Regulator of power and speed of rotation of a single-phase collector electric motor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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The regulator of power and speed of rotation of the rotor of a single-phase collector motor is designed for ease of operation (expansion of capabilities) of the IE1032 electric drill and other household electrical machines using AC collector motors with a power of up to 1,2 kW. Single-phase collector electric motors with series excitation are widely used in household appliances when high rotation speeds are required: vacuum cleaners, floor polishers, sewing machines, juicers, coffee grinders, universal kitchen machines, hand-held woodworking tools (electric drills), electric planes and much more.

Single-phase collector motors are described in [1]. They are powered by both AC mains and both AC and DC mains (universal). If the electric motor is universal, then its excitation windings have taps (Fig. 1).

The IE1032 drill uses a KNII-420/220-18 type motor, which is not universal. It is made according to the scheme of Fig. 2 and can only be powered by an alternating current, but not from a direct current and not from a pulsating one with a frequency of 100 Hz, as described in [2]. This scheme was made, but did not work.

The regulation of the power and speed of rotation of the rotor for such motors can be carried out by regulating the supply voltage using an autotransformer (for example, LATR) or by the amplitude-phase method using a power controller (in this case, on a thyristor).

When choosing a regulator circuit, the following should be taken into account: ease of manufacture; the possibility of smooth regulation of rotation speed and power in the entire control range; convenient and correct inclusion of the electric motor in that section of the circuit in which a sinusoidal current with a frequency of 50 Hz flows; reliability in work.

Figure 3 shows in which section of the circuit the electric motor cannot be turned on, in Figure 4 - which one should be turned on.

To control the thyristor of the regulator, a relaxation oscillator circuit based on a single-junction transistor was chosen [3].

Advantages of the regulator: minimum number of elements, ease of manufacture, small dimensions, smooth adjustment, high stability in operation, high reliability (for 5 years of operation there was not a single failure), the absence of a constant component in the load, since a symmetrical current flows through the thyristor in positive and negative half cycles of the supply voltage. The schematic diagram of the regulator is shown in Fig.5.

(click to enlarge)

Specifications of the regulator:

• Supply voltage ....... 220 V
• Supply voltage frequency ...... 50 Hz
• Load power: 1st option......550 W
• 2nd option.......1200 W
• Thyristor firing angle: minimum.......6°
• maximum......37°

When the controller is running, the thyristor is under a rectified pulsating voltage with a maximum amplitude Umax = 1,4Uef = 310 V. Therefore, the reverse voltage of the thyristor must be greater than this value.

The relaxation generator is powered by the same voltage, but limited by two D814V zener diodes connected in series up to 20 V.

The regulator works as follows. When connected to the network from the output of the rectifier, a pulsating voltage is applied to the thyristor, and a limited sinusoidal voltage is applied to the relaxation generator.

Capacitor C1 starts charging through resistors R1 - R4. The total resistance of these resistors is 46 kOhm. As the capacitor charges, the voltage across it increases, and when the trigger voltage at the emitter VT1 (UC1 = UE.on) is reached, the unijunction transistor unlocks and capacitor C1 is discharged through the emitter-base1 circuit VT1, resistor R6. The emitter-base resistance in the open state is from 5 to 20 Ohm [3], the resistance of the resistor R6 = 150...200 Ohm. The time constant of the capacitor discharge circuit is small, and a short pulse of positive polarity is formed on the resistor R6.

By selecting the resistance of the resistor R6, you can adjust the trigger threshold UE.on the transistor and the amplitude of the control pulse, which should be 5-7 V (optimal for stable operation of the thyristor.

A short pulse of positive polarity from resistor R6 is applied to the control electrode of the thyristor, the latter opens, including the load.

In the open state, the voltage drop across the thyristor is 1,5-2 V. This voltage is supplied as a power supply for the relaxation generator, shunts and turns it off.

Thus, the relaxation oscillator does not go into self-oscillatory mode, but for one half-cycle of the mains voltage it produces only one control pulse and turns off before the next one arrives. The thyristor remains open until the end of the half-cycle and closes at the end of the half-cycle.

With the arrival of the next half-cycle at the anode of the thyristor, which is still closed, the rectified voltage through the resistors R7, R8, limited by the zener diodes VD1 VD2, enters the power circuit of the relaxation generator. Capacitor C1 begins to charge, and the cycle repeats.

The moment of opening the thyristor is determined by the time constant of the charge circuit of the capacitor C1. In this circuit there is a variable resistor R1, with which you can change the moment of unlocking, therefore, adjust the speed of rotation of the motor shaft and its power.

At the minimum unlocking angle (ϕ min), the engine develops maximum speed, and the unlocking angle depends on the type of engine (within the technical characteristics of the regulator) and does not change within the regulation.

At the maximum firing angle ϕmax. the engine develops a minimum speed, and the opening angle depends on the type of engine (on its power, rotor weight, friction in brushes and bearings, etc.).

The greater the engine power, the heavier the rotor, the greater the friction, the greater the current required from the regulator, therefore, the smaller the maximum firing angle will be. Each type of motor has its own maximum firing angle of the thyristor.

We select the elements of the charging circuit of the capacitor C1 and determine the range of change in the control angle ∆ϕ: ∆ϕ = ϕmax - ϕ min.

Figure 6 shows one half-cycle of a sinusoidal mains voltage and a voltage limited to 20 V. Since the ratio 20/310 = 0,0645, the minimum possible angle ωt = 0,0645°3' was found for sinωt = 45.

The variable resistor R1, with the help of which the firing angle is changed in the range ∆ϕ, is high-resistance and has an initial jump in resistance, i.e. when turning the knob, for example, from the extreme left position, the resistance jumps from 0 to 5 kOhm. There is also a jump from the right extreme position, and it is different from the left one. The value of this jump for each variable resistor is individual.

The resistance R3 is chosen equal to the value of the initial jump, i.e. 5,1 kOhm It determines the minimum firing angle of the thyristor ϕ min. If the slider of the resistor R1 is in the lowest position according to the diagram, then the resistance of the charge circuit of the capacitor C1 will consist of resistors R3 and R4 connected in parallel with a total resistance of 4,85 kOhm (in the other extreme position, as already indicated, the total resistance is 46 kOhm) .

We will carry out an estimated calculation of two capacitor charge curves (exponential) at the extreme positions of the potentiometer R1 engine, plot graphs (Fig. 7), determine the angles fmin, fmax and the control range f.

To simplify the calculation and the convenience of plotting, we will make some simplifications: we accept Rtot. min = 5 kOhm, not 4,858 kOhm (3% error), we accept Rtot. max \u46d 45,858 kOhm, and not 3 kOhm (2% error), we also accept a limited sinusoidal voltage as a rectangular pulse of the same duration, as well as one half-cycle of the mains voltage T / 10 \uXNUMXd XNUMX ms.

Voltage across capacitor C1 at time t

Us \u1d U (XNUMXst ^-t/RC),

where U = 20 V is a limited sinusoidal voltage.

Charging circuit time constant at Rtot min = 5 kOhm

at τ1 = Rtot minC1= 5 H 0,1 = 0,5 ms,

at Rtotal max = 46 kOhm

τ2 = Rtotal maxC1 = 46 H 0,1 = 4,6 ms.

For example, we give a detailed procedure for calculating the voltage across the capacitor, for example, for the first point t = RС/2. Us = U(1st ^-t/RC) = U(1st ^-1/2) = U(1 - 1/√e) = 20(1 - 1/√2,7183) = = 20 (1 - 1/1,6487) = 20 (1 - 0,6) = 20 x 0,4 = 8 V.

This means that during the time t = τ1/2 = 0,5/2 = 0,25 ms, the capacitor C1 will charge up to a voltage of Uc = 8 V.

The calculated data are summarized in the table.

The graph in Fig. 7 shows:

• one half-cycle of the approximate limited mains voltage;
• curve U'с = f (τ1) - exponent for the time constant;
• straight line 0A characterizes the initial section of the exponent U's, close to linear;
• curve U''c = f (τ2) - exponential for the time constant τ2; straight line 0B characterizes the initial section of the exponent U''c close to linear.

In addition, Ue.on is marked on the y-axis - the operating threshold of the unijunction transistor VT1; on the abscissa axis - τ1 and τ2 (in milliseconds and electrical degrees), the duration of the pulse feeding the relaxation generator (in milliseconds and electrical degrees) are marked ϕmin, ϕmax and ∆ϕ for the real controller.

On the phase scale, the price of a large division of 1 cm with a resistance of -18 °, the price of a small division of 1 mm is 1,8 °.

Let's determine graphically the minimum and maximum thyristor firing angles

ϕmin = 2⋅1,8° = 3,6° = 3°36'.

ϕmax = 20⋅1.8°° = 36°°.

Let us take into account the error by approximating the limited sinusoidal voltage into a rectangular one. Let's determine sinωt when the voltage across the capacitor C1 is equal to the trigger threshold of the transistor VT1.

Us \u7d Ue.on \uXNUMXd U \uXNUMXd XNUMX V;

sinωt = 7/310 = 0,0226.

According to the table of sines, we determine the angle ωt = 1°18'.

Then ϕmin = 3°36' + 1°18' = 4°54';

ϕmax = 36° + 1°18' = 37°18'.

Taking into account other errors associated with the accepted simplifications in the construction of graphs in Fig. 7, with a sufficient degree of reliability, it is possible to accept the angles ϕmin = 6°; ϕmax = 37°.

Thus, the firing angle of the thyristor can be controlled from 6 to 37°.

Control Angle Range

∆ϕ = ϕmax - ϕmin = 31°,

but not 170°, as stated in [4, p. 202]. At an angle ϕmax = 170°, no motor designed for an operating voltage of 220 V will work.

Setting the regulator consists in selecting the resistance of the resistors of the charge circuit of the capacitor C1 (R1, R2, R3, R4) for a specific single-phase collector motor at the maximum thyristor firing angle (the R1 engine is in its extreme upper position). With a minimum opening angle, no adjustment is required.

When the engine of the resistor R1 is set to the lowest position according to the scheme (R1 is shorted), the thyristor firing angle is minimal, the electric motor develops maximum speed. By moving the engine up, we increase the resistance of the charge circuit, the rotation speed drops, and in the highest position of the engine, the electric motor should work stably at minimum speed.

If the engine is unstable and stops with slight fluctuations in the mains voltage, then it is necessary to reduce the resistance of the charge circuit, i.e. reduce the resistance of the resistor R1 by connecting instead of R2 = 390 kΩ a resistor of lower resistance 360, 330 kΩ, ... etc.

And vice versa, if at the upper position of the engine the rotation speed is still high and it needs to be lowered, then the resistor R2 must be replaced with a resistor of greater resistance 430, 470 kOhm, etc., up to removing it from the circuit. This completes the adjustment.

The regulator made according to this scheme works stably and for 5 years of operation there was not a single failure, it showed good results both at high and low speeds with a variable load on the drill.

In the manufacture of the regulator, it is necessary to provide that when the knob of the speed regulator (resistor R1) is turned to the right, the rotation speed increases, for this it is necessary to crucify the resistor R1 so that when the knob is turned to the right, the resistance decreases.

The use of the amplitude-phase method leads to a significant distortion of the sinusoidal voltage and the appearance of many higher harmonics, so there is a need for additional protection against interference by introducing two additional filters into the power supply circuit of the drill C2, R9 and into the power supply circuit of the regulator C3, R10.

Regulator design.

The regulator is made in two versions. The first option is described above, the difference lies only in the type of rectifier diodes used (indicated in brackets on the circuit diagram).

Printed circuit boards are made of foil fiberglass and getinaks with a thickness of 1,5-2 mm.

Figure 8 shows two printed circuit boards for the first version of the regulator.

The board in Fig. 8, a is used when filters C2, R9 and C3, R10 are made by hanging mounting, the board in Fig. 8, b - when the filters are placed on the board.

Figure 9 shows one printed circuit board for the second version of the regulator.

Filters are made by hinged installation. You can make a board together with filters like (Fig. 8, b) for the first option.

The printed circuit board and other parts of the regulator are placed in a plastic box. A variable resistor R1 with R2, a socket for connecting a drill are fixed on the box body, a 1,5 m long power cord with a plug at the end is rigidly fixed. Filters C2, R9 and C3, R10 are mounted on mounting racks in close proximity to the power cord and socket for connecting a drill. A scale with conditional divisions is fixed on the box body under the handle of the resistor R1.

Details. The rectifier uses KD202R diodes, designed for an average rectified current of 5 A. Instead, you can use KD202K, KD202M. In the second version of the regulator, diodes D231 are used. You can use D231A, D231B, D232, D233, D234 with any letter indices and other types of diodes, designed for an average rectified current of 10 A and a reverse voltage of 300 V or more.

Thyristor KU202M can be replaced with KU202N, zener diodes D814V - with any others with a total stabilization voltage of 18-20 V. KT117 can be used with any letter index. Capacitor C1 can be used types KLS, KM, K10U-5. Capacitors C2 and C3 of the K40P-2B type can be replaced with any paper ones with an operating voltage of at least 400 V. A variable resistor of the SP-1 type can be replaced with a resistor of any other type and any size.

To operate a drill with this regulator, no additional switches need to be installed. A two-pole switch installed in a drill is quite enough. Voltage is supplied to the regulator and removed by the drill switch.

Despite the fact that the regulator was designed to power single-phase collector electric motors, if necessary, any active load (heaters) of the appropriate power can be connected to it.

References:

1. Woldek A. I. Electric machines.-L .: Energy, 1978.
2. Denisov G. Trinistor regulator for a collector electric motor//Radio. -1990.-№1.-S. 61, 62.
3. Kublanovskiy Ya.S. Thyristor devices.-M.: Radio and communication. 1987.
4. Encyclopedia of modern technology. "Automation of production and industrial electronics". Owls. encyclopedia. T.4, 1965.

Author: V. V. Pershin

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