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High temperature power electronics is an advancing area of research, especially given the widespread availability of wide bandgap semiconductors. In this work a suitability analysis of (1−x)BiScO3–xPbTiO3 (BSPT) as a material for high temperature piezoelectric transformers (PTs) is presented and compared to state-of-the-art Pb(Zr1−xTix)O3 (PZT). Initially, both materials will be compared using a variety of metrics to prove the suitability of BSPT as a material for constructing PTs specifically for high temperature applications. PTs based on the two materials are designed and fabricated, and then subsequently characterised using impedance measurements. Finally, half-bridge resonant inverters are constructed using both PTs and the performance of each inverter measured over a range of ambient temperatures. The result of these experiments confirm the suitability of BSPT for PT applications and show the excellent performance of BSPT PTs at temperatures in excess of that possible with PZT based PTs.

Hard‐switched high‐gain DC‐DC converters such as the boost converter play an important role in renewable energy systems. Research to increase their efficiency is important and can be achieved using soft‐switching techniques; however, that approach requires an auxiliary circuit. The auxiliary circuit decreases power density and reliability while increasing the cost. Moreover, soft‐switching topologies usually cannot improve the efficiency for all power and voltage ranges. Wide bandgap (WBG) devices, such as gallium nitride (GaN), result in lower switching losses than silicon (Si), can be used while retaining the simple structure of a hard‐switched topology. However, the high cost of these devices is problematic for their frequently cost‐sensitive applications. To quantify the cost and efficiency, this study compares soft‐switching techniques and WBG‐based switches in DC‐DC boost converters for a photovoltaic (PV) energy application. The performance of four prototypes including the soft‐switched and hard‐switched DC‐DC converters with both state‐of‐the‐art Si and GaN switches are evaluated in terms of cost, power density, efficiency, and reliability using theoretical analysis, simulation and experimental results. It is shown that the GaN‐based hard‐switched converter provides higher efficiency and power density; it is more expensive than its Si‐based counterpart, yet is cheaper than soft‐switched converters.

A single‐active switch high‐voltage gain non‐coupled inductor DC–DC converter is presented. The introduced converter achieves high step‐up gain without using any coupled inductors or transformers, provides high efficiency, and has a simple control system. The converter also achieves low voltage stress on the switch and diodes without clamping circuits, reducing cost, conduction losses, and complexity. The input current of the introduced converter is continuous with low ripple, and is therefore suitable for renewable energy applications in which the fast dynamic response of the converter is necessary. The principle of operation and design considerations of the introduced converter are investigated. A 200 W prototype circuit with 40 kHz switching frequency, 40 V input voltage, and 250 V output voltage is implemented. The prototype operates at 93.2% efficiency, with voltage and current error of less than 4% compared to theoretical values.

A control system to achieve zero-voltage switching (ZVS) for an inductorless half-bridge piezoelectric transformer-based resonant power supply is presented. Both the phase and frequency of the resonant current are locked to the switching waveform using an analogue phase-locked loop (PLL) to ensure ZVS operation. We present two resonant current estimation circuits which generate the reference signals for the PLL. We also present three PLL feedback designs to produce the in-phase gate drive signals with adequate deadtime. The operating principle of the control system and its ability to achieve ZVS operation is discussed. Experimental results of the PLL circuit verify the successful operation of the proposed system. The six permutations of current estimation and feedback are contrasted and conclusions for application-specific usage are made.

Existing equivalent circuit extraction techniques are inaccurate for piezoelectric transformers (PTs) with low-input capacitance or high damping. A new method is presented, offering improved accuracy in both damping resistance and resonant frequency extraction compared with state-of-the-art methods. Effectiveness is evaluated on two sample PTs, with the proposed method achieving up to 84% decrease in error compared with previous methods.

Inductorless half-bridge, piezoelectric transformer (PT) resonant power supplies require careful control if zero voltage switching of the MOSFETs is to be achieved. Here we describe how a phase-locked loop may be used to achieve this by ensuring adequate deadtime exists between the two MOSFETs to allow the PT input voltage to fully charge to the DC link. Experimental results demonstrate the operation of the system.

This paper presents a technique to estimate the temperature of each power electronic device in a thermally coupled, multiple device system subject to dynamic cooling. Using a demonstrator system, the thermal transfer impedance between pairs of devices is determined in the frequency domain for a quantised range of active cooling levels using a technique based on pseudorandom binary sequences. The technique is illustrated by application to the case temperatures of power devices. For each cooling level and pair of devices, a sixth order digital IIR filter is produced which can be used to directly estimate temperature from device input power. When the cooling level changes, the filters in use are substituted and the internal states of the old filters are converted for use in the new filter. Two methods for filter state conversion are developed—a computationally efficient method which is suited to infrequent changes in power dissipation and cooling, and a more accurate method which requires increased memory and processing capacity. Results show that the temperature can be estimated with low error using a system which is suitable for integration on an embedded processor.

A methodology for predicting the ability of inductor-less driven piezoelectric transformer (PT) based power supplies to achieve zero voltage switching (ZVS) is presented. A describing function approach is used to derive an equivalent circuit model of the PT operating in the vicinity of ZVS and the subsequent application of the model provides a quantitative measure of a PT's ability to achieve ZVS when driven by an inductor-less half-bridge inverter. Through detailed analysis of the analytical model, the limitations of the inductor-less half-bridge driven PT are exposed from which guidelines for designing both the PT and inverter are derived.