Discontinuous Current Mode Operation Research Articles

A Single-Stage Bridgeless Isolated AC–DC Conversion System for Light Electric Vehicles Charging Application

A 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\phi $ </tex-math></inline-formula> single-stage ac–dc power conversion unit employing bridgeless isolated modified single-ended primary inductor converter (BLIMSEPIC) is presented in this work for the light electric vehicles (LEVs) charger applications. Unlike the existing SEPIC and Cuk high-power factor (HPF) ac–dc converters, the presented BLIMSEPIC HPF ac–dc converter incorporates continuous input and output current features while operating under discontinuous current mode (DCM) condition. Therefore, it demonstrates excellent applicability in charging applications. The DCM operation considerably simplifies overall control architecture, as the presented BLIMSPEIC ac–dc converter exhibits inherent power factor correction capability under DCM operation, and therefore, significantly reduces the cost of control implementation. Besides, the continuous input and output currents attribute lessen the filter’s size and associated losses. Furthermore, the reduced voltage stress and zero current switching of semiconductor devices, together with the front-end bridgeless structure, considerably improve the conduction and switching losses of the charger. The operation, design, control, and performance of the BLIMSEPIC HPF ac–dc converter are experimentally verified, and corresponding results are presented to justify its efficacy for LEVs charging applications.

Comparative study of a bidirectional multi-phase multiinput converter for electric vehicles

Multiinput converters allow to create hybrid energy systems in electric vehicles with a reduced part count. In addition, interleaved structures help to build efficient converters with several possible benefits, such as low current ripple and high power density. This paper proposes utilizing a multiphase multiinput converter (MPMIC), which concentrates the aforementioned advantages and presents a comprehensive comparison with its single-phase version, called single phase multiinput converter (SPMIC). After analysing their steady-state characteristics, SPMIC and MPMIC are designed considering same conditions. Then, two laboratory prototypes rated at 2.5kW output power are implemented to validate the analysis. Finally, these prototypes are compared in terms of voltage-gain, input current ripple, efficiency, complexity, cost, and power density. The results show that MPMIC surpasses SPMIC in efficiency and in input current ripple at the expense of increments in the complexity and cost. Besides, MPMIC results in comparatively high voltage gain in low power region thanks to the discontinuous current mode operation. On the other hand, it is explored that SPMIC can reach higher power density in the event of effective cooling.

Discontinuous Current Mode Modeling and Zero Current Switching of Flyback Converter

The flyback converters are widely used in low power applications. The switch typically requires 600 V breakdown voltage in order to perform large step-down voltage. Thus, slight variation on the switch control can either permanently damage the switch or decrease the efficiency of the power conversion. In order to achieve higher power efficiency, the previous literature suggested operating the flyback converter in the discontinuous current mode (DCM). It is then required to understand the critical conditions of the DCM through analyzing the dynamic behavior and discontinuous current mechanism. This paper started from the current waveform analyses, proceeded to the derivation of zero current switching (ZCS) formulation, and finally reached the necessary conditions for the DCM. The entire DCM operation was divided into three phases that subsequently affect the result of the zero voltage switching (ZVS) and then to the ZCS. The experiment shows a power efficiency of over 96% when the output power is around 65 W. The switch used in this paper is a Gallium Nitride High-Electron-Mobility Transistor (GaN HEMT) that is advantageous at the high breakdown voltage up to 800 V. The important findings from the experiments include that the output power increases with the increasing input DC voltage and the duty cycle is rather linearly decreasing with the increasing switching frequency when both the zero voltage switching (ZVS) and ZCS conditions are satisfied simultaneously.

EMI Attenuation in a DC–DC Buck Converter Using GaN HEMT

A dc-dc buck converter using gallium nitride (GaN) high electron mobility transistors (HEMTs) is experimentally investigated at the discontinuous-current-mode (DCM) and the triangular-current-mode (TCM) operations. The objective of this article is to specify the power conversion efficiency and attenuation of common-mode (CM) and differential-mode (DM) noise voltage, measured at the line impedance stabilization network (LISN) for the compared control strategies. Zero-voltage switching achieved for the TCM operation improves efficiency with reference to the DCM operation. However, significant attenuation of electromagnetic interference (EMI) spectra is obtained for TCM operation with capacitive snubber. Sizing of capacitor snubber dependent on parasitic inductances of the commutation circuit and rapid switching of GaN HEMTs are illustrated.

Design for continuous‐current‐mode operation of inductive‐power‐transfer converters with load‐independent output

The control design of inductive power transfer (IPT) converters can be greatly simplified by exploring the property of load-independent output. However, IPT converters can easily enter a discontinuous current mode (DCM) operation due to the non-linearity of the output diode rectification circuit at some loading conditions. The switching between operations of continuous current mode (CCM) and DCM within a switching cycle is highly non-linear, making the converter behaviour difficult to predict and analyse. The well-known first harmonic approximation (FHA) analysis method and the load-independent output property are no longer applicable when the converter enters DCM operation. This paper presents a simple and yet effective harmonic analysis method to reveal the main reason for the converter to enter DCM operation. Subsequently, the load boundary between CCM and DCM operations is derived in detail as a design criterion. A solution by increasing the input impedances at some higher order harmonic frequencies is also suggested to extend the load range against DCM operation. Finally, IPT prototypes using two higher order compensation circuits, having load-independent voltage output and capacitor filter, are demonstrated to verify the theoretical analysis.

Discontinuous-Current Mode Operation of a Two-Phase Interleaved Boost DC–DC Converter With Coupled Inductor

A two-phase interleaved boost dc–dc converter with an inversely coupled inductor in a discontinuous-current mode (DCM) is analyzed by the equivalent inductance method. Coupling effects on the circuit statuses are described, and a forced conduction of the power diode or reverse-paralleled diode of MOSFET is caused by coupling. As a result, three major circuit statuses are figured out according to the physical relationship between the input–output voltage ratio and the coupling coefficient, and their condition boundaries are used to classify the DCM operation modes. Then, considering the load (duty cycle) variation, ten DCM operation modes are comprehensively analyzed. The analysis can be used to make an easy prediction of operation modes, and extended to the analysis of an interleaved buck converter or buck/boost bidirectional converter with a coupled inductor in DCM. At last, a 300-W prototype is built and tested in the lab to verify the analysis.

Phase Current-Balance Control Using DC-Link Current Sensor for Multiphase Converters With Discontinuous Current Mode Considered

This paper presents a new phase current-balance control method of unbalanced phase currents in multiphase converters. The phase current reconstruction process, in which the sampled dc-link current from a dc-link current sensor is used to reconstruct the phase currents, is comprehensively investigated, taking account of both the region of duty ratio and the operating mode of the continuous current mode (CCM) and discontinuous current mode (DCM). DCM operation reveals that the phase current reconstruction cannot coincide with the average value of the respective phase current. Eventually, it is confirmed that this proposed balance control based on a circular chain control makes it possible to establish an exact current sharing among the phase currents all over the operating condition including the DCM. The actual phase currents do not show any distorted waveforms due to the multisamplings of dc-link current that do not provoke any extra switching of the converter switches at all. The validity and effectiveness of the proposed phase current-balance control are illustrated through the experimental results.

Analysis and Design of a High-Frequency Isolated Dual-Tank LCL Resonant AC-DC Converter

An integrated single-phase single-stage high-frequency transformer isolated dual-tank LCL-type series resonant ac-dc converter with fixed-frequency phase-shift control strategy is presented. The circuit configuration combines a diode rectifier, a boost converter, and two identical half-bridge dc-dc LCL resonant converters. A high power factor and a low total harmonic distortion are achieved by discontinuous current mode operation of the front-end power factor correction circuit. The output voltage is regulated by the fixed-frequency phase-shift between two identical half-bridge LCL resonant converters. Soft-switching operation is achieved for all of the switches. The operation of intervals and steady-state analysis are presented briefly. A design example of a 100-W proposed converter is given, together with its simulated and experimental results for different input voltages.

Fault diagnosis algorithm based on switching function for boost converters

A fault diagnosis algorithm, which is necessary for constructing a reliable power conversion system, should detect fault occurrences as soon as possible to protect the entire system from fatal damages resulting from system malfunction. In this paper, a fault diagnosis algorithm is proposed to detect open- and short-circuit faults that occur in a boost converter switch. The inductor voltage is abnormally kept at a positive DC value during a short-circuit fault in the switch or at a negative DC value during an open-circuit fault condition until the inductor current becomes zero. By employing these abnormal properties during faulty conditions, the inductor voltage is compared with the switching function to detect each fault type by generating fault alarms when a fault occurs. As a result, from the fault alarm, a decision is made in response to the fault occurrence and the fault type in less than two switching time periods using the proposed algorithm constructed in analogue circuits. In addition, the proposed algorithm has good resistivity to discontinuous current-mode operation. As a result, this algorithm features the advantages of low cost and simplicity because of its simple analogue circuit configuration.

Novel Online Parameter Tuning Method for Digital Boost PFC With Transition Current Mode

A new online parameter tuning method for digital power factor corrector (PFC) with transition current mode (TCM) control is proposed in this paper. The proposed method copes with the parameter variation issue, which results in discontinuous current mode operation and larger current ripple. The proposed method is to give one more current sample in one sampling period in order to estimate the inductance of a boost inductor online, thereby tuning the parameter of the predicted switching period. It will be shown by experimental results that the proposed online parameter tuning method can retain TCM operation even under full-load condition and slightly increase the converter efficiency. Experimental results derived from a digital-signal-processor-based controller are presented for confirmation. The PFC is with 270-W power rating, 100-V/50-Hz input, and 385-V/dc output. Experimental results demonstrate the effectiveness of the proposed online parameter tuning method for digital PFC under TCM control.

Soft-Switching Single-Phase Grid-Connecting Converter Using DCM Operation and a Turn-Off Snubber Capacitor

This paper proposes a new single-phase dc/ac converter topology with soft-switching operation. The proposed converter achieves soft-switching by using DCM (discontinuous current mode) operation and a common turn-off snubber capacitor connected to the dc terminals of a full-bridge configuration. One additional semiconductor switch is used to disconnect the snubber capacitor from the dc side, and allows the snubber capacitor to be discharged. The DCM operation realizes zero-current turn-on and the snubber capacitor achieves zero-voltage turn-off. The proposed converter can be applied to a grid-connected converter for domestic renewable energy and energy storage, including Photovoltaic and battery energy storage devices. This paper describes operation principles, control and modulation techniques as a grid-connecting converter. Experimental verification including loss analysis with a 1-kW pilot device is provided.

Quadratic boost converter with low buffer capacitor stress

A new quadratic boost converter is presented in this study. Compared with the conventional quadratic boost converter, the proposed converter has the feature of lower buffer capacitor voltage stress. This advantage is very valuable for high voltage and high-voltage gain applications. The proposed converter also employed only one active switch and two LC (inductor-capacitor) filters. Detailed analysis for its continuous current mode operation and discontinuous current mode operation both are presented. In addition, modelling for the proposed converter is also developed in this study. A prototype circuit is built and the experimental results confirm the feasibility and performance of the high step-up converter.

Primary side feedforward control for TRIAC dimmable light emitting diode driver with Constant Power

This study proposes a primary side feedforward control scheme for low-power Triode AC semiconductor switch dimmable light emitting diode (LED) driver. The LED driver is a Flyback converter operated in constant frequency (CF) discontinuous current mode (DCM). With the proposed control scheme, the input power of the Flyback converter can be controlled by the TRIAC dimming angle, which is not affected by the AC input voltage. That is to say, the input power is constant with certain dimming angle. Besides, the output power is determined by the input power with a given conversion efficiency. For LED load, since the output voltage is almost constant, the output current can be regulated by TRIAC dimming angle without any secondary side feedback circuit. Almost linear dimming curve can be achieved. Also, the input current automatically follows the input voltage because of CF DCM operation, resistive input characteristic can be achieved and no dummy load is required for TRIAC dimming angle detection. Considering the LED forward voltage drop tolerance existed in the practical application, the related compensation method is also discussed in this study, which can further improve the performance of the proposed control scheme. A prototype with 27 V/0.5 A output and 180–265 V AC input has been built. Moreover, the experimental results from the prototype are presented to verify the theoretical analysis.

Boost-Chopper-Derived PFC Rectifiers: Interest and Reality

This work presents an overview of single-phase boost-chopper-derived power-factor-correction rectifiers. Converters are presented for several control strategies in continuous and discontinuous current mode operations. The presentation highlights the main characteristics of the converters and underlines harmonic content over a wide frequency range. A methodology is derived to compute these harmonics in order to facilitate the analysis and performance evaluation of the converters. Based on this methodology, a comparison is conducted in order to highlight advantages and drawbacks of the most popular converters and control strategies. A table is given where main converter critical parameters are summarized in order to help the designer, in converter and operating mode selections. Practical results are provided to validate the modeling technique.

Matlab™ Simulation of an Exact Mathematical Model of the Permanent Magnet Synchronous Motor With a Discontinuous Current Mode Operation

An exact model of a permanent magnet synchronous motor operating in the discontinuous current mode is developed. This motor behaves differently under light-and heavy-load conditions. Our mathematical model, based on this exact model, can represent motor responses under all of the different load conditions. Moreover, it can explain the flux-weakening effect with the phase-advanced angle. The model is implemented by using MATLAB™, which can solve the initial value problem of the represented systems described with complicated differential equations. In comparison with the PSPICE ™ platform, MATLAB™ is more convenient for designers to predict and evaluate the performance of their systems.

Current and speed digital control of commutationless DC drives

The digital control of commutationless DC drives using a minimal hardware structure is discussed. The authors present a low-cost monochip microcomputer-based control system for speed regulation and current limitation that has no current measurement of a DC motor fed by thyristors in discontinuous current-mode operation. With this system, the speed of the drive is controlled by a classical algorithm using the Z transform. The thyristor firing is synchronized with the power supply and controlled by internal interrupts of the microcomputer. The current limitation is augmented by an estimation algorithm using an experimental simplified model. Results are presented for a 1 kW DC drive. >