RU1786626C - D c electric motor drive - Google Patents

Description

The alternating current contains an electric motor, the root winding of which through the first rectifier is connected to the first capacitor bank, and the independent winding is connected to the DC 5 terminals of the second rectifier, which is connected via the transformer to the terminals of the second capacitor battery, the first and second capacitor batteries being connected to serial circuit 10 and are intended for connection to a single-phase AC network.

A DC electric drive device for a variant of a three-phase alternating current circuit comprises an electric motor 15, the root winding of which through a three-phase rectifier is connected to the first three-phase capacitor bank connected in the star circuit or in the triangle circuit, which is connected to each of the three phases 20 to the AC mains through a phase-phase connected three-phase second battery of capacitors. The independent motor winding is connected to the DC terminals 25 of a single-phase rectifier , Kbtory via a transformer connected to terminals of a second capacitor bank in one of three phases.

The proposed solution 30 meets the criteria of the invention, significant differences, because no other technical solutions with similar properties have been identified.

Figures 1 and 2 are schematic diagrams of an electric drive device for turning on a DC motor, respectively, for variants of single-phase and three-phase AC circuits.

Fig. 3 shows a vector diagram of current and voltage diagrams for a device circuit with a single-phase alternating circuit

current.

Fig. 4 is a current vector diagram for a circuit of a device with a three to 45 phase AC circuit.

Figures 5a and 5b show, respectively, the mechanical and speed characteristics of the engine with independent excitation when the prototype is turned on (dashed lines) and when turned on according to the device of Fig. 2d (solid lines).

Presented in FIG. 1, the motor switching circuit for a variant of a single-phase alternating current circuit 55 contains capacitors 1 connected in series to the alternating current circuit (in general, this is a 1-t capacitor bank), the first rectifier 2, to the output of which

the main circuit of the motor 3 is connected, and capacitors 4 are connected in parallel with the input (in the general case, this is a capacitor bank 1-p) and the second rectifier 5, to the output of which are connected in parallel independently. The excitation coil b and the capacitance of the smoothing capacitors 7 (the latter may be absent), and the input of the rectifier 5 is connected to the output of the matching transformer 8, which is connected in parallel with the capacitors 1 in the alternating current circuit.

The device operates as follows. . , -

In accordance with the first Kirchhoff law for the network current H (and neglecting the magnitude of the current of the excitation circuits, and for the current of capacitors 1), current r of capacitors 4 and current ID of rectifier 2, we have:

IH2 + ID (1)

For a single-phase rectifier 2, the T9s of its input ID and output Id are equal, moreover, the current Id is the core current, and the voltage of its output Ud and input U2 are connected by a known relation: . , 9U2 (2)

The voltage on the field winding is related to the voltage at the input of the matching transformer 8 by the ratio:

, (3) where Kc is the matching coefficient, taking into account the value of the transformation coefficient Kt of the transformer 8 and a ratio similar to expression (2) for the output and input voltages of rectifier 5.

With ideal idling of the motor 3, there is no current ID, the currents f i and h are equal to each other and their value is determined by the voltage of the network and the resistances Xi and X2 of the batteries of the capacitors 1 and 4:

( (4)

The mains voltage is distributed between the capacitor banks 1 and 4 in proportion to their resistance.

In this case, the voltage on the motor core (taking into account (2)) and the voltage on the field winding (taking into account (3)) are equal to:

 1xx X1 (5) X2 (b)

The ratio of these voltages uniquely determines the excitation flux of the engine and its ideal idle speed n0.

At the moment of starting (starting) the engine, when its engine speed. and there is no EMF (stop mode), the rectifier 2 and the capacitors 4 turn out to be shorted (points D and B) by the resistance P of the motor core circuit, the value of which can be neglected as a first approximation compared to the resistance Xi of the battery 1. In this case, the current 2 can be neglected, and

the current I in in the network is equal to the current bn and the current Idn in the core circuit and is determined by the ratio of the voltage and resistance Xi of the battery and capacitors 1, i.e.:

(7)

liri

, ig

HT

Obviously, in this case, the voltage on the field winding is determined by the magnitude of the mains voltage:

.U.m "Uc ...;. (8). The circuit parameters determine the outcome of the following. Specifying the desired value K of the frequency of the starting current of the motor

 -.

to its rated current dv is calculated

Desired current value Ip:

  dv (9) Then, from (7), the required value of the resistance Xi of the capacitors of the battery 1 (and therefore the capacitance Ci of this battery) is determined, which provides, similarly to the prototype, a limitation of the starting current of the motor.

The value X2 of the resistance, which determines its capacity C2, of the battery 4 is determined from a given value of the voltage U2xx on the core during idling from (4) and (6). The maximum voltage values for the batteries 1 and 4 are equal to Uc and

U2xxH3 (6).

With a smooth transition from stop mode to ideal idle

engine its current 1DV, (and hence the current about)

varies from the starting value Hn to zero.

In this case, the state of the system is described by equation (1), as well as by equations

 (7)

fifteen

twenty.

25

30 35

40

45

  F 1Dv (12)

(thirteen)

where ed. - EMF of the engine, which in this case, taking into account (2), is determined by the already known parameters:

, 9 and 2-1dV -Ra ./(14) 10 In this case, in the proposed scheme for switching on the field winding, the value of the field current is taken into account (3). a function of the already known parameter Ui, for which a universal magnetization curve can be used for parallel excitation motors.

When a matching factor is selected in (3), for example, under the condition of providing a nominal excitation flux at a rated current in the motor core, the behavior of the motor is similar to the behavior of a gray motor, taking into account the following.

At the rated motor current, the flux is equal to the rated value. With an increase in the motor current, the flux increases, however, nonlinearly, since The motor magnetic circuit operates in the region of appreciable saturation. In this case, as with a gray engine, the magnitude of the torque per unit current is higher than that of an engine with an independent (parallel) field winding. The increase in the excitation flux is due to the increase in the voltage drop Ui on the battery 1 at

increasing current li.

With a decrease in the motor current, the excitation flux decreases, providing an increase in the rotation frequency similarly to a series engine, but, in contrast, only to a certain value, because even with perfect idling of the engine, the excitation flux is provided by the voltage drop across the battery 1 due to the cold current

U Ui + U2

. . and, .-

 X2

The problem is solved by a numerical method (iteration) and allows us to uniquely determine the dependences Ui; U2 and I 2 from I D, i.e. from I dv. The moment M and the engine speed r are determined by the value of I dv and the magnitude of the excitation flux Φ from the known expressions (1)

stagnation of Hxx determined by expression (4). Thus, the engine idling speed in the proposed device is significantly higher than in the prototype for an engine with an independent excitation winding, but, unlike a gray engine with such properties, has a completely limited fixed value,

In the device of FIG. 2, for a variant of a three-phase AC circuit, the first three-phase rectifier is connected in series with capacitors 1 in series with capacitors 1 in each of the three phases

55

2, to the output of which the core of the motor 3 is connected, and parallel to its three-phase input, capacitors 4 are connected in the star circuit (as shown in the figure) or in the triangle circuit (not shown in the figure), and the second single-phase rectifier 5, to the output of which is connected in parallel independent field winding b and the capacity of smoothing capacitors 7 (the latter may be absent), is connected by its input to the output of the matching transformer 8, which is connected in parallel with capacitors 1 in one of the phases of the AC circuit (in the drawing, parallel to the capacitors 1-1 in phase A).

The operation of the circuit is fundamentally completely identical to the operation of the circuit of FIG. 1, taking into account the features introduced by the three-phase execution of the alternating current circuit,

In accordance with the known relations for three-phase rectifier 2 and the accepted notation in Fig. 2, we have:

, 82 -Id

or, given that cos35 ° 0.82:., -cos35 ° (15).

, 74 Ud (16) where UD is the linear voltage module at the input of rectifier 2,

In accordance with the first Kirchhoff law for point D

ilA lp + l2A. ,. (17)

The parameters of capacitances 1 (their resistance Xi and others) are determined from expression (7) from the phase voltage of the network L f, taking into account relation (15) and a given value of the starting current 1Dp, i.e. from the expression:

-O „C)

1 ht

1d.v COS35C

(eighteen)

because in stop mode, the main circuit of the motor 3 through the bridge 2 shorts the capacitance 4 (points D, E and F) and the capacitance 1 turns out to be connected to the network according to the star scheme.

The resistance (capacitance) of the capacitors 4 is determined based on the provision (taking into account expression (16), the mains voltage and the resistance of the capacitors 1) of a given value of the voltage on the engine in idle mode, which uniquely determines the frequency of rotation of the ideal idle speed of the engine,.

Fig. 3 is a vector diagram of the currents and voltages of the motor mode region according to the calculation results for the circuit of the device of Fig. 2. The calculations were carried out for a 27 kW engine with a voltage of 250 V under the following design conditions,

All calculations for the convenience of analysis are carried out in relative units.

The basic parameters are the rated motor parameters (voltage, current, resistance, speed).

The relative value of the mains voltage is 92 (with a standard supply transformer voltage of 230 V).

The multiplicity of the starting current is 2.25 (determines the choice of Xi 10). It is accepted, 3885 (hereinafter all values are in relative units) .- .. The ratio of the resistances of the capacitors 1 and 4 is equal to Xi: X2 1: 2 (determine the 15 open-circuit voltage).

The calculations were carried out by a numerical meter at various given values of the motor current h and are presented in Fig.Z. 20 Curve AiA.2A3 is the hodograph

current vectors h with origin at point O. Points

I 2 and ID are the projections of the current AND onto the ordinate axis and the abscissa axis, taken as the real axis, respectively.

The motor current is aligned with the real axis. Current 2 is determined from expression (11) by the corresponding values of voltage - OQ of voltage U2 (not shown in the diagram) obtained as a result of calculation by iteration and ahead of this voltage (coinciding

phase with active current of motor ID) by 90 °, i.e. coincides with the direction of the axis of the 5-axis. The current And is determined from the expression (1). The voltage vector DI is the voltage drop in the resistance capacitance Xi from the current h and is 90 ° behind. The hodograph of the ends of the vectors Ui having a origin at point O is the curve C - | C2C3. The calculations take into account the influence of the resistance of the core circuit, therefore, in the starting mode (points Ai, Ci), the current And does not coincide in

45 phase with ID-.: ..... The rated current of the motor in the diagram corresponds to points A2 and C2, and the idling mode corresponds to points Az and Cz.

50 Fig. 4 is a current vector diagram for the circuit of the apparatus of Fig. 2.

For convenience, the current vector ID is aligned with the real axis, and the TOKS pseudovector

55 Id of the engine, in accordance with expression (15), is 35 ° behind the abscissa axis. Under these conditions, the diagram in principle

. 4 is identical to the diagram in. Fig. 3 for a single phase AC circuit.

40

The diagram in Fig. 4 is constructed for the ratio of the resistances Xi and Xa of capacities 1 and 2 equal to 1: 0.5. The voltages in the diagram are not shown in order to simplify the reading of the diagram since the voltage of interest LH is determined similarly to the diagram in Fig. 3 ..

Figure 5 shows the mechanical (Fig. Ba) and speed (Fig. 56) characteristics of the engine according to the results of calculating the circuit of the device of Fig. 1 for the conditions in the diagram of FIG. Z. The solid lines show the characteristics of the proposed method for switching on the field winding (Fig. 11), and the dashed lines show the independent nominal excitation () in the prototype circuit. The characteristics of the proposed device are obtained under the following conditions:

1. Resistance of the root chain - according to generalized data.

2. The dependence of the excitation flux on the input current (voltage) of the excitation winding is based on the generalized magnetization curve.

3. The coordination coefficient Kc in (3) is taken equal to 08 from the condition that the rated value of the voltage on the field winding is ensured at the rated current in the motor core, when the voltage across the capacitors 1, according to the calculation, is 48.

From Fig. 5a, it follows that in the proposed device, due to the automatic change of the voltage Ui at the input of the field winding in accordance with the diagram of FIG. 3, the characteristic of the motor in comparison with the prototype circuit (with independent supply to the field winding) acquires positive properties:

1. Increases the multiplicity of the starting torque per unit current during overloads. In particular, the stopping torque value at the same starting current under the accepted calculation conditions increases from 2.2 to 3.6, i.e. 1.64 times.

2. Increases rotational speed at loads lower than rated. In particular, the idle speed increases from a value of 0.55 to a value of 0.7 i.e. 1.27 times.

By changing the coordination coefficient Kc in expression (3), it is possible to change the shape of the mechanical and speed characteristics of the engine in the proposed device, ceteris paribus, namely; with a decrease in Ks, the overload capacity in time decreases and the frequency of rotation of the idling increases, and vice versa, with an increase in Ks it increases (taking into account

saturation of the motor magnetic system) torque overload capacity and idle speed decreases; .-; : .. -

The matching coefficient can be changed by changing the transformation coefficient of the matching transformer.

The calculation of the magnetic circuit of the matching transformer must be performed according to the full voltage of the network in the device by

fig. 1 or according to the phase voltage of the network in the device according to fig. 2, because in stop mode, it is these maximum voltage drop values across capacitors 1 that occur in the respective circuits.

The economic efficiency of the proposed technical solution is due to an increase in the overload capacity of the drive motor and, accordingly, to the torque mechanism and to an increase in the rotational speed at low loads, which makes it possible to increase the productivity of the mechanism. Formulas and inventions A DC electric drive comprising an electric motor, the root winding of which is connected to the first capacitor bank through a first rectifier, and an independent field winding is connected to the DC terminals

the second rectifier, characterized in that, in order to increase reliability and improve the quality of control, a second capacitor bank and a transformer are inserted into it, connected between the terminals of the second capacitor battery and the AC terminals of the second rectifier, the capacitor banks being connected in series and designed to connect to the network

alternating current.

i. L

i L

i b / - /

Pwe.z

0.4 0.8 f, Z 1.6. 2.0 2.4, 8 3, g J, G 4.0 M,

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