In
The single-phase permanent magnet motor 2 includes a stator 3 and a rotor 4. In the ensuing description, it is supposed that the motor is the so-called outer rotor type motor in which the stator 3 is disposed on an inner circumference and the rotor 4 is disposed on an outer circumference. However, similar description holds true of the inner rotor type motor or other motors. In the shown example, the number of poles of the permanent magnets in the rotor 4 is four. However, the effects of the present invention do not depend upon the number of poles.
In
The rotor 4 includes permanent magnets 7 and a rotor core 8 disposed around the permanent magnets 7 to constitute a magnetic circuit for the permanent magnets 7 and fulfill a role of mechanical coupling to an output shaft (not illustrated). As for the magnets, ferrite rubber magnets or plastic magnets are typically used because of their low prices.
In
In a typical single-phase permanent magnet motor, a position detector is disposed on the stator 3 so as to be located near the shaft end of each of the permanent magnets 7 in the rotor 4. (Typically, a hall element is used to detect the magnetic flux of the permanent magnet 7.) The position detector functions to detect the position of the permanent magnet 7 and let flow an effective current through the single-phase permanent magnet motor 2 via the conversion circuit 5. In applications such as automobiles, however, the use environment is high in temperature and hall elements cannot be used in some cases. If it is difficult to dispose the position detection elements because of circuit mounting, the senseless drive scheme described in the disclosure example is conceivable.
In accordance with an aspect of the present invention, a control circuit 6 includes an induced voltage calculation unit 14 for calculating an induced voltage of the single-phase permanent magnet motor 2 on the basis of information of a current sensor 16 and previously stored winding resistance information 11 and inductance information 12 of the stator windings 10, a velocity control circuit 13, and a drive signal computing and producing circuit 15 for synthesizing signals from the velocity control circuit 13 and so on. In accordance with the present invention, the position of the rotor is determined and timing of applied voltage is determined on the basis of information obtained by the induced voltage calculation unit 14. As a result, continuous energization is possible and single-phase sensorless operation with little torque ripple is made possible. Therefore, magnetic pole position detectors are made unnecessary and sensorless operation is made possible.
Hereafter, operation in the present invention will be described with reference to
The induced voltage has a feature that the waveform is bilaterally asymmetric because of the shape of the stator core on the gap face. The induced voltage calculation unit 14 calculates an induced voltage E0(θ) according to the following equation by using information of the terminal voltage Et(θ), a current i(θ) of a current sensor, winding resistance r and winding inductance L.
where
Et(θ) is the terminal voltage shown in
r is winding resistance,
L is winding inductance, and
i(θ) is a current value measured by the current sensor 16.
where
ω represents information of rotation angular velocity,
E0(θ) represents induced voltage information for an angle θ at each velocity ω, and
I(θ) represents current information obtained by the current sensor.
Tt(θ)=Tcog(θ)+Tw(θ) (3)
where Tcog(θ) represents the cogging torque for the rotation angle.
In accordance with the present invention, the single-phase permanent magnet motor shown in
In accordance with the present invention, the positive-negative changeover of the terminal voltage Et(θ) is conducted on the basis of the induced voltage information obtained by the induced voltage calculation unit 14 according to the equation (1). For example, the terminal voltage is changed over from positive to negative when the induced voltage falls from a highest positive part and reaches a predetermined value or less. The terminal voltage thus controlled is shown in
The voltage is controlled to become constant until the next changeover point. As occasion demands, however, it is also possible to provide the rising part or the falling part with a voltage change near the changeover point. The current can be controlled continuously by such control.
Since the current quiescent period for detecting the terminal voltage is provided during half cycle, a steep torque change occurs in the output torque. Furthermore, since the current stop period is provided, it becomes necessary to increase the current in other energization periods, resulting in a lowered efficiency.
As a result of the control described heretofore, it is possible to provide a low torque ripple, low noise, low vibration, high efficiency single-phase position permanent magnet motor.
In this way, the present invention provides a single-phase permanent magnet motor control apparatus for driving a single-phase permanent magnet motor by using a DC power supply, a converter for converting DC to AC, and a control circuit for controlling the converter, wherein a motor current measuring unit, a terminal voltage measuring unit, a correction unit for correcting an impedance drop in motor constants, and a calculation unit for finding an induced voltage to be obtained by control are included, and a polarity of a terminal voltage is determined on the basis of a value of the found induced voltage. As compared with an ordinary three-phase motor, therefore, only one set of windings and one hall element are required as shown in
By using the single-phase permanent magnet motor control apparatus in an electromotive fan and electromotive pump, it is possible to provide a low price, small-sized, light weight, low noise, low vibration electromotive fan and electromotive pump with a single configuration. (For example, when the fan and pump are disposed in a passenger room of a vehicle, the low noise and low price form powerful weapons.)
Description has been given heretofore with a mind to a system using a microcomputer as the control circuit 6. However, it is possible to implement a single-phase position sensorless permanent magnet motor control apparatus having the control circuit 6 which includes the induced voltage calculation unit 14, even if the control circuit 6 is constituted by using a discrete circuit including amplifiers, resistors and capacitors. In this case, the single-phase position sensorless permanent magnet motor control apparatus can be implemented with a more inexpensive configuration.
At the time of start, there is no information of induced voltage and the voltage energizing method is unknown. However, a mechanism for letting flow a current through the stator windings is included. As a result, stable start can be made possible by utilizing polarity discrimination for discriminating a current direction in which the rotor can output positive torque.
In
The single-phase permanent magnet motor 2 includes a stator 3 and a rotor 4. In the ensuing description, it is supposed that the motor is the so-called outer rotor type motor in which the stator 3 is disposed on an inner circumference and the rotor 4 is disposed on an outer circumference. However, similar description holds true of the inner rotor type motor or other motors. In the shown example, the number of poles of the permanent magnets in the rotor 4 is four. However, the effects of the present invention do not depend upon the number of poles.
In
The rotor 4 includes permanent magnets 7 and a rotor core 8 disposed around the permanent magnets 7 to constitute a magnetic circuit for the permanent magnets 7 and fulfill a role of mechanical coupling to an output shaft (not illustrated). As for the magnets, ferrite rubber magnets or plastic magnets are typically used because of their low prices.
In
A position detector 111 is disposed on the stator 3 so as to be located near the shaft end of each of the permanent magnets 7 in the rotor 4. (Typically, a hall element is used to detect the magnetic flux of the permanent magnet 7.) The position detector 111 functions to detect the position of the permanent magnet 7 and let flow an effective current through the single-phase permanent magnet motor 2 via the conversion circuit 5. A current sensor 18 is included in the stator windings 10 of the single-phase permanent magnet motor or the conversion circuit 5. The current let flow through the stator windings 10 is always monitored by the current sensor 18.
The control circuit 6 controls the conversion circuit 5 which supplies power to the single-phase permanent motor, on the basis of information of the position detector 111 and a current sensor 118, and previously stored cogging torque information 113 and induced voltage information 114.
An angle conversion unit 112 is a calculation unit for estimating an electric angle θ of the rotor 4 on the basis of the information of the position detector 111. The angle conversion unit 112 can calculate the average velocity of the rotor 4 on the basis of the period of the positive-negative changeover of an output signal of the position detector 111, and calculate and estimate the angle of the rotor on the basis of time elapse in the control period. Furthermore, the positive-negative energization of the conversion circuit 5 is determined by positive-negative information of the position detector 111.
Hereafter, a method for calculating the pulsating torque will be described in detail.
Electromagnetic torque Tw(θ) which is generated by the magnetic flux generated by the permanent magnet and a current which flows through the stator windings can be represented by using the following equation.
where
ω represents information of rotation angular velocity,
E0(θ) represents induced voltage information for an angle θ at each velocity ω, and
I(θ) represents current information obtained by the current sensor.
Therefore, total torque Tt(θ) generated by the single-phase permanent magnet motor is represented by the following equation.
Tt(θ)=Tcog(θ)+Tw(θ) (5)
On the other hand, average torque Tav can be calculated according to the following equation by finding an average of the total torque Tt(θ) over one cycle of electrical angle (which may be half a cycle as occasion demands).
Therefore, pulsating torque Tac(θ) can be represented by the following equation.
Tac(θ)=Tt(θ)−Tav (7)
In
The drive signal calculation producing circuit 51 combines an output of the velocity control unit 115 and an output of the pulsating torque calculation unit 116 to produce a signal for controlling the conversion circuit 5. As a result of the control heretofore described, torque ripple in
The above-described control is control of the fan and pump. The response frequency of the control is as low as several Hz. Therefore, control is exercised stably.
It is also possible to make the period of the velocity control equal to one electric cycle and conduct pulsating torque correction at an integer times the period. Furthermore, it is also possible to stop the control at the time of transition in largely changing the velocity command Ns signal as occasion demands.
As compared with an ordinary three-phase motor, only one set of windings and one hall element are required in the single-phase permanent magnet motor as shown in
In the configuration heretofore described, the cogging torque information 113 and the induced voltage information 114 are information that is proportional to square of the gap magnetic flux density or proportional to the gap magnetic flux density. The gap magnetic flux density is information that is proportional to the temperature. If, for example, a temperature sensor is provided in the single-phase permanent magnet motor control apparatus and the cogging torque information 113 and the induced voltage information 114 are corrected thereby, therefore, control with better precision can be exercised.
Furthermore, control with high precision is made possible by exercising the velocity control at half periods of electrical angle and dividing the period into a plurality of parts to exercise pulsating torque correction control.
Considering precisions of constants and their dependence upon the temperature as to the pulsating torque correction control, it is possible to select the case where stable control can be achieved when only proportional control is exercised although a larger deviation remains as compared with zero deviation control using integral control.
It is possible to provide a low price, small-sized, light weight, low noise, low vibration electromotive fan and electromotive pump with a simple configuration by adopting the single-phase permanent magnet motor control apparatus in the electromotive fan and electromotive pump.
Yet another embodiment of the present invention will now be described.
The embodiment differs from the foregoing embodiments only in the pulsating torque calculation unit 116.
Pulsating torque shown in
In the present embodiment, the pulsating torque is decomposed into frequency components and control is exercised every frequency component. Herein, a method for reducing the torque ripple at two frequencies, for example, at a frequency that is twice the fundamental wave in the electrical frequency and a frequency that is four times the fundamental wave will be described.
Basically, the ripple in the total torque can be reduced by calculating the phase and magnitude at each of two frequency components in the pulsating torque and exercising proportional integral control at each of the frequencies.
Hereafter, a concrete embodiment and operation will be described with reference to the drawings.
In the configuration shown in
As for the component corresponding to four times the fundamental frequency of the pulsating torque as well, a second calculation unit 23 for phase and magnitude of a component corresponding to four times the fundamental frequency can calculate its phase and magnitude by using the Fourier integral in the same way. In addition, a second correction signal generation unit 24 for a component corresponding to four times the fundamental wave exercises control with the goal of the component corresponding to four times the fundamental wave set to 0 and thereby generates correction torque for the component corresponding to four times the fundamental wave of the calculated pulsating torque. In addition, a correction signal synthesis unit 25 exercises control. As a result, it is possible to selectively suppress the torque ripple of the two frequency components.
In general, vibration and noise generated in the electromotive pump and electromotive fan are based on factors having relations of integer times in electrical angle, in many cases. Therefore, it is considered that the present scheme capable of reducing the factors every frequency is effective.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
2006-198879 | Jul 2006 | JP | national |
2006-198880 | Jul 2006 | JP | national |