Nidec Unidrive M600 Series Design Manual

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Nidec Unidrive M600 Series Design Manual Manual pdf 143 page image

Safetyinformation Introduction ProductInformationSystemdesignMechanicalInstallationElectricalInstallationGettingstarted Optimization Parameters TechnicaldataComponentsizing Diagnostics ULInformationUnidrive M Regen Design Guide 143Issue Number: 18.2 Regen controllersThe Regen drive uses a DC bus voltage controller with inner currentcontrollers as shown in Figure 8-2:Figure 8-2 Regen controllersThe gains of the voltage and current controllers affect the stability of theRegen system, with incorrect settings resulting in over-voltage or over-current trips.8.3 Current loop gainsThe defaults current loop gains (Kp, Pr 04.013 and Ki, Pr 04.014) aresuitable for most standard Regen systems. However if the inputinductance is significantly higher the proportional gain may need to beadjusted as described following.The most critical parameter for stability is the current controllerproportional gain, Pr 04.013. The required value for this is dependentupon the Regen drives input inductance. If the inductance of the supplyis a significant proportion of the recommended Regen inductori.e. 60/IDR mH per phase,Where:I DR is the drive rated currentthen the proportional gain may need to be increased.The supply inductance is likely to be negligible compared to the Regeninductor value with small drives, but is likely to be significant with largerdrives. The proportional gain, Pr 04.013 should be adjusted asdescribed following using the total inductance per phase.The proportional gain, Pr 04.013 can be set by the user so thatPr 04.013 = Kp = (L / T) x (I fs / V fs ) x (256 / 5)Where:T is the sample time of the current controllers. The drive compensatesfor any change of sample time, and so it should be assumed that thesample time is equivalent to the lowest sample rate of 167 μs.L is the total input inductance.I fs is the peak full-scale current feedbackI fs = Full Scale Current Kc (11.061) x √2Vfs is the maximum DC bus voltage.Therefore:Pr 04.013 = Kp = (L / 167 μs) x (Kc x √2 / Vfs) x (256 / 5)= K x L x KcWhere:K = [√2 / (Vfs x 167 μs)] x (256 / 5)There is one value of the scaling factor K for each drive voltage rating asshown in the table below.This set-up will give a step response with minimum overshoot after astep change of current reference. The approximate performance of thecurrent controllers will be as given below. The proportional gain can beincreased by a factor of 1.5 giving a similar increase in bandwidth,however, this gives a step response with approximately 12.5 %overshoot.Table 8-1 Current loop sample timesAs previously detailed the current controller integral gain, Pr 04.014 isnot so critical with the recommended value being the default setting.8.4 Voltage controller proportional gainKp (Pr 03.006)The DC bus voltage is controlled by a PI controller, which provides thereference for the real component of current from the inverter terminals tothe supply. The power input parameters (Power Input 1 (03.010),Power Input 2 (03.013), Power Input 3 (03.014) or Power Input kW(03.018)) are provided to give a power feed forward term, at the outputof the PI controller, from the motor drives connected to the DC bus.If possible the power feed forwards should be used so that the PIcontroller is simply providing a trim to the DC bus voltage. In most casesthe default voltage controller gains can be used, however the effect ofthe gains and the response of the voltage controller is discussed below.For the purpose of analyzing the voltage controller response it isassumed that a power feed-forward term is not provided. If the powerflow from the DC bus is increased (i.e. motor is accelerated by a motordrive connected to the DC bus) the DC bus voltage will fall, but theminimum level will be limited to just below the peak rectified level of thesupply provided the maximum rating of the unit is not exceeded. If thepower flow to the DC bus is increased (i.e. motor is decelerated by amotor drive connected to the DC bus) the DC bus voltage will rise. If thepeak of the DC bus voltage reaches the over voltage level the Regendrive will trip. A rapid transient where power into the DC bus is increasedis shown below in Figure 8-3.Figure 8-3 DC Bus transientThe example shown is for a very rapid load change where the torquereference of the motor drive has been changed instantly from one valueto another.Drive voltage rating (11.033) Vfs K200 V 415 V 1045400 V 830 V 522575 V 990 V 438690 V 1190 V 364VoltagecontrollerCurrentcontrollers- -DC busvoltagefeedbackCurrentfeedbackPr DC03.005bus voltageset pointSwitching frequency kHz Current control sample time (T)μs3 1674 1256 838 62.512 8316 62.5Regen unitDC bus voltageReal current100ms/div