Sliding-Mode-Based Direct Power Control of Grid-Connected Wind-Turbine-Driven Doubly Fed Induction Generators Under Unbalanced Grid Voltage Conditions

Abstract

This paper proposes an improved direct power control (DPC) strategy of grid-connected wind-turbine-driven doubly fed induction generators (DFIGs) when the grid voltage is unbalanced. The DPC scheme is based on the sliding mode control (SMC) approach, which directly regulates the instantaneous active and reactive powers in the stator stationary reference frame without the requirement of either synchronous coordinate transformation or phase angle tracking of grid voltage. The behavior of DFIGs by the conventional SMC-DPC, which takes no negative-sequence voltage into consideration, is analyzed under unbalanced grid voltage conditions. A novel power compensation method is proposed for the SMC-based DPC during network unbalance to achieve three selective control targets, i.e., obtaining sinusoidal and symmetrical stator current, removing stator interchanging reactive power ripples and canceling stator output active power oscillations, respectively. The active and reactive power compensation components are calculated via a simple method and the proposed three control targets can be achieved, respectively, without the need of extracting negative-sequence stator current components. Experimental results on a 2 kW DFIG prototype are presented to verify the correctness and validity of the proposed control strategy and power compensation method.Index Terms-Direct power control (DPC), doubly fed induction generator (DFIG), power compensation, sliding mode control (SMC), unbalanced grid voltage, wind turbine. NOMENCLATURE U s , V r

First Order Integral Sliding Mode Control for Active and Reactive Current of A Multilevel Inverter Based Distributed Generation Unit

“…The adaptive total sliding SMC is particularly used to achieve minimum total injected harmonics and maximum power factor. A regular sliding mode control is utilized with the inverter to control its output instantaneous power and stabilize its output voltage, but it suffers from high chattering with steady state error [5]. Recently, a new control scheme called Direct Power Control, DPC, has been applied to the regular inverter based DGU, to directly control the injected active and reactive power [6], [7].…”

Sliding Mode Control of a Grid-Connected Distributed Generation Unit under Unbalanced Voltage Conditions

“…Therefore, the interaction between DG units and main-grid during voltage unbalanced conditions is very important and it must be considered when designing a proper control strategy [12]. In the literature, it can be seen that a part of research effort in the area of DG systems has been dedicated to the gridconnected-mode control of inverter-based DG units under unbalanced voltage conditions [13][14][15][16][17]. A vector control approach for controlling the voltage sourced converter (VSC) which is capable of mitigating the harmonics under unbalanced operating conditions is proposed in [13].…”

“…Early publications related to control of VSCs during unbalanced conditions [14][15][16][17], have presented generalized discussions on how to derive current references corresponding to different objectives for control of active and reactive powers during unbalanced conditions [15]. The control scheme proposed in [14,15] is based on either grid voltage oriented [14] or grid virtual-flux-oriented [15] vector control.…”

“…One main drawback for this control scheme is that the performance highly relies on the tuning of the PI or PR parameters and accurate system parameters. Hence, performance may degrade when actual system parameters deviate from values used in the control system [17].…”

“…A direct power control (DPC) strategy has been presented in [16,17] for a grid-connected VSC under voltage unbalanced conditions. The DPC scheme is based on the SM control approach, which controls the instantaneous active and reactive powers in the stationary reference frame.…”