RU2173931C1 - Device for automatic control over dc brushless motor - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: technical result of invention consists in development of circuit for automatic control over brushless motor that provides for conditions of retunable stabilized rotational speed and stable operation of motor during start and variation of load torque. Device for realization of invention has rotor position pickup, regulator of pulse length, electronic switch and feedback circuit. Feedback circuit is inserted with former of voltage setting, regulator of depth of feedback and integrator and outputs of feedback circuit are connected to inputs of comparators inserted into regulator of pulse length which outputs are connected to inputs of electronic switch of armature windings of motor via detectors. EFFECT: improved functional reliability of device. 4 dwg

Description

 The invention relates to the field of automation and robotics and can be used both in these areas and in a number of others, where controlled brushless motors are used as an actuating element.

 A DC brushless motor is an electromechanical system in which the magnetic flux of the excitation is created by permanent magnets located on the rotor, and the anchor windings are placed on the stator. Switching the windings of the armature of the machine is carried out by a controlled switch according to the signals of the position sensor. The presence of an electronic control unit, with which it is possible to regulate the parameters of the engine’s performance, a non-contact way of transferring energy to the armature windings and a number of other factors makes it possible to use brushless motors in technology [1 - 3].

 As an example, we can cite the engine according to the application of Germany N 2927958, class. H 02 K 29/02, where a tachogenerator or engine according to UK patent N 21022222 of 07.13.82, in which the correction of the mechanical characteristic is carried out by switching the anchor windings according to the signal from the speed sensor, is used to control the speed. A known control circuit of a brushless motor according to the patent of Russia N 1748607, class. H 02 K 29/14, in which pulse-width modulation of the currents of the armature windings is used to stabilize the speed. The duration of the switching pulses is formed using a controlled position sensor, one of the inputs of which receives a speed feedback signal. The disadvantage of such a scheme is its low reliability, associated with the structural and circuit complexity of the implementation of such a sensor and the need to compensate for destabilizing factors in it.

 Closest to the proposed technical solution is a brushless motor control device according to the USSR copyright certificate N 256038, cl. H 02 K 29/06. This device includes: a rotor position sensor, amplifiers on multivibrators, pulse width controllers according to the number of motor windings, an electronic switch and a speed feedback circuit, in which a speed feedback signal is generated using an additional winding in the transformer of one of the multivibrators of the amplifier, rectifier and elements of the pulse duration controller. The signal from the output of the pulse duration controller is fed to the second multivibrator of the amplifier and changes the time interval of its open state, thereby performing latitudinal modulation of the switching pulses.

 The main disadvantages of the known solution are: the complexity of the circuit for generating switching pulses in the control device of a brushless motor and the presence of a large number of transformers in it, which reduces the reliability of the control device and virtually eliminates the possibility of its integral design. The absence in the device of elements of electronic adjustment of the parameters of the feedback circuit narrows its scope.

 The purpose of this proposal is to eliminate these disadvantages of the prototype and expand the scope of brushless motors by providing the ability to correct the mechanical characteristics of the motor using controlled feedback. This goal is achieved by the fact that in the device for automatic control of a brushless DC motor containing a rotor position sensor, pulse width controllers according to the number of motor armature windings, an electronic switch and a feedback circuit containing a speed signal generation circuit, an additional circuit is introduced into the feedback circuit comparison, a voltage driver defining a threshold for the comparator of the comparison circuit, a feedback depth regulator and an integrator. Each pulse duration controller is made in the form of two controlled comparators, a detector with a back-on diode and a detector with a directly-connected diode. The input of the signal conditioning circuit for speed is connected to one of the outputs of the pulse width controller, and its output is connected to the first input of the comparison circuit, the second input of the comparison circuit is connected to the output of the voltage driver determining the threshold of the comparison circuit, the output of the comparison circuit is connected to the first input of the depth controller feedback, the second input of which is connected to the second output of the voltage driver, which determines the threshold of the comparator of the comparison circuit, the output of the depth regulator atnoy communication via an integrator and the resistors connected to the first input of the second comparator and managed to the second input of the first comparator of each managed control pulse duration. External sources of control signals are connected to the first and second inputs of the voltage driver, which determines the response threshold of the comparator of the comparison circuit. The outputs of the rotor position sensor, made in the form of an angle sensor, are connected through resistors to the first inputs of the first and second controlled comparators of the corresponding pulse duration controller. The second inputs of the second controlled comparators are combined and connected to a common bus of the device for automatic control of a brushless motor. The output of the first controlled comparator of each pulse width controller through a detector with a back-on diode is connected to the corresponding first input of the electronic switch, the output of the second controlled comparator of each pulse width controller through a detector with a directly connected diode is connected to the second corresponding input of the electronic switch, the outputs of the electronic switch are connected to the corresponding inputs of the armature windings of the motor, the second inputs of the armature windings are combined and connected us to the common bus brushless motor control device.

 The operation of the device is illustrated by the drawings depicted in FIG. 14.

 In FIG. Figure 1 shows the natural mechanical characteristic of the engine (direct CD) and the family of artificial mechanical characteristics (CAB, CA'B ') at various values of the installation voltage, which determines the feedback threshold.

 In FIG. 2 shows a block diagram of a device for automatic control of a brushless motor for a variant with a two-phase anchor winding.

 In FIG. 3 shows options for timing diagrams of switching pulses when changing the value of the feedback signal U.

 In FIG. 4 shows time diagrams of voltages at the output of elements of a device for automatic control of a brushless motor.

The brushless motor is automatically controlled by jointly processing the signals from the rotor position sensor and the feedback circuit. Using adjustable feedback allows you to change the parameters of the mechanical characteristics in accordance with the required control law. The natural mechanical characteristic of a DC motor not covered by feedback is described by a well-known equation of the form n = n ₀ - k ₁ M, or M (n ₀ -n) / k ₁ , where n ₀ is the idle speed, M is the engine moment , k ₁ - coefficient of rigidity of the mechanical characteristics of the engine. When a feedback signal is introduced into the engine control circuit (see the appendix below), which corrects the duration of the working pulses, the mechanical characteristic changes and takes the form
M = [(n ₀ -n) / k ₁ ] [l - k ₂ (nn _os )], for n ≥ n _os ,
where k ₂ is the coefficient of feedback depth :, n _os is the number of engine revolutions, above which the correction signal begins to enter the control circuit.

The mechanical characteristics of the engine for various values of _nos are shown in FIG. 1. As can be seen from the graph, at a speed of n <n _{os, the} engine runs in an uncontrolled engine mode, for n ≥ n _os - it goes into stabilization mode (section AB). The parameters k and n _{os are} regulated by changing the voltage supplied to the control inputs of the voltage generator of the installation.

 A brushless motor automatic control device generally has m control channels by the number of phases of the armature windings, and therefore, the rotor position sensor used in the device must have m outputs, similarly to an electronic switch 2m inputs and m outputs.

 Angle sensors are used as a position sensor, the output signal of which is determined by the angular mismatch of the position of the rotor relative to the stator. For these purposes, it is most advisable to use inductive or capacitive sensors. It is possible to use Hall sensors, or rotating transformers. The advantage of such sensors is that the value of the output signal is uniquely determined by the angular mismatch of the stator and rotor and does not depend on the rotor speed and other factors. The output signal, depending on the angle of mismatch, is described either by a sinusoid or by a sequence of alternating isosceles pulses.

Consider the operation of the device for the case of a two-phase brushless motor of FIG. 2, in which the rotor position sensor generates a sinusoidal waveform. It contains a rotor position sensor 1, pulse width controllers 2 and 3, an electronic switch 4 and a feedback circuit 5. The pulse width controller of the first channel 2 includes: a first controlled comparator 6, a second controlled comparator 7, a detector with a back-on diode 8, a detector with directly connected diode 9. The pulse width controller of the second channel 3 includes: the first and second controlled comparators 10 and 11, a detector with a back-on diode 12, a detector with a directly connected diode 13. Feedback circuit 5 contains: a signal generation circuit for speed 14, a comparison circuit 15, a voltage driver defining a threshold for the comparator of the comparison circuit 16, a feedback depth regulator 17, and an integrator 18. FIG. 2 also shows the anchor windings of the motor 19 that are not included in the automatic control device. In this embodiment of the engine, two anchor windings are placed on the stator, offset by 90 ^° from each other in space. Conventionally, these windings are called sine and cosine. The rotor position sensor 1 has two outputs. A signal is generated at the first output of the position sensor, which is proportional to the sine of the mismatch angle, and at the second, the cosine.

When the engine is turned on, the feedback circuit 5 is blocked, so the engine operates in uncontrolled mode. Its mechanical characteristic corresponds to the natural characteristic of a DC motor. The operation of the controlled comparators 6, 7, 10 and 11 in both managed and uncontrolled modes is the same. To exclude the appearance of through currents in the electronic switch 4 at the moments of switching of the armature windings of the motor to the output of the integrator 18, voltage boosting is possible. This voltage, combined with the feedback signal, separates the moments of disconnection of one of the armature windings and the inclusion of another. When the engine accelerates, the voltage at the output of the signal conditioning circuit at a speed of 15 increases. When the engine speed reaches a value of _nos (Fig. 1), the signal generated by the signal conditioning circuit at speed 14 causes the comparator to go into the comparison circuit 15. determined by the signal from the voltage shaper 16, which determines the threshold of the comparator of the comparison circuit. From this moment, the feedback circuit is turned on and its signal, taken from the output of the integrator 18, begins to flow to the inputs of the controlled comparators 6, 7 of the first pulse width controller 2, and also to the inputs of the comparators 10, 11 of the second pulse width controller 3.

 In the automatic control device of a brushless motor, pulse-width modulation of the voltage supplying the armature windings is used to correct the mechanical characteristic. The modulation is carried out using the pulse duration controllers 2 and 3 according to the signals received from the rotor position sensor 1 and from the feedback circuit 5. When the feedback signal level changes, the time interval during which the operating current in the armature windings flows, and therefore the average for the period the electromagnetic moment developed by the engine. In FIG. Figure 3 shows how the interval of the open state of one of the shoulders of the comparator changes when the feedback voltage changes.

 The purpose and operation of the individual elements of the feedback circuit 5 is as follows. The signal generating circuit for speed 14 is connected by its input to one of the outputs of the pulse width regulators 2 or 3, the output signal of which is a sequence of rectangular pulses with a frequency proportional to the engine speed. From the output of the signal conditioning circuit at a speed of 14, a sequence of pulses is taken, the frequency of which corresponds to the frequency of the input pulses, and hence the engine speed.

 The signal generation circuit for speed 14 can be implemented (as an option) using a series-connected detector, a differentiating chain, and a single-shot. The signal at the output of the differentiating chain represents a sequence of short pulses corresponding to the leading edge of the pulses arriving after detection from the output of the pulse duration controller. These pulses are fed to the input of a single-shot, which converts them into a sequence of pulses of constant amplitude and duration.

 The comparison circuit 15 may consist of an integrator, a comparator and a key. In this embodiment, the signal coming from the output of the signal conditioning circuit at a speed of 14 to the first input of the comparison circuit 15 is fed to a key and an integrator. In the integrator, a constant voltage proportional to the engine speed is formed from a sequence of pulses. This voltage is supplied to the comparator, where it is compared with the voltage supplied to the comparison circuit 15 at its second input from the first output of the voltage shaper, which determines the threshold of the comparator of the comparison circuit 16. When the comparator is activated, a signal is generated that opens the key. From this moment, the signal generated by the signal conditioning circuit at speed 14 begins to pass through the comparison circuit 15 to the first input of the feedback depth adjuster 17. The second input of the feedback depth adjuster 17. made in the form of a divider with a variable division ratio, receives a signal from the second the output of the voltage shaper 16. The output signal from the feedback depth regulator 17 is fed to the input of the integrator 18, the output voltage of which starts to change in accordance with the feedback signal tie. This voltage is supplied through the resistors to the inputs of the controlled comparators 6, 7, 10, 11.

 The parameters of the response threshold of the comparison circuit 15 and the transfer coefficient of the feedback depth regulator 17 are determined by external sources at the inputs 1 and 2 of the voltage shaper, which determines the response threshold of the comparator of the comparison circuit 16, or, as an option, can be changed using variable resistors in this shaper. The feedback depth controller 17 provides the required level of the feedback signal in the tunable stabilized speed mode or, if necessary, the correction of the mechanical characteristics.

 The work of the regulators of the duration of pulses 2 and 3 is as follows. The signal from the output of the rotor position sensor 1 (Fig. 4a) is fed through resistors to the first (inverting) inputs of the controlled comparators 6 and 7, 10 and 11, which are respectively included in the pulse width controllers 2 and 3. At the same time, a control voltage is supplied from the output of the feedback circuit to the second (non-inverting) inputs of the comparators 6 and 10, as well as to the first inputs of the comparators 7 and 11.

 Comparators 6 and 10 are triggered when the voltages at their inputs match. Either positive or negative voltage is set at the output of the comparator, depending on which of these voltages is of greater importance at input 1 or input 2 of the comparators. A timing diagram of this voltage is shown in FIG. 4b.

 Comparators 7 and 11 has a slightly different connection scheme, in it both signals from the position sensor 1 and from the output of the feedback circuit 5 are fed to the inverting input. The non-inverting input is earthed. Therefore, the operation of the comparators 7 and 11 occurs at those moments when the signals at their inverting inputs are mutually compensated. A timing diagram of the voltage at the output of the comparators is shown in FIG. 4c.

 The voltages from the output of the comparators 6 and 7 are supplied to the detectors 8 and 9, which are rectifiers assembled on the basis of the back-connected and directly-connected diodes. The voltages at their outputs are shown in the time diagrams of FIG. 4g, 4d.

 Voltage pulses from the output of the detector 8 and detector 12 are supplied to the first inputs of the corresponding channels of the electronic switch 4, and voltage pulses from the outputs of the detectors 9 and 13 are applied to the second inputs of the electronic switch 4. As a result, a sinus supply voltage is generated at the first output of the electronic switch motor anchor winding (Fig. 4e). Similarly, the operating mode is also provided on the cosine anchor winding along the second output of the electronic switch. The circuit of the electronic switch 4 depends on the power source used. This problem is most easily solved by using a bipolar power source with an average grounded point. In this case, the anchor windings are connected at one end to the corresponding outputs of the electronic switch, and the second to the common ground point of the device. The control signals arriving in series to the inputs 1 and 2, 1 'and 2' of the switch commute its respective shoulders, connecting either positive or negative voltage to the armature windings (Fig. 4e) and thereby changing the direction of the current in the armature windings. For motors with an m-phase anchor winding, a switch is used that has 2m inputs and m outputs. The operation of the switch in this case proceeds in the same way.

 Using the proposed technical solution will expand the scope of possible applications of brushless motors and increase their reliability. The analysis of the available technical information showed that at the moment a similar solution with the given composition of essential features (blocks and connections between them) is not known. This allows us to conclude that the application materials meet the criterion of the novelty of the technical solution to the problem.

 Bibliographic data.

 1. Ovchinnikov I.E., Lebedev N.I. Contactless DC motors. - L .: Science, 1973.

 2. Kosulin V.D., Mikhailov G.B. and others. Low-power valve motors for industrial robots. - L .: Energoizdat, 1998.

 3. Tsatsenkin V.K. Gearless automated electric drive with valve motors. - M .: MPEI, 1991

 Application.

 The mechanical characteristic of a feedback motor.

где U - напряжение питания,
n - число оборотов двигателя,
R_я - сопротивление в цепи якоря,
Φ - поток возбуждения,
C_E, C_M - постоянные двигателя.The natural mechanical characteristic of a DC motor is described by an equation of the form

where U is the supply voltage,
n is the engine speed,
R _i - resistance in the chain of the anchor,
Φ is the excitation flux,
C _E , C _M - engine constants.

The moment developed by the motor is proportional to the armature current,
M = C _M Φ I _i ,
it is assumed that the magnitude of the armature current does not change within one revolution. The moment developed by the engine can be varied if, within a revolution, the value of the armature current is changed using its modulation.

M = M _n.o. [1 + f (x)],
where M _n.o. - moment developed by an uncontrolled engine,
x is the control factor.

где τ - длительность импульса тока в управляемом двигателе,
τ₀ - длительность импульса при отсутствии управляющего сигнала.Current control in the armature winding can be implemented using one or another modulation of the current. From the point of view of maximum efficiency and ease of implementation, PWM is most preferable when the ratio of the pulse duration of the armature winding to the maximum possible is determined by a controlling factor, for example, the current value of the engine speed. Since in this case the moment developed by the engine is determined by the pulse duration, we can write the relation

where τ is the duration of the current pulse in the controlled motor,
τ ₀ - pulse duration in the absence of a control signal.

Анализ этих характеристик показывает, что, хотя механическая характеристика двигателя, охваченного обратной связью, обладает большей жесткостью, чем исходная, она не удовлетворительна, так как рабочий момент двигателя при тех же габаритно-весовых характеристиках в номинальном режиме оказывается существенно заниженным. Напрашивается вывод - обратная связь должна быть сильной, но задержанной, т.е. включаемой, когда двигатель разгоняется до числа оборотов, близкого к номинальному.Assuming that τ = τ (lk ₂ n), which is true for linear control, we obtain the mechanical characteristic of the controlled engine in the form

An analysis of these characteristics shows that, although the mechanical characteristic of the motor covered by the feedback has greater rigidity than the initial one, it is not satisfactory, since the working moment of the engine with the same overall weight and weight characteristics in the nominal mode is significantly underestimated. The conclusion suggests itself - the feedback should be strong, but delayed, i.e. included when the engine accelerates to a speed close to the nominal.

Как видно из фиг. 1 двигатель, охваченный задержанной обратной связью, может обеспечить стабильную скорость вращения в широком диапазоне колебаний момента нагрузки. В то же время, меняя значение установленного числа оборотов, можно регулировать номинальное значение стабилизированной скорости.In this case, the mechanical characteristic of the engine is described by the equation

As can be seen from FIG. 1 motor covered by delayed feedback can provide a stable rotation speed in a wide range of oscillations of the load moment. At the same time, changing the value of the set speed, you can adjust the nominal value of the stabilized speed.

Claims (1)

 A device for automatic control of a brushless DC motor containing a rotor position sensor, pulse width controllers according to the number of motor windings, an electronic switch and a feedback circuit containing a speed signal generation circuit, characterized in that a comparison circuit and a shaper are additionally introduced into the feedback circuit voltage determining the threshold of operation of the comparator of the comparison circuit, a feedback depth regulator and an integrator, and each duration controller The pulses are made in the form of two controlled comparators, a detector with a reverse-connected diode and a detector with a direct-connected diode, and the input of the signal conditioning circuit for speed is connected to one of the outputs of the pulse duration controller, and its output is connected to the first input of the comparison circuit, the second input of the comparison circuit is connected to the first output of the voltage driver, which determines the threshold of the comparator of the comparison circuit, the output of the comparison circuit is connected to the first input of the feedback depth controller, the second the path of which is connected to the second input of the voltage driver, which determines the threshold of the comparator of the comparison circuit, the outputs of which are connected to external sources of the installation voltage, the output of the feedback depth controller through the integrator and resistors is connected to the first input of the second controlled comparator and to the second input of the first controlled comparator of each controller pulse duration, with each of the outputs of the rotor position sensor, made in the form of an angle sensor, through resistors it is connected to the first inputs of the first and second comparators of the corresponding pulse width controller, the second input of the second controlled comparator of each pulse width controller is connected to the common bus of the automatic control device, the output of the first controlled comparator of each pulse width controller is connected to the corresponding first inputs of the electronic switch through detectors with reverse-connected diodes , output of the second controlled comparator of each pulse duration controller Erez detectors pryamovklyuchennymi diodes are connected to second inputs of the electronic switch, the electronic switch outputs connected to inputs of respective armature coils brushless motor, and the second inputs of the armature coils are combined and connected to a common bus automatic engine control device.

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