Jianjiang Shi

Single-Switch High Step-Up Converters With Built-In Transformer Voltage Multiplier Cell

In this paper, a built-in voltage gain extension cell is proposed to give a universal topology derivation on next-generation high step-up converters for large voltage gain conversion systems. Several improved single-switch high step-up converters with built-in transformer voltage multiplier cell are derived with some advantageous performance, which includes extremely large voltage conversion ratio, minimized power device voltage stress, effective diode reverse-recovery alleviation, and soft-switching operation. The turns ratio of the built-in transformer can be employed as another design freedom to extend the voltage gain, which shows great design flexibility. Compared with their active clamp counterpart, only one MOSFET is required to simplify the circuit configuration and improve the system reliability. The over resonance frequency and the below resonance frequency operation modes are studied to explore the circuit performance, and the key parameter design criterion is provided to show a valuable guidance for future industrial applications. Finally, the experimental results from a 500 W 36-380 V prototype are provided to validate the effectiveness of the main contributions in this paper.

Common-Duty-Ratio Control of Input-Parallel Output-Parallel (IPOP) Connected DC–DC Converter Modules With Automatic Sharing of Currents

Input-parallel output-parallel (IPOP) connected converter systems allow the use of low-power converter modules for high-power applications, with interleaving control scheme resulting in smaller filter size, better dynamic performance, and higher power density. In this paper, a new IPOP converter system is proposed, which consists of multiple dual-active half-bridge (DAHB) dc-dc converter modules. Moreover, by applying a common-duty-ratio control scheme, without a dedicated current-sharing controller, the automatic sharing of input currents or load currents is achieved in the IPOP converter even in the presence of substantial differences of 10% in various module parameters. The current-sharing performance of the proposed control method is analyzed using both a small-signal model and a steady-state dc model of the IPOP system. It is concluded that the equal sharing of currents among modules can be achieved by reducing the mismatches in various module parameters, which is achievable in practice. The current-sharing performance of the IPOP converter is also verified by Saber simulation and a 400-W experimental prototype consisting of two DAHB modules. The common-duty-ratio control method can be extended to any IPOP system that consists of three or more converter modules, including traditional dual-active bridge dc-dc converters, which have a characteristic of current source.

LCC Resonant Converter Operating under Discontinuous Resonant Current Mode in High Voltage, High Power and High Frequency Applications

The full-bridge series-parallel resonant converters (also known as LCC resonant converters) with capacitive output filter is evaluated in high output voltage (≫50kV), high power (≫50kW) and high frequency (20 kHz) ESP (Electrostatic Precipitator) power supply applications. By using the leakage inductance and the winding capacitance of the transformer as the resonant elements only an additional series resonant capacitor is needed to form the LCC topology. ZCS turn-on and ZVZCS turn-off of the power switches are achieved by adopting the DCM (discontinuous current mode) control method. The concept of critical load is introduced as a key parameter to aid the circuit design. A prototype has been built to verify the operation principle of the circuit. Experimental results are given.

Design of High Voltage, High Power and High Frequency Transformer in LCC Resonant Converter

The design of a high voltage, high power and high frequency transformer is introduced considering its operation in the LCC resonant converter. The leakage inductance and winding capacitance of the transformer are used as the resonant elements. An additional series resonant capacitor is added to form the LCC topology. The discontinuous current mode (DCM) is adopted to achieve the ZCS turn-on and ZVZCS turn-off of the power switches. Smaller value of the winding capacitance is preferred because it has the effect of decreasing the peak value of the resonant current at almost the same output voltage. The theoretic calculation of the winding capacitance and leakage inductance of the transformer is given. The error between the theoretical calculation and practical measurement is within 15%. So optimization design of the parasitic resonant elements can be achieved to meet requirement of the circuit. A prototype of LCC resonant converter with 60kW and 60kV output is built based on the designed transformer. Experiment results are given.

Automatic Current Sharing of an Input-Parallel Output-Parallel (IPOP)-Connected DC–DC Converter System With Chain-Connected Rectifiers

Input-parallel output-parallel (IPOP)-connected converter systems allow the use of low-power converter modules for high-power applications. An IPOP converter topology with half-wave, daisy chain-connected rectifiers is presented which consists of multiple half-bridge (HB) dc-dc converter modules. By utilizing a common-duty-ratio control scheme, without a dedicated current-sharing controller, automatic sharing of input current and load current in the IPOP converter is achieved even in the presence of differences of more than 10% in various module parameters. The steady-state and dynamic-state current-sharing performance of the proposed IPOP converter is analyzed by using a steady-state dc model and a small-signal model of the system, respectively. It is concluded that steady-state current sharing among modules can be realized by applying a common-duty-ratio control scheme and by reducing the difference in transformer turn ratios, while dynamic-state current sharing is only slightly affected by substantial module parameter mismatches. The stability and current-sharing performance are verified by Saber simulation and an 800-W prototype consisting of two HB modules. The IPOP converter topology under the common-duty-ratio scheme can be extended to any system of three or more converter modules, including full-bridge dc-dc converters.

An isolated interleaved active-clamp ZVT flyback-boost converter with coupled inductors

The fundamental limitations of interleaved flyback converters for high step-up DC/DC applications are analyzed in this paper. A novel interleaved flyback-boost converter is derived with further modifications on the interleaved flyback converter, which extends the voltage gain and reduces the voltage stress of the switch. The active-clamp circuits are employed to recycle the leakage energy. Both the main and the auxiliary switches can realize ZVT soft switching condition. The turn-off voltage spikes of the main switch are clamped by the active-clamp circuits. Due to the leakage inductance of the coupled inductors, the output diode reverse-recovery problem is alleviated dramatically. A 1 kW prototype with 40V-input-to-380V-output operating at 50 kHz switching frequency built in the lab verifies the effectiveness of the proposed converter. The efficiency of nearly 90% at full load is achieved. More than 7% efficiency improvements with active-clamp circuits are achieved compared with the case with RCD snubbers.

A ZCS PWM Switch Circuit for the Interleaved Boost Converters

A ZCS PWM switch circuit for the interleaved boost converters is proposed in this paper. Only one auxiliary switch is used in the active soft switching circuit. By using this ZCS converter topology, zero current turn-on and zero current turn-off of the main switches can be achieved and the reverse-recovery loss of boost diode can be reduced. In addition, the auxiliary switches are ZCS during the turn-on and turn-off switching transition. A prototype of boost converter rated at 500W has been built to confirm the effectiveness of the converter.

Voltage and power balance control strategy for three-phase modular cascaded solid stated transformer

The three-phase modular cascaded solid stated transformer (SST) is an important element in the micro-grid systems as its outstanding adventures compared with conventional power transformer. It consists of three stages, the three-phase cascaded modular rectifier stage, the dual active bridge (DAB) converter stage and the three-phase inverter stage. Three output-paralleled DAB converters offer three dc-buses, which forming the interfaces of renewable energy. However, unbalanced modular voltage or transferred power causes overvoltage or overcurrent issues, which increase the stress of the semiconductor switches and even the instability of SST system. Focusing on the imbalance issues, this paper proposes a systematic control strategy for the three-phase modular cascaded SST. A d-q vector-based common-duty-ratio controller is applied to the rectifier stage aiming at balancing the modular current in each phase. Voltage controller for DAB stage achieves the balanced dc-link and dc-bus voltage, and proportional-resonant controller is applied to inverter stage. The effect of this proposed control method has been verified theoretically. In addition, a scaled-down experimental prototype is built to prove the performance.

Performance analysis of a single stage single phase high step-up soft switching boost converter

In this paper, a voltage multiplier cell with built-in transformer is inserted into the conventional single switch boost converter, which can extend the voltage gain by regulating not only the duty cycle, but also the turns ratio of the built-in transformer. Furthermore, the switch voltage stress can be reduced greatly by increasing the turns ratio of the built-in transformer. Therefore, the switch conduction losses can be minimized by employing low voltage rated power devices. Furthermore, Zero current switching (ZCS) turn-on for the switch and reverse-recovery problem alleviation for the diodes are achieved to reduce the switching losses. As a result, the proposed converter is suitable for high step-up and high output voltage applications. Finally, the experimental results from a 500W 36V-380V prototype are provided to validate the effectiveness of the proposed converter.

Performance Analysis of an Isolated ZVT Boost Converter with Primary-Parallel-Secondary-Series (PPSS) Structure

The primary-parallel-secondary-series structure is employed in this paper to share the large current at the primary side and to sustain the high voltage at the secondary side in the isolated low-input-to-high-output applications. A novel boost converter with coupled inductors and an active-clamp circuit is proposed for high power and high step-up conversion. Only one set of clamp circuit is necessary to serve for the interleaved two phases, which reduces the auxiliary switch number and simplifies the circuit. ZVT soft switching performance is achieved to reduce the switching losses for both the main and the auxiliary switches during the whole switching transition. The leakage energy of the coupled inductors is recycled and the output diode reverse-recovery problem is alleviated. The steady operation and the circuit performance are analyzed. And the design considerations are given. At last, the simulated and experimental results for a 40V-to-760V converter verify the converter performance.