Implement Self-Controlled Synchronous Motor Drive

Electric Drives/AC drives

The Self-Controlled Synchronous Motor Drive (AC5) block represents a classical vector control drive for wound-field synchronous motors. This drive features unity power factor operation and closed-loop speed control, based on the vector control method. The unity power factor operation is achieved through a voltage controlled, three-phase active rectifier. The speed control loop outputs the reference electromagnetic torque and stator flux of the machine. The reference direct and quadrature (dq) components of the stator current corresponding to the commanded stator flux and torque are derived based on the vector control strategy. These reference dq components of the stator current are then used to obtain the required gate signals for the inverter through a hysteresis-band current controller. The field voltage required by the machine is obtained from the stator flux control loop.

The main advantage of this drive compared to scalar-controlled drives is its fast dynamic response. The inherent coupling effect (between the torque and flux) in the machine is managed through decoupling (stator flux orientation) control, which allows the torque and flux to be controlled independently. However, due to its computation complexity, the implementation of this drive requires fast computing processors or DSPs.

In Simscape™
Power Systems™ software, the Self-Controlled
Synchronous Motor Drive block is commonly called the `AC5`

motor
drive.

The Self-Controlled Synchronous Motor Drive block uses these blocks from the Electric Drives / Fundamental Drive Blocks library:

Speed Controller (AC)

Vector Controller (WFSM)

Active Rectifier

Inverter (Three-Phase)

The model is discrete. Good simulation results have been obtained
with a 2 *µ*s 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.

**Output bus mode**Select how the output variables are organized. If you select

`Multiple output buses`

(default), 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.**Model detail level**Select between the detailed and the average-value inverter. Default is

`Detailed`

.**Mechanical input**Select between the load torque, the motor speed and the mechanical rotational port as mechanical input. Default is

`Torque Tm`

.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.

**Use signal names as labels**When you select this check box, the

`Motor`

,`Conv`

, and`Ctrl`

measurement outputs use the signal names to identify the bus labels. Select this option for applications that require bus signal labels to have only alphanumeric characters.When this check box is cleared (default), the measurement output uses the signal definition to identify the bus labels. The labels contain nonalphanumeric characters that are incompatible with some Simulink

^{®}applications.

The **Synchronous Machine** tab
displays the parameters of the Synchronous Machine block
of the Fundamental Blocks (powerlib) library.

The **Rectifier** section of the **Converters
and DC Bus** tab displays the parameters of the Universal
Bridge block of the Fundamental Blocks (powerlib) library.
For more information on the Universal Bridge parameters, refer to
the Universal Bridge reference page.

The average-value rectifier uses the three following parameters.

**Source frequency**The frequency of the three-phase voltage source (Hz). Default is

`60`

.**Source voltage**The RMS line-to-line voltage of the three-phase voltage source (V). Default is

`460`

.**On-state resistance**The on-state resistance of the rectifier devices (ohms). Default is

`1e-3`

.

**Capacitance**The DC bus capacitance value (F). Default is

`7500e-6`

.

Input chokes reduce line current harmonics.

**Resistance**The input choke resistance value (ohms). Default is

`0.05`

.**Inductance**The input choke inductance value (H). Default is

`1e-3`

.

The **Inverter** section of the **Converters
and DC Bus** tab displays the parameters of the Universal
Bridge block of the Fundamental Blocks (powerlib) library.
For more information on the Universal Bridge parameters, refer to
the Universal Bridge reference page.

The average-value inverter uses the two following parameters:

**On-state resistance**The on-state resistance of the inverter devices (ohms). Default is

`1e-3`

.**Forward voltages [Device Vf, Diode Vdf]**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.

**Regulation type**This drop-down menu allows you to choose between speed and torque regulation. Default is

`Speed regulation`

.**Schematic**When you click this button, a diagram illustrating the speed, rectifier, and vector controllers schematics appears.

**Speed ramps — Acceleration**The maximum change of speed allowed during motor acceleration. An excessively large positive value can cause DC bus under-voltage (rpm/s). Default is

`100`

.**Speed ramps — Deceleration**The maximum change of speed allowed during motor deceleration. An excessively large negative value can cause DC bus over-voltage (rpm/s). Default is

`-100`

.**Speed cutoff frequency**The speed measurement first-order low-pass filter cutoff frequency (Hz). Default is

`5`

.**Speed controller sampling time**The speed controller sampling time (s). The sampling time must be a multiple of the simulation time step. Default is

`7*20e-6`

.**PI regulator — Proportional gain**The speed controller proportional gain. Default is

`75`

.**PI regulator — Integral gain**The speed controller integral gain. Default is

`100`

.**Torque output limits — Negative**The maximum negative demanded torque applied to the motor by the vector controller (N.m). Default is

`-1200`

.**Torque output limits — Positive**The maximum positive demanded torque applied to the motor by the vector controller (N.m). Default is

`1200`

.

**PI regulator — Proportional gain**The DC bus voltage controller proportional gain. Default is

`10`

.**PI regulator — Integral gain**The DC bus voltage controller integral gain. Default is

`100`

.**Line current d component limits — Minimum (negative)**The maximum current flowing from the DC bus capacitor towards the AC line (A). Default is

`-800`

.**Line current d component limits — Maximum (positive)**The maximum current flowing from the AC line towards the DC bus capacitor (A). Default is

`800`

.**Voltage measurement cutoff frequency**The bus voltage measurement low-pass filter cutoff frequency (Hz). Default is

`100`

.**Active rectifier sampling time**The DC bus voltage controller sampling time (s). The sampling time must be a multiple of the simulation time step. Default is

`20e-6`

.**Current hysteresis bandwidth**The current hysteresis bandwidth. Default is

`10`

. 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.

**Controller sampling time**The vector controller sampling time (s). The sampling time must be a multiple of the simulation time step. Default is

`20e-6`

.**Machine nominal flux**The motor stator nominal flux (Wb). Default is

`0.98`

.**Current hysteresis bandwidth**The current hysteresis bandwidth (for details, see the

**DC Bus Controller**subtab). Default is`10`

.

**PI regulator — Proportional gain**The flux controller proportional gain. Default is

`1000`

.**PI regulator — Integral gain**The flux controller integral gain. Default is

`1000`

.**Voltage limits — Minimum**The minimum voltage applied to the motor excitation field (V). Default is

`-300`

.**Voltage limits — Maximum**The maximum voltage applied to the motor excitation field (V). Default is

`300`

.**Flux estimation lowpass cutoff frequency**The flux estimation first-order filter cutoff frequency (Hz). Default is

`2`

.

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.

**Field magnetization voltage**The field magnetization voltage applied in order to establish the stator flux (V). Default is

`600`

.**High voltage field magnetization time**The field magnetization high voltage application time (s). Default is

`0.2`

.**Field nominal voltage**The field nominal voltage (V). Default is

`30`

.**Total field magnetization time**The total time before the drive is ready to produce a torque (s). Default is

`1`

.

`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 | ||
---|---|---|---|

| |||

Amplitude | 460 V | 460 V | |

Frequency | 60 Hz | 60 Hz | |

| |||

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.

[1] Bose, B. K. * Modern
Power Electronics and AC Drives*. Upper Saddle
River, NJ: Prentice-Hall, 2002.

[2] Krause, P. C. * Analysis
of Electric Machinery*. New York: McGraw-Hill,
1986.

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