Hiromi Hosoda

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.

Multi-level converters for large capacity motor drive

The two-level PWM inverter has expanded in industrial applications because it was able to achieve maintainability and high performance to surpass the DC drive by the development of the vector control and the IGBT (Insulated Gate Bipolar Transistor). However, as the main motor drive of the metal plant rolling mill, the two-level inverter output voltage was too low and capacity was too small, so the DC drive was used for a long time as the main drive. The 3-level NPC circuit (Neutral Point Clamped) was introduced as a new circuit which can output two times higher voltage and the two times cleaner waveform than the 2-level circuit. The improved power devices such as GCT (Gate Commutated Turn-off) Thyristor and IEGT (Injection Enhanced Gate bipolar Transistor) were developed and applied to 3-level inverter after 2000. The switching performance was improved and the efficiency of the inverter was improved to about 99%. Now, most of the new main drives of the metal plant rolling mill are using the 3-level inverters. There are other large motor drive applications, such as fans, pumps, and compressors. Usually, these motors are directly connected to the commercial power line and flow is changed by the mechanical means, such as dampers and bypass valves, which are inefficient. Recently, our society is becoming more focused on saving energy, and MV inverters, directly operating (without mechanical means) the electric motors in these applications at adjustable speed, are used to save energy. Recently, LNG (Liquefied Natural Gas) is considered as an important energy source that can be transported from the gas fields to the consumers that need it. The LNG compressors are often very large capacity of 75MW or greater. Initially it was driven by the gas turbine system. Now, it is changing to an all electric motor drive system because of higher efficiency and maintainability. To meet the very large capacity required, a 5-level inverter was developed, with the rating of 7.2kV and 30MVA. It can be applied in parallel up to 4 sets, for a maximum capacity of 120MVA. The 5-level inverter has an excellent performance of high voltage and clean output voltage waveform.

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.

Trends in MW-rated VSI technology and reliability for adjustable speed drives

In recent years, the drive equipment capacity has been developed to more than megawatt based on demands in various industries. High reliability is indispensable for such large scale equipment to make the total system reliability high. The paper reports trends of the voltage source inverter now applied to very large scale drive equipment. The paper also reports trends of the high capacity self-turn-off semiconductor devices and the inverter circuit configuration, which realize both large and reliable drive equipment. In the paper, reliability factors in manufacturing process of drive equipment are discussed and an example of field experiences is introduced.

New Control Strategy In Tandem Cold Mill With Ac Drives

The gage accuracy of strip coil in the tandem cold mills has much possibility of improvement with the advanced control techniques. In conventional dc motor mill drives, however, the limit on speed control response makes it difficult to achieve the higher accuracy in the gage control. The circulating current cycloconverter-fed squirrel cage induction motor drive system with entirely digital control scheme has been employed at Mizushima No.2 tandem cold mil for the purpose of improvement in the gage accuracy.

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

Large voltage source inverter for Hot Strip Mill

The rolling mill of metal industry is one of large markets of the large capacity motor drive system. The DC motor and thyristor Leonard was long used because rolling mill required the speed control accuracy, speed control response and torque control accuracy and the AC drive lacked enough capability. Then the vector control was developed and the control performance was improved and the vector control type cycloconverter was applied. The control performance was better than that of the DC drive, but the cycloconverter generated large harmonics and large amount of reactive power.

Application of Large Capacity Voltage Source Inverter to cylindrical rotor synchronous motor

The Large Capacity Voltage Source Inverter (LCVSI) application started early 90s. The inverters are getting old and are beginning to be replaced with more recent drives. In March of 2010, a contract was awarded to replace the existing GTO (Gate Turn-Off thyristor) Inverter drives applied to cylindrical rotor synchronous motors on a two stand reversing cold rolling mill. New IEGT (Injection Enhanced Gate Transistor) drives were applied on the two rolling stands and both tension reels. Previous voltage source inverter was the GTO Inverter. Previous synchronous motor applications had been with salient pole type synchronous motor. The differences between GTO inverter and IEGT inverter are discussed. Cylindrical rotor and salient pole motor, design considerations for application of large scale voltage source inverters to cylindrical rotor motors, and results obtained during testing and commissioning are discussed.

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