The coupling between the boost control and neutral-point voltage balance control of a quasi-Z-source three-level inverter seriously limits its control performance. To solve this problem, a neutral-point voltage balance control strategy based on a virtual space-vector pulse width modulation method is proposed. The neutral-point voltage balance control is realized through a closed-loop control of the DC-bus capacitor voltage, and the low-frequency fluctuations in the neutral-point voltage are eliminated. Meanwhile, a constant shoot-through boost modulation strategy is employed, which avoids the adverse impact on the neutral-point voltage and guarantees an ample boosting capacity of the quasi-Z-source network. Finally, simulation and experimental results verified the validity of the proposed control strategy.

In view of the recent situation in which power sources gradually reach their service terms in China, an evaluation method based on improved fuzzy analytical hierarchy process (FAHP) and entropy weight method (EWM) is proposed. First, an appropriate hierarchical structure is constructed based on the analytic hierarchy process to form a judgment matrix. Then, FAHP is used to process the judgment matrix between various layers, and the importance-oriented weight vector is obtained. At the same time, the Delphi survey method is used to form an evaluation matrix for the last sub criterion layer and the target layer. After normalization, EWM is used to obtain the value-oriented weight vector. The two weight vectors are synthesized to form a comprehensive weight vector. Finally, the final weight vector of the scheme layer to the target layer is formed, and the best scheme is given. The result of an example shows that the proposed evaluation method has strong flexibility and wide applicability. In addition, it also has a clear and reasonable process, as well as intuitive and accurate results.

Three-phase chain-link energy storage converters (TPCLESCs) are promising in enhancing the controllability of renewable energy in power grid, such as wind and solar power. Aimed at the problem of state-of-charge (SOC) imbalance of energy storage battery among phases of a TPCLESC, a phase-to-phase SOC balance method based on phase-to-phase circulating current power closed-loop control is proposed. Through the zero-sequence voltage injection into phases a, b and c, the active circulating current among phases is generated to realize the SOC balance in the three-phase energy storage battery groups. A mathematical model of the maximum phase-to-phase circulating current power of the chain-link energy storage converter and SOC deviation is established. On this basis, the phase-to-phase SOC balance in battery groups is realized at the maximum circulating current power through the phase-to-phase circulating current active power closed-loop control. As a result, the phase-to-phase SOC reaches its balance at the maximum speed, and the process of phase-to-phase SOC balance is accelerated. Finally, the correctness and feasibility of the proposed method were verified by a MATLAB simulation model and an experimental platform.

When a modular multilevel converter (MMC) adopts the traditional carrier phase-shifted pulse width modulation strategy, the additional capacitor voltage balance strategy for submodules will cause the number of submodules in each phase circuit of the MMC to jump at a high frequency. Therefore, a large induced pulse voltage will appear on the inductance of the bridge arm, which will generate a high-frequency harmonic circulating current, thereby increasing the voltage and current stress of components. Based on the study of the traditional carrier phase-shifted modulation strategy and its application to the MMC, the implementation process is improved to ensure that the number of submodules in each phase circuit of the MMC is constant at any time, so as to avoid the above problems. The improved carrier phase-shifted modulation strategy is analyzed in detail, and the corresponding capacitor voltage balance control strategy is given. Simulation and experimental results show that the circulating current amplitude of the bridge arm is reduced after adopting the improved carrier phase-shifted modulation strategy.

A novel two-channel light emitting diode (LED) driver is proposed, and its operating principle and characteristics are analyzed in detail. This driver uses a novel Z-source resonant network and an active switch which has the same ground properties as the power supply, and the current balance is automatically realized by balancing capacitors, so its current control is simple. At the same time, owing to the use of Z-source resonant network to transfer energy, the proposed driver has advantages such as soft switching, high efficiency, small volume and low voltage stress. To verify the effectiveness of this driver, a 80 W prototype was built and tested.

Aimed at the problems such as voltage sag/surge resulting from strong fluctuations of high-permeability renewable energy, which cannot be dealt with by using the existing transformers, a novel hybrid distribution transformer (HDT) based on a three-bridge arm power converter is proposed. This method is realized by adding a series three-bridge arm power converter to the primary side of the existing distribution transformer. The proposed novel HDT has two advantages, i.e., it can reduce the rated power of the power converter, and it can improve the transformer’s degree of freedom by adding an additional current loop. In addition, to further improve the power quality of the transformer, the proposed method integrates the voltage vector, which can compensate the adverse effects of voltage sag/surge and grid voltage harmonics on the transformer. Therefore, it improves the power factor of power grid, as well as the transmission efficiency of the distribution network. Finally, the configuration and control strategy for the proposed HDT are discussed, and the effectiveness and superiority of the proposed method are verified by simulation analysis.

Aimed at the problem that the traditional control methods are difficult to achieve soft-switching in a wide load range due to the limitation of resonant inductor volume and duty cycle loss in phase-shifted full-bridge converters, a hybrid control method based on peak current and Burst mode is proposed. The output voltage is stabilized to a reference value by adjusting the Burst duty cycle, and the phase shift angle is changed to maintain the minimum primary current so as to realize the lagging bridge arm zero voltage switching. A simulation platform was built for the proposed control method, and a 250 W prototype was developed. The hybrid control of a phase-shifted full-bridge converter was realized through a digital signal processor, and the feasibility of the control method was verified by simulation and experimental results.

To reduce the cost and the number of components while ensuring the safe operation of the circuit, a single-phase isolated Δ-source AC-AC converter is proposed. This novel converter can provide a wider range of Buck-Boost output voltage, and the input voltage and output voltage can be in-phase or out-phase. Meanwhile, the surge and harmonic currents are suppressed, and the circuit reliability is improved. The working principle for the proposed circuit is analyzed, the voltage values of main components in each working process are deduced, and the relationship between input voltage and output voltage is formulated, which is further compared with those of other improved AC-AC converters. The theoretical analysis proves the performance of the novel AC-AC converter. A simulation model and an experimental model were built according to the designed parameters for verification, and simulation and experimental results verified the correctness and feasibility of the theoretical analysis.

The converters, switching power supply and other power electronic equipment will inject a large quantity of supraharmonics into distribution network when they are connected to the grid on a large scale, resulting in the problem of power quality which becomes more and more serious. On this basis, the supraharmonics emission mechanism for an ordinary two-stage single-phase frequency converter is studied in depth. First, the Fourier series expression of harmonic current on the grid side is derived using the switching function method. Then, the ratio of supraharmonics is calculated, and its influencing factors are analyzed. Finally, the theoretical analysis is verified by simulation and measurement results. The research can provide a reference for the quantification, detection and monitoring of supraharmonics in distribution network.

The double-sided LCC compensated inductive power transfer (IPT) system with constant-voltage (CV) output suffers from the problem of low efficiency under light load. To solve this problem, based on the idea of approximate optimal solution, a parameter design method for double-sided LCC compensation topology was proposed. The zero phase angle condition in CV output mode and the loss of a loosely coupled coil were analyzed, and a 6.6 kW prototype was built to verify the proposed method. Experimental results show that the system efficiency can be improved with the proposed compensation parameter design method, especially in the case of light load. The system efficiency can reach 95% under full load of 6.6 kW and 93% under light load of 1.32 kW.