional-order Boost converter are studied. The predictor-corrector model of the Boost converter is established using the predictor-corrector algorithm of fractional-order calculus. On this basis, the bifurcation diagrams with the reference current, input voltage and orders of capacitance and inductance as bifurcation parameters are obtained. The period doubling bifurcation and chaotic behaviors of the fractional-order Boost converter are studied, and its nonlinear dynamic behavior is compared with that of an integer-order Boost converter at the same time. Results show that under certain operating conditions, some nonlinear phenomena such as bifurcation and chaos will appear in the fractional-order Boost converter with changes in some circuit parameters. Under the condition of the same circuit parameters, the parameter stability domains of integer-and fractional-order converters are different. Compared with that of the integer-order converter, the parameter stability region of the fractional-order converter is smaller, which more truly reflects the nonlinear dynamic characteristics of the Boost converter.

A flux-weakening control method for permanent magnet synchronous motor (PMSM) used in electric vehicles is put forward on the basis of current prediction to improve the dynamic performance in the flux-weakening region of PMSM. The voltage boundary problem in the flux-weakening region is analyzed in detail, and the stability problem under different voltage selection criteria is also introduced. On this basis, a dynamic overmodulation strategy considering the stability and dynamic characteristics is proposed. Furthermore, a model-based predictive current control algorithm is investigated, in which the advantages of fast dynamic response and manageable constraints help to improve the dynamic performance in the flux-weakening region while guaranteeing the stability. Finally, the effectiveness of the proposed algorithm was verified on a simulation platform and an experimental platform, respectively.

Silicon carbide (SiC) switching devices are widely applied in DC/DC converters owing to their faster switching speed and higher operating frequency. However, the high working frequency of SiC devices will result in strong electromagnetic radiation interference. To optimize the internal structure of DC/DC converter and achieve a higher power density, an optimization method for the electromagnetic radiation interference of SiC DC/DC converter is proposed. First, the characteristics of the converter's electromagnetic radiation interference source are analyzed, and a space electromagnetic radiation model is established according to the topology of DC/DC circuit. Then, based on the electromagnetic radiation model and simulated annealing algorithm, the low electromagnetic radiation optimization is carried out for the layout of components within the DC/DC converter. The optimized layout scheme reduces the length of high-frequency wire by 60.2%. Finally, the three-dimensional finite element simulation is carried out, and it is verified that the proposed method can optimize the circuit layout of SiC DC/DC converter and reduce the electric field intensity produced on the sensitive circuit by two orders of magnitude.

The fast on-off switching signal is the main cause of electromagnetic interference (EMI). At present, the research on EMI suppression by chaos mainly focuses on the suppression of conducted EMI by integer-order chaos. On this basis, the suppression by fractional-order chaos on radiated EMI and the selection of optimal order are studied in this paper. First, through the analysis of spectrum characteristics of fractional-order Lorenz and Lyapunov exponent spectrum, 1.8-order Lorenz signal is selected as the best spread spectrum series. Second, based on the principle of EMI suppression technology with variable switching frequency, Lorenz chaotic spread spectrum PWM signals with fixed frequency, integer-order, 2.7-order and 1.8-order are implemented in an STM32 single chip microcomputer. A near-field radiation experiment was carried out on a 5 W flyback converter, which proved that the 1.8-order Lorenz signal had the strongest suppression effect on the near-field magnetic field radiation. Finally, experimental results showed that the prototype's overall efficiency was about 2% different when it was under the fractional-order Lorenz Chaos PWM control and constant-frequency PWM control, respectively, which verified the superiority of the fractional-order chaotic PWM in radiated EMI suppression performance.

The silicon carbide (SiC) device is considered as a semiconductor device with high temperature resistance, and a careful study on its loss and heat dissipation is required when it is applied to high-power-density and high-temperature scenarios. The maximum current conduction capability of SiC MOSFET power module at high temperature is studied, and the relationship between electrical performance and heat dissipation is taken into account. Based on an electro-thermal coupling model of SiC MOSFET device and a heat dissipation model of the cooling system, the mechanism of thermal runaway process is analyzed. A co-simulation is conducted to determine the current conduction capability of one SiC power module at high temperature, and the simulation error with respect to the experimental result is about 4%, which verifies the effectiveness of the proposed method.

In response to the high-voltage steep pulse application demands such as those in the biomedical industry, a series and parallel high-voltage steep pulse generator circuit based on solid-state switches is designed, and a novel pulse steepening method is proposed by combining the timing control technology. The key to pulse steepening, the system's working process and the main points of design are analyzed theoretically. This method can better reduce the influences of stray parameters, wiring inductance and wire inductance on the switching speed after adding the switching tubes. An experiment was carried out with a 2 kV high-voltage DC power supply and a load resistance of 110 Ω, and experimental results show that the rising edge of load pulse signal was 50 ns approximately, the falling edge was 70 ns approximately, and the output current amplitude was 18 A approximately. The half-height width of the minimum pulse width signal was 100 ns, and the system's minimum resolution was 5 ns, which can realize a flexible adjustment of 5 ns pulse width step by step. The maximum pulse width was related to the energy storage capacitor.