Hardware Systems Versus Microprocessor Control:

The Hardware Systems Versus Microprocessor Control control of electric drives offers the following advantages when compared to the dedicated hardware control.

As has already been discussed, the use of microprocessors reduces the com­plexity of the system. The software supported control using microprocessors to perform the functions of controllers eventually result in the least hardware making the system economically viable. The present day developments in this area will make the system cost effective.

The reliability of the control of the drives is higher with microprocessors than with dedicated Hardware Systems Versus Microprocessor Control. The number of parts is reduced. Soft­ware programs are employed for various controls. The control equipment can be realised as a unified hardware.

The control is free from drift and parameter variations due to temperature while in operation using microprocessors whereas the control is affected by these when the control is implemented with dedicated hardware. The calcu­lations are exact except for the errors in the ADD converters.

The information can flow in both forward and backward directions. This property is very important and has significance in the control using micropro­cessors. Proper shielding may minimise the EMI problems. The control may be extended as it is compatible with the host computer.

The speed detection schemes are completely digital, avoiding the errors of measurement. This improves the accuracy even at very low speeds. Control efficiency is more. The concepts of modern control theory can be used in the control.

A generalised Hardware Systems Versus Microprocessor Control supported by a flexible software can take care of a particular application. The software will have possibilities of addition , deletion and upgrading.

Microprocessor control is capable of performing the control functions, such as decision making, complicated computations, etc. These enhance the power of the microprocessors and are not possible With dedicated hardware. The role of a microprocessor is to replace the logic circuits that control the fir­ing angle of SCRS. In some instances it performs, in addition, the control computations. Since a control cannot be applied until it is calculated or com­puted, there is invariably a delay between the beginning of computation and application of control. In the case of SCR control, if the delay is too long the time corresponding to a particular firing time may have already passed. The controller must then fire at a different instant of time in the present cycle or wait for the correct time in the next cycle. A suboptimal control will result in both cases. Thus in order to avoid long delays and particularly with slow microprocessors, the control law, if to be implemented by a micro­processor, must be simple. Ideally determining the necessary controls should require only table look-up operations and any computations should be kept to a minimum.

Microprocessor control also permits several other functions, such as data acquisition, monitoring and warning, diagnosis, etc. The fault diagnosis of digital control systems is easier than that of a dedicated Hardware Systems Versus Microprocessor Control system. It is easy to maintain the system. However, the microprocessor control has also certain disadvantages.

The communication between the microprocessor and the analog circuitry is accomplished by A/D or D/A converters. There are sampling or quantizing errors. These, however, can be minimised by increasing the bit size.

The response is more sluggish and slower than that of a dedicated hard­ware. This is mainly because the dedicated Hardware Systems Versus Microprocessor Control can handle the signals and process them almost simultaneously, without any time delay. The micro­processors on the other hand can process the signals only in a sequence or in a serial manner, causing a delay in processing. Higher sophisticated sys­tems, using microprocessor control to perform different functions may exhibit stability problems. Special techniques are required to enhance the speed and assure stable operation.

The development of necessary software may be costly and time consuming. The cost may be justified depending on the size of the production.

The variables are not a ressible for measurement using instruments. The parameters cannot be easily monitored or changed under operating conditions.

Modifications in the system are possible to overcome several of these disad­vantages. Multiprocessor control increases the speed of the system. Resolu­tion can be increased by increasing the bit size. A microprocessor based digital control system, which is priced at the same level as an analog control system but compares favourably with the latter in terms of controlability, reliability and available functions, has become practical.