Current Controlled Voltage Source Inverter under Saturation-Analysis and New Algorithms

M. Dighrasker and P.S. Sensarma (India)

Keywords

Saturation algorithm, Current controller, Voltage source converter, PWM. 1 Nomenclature ¯ Superscript showing steady state quantities. d Subscript showing daxis component of the quantities transformed to two axes dq frame. q Subscript showing qaxis component of the quantities transformed to two axes dq frame. dq Subscript showing the quantities transformed to two axes dq frame. ref Subscript showing reference quantities. v Instantaneous value of VSI output voltage. vp

Abstract

This paper presents the dynamic analysis of the currents during controller saturation of a three phase Voltage Source Inverter (VSI), connected to the Point of Common Cou pling (PCC). Closed-form solutions of the VSI currents are obtained using a piecewise linear, state-space averaged model of the VSI under the linear and saturated regimes of the current controller. Using these results, two new algorithms are proposed which best improve current dy namics during controller saturation, while simultaneously limiting the reference voltage within the modulation range. This ensures that no lower order harmonics are introduced in the VSI currents, resulting in simplification of the rip ple filter design. Simulation results obtained are compared with those from existing algorithms. The simulation model includes device switching and uses multi-rate sampling, for the physical plant and controller, to reflect major non idealities of a practical system. It is shown that the pro posed algorithms result in decoupled current control and faster current dynamics.

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