Design and analysis of a full bridge LLC DC-DC converter for auxiliary power supplies in traction

This paper focuses on an 8 kW LLC resonant full bridge DC-DC converter topology using a high frequency transformer for auxiliary power supply systems in traction. The full bridge DC-DC converter with the LLC resonant network has been tested under hard switching and zero current switching conditions with 100 kHz switching frequency. In addition to this, an observation made for the effect of dead time variation of the power switches to improve the overall system efficiency. This paper describes the efficiency of the ZCS full bridge converter by considering different input power levels and also compared with hard switched topology. This paper presents the operating principles, simulation analysis, and experimental verification for 3 kW to 8 kW LLC resonant full bridge converter with 1200 V/40 A IGBTs, and its efficiency comparison.     

SAW filters based on parallel-connected coupled resonator filters with offset frequencies

The concept of coupled resonators is applied to synthesize surface acoustic wave filters. Employing two parallel-connected filter tracks, with a frequency shift imposed between them, a wide passband with low insertion loss together with well-controlled rejections is achieved. The operation of the two-track device is based on the mutual interaction of the individual transfer functions for the pair of tracks. Each track serves to contribute a part of the passband, enabling a wide band. Outside of the passband, the signals passing through the two channels may cancel each other, thus facilitating efficient control over the rejections. However, obtaining rejection stopbands at just the predetermined frequencies requires precise values for the materials parameters and a reliable fabrication process. Prototype devices fabricated with this approach are demonstrated both on quartz and, for the first time, on 42 degrees-LiTaO3. Results for two-track devices having either two or three transducers per track and operating either single-ended or with a balanced output are presented. The devices are designed employing the coupling-of-modes model and transmission-matrix approach, and the separate tracks are optimized simultaneously and independently. The center frequencies are 868 MHz and 1960 MHz. On quartz, a minimum insertion loss of 4 dB and a passband width of 0.23% are achieved at 868 MHz. On 42 degrees-LiTaO3, the corresponding figures of merit are 1.3 dB for minimum insertion loss and 4.1% bandwidth at 1960 MHz. The filters on 42 degrees-LiTaO3 also have remarkably flat passbands.     

Sensitivity analysis with full-wave electromagnetic solvers based on structured grids

Recently, we proposed a novel technique for design sensitivity analysis of high-frequency structures with respect to localized perturbations in conductive parameters. Here, we generalize the technique to include shape and material variations and utilize the response sensitivities in gradient-based optimization. Our technique belongs to the class of adjoint-variable methods. Thus, it computes the response and its gradient with only two electromagnetic (EM) simulations-of the original and the adjoint problems-regardless of the number of design parameters. For the first time, adjoint sensitivities with respect to conductive, dielectric-magnetic material and shape perturbations are computed via EM solvers on structured grids. Our approximate sensitivity analysis does not require analytical derivatives of the system matrix. This makes the technique versatile and easy to implement. The technique defaults to exact sensitivities with analytical system matrix derivatives when global design parameters are being perturbed. We discuss the accuracy of the approximate sensitivities, as well as the practicality of the exact sensitivities in specific design problems. We also discuss implementations in gradient-based optimization and illustrate them through simulation and design with the frequency domain transmission line method (FD-TLM).     

Soft-switching flyback inverter with enhanced power decoupling for photovoltaic applications

A novel single-phase flyback inverter for photovoltaic applications is proposed to achieve low-frequency ripple current reduction on the DC busbar and to draw sinusoidal current into the AC grid. Based on capacitive idling techniques, the proposed circuit topology is derived from a single-ended primary-inductance converter and two-switch flyback inverter to obtain soft-switching operation for all of the active switches. Compared with a buck-boost inverter and other flyback inverter topologies for AC photovoltaic module systems, no extra active switches are used in the proposed inverter to realise both soft-switching and enhanced power decoupling with only four active switches. Peak-current mode control method is employed in the control schemes to ensure pure sinusoidal current with unity power factor on the AC grid. Laboratory experimental results based on a 500 W prototype are provided to verify the effectiveness of the proposed inverter     

Displacement-phase-code converter with error correction

Conclusions 1) The use of phase converters with multichannel outputs enables us to calculate automatically the components of the error in a phase converter and use them for correcting the error. 2) The use of two-channel phase converters enables us to correct for only of the components of the error. 3) For full error correction, we need to use a phase converter with three or more output channels.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 31–33, July, 1978.     

A frequency converter with controllable characteristics

The area of practical application of measuring instruments with frequency conversion, in which the economic costs of their operating cycle are related to the control of the accuracy of the converters, is considered. Methods of constructing stroboscopic frequency converters, adapted to a specific class of measurement problems with respect to the “accuracy” parameter, are described. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 47–51, January, 2008.