Power Electronics & Drives IV
Power Electronics & Drives 4/M
Copyright By PowCoder代写 加微信 powcoder
Laboratory 2: Variable Speed 3 Phase Induction Motor Drives
version 1.0
Dr Mohammad Yazdani-Asrami
24th Oct 2022
Introduction
The induction motor has been the ‘workhorse of industry’ since its invention in the late 1800’s
primarily due to its low maintenance and high reliability compared with early brushed motors.
The one drawback of the induction machine however was its ‘fixed speed’ operation when
operating off a fixed frequency AC supply. This dominance continued until the 1980’s when the
development of economic power electronic converters facilitated a new generation of
commercially available brushless motors (brushless DC, permanent magnet AC and switched
reluctance) which offered low maintenance alternatives AND variable speed operation.
Fortunately for the induction motor it too could now operate at variable speed with the inclusion
of a power electronic converter thus opening up a whole new range of applications (e.g. traction)
and allowing energy efficient variable speed operation in the traditional fixed speed applications
(e.g. fans and pumps).
Aims and Objectives:
Model 1: Grid connected ‘fixed speed’ induction motor
• Torque vs speed curve for Grid connected operation
• Output power, input power and efficiency at a given value of slip
• Comparison with equivalent circuit calculations
Model 2: Variable speed 3 phase induction motor drive
• 3 phase inverter (DC-AC) topology
• Sinusoidal PWM control
• Variable speed control
• Constant V/Hz control and resultant torque vs speed curves
Power Electronics & Drives 4/M
Model 1: Grid connected ‘fixed speed’ induction motor
The Electrical Machines library contains an Induction Machine model (see Figure 1) which can be applied to both
motoring and generating modes of operation. We will subsequently use this model in our investigations into inverter
connected variable speed operation but it would be worthwhile first having a look at it in Grid connected (fixed
supply frequency) operation and validating its performance against hand calculations based on the equivalent circuit.
Figure 1: Portunus Induction Machine Model
There are slight differences between the Portunus equivalent circuit and the one outlined in the lecture notes so they
will not give exactly the same results at a given operating point but they are close enough for the purposes for which
these models are used.
Example Motor
The motor we want to investigate in this exercise has parameters outlined in Table 2 with an accompanying
explanation as to how these parameters are related to equivalent circuit values (just different ways of doing the same
Portunus Model Parameter Value Equivalent Circuit Parameter Value
Stator Resistance (Rs) (Ω) 0.8 Stator Resistance (Rs) 0.8Ω
Rotor Resistance (Rr) (Ω) 0.3 Rotor Resistance (Rr) 0.3Ω
Stator Leakage Inductance (Ls) (H) 2.23m Total Leakage Reactance (Xeq) 1.4Ω
Rotor Leakage Inductance (Lr) (H) 2.23m Magnetising Inductance (Xm) 62.8Ω
Main Inductance (Lm) (H) 0.2 Core Loss Resistance (Rc) ignore
Pole Pairs 3 (NOTE!!) Number of Poles 6
Moment of Inertia (kg.m^2) 1
rms Supply Voltage (Vsrms) 240V
Supply Frequency (fs) 50Hz
Table 2: Induction Motor Parameters
1. Xeq = ω.(Ls+ Lr) (where ω = 2.π.fs)
2. Xm = ω.Lm
3. Poles = 2.Pole_Pairs
4. The Portunus model does not include a Core Loss Resistance – I don’t know why!
From this information determine the synchronous speed (Ns) for this machine operating off a 50Hz supply:
Synchronous Speed (rpm)
Power Electronics & Drives 4/M
Exercise 1.1 Torque v Speed Curve
Create a model which connects a 3-phase induction motor to a 3-phase electrical supply (E1, E2 & E3) and a
mechanical speed source (NSRC1) as outlined in Figure 2 and Table 3.
Figure 2: Grid connected induction motor
Symbol Model Directory Parameters
E1 Voltage Source Sources Voltage –TR [V] = SINE1.OUT
E2 Voltage Source Sources Voltage –TR [V] = SINE2.OUT
E3 Voltage Source Sources Voltage –TR [V] = SINE3.OUT
SINE1 Time Function Frequency = 50
Amplitude = 339
Phase Shift = 0
Offset = 0
SINE2 Time Function Frequency = 50
Amplitude = 339
Phase Shift = 240
Offset = 0
SINE3 Time Function Frequency = 50
Amplitude = 339
Phase Shift = 120
Offset = 0
NSRC1 Speed Source Mechanics – Rotational Speed (rpm) = 1000
Table 3: Component Parameters
IMPORTANT Note:
1. In Portunus the stated amplitude of the Sinewave is the PEAK value = √2. Vrms (where Vrms = 240V)
Setup the IM1 parameters according to Table 2. Note that the phasing of the 3-phase supply (E1, E2 & E3) should
look like that shown on Figure 3 – to confirm this you can put these voltages onto an On Sheet Display and simulate
(TEND = 0.04) to verify.
Figure 3: 3 phase grid voltages
Power Electronics & Drives 4/M
We now want to use this model to investigate the torque v speed (slip) relationship between zero and synchronous
speed. The IM1 model outputs a parameter IM1.T_SHAFT which shows instantaneous motor torque, however at the
start of any simulation this value goes to a ridiculously high value (this does not happen in reality so its always
worth being aware when a simulation is being silly!) so to remove this and make the output graph of torque more
usable we can multiply this shaft torque with a step function which is zero for the first 0.1s of the simulation and
then goes to a 1 and allows IM1.T_SHAFT to be output on MUL1 (see Figure 4). Include this in your simulation
Figure 4: Removing initial spike on Shaft Torque
OK we are now ready to determine the motor torque as a function of speed. To do this we set the motor speed in the
NSRC1 block, simulate at that speed and determine motor torque. Output MUL1.OUT on an On Sheet Display to
display motor torque.
Set TEND = 1s in the simulation setup panel [F9] and perform a series of simulations at the following motor
speeds to determine motor torque (note: as it turns out the Portunus convention is that motoring torque is negative,
but for the purposes of this exercise just make it positive in the table):
Motor Speed (rpm) Slip Torque (Nm)
Note: Calculate slip for each of the motor speeds using the formula:
Ns = Synchronous Speed
Nr = Actual motor speed
Power Electronics & Drives 4/M
Create a graph of torque v speed from these results and determine the following:
Parameter Value (Nm) Speed at which this occurs (rpm)
Starting Torque (Nm)
Breakdown Torque (Nm)
Torque at Rated Slip (0.03)
We now want to validate the Portunus induction machine model against equivalent circuit calculations.
Exercise 1.2 Rated Operating Point Comparison
Adding additional calculation blocks (include these in Lab Report) in the Portunus model (see below for reference)
determine the following for the simulation model at the ‘rated operating point’ for this machine:
Parameter Simulation Model Equivalent Circuit
(do this later)
Speed (rpm)
Torque (Nm)
Output (mech) Power (kW)
rms Phase Current (A)
Total input (elec) Power (kW)
Efficiency (%)
Get a demonstrator to check your results. Determine the performance based on Equivalent Circuit calculations and
include the calculations and results in Lab Report.
1. Ignore the parallel magnetising reactance and core loss resistance in the equivalent circuit calculations for
simplicity.
With this understanding of operation from a fixed frequency Grid connected induction motor we will now turn out
attention to inverter connected machines.
Power Electronics & Drives 4/M
Model 2: Inverter connected 3 phase induction motor drive
OK we now want to produce a variable speed induction motor drive using a power electronic inverter as shown on
Figure 5. (note that the AC-DC rectifier shown in the lecture is not included here).
To save you time I have already created an Inverter/Motor model Lab2_Model2.bak (Fig 5) and you can access this
from Moodle as outlined in the Appendix. Open this and ensure the various components are setup according to
tables 4 and 5.
So why the need for all these diodes? Well 2 reasons: 1] the induction motor contains inductive elements so when
switches are turned off there has to be a current path for this current to ‘freewheel’ as outlined in Lab 1 (D2, D4 etc),
and 2] real semiconductor switches (e.g. MOSEFET, IGBT) can only conduct current in one direction so a diode
(D1, D3 etc) is placed in series with each ideal switch to model this.
Figure 5: Variable Speed Induction Motor Drives
Set up the various model components as outlined in Tables 4 and 5.
Model Directory Parameters
E1 Voltage Source Sources Voltage –TR [V] = 680
C1 Capacitor Passive Components Capacitance = 1000e-6
NSRC1 Mechanics – Rotational Speed Source Speed (rpm) = 970
S1-S6 Ideal Switch Switches & Relays Need to allocate Control inputs – see
D1-D13 Diode Semiconductors Characteristic = EQUL1
AM1 Ammeter Measurement Devices
VM1 Voltmeter Measurement Devices
Table 4: Component Parameters
IM1 Parameter Value
Stator Resistance (Ω) 0.8
Rotor Resistance (Ω) 0.3
Stator Leakage Inductance (H) 2.23m
Rotor Leakage Inductance (H) 2.23m
Main Inductance (H) 0.2
Number of Pole Pairs 3
Moment of Inertia (kg.m^2) 1
Table 5: Induction Motor Parameters
Power Electronics & Drives 4/M
Sinusoidal PWM Control
The lecture outlined the principles of Sinusoidal PWM control so refer to this for a basic understanding of this
control mode.
We now need to construct the Sinusoidal PWM control block in Portunus, the per phase implementation being
shown on Figure 6.
Figure 6: Per Phase Sinusoidal PWM Control
Implement these blocks for each of the 3 phaselegs according to Table 6 and allocate the relevant control signal to
each of the 6 inverter switches. For each phaseleg the INVERSE of the upper switch control signal is used to control
the respective lower switch. The inverter is implemented by the three blocks on the right-hand side of Figure 6. Note
the -1 (negative one) gain in GAIN1 block.
Phase Model Directory Parameters
1 (SINE1) Time Function Frequency (Hz) = 50
Amplitude = 1
Phase Shift = 0
Offset = 0
1 Source Blocks Value –TR = SINE1.OUT
1 Comparator Blocks Threshold = TRIANG1.OUT
2 (SINE2) Time Function Frequency (Hz) = 50
Amplitude = 1
Phase Shift = 240
Offset = 0
2 Source Blocks Value –TR = SINE2.OUT
2 Comparator Blocks Threshold = TRIANG1.OUT
3 (SIN3) Time Function Frequency (Hz) = 50
Amplitude = 1
Phase Shift = 120
Offset = 0
3 Source Blocks Value –TR = SINE3.OUT
3 Comparator Blocks Threshold = TRIANG1.OUT
All Triangular Wave (TRIANG1) Time Function Frequency = 2e3
Amplitude = 1
Phase Shift = 0
Offset = 0
1 Ideal Switch (Upper) Control Signal = Phase 1 Comp’X’.OUT
1 Ideal Switch (Lower) Control Signal = Phase 1 Sum’A’.OUT
2 Ideal Switch (Upper) Control Signal = Phase 2 Comp’Y’.OUT
2 Ideal Switch (Lower) Control Signal = Phase 2 Sum’B’.OUT
3 Ideal Switch (Upper) Control Signal = Phase 3 Comp’Z’.OUT
3 Ideal Switch (Lower) Control Signal = Phase 3 Sum’C’.OUT
Table 6: WM Control Parameters
Power Electronics & Drives 4/M
Exercise 2.1 Inverter based operation at Rated Operating Point
To match the conditions of the direct grid connected machine earlier we require the Inverter based drive to operate at
a synchronous speed of 1000rpm and an rms phase voltage of 240V. Determine the necessary controller parameters
to achieve this given the following relationships:
Figure 7: PWM Control
_ ( ) 3. _ ( )L phLine Voltage V Phase Voltage V=
PWM Control Parameter Value
Sinewave Frequency (fs)
Sinewave Amplitude (Ma)
Using these control values, and adding calculation and measurement blocks where necessary, determine through
simulation (set TEND = 0.4s) the performance for the inverter-based drive at the rated operating point:
Parameter Simulation Model
Slip 0.03
Speed (rpm)
Torque (Nm)
Output (mech) Power (kW)
rms Phase Current (A)
Average DC Power Supply Current (A)
Total input (elec) Power (kW)
Efficiency (%)
Note: the DC Power Supply current should be averaged over a 20ms period (50Hz). Note also there is a large spike
at start-up in the DC Link current so this should be removed by multiplying the current (E1.I) with a step function.
(as we did to remove initial spike in motor torque output)
How these compare with the grid connected case, why might the efficiency be lower for the inverter drive case?
Power Electronics & Drives 4/M
Exercise 2.2: Variable Speed Control
As outlined in the lecture the main purpose of connecting the inverter to an induction machine is to achieve variable
speed operation. This is achieved by controlling the synchronous speed via the phase voltage frequency, but with the
additional requirement of controlling the rms phase/line voltages using Ma such that a constant V/Hz ratio is
maintained and saturation of the magnetic circuit avoided. What does constant V/Hz mean? Well for example if the
synchronous speed is halved then the rms phase/line voltages needs to half as well. How is this achieved? Answer,
by controlling the value of the Modulation Index (Ma), so for this example it has to halved too.
In this exercise we want to determine the torque v speed curves for operation around the rated operating point at 3
different synchronous speeds. What you should obtain is a set of curves which looks like the theoretical values
shown on figure 8:
Figure 8: Torque v Speed curves for Variable Speed Operation under constant V/Hz
Constant Torque #1 = 140Nm
Replace the Constant Speed Source NSRC1 with a Constant Torque Source TRQSRC1 found in the Mechanics-
Rotational Library and set the Torque –TR (Nm) parameter = -140 (NOTE THE NEGATIVE SIGN) and connect to
the IM1 model – ALSO change the Triangle Oscillator frequency to 2kHz as this will quicken up the simulations.
Open the IM1 model parameters and set the initial speed = 1000rpm (you will subsequently have to change this
to equal the synchronous speed every time you change the Synchronous speed)
Set TEND = 0.5s
Determine the necessary control parameter for each of the following 3 test points and simulate in Portunus to
determine the actual motor speeds (IM1.N parameter – display this on an On Sheet Display)
Control Parameter Value #1 Value #2 Value #3
Synchronous Speed (rpm) 1000 750 500
Phase Voltage Frequency fs (Hz) 50
Modulation Index (Ma) 1
Sinewave Frequency (Hz)
Sinewave Amplitude
Simulation Result:
Actual Motor Speed (rpm)
Slip Speed ∆N (rpm)
Where Slip speed ∆N (rpm) = Synchronous speed (rpm) – Actual Motor Speed (rpm)
Power Electronics & Drives 4/M
Now recognising that that torque = 0 when operating at Synchronous Speed create a graph of these results (hint –
this should look something like that shown on figure 8)
Exercise 2.3: Operating Point Parameter Selection
Using theory and the graphs you have just obtained determine the required Control parameters to operate this
induction motor at 800rpm actual speed (+/-5rpm) for a load torque of 150Nm. Simulate using these control
parameters to confirm operation:
Control Parameter Value
Synchronous Speed (rpm)
Phase Voltage Frequency fs (Hz)
Modulation Index (Ma)
Sinewave Frequency (Hz)
Sinewave Amplitude
Simulation Result:
Actual Motor Speed (rpm)
Power Electronics & Drives 4/M
Accessing Existing Models
In this laboratory session you are required to access an existing Portunus model
(Lab2_Model2.bak) from Moodle page ENG4187. Copy this file into a known directory on your
PC. To open this file in Portunus select ‘File-Open’ and go to the directory where you have
stored Lab2_Model2.bak. Note that in Portunus you should select ‘all files’ in the Open File
panel to access the .bak file. If you subsequently want to save models then choose the relevant
Lab2_Model’X’.bak file as it is MUCH smaller than the corresponding .ecd file but contain all
the necessary information and can be subsequently opened from Portunus using the select ‘all
files’ in the Open File panel.
程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com