Laboratory type PWM grid emulator for generating disturbed voltages for testing grid connected devices

This paper presents the design and performance of a test bench to generate grid faults and disturbed grid voltage conditions to test grid connected devices. The test bench is applied to generate different reproducible types of disturbed grid voltages like symmetrical and unbalanced voltage dips, overvoltage, frequency variations and harmonic disturbances. By means of this grid emulator the behavior of active front end converter, grid converter for renewable energy generation systems and also grid connected generators like doubly fed induction generators can be analyzed during voltage disturbances. The laboratory type grid emulator is rated to a nominal power of 30 kVA and is able to handle peak currents up to 150 amps. The nominal output voltage of the grid emulator is 400 volts. The voltage source converter based grid emulator is controlled by means of a dynamically and a static control method depending from the particular test in progress. State space control method has been chosen for good dynamic performance. This paper illustrates the structure of the grid emulator, the design of main components, the dynamic control method applied, and the design of the controller parameters. Furthermore results of the dedicated measurements are presented and discussed.