Input-Series Output-Parallel (ISOP) connected Dual-Active-Bridges (DABs) form an interesting topology which enable step down MVDC to LVDC by employing medium frequency transformers. Si-IGBT semiconductor devices are commonly used in power distribution grid applications such as Smart Transformers (STs) where both MVDC and LVDC energy ports can be presented. In this paper, Si-IGBT semiconductor loss components such as conduction, switching and gate driver losses behavior are theoretically evaluated in a wide range of blocking voltage, switching frequency and phase-shift angle of DAB converters. In addition, gate driver losses are approximated as a continuous function of blocking voltage based on available datasheets. The behavior of the loss components are analyzed for two 50 and 500 kW ISOP-DAB converters where DC voltage ratio is 10 kV/400V.

https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/macau_derivate_00002403/Theoretical Evaluation of Semiconductor Loss.pdf

Theoretical Evaluation of Semiconductor Loss Components Behavior in ISOP-DAB Converters

A novel input-series output-series high gain Boost converter was proposed in this paper.Operation principle and property of this converter were analyzed.The new topology was composed of two identical high gain subtopologies with input-series and output-series connection.As the Cf1 and Cf2,the new topology not only had high voltage gain,but also automatically evenly could share current without any sensing when the duty cycle was greater than or equal to 0.5.Compared with the traditional two phase interleaved Boost converter,the ripple of the inductor current,the ripple of the input current and the voltage stress of the switches were reduced because of the double-series structure of the new topology.Consequently,the new topology is very suitable for the application (for example,the fuel cell power system) in which it has low input voltage but high output voltage.Finally,the experiment was built to verify the theoretical analysis.

Input-series Output-series High Gain Boost Converter

A high ratio DC/DC converter for medium voltage DC distribution is put forward first. The DC/DC converter is built with state-of-the-art Silicon Carbide (SiC) Insulated Gate Bipolar Transistor (IGBT). The DC/DC converter is made up of a two-stage structure, in which the high-voltage stage is a three-level neutral-point clamped (NPC) circuit to reduce the breakdown voltage of the switches. Low-voltage stage uses two-level VSC circuit. These two stages are connected by a high-frequency transformer to improve utilization of the core material, while it can also help reduce the size of DC/DC converter; The control schemes for different stages of the DC/DC converter are designed in detail, the effectiveness of which is proved by theoretical analysis. Then simulation based on PSCAD is carried out according to different load condition and power flow direction to verify the dynamic performance of whole system. The simulation results show that the DC/DC converter proposed in this paper can not only realize bidirectional power flow and high conversion ratio (10kV / 400V) of energy, but also have good dynamic performance when the load changes on the low-voltage side, which can well satisfy the needs of DC power distribution.

A SiC IGBT-Based DC/DC Converter for Medium-Voltage DC Distribution

The electric load integrated in DC micro-grid is typically with the property of constant power which demonstrates negative resistor characteristics and can be a challenge for DC micro-grid stability control. Based on a large capacity DC micro-grid with variety of sources and loads and converters, the presented paper established an equivalent circuit model of the DC micro-grid system with droop control and discussed the stability issues of the system. Considering the nonlinearity of the system, this paper firstly determined the stability of the system equilibrium points. Secondly, the influence of constant power load and system parameters on the stability of the system was analyzed, and the load carrying capacity of the system under different system parameters was quantified and verified by simulation. Finally, according to the results of the stabilization mechanism analysis, the selection of control system parameters in the planning and design is discussed, and the stability control strategy of DC micro-grid was proposed from the system level combining with the hierarchical control of micro-grid, and the simulation and experimental verification were carried out.

Stability Control Strategy for DC Micro-grid Considering Constant Power Load

The invention belongs to the field of DC micro-grids, and in particular to a DC micro-grid isolated island detection method based on an additional impedance The method includes the following steps: implementing shunt by connecting an additional impedance in parallel at an inverter port, using a microcomputer to analyze a branch current which is connected to a PCC and the changes to the voltage on the additional impedance so as to implement the detection of the isolated island and address the problems of the effects of isolated island existed in an AC power distribution grid if a networked circuit breaker is cut off due to breakdown or maintenance, etc According to the invention, the method combines the advantages of active measurement methods and passive measurement methods, realizes detection through the additional impedance, and is noticeably better than passive detection methods which directly measure changes to electrical quantities at an inverter exit The method, on the basis of the impact of the changes to network topology on the electrical quantities, obviates the need for changing the working methods of the inverter and does not impact the output current waveform of the inverter in the state of grid-connection operation, such that the method has the advantages that are absent in the active frequency shift and power interference strategy in the active measurement

Wenqiang Xie

Papers

A SiC IGBT-Based DC/DC Converter for Medium-Voltage DC Distribution

Stability Control Strategy for DC Micro-grid Considering Constant Power Load

DC micro-grid isolated island detection method based on additional impedance