The technology of solid-state adjustable speed ac drives was launched in the 1960's. Since then many innovations in devices, circuits, control theory, and signal electronics have made a considerable contribution to this technology. With the heritage of past experience, and the projection of present trends, an almost certain prediction can be made that adjustable speed ac drives will find widespread applications in industry before the end of this decade. The paper reviews the present status of ac drives technology in which the salient technical features of ac machines, converters, controls, and performances of the integrated drive systems have been discussed, and wherever possible, the appropriate trend of the technology has been indicated.

Adjustable speed AC drives&#8212;A technology status review

With thyristor-based full-bridge module (TFBM) embedded in the converter valve, an evolutional line-commutated converter (ELCC) is proposed to enhance the commutation failure (CF) immunity. The operating principle of the TFBM and the coordinated control strategy between the TFBM and series-connected valve are presented. The voltage–current stress of the TFBM is analyzed, and the method to select the capacitor parameter is also presented. Then, the ELCC high-voltage direct current (HVDC) under the presented control strategy is developed in PSCAD/EMTDC, and its dynamic responses under ac fault condition are compared with that of capacitor-commutated converter-based HVDC (CCC-HVDC) and conventional line-commutated converter (LCC) HVDC. A dual-infeed HVDC system with TFBM embedded in one HVDC link is also developed to further investigate the merits of TFBM. Finally, the increased capital cost and power loss of the ELCC-HVDC are discussed. The results show that the presented ELCC-HVDC has the ability to reduce the CF risk effectively and also exhibits favorable steady-state and dynamic performances.

An Evolutional Line-Commutated Converter Integrated With Thyristor-Based Full-Bridge Module to Mitigate the Commutation Failure

A method of providing a unified power control of a motor including providing a first inverter system, a second inverter system, and a motor coupled therebetween; coupling the first inverter system coupled to a first energy source; coupling the second inverter system coupled to a secondary energy source; generating a first pulse width modulated signal; and generating a second pulse width modulated signal. The first inverter system and the second inverter system are driven with the first pulse width modulated signal and the second pulse width modulated signal respectively in order to control a fundamental component of an output voltage of the first inverter system and the second inverter system to control the motor.

Unified power control method of double-ended inverter drive systems for hybrid vehicles

A high speed compressor (10) includes a gear box (11), two compressing units (12, 13) supported on opposite side walls of the gear box (11) and a bull gear (32) rotatably placed in the gear box (11). Each compressing unit includes a scroll (15, 16) and an impeller (18, 19) rotatably housed in the scroll (15, 16). The impellers (18, 19) share an impeller shaft (22) extending into the gear box (11). A pinion gear (23) is mounted on the impeller shaft (22) such that it engages with the bull gear (32). A drive shaft (30) extends from the bull gear (32) out of the gear box (11) along a center axis of the gear box (11). An induction motor (35) is connected with the drive shaft (30) for causing the impellers (18, 19) to rotate by way of the bull gear (32) and the pinion gear (23). An inverter (40) is connected with the induction motor (35) at its one end and with a commercial power source (43) at the other end for converting an A.C. power from the commercial power source (43) into an A.C. power having a desired frequency and feeding it to the induction motor (35) for driving of the induction motor (35).

Method for driving a high speed compressor

Certain exemplary embodiments can comprise a system comprising an electric drive system for a machine. The system can comprise a rectifier adapted to convert AC power from an alternator to DC power. The system can comprise an inverter adapted to receive DC power from the rectifier and provide power to a traction motor and/or auxiliary devices. Certain exemplary embodiments can comprise a system and method for dissipating excess energy from a machine.

Auxiliary bus method

An arrangement to provide variation of the speed or other operating parameters of an electrical machine without connection to the rotor. The machine is of the induction type having a winding in separate parts to create a flux movable in the air-gap different speeds by the alteration of current in a part of the winding. In one example the current is altered by a variable impedance connected to one winding part, the other part being connected to an electrical supply. Another example, FIG. 6, shows two machines (NM 1 , NM 2 ) arranged to drive a rail vehicle through smooth rail wheels attached to the machine rotor axles. A single, variable-frequency, inverter (NI) drives both machines and is connected to part (MP) of each machine winding. Other parts (AP) of each machine winding are connected together by a link (NC). In operation power (real or reactive) is transferred between the machines along the link to equalize the torque of the machines. Run-away of one machine while the other stalls is thereby avoided.

Variable-speed electrical machines

A new mechanism of continuously generating reactive kVA from the stator of abrsh ess induction machine is formulated and tested on 10 kW and 35 H. P. laboratory machines. A space-transient magnetic wave, travelling at rotor speed must be artificially created and at least two distinct windings of different pole-pitch must be incorporated. The per -unit kvar generation effect increases with machine rating, and leading power factor operation of the entire machine is viable for large industrial motors and power system induction generators.

The Asynchronous Condenser: A Brushless, Adjustable Power Factor Induction Machine

Several designs detailing the construction of brushless cage-rotor induction machines operating at unity or leading power factor at the 35-hp level have recently been published [1]-[3]. The experimental machine combines the torque characteristics of a conventional cage induction machine with the leading power-factor (PF) capability of an overexcited dc field synchronous condenser into one unit using a common cage rotor and a common stator core. The ability of this machine to naturally commutate a high-power current-source thyristor inverter is apparent without any need for capacitors. The preferred adjustable speed propulsion arrangement consists of a mains-fed phase-delay-rectifier (PDR), high-voltage dc link, and a current-source inverter powering a ten-pole traction motor with constant V/Hz control. The drive system provides continuously variable torque during motoring, and regenerative braking modes and specific details are given for a 150-hp cage-rotor traction motor and converter, capable of natural commutation up to 200 Hz, currently under development.

Development of an Induction Machine Commutated Thyristor Inverter for Traction Drives

The theory of continuously generating large amounts of reactive kVA from the stator of brushless, cage-rotor induction machines in which the total input current may be at a unity or leading power factor, has recently been published with initial results from a 35 H. P. machine[1-5]. The only major difference between this machine and conventional rotary motors or induction generators is in the stator winding layout. A space-transient magnetic wave travelling at rotor speed is artificially introduced by using at least two distinct stator pole-pitches. This paper concentrates on the first test results obtained from a second prototype machine rated at 150 H. P. which operates at unity power factor directly on the 50 Hz mains.

Test Results Obtained from a Brushless Unity-Power-Factor Induction Machine

A variable-speed thyristor inverter system using a cage-rotor induction motor for natural commutation and as the prime mover has been built. The development has concentrated on the 35 and 150 H.P. machines rather than in the inverter units which are simply 6-device bridge circuits. It is fully anticipated to extend development beyond the 150 H.P. range.

Stephen B. Kuznetsov

Papers

Variable-speed electrical machines

The Asynchronous Condenser: A Brushless, Adjustable Power Factor Induction Machine

Development of an Induction Machine Commutated Thyristor Inverter for Traction Drives

Test Results Obtained from a Brushless Unity-Power-Factor Induction Machine

Development of an induction machine commutated thyristor inverter for traction drives