Motors & Drives Information

Direct Torque Control (DTC) is widely used as a method for controlling AC motors in many demanding applications. It is a unique method for controlling AC. motors. In pulse-width modulation (PWM) drives, the output frequency and voltage are the primary control reference signals for the power switches, rather than the desired torque in/of the motor shaft. For those who are not familiar with inverter technology, the DTC principle can be illustrated most accurately via this mechanical analogy: the continuous calculation of the best angle at which to rotate a shaft, with a given arm length and the forces available. These electrical "force vectors" are generated with the help of semiconductor switches called Integrated Gate Bipolar Transistors (IGBT).

Testing of rotating machines like gears, engines, and complete cars is a demanding task. Iligli accuracy and dynamic load control - that is, control of torque - is needed both for day-in-day-out testing, but excels., specifically, on those tests with new complex electronic functions, such as ABS, EPS - or electromechanical innovations like final - clutch transmissions being introduced in the current generation of automobiles. AC motors drive these test rigs. When manufacturing test rigs for engines, transmission, or chassis dynamometers with high-performance requirements, careful consideration must be given to the AC machines and drives used in such applications (control of speed and torque are paramount). The way the AC; motor is controlled by the drive has a primary effect on these considerations.

Chassis dynamometers are typically used to test the performance of vehicle, exhaust emission, fuel consumption, noise, and fine-tuning of exhaust, catalyst, and motor fuel-injection system. It is well known that dynamometers with AC motor technology offer the best platform to realize high accuracy, dynamics, and energy savings.

Dynamometers should simulate the real highway precisely. This requires that, during acceleration and deceleration, the roll inertia be compensated dynamically to match the mass of the tested vehicle and the real road. To be able to realize such high-dynamic online compensation (real-world, real use), the load torque of the roll motor must be controlled accurately and with extreme precision at every speed point.

Testing geai-shifting-and-synchronization, calibration of automatic transmissions, clutching, and durability - these are typical testing needs. Inherently, these cases require a capability to change load torque very quickly. And, transmission test-stand configuration can include several motors - one simulating the engine, and two or even more for the simulation of the load. This requires mutual coordination of drives operation; the faster and more accurate it is, the better it simulates real-world conditions like differential-gear operation.

For engine dynamometers, the dynamic performance is the key issue to ensure that you can simulate real systems dynamically and accurately. DTC drive technology answers this challenge directly. The test system's overall dynamic performance can be quantified by looking at the delay from reference change to change in AC motor torque.

The dynamics of the electrical system are defined by several fundamental elements: the electrical and mechanical characteristic of the AC machine (leakage inductance and inertia); the torque-control cycle of the AC drive; and any delay from speed/torque reference via any drive interface to the control-cycle loop itself. DTC controls motor torque every 25 µs (microseconds).

Once the torque reference is changed, DTC automatically selects the best voltage vector to achieve the desired torque, and checks every 25 µs if this vector is still the hest one to maximize torque rise, or whether another vector should be used. The actual rise then is solely dependent on motor characteristics, such as leakage inductance. The torque rise time with a standard motor is between 1-2 milliseconds (ms), measured from current rise. For high-speed dynos, the leakage inductances are typically smaller, thus requiring shorter current- and torque-rise times.

The repeatability of testing is always important, but it is of particular importance when testing engines and complete cars for emissions. DTC has torque repeatability of less than ±0.5% of nominal torque. This means that the load applied will be the same time after time, and the measurement results from a test cell are comparable with each other. The benefits are reduced testing requirements, improved test data quality, i.e., reduced overall testing time.

# posted by Medical Information : 11:24 PM