Apparatus, system and method of fault diagnosis for permanent magnet motor
Disclosed are an apparatus, system and method for detecting, based on a mathematical model, a fault of a permanent magnet motor driven by a square wave. A fault diagnosis apparatus for the permanent magnet motor includes a current voltage measurement unit, a phase shift time calculation unit, and a control unit.
1. An apparatus for diagnosing a short-circuit in a motor that comprises a rotor of permanent magnet and stators of three-phases, the apparatus comprising:
a current voltage measurement unit connected to an inverter configured to drive the motor, the current voltage measurement unit configured to measure a current input and a voltage input to the motor received from the inverter; and
at least one controller configured to, for each phase of the motor;
compute a phase shift time of the motor indicating a time between a start and an end of a phase shift in the motor,
compute an inductance using the phase shift time, the current input and the voltage input,
compute an error value between the computed inductance and a predetermined reference inductance, and
when the error value is out of a predetermined range of normal operation, determine that a stator of the motor in a corresponding phase is short-circuited such that a short-circuited stator is detected while the motor is in operation,
wherein the system further comprises an output unit configured to generate a visual or audible alarm when a short-circuited stators detected.
2. The apparatus of claim 1 , wherein the least one controller is configured to compute the inductance using Equation 1:
{
v
us
=
Ri
u
+
L
1
di
u
dt
+
e
u
v
vs
=
Ri
v
+
L
2
di
v
dt
+
e
v
v
ws
=
Ri
w
+
L
3
di
w
dt
+
e
w
[
Equation
1
]
where v us , v vs , and v ws denote a u-phase voltage, a v-phase voltage, and a w-phase voltage of the motor, respectively, where i u , i v , and i w denote a u-phase current, a v-phase current, and a w-phase current of the motor, respectively, where L 1 , L 2 , and L 3 denote a u-phase inductance, a v-phase inductance, and a w-phase inductance of the motor, respectively, where e u , e v , and e w denote a u-phase back electromotive force, a v-phase back electromotive force, and a w-phase back electromotive force of the motor, respectively, and where R denotes a resistance of the motor.
3. The apparatus of claim 2 , wherein the at least one controller is configured to compute inductance of each phase by using Equation 2 derived from Equation 1:
L
1
=
(
t
2
-
t
1
)
(
DV
d
c
3
-
2
E
)
(
I
dc_e
-
I
dc_s
)
[
Equation
2
]
where L n denotes the inductance of each phase, where n is from 1 to 3, where t 2 -t 1 denotes the phase shift time, where t 1 denotes a start time of the phase shift and t 2 denotes an end time of the phase shift, where D denotes a PWM duty ratio, where V dc denotes the input voltage, where E denotes an effective value of the back electromotive force, where I dc _ s denotes an input current at the phase shift start, and where I dc _ e denotes an input current at the phase shift end.
4. The apparatus of claim 1 , wherein the at least one controller is further configured to determine that a degree of short circuit using the error vale, and wherein the greater the error value is, the greater the degree of short circuit.
5. The apparatus of claim 1 , wherein the at least one controller is further configured to determine a rating of short circuit and generate an alert corresponding to the rating of short circuit.
6. A motor diagnosis system comprising:
a motor comprising a rotor of permanent magnet and stators of three-phases;
an inverter configured to drive the motor;
a current voltage measurement unit connected to the inverter and configured to measure a current input and a voltage input to the motor received from the inverter; and
at least one control unit configured to, for each phase of the motor:
compute a phase shift time of the motor indicating a time between a start and an end of a phase shift in the motor,
compute an inductance using the phase shift time, the current input and the voltage input,
compute an error value between the computed inductance and a predetermined reference inductance, and
when the error value is out of a predetermined range of normal operation, determine that a stator of the motor in a corresponding phase is short-circuited such that a short-circuited stator is detected while the motor is in operation.
7. A method of diagnosing a short-circuit in a motor that has a rotor of permanent magnet and stators of three-phases, the method comprising:
measuring, using a current voltage measurement unit connected to an inverter for driving the motor, a current input and a voltage input to the motor by the inverter;
computing, by a controller, a phase shift time of the motor indicating a time between a start and an end of a phase shift in the motor;
computing, by the controller, an inductance using the phase shift time, the current input and the voltage input;
computing, by the controller, an error value between the computed inductance and a predetermined reference inductance; and
determining, by the controller, that a stator of the motor is short-circuited when the error value is out of a predetermined range of normal operation such that a short-circuited stator is detected while the motor is in operation.
8. The method of claim 7 , further comprising generating, by the controller, a visual or audible alarm when a short-circuited stator is detected.
9. The system of claim 6 , further comprising an output unit configured to generate a visual or audible alarm when a short-circuited stator is detected.