CN105915149B - The accurate discrimination method of motor speed after being powered off in discontinuous power supply Energy Saving Control - Google Patents

Abstract

The invention belongs to the technical field of energy-saving control of electric motors, and in particular relates to a method for accurately identifying the rotational speed of a motor after a power outage for energy-saving control of intermittent power supply. When the voltage is 10%, use the single-chip microcomputer to control the thyristor device to energize any phase winding of the stator, so that the rotor bar induces electromotive force and current; The magnetic field that rotates with the rotor is generated to cut the stator winding, and the induced electromotive force corresponding to the rotor speed is induced. The frequency of the induced electromotive force can be judged by the single-chip computer to complete the accurate identification of the rotor speed in the process of intermittent power supply energy-saving control. The present invention ensures that the residual voltage does not attenuate too low during the power-off control process without changing the operating parameters of the motor and at the same time reduces energy consumption as much as possible, and ensures stable and accurate detection of the motor speed.

Description

Intermittent power supply energy saving control method for accurate identification of motor speed after power failure

technical field

The invention belongs to the technical field of electric motor energy-saving control, and in particular relates to a method for accurately identifying the rotational speed of a motor after power interruption for intermittent power supply energy-saving control.

Background technique

Most oil production equipment in oilfields at home and abroad are beam pumping units. When the motor drives this type of load, the motor is usually under heavy load during the upstroke of the pumping unit. Due to the action of the sucker rod and the gravity of the liquid column during the downstroke, The motor will enter light-load or even power-generating conditions. In view of the characteristics of this periodic potential energy load, a large number of literatures have proposed and studied various energy-saving technologies for pumping unit motor systems from the perspective of different energy-saving mechanisms. These energy-saving technologies can be roughly divided into two aspects in terms of operation mode. One is to basically not change the stroke times of the pumping unit, and to achieve energy saving by improving the operating efficiency of the motor and the power factor of the line, including intermittent power supply, voltage regulation and energy saving, star angle Conversion, capacitance compensation, high-efficiency motor, linear motor, etc.; the other is to control the motor or use motors with different functions in combination with the downhole liquid level and liquid supply volume, etc., and then change the stroke times of the pumping unit to achieve the purpose of energy saving, including Multi-speed motors, variable frequency speed regulation, ultra-high slip motors, intermittent pumping, etc.

Among them, intermittent power supply technology has been widely used in oil fields. The starting point of its design is to cut off the power supply in the power generation area and connect the power supply in the electric area to realize energy-saving control. The main control links and their characteristics are as follows:

1) When the power supply of the motor is disconnected in the state of power generation and light load, the winding voltage and current of the motor are zero at this time, which reduces the loss of the motor to the greatest extent. When re-entering the electric working condition, turn on the power to allow the motor to continue to run. If the pumping unit can reasonably select the power-off time during a mechanical cycle of the pumping unit, after the pumping unit is powered off, the motor will continue to rotate by utilizing the potential energy and inertia of the pumping unit, and the energy-saving control of "no power-off without stopping" is realized.

2) After the power is cut off, by detecting the running speed of the motor, when the motor enters the electric working condition and is near the synchronous speed, the "fast soft input" control method is used to realize the power input without impact, and the "power-on without impact" control is realized, and the energy saving effect is remarkable.

In the process of completing the control link of "non-stop when power is off, no impact when power is on", in order to realize the control of "no impact when power is on", it is required that the power at the time of power supply is in a non-heavy-load operation state, and the motor speed should be as close as possible to the synchronous speed. In order to achieve It is particularly important to accurately detect the motor speed after power failure when the power is switched on near the synchronous speed. Inaccurate detection will not only affect the inrush current at the time of switching on, but in severe cases will lead to mechanical connection failure or even shutdown of the pumping well. Although relevant literature has proposed the use of Participated in the method of detecting the motor speed, but did not consider the problem that the motor speed cannot be detected after the power-off time is too long and the residual voltage decays too small.

Contents of the invention

Aiming at the problem of too low attenuation of the residual voltage of the pumping unit mentioned in the above background technology, the present invention proposes a method for accurately identifying the motor speed after a power interruption with intermittent power supply energy-saving control, including:

When the power supply of the motor is cut off, the residual voltage of the motor stator winding is used to detect the speed. When the residual voltage decays to 10% of the rated voltage, the SCM is used to control the thyristor device to energize any phase winding of the stator, so that the rotor bar induces the electromotive force and current;

When any phase winding of the stator is energized, the current induced by the rotor side generates a magnetic field that rotates with the rotor in space to cut the stator winding, and induces the induced electromotive force corresponding to the rotor speed, and judges the frequency of the induced electromotive force through a single-chip computer The precise identification of the rotor speed in the energy-saving control process of intermittent power supply can be completed.

The conditions for energizing any one phase winding of the stator should satisfy that the voltage phase angle is 120°-150°, and the energization time lasts 5ms-10ms.

The precise identification method of the rotor speed includes:

During power-off operation, the residual voltage analog signal is converted into a square wave by a comparator, and then the external interrupt and time timer interrupt functions of the single-chip microcomputer are used to detect and calculate the duration between two adjacent zero-crossing points in the residual voltage waveform of the stator winding. Time T _c , the calculation formula is as follows:

T _c =k×T ₀

In the formula, T _c represents the duration of one cycle of residual pressure; k represents the number of timer interruptions during two external interruptions; T ₀ is the duration of each interruption of the timer;

After detecting _Tc , the motor speed can be solved by the following formula:

n _r =60/(P×T _c )

In the formula, n _r is the identified rotor speed; P is the number of pole pairs of the motor.

The moment when the residual voltage decays to 10% of the rated voltage can be obtained by detecting the residual voltage waveform, and the residual voltage amplitude of different cycles is predicted by exponential function fitting, and the calculation is as follows:

U _res = U ₀ ×e ^-t/τ

In the formula, U _res is the amplitude of the residual voltage; U ₀ is the voltage amplitude of the first cycle of detecting the residual voltage; t is the time; τ is the decay time constant, obtained by curve fitting.

The beneficial effects of the present invention are:

The method for accurately identifying the motor speed during power-off operation proposed by the present invention can well adapt to the complex and changeable motor load of the pumping unit. No matter how the load fluctuates, the method described in the present invention can accurately identify the Motor speed;

The method proposed by the present invention can not only accurately identify the motor speed, but also can properly slow down the motor speed that increases sharply when the load releases potential energy, so as to prevent the motor rotor from rotating too fast and damage the motor;

The method of the present invention can not only obtain a good energy-saving effect by accurately determining the rotational speed, but also ensure the normal and stable operation of the motor;

The invention is not only applicable to the accurate identification of the motor speed in the energy-saving control of the intermittent power supply of the motor of the pumping unit, but also applicable to the accurate identification of the motor speed when other technologies are powered off.

Description of drawings

Fig. 1 is the flow chart of the speed identification method of the present invention;

Figure 2 is the residual voltage waveform after the motor of the 5.5kW pumping unit is powered off;

Figure 3 is the residual voltage waveform after the motor of the 22kW pumping unit is powered off;

Fig. 4 is the hardware circuit diagram of single-chip analog signal conversion digital signal;

Fig. 5 is a schematic diagram of a square wave converted into a residual voltage analog signal during power-off operation of the present invention;

Fig. 6 is a waveform diagram of converting the residual voltage analog signal into a square wave signal during the actual power-off operation process of the present invention;

Fig. 7 is the hardware circuit diagram of single-chip microcomputer and output trigger signal;

Fig. 8 is a circuit diagram of a thyristor trigger circuit;

Fig. 9 is the winding voltage and current waveform when the present invention electrifies any phase winding of the stator;

Figure 10 is the residual voltage waveform of the present invention after power off for 3s and power on again;

Fig. 11 shows the motor speed obtained by identifying the time interval between zero-crossing points of the residual voltage waveform according to the present invention.

Detailed ways

Below, in conjunction with the accompanying drawings, a 5.5kW motor and its drawings will be described in detail for the implementation plan and steps, as shown in Figure 1.

(1) The control device detects whether the power-off operation is satisfied, and if it meets the power-off operation;

(2) After the power is cut off, the single-chip microcomputer first detects the residual voltage amplitude of the motor winding, and the detected residual voltage waveforms are shown in Figure 2 and Figure 3, which are respectively the residual voltage waveforms of the 5.5kW and 22kW pumping unit motors after power failure; detection At the same time as the residual voltage, it is also necessary to predict the possible moment when the residual voltage amplitude of the winding is lower than 10% of the rated value by fitting the residual voltage amplitude; U _res ＝U ₀ *e ^-t/τ for fitting, τ can be obtained as 3.8, and it can be preliminarily calculated that it takes about 7.8s when the residual voltage amplitude is lower than 10%; the residual voltage of the 22kW motor in Attached Table 2 The data is fitted by U _res = U ₀ *e ^-t/τ , and τ is 0.34. It can be preliminarily calculated that when the residual pressure amplitude is lower than 10%, it takes about 0.88s;

Table 1 Variation value of residual voltage amplitude of 5.5kW motor with time

Table 2 Variation value of residual voltage amplitude of 22kW motor with time

point in time Amplitude 1.167 466 1.187 434 1.207 408 1.248 367 1.268 346 1.288 327 1.309 310 1.329 293 1.349 278 1.37 262 1.39 249

(3) When the amplitude of the residual pressure detected by the sensor is greater than 10%, use the comparator shown in Figure 4 to convert the residual pressure analog signal in Figure 5 into a square wave, as shown in Figure 6, use the external interrupt and time of the motor microcontroller The timer interrupt function detects and calculates the interval time _Tc between two adjacent zero-crossing points in the residual voltage waveform of the stator winding, and identifies the motor speed according to the detected duration _Tc of the zero-crossing point of the residual voltage waveform;

(4) When the sensor detects that the residual voltage has decayed to 10% of the rated voltage, use the single-chip microcomputer shown in Figure 7 and Figure 8 to control the thyristor device to detect the voltage phase, and when the voltage phase angle is 120°-150° The phase windings are energized, and the energization time lasts for 5ms to 10ms. As shown in Figure 9, the time from t ₁ to t ₂ is the conduction interval of the thyristor, and the thickened part of the curve is the voltage waveform of the one-phase winding and the current waveform of the one-phase winding respectively, as shown in Fig. The ratio of the voltage amplitude in 9 is reduced by 20 times, and the winding voltage and current can be clearly expressed in the same coordinate system. The residual voltage waveform of short power-on after power-off is shown in Figure 10, and the residual voltage waveform after power-on again is further detected Zero-crossing duration T _c , identify the motor speed according to T _c , and the subsequent steps are as described in (3);

(5) After the above steps (3) and (4), the detected motor speed is shown in Figure 11 .

(6) It is detected that the power-on condition is met, and the three-phase power supply is connected by using the fast soft switching technology.

This embodiment is only a preferred specific implementation of the present invention, but the scope of protection of the present invention is not limited thereto, any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention , should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (4)

1. A method for accurately identifying the motor speed after an intermittent power supply energy-saving control power failure, characterized in that it includes: When the power supply of the motor is cut off, the residual voltage of the motor stator winding is used to detect the speed. When the residual voltage decays to 10% of the rated voltage, the single-chip microcomputer is used to control the thyristor device to energize any phase winding of the stator, so that the rotor bar induces the electromotive force and current; When any phase winding of the stator is energized, the current induced by the rotor side generates a magnetic field that rotates with the rotor in space to cut the stator winding, and induces the induced electromotive force corresponding to the rotor speed, and the frequency of the induced electromotive force is judged by the single-chip computer The precise identification of the rotor speed in the energy-saving control process of intermittent power supply can be completed. 2 . The method according to claim 1 , wherein the conditions for energizing any phase winding of the stator are that the voltage phase angle is 120°-150°, and the energization time lasts 5 ms-10 ms. 3. The method according to claim 1, wherein the precise identification method of the rotor speed comprises: During power-off operation, the residual voltage analog signal is converted into a square wave by a comparator, and then the external interrupt and time timer interrupt functions of the single-chip microcomputer are used to detect and calculate the duration between two adjacent zero-crossing points in the residual voltage waveform of the stator winding. Time T _c , the calculation formula is as follows: T _c =k×T ₀ In the formula, T _c represents the duration of one cycle of residual pressure; k represents the number of timer interruptions during two external interruptions; T ₀ is the duration of each interruption of the timer; After detecting _Tc , the motor speed can be solved by the following formula: n _r =60/(P×T _c ) In the formula, n _r is the identified rotor speed; P is the number of pole pairs of the motor. 4. The method according to claim 1, characterized in that the moment when the residual voltage decays to 10% of the rated voltage can be obtained by detecting the residual voltage waveform, and the residual voltage amplitude of different cycles is predicted by fitting an exponential function , calculated as follows: U _res = U ₀ ×e ^-t/τ In the formula, U _res is the amplitude of the residual voltage; U ₀ is the voltage amplitude of the first cycle of detecting the residual voltage; t is the time; τ is the decay time constant, obtained by curve fitting.