Prior Art Known is a fact that the power consuming devices (e. g. an electric motor) are connected to the mains supply by means of a power switch.

The disadvantage of such connections is the impossibility to control an electric motor speed.

Known is a method of decreasing the rotational speed of an alternating-current drive motor [Masandilov L. B., Moskalenko V. V. Rotational Speed Control Of Asynchronous Motors. , M., "Energija", 1969, pp. , 25-34. ] by means of serially connecting a pure resistance (a resistor).

The disadvantage of an alternating-current drive of the type described is its low efficiency due to the substantial drop of an active power and the conversion of the latter into the heat power.

The operating mode of such an alternating-current drive with the decreased rotational speed is used only for a short-term switching.

The nearest to the device filed Prior Art reference is an alternating-current drive [Russian Patent No. 2006172, Int. Cl.: H02P5/16, published 15.01. 1994] comprising a single-phase collector motor, a power switch, two capacitors and a double-pole switch with each contact of the latter being connected respectively to the opposite leads of an electric motor and the mains supply. The power switch being closed and the double-pole switch being opened, each lead of an electric motor appears to be serially connected to the mains supply through the capacitor.

In this case the current in the power supply chain of the motor is limited by the capacitors in such a manner that the motor rotational speed reaches the level of 6-10% of the rating value.

Under the closure of the double-pole switch the motor is connected directly to the supply mains and reaches the rotational speed rating.

The disadvantage of the technical solution filed is its rigidity and impossibility to achieve a multi-step control of a motor rotational speed.

Summary of the Invention It is the aim of the present invention to design a modified alternating-current drive with the possibility of providing a multi-step control of its motor rotational speed.

The above-described aim in an alternating-current drive comprising a single-phase electric motor, at least one capacitor, at least one key and the power supply terminals for connecting to A. C. supply mains, is achieved by means of the first lead of an electric motor being connected to the first power supply terminal through the key and the capacitor connected in parallel, while the second lead of an electric motor is directly connected to the second power supply terminal.

An drive may be supplied with a capacitor directly connected between the first and the second leads of an electric motor.

An alternating-current drive may also be supplied with three power switches, while the winding of an electric motor is made with two additional leads with each of said winding leads being coupled to the connection point of the key and the capacitor through an corresponding power switch.

An alternating-current drive may be additionally supplied with two keys and three power switches, and the winding of an electric motor can be made with two additional leads, while all the keys are connected in parallel to the capacitor in such a manner that the second lead of each of said keys is connected to an appropriate winding lead of an electric motor with each of the latter leads being connected to the second capacitor lead through an corresponding power switch.

An alternating-current drive may be supplied with a chain comprising a second capacitor and a second key connected in parallel, while said chain is connected between the first lead of an electric motor and the first power supply terminal.

An alternating-current drive is preferably supplied with a second capacitor and the second and third keys, while the second key is connected in series with the first capacitor, and at least one chain comprising the third key and the second capacitor is connected in parallel to the first key.

An alternating-current drive may be supplied with a second capacitor and the second, the third and the forth keys, while the second key is coupled between the connection point of a first key and a first capacitor and the first power supply terminal, the latter being coupled through serially connected the third key and the second capacitor to the connection point of the second lead of the first key and of the first lead of the forth key, while the second lead of the latter is connected to the second lead of the first capacitor.

An alternating-current drive may also be supplied with the second and the third capacitors and the first, the second, the third, the forth, the fifth, the sixth, the seventh, the eighth, the ninth, the tenth, the eleventh and the twelfth keys, while the connection point of the first leads of the first key and the first capacitor is coupled to the first power supply terminal through the second key, the first chain comprising connected in series the third key, the second capacitor and the forth key is connected between the first power supply terminal and the first lead of an electric motor, which is coupled to the second lead of the first capacitor through the fifth key. and the second chain comprising connected in series-the sixth key, the third capacitor and the seventh key is connected in parallel to the to the first chain between the first power supply terminal and the first lead of an electric motor, while the connection point of the first capacitor and the fifth key is coupled through the eighth key to the connection point of the third capacitor and the sixth key and through the ninth key to the connection point of the second capacitor and the third key, the latter connection point through the tenth key being coupled to the connection point of the third capacitor and the seventh key, the latter connection point in its turn being coupled by the eleventh key to the connection point of the first leads of the first capacitor and the first key, while the second lead of the first key is coupled to the connection point of the second capacitor and the forth key, the latter connection point being also coupled to the connection point of the sixth key and the third capacitor through the twelfth key.

Parallel to the capacitors there the resistors may be connected.

At-least one of the keys is preferably made in the form of an electronic switch.

The following drawings illustrate the non-limiting implementation examples of an A. C. electronic drive filed.

Brief Description of the Drawings Fig. 1 is a block diagram of the first implementation of an Alternating-current drive filed.

Fig. 2 is a block diagram of another version of the first implementation of an Alternating- current drive filed.

Fig. 3 is a block diagram of one more version of the first implementation of an Alternating- current drive filed.

Fig. 4 is a block diagram of the implementation of an Alternating-current drive filed featuring four speeds and the in-series capacitors.

Fig. 5 is a block diagram of the implementation of an Alternating-current drive filed featuring four speeds the in-parallel capacitors.

Fig. 6 is a block diagram of the implementation of an Alternating-current drive filed featuring five speeds and the capacitors connected either in series or in parallel.

Fig. 7 is a block diagram of the implementation of an Alternating-current drive filed featuring eighteen speeds and the capacitors connected either in series or in parallel or in series-parallel.

Detailed Description of the Invention and Preferable Examples According to the most comprehensive implementation example (See Fig. 1) an alternating- current drive filed comprises an electric motor 1, a capacitor 2 and a key 3. The capacitor 2 and the key 3 connected in parallel are coupled between one of the leads of an electric motor and an appropriate lead of a power switch 4, which as in the example described is coupled between the connection point of the first leads of the capacitor 2 and the key 3 and an appropriate one of the power supply terminals 5 for connecting to A. C. mains e. g. a single- phase one. The second lead of an electric motor 1 is directly connected to the second 6 of the power supply terminals for connecting to A. C. mains. In parallel to the capacitor 2 there is connected a resistor 7 for removing a residual charge from the capacitor 2 after the latter has been switched off. The use of this resistor is not binding. In some cases an interference cancellation capacitor 8 may be required, which is directly connected between the first and the second leads of an electric motor i. e. , as it is shown in the example described, between the connection point of the second leads of the capacitor. 2 and the key 3 and the second lead of an electric motor 1.

A power switch may be connected between the second lead of an electric motor and the power supply terminal or between the connection point of the capacitor 2 and the key 3 and one of the leads of an electric motor, as for example in Fig. 2, where it is shown all implementation example of an alternating-current drive filed for use in a ventilator. The winding of a ventilator electric motor is made with two additional leads in such a manner that the first lead of an electric motor is produced respectively by three leads A, B, C. An alternating-current drive comprises also three power switches 4A, 4B, 4c coupled between the connection point of the capacitor 2 and the key 3 and the appropriate lead of the electric motor 1. In the described example an electric light bulb 9 performs the function of a resistor.

Fig. 3 illustrates another implementation example of an alternating-current drive filed for use in a ventilator. The winding of a ventilator electric motor is made with two additional leads in such a manner that the first lead of an electric motor is produced respectively by three leads A, B, C. An alternating-current drive comprises three keys 3A, 3B, 3C and three power switches 4A, 4B, 4c while all the keys are connected in parallel to the capacitor 2 in such a manner that the second lead of each of said keys is connected to the similar lead of an electric motor winding with each of latter being connected to the second lead of the capacitor 2 through a similar power switch.

An alternating-current drive shown in Fig. 4 comprises an electric motor 1, a first capacitor2 and a first key 3. The power switch is not shown. Coupled in parallel the first capacitor 2 and the first key 3 are connected between one of the electric motor leads and the first power supply terminal 5. An alternating-current drive is additionally supplied with the chain of coupled in parallel the second capacitor 10 and the second key 11 connected between the first lead of the electric motor 1 and the first power supply terminal 5. The second lead of the electric motor 1 is directly connected to the second one 6 of the power supply terminals for connecting to a single-phase A. C. mains.

A preferable implementation of an alternating-current drive shown in Fig. 5 comprises an electric motor 1, a capacitor 2 and a key 3. Coupled in parallel the first capacitor 2 and the first key 3 are connected between one of the electric motor leads and the first power supply terminal. The second key 11 is connected in series with the first capacitor 2, while the chain comprised of seriously connected a third key 12 and a second capacitor 10 is connected in parallel to the first key 3. The second lead of the electric motor 1 is directly connected to the second one 6 of the power supply terminals for connecting to a single-phase A. C. mains.

If necessary the number of additional chains comprised of seriously connected additional key and additional capacitor connected in parallel to the first key could be extended (not shown in the drawings).

Fig. 6 illustrates the most preferable implementation of an alternating-current drive filed making it possible with the help of only two capacitors and four keys to provide the five speeds of the drive rotation. An alternating-current drive described comprises an electric motor 1, a first capacitor 2 and a second capacitor 10 and a first key3, a second key 11, a third key 12 and a forth key 13. The power switch is not shown. Coupled in parallel the first capacitor 2 and the first key 3 are connected between one of the leads of an electric motor 1 and the first power supply terminal 5. The second key 11 is connected between the connection point of the first key 3 and the first capacitor 2 and the first power supply terminal 5. The first power supply terminal 5 through the seriously connected the third key 12 and the second capacitor 10 is coupled to the connection point of the second lead of the first key 3 and the first lead of the forth key 13, while the second lead of the latter is connected to the second lead of the first capacitor 2.

Fig. 7 illustrates an original circuit of an alternating-current drive filed making it possible with the help of only three capacitors and twelve keys to provide the eighteen speeds of the drive rotation. An alternating-current drive described comprises an electric motor 1, a first capacitor 2, a second capacitor 10, a third capacitor 14 and a first key 3, a second key 11, a third key 12, a forth key 13, a fifth key 15, a sixth key 16, a seventh key 17, an eighth key 18, a ninth key 19, a tenth key 20, an eleventh key 21 and a twelfth key 22. The power switch is not shown.

Coupled in parallel the first capacitor 2 and the first key 3 are connected between one of the leads of the electric motor 1 and the first power supply terminal 5, while the connection point of their first leads is coupled to the power supply terminal 5 through the second key 11. A first chain comprised of coupled in series the third key 12, the second capacitor 10 and the forth key 13 is connected between the first power supply terminal 5 and the first lead of the electric motor 1, which is coupled to the second lead of the first capacitor 2 through the fifth key 15. A second chain comprised of coupled in series the sixth key 16, the third capacitor 14 and the seventh key 17 is connected in parallel to the first chain between the first power supply terminal 5 and the first lead of the electric motor 1. The connection point of the first capacitor 2 and the fifth key 15 is coupled through the eighth key 18 to the connection point of the third capacitor 14 and the sixth key 16 and through the ninth key 19 to the connection point of the second capacitor 10 and the third key 12, which through the tenth key 20 is coupled to the connection point of the third capacitor 14 and the seventh key 17, said point coupled in its turn to the connection point of the first leads of the first capacitor 2 and the key 3 by the eleventh key 21. The second lead of the first key 3 is connected to the connection point of the second capacitor 10 and the forth key 13, said connection point being also coupled to the connection point of the sixth key 16 and the third capacitor 14 through the twelfth key 22.

A resistor similar to the one shown in Fig 1 may be connected parallel to any of the capacitors in the examples illustrated in Fig. 3 to 8, however, in the examples described this (these) resistor is not present.

The keys and the power switches may be made in the form of mechanical keys, relay contacts, but more preferably in the form of electronic switches, possibly in the form of microcircuits.

An alternating-current drive filed operates as follows.

The most comprehensive implementation example is'shown in Fig. l.

In the first state mode the key 3 is opened, and the power switch 4 is closed. Power supply to an electric motor 1 from the power supply source (not shown) is provided through the terminals 5 and 6 and the capacitor 2. In this case the current in the chain is defined by the formula where U is the power supply voltage, Xc is the resistance of the capacitor 2, while SYc=l/coC, where C is the capacitance value of the capacitor co is the circular frequency of the power supply voltage, = 2 ? !/' where f=50Hz.

The required decreased rotational speed is to be chosen in the range providing the stable rotations. The capacitance value of the capacitor 2 is chosen in accordance with the above- mentioned equations in such a manner that said value limits the current at the level providing the pre-defined rotational speed of an electric motor 1.

To switch over an electric motor 1 to the rated operation mode a key 3 is closed, while an electric motor 1 appears to be directly connected to the power supply source. A capacitor 8 is intended for cancellation of the interferences that may arise during operation of the electric motorl. To remove a residual charge from the capacitor 2 after its switching-off a resistor 7 is included into the circuit.

An implementation version of an alternating-current drive filed as in Fig. 2 when operated makes it possible to double the number of possible rotational speeds of an electric motor, e. g. a ventilator. During the closure any of the power switches 4A, 4B, 4c a respective winding of an electric motor 1 is switched on, this defining one of the three operation speed ratings of a ventilator. Each of these speeds appears to be decreased in the pre-defined proportion due to connection of this winding to the power supply source through the capacitor 2. The closure of the key 3 provides a rotational speed rating for this specific winding of an electric motor 1.

The circuit described was implemented on the base of the consumer stand-type ventilator having the power of 50W, and the capacitance value C of the capacitor 2, C=2 yF. The operation of an alternating-current drive thus received is shown in Table 1.

Table 1 Operation Mode Electric Motor Rotational Closed Key Winding Connection Number Speed, rotations per min of Electric Motor I (approximate values) 1 4A A through capacitor 450 2 2 4B B through capacitor 2 600 3 4c C through capacitor 2 750 4 3,4A A direct connection 900 5 3, 4B B direct connection 1000 6 3, 4c C direct connection 1200 Operation of other implementations is shown in the Tables from 2 to 6.

An Implementation Example according to Fig. 3.

The circuit described was also implemented on the base of the consumer stand-type ventilator having the power of 50W, and the capacitance value C of the capacitor 2, C=2 uF. The operation of an alternating-current drive thus received is shown in Table 2.

Table 2 Operation Mode Electric Motor Rotational Closed Key Winding Connection Number Speed, rotations per min of Electric Motor 1 (approximate values) 1 4A A through capacitor 450 2 2 4B B through capacitor 2 600 3 4C C through capacitor 2 750 4 3A A direct connection 900 5 3B B direct connection 1000 6 3c C direct connection 1200 An Implementation Example According to Fig. 4.

The power switch is not shown, but it is considered as a closed one. For the convenience of presentation the capacitance values of the first and the second capacitors 2,10 are considered as differing ones and relating in such proportion as for example. C2 calo=3 : 5.

Table 3 Operation Closed Capacitor Used Total Current Electric Motor Mode Key to Provide Power Limiting Capacitance Rotational Speed, Number Supply to Electric'relative valuation Motor I Keys 3 2 and 10 in series C2xC10 The First and 11 C=--------- = Opened Cs+Cjo 2 11 C-The Second 3 Clo=5 The Third 4 3 and 11 Rated An Implementation Example According to Fig. 5.

A power switch in the example described may not be present as all of the above-mentioned keys are opened, an alternating-current drive is in an off-state, while the closure of at least one of said keys causes an alternating-current drive to be switched on. For the convenience of presentation the capacitance values of the first and the second capacitors 2,10 are considered as differing ones and relating in such proportion as for example. C2 : C10 = 1 : 2.

Table 4 Operation Closed Capacitor Used Total Current Electric Motor Mode Key to Provide Power Limiting Capacitance Rotational Speed, Number Supply to Electric relative valuation Motor JH2C2= ! The First 2 12 10 C, o=2 The Second 3 11 and 2 and 10 in parallel C=C2+C10=3 The Third 12 4 3 Rated An Implementation Example According to Fig. 6.

A power switch is not shown and is considered as a closed one. A power switch in the example described may not be present as all of the above-mentioned keys are opened, an alternating-current drive is in an off-state, while the closure of the below-mentioned keys causes an alternating-current drive to be switched on. For the convenience of presentation the capacitance values of the first and the second capacitors 2,10 are considered as differing ones and relating in such proportion as for example. C2 : C10 = 3 : 5.

Table 5 Operation Closed Capacitor Used Total Current Electric Motor Mode Key to Provide Power Limiting Capacitance Rotational Speed, Number Supply to Electric relative valuation Motor 1 12 and 3 2 and 10 in series CxCfo The First c=-------- = 1, 9 C2+C10 2 11 2 C2=3 The Second 3 12 and 10 Ciao=5 The Third 13 4 12,11, 13 2 and 10 in C-C2+Clo=8 The Forth parallel 5 11,3,13 Rated An Implementation Example According to Fig. 7.

A power switch is not shown and is considered as a closed one. A power switch in the example described may not be present as all of the above-mentioned keys are opened, an alternating-current drive is in an off-state, while the closure of the below-mentioned keys causes an alternating-current drive to be switched on. For the convenience of presentation the capacitance values of the first, the second and the third capacitors 2,10, 14 are considered as differing ones and relating in such proportion as for example. C2 : C10:C14 = 4 : 5: 6.

Table 6 Operation Closed Key Capacitor Used Total Current Limiting Electric Motor Mode to Provide Power Capacitance Rotational Speed Number Supply to Electric relative valuation Motor 1 11, 19,22, 17 2,10 and 14 in series C2xC10xC14 C=-------------------= 1,6 C2xC10+C2xC14+C14xC10 2 11, 19, 13 2 and 10 in series C2xC10 2m c=---------=2,2 C2+C10 3 11, 18,17 2 and 14 in series C2xC10 @ C=--------- C2+C14 4 12, 22,17 10 and 14 in series C10xC14 4th C=---= 2, 7 CIO+CI4 5 11, 18,19, 13,17 (10 and 14 in parallel) in C2x (C10+C14) 5th series 2 C=----------------= 2,9 C2+ C10+C14 6 12, 3, 22,15, 17 (2 and 14 in parallel) in C, ox (C2+C, 4) 6 series 10 C=------=3. 3 C2+C10+C14 7 16, 20,21, 15,13 (2 and 10 in parallel) in C14x (C +Clo) series 14 C=------=3, 6 C2+C, p+C, 4 8 11 and 15 2 C2=4 9 12 and 13 10 Clo= 5 9" 10 16 and 17 14 C14=6 11 11, 15,12, 22,17 (10 and 14 C10xC14 in series) in parallel 2 C=C2+--------= 6,7 C10+C14 12 12, 13, 11,18, 17 (2 and 14 in series) in C2xC14 parallel 10 C=C10 + -----------=7,4 C, +C14 13 16, 17, 11,19, 13 (2 and 10 C2xC10 13th in series) in parallel 14 C=C14 + --------= 8, 2 C2+C10 14 11, 12, 15, 13 2 in parallel 10 C2+C10=9 14th 15 11,16, 15, 17 2 in parallel 14 C2+C14=10 15th 16 12, 16,13, 17 10 in parallel 14. C, o+C, 4= 1116'" 17 11,12, 16,15, 13,17 2, 10 and 14 C=C2+C10+C14= 15 17th in parallel 18 11,3, 13 - - Rated In this implementation example the speeds are switched over with such a number of intermediate states that this mode can be considered with a certain degree of approximation as a continuous control.

The examples listed above illustrate high flexibility and wide modification opportunities of an alternating-current drive circuit filed.

Moreover, no active heat losses are observed due to capacitance nature of a current limiting load.