CN102904510B - Permanent magnetism single-phase synchronous motor starting method and realize the electronic equipment of the method - Google Patents
Permanent magnetism single-phase synchronous motor starting method and realize the electronic equipment of the method Download PDFInfo
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- CN102904510B CN102904510B CN201210258481.7A CN201210258481A CN102904510B CN 102904510 B CN102904510 B CN 102904510B CN 201210258481 A CN201210258481 A CN 201210258481A CN 102904510 B CN102904510 B CN 102904510B
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/26—Arrangements for controlling single phase motors
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
- H02P1/46—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual synchronous motor
- H02P1/465—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual synchronous motor for starting an individual single-phase synchronous motor
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/02—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using supply voltage with constant frequency and variable amplitude
- H02P27/024—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using supply voltage with constant frequency and variable amplitude using AC supply for only the rotor circuit or only the stator circuit
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/14—Electronic commutators
- H02P6/16—Circuit arrangements for detecting position
- H02P6/18—Circuit arrangements for detecting position without separate position detecting elements
- H02P6/182—Circuit arrangements for detecting position without separate position detecting elements using back-emf in windings
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Ac Motors In General (AREA)
- Control Of Motors That Do Not Use Commutators (AREA)
- Motor And Converter Starters (AREA)
Abstract
The method of the startup permanent magnetism single-phase synchronous motor that can simply and efficiently realize, described motor comprises p-m rotor and the stator that is provided with the winding being connected with electrical network by switch; Said method comprising the steps of: first starts and attempt (100), wherein, winding is fed to electric current with one or more the first starting impulses that only produce during the half period of the first polarity of line voltage; Whether first controls step (200), wherein, detect and attempt having obtained entry condition in (100) process in the first startup; If not detecting in (100) time limit is attempted in the first startup, described the first control step (200) obtains entry condition, attempt in (300) in the second startup, winding is fed to electric current with one or more the second starting impulses that only produce during described line voltage and half period described first opposite polarity the second polarity.
Description
Technical Field
The present invention, in its general aspects, relates to a method for starting a single-phase permanent-magnet synchronous motor, and to an electronic device that can be associated with the motor to implement said starting method.
In particular, the method relates to the starting of a unidirectional synchronous motor used in applications characterized by a great need to reduce costs and bulk. For example, the method relates to the starting of electric motors used in household appliances such as washing machines and dishwashers.
Background
As is known, synchronous motors, while benefiting from high energy efficiency and excellent running speed stability, also have substantial drawbacks related to their difficulty in starting.
In fact, during the starting step, the rotor must be brought from zero speed to a condition in which its frequency is coupled to the machine power supply. In practice, in order to achieve said frequency coupling, mechanical and/or electronic specifications are adopted, which necessarily involve considerable production and installation costs.
On the one hand, when mechanical adaptations are made and when widely used, problems of efficiency and noise result, on the other hand, electronic systems generally have higher costs and are more dependent.
In particular, the electronic circuit comprising the inverter and the circuit breaker, which makes it easy to vary the amplitude and frequency of the grid voltage, varying them in the starting step, is extremely burdensome and is also unsuitable for the control of low-power single-phase synchronous motors, which are prioritized for use in electrical appliances for reasons of low cost.
Therefore, with a low-cost circuit based starting method, the motor phase is switched, for example with a switch, with the alternating current powering the motor phase with a start pulse ramp of the same sign intended to start the initial rotation of the rotor.
In this type of solution, however, the initial position of the rotor must be known to determine which sign the starting pulse should have. In fact, the rotor of a single-phase synchronous permanent-magnet motor can occupy two distinct rest positions, which are separated by half a turn in the case of a typical 2-pole machine; in the first position, the rotor is excited with a negative current pulse and in the opposite position with a positive current pulse.
The starting position of the rotor may be determined by means of a position sensor, for example a hall effect (hall) sensor reading the magnetic field locally defined by the rotor magnets. However, this solution requires the use of additional components and is relatively expensive.
A more economical solution that does not require a position sensor is described in patent EP 0945973. This patent proposes that a brief sequence of alignment pulses of opposite sign is applied before the above-mentioned start pulse ramp in order to aim at bringing the rotor into a predetermined start position. In fact, in the case where the rotor is in a rest position different from the predetermined starting position, the pulses will cause it to rotate; in the opposite case, the pulse will have no effect. Thus, the subsequent start ramp determines the start based on the predetermined position.
For the method described in EP0945973 to work correctly, the number and amplitude of the pulses must be determined with high precision so that the pulses produce the desired rotor rotation (180 ° in the case of a typical 2-pole machine). In practical applications, there are various uncertain intervention factors, such as unforeseen load changes or fluctuations in the grid voltage, which form also considerable deviations from the planned parameters. Thus, a deviation situation occurs in which the alignment pulse does not fulfill its purpose: this is due to the fact that the pulse intensity is not high enough to push the rotor to the predetermined position, or conversely, the intensity is too high to return the rotor past the predetermined position to the original position. Both of these circumstances mean that the motor fails to start.
The technical problem forming the basis of the present invention is therefore to devise a starting method and a corresponding electronic device implementing the method which enable starting of a permanent-magnet single-phase synchronous motor with low production and installation costs, while eliminating the problem of starting failures observed in the method proposed in EP 0945973.
Disclosure of Invention
The technical problem mentioned above is solved by a method for starting a single-phase synchronous motor comprising a permanent-magnet rotor and a stator provided with windings connected to a power grid by means of switches.
The method comprises the following steps:
a first start attempt, wherein the winding is fed with current using one or more first start pulses generated only during a half-cycle of a first polarity of the grid voltage;
a first control step in which it is detected whether a start-up condition has been obtained during the first start-up attempt;
feeding current to the winding in a second start attempt using one or more second start pulses generated only during half-cycles of a second polarity of the grid voltage, opposite to the first polarity, if the first control step does not detect that a start condition has been obtained within the first start attempt period;
the control logic described above can also be implemented in a sensorless mode with low cost components, enabling simple and efficient starting of single phase synchronous motors.
In fact, two successive starting attempts ensure that the rotor is started in any of said possible rest positions, without having a position sensor to detect the position in which the rotor finds itself.
Furthermore, there is no critical step of rotor alignment, which avoids failed starts due to incorrect calibration of the alignment pulses.
The starting condition, which detects its attainment during the first control step, can advantageously be represented by the back emf signal exceeding a control threshold.
The back emf signal can be easily obtained without the help of a sensor, for example as the difference between the voltage across the switch and the grid voltage during the period when the current fed to the winding is zero. The zero current condition can be evaluated by ensuring that the voltage across the switch is sufficiently different from zero or by a shunt resistance.
Note that since the start-up attempt is preset to overcome the pull-back of the cogging torque, the back emf threshold is chosen in such a way that: which in a subsequent transition phase establishes synchronous operation (using specific control logic described hereinafter) over a rotation angle of the rotor which is the same as the angle sandwiched between two successive interpole axes of the stator. For the particular case of a single phase motor with two poles, the control logic therefore begins within the first 180 of rotor rotation.
In particular, it can be advantageously established that: the control logic is implemented when the back emf exceeds a threshold value between 10% and 20% of the peak value of the back emf at operating speed.
In the above-mentioned method, the first start pulse is preferably plural, and in this case the first control step may include: after each start pulse it is detected whether a start condition has been reached.
In this way, the sequence of pulses can be interrupted rapidly, switching to a control mode more suitable for the state of motion of the rotor in the successive transition phases.
The first start pulse and the second start pulse may be a plurality of pulses of gradually increasing intensity (e.g. modulated by phase control) to define a ramp against cogging torque in the first start-up phase of the rotor.
Preferably, the method comprises a waiting step, which separates the first start attempt from the second start attempt, said waiting step being of sufficient length to ensure the stability of the rotor.
In fact, even if the rotor on which the first start attempt acts is oriented in such a way that it cannot be started by the polarity of the pulses employed, these pulses cause oscillations of the armature in the rest position, which preferably disappear before the next start attempt.
Furthermore, the first starting pulses must be configured in number and intensity in such a way that: the first start pulse starts the rotor against cogging torque if the rotor finds itself in a first rest position, and does not change the rotor position if the rotor finds itself in a second rest position.
The method may advantageously comprise a second control step in which a possible acquisition of a starting condition is detected during a second starting attempt. Thus, when the start condition is detected in the first or second control step, the control logic of the electric motor is employed until the step of obtaining the synchronization state is activated.
The control logic may employ two conditions for switching on, intended to ensure that the sign of the current circulating in the winding is substantially (i.e. for most of the time) the same as the sign of the back emf generated by the motor.
Hereafter we explain briefly why such a sign ensures a good start of the motor.
Driving torque C instantaneously generated by current in windingMBy product CMGiven by (i) (t) Φ · sin (θ (t)).
Where Φ is the peak of the flow induced by the magnets in the windings and θ is the angular displacement of the rotor.
On the other hand, the back electromotive force is:
fcem＝-Φωm·sin(θ(t))
thus:
CM·ωm＝fcem·i(t)
to obtain a speed of rotation omegamUniform torque value CMThat is, in order to ensure the driving torque rather than the braking torque during the starting, it is necessary to make the sign of the current flowing through the winding the same as the sign of the back electromotive force as described above.
The first condition for switching on the switch is checked when the detected back emf signal has the same sign as the grid voltage signal, and the second condition is checked when the back emf signal has the same sign as its first derivative value.
Furthermore, assuming that the above-mentioned control logic only controls the conditions for switching on the switches, for implementing the control logic, the switches used may be simple TRIAC switches which are disconnected at the moment of zero crossing of the current.
On the other hand, more sophisticated control logic (which includes conditions for opening the switch when the sign of the current and the back emf are different) requires a switch that enables interruption of the current, and a suitable circuit for absorbing the energy dissipated in the inductance of the stator winding. Such logic also requires acquisition of current signals and estimation of back emf by implementation of complex circuitry as the current circulates through the windings.
In fact, however, the second condition of the control logic according to the invention prevents the stator current from being different from the counter-electromotive force, so that the opening condition of the switches is rendered superfluous and the control architecture and its implementation are substantially simplified.
The verification of said first condition can be easily achieved by implementing an XNOR logic operation on the rectangular back emf signal and on the grid synchronization signal.
The second condition can also be easily verified by implementing an XNOR logic operation on the rectangular back emf signal and on the back emf first derivative signal of the rectangle.
As a variant, the first and second conditions can be verified simultaneously by implementing an XNOR logical operation between the grid synchronization signal and a second rectangular signal, which is derived from the sum of the first derivative signals with which the back emf signal is suitably scaled.
Since the first derivative of the back emf leads the back emf, the sum of the rectangles of the two signals also leads the rectangular signal of only the rectangular back emf; the lead increases with the scaling factor that the first derivative has; the threshold rectangle value also makes it possible to delay the rising edge and advance the falling edge; with only two parameters, the range of permissible switch-on conditions can thus be set according to the needs of the situation (moment of inertia, hydro-mechanical load, risk of damage, etc.).
The switch may be turned on in advance with respect to the occurrence of the first condition of the control logic, and the switch may be turned on slightly in advance of the moment when the back emf changes sign to have the same sign as the grid voltage.
This solution is feasible in view of the sinusoidal correlation of the torque with the rotor azimuth angle and the delay of the current signal with respect to the voltage signal in the ohmic-inductive circuit represented by the stator windings. The azimuth angle is always the opposite, and the braking torque is negligible. However, early turn-on does provide more time for the circuit to allow the current to grow, taking it when the sine of the azimuth angle becomes equally wide.
In order to avoid that the second condition inhibits the switch-on in case of a local slowdown due to cogging torque or motor load, the aforementioned second condition may be relaxed so as to allow the switch to be switched-on even when the peak of the back emf signal (although the back emf signal has assumed a sign different from its first derivative value) coinciding with the last change in sign of the first derivative of the back emf has a modulus lower than a threshold value.
A second condition of the control logic is to inhibit the switch from turning on when the rotor poles are close to the stator poles (the situation before the sign of the back emf changes).
However, the aforementioned local slow down may cause a negative first derivative of the signal, but the critical condition does not necessarily occur. However, such circumstances can be recognized from the following: the absolute value of the back emf peak has a low value (typically less than 20% of the back emf peak at nominal speed) before self-slowing occurs. This is why the control logic can advantageously provide the switching-on of the TRIAC switch (contrary to the previous indication) if said value does not reach a certain threshold value.
The aforementioned technical problem is also solved by an electronic device for starting a synchronous motor comprising a processing unit, a switch for feeding said synchronous motor controlled by said processing unit, said control unit receiving a grid voltage signal and a voltage signal across the switch, said electronic device being adapted to implement the above-mentioned method. As previously mentioned, the switch may be a TRIAC type switch.
Other features and advantages of the present invention will be readily appreciated from the following description of the preferred embodiments, which is given by way of illustration and not of limitation with reference to the accompanying drawings.
Drawings
FIG. 1 schematically illustrates a synchronous motor controlled using start-up logic according to the present invention;
fig. 2 schematically shows an electronic device according to the invention applied to the synchronous motor shown in fig. 1;
FIG. 3 shows a block diagram depicting various steps of a boot method according to the invention;
fig. 4 shows a time profile of several parameters related to the synchronous motor of fig. 1 during a first step of the starting method according to the invention;
fig. 5 shows a time profile of several parameters related to the synchronous motor of fig. 1 during a first step of the starting method according to the invention;
fig. 6 shows a time profile of several parameters related to the synchronous motor of fig. 1 during a second step of the starting method according to the invention;
FIG. 7 compares the time profile of the drive torque generated during the second step of two alternative embodiments of the starting method according to the invention;
fig. 8 compares the time profiles of several parameters related to the synchronous motor of fig. 1 during the second step of two alternative embodiments of the starting method according to the invention;
fig. 9 shows a time profile of several signals used in the start-up logic according to the invention.
Detailed Description
Referring to fig. 1 of the drawings, reference numeral 1 denotes a permanent magnet single-phase synchronous motor including a stator 10 and a cylindrical rotor 15 rotatable relative thereto.
The stator 10 defines a magnetic circuit that surrounds a rotor 15, which rotor 15 is rotatably arranged between a first pole extension 12a and a second pole extension 12b of the stator itself. The stator has two windings 11 fed by the electronic device 20.
The rotor 15 comprises permanent magnets arranged to define two diametrically opposed poles on the outer periphery of the element. We use the term "rotor axis AR" to define the diameter of the rotor in the ideal separation plane between the two poles thus defined.
The pole expansions 12a, 12b arranged according to the pole axis AP of the stator 10 are not referred to as features in form, so that the rotor 15 at rest is arranged: the rotor shaft AR is inclined at an asymmetric angle θ R with respect to the inter-pole axis AI of the stator 10. This asymmetry is known to ensure unidirectional starting of the synchronous motor. In this example, the rotor axis AR is tilted by 6 ° in the counterclockwise direction with respect to the interpole axis, which facilitates the rotor starting in the same direction.
The electronic device 20, which preferably takes the form of a control panel, has a static switch 21, in this particular case a TRIAC switch, which is arranged for regulating the supply of power to the stator windings 11 provided by an alternating current network 22.
The TRIAC switch 21 is connected to a PWM output 33 of the processing unit 30, the processing unit 30 preferably taking the form of a microprocessor. The processing unit 30 implements the method for starting the synchronous motor 1 described below.
The processing unit 30 has: a first input 31 receiving the grid voltage signal 23 and, on the other hand, a second input 32 receiving the voltage signal 24 over the switch.
By processing such a signal, the processing unit 30 is able to make an indirect measurement of the back emf generated by the synchronous motor 1 at the instant when the current is zero, obtained as the difference between the grid voltage signal 23 and the voltage signal 24 on the switch. The control unit 30 detects the zero-current condition while evaluating the voltage signal 24 across the switch, in particular ensuring that the signal is sufficiently far from a zero value.
From the back emf measurements during the zero current period, the processing unit 30 can estimate the time profile of the emf. A rectangular back emf signal 26 (which has a single value when the back emf is positive and zero otherwise) and a rectangular back emf first derivative signal 27 (which has a single value when the function of the back emf has a positive derivative and zero otherwise) are thus generated.
The electronic device 20 also has a section 35 for synchronizing with the power supply grid, which section 35 takes the grid synchronization signal 25 (i.e. a signal that is a single value when the grid voltage has a positive value and zero when the grid voltage has a negative value) and sends it to the processing unit 30.
The time profiles of the grid synchronization signal 25, the rectangular back emf signal 26 and the rectangular back emf gradient signal 27 are schematically illustrated in comparison to the time profiles of the back emf in fig. 9.
The electronic device 20 further has a feeding portion 36 of the processor 30, also arranged for providing the unit with a voltage reference signal.
In the rest state, the rotor 15 is arranged: the two poles face the first pole extension portion 12a and the second pole extension portion 12b, respectively. Thus, two possible rest positions are given, in the first position the north pole of the rotor 15 faces the second pole extension 12b of the stator 10, and in the second position the north pole of the rotor 15 faces the first pole extension 12a instead.
The first step of the method for starting the synchronous motor 1 comprises a first start attempt 100 in the following manner.
The electronic device 20 controls the TRIAC switch 21 so as to feed the winding 11 with a sequence of current pulses, referred to herein as first starting pulses 50, generated only during a determined half-cycle (positive in the particular embodiment described herein) of the voltage signal of the grid 22. In application, the TRIAC switch must only be turned on when the grid synchronization signal 23 has a positive value.
The first start pulse 50 generated preferably has an increased intensity and thus defines a positive start ramp. The intensity is adjusted by means of phase control, i.e. the starting angle of the TRIAC switch 21 is changed.
If the rotor 15 finds itself in the first rest position described above, the first start pulse 50 causes a rotation of said rotor, ideally not more than an angle of up to 180 °.
First, the rotor 15 is braked by a cogging force which is intended to bring it back into the starting position, in particular during the first (90+ θ R) ° movement (96 ° in the embodiment discussed here). Thus, the back emf that increases during the start pulse 50 returns to zero at the end of each pulse according to the known formula:
wherein,is the instantaneous flow induced by the magnets in the winding 11, phi is the peak of this instantaneous flow, omegamIs the rotational speed of the rotor and theta is the angular displacement of the rotor.
The cogging force is at a rotor angle of (45+ θ)R) Reaches its maximum value at DEG, where thetaRIs the angle the rotor has at rest (with zero current), however only because the torque due to the current action increases up to 90 ° with the sinusoidal profile, beyond a certain angle the current pulse causes the drag backwards against the cogging force to be overcome and the back emf increases substantially beyond a control threshold, typically equal to 10-20 of its maximum value in normal operation％。
Thus, between one start pulse 50 and the next, the electronic device 20 monitors the profile of the back emf signal in a first control step 200; and if when the signal exceeds the control threshold, electronics 20 interrupts the pulse train and passes to motor control logic 500, described hereinafter.
The first case described above is illustrated in the diagram of fig. 4, in which the rotor 15 finds itself in the first rest position and causes it to rotate during the first start attempt 100, which represents the profile of the current i, the grid voltage T and the rotor rotation angle θ.
However, if the rotor 15 finds itself in the second rest position described above, the first start pulse 50 has a relatively negligible effect on it, provoking a moderate oscillation thereof in the vicinity of this rest position. It should be noted that in fact the number and intensity of the first start pulses 50 are defined such that they do not provoke excessive oscillations, so that the transition from the second rest position to the first rest position never occurs.
In this manner, if the rotor 15 finds itself in the second rest position, it does not move in any substantial way during the first start attempt 100, the back emf remains zero, and, at the termination of the predetermined number of first start pulses 50 forming a ramp, the control threshold is not breached and the electronic device 20 does not activate the control logic 500.
In this case, the method comprises a waiting step for the oscillation of the rotor 15 in the vicinity of the second rest position to be gradually eliminated.
Of course, the waiting time depends on various factors, above all the friction and the moment of inertia of the rotor 15. The time period possible for a small permanent magnet synchronous motor is in any case about 700 ms.
At the end of the waiting step, the method comprises a second start-up attempt 300, performed in the same way as the first start-up attempt, but with a sequence of second start-up pulses 60, this time generated during the negative half-cycles of the grid voltage signal 22.
The negative start ramp thus generated exhibits the same characteristics as described above with respect to the positive ramp, but with the single obvious exception of signal polarity. For the sake of brevity, the characteristics of the negative slope will not be described extensively, implying that the description of the positive slope can also apply mutatis mutandis to the negative slope.
Also in this case, exactly as described with reference to the positive ramp, between one start pulse 60 and the next, the electronic device 20 monitors the profile of the back emf signal (second control step 400) to detect the exceeding of the control threshold that determines the passage to the control logic 500.
Assuming that the rotor 15 in the first rest position has started during the first start-up attempt 100, it should be assumed that the rotor 15 finds itself in the second rest position and that the back emf exceeds the control threshold during the second start-up attempt 300.
The second case described above is illustrated in the diagram of fig. 5, in which the rotor 15 finds itself in the second stationary state and rotates it during the second start attempt 300, which depicts the distribution of the current i, the grid voltage T and the rotor rotation angle θ.
However, if the control threshold for back emf has not been reached at the termination of the predetermined number of second start pulses 60 forming a negative ramp, the method may include starting the restart or eventually stopping the motor with the first start attempt 100, but this may be after a series of negative tests and/or diagnostic steps regarding possible damage or failure.
However, if the electronic device 200 detects that the control threshold of the electromotive force has been exceeded, the method proposes to apply a control logic 500 which determines a transition towards normal operation of the electric motor 1.
In this final starting step, the electronic device 20 controls the TRIAC switch 21, allowing it to be switched on only when both of the following two conditions occur:
a) the estimated back emf signal must have the same sign as the grid voltage (first condition);
b) the estimated back emf signal must be far from zero (second condition).
The first condition is achieved by the electronic device 20 through an XNOR operation performed on the grid synchronization signal 25 and the rectangular back emf signal 26.
The second condition is also realized by an XNOR operation between the rectangular back emf signal 26 and the rectangular back emf first derivative signal 27. When two operands have the same value in sign (i.e., if the sign of the first derivative is the same as the sign of the function), the XNOR operation gives a positive result; the resolution condition for the function is constrained away from zero.
Fig. 6 shows the time profile of the back electromotive force e, the grid voltage T, the rotor rotation angle θ and the stator current i during the course of the steps of applying the control logic 500.
The aforementioned switch-on logic tends to keep the TRIAC switch 21 conductive only when the current transfer in the winding 11 determines the driving torque in the direction of rotation of the rotor 15, as will become clearer from the following formulation considerations.
The drive torque produced by the stator current is given by the product CMGiven by-i (t) Φ · sin (θ (t)),
and the back electromotive force is fcem ═ Φ ωm·sin(θ(t))
Thus, CM·ωm＝fcem·i(t)。
In order to obtain a driving torque value CMAnd omegamThe current flowing in the winding must therefore also have the same sign as the sign of the back emf.
Based on this consideration, the advantageous control logic of the electric motor can cause the feed switch to be switched on when the counter-electromotive force and the grid voltage have the same sign (the first condition of the switch-on logic is actually fulfilled) and to be switched off when the counter-electromotive force and the current have different signs. Such control logic generates a driving torque towards the direction of rotation of the rotor 15, i.e. never brakes, if the switches used allow almost instantaneous breaking of the current.
On the other hand, however, such control logic (which we call on/off logic to distinguish it from the actual implementation of only on logic) cannot be replicated by the electronic device 20 according to the embodiments described herein. In practice, the electronic device 20 does not provide an input for the current signal necessary to detect the open condition, and also uses a TRIAC switch 21 that does not adequately enable such opening.
The on-only logic actually replaces the control of the off with the second on condition. In this way, it is assumed that in such a case, where the variable is in the process of changing sign and would soon be different from the current pulse generated by the switching on of the switch, the TRIAC switch 21 is not switched on in the case where the periodic profile of the back emf has exceeded its peak value. In other words, the second condition inherently avoids a situation that may result in a switch-off according to the on/off logic.
Thus, thanks to the second condition, the switch-on logic only avoids the generation of a braking torque on the rotor 15 of the synchronous motor 1.
It should be noted that the first condition of the switch-on logic only can be changed by causing the switch 21 to switch on in advance when the back emf different from the grid voltage is in the process of a sign change. In this case, the first condition allows the switch 21 to be switched on when the back emf signal (even if of different sign from the grid voltage) is close to zero and has an absolute value lower than a predetermined threshold.
This first condition does not significantly affect the sign matching between back emf and current even if the current is considered to have a delay with respect to the grid voltage if the allowed advance behaviour is not excessive. In this way, the current peaks arrive earlier, facilitating start-up.
Fig. 8 compares the time profiles of back emf e, stator current i, and torque C during application of the control logic with or without early start. The values relating to early start are identified by the subscript 1, while the values relating to non-early start have the subscript 2.
It should also be noted that the second condition of the switch-on logic alone may also inhibit the switch-on of the switch 21, in addition to being accompanied by a slowing down of the rotor 15 that does not correspond to the absolute peak of the back emf (for example due to cogging torque or load on the rotor). In this case, this second condition proves to be too restrictive, provided that the current pulses generated generate a driving torque on the rotor 15.
The second condition, while undesirably forbidden, substantially improves the starting performance of the motor. In this regard, referring to FIG. 7, the torque C generated by this FIG. 7 will only be taken as the first condition of the on logicaAnd torque C generated using the first and second conditions of the logicabA comparison was made.
During application of the control logic 500 it is monitored whether the synchronization state 700 is reached (third control step 600) depending on a measurement of the phase difference between the voltage and the current. If the phase difference remains nearly constant for some continuous period of time, then the synchronous condition 700 is deemed to have been reached and the start of the motor is completed.
Of course, a man skilled in the art can bring numerous modifications and variants to the method and to the washing machine described above, in order to satisfy contingent and specific requirements, all of which are covered by the scope of protection of the invention, as defined by the following claims.
Claims (14)
1. A method of starting a single-phase synchronous motor comprising a permanent-magnet rotor and a stator provided with windings, said windings being connected to an electric network by means of switches; the method comprises the following steps:
a first start-up attempt, wherein the winding is fed with current using one or more first start-up pulses generated only during a half-cycle of a first polarity of the grid voltage;
a first control step in which it is detected whether a start-up condition has been obtained during the first start-up attempt;
feeding current to the winding in a second start-up attempt using one or more second start-up pulses generated only during half-cycles of a second polarity of the grid voltage, opposite to the first polarity, if the first control step does not detect that a start-up condition has been obtained within the first start-up attempt period;
wherein the one or more first start pulses are configured in number and strength such that the first start pulse starts the rotor against cogging torque if the rotor finds itself in a first rest position, and in such a way that the first start pulse does not change the rotor position if the rotor finds itself in a second rest position.
2. A method according to claim 1, wherein the start-up condition is a back emf signal exceeding a control threshold, wherein the achievement of the start-up condition is verified during the first control step.
3. A method according to claim 2, wherein the back emf signal is obtained as the difference between the voltage across the switch and the grid voltage during a period when the current fed to the winding is zero.
4. Method according to one of the preceding claims, wherein said first activation pulse is plural, said first control step providing, after each first activation pulse, a detection of the possibility of obtaining said activation condition.
5. The method of any of claims 1-3, wherein the first and second initiation pulses are a plurality of pulses of increasing intensity.
6. The method of claim 5, wherein the intensities of the first and second activation pulses are modulated by phase control.
7. A method according to any one of claims 1 to 3, comprising a waiting step separating the first and second start attempts, the waiting step being of sufficient length to ensure stabilisation of the rotor.
8. The method of any one of claims 1 to 3, wherein the switch is a TRIAC switch.
9. The method according to claim 1, further comprising a second control step, wherein it is detected whether the start-up condition has been obtained during the second start-up attempt; and a step of applying control logic of the electric motor until a synchronous state, the step of applying control logic being triggered when a start condition is detected during the first control step or the second control step.
10. The method of claim 9, wherein the control logic provides a first condition and a second condition for turning on a switch, the first condition and the second condition aiming to: during the application of said control logic, ensuring that the current circulating in the winding has the same sign as the back emf generated by said motor; verifying the first condition when the detected back emf signal has the same sign as the grid voltage signal; the second condition is checked when the detected back emf signal has the same sign as its first derivative value.
11. The method of claim 10, wherein the first condition is verified by applying an XNOR logic operation on a back emf signal and a grid synchronization signal of a rectangular shape.
12. The method of claim 10 or 11, wherein the second condition is verified by applying an XNOR logic operation on a back emf signal of a rectangle and a first derivative signal of the back emf of a rectangle.
13. The method of claim 10, wherein the first and second conditions are verified simultaneously by applying XNOR logic operations to a grid synchronization signal and a second rectangular signal from the sum of the back emf signal and its appropriately scaled first derivative signal.
14. An electronic device for starting a synchronous motor, comprising a processing unit, a switch for feeding the synchronous motor controlled by the processing unit, the processing unit receiving a grid voltage signal and a voltage signal across the switch, the electronic device being adapted to implement the method according to claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP11175224.2A EP2421144B1 (en) | 2010-07-23 | 2011-07-25 | Method for starting a permanent magnet single-phase synchronous electric motor and electronic device for implementing said method |
| EP11175224.2 | 2011-07-25 |
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| CN102904510A CN102904510A (en) | 2013-01-30 |
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| KR (1) | KR101945888B1 (en) |
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| CN105134617B (en) * | 2015-08-24 | 2016-10-19 | 江门市地尔汉宇电器股份有限公司 | The small-size centrifugal pump that a kind of permasyn morot drives |
| CN105490589B (en) * | 2015-12-03 | 2017-08-15 | 深圳市本特利科技有限公司 | D.c. motor static state is taken advantage of a situation starter, control method and d.c. motor |
| WO2019052640A1 (en) * | 2017-09-13 | 2019-03-21 | Siemens Aktiengesellschaft | Operating a permanently excited synchronous machine |
| JP2019097315A (en) * | 2017-11-23 | 2019-06-20 | 株式会社デンソー | Control apparatus |
| CN110932616B (en) * | 2018-08-30 | 2021-04-02 | 广东威灵电机制造有限公司 | Method and device for determining angle position of rotor of permanent magnet synchronous motor and motor |
| EP3663870B1 (en) * | 2018-12-06 | 2021-08-11 | The Swatch Group Research and Development Ltd | Dc electric motor with asymmetrical stator inductors |
| CN113411017B (en) * | 2021-08-06 | 2022-08-12 | 北京航空航天大学宁波创新研究院 | Fault-proof starting method and system for electronic oil pump permanent magnet brushless motor |
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| EP0945973A2 (en) * | 1998-03-25 | 1999-09-29 | AKO-Werke GmbH & Co. KG | Control device for a single phase synchronous motor |
| CN101711453A (en) * | 2007-06-26 | 2010-05-19 | 阿思科尔P&C责任有限公司 | A control system without position sensors for a synchronous electric motor |
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| EP1351376A1 (en) | 2002-03-11 | 2003-10-08 | Askoll Holding S.r.l. | Electronic device for starting and controlling a permanent-magnet synchronous motor |
| AU2010343096A1 (en) | 2009-12-28 | 2012-08-16 | Flyback Energy, Inc. | Controllable universal power supply with reactive power management |
| PL2410651T4 (en) | 2010-07-23 | 2013-12-31 | Askoll Holding Srl | Method for starting a permanent magnet single-phase synchronous electric motor and electronic device for implementing said method |
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- 2012-07-24 KR KR1020120080413A patent/KR101945888B1/en active IP Right Grant
- 2012-07-24 BR BR102012018390-0A patent/BR102012018390B1/en active IP Right Grant
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| US5675226A (en) * | 1995-09-06 | 1997-10-07 | C.E.Set. S.R.L. | Control circuit for an synchronous electric motor of the brushless type |
| EP0945973A2 (en) * | 1998-03-25 | 1999-09-29 | AKO-Werke GmbH & Co. KG | Control device for a single phase synchronous motor |
| CN101711453A (en) * | 2007-06-26 | 2010-05-19 | 阿思科尔P&C责任有限公司 | A control system without position sensors for a synchronous electric motor |
| CN201554658U (en) * | 2009-07-10 | 2010-08-18 | 邓荣星 | Unidirectional pump |
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| KR20130012561A (en) | 2013-02-04 |
| BR102012018390B1 (en) | 2020-11-24 |
| CN102904510A (en) | 2013-01-30 |
| MX2012008607A (en) | 2013-01-24 |
| BR102012018390A2 (en) | 2014-06-10 |
| KR101945888B1 (en) | 2019-02-11 |
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