This block implements a squirrel-cage induction machine (SCIM)

The SCIM block implements a three-phase induction machine (asynchronous machine) with a squirrel-cage rotor model with resolvers and encoders. The machine can operate in both motoring mode, when the mechanical torque is positive, and generating mode when the mechanical torque is negative.

Model Formulation

Q-d Transformation

The 3-phase to q-d transformation and the inverse used for the model are:

required for the q-d transformation depends on the chosen reference frame as follows:

Rotor reference frame: θ=θr,
Stationary reference frame: θ=0,
Synchronous reference frame: θ=θe.

Since the Induction Machine is modeled in rotor reference frame, the θ required for the q-d transformation is the rotor electrical angle (θr).

Induction Machine Electrical Model

Induction machine models in state space framework are based on magnetic fluxes as the state variables and winding currents as the outputs, and can be represented as follows:

where the coefficient matrices are as follows:

with being the Identity matrix, a square matrix with ones on the main diagonal and zeros elsewhere,

and

The Induction Machine is modeled in rotor reference frame so ω=ωr.

In the model, all the rotor parameters and variables are seen from the stator distinguished by a prime sign. Since the squirrel-cage rotor type is not supplied by an external source, then it is always the case that V'rq=V'rd=0.

The electrical torque can be calculated as follows:

Resolver Encoder Model

The equations of the resolver encoder can be expressed as follows:

where θ_resis the resolver angle, θ_mecis the mechanical angle of the machine, θ_offsetis the angle offset, R_pp is the Number of pole pairs of the resolver and R_k are the resolver sine cosine gains.

Parameters and Measurements

The SCIM's parameters and measurements are separated in 4 different tabs, Electrical, Mechanical, Resolver and Encoder.

Electrical Parameters and Measurements

Symbol	Name	Description	Unit	Type

Symbol	Name	Description	Unit	Type
R_s	Stator resistance	Stator winding resistance of phase a, b, and c	Ω	Edit-input
L_ls	Stator leakage inductance	Stator winding leakage inductance of phase a, b, and c	H	Edit-input
R_r'	Rotor resistance	Equivalent rotor winding resistance referred to the stator of phase a, b, and c	Ω	Edit-input
L_lr'	Rotor leakage inductance	Equivalent rotor winding leakage inductance referred to the stator of phase a, b, and c	H	Edit-input
L_m	Mutual inductance	Stator-rotor mutual (magnetizing) inductance of phase a, b, and c	H	Edit-input
pp	Number of pole pairs	Number of pole pairs	N/A	Edit-input
i_s	Stator phase currents	Stator currents measured at phases a, b and c	A	Measurement
i_sqd	Stator qd currents	Stator currents in qd frame	A	Measurement
Φ_sqd	Stator qd fluxes	Stator fluxes in qd frame	Wb	Measurement
V_sqd	Stator qd voltages	Stator voltages in qd frame	V	Measurement
i_r'	Rotor phase currents	Rotor equivalent phase a, b, and c currents, referred to the stator	A	Measurement
i_rqd	Rotor qd currents	Rotor currents in qd frame, referred to the stator	A	Measurement
Φ_rqd'	Rotor qd fluxes	Rotor fluxes in qd frame, referred to the stator	Wb	Measurement
R_sn	Snubber resistance	Resistances of the snubber on phase A, B and C	Ω	Input
C_sn	Snubber capacitance	Capacitance of the snubber on phase A, B and C	F	Input

Mechanical Parameters and Measurements

Symbol	Name	Description	Unit	Type

Symbol	Name	Description	Unit	Type
J	Rotor inertia	Moment of inertia of the rotor	kg*m²	Input
F_v	Viscous friction coefficient	Viscous friction	Nms/rad	Input
F_s	Static friction torque	Static friction	N*m	Input
ctrl	Mechanical control mode	Control mode of the mechanical model. Has two possible values: speed or torque. In speed mode, the mechanical model is bypassed and the speed command is sent directly. In torque mode, the torque command is used to measure the speed using the mechanical parameters of the machine.		Input
T	Torque command	Torque command sent to the mechanical model	N*m	Input
ω_rc	Rotor speed command	Speed command sent to the mechanical model	rpm	Input
ω_r	Rotor speed	Speed of the rotor	rpm	Measurement
T_e	Electromagnetic torque	Torque measured at the rotor	N*m	Measurement
θ₀	Initial rotor angle	Rotor position at time t = 0	°	Input
θ	Rotor angle	Rotor position from 0 to 360 degrees	°	Measurement

OPAL-RT's resolver models are based off of the following sets of equations:

Where Sin.Sin, Sin.Cos, Cos.Sin, and Cos.Cos represent gains that are applied to simulate a non-ideal resolver. To simulate an ideal resolver, set the Sin.Sin and Cos.Cos gains to 1, set the Sin.Cos and Cos.Sin gains to 0, set the pp to 1, and set the θ_Offset to 0. This results in the following equations:

Resolver Parameters and Measurements

Symbol	Name	Description	Unit	Type

Symbol	Name	Description	Unit	Type
R_en	Enable resolver	Whether or not to enable the resolver	N/A	Input
R_sc	Resolver feedback signals	The two two-phase windings producing a sine and cosine feedback current proportional to the sine and cosine of the angle of the motor	N/A	Measurement
R_pp	Number of resolver pole pairs	Number of pole pairs of the resolver	N/A	Input
R_dir	Direction of the sensor rotation	Direction in which the sensor is turning, either clockwise or counterclockwise	N/A	Input
R_θ	Angle offset Δθ ( Sensor- Rotor )	Angle offset between the resolver and the rotor position from 0 to 360 degrees	°	Input
R_k	Resolver sine cosine gains	The sine/cosine modulation output sine/cosine component amplitude. Default value are 1, 0, 0 and 1	N/A	Input
E_type	Excitation source type	The source from which the excitation of the resolver is generated. Can either be AC, which is generated inside the FPGA with the specified frequency, DC, which is generated with a 90° from the rotor and External, which is generated from outside the model	N/A	Input
E_f	Excitation frequency	Frequency of the excitation when in AC mode	Hz	Input
E_src	Excitation source	Source of the external excitation source when in External mode	N/A	Input
E_ts	Excitation time shift	This parameter is used to compensate the time offset between the carrier generation's input in the system and modulated signals' output	s	Input

Encoder Parameters and Measurements

Symbol	Name	Description	Unit	Type

Symbol	Name	Description	Unit	Type
Enc_en	Enable encoder	Whether or not to enable the encoder	N/A	Input
Q_ABZ	A B Z encoder signals	A B and Z signals of the encoder	N/A	Measurement
Q_ppr	Number of pulses per revolution	Number of pulses in one full revolution of the encoder	N/A	Input
Q_dir	Direction of the sensor rotation	Direction in which the sensor is turning, either A leads B or B leads A	N/A	Input
θ_offset	Angle offset Δθ ( Sensor - Rotor )	Angle offset between the encoder and the rotor position from 0 to 360 degrees	°	Input

Visualization of Resolver Encoder Parameters Effects

Number of resolver pole pairs affects the number of electrical turns per mechanical turns. On the left figure, the number of resolver pole pairs is 2, on the right figure, the number of resolver pole pairs is 4.

Resolver sine cosine gains affect the sine ( first axe ) and cosine ( second axe ) modulation output. Default values set to 1, 0, 0, 1 make it so the sine modulation has a sine form and the cosine modulation has a cosine form. If set to 0, 1, 1, 0, the sine modulation would have a cosine and the cosine modulation would have a sine form.

Excitation frequency, in AC excitation source type, affects the frequency of the carrier signal. We can see the time step highlighted in red. ( Figure 3 is a zoomed in view of Figure 2 )

Number of pulses per revolution (Q_ppr) defines how many times signals A and B pulse between two Z pulses ( one full rotation ).

Direction of the sensor rotation describes if A leads B ( Clockwise ) or if B leads A ( Counterclockwise )

Electrical ports

This block has three electrical ports, the three terminals of the stator.

OPAL-RT Schematic Editor Documentation

Squirrel-Cage Induction Machine