The integrated operation and design of the DC distribution systems combined wind turbine and photovoltaic power systems Shin,Soo Cheol Department of Electrical and Computer Engineering Sungkyunkwan University

( Abstract )
 Because DC distribution system has more numerous advantages than AC distribution system, aircraft and ships have been applied to the DC distribution system. because consumer and office equipment consisting of the electronic systems use DC power, the power can be easily supplied to the load using simple power conversion system. especially, high efficiency power transmission is possible because the power conversion step supplying the power to the electronic load is small in DC distribution system. however, due to the power grid of land consisting of AC power grid, most of the land power system are applied to the AC distribution system except for special cases such as IDC(Internet Data Center) and etc. In this paper, design and control method of DC distribution system which can be connected with AC distribution system of land is proposed. In addition, it proved that the connection of renewable energy can be more easily connected with DC distribution system than AC distribution system by connecting DC distribution grid with renewable energy such as wind power of PMSG type and photovoltaic system through the simulation and experiment. Three-phase AC/DC PWM converter can supply DC 380[V] to the DC bus in case that AC power distribution voltage is AC 220[V]. however, because the secondary side of the transformer consists of Y connection and 380[V] in most of the commercial building, in order to configure a DC distribution system, it is boosted to DC 700[V] using three-phase AC/DC PWM converter. And then, the DC distribution system of DC 380[V] was constructed using non-isolated bidirectional DC/DC converter. In this paper, considering the stable operation of DC distribution system, three control algorithm and a topology of DC distribution system were proposed. And a thermal model was proposed to simulate the heat of the semiconductor in PSIM software. Also, it proved that generated power can be easily connected to DC distribution grid by connecting DC distribution system with renewable distributed generation systems such as wind power and photovoltaic system. First, parallel control method is proposed for 50[kW] voltage source DC/DC power converter. Traditionally, parallel operation of two converters has been used to method which commonly combined voltage source converter with current source converter. The reason is that voltage source power converter has very small impedance to the output capacitor. Therefore, excessive inrush current occur and it cause destruction on the power converters when two voltage source converters are connected each other. Also, traditionally parallel operation method of combining voltage source converter with current source converter has disadvantages of a stop for whole systems when voltage source converter has broken. The reason is that voltage source converter is only possible to control the voltage of DC bus. Also, voltage and current source converter have to be designed respectively to operate parallel systems. In order to solve this problem, this paper proposed control algorithm that can connect two voltage source converters in parallel. Hardware parameters of two voltage source converter are equally designed and it is separated to main system and slave system in control aspects. The main system control the voltage of DC bus and slave system performs power control to share loads of the main system. Because the hardware is equal, slave system is able to perform the role of the main controller when the main system is broken. Therefore, the proposed method has advantage of improved reliability. Second, in DC distribution system, bidirectional DC/DC converter is unnecessary in case that AC input voltage is 220[Vrms]. The reason is that three-phase AC/DC PWM converter is available to supply 380[V] to DC link. Therefore, this paper proposed a novel multi-parallel control algorithm of voltage source three-phase AC/DC PWM converter having the same structure in DC distribution system with three-phase AC/DC PWM converter only.
FULL THESIS:
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