Novel High-Efficiency Three-Port Bidirectional Step-Up/Step-Down DC–DC Converter for Photovoltaic Systems

This paper presents a novel high-efficiency three-port bidirectional DC–DC converter for photovoltaic (PV) systems. A PV system’s output is stepped up to supply a DC bus or DC load while charging the battery. When the PV output is insufficient, the battery voltage is stepped up to the DC bus; when the DC bus has excess energy, it is stepped down to charge the battery. Thus, a high-efficiency three-port bidirectional step-up/step-down converter is achieved. A common-core coupled inductor was designed and adopted in the proposed converter. Power switches and diodes in the circuit are shared to achieve bidirectional operation. In step-up mode, the clamp capacitor is used to reduce the voltage spike on the main switches. Moreover, the voltage-doubling capacitor recovers energy from the secondary-side leakage inductance. Furthermore, the input capacitors recover the primary-side leakage inductance energy in step-down mode. Thus, the converter can improve its conversion efficiency. Finally, this paper details the implementation of a 500 W three-port bidirectional converter to verify the feasibility and the practicability of the proposed topology. According to the measurement results, the highest efficiency levels of the PV and the battery in step-up mode were 94.3% and 94.1%, respectively; the highest efficiency in step-down mode was 95.2%.

Non-isolated high step-up DC/DC power converter with coupled-inductor

This paper presents a non-isolated single switch converter with high voltage gain. Its circuit topology is combined with coupled-inductor, clamp circuit, and voltage lift capacitor techniques. The proposed converter has several advantages: First, the circuit is controlled by only single pulse width modulation (PWM) for the power switch, which keeps the circuit simple. Secondly, the proposed converter is used as a clamping circuit,which let the energy of the leakage inductance can be circulated to the capacitor, so that the voltage spike on the active switch can be suppressed, and improves efficiency. This paper will introduce the principle of action, theoretical analysis, and experimental waveform in order. Finally, in the case of input voltage of 48 V, output voltage of 400 V, and output power of 1 kW, the performance of the proposed converter is verified. As a result, the maximum efficiency is up to 96.5% and full load efficiency is 92.3%.

Development of universal algorithm of voltage circuits detecting faults of microprocessor protection and automation devices

Reliability, along with response speed, sensitivity, and selectivity, is the key requirement for relay protection (RP) devices. The reliability of modern RP digital terminals is understood as protection operation for all estimated failure modes and failure of protection equipment to operate in all other modes, in which this protection is not provided. Analysis of the secondary voltage schemes and algorithms of detecting faults in these circuits reveals several disadvantages of the implementation of blocking in case of faults in voltage circuits. All existing algorithms and blocking schemes in case of faults in voltage circuits suffer from several disadvantages. In this regard, it is relevant to develop a universal relay protection terminal, which can be used with any types of voltage transformers. The MatLAB Simulink is used to simulate the primary failure of secondary circuits for the connection schemes of the voltage transformer load on phase and electric line voltages. The authors propose the algorithm that allows us to create a typical universal RP terminal, which can be used with any type of voltage transformers. To detect the neutral conductor interruption of the «star» circuits, it is proposed to create an artificial asymmetry at the input voltage circuits of the relay protection and automation (RPA) terminal and develop a group of fault detectors that analyze the position of the offset neutral on the voltage complex plane. Using a simulation model of various types of failure of voltage transformer secondary circuits and the logic diagram of the unit that implements the proposed algorithm, the authors graphically show that the detection of a break in the neutral wire is possible due to monitoring the zero-sequence voltage spike (triggering of the pulsed dU0 fault detector) with neutral displacement to the complex plane area, which is set by the setpoints. The results obtained allow us to implement a universal scheme of blocking faults in voltage circuits. This scheme does not depend on the voltage transformer secondary load connection method and exclude the disadvantages of existing solutions discussed in the article. This algorithm allows us to develop a typical universal RPA terminal. Due to its connection scheme and functional and logical implementation, this terminal can be used with any types of voltage transformer without reprogramming. Also, the proposed algorithm fully complies with the requirements of the current regulatory and legal documents.

An Interleaved Phase-Shift Full-Bridge Converter with Dynamic Dead Time Control for Server Power Applications

A compact and high-efficiency power converter is the main business of today’s power industry for server power applications. To achieve high efficiency with a low-output ripple, an interleaved phase-shift full-bridge (PSFB) converter is designed, built, and tested for server power applications in this study. In this paper, dynamic dead time control is proposed to reduce the switching loss in the light load condition. The proposed technique reduces the turn-off switching loss and allows a wide range of zero-voltage switching. Moreover, the current ripple of the output inductor can be reduced with the interleaved operation. To verify the theoretical analysis, the proposed PSFB converter is simulated, and a 3 kW prototype is constructed. The experimental results confirm that the conversion efficiency is as high as 97.2% at the rated power of 3 kW and 92.95% at the light load of 300 W. The experimental transient waveforms demonstrated that the voltage spike or drop is less than 2 V in the fast-fluctuating load conditions from 0% load to 60% load and 40% load to 100% load.

Active Clamp Boost Converter with Blanking Time Tuning Considered

An active clamp boost converter with blanking time auto-tuned is presented herein, and this is implemented by an additional auxiliary switch, an additional resonant inductor, and an additional active clamp capacitor as compared with the conventional boost converter. In this structure, both the main and auxiliary switches have zero voltage switching (ZVS) turn-on as well as the output diode has zero current switching (ZCS) turn-off, causing the overall efficiency of the converter to be upgraded. Moreover, as the active clamp circuit is adopted, the voltage spike on the main switch can be suppressed to some extent whereas, because of this structure, although the input inductor is designed in the continuous conduction mode (CCM), the output diode can operate with ZCS turn-off, leading to the resonant inductor operating in the discontinuous conduction mode (DCM), hence there is no reverse recovery current during the turn-off period of the output diode. Furthermore, unlike the existing soft switching circuits, the auto-tuning technique based on a given look-up table is added to adjust the cut-off time point of the auxiliary switch to reduce the current flowing through the output diode, so that the overall efficiency is upgraded further. In this paper, basic operating principles, mathematic deductions, potential designs, and some experimental results are given. To sum up, the novelty of this paper is ZCS turn-off of the output diode, DCM operation of the resonant inductor, and auto-tuning of cut-off time point of the auxiliary switch. In addition, the efficiency of the proposed converter can be up to 96.9%.