Special Issue: New Technologies for Power Electronic Converters and Inverters

1. Introduction

Efficient power conversion is one of the most critical problems in power electronics. In 2019, the European Parliament adopted a resolution declaring a climate and environment crisis, making the reduction of power loss increasingly important. DC/DC converters and DC/AC inverters are essential devices for power conversion. However, many other devices are also used, including active rectifiers and power conditioning equipment such as active power filters and power factor correctors. The specific converters are employed in energy harvesting systems, where the voltage source has a high output resistance and provides a wide range of low voltages. The other power converters are predicted to work with renewable energy sources as photovoltaic modules, where, following the current–voltage curve of the source, should lead to maximum power point tracking that can be realised in many ways.

Today, only switching mode solutions are used because of the low power losses. Discrete or discretised systems digitally control the inverters. The discrete models of the plants, based on solving their state space equations or discretized from the continuous models, are required for the design of the sophisticated, microprocessor or FPGA-based, multi-input control of inverters and converters. The control systems, such as Passivity-Based Control almost predicted for power systems, can be utilized. Modern metaheuristic algorithms inspired by natural phenomena such as genetics, swarm behavior, and evolution—such as Particle Swarm Optimization and Cuckoo Search Optimization—can be applied to power conversion control. However, their performance compared to traditional control systems remains a subject of discussion. New technologies in switching components, such as wide band gap transistors (SiC, GaN) and new magnetic materials (e.g., alloy powders, nanoperm), enable faster switching with lower static and dynamic losses. The high-frequency low-power supplies in package (PSiP) with air-core inductors are a power conversion novelty. The higher switching frequency of inverters reduces delays in the measurement channels, which can be modelled as simple delays in the low-frequency range. Using the different types of fuzzy logic enables control of the power converter with an unknown nonlinear model.

The inverters with the new components can drive high-speed electrical machines, where both smart control (e.g., modified SVM for the four-leg bridge), fast-switching components, and additional circuits (the sinusoidal output filters that are absent in the standard motor drives) should be used. Supplying single-stage microinverters from renewable energy sources as photovoltaic modules, requires a new inverter architecture (to reduce the common mode current from PV), new sinusoidal PWM schemes, and new maximum power point tracking techniques. The usage of supercapacitors in power conversion systems is a new solution. The new “redundant” architectures of multilevel inverters should lead to improved reliability. DC/DC converters can work in zero-voltage or zero-current switching modes to improve power efficiency. The impedance networks are often today’s DC/DC converter solutions, increasing the input voltage of inverters. The use of real-time interfaces (for MATLAB/Simulink) for experimental verification leads to a much faster design process. Improving the EMC of switching-mode power devices is very important and can be useful for the hardware design and the software schema of the PWM modulation as well. Automotive applications of power conversion devices in hybrid or electric cars require the development of power conversion designs. The most useful in practice are the different types of tests of the power devices manufacturing process, particularly in the case of the required lead-free soldering with SAC solders. The important thing for design engineers is charging batteries from the AC power grid, when the input current’s total harmonic distortions result in a lower power factor, and the power efficiency is crucial.

Eight papers were submitted for the Special Issue of Applied Sciences: New Technologies for Power Electronic Converters and Inverters, and five were published in this SI.

2. A Brief Description of the Papers Published in the Special Issue

The paper [1] concerns the problem of the high-frequency harmonics suppression using an additional LC filter when driving the high-speed permanent magnet synchronous motor (HPMSM) that has a low inductance. Such an LC filter between the inverter and the HPMSM introduces additional system resonance. Therefore, the adaptive notch filter with the frequency tracking capability is designed in the control system to offset specific resonant peaks by constructing an antiresonant peak. The harmonic contents of HPMSM are significantly reduced, and the dynamic response performance of the control system is improved. Simulation and experiment results prove the effectiveness of the proposed scheme.

The paper [2] investigates the roadmap for power loss optimisations of switches and inductors in high-frequency power supply in package (PSiP). Power losses of the integrated Si LDMOSFET switches and air-core inductors are calculated with switching frequency up to 100 MHz and the output power up to 10 W. The paper predicts the efficiency boundaries of PSiPs. The presented power loss optimisations improve the efficiency, which provides potential roadmaps for achieving high-frequency PSiPs.

The research [3] introduces an improved control strategy for an active power filter (APF) system. It utilises an adaptive super-twisting sliding mode control (STSMC) scheme. The proposed approach integrates an interval type-2 fuzzy neural network with a self-feedback recursive structure (IT2FNN-SFR) to enhance the overall performance of the APF system. The IT2FNN-SFR estimator is used to approximate the unknown nonlinear function within the APF. Simultaneously, the STSMC component is integrated to reduce system chattering, improving control precision and overall system performance. STSMC combines the robustness and simplicity of traditional sliding mode control, effectively addressing the chattering problem. An adaptive law of sliding mode gain is formulated to achieve optimal gain solutions. Experimental validation is successfully conducted to verify the harmonic suppression capability of the control strategy.

In the paper [4], the issue of an ageing process’s influence on power LEDs’ properties is considered. Some measured DC characteristics of these devices and their thermal and optical parameters obtained are presented after considering different values of the ageing process duration. Components soldered using different metal–ceramic composite pastes, e.g., with TiO₂, were tested. It is shown that after the ageing process at elevated temperatures, worse properties were observed for the power LEDs soldered using classical SACX0307 alloy. Most of the samples soldered with reference alloy (not composite) were damaged during the test. The best properties were obtained for the samples soldered with solder paste with the addition of titanium oxide. It is very important because most diodes soldered with classical SACX0307 alloy failed before testing was completed, and some were damaged after 100 h of the test. The paper [4] was distinguished as a Featured Application because the presented results can be useful for engineers working on the reliability of the soldering process.

The paper [5] aims to enhance the performance of photovoltaic (PV) systems by developing and evaluating maximum power point tracking (MPPT) algorithms capable of operating effectively under both uniform irradiance and partial shading conditions (PSCs). Two metaheuristic algorithms—Particle Swarm Optimisation (PSO) and Cuckoo Search Optimisation (CSO)—are modelled, implemented, and tested for tracking the global peak power (GPP) in various static and dynamic scenarios. Simulation results indicate that both algorithms accurately and efficiently track the GPP under static uniform and PSCs. Under dynamic conditions, while both the PSO and CSO can initially locate the GPP, they fail to maintain accurate tracking during subsequent intervals. CSO exhibits reduced oscillations and faster response time compared with PSO. Metaheuristic MPPT methods are effective in static environments, but their performance in dynamic conditions requires further enhancement.

3. Conclusions

The problem of designing and modelling devices for switching-mode power conversion is significant in the development of renewable energy sources, the requirements for high efficiency of power conversion, and the improvement of power converters’ electromagnetic compatibility. The wide spectrum of the topics in the Special Issue of the Applied Sciences: New Technologies for Power Electronic Converters and Inverters shows that there is a need for the further research in power electronics devices and systems, e.g., in their control strategy reducing the output voltage distortions and increasing the power efficiency, testing the novel packaging of the power devices, and finally the estimation of the reliability of the manufacturing process.