Can a Utility scale PV Inverter be used as a STATCOM?

The integration of utility-scale photovoltaic (PV) systems into the power grid has prompted a re-evaluation of voltage regulation and reactive power compensation strategies. The conventional grid, primarily designed for centralized power generation, is now transitioning to accommodate distributed energy resources (DERs), including solar and wind. This shift introduces challenges, such as poor power factor, voltage fluctuations, and increased overvoltage risks, particularly given the limited capacity of existing transmission lines.

Traditionally, shunt capacitors have been employed for reactive power compensation to elevate system voltage levels to meet operational standards. During periods of light load, inductive compensation is utilized to mitigate voltage rise. However, these methods are static and lack the flexibility required to respond to the dynamic nature of power generation from renewable sources.

Flexible AC Transmission Systems (FACTS) devices, and specifically Static Synchronous Compensators (STATCOMs), offer an advanced solution. STATCOMs provide fast, continuous reactive power support, thereby improving the power factor and maintaining regulated system voltage. This makes them particularly suitable for addressing the voltage fluctuations introduced by solar plant integration into the grid.

In the context of PV farms, STATCOMs can perform voltage regulation and reactive power compensation, especially during non-generating hours, such as nighttime, and partially generating hours like early morning and late evening. This not only increases the utilization factor of the farm but also enhances cost-effectiveness.

The technical feasibility of using a PV inverter as a STATCOM is rooted in the inverter's ability to inject sinusoidal current into the grid, behaving as either an inductive or capacitive source of reactive power. During nighttime, the inverter can use its full capacity for reactive power compensation, and during the day, it can use the remaining capacity after real power generation.

Our approach is to design and develop a 10MW PV farm with an integrated +/-10 Mvar STATCOM using a voltage-sourced converter (VSC) connected to the grid. The objective is to evaluate the performance enhancements through simulation, focusing on reactive power compensation and voltage regulation.

The technical methodology involves constructing a SIMULINK model of a 10MW solar farm, comprising four units of 2.5MW Solar PV, interfaced with a 25kV grid via a DC-DC boost converter and a GTO based 3-level, 12 pulse Inverter. We calculate modulation indices, converter currents, and inductance values to fine-tune the PV farm's interaction with the grid, ensuring an optimized balance between power quality and efficiency.

Our findings indicate that integrating a STATCOM with a solar farm significantly improves reactive power compensation and voltage regulation, particularly during periods when the solar farm is not generating power. This integration has the potential to enhance grid stability and power quality, leading to a more resilient and efficient power system.

Voltage Regulation

Reactive Power Compensation

Temporary Overvoltage Control

In essence, a voltage source converter is a key component in both STATCOM and PV farms. A STATCOM can be effectively utilized in PV farms to serve both purposes. With the above analysis, it is evident that during low generation periods and night time, STATCOM can be used to compensate for reactive power. During normal operation, the STATCOM can be used for voltage regulation and stabilization. This will improve the power factor in the grid with reduced transmission losses.  This can be effectively utilized to improve the performance of low-voltage and medium-voltage distribution systems.