AC Motor Drive System

The two AC drive systems used on extruders are the adjustable transmission ratio drive and the adjustable frequency drive. The adjustable transmission ratio drive can be either a mechanical adjustable speed drive or an electric friction clutch drive. 

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David Finney, Variable frequency ac motor drive systems. Peter Peregrinus Ltd (1991). ISBN 0 863-41114-2... 

Ribeiro, R.L.A., Jacobina, C.B., da Silva, E.R.C., Lima, A.M.N. Faulttolerant voltage-fed pwm inverter ac motor drive systems. IEEE Transactions on Industrial Electronics 51(2), 439-446 (2004)... 

Inverter-AC Motor Drives. An adjustable-frequency control of AC motors provide efficient operation with the use of brushless, high-performance induction, and synchronous motors. A typical system is shown in Figure. 3-14. Such a system consists of a rectifier (which provides DC power from the AC line) and an inverter (which converts the DC power to acljustable-frequency AC power for the motor). Inverter cost per kilowatt is about twice that of controller rectifiers thus the power convertor for an AC drive can approach three times the cost of a DC drive. 

One of the oldest adjustable-speed drives is the Ward-Leonard system. This consists of an ac to dc motor-generator set and a shunt or compound-wound dc motor. Speed is adjusted by changing the generator voltage. A functional equivalent of this drive uses an adjustable-voltage rectifier feeding a dc motor. This system has only one rotating machine in contrast to the three of a conventional Ward-Leonard system. 

Most induction ac motors are fixed-speed. However, a large number of motor applications would benefit if the motor speed could be adjusted to match process requirements. Motor speed controls are the devices which, when properly applied, can tap most of the potential energy savings in motor systems. Motor speed controls are particularly attractive in applications where there is variable fluid flow. In many centrifugal pump, fan, and compressor applications mechanical power grows roughly with the cube of the fluid flow. To move 80 percent of the nominal flow only half of the power is required. Centrifugal loads are therefore excellent candidates for motor speed control. Other loads that may benefit from the use of motor speed controls include conveyers, traction drives, winders, machine tools and robotics. 

These AC drive systems require the inverters to operate with either low-slip induction motors or reluctance-type synchronous-induction motors.. Such systems are u.sed where DC commutator motors are not acceptable. Examples of such applications are motor operations in hazardous atmospheres and high motor velocities. 

Solid-State DC Drives. The controlled-thyristor rectifier and separate-field DC motor is the solid-state motor drive in greatest use. The combination provides control over at least a 10 1 speed range, plus an additional two to three times by field weakening. Depending upon the power level, the rectifier is operated directly from the AC supply lines, or via a transformer. Typical speed regulation of 2% can be accomplished with a single control system. The horsepower and speed limitations are set by the DC motor, not by the semiconductor rectifiers. The DC motor and rectifier can be combined to any required power level. 

AC vector motors typically operate with a power factor In the range of 0.90 to 0.98 [20]. The power factor for a DC drive system can be considerably lower and as low as 0.5. Replacing an older DC motor with an AC vector motor can be economically attractive due to an Increase In both the efficiency and the power factor. 

Developments in web tension control systems are providing increased capability and function to eliminate problems (Fig. 3-34). They include ultrasonic roll diameter sensors, pneumatic pressure gauge tension monitors, capston-Mt. Hope tension systems, and so on. As an example, replacement of a web-tensioning system s conventional electromechanical drive with an ordinary ac motor enables processors to lower system cost and improve web consistency, as has been done for many years. A vector control system uses a belt and pulley arrangement to remotely couple an encoder to the shaft of the ac induction motor. This approach provides closed-loop feedback, without requiring that one modify the relatively inexpensive motor by installing a special feedback device on it. 

The previous chapters address various aspects of quantitative bond graph-based FDI and system mode identification for systems represented by a hybrid model. This chapter illustrates applications of the presented methods by means of a number of small case studies. The examples chosen are widely used switched power electronic systems. Various kinds of electronic power converters, e.g. buck- or boost converters, or DC to AC converters are used in a variety of applications such as DC power supplies for electronic equipment, battery chargers, motor drives, or high voltage direct current transmission line systems [1]. 

Clearly, a bond graph approach to FDI of systems modelled as a hybrid system is not limited to switched power electronic systems but may be applied to other engineering systems as well for which a hybrid model is appropriate. In the following, the case studies consider faults in a DC to DC boost-converter, in a three-phase DC to AC inverter and in a three-phase rectifier AC to DC. In some motor drives, a rectifier and an inverter are used back-to-back [8], Computations have been performed by means of the open source software program Scilab [21],... 

Mine hoist drive systems have evolved from DC-based systems to AC systems in the majority of new apphcations. Early AC apphcations involved the use of cycloconverter drive systems, however the trend in modern hoisting systems is to utihze cage induction motors on many new installations coupled with Pulse Width Modulated (PWM) style Vcuiable frequency drives (VFDs) complete with Active Front End (AFE) technology. 

The hoist drive solution presented in this work, which is based on the Ingedrive MVlOO medium voltage AG frequency converters, contains two completely independent Active Front End Rectifier and Inverter sets under the well-known AC-DC-AC topology. The entire drive system solution allows the operation at full speed and full load (then full hoist performance, with no limitation) even in the case that one frequency converter (AG-DC-AC set) is unavailable. The solution presents some extra benefits comparing to the original hoist system solution that was based on two slip ring rotor wound induction motors in which the speed control... 

The hoist was supphed with a high voltage AC PWM drive, coupled to a 76.4 rpm overhung synchronous motor. A pony drive was provided to allow controlled movement of the hoist should personnel become stranded in the shaft on a conveyance during maintenance activities, due to a power outcige or fculme of the main drive system. 

The use of an adjustable-frequency power supply (ac inverters) in conjunction with the induction motor results in an adjustable-speed drive system.The speed of the motor is adjusted by controlling the output frequency of the ac inverter.Thus the induction motor can be used on many adjustable-speed apphcations. The speed-torque motor performance at different input motor frequencies is Ulustrated by Fig. 5.127a. This permits the apphcation of induction motor adjustable-speed systems to loads such as fans and pumps for flow control with considerable power savings over fixed-speed systems with dampers or valves for flow control. Figure 5.127Z) shows the performance of a 10-hp motor adjustable-frequency system driving a fan load. 

The drive system has a frictionless asynchronous AC motor and inductive position sensor. The ranges are listed, accuracy is better than +10% at 0.00002 mN-m. 

Conventional back-drive systems on decanters perform a braking duty. As such many of them have the ability to regenerate power. Although an eddy current brake is unable to do this. AC. DC. and inverter motors, and hydraulic systems are. The braking process causes the electric motor to act as a generator and so returns power to the grid. In the case of the DC and inverter motor, the power regenerated is usually considered dirty unless electric filters are fitted which smooth out unwanted harmonics. 

Toyota Motor Corporation has also been developing zinc/bromine batteries for electric vehicles. - A concept urban transportation vehicle, called the EV-30, has been designed for use with Toyota s zinc/broinine battery and has been displayed at motor shows in Japan. This two-seater vehicle would transport people in buildings, shopping centers, small communities, and to and from train stations—a horizontal elevator concept. The front-wheel-drive system uses an AC induction motor built by Toyota Motor Corporation. The battery system is modular zinc/bromine at 106 V and 7 kWh. 

The initial pilot plant agitation system was powered by a 40-kW AC motor with a standard gearbox. A problem with AC drives is that they do not deliver full power below 10 rpm. In the situation where the processing conditions produce a tacky material the rotational speed falls to below 10 rpm and the system does not... 

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