This paper analyzes a non-isolated bidirectional converter with hand-in-hand fractional-stage conversion for battery storage applications. This converter contains two partial power conversion units. Each unit consists of a non-isolated converter, and its output port is serially connected to a set of batteries. Meanwhile, the two series-connected partial power conversion units are connected in parallel. In this configuration, the batteries of one unit are operated as the source of the converter in the other unit, forming a hand-in-hand structure that enables mutual support for correct operation. Due to the unique series-parallel connection of the converter, partial power conversion is achieved using simple non-isolated converters, making the converter feature high efficiency and high power density. Moreover, the special structure of the analyzed converter endows it with the ability to regulate the voltage and current and manage the battery energy through the coordinated operation of the two non-isolated converters. To demonstrate the effectiveness and correctness of the converter, the simulation and experimental verification results are presented in this paper.

Bulky electrolytic capacitors are equipped on the conventional stand-alone high peak-to-average-ratio (PAPR) pulsed power system. Although there are some active schemes have been proposed to reduce the capacitance, they also have the negative impact on system efficiency. Therefore, in this article, a topology adopted for pulsed power suppression based on ripple voltage compensation and partial power conversion is introduced, in which a direct power path is constructed between the high voltage direct current (HVDC) bus and the energy storage capacitor (ESC) to improve the system efficiency, the output series structure compensates for voltage fluctuations in the ESC, which stimulates the energy storage potential of the capacitors. The structure and operating principle of the topology is introduced, the power flow and distribution are analyzed. Then, the design consideration and control strategy are explained, Finally, a simulation model is built in PSIM and an experimental prototype is built in the lab to verify the accuracy of theoretical analysis and the effectiveness of the topology.

High-frequency variation of the common-mode voltage (CMV) causes severe leakage current and electromagnetic interference (EMI) in photovoltaic (PV) generation and motor drive systems. This paper proposes a discontinuous PWM (DPWM) to reduce CMV for three-phase three-level inverters under different NP voltage conditions. Firstly, the relationship between the CMV and NP voltage is revealed. Then, the switching-state sequence is optimized to reduce the magnitude and frequency variations of the CMV. Furthermore, since the switching state of one phase is clamped at each switching cycle, the switching loss is also reduced. Finally, a 6-kW inverter prototype is built, and experimental results show that the proposed scheme features lower CMV, lower leakage current, and higher efficiency.

Neutral-point (NP) voltage imbalance causes severe alternating output current distortion in three-phase three-level inverters when conventional discontinuous PWM (DPWM) schemes are employed. Existing improved DPWM schemes can not achieve low total harmonic distortion (THD) and simple digital implementation simultaneously. In this paper, a pulse-width compensation (PWC) scheme is proposed to improve the THD performance of DPWM-based three-level inverters under unbalanced NP voltage conditions. By using the proposed PWC scheme, the pulse width of the bridge-leg voltage of the unclamped phases is compensated according to the NP voltage. As a result, the fundamental component of the bridge-leg voltage is not affected by the NP voltage, and the alternating output current distortion is improved. Finally, a 6-kW inverter prototype is built, and experimental results show that the proposed PWC scheme can achieve low THD and simpler digital implementation than the existing improved DPWM scheme.

As Boost-type topology, three-phase Vienna rectifier has the inherent problem of increasing output voltage at partial load. In this paper, a duty-ratio feedforward strategy based on dual-loop control is proposed to solve this problem. The comparison between a three-phase three-wire system and a three-phase four-wire system reveals that the main feature of the former is the zero-sequence component, which will not affect THD. It provides a theoretical basis for calculating three-phase feedforward respectively and carry it out in abc-domain. The feasibility of duty-ratio feedforward in other coordinate systems has also been demonstrated. Finally, the simulation and experimental results are given, which are compared with the commonly used grid-voltage feedforward in the dq-domain, to verify that the proposed feedforward strategy can not only operate stably at partial load, but also optimize THD to a certain extent.

A semi-two-stage transformerless PV grid-tied inverter based on H5 is proposed in this paper. By introducing the front-end Boost converter, the PV module and the output of the front-end Boost can be used as two different inputs of the H5 converter respectively. Therefore, the proposed topology can operate in a wide input range and part of the PV module power can be transmitted to the utility grid directly without being transferred through the path of the front-end Boost converter. The efficiency can be higher than that of the conventional two-stage H5 inverter. A modulation strategy for this topology is presented and analyzed in detail. The common-mode (CM) voltage varies with a low frequency which results in a low leakage current. An experimental prototype is built to verify the effectiveness of the proposed topology and modulation strategy.

A SiC device-based dual-input Buck-Boost converter (DI-BBC) is analyzed and evaluated for high efficiency photovoltaic (PV) power system applications. The DI-BBC is built by cascading a dual-input Buck converter and a Boost converter. Independent maximum power point tracking (MPPT) of two PV inputs can be achieved within a wide PV voltage range. SiC devices are employed to reduce losses and improve conversion efficiency. Operation principles, modulation strategies, control and design considerations of the DI-BBC are analyzed in detail. Experimental tests were carried out to evaluate the performance of the DI-BBC-based PV system.

A quasi single-stage power factor correction converter, which is composed of a three-level (TL) Boost converter and a DC-DC transformer (DCX), is presented and analyzed in this paper. The DC output load is connected to one of the dividing capacitors of the TL Boost converter, so that the load voltage can be lower than the peak amplitude of the AC line voltage and part of the AC input power can be processed within only single conversion stage. Power factor correction and output voltage regulation are realized by adopting a dual-carrier-based modulation strategy. Voltage and power balance between the two dividing capacitors of the TL Boost converter is implemented by the open-loop controlled DCX. Smooth mode transition between single-stage mode and two-stage mode is achieved. The operation principles, characteristics and design considerations of the converter are analyzed and verified with simulation experimental results.

Performance of a current-fed bidirectional LLC resonant converter for energy storage system in DC grid applications is analyzed and tested. The well match of the voltages on two sides of the LLC circuit is ensured by varying the duty cycle of buck-boost circuit under wide battery voltage range. Hence LLC circuit is operated like a DC transformer to improve efficiency. In the battery discharging mode, the pulse-width modulation (PWM) control is employed. While in the battery charging mode, the phase-shift modulation (PSM) and PWM control is adopted. To achieve the zero-voltage-switching (ZVS) of all the MOSFETs, a frequency feed-forward loop is introduced in the battery charging mode. Compared with conventional bidirectional LLC converter, the frequency regulation range of this converter is narrowed which is beneficial for the design of magnetic components. The operation principles are introduced, the main features such as current ripple of battery, and the zero-voltage-switching (ZVS) of the two modes are analyzed and compared with conventional solutions. A 1.6-kW prototype with a battery voltage of 160V–240V and a DC-bus voltage of 400V has been built and tested to verify the operational principle analysis.

A light load efficiency improvement approach for distributed battery energy storage system (BESS) is analyzed in detail. The system is constructed by the non-isolated bidirectional DC-DC converters (BDC) integrated a buck-boost BDC with a dual-active half-bridge (DAHB) BDC. With the equivalent DAHB BDCs in parallel connection and the buck-boost BDCs high voltage side in parallel connection, the independent battery charging and discharging can be realized to obtain the state of charge (SOC) balance. Meanwhile, an additional low voltage DC-bus is generated. Hence the high voltage side circuit in some DAHB BDCs can remain off at light load to decrease the total power losses while the battery input or output power can be transferred through this low voltage DC-bus to ensure the battery balance. While at heavier load, all the non-isolated BDCs are operated independently with no power transferred through the low voltage DC-bus. System architecture and the light load efficiency improvement method are analyzed. Experimental tests based on two 1kW prototypes verify the effectiveness of the approach.

A novel interleaved-series/parallel forward converter (ISP-FC) is proposed. The ISP-FC is composed of two low-voltage switching-legs and a high-voltage switching leg. The three switching-legs construct two forward cells. The voltage stress on the low-voltage switching-legs is only half of the input voltage while that on the high-voltage switching-leg is the input voltage. The maximum duty cycle of the ISP-FC can achieve 0.67, 1.33 times of that of the two-switch forward converter, which leads to wide input voltage range. The high-voltage leg switches can be soft-switched when duty cycle less than 0.5 while the low-voltage leg switches can be soft-switched when duty cycle larger than 0.5. As a result, high efficiency is achieved over a wide voltage range. The operation principles and characteristics of the ISP-FC proposed is analyzed in detail and verified with experimental results.

A novel non-isolated three-port converter (NI-TPC) is proposed interfacing one PV port, one bidirectional battery port and one load port. Single stage power conversion between any two of the three ports is achieved. The topology is derived by decoupling the bidirectional power flow path of the conventional structure into two unidirectional ones. Two of the three ports can be tightly regulated to achieve maximum power harvesting for PV or charge control for battery, and maintain the load voltage constant at the same time, while the third port is left flexible to compensate the power imbalance of the converter. Operation states are analyzed. The multi-regulator competition control strategy is presented to achieve autonomous and smooth state switching when the PV input power fluctuates. The analysis is verified by the experimental results.