The Solid State Transformer (SST) is an attractive solution for highly flexible, cost-effective, compact and efficient power transfer among different grids. Furthermore, a three-port topology is proven as a suitable solution to integrate energy storage resources, the key functionality of emerging SST concept. Among other alternatives, the resonant LLC series resonant converter (SRC) is the cost-effective solution to implement the DC-transformer functionality, which is a core part of the SST. This paper addresses the power sharing characteristics and the zero-voltage switching (ZVS) conditions of a galvanically isolated three-port SRC, operated in DC-transformer mode. A mathematical model, which effectively decouples principal from circulating currents and power flows, is proposed and developed. This new mathematical framework eases the analysis; and reveals a constant power sharing characteristic tightly dominated by the resonant tank parameters even though some degrees of freedom are allowed thanks to the introduction of a differential voltage at the input terminals. Subsequently, design aspects and assessments of working operation conditions are also reported. The accuracy of the proposed model is verified by experimental validation on a lab-scale prototype.

In order to improve the performance of dc-dc converter circuit in renewable energy power generation system, and overcome the problems of input current discontinuity and high inrush current in traditional Y-source converter, an improved Y-source dc-dc boost converter topology is presented in this paper. The voltage gain formula is derived by analyzing the topology and operating principle of the converter circuit. The proposed circuit topology inherits all the benefits of the existing Y-source converter and has several more advantages, including the higher voltage gain, continuous input current and small inrush current. The simulation and the experiments based on the prototype are performed. And the simulation and experimental results verify the rationality and superiority of the circuit topology.

The dual-active-bridge (DAB) converter attracts more and more attentions due to its ability of bidirectional power transmission and high conversion efficiency. The adoption of high-frequency transformer provides galvanic isolation, but also brings the possibility of dc bias. In this paper, the causes of dc bias have been analyzed and relevant calculation methods are derived in details. With the calculation methods, the dc bias magnetizing current can be predicted considering the inconsistency of semiconductor switches and driver signals. In other words, if the maximum permitted dc bias of the transformer is given, the range of the inconsistency of semiconductor switches and driver signals can be obtained which helps guide the selection of semiconductor devices and design of the transformer. Therefore, extra flux balancing method can be avoided and the overall cost and volume will be further reduced. Additionally, simulation and experimental results show great agreement with the theoretical analysis.

The hardware-in-the-loop (HIL) simulation is an effective method to verify the overall function of the flexible HVDC transmission control and protection device. With this method, debugging the control and protection device can make the system run safely and stably after being put into operation. Therefore, a hardware-in-the-loop simulation platform modular multilevel converter (MMC) based on RT-LAB is established in this paper. Data merging between a converter valve control system and the real-time simulator is realized by high-speed optical fiber communication protocol conversion chassis, and the high-speed communication interface is designed to meet the requirements of the communication rate. Aiming at the control performance of the physical device, the test scheme is designed, and the test methods of voltage balance control and circulating current suppression are proposed. The closed-loop test of control and protection device is carried out by the active power step and AC/DC fault test. The above test verifies the validity of the HIL simulation platform of the MMC and the rationality of the testing scheme, and can meet the performance testing requirements of the control and protection device.

In this paper, an analytical small-signal model applied for hybrid hysteretic charge (HHC) control has been proposed and analyzed with the advantages over direct frequency control (DFC). Based on the approach of extended describing function method and average concept, for the first time, the systematical analytical open-loop transfer functions from control to output, input to output, output impedance and the closed-loop transfer functions of the overall loop, audio susceptibility and output impedance are proposed and verified through simulation. Additionally, some important physical insights have been extracted, analyzed and verified. Finally, the experiments on a design example of 12 V DC & 12 A output power are conducted and verified. It shows that the calculations match well with the results from both the simulation and experiment, which reveals the proposed analytical transfer functions are very useful for the practical power design to achieve good prediction result.

Comparing to the traditional synchronous or induction electric machines, the doubly-fed induction machine (DFIM) with the partially rated converter is a good solution for a shaft generator system which normally operates within a relatively small adjustable speed range. However, the application of DFIM is limited in the real systems due to the lack of self-start capability under the power take me home (PTH) mode when the main engine fails. To overcome this problem, an approach is proposed in this paper. The basic idea is first to start the machine in the induction machine (IM) mode feeding from the ship-borne power grid (SPG) and then to switch over into the DFIM mode when the speed reaches its normal speed range. The hardware scheme, start procedure and control algorithm of the start approach are presented in the paper. Simulation and experimental studies were carried out to validate the feasibility and effectiveness of the approach.

Distributed Photovoltaic Generation (DPVG) systems have become more important in recent years because of energy pinch and air pollution. Grid-tied inverters, as the indispensable parts of the DPVG systems, have drawn a lot of research attentions. Among various constructors, the Aalborg inverter was proposed as a candidate for the interface between the PV arrays and the power grid for some potential advantages, such as the wide range of input DC voltages, high efficiency, low cost and no leakage current. For a conventional Aalborg inverter, however, in order to gain a symmetrical grid-injected current, when the input DC voltages generated by the PV arrays are not equal, part of the input DC energy has to be discarded, which will reduce the conversion efficiency of the whole system. In this paper, a modified Aalborg inverter with a single input DC source is proposed to extract the maximum DC energy of PV arrays. The operating principle is illustrated via equivalent circuits. The control strategy is designed to balance the capacitor voltages and smooth the grid-injected current. A 110 V/50 Hz/800 W prototype has been built to verify the validity of the proposed inverter together with the effectiveness of the control strategy.

Aims to complete the test of the International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) converter system, and to meet future continuous upgrading needs of a modern industrial power system and scientific research, direct current (DC) high-power test facility of Hefei Institutes of Physics Science, Chinese Academy of Sciences (CASHIPS) is built in 2011. As the largest DC high-power test facility in China, the rated steady state DC current is 120 kA and the pulse peak current is 500 kA. Four thyristor-based AC/DC converter modules are paralleled to handle this huge current. In May 2017, 15 testing items are accredited by the China National Accreditation Service (CNAS) for Conformity Assessment. Up to now, the test for 17 devices of 16 companies and manufacturers in the world have been completed. In this paper, the topology and the control of DC High-Power test facility are presented. In addition, the testing capability and the completed tests of DC high-power test facility are illustrated.