RU221770U1 - Device for sensorless determination of the speed of an asynchronous electric motor based on injection of a high-frequency signal - Google Patents

Abstract

The utility model relates to the field of electrical engineering and can be used for vector control of an asynchronous electric drive, specially designed for very low speeds. The technical result of the utility model is to reduce the error in determining the speed at low speeds of an electric motor without sensors structurally connected to the electric motor. A device for sensorless determination of the speed of an asynchronous electric motor based on the injection of a high-frequency signal, containing an asynchronous electric motor to which voltage sensors and phase current sensors are connected, an autonomous voltage inverter, the output of which is connected to voltage and current sensors, the input of an autonomous voltage inverter is connected to the output of a vector control system on the rotor flux linkage base, and its input is connected to the speed controller and the flux linkage controller; first and second coordinate converters connected, respectively, at the input to voltage and current sensors; a bandpass filter connected in series with an amplitude detector, a PI controller and a coordinate shift unit, according to the utility model, additionally contains a third coordinate converter, a module for calculating the objective function, a module for determining the correction angle, a module for calculating the speed correction and an MRAS observer, wherein the third coordinate converter is connected at the input with a second coordinate converter, and at the output with a bandpass filter; the module for calculating the target function is connected by its input to the amplitude detector, and its output to the module for determining the correction angle, connected at the output to the PI controller; the speed correction calculation module is connected at the input to the third coordinate converter, and the MRAS observer at the input is connected through the first and second coordinate converters to current and voltage sensors, and at the output - to the input of the coordinate shift module and the output of the correction angle calculation module. The use of the proposed device will reduce the error in determining the speed at low frequencies of the electric motor to 4.6%. 2 ill.

Description

The utility model relates to the field of electrical engineering and can be used for vector control of an asynchronous electric drive, specially designed for very low speeds.

A device for sensorless determination of the speed of an electric motor is known [Fang-Zheng Peng and T. Fukao, “Robust speed identification for speed-sensorless vector control of induction motors,” in IEEE Transactions on Industry Applications, vol. 30, no. 5, pp. 1234-1240, Sept.-Oct. 1994, doi: 10.1109/28.315234], containing an asynchronous motor, inverter, coordinate converter, speed controller, observer. The authors of the device propose to use an observer based on a model-reference adaptive system (MRAS) for sensorless determination of the speed of an electric motor, built on the basis of a comparison of the rotor EMF, but using the reactive power value as the target function. This will allow not only to exclude the integrating component from the observer, but also the stator resistance parameter, which is subject to temperature influence. The disadvantages of this device include the high relative error in determining the speed when operating at frequencies close to zero, which is associated with low EMF values in the specified range.

A known device for sensorless speed detection [Jung-Ik Ha and S. -K. Sul, “Sensorless field-orientation control of an induction machine by high-frequency signal injection,” in IEEE Transactions on Industry Applications, vol. 35, no. 1, pp. 45-51, Jan.-Feb. 1999, doi: 10.1109/28.740844], which in terms of technical essence and achieved results is the closest analogue (prototype) to the proposed utility model. The device includes an asynchronous motor, to the stator windings of which voltage sensors are connected in parallel, to which phase current sensors are respectively connected , and they, in turn, are connected to the power outputs of an autonomous voltage inverter. The first and second coordinate converters are connected in series to the power outputs of the current sensors. After the second coordinate converter, the signal enters the coordinate shift block, the output of which is connected in series to a bandpass filter. The output signal of the bandpass filter is connected in series to the amplitude detector, which in turn is connected to the impedance calculation block. The impedance calculation unit is connected in series to the speed estimation PI controller, the output of which generates the value of the motor rotation speed. This value is fed into the pulse width modulation system, which is connected in series with the speed estimation controller. The operating principle of this device is that an alternating signal is injected into the current component of the flux linkage axis. Next, the difference between the impedance values along the d and q axes is evaluated. Typically the difference is not measurable at the fundamental frequency, but can be measured at the injected high frequency. Based on the difference in the impedance signal and the known objective function, the rotation speed of the electric motor is calculated. The disadvantages of this known method include the high error in determining the speed during prolonged operation of the electric drive at low speeds.

In this regard, technical The task and result of the utility model was to reduce the error in determining the speed at low speeds of an electric motor without sensors structurally connected to the electric motor.

The required technical result is achieved by the fact that a device for sensorless determination of the speed of an asynchronous electric motor based on the injection of a high-frequency signal, containing an asynchronous electric motor to which voltage sensors and phase current sensors are connected, an autonomous voltage inverter, the output of which is connected to voltage and current sensors, the input of an autonomous voltage inverter connected to the output of the vector control system based on the rotor flux linkage, and its input is connected to the speed controller and the flux linkage controller; first and second coordinate converters connected, respectively, at the input to voltage and current sensors; a bandpass filter connected in series with an amplitude detector, a PI controller and a coordinate shift unit, according to the utility model, additionally contains a third coordinate converter, a module for calculating the objective function, a module for determining the correction angle, a module for calculating the speed correction and an MRAS observer, wherein the third coordinate converter is connected at the input with a second coordinate converter, and at the output with a bandpass filter; the module for calculating the target function is connected by its input to the amplitude detector, and its output to the module for determining the correction angle, connected at the output to the PI controller; the speed correction calculation module is connected at the input to the third coordinate converter, and the MRAS observer is connected at the input through the first and second coordinate converters to current and voltage sensors, and at the output - to the input of the coordinate shift module and the output of the correction angle calculation module.

The essence of the device is illustrated using Figs. 1, 2, which shows:

Fig. 1 shows a block diagram of a device for sensorless determination of the speed of an asynchronous electric motor based on the injection of a high-frequency signal;

Figure 2 shows a vector diagram of injected currents.

All elements devices for sensorless determination of the speed of an asynchronous electric motor based on the injection of a high-frequency signal are fixed on a common base (not shown in Fig. 1). The block diagram of the device is shown in Fig. 1, it contains a three-phase alternating voltage source 1, which is connected in series with an autonomous voltage inverter 2, which is connected in series with an asynchronous motor 5, connected in series with phase voltage sensors 3 and phase current sensors 4. Speed controller 7 and the flux linkage setter 8 are connected in series with an autonomous voltage inverter 2 through a vector control system based on the rotor flux linkage 6. Phase voltage sensors 3 are connected to an additionally installed observer MRAS 19 through the first coordinate converter 9. Phase current sensors 4 are connected to the bandpass filter 12 through the second 10 and the third, additionally installed 11, coordinate converters. The output of the third coordinate converter 11 is connected to the bandpass filter 12.

The bandpass filter 12 is connected to the amplitude detector 13, which is connected to an additionally installed module for calculating the objective function 14. The module for calculating the objective function 14 is connected to the PI controller 16 through an additionally installed module for determining the correction angle 15. The output signal of the PI controller 16 simultaneously enters the third converter coordinates 11, an additionally installed module for calculating the speed correction 18 and to the adder 20. The MRAS observer 19 is connected to the coordinate shift module 17 and the adder 21. The output signals of the adders 20 and 21 enter the vector control system based on the flux linkage of the rotor 6.

The device works as follows.

First of all, from the source of three-phase alternating voltage 1, the signals are supplied to an autonomous voltage inverter 2, which receives control signals from a vector control system based on the rotor flux linkage 6, which processes the speed and flux linkage task signals from the speed controller 7 and the flux linkage controller 8. The generated signals with voltage inverter 2, are supplied to the asynchronous motor 5 and measured using voltage sensors 3 and current sensors 4. The injected signal is added to the current command signal I _d , which determines the rotor flux linkage in a vector control system based on the rotor flux linkage 6. The frequency of the injected signal is 250 Hz , the amplitude is 5% of the rated motor current.

Current signals measured using current sensors 4 enter the second coordinate converter 10, which converts the phase currents of the motor into a stationary orthogonal coordinate system, then the currents are projected into a rotating coordinate system in the third coordinate converter 11. Position of coordinate axes shifted by -45° using the coordinate shift module 17 relative to the base rotating coordinate system, as shown in Fig.2. Using a bandpass filter 12, high-frequency components of the injected current are isolatedAnd, which can be determined (according to Fig. 2) by the expressions:

,

.

Using amplitude detector 13, the values are determined And , which are used to find the objective function ε. In the module for calculating the objective function 14 , the expression of the objective function is implemented:

.

In the module for determining the correction angle 15, the correction angle is calculated, which is determined by the expression

.

To accelerate transient processes in the correction system, the error signal is introduced through the PI controller 16 into the third coordinate converter 11.

In the speed correction calculation module 18, the speed correction signal is calculated, determined by the dependence

.

Voltage signals measured using voltage sensors 3 are supplied to the MRAS 19 observer, which implements the adaptation law according to the expression:

,

Where

allows you to get the speed estimate value and the value of flux linkage assessment .

In the adder 20, the adjusted angle of rotation of the rotor flux linkage is calculated, based on the values of the flux linkage evaluation signal observer MRAS 19 and flux linkage error signal from the output of the PI controller 16 :

.

Resulting speed signal is determined at the output of adder 21 as the sum of speed estimation signals , received at the output of the observer MRAS 19 and the speed correction signal , obtained at the output of the speed correction calculation module 18.

Generated speed signals and rotor flux angle are fed into a vector control system based on rotor flux linkage 6, allowing feedback on the speed and rotor flux linkage to be generated.

The use of the proposed device makes it possible to reduce the error in determining the speed at low operating frequencies of the electric motor to 4.6%.

Claims (1)

A device for sensorless determination of the speed of an asynchronous electric motor based on the injection of a high-frequency signal, containing an asynchronous electric motor to which voltage sensors and phase current sensors are connected, an autonomous voltage inverter, the output of which is connected to voltage and current sensors, the input of an autonomous voltage inverter is connected to the output of a vector control system on the rotor flux linkage base, and its input is connected to the speed controller and the flux linkage controller; first and second coordinate converters connected, respectively, at the input to voltage and current sensors; a bandpass filter connected in series with an amplitude detector, a PI controller and a coordinate shift unit, characterized in that it additionally contains a third coordinate converter, a module for calculating the objective function, a module for determining the correction angle, a module for calculating the speed correction and an MRAS observer, wherein the third coordinate converter is connected at the input with a second coordinate converter, and at the output with a bandpass filter; the module for calculating the target function is connected by its input to the amplitude detector, and its output to the module for determining the correction angle, connected at the output to the PI controller; the speed correction calculation module is connected at the input to the third coordinate converter, and the MRAS observer at the input is connected through the first and second coordinate converters to current and voltage sensors, and at the output - to the input of the coordinate shift module and the output of the correction angle calculation module.