Search

This letter proposes a three-switch ac–dc converter with buck/boost ability, low leakage current, and continuous input/output currents. Therefore, a wide output voltage range and no bulky electromagnetic interference filters can be achieved. Furthermore, the proposed topology can transfer pulsating power, reducing the demand for the output capacitance. Without a complex structure, the total component count is only nine and a high power density can be obtained. In addition, benchmarking is provided to compare various performance aspects with existing topologies. Finally, the validity of the topology is verified by the experimental results.

The single-phase unified power quality conditioner (UPQC) is an advanced solution capable of compensating voltage sag/swell and current harmonics simultaneously in electrical systems, garnering considerable interest from experts. However, the compensation performance of UPQC can be adversely affected by the fluctuation of dc side capacitor voltage and the presence of nonlinear loads. In this article, we conduct a thorough analysis of the influence of dc voltage fluctuation and nonlinear loads on the series-parallel converter of UPQC. To mitigate these effects, a dynamic control strategy is proposed for the single-phase UPQC. For the series converter, a specific order harmonics compensation (SOHC) scheme is introduced in the outer-voltage loop to reduce grid voltage harmonics. In addition, a moving average calculation method is proposed for the parallel converter to determine the real-time average value of the subcapacitor voltage, effectively minimizing voltage errors in the proportional integral voltage equalization control. Finally, simulation and experimental results validate the efficacy of the proposed control method.

The modular multilevel matrix converter ($\mathrm{{\mathbf{M}}}^{3}$C) is a topology suitable for ac–ac fields, such as wind power conversion systems, large-capacity electric drives, etc. However, when the input frequency of the system is close to or equal to the output frequency, large voltage fluctuations even unbalancing will produce on the dc capacitors of the submodules, which limits the application range of $\mathrm{{\mathbf{M}}}^{3}$C. This article proposes a low-frequency circulating current injection method to address the issue of dc capacitor voltage fluctuations in $\mathrm{{\mathbf{M}}}^{3}$C under equal frequency operating condition. The frequencies present within the $\mathrm{{\mathbf{M}}}^{3}$C are used to consist of the low-frequency circulation current. Therefore, the proposed method does not require injecting common mode voltage or applying reactive power. Experimental results based on the $\mathrm{{\mathbf{M}}}^{3}$C platform verify the effectiveness of the proposed method. Moreover, the dynamic performance is also good with the proposed control strategy under the conditions of output voltage or frequency change.

Voltage equalizer is essential for mitigating the inconsistencies of series-connected lithium-ion batteries in electric vehicles to ensure operation life and work safety. To keep voltage balancing, voltage equalizers are widely adopted in the battery string application. However, traditional voltage equalizers have high circuit costs and large sizes due to the need for a large number of MOSFETs and isolated gate drivers. Moreover, as the voltage difference between the batteries in the series decreases towards the end of the equalization process, the equalization current also decreases, which can affect the speed of voltage equalization. To overcome these problems, an isolated multiple half-bridge converter with a multiport transformer is proposed. The balancing circuit has two power transfer paths, allowing for energy transfer among multiple cells simultaneously, which could achieve a significant equalization current even when the voltage difference is close to zero. In the proposed equalizer, only one MOSFET is needed for one cell and two cells can share one transformer winding. Hence, it is more applicable for a large number of battery stacks, such as electric vehicles. Finally, to improve the equalization speed and efficiency, three equalization control strategies, i.e., average voltage, predicted voltage, and boundary voltage control strategies are introduced and verified by a 100 kHz 24-cell voltage equalization prototype.