独立微电网有功功率自主与协调控制

为了实现微电网内各单元的协调控制,针对独立微电网设计了有功功率自主与协调控制方法。该方法基于分层控制结构,1次调整由风力分布式发电单元、光伏分布式发电单元、储能单元完成,根据电压-有功功率控制曲线自主控制。2次调整由微电网控制器完成,对风力分布式发电单元、光伏分布式发电单元、储能单元及负荷单元协调控制,实时监测储能单元的电压、有功功率,如果在2次调整允许的波动范围内,微电网控制器不下发控制指令;否则,电压越限时将储能该时刻的瞬时功率作为功率基准值实现工作曲线的平移,功率越限时,微电网控制器通过改变间歇性分布式发电单元的发电功率及投入或切除负荷完成2次调整。并建立了微电网状态转换协调控制模型,更加适用于计算机处理和工程化的实现。通过Matlab算例验证了所提出控制方法的有效性。

Autonomous and coordinated control of active power in standalone microgrid

Abstract: Usually, a microgrid is connected to a power grid as a complement that enhances the flexibility and safety of a system. However, in some cases, for example grid faults, remote rural areas, or islands away from the continent, the microgrid has to operate independently. Because of a large number of power electronic components in the microgrid, the fluctuant distributed generation, and the bidirectional power flow, the unified coordination control of the units in each case is very important for the security and stability in the operation of each standalone microgrid. Aiming at the standalone microgrid, an autonomous and coordinated control method is designed in the paper. The primary adjustment is an independent local control strategy that allows each DG unit to operate autonomously. Also, for reliability reasons, communication is avoided in the primary adjustment, similar to the conventional grid control. Hence, it is based only on local measurements, being conceived as a local control strategy. With respect to the primary adjustment, in islanded mode, the DG units need to dispatch their power to enable power sharing and voltage control, thereby ensuring a stable microgrid operation. According to the voltage and active power control curve in autonomous control, the primary adjustment is completed by wind unit controller, solar unit controller, and energy storage controller. For the fast response of energy storage devices and large random fluctuations of intermittently distributed generations in the standalone microgrid without any continuous power supply, the voltage-frequency control method is adopted in energy storage devices to allocate automatically and absorb the transient imbalance power of the system during real time operating. Meanwhile, the PQ control method is adopted in intermittently distributed generations. The secondary adjustment is completed by the microgrid controller. According to the upper and lower limits of voltage and current of energy storage, the work space of the V/f unit is divided into areas by microgrid controller for diffident suitable control. Firstly, in the stable area, such as the area 1, voltage and active power of energy storage is in bounds so no control is carried out by the secondary adjustment. Secondly, in the voltage adjustment area, such as areas 2, 3, 6, 7, 8, 9, the power reference of energy storage is replaced by a frozen output power of itself to translate droop curve, meanwhile intermittently distributed generation are at the maximum power output. Thirdly, in the power control area, if the discharge current is over the upper bound, such as areas 4, 6, 7, the procedure is performed as follows: 1) intermittently distributed generations increase power output to the maximum, 2) loading relief according to importance and power matching. If the charge current of energy storage is less than the lower bound, such as areas 5, 8, 9, the procedure is performed as follows: 1) increased loads according to importance and power matching until full loads, 2) according to priority of intermittently distributed generations, reducing the active power output. In order to make the microgrid controller achieve better management of working space, a mathematical model based on finite state machine is established for computer processing and engineering. The proposed control method is validated in simulated examples and show that microgrids can undertake power fluctuation of loads and intermittently distributed generations to achieve active power balance. The first and secondary adjustment not only realized coordinated control of wind, solar, and energy storage units to provide a valuable reference for optimization control of units, but also ensured security and stability of the standalone microgrid while also realizing hierarchical control idea.