This paper utilised a solid‐state transformer (SST) with an active clamped L‐L type current fed front‐end converter for maximum power extraction (MPE) and voltage boost operation. The proposed system employed perturb and observe (P&O) based MPE and upheld the ZVS operation of all primary side switches and ZCS operation of all secondary side rectifier diodes for various insolation conditions. The proposed system developed a new fundamental extractor titled multi‐level cascaded dual double fundamental signal extractor (MCDDFSE) and is utilized in the control algorithm for synchronization with the utility grid. The main objective of the proposed system was to deliver a compact size, reduced weight and cheaper magnetic components‐based front‐end converter of SST on the photovoltaic (PV) array side and a fast, secure and trustworthy mitigation technique for the grid current harmonics on the utility grid side. The proposed system was trialled on the platform of OPAL‐RT (RT‐LABv2021.3.2.307) for various grid abnormalities and its behaviour was found well within the IEEE 519 standards.

The presented work utilized a solid‐state transformer with an active clamped L‐L type current fed front‐end converter for maximum power extraction from PV arrays by providing ZVS operation to primary side switches and ZCS operation to secondary side rectifier diodes. Further, the generated power is supplied to non‐linear load and utility grid at unity power factor and improved power quality by applying a new fundamental extractor topology titled multi‐level cascaded dual double fundamental signal extractor (MCDDFSE) based grid control technique. Finally, the proposed system was trialled on the platform of OPAL‐RT (RT‐LABv2021.3.2.307) for various grid abnormalities and its behaviour was found well within the IEEE 519 standards.image

Buck converter is a good candidate for the non‐isolated auxiliary power supply (APS) due to its simple structure and high efficiency. However, it can hardly be adopted in applications that required a very high step‐down ratio due to the difficulty to realize an ultra‐low duty cycle, especially when the switching frequency becomes higher and higher. Here, an improved Buck converter is proposed for high‐frequency and high‐step‐down‐ratio APS application. With the control method based on energy extraction, the proposed topology can achieve an ultra‐low equivalent duty cycle. Thus, a high step‐down ratio can be achieved under a high switching frequency. Moreover, the proposed structure can be applied on several types of the main power stage through the power switch sharing technique. Finally, the prototype with the switching frequency of 1 MHz and the step‐down ratio of 18:1 is verified by the experimental results.

An improved Buck converter is proposed for high‐frequency and high‐step‐down‐ratio application. With the control method based on energy extraction, the proposed topology can achieve an ultra‐low equivalent duty cycle and thus a high step‐down ratio under a high switching frequency.image

In the three‐phase grid‐connected current‐source inverters (CSIs), the resonance result from the AC‐side CL filter and the quality of the grid‐current waveform under the unbalanced and harmonic grid voltage conditions are two issues deserving attention. To solve the two problems, a continuous control set‐model predictive control (CCS‐MPC) method based on the optimization theory is proposed in the two‐phase synchronous coordinate frame in this paper. The constructed cost function takes grid‐connected current and output current of the inverter as control target, and obtains its optimal solution under the least‐squares method, where the optimal inverter‐side current reference is composed of inductor‐current proportional feedback, capacitor‐voltage proportional feedback, and inverter‐side current steady‐state value feedforward. The proposed method can easily realize the normal operation of three‐phase grid‐connected CSIs because the method can be determined by only one parameter under the unbalanced and distorted grids. Furthermore, in the proposed method, the proportional feedback of capacitor voltage can effectively suppress the CL filter resonance. Finally, simulation and experimental results verify the effectiveness of the proposed control strategy.

For the control under unbalanced and harmonic grids, this paper discusses in detail about the suppression mechanism and specific implementation methods of the proposed method for grid voltage harmonics. Furthermore, the necessary parameters are designed according to the Bode diagram of the control system, and the position map of the closed‐loop pole also shows that the proposed method has good anti‐disturbance to AC‐side inductance parameters. Finally, the simulation and experimental results demonstrate the excellent performance of the proposed method. image

Here, an ultra‐high gain quadratic boost DC–DC converter (UQBC) based on the conventional quadratic boost converter (CQBC) and a three‐winding coupled inductor (TWCI) has been proposed. It benefits from an extensive voltage gain range and low voltage stress on semiconductors. In addition, the converter requires a reasonable number of components. This structure is suitable for connecting renewable DC power sources like fuel cells to a DC‐bus in DC microgrids. Unlike CQBC, the produced conversion ratio has been improved to [1+n+m+d(1+n)]/(1−d)² thanks to integrating a TWCI into CQBC. As a result, the proposed quadratic boost converter gives a better step‐up factor than previously presented quadratic boost converters (QBC). Meanwhile, the employed improvement method has not adversely affected some critical parameters like voltage stress on semiconductors or the input current ripple. This paper presents the mathematical analysis and operating principle of the proposed topology for both continuous and discontinuous current modes (CCM and DCM). Experimental results are represented to validate the converter theory and its performance. Results indicate that a high gain and efficiency have been obtained. Also, the voltage stress on the power switch is reduced by one‐fourth by choosing a proper duty cycle and winding coefficient.

A single‐switch non‐isolated step‐up DC–DC converter based on the conventional quadratic boost converter and a three‐winding coupled inductor has been introduced. High boost factor, high efficiency, continuous input current with low ripple, reduced voltage stresses on the switch and power diodes, and a suitable number of elements compared to the obtained gain are the most significant achievements of this topology. image

This paper presents an auto‐tuning method for dc‐ac voltage source converters (VSCs) with an inductive load that is based on the modified relay feedback test (MRFT). Controllers tuned by the proposed method can produce near‐optimal dynamic performance for dc–ac VSCs without requiring knowledge of the plant's parameters. The controller consists of a PID cascaded with a digital notch filter. The tuning involves two steps. In the first step, the MRFT is used to tune the digital notch filter to compensate for the LCL resonance resulting from the LC filter's interaction with the inductive load. In the second step, one more MRFT is used to tune the PID controller using optimal tuning rules that are derived in advance (offline). The proposed optimal for the class of the dc–ac VSCs tuning rules can guarantee a specified phase margin and near optimal transient performance for any randomly picked VSC. The performance of the proposed tuning of the PID + notch filter is verified by simulations and experiments. The dynamic response of the auto‐tuned controller compares well to the response of a theoretically optimal but non‐auto‐tuned PID + notch filter designed using the full knowledge of the LC filter and the load.

This paper presents an auto‐tuning method for dc–ac voltage source converters (VSCs) with an inductive load that is based on the modified relay feedback test. Controllers tuned by the proposed method can produce near‐optimal dynamic performance for dc–ac VSCs without requiring knowledge of the plant's parameters. image