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In this paper, a voltage balance control strategy based on dual active bridge (DAB) dc/dc converters in a power electronic traction transformer (PETT) is proposed. Based on this strategy, the output-parallel DAB converters can be equivalent to an input-series-output-parallel system. Furthermore, a PETT starting control method is put forward, which can effectively avoid risks of overcurrent and overvoltage in the PETT starting process. In order to carry out the controller design and system stability analysis, three different kinds of mathematical models of DAB converters are set up. The first model is related to a single DAB converter, the second model reflects the equivalent relation between an output-parallel DAB system and a single DAB converter in terms of the output-voltage control loop, and the third model indicates that the voltage balance control system based on DAB converters is a multiinput-multioutput system. Due to the nonzero off-diagonal elements of the controlled plant, there is a mutual effect between different control loops, which is defined as “interaction” in the multivariable feedback control theory. The stability of the voltage balance control system is made up of two parts, including the stability of each single-input-single-output (SISO) control loop and the influence of the interaction on the system stability. The research is carried out to measure the intensity of the interaction in this paper, and a criterion directly based on the controlled plant is proposed to predict the influence of the interaction, which can obviously simplify the system stability analysis. Considering the particular traction onboard application, a new control structure toward the voltage balance controller is introduced. Based on the new structure, the controller is designed and the stability of the SISO system is analyzed. Finally, a five-cell PETT prototype with rated power of 30 kW is taken to carry out further research, and the experiment results verify the effectiveness and correctness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

To solve some problems caused by the ac control method used for the existing modular multilevel dc–dc converter (MMDC), this paper has proposed a new MMDC topology with a wide range of output voltage by means of dc control. By reconstructing the submodule structure, the converter has a power branch and an auxiliary balance branch, which are used to transmit dc power and balance the capacitor voltage, respectively. Both dc analysis and control method are adopted to establish a mathematical model so as to deduce the mathematical relationships between the key electrical parameters. Moreover, what have been done include analyzing the self-balancing principle of the capacitor voltage and the mechanism of the auxiliary balance branch, calculating the related parameters of the capacitor voltage fluctuation, and presenting a dc closed-loop control strategy based on a small-signal model. The analyses of the steady and dynamic states in combination with simulation and experiment show that the proposed converter can stably operate in the mode of dc control, with a large adjustable range of output voltage, a small fluctuation in voltage of the capacitor, and the ability of the inductor to suppress the spike of the auxiliary balance current effectively so as to reduce the impact on the device. [ABSTRACT FROM AUTHOR]

The resonant converter (RC) is finding wide applications in many space and radar power supplies. Among various RCs LCL, LCC, and LCL-T topologies are broadly used. This manuscript presents a comparative evaluation of steady-state stability of LCL, LCC, and LCL-T resonant configurations. Careful analysis favors LCL RC among the aforementioned three configurations since the stability region is good for the LCL RC over the other configurations. Also, this paper presents a comparative evaluation of proportional integral (PI) controller and fuzzy logic controller for a modified LCL RC. The aforementioned controllers are simulated using MATLAB and their performance is analyzed. The outcome of the analysis shows the superiority of fuzzy control over the conventional PI control method. The LCL RC is proposed for applications in many space and radar power supplies. Design, simulation, and experimental results for a 133-W, 50-kHz LCL RC are presented in this manuscript which provide high efficiency (greater than 89%) even for 50% of load. Efficiencies greater than 80% are obtained at significantly reduced loads (11%). In this paper, the applicability of the Philips advanced RISC machine processor LPC 2148 is also investigated for implementing the controller for an RC. [ABSTRACT FROM AUTHOR]

This paper presents the high-performance quasi-Z-source series resonant dc–dc converter as a candidate topology for the photovoltaic module-level power electronics applications. The converter features a wide input voltage and load regulation range thanks to the multimode operation, i.e., when the shoot-through pulse width modulation and phase-shift modulation are combined in a single switching stage to realize the boost and buck operating modes, respectively. Our experiments confirmed that the proposed converter is capable of ensuring ripple-free 400 V output voltage within the sixfold variation of the input voltage (from 10 to 60 V). The converter prototype assembled achieved a maximum efficiency of 97.4%, which includes the auxiliary power and control system losses. [ABSTRACT FROM AUTHOR]

This paper introduces a module-integrated distributed battery energy storage and management system without the need for additional battery equalizers and centralized converter interface. This is achieved by integrating power electronics onto battery cells as an integrated module. Compared with the conventional centralized battery system, the modular design brings several advantages such as reduced power rating and voltage stress of power electronics, no extra equalizers or centralized converters, active thermal distribution control ability, enhanced safety and reliability, etc. The battery system can now be built by simply attaching integrated modules together. The integrated module is implemented by a synchronous bidirectional dc/dc converter with digital control techniques. The design considerations and control strategy of the system are discussed. A prototype is built that the power electronics are integrated onto the battery cell. Experimental results of a three-module system verified that the module-integrated distributed system provides satisfied functional performance without extra equalizers, centralized charger, or bidirectional dc/dc converter. [ABSTRACT FROM AUTHOR]

This paper describes the design and performance of a 6-kW, full-bridge, bidirectional isolated dc-dc converter using a 20-kHz transformer for a 53.2-V, 2-kWh lithium-ion (Li-ion) battery energy storage system. The dc voltage at the high-voltage side is controlled from 305 to 355 V, as the battery voltage at the low-voltage side (LVS) varies from 50 to 59 V. The maximal efficiency of the dc-dc converter is measured to be 96.0% during battery charging, and 96.9% during battery discharging. Moreover, this paper analyzes the effect of unavoidable dc-bias currents on the magnetic-flux saturation of the transformer. Finally, it provides the dc-dc converter loss breakdown with more focus on the LVS converter. [ABSTRACT FROM AUTHOR]

This paper describes an integrated power management IC with bidirectional current capability, aimed at compensating differences in output current between series-connected cells in concentrating photovoltaic (CPV) systems. The integrated 3.6-MHz power stage allows building a small-form-factor converter per cell. A hysteretic current-mode controller regulates the bidirectional converter's current to equalize neighboring cell voltages. A phase-locked loop controls the inductor current ripple around the average value to stabilize the switching frequency. The use of hysteretic current-mode control with a novel bidirectional senseFET scheme provides inherent current protection and high reliability. The converter can operate from an input voltage as low as 1.8 V and with an inductor current up to $\pm$1.5 A, while achieving a system efficiency above 90% for current mismatches between cells up to 60%. Measurement results show that the converter maximizes the output power of series-connected CPV cells with mismatched output currents. [ABSTRACT FROM AUTHOR]

A pulse dropping switching technique (PDT) has been presented in this paper to accomplish variable conversion ratio (CR) in a multilevel modular capacitor-clamped dc-dc converter in the step-up conversion mode. The switching pattern is generated by comparing a triangular wave with a rectangular wave, and a proper output voltage regulation can be obtained by controlling the relative frequency and amplitude of these two waveforms. A state-space modeling technique has been applied here to estimate the variation in equivalent output resistance (EOR) for different operating conditions of the PDT. The EOR can be varied in a wide range without changing the operating frequency of the converter, and thereby the PDT enhances the degrees of freedom to accomplish voltage regulation in a two-phase switched-capacitor converter. Slow-switching limit of the converter has been derived to define the boundary of the EOR. Different challenges and limitations of the proposed modulation scheme has been discussed in detail, and the proposed analysis has been verified by comparing the analytical expressions with the simulation and experimental results for different switching frequencies, modulation indices, and number of active modules. In addition, variations in the CR, efficiency and ripple voltage for different number of active modules and switching conditions have been described in detail. [ABSTRACT FROM AUTHOR]

Peak current mode bifrequency (PCM-BF) control, a novel control technique for switching dc-dc converters in the discontinuous conduction mode (DCM), is proposed in this paper. It realizes output voltage regulation by employing high- and low-frequency control pulses with preset switching frequencies. At the beginning of each control pulse cycle, the output voltage is sampled and compared with reference voltage to determine whether high- or low-frequency control pulse should be generated as control pulse. Compared with conventional pulse-width-modulation-based PCM control (hereafter called PCM-PWM), which realizes output voltage regulation by adjusting the duty ratio of the control pulse cycle by cycle, the PCM-BF control is simple, cost effective, and enjoys fast transient response. Moreover, more low-frequency control pulses are generated for light load, which improve the power conversion efficiency at light load. Besides, high- and low-frequency control pulses with different switching frequencies spread the spectrum over discrete frequencies, resulting in low electromagnetic interference. A buck converter operating in the DCM is taken as an example to illustrate the applications and benefits of the PCM-BF control technique. Simulation and experimental results are presented to verify the analytical results. [ABSTRACT FROM AUTHOR]

This paper proposes an active technique to reconstruct and balance the phase currents in multiphase dc-dc converters implementing both of voltage- and current-mode controls. Only one current sensor at the dc link is required to measure and reconstruct the phase currents. Multiple current samples in the pulsewidth modulation switching period are synchronized with the carrier waveforms to actively reconstruct the phase currents using a simple active balancing algorithm that is implemented in a digital controller. The proposed technique improves system performance, stability, and efficiency, and prevents inductor saturation. A 5-kW four-phase dc-dc converter prototype for battery charging application is built to experimentally verify the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, a new technique for controlling dc-dc resonant converters is investigated. A variable inductance is used to control and regulate the dc output voltage maintaining constant switching frequency for the half-bridge transistors. The output voltage characteristics of the series resonant and parallel resonant converters under the proposed magnetic control are obtained and analyzed. In order to evaluate the proposed technique, a laboratory prototype for a 48 V-input 5 V/10 A-output 500 kHz parallel resonant converter is presented. A methodology for obtaining the converter dynamic response using a step response test is carried out. From the dynamic response, a compensator for operating the converter at closed loop is developed and tested in the laboratory. The results prove that the proposed technique is suitable for controling resonant inverters at constant frequency using a low-cost half-bridge inverter. [ABSTRACT FROM AUTHOR]

Multiport dc/dc converters are widely employed in hybrid energy generation systems to provide stable power to key loads with high power density. In this paper, the switch duty cycle and the phase angle of the interleaved converters are employed as two control freedoms to achieve decoupled voltage regulation within a certain operating range among different ports, which is referred to as pulsewidth modulation plus phase angle shift (PPAS) control scheme. An interleaved bidirectional buck-boost converter and a full-bridge converter are integrated together to derive a combined three-port dc/dc converter for photovoltaic (PV)-battery hybrid energy systems, which is adopted as a typical example to explore the clear performance of the proposed PPAS control strategy. The bidirectional buck-boost converter and the full-bridge converter share the same power MOSFETs in the primary side, which simplifies the circuit structure and improves the power density. The duty cycle of the interleaved bidirectional buck-boost converter is adopted to realize the maximum power point tracking and the voltage balance between the battery and the PV cell in the primary side. Furthermore, the phase angle of the interleaved buck-boost converter is employed as another control freedom to achieve accurate secondary output voltage regulation. Finally, a 100-W PV-Battery energy system is designed and tested to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

The existing infrastructures of electrical power systems are still dominated by ac. The challenge in the coming years lies in developing new infrastructures and power modules, setting up safety standards and regulations, and investigating system stability and dynamics for dc distribution systems, to which this Special Issue is dedicated. A perspective of the challenge is broken down as follows: 1) infrastructures of dc distribution systems; 2) power modules; 3) energy management system; 4) safety standard and regulation; 5) DC-bus voltage regulation; 6) modeling and control; 7) interface of dc-bus to ac-grid; 8) energy storage and compensation; 9) DC appliances and electronic products; 10) accessories for dc distribution systems. For this Special Issue, there was a record number of over 100 manuscripts. From these high-quality papers submitted, the editorial team selected 37 papers for publication in this Special Issue, and they cover five major topic areas, as follows: 1) infrastructure, energy storage and management (8 papers); 2) interface of dc-bus to ac-grid (7 papers); 3) converter modules (11 papers); 4) modeling and control (8 papers); 5) DC-bus voltage regulation (3 papers). [ABSTRACT FROM AUTHOR]