Academic literature on the topic 'Current-fed push-pull'

Three-phase current-fed flyback push-pull dc-dc converter is proposed in this paper, which is a new circuit topology putting into practice based on current-fed flyback push-pull dc-dc converter. Structure is simplified; cost is cut down; efficiency and reliability are improved all by the high frequency three-phase transformer technique that carries out functions of flyback transformer as well as push-pull transformer at the same time. Three-phase transformer can be separated into relatively independent functions of flyback transformer and push-pull transformer with the reluctance produced by the magnetic gap in the central phase; the flyback transformer produces only common-mode flux in the magnetic circuit of push-pull transformer and does not influence its output signal; the magnetic flux in push-pull transformer is blocked by the magnetic gap and can only flow through the outer magnetic loop. Investigational device is designed; static and dynamic characteristics are observed and test results are verified by the experimentation.

A bidirectional dc-dc converter with multiple outputs are concatenated with a high frequency current source parallel resonant push pull inverter is presented in this paper. The two outputs are added together and it is taken as the input source for the inverter. The current source parallel resonant push pull inverter implemented here with high frequency applications like induction heating, Fluorescent lighting, Digital signal processing sonar. This paper proposes a simple photovoltaic power system consists of a bidirectional converter and a current fed inverter for regulating the load variations. Solar power is used as the input source for the system. Simulation of the proposed system is carried out in PSIM software and experimentally verified the results.

This work presents a modified version of the current-fed dc–dc push–pull converter associated with an active clamping circuit for mitigating voltage spikes on the primary-side switches. Unlike the traditional push–pull topology, saturation due to asymmetrical gating signals applied to the active switches is not likely to occur in the high-frequency transformer because the converter allows for connecting a blocking capacitor in series with the primary winding. In addition, the leakage inductance will not cause high voltage spikes on the primary-side semiconductors owing to the clamping capacitors. Since all active switches operate under the zero-voltage switching (ZVS) condition, one can obtain a high efficiency over a wide load range when comparing the structure with its hard-switching counterpart. Experimental results obtained from a laboratory prototype rated at 1 kW are presented and discussed to validate the theoretical claims.

The inherent difficulty in designing high voltage power supplies is often compounded by demands of high reliability, high performance, and safe functionality. A proposed high step-up ratio DC-DC converter meets the exacting requirements of applications such as uninterruptible power systems, radar, and pulsed power systems. The proposed DC-DC converter topology combines a multi-phase buck input stage with a novel self-tracking zero-voltage-switching (ZVS) resonant output stage. Traditionally, the inclusion of multiple power processing stages within a power supply topology severely degrades the overall converter efficiency. Due to the inherent high efficiency per stage, however, this effect is minimized. The self-tracking switching scheme ensures that ZVS occurs across the full range of load variation. Furthermore, the switching scheme allows significantly increased flexibility in component tolerances compared to traditional resonant converter designs. The converter also demonstrates indefinite short-circuit protection and true ZVS during transient processes. Computer simulation and hardware analysis verify the efficacy of the topology as a rugged and efficient converter.

ABSTRACT Bridgeless Active Power Factor Correction Using a Current Fed Push Pull Converter Jeramie Seth Bianchi Switched Mode Power Supplies have become increasingly popular for efficient methods of delivering power to an assortment of electronic devices. This thesis proposes a method of using a current fed push pull converter to provide active power factor correction and rectification in a single stage. While most AC-DC converters utilize a bridge rectifier to convert AC-DC and then perform DC-DC conversion, the proposed circuit will utilize its output diodes to perform rectification, thus eliminating the need for a bridge rectifier. This circuit will also inherently provide power factor correction because the input current has a continuous path for current flow due to the current fed topology where no time exists for both switches to be off. Through analog circuitry for the controller, multiple methods of AC main switching are tested, including isolation techniques using optocouplers, to prove the most efficient way to control a bidirectional switch. Simulations with PSPICE and hardware implementation of the design prove that alternative methods to provide quality power conversion for Switched Mode Power Supplies are available. Keywords: Active Power Factor Correction, Current Fed Push Pull Converter, SMPS, Bidirectional Switching, IGBT, Bridgeless Rectification

High-frequency and large amplitude current is a driving requirement for applications such as induction heating, wireless power transfer, power amplifier for magnetic resonant imaging, electronic ballasts, and ozone generators. Voltage-fed resonant inverters are normally employed, however, current-fed (CF) resonant inverters are a competitive alternative when the quality factor of the load is significantly high. The input current of a CF resonant inverter is considerably smaller than the output current, which benefits efficiency. A simple, parallel resonant tank is sufficient to create a high-power sinusoidal signal at the output. Additionally, input current is limited at the no-load condition, providing safe operation of the system. Drawbacks of the CF resonant inverter are associated with the implementation of the equivalent current source. A large input inductor is required to create an equivalent dc current source, to reduce power density and the bandwidth of the system. For safety, a switching stage is implemented using bidirectional voltage-blocking switches, which consist of a series connection of a diode and a transistor. The series diode experiences significant conduction loss because of large on-state voltage. The control of the output current amplitude for constant-frequency inverters requires a pre-regulation stage, typically implemented as a cascaded hard-switched dc/dc buck converter. The pre-regulation also reduces the efficiency. In this dissertation, a variety of CF resonant inverters with two input inductors and two grounded switches are investigated for an inductive-load driver with loaded quality factor larger than ten, constant and high-frequency (~500 kHz) operation, high reactive output power (~14 kVA), high bandwidth (~100 kHz), and high efficiency (over 95 %). The implementation of such system required to question the fundamental operation of the CF resonant inverter. The input inductance is reduced by around an order of magnitude, ensuring sufficient bandwidth, and allowing rich harmonic content in the input current. Of particular importance are fundamental and second harmonic components since they influence synchronization of the zero-crossing of the output voltage and the turn-on of the switches. The synchronization occurs at a particular frequency, termed synchronous frequency, and it allows for zero switching loss in the switches, which greatly boosts efficiency. The synchronous conditions were not know prior this work, and the dependence among circuit parameters, input current harmonics, and synchronous frequency are derived for the first time. The series diode of the bidirectional switch can reduce the efficiency of the system to below 90 %, and has to be removed from the system. The detrimental current-spikes can occur if the inverter is not operated in synchronous condition, such as in transients, or during parametric variations of the load coil. The resistance of the load coil has a wide variance, five times or more, while the inductance changes as well by a few percent. To accommodate for non-synchronous conditions, a low-loss current snubber is proposed as a safety measure to replace lossy diodes. The center-piece of the dissertation is the proposal of a two-phase zero-voltage switching buck pre-regulator, as it enables fixed frequency and synchronous operation of the inverter under wide parametric variations of the load. The synchronous operation is controlled by phase-shifting the switching functions of the pre-regulator and inverter. The pre-regulator reduces the dc current in the input inductors, which is a main contributor to current stress and conduction losses in the inverter switches. Total loss of the inverter switches is minimized since no switching loss is present and minimal conduction losses are allowed. The dc current in the input inductors, once seen as a means to transfer power to load, is now contradictory perceived as parasitic, and the power is transferred to the load using a fundamental frequency harmonic! The input current to the resonant tank, previously designed to be a square-wave, now resembles a sine-wave with very rich harmonic content. Additionally, the efficiency of the pre-regulator at heavy-load condition is improved by ensuring ZVS for with an additional inductive tank. The dissertation includes five chapters. The first chapter is an introduction to current-fed resonant inverters, applications, and state-of-the-art means to ensure constant frequency operation under load's parametric variations. The second chapter is dedicated to the optimization of the CF resonant inverter topology with a dc input voltage, two input inductors, and two MOSFETs. The topology is termed as a boost amplifier. If the amplifier operates away from the synchronous frequency, detrimental current spikes will flow though the switches since the series diodes are eliminated. Current spikes reduce the efficiency up to few percent and can create false functioning of the system. Operation at the synchronous frequency is achieved with large, bulky, input inductors, typically around 1-2 mH or higher, when the synchronous frequency follows the resonant frequency of the tank at 500 kHz. The input inductance cannot be reduced arbitrarily to meet the system bandwidth requirement, since the synchronous frequency is increased based on the inductance value. The relationship between the two (input inductance and the synchronous frequency) was unknown prior this work. The synchronous frequency is determined to be a complicated mathematical function of harmonic currents through the input inductors, and it is found using the harmonic decomposition method. As a safety feature, a current snubber is implemented in series with the resonant tank. Snubber utilizes a series inductance of cable connection between the tank and the switching stage, and it is more efficient than the previously employed series diodes. Topology optimization and detailed design procedure are provided with respect to efficiency and system dynamics. The mathematics is verified by a prototype rated at 14 kVA and 1.25 kW. The input inductance is reduced by around an order of magnitude, with the synchronous frequency increase of 2 %. The efficiency of the power amplifier reached 98.5 % and might be improved further with additional optimization. Silicon carbide MOSFETs are employed for their capability to operate efficiently at high frequency, and high temperature. The third chapter is dedicated to the development of the boost amplifier's large signal model using the Generalized State-space Averaging (GSSA) method. The model accurately predicts amplifier's transient and steady-state operation for any type of input voltage source (dc, dc with sinusoidal ripple, pulse-width modulated), and for either synchronous or non-synchronous operating frequency. It overcomes the limitation of the low-frequency model, which works well only for dc voltage-source input and at synchronous frequency. As the measure of accuracy, the zero-crossing of the resonant voltage is predicted with an error less than 2° over a period of synchronous operation, and for a range of interest for input inductance (25 μH – 1000 μH) and loaded-quality factor (10 – 50). The model is validated both in simulation and hardware for start-up transient and steady-state operation. It is then used in the synthesis of modulated output waveforms, including Hann-function and trapezoidal-function envelopes of the output voltage/current. In the fourth chapter, the GSSA model is employed in development of the PWM compensation method that ensures synchronous operation at constant frequency for the wide variation of the load. The boost amplifier is extended with a cascaded pre-regulator whose main purpose is to control the output resonant voltage. The pre-regulator is implemented as two switching half-bridges with same duty-cycle and phase-shift of 180°. The behavior of the cascaded structure is the same as of the buck converter, so the half-bridges are named buck pre-regulators. ZVS operation is ensured by putting an inductive tank between the half-bridges. Each output of half-bridges is connected to each of input inductors of the boost to provide the PWM excitation. Using the GSSA model, the synchronous condition and control laws are derived for the amplifier. Properties of the current harmonics in the input inductors are well examined. It is discovered that the dc harmonic, once used to transfer power, is unwanted (parasitic) since it increases conduction loss in switches of the boost. A better idea is to use the fundamental harmonic for power transfer, since it does not create loss in the switches. Complete elimination of the dc current is not feasible for constant frequency operation of the amplifier since the dc current depends on the load coil's resistance. However, significant mitigation of around 55 % is easily achievable. The proposed method improves significantly the efficiency of both the buck pre-regulator and the boost. Synchronous operation is demonstrated in hardware for fixed switching frequency of 480 kHz, power level up to 750 W, input voltage change from 300 V to 600 V, load coil's resistance change of three times, and load coil's inductance change of 3.5 %. Measured efficiency is around 95 %, with a great room for improvements. Chapter five summarizes key contributions and concludes the dissertation.<br>Ph. D.

碩士<br>國立成功大學<br>電機工程學系碩博士班<br>94<br>This thesis mainly studies and implements a current-fed push-pull converter, which is two-stage power supply. The first stage is a buck converter with the output voltage regulator function, and the second is a push-pull converter with the electrical isolation and step-down function. The topology is very suitable for low-output-voltage, high-output-current applications with a wide input voltage range. First, the characteristics of the topology are discussed, and the operation principle of the push-pull converter with a 50% duty cycle is studied in this thesis. Finally, a current-fed push-pull buck converter with a 36~72VDC input voltage range and 1.5V/70A output is performed. The experimental results show that efficiency of the proposed converter is 82.3% at full load condition and the maximum efficiency is 91.3% at 20A output current.

碩士<br>崑山科技大學<br>電機工程研究所<br>97<br>Fluorescent lamps have been very popular for current lighting. This paper develops an alternative electronic ballast. This ballast can accept 12V DC voltage input to provide the power that lamp needs. Will develop in addition the kind of electronic stabilizer, Changes into the high-pressured alternating current the low pressure current phonograph, provides power source which needs for the tube. This paper proposed a current sourcing push-pull resonant inverter fluorescent lamp ballast. This inverter will produce a sufficiently high ac voltage to drive a 40W fluorescent lamp, and it is able to solve the common ground problem that single dc source with two power switches will encounter. Ispice is used to simulate the photovoltaic power driven ballast. The simulation resulted parameters are applied for experiments. The experimental results show that this circuit has efficiency as high as 88%.

碩士<br>南台科技大學<br>電機工程系<br>96<br>A current-fed zero-voltage-switching (ZVS) and zero-current-switching (ZCS) push-pull dc/dc converter is presented in this paper. The proposed push–pull converter topology is suitable for unregulated low-voltage to high-voltage power conversion with low ripple input current. The resonant frequency of both capacitor and inductor is operated at approximately twice the main switching frequency. In this topology, the main switches are operated under ZVS due to commutation of the transformer magnetizing current and the parasitic drain-source capacitance. Due to the leakage inductance of the transformer and resonant capacitance from the resonant circuit, both main switches and output rectifiers are operated implementing ZCS. The operation and performance of the proposed converter has been verified on a 400W with 12V input voltage, 408~426V output voltage and 65.8kHz operated in frequency ZVS ZCS push-pull dc/dc converter. Experimental results in efficiency of 92.5% at a full load.

碩士<br>國立成功大學<br>電機工程學系碩博士班<br>96<br>In this thesis, a current-fed push-pull high voltage converter with zero-current switching (ZCS) is studied and implemented. The first stage is a buck converter that utilizes pulse width modulation (PWM) to regulate the output voltage. The second stage is a push-pull converter which is used to transfer energy from low voltage side to high voltage side. Moreover, the stray components of the high voltage transformer are integrated into the resonant tank of the current-fed push-pull converter. Thus, the proposed converter can achieve ZCS operation of the active switches of the push-pull converter, and the unpredictable resonant phenomenon can be avoided. The characteristics of the various topologies are expressed. The operating principles of the proposed converter are presented, and the steady-state analysis is also discussed in this thesis. Finally, a laboratory prototype with 400 V input and 5 kV/1 kW output is implemented to verify the theoretical analysis.

碩士<br>國立聯合大學<br>電機工程學系碩士班<br>104<br>PV charger is an essential part for the stand-alone and hybrid systems to transform the solar power. This aim of this thesis is to develop an isolated 2kW PV charger with 4 to 8 modules and 48V battery. For achieving wide input voltage to generate power even under low insulation condition, the charger employs the current-fed push-pull converter with buck-boost feature and active clamp for ZVS. The charger charges the battery with three-stage strategy based on the SOC and PV power condition. This thesis presents an improved MPPT control of the incremental conductance method. In addition a fully digital control is adopted for cope with the operation condition variation. The TI F28335 DSP is employed. Some simulation and experimental results are provided for demonstrating the effectiveness of the proposed method.

碩士<br>國立臺灣科技大學<br>電子工程系<br>100<br>This thesis aims to study soft-switched high-voltage buck current-fed push pull resonant converters. The comparisons between the soft-switched and the conventional hard-switched converters are presented. The additional resonant tank of the soft-switched high- voltage buck current-fed push pull resonant converter is added to achieve the ZCS (zero-current switching) and ZVS (zero-voltage switching) features. The conversion efficiency can thus be raised and the voltage spike on the switch can be reduced. A soft-switched high voltage buck current-fed push pull resonant converters with an output rating of 1kV/300W is implemented and tested in the lab. The experimental results are agreed with the theoretical analysis.