FPeT: Framework for designing piezoelectric transformer power supplies

Publications related to piezoelectric transfomers

The following is a list of the publications relating to FPeT work. Updated May 2022.

  1. Performance of PZT-based piezoelectric transformers for us in high-temperature converters
    J. Forrester, L. Li, J. N. Davidson, M. P. Foster, D. A. Stone, I. M. Reaney & D. C. Sinclair
    IET Power Electronics, Machines & Drives (PEMD) 2022
    Piezoelectric transformers (PTs) are ideally suited for resonant converter applications, owing to their inherent resonant tank circuit, high power density and efficiency. High temperature electronics is an area of research that is increasing in popularity, due to SiC and GaN devices. However, high temperature power electronic conversion is difficult to achieve using traditional passive components due to the novel materials required. In this paper, a PT made from lead zirconate titanate (PZT) is proposed for use in high temperature power conversion.
    Awaiting DOI.
  2. RadPTDesigner: A program for designing radial mode piezoelectric transformers for inductorless inverters
    J. Forrester, J. N. Davidson, M. P. Foster & D. A. Stone
    European Conference on Power Electronics and Applications (EPE'21 ECCE-Europe), 2021
    Piezoelectric transformers (PTs) offer the possibility for designing compact and efficient power supplies featuring few components. PT power supplies are difficult to design owing to the fusion between resonant power conversion and materials science. This paper presents a program for designing radial-mode PTs.
    DOI not issued. Click here to access the paper. Click here to access the software.
  3. Output voltage regulation for piezoelectric transformer-based resonant power supplies using phase-locked loop control
    Z. Yang, J. N. Davidson & M. P. Foster
    IET Power Electronics Machines and Drives Conference (PEMD), 2020
    This study proposes an output regulation method for a piezoelectric transformer (PT)-based power converter that employs an inductorless half-bridge topology for achieving zero-voltage switching (ZVS). The resonant current is first estimated at the input section of the PT. These data are used to indicate the effective signs for zero-voltage switching, applied to a phase-locked loop (PLL) as a reference input, to generate the in-phase gate drive signals with an adequate deadtime. Practical results show successful operation of the PLL controller. This technique is extended to achieve output regulation by a burst-mode hysteresis control. Experimental results demonstrate good agreement with the SPICE-based simulation for output regulation while achieving zero-voltage switching.
  4. Influence of spurious modes on the efficiency of piezoelectric transformers : a sensitivity analysis
    J. Forrester, J. N. Davidson, M. P. Foster & D. A. Stone
    IEEE Transactions on Power Electronics, 2020
    An analysis of the efficiency degradation resulting from spurious modes in piezoelectric transformers (PTs) is presented in this article. Circuit analysis is performed on PT equivalent circuit models with both a single resonant branch and with two resonant branches (spurious mode included), allowing the efficiency degradation from a spurious mode to be analyzed. Multiple sensitivity analyses were then performed, highlighting frequency difference (between modes) and characteristic impedance of the spurious resonant circuit (√L2/C2) as critical design parameters for minimizing efficiency degradation from spurious modes. These two parameters are further analyzed to determine optimum design conditions to ensure minimal efficiency degradation. Results of this analysis provide a method of estimating whether a spurious mode will degrade efficiency and consequently provide a method for improving PT designs.
  5. Resonant current estimation and phase-locked loop feedback design for piezoelectric transformer-based power supplies
    Z. Yang, J. Forrester, J. N. Davidson, M. P. Foster & D. A. Stone
    IEEE Transactions on Power Electronics, 2020
    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.
  6. Lead-free (Ba, Sr) TiO3–BiFeO3 based multilayer ceramic capacitors with high energy density
    G. Wanga, Z. Lu, J. Li, H. Ji, H. Yang, L. Li, S. Sun, A. Feteira, H. Yang, R. Zuo, D. Wang, I. M. Reaney
    Journal of the European Ceramic Society 40, no. 4 (2020): 1779-1783
    High recoverable energy density (10 J cm−3) multilayers have been fabricated from lead-free 0.61BiFeO3-0.33(Ba0.8Sr0.2)TiO3-0.06La(Mg2/3Nb1/3)O3 ceramics. High breakdown strength > 730 kV cm-1 was achieved through the optimisation of multilayer processing to produce defect-free dielectric layers 7 μm thick. Excellent temperature, frequency, fatigue stability and fast charge-discharge speed were observed in the multilayer, critical for their potential use in power electronics.
  7. Equivalent circuit parameter extraction methods for piezoelectric transformers
    J. Forrester, J. N. Davidson, M. P. Foster & D. A. Stone
    European Conference on Power Electronics and Applications (EPE'19 ECCE-Europe), 2019
    Three methods for extracting the equivalent circuit components of a piezoelectric transformer areproposed. Each of the methods is presented in detail, describing both the measurement setup and thealgorithm used for extraction. A full comparison of the implementation complexity and extractionaccuracy is performed using experimentally measured data. Finally, the performance of each techniquein the presence of measurement noise is explored. The comparison presented allows the reader todetermine which technique is most suitable for their application.
  8. Critical Design Criterion for Achieving Zero Voltage Switching in Inductorless Half-Bridge-Driven Piezoelectric-Transformer-Based Power Supplies
    M Foster, J Davidson, E Horsley, D Stone
    IEEE Transactions on Power Electronics 31, (7), July 2016
    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.
  9. A PLL controller for achieving zero voltage switching (ZVS) in inductorless half-bridge drive piezoelectric transformer resonant power supplies
    M Foster, J Davidson, D Stone, R Yappa
    The Journal of Engineering (Volume: 2019, Issue: 17, 2019)
    Inductorless half-bridge, piezoelectric transformer (PT) resonant power supplies require careful control if zero-voltage switching (ZVS) of the MOSFETs is to be achieved. Here, the authors describe how a phase-locked loop (PLL) 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.
  10. Automated design tools for piezoelectric transformer-based power supplies
    J Forrester, J Davidson, M Foster, D Stone, E Horsley
    The Journal of Engineering (Volume: 2019, Issue: 17, 2019)
    This paper proposed a design approach for piezoelectric-transformer-based power supplies. Initially, an analytical approach is used to derive the Mason equivalent circuit parameters of a PT. This is coupled with a semi-automated procedure to decide the appropriate physical dimensions of the PT. The procedure is applied to a typical low-power power supply specification, whereupon a specific transformer is design, verified using COMSOL and used as a simulated converter in SPICE. Results show that the design can be successfully implemented while maintaining efficient zero-voltage switching operation.
  11. Effect of Spurious Resonant Modes on the Operation of Radial Mode Piezoelectric Transformers
    J Forrester, J Davidson, M Foster
    PCIM Europe 2018
    This paper analyses both the intentional and unwanted resonant modes of radial piezoelectric transformers (PTs). Initially, finite element analysis is performed to discover the type of spurious modes prevalent is radial mode PTs. From this, analysis is performed on these modes and a relationship between resonant frequency and geometry is found. The effect of spurious modes on the efficiency of a typical PT is simulated using an equivalent circuit model in LTSpice and Simulink. A number of design rules are generated based on the findings. Results show that, in most cases and by careful design, spurious modes can be avoided.
    Click here for more details
  12. Equivalent circuit parameter extraction of low-capacitance high-damping PTs
    J Forrester, L Li, J Davidson, M Foster, D Stone, D Sinclair, I Reaney
    IET Electronics Letters, 2020
    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.