Full-scale Power Converter Research Articles

Operating and Loading Conditions of a Three-Level Neutral-Point-Clamped Wind Power Converter Under Various Grid Faults

In order to fulfill the growing demands from the grid side, full-scale power converters are becoming popular in the wind turbine system. The low-voltage ride-through (LVRT) requirements may not only cause control problems but also result in overstressed components for the power converter. However, the thermal loading of the wind power converter under various grid faults is still not yet clarified, particularly at megawatt power level. In this paper, the impacts by three types of grid faults to a three-level neutral-point-clamped (3L-NPC) wind power converter in terms of operating and loading conditions are analytically solved and simulated. It has been found that the operating and loading conditions of the converter under LVRT strongly depend on the types/severity values of grid voltage dips and also the chosen control algorithms. The thermal distribution among the three phases of the converter may be quite uneven, and some devices are much more stressed than the normal operating condition.

Open-Circuit Fault Diagnosis in PMSG Drives for Wind Turbine Applications

Condition monitoring and fault diagnosis are currently considered crucial means to increase the reliability and availability of wind turbines and, consequently, to reduce the wind energy cost. With similar goals, direct-drive wind turbines based on permanent magnet synchronous generators (PMSGs) with full-scale power converters are an emerging and promising technology. Numerous studies show that power converters are a significant contributor to the overall failure rate of modern wind turbines. In this context, open-circuit fault diagnosis in the two power converters of a PMSG drive for wind turbine applications is addressed in this paper. A diagnostic method is proposed for each power converter, allowing real-time detection and localization of multiple open-circuit faults. The proposed methods are suitable for integration into the drive controller and triggering remedial actions. In order to prove the reliability and effectiveness of the proposed fault diagnostic methods, several simulation and experimental results are presented.

Thermal Analysis of Multilevel Grid-Side Converters for 10-MW Wind Turbines Under Low-Voltage Ride Through

As the power level of a single wind turbine is continuously pushed up even to 7 MW, the wind power generation systems are required to be more reliable and able to withstand extreme grid disturbances. Moreover, it is becoming a need that the wind power generation system should be more active in the power network and able to contribute to the grid recovery by injecting reactive current during grid faults. Consequently, the full-scale power converter solutions are becoming more and more popular to fulfill the growing challenges in the wind power application. Nevertheless, the loading of the power devices in full-scale power converters, particularly during grid faults, may compromise the reliability performance and further increase the cost of the system. In this paper, three promising grid-side multilevel converter topologies for the next-generation 10-MW wind turbines are proposed and basically designed as case study. The operation status, as well as the reliability-related performances, is investigated aimed at various low-voltage ride through (LVRT) conditions. It is found that all of the proposed converter topologies will suffer from higher junction temperature in some heavily loaded power devices (particularly the diodes) under LVRT operation. Moreover, the three-level and five-level H-bridge topologies show more potential to reduce the inequality and level of device stress than the well-known three-level neutral point clamped topology.

Thermal Cycling Overview of Multi-Megawatt Two-Level Wind Power Converter at Full Grid Code Operation

In this paper, two promising multi-megawatt wind turbines equipped with a doubly-fed induction generator-based partial-scale and a permanent magnet synchronous generator-based full-scale two-level power converter are designed and compared. Simulations of the two configurations with respect to loss distribution and junction temperature variation for the power device over the entire wind speed range are presented and analyzed both for normal operation and operation with various specific grid codes. It is concluded that in both partial-scale and full-scale power converters, the most thermal stressed power device in the generator-side converter will have a higher mean junction temperature and also junction temperature variation compared to the grid-side converter at the rated wind speed, and the thermal performance of the generator-side converter in the partial-scale power converter becomes crucial around the synchronous operating point and needs to be considered carefully. Moreover, reactive power injection directed by the grid codes will affect the thermal profile of the power semiconductors, especially at lower wind speeds.

Wind energy conversion system with full-scale power converter and squirrel cage induction generator

This paper describes a modeling and control of a variable speed squirrel-cage induction generator with back to back power electronics converters used in variable speed wind energy conversion system. The power electronics is composed of the generator side converter (GSC) coupling to the grid connected converter (GCC) together via DC bus capacitor. The generator side converter (GSC) is controlled by direct torque control (DTC).The control objectives of the generator side converter (GSC) are to optimize the energy capture from the wind turbine and supply the magnetic flux to the squirrel cage induction generator (SCIG). The GCC converter delivering the energy from the machine side to the utility grid regulated the DC link voltage and the power flows to the grid. The basic idea of P-Q control method used is based on voltage vector oriented control and decoupling in the d-q axis reference frame. The complete control system has been developed; analyzed and validated by Matlab simulation. The two operating modes of GCC converter and the performance under active and reactive power variations are also presented. The low voltage ride-through (LVRT) performances of the variable speed wind turbine (VSWT) is tested, when the grid voltage has dropped to a very low value. Simulation results confirmed the effectiveness of the proposed control strategies and their capability under different case study. Key words: Variable speed wind turbine, converter control, power quality, back to back converters, vector oriented control.

Based Flying Capacitor Converter Wind Power Generator System

Direct drive wind power system need full-scale high power converter, such as flying capacitor multilevel converter. On the realization of high power electronic equipment, an important problem is that the working frequency of high power devices is too low to apply excellent modulated technique such as PWM. In large-power equipment, the switching frequency of power electronics devices is such low that good control performance can't be obtained with a single converter. In order to overcome this problem, Carrier phase-shifted SPWM technique (CPS-SPWM) has been researched. Reactive power compensation and harmonic reduction are two relevant research problems that exist in wind power system. With the advancement of modern power electronics technology in both circuits and devices, new and better solutions are being proposed and applied to solve these two problems. To compensate reactive power, a flying capacitor type multilevel inverters with a Carrier Phase-Shifted SPWM(CPS-SPWM) switching scheme is proposed. All this verified by simulation and experiment.

Hardware Simulator Development for a 3-Parallel Grid-Connected PMSG Wind Power System

This paper presents the development of a hardware simulator for a 3-parallel grid-connected PMSG wind power system. With the development of permanent magnetic materials in recent years, the capacity of a PMSG based wind turbine system, which requires a full-scale power converter, has been raised up to a few MW. Since it is limited by the available semiconductor technology, such large amounts of power cannot be delivered with only one power converter. Hence, a parallel connecting technique for converters is required to reduce the ratings of the converters. In this paper, a hardware simulator with 3-parallel converters is described and its control issues are presented as well. Some experimental results are given to illustrate the performance of the simulator system.

Development of a 1 kA, 50 Hz superconducting converter

A single-phase, thermally switched superconducting power converter operating at mains frequency is being developed and tested by the authors. Typical design values of the device are: input voltage of 220 V; input current of 7 A; output voltage of 1 V; and output current of 1 kA. The average output power is about 750 VA, with an efficiency better than 96%. Test results of the full scale power converter while ramping up and down a superconducting magnet and a comparison with the theory are presented. The power converter will be installed as a part of a power supply system controlling the current of a separator magnet located in Ukraine for an iron ore recycling process. >