Method and device for detecting winding temperature, method and device for thermal protection of a motor
View Patent ↗A method and device for detecting the temperature of a motor winding, a method and device for thermal protection of a motor are provided, the method for detecting the temperature of a motor winding includes: obtaining the temperature of the motor winding at a first time before a time step; calculating the temperature rise of the rotor equivalent body after the motor runs for the time step; then calculating the temperature of the motor winding after the motor runs for the time step by superposing the temperature rise of the rotor equivalent body after the motor runs for the time step on the temperature of the motor winding obtained at the first time. By the method for detecting the temperature of a motor winding, the real-time monitoring on the temperature of the winding is achieved, thus applying the ability of the motor and improving sensitivity.
1. A method for thermally protecting a motor based on determining a simulated temperature of a winding of the motor, comprising the following steps:
A) obtaining the temperature T i-1 of the winding at a first time before a time step Δt;
B) detecting the voltage U and the rotation speed ω of the motor during the time step, acquiring the equivalent thermal power Q W and the heat dissipation power Q out of the motor; and calculating, by using a first expression, the temperature rise ΔT of the rotor equivalent body after the motor runs for the time step Δt, wherein
the first expression is:
Δ
T
=
(
Q
w
-
Q
out
)
Δ
t
CM
,
wherein C is the equivalent specific heat capacity of the motor rotor, M is the mass of the motor rotor;
the equivalent thermal power Q W of the motor is calculated from the voltage U and the rotation speed ω of the motor from expression
Q
w
=
K
t
ω
U
-
K
t
ω
R
(
1
-
η
)
η
,
wherein R is the resistance of the winding, η is the mechanical efficiency of the motor, and K t is a current coefficient;
C) calculating, by using a second expression, a simulated temperature T i of the winding after the motor runs for the time step Δt; wherein
the second expression is: T i =T i-1 +ΔT; and
D) comparing the simulated temperature T i with a temperature threshold, and starting thermal protection for the motor if the simulated temperature T i is greater than the temperature threshold.
2. The method according to claim 1 , wherein in the step B, the equivalent thermal power Q W of the motor is equal to the sum of copper loss power T Cu and iron loss power P F e , wherein the copper loss power P Cu is calculated from a fourth expression, and the iron loss power P F e is calculated from a fifth expression, and wherein
the fourth expression is:
P
Cu
=
(
U
-
K
t
ω
)
2
R
,
wherein R is the resistance of the winding, U is a motor voltage, K t is a current coefficient, and ω is a rotation speed of the motor;
the fifth expression is:
P
F
e
=
Kp
1
/
50
B
2
(
f
f
0
)
1.3
G
Fe
,
wherein p 1/50 is a loss per unit of the iron core material at the frequency of 50 Hz and the flux density of 1 Tesla, B is the flux density of the iron core, f is an alternative frequency, G Fe is the mass of the iron core, K is a correction factor of the iron loss, and f 0 is 50 Hz.
3. The method according to claim 1 , wherein the step B further comprises detecting the ambient temperature T e , wherein the heat dissipation power Q out of the motor is calculated from a sixth expression, wherein
the sixth expression is:
Q
out
=
T
i
-
1
-
T
e
R
t
,
wherein R t is the equivalent thermal resistance of the motor.
4. The method according to claim 1 , wherein in the step B, the equivalent specific heat capacity C of the motor rotor is fit into a linear function of the temperature T i-1 of the winding, and in the time step, the value of the equivalent specific heat capacity C obtained from the linear function is substituted into the first expression for performing the calculation.
5. A device for thermally protecting a motor based on determining a simulated temperature of a winding of the motor, comprising:
a motor winding temperature recording unit configured to obtain a temperature T i-1 of the winding at a first time before a time step Δt;
a motor winding temperature calculating unit configured to detect the voltage U and the rotation speed ω of the motor during the time step, calculate, by using a first expression, the temperature rise ΔT of the rotor equivalent body after the motor runs for the time step Δt from a acquired equivalent thermal power Q W and a acquired heat dissipation power Q out of the motor; and calculate, by using a second expression, a simulated temperature T i of the winding after the motor runs for the time step Δt; and
a controller for starting thermal protection of the motor when the simulated temperature T i exceeds a temperature threshold,
wherein
the first expression is:
Δ
T
=
(
Q
w
-
Q
out
)
Δ
t
CM
,
wherein C is the equivalent specific heat capacity of the motor rotor, M is the mass of the motor rotor;
the second expression is: T i =T i-1 +ΔT, and
wherein the equivalent thermal power Q W of the motor is calculated from the voltage U and the rotation speed ω of the motor from expression
Q
w
=
K
t
ω
U
-
K
t
ω
R
(
1
-
η
)
η
,
wherein R is the resistance of the winding, η is the mechanical efficiency of the motor, and K t is a current coefficient.
6. The device according to claim 5 , further comprising a second equivalent thermal power calculation unit configured to calculate the value of the equivalent thermal power Q W from the sum of the copper loss power P Cu and the iron loss power P F e , wherein the copper loss power P Cu is calculated from a fourth expression, and the iron loss power P F e is calculated from a fifth expression, and wherein
the fourth expression is
P
Cu
=
(
U
-
K
t
ω
)
2
R
,
wherein R is the resistance of the winding, U is the motor voltage, K t is a current coefficient, ω is the rotation speed of the motor;
the fifth expression is
P
F
e
=
Kp
1
/
50
B
2
(
f
f
0
)
1.3
G
Fe
,
wherein p 1/50 is the loss per unit of iron core material at the frequency of 50 Hz and the flux density of 1 Tesla, B is the flux density of the iron core, f is alternative frequency, G Fe is the mass of the iron core, K is a correction factor of the iron loss, and f 0 is 50 Hz.
7. The device according to claim 5 , further comprising a temperature sensor and a heat dissipation power calculating unit, wherein
the temperature sensor is configured to acquire the ambient temperature T e ;
the heat dissipation power calculating unit is configured to obtain the heat dissipation power Q out from a sixth expression, wherein
the sixth expression is:
Q
out
=
T
i
-
1
-
T
e
R
t
,
wherein R t is the equivalent thermal resistance of the motor.