A Control Method of a Small-Scale DC Power System Including Distributed Generators
A Control Method of a Small-Scale DC Power System Including Distributed Generators
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一种包括分布式发电机的小型直流电力系统的控制方法
DOI：
10.1541/ieejias.126.1236
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
H. Akagi
中科院分区：
文献类型：
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作者：
Youichi Ito;Zhongqing Yang;H. Akagi
本文描述了一种连接到直流微电网的多台分布式发电机的控制方法。该直流微电网系统需要建设专门的直流输电线路。然而，如果其安装地点仅限于建筑物、工厂和小城市或城镇等局部区域，则这不会对直流电网系统所连接的交流电网系统造成大的故障。与交流电网系统相比，直流电网系统具有以下优点： 1）连接到直流电网的每台发电机可以轻松地协同运行，因为它仅控制直流电网电压。 2）当交流电网系统出现异常或故障情况时，直流电网系统与交流电网系统断开，然后切换到独立运行，将产生的电力供应给连接到直流电网的负载。 3）仅需单个交流并网逆变单元，可降低系统成本和损耗。图 1 显示了本文考虑的直流电网系统。该系统由以下五个生成和控制单元组成；太阳能电池发电单元、风力发电单元、电池储能控制单元、飞轮均平单元、交流并网逆变单元。在系统可靠性、可扩展性和可维护性方面，这些连接到直流电网的功率单元需要满足以下要求： 1）这些单元可以连接到有源直流电网或从有源直流电网断开。 2）其他不同额定功率的发电和控制单元在不久的将来可以轻松连接到直流电网。 3）现有单元之间不进行信号或数据通信。为了满足这些需求，所提出的控制方法可以通过仅检测直流电网电压作为公共信息来实现。考虑以下因素； 1）连接到直流电网的单元之间的环流，以及2）交流电网逆变单元和电池单元之间的协同控制。当单元之间存在电压差时，循环电流可能在单元之间流动。为了抑制环流，该方法关注每个单元的直流侧输出特性。太阳能电池和风力涡轮机单元作为电流源进行控制。控制交流电网逆变器和电池单元以向直流侧提供等效阻抗。这些单元中的输出直流电流和直流电网电压之间的关系取决于等效阻抗。然而，交流并网逆变器单元和电池单元可以分配它们的输出功率。最好从交流电网系统中获取尽可能小的电力。然后，交流电网逆变单元和电池单元的等效电阻特性根据直流电网电压而变化，如图2所示。10kW原型系统的实验结果验证了所提出控制方法的有效性和有效性。下面分两种情况进行说明；情况1：当太阳能发电机组的发电量逐渐增加时，由于储能单元的等效电阻小于交流电网逆变单元的等效电阻，电池单元继续对该电力进行充电。当电池单元达到充满电状态后，交流电网逆变单元将太阳能电池单元产生的电力提供给交流电网。情况2：当交流电网出现故障时，交流电网逆变器检测到故障并停止15秒。剩余功率保留在直流电网中。太阳能电池单元减少了发电量。电池单元向直流电网供电。此时，飞轮单元对突然的功率变化进行补偿。随着太阳能电池单元产生的电力增加，电池单元馈送的电力减少。
This paper describes a control method of multiple distribution power generators connected to a dc micro-grid. This dc micro-grid system needs to construct a special dc transmission line. However, if its installation place is limited to a local area such as a building, a factory and a small city or town, this will not cause a big fault to the ac grid system to which the dc grid system is connected. The dc grid system takes the following advantages over the ac grid system: 1) Each power generator connected to the dc gird can be easily operated cooperatively because it controls only the dc-grid voltage. 2) When the ac grid system falls into abnormal or fault conditions, the dc-grid system is disconnected from the ac-grid system, and then it is switched to stand-alone operation in which the generated power is supplied to the loads connected to the dc grid. 3) The system cost and loss can be reduced because only a single ac-grid-connected inverter unit is needed. Fig. 1 shows a dc grid system considered in this paper. The system consists of the following five generation and control units; a solar-cell generation unit, a wind-turbine generation unit, a battery energy-storage control unit, a flywheel power-leveling unit, and an ac grid-connected inverter unit. In terms of system reliability, extendibility and maintainability, the followings are required for these power units connected to the dc grid: 1) These units can be connected to, or disconnected from, the active dc gird. 2) Other generation and control units with different power ratings can be easily connected to the dc gird in the near future. 3) Neither signal nor data communication is made among the existing units. To meet these demands, the proposed control method can be achieved by detecting only the dc-grid voltage as common information. The followings are taken into account; 1) the circulating current among the units connected to the dc gird, and 2) cooperative control between the ac-grid inverter unit and the battery unit. The circulating current may flow among the units when a voltage difference exists among them. To suppress the circulating current, the proposed method pays attention to the dc-side output characteristic of each unit. The solar-cell and wind-turbine units are controlled as current sources. The ac-grid inverter and battery units are controlled to give an equivalent impedance to the dc side. The relation between the output dc current and the dc-grid voltage in these units depends on the equivalent impedance. However, the ac-gird inverter unit and the battery unit can assign their output power. It is better to take as small power as possible from the ac-grid system. Then, the equivalent resistance characteristics in the ac-grid inverter unit and the battery unit are changeable according to the dc-gird voltage, as shown in Fig. 2. Experimental results from a 10-kW prototype system verify the validity and effectiveness of the proposed control method. Two cases are demonstrates as follows; Case 1: When the generation power from the solar generator unit increases gradually, the battery unit continues charging this power because the equivalent resistance of the storage unit is smaller than that of the ac grid inverter unit. After the battery unit reaches a fully-charged condition, the ac-gird inverter unit supplies the power generated by the solar cell unit to the ac gird. Case 2: When the ac grid falls in fault, the ac grid inverter detects the fault and is stopped for 15 sec. The surplus power remains in the dc gird. The solar-cell unit reduces the generated power. The battery unit supplies the power to the dc gird. At this time, the flywheel unit compensates for a sudden power change. As the power generated by the solar-cell unit increases, the power fed by the battery unit decreases.