Dongsheng Yang

Synthesis of Multiple-Input DC/DC Converters

Hybrid power systems continuously deliver power to the load from several renewable energy sources. For such systems, the use of a multiple-input converter (MIC) has the advantage of simpler circuit structure and lower cost, compared to the use of several single-input converters. By decomposing converters into basic cells, namely, pulsating source cells and output filters, a set of basic rules for generating multiple-input converter topologies is proposed. Specifically, two families of multiple-input converters are systematically generated. In the first family of MICs, all the input sources can power the load simultaneously or individually. In the second family, only one power source is allowed to transfer energy to the load at a time. Furthermore, some isolated MICs are simplified for reducing the complexity of the circuit configuration.

Impedance Shaping of the Grid-Connected Inverter with LCL Filter to Improve Its Adaptability to the Weak Grid Condition

The current-controlled grid-connected inverter with LCL filter is widely used in the distributed generation system (DGS), due to its fast dynamic response and better power quality features. However, with the increase of power injected into the grid, control performances of the inverter will be significantly influenced by the nonideal grid conditions. Specifically, the possible wide variation of the grid impedance challenges the system stability. Meanwhile, background harmonics of the grid can greatly distort the injected current. Therefore, the control of the inverter should be designed with strong stability-robustness and high harmonic-rejection-ability, both of which correlate closely with the inverter output impedance. However, it is difficult to shape the output impedance into the one with a desirable characteristic simply by adjusting the current loop gain. In this paper, an impedance shaping method is proposed with virtual impedances, and the current control loop can be designed independently. The implementation and parameter design of the virtual impedances are studied under the practical considerations. With this proposed method, the grid-connected inverter can work stably over a wide range of the typical inductive-resistive grid impedance and exhibit strong rejection ability of grid-voltage harmonics. Experimental results from a 6-kW single-phase grid-connected inverter confirm the effectiveness of the proposed method.

One-Cycle Control for a Double-Input DC/DC Converter

In hybrid power systems, the use of a multiple-input converter (MIC) instead of several single-input converters leads to a simpler circuit and lower cost. Energy management is always required for the MICs in order to ensure the highest utilization of renewable energy. The MIC-based hybrid power system is a typical multiple-input multiple-output coupling system, and it has multiple operating modes. As a result, the design of the controllers is very complicated. This paper proposes one-cycle control (OCC) for double-input buck converter (DIBC) to eliminate the interactions of the control loops and, thus, to simplify the design of the controllers. The mode transition circuit is further proposed to realize seamless mode transition, according to the available renewable energy and the output power. Small signal models of DIBC in different operating modes are derived. It can be seen that with OCC, the two control loops are independent of each other, and no current regulator is required. Moreover, the design conditions of the output voltage regulator in different operating modes are the same. As a result, the controller design is greatly simplified. An 800-W prototype has been built and tested in the lab and the experimental results validate the proposed OCC.

Small-Signal Modeling and Parameters Design for Virtual Synchronous Generators

The concept of the virtual synchronous generator (VSG) is emerging as an attractive solution for controlling the grid-connected inverter when the renewable energy has a high penetration level into the grid. This paper focuses on the small-signal modeling and parameters design of the power loop of the VSG, and points out that the bandwidth of the power loop should be far less than twice the line frequency for the purpose of avoiding the VSG output voltage to be severely distorted. Consequently, the line-frequency-averaged small-signal model of the VSG is derived for system analysis and parameters design. Based on the model, the decoupling conditions between the active power loops (APLs) and the reactive power loops (RPLs) of the VSG are given. Finally, a step-by-step parameters design method is proposed to facilitate the design of the control parameters of the VSG. A 10-kVA prototype is built and tested in the laboratory, and the experimental results are given to verify the effectiveness of the theoretical analysis and the proposed parameters design method.

Multiple-input full bridge dc/dc converter

In the renewable power system with two or more sources, the application of multiple-input converter (MIC) instead of several single-input converters can simplify the circuit and reduce the cost. A novel multiple-input full bridge dc/dc converter is proposed in this paper. Taking the two inputs as the example, the operation principles and characteristics of the double-input full bridge dc/dc converter are presented. By applying the proposed double phase-shift control strategy, the soft-switching technology is accessible. Power management method of the new converter is also introduced. Finally, a 800W prototype is built to verify the theoretical analysis and the effectiveness of the control strategy.

A systematic method for generating multiple-input DC/DC converters

A multiple-input converter (MIC) is devoted to combining on-board energy sources in the electric vehicles (EVs) and hybrid-electronic vehicles (HEVs). By analyzing the structure of the single-input converters, the basic cells including the pulsating source cells (PSCs), the buffer cells (BCs) and the output filter are proposed for deriving various MIC topologies. MIC can be categorized into two lists, MIC without BCs and MIC with BCs. According to the presented combination and cascade rules, two families of MICs without BCs and with BCs can be systematically generated.

Modeling, analysis and design for hybrid power systems with dual-input DC/DC converter

Hybrid power systems derive power simultaneously from several renewable energy sources and deliver power continuously to the load. For such systems, the use of a multiple-input converter (MIC) has the advantage of simpler circuit design and lower cost, compared to the conventional use of several single-input converters. Taking dual-input Buck converter as the example in this paper, a new power management strategy is first proposed and the multiple operation modes of the system are analyzed. Based on the small signal modeling, a new approach for designing the closed-loop system can be proposed. The system with the designed regulators can operate stably in each operation mode and switch smoothly among the multiple operation modes.

Isolated Multiple-Input DC/DC Converter Using Alternative Pulsating Source as Building Cells

Multiple-input dc/dc converters (MICs) serving as the interface of several sources with a load provide the energy to the load simultaneously or individually, which can optimize the utilization of sources, simplify the system structure and reduce the overall cost, so they are attractive for the hybrid renewable power system. In this paper, a novel method using the alternative pulsating sources as the building cells to generate the isolated MICs is proposed. The basic isolated MICs are deduced, and the control strategy is proposed to realize the maximum power transfer, leading to further simplification of the basic isolated MICs. Taking the double-input converter incorporating a half-bridge three-level cell and a full-bridge cell as the example, the operation principles and characteristics of the converter are presented and the power management strategy is introduced. Finally, the theoretical analysis is validated by the simulation and experimental results from a 1000 W prototype.

Interleaved dual-edge modulation scheme for double-input converter to minimize inductor current ripple

In the power system with two or more renewable energy sources, it can simplify the circuit configuration and reduce the cost by using a multiple-input converter instead of several single-input converters. Taking double-input buck converter (DIBC) as the example, this paper discusses the relationship between the inductor current ripple and the phase difference among the drive signals, and an interleaved dual-edge modulation (IDEM) is proposed in order to minimize the ripple. As a result, the filter inductor can be reduced significantly, leading to a fast dynamic response and a high power density. The IDEM can be applied in other double-input converters. A 400 W prototype of a DIBC is fabricated to verify the effectiveness of the IDEM.

Neutral Point Voltage Ripple Suppression for a Three-Phase Four-Wire Inverter With an Independently Controlled Neutral Module

An independently controlled neutral module (ICNM) can be adopted in a three-phase four-wire inverter to form the neutral line and provide the path for zero-sequence current when the loads are unbalanced. The original control objective of the ICNM is to stabilize the neutral point voltage. Since there is a −180° phase jump at the resonant frequency of the neutral inductor and split dc-link capacitors in the system loop gain, system instability may occur. In order to ensure system stability, the inductor current feedback scheme (ICFS) can be incorporated, which is equivalent to introducing a resistor in series with the inductor branch. However, it will lead to increased zero-sequence current flowing through the dc-link capacitors, thus increasing the neutral point voltage ripple. In this paper, three improved control schemes, namely, notch-filter-incorporated inductor current feedback scheme (NF-ICFS), proportional resonant cascaded regulator plus inductor current feedback scheme (PR+ICFS), and neutral current feed-forward plus inductor current feedback scheme (NCFF+ICFS), are proposed, which not only ensure system stability, but also maintain a small neutral point voltage ripple. A 10-kW prototype of the three-phase four-wire inverter with ICNM is built and tested in the laboratory, and the experimental results verify the effectiveness of the proposed control schemes.