柔性中压直流配电网电压控制的研究

发布时间：2018-05-25 16:30

本文选题：直流配电网 + 运行方式　；参考：《西安理工大学》2017年硕士论文

【摘要】：中压直流配电网具有很大的应用前景,既能为高压输电向配电的发展提供并网接口,或通过AC/DC变换隔离交流输配电系统的电压跌落、为交流电网补偿无功功率;又能为大容量储能系统、光伏系统和低压直流配电网提供并网接口,减少电压变换环节,提高系统可靠性。但中压直流配电网结构复杂,存在多个端口、多个电压等级和多种运行方式,给其电压控制带来了困难。如何确定合适的电压控制策略,在中压直流配电网多种运行方式下,保证直流母线电压的稳定是亟需解决的问题。本文对柔性中压直流配电网的电压控制进行研究,以两端型直流配电网为研究对象,中压直流母线通过两侧电压源换流器(voltage source converter,VSC)与交流电网相连,通过3个基于输入串联输出并联(input-series-output-parallel,ISOP)高频隔离双主动全桥(dual active bridge,DAB)变换器的直流固态变压器(DC solid state transformer,DCSST)分别为光伏系统、储能系统和低压直流配电网提供并网接口。首先分析了两端直流配电网的运行方式及各接口设备在不同运行方式下的控制模式,分别设计了 VSC的功率、电压控制器、光伏系统的MPPT控制器、储能系统的恒功率充放电控制、定电压控制器和DCSST的电压电流双闭环控制、高压串联侧均压控制器。其次,针对传统借鉴多端直流输电的柔性中压直流配电网的电压控制,无法适应柔性中压直流配电网多种运行方式的变化,提出了改进的电压裕度控制策略,该策略包括对主站VSC、从站VSC和次从站DCSST的控制。主站VSC采用定直流电压控制,从站VSC作为备用站采用电压裕度控制,正常情况下工作在定功率控制模式下,主站VSC退出运行时,具有接替主站控制系统中压侧电压的能力。次从站DCSST作为备用站采用电压裕度控制,正常情况下工作在定低压直流电压控制模式,电压失控时,具有稳定中压直流电压3能力,动作优先级低于从站VSC。最后,在PSCAD/EMTDC下搭建了采用该控制策略的两端柔性中压直流配电网在双端供电、单端供电、双端隔离和孤岛运行四种运行方式下的仿真模型,仿真结果表明该电压裕度控制下的直流配电网在运行方式切换过程中,电压能很好地保持稳定,并降低了系统对于通信的依赖。
[Abstract]:The medium voltage DC distribution network has a great application prospect. It can provide grid-connected interface for the development of high voltage transmission and distribution, or isolate voltage drop of AC transmission and distribution system by AC/DC transform, and compensate reactive power for AC power network. It can also provide grid-connected interface for large capacity energy storage system, photovoltaic system and low-voltage DC distribution network, reduce voltage conversion link and improve system reliability. However, the structure of medium voltage DC distribution network is complex, there are many ports, multiple voltage levels and various operation modes, which brings difficulties to voltage control. How to determine the appropriate voltage control strategy and how to ensure the stability of DC bus voltage is an urgent problem under the operation mode of medium voltage DC distribution network. In this paper, the voltage control of the flexible medium voltage DC distribution network is studied. The middle voltage DC bus is connected to the AC network by voltage source converter. Three DC solid-state transformer DC solid state transformers-DCSSTs based on three input series output parallel series parallel active converters are used for photovoltaic system, energy storage system and low-voltage direct current distribution network respectively to provide grid-connected interface. Firstly, the operation mode of DC distribution network at both ends and the control mode of each interface device under different operation modes are analyzed. The power and voltage controllers of VSC and the MPPT controller of photovoltaic system are designed, respectively. The constant power charge and discharge control, the constant voltage controller, the voltage and current double closed loop control of DCSST, and the voltage sharing controller of the high voltage series side are presented in this paper. Secondly, in view of the traditional voltage control of flexible medium voltage DC distribution network based on multi-terminal DC transmission, which can not adapt to the variety of operation mode of flexible medium voltage DC distribution network, an improved voltage margin control strategy is proposed. The strategy includes the control of master station VSC, slave station VSC and secondary station DCSST. The main station VSC adopts the constant DC voltage control, the slave station VSC uses the voltage margin control as the backup station. Under the normal condition, the master station VSC can replace the voltage side voltage of the master station control system when it exits operation in the fixed power control mode. The secondary slave station (DCSST) uses voltage margin control as the backup station, and normally works in the constant low voltage DC voltage control mode. When the voltage is out of control, the secondary slave station has the ability of stabilizing the middle voltage DC voltage, and the priority of operation is lower than that of the slave station. Finally, the simulation model of the flexible medium voltage DC distribution network with this control strategy is built under the four operation modes of double end power supply, single end power supply, double end isolation and island operation. The simulation results show that the voltage of the DC distribution network controlled by the voltage margin can be kept stable in the switching mode and the dependence of the system on communication is reduced.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1;TM714.2

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