Implement Self-Controlled Synchronous Motor Drive
Electric Drives/AC drives
This block models a wound field synchronous motor (WFSM) vector control drive model. The high-level schematic shown below is built from six main blocks. The WFSM motor, the three-phase inverter, and the three-phase rectifier models are provided with the Simscape™ Power Systems™ library. More details are available in the reference pages for these blocks. The speed controller, the rectifier controller, and the vector control models are specific to the drive library. It is possible to use a simplified version of the drive containing average-value models of the inverter and rectifier for faster simulation.
Note
In Simscape Power Systems software, the Self-Controlled Synchronous
Motor Drive block is commonly called the |
The speed controller is based on a PI regulator, shown below. The outputs of this regulator are set points for the torque and the flux applied to the vector control block.
The rectifier controller is based on a PI regulator of the DC bus voltage. The output of this regulator is the direct (active) component of the AC line current. The reactive component of the AC line current is set to zero in order to operate at unity power factor.
The dq-abc block performs the conversion of the dq current components into abc phase variables.
The current regulator is a bang-bang current controller with adjustable hysteresis bandwidth.
The vector control contains five main blocks shown in this figure. These blocks are described below.
The flux estimator block is used to estimate the motor stator flux .
The flux PI controller is used to regulate the flux in the machine.
The dq2abc block performs the conversion of the dq current components into abc phase variables.
The current regulator is a bang-bang current controller with adjustable hysteresis bandwidth.
The magnetization control unit contains the logic used to switch between the magnetization and normal operation mode.
The average-value inverter/rectifier internal architecture is shown in the following figure.
It is composed of one controlled current source on the DC side and of two controlled current sources and three controlled voltage sources on the AC side. The DC current source allows the representation of the average DC bus current behavior following the next equation:
I_{dc} = (P_{ac} + P_{losses}) / V_{dc}
with P_{ac} being the AC side instantaneous power, P_{losses} the losses in the power electronics devices, and V_{dc} the DC bus voltage.
On the AC side, the current sources represent the average phase currents fed to the motor. The regulation being fast, the current values are set equal to the current references sent by the current regulator. A small current is injected to compensate for the current drawn by the three-phase load (needed because of the inverter current sources in series with the inductive motor).
During loss of current tracking due to insufficient inverter voltage, the currents are fed by three controlled voltage sources. These voltage sources represent the square wave mode and allow good representation of the phase currents during inverter saturation. Each voltage source outputs either Vin or 0, depending on the values of the pulses (1 or 0) send by the current controller.
The model is discrete. Good simulation results have been obtained with a 2 µs time step. To simulate a digital controller device, the control system has two different sampling times:
Speed controller sampling time
Active rectifier controller and vector controller sampling time
The speed controller sampling time has to be a multiple of the vector controller sampling time. The latter sampling time has to be a multiple of the simulation time step. The average-value inverter and rectifier allow the use of bigger simulation time steps since they do not generate small time constants (due to the RC snubbers) inherent to the detailed converters. For a vector controller and active rectifier controller sampling time of 50 µs, good simulation results have been obtained for a simulation time step of 50 µs. This time step can, of course, not be higher than the smallest controller sampling time.
The torque sign convention of the synchronous machine is different from the one of the asynchronous and PM synchronous machines. That is, the synchronous machine is in the motor operation mode when the electric torque is negative and in the generator operation mode when the electric torque is positive.
The Synchronous Machine tab displays the parameters of the Synchronous Machine block of the Fundamental Blocks (powerlib) library.
Select how the output variables are organized. If you select Multiple output buses, the block has three separate output buses for motor, converter, and controller variables. If you select Single output bus, all variables output on a single bus.
Select between the detailed and the average-value inverter.
Select between the load torque, the motor speed and the mechanical rotational port as mechanical input. If you select and apply a load torque, the output is the motor speed according to the following differential equation that describes the mechanical system dynamics:
$${T}_{e}=J\frac{d}{dt}{\omega}_{r}+F{\omega}_{r}+{T}_{m}$$
This mechanical system is included in the motor model.
If you select the motor speed as mechanical input, then you get the electromagnetic torque as output, allowing you to represent externally the mechanical system dynamics. The internal mechanical system is not used with this mechanical input selection and the inertia and viscous friction parameters are not displayed.
For the mechanical rotational port, the connection port S counts for the mechanical input and output. It allows a direct connection to the Simscape environment. The mechanical system of the motor is also included in the drive and is based on the same differential equation.
The rectifier section of the Converters and DC bus tab displays the parameters of the Universal Bridge block of the Fundamental Blocks (powerlib) library. Refer to the Universal Bridge for more information on the universal bridge parameters.
The inverter section of the Converters and DC bus tab displays the parameters of the Universal Bridge block of the Fundamental Blocks (powerlib) library. Refer to the Universal Bridge for more information on the universal bridge parameters.
The average-value rectifier uses the three following parameters.
The frequency of the three-phase voltage source (Hz).
The RMS line-to-line voltage of the three-phase voltage source (V).
The on-state resistance of the rectifier devices (ohms).
The average-value inverter uses the two following parameters:
The on-state resistance of the inverter devices (ohms).
Forward voltages, in volts (V), of the forced-commutated devices and of the antiparallel diodes. These values are needed for startup and for square wave mode.
The DC bus capacitance value (F).
Input chokes reduce line current harmonics.
The input choke resistance value (ohms).
The input choke inductance value (H).
This drop-down menu allows you to choose between speed and torque regulation.
When you click this button, a diagram illustrating the speed, rectifier, and vector controllers schematics appears.
The speed measurement first-order low-pass filter cutoff frequency (Hz).
The speed controller sampling time (s). The sampling time must be a multiple of the simulation time step.
The maximum change of speed allowed during motor acceleration. An excessively large positive value can cause DC bus under-voltage (rpm/s).
The maximum change of speed allowed during motor deceleration. An excessively large negative value can cause DC bus over-voltage (rpm/s).
The speed controller proportional gain.
The speed controller integral gain.
The maximum negative demanded torque applied to the motor by the vector controller (N.m).
The maximum positive demanded torque applied to the motor by the vector controller (N.m).
The DC bus voltage controller proportional gain.
The DC bus voltage controller integral gain.
The maximum current flowing from the DC bus capacitor towards the AC line (A).
The maximum current flowing from the AC line towards the DC bus capacitor (A).
The bus voltage measurement low-pass filter cutoff frequency (Hz).
The DC bus voltage controller sampling time (s). The sampling time must be a multiple of the simulation time step.
The current hysteresis bandwidth. This value is the total bandwidth distributed symmetrically around the current set point (A). The following figure illustrates a case where the current set point is Is^{*} and the current hysteresis bandwidth is set to dx.
This parameter is not used when using the average-value inverter.
Note This bandwidth can be exceeded because a fixed-step simulation is used. A rate transition block is needed to transfer data between different sampling rates. This block causes a delay in the gate signals, so the current may exceed the hysteresis band. |
The vector controller sampling time (s). The sampling time must be a multiple of the simulation time step.
The motor stator nominal flux (Wb).
The current hysteresis bandwidth (for details, see the DC Bus Controller subtab).
The flux controller proportional gain.
The flux controller integral gain.
The minimum voltage applied to the motor excitation field (V).
The maximum voltage applied to the motor excitation field (V).
The flux estimation first-order filter cutoff frequency (Hz).
When you start the self-controlled synchronous motor, the magnetic flux of the motor must be first established before the motor is allowed to produce an electric torque. Since the motor field time constant is high, a field voltage much higher than nominal is applied in order to accelerate the building of the magnetic flux in the synchronous motor. After the period during which the high voltage is applied, the field voltage is lowered down to its nominal value during a second short period that adds to the latter period giving the total magnetization period. This procedure gives a smooth startup of the self-controlled synchronous motor.
The field magnetization voltage applied in order to establish the stator flux (V).
The field magnetization high voltage application time (s).
The field nominal voltage (V).
The total time before the drive is ready to produce a torque (s).
SP
The speed or torque set point. The speed set point can be a step function, but the speed change rate will follow the acceleration / deceleration ramps. If the load torque and the speed have opposite signs, the accelerating torque will be the sum of the electromagnetic and load torques.
Tm
or Wm
The mechanical input: load torque (Tm) or motor speed (Wm). For the mechanical rotational port (S), this input is deleted.
A, B, C
The three phase terminals of the motor drive.
Wm
, Te
or S
The mechanical output: motor speed (Wm), electromagnetic torque (Te) or mechanical rotational port (S).
When the Output bus mode parameter is set to Multiple output buses, the block has the following three output buses:
Motor
The motor measurement vector. This vector allows you to observe the motor's variables using the Bus Selector block.
Conv
The three-phase converters measurement vector. This vector contains:
The DC bus voltage
The rectifier output current
The inverter input current
Note that all current and voltage values of the bridges can be visualized with the Multimeter block.
Ctrl
The controller measurement vector. This vector contains the values for the active rectifier and for the inverter.
For the active rectifier:
The active component of the current reference.
The voltage error (difference between the DC bus voltage reference and actual DC bus voltage)
The DC bus voltage reference
For the inverter:
The torque reference
The flux reference
The speed error (difference between the speed reference ramp and actual speed)
The speed reference ramp or torque reference
When the Output bus mode parameter is set to Single output bus, the block groups the Motor, Conv, and Ctrl outputs into a single bus output.
The library contains a 200 hp drive parameter set. The specifications of the 200 hp drive are shown in the following table
14 HP and 200 HP Drive Specifications
14 HP Drive | 200 HP Drive | ||
---|---|---|---|
Drive Input Voltage | |||
Amplitude | 460 V | 460 V | |
Frequency | 60 Hz | 60 Hz | |
Motor Nominal Values | |||
Power | 14 hp | 200 hp | |
Speed | 1800 rpm | 1800 rpm | |
Voltage | 460 V | 460 V |
.
The ac5_example
example illustrates
an AC5 motor drive simulation with standard load condition for the
detailed and average-value models. At time t = 1.5 s, the speed set
point is 200 rpm.
As shown below, the speed precisely follows the acceleration ramp. At t = 3 s, the nominal load torque is applied to the motor. At t = 4 s, the speed set point is changed to 0 rpm. The speed decreases along the prescribed deceleration ramp to 0 rpm. At t = 5.5 s., the mechanical load passes from −792 N.m to 792 N.m. Notice that the results of the average-value model are similar to those of the detailed model except that the higher frequency signal components are not represented with the average-value converter.
AC5 Example Waveforms (Blue : Detailed Converter, Red : Average-Value Converter)
[1] Bose, B. K., Modern Power Electronics and AC Drives, Prentice-Hall, N.J., 2002.
[2] Krause, P. C., Analysis of Electric Machinery, McGraw-Hill, 1986.