What is Reactive Power and How can Smart Inverters Use it to Create a Reliable Electric Grid?
Remember the blackout of August 2003? It was the largest in North American history — affecting over 50 million people across eight U.S. states and two Canadian provinces.
The North American Electric Reliability Council found that a shortage of reactive power — the power needed to keep electric current flowing — was a significant factor that contributed to the blackout.
Renewable energy sources, such as solar power, provide not only electricity, but can also be used to generate reactive power. To prevent blackouts, renewable energy systems also need smart inverters to control the energy flux and manage the passive power of electrical grids.
To meet this need, researchers from the University of Pittsburgh have designed smart inverters that regulate the reactive power and voltage of power grids.
What is Reactive Power?
Similar to the pressure that pushes water through a pipe, voltage acts as the pressure that pushes electrical current through power lines. To do this, voltage draws on reactive power.
Without enough reactive power, voltage drops threaten the grid’s stability. Therefore, reactive power doesn’t actively keep our lights and electronics on. Think of it as the power that the AC grid uses to keep the current flowing to those devices.
So, how do we generate more reactive power? Solar photovoltaic (PV) systems might be the answer. Over 55 gigawatts of solar power generation potential is installed in the U.S. — enough to power over 10 million homes.
Connecting PV power to the electrical grid introduces unique challenges — including overvoltage which requires reactive power absorption. PV power output can also dip due to environmental factors. These voltage swings stress legacy power management equipment leading to high maintenance, operational and replacement costs.
To mitigate these disturbances, utility companies are requiring that PV systems integrate smart inverters to generate or consume reactive power.
Using Smart Inverters to Regulate Reactive Power
Similar to traditional inverters, smart inverters convert direct current (DC) into alternating current (AC). The key difference is their ability to absorb and output reactive power. This process is also known as reactive power compensation.
Tasking inverters with reactive power compensation creates heat which could cause the device to reduce its operational life — or fail.
Designing the inverters typically involves building many prototypes and performing lengthy, expensive experiments. However, with simulation, the University of Pittsburgh’s researchers sought to circumvent this substantial effort.
Simulating Reactive Power Stresses on Smart Inverters
Using multi-domain system simulation, (now contained in Ansys Twin Builder) the University of Pittsburgh’s researchers developed electrothermal models to evaluate the smart inverter’s circuits and control algorithms.
When the researchers modeled the inverter, the electrical performance matched the expected performance. This comparison proved that the models provide accurate predictions of the inverter’s electrical and thermal performance.
The researchers then conducted characterization studies to reduce the need to physically prototype the inverter’s thermal dynamics — resulting in significant cost savings.
The simulation also enabled the researchers to evaluate different design configurations. Studying these configurations gave the researchers the ability to optimize the inverter’s critical trade-off between reactive power performance and device lifetime.
To learn more about how the University of Pittsburgh’s researchers are using Ansys simulation to optimize smart inverter designs, read: Preserving the Life of Solar Power Inverters.