FC 300 Design GuideIntroduction to FC 300Optimization of the process regulatorThe basic settings have now been made; all that needs to be done is to optimize the proportionalgain, the integration time, and the differentiation time (par. 7-33, 7-34, 7-35). In mostprocesses, this can be done by following the guidelines given below.1. Start the motor2. Set par. 7-33 (Proportional Gain) to 0.3 and increase it until the feedback signal againbegins to vary continuously. Then reduce the value until the feedback signal hasstabilized. Now lower the proportional gain by 40-60%.3. Set par. 7-34 (Integral Time) to 20 sec. and reduce the value until the feedback signalagain begins to vary continuously. Increase the integration time until the feedbacksignal stabilizes, followed by an increase of 15-50%.4. Only use par. 7-35 for very fast-acting systems (differentiation time). The typical value is four timesthe set integral time. The differentiator should only be used when the setting of the proportionalgain and the integral time has been fully optimized. Make sure that oscillations in the feedbacksignal are sufficiently damped by the low-pass filter on the feedback signal.NOTEIf necessary, start/stop can be activated a number of times in order to provokea variation of the feedback signal." Ziegler Nichols Tuning MethodIn order to tune the PID controls of the adjustable frequency drive, several tuning methods can be used.One approach is to use a technique which was developed in the 1950s but which has stood the test oftime and is still used today. This method is known as the Ziegler Nichols tuning.NOTEThe method described must not be used on applications that could be damaged by theoscillations created by marginally stable control settings.The criteria for adjusting the parameters arebased on evaluating the system at the limit ofstability rather than on taking a step response.We increase the proportional gain (Ku ) until weobserve continuous oscillations (P u ) (as measuredon the feedback), that is, until the systembecomes marginally stable. The correspondinggain (called the ultimate gain) and the period ofoscillation (also called the ultimate period) aredetermined as shown in Figure 1. Figure 1: Marginally stable systemP u should be measured when the amplitude of oscillation is quite small. Then we "backoff" from this gain again, as shown in Table 1.K u is the gain at which the oscillation is obtained.39MG.33.B6.22 - VLT is a registered Danfoss trademark
