Abstract
Conventional direct power control (DPC) presents highly distorted grid currents and twice grid-frequency ripple in the dc bus voltage under unbalanced network. Various improved DPC methods have been proposed to tackle the problems above. However, they are usually complicated and not easy to use due to the positive/negative sequence extraction of grid and converter voltages/currents, additional controllers and filters, more tuning work, and so on. This paper proposes an improved DPC by simply adding a compensation term to the original power references. The compensation power is obtained by analyzing the power ripple in the input line inductance based on extended power theory. The reference voltage vector is subsequently calculated from the new power reference and synthesized by space vector modulation (SVM). To improve the robustness of the proposed DPC against inductance variation, an online inductance identification technique based on gradient correction method is proposed and combined with the proposed DPC. The presented simulation and experimental results prove that the proposed method can achieve sinusoidal grid currents and reduce the de voltage ripple significantly even with mismatched inductance.
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