Transformer-Less UPFC for Wind Turbine Applications

In this paper, an innovative technique with a new concept of transformer-less unified power flow controller (UPFC) is implemented. The construction of the conventional UPFC that consists of two back-to-back inverters which results in complexity and bulkiness which involves the transformers which are complication for isolation & attaining high power rating with required output waveforms. To reduce a above problem to a certain extent, a innovative transformer-less UPFC based on less complex configuration with two cascade multilevel inverters (CMIs) has been proposed. Unified power flow controller (UPFC) has been the most versatile Flexible AC Transmission System (FACTS) device due to its ability to control real and reactive power 80w on transmission lines while controlling the voltage of the bus to which it is connected. UPFC being a multi-variable power system controller it is necessary to analyze its effect on power system operation. The new UPFC offers several merits over the traditional technology, such as Transformer-less, Light weight, High efficiency, Low cost & Fast dynamic response. This paper mainly highlights the modulation and control for this innovative transformer-less UPFC, involving desired fundamental frequency modulation (FFM) for low total harmonic distortion (THD), independent active and reactive power control over the transmission line, dc-link voltage balance control, etc. The unique capabilities of the UPFC in multiple line compensation are integrated into a generalized power flow controller that is able to maintain prescribed, and independently controllable, real power & reactive power flow in the line. UPFC simply controls the magnitude and angular position of the injected voltage in real time so as to maintain or vary the real and reactive power flow in the line to satisfy load demand & system operating conditions. UPFC can control various power system parameters, such as bus voltages and line flows. The impact of UPFC control modes and settings on the power system reliability has not been addressed sufficiently yet. Cascade multilevel inverters has been proposed to have an overview of producing the light weight STATCOM’s which enhances the power quality at the output levels.When the multilevel converter is applied to STATCOM, each of the cascaded H-bridge converters should be equipped with a galvanically isolated and floating dc capacitor without any power source or circuit. This enables to eliminate a bulky, heavy, and costly line-frequency transformer from the cascade STATCOM. When no UPFC is installed, interruption of either three-phase line due to a fault reduces an active power flow to half, because the line impedance becomes double before the interruption. Installing the UPFC makes it possible to control an amount of active power flowing through the transmission system. Results has been shown through MATLAB Simulink