Digital Current Controller for a 1 MHz, 10 kW Three-Phase VIENNA Rectifier

Abstract

Active three-phase rectifiers operated at switching frequencies of 500 kHz and above, in order to increase their power density, require high-speed current controllers. If these current controllers are implemented purely digitally, which is well established today for 20-200 kHz converter systems, then very high numerical data processing demands result. In this paper, two different types of field-programmable gate arrays (FPGAs) are evaluated for realizing high-speed converter current control. For the implementation of such controllers, not only the FPGA has to be considered but rather the entire signal chain. Two alternative A/D interfaces (including high-speed low-voltage differential signaling data transmission) that are able to handle data sampling rates up to 25 MSa/s are verified. Subsequently, a digital current controller is designed and it is shown how hardware multiplier blocks of modern FPGAs can be used advantageously. Furthermore, the FPGA implementation of high-resolution pulsewidth modulation providing symmetrical pulse patterns for high switching frequencies is described. Measurements taken from a 10 kW VIENNA rectifier laboratory prototype finally demonstrate the high performance of the proposed control concept and show that a low mains current total harmonic distortion of 1.4% can be achieved for such ultrahigh switching frequency converters.