Characterization of inverter-grid interactions using a hardware-in-the-loop system test-bed

Renewable energy, such solar and wind, and other distributed generation (DG) resources are usually connected to the power grid through an inverter. As the penetration level of such inverter-based DG increases, their effects on, and interactions with the grid become an important concern for grid stability and power quality. In addition to the intermittent nature of renewable energy generation, which poses an challenge for system operation and power flow control, dynamics of the inverters have also been found to cause high-frequency stability problems. One particular issue is the harmonic resonance formed between the inverter output impedance and the grid impedance, which presents a system power quality problem and can lead to false tripping of inverters and other devices connected to the grid. This paper describes a hardware-in-the-loop system test-bed that has been developed to study such inverter-grid interactions and other system issues involving DG sources. Design considerations of the test-bed are presented along with its programming and control capabilities. Operation of grid-parallel inverters under different configurations and conditions of the test-bed is measured and their modes of interaction with the simulated grid are investigated. The effects of grid impedance and local loads on the stability and performance of grid-parallel inverters are also presented.