Optimized Direct Power Control Strategy using Output Regulation Subspaces and Pulse Width Modulation

Abstract

-In this paper, a Direct Power Control (DPC) using Output Regulation Subspaces (ORS) for a three-phase two-level converter is presented. An optimal controller design and the use of optimized modulation techniques permit to improve the system performance minimizing the necessary grid-connection inductance. ORS plus proportional controllers are proposed for the generation of the reference vector to decrease active and reactive power errors and to achieve unity power factor. The generation of the reference vector is carried out thanks to simple Pulse Width Modulation techniques. The computational cost of the proposed control is really low and all the calculations can be done online allowing its implementation in low cost microprocessors. Simulation and experimental results are shown in order to illustrate the good performance of the proposed control strategy.

Model Based Adaptive Direct Power Control for Three-Level NPC Converters

“…To design this control loop it is assumed that the difference between the capacitors voltages values is small (x 2 ∼ 0) so the inductors currents dynamics can be approximated by (8). That equation is similar to that from a conventional three-phase two-level converter [15].…”

“…Assuming that the input AC voltages are balanced and without harmonic content, and using the instantaneous active (13) and reactive (14) power definition given in [26], the instantaneous active power first derivate over the time,ṗ, and the instantaneous reactive power first derivative over the time, q, can be calculated as (15) and (16), respectively.…”

“…Solving the equations (15) and (16) for the condition ofṗ anḋ q to be zero yields (17) and (18). Those equations represent the two straight lines in the αβ plane that define the ORS and c 1 and c 2 are two variables that represent the displacement over each line.…”

“…Taking into account the ORS division defined by (17) and (18) and the equilibrium point (19), the controller (20) is proposed to solve the instantaneous power tracking problem [15].…”

“…The controller design is based in the converter model [29], and supported by adaptive strategies [7] presented in previous works, improving the performance of three-level three-phase voltage source inverters working in direct power control mode. The MB-ADPC strategy proposed is an extension of the controller presented in [15] for the two-level converter. When compared with controllers based on current loops, the proposed controller presents faster response in transients as it is based on DPC strategies.…”