Motor drive inverter

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. 

Figure 3-14. Typical invester AC motor drive consisting of rectifier-DC link, adjustable-frequency inverter, and induction of synchronous motor [10].

Ziang, Y. Q., Instability Compensation of V/Hz PWM Inverter-Fed Induction Motor Drives, Conference Record of the 1997 IEEE 32nd IAS Annual Meeting, 1997, pp. 613-620. 

Modern frequency converters now make it possible to handle smaller automation tasks via the motor drive alone. Here, the controller intended for controlling the inverter assumes monitoring and control tasks that it can communicate externally via the available (or expandable) I/O. Moreover, it is also possible to connect various bus systems. Sometimes the functioning of small programmable logic controls can be integrated into the inverter. Parameters and control function programming can be entered via a small user interface. It may be even more convenient to connect to a laptop with an RS 232 interface. 

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],... 

In a paper on fault tolerant power inverter topologies used for alternating current (AC) motor drives [30], Welchko et al. distinguish the following faults inside the... 

The drive inverter supplies motor current at varying voltage and frequency. The inverter section provides power at a power factor which is a function of motor power factor, load, magnetization current and operating speed. 

Figure 4 shows both the motor current (inverter output) and the converter power (drive input kVA or kW). The converter provides current to the DC bus at unity power factor. Current is supplied at rated drive input voltage and power utility frequency. Because of the separation of the drive input and output sections provided by the DC bus, the average input current at rated input voltage will be less than the average motor current, which is supplied at a lower average output voltage. 

The input RMS kVA appears to be less than the motor power rating. This apparent anomaly is because a large amount of motor current is apphed by the inverter (output) at low motor voltage diuing the hoist creep and acceleration phases. This kVA demand is supplied by the converter at the drive input voltage (3,550V), and so the input current is lower than the motor current dming these phases. While the inverter is subject to the motor ciurent, the converter supplies the only the real power (plus losses) to the drive inverter and motor at unity power factor. 

In the case of constantly fluxed synchronous motors, the stator cmrent will follow the motor torque more closely. After adding excitation losses, the synchronous motor efficiency is still shghtly better than the induction motor. The drive inverter for a synchronous motor supplies the armature or torque producing current, compared to the induction motor apph-cation where the inverter must supply torque producing current and magnetising current In the synchronous motor application, the motor operates at unity power factor, which reduces current demand in the inverter section. As a result, there are fewer losses in the inverter and motor, and to a lesser extent fewer losses in the converter. 

By operating a geared hoist drive above rated speed, the drive inverter and motor rating can be optimised. 

SEPARATE DUTY CYCLE MODEL FOR DRIVE INVERTER AND MOTOR... 

Hoist RMS Power calculations must therefore be different for motor and drive components. Motor current is provided by the drive inverter, which is subject to the same duty cycle as the motor. A model giving the 5 minute RMS as well as the 20 minute RMS duty is required in order to correctly model the heating for both the drive inverter (output) section and the motor. By calculating the 5 minute and 20 minute RMS thermal duty over a period of 30 minutes, a more accurate estimate of the component thermal loading can be studied. 

The maximum value of the 20 minute RMS for the duty in the example used is 955 A, and the maximum value of the 5 min RMS is 1,130 A. For this application the drive inverter must be rated 22% higher than the calculated motor Constant RMS current. 

While it is generally accepted that the motor electrical thermal cycle be approximated with a steady state calculation, this assumption ignores the shorter time constant of the drive, as well as some parts of the motor. Close attention must therefore be paid to the short term RMS duty of the drive inverter. 

As has been demonstrated in examples above, the converter RMS kVA loading is less than the inverter and motor RMS loads in mine hoisting apphcations. In the example summcuized in Table 1, a 3,000 kW drive, motor cuid inverter apphed to a selected mine hoist duty required an RMS current in the motor of 591 A, while the input converter RMS current was calculated... 

Tadakuma et al, S., Fundamental Approaches to PWM Control based GTO Inverters For Linear Synchronous Motor Drives, in Proc. IEEE IAS Annual Meeting, pp. 847-852,... 

The function of an inverter is to convert a DC input voltage to an AC output voltage. The output voltage and frequency may be fixed or variable depending on the application. Inverters find several applications, some of them are in variable speed AC motor drives, uninterruptible power supplies (UPS), mobile AC power supplies (operating on a battery), induction heating, etc. They are also used as the front stage in DC-to-DC converters. 

Figure 10.70 shows a single-phase CSI using thyristors. A three-phase version of this type of inverter is widely used in induction motor drives. 

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)... 

A standard gear pump can have one or more exit streams as needed. Each stream has a constant volumetric output based on the rotational speed (RPM) of the gears. The gear pump is driven by an AC motor with inverter or vector drive speed control. The exit pressure from a metering pump in a typical spinning process will range from approximately 7000 kPa (1000 psi) to 25 000 kPa (3500 psi). Once the pressure reaches 25 000 kPa (3500 psi), the process is typically shut down and the filter media replaced. 

The average prices of the batch centrifuge are shown in Fig. 18-154. All the models include the drive motor and control. In Fig. 18-154, the inverting filter, horizontal peeler, and the advanced vertical peeler are the premium baskets especially used for specialty chemicals and pharmaceuticals. Control versatility with the use of programmable logic control (PLC), automation, and cake-heel removal are the key features which are responsible for the higher price. The underdriven, top-driven, and pendulum baskets are less expensive with fewer features. 

A converter unit is used for the control of d.c. machines and also to provide a d.c. source to an inverter unit controlling an a.c. machine. In d.c. drives the d.c. voltage after tlie converter unit should be variable, whereas for in a.c. drive it is kept fixed. The voltage is varied by the invener unit. A convener unit is the basic power conversion scheme to convert an a.c. supply to a d.c. supply. Conventionally they are also known us rectifier units and c in be arranged in four different modes to suit dilTerent applications of a motor as follows ... 

In addition to the above inverter systems there is one more system, called a cyclo converter system. These drives tire employed for very large motors, when IGBTs in such ratings are a limitation. It converts the fixed a.c. supply frequency to a variable frequency, generally lower than rated, directly and without rectifying it to a d.c, source. They are basically frequency converters. This system is more complex and expensive and has only... 

A relatively new innovation for use in electric motor compressor drives is the variable frequency power source. Fundamentally, the power source converts an existing three-phase source into DC then uses an inverter to convert back to a variable frequency supply. Thyristors or transistors are used to switch the output at the required frequency. 

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