Overview

GPM PPC acts as a master to drive all photovoltaic (PV) devices in a plant.The GPM PPC coordinates the local controls of the (PV) inverters, to achieve the desired setpoints at the point of interconnection (POI).

The GPM PPC is an overall control that allows the plant to be friendlier with the grid and meet the requirements imposed by the Transmission System Operator (TSO). It implements a closed-loop control in real time, which allows sending fast and refreshed commands to the inverters, to achieve the setpoints. The data acquisition and the sending of commands relies on the RTU SmartBridge (RTUSMB) system that connects the GPM PPC and the drivers of the inverters.

The GPM PPC reads the measurement from the POI and sends orders (active and reactive setpoints) to all inverters or FACTS. If there are capacitor banks present in the plants, it sends them orders to connect or disconnect. Then, the inverters perform their own controls to follow their master (GPM PPC) orders.
Important: In the case of fault ride through (FRT), inverters and FACTS omit the orders from the GPM PPC, because grid codes require rapid response during fault events and communication delays would lead the PV plant to FRT requirement non-compliance.

Structure

The GPM PPC contains two main plant control structures, one for active power control and one for reactive power control. Once GPM PPC calculates the commands to accomplish the enabled setpoints or controls, it sends them to the RTUSMB, which adapts them at each inverter and STATCOM.

The GPM PPC controls power generation and output by measuring actual power production, comparing it to the expected power setpoint, and sending a new setpoint to correct any deviations.

Figure 1. Typical large-scale PV plant layout including the proposed power plant control schemes

Commands

The GPM PPC delivers the commands to the SMB, based on the measurements of point of interconnection (POI). The SMB distributes the commands of active and reactive power in the whole plant. This guarantees the correct active and reactive power values to fulfill the requirements in the POI.

The plant operator and the system operator can send setpoints and enable or disable controls by means the PV SCADA or the Substation RTU, respectively.

After sending the endpoints, the GPM PPC uses the measurements of the POI, calculates and delivers the commands needed to fulfill the necessities, lowering or augmenting the active and reactive power at the POI. The command is unique to all inverters, enabling different inverters ratings and cloud coverage conditions, as the GPM PPC readjusts the percentage commands to meet the requirements.

The GPM PPC can control not only inverters, but all devices in a plant (STATCOMS, battery inverters and capacitor banks).