Osman Selcuk Senturk

Converter Structure-Based Power Loss and Static Thermal Modeling of The Press-Pack IGBT Three-Level ANPC VSC Applied to Multi-MW Wind Turbines

Wind turbine converters demand high power density due to nacelle space limitation and high reliability due to high maintenance cost. Depending on the converter structure, the converter thermal performance determines the converter power density and reliability. To estimate the converter thermal performance, the converter structure-based power loss and thermal models are developed in this study for the medium-voltage (MV) three-level active neutral-point-clamped voltage source converter (3L-ANPC-VSC) utilizing 4500 V-1800 A press-pack insulated-gate bipolar transistor-diode pairs and interfacing a 6 MW wind turbine to a MV grid. The switching power loss models are built using the experimental switching power loss data acquired via the double-pulse tests conducted on a full-scale 3L-ANPC-VSC prototype. The converter static thermal model is developed based on the double-sided water-cooled press-pack switches. Via a single-phase test setup with two full-scale 3L-ANPC-VSC legs, the developed power loss and thermal models are validated experimentally. Employing the validated models, the 3L-ANPC-VSCs thermal performance is demonstrated on simulation for a 6 MW wind turbine grid interface. Hence, these converter structure-based models developed and validated in this study are proven to be suitable for the converter power density and reliability studies based on converter thermal performance.

Performance Enhancement of the Single-Phase Series Active Filter by Employing the Load Voltage Waveform Reconstruction and Line Current Sampling Delay Reduction Methods

This paper proposes the waveform reconstruction method (WRM), which is utilized in the single-phase series active filters (SAFs) control algorithm, in order to extract the load harmonic voltage component of voltage harmonic type single-phase diode rectifier loads. Employing WRM and the line current sampling delay reduction method, a single-phase SAF compensated system provides higher harmonic isolation performance and higher stability margins compared to the system using conventional synchronous-reference-frame-based methods. The analytical, simulation, and experimental studies of a 2.5 kW single-phase SAF compensated system prove the theory.

Electro-thermal modeling for junction temperature cycling-based lifetime prediction of a press-pack IGBT 3L-NPC-VSC applied to large wind turbines

Reliability is a critical criterion for multi-MW wind turbines, which are being employed with increasing numbers in wind power plants, since they operate under harsh conditions and have high maintenance cost due to their remote locations. In this study, the wind turbine grid-side converter reliability is investigated regarding IGBT lifetime based on junction temperature cycling for the grid-side press-pack IGBT 3L-NPC-VSC, which is a state-of-the art high reliability solution. In order to acquire IGBT junction temperatures for given wind power profiles and to use them in IGBT lifetime prediction, the converter electro-thermal model including electrical, power loss, and dynamical thermal models is developed with the main focus on the thermal modeling regarding converter topology, switch technology, and physical structure. Moreover, these models are simplified for their practical implementation in computation platforms. Finally, the converter lifetimes for wind power profiles are predicted using the IGBT lifetime model available. Hence, the developed electro-thermal models suitability for the lifetime predictions is shown.

A Simple Sag Generator Using SSRs

Power line voltage sags are among the most frequent and costly power quality problems. Most equipment must be designed such that they can tolerate voltage sags (within limits defined according to some standards). Furthermore, some equipment must continue proper operation even under extreme sag conditions (critical loads) and this property often may not be accommodated inside the device itself and sag compensating power conditioners have been developed for such purposes. While in practice voltage sags are not wanted, generating sags becomes necessary for the purpose of experimentally verifying the performances of the equipment (both the equipment under sag condition and the sag compensating power conditioner) under sag conditions. In this work, a simple and economical, yet highly performing sag generator is developed, its design discussed, and its feasibility demonstrated by experiments. The proposed SSR (solid state relay, a semiconductor power module of triac characteristics) and variable transformer (variac) based sag generator is built for three-phase 10kVA ratings and balanced/imbalanced voltage sags are demonstrated in the laboratory. The performance under resistive and inductive loads is evaluated and finally the utilization of the sag generator in the test of a series active filter based power quality conditioner is demonstrated. The proposed approach provides an effective solution for voltage sag generation.

Special tests for the power electronic converters of wind turbine generators

Power electronic converters for wind turbines are characterized by high specific power density and high reliability. Special tests for such converters are performed in order to determine the power loss and thermal models, which are dependent of the load profile and converter structure. Two multi-level medium-voltage source converter topologies, of the 3L-ANPC-VSC and 3L-HB-VSC type, are considered in the paper. Both converters employ press-pack IGBT-diode pairs and interface a 6 MW wind turbine to a medium voltage grid. The power loss and thermal model data applicable for both grid and generator-side VSCs is used to estimate the switch junction temperatures through the simulation of wind turbine grid interface operation. A discussion of the power density and reliability of the grid-side VSCs with respect to press-pack switches, gate driver, and cooling plate is included. A test set-up for a single-phase full-scale 3L-ANPC-VSC being able to emulate both grid and generator-side VSCs is also described.

High-Performance Harmonic Isolation and Load Voltage Regulation of the Three-Phase Series Active Filter Utilizing the Waveform Reconstruction Method

This paper develops the waveform reconstruction method (WRM) for high accuracy and bandwidth signal decomposition of voltage harmonic type (V-type) three-phase diode rectifier load voltage into its harmonic and fundamental components, which are utilized in the series active filter (SAF) control algorithms. The SAF compensated system utilizing WRM provides high performance load harmonic voltage isolation and load voltage regulation at steady-state and during transients compared to the system utilizing the synchronous reference frame based signal decomposition. Additionally, reducing the line current sampling delay in the discrete-time implementation enhances the stability of the SAF. The simulations and experimental studies of a 10 kW three-phase SAF compensated system prove the theory.

Converter structure-based power loss and static thermal modeling of the press-pack IGBT-based three-level ANPC and HB VSCs applied to Multi-MW wind turbines

The wind turbine converters demand high power density due to nacelle space limitation and high reliability due to high maintenance cost. Once the converter topology with the semiconductor switch technology is selected, the converter power density and reliability are dependent on the component count and the switch thermal performance which is determined by the converter load profile and the converter structure. In this study, the converter-structure based power loss and thermal models are developed for the medium voltage full-scale 3L-ANPC-VSC and 3L-HB-VSC utilizing press-pack IGBT-diode pairs and interfacing a 6MW wind turbine to a medium voltage grid. The switching power loss models are built using the experimentally obtained switching power loss data from a full-scale 3L-ANPC-VSC leg. The static thermal models are developed considering the double-sided cooling of the switches by the cooling plates. For the experimental model verifications, a test setup with a single-phase full-scale 3L-ANPC-VSC is introduced. Using the power loss and thermal models, the switch junction temperatures are obtained on simulation for the wind turbine grid interface. The power density and reliability of the VSCs are discussed and compared with respect to these junction temperatures as well as the counts of press-pack switches, gate driver, and cooling plate.

High voltage cell power supply for modular multilevel converters

Modular multilevel converters (MMCs) require isolated power supplies at their cells (modules). For high voltage MMC cells with considerable power consumption, simple flyback converters are no more applicable as power supplies; however, input-series output-parallel (ISOP) flyback converters are suitable provided that simplicity and cost-effectiveness are preserved. In this paper, a simple 100W 2.8kV-to-36V 3-stage ISOP flyback converter is proposed as high voltage cell power supply (HV-CPS). In this paper, the HV-CPSs implementation challenges are addressed and their solutions are provided. Via the full-scale prototype of the proposed HV-CPS, its successful operation is experimentally demonstrated.

Converter-fed synchronous machine for pumped hydro storage plants

Pumped hydropower is gaining importance as a key technology for the integration of large quantities of renewable electricity, in particular from wind and solar sources. With the progress in power electronics, it has recently become possible to build frequency converters with a rated power in excess of 100 MVA, paving the way for a new variable speed pumped hydropower solution based on synchronous machines whose stator is driven with a variable frequency. This solution, refered to as converter fed synchronous machine (CFSM), is offering even higher flexibility and efficiency than DFIM (doubly-fed induction machine). A first CFSM plant with a rated power of 100 MVA has been installed in Switzerland and has been in productive operation since late spring 2013. As a further step a new CFSM power converter type based on modular multi-level converter (MMC) technology is proposed. This topology, powered by advanced IGCT (integrated gate-commutated thyristor) power semiconductor devices, enables a total power conversion efficiency greater than 98.5%. Very smooth waveforms and special starting algorithms make it possible to use standard generator and transformer insulation schemes. Due to a modular converter construction, the accessible range of rated power spans from approximately 50 MVA up to 500 MVA. Built-in redundancy enables a very high availability.

A simple sag generator using SSRs

Power line voltage sags are among the most frequent and costly power quality problems. Most equipment must be designed such that they can tolerate voltage sags (within limits defined according to some standards). Furthermore, some equipment must continue proper operation even under extreme sag conditions (critical loads); this property often may not be accommodated inside the device itself, and sag-compensating power conditioners have been developed for such purposes. While, in practice, voltage sags are not wanted, generating sags becomes necessary for the purpose of experimentally verifying the performances of the equipment (both the equipment under sag condition and the sag-compensating power conditioner) under sag conditions. In this paper, a simple and economical, yet highly performing, sag generator is developed, its design is discussed, and its feasibility is demonstrated by experiments. The proposed solid-state relay (a semiconductor power module of triac characteristics) and variable transformer (variac)-based sag generator is built for three-phase 10-kVA ratings, and balanced/imbalanced voltage sags are demonstrated in the laboratory. The performance under resistive, inductive, and nonlinear loads is evaluated, and finally, the utilization of the sag generator in the test of a series-active-filter-based power quality conditioner is demonstrated. The proposed approach provides a very simple, yet highly effective, solution for voltage sag generation.