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In this paper, an improved bridgeless single-ended primary inductance converter (SEPIC) power factor correction (PFC) rectifier is introduced. By introducing an additional output diode into conventional bridgeless SEPIC PFC rectifier, an undesired capacitive coupling loop is removed, not only eliminating the circulating loss but also reducing the sensing noise. Moreover, an integrated magnetics with symmetrical structure could be utilized so as to reduce the system size and increase the circuit power density. The operation principle of the proposed converter is investigated, and simulation results are provided. A 100-W prototype with 110Vrms input line voltage and 50V dc output voltage is built and tested. A peak efficiency of 91% and power factor above 0.98 are achieved under 100kHz switching frequency operation condition.

The trend for photovoltaic (PV) inverter is toward low cost, high efficiency, high reliability, low ground leakage current, and low-output ac-current distortion. This paper would introduce high efficiency and low cost dual buck PV inverter, which has no reverse recovery problem for MOSFET and is very suitable for Super-junction power MOSFETs application. However, due to the duty cycle would be 50% at zero-crossing, current would have a significant distortion when it adopts bipolar PWM for PV application. This paper would propose a novel modulation method for bipolar PWM, which provides 0% duty cycle at zero-crossing. With this modulation method, the current zero-crossing distortion would be eliminated, but the total current would have distortion due to nonlinear modulation. In the last part, combined with proposed PWM modulation method, a repetitive current controller is introduced to eliminate the distortion from nonlinear modulation. All the experiment results in standalone (380Vdc, 208Vac) verified the analysis and proposed method for current distortion correction in dual buck PV inverter.

Implementing variable frequency modulation using low-cost digital signal processors introduces two main design issues: variability in the converter response due to the modulator delay, and a widely varying controller response due to the changing sampling period. While the first issue has been modeled several times in literature, the second has been largely ignored, and becomes an even greater issue as the frequency range is increased. As a solution, a digital compensator with adaptive gains that is normalized against frequency variations is proposed. A method for calculating the coefficients is also provided, along with a theoretical analysis of the converter frequency response. The frequency-normalized compensator is then implemented on a 180W prototype dc-dc converter, and the improvements in converter stability and system bandwidth are verified experimentally using a frequency response analyzer. For a frequency range of 25-75kHz, bandwidth improvements of up to 300% are shown for the prototype system.

This paper presents a high boost ratio dc-dc converter with hybrid transformer for non-isolated photovoltaic (PV) microinverters. The proposed converter incorporates the resonant operation mode into the traditional high boost ratio active-clamp coupled-inductor PWM converter, achieving ZVS turn-on of the switches and ZCS turn-off of the diodes. As a result of the inductive and capacitive energy being transferred simultaneously within both turn-on and turn-off intervals of the main switch, the dc bias of the magnetizing current is reduced and hence the size of magnetics can be reduced. The magnetizing inductance is designed with a small value to utilize ripple magnetizing current to assist ZVS of main switch, while maintaining low RMS conduction losses. The voltage stresses on the active switches and diodes are maintained at a low level and are independent of the wide changing input PV voltages as a result of the resonant capacitor in series in the energy transfer loop. The experimental results based on 250 W prototype circuit show system CEC efficiencies greater than 96.7% over 20 V to 45 V PV voltage range.

This paper presents a comprehensive digital control strategy for a single-switch bridgeless SEPIC PFC converter which employs the damping circuit to improve the stability of the converter. To do this, first, the 5th order control-to-inductor current model and control-to-output model are derived mathematically in both the s- and the z-domains, in where the digital delay effects are included. After that, it is confirmed that the damping circuit assists to stabilize the control loops from the loop-gain analysis of the derived models. The design procedures of the digital voltage and the current feedback controllers and the current feed-forward controller are explained in detail. The experimental results show that the designed controller is very well adopted for a 150 W LED drive application. The experimental results show that the input current THD meets EC61000 standard as well as verifying the designed digital controller under the given specification.

Driven by worldwide demands for renewable energy source, photovoltaic (PV) inverters, which are the most important part for energy conversion, have seen a considerable amount of innovations in recent years. The trends for PV inverters are toward high efficiency, high reliability, low ground leakage current, low-output ac-current distortion, and reactive power capability. This paper provides an efficiency optimized design of an Auxiliary Resonant Snubber with Coupled-Magnetic Reset Zero-voltage switching (ZVS) inverter for PV application. The main device is Power MOSFETs, which have low conduction loss and could achieve ZVS in all load condition. The auxiliary devices are low current, low cost IGBTs and Diodes, which could achieve zero-current switching (ZCS). To achieve high efficiency, resonant circuit is analyzed to optimally design the resonant components, which is based on the guarantee of full range ZVS, gating delay-time design, and lower power loss in auxiliary circuit. The power loss model is also analyzed to select suitable power device and further improve the efficiency. At last, experiment results of a 5kW single phase inverter in PV system was presented, which has more than 99% CEC efficiency and work in full load condition without cooling fan. Besides, reactive power capability is also demonstrated.

In this paper, a 5-kW photovoltaic (PV) inverter with more than 99% peak efficiency is presented. The inverter utilizes two coupled inductors in one resonant pole to ensure the zero-voltage switching (ZVS) for main switches, and zero-current switching (ZCS) for auxiliary switches. Due to the favorable cooling and ease of fabrication characteristics, PCB planar magnetics are employed as the coupled resonant inductors. In addition, super-junction MosFETs with low on-state resistance is selected in order to reduce the inverter conduction loss. The optimization design of planar resonant inductors is described and verified by finite element analysis (FEA) software. During the experiment on the 5-kW inverter prototype, the temperature rise of planar inductors is below 15°C without fan cooling at full load.

This paper presents a high-efficiency zero-voltage-switching (ZVS) dc-dc converter combing resonant and pulse-width-modulation (PWM) power conversions for electric vehicle battery chargers. A half-bridge LLC circuit, which operates at series resonant frequency, shares the lagging-leg with a phase-shift-full-bridge (PSFB) dc-dc circuit to guarantee ZVS of the lagging-leg switches of the full bridge from zero to full load. A secondary-side hybrid-switching circuit, which is formed by the leakage inductance, output inductor of the PSFB dc-dc circuit, a small additional resonant capacitor and two additional diodes, is incorporated at the secondary side of the PSFB dc-dc circuit. With the hybrid-switching circuit providing a clamp path, the voltage overshoots that arise during the turn-off of the rectifier diodes are eliminated and the voltage stress of bridge rectifier is clamped to the minimal achievable value, which is equal to secondary-reflected input voltage of the transformer. The sum of the output voltage of LLC resonant circuit and the resonant capacitor voltage of the hybrid-switching circuit is applied between the bridge rectifier and the output inductor of the PSFB dc-dc circuit during the freewheeling phases. As a result, the primary-side circulating current of the PSFB dc-dc circuit is instantly reset to zero achieving minimized circulating losses. The experimental results based on a 4 kW prototype circuit show 98.6% peak efficiency and high efficiency over wide load and output voltage ranges.