Direct Current Control for Grid-Connected Diode-Clamped Inverters

Abstract

Abstract-The accurate control of the line current, robust and dynamic behavior even under distorted grids and other system faults are the most important requirements for grid connected inverters. Applying direct current control to multilevel inverters combines the advantages of both and is an enabling step towards improved inverter performance. Direct current controllers suffer from high complexity at increased level count, which is resolved using geometrical principles and simple analytical calculations for switching vector selection within the space vector diagram. The simplified, novel parametric controller concept is scalable to inverters with arbitrary level count, does not require any switching tables and the new fully symmetric setup guarantees equal switching frequencies among the three phases. The hypotheses are further confirmed on a real hardware test setup on the example of a 3-level NPC inverter hardware and a Xilinx development platform. Experimental results prove the expected behavior of the direct current control under various conditions, shows a general approach to balance the DC-link capacitors of diode-clamped inverters within the theoretical limits and demonstrates the benefits of using Field Programmable Gate Arrays (FPGA) as a controller platform.

Operation of grid‐connected DFIG using SPWM‐ and THIPWM‐based diode‐clamped multilevel inverters

“…The total voltage across all capacitors is DC voltage V dc, which is equal to 1150 V. Each switching device has a limited voltage stress across it which is equal to V dc via the clamping diodes. An nlevel inverter needs 2(n − 1) switching devices, (n − 1)(n − 2) diodes, and (n − 1) voltage sources or capacitors [19,20]. The fivelevel DCMLI is illustrated in Fig.…”

Comparative Study on Performance Improvement of SPWM/THIPWM based DCMLI Grid Connected DFIG

“…The total voltage across all capacitors is DC voltage Vdc which is equal to 1150 V. Each switching device has a limited voltage stress across it which is equal to Vdc via the clamping diodes. An n level inverter needs 2(n-1) switching devices, (n-1) (n-2) diodes, and (n-1) voltage sources or capacitors [10,11]. The five-level DCMLI is illustrated in Fig.…”

Power conversion interface with harmonic suppression for a DC grid and single‐phase utility

“…However, it also results in increasing the switching loss and degrading power conversion efficiency. A multi‐level power converter integrates several power converters in series to reduce the switching harmonics by increasing the level of the output voltage [6–8]. Many capacitors are used in a multi‐level power converter to produce different voltage levels.…”