KR100618218B1 - Inverter apparatus - Google Patents

Abstract

The inverter device includes a rotor position speed detection unit 8 for detecting the position speed of the rotor from the terminal voltage of the motor 4, a speed control unit 10 for controlling the speed of the motor to a target speed, and a current carrying width for the motor. And an energization control section 8 for controlling energization to the motor. The energization control unit 9 controls the energization according to the position of the magnetic pole of the rotor, at which time the conduction width is set to a range of 120 degrees or more or less than 180 degrees, and PWM control the switching element in the first portion which is one energization section. And a second section in which the switching element is always on after the first section, and a third section in which the PWM is controlled by the switching element.

Description

Inverter device {INVERTER APPARATUS}

The present invention relates to an inverter device for driving a motor used for an air conditioner or the like at an arbitrary frequency.

In recent years, the need for reducing the power consumption in the air conditioner in terms of global environmental protection is increasing. Among them, as one of power-saving techniques, an air conditioner using an inverter that drives an electric motor of a compressor at an arbitrary frequency is widely used.

As a motor used in an air conditioner, an efficient DC brushless motor with high efficiency is widely used, but this is composed of a stator made of a coil and a rotor, which is a rotor equipped with a magnet. On the other hand, as an inverter device for driving such a DC brushless motor, a direct current obtained by rectifying an AC power source by a rectifying circuit is converted to a desired alternating current by turning on / off a switching element connected to the rectifying circuit, and the output is converted into a three-phase motor. It is common to drive a motor by inputting it to a coil. 15 shows a configuration of a general inverter device.

In FIG. 15, the DC voltage obtained by rectifying the voltage from the AC power supply 1 by the rectifier circuit 2 is switched by switching elements 5a-5f in which the flyback diodes 6a-6f are connected in parallel, respectively. Then, it is modulated by a modulation method such as PWM (Pulse Width Modulation) to form an AC voltage of three phases.

The three phase alternating current is input to the motor 4, and the motor 4 rotates at the desired alternating frequency specified by the switching elements 5a to 5f. When the DC brushless motor is rotated, it is necessary to generate an AC voltage synchronized with the magnetic pole position of the rotor of the brushless motor, and thus the zero cross position of the induced voltage of the motor from the terminal voltage of the motor. Is detected and a timer is processed so as to have a predetermined phase angle from the zero cross position to switch the energization pattern. Fig. 16 shows the timing at which the induced voltage of each phase, the zero cross detection signal of the induced voltage, the timer for phase control, and the six switching elements are turned on when the general three-phase DC brushless motor is driven. In this way, the zero crossing point of the induced voltage of each phase is detected, the timer is started and delayed by the timing, and the on / off of the six switching elements is controlled in a desired phase.

As described above, 120-degree conduction drive, which is a drive having a section of 120-degree as an electric angle for each phase, is realized.

(Technical problem to be solved by the invention)

In the conventional inverter device as described above, the current waveform flowing through the motor becomes a square wave having a conduction angle of 120 degrees. For this reason, the current fluctuates greatly every 60 degrees in the electric angle, and the noise due to it, that is, the noise of the cogging component, becomes considerably large. In addition, in order to maximize the motor efficiency, it is necessary to drive by a current having the same shape as the induced voltage of the motor, but maximization of efficiency has not been realized because of the square wave current.

17A to 17C are waveform diagrams showing an example of the current when driven by the conventional method. 17A shows the terminal voltage, FIG. 17B shows the motor current, and FIG. 17C shows the current of the DC portion of the inverter device. In this way, the current waveform becomes a square wave shape. In addition, there is a reverse current in the direct current section of the inverter device as a factor that the current waveform becomes a square wave shape. 18A to 18D show the paths of currents flowing through the switching element and the motor in the case of the 120-degree energization method shown in FIG. 16. 18A, 18B, 18C, and 18D correspond to the switching sections of (a), (b), (c), and (d) in FIG. In this figure, the solid line shows the path when chopping and on, and the thin broken line shows the current path when chopping and off. Incidentally, the thick broken line is a continuous current due to the motor inductance of the current in the previous mode. As can be seen from this, in the periods of FIGS. 16B and 16D, a part of the current flowing through the motor coil flows through a diode parallel to the switching element, and the rectifier circuit is different from the normal direction. It flows back toward the condenser inside. At this timing, the current flowing through the motor coil is rapidly decayed, whereby the current waveform is closer to the square wave.

As described above, in the conventional driving method, since the current waveform has a square wave shape, the efficiency decreases and the vibration noise becomes large.

(Solution)

MEANS TO SOLVE THE PROBLEM This invention solves the said subject, When driving a motor by a variable frequency by three-phase alternating current, it improves motor efficiency, reduces torque ripple, suppresses noise and vibration, and is stable motor operation. An object of the present invention is to provide an inverter device.

An inverter device according to the present invention is an inverter device for driving a motor by an alternating current having a desired frequency, the switching device comprising a plurality of switching elements and a plurality of diodes connected in parallel to the switching element, and driving the motor at a desired frequency. To control the operation of the switching means to control the energization to the motor coil, the voltage detection means for detecting the terminal voltage of the motor, the detected voltage and the reference voltage, and the magnetic pole position of the rotor of the motor. And position speed estimating means for estimating speed and speed control means for outputting a voltage for controlling the speed of the motor to a given target speed to the energization control means. In particular, the energization control means controls the energization in accordance with the magnetic pole position of the rotor estimated by the position speed estimating means, and sets the energization width to a range of 120 degrees or more or less than 180 degrees, and further, one energization. In the first part of the section, a first section for PWM control of the switching element is formed, and a second section for always turning on the predetermined switching element is formed after the first section, and the second section of the second section is Thereafter, a third section for PWM controlling the switching element is formed.

The inverter device may further include a PWM position setting means for shifting the start position of the second energizing section in accordance with the output voltage value output by the speed control means.

Preferably, the PWM positioning means shifts the start position of the second energization section forward in the energization section as the output voltage value output by the speed control means becomes larger.

In addition, the inverter device may further include a conduction width setting means for changing the conduction width of the conduction section in accordance with the output voltage value output by the speed control means.

Preferably, the conduction width setting means makes the conduction width of the conduction section narrow as the output voltage value output by the speed control means becomes larger.

In addition, the inverter device includes a reflux period detecting means for detecting a reflux period that is a period in which a current flowing through the motor refluxs the diode, and an energization width for determining an energization width of the energization section according to the length of the reflux period output by the reflux period detection means. You may also be provided with a setting means.

The inverter device further includes a reflux period detecting means for detecting a reflux period that is a period in which a current flowing through the motor refluxs the diode and a second recirculation period in the energizing section according to the length of the reflux period output by the reflux period detecting means. You may also provide PWM position setting means for determining the start position of the section.

(Effective effect than conventional technology)

According to the inverter device of the present invention, energization is performed in an electric angle of more than 120 degrees and less than 180 degrees, and the pulse width modulation of the switching element of the phase in which no switching occurs when switching of motor current occurs. By doing so, high efficiency, low vibration, and noise level can be realized by a smooth current waveform.

In addition, by changing the position of the section in which the pulse width modulation is not performed in accordance with the output voltage value output by the speed controller, stable motor driving can be realized in any load operation.

In addition, the energization width of the energization section is changed according to the voltage value corresponding to the speed to be controlled. Accordingly, stable and high efficiency, low vibration, and low noise motor driving are realized in any load operation.

Furthermore, by detecting the reflux period of the motor current and determining the energization width of the energization section according to the length of the reflux period, stable and high efficiency, low vibration, and low noise motor driving are realized in any load operation.

Alternatively, by detecting the reflux period of the motor current and determining the position of the section in which the pulse width modulation is not performed according to the reflux period length, stable motor driving is realized in any load operation.

1 is a block diagram showing a configuration of a first embodiment of an inverter device according to the present invention.

FIG. 2A is a diagram illustrating an electricity supply method in the conventional inverter device, and FIG. 2B is a diagram explaining the electricity supply method in the inverter device according to the first embodiment.

3A is a diagram showing a current waveform under control of a conventional inverter device, and FIG. 3B is a diagram showing a current waveform of motor current under control of an inverter device of the present invention.

4 is a time chart showing an induced voltage during driving of a motor by the inverter device according to the present invention, ON / time of switching elements, and the like.

5A to 5D are diagrams showing a path of a current flowing through a switching element and a motor in the embodiment of the inverter device according to the present invention.

6A to 6C are diagrams showing a path of a current flowing through a switching element and a motor in the embodiment of the inverter device according to the present invention.

Fig. 7A is a diagram showing an example of the waveform of the terminal voltage by the inverter device of the present invention, Fig. 7B is an example of the waveform of the motor current, and Fig. 7C is a view showing an example of the waveform of the current of the DC section of the inverter device.

8 is a view for explaining a detectable range of induced voltages for respective load torques at different PWM position shift amounts.

9 is an operation characteristic diagram of a PWM positioning unit of the inverter device according to the first embodiment.

FIG. 10 is an operation characteristic diagram of an energization width setting unit of the inverter device according to the first embodiment. FIG.

11 is a block diagram showing the construction of a second embodiment of an inverter device according to the present invention.

12 is a view for explaining the principle of detection of the reflux period by the motor terminal voltage.

13 is an operation characteristic diagram of a PWM positioning unit in one embodiment of the inverter device of the present invention.

14 is an operational characteristic diagram of an energization width setting unit of the inverter device according to the second embodiment.

15 is a block diagram showing the structure of a conventional inverter device.

Fig. 16 is a time chart showing an induced voltage during driving of a motor by a conventional inverter device, on / time of a switching element, and the like.

17A is a diagram showing an example of a waveform of a terminal voltage of a conventional inverter device, FIG. 17B is a diagram showing an example of a waveform of a motor current, and FIG. 17C is a diagram showing an example of a waveform of a current of a DC section of the inverter device.

18A to 18D are diagrams showing current paths of currents flowing through a switching element and a motor of a conventional inverter device.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of the inverter apparatus which concerns on this invention is described in detail with reference to attached drawing.

(First embodiment)

The structure of one Embodiment of the inverter device of this invention is shown in FIG. In FIG. 1, the inverter device 3 includes switching elements 5a to 5f and switching portions 6 each consisting of reflux diodes 6a to 6f connected in anti-parallel to each of the switching elements 5a to 5f. . In addition, in order to control the switching operation of each switching element 5a to 5f of the switching unit 6, the inverter device 3 includes a voltage detector 7, a rotor position detector 8, an energization control unit 9, The speed control part 10, the electricity supply width | variety setting part 11, and the PWM position setting part 12 are provided.

The inverter device 3 converts the DC voltage after rectifying the input from the AC power supply 1 into the DC in the rectifier circuit 2 by the switching operation of the switching elements 5a to 5f of the switching unit 6 in three phases. It converts into an AC voltage and outputs it, and accordingly drives the brushless DC motor (henceforth "motor") 4 at a desired frequency.

The voltage detector 7 detects the terminal voltage of each phase of the coil of the motor 4. The rotor position speed detector 8 estimates and detects the magnetic pole position and speed of the rotor of the motor 4 using this detection voltage.

The energization control unit 9 switches the switching elements 5a to 5f in accordance with a drive signal for driving the motor 4 based on the information on the magnetic pole position of the rotor estimated by the rotor position speed detection unit 8. Outputs a base signal for driving the switch to the switching unit (6). The speed control unit 10 calculates the output voltage so that the speed of the rotor of the motor 4 becomes the target speed from the deviation between the speed of the rotor estimated by the rotor position speed detection unit 8 and the target speed provided from the outside. To control.

The energization width setting unit 11 selects an optimum energization width in accordance with the output voltage information from the speed controller 10 and outputs it to the energization control unit 9. In addition, the PWM position setting unit 12 is similarly based on the output voltage information from the speed control unit 10, the position at which the driving of the switching element by the PWM control starts (hereinafter referred to as "PWM starting position", and will be described in detail later). ) Is determined and output to the energization control unit 9. The energization control unit 9 controls the switching elements 5a to 5f and drives the motor 4 in accordance with the supplied energization width and the PWM start position.

FIG. 2A shows a base signal waveform in a general 120 degree energization method, and is a diagram showing the output voltage of one phase centered on the one energization section. 2B shows a base signal waveform in the energization method of the inverter device in this embodiment.

As shown in Fig. 2A, in the current-carrying method, in a current-carrying section of 120 degrees as an electric angle, 60 degrees of the first half drives the switching element to always on, and 60 degrees of the second half PWM the switching elements 5a to 5f. Drive by control. Thereby, the energization section of each phase is switched every 120 degrees, and a certain phase is always in an energized state, so that electricity supply to the motor 4 is performed continuously and rotational force is provided.

On the other hand, in the electricity supply system of this embodiment, as shown to FIG. 2B, an electricity supply section is set to 120 degree | times or more ((120+ (alpha)), (alpha) ≥0) per phase. This results in a section in which the energized state overlaps between each phase. Further, in the energization section at (120 + α) degrees, the energization drive is executed by the PWM control between the first predetermined time periods, and the energization drive is always turned on without executing the PWM control after the predetermined time elapses. Afterwards, the energization drive is executed by the PWM control. In this manner, the section which is always turned on without executing the PWM control is started after a predetermined time has elapsed from the start of the energizing section, that is, after a predetermined electric angle (hereinafter referred to as "PWM position shift angle") φ. At this time, in the present embodiment, the start of the section to be always on without performing the PWM control is shifted by a predetermined shift angle φ with respect to the start of the section to be always on without performing the conventional PWM control. The energization section length at this time is set by the energization width setting section 11, and the PWM start position (ie, the PWM position shift angle) is set by the PWM position setting section 12.

In this manner, in the inverter device according to the present invention, the energization width is set wider to 120 degrees or more, and the energization control at all times is performed after the energization driving is first performed by the PWM control in the energization section. As a result, when the switching of the energized phase of the motor current occurs, the energized driving is performed in which the pulse width modulation of the switching element is not performed in the phase in which the switching does not occur, so that the current waveform is smoothed and the motor efficiency is improved. In addition, torque ripple can be reduced, noise and vibration can be suppressed, and stable motor operation can be performed.

3A and 3B, differences in waveforms of motor currents by the inverter devices of the prior art and the present invention will be described. Fig. 3A is a diagram showing the shape of a current waveform at the time of driving by the conventional 120 degree energization method. As shown in the figure, conventionally, in a section slightly wider than the conduction section, the current flows in the motor coil in a substantially square wave shape. The motor current flows in the section added by the delay of the current rise and fall by the inductance of the motor in addition to the energization section. 3B is a view showing the current form of the electricity supply method according to the present invention. Thus, the motor current flows in a long section exceeding 120 degrees. At this time, the current flowing through the inductance component (hereinafter referred to as the "reflux component") increases by driving a phase switching element in which the switching of the energized phase does not occur without performing pulse width modulation. Therefore, the current waveform becomes smoother.

4 is a diagram illustrating an example of the energization method in the inverter device of the present embodiment. The induced voltage of each phase at the time of energization in the inverter device of this embodiment, the zero cross detection signal of the induced voltage (refer to "comparison of U, V, W phase" in drawing), phase It is a figure which shows the timer operation | movement for control, and the on timing of six switching elements (it describes as U, V, W phase drive in drawing). In this way, the zero crossing point of the induced voltage of each phase is detected, and the on / off of six switching elements is switched using a timer multiple times according to the timing.

In FIG. 4, for example, when attention is paid to the U phase switching element 5a of the upper arm, PWM control is started just before the phase is 0 degrees (sections (a) and (b)). , The section of the always-on (section (c) to (e)) is continued, and then again becomes a PWM control section (section (f), (g)). In addition, since the energization section is set to 120 degrees or more, for example, where the phase slightly passes from 120 degrees in phase, the U phase is also in the energized state in addition to the V phase and the W phase.

5A-5D and 6A-6C show the electric current which flows through a switching element and a motor coil in each electricity supply section in the inverter device when it drives by the electricity supply system shown in FIG. In each section, the path of the current flowing through the motor coil (that is, the energized phase) is switched according to the conduction state of the switching element. Each path diagram of FIGS. 5A to 5D corresponds to the switching sections a to d shown in FIG. 4, and each path diagram of FIGS. 6A to 6C corresponds to the switching sections e to g shown in FIG. 4. Respectively). 5A to 5D and 6A to 6C, the solid line shows the path when chopping and on, and the thin broken line shows the current path when chopping and off. In addition, a thick broken line is a continuous current by the inductance of the current immediately before it. In this system, by not performing pulse width modulation of a phase switching element in which switching does not occur, a reverse current flowing through the DC portion of the inverter device that has been generated in the conventional 120 degree energization does not occur. It can be seen that the current flows smoothly. As a result, a smooth current waveform as shown in FIG. 3B is realized.

7A to 7C show waveforms of the current of the motor 25 driven by the inverter device according to the present embodiment, the terminal voltage, and the DC portion current I of the inverter device. In the conventional 120-degree energization shown in Figs. 17A to 17C, for a 120-degree conduction width, a current having substantially the same width is generated in the shape of a square wave, and the current of the DC part is added by three phases to turn on and off the PWM. Almost smooth current flows at the timing, and a large reverse current (the lower peak current sometimes seen in Fig. 17C) is generated every 60 degrees. However, according to the inverter device of the present embodiment, the energization width is widened (in this example, 130 degrees energized), and the timing of PWM control start is wider than 120 degrees with respect to the voltage drive waveform set at the center. It can be seen that a current waveform with a smooth width is flowing. In addition, although a constant current flows also in the electric current of the direct current | flow part of an inverter device at that time, the reverse current does not generate | occur | produce every 60 degrees at that time. As a result, a smooth current waveform is realized.

The operation of the position setting unit 12 will be described below.

As described above, the PWM position setting unit 12 optimally determines the position (PWM start position) for starting the pulse width modulation. The optimal PWM starting position is determined in consideration of the improvement in efficiency and control stability. By moving the PWM start position from the normal position (switching position every 120 degrees in the conventional 120 degree energization method), a DC reverse current does not occur, thereby making the current waveform smoother and improving the efficiency.

On the other hand, in order to secure control stability, it is necessary to reliably realize phase estimation of the motor in driving the inverter. In other words, if the phase estimation cannot be performed, it cannot be driven because the position of the rotor of the motor is not known. Therefore, the inverter device estimates the phase by detecting the terminal voltage of the motor in the non-energizing section of the motor coil. However, when this non-energizing section is narrowed, it becomes difficult to estimate the position of the motor. 8, the change of the detectable range of the induced voltage with respect to load torque in 0 degree, 10 degree, and 20 degree in PWM starting position shift amount is shown. From the same figure, it turns out that the detectable range of an induced voltage becomes narrower, so that the shift amount of a PWM start position increases, and the load torque increases. As the detectable range of the induced voltage is narrowed, the driving stability is lowered. Therefore, the driving stability is lowered as the load torque is increased. Therefore, in order to ensure drive stability at a certain level, it is preferable to change the shift amount of the PWM position in accordance with the increase of the load so that the detectable range of the induced voltage does not narrow even if the load increases.

9 is a diagram for explaining the control of the shift amount of the PWM start position of the PWM position setting unit 12 for coping with the above problem. Since the load torque can be estimated by the output voltage value output by the speed control part 10, the PWM position setting part 12 determines a PWM starting position according to the output voltage value of the speed control part 10. FIG. That is, as shown in FIG. 9, when the output voltage value is below the predetermined value D1, the shift angle of the PWM position is set to the predetermined angle φ1, the current waveform is smoothed, and the efficiency is improved. Further, when the output voltage is from the predetermined value D1 to the predetermined value D2, when the load of the motor increases and the output voltage value output by the speed controller 10 increases, the PWM position shift angle is gradually decreased. The PWM position shift angle at this time is set to a value that can sufficiently secure the detectable range of the induced voltage. And when the output voltage becomes more than predetermined value D2, the shift amount of a PWM start position shall be zero. As described above, by changing the shift amount according to the load size, the PWM positioning unit 12 can secure the detectable range of the induced voltage at a certain level even when the load increases, thereby stably driving the motor. have.

In addition, similarly to the relationship of the detectable range of the induced voltage with respect to the shift amount of the PWM start position, it is also apparent that the detectable range of the induced voltage is changed by the conduction width. In other words, the wider the conduction width is, the narrower the detection range of the induced voltage is, and vice versa. For example, when the energization width is 120 degrees, since the non-energization section is 60 degrees, the range for detecting the induced voltage also becomes a range excluding 60 degrees from the reflux current section. In the case where the energization width is 140 degrees wider than this, the detectable range becomes a narrow range except for the reflux current section from 40 degrees. Therefore, when the energization width is wide, the detectable range is narrowed and the driving stability is further lowered. Therefore, in order to ensure drive stability more fully, it is preferable to change an energization width with increase of load.

10 is a diagram for explaining control of the energization width by the energization width setting unit 11. The electricity supply width setting part 11 estimates a load torque by the output voltage value which the speed control part 10 outputs, and determines an electricity supply width according to the output voltage value. As shown in this figure, when the output voltage value output by the speed controller 10 is equal to or less than DA, the current width is set to φ MAX, and the current waveform is smoothed to improve efficiency. When the output voltage value is in the range between the predetermined value DA and the predetermined value DB, the conduction width gradually decreases as the output voltage value increases. When the output voltage value is greater than or equal to the predetermined value DB, the conduction width is fixed to 120 degrees. Thus, by controlling the energization width according to the magnitude | size of a load, even if the load increases, the detectable range of an induced voltage can fully be ensured, and a motor can be driven stably.

(2nd embodiment)

Another embodiment of the inverter device according to the present invention will be described.

11 shows a block diagram of the inverter device according to the second embodiment. In FIG. 11, the inverter device 3a is provided with the reflux period detection part 13 in addition to the structure of the apparatus of 1st Embodiment. In the inverter device 3a, the direct current voltage rectified by the direct current from the AC power supply 1 to the rectifier circuit 2 is converted into a three-phase AC voltage in the switching section 6 to the voltage. The motor 4 is driven in the same manner as in the first embodiment.

The reflux period detection unit 13 uses the voltage of the motor 4 detected by the voltage detector 7, and the time length of the period in which the reflux current of the coil of the motor 4 flows (hereinafter referred to as a "reflux period"). Detect. The energization width setting unit 11 determines the energization width using the time length information of this reflux period, and instructs the energization control section 9 of the energization width. In addition, the PWM position setting unit 12 determines the optimal PWM position using the time length information of this reflux period, and instructs the power supply control unit 9 to position the PWM.

12 is a diagram for explaining the operation of detecting the length of time in the reflux period by the reflux period detection unit 13. FIG. 12 is a diagram showing waveforms of terminal voltages at certain timings in one phase of the motor 4. In the non-energization section set before the energization section, the induced voltage generated by the coil of the motor 4 is detected at the timing of energizing ON of the PWM control, but before the inductance of the current flowing through the coil of the motor 4 is detected. The reflux current generated by Since the terminal voltage of the motor 4 becomes a high voltage by this reflux current, the reflux period which becomes a high voltage appears in the previous part of a non-energization section. Therefore, it is possible to monitor the motor terminal voltage and determine that the reflux period has ended when the motor terminal voltage is lowered from a value higher than a predetermined level (referred to as "reflux determination level"). Therefore, the reflux period detection unit 13 detects the terminal voltage of the motor 4, and determines that the reflux period has ended when the value becomes below the predetermined reflux determination level. For example, in FIG. 12, when the terminal voltage at time tA is VA, the terminal voltage at time tB is VB, and the reflux determination level is VK, the reflux period detecting unit 13 is VA> VK or VB. When terminal voltages VA and VB, which are <VK, are detected, it is determined that the reflux period has ended between the time tA and the time tB.

The PWM position setting unit 12 operates as follows. The PWM position setting unit 12 determines the optimum PWM position as in the case of the first real form. The optimal PWM position is determined by considering the efficiency improvement and control stability by the PWM starting position. Control stability is determined by the detectable range of the induced voltage, and the narrower the range, the lower the drive stability. Therefore, drive stability is ensured by changing the PWM start position in accordance with the length of the reflux period detected by the reflux period detection unit 13.

FIG. 13 is a diagram for explaining the control of the PWM start position by the PWM position setting unit 12 of the present embodiment. The PWM position setting unit 12 estimates the load torque by the reflux period length, and determines the PWM starting position accordingly. As shown in this figure, when the reflux period length is L1 or less, the shift angle of the PWM start position is set to φ1. Accordingly, the current waveform is smoothed to improve efficiency. When the load of the motor increases and the reflux period length is in a predetermined range, that is, when the reflux period length is between L1 and L2, the PWM position shift angle is gradually decreased in accordance with the load of the motor. If the reflux period length is equal to or greater than the predetermined value L2, the PWM position shift angle is set to zero. Thereby, even if the load increases, the detectable range of sufficient induced voltage can be ensured and a motor can be driven stably.

As described in the first embodiment, the detectable range of the induced voltage also changes depending on the conduction width. In other words, the wider the conduction width is, the narrower the detection range of the induced voltage is, which lowers the driving stability. In addition, the stability decreases further as the load torque increases and the reflux period becomes long. Therefore, in order to secure driving stability, it is desirable to change the current carrying width as the reflux period length increases.                 

14 is a view for explaining the control of the energization width of the energization width setting unit 11 according to the present embodiment. The energization width setting unit 11 determines the energization width according to the reflux period length. As shown in the figure, when the reflux period length is equal to or less than LA, the current width is set to φ MAX, and the current waveform is smoothed to improve efficiency. In addition, when the load of the motor increases and the reflux period length is in a certain range (between LA and LB), the conduction width gradually decreases along the reflux period length. Thus, when the reflux period length is more than the predetermined value LB, the energization width is fixed to 120 degrees. Thus, by varying the conduction angle width depending on the length of the reflux period, even if the load increases, a detectable range of sufficient induced voltage can be ensured and the motor can be stably driven.

It goes without saying that the inverter device according to the present embodiment may be implemented as a dedicated hardware circuit or software using a microcomputer.

While the present invention has been described with respect to specific embodiments, many other variations, modifications, and other uses are apparent to those skilled in the art. Therefore, the present invention is not limited to the specific disclosure herein but may be limited only by the appended claims.

Claims (7)

In the inverter device which drives a motor by the alternating current of a desired frequency, Switching means comprising a plurality of switching elements and a plurality of diodes connected in parallel to the switching elements; Energization control means for controlling the operation of the switching means by controlling the operation of the switching means to drive the motor at a desired frequency; Voltage detecting means for detecting a terminal voltage of the motor; Position speed estimating means for estimating magnetic pole positions and speeds of the rotor of the motor by comparing the detected voltage with a reference voltage; Speed control means for outputting a voltage to the energization control means for controlling the speed of the motor to a given target speed, The energization control means controls the energization in accordance with the magnetic pole position of the rotor estimated by the position speed estimating means, and sets the energization width to a range of 120 degrees or more and less than 180 degrees, and at the beginning of one energization section A first section for PWM control of the switching element is formed in a portion of the second section, a second section for always turning on a predetermined switching element is formed after the first section, and a switching element is placed behind the second section. And a third section for PWM control. The inverter device according to claim 1, further comprising PWM position setting means for shifting the start position of said second energizing section in accordance with an output voltage value output by said speed control means. The inverter device according to claim 2, wherein the PWM position setting means shifts the start position of the second energizing section forward in the energizing section as the output voltage value output by the speed control means is larger. The inverter device according to claim 1, further comprising a conduction width setting means for changing the conduction width of the conduction section in accordance with an output voltage value output by the speed control means. 5. The inverter device according to claim 4, wherein the energization width setting means narrows the energization width of the energization section as the output voltage value output by the speed control means is larger. 2. The energizing width of the energizing section is determined according to claim 1, wherein the reflux period detecting means detects a reflux period in which the current flowing through the motor is a reflux period of the diode, and the length of the reflux period output by the reflux period detecting means. An inverter device further comprising a conduction width setting means. 2. The apparatus according to claim 1, further comprising: a reflux period detecting means for detecting a reflux period in which a current flowing through the motor is a reflux period for the diode and a length of the reflux period output by the reflux period detecting means; Inverter device further comprises a PWM position setting means for determining the start position of the interval of 2.

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