RU2038689C1 - Device for determining vector phase of a c motor emf - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: device has resistive phase modifier unit 4, signal shapers 32-34, and decoder with 24 outputs. EFFECT: improved accuracy of digital check of motor emf vector phase due to reduction of digital check-up region to 15 deg. 3 dwg, 1 tbl

Description

 The invention relates to electrical engineering and can be used for vector-pulse control of an asynchronous electric drive operating in a pulsed mode, or in reconnecting the electric motor to a network or a frequency converter.

 A device is known for generating the phase position of stator voltage vectors or currents for a system, an asynchronous electric motor frequency converter [1] comprising a sinusoidal function sensor, a torque measuring unit, a stator voltage amplitude measuring unit, an electric motor rotor speed measuring unit, a first and second integrator, an adder.

 The disadvantage of this device is its complexity and low accuracy of measuring the phase of the voltage. In addition, a speed sensor must be installed on the motor shaft, and the accuracy of measuring the position of the EMF vector depends on the number of poles of the motor.

 Closest to the technical nature of the proposed device is a discrete phase control device for the EMF vector of an induction motor induced in the stator windings by a damped rotor flow [2] containing phase and linear EMF transformers of the motor, signal conditioners connected to the secondary windings of the transformers of phase and linear EMF of the motor, a decoder that converts a 6-bit input code to "1" on one of 12 outputs.

The disadvantage of this device is the low accuracy of controlling the spatial position (phase) of the electric motor EMF vector, due to the formation of only six controlled zones. The best accuracy of phase control of the EMF vector is 30 ^about .

 The purpose of the invention is to improve the accuracy of discrete control of the phase of the EMF vector of the electric motor.

This goal is achieved by the fact that a phase conversion resistor block is introduced into the device for discrete phase control of the EMF vector of the AC motor, while the terminals of the primary winding of the three-phase connection transformer connected by a star are connected to the terminals for connecting the terminals of the corresponding phase windings of the studied motor, the terminals of the secondary transformer connected by a star are connected to the three inputs of the phase conversion unit, the twelve outputs of which are connected to the inputs signal shapers and with the second conclusions of the resistors, the first conclusions of which are connected to the bus of zero potential, and the phase conversion unit contains three circuits of five series-connected resistors each, which are connected to the inputs of the phase conversion unit according to the triangle circuit, while the connection points between the resistors of each circuit the phase conversion unit is its outputs, the outputs of the signal conditioners are connected to the corresponding inputs of the decoder, made twenty-four-output, the outputs of which connected to the output terminals of the device. The phase conversion unit converts a three-phase voltage system into a twelve-phase one, due to which 24 combinations of signals appear at the decoder inputs during a period. Each combination of signals corresponds to a signal of a logical unit at one of the 24 outputs of the decoder. This signal reflects the position of the phase of the EMF vector of the electric motor in a certain discrete control zone. The width of each zone is 360 ^about 24 15 ^o , which means an increase in accuracy by 2 times compared with the prototype.

Figure 1 presents a schematic diagram of the proposed device; in FIG. 2 vector-topographic voltage diagram of the phase conversion unit; in FIG. 3 wave voltage diagrams of U _2-1 -U _2-12 , combined with waveforms of pulse shapers U _3-1 -U _3-12 .

 The correspondence of the output signals of the decoder and the phase zone of the EMF vector to the input signals of the decoder is presented in the table.

The device comprises a connection transformer 1, terminals 2 for connecting the windings of the studied electric motor 3, a phase conversion unit 4, consisting of resistors 5-19, resistors 20-31, signal conditioners 32-43, a decoder 44. In this case, the conclusions of the primary winding W _{1 of} transformer 1 connected by a star are connected to terminals 2 for connecting the terminals of the corresponding phase windings of the studied motor, the terminals of the secondary winding W _{2 of the} transformer 1 connected by a star are connected to three inputs of the phase conversion unit 4, twelve the outputs of which are connected to the second terminals of the resistors 20-31 and to the inputs of the signal conditioners, and the phase converting unit 4 contains three circuits of five series-connected resistors each, these circuits are connected to the inputs of the phase converting unit 4 in the form of a triangle, while the connection points between the resistors each circuit of the phase conversion unit are its outputs.

=

R₂₀=R₂₁=R₂₂=R₂₉=R₃₀=R₃₁

cos7,5^°

=

где U фазное напряжение вторичной обмотки трансформатора;
I линейный ток вторичной обмотки трансформатора;
α α₁ углы (фиг.2), которые задаются в пределах 0 < α < 30^о;
(7,5^о + α) < α₁ < 37,5^о.To vectors phase voltage from the load resistors 20-31, m. E. The voltage output unit 4, the phase transformation, are shifted from each other by ^about 15, the resistor values are selected from the conditions
R ₅ = R ₉ = R ₁₀ = R ₁₄ = R ₁₅ = R ₁₉

=

R ₂₀ = R ₂₁ = R ₂₂ = R ₂₉ = R ₃₀ = R ₃₁

cos7.5 ^°

=

where U is the phase voltage of the secondary winding of the transformer;
I line current of the secondary winding of the transformer;
α α ₁ angles (figure 2), which are set within 0 <α <30 ^about ;
(7.5 ^about + α) <α ₁ <37.5 ^about .

When these conditions are met, the vector diagram of the voltages U _2-1 -U _2-12 , removed from the load resistors 20-31, has the form shown in figure 2. The vectors U _2-1 -U _{2-12 are} shifted relative to each other in phase by 15 ^about .

 The device operates as follows.

If conditionally the moment of transition of the phase voltage U _2-1 (Fig. 3), taken from the resistor 20, through zero from negative to positive values, then in the range of 0-15 el. hail. from the load resistors 20, 22, 25, 27, 28, 30, 31, the positive half-wave voltages of the phase voltages U _2-1 , U _2-9 , U _2-10 , U _2-7 , U _2-11 , U _2- are removed ₈ , U _2-12 , and negative half-waves are removed from the remaining resistors. As a result, the outputs of the signal conditioners 32, 34, 37, 39, 40, 42, 43 will receive signals in the form of rectangular pulses U _3-1 , U _3-8 , U _3-11 , U _3-3 , U _3-6 , U _3-9 , U _3-12 , corresponding to the standard logical unit, and there are no signals at the outputs of the signal conditioners 35, 38, 41, 33, 36, i.e. there is a logical zero (Fig.3 and 4). According to the table, at the output of the decoder 44, a single signal U _4-1 appears, indicating that the phase of the EMF vector of the investigated electric motor 3 is in the range 0-15 el. hail. On all other outputs of the decoder 44, the signals U _4-2 -U _4-24 are equal to zero. In the transition phase of the EMF vector of the test electric motor 3 in another range ^of 15-30 to the input signal generator 35 with the load resistor 23 is supplied positive half-wave voltage U _2-2 and its output signal appears U _3-4, the corresponding logical unit. The state of the outputs of the other signal conditioners does not change. When the signal U _3-4 appears at the input of the decoder 44, the signal U _4-1 disappears at its output and the signal U _4-2 appears (see the table), which indicates that the phase of the EMF vector of the studied electric motor 3 lies in the interval 15-30 ^about .

 Thus, the signals at one of the outputs of the decoder 44 appear only when the phase of the investigated electric motor 3 lies in the corresponding interval. The table shows how in the proposed device for determining the phase of the EMF vector of the investigated electric motor 3, the signals at the input of the decoder 44 are correlated with the signals at its output and the position of the controlled phase of the EMF vector of the studied electric motor.

 Thus, the device provides an increase in accuracy by half.

Claims (1)

 DEVICE FOR PHASE DETERMINATION OF EMF VECTOR VECTOR OF AC Alternating Current Transformer, comprising a connection transformer, phase terminals of the primary windings of which are connected to terminals for connecting the terminals of the respective phase windings of the studied electric motor, signal conditioners, resistors and a decoder, characterized in that a three-phase conversion resistor circuit is introduced connected to the inputs of the phase conversion unit according to the triangle circuit, each circuit consists of five series-connected resistors , the connection points between which are the outputs of the phase conversion unit, and the terminals of the secondary windings of the connection transformer are connected to the inputs of the phase conversion unit, the outputs of which are connected to the inputs of the signal conditioners and second outputs of the resistors, the first conclusions of which are connected to the zero potential bus, the outputs of the signal conditioners are connected to the corresponding inputs of the decoder, made twenty-four output, the outputs of which are connected to the output terminals of the device.

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