SU1365226A1 - Method of thermal protecting of electric motor of follow-up system - Google Patents

Abstract

The invention relates to electrical engineering and can be applied, in particular, for electric motors of direct current of follow-up systems. The aim of the invention is to increase reliability by ensuring continuous monitoring of the thermal state of the engine and improving accuracy. Result aperiodic. the averaging of the current squared, reflecting the thermal state of the motor, is compared with the upper setpoint level and a signal is generated to turn off the control signal of the protected motor. When the engine temperature is subsequently lowered to the low setpoint level, the control signal is automatically re-activated. If it is necessary to maintain motor control in overload modes, vibration mode is possible. 3 il. (L

Description

The invention relates to the field of electrical engineering and can be applied, in particular, for the protection of direct current electric motors of nuclear systems.

The purpose of the invention is to increase reliability by ensuring continuity of monitoring the thermal state of the engine and improving accuracy,

Figure 1 shows a graph of a pulse train that is used as a signal proportional to the square of the current; Fig. 2 shows the processes of changing the superheat temperature T (t) (proportional to the result of the filterdiah) when the engine is loaded with a rated current i, and a current of 1; 1.5; in FIG. 3, a diagram of the device that implements the proposed method.

The proposed method consists in continuously measuring the current of the protected motor, generating a signal proportional to the absolute value of the current, comparing it with a single polarizing triangular signal, interrupting it for those periods of time when the reference signal is longer than measured current. The current result of the averaged pulse sequence is compared with the setpoint and forms a stop signal, in the case of being above the upper setpoint level or the next one. enabling the control signal of the overheating motor in case of averaging a result lower than the setpoint level, the upper setpoint level being determined by the established value of the averaging result at the rated motor current, and the time averaging constant realized by aperiodic filtering is

tK

-ln (l- f, -)

(one)

where tj, is the maximum allowed. operation time interval at current IK IH.

As can be seen from figure 2, the signal is proportional to the absolute value, i.e. to the current module of the motor being protected, is compared with the periodic recalculation of ms ms to zero with the unipolar reference signal Ugn of a triangular shape and

interrupt for those periods of time when the reference signal is larger, the resulting pulses (in FIG. 2 are shaded) form a sequence, which is used as a signal proportional to the square of the current. It is obvious that the duration of the pulses of the formed sequence with a constant in time modulus of the current is strictly proportional to their amplitude, which means that the area of the pulses is strictly proportional to the square of the current. If the current and its modulus change in time, then this severity is violated, however, the resulting error can be neglected, keeping in mind that the period of the reference signal can be easily made one to three orders less than the minimum interval time (for example, 3-10 s), which it is considered necessary to measure the thermal effect of the current. I

Since the time integral of

signal K, 1, proportional to the square of the current, corresponds only to the amount of heat QK that heats the engine, and the amount of heat Qp, dissipating and discharging, can be taken into account by the integral of the signal proportional to the engine overheating temperature T above the environment, then the temperature T value is proportional to differences QH - QP means that cG as the result of averaging a sequence of pulses can be found by aperiodic

filterdia t

 J (K; i -) dt.

(2)

since the transformation (2) with K, ---, K2 corresponds to the differential equation of the aperiodic filter

, (3)

K i T + Too

If before the start of the process T (0) 0 (the engine temperature is equal to the ambient temperature), then the motor is loaded with a nominal current 1c, then the change process 6 corresponds to the curve 1 ,, shown in FIG. 2

(t) (1-e),

(BUT)

The established maximum value of c is taken as the upper level of the setpoint U,, KoiJ, - It is obvious that if the operating current is at least 1% less than the rated current, then c (t will never reach the setpoint level and the response will never happen, which corresponds to the permissibility of long-term engine operation at a current lower than the rated value. If now, starting from T (0) 0, the engine is loaded with a current of 1.1 c, then the process of changing G will proceed, as indicated in Figure 2, curve II

t

T (t) K „1 (1st),

(five)

which reaches the setting level Uijj. at time t | defined by the equation

B

and ,,. ,, ,, to „1 и кУ, (1-е) о (6)

.ICT.I

-n

Therefore, if the admissible t | 4 of engine operation with a current 1 is known, then the time constant T is determined from equation (6), i.e. according to the formula (l). Thus, if the upper setpoint UUCT.O level is reached, the engine is turned off, which can be done by interrupting the control signal, then C will be reduced according to the law of discharge of the aperiodic filter (curve III in Fig. 2). t

(t) and e

(7)

which corresponds to the process of cooling the engine. After a time interval defined by the formula

t - T In% gkl T in - (8)

t reaches the lower level of Uucyi, and the engine is switched on again by closing the control signal circuit of the protected engine. If the time t to stay in the off state is set, the lower setpoint level is determined by the formula

off

The process is repeated.

In the case when it is necessary to continue engine control under overload conditions, but without exceeding the permissible overheating i, -, 5

lower setting level IL ,,,, select

3

365226. 4

equal to the upper U,, In this case, after the first disconnection, a vibratory mode of current limitation occurs on the overheating, and the average square of it will not exceed the nominal one.

Sensor 1 of the absolute value of the motor current through the first breaker 2 is connected to the input of the inverting integrator 3, the other input of which is connected to its output. The output of this integrator is in turn connected to the input of the first comparator 4, the other input of which is connected to a constant voltage source.

ten

15

 The output of this comparator is connected to the signal input of the second chopper 5 is connected to the signal circuit U

20

which 1 is right25

thirty

40

not a single engine. In addition, the reference signal generator 6 and the absolute current sensor 1 are connected to the inputs of the second comparator 7, the output of which is connected to the control input of the first breaker 2.

The device works as follows.

The signal (i) from the output of sensor 1 of the absolute value of the current and the reference signal Ugn from the output of generator 6 is compared at comparator 7, the output of which produces a square-shaped voltage U, a constant amp2g volume and a variable duty cycle, and the pulse duration, for example, positive polarity is proportional to signal (1). The voltage and supplied to the control input of predolgoitel 2 and pulses (in this case) of negative polarity interrupts the signal (ij, which passes through the interrupter only when the polarity is positive .g nn. Thus, at the output of interruptor 2 get pulse sequence 1

the amplitude and duration of which is almost proportional (i). This process is described gQ graphically presented in figure 2,

J h Pulse sequence i

is fed to the input of the inverting integrator 3, which, being covered by resistor feedback

55

through the input resistor of the second input, is an aperiodic filter averaging sequence 1.

The result of averaging tr, which is obtained at the output of integrator 3, is compared at comparator 4 with a constant voltage equal to the upper level of the setpoint U ,,,. As long as the signal C UucTi, the signal W from the output of the comparator 4 does not affect the switch 5, through which the control signal of the protected engine passes, and the tracking system operates in normal mode. As soon as the signal G exceeds the upper level of the setpoint 1) ,,, the signal Vf from the output of the comparator 4. changes polarity and affecting the control input of the breaker 5 breaks the control signal circuit of the protected motor. The current through the motor ceases. The signals (i) and i go to zero, and the signal t begins to decrease due to the action of the integrator feedback, 3.

After reducing the signal t to the lower setting level j, the value of which can be set by the positive feedback factor of the comparator 4, the voltage at its output returns to the original polarity, and the interrupter 5 closes the control signal circuit U s again. The following system continues.

If the coefficient of positive feedback of comparator 4 is set to zero, then the lower level of the matching coincides with the upper level and instead of repeating cycles on or off with the load on or off, a vibration current limiting mode occurs at which the average square of the current does not exceed the nominal semiconductor power amplifiers (PA) are fully acceptable.

The proposed protection device is used both to protect the engines of follow-up systems operating in the continuous mode of testing the driving effects, and for engines operating in the intermittent mode. In the latter case, it is necessary not to turn off the device for a period of pauses to monitor the thermal state during the entire cycle.

The invention was used to design the thermal protection of the EDM-34 low-inertia motor, with the upper and lower levels of the usaka being equal and constant

the time of the thermal protection device was determined by the requirements of the technical conditions at currents 1.5 and 3 times higher than the nominal, the duration of the engine should not exceed 60 and 12 s, respectively.

The time constant for this thermal protection device is set to 100 s.

The proposed method makes it possible to significantly simplify the procedure for monitoring the thermal state of an electric motor.

Improving the accuracy of motor thermal monitoring improves the operational reliability of the tracking system and is achieved by selecting the P value of the input resistor.

Claims (1)

Invention Formula The method of thermal protection of the follow-up motor, in which the current of the protected motor is measured continuously, forms a signal proportional to the square of the current of the motor, averages the specified signal comparing the result of averaging with a predetermined setpoint, and if it is above a predetermined setpoint, a signal is generated to shut off the engine, characterized in that, in order to increase reliability by ensuring the continuity of monitoring the motor thermal state and increasing accuracy, a signal is proportional to the absolute magnitude, compare it with a unipolar, periodically triangular-shaped reference signal of a triangular shape, break it for those periods when the reference the signal is larger than the measured current, the current averaging result of the obtained pulse sequence is compared with the setpoint and forms a stop signal in case of exceeding the upper setpoint level or subsequent activation of the control signal of the protected engine in case of averaging lower than the lower setpoint level, the upper setting level is determined by the steady-state value of the averaging result at the nominal motor current, and the constant of the averaging time is determined by the formula ft fzg.1 ST Phage. 2 original