Masahiko Tsukakoshi

Introduction of a large scale high efficiency 5-level IEGT inverter for oil and Gas industry

In the Oil and Gas Industry, there is a trend towards all electrically-driven compressor power train equipment, instead of gas turbine operated equipment; and simultaneously higher system availability is required with smaller installation space, considering environmental issues for the compressor driven equipment. In general, tens of MW capacity compressors are used in the LNG plant, so the electrically-driven power train AC motor and drive equipment must have large capacity and capability for high speed operation. In this study, we will introduce our development of a 5-level IEGT (Injection Enhanced Gate Transistor) inverter which is applicable in the Oil and Gas Industry as a high speed, large capacity power train with high efficiency, high reliability, and smooth output voltage waveform. One unit of this inverter has a capacity of 20MVA, so by connecting four units in parallel it is possible to obtain 80MVA rating. This paper also reports the results of a full power inverter and motor combined test which illustrates the principles and mechanisms of a 5-level inverter system.

Performance evaluation of a large capacity VSD system for Oil and Gas industry

Reduction of energy consumption and CO2 emissions are recognized as important environmental issues in todays world. In addition, Oil and Gas companies are striving for ways to increase their capacity and maximize system uptime in order to meet the global energy demand. To realize these goals, Oil and Gas utilities are looking for electrical solutions as prime movers on their compressor trains. These solutions make use of large scale Variable Speed Drive (VSD) system such as Voltage Source Inverter (VSI) with high power AC motor drive systems. Since large electrical drive systems are a relatively new technology with limited field data, the full load test of 30MVA 5-level VSI system was carried out on a test stand to measure critical data necessary to evaluate system performances. This paper reports the results of motor combined test which illustrate the principle and mechanism of 5-level inverter system.

Experimental Comparisons Between Modular Multilevel DSCC Inverters and TSBC Converters for Medium-Voltage Motor Drives

This paper makes an intensive comparison in operating performance between a modular multilevel double-star chopper-cells (DSCC) inverter and a modular multilevel triple-star bridge-cells (TSBC) converter. Both inverter and converter are intended to drive medium-voltage motors in industrial applications. First, it makes numerical comparisons, thus, resulting in revealing that the torque and frequency of a driven motor produce a significant effect on capacitor-voltage fluctuation and arm or cluster current in the individual DSCC inverter and TSBC converter. Next, a three-phase DSCC inverter and a three-phase TSBC converter with the same rating as 400 V and 15 kW are designed and compared to drive the following two general purposes and specially-designed induction motors; one is rated at the 380-V, 15-kW, 50-Hz four-pole motor, and the other is at the 320-V, 15-kW, 38-Hz six-pole motor. This experimental comparison based on the two downscaled drive systems confirms the validity of the numerical comparison. Finally, this paper concludes that the DSCC inverter is more suitable for driving medium-voltage high-speed motors loaded with quadratic-torque-to-speed profiles like fans, blowers, pumps, and centrifugal compressors. On the other hand, the TSBC converter is more suitable for driving medium-voltage low-speed high-torque motors like mills, kilns, conveyors, and extruders.

Which is more suitable for MMCC-based medium-voltage motor drives, a DSCC inverter or a TSBC converter?

This paper provides theoretical, numerical, and experimental comparisons in electrical-drive performance between a double-star chopper-cells (DSCC) inverter and a triple-star bridge-cells (TSBC) converter. The inverter and converter are two of the most promising members of the modular multilevel cascade converter (MMCC) family. Two sets of downscaled electrical drives using the DSCC inverter and the TSBC converter are designed, constructed, and tested, along with the common three-phase four-pole induction motor rated at 380 V, 15 kW, and 50 Hz. This paper presents experimental waveforms of the electrical drives loaded with a quadratic torque-to-speed profile and at the rated torque.

Redundancy system for continuous driving large motor drive equipment

A compressor which is used in liquefied natural gas (LNG) plant is mainly driven by turbine engine, but consideration for electrically driven compressor by a motor is increasing. Particularly, application of a motor driven by an inverter has the advantage of adjustable speed control of compressor. However, there is a concern of compressor train stop due to inverter failure. To eliminate this concern, various redundancy system for continuous driving large capacity inverter TMdrive™-XL series are developed. The redundancies including the main inverter circuits realize inverter continuous operation even if a failure is occurred to some parts.

Study Of Large VSI Drive System For The Oil And Gas Industry.

Reduction of energy consumption and CO2 emissions are recognized as important issues in today’s world. In addition, oil and gas companies are looking for ways to increase their capacity and maximize system uptime in order to meet the global energy demand. To realize these goals, oil and gas facilities are looking for 261 STUDY OF LARGE VSI DRIVE SYSTEM FOR OIL AND GAS INDUSTRY

Study of subsynchronous torsional interaction with voltage source inverter drive for LNG plant

Electrical drives for large capacity compressors in a liquefied natural gas (LNG) plant have been investigated. There are mainly two topologies for such an electrical drive; load commutated inverters (LCIs) and voltage source inverters (VSIs). Due to commutation of the thyristors, LCIs produce current harmonics with variable frequencies, and their interharmonics are significant. Therefore, torsional interactions should strongly be concerned. The VSI systems have low harmonics of voltage and current, and become a matured and reliable technology. So this technology is getting attractive to the very large capacity motor drives. This paper shows characteristics of proposed variable speed drive system (VSDS) using VSIs technology comparing with LCIs at first for subsynchronous torsional interactions(SSTI). Second, interharmonics are considered. This study shows that the SSTI is less concerned with the proposed VSI-VSDS that would be suitable to apply large capacity drive applications in LNG plant.

Innovation of a large capacity 5-level IGBT inverter for Oil and Gas Industry

All the companies of electrically-driven equipments are looking for the solutions with high reliability, low maintenance cost, and maximum efficiency with smaller installation space considering environmental issues. In this study, the development of a 5-level IGBT (Insulated Gate Bipolar Transistor) inverter is introduced which is applicable in the field of Oil and Gas Industry as a high speed, large capacity with high efficiency motor drive equipment. By decreasing the floating inductance from the unit, we materialize to develop the snubberless main circuit block. Thus, it is possible to downsize the equipment by reducing the parts. As one bank of this inverter capacity is 8MVA, it is possible to obtain 16MVA by connecting two banks in parallel. This paper also reports the results of motor combined test which illustrate the principle and mechanism of the 5-level inverter system.

Novel Torque Ripple Minimization Control For 25 MW Variable Speed Drive System Fed By Multilevel Voltage Source Inverter

Continuous improvements in the power rating and switching characteristics of power semiconductor devices have enabled the use of power electronics converters in high power variable speed drives (VSDs). These multimegawatt drives are needed for driving large capacity compressors in liquefied natural gas (LNG) plants. However, the generated harmonics and their associated torque ripples may result in serious drawbacks in the application of VSDs in the oil and gas industry. The torque ripples may lead to torsional vibrations that may in turn cause damage to the load-motor coupling. To overcome these drawbacks, a new speed control technique, which is based on a synchronized pulse width modulation (PWM) control method, is proposed. A 25 MW five level VSD system was developed to verify the new approach using two experimental tests, namely, back-to-back and full load tests. The tests validated the feasibility of the proposed method in reducing the torsional vibration. INTRODUCTION LNG is in great demand globally because it is a clean fuel that is friendly to the environment. To obtain LNG, the natural gas is chilled to !162 C to produce a clear liquid that occupies up to 600 times less space than the corresponding gas. To achieve the necessary cryogenic temperatures, refrigerating turbocompressors are traditionally driven by industrial heavy-duty gas turbines (GTs). Besides their low efficiency, GT need regular maintenance. Furthermore, the necessary shutdown periods and the unscheduled outages interrupt the LNG production and reduce LNG plant productivity. As electrical drives such as VSDs are maintenance free and more efficient than GT, efforts are being made by major LNG plant operators, contractors and manufacturers to develop VSDs suitable for LNG compressors. On the other hand, VSDs have been used in various industries such as steel and paper mills. In the megawatt capacity ranges, these industries prefer multilevel voltage source inverter (VSI) over the load commutated inverter (LCI) as a power converter for VSD applications. VSIs are preferred due to their lower harmonics, better power factor, and smaller torque ripples at the motor side. These same features make the VSI fed VSD systems the most attractive solution for driving LNG plant compressors. A new control method is proposed to reduce the harmonics and the torque ripples of a VSI-based VSD drive system. From previous experience, the installation of a VSI-based drive system for a large capacity compressor of an LNG plant led to several technical issues related to ripples and torsional vibrations in a centrifugal LNG compressor train with a gearbox. Kita, et al. (2007), reported that the torsional vibration was transferred to the lateral vibration at the gear mesh. Based on the knowledge of previous coupling failure of a compressor driven by a VSD fed by a three-level inverter, the following two methods were implemented to solve the problem: • Synchronized pulse width modulation control for the output frequency and • V/F constant control (Shimakawa and Kojo, 2007). The compressor train has been operating properly after the implementation of the above-mentioned two methods. The objective of this study was to improve the new techniques and to apply them to a five-level large capacity inverter instead of a three-level inverter, which resulted in even higher performances. An improved control method, based on a fixed pulse pattern, was also applied to further improve the waveform of the five-level inverter. The effectiveness of the improvements was validated by torque ripple measurement during the motor combined experimental test. The authors built a 25 MW motor drive system and evaluated the system in a back-to-back test using a 7.2 kV 30 MVA VSI bank along with a 25 MW synchronous motor (SM). A power recovery system with a synchronous generator (SG) and a regenerative PWM inverter were used to load the high power SM. The relationship between the VSI output voltage pulse pattern and the torque ripple was examined. The effectiveness of the implemented control method was also experimentally verified. DRIVE SYSTEM APPLICATION BACKGROUND Stable speed and torque control is essential for a large adjustable-speed motor-driven compressor train. In order to achieve the stable control, however, highly advanced control techniques are required. In this section, will be introduced the influence of and issues involved with motor speed control of an adjustable speed drive that were experienced. Fuel Gas Compressor System and Analysis of a Coupling Failure A schematic diagram of the studied fuel gas compressor system is shown in Figure 1. A 13.65 MW induction motor was driven by PROCEEDINGS OF THE THIRTY-NINTH TURBOMACHINERY SYMPOSIUM • 2010 194