Isolated three-phase rectifier with high power factor using the Zeta converter in continuous conduction mode

This paper presents the analysis of an isolated three-phase rectifier with high power factor using a Zeta converter operating in the continuous conduction mode (CCM). The structure is particularly simple and robust. Its main features are: one power processing stage; lower harmonic distortion in the current; and natural isolation. Its principle of operation, design procedure and experimental results are presented.

The growing demand on the renewable energy systems that work through battery cells has provided a high interest in the DC/DC Buck-Boost converters due to their capability to both amplify and attenuate the voltage that is supplied from such cells. An important feature in the design of these converters is the ability to operate in continuous conduction mode (CCM) so as to lower harmonic distortion and avoid the need for active control on inductors. In this paper, we investigate the design requirements for CCM operation in a reported single switch quadratic DC/DC converter by constructing a simulation model to validate the theoretical gain equations of the converter and check their agreement with the reported results. The simulation results obtained not only revealed inaccuracies in the reported gain equations but also confirmed the agreement between the proposed gain equations in this paper with the expected behavior of the converter.

Due to the ever-expanding use of light emitting diodes (LED) lamps and the necessity of constant current to operate properly, a drive circuit is required for these types of lamps. Also, power factor correction (PFC) to eliminate harmonics, is required and must be included in these types of drivers based on the existing standards. Soft switching can effectively reduce the switching losses and electromagnetic noise. Consequently, high switching frequency operation is possible which reduces the converter weight and size, effectively and high power density is achieved. In this paper, continuous conduction mode (CCM) operation of a single-stage boost-flyback converter with active-clamp for LED driver applications is introduced. Its CCM operation leads to low input current ripple which reduces the input filter volume effectively. Also, low voltage and current stresses on the components are obtained. As a result, the converter can be used for high power applications compared with previously proposed discontinuous conduction mode (DCM) operation. Theory, simulation as well as practical results are presented below.

This paper presents a control method for three-phase inverter under grid fault condition based on a novel critical conduction mode (CRM)-based soft-switching modulation. In the soft-switching modulation, one phase is clamped to dc bus, other two phases operate in CRM and discontinuous conduction mode (DCM), respectively. The soft-switching technique with silicon carbide (SiC) power devices allows the inverter to operate at hundreds of kHz with high efficiency by reducing switching loss. In order to extend the modulation scheme to more practical cases, behavior of the inverter under grid fault conditions, specifically voltage sag, is investigated. During voltage sag, the grid voltage becomes unbalanced requiring unbalanced ac current reference for the avoidance of output active power oscillation. With the unbalanced grid voltage and ac current reference, continuous conduction mode (CCM) operation occurs where DCM operation is intended leading to high turn-on loss. To eliminate the CCM operation and reduce the turn-on loss, an improved modulation technique is proposed by using off-time extension concept in CRM phase. In this paper, how the CCM operation appears under grid fault condition, and details of the proposed control are discussed. Performance of the proposed control method is validated experimentally with SiC-based three -phase inverter laboratory prototype.

This paper presents a high power factor single-stage driver powering a high-power-LED. The driver employs a PFC based on a Zeta converter, using the One-Cycled Control (OCC) technique. A design procedure for Zeta converter is presented, which is based on the flyback converter as proposed by (Lamar, et al. [1]). Through simulation results of Zeta converter working as PFC, classical OCC and exponential ramp OCC approaches are compared and discussed. Showing that the ramp OCC approach results in better performance of the PFC, in relationship to conventional OCC. This paper also presents the stages of operation of the Zeta converter in the continuous conduction mode (CCM).

This paper presents a small-signal analysis of the pulse-width modulated (PWM) boost dc-dc converters operating in continuous-conduction mode (CCM) and subject to complex impedance load. Using the existing knowledge on the small-signal model of the boost converter obtained through the circuit averaging approach, this paper presents an extended analysis of the small-signal transfer functions, under the influence of resistive and inductive load impedances. The expressions for the control-to-output, input-to-output voltage transfer functions, and the output impedance of the boost converter operating in CCM are derived. The characteristics of these transfer functions are analyzed and the effect of the added inductance on the location of poles and zeros is discussed. It is shown that the inherent right-half plane (RHP) zero shifts to the left-half of the s-plane, when the load inductance is increased beyond a specific value. The theoretical results are validated by simulations of a boost converter with suitable design specifications.

This paper introduces small signal modeling of the restructured boost converter (RBC) in continuous conduction mode (CCM) by using the circuit averaging technique. The averaging technique produces linear transfer functions of the converter. The transfer functions relating the duty cycle to output voltage, duty cycle to inductor current, input voltage to output voltage, and input voltage to inductor current are obtained. To validate the converter model, power simulation (PSIM) simulations are developed, and experiments are conducted. The function of RBC is similar to a conventional boost converter, i.e., to level up the input voltage. A comparative analysis between the RBC and conventional boost converter is performed. The results highlight the advantages of RBC over a conventional boost converter.

This paper discusses experimental validation of semi-bridgeless boost rectifier (SBBR) operation of continuous conduction mode (CCM) & discontinuous conduction mode (DCM) for power quality improvement in uninterrupted power supply (UPS) system. The double stage conversion in UPS attenuates power quality at the input side and output configuration of the system. Many researchers have proposed the improvement of power quality with CCM and DCM operations for ac-dc conversion stage in bridge and bridgeless rectifier, but there is lack of knowledge about their performance and drawbacks of CCM and DCM operation with SBBR topology. This paper focuses on experimental analysis of SBBR topology operating in CCM and DCM under different load ranges. The performance of power quality factors and efficiency of SBBR operating in CCM and DCM are addressed. To study the stability analysis of SBBR operation in CCM and DCM, a comprehensive small signal model is derived by analyzing the inductor current waveforms. PSCAD simulations have obtained theoretical study of SBBR with CCM and DCM operations and experimental validation is carried out through FPGA Spartan 3A processor.

This paper introduces an LED drive circuit implemented by series input connected converter cells with a common duty cycle control approach operating from a dc voltage bus. With this structure, low voltage high frequency ICs and low profile components can be applied in high voltage applications. Flexibility is provided for the cells to work under different voltage supply conditions by simply changing the number of series converters. With the converters operating in continuous conduction mode (CCM), the common duty cycle control approach enables automatic line voltage sharing and output current copying. The approach results in a control-to-output transfer function of the system that is close to that of a single converter for ease of feedback loop design. The modular approach also allows continued operation in the presence of open circuit LED failures. Design considerations and experimental results are presented for a 25 W 3-cell system with 9 Luxeon K2 high brightness LEDs, demonstrating line voltage sharing, output current copying and LED failure response.

In this paper, a high gain modular multilevel dc-dc converter topology is proposed. As compared with the conventional modular multilevel step-up converters, the proposed converter offers an additional degree of control-freedom and higher steady-state voltage gain. The proposed converter operates in continuous conduction mode. A detailed small-signal modeling for the proposed converter based on state-space average modeling is presented. In addition, this study covers both the small-signal and steady-state analysis for the high gain modular multilevel dc-dc converter operating in continuous conduction mode. The performance of the proposed converter is compared with conventional modular multilevel dc-dc converter. To confirm this design, simulations have been carried out on a 1 kW, 48 V to 288 V converter system. Finally, the validity of the converter is verified by simulation results.

It is the design criteria of driving LEDs at constant current and keeping the input current’s harmonics low, attaining a high power factor, and maximizing efficiency. For low power general purpose lighting buck converter can be chosen for simplicity and reduced cost. It is a difficult to improve power quality parameter like, the THD (total harmonic distortion) and power factor of ac mains. In the proposed topology, the operation for high power factor and low THD at the AC mains’ input is accomplished through buck converter operation in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM) with a suitable control circuit. This paper assures constant current in both cases for suitable design of control circuit. Over voltage protection has been incorporated. To validate the LED driver circuit, simulation studies are carried out.

Small-signal modeling of switched-mode converters has been developed in early 70s, when the state-space averaging (SSA) method was introduced for assessing the dynamics of direct-duty-ratio controlled converters in continuous conduction mode (CCM). It turned out that the direct circuit theoretical approach could not be applied to get accurate models also for discontinuous operation mode (DCM). We present in this paper a unified and consistent method for the modeling of switched-mode converters under direct-on-time control applicable to fixed-frequency and variable-frequency operation in DCM and CCM. The method is based on the direct estimation of the state-variable derivatives using their physical and circuit-theoretical dependence on the corresponding circuit elements.

This paper proposes a new multi-mode three-phase bridgeless AC/DC high power factor step-up resonant converter with a new adaptive active-controlled auxiliary circuit and regulated output voltage for MVDC grid application. In the proposed design, the integrated boost rectifier operates in a hybrid Discontinuous Conduction Mode (DCM)/Continuous Conduction Mode (CCM) operation to lower the inductor and EMI filter losses. To ensure soft-switching operation during the CCM operation of the converter, a closed-loop adaptive active auxiliary circuit is proposed to provide the required lagging current for the switches whenever needed. The duty ratio of the switches changes based on the input current equation in a closed-loop manner to ensure an almost sinusoidal input current with a high power factor. A variable frequency control algorithm is also implemented on the proposed converter to regulate the converter's output voltage. The converter's performance is verified through a 1.2MW, 690Vac/27kVdc design.

The flyback converter is widely used in modern power conversion systems due to its simple topology, single switch, low component count, and inherent galvanic isolation. This paper investigates the performance characteristics of flyback converters by analyzing their operation in Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM), with particular emphasis on voltage spike behavior. The main contribution of this study is the development of a mathematical model that correlates the operating mode (CCM or DCM) with the voltage spike across the power switch. In addition, the study examines the impact of duty cycle variations on voltage spike behavior. The results show that, for comparable operating conditions and moderate duty cycles, CCM operation generally results in lower voltage spikes than DCM due to reduced peak magnetizing current, while at higher duty cycles and load levels, CCM may exhibit increased voltage stress. The proposed approach was validated through MATLAB/Simulink simulations and a scaled-down experimental prototype. A proportional integral (PI) controller is implemented in simulation to ensure regulated output voltage under practical operating conditions. The results demonstrate that optimizing the duty cycle and accounting for the influence of conduction mode can enhance the reliability of flyback converters, making them suitable for applications requiring galvanic isolation and cost-effective solutions.

An extensive small-signal analysis of a single-loop current-mode control strategy for a pulse-width-modulated (PWM) boost DC-to-DC power converter operating in continuous conduction mode (CCM) is proposed using a new non-symmetric phase controller. To model the boost power stage, a linear circuit model is used which includes all parasitic components such as the equivalent series resistance (ESR) of the filter capacitor, the ESR of the inductor, the transistor ON-resistance, and the diode forward resistance and offset voltage. A boost power stage design example gives component design equations and will serve to illustrate the closed-loop converter design. A design procedure for the new non-symmetric phase controller is presented. Open-loop and closed-loop circuit models and transfer functions are derived for the boost PWM converter and illustrated by Bode plots. An approach is presented for simplifying closed-loop transfer functions, using Euler's identity, into a format which is conducive to modeling in any high level programming language on a personal computer. Bode plots are obtained using a data analysis software package Axum 3.0 which combines a programming language, spread-sheet, and publication quality technical graphics. The proposed control scheme directly controls the inductor current and indirectly controls the load current and output voltage. The closed-loop transfer functions of the proposed control scheme do not contain a righthalf plane (RHP) zero, in contrast to the closed-loop transfer functions of a single-loop voltage-mode control scheme. The absence of the RHP zero provides better stability by making it easier to obtain large or specified gain and phase margins.