PM Synchronous Motor Drive - Implement Permanent Magnet Synchronous Motor (PMSM) vector control drive

Library

Electric Drives/AC drives

Description

The high-level schematic shown below is built from six main blocks. The PMSM motor, the three-phase inverter, and the three-phase diode rectifier models are provided with the SimPowerSystems library. More details are available in the reference pages for these blocks. The speed controller, the braking chopper, and the vector controller models are specific to the drive library. It is possible to use a simplified version of the drive containing an average-value model of the inverter for faster simulation.

Note In SimPowerSystems software, the PM Synchronous Motor Drive block is commonly called the AC6 motor drive.

High-Level Schematic

Simulink Schematic

Speed Controller

The speed controller is based on a PI regulator, shown below. The output of this regulator is a torque set point applied to the vector controller block.

Vector Controller

The vector controller contains four main blocks, shown below. These blocks are described below.

The dq-abc block performs the conversion of the dq current component in the rotor reference frame into abc phase variables.

The current regulator is a bang-bang current controller with adjustable hysteresis bandwidth.

The angle conversion block is used to compute the electrical rotor angle from the mechanical rotor angle.

The Switching control block is used to limit the inverter commutation frequency to a maximum value specified by the user.

When using the average-value inverter, the ab current references are sent to the inverter, as well as switching pulses from a slightly modified Switching control block.

Braking Chopper

The braking chopper block contains the DC bus capacitor and the dynamic braking chopper, which is used to absorb the energy produced by a motor deceleration.

Average-Value Inverter

The average-value inverter 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 two 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:

with being the output power, the losses in the power electronic devices, and 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 inductive motor).

During loss of current tracking due to insufficient inverter voltage, the currents are fed by two 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) sent by the current controller.

Remarks

The model is discrete. Good simulation results have been obtained with a 2 time step. To simulate a digital controller device, the control system has two different sampling times:

Speed controller sampling time
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 allows the use of bigger simulation time steps since it does not generate small time constants (due to the RC snubbers) inherent to the detailed converter. For a vector controller sampling time of 75 µs, good simulation results have been obtained for a simulation time step of 75 µs. The simulation time step can, of course, not be higher than the vector controller time step.

The stator current direct component id* is set to zero inside the vector controller block because the rotor flux is supplied by the permanent magnets.

Dialog Box

PM Synchronous Machine Tab

The PM synchronous machine tab displays the parameters of the PM synchronous machine block of the powerlib library. Refer to Permanent Magnet Synchronous Machine for more information on the PM synchronous machine parameters.

Model detail level

Select between the detailed and the average-value inverter.

Mechanical input

Allows you to select either the load torque or the motor speed as mechanical input. Note that if you select and apply a load torque, you will obtain as output the motor speed according to the following differential equation that describes the mechanical system dynamics:

This mechanical system is included in the motor model.

However, if you select the motor speed as mechanical input then you will get the electromagnetic torque as output, allowing you to represent externally the mechanical system dynamics. Note that the internal mechanical system is not used with this mechanical input selection and the inertia and viscous friction parameters are not displayed.

See for example Mechanical Coupling of Two Motor Drives.

Converters and DC Bus Tab

Rectifier section: The rectifier section of the Converters and DC bus tab displays the parameters of the Universal Bridge block of the powerlib library. Refer to the Universal Bridge for more information on the universal bridge parameters.
Inverter section: The inverter section of the Converters and DC bus tab displays the parameters of the Universal Brige block of the powerlib library. Refer to the Universal Bridge for more information on the universal bridge parameters.

The average-value inverter uses the following parameters.

Source frequency: The frequency of the three-phase voltage source (Hz).
On-state resistance: The on-state resistance of the inverter devices (ohms).
DC Bus Field — Capacitance: The DC bus capacitance (F).

Braking Chopper Section

Resistance

The braking chopper resistance used to avoid bus over-voltage during motor deceleration or when the load torque tends to accelerate the motor (ohms).

Frequency

The braking chopper frequency (Hz).

Activation Voltage

The dynamic braking is activated when the bus voltage reaches the upper limit of the hysteresis band. The following figure illustrates the braking chopper hysteresis logic.

Deactivation Voltage

The dynamic braking is shut down when the bus voltage reaches the lower limit of the hysteresis band. The chopper hysteresis logic is shown in the following figure.

Controller Tab

Regulation Type: This pop-up menu allows you to choose between speed and torque regulation.
Schematic Button: When you press this button, a diagram illustrating the speed and vector controllers schematics appears.

Speed Controller section

Speed cutoff frequency: The speed measurement first-order low-pass filter cutoff frequency (Hz). This parameter is used in speed regulation mode only.
Speed controller sampling time: The speed controller sampling time (s). The sampling time must be a multiple of the simulation time step.
Speed Ramps — Acceleration: The maximum change of speed allowed during motor acceleration (rpm/s). An excessively large positive value can cause DC bus under-voltage. This parameter is used in speed regulation mode only.
Speed Ramps — Deceleration: The maximum change of speed allowed during motor deceleration (rpm/s). An excessively large negative value can cause DC bus overvoltage. This parameter is used in speed regulation mode only.
PI Regulator — Proportional Gain: The speed controller proportional gain. This parameter is used in speed regulation mode only.
PI Regulator — Integral Gain: The speed controller integral gain. This parameter is used in speed regulation mode only.
Torque output limits — Negative: The maximum negative demanded torque applied to the motor by the current controller (N.m).
Torque output limits — Positive: The maximum positive demanded torque applied to the motor by the current controller (N.m).

Vector Controller Section

Sampling Time

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

Current controller hysteresis band

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.

Maximum switching frequency

The maximum inverter switching frequency (Hz). This parameter is not used when using the average-value inverter.

Block Inputs and Outputs

SP

The speed or torque set point. Note that 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).

A, B, C

The three phase terminals of the motor drive.

Wm or Te

The mechanical output: motor speed (Wm) or electromagnetic torque (Te).

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 torque reference
The speed error (difference between the speed reference ramp and actual speed)
The speed reference ramp or torque reference

Model Specifications

The library contains a 3 hp drive parameter set. The specifications of the 3 hp drive are shown in the following table

3 HP Drive Specifications

Drive Input Voltage
	Amplitude	220 V
	Frequency	60 Hz
Motor Nominal Values
	Power	3 hp
	Speed	1800
	Voltage	300

Example

The ac6_example demo illustrates an AC6 motor drive simulation with standard load condition. At time t = 0 s, the speed set point is 300 rpm.

As shown in the following figure, the speed precisely follows the acceleration ramp. At t = 0.5 s, the nominal load torque is applied to the motor. At t = 1 s, the speed set point is changed to 0 rpm. The speed decreases to 0 rpm. At t = 1.5 s., the mechanical load passes from 11 N.m to -11 N.m. Average voltage, current, torque, and speed values are identical for both models. Notice that the higher frequency signal components are not represented with the average-value converter.

AC6 Example Waveforms (Blue: Detailed Converter, Red: Average-Value Converter)