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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, you:

Open the example:

`ac3_example`

. (Type`ac3_example`

in the MATLAB^{®}Command Window).The parameters are set for a 200 hp motor.

Simulate the model in Accelerator mode and observe the results.

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.

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

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.

Set the

**Lowpass filter cutoff frequency**to 10 kHz to avoid limiting the flux frequency. The highest flux frequency depends of the switching frequency.Also set the

**Flux output limits**to 150% of the**Nominal flux**, the**Proportional gain**to 1, the**Integral gain**to 0, the**hysteresis band**to 1, and the**Machine flux**to 0.705. Machine flux is based on this computation:$$\frac{{V}_{LL}\left(rms\right)}{\sqrt{3}\cdot 2\cdot \pi \cdot f}=\frac{460}{\sqrt{3}\cdot 2\cdot \pi \cdot 60}$$

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.

Set the

**Sampling Decimation**of the scope block to`1`

, and the**Variable name**to`simout1`

. Select**Save data to workspace**and set**Format**to`Structure with time`

.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.Note that the switching frequency is about 5 kHz. To attenuate this frequency, set the Flux controller

**Lowpass filter cutoff frequency**parameter to 500 Hz.Open the Scope block and observe the flux signal. Note that the steady-state error is high.

Gradually increase the

**Proportional gain**parameter of the controller 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.Gradually increase the

**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.

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.Set the

**Torque output limits**to`150%`

of the nominal torque, the**Proportional gain**to`1`

, the**Integral gain**to`0`

, and the**Speed cutoff frequency**to`500`

.The highest speed frequency depends also on the switching frequency, so set the

**Maximum switching frequency**parameter to`500`

Hz.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:

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

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.

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.

Gradually increase the

**Proportional gain**parameter of the 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.Gradually increase the

**Integral gain**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.

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.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:

is the nominal power of the motor drive (W).*P*_{motor}is the frequency of the AC source (Hz).*f*Δ

_{V}is the desired voltage ripple (V).is the average DC Bus voltage (V).*V*_{DC}

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:

= 1.35·*V*_{DC},*V*_{LL}where

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*_{LL}.*V*= 621 V_{DC}The required capacitor is then equal to

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

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.Set the Braking chopper

**Resistance**to 131 ohms.The braking chopper resistance is calculated using this equation:

$$R=\frac{{V}_{act}^{2}}{{P}_{motor}}=\frac{{700}^{2}}{3728}=131\text{}\Omega $$

The final DC bus parameters are shown in the next figure.

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

No-load acceleration

Nominal load torque is applied

Steady state speed

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

Deceleration

Negative speed acceleration

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