DE1949667C3 - Circuit arrangement for supplying a single-phase series commutator motor (universal motor) - Google Patents

Description

The invention relates to a circuit arrangement for supplying a power source connected to an alternating current source Single-phase series commutator motor (universal motor) with at least two excitation windings, at least one of which can be switched on and off by a switch.

So-called high-frequency machines are mainly used for machine tool drives, d'.c are mostly designed as asynchronous squirrel cage motors with a nominal frequency of about 600 Hz and have a low power-to-weight ratio at constant speed over the entire working range. Since these motors are relatively expensive, so-called universal motors, which are AC single-phase series commutator motors, are often used, which are controlled by an electronic .vi control circuit, e.g. B. be fed via a tachometer generator in order to achieve a constant speed.

Devices for speed setting, speed control and current limitation are per se for motors known of the type mentioned. For example, the DT-Gbm has 18 15 465 for speed setting the series connection of several field windings with the armature of an electric motor is known, wherein a switch is also provided with which said field windings are connected in series can be added or removed.

In contrast to the circuit arrangement according to the present invention, this known circuit arrangement permits Invention not the universal speed control and current limitation and is therefore for many use cases disadvantageous.

Basically the same also applies to a further known circuit device for setting the speed, which is shown in FIG of the magazine »Deutsches Elektrohandwerk, 44 ^ 1969), Issue 8, on pages 229 and 230 which only deals with speed control. This speed control is carried out by that the excitation winding is switched on and off by a thyristor.

Circuit arrangements for speed control are also known per se (cf. CH-PS 4 48 233). the However, the number of circuit elements required for this is considerable, so that the cost is very high high and the risk of interference is quite great. For example, those with 10 to 12, 15 and 17 to 19 denote components a ramp voltage generator to which the armature tacho voltage is fed. This type of regulation is more sensitive in terms of the components required but quite complex. A disadvantage of this circuit arrangement is that for the Kunischlußstrom- and starting current limitation requires two different complex circuit arrangements will. An ohmic resistor in the armature circuit is used to limit the short-circuit current required for armature current measurement, its voltage drop across a capacitor, a resistor and a diode is taken out and used to control a transistor that is in communication with causes the timing capacitor to change the timing of the ignition pulses. For one Starting current limitation requires an additional device consisting of a diode, a resistor and a capacitor, the ramp jump is delayed and thus the triggering time is delayed shifts. Functionally, these two separate bodies for the two fulfill different Current limitation types do their job, however, from a cost standpoint, especially for inexpensive control equipment, useless.

In GB-PS 11 53 929, finally, is a device specified, at which a voltage value proportional to the speed on a transistor such acts that the timing circuit containing a capacitor, the firing pulses for the thyristor in The sense of the regulation changed depending on the time. This circuit does not contain the mentioned current limiting devices, so that it cannot be used for these purposes.

As the mentioned prior art shows, b.sher no institution has become known, all of them contains the functions mentioned and in a single circuit arrangement on particularly economical Way realized.

The invention has therefore set itself the task of providing a simply constructed and thus inexpensive and Circuit arrangement not susceptible to failure for speed setting and regulation as well as for current limitation for a single-phase series-wound commutator motor equipped with two field windings.

This object is achieved on the basis of the circuit arrangement of the type mentioned at the beginning by the fact that at the alternating current source a series

circuit consisting of the first excitation winding, the armature winding, a current measuring resistor, the second excitation winding and a diode is connected that as a switch to the series circuit of the current measuring resistor, the second excitation winding and the diode in anti-parallel direction to the diode switched thyristor is, the ignition pulses from a unijunction transistor, a time capacitor and an ignition circuit containing a setpoint potentiometer, the supply voltage of which corresponds to that at the Thyristor is applied voltage, are supplied that a the charging time of the time capacitor determining npn transistor with its emitter through a diode at the junction between the second Excitation winding and the current measuring resistor and with its collector on the egg.ien side of the Time capacitor is connected, the other side of which is connected to the cathode of the thyristor, and that the base of the transistor via another diode with the connection point of the armature winding and the first excitation winding is connected.

The invention is only seen in the entirety of the features of the claim.

The advantage achieved by the invention is in a relatively simple electronic control circuit visible, which allows both speed control with relatively little effort, as also already includes a current limitation, so that a separate starting current limiting circuit can be dispensed with.

An exemplary embodiment of the invention is shown in the drawing. It shows

F i g. 1 a motor with series-connected Excitation windings,

F i g. 2 the relationship between speed and torque for this motor and

F i g. 3 a circuit proposal according to the invention.

The invention is based on a universal motor which has two separate field windings / and / _ä . It is essential here that an excitation winding, e.g. B. / ,, high resistance and the other field winding, z. B. /. "Is designed with low resistance, but because of the armature reaction, the two windings are evenly distributed over the poles of the motor. If now the engine, as in FIG. 1 is shown, connected so that both windings /, and f _{2 are} in series, then there is a speed-Z torque characteristic for the motor that follows the curve Λ in FIG. If the switch S, which is connected in parallel to the excitation winding /, is closed, this winding is de-energized. This causes a weakening of the field Φ in the motor.

Since the following relationship applies to the speed of the main current motor:

U-IR ₁

η = c, -

a higher speed will set, which is approximately the course of the curve K., in F i g. 2 follows.

If an electronic switch is used in place of the mechanical switch S, e.g. B. a thyristor, or a triac, ie a component with Thyiatron characteristics that is controlled by the operating state of the engine, it is possible to enforce a speed / torque characteristic that acts as a straight line connecting the points P ₁ (idle speed of the motor when the windings /, and / _{2 are} in series) and P ₂ (full load at the rated torque of the machine when the field winding /, is short-circuited) in FIG. 2 is reproduced.

The in F i g. 3 circuit arrangement shown contains a potentiometer P, via which the capacitor C _{1 is} charged until the ignition voltage of the trigger element T, z. B. a unijunction transistor is achieved. The time required for this can be delayed depending on the operating point of the transistor T _r. If the trigger element T ignites, a positive control pulse is generated at the control electrode ST of the thyristor Th, which ignites the thyristor. The forward resistance of the thyristor, which has now become very low, shorts the field winding /,. As a result, ^{the operating point of the motor for the remaining part 1 of} the positive half-wave is from P ₁ in the direction of P ₂ in FIG. 2 postponed.

In the following negative half-cycle, a current flows through the diode D ₁ , the field winding / ,, the resistor R ₁ , the armature A and the field winding / ". The operating point of the motor is now moving again on the characteristic curve K ₁ in FIG. 2. A _{voltage drop occurs at resistor A 1 which} is proportional to the magnitude of the motor current. If this voltage drop increases z. B. to values greater than 0.7 V, so builds up across the diode D. ,, if it is a silicon diode, on the capacitor C., a voltage that, with the appropriate size (start-up or short circuit of the motor), the transistor Makes T _r conductive via the resistors R ₂ , /?., And R _t and thus prevents the capacitor C ₁ from being charged. In addition, a voltage of the same magnitude arises at anchor A.

U ₁₁ = e + I ■ R ₁₁ = c · Φ · η + I ■ R _a

a, where / is the current, c is a constant of proportionality, Φ is the flux of the magnetic field and R _{a is} the internal resistance of the armature. It can be seen from this that the speed of the motor is proportional to this voltage. This voltage is then _{processed accordingly via the diode O 1} , the capacitor C., the resistor As, the resistor R ₄ and the capacitor C ₄ and also the transistor T ₁ . fed through the resistors Ä _s and R _2. If the speed of the motor increases, then this voltage also increases, and the transistor T _r becomes conductive, which means an ignition angle adjustment of the thyristor towards a smaller current conduction angle. In this way, a change in speed is corrected.

With an appropriate design of the circuit, a control is possible that limits the starting and short-circuit current with simple means and also keeps the speed η constant in the target range.

1 sheet of drawings

Claims (1)

Claim: Circuit arrangement for supplying a single-phase series commutator motor (universal motor) connected to an alternating current source with at least two excitation windings, at least one of which can be switched on and off by a switch, characterized in that a series circuit consisting of the first excitation winding ( /,; Fig. 3), the armature winding (A), a current measuring resistor (A ₁ ), the second excitation winding (/,) and a diode (D ₁ ) is connected that a switch to the series connection of the current measuring resistor, the second Excitation winding and the diode in antiparallel direction to the diode connected thyristor (Th) is located, the ignition pulses from a unijunction transistor (T), a time capacitor (C ₁ ) and a setpoint potentiometer (P) containing ignition circuit The supply voltage, which is the voltage applied to the thyristor, is supplied so that an npn-trans which determines the charging time of the time capacitor istor (Tr) is connected with its emitter via a diode (D.,) to the connection point between the second excitation winding and the current measuring resistor and with its collector on one side of the time capacitor, the other side of which is connected to the cathode of the thyristor, and that the base of the transistor is connected to the connection point of the armature winding and the first excitation winding via a further diode (D ₃ ).