Development of power electronic converters tend to achieve high efficiency and at the same time high power density in many industrial applications. In recent years, with emerging third-generation semiconductor materials i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN), the switching frequency of several MHz has become a widely studied frequency band, therefore traditional technology can no longer meet the demand, and many new challenges appear. This paper presents a comprehensive review of high frequency (HF) converters, the essential challenges are analyzed such as topology selection, soft-switching technologies, resonant gate drivers, magnetic components design and optimization.

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A Review of High Frequency Power Converters and Related Technologies

An interleaved zero-voltage zero-current switching (ZVZCS) high step-up DC-DC converter is proposed for modern photovoltaic power generation systems. The proposed converter can achieve high voltage conversion gain without operating under extreme duty cycles. The voltage conversion gain can be readily adjusted by selecting different numbers of the diode-capacitor multiplier (DCM) cells in the circuit at the design stage. Moreover, with the passive snubber circuit in the proposed converter, all power switches and diodes in the DCMs can achieve zero-voltage turn-off and zero-current turn-on, which effectively reduces switching losses and increases the overall converter efficiency. The operational principles and analysis of the performance analysis with two DCMs are presented for demonstrative purpose. The effectiveness of the proposed ZVZCS DC-DC converter is validated using an 800W experimental prototype.

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An Interleaved Zero-Voltage Zero-Current Switching High Step-Up DC-DC Converter

The invention relates toDC-DC power converters and methods of operating DC-DC power converters. A DC-DC power converter includes an input, an output, a transformer, a primary field-effect transistor (FET), and a synchronous rectifier. The synchronous rectifier includes a drain that experiences multiple resonant voltage valleys during each dead-time period of the converter. The converter further includes a synchronous rectifier drive circuit configured to turn on and turn off the synchronous rectifier, and a primary control circuit. The primary control circuit is configured to operate the primary FET in a valley skipping mode, and to transmit a drive signal to the synchronous rectifier drive circuit to turn on the synchronous rectifier during a specified one of the multiple resonant voltagevalleys to generate a negative current through the synchronous rectifier. Methods of operating a DC-DC power converter are also disclosed.

DC-DC power converters and methods of operating DC-DC power converters

In the conventional peak current controlled active-clamped flyback converter, the primary side current sampling resistor R s brings many problems, among which the additional power consumption and instability are the most obvious ones. A new peak current control method without sampling resistor is proposed, which is suitable for both analog control (based on Analog IC or discrete components) and digital control (based on FPGA, ASIC, MCU, DSP, etc.). To exemplify, the FPGA-based digital control method is taken as case study, and the proposed control method is verified by experimental results. In a GaN-based 12V-3A ACF, the average efficiency is improved by upto 2.92% compared to the conventional peak current control methods. In addition, the dynamic response is greatly improved, and analysis is given to explain this improvement.1

An Improved Peak Current Control Method for GaN-based Active-clamped Flyback Converter

This chapter is devoted to multilevel resonant and impedance-source converters. First of all, the general operating principle of resonant circuits is disclosed, the main goal of their application being to provide a soft-switching operation. The same is done for impedance-source networks, which have unique features of both current and voltage source networks, along with inherited advantages. A brief overview of multilevel inverters describes the main types and the general means of further derivation. Finally, the combination of resonant circuits and impedance networks with multilevel inverters are discussed in the final sections.

Resonant and Z-source multilevel inverters

The demand of miniaturization of power systems has accelerated the research on high-switching-frequency power converters. A single-switched quasi-resonant flyback converter that features low switching loss and low switching noise at high switching frequency is investigated in this paper. In order to realize near fully soft switching, a resonant inductor of primary side and a resonant capacitor of secondary side are utilized to recycle the transformer leakage energy and realize zero-current switching (ZCS) at turn off and valley switching (VS) at turn on of the primary switch, and ZCS at turn off of diode. The VS is utilized based on the resonance between the resonant inductor and the equivalent switch drain capacitor. In the closed-loop control, a pulse frequency modulation mode with time fluctuation of switching period is implemented to realize VS at turn on of switch and an on – off control mode is utilized to improve the overall efficiency. Low cost, low losses, and low switching noise are all realized in the proposed prototype. The proposed concept has been validated on a 1 MHz 12 V/3 A prototype with 80 V dc input. The peak efficiency is 90.3% in the on – off mode by using GaN device without synchronous rectification.

A Single-Switched High-Switching-Frequency Quasi-Resonant Flyback Converter

Provided is a constant voltage output control system of a synchronous rectification primary side feedback flyback power source. The control system comprises a single output DAC midpoint sampling module, a sampling error compensation module, a current detection module, a digital control module and a PWM driver module. The single output DAC midpoint sampling module samples a voltage signal Vsense ofan auxiliary winding. The voltage signal Vsense (tmid) at the secondary side current rectification time Tr midpoint moment is output. Midpoint sampling errors are calculated by a compensation algorithm based on the current detection module to correct the sampling voltage on the auxiliary winding at a midpoint. The digital control module utilizes a proportion and an integral to calculate a controlquantity to output the control quantity to the PWM driver module to control a primary side switch tube and a secondary side synchronous rectification tube separately through the compensated midpointvoltage signal and errors e (n) of a fixed value VREF preset by the system, and therefore constant voltage output control on the synchronous rectification primary side feedback flyback power source isachieved.

Constant voltage output control system of synchronous rectification primary side feedback flyback power source

The invention relates to a fly-back power source CCM and DCM mode constant current control system. The control system comprises a current detection module, an output feedback module, a current calculation module, an error calculation module, a PID module, a PWM module and a driving module. Connection with a controlled switch power source is carried out to form a closed loop, basic parameters for realizing a constant current algorithm are acquired by the current detection module and the output feedback module, the current calculation module is mainly used for calculating an average output current value, the output value realizes compensation in the PID module, a compensation value is transferred to the PWM control module, a proper duty ratio is outputted through the driving module, and thereby a high precision constant current of a digital power source is controlled.

Fly-back power source CCM and DCM mode constant current control system

A MHz single-switched resonant flyback converter with quasi-ZVS is applied to improve the power density. In the quasi-ZVS control, as the control parameters are adjusted and varying continuously, the conventional efficiency calculation is no longer applicable. A dynamic analytical loss model is thus proposed for the quasi-ZVS control, and an optimized on-off control algorithm is further used for efficiency improvement. Based on the loss model with variable parameters, the efficiency of the quasi-ZVS control under different load can be calculated by iteration of multiple switching cycles, and the highest efficiency working condition can be obtained and used for on-off control to improve the overall efficiency. The efficiency is greatly improved with the optimized on-off control. A FPGA controlled 12V/3A resonant converter with eGaN HEMTs is established to verify the proposed control method. The peak efficiency under the proposed optimized on-off control without synchronous rectification is 90%, and the light load efficiency is more than 80%. Compared with the quasi-ZVS control, there is an improvement of 1.2% under full-load condition, and increases by 6.2% under 10% load condition.

An efficiency optimization method for a high frequency quasi-ZVS controlled resonant flyback converter

A method for improve that dynamic response of switching power supply to heavy load shedding and light load, in accordance with an embodiment of that present invention, dynamic control module, error calculation module, PID module, a control system composed of a mode control module and a PWM module, the control system is connected with the controlled switching power supply to form a closed loop, Asthat output voltage of the switch power supply exceed its set upper limit voltage, the output is quickly stabilized by a low energy heavy load shedding light load mode, The change of output voltage ismonitored in the heavy load shedding and light load mode, and then the period of the next switching cycle is calculated. According to the switching cycle, the load is obtained. After jumping out of the dynamic mode, the load jumps to the working state of the corresponding load point, and the energy consumption after the jump is not different from the load steady state, which eliminates the subsequent voltage oscillation and reduces the dynamic recovery time.

Shen Weidong

Papers

A Single-Switched High-Switching-Frequency Quasi-Resonant Flyback Converter

Constant voltage output control system of synchronous rectification primary side feedback flyback power source

Fly-back power source CCM and DCM mode constant current control system

An efficiency optimization method for a high frequency quasi-ZVS controlled resonant flyback converter

A control method for improving the dynamic response of heavy load cutting and light load of a switching power supply