Approximate small-signal analysis of the series and the parallelresonant converters

Approximate transfer functions of series and parallel resonant converters are given which are in good agreement with the results of exact analysis as well as the results of experiments. It is shown that the dominant behavior of these transfer functions is determined by the output low-pass filter modified by the internal impedance of the converter. The high-frequency behavior, on the other hand, is given by a second-order response whose frequency is at the difference between the resonant and the switching frequencies and whose Q is the original resonant Q modified by the internal impedance of the converter     

Equivalent circuit models for resonant and PWM switches

The nonlinear switching mechanism in pulsewidth-modulated (PWM) and quasi-resonant converters is that of a three-terminal switching device which consists only of an active and a passive switch. An equivalent circuit model of this switching device describing the perturbations in the average terminal voltages and current is obtained. Through the use of this circuit model the analysis of pulsewidth modulated and quasiresonant converters becomes analogous to transistor circuit analysis where the transistor is replaced by its equivalent circuit model. The conversion ratio characteristics of various resonant converters and their relationship to a single function, called the quasi-resonant function, is easily obtained using the circuit model for the three-terminal switching device. The small-signal response of quasi-resonant converters to perturbations in the switching frequency and input voltage is determined by replacing the three-terminal switching device by its small-signal equivalent circuit model     

A new phase-controlled parallel resonant converter

A phase-controlled resonant converter was obtained by connecting in parallel the AC loads of two identical parallel resonant inverters. A phase shift between the drive signals of the two inverters controls the amplitude of the output voltage of the new inverter. A voltage-driven rectifier is used as an AC load of the inverter, which results in a phase-controlled parallel resonant DC-DC converter. A frequency-domain analysis is performed for the steady-state operation of the inverter, and two types of voltage-driven rectifiers and design equations are derived. The converter can be operated at a constant switching frequency, which reduces EMI problems. It is found that for switching frequencies higher than the resonant frequency by a factor of 1.07, the load of each switching leg is inductive. The converter is capable of regulating the output voltage in the range of load resistance from full-load to no-load. Experimental results are presented for a prototype of the phase-controlled parallel resonant converter with a center-taped rectifier tested at an output power of 50 W and a switching frequency of 116 kHz     

Optimal Design of Resonant Gate Driver for Buck Converter Based on a New Analytical Loss Model

In this paper, the advantages of a new resonant driver are verified thoroughly by the analytical analysis, simulation and experimental results. A new accurate analytical loss model of the power metal oxide semiconductor field effect transistor driven by a current-source resonant gate driver is developed. Closed-formed analytical equations are derived to investigate the switching characteristics due to the parasitic inductance. The modeling and simulation results prove that compared to a voltage driver, a current-source resonant driver significantly reduces the propagation impact of the common source inductance during the switching transition at high (>1 MHz) switching frequency, which leads to a significant reduction of the switching transition time and the switching loss. Based on the proposed loss model, a general method to optimize the new resonant driver is proposed and employed in the development of a 12 V synchronous buck voltage regulator (VR) prototype at 1 MHz switching frequency. The level-shift circuit and digital implementation of complex programmable logic device (CPLD) are also presented. The analytical modeling matches the simulation results and experimental results well. Through the optimal design, a significant efficiency improvement is achieved. At 1.5 V output, the resonant driver improves the VR efficiency from 82.7% using a conventional driver to 86.6% at 20 A, and from 76.9% using a conventional driver to 83.6% at 30 A. More importantly, compared with other state of the art VR approaches, the new resonant driver is promising from the standpoints of both performance and cost-effectiveness.     

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     

A circuit model for the class E resonant DC-DC converter regulatedat a fixed switching frequency

An averaging circuit model is developed for the class E resonant DC-DC converter regulated at a fixed switching frequency. The regulation is achieved by use of an auxiliary switch. The model is obtained based on the circuit analysis using the Fourier series expansion. Steady-state and small-signal dynamic analysis is presented, which reveals that the DC output is well controlled by the control angle of the auxiliary switch and that there exists a right-half-plane zero in the control-to-output transfer function. The analysis results are verified by the experiments     

Finite element modeling and modal analysis of the human spine vibration configuration

This study was designed to investigate the modal characteristics of the human spine. A 3-D finite element model of the spine T12-Pelvis segment was used to extract resonant frequencies and modal modes of the human spine. By finite element modal analysis and harmonic response analysis, several lower vibration modes in the flexion-extension, lateral bending, and vertical directions were obtained and its vibration configurations were shown in this paper. The results indicate that the lowest resonant frequency of the model is in the flexion-extension direction. The second-order resonant frequency is in the lateral bending direction and the third-order resonant frequency of the T12-Pelvis model is in the vertical direction. The results also show that lumbar spinal vertebrae conduct the rotation action during whole body vibration (WBV). The vibration configurations of the lumbar spine can explore the motion mechanism of different lumbar components under WBV and make us to understand the vibration-induced spine diseases. The findings in this study will be helpful to understand WBV-related injury of the spine in clinics and the ergonomics design and development of mechanical production to protect human spine safety.     

Efficient resonant power conversion

The DC analysis of a series-resonant converter operating above resonant frequency is presented. The results are used to analyze the current form factor and its effect on the efficiency. The selection of the switching frequency to maximize the efficiency is considered. The derived expressions are generalized and can be applied to calculations in any of the switching modes for a series-resonant circuit. For switching frequencies higher than the resonant frequency, an area of more efficient operation is indicated which will aid in the design of this class of converters and power supplies. It is pointed out that (especially for power MOSFETs where ohmic losses dominate) it is more attractive to select switching frequencies that are higher than the resonant frequency because of the possibility of nondissipative snubbers. Slowing down the rise of the gate voltage and, hence, the slow decrease of ON resistance during turn-on is also not a drawback to high-frequency switching. Because of this safer operation, the standard intrinsic diode of the power MOSFET could be used at high frequencies instead of the more expensive FREDFET     

高功率CO2激光器谐振开关变换型电源的计算仿真

研究了高功率CO2激光器用零电流开关准谐振开关电源,讨论了电源的工作原理和电路结构,进行了激光电源的计算仿真研究,得到了谐振电路的工作波形,通过谐振开关方式与PWM硬开关方式的比较,论述了零电流开关准谐振变换器的技术特点及优势。     

A Novel Control Method for Piezoelectric-Transformer Based Power Supplies Assuring Zero-Voltage-Switching Operation

In this paper, a new control strategy that allows zero-voltage-switching (ZVS) operation of power converters using piezoelectric transformers (PTs) is proposed. The control circuit operates in a closed loop by measuring the phase between the PTs resonant current and the switching pattern and adjusting the switching frequency to the optimum value so that ZVS operation is assured. An innovative nonlinear regulator based on an analog multiplexer is presented. The regulator automatically swaps the signs of the sensed signal and the reference signal to allow generation of the adequate control action. A laboratory prototype for a 6 W resonant inverter was tested; obtained experimental results are also shown.     

High-Frequency Resonant Transistor DC-DC Converters

Transistor dc-dc converters which employ a resonant circuit are described. A resonant circuit is driven with square waves of current or voltage, and by adjusting the frequency around the resonant point, the voltage on the resonant components can be adjusted to any practical voltage level. By rectifying the voltage across the resonant elements, a dc voltage is obtained which can be either higher or lower than the input dc voltage to the converter. Thus, the converter can operate in either the step-up or step-down mode. In addition, the switching losses in the inverter devices and rectifiers are extremely low due to the sine waves that occur from the use of a resonant circuit (as opposed to square waves in a conventional converter); also, easier EMI filtering should result. In the voltage input version, the converter is able to use the parasitic diode associated with an FET or monolithic Darlington, while in the current input version, the converter needs the inverse blocking capability which can be obtained with an IGT or GTO device. A low-power breadboard operating at 200-300 kHz has been built. Two typical application areas are switching power supplies and battery chargers. The converter circuits offer improvements over conventional circuits due to their high efficiency (low switching losses), small reactive components (high-frequency operation), and their step-up/stepdown ability.     

Resonant gate driver with efficient gate energy recovery and switching loss reduction

This article describes a novel resonant gate driver for charging the gate capacitor of power metal-oxide semiconductor field-effect-transistors (MOSFETs) that operate at a high switching frequency in power converters. The proposed resonant gate driver is designed with three small MOSFETs to build up the inductor current in addition to an inductor for temporary energy storage. The proposed resonant gate driver recovers the CV² gate loss, which is the largest loss dissipated in the gate resistance in conventional gate drivers. In addition, the switching loss is reduced at the instants of turn on and turn off in the power MOSFETs of power converters by using the proposed gate driver. Mathematical analyses of the total loss appearing in the gate driver circuit and the switching loss reduction in the power switch of power converters are discussed. Finally, the proposed resonant gate driver is verified with experimental results at a switching frequency of 1 MHz.     

A new method to regulate resonant converters

A resonant frequency-modulation method is presented as an alternative to the switching frequency-modulation method to regulate resonant converters. A switch-controlled inductor and switch-controlled capacitor, in which switching losses are found to be very low due to zero-current or zero-voltage switching, are developed to do so. A new family of resonant converters that are regulated at a fixed switching frequency is proposed. A steady-state analysis of the Class E resonant converter regulated by a switch-controlled capacitor is presented. Theoretical and experimental results verify the validity of the proposed method. The efficiency measured from a breadboard of 1 MHz, 5 V, 25 W Class E regulated resonant DC-DC converter is up to 83%     

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     

Self-sustained phase-shift modulated resonant converters: modeling, design, and performance

This paper presents an improved control technique for the full bridge series, parallel, and series-parallel resonant converters. This control technique combines a self-sustained oscillation mode with a phase shift modulation technique that can significantly reduce the range of frequency variation necessary for obtaining zero voltage switching in the resonant converters. This frequency reduction provides optimized component ratings and operating frequency. A simple and accurate low order mathematical model based on the sampled data technique that fully describes the steady-state, and dynamic performance of the resonant converters, has been developed. A refinement algorithm is developed to enhance the accuracy of the modeling technique and the converter design. The improved converter performance and the feasibility of the developed dynamic model have been investigated using the series-parallel resonant converter topology with a capacitive output filter. Finally, MATLAB numerical solutions, PSIM simulation results, and experimental results are given to highlight the merits of the proposed work.     

Loss performance and efficiency comparison of resonant gate drivers

In an effort to reduce switching and gate-drive losses in power converters when the energy density is increased by increasing the switching frequency, various resonant gate drivers (RGDs) based on a current source have been proposed to drive metal–oxide–semiconductor field-effect transistors in low-voltage high-current power converters. The resonant gate drivers enable high efficiency owing to energy recovery and the reduction of switching losses. Recently, many studies have been performed on the design of new topologies and loss analyses. Despite numerous proposed studies on RGDs, a comparative study based on a theoretical analysis has not been carried out. In this paper, a theoretical loss analysis in terms of the conduction, switching and gate-drive losses is presented according to the operation stages. In particular, the conduction loss has been expressed in terms of a general loss model that can generally applied to all topologies. Five RGD topologies are evaluated for their efficiency performance with analytical expressions and features based on several operating conditions.     

Characteristics and Design of an Asymmetrical Duty-Cycle-Controlled LCL-T Resonant Converter

The characteristics of an asymmetrical duty cycle (ADC) controlled LCL-T resonant converter operating at the resonant frequency are studied by solving the state-space model of the converter. Four operating modes are identified having different circuit waveforms representing different device conduction sequences, thereby creating different conditions during the device switching. The mode boundaries are obtained and plotted on the D–Q plane. A region on the D–Q plane is identified for the converter design, where the switches operate under zero-voltage-switching condition. A prototype 500 W, 100 kHz converter is designed and built to experimentally demonstrate the operating modes, control characteristics, and performance of ADC-controlled LCL-T resonant converter.      

A Novel Robust Control Method for the Series–Parallel Resonant Converter

A novel robust control method for the series–parallel resonant converter (SPRC), which moves the inverter switching point to switch in advance or with lag w.r.t. the rectifier commutation point (RCP), thereby varying the converter gain around the load-independent point, is presented. The converter gain is derived using a novel analytical tool that combines state-plane analysis and superposition with added RCP constraint. Unlike traditional fundamental harmonic analysis , the exact gain and frequency expressions for the SPRC at the load-independent point and its neighborhood are obtained with this method. The proposed gain adjustment technique is combined with feedback to form a simple resonant converter controller. This control method is shown to be highly robust to resonant tank parameter uncertainty and circuit/switching delay. It also significantly simplifies the resonant converter controller's design.      

Design and analysis of an IC-less self-oscillating series resonant inverter for dimmable electronic ballasts

This paper presents a low-cost solution of converting the popularly adopted nondimmable electronic ballast circuit for fluorescent lamps with self-oscillating series resonant inverter into a dimmable one. The dimming function is achieved by increasing the switching frequency of the inverter from the natural frequency of the resonant tank, so that less energy is coupled to the lamp. Control of the switching frequency is based on deriving an adjustable dc current source from the resonant inductor in the resonant tank to control the operating point of the saturable transformers for driving the switches in the inverter. The overall implementation does not require any integrated circuit. A 17-W prototype has been built and studied. Theoretical predictions have been verified with experimental results. The lamp can be dimmed down to 10% of the full power.     

Self-oscillating dimmable electronic ballast for fluorescent lamps

This letter presents a low-cost solution for converting the popularly adopted nondimmable electronic ballast circuit for fluorescent lamps with self-oscillating series resonant inverter into a dimmable one. The dimming function is achieved by increasing the switching frequency of the inverter from the natural frequency of the resonant tank, so that less energy is coupled to the lamp. Control of the switching frequency is based on deriving an adjustable dc current source from the inductor in the resonant tank to control the operating point of the saturable chokes for driving the switches in the inverter. The overall circuit does not require any integrated circuit. A 17-W prototype has been built and tested. Theoretical predictions have been verified with experimental results. The lamp can be dimmed to 10% of the full brightness.