Boundary Current Mode Research Articles

Optimization of Minimum Negative Current BCM Synchronous Buck Converter

Non-isolated DC-DC converters are widely used in renewable energy applications, such as the hybrid energy storage system (HESS), charging and discharging system of batteries and supercapacitors and the photovoltaic power generation. With the advantages of achieving zero-voltage-switching (ZVS), high efficiency and power density, low cost, and fast dynamic response, the converters operating in boundary current mode (BCM) have caught researchers' eyes recently. Taking the synchronous buck converters as an example, this paper briefly introduces the working principle and advantages of BCM converter realize soft switching. Firstly, it is pointed out that the phenomenon of circulating energy exists in the BCM converter. Then, the relationship between circulating energy and negative current is analyzed, and an optimal control strategy of negative current minimization is proposed to reduce the circulating energy. In the condition of realizing ZVS, negative current minimization not only improves the efficiency of the converter, but also reduces the ripple of inductor current to a certain extent. Finally, the experimental platform of 100 W synchronous buck converter is built. Experimental results validate that the optimal control of minimum negative current has good effect on improving efficiency of converter and reducing the ripple of inductor current.

Study of the operating modes of the high voltage power source for barrier type discharge excitation

The issues related to the features of operation and modes setting of a high-voltage switching power source based on a sequential autonomous resonant inverter with reverse diodes used to excite an atmospheric pressure barrier type discharge are discussed in the article. It is indicated that the characteristic features of the autonomous resonant inverters operation are the occurrence of damped voltage fluctuations in the LC circuit of the inverter, as well as the dependence of the output alternating voltage on the ratio of the inverter operating frequency (thyristor switching frequency) to the natural resonant frequency of the LC circuit. Depending on this ratio, the inverter can operate in discontinuous, boundary and continuous current mode. The amplitude and shape of the inverter output voltage were controlled using a 1:1000 voltage divider with a C1-65A oscilloscope. The shape of the gate trigger pulses was obtained using a C1-167 oscilloscope. It is established that when the gate trigger pulses are asymmetrical relative to each other due to the operation features of the step-up transformers, the value of the alternating high-voltage at the inverter output is insufficient to excite the atmospheric pressure barrier type discharge. In the case of the gate trigger pulses symmetry, the output voltage of the inverter stage reaches the values required for the breakdown of the dielectric medium. Oscillograms of the inverter output voltage while adjusting its operating frequency are obtained. It is shown that the amplitude value of the voltage at the gas-discharge load increases as the operating frequency of the inverter increases. For the gate trigger pulses frequency of 250 Hz the value of the inverter output voltage amplitude was 3.4 kV, for 460 Hz – 4.0 kV, and for 550 Hz – 4.2 kV.

Variable-Frequency Control Strategy of Isolated Buck–Boost Converter

A control strategy with three control variables that contain switching frequency and two duty cycle ratios for an isolated buck–boost converter is proposed in this paper. The converter only operates in the discontinuous current mode (DCM) and the boundary current mode (BCM) in the whole voltage range and load range which can achieve an excellent soft-switching performance, a low energy circulation, and a high efficiency. On the basis of the operational principle and variables simplification, the optimal operating point that has a minimum clamped inductor peak current value is obtained. Under the variable-frequency control strategy, the converter characteristics are analyzed, such as the direct energy transfer time ratio, peak current value of the clamped inductor, and switching frequency. Moreover, the implementation of the closed-loop variable-frequency control strategy is given with three operational modes: variable-frequency BCM mode, constant-frequency BCM mode, and variable-frequency DCM mode. A 380-V 1-kW output prototype is fabricated, and the experimental results indicate that high efficiency over overall load range has been achieved under the variable-frequency control strategy due to the excellent soft-switching performance in the whole range. What is more, a smooth transition between three operational modes is achieved.

Implementation of zero current switch turn-ON based buck-boost-buck type rectifier for low power applications

ABSTRACTA single-stage single-switch AC–DC integrated converter is proposed in this paper, as a tight DC voltage regulator with unity input power factor for the fundamental component of the input current. Proposed converter is formed by the integration of buck-boost configuration with a buck converter operated by a single switch. The buck-boost section of the proposed configuration is operated in current discontinuous conduction mode (DCM) to get unity input power factor at the supply terminals and the buck section is operated up to boundary current conduction mode (BCM). The features acquired by the converter operating in complete discontinuous conduction mode (DCM) are unity input power factor, zero-current turn-ON for the Switch, fast and good DC output voltage regulation with extensive conversion range and low voltage stress on the switch. Additionally, the intermediate capacitor voltage stress is independent of converter load variations and so the switch also is subjected to constant peak voltage stress. A comprehensive study is carried out to obtain the necessary design equations. A design model is implemented using simulation and hardware. The results confirm the performance of the proposed configuration.

Hybrid Three-Level Full-Bridge Isolated Buck–Boost Converter With Clamped Inductor for Wider Voltage Range Application

An isolated buck–boost (IBB) converter with a hybrid three-level full-bridge primary-side circuit is proposed to achieve wider voltage range regulation. The primary-side circuit is composed of a three-level leg and a two-level leg. The output voltage of the primary-side circuit is five level (i.e., $\pm V_{{\text{in}}}$ , $\pm V_{{\text{in}}}{\text{/ 2}}$ , and zero), and the secondary-side circuit is a semiactive full-bridge rectifier with two active switches and two diodes. The input voltage of the secondary-side circuit is three level (i.e., $\pm V_{{\text{o}}}$ and zero). Hence, the operation voltage range can be wider than the normal IBB converter's with three voltage levels in the primary-side circuit and secondary-side circuit. This paper focuses on the control strategy allowing the converter to operate in boundary current mode at heavy load and in discontinuous current mode at light load with smooth mode transition. The soft-switching performance and output characteristics of the proposed converter are presented in detail. Compared with the semi-dual active bridge converter, the voltage range is doubled and the peak current of the clamped inductor is decreased. An 800-W prototype with 100–400-V input voltage and 380-V output voltage is built and tested to verify the feasibility of the proposed control strategy.

Controlled-Type ZVS Technique without Auxiliary Components for Micro-inverters

This paper proposes a Boundary Current Mode (BCM) control scheme to realize soft switching on a conventional single phase full bridge DC/AC inverter. This technique with the advantages of no auxiliary components, low cost, high efficiency, and simple in control, is attractive for micro-inverter applications. The operation principle and characteristic waveforms of the proposed soft switching technique are analyzed in theory. A digital controller is provided based on that theory. To balance the requirements of efficiency, switching frequency, and inductor size, the design considerations are discussed in detail to guide in BCM inverter construction. A 150W prototype is built under these guidelines to implement the BCM control scheme. Simulation and experiment results demonstrate the feasibilities of the proposed soft switching technique.

A Controlled-Type ZVS Technique Without Auxiliary Components for the Low Power DC/AC Inverter

This paper proposes a soft switching technique for dc/ac inverters, by using duty cycle and frequency modulation. Zero voltage switching (ZVS) is achieved through controlling the inductor current bidirectional in every switching cycle. This technique requires no additional resonant components and can be employed for various low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes are derived from the basic theory of the proposed technique. They are referred to as boundary current mode (BCM), variable hysteresis current mode (VHCM), and constant hysteresis current mode (CHCM) in this paper and their advantages and disadvantages are compared. Simulation and experimental results demonstrate the feasibilities of the proposed soft-switching technique and its control schemes.

A Family of Predictive Digital-Controlled PFC Under Boundary Current Mode Control

One of the advantages of power factor corrector with boundary current mode control is the reduction of reversal recovery loss of diode. This paper proposes a family of predictive methods adapted to digital pulse-width modulations for digital-controlled PFC operated under boundary current mode. The DPWM methods include leading-edge modulation, trailing-edge modulation and triangular modulation. For the proposed control method, the switching period retaining zero current switching is predicted and the turn-on period is determined by the voltage controller. Therefore, neither zero-current detection nor high-frequency A/D converter for current sampling is required for the proposed control method.proposed control method. Experimental results derived from a DSP-based controller are presented for confirmation. The power factor corrector is with 250 W power rating, 100 V/AC/50 Hz input, and 385 V/DC output. Experimental results demonstrate the effectiveness of the proposed predictive digital-controlled PFC under boundary current mode control.