Nidec Digitax HD M753 User Manual

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Nidec Digitax HD M753 User Manual Manual pdf 92 page image

SafetyinformationProductinformationMechanicalinstallationElectricalinstallationGettingstartedBasicparametersRunningthe motor Optimization EtherCATinterfaceSD CardOperationOnboardPLCAdvancedparameters Diagnostics UL listinginformation92 Digitax HD M753 Control User GuideIssue Number: 38.2 Current limitsThe default setting for the current limit parameters is:• 165 % x motor rated torque producing current for open loop mode• 250 % x motor rated torque producing current for RFC-A and RFC-Smodes.There are three parameters which control the current limits:• Motoring current limit: power flowing from the drive to the motor• Regen current limit: power flowing from the motor to the drive• Symmetrical current limit: current limit for both motoring and regenoperationThe lowest of either the motoring and regen current limit, or thesymmetrical current limit applies.The maximum setting of these parameters depends on the values ofmotor rated current, drive rated current and the power factor.The drive can be oversized to permit a higher current limit setting toprovide higher accelerating torque as required up to a maximum of1000 %.8.3 Motor thermal protectionA dual time constant thermal model is provided to estimate the motortemperature as a percentage of its maximum allowed temperature.The motor thermal protection is modelled using losses in the motor. Thelosses in the motor are calculated as a percentage value, so that underthese conditions the Motor Protection Accumulator (04.019) wouldeventually reach 100 %.Percentage losses = 100 % x [Load related losses + Iron losses]Where:Load related losses = (1 - Kfe ) x [(I / (K 1 x IRated )] 2Iron losses = K fe x (w / wRated ) 1.6Where:I = Current Magnitude (00.012)I Rated = Rated Current (00.046)K fe = Rated Iron Losses As Percentage Of Losses (04.039) / 100 %The Motor Protection Accumulator (04.019) is given by:Pr 04.019 = Percentage Losses x [(1 - K2 ) (1 - e-t/) + K 2 (1 - e- t/)]Where:T = Motor Protection Accumulator (04.019)K 2 = Motor Thermal Time Constant 2 Scaling (04.038) / 100 %1 = Motor Thermal Time Constant 1 (00.053)2 = Motor Thermal Time Constant 2 (04.037)K 1 = Varies, see belowIf Rated Current (00.046)  Maximum Heavy Duty Current (00.032)Figure 8-1 Motor thermal protection (Heavy Duty)If Pr 04.025 is 0 the characteristic is for a motor which can operate atrated current over the whole speed range. Induction motors with thistype of characteristic normally have forced cooling. If Pr 04.025 is 1 thecharacteristic is intended for motors where the cooling effect of motorfan reduces with reduced motor speed below 50 % of base speed/frequency. The maximum value for K1 is 1.05, so that above the knee ofthe characteristics the motor can operate continuously up to 105 %current.When the estimated temperature in Pr 04.019 reaches 100 % the drivetakes some action depending on the setting of Pr 04.016. If Pr 04.016 is0, the drive trips when Pr 04.019 reaches 100 %. If Pr 04.016 is 1, thecurrent limit is reduced to (K - 0.05) x 100 % when Pr 04.019 reaches100 %.The current limit is set back to the user defined level when Pr 04.019falls below 95 %. The thermal model temperature accumulatoraccumulates the temperature of the motor while the drive remainspowered-up. By default, the accumulator is set to the power down valueat power-up. If the rated current defined by Pr 00.046 is altered, theaccumulator is reset to zero.The default setting of the thermal time constant (Pr 00.053) is 89 s whichis equivalent to an overload of 150 % for 100 s from cold.8.4 Switching frequencyThe default switching frequency is 8 kHz, however this can be increasedup to a maximum of 16 kHz by Pr 00.041 (dependent on drive size). Theavailable switching frequencies are shown below.Table 8-1 Available switching frequenciesIf switching frequency is increased from 8 kHz the following apply:1. Increased heat loss in the drive, which means that derating to theoutput current must be applied.See the derating tables for switching frequency and ambienttemperature in the Digitax HD M75X Series Installation andTechnical Guide.2. Reduced heating of the motor - due to improved output waveformquality.3. Reduced acoustic noise generated by the motor.4. Increased sample rate on the speed and current controllers. A tradeoff must be made between motor heating, drive heating and thedemands of the application with respect to the sample time required.Table 8-2 Sample rates for various control tasks at eachswitching frequency0.000.701.00Pr = 0Pr = 104.02504.0251.00 1.05Base speed/frequency50% of basespeed/frequencyKDrivesize Model 2kHz3kHz4kHz6kHz8kHz12kHz16kHz1All       23Level 3, 6, 12 kHz 2, 4, 8, 16 kHz OpenloopRFC-ARFC-SLevel 13 kHz - 167 μs6 kHz - 83 μs12 kHz - 83 μs2 kHz - 250 μs4 kHz - 125 μs8 kHz - 62.5 μs16 kHz - 62.5 μsPeak limit CurrentcontrollersLevel 2 250 s2 kHz - 500 μs4 kHz - 250 μs8 kHz - 250 μs16 kHz - 250 μsCurrentlimit andrampsSpeedcontrollerand rampsLevel 3 1 ms Voltage controllerLevel 4 4 ms Time critical userinterfaceBackground Non-time critical userinterface