mcc regulation - General structure

The structures of the regulations are chosen to meet several needs:

• First, the machine must be controlled (or servo-controlled) in such a way as to impose the desired speed, position or torque on the load;

• it is also necessary to provide certain additional functions, the most important of which concern safety. The structures are chosen so that the current amplitude can be limited (protection in I _max where I is the current) "actively" by the control and not by protections such as circuit breakers or fuses. In addition, we can limit the current variation [protection in ${(\text{d}i\text{/d}t)}_{\text{max}}$ ] to enable the commutator to switch correctly, even when operating at the limits. We can also limit heating due to Joule effect losses (protection in $\int i^2\text{d}t$ ) or impose particular torque profiles, for example to avoid exciting certain natural frequencies in the mechanical transmission chain. There are various types of protection, used or not, depending on the application or motor type;

• secondary functions, necessary for converter operation, must also be implemented (e.g. regulation can provide the sign of the desired current, so that the logic driving bidirectional thyristor converters can choose which bridge to drive); similarly, overspeed operation requires action on machine excitation.

Controls will therefore have more tasks than those usually considered in traditional servo-controls. In addition, the converter is not a true linear amplifier, and its possible non-linear operation must be taken into account.

These problems have been solved by the widespread use of multiple loops. The aim is to regulate each useful machine variable separately, which also allows it to be limited (i.e. active protection) or used for the various functions required. Furthermore, the order of the overall transfer function of the system is quite high, but the internal loop structure enables the system to be decoupled into several sub-systems whose elementary transfer functions are of sufficiently low order to make it easy to synthesize correctors.

In this article, we first present the sensors used to measure the various quantities required for control systems. Then we'll define the representative control...