Retune the Drive Parameters

This example shows how to modify the parameters of an electric drive using the AC3 drive model. In this example, the nominal power of the motor changes from 200 hp to 5 hp. To retune the drive parameters:

• Modify Motor Parameters

• Retune Parameters of the Flux Regulator

• Retune Parameters of the Speed Regulator

• Retune Parameters of the DC Bus Voltage

• Simulate and Analyze the Results

Modify Motor Parameters

1. Open the example: ac3_example. Type ac3_example in the MATLAB^® Command Window.

   The parameters are set for a 200 hp motor.

2. Simulate the model in Accelerator mode and observe the results.

3. Double-click the Field-Oriented Control Induction Motor Drive block and select the Asynchronous Machine tab. Copy these parameters of the 5 hp motor into the drive's mask.

   Parameter	Value
   Reference frame	Rotor
   Discrete solver model	Forward Euler
   Electrical parameters > Nominal values > Power	3730
   Electrical parameters > Nominal values > Voltage	460
   Electrical parameters > Nominal values > Frequency	60
   Electrical parameters > Equivalent circuit values > Main winding stator > Resistance	1.115
   Electrical parameters > Equivalent circuit values > Main winding stator > Leakage inductance	0.005974
   Electrical parameters > Equivalent circuit values > Main winding stator > Mutual inductance	0.2037
   Electrical parameters > Equivalent circuit values > Main winding rotor > Resistance	1.083
   Electrical parameters > Equivalent circuit values > Main winding rotor > Leakage inductance	0.005974
   Electrical parameters > Initial Currents > Ia_Magnitude	0
   Electrical parameters > Initial Currents > Ia_Phase	0
   Electrical parameters > Initial Currents > Ib_Magnitude	0
   Electrical parameters > Initial Currents > Ib_Phase	0
   Electrical parameters > Initial Currents > Ic_Magnitude	0
   Electrical parameters > Initial Currents > Ic_Phase	0
   Mechanical parameters > Inertia	0.02
   Mechanical parameters > Friction factor	0.005752
   Mechanical parameters > Pole pairs	2
   Initial values > Slip	1
   Initial values > Angle	0

Retune Parameters of the Flux Regulator

1. To measure the signals associated to the flux regulator, add these blocks into the demux subsystem.

   

2. Select the Controller tab in the mask of the Field-Oriented Control Induction Motor Drive block. Set the Regulation type to Torque regulation to access the controller parameters.

   The torque regulation mode is required to bypass the speed regulator parameters and act directly on the field-oriented control (FOC) controller.

   The current controlled by the FOC controller depends of the machine flux. The flux controller ensures that the required flux is correctly applied to the machine.

3. Copy these parameters into the drive’s mask:

   Parameter	Value
   Machine flux > Initial	0.705
   Machine flux > Nominal	0.705
   Field oriented control > Flux controller > Proportional gain	1
   Field oriented control > Flux controller > Integral gain	0
   Field oriented control > Flux controller > Low-pass filter cutoff frequency	10e3
   Field oriented control > Flux controller > Flux output limits > Negative	-0.705*1.5
   Field oriented control > Flux controller > Flux output limits > Positive	0.705*1.5
   Field oriented control > Current controller Hysteresis bandwidth	1

4. To apply the nominal torque to the motor, modify the parameters of the Stair Generator blocks in the Speed reference subsystem and in the Load torque subsystem.

   

5. On the Logging tab of the Scope block, set Decimation to 1 and Variable name to simout1. Select Log data to workspace and set Save format to Structure With Time.

6. Simulate the system for 0.5 s. Open the FFT Analysis tool of the powergui block.

   In the Input list, select the Stator current signal and set Start time to 0.23, Number of cycles to 1, Fundamental frequency to 7.5, and Max Frequency (Hz) to 20000 Hz.

   Click Display to get the FFT graph.

   

7. Note that the switching frequency is about 5 kHz. To attenuate this frequency, set the Flux controller Low-pass filter cutoff frequency parameter to 500 Hz.

8. Open the Scope block and observe the flux signal. Note that the steady-state error is high.

   

9. Gradually increase the Flux controller Proportional gain parameter and simulate until you obtain a satisfactory response. Increasing the gain above a certain value can cause a saturation of the Flux controller. The curve at the next plot is based on a proportional gain of 100.

   

10. Gradually increase the Flux controller Integral gain and simulate until you obtain a satisfactory steady-state result with minimal error. The next plot is based on an integral gain of 90.

    

Retune Parameters of the Speed Regulator

1. Select the Controller tab in the mask of Field-Oriented Control Induction Motor Drive block and set the Regulation type to Speed regulation to edit the controller parameters.

   Parameter	Value
   Speed controller > Torque output limits> Negative	-1200*1.5
   Speed controller > Torque output limits> Positive	1200*1.5
   Speed controller > PI regulator > Proportional gain	1
   Speed controller > PI regulator > Integral gain	0
   Speed controller > Speed cutoff frequency	500
   Field oriented control > Maximum switching frequency	500

   The speed ramp acceleration must be calculated to avoid exceeding the torque output limit. The required torque to accelerate the motor at 1750 rpm/s is given by:

   $$\begin{array}{l}{T}_{accel}=J\cdot \frac{Accel\left(\left(rpm\right)/s\right)}{30}\cdot \pi \\ T_{accel}=0.02\cdot \frac{1750}{30}\cdot \pi =3.67\text{ Nm}\end{array}$$

2. To apply the nominal torque to the motor, modify the parameters of the Stair Generator blocks in the Speed reference subsystem and in the Load torque subsystem.

   

3. Set the scope decimation to 25 to prevent memory overload. Start the simulation.

   Observe the speed signal on the Scope block. The steady state error is high and the response time is not acceptable.

   

4. Gradually increase the Proportional gain parameter of the speed controller and simulate until you obtain a satisfactory response time without overshoot. Note that if the gain is too high, the system will be oscillatory. The next plot is based on a proportional gain of 3.

   

5. Gradually increase the Integral gain of the speed controller and simulate until you obtain a satisfactory steady state value with a minimal steady-state error. This curve is based on an integral gain of 100.

   

Retune Parameters of the DC Bus Voltage

1. Select the Converter and DC bus tab in the mask of the Field-Oriented Control Induction Motor Drive block to tune the DC bus capacitor and the braking chopper parameters.

2. Set the DC Bus Capacitance parameter to 167e-6.

   The DC bus capacitance is calculated in order to reduce the voltage ripple.

   $$C=\frac{P_{motor}}{12\cdot f\cdot {\Delta }_V\cdot V_{DC}}$$

   where:

   • P_motor is the nominal power of the motor drive (W).

   • f is the frequency of the AC source (Hz).

   • Δ_V is the desired voltage ripple (V).

   • V_DC is the average DC Bus voltage (V).

   This equation gives an approximate value of the capacitor required for a given voltage ripple level. Here the desired voltage ripple is 50 V.

   The motor drive of 5 hp (3728 W) is fed by a 60 Hz three-phase source. The average DC bus voltage is given by:

   V_DC = 1.35·V_LL,

   where V_LL represents the line to line rms voltage of the source. The source line to line voltage is 460 Vrms so the DC voltage is V_DC = 621 V.

   The required capacitor is then equal to

   $$C=\frac{3728}{12\cdot 60\cdot 50\cdot 621}=167\mu \text{F}\text{.}$$

3. Set the Braking chopper Shutdown voltage to 660V and the Braking chopper Activation voltage to 700 V.

   In motor mode, the peak voltage of the DC bus is equal to

   $$V_{peak}=V_{LL}\cdot \sqrt{2}=460\cdot \sqrt{2}=650\text{ V}\text{.}$$

   The shutdown voltage (V_shut) of the braking chopper should be a little bit higher than this value. To limit the voltage increase during regenerative braking, shutdown voltage is set to 660 V, and the activation voltage (V_act) is set to 700 V.

4. Set the Braking chopper Resistance to 131 ohms.

   The braking chopper resistance is calculated using this equation:

   $$R=\frac{V_{act}^2}{P_{motor}}=\frac{{700}^2}{3728}=131\Omega$$

Simulate and Analyze the Results

Simulate the system and observe six sections of the simulation results.

1. No-load acceleration

2. Nominal load torque is applied

3. Steady state speed

4. Nominal generation torque is applied: Observe the DC bus voltage overshoot

5. Deceleration

6. Negative speed acceleration