Parameter Setting of Analog Speed Controllers

Abstract

Practical speed controlled systems comprise delays in the feedback path. Their torque actuators, with intrinsic dynamics, provide the driving torque lagging with respect to the desired torque. Such delays have to be taken into account when designing the structure of the speed controller and setting the control parameters. In this chapter, an insight is given into traditional DC-drives with analog speed controllers, along with practical gain-tuning procedures used in industry, such as the double ratios and symmetrical optimum. In the previous chapter, the speed controller basics were explained with reference to the system given in Fig. 1.2, assuming an idealized torque ac-tuator (A the parameter settings are discussed for the realistic speed-control systems, including practical torque actuators with their internal dynamics A (). Traditional DC drives with analog controllers are taken as the design example. Delays in torque actuation are derived for the voltage-fed DC drives and for drives comprising the minor loop that controls the armature current. Parameter-setting procedures commonly used in tuning analog speed controllers are reviewed and discussed, including double ratios, symmetrical The driving torque T em , provided by a DC motor, is proportional to the ar-mature current i a and to the excitation flux Φ p. The torque is found as T em = k m Φ p i a , where the coefficient k m is determined by the number of rotor conductors N R (k m = N R /2/π). The excitation flux is either constant or slowly varying. Therefore, the desired driving torque T ref is obtained by injecting the current i a = T ref /(k m Φ p) into the armature winding. Hence, the torque response is directly determined by the bandwidth achieved in controlling the armature current. In cases when the response of the current is faster than the desired speed response by an order of magnitude, neglecting the torque 3.1 Delays in torque actuation W s W (s) = 1). In this chapter, the structure of the speed controller and optimum, and absolute value optimum. The limited bandwidth and performance limits are attributed to the intrinsic limits of analog implementation.