Series-parallel resonant converter operating in discontinuous current mode. Analysis, design, simulation, and experimental results

This paper presents the operating principle, analysis, design, simulation and experimental results for a high frequency (HF) transformer isolated AC-to-DC series-parallel resonant converter (SPRC) operating on the utility line, in discontinuous current mode (DCM). The equivalent models, the state space analysis of the SPRC in DCM are presented. PROMATLAB software is used to solve the equations and to obtain important design parameters. SPICE simulation and experimental results obtained from a 150 W prototype are presented to verify the analysis. High power factor operation (>0.99) with low harmonic distortion ( >

The series parallel resonant converter (SPRC) is known to have combined merits of the series resonant converter (SRC) and parallel resonant converter (PRC). However, the presence of a three-element LCC structure makes the SPRC's transient dynamics complex and its quick control difficult. This paper provides an analysis and a solution for this problem. It firstly presents the SPRC dynamics using the state-plane analysis technique and then provides a method to derive the optimal trajectory during transients for the SPRC. The method minimizes the transient response of the SPRC to within one switching cycle by deriving two optimal switching instances. The derivation of the optimal state trajectory during transients for the SPRC is described. Simulation results validate the method and show significant improvement in transient response compared to that of a step change in frequency control.

The state-space modeling and related order reduction problems of switching DC-DC converters operating in discontinuous (D) mode are treated in this paper. A unified discrete-time full-order model is proposed assuming the discontinuous current and voltage mode (DCVM) as a general operation mode from which the discontinuous current mode (DCM), the discontinuous voltage mode (DVM), and continuous made (CM) derive as special cases. Such a model permits a straightforward study of the control-to-output response, in each operation mode. The order reduction of the transfer function is carried out by means of the principal component analysis considering the joint controllability and observability properties of the circuit. It is shown that a proper order reduction can be gained not only in DC mode, as expected, but also in DV and DCV modes. A substantial difference between DC and DV modes is also evidenced in terms of controllability. The frequency analysis and state-space model order reduction for a Cuk converter are proposed to show that the method is free of the limitations affecting other methods of analysis and that its predictions fit experimental measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fixed and variable frequency operation of a high-frequency transformer isolated DC-to-DC converter employing a hybrid parallel-series resonant converter bridge operating in continuous current mode is proposed. A state space analysis method is used to analyze the converter for continuous and discontinuous capacitor voltage modes of operation. Based on the analysis, normalized design curves for the converter gain, and other peak component stresses are obtained. A design example is presented. All the results obtained from the analysis are verified with SPICE3 simulation and experimental results, for a 300 W output converter.

The inductor inductor capacitor (LLC) resonant topology has become more popular for deployment in high power density and high-efficiency power converter applications due to its ability to maintain zero voltage switching (ZVS) over a wider input voltage range. Due to their ease of operation and acceptable accuracy, frequency domain-related analytical methods using fundamental harmonic approximation (FHA) have been frequently utilized for resonant converters. However, when the switching frequency is far from the resonant frequency, the circuit currents contain a large number of harmonics, which cannot be ignored. Therefore, the FHA is incapable of guiding the design when the LLC converter is used to operate in a wide input voltage range applications due to its inaccuracy. As a result, a precise LLC converter model is needed. Time domain analysis is a precise analytical approach for obtaining converter attributes, which supports in the optimal sizing of LLC converters. This work strives to give a precise and an approximation-free time domain analysis for the exact modeling of high-frequency resonant converters. A complete mathematical analysis for an LLC resonant converter operating in discontinuous conduction mode (DCM)—i.e., the boost mode of operation below resonance—is presented in this paper. The proposed technique can confirm that the converter operates in PO mode throughout its working range; in addition, for primary MOSFET switches, it guarantees the ZVS and zero current switching (ZCS) for the secondary rectifier. As a function of frequency, load, and other circuit parameters, closed-form solutions are developed for the converter’s tank root mean square (RMS) current, peak stress, tank capacitor voltage, voltage gain, and zero voltage switching angle. Finally, an 8 KW LLC resonant converter is built in the hardware-in-loop (HIL) testing method on RT-LAB OP-5700 to endorse the theoretical study.

This paper proposes a discontinuous current mode (DCM) feedback current control for a single-phase grid-tied inverter in order to minimize a LCL filter without worsening total harmonic distortion (THD) of a grid current. In DCM, there are two nonlinearities occurring in the transfer functions; the first non-linearity occurs in the duty-ratio-to-current transfer function which worsens the current command response, whereas the second nonlinearity occurs in the disturbance-to-current transfer function which reduces the disturbance effect. In the proposed DCM current control, the first nonlinearity is compensated by utilizing the duty ratio at the previous calculation period in order to achieve the same control performance of the current command response as in continuous current mode. Meanwhile, the second nonlinearity is utilized in order to reduce the disturbance effect when the LCL filter with a small impedance is applied. Furthermore, a design procedure of the LCL filter is introduced under the condition that the impedance of the LCL filter can be minimized without worsening the grid current THD by applying the proposed DCM control. A 1-kW 100-kHz inverter with several LCL filters of different impedances (3.0%, 0.6% and 0.04%) is constructed in order to confirm the operation of the proposed DCM current control. As a result, the grid current THD is reduced from 8.5% to 3.7% at rated load. Furthermore, the inductor volume is reduced by 77.0%, whereas the converter loss is reduced by 17.1%.

The main focus of this work is the integration of the communication and power management functions of a 80W smart LED module. The luminair provides high-efficiency programmable ambient lighting and can also act as a networked sensor node to gather a variety of local measurements, which leads to improved safety, comfort and efficiency in future lighting systems. A dimmable LED driver based on the LLC resonant dc-dc converter topology is proposed to implement an emerging communication scheme, Visible Light Communication (VLC). VLC capitalizes on the high switching-speed of LEDs and offers several compelling advantages over conventional RF and wired communication schemes. The digitally controlled LLC converter operates in constant-current burst mode, where the burst is sequenced to independently control the dimming and transmission the data using the Variable Pulse Position Modulation (VPPM) protocol. A receiver circuit is designed to demodulate and decode the visible light signal. The 50 kb/s system is successfully demonstrated on a 308 LED Luminair with a digitally controlled LLC dc-dc converter.

A three-phase DC-to-DC series-parallel resonant converter is proposed and its operating modes for a 180/spl deg/ wide gating pulse scheme are explained. A detailed analysis of the converter using a constant current model and the Fourier series approach is presented. Based on the analysis, design curves are obtained and a design example of a 1-kW converter is given. SPICE simulation results for the designed converter and experimental results for a 500-W converter are presented to verify the performance of the proposed converter for varying load conditions. The converter operates in lagging power factor (PF) mode for the entire load range and requires a narrow variation in switching frequency, to adequately regulate the output power.

Full-bridge resonant converters have gained widespread adoption due to their excellent performance characteristics. However, these converters face limitations in terms of gain expansion. To address this issue, this paper proposes a switch-multiplexed resonant converter with wide voltage gain. By employing an auxiliary capacitor and inductor, the converter can achieve pseudo partial power processing and effectively expand its voltage gain. To regulate the voltage of the converter, the duty cycle of the switching devices is designed to be modulated, which is different from the conventional resonant converter. By optimizing the design parameters, the resonant current of converter can operate in discontinuous current mode (DCM), eliminating reverse recovery losses and/or minimizing reactive current. All switching devices achieve soft switching, thereby removing switching losses and further enhancing efficiency. Finally, a 1 kW prototype is built to validate the effectiveness of the proposed converter.

This paper presents a theoretical analysis of a resonant LLC DC-DC converter operating in continuous current mode with zero voltage switching (ZVS). On the base of modeling the processes in the tank circuit with differential equations, expressions for the fundamental quantities for both step-down and step-up modes are derived. The conditions for the transition to the discontinuous current mode are determined. The boundary of the ZVS operating area is defined. Output characteristics of the converter are plotted graphically for different values of circuit and control parameters.

The load parameter, Q, and the ratio of the switching frequency to the resonant frequency, Fs/Fo, characterize the operation of resonant converters. An accurate do analysis of the series and parallel resonant converters is given in terms of these parameters whereby the conversion ratio, peak stresses, and diode conduction time are determined. An exact and systematic method of small-signal analysis is given whereby the control-to-output transfer function, audio susceptibility, and input impedance are determined at a given operating point. In addition, simple and approximate transfer functions are obtained under high-Q assumption.

The aim of the work is to determine promising converters for supplying consumer devices with the required voltage level. As part of the task implementation, a mathematical description of the resonant converter with a series LC resonant circuit is made. The equivalent replacement circuit of the converter is given, as a result of its analysis analytical expressions are determined that describe the main dependences of this converter on the load and switching frequency of the keys. In the process of analyzing the resonant converter operation with a series LC resonant circuit, mathematical modelling methods are used. The result of the work is the obtained analytical expressions that allow determining the oscillatory circuit parameters for the resonant converter operation with a series LC resonant circuit in the mode with the highest efficiency. The presented graphs demonstrate the key parameter dependence of the oscillatory circuit on the load magnitude and on the switching frequency of semiconductor keys, and, accordingly, on the oscillatory circuit frequency. Applying a resonant converter with a series LC resonant circuit is possible in those areas where a static load is used that changes little over time. Applying this converter is not optimal for a dynamic load, because to maintain the output voltage at the required level, it will be necessary to complicate the control system and introduce pulse-width modulation in addition to pulse-frequency one and to control the converter by means of skipping control pulses in the case when an operating mode is close to the idle one.

A half-bridge resonant converter with zero-current switching (ZCS) and pulsewidth modulated (PWM) control is presented. The converter is derived from the parallel resonant converter (PRC), and the PWM control is obtained by the addition of a third ZCS switch in series with the resonant capacitor. The converter operates at fixed frequency, in the discontinuous current mode. A simplified theoretical steady-state analysis is developed and the converter characteristics are presented. Design considerations are outlined, and a design example, illustrated by digital simulation results, is presented and discussed. >

A generalized small-signal analysis approach that is based on both the Taylor's series expansion and the state-plane diagram is presented. A generalized discrete small-signal model for a double-ended DC-to-DC resonant converter operating in the continuous conduction mode is also given. Based on the model derived, the frequency responses for two transfer functions, namely, the line-to-output and the control-to-output transfer functions, are obtained. The technique is verified by applying it to the conventional series resonant converter whose small-signal analysis is known. >

Series-connected integrated gate-commutated thyristors (IGCTs) find application in hard-switched commercial power converters at the megawatt power levels. Expanding the application of these devices to medium-voltage dc&#x2013;dc resonant converters is of great interest due to the IGCT&#x0027;s low conduction losses. This requires a deeper understanding of the device&#x0027;s behavior in series connection and under switching conditions different than those in hard-switched converters. In particular, the voltage sharing between series-connected IGCTs must be achieved with significantly reduced turn-<small>off</small> currents, typical for resonant converters. Relying on a versatile IGCT test setup, this article explores the operational performances of series-connected IGCT operation at very low turn-<small>off</small> current and with snubber capacitance in the range of a few tens of nanofarad. The results presented in this article are obtained from commercially available 4.5-kV 68-mm reverse-conducting IGCTs (with standard irradiation), as well as two customized engineering samples (high irradiated variants), optimized on their technology curve for high switching frequencies. The IGCTs are successfully operated in series connection at 5 kHz, with device voltage being effectively shared in resonant converter operation.