Self-sustained oscillating resonant converters operating above theresonant frequency

This paper presents a new control technique for resonant converters. Unlike conventional variable frequency control which externally imposes the switching frequency, the proposed scheme is based on controlling the displacement angle between one of the resonant circuit variables, typically the current through the resonant inductor, and the voltage at the output of the inverter. As a result, zero-voltage switching (ZVS) can be ensured over a wide operating range. The proposed control technique cam be applied for series, parallel, and series-parallel resonant converters. As an example, the static characteristics and dynamic model of a series-parallel resonant converter with the proposed controller are derived and the system behaviour is investigated in detail. Experimental results are given to demonstrate the operation of resonant converters with the proposed controller and to validate the analysis     

New method of power control for series-parallel load-resonantconverters maintaining zero-current switching and unity power factoroperation

A power supply incorporating a series-parallel load-resonant converter capable of efficient operation over a wide range of output power is presented. The series-parallel resonant converter is shown to have three resonant frequencies. Operation of the circuit at each of these resonant frequencies maintains zero-current switching and high-frequency operation. The resonant circuit is designed to have different circuit resistances at each resonant frequency. The power delivered to the circuit, and hence the load, will therefore vary depending on which resonant frequency the circuit is excited at. This is the basis of a new method of power control for load-resonant converters disclosed in this paper. A welding power supply is designed and constructed which delivers pulsed output currents of 150 A while operating at 100 kHz and 60 A at 65 kHz. The power supply contains an active rectifier and draws near unity power factor     

Optimum Trajectory Switching Control for Series-Parallel Resonant Converter

The series-parallel resonant converter (SPRC) is known to have combined merits of the series resonant converter (SRC) and PRC. However, the SPRC has a three-element LCC structure with complex transient dynamics, and without control of the resonant circuit's dynamics, the converter's closed-loop bandwidth to switching-frequency ratio will be much reduced compared to that of pulsewidth-modulation (PWM) converters. This paper presents the optimal trajectory enabling any SPRC's steady state be achieved within one cycle. Dynamics using the state-plane analysis is presented, and the optimal state trajectory for transients is derived. Experimental results with comparison to frequency control show much reduced resonant circuit response time for step changes in output voltage. This improved resonant circuit control allows subsequent current and voltage-loop controls of the SPRC to be treated as that of a conventional PWM voltage source     

Performance Comparison of Single-Stage Three-Level Resonant AC/DC Converter Topologies

In this paper, the performance of different three-level resonant converters is studied for single-stage power factor correction operation. These converters are suitable for power ranges higher than that in the currently available single-stage converters, due to their high efficiency and reduced component stresses. All the converters presented here are characterized by their ability to regulate the output voltage as well as the dc bus voltage. This leads to lower voltage stresses, wider input voltage range, higher output power applications, and improved efficiencies compared to existing single-stage topologies. Due to the availability of more degrees of freedom in the presented converters, two types of control strategies can be used for this purpose: variable frequency asymmetrical pulsewidth modulation control and variable frequency phase-shift modulation control. Three resonant converters will be studied in this paper and their performances as well as the applicability of the aforementioned control methods for each converter are compared. A 2.3-kW, 48-V converter with input voltage range of 90-265 V_rms is used to study the performance of each case.     

A comparison of half-bridge resonant converter topologies

The half-bridge series-resonant, parallel-resonant, and combination series-parallel resonant converters are compared for use in low-output-voltage power supply applications. It is shown that the combination series-parallel converter, which takes on the desirable characteristics of the pure series and the pure parallel converter, avoids the main disadvantages of each of them. Analyses and breadboard results show that the combination converter can run over a large input voltage range and a large load range (no load to full load) while maintaining excellent efficiency. A useful analysis technique based on classical AC complex analysis is introduced     

Series–Parallel Resonant Converter in Self-Sustained Oscillation Mode With the High-Frequency Transformer-Leakage-Inductance Effect: Analysis, Modeling, and Design

An accurate modeling of the series-parallel resonant converter operating in self-sustained oscillation mode including the overlap effects of the output rectifying stage due to the leakage inductance of the transformer is presented. This paper presents a systematic procedure to study the aforementioned effects on the converter dynamic and steady-state performance. Such information is critical in designing isolated high-frequency resonance-based voltage-regulator modules for powering future subvoltage very large scale integration circuits such as microprocessors. The extended describing function technique is used to extract the steady-state characteristics in order to get an optimum converter design. Averaging state-space techniques are employed to derive a small-signal model that can describe the converter dynamics accurately. Analytical and simulation results are given. Finally, a 1-kW experimental prototype is built to verify the validity of the proposed work     

Analysis, design, and resonant current control for a 1-MHzhigh-power-factor rectifier

Fundamental frequency analysis is used to examine the LCC series-parallel loaded resonant converter with a capacitive output filter when operating as a high-power-factor rectifier. Optimum values are identified for the Q factor and voltage conversion ratio such that zero-voltage switching is just maintained, while minimizing the resonant circuit conduction losses. A simple resonant current control loop is shown to provide an effective mechanism of active control, achieving a high-quality input current waveform over a wide load range. Results are presented from a 1 MHz 160 W prototype     

Characteristics of load resonant converters operated in ahigh-power factor mode

The performance of the parallel resonant power converter and the combination series/parallel resonant power converter (LCC converter) when operated above resonance in a high power factor mode are determined and compared for single phase applications. When the DC voltage applied to the input of these converters is obtained from a single phase rectifier with a small DC link capacitor, a relatively high power factor inherently results, even with no active control of the input line current. This behavior is due to the pulsating nature of the DC link and the inherent capability of the converters to boost voltage during the valleys of the input AC wave. With no active control of the input line current, the power factor depends on the ratio of operating frequency to tank resonant frequency. With active control of the input line current, near-unity power factor and low-input harmonic currents can be obtained     

Analysis of RCD snubber based non-ideal Z-source inverter using average modelling approaches

ABSTRACT

Z-Source inverters (ZSIs) are one of the most promising single-stage power converters in modern industrial applications. However, these ZSIs exhibit non-minimum phase behaviour as a result of right half-plane (RHP) zero in the converter transfer functions and impose a constraint on the controller design. A detailed mathematical model of the converter plays a crucial role in the design of an efficient control strategy. This paper presents a detailed mathematical model of non-ideal ZSI using averaged modelling approaches and its comparisons are summarised. The pole-zero and step response plots reveals the impact of parasitic elements and parameter variations on system steady-state and dynamic performance. Finally, the effects are outlined, which gives a basic guideline to the designers in the converter performance optimisation such as the feedback control bandwidth, damping factor, resonant frequency, and overshoot/undershoot in the desired output. The sensitivity function is defined for a voltage gain of ZSI with respect to system parasitic elements and snubber parameters. In order to validate the theoretical analysis of converter dynamics, a laboratory prototype model of 50 watts ZSI is developed. Further, a hardware implimentation of PID-based capacitor voltage control is shown to check the effectiveness of the derived transfer functions on closed-loop performance.     

A LLC resonant converter with dual resonant frequency for high light load efficiency

This paper presents a new approach to achieve high light-load efficiency for inductor-inductor-capacitor (LLC) resonant converters. Compared with the conventional LLC resonant converters, an additional active resonant network is employed to give the proposed converter another resonant frequency and another steady state. Thereby, the proposed converter has advantages of narrow switching frequency range and high light-load efficiency. The operation principle and the resonant network switching strategy of the proposed converter are analysed, as well as the design considerations. A 1.2-kW prototype with silicon carbide (SiC) MOSFETs is built to verify the proposed converter. The peak efficiency is tested as 94.4% at 680 kHz. Especially, the light-load efficiency is improved from 89% to 91%.     

Output plane analysis of load-sharing in multiple-module convertersystems

This paper explores the origin of the DC current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems. Both problems may be studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems. Furthermore, a broad class of converters whose output voltage is load-dependent, i.e., those that have a moderate value of output resistance, all exhibit good voltage- and current-sharing characteristics. Such converters are often suitable for a×b arrays of converters that can meet a large range of power-conversion requirements. The output planes of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A simple small-signal model of the modular converter system is developed. Experimental confirmation of load sharing and the small-signal model is given for the clamped series resonant converter and the series resonant converter for various configurations of four converters     

A Multipulse-Structure-Based Bidirectional PWM Converter for High-Power Applications

Multipulse converters are suitable for high-power application with the merits of low switching frequency and perfect harmonic performance. But less controllability and poor regulation lead the restriction on its application. A bidirectional pulsewidth modulation (PWM) converter based on multipulse structure is proposed in this paper, which has the same perfect harmonic performance with very low switching frequency. A special sequential sampling space vector modulation technique, which has the sampling sequence from the lagging module to the leading module, is proposed to make the converter controllable like conventional PWM converters. The harmonic performance and linear regulation capability are analyzed theoretically. The converter is modeled in detail, and an instantaneous feedback control strategy with phase delay compensation and decoupling control is also proposed. The controller parameters are optimized to get high dynamic performance with adequate phase margin and gain margin. A 3-kVA prototype is built, and the simulation and experiment results validate that the proposed converter is quite suitable for high-power conversion.     

Phase-controlled series-parallel resonant converter

A constant-frequency, phase-controlled, series-parallel resonant DC-DC converter is introduced, analyzed in the frequency domain, and experimentally verified. To obtain the DC-DC converter, two identical series-parallel resonant inverters are paralleled and the resulting phase-controlled resonant inverter is loaded by a voltage-driven rectifier. The converter can regulate the output voltage at a constant switching frequency in the range of load resistance from full-load resistance to infinity while maintaining good part-load efficiency. The efficiency of the converter is almost independent of the input voltage. For switching frequencies slightly above the resonant frequency, power switches are always inductively loaded, which is very advantageous if MOSFETs are used as switches. Experimentally results are given for a converter with a center-tapped rectifier at an output power of 52 W and a switching frequency of 127 kHz. The measured current imbalance between the two inverters was as low as 1.2:1     

Smart Internet of Things (IOT) System for Performance Improvement of Dual Bridge LLC Resonant Converter by Using Sophisticated Distribution Control Method (SDC)

A resonant converter is a kind of electric power converter that contains a system of inductors and capacitors called a resonant tank, tuned to resonate at a particular frequency in this work recommends a better-quality dual bridge LLC resonant converter with a novel controller technique. The resonant converters include the serial or parallel connections of inductors and capacitors to activate the switch to realize the Zero Current Switching (ZCS) and Zero Volt Switching (ZVS) under resonance conditions. The resonant effects are switching sufferers, turning strain and electromagnetic interference problems the switching resonant converter controls the output voltage through changing frequency and generally can be sub classified in ZCS converter and ZVS converter. This scheme had combined wireless monitoring for dual bridge LLC resonant converter for dc distribution applications based on sophisticated distribution controller (SDC) through the internet of things and embedded structure access and other mechanisms. The consequence of our exhibition demonstrates that the framework can monitor and store the manipulate data from the converter. Thus, the wireless monitoring functions are realized in real-time. This converter permits both forward and reverses power exchange between the source and the load, to keep up the output voltage consistent, regardless of load and line unsettling influences, it is important to work the converter as a closed loop system. The proposed SDC based dual bridge resonant converter has validated through simulation in Matlab Simulink environment. A hardware setup is also developed to validate the simulation. General 97% effectiveness accomplished at full load condition in light of the dual bridge resonant converter.     

Analysis, modeling, and simulation of series-parallel resonantconverter circuits

This paper presents a SPICE macromodel for a generic series-parallel resonant converter circuit. The model is derived from the averaged time-invariant state-space equations obtained from a Fourier transform. The conditions are derived under which all but the fundamental harmonic may be discarded, and the model developed based solely on the fundamental Fourier component. The single macromodel developed has a wide range of validity, and allows DC, AC, and transient analyses to be carried out in a fast, easy, and familiar manner. It also permits the converter to be incorporated alongside its control circuitry into an entire system. The simulation results from the model have been compared to results from a full simulation, and the agreement is found to be excellent, with the macromodel simulation running between 37 and 4700 times faster than the full simulation     

A simple control technique for series resonant converters

A control strategy for series resonant converters, based on the control of the state space trajectory, is proposed. Its simple implementation allows high frequency applications and requires only resonant current sensing. Quite linear and load independent control characteristics are obtained. Simulated and experimental results show good steady-state stability, fast dynamic response for wide reference step variations, and well-controlled converter start-up     

Transistor Selection and Design of a VHF DC-DC Power Converter

This paper explores the design and performance of dc-dc power converters operating in the very high frequency (VHF, 30-300 MHz) range. Methods are presented for assessment and comparison of device losses in VHF operation under soft switching and soft gating conditions. These methods are applied to the development of a 2 W resonant boost converter operating at a switching frequency of 30 MHz. Design of the power stage, resonant gate drive, and control circuitry are treated in detail, and experimental results demonstrating the performance of the converter are presented.     

Series resonant converter with auxiliary winding turns: analysis,design and implementation

Conventional series resonant converters have researched and applied for high-efficiency power units due to the benefit of its low switching losses. The main problems of series resonant converters are wide frequency variation and high circulating current. Thus, resonant converter is limited at narrow input voltage range and large input capacitor is normally adopted in commercial power units to provide the minimum hold-up time requirement when AC power is off. To overcome these problems, the resonant converter with auxiliary secondary windings are presented in this paper to achieve high voltage gain at low input voltage case such as hold-up time duration when utility power is off. Since the high voltage gain is used at low input voltage cased, the frequency variation of the proposed converter compared to the conventional resonant converter is reduced. Compared to conventional resonant converter, the hold-up time in the proposed converter is more than 40ms. The larger magnetising inductance of transformer is used to reduce the circulating current losses. Finally, a laboratory prototype is constructed and experiments are provided to verify the converter performance.     

PWM-controlled SRC with inductive output filter at constantswitching frequency

By using the PWM control scheme in the series resonant power converter (SRC) with inductive output filter, the converter can be operated at a constant frequency. This converter has lower switching loss than the PWM converter and better control characteristics than the ordinary SRC. Since the peak current in the present converter equals the load current, it has the lowest possible peak current stress among converters. The analysis and the performance characteristics of the converter operating at a constant switching frequency are presented. Experimental results are given to confirm the analytical work     

Modeling and improved current control of series resonant converterwith nonperiodic integral cycle mode

A dynamic modeling and an improved current control technique for a series resonant power converter with nonperiodic integral cycle mode are proposed to overcome the disadvantages of an integral cycle mode-controlled series resonant converter. The internal operational characteristics, are investigated in detail and an improved current control technique is developed based on this analysis. Using the proposed control technique, the minimized current ripple with reduced offset current and the fast transient response with negligible overshoot can be obtained. Furthermore, the continuous output voltage levels can also be available by accurately controlling the average filter input current. The usefulness of the proposed technique is verified through computer simulations and experiments