Design of a Back-to-Back NPC Converter Interface for Wind Turbines With Squirrel-Cage Induction Generator

Abstract

As the number of wind power applications with power electronic interfaces in the grid increases, it is becoming unacceptable to disconnect the generating units every time disturbances occur, especially under voltage dips, as was a common practice in the past. Keeping the converter online during unbalanced voltage, and guaranteeing the actual standards of the converter connected to the grid, is becoming a very critical issue. From these goals, the design of a robust back-to-back neutral point clamped (three levels) voltage source converter of 150 kVA is developed in this paper. The converter is divided into two main parts: the power electronic system and the control electronic system. Concerning the first part, on the one hand, the paper presents the designs of active and passive components as insulated gate bipolar transistor, free-wheeling diodes, clamping diodes, grid filter, dc-bus capacitors, etc.; and on the other hand, the converter requirements are analyzed to ride through real grid conditions, i.e., unbalanced voltage dips. Concerning the control electronic system, the chosen electronic structure and the task distribution between the two processors used are shown.Index Terms-Back-to-back neutral point clamped (NPC) converter, dc-bus capacitors, DSP and field-programmable gate array (FPGA), local control level (LCL) filter, voltage dip.

A New Space-Vector-Modulation Algorithm for a Three-Level Four-Leg NPC Inverter

“…In addition, lower dv/dt values, higher efficiency and less stress on the devices are also considered important advantages of the NPC converter over the conventional two-level topology [3], [5]. There are several applications of the three-level VSI reported in the literature, for instance in Wind Energy Conversion Systems (WECSs) [4], [6], [7], where the nominal power of single WECs approaches 10MW. In Photovoltaic (PV) applications the three-level NPC is also used because of its good efficiency [1].…”

Back to Back Connected Multilevel Converters: A Review

“…In this review some specific and important applications on BTB connection are presented which clearly shows that this technology is now capable enough to handle the pressure of fast moving technology in this area and this is only possible due to major development in multilevel topologies, modulation technology and control methodology [63][64][65][66][67][68][69][70][71][72][73][74][75][76][77]. Some important applications are tabulated in Table 5.…”

Discrete Wavelet Transforms for Synchronization of Power Converters Connected to Electrical Grids

“…The power stage of the dc/ac converter consists of an IGBT full-bridge with diodes, which synthesizes a low frequency ac voltage by changing the IGBTs' switching states, the gate circuit, which applies the required gate signals in order to 217 Discrete Wavelet Transforms for Synchronization of Power Converters Connected to Electrical Grids switch on and off the controlled power devices, an LCL-filter, employed as a second-order low pass filtering stage which allows the high frequency ripple of the full-bridge output voltage to be filtered out and a dc-side filtering stage, which can be implemented by means of one shunt capacitor (first order) or a series inductance plus a shunt capacitor (second order). Depending on the application characteristics, the converter controller functionalities are implemented using analog or digital circuitries and, in the second case, FPGAs, DPSs and microcontrollers (µCs) allow more flexible and complex controllers to be designed and implemented (Bueno et al, 2008;Koizumi et al, 2006;Kojabadi et al, 2006). In case of grid-connected power converters, both inverters and controlled rectifiers switching at relatively high frequencies (around 10 kHz), the main functionalities that must be implemented are grid synchronization, evaluation of the reference for current injection/consumption, grid side current control and pulse width modulation (PWM) (Kazmierkowski et al, 2002).…”