Utility-scale PV Power Plant Control PPC Cooperate with EMS(Part II)

Author: Yuyao

2022-10-17 13:41

4、Energy Storage EMS System Operation Mode

4.1、Active Power Control

Active power control is mainly used to set the active power operation mode of EMS, as well as the status and real-time irradiance of each inverter in the photovoltaic power station corresponding to the integrated energy storage power station, issue active power control instructions to the energy storage unit, and dynamically allocate the active power output of each energy storage unit. The active power control function can be enabled and disabled separately through the console interface. When enabled, the active power control mode can be selected into three modes: dispatching, centralized control or local control. In the dispatching mode, the active power target value is the dispatching command value issued by the superior PPC system; In the centralized control mode, the active target value is the command value issued by the superior centralized control center; In the local mode, the active target value is the command value manually entered by the user in the control interface.

The active power control algorithm mainly includes the following contents: real-time dispatching control, peak shaving and valley filling control, remote and local control, power prediction auxiliary control, change rate control, black start control, etc.

4.1.1、Real time scheduling Control

The energy storage EMS supports receiving and dispatching the control target value sent by the multi energy cooperative controller of PPC master station or local PPC sub station in real time. According to the control target value received in real time, the power target is allocated to each energy storage control unit based on the optimal allocation strategy, so as to realize the real-time control of PCC grid connection point of energy storage system.

The real-time dispatching control distributes the active power command to the PCS equipment according to the health priority of the energy storage unit. The determinants of the health of energy storage unit include: working condition of energy storage unit, theoretical power generation capacity, actual follow-up capacity, etc. In the program, the power allocation priority of each energy storage unit will be comprehensively estimated according to the real-time data acquisition, state estimation storage data and user settings, and then the power output will be allocated. The energy storage unit with high priority is allocated a larger power target value share, and the remaining power target value share is allocated to the energy storage unit with low priority.

4.1.2、Peak shaving and valley filling control

Based on the peak shaving and valley filling strategy, the energy storage EMS system sets the time strategy, SOC strategy, charge and discharge strategy, etc. Without affecting the PPC regulation target and the active power processing of the inverter has surplus, it regularly schedules the battery charge and discharge control with 1 minute as the control interval, which makes full use of the surplus wind power generation and responds to the auxiliary services of the power grid at the same time. When the function is enabled on the power side, the control priority is lower than the real-time scheduling control.

4.1.3、Remote Local Control

EMS supports remote and local control, that is, it accepts the manual input of command value by local operators in the control interface for control; Centralized control means that the regional centralized control center issues control values, which are automatically executed locally.

During EMS remote control, receive and dispatch PPC command in real time or operate according to the dispatching command of sub station PPC controller under the planning curve.

During EMS local control, the energy storage system operates normally according to the local operation strategy set by EMS and does not participate in power grid PPC regulation.

4.1.4、Power predictive auxiliary control

This function is applicable to the operation scenario of photovoltaic power station with power prediction data. For short-term or ultra short-term power prediction data, combined with the actual output of the current section of photovoltaic power station, through the two-way adjustment capacity of energy storage battery, reduce the deviation of power prediction assessment and improve the operation income of photovoltaic power station.

4.1.5、Rate of change Control

The change rate control of energy storage power station is mainly for new energy power station, which is mainly used to solve the output instability of photovoltaic and other new energy power generation systems. Through the set change rate index, the energy storage system provides a charge discharge control strategy opposite to the output deviation in case of abnormal output fluctuation of photovoltaic power station, so as to alleviate the output fluctuation of new energy power station and make the change of active power of new energy power station meet the requirements of safe and stable operation of power system.

Power grid companies in some provinces in China have requirements for the change rate of new energy power stations. EMS regulates the stable change of active power of energy storage power stations to avoid short-term impact on the power grid. The control objectives include 1-minute change rate and 10-minute change rate. The change rate of active power can be adjusted by configuring energy storage batteries with an installed capacity of 10%.

The change rate control of energy storage power station is mainly for new energy power station, which is mainly used to solve the output instability of photovoltaic and other new energy power generation systems. Through the set change rate index, the energy storage system provides a charge discharge control strategy opposite to the output deviation in case of abnormal output fluctuation of photovoltaic power station, so as to alleviate the output fluctuation of new energy power station and make the change of active power of new energy power station meet the requirements of safe and stable operation of power system.

Power grid companies in some provinces in China have requirements for the change rate of new energy power stations. EMS regulates the stable change of active power of energy storage power stations to avoid short-term impact on the power grid. The control objectives include 1-minute change rate and 10-minute change rate. The change rate of active power can be adjusted by configuring energy storage batteries with an installed capacity of 10%

4.1.6、Black Start Control

For energy storage power station, when the whole system is shut down due to fault, it does not rely on the help of large power grid and is started by the generator set with self starting ability in the system. Facing the booster station system, the energy storage system provides stable power supply for the start-up and operation of inverter, gas turbine, thermal power unit and other equipment through the effective control of load switch, bus voltage and power frequency, so as to realize the power supply for important loads in the region.

For energy storage power station, when the whole system is shut down due to fault, it does not rely on the help of large power grid and is started by the generator set with self starting ability in the system. Facing the booster station system, the energy storage system provides stable power supply for the start-up and operation of inverter, gas turbine, thermal power unit and other equipment through the effective control of load switch, bus voltage and power frequency, so as to realize the power supply for important loads in the region.

 

4.2 Reactive Power Control

Reactive power control is independent of active power control, and reactive power control function can be enabled and disabled separately. After enabling, the reactive power control mode can be selected as receiving dispatching mode or manual setting mode. In the receiving dispatching mode, the target value of reactive power (voltage or power factor) is the command value issued by the superior PPC system; In manual setting mode, the target value of reactive power (voltage or power factor) is the command value manually entered by the user in the control interface.

Similar to active power control, EMS also supports single energy storage unit control when controlling reactive power. The user can set the single energy storage unit into three types: automatic control, free power generation and manual setting. EMS will automatically assign reactive power command to the automatically controlled energy storage unit; EMS will not control reactive power of energy storage unit for free power generation; For the energy storage unit with manual setting value, EMS will carry out reactive power control according to the instruction of manual setting value.

4.2.1 Reactive Power Control

The working mode is similar to the real-time scheduling mode of active power control. The energy storage EMS supports receiving and scheduling the control target value sent by PPC sub station or multi energy cooperative controller in real time. According to the control target value received in real time, the reactive power target is allocated to each energy storage control unit based on the optimal allocation strategy.

4.2.2 Reactive Power Planning Curve Following

The working logic is similar to the peak shaving and valley filling mode of active power, that is, in the reactive power scenario, the reactive power is controlled according to the preset reactive power operation work plan curve, and the system will automatically execute the preset reactive power target value according to the time.

4.2.3 Remote Local Control

Similar to active power control, reactive power control supports the control mode of following the dispatching command value in real time, and the actual reactive power changes according to the change of dispatching command value; At the same time, reactive power control also supports local manual setting.

4.2.4 Power Factor/Voltage Control

In the reactive power control scenario, the operation mode can select the power factor or voltage mode, calculate the reactive power demand under this mode, and carry out object control according to the reactive power distribution mode to make the whole field control target reach the set power factor or voltage setting target value.

4.2.5 Voltage Droop Control

EMS adjusts the actual reactive power output of the energy storage station according to the current actual voltage value of the energy storage station and the set Vdrop curve, so as to achieve the purpose of reverse voltage regulation.

 

5、PPC coordinate EMS Internet Topology Structure

With the continuous increase of photovoltaic

                                                                                   

With the continuous increase of photovoltaic power generation capacity, the phenomenon of large power fluctuation in the power grid system caused by the intermittence and instability of new energy power generation is extremely unfriendly to the power grid. The new energy power generation project supporting a certain capacity of energy storage can greatly alleviate the current situation of intermittence and instability of new energy power generation. Under the regulation of power grid dispatching through PPC and EMS, Energy storage system can provide fast energy buffer for power grid, so as to keep the voltage and frequency of power grid stable. Therefore, the role of energy storage technology in microgrid is becoming increasingly prominent.

Please click here to read Part I of this article.

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