Device, system and method for starting a single-phase induction motor

Abstract

A device, system and method for starting a single-phase induction motor. The method includes: i) energizing the start winding (50b) and continuously estimating an operating rotation (R.sub.1) of the motor throughout its operation; ii) measuring a first phase shift level (D.sub.1) between at least two electrical quantities along a first stability stage (E.sub.1); iii) monitoring the variation of the first phase shift level (D.sub.1) according to the increase of the operating rotation of the motor along the first stability stage; iv) detecting an inflection stage (E.sub.inf) from the first phase shift level to a second phase shift level (D.sub.2), when the operating rotation is close to a regime rotation (R.sub.2); v) measuring the second phase shift level (D.sub.2) between at least two electrical quantities of the motor along a first stability stage (E.sub.2); and vi) de-energizing the start winding when the operating rotation reaches the regime rotation.

Claims

1. A method of starting a single-phase induction motor, the motor comprising a rotor and a stator (50), the stator comprising a main winding (50a) and a starting winding (50b), the main winding (50a) and the starting winding (50b) being energized by means of an alternating voltage source (F), the starting winding (50b) being selectively activated and deactivated by a starting device (100) comprising a microprocessor (70), the method comprising the steps of: i) energizing the start winding (50b) and using the microprocessor (70) to continuously estimate an operating rotation (R.sub.1) of the single-phase induction motor throughout its operation through the phase shift between at least two electrical quantities; ii) using the microprocessor (70) to measure a first phase shift level (D.sub.1) between at least two electrical quantities of the motor along a first stability stage (E.sub.1); iii) monitoring the variation of the first phase shift level (D.sub.1) according to the increase of the operating rotation (R.sub.1) of the single-phase induction motor along the first stability stage (E.sub.1); iv) detecting an inflection stage (E.sub.inf) from the first phase shift level (D.sub.1) to a second phase shift level (D.sub.2), when the operating rotation (R.sub.1) of the single-phase induction motor is close to a regime rotation (R.sub.2); v) using the microprocessor (70) to measure the second phase shift level (D.sub.2) between at least two electrical quantities of the motor along a second stability stage (E.sub.2), after the inflection stage (E.sub.inf) of the first phase shift level (D.sub.1); and vi) de-energizing the start winding (50b) when the operating rotation (R.sub.1) reaches the regime rotation (R.sub.2).

2. The method according to claim 1, wherein the starting device (100) further comprises a switch (60) and a zero-crossing detection circuit (90).

3. The method according to claim 2, wherein the steps ii) to v) of measuring and monitoring the first phase shift level (D.sub.1) and measuring the second phase shift level (D.sub.2) between at least two electrical quantities of the motor are performed by means of the zero-crossing circuit (90) of the start device (100) and of the microprocessor (70).

4. The method according to claim 3, further comprising an intermediate step between steps v) and vi) of determining whether the first phase shift level (D.sub.1) is different from the second phase shift level (D.sub.2).

5. The method according to claim 2, wherein the microprocessor 70 sends the command signals to the switch (60).

6. The method according to claim 5, wherein the switch (60) comprises a TRIAC.

7. The method according to claim 5, wherein the switch (60) comprises at least one silicon-controlled rectifier.

8. The method according to claim 5, wherein the switch (60) remains initially activated before starting of the single-phase induction motor.

9. The method according to claim 1, wherein the at least two electrical quantities of the motor of the first phase shift level (D.sub.1) and the second phase shift level (D.sub.2) are selected from a group comprising: input voltage of the alternating voltage source (F), input current of the alternating voltage source (F), voltage in the main winding (50a), current in the main winding (50a), voltage in the start winding (50b) and current in the start winding (50b), the voltage between the main winding (50a) and the start winding (50b).

10. A system of starting a single-phase induction motor, the motor comprising a rotor and a stator (50), the stator comprising a main winding (50a) and a start winding (50b), the main winding (50a) and the start winding (50b) being energized by means of an alternating voltage source (F), the start winding (50b) being selectively activated and de-activated by a starting device (100), wherein the system is configured to energize the start winding (50b) and continuously estimating an operating rotation (R.sub.1) of the single-phase induction motor throughout its operation through the phase shift between at least two electrical quantities, the system comprising a microprocessor (70), the microprocessor (70) being further configured to measure a first phase shift level (D.sub.1) between at least two electrical quantities of the motor along a first stability stage (E.sub.1) and to detect an inflection stage (E.sub.inf) from the first phase shift level (D.sub.1) to a second phase shift level (D.sub.2), when the operating rotation (R.sub.1) of the single-phase induction motor is close to a regime rotation (R.sub.2), the first phase shift level (D.sub.1) varying according to the increase of the operating rotation (R.sub.1) of the single-phase induction motor, the system being further configured to measure, by means of the microprocessor (70), the second phase shift level (D.sub.2) between at least two electrical quantities of the motor along a second stability stage (E.sub.2), after the inflection stage (E.sub.inf) of the first phase shift level (D.sub.1), and configured to de-energize the start winding (50b) when the operating rotation (R.sub.1) reaches a regime rotation (R.sub.2).

11. A starting device (100) for a single-phase induction motor, the motor comprising a rotor and a stator (50), the stator comprising a main winding (50a) and a starting winding (50b), the main winding (50a) and the starting winding (50b) being energized by means of an alternating voltage source (F), the starting winding (50b) being selectively activated and de-activated by the starting device (100), the starting device (100) comprising a microprocessor (70), the microprocessor (70) being configured to energize the start winding (50b) and continuously estimate an operating rotation (R.sub.1) of the single-phase induction motor throughout its operation throughout the phase shift between at least two electrical quantities, the starting device (100) being further configured to measure, during a first stability phase (E.sub.1), the variation of first phase shift level (D.sub.1) between at least two electrical quantities of the motor until the first phase shift level (D.sub.1) reaches the second phase shift level (D.sub.2) along an inflection stage (E.sub.inf), when the operating rotation (R.sub.1) of the single-phase induction motor is close to a regime rotation (R.sub.2), the first phase shift level (D.sub.1) varying according to the increase of the operating rotation (R.sub.1) of the single-phase induction motor, and the starting device (100) being further configured to measure, by means of the microprocessor (70), the second phase shift level (D.sub.2) between at least two electrical quantities of the motor along a second stability stage (E.sub.2), after the inflection stage (E.sub.inf) of the first phase shift level (D.sub.1), and the starting device (100) de-energizing the start winding (50b), when the operating rotation (R.sub.1) reaches a regime rotation (R.sub.2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be further described in more detail based on one example of embodiment represented in the drawings. The figures show:

(2) FIG. 1 illustrates a schematic view of the starting system for a single-phase induction motor object of the present invention;

(3) FIG. 2 illustrates the equivalent circuit of a single-phase induction motor;

(4) FIG. 3 represents graphs of the rotation and of the phase behavior between the motor electrical quantities over a first stage of stability, an inflection stage and a second stability stage, the graphs demonstrating a clear relationship between the phase variation and the increase of the motor rotation until it reaches a regime rotation, situation which constitutes the starting of the motor.

(5) FIG. 4 illustrates graphs of the rotation and phase behavior between motor electrical quantities along a first stage of stability, as well as the state of the starting system object of the present invention prior to starting the motor (start winding energized).

(6) FIG. 5 illustrates graphs of the rotation and phase behavior between motor electrical quantities along an inflection state, as well as the starting system object of the present invention prior to starting the motor (start winding energized); and

(7) FIG. 6 illustrates graphs of the rotation and phase behavior between motor electrical quantities along a second stage of stability, as well as the starting system object of the present invention prior to starting the motor (start winding de-energized).

DETAILED DESCRIPTION OF THE INVENTION

(8) A great advantage of the present invention over the prior art is the fact that the starting method can be used in different types of single-phase induction motors, there being no need for specific components for a given motor. In other words, the present invention allows that both large and small motors to have an optimal adaptive starting from the proposed methodology, regardless of the supply voltage or the load coupled to the shaft.

(9) In a preferred embodiment, the method of the present invention is implemented by means of a system composed of a single-phase induction motor, an alternating voltage source F and a starting device 100.

(10) As can be seen from FIG. 1, the motor is provided with a rotor (not shown) and a stator 50, the latter being provided with a main winding 50a and a start winding 50b. With respect to the alternating voltage source F, it is noted that this may be any known source of the prior art capable of supplying electrical power to the motor. Finally, the starting device 100 preferably comprises a microprocessor 70, a switch 60, a zero-crossing detection circuit 90 and a DC source 80.

(11) Still in a preferred embodiment, the microprocessor 70 is a signal processing circuit fed by the DC source 80 and the switch 60 is a TRIAC or is formed by at least one silicon-controlled rectifier configured to selective energize and de-energize a start winding 50b. It should be noted that the electronic switches 60 are merely examples of switching components, which do not represent any obligation nor limit the invention.

(12) The zero-crossing detection circuit 90 is configured to detect time periods, or instants, where the current or voltage of the motor crosses zero.

(13) Still referring to FIG. 1, it is noted that this illustrates the connections of the elements described above. As can be seen, the alternating voltage source F is preferably connected in parallel with the main winding 50a for energizing thereof.

(14) On the other hand, the start winding 50b has one of its ends electrically connected to one of the nodes of the alternating voltage source F and the other end is connected to the switch 60 of the starting device 100, the switch 60 being connected to the other node of the alternate voltage source F.

(15) It is thus observed that the start winding 50b is only energized by the alternating voltage source F, when the switch 60 is activated, that is, when the motor is initially energized to start.

(16) Still in connection with the connections of the system elements of the present invention, it is noted that the zero-crossing detection circuit 90 is configured to measure and monitor periods of time, or instants, in which electrical quantities, coming from the alternating voltage source F, of the main winding 50a or from the start winding 50b, cross zero.

(17) After detecting periods of time, or instants, when the electric quantities cross zero, the microprocessor 70 calculates a first phase shift level D.sub.1 between at least two electrical quantities based on the signals received from the zero-crossing detection circuit 90. If the first phase shift level D.sub.1 changes in accordance with the increase of the operating rotation R.sub.1 of the single-phase induction motor, the microprocessor 70 waits for the occurrence of a second phase shift level D.sub.2 between at least two quantities in such a way that the latter has null variation.

(18) The electric quantities used may be the most different, these not establishing a limiting character of the present invention. Two, three, a plurality or combinations of electrical quantities may be used in the present invention depending on the user's choice.

(19) By way of example only, the first phase shift level D.sub.1 and the second phase shift level D.sub.2 can be calculated i) between the input voltage of the alternating voltage source F and the current in the main winding 50a; ii) between the input voltage of the alternating voltage source F and the current in the start winding 50b; iii) between the current in the main winding 50a and the current in the start winding 50b; iv) between the voltage in the start winding 50b and the current in the start winding 50b and so on.

(20) The second phase shift level D.sub.2 must have a significant difference from the first phase shift level D.sub.1, thereby ensuring that the motor has left the locked rotor condition. The phase shift levels D.sub.1 and D.sub.2 vary depending on the design of the motor and the configuration thereof (with or without a starting capacitor). Starting from the value D.sub.1 initially defined, a percentage value is calculated for a minimum value for D.sub.2, thereby ensuring the engine acceleration.

(21) Preferably, the microprocessor 70 is configured to selectively energize and de-energize a start winding 50b, when the operating rotation R.sub.1 reaches the operating rotation R.sub.2, estimated by varying the phase shift levels D.sub.1 and D.sub.2, as will be better described below.

(22) As outlined above, the starting system described above has been developed to optimize startup through a single starting device 100, which can carry out startup of different types of single-phase induction motors. The starting device 100 allows that an adaptive startup is carried out in any type of a single-phase induction motor, whether they are motors requiring longer connection time or shorter connection time with start winding 50b.

(23) For a better understanding of the present invention, it is important to refer to the equivalent circuit of a single-phase induction motor shown in FIG. 2. As can be seen, the variable elements are the input voltage, rotor speed, and load torque (not shown). Since the input voltage and the load torque are practically constant during the starting period of the motor, it is noted that the phase relationship between electric quantities (voltages and currents) depends only on the variation of the motor speed.

(24) Taking into account such a condition, it is noted that the present invention has the advantage of monitoring the rotation of the motor through the phase between electrical quantities over three stages during the starting of the motor. The simulations of FIG. 3 represents graphs of the rotation and of the phase behavior between the motor electrical quantities over a first stage of stability E.sub.1, an inflection stage E.sub.inf and a second stability stage E.sub.2, the graphs demonstrating a clear relationship between the phase variation and the increase of the motor rotation until it reaches a regime rotation, situation which constitutes the starting of the motor.

(25) It can be observed that in the first stage of stability E.sub.1, the first phase shift level D.sub.1 is practically constant, while the operating rotation R.sub.1 of the single-phase induction motor increases. As clearly shown in FIG. 4, this stage is the beginning of the starting period of the motor, situation in which the switch 60 is already closed from the start, for energizing the start winding 50b. Preferably, the first stage of stability E.sub.1 is between 0% and 40% of the total time of a startup under normal conditions of supply voltage and load.

(26) Referring now to FIG. 5, it can be noted that in the inflection stage E.sub.inf, the first phase shift level D.sub.1 begins to vary significantly, for example, after the operating rotation R.sub.1 of the single-phase induction motor reaches about 50% of the regime rotation R.sub.2. The first phase shift level D.sub.1 reaches the second phase shift level D.sub.2 when the operating rotation R.sub.1 is close to the regime rotation R.sub.2. As clearly shown in FIG. 5, this stage is the intermediate period of startup of the motor, situation in which the switch 60 is still closed for energizing the start winding 50b. Preferably, the inflection stage E.sub.inf lasts between 40% and 90% of the total starting time. Alternatively, the inflection stage E.sub.inf can be obtained by a minimum waiting time between the first stage of stability (E.sub.1) and the second stage of stability (E.sub.2).

(27) Finally, one can note from FIG. 6 that, in the second stability stage E.sub.2, the operating rotation R.sub.1 of the single-phase induction motor preferably reaches the regime rotation R.sub.2, which is very close to the synchronous rotation of the motor. The operating rotation R.sub.1 and the second phase shift level D.sub.2 remain constant along the second stabilization stage E.sub.2. As clearly shown in FIG. 6, this stage is the end of the motor starting period, situation in which the switch 60 opens for de-energization of the start winding 50b. Preferably, the second stability stage E.sub.2 lasts between 90% and 100% of the total starting time.

(28) Considering the three stages of the starting time above the single-phase induction motor, it is observed that the system is operated in the following manner:

(29) Initially, the single-phase induction motor is energized, which is the beginning of the first stability stage E.sub.1, the main winding 50a and the start winding 50b being energized by means of an alternating voltage source F, the start winding 50b being initially energized by the switch 60 of the starting device 100. The microprocessor 70 continuously estimates the operating rotation R.sub.1 of the single-phase induction motor through the signals received from the zero-crossing detection circuit 90, the microprocessor 70 defining the first phase shift level D.sub.1 between at least two electrical quantities of the motor, as shown in FIG. 4 (first stability stage E.sub.1).

(30) The microprocessor 70 is further configured to verify whether the first phase shift level D.sub.1 has varied to a second phase shift level D.sub.2, when the operating rotation R.sub.1 of the single-phase induction motor is close to a regime rotation R.sub.2, As illustrated in FIG. 5 (inflection stage E.sub.inf);

(31) During the inflection stage E.sub.inf, the microprocessor 70 determines whether the first phase shift level D.sub.1 is different from the second phase shift level D.sub.2. If that is true (FIG. 6second stability stage E.sub.2), the microprocessor 70 remains estimating the operating rotation R.sub.1 of the single-phase induction motor until it preferably achieves the regime rotation R.sub.2. The microprocessor 70 generates command signals and sends them to the switch 60, the latter being opened so as to de-energize the start winding 50b. The end of the second stage of stability E.sub.2 establishes the end of the start period of the single-phase induction motor.

(32) After one example of a preferred embodiment has been described, it should be understood that the scope of the present invention encompasses other possible embodiments and is limited only by the content of the appended claims, which include their possible equivalents.