Abstract
A passivity-based control (PBC) strategy with improved robustness for single-phase three-level rectifiers feeding resistive and constant power loads (CPLs) is proposed. It is shown that the control of the rectifier can be achieved if the damping injection is applied to the grid current only. In this case, the knowledge of load resistance is required in the computation of reference grid current amplitude. Since the output voltage and load current are dc quantities, the load resistance can be estimated easily. Then, the amplitude of the reference grid current is calculated from the power balance equation of the rectifier. The transfer function from reference grid current to actual grid current is derived. The derived transfer function is analyzed under variations in the filter inductance. The results reveal that the proposed PBC offers strong robustness to variations in the filter inductance when a suitable damping gain is selected. The performances of the proposed PBC strategy under undistorted and distorted grid voltage as well as, variations in inductor are investigated via experimental studies during steady-state and transients caused by the resistive load and CPL changes. In all cases, the output voltage is regulated at the desired value, and grid current tracks its reference.
Highlights
Due to the well-known features such as controllable dc-link voltage, sinusoidal grid current with reasonably small total harmonic distortion (THD), bidirectional power flow capability and ability of unity power factor operation, the pulse width modulation (PWM) rectifiers are widely used in many applications such as motor drives [1], energy storage systems [2], renewable power generation systems [3], microgrids [4], and battery charger in hybrid electric vehicles [5]
It is pointed out that both dc output voltage and grid current of the rectifier can be controlled if the damping injection is applied to the grid current only
It is shown that the proposed passivity-based control (PBC) strategy possesses strong robustness to variations in the inductance when the damping gain is selected in accordance with the grid current transfer function magnitude
Summary
Due to the well-known features such as controllable dc-link voltage, sinusoidal grid current with reasonably small total harmonic distortion (THD), bidirectional power flow capability and ability of unity power factor operation, the pulse width modulation (PWM) rectifiers are widely used in many applications such as motor drives [1], energy storage systems [2], renewable power generation systems [3], microgrids [4], and battery charger in hybrid electric vehicles [5]. Among the multilevel converter topologies, the three-level T-type converter has important advantages such as reduced component count, highest post fault operation capability, and lower losses These advantages are meaningful in low voltage applications if the efficiency and cost are important [8], [9]. A PBC with an improved robustness feature is proposed for single-phase three-level T-type rectifiers feeding resistive load and CPL. The proposed PBC strategy possesses the following features: i) It exhibits excellent steady-state and dynamic performances under load and reference changes, ii) Despite the use of inductance L in the switching function, the proposed PBC offers strong robustness against variations in L with suitably adjusted damping gain, iii) It stabilizes the system when R > RCPL , iv) It requires only one controller gain (damping gain), which leads to simplification in the implementation. Experimental results obtained from a prototype are presented to validate the effectiveness of the proposed PBC strategy
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