PPC – Power Plant Controller

2. Normative References

The following normative references are applicable for Power Plant Controller (PPC) modelling, simulation, and grid compliance studies.

• Central Electricity Authority (CEA), Technical Standards for Connectivity to the Grid Regulations, 2019, including subsequent amendments.
• IEEE Std 2800™-2022, IEEE Standard for Interconnection and Interoperability of Inverter-Based Resources with Associated Transmission Electric Power Systems.

3. Introduction

Power Plant Controller helps maintain overall system stability in solar and wind power plants. The control process is largely automated rather than manual, enabling centralized monitoring and regulation of all signals across the entire power plant. The PPC manages not only key parameters such as frequency, voltage, and active power, but also supervises and coordinates all operational parameters of the plant.

4. Analysis Objectives

The objectives of the Power Plant Controller (PPC) analysis are as follows:

1. Verification of plant-level active and reactive power control through the PPC.
2. Assessment of steady-state voltage, frequency, and real and reactive power response at the Point of Interconnection (POI).
3. Evaluation of active power ramp-rate limiting in accordance with grid code requirements.
4. Verification of PPC voltage control, reactive power control, and power factor control modes.
5. Assessment of frequency response performance with and without droop control.
6. Evaluation of plant response to frequency deviations, including compliance with droop and deadband requirements.
7. Verification of active power set-point tracking and plant output limiting.
8. Assessment of under-voltage and over-voltage response in coordination with inverter and SVG controls.
9. Performance evaluation under maximum, nominal, minimum, and start-up operating conditions.
10. Verification of PPC compliance with applicable grid code and CEA connectivity requirements.

5. Representative PPC

Using the PPC, the entire plant can be controlled from a master computer. It also enables plant operation through SCADA using a similar control approach. The mechanical model is developed by the OEM, followed by the development of unit-level models, and subsequently the corresponding PSCAD and PSS®E simulation models.

In the PPC, a plant-level model is used in which the entire power plant is built and controlled through the controller. The model provided by the vendor (OEM) contains default parameter values, which must be modified to comply with the Indian Grid Code. Parameters such as thresholds, gains, and limits are adjusted based on project requirements. In some cases, data-related issues may arise not only in PPCs but also in SVGs and inverters. Therefore, for validation and benchmarking, the configured parameters are carefully verified to ensure they are correctly implemented.

When developing a plant-level model for a solar or wind farm, the control requirements and parameters should be adjusted as required to suit the power system conditions.

5.1 Power Plant Controller – Control Functions and Monitoring

PPCs are primarily used in renewable power plants, and to effectively control all plant parameters, they must comply with the applicable grid code. For instance, when deployed in India, the PPC parameters need to be configured in accordance with the Indian Grid Code. Similarly, for projects in other countries, the respective national grid codes must be followed. In this way, the PPC serves as a key tool for integrating renewable energy plants with the grid. During grid compatibility studies, the performance of the PPC has a direct impact on the overall system performance. PPCs are responsible for managing all control responses of the power plant. In dynamic studies, various cases are evaluated, including LVRT, HVRT, frequency response, active power ramping, frequency response with and without droop, and active power set-point control. PPCs handle most of these control functions, except voltage ride-through. During voltage rise or dip events, inverter-level controls support the ride-through capability. However, for frequency response, active power ramping, and related controls, the PPC is solely responsible.

One of the key features of PPCs is continuous monitoring, as the system is fully digitalized and operates on a 24/7 basis. In the event of any disturbance in the power system, the PPC communicates through various control signals to the plant operator. It continuously monitors all plant parameters and ensures they remain within nominal operating limits. Whenever deviations occur, the PPC responds accordingly to restore normal operation.

5.2 PPC Control Selection Options and Operating Modes

The F-select option determines whether the PPC operates with or without droop control. The slave-enable function is used for master–slave control configuration. The Q-select option provides an operator-selectable control mode, where 0 corresponds to voltage control, 1 to reactive power (MVAr) control, and 2 to power factor control. Selecting the respective value activates the corresponding control mode. It should be noted that not all PPCs offer identical control options, as functionalities vary by manufacturer. The client-provided PPC manual details the available controls and their usage. Active power ramp rates and other configurable parameters must be entered in accordance with grid code requirements.

The OEM supplies the PPC as a black-box model, where internal control logic is not accessible to the user. Only selected configurable parameters are made available. The OEM also develops equivalent PSCAD and PSS®E models and performs benchmarking. Benchmarking involves validating simulation results against field measurements. Control functions such as active power ramping, voltage droop control, reactive power control, power factor control, and frequency support must show close agreement between simulation and actual plant performance.

5.3 Grid Code–Based Ramping and Droop Control Requirements

As per the Indian Grid Code, the allowable ramp rate is 10% per minute, which corresponds to 0.001667 pu/s when converted to per-unit per second. This value must be configured in the PPC settings. For example, if a plant has an operating limit of 400 MW, a 10% ramp rate allows a maximum change of 40 MW within one minute. Accordingly, the plant output should not exceed 440 MW or fall below 360 MW during ramp-up or ramp-down conditions.

The PPC configuration is common for both PV and WTG plants. Active power (P) control applies to both PV and WTG units, reactive power (Q) control is applicable to both, and reactive power support from SVGs along with voltage droop control is also included.

The specified voltage droop is 5%, i.e., 0.05 pu. Droop represents the proportional relationship between changes in frequency or voltage and the corresponding change in power output. For example, consider a 200 MW plant operating at a nominal frequency of 50 Hz with a 4% frequency droop. A 4% droop corresponds to a 2 Hz frequency variation. This results in a power change rate of 100 MW/Hz (200 MW / 2 Hz). At 50 Hz, the output is 200 MW; at 51 Hz, it reduces to 100 MW; and at 52 Hz, the output drops to zero. This illustrates the droop control behavior. Both droop-enabled and droop-disabled cases must be simulated during studies.

The maximum per-unit active power setting for PV plants is 1.0 pu. For a 300 MW solar plant, this corresponds to a maximum output of 300 MW. If the per-unit limit is set to 0.5 pu, the output is restricted to 150 MW. Active and reactive power limits are configured accordingly, and reactive power limits are also defined for SVGs.

5.4 Frequency Droop and Deadband Requirements

While the nominal frequency setting can be modified, the sampling frequency cannot be changed. The voltage deadband is specified as 10%, and the frequency deadband is specified as 3%, in line with grid code requirements.

According to the grid code, frequency droop values typically range from 3% to 6%. Manufacturers supplying equipment to the Indian grid validate their models for both droop limits (3% and 6%). The frequency deadband must not exceed 0.03 Hz.

PPCs are applicable to both solar power plants and Type-4 WTG models. When performing grid compliance studies for a Type-4 WTG or solar plant, the relevant control flag must be enabled. Control parameters vary across manufacturers, and identical settings should not be expected for different PPC implementations.

6. Conclusion Summarizing PPC Modelling as per Indian Grid Code

Power Plant Controller (PPC) modelling provides a structured approach for validating plant-level control performance of renewable energy generating stations connected to the grid. It emphasizes accurate representation of control functions such as active power ramping, frequency response with droop, voltage and reactive power control, and coordination with inverter and SVG controls. PPC studies support the use of time-domain simulation tools such as PSCAD and PSS®E to evaluate dynamic plant behavior under normal, disturbed, and contingency operating conditions. The modelling framework guides engineers in assessing grid code compliance under various operating scenarios and plant configurations. Overall, PPC modelling ensures reliable, secure, and standards-compliant integration of renewable energy plants in accordance with the CEA (Technical Standards for Connectivity to the Grid) Regulations, 2019 and the Indian Electricity Grid Code (IEGC).

6.1 Recommended References

• Central Electricity Authority, Technical Standards for Connectivity to the Grid Regulations, 2019.https://cea.nic.in/technical-standards-for-connectivity-to-the-grid-regulations-2019/
• Central Electricity Regulatory Commission, Indian Electricity Grid Code (IEGC), 2023.https://cercind.gov.in/2023/regulation/IEGC_2023.pdf