WO2012137399A1

WO2012137399A1 - Motor drive device and electric appliance using same

Info

Publication number: WO2012137399A1
Application number: PCT/JP2012/001050
Authority: WO
Inventors: 義典竹岡; 田中　秀尚
Original assignee: パナソニック株式会社
Priority date: 2011-04-04
Filing date: 2012-02-17
Publication date: 2012-10-11
Also published as: JP2012222842A; BR112013024711A2; CN103460596B; CN103460596A

Abstract

Provided is an inexpensive, small motor drive device (22) that can drive stably and smoothly without sudden increases in bus voltage even though small capacity flat capacitors are provided. The motor drive device (22) has a rectification and smoothing circuit (2), an inverter (3) that converts direct current power obtained from the rectification and smoothing circuit (2) to alternating current power and provides the same to a brushless DC motor (4), and a control unit (30) that outputs a drive signal to the inverter (3). During a period in which a switching element for one arm of a plurality of arms has a PMW output, the drive signal controls the inverter (3) such that a switching element for another arm of the plurality of arms, for which upper and lower are on the opposite side to the one arm, forms ON output. When the control unit (30) switches the phase of the electrification of the brushless DC motor (4), the drive signal is output such that the switching element for the arm on the opposite of the arm for which the ON output is complete starts an ON output.

Description

MOTOR DRIVE DEVICE AND ELECTRIC DEVICE USING THE SAME

The present invention relates to a motor drive device for driving a brushless DC motor and an electric device using the same.

The first conventional motor drive apparatus performs speed feedback drive and square wave drive according to the drive speed. FIG. 7 is a block diagram of a first conventional motor driving apparatus that performs rectangular wave driving. FIG. 8 is a diagram showing a waveform of a drive signal in the first conventional motor drive device.

7, the AC power from the AC power source 201 is converted into DC power by the rectifying / smoothing unit 202 including the four rectifying diodes 202 a to 202 d and the smoothing capacitor 202 e, and the DC power is input to the inverter 203. The inverter 203 is configured by connecting six arms including six switching elements 203a to 203f and six return current diodes 203g to 203l in a three-phase bridge connection. The inverter 203 converts the input DC power into AC power having a predetermined frequency and outputs the AC power to the brushless DC motor 204.

The position detection unit 205 acquires information on the induced voltage generated by the rotation of the brushless DC motor 204 based on the voltage at the output terminal of the inverter 203. Based on this information, the position detection unit 205 detects the relative position of the rotor 204a of the brushless DC motor 204. The speed estimation unit 206 calculates the rotation speed of the brushless DC motor 204 based on the signal from the position detection unit 205. The waveform generation unit 207 calculates the duty on width in PWM (Pulse Width Modulation) according to the speed calculated by the speed estimation unit 206, determines the arm to be energized in the inverter 203 based on the signal from the position detection unit 205, A waveform signal indicating the result is generated. The drive unit 208 drives the switching elements 203a to 203f of the inverter 203 based on the waveform signal from the waveform generation unit 207. At that time, the drive signal output from the drive unit 208 has a switching waveform as shown in FIG. FIG. 8 shows waveforms of drive signals inputted to the gates of the six switching elements 203a to 203f. As shown in FIG. 8, the switching element of one of the three upper arms outputs a PWM signal that repeatedly turns on and off based on pulse width modulation, and the lower arm of one of the three lower arms. The ON output is always turned on. As a result, the current flowing to the brushless DC motor 204 is adjusted by the PWM duty on width of the

upper switching elements

203a, 203c and 203e constituting the upper arm, and the change in the rotational speed of the brushless DC motor 204 and the change in the load are dealt with. enable.

The first conventional configuration can provide a motor drive device that drives the brushless DC motor while arbitrarily changing the speed.

As a second conventional motor drive device, for example, as disclosed in Patent Document 1, it has the characteristics of the first conventional motor drive device and is smoother than the first conventional motor drive device. Some capacitors are driven with a large ripple component in the bus voltage (the output voltage of the rectifying / smoothing unit, that is, the direct-current voltage applied to the inverter) with a small capacity. FIG. 9 shows a block diagram of a second conventional motor driving apparatus using such a small-capacity smoothing capacitor.

In FIG. 9, the AC power from the AC power supply 301 is rectified by the rectifying diodes 302a to 302d of the rectifying and smoothing unit 302, and then smoothed by the smoothing capacitor 302e. Here, since the capacity of the smoothing capacitor 302e is small, the voltage (bus voltage) from the rectifying / smoothing unit 302 is input to the inverter 303 in a state including a large ripple component. The inverter 303 is configured by connecting six arms including six switching elements 303a to 303f and six return current diodes 303g to 303l in a three-phase bridge connection. The inverter 303 converts the input DC power including ripples into AC power having a predetermined frequency and outputs the AC power to the brushless DC motor 304 (strictly, the stator 304b).

The position detection unit 305 acquires information on the induced voltage generated by the rotation of the brushless DC motor 304 based on the voltage at the output terminal of the inverter 303. Based on this information, the position detector 305 detects the relative position of the rotor 304a of the brushless DC motor 304. Further, in the voltage including a large ripple output from the rectifying / smoothing unit 302, it is difficult for the position detection unit 305 to accurately detect the relative position when the voltage is low. The position estimation unit 306 estimates the relative position of the rotor 304a. That is, when the output voltage of the rectifying / smoothing unit 302 detected by the voltage detection unit 307 is equal to or lower than a predetermined value, the switching unit 308 adopts the signal from the position estimation unit 306 as the position detection signal, and the waveform generation unit 309 In 303, the arm to be energized and the PWM duty width are determined, and a waveform signal indicating the result is generated. The drive unit 310 drives the switching elements 303 a to 303 f of the inverter 303 based on the waveform signal generated by the waveform generation unit 309.

According to the second conventional configuration, the load can be driven while arbitrarily changing the speed of the brushless DC motor even if the bus voltage output from the rectifying and smoothing unit 302 includes a large ripple. Since the capacity of the smoothing capacitor 302e can be made smaller than that of the first conventional motor driving device, a smaller and smaller motor driving device can be provided than the first conventional motor driving device.

JP 2005-198376 A

However, the second conventional motor driving device has a problem that the bus voltage suddenly increases when the energized phase of the brushless DC motor is switched, and smooth driving of the brushless DC motor becomes difficult. In particular, when the current is large, such as high-speed driving or high-load driving, there is a problem that the circuit is destroyed by overvoltage in the worst case. Specific examples of such problems will be described with reference to FIGS. FIG. 10 shows the driving signal and current waveform of the second conventional motor driving apparatus, and FIG. 11 shows the current path of the second conventional motor driving apparatus.

Here, the phase at the stator 304b of the brushless DC motor 304 connected to the switching element 303c and the switching element 303d of the inverter 303 in FIG. 9 will be described as the V phase. In FIG. 10, times (1) to (5) are periods in which the energized phases in the brushless DC motor 304 are the same. In this period, the switching element 303a performs switching (that is, PWM output), and the switching element 303d 100% energization (that is, ON output) (strictly speaking, the switching element 303d is ON output in time (1) to (4)). At times (1) and (3) in FIG. 10, the same switching pattern is obtained, and the current path is the path shown in FIG. At times (2) and (4) in FIG. 10, the same switching pattern is obtained, and the current path is as shown in (b) of FIG.

At time (5) in FIG. 10, the switching element 303d in the lower arm is switched from on to off, and the switching element 303f is switched from off to on. At this time, the switching element 303a in the upper arm is off. Therefore, the current passing through the return current diode 303h flows to the brushless DC motor 304, while the current from the brushless DC motor 304 flows through the return current diode 303i. As a result, the current passes through the path shown in FIG. A current flows into the smoothing capacitor 302e. At this time, since the smoothing capacitor 302e has a small capacity, the voltage across the smoothing capacitor 302e, that is, the bus voltage rises rapidly. As described above, the second conventional motor driving device has a problem that the bus voltage rapidly increases when the energized phase of the brushless DC motor is switched, and it is difficult to smoothly drive the brushless DC motor.

Therefore, the present invention solves the above-described conventional problems, and is inexpensive and small in size, which enables more stable and smooth driving without rapidly increasing the bus voltage despite having a small-capacity smoothing capacitor. An object of the present invention is to provide a simple motor drive device.

A motor driving apparatus according to an aspect of the present invention is a motor driving apparatus that rotates and drives the brushless DC motor by switching an energized phase of a brushless DC motor that is connected to an AC power source and has a plurality of windings. A rectifier circuit that rectifies AC power input from an AC power source, a capacitor and a reactor whose values are determined to have a resonance frequency higher than 40 times the frequency of the AC power, and smoothes the output from the rectifier circuit. When a circuit composed of a smoothing section, a switching element and a return current diode is used as one arm, the upper arm and the lower arm have a plurality of legs connected in series, and are obtained from the smoothing section. An inverter that converts direct current power into alternating current power and supplies the brushless DC motor, and the inverter serves as the brushless DC motor A control unit that outputs to the inverter a drive signal instructing a supply timing of power to be supplied, and the drive signal is turned on when a switching element of one of the plurality of arms is based on pulse width modulation. During the period in which PWM output is repeatedly turned off, the inverter is controlled so that the switching element of one arm among the plurality of arms opposite to the upper and lower sides is always turned on. The control unit outputs the drive signal so that when the energized phase of the brushless DC motor is switched, the switching element of the arm on the opposite side to the arm on which the on-output is completed starts on-output. To do.

According to such a configuration, even when the energized phase of the brushless DC motor is switched, there is always a path for the current flowing in the energized phase that has been turned off to return to the brushless DC motor, so there is no current path to return to the small-capacity smoothing capacitor. , A rapid rise in the bus voltage is suppressed.

The motor drive device of the present invention can provide an inexpensive and small motor drive device that can suppress a rapid rise in the bus voltage when switching the energized phase and can realize more stable and smooth motor drive.

FIG. 1 is a block diagram of a motor driving apparatus according to an embodiment of the present invention. FIG. 2 is a timing chart showing the waveform of the drive signal in the same embodiment. FIG. 3 is a diagram showing a drive signal and current waveforms in the same embodiment. FIG. 4 is a diagram showing a current path in the same embodiment. FIG. 5A is a diagram showing the waveform of the bus voltage in the conventional motor driving apparatus, and FIG. 5B is a diagram showing the waveform of the bus voltage in the same embodiment. FIG. 6 is a cross-sectional view of a main part of the brushless DC motor in the same embodiment. FIG. 7 is a block diagram of a first conventional motor drive device. FIG. 8 is a timing chart showing the waveform of the drive signal in the first conventional motor drive device. FIG. 9 is a block diagram of a second conventional motor driving device. FIG. 10 is a diagram showing the drive signal and current waveforms of the second conventional motor drive device. FIG. 11 is a diagram illustrating a current path of a second conventional motor drive device.

As a result, even when the energized phase of the brushless DC motor is switched, the energy does not return to the small-capacity smoothing capacitor because there is always a path in the inverter where the energy accumulated in the energized off phase is returned to the brushless DC motor. Thus, it is possible to provide a small and inexpensive motor driving device capable of suppressing a rapid increase in bus voltage and capable of stably and smoothly driving the brushless DC motor.

Here, the control unit further includes an arm in which the on-output is completed until a bus voltage that is a voltage output from the smoothing unit rises to a predetermined voltage when the energized phase of the brushless DC motor is switched. The on-output of the switching element of the arm on the opposite side may be started. By adopting such a configuration, the bus voltage is suppressed to a voltage increase value that does not cause adverse effects such as overvoltage and drive rattling, which are problems due to the bus voltage rising, and a stable motor driving device can be provided. .

Further, the period during which the switching element of the arm on the opposite side of the arm where the on output has been completed continues the on output may be at least until the current flowing through the arm where the on output has been completed becomes equal to or less than a predetermined value. As a result, a current equal to or lower than the current value that does not cause a problem even when the bus voltage rises can flow into the capacitor, and more stable driving is possible.

Further, the period during which the switching element of the arm opposite to the arm on which the ON output is completed continues the ON output may be until the energized phase of the brushless DC motor is next switched. This facilitates the setting of the energization pattern and simplifies the software and system for driving, thereby improving the maintainability and quality.

Further, the rotor of the brushless DC motor is configured by embedding a permanent magnet in an iron core, and may further have saliency. This enables effective use of reluctance torque due to saliency as well as magnet torque due to permanent magnets in the drive of brushless DC motors, thus reducing the output torque by increasing the advance angle when the bus voltage drops. Can be mitigated, and more stable driving becomes possible.

The brushless DC motor may drive a compressor. In the drive control of the compressor, there is no need for high-precision rotation speed control or acceleration control like industrial servo motor control, etc., and the compressor is a load with relatively large inertia, so it can be done in a short time. Speed fluctuations are very light loads. Therefore, even when the bus voltage is lowered, the speed variation is small and more stable driving is possible.

Further, the compressor may be a reciprocating compressor. As a result, the reciprocating type that performs reciprocating motion is structurally connected to the rotor, which is metallic and heavy, with a heavy crankshaft and piston. Therefore, the inertia is very large and operates more stably when the voltage drops. be able to.

Further, the refrigerant used in the compressor may be R600a. As a result, the cylinder volume and the inertia are increased in order to obtain the refrigerating capacity, and further, stable driving that is hardly affected by fluctuations in the applied torque becomes possible.

Another embodiment of the present invention may be an electric device including the motor driving device and a brushless DC motor driven by the motor driving device. As a result, when used in a refrigerator as an electrical device, the motor drive device can be reduced in size so that the motor drive device can be stored in a small space of the refrigerator that is driven at a constant speed, and the speed can be changed more efficiently. A good refrigerator can be provided at low cost. Further, when the blower is used as an electric device, since the blower has a very large inertia, a small blower that is easy to carry can be realized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Each of the embodiments described below shows a preferred specific example of the present invention. Numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of constituent elements, signal waveforms, signal timings, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. The invention is specified by the claims. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept of the present invention are not necessarily required to achieve the object of the present invention. It will be described as constituting a preferred form.

FIG. 1 is a block diagram of a motor drive device 22 according to an embodiment of the present invention. In FIG. 1, an AC power source 1 is a general commercial power source, and in Japan, a power source of 50 or 60 Hz with an effective value of 100V. The motor driving device 22 is connected to the AC power source 1 and drives the brushless DC motor 4. Hereinafter, the motor drive device 22 will be described.

This motor drive device 22 employs PWM control that can arbitrarily change the rotation speed of the brushless DC motor 4, and stably and smoothly drives the brushless DC motor 4 despite having a smoothing capacitor with a small capacity. The motor drive device can include a rectifying and smoothing circuit 2, an inverter 3, and a control unit 30.

The rectifying / smoothing circuit 2 is a circuit that rectifies and smoothes AC power from the AC power source 1 into DC power, and includes four bridge-connected rectifier diodes 2a to 2d, a smoothing capacitor 2e, and a reactor 2f. . The output from the rectifying / smoothing circuit 2 is input to the inverter 3. Here, in the rectifying / smoothing circuit 2, the four rectifying diodes 2 a to 2 d constitute a rectifying unit that rectifies AC power from the AC power supply 1.

Further, the smoothing capacitor 2e and the reactor 2f are set such that the resonance frequency is higher than 40 times the frequency of the AC power from the AC power supply 1, and constitutes the smoothing unit 2g. As a result, the current at the resonance frequency is outside the range of the power supply harmonic regulation, and the harmonic current can be reduced. Further, by setting the smoothing capacitor 2e to such a value (small capacity, details will be described later), the bus voltage includes a large ripple component, and the current flowing from the AC power source 1 to the smoothing capacitor 2e is also a frequency component of the AC power source 1. The harmonic current can be reduced because the current is close to.

In addition, since the reactor 2f is inserted between the AC power supply 1 and the smoothing capacitor 2e, it may be either before or after the rectifier diodes 2a to 2d. Further, the reactor 2f corresponds to a combined component with the reactance component of the high frequency removing means when the common mode filter constituting the high frequency removing means is provided in the rectifying and smoothing circuit 2.

The inverter 3 converts the DC power containing a large ripple component into the voltage from the rectifying / smoothing circuit 2 in a cycle twice the power cycle of the AC power source 1 into AC power. The inverter 3 is configured by connecting six switching elements 3a to 3f in a three-phase bridge. The six return current diodes 3g to 3l are connected in parallel to the switching elements 3a to 3f in the reverse direction. In other words, the inverter 3 has one upper arm and one lower arm in series when a circuit composed of a parallel connection of one switching element and one return current diode is used as one arm. There are 3 legs connected to.

The brushless DC motor 4 includes a rotor 4a having a permanent magnet and a stator 4b having a three-phase (U-phase, V-phase, W-phase) winding. The brushless DC motor 4 rotates the rotor 4a when the three-phase alternating current generated by the inverter 3 flows in the three-phase winding of the stator 4b.

The control unit 30 is a circuit that outputs to the inverter 3 a drive signal that instructs the supply timing of the power supplied from the inverter 3 to the brushless DC motor 4. The position detection unit 5, voltage detection unit 6, speed estimation unit 7, switching Unit 8, position estimation unit 9, switching arm determination unit 10, waveform generation unit 11, and drive unit 12.

Here, the drive signal output from the control unit 30 is a PWM output in which the switching element of one of the plurality of arms constituting the inverter 3 repeats on and off based on pulse width modulation (PWM). In this period, the control signal is for controlling the inverter 3 so that the switching element of one of the plurality of arms on the opposite side to the arm is always turned on. Thereby, the speed of the brushless DC motor 4 can be arbitrarily changed by changing the PWM duty on width.

At this time, when the energized phase of the brushless DC motor 4 is switched, the control unit 30 outputs a drive signal so that the switching element of the arm on the opposite side to the arm on which the ON output is completed starts the ON output. That is, the arm (that is, the switching element) that is the target of the on output is switched so that the on output is seamlessly continued. Thereby, when the energized phase is switched, a current path through which a current flows through the small-capacity smoothing capacitor 2e does not occur, so that a rapid rise in the bus voltage is suppressed. Hereinafter, each component which comprises the control part 30 is demonstrated in detail.

The position detection unit 5 acquires the terminal voltage of the brushless DC motor 4 in the present embodiment. That is, the magnetic pole relative position of the rotor 4a of the brushless DC motor 4 is detected. Specifically, the position detector 5 detects the relative rotational position of the rotor 4a based on the induced voltage generated in the three-phase winding of the stator 4b. As another position detection method, there is a method of estimating the magnetic pole position by performing vector calculation on the detection result of the motor current (phase current or bus current).

The voltage detector 6 detects the voltage across the smoothing capacitor 2e, which is the voltage between the DC buses (bus voltage).

The speed estimation unit 7 estimates the driving speed of the brushless DC motor 4 from the speed of the position change detected by the position detection unit 5. However, the speed estimation unit 7 stops the speed estimation when the voltage detected by the voltage detection unit 6 is equal to or lower than a predetermined threshold, and is performed by the position detection unit 5 after the bus voltage becomes equal to or higher than the threshold again. The speed estimation is resumed after the first position is detected. The threshold value for stopping the speed estimation is a value of the bus voltage at which the position detection by the position detection unit 5 becomes unstable, and is determined in advance by the system.

Since the position information from the position detection unit 5 becomes unstable when the bus voltage becomes a predetermined voltage or less, the switching unit 8 detects the position when the detected value of the bus voltage detected by the voltage detection unit 6 becomes a threshold value or less. The position information of the position estimation unit 9 is selected and output instead of the position information of the unit 5. When the voltage value detected by the voltage detection unit 6 exceeds the threshold value, the switching unit 8 selects and outputs the position information of the position detection unit 5 again.

The position estimation unit 9 estimates and outputs the relative position of the rotor 4a of the brushless DC motor 4 from the position information output from the switching unit 8 and the speed estimated by the speed estimation unit 7. For example, when the control cycle is 100 μs, the relative position indicated by the position information from the switching unit 8 is 60 degrees in electrical angle, and when the speed estimated by the speed estimation unit 7 is 50 r / s, the brushless DC Since the motor 4 has a four-pole configuration in this embodiment and the current frequency is 100 Hz, which is twice the speed, the position estimation unit 9 advances the signal of 100 Hz in 100 μs to 60 degrees. The sum of the phases (3.6 deg), that is, position information of 63.6 deg is output.

Based on the position information output from the switching unit 8, the switching arm determination unit 10 switches either the upper arm including the

switching elements

3a, 3c and 3e or the lower arm including the

switching elements

3b, 3d and 3f to perform PWM. Decide whether to output. These can be easily realized by providing in advance a table for position information. In the present embodiment, the switching arm determination unit 10 determines whether the arm that performs PWM output is changed (that is, whether the upper arm performs PWM output or the lower arm performs PWM output). Determine at the same time as the phase is switched.

In the present embodiment, the PWM output and the ON output are set to 60 degrees as the phase angle of the brushless DC motor 4 during the period in which the upper and lower arms continue respectively. When position detection is performed on the basis of 0 cross by induced voltage, the current value of the energized phase whose output is stopped during 60 deg becomes 0 within the drivable range. That is, the on-output is continued until the current value is at least equal to or less than a predetermined current value of 0.

The waveform generation unit 11 determines the energized phase of the brushless DC motor 4 from the position information from the switching unit 8 and outputs a waveform signal that PWM-controls the arm on the side determined by the switching arm determination unit 10. The waveform generation unit 11 determines the PWM duty width from the difference between the target speeds managed by the speed estimation unit 7 and the waveform generation unit 11. In the present embodiment, the target speed is managed by the waveform generation unit 11, but there is no problem even if the target speed is input from the outside. Thereby, the rotational speed of the brushless DC motor 4 can be changed by an instruction from the outside.

Further, the waveform generation unit 11 uses the bus voltage detected by the voltage detection unit 6 and performs control so that the advance angle becomes large when the voltage drops.

The drive unit 12 outputs a drive signal that instructs the supply timing of the power that the inverter 3 supplies to the three-phase winding of the brushless DC motor 4 based on the waveform signal output from the waveform generation unit 11. Specifically, the drive signal turns on or off switching elements 3a to 3f of inverter 3 (hereinafter referred to as on / off). As a result, optimum AC power is applied to the stator 4b, the rotor 4a rotates, and the brushless DC motor 4 is driven.

Next, an electrical device using the motor drive device 22 in the present embodiment will be described. A refrigerator 21 will be described as an example of the electric device.

Although the compressor 17 is mounted in the refrigerator 21, the rotational motion of the rotor 4a of the brushless DC motor 4 is converted into a reciprocating motion by a crankshaft (not shown). A piston (not shown) connected to the crankshaft reciprocates in a cylinder (not shown) to compress the refrigerant in the cylinder. That is, the compressor 17 is configured by the brushless DC motor 4 and the crankshaft, piston, and cylinder.

As the compression method (mechanism method) of the compressor 17, an arbitrary method such as a rotary type or a scroll type is used. In this embodiment, the case of the reciprocating type will be described. Since the reciprocating compressor 17 compresses the refrigerant by changing the volume of the cylinder due to the reciprocating motion of the piston, the inertia is large. For this reason, even when the bus voltage drops and the torque decreases, the fluctuation of the rotational speed of the brushless DC motor 4 is small, so that the drive of the compressor 17 is stabilized.

The refrigerant used in the compressor 17 is generally R134a (HFC; Hydro Fluoro Carbon) or the like, but in this embodiment, R600a (isobutane) is used as the refrigerant. R600a has a lower global warming potential than R134a, but has a low refrigeration capacity. In the present embodiment, the compressor 17 is constituted by a reciprocating compressor, and the cylinder volume is increased in order to ensure the refrigerating capacity. Since the compressor 17 having a large cylinder volume has a large inertia, the brushless DC motor 4 is rotated by the inertia even when the bus voltage drops. As a result, fluctuations in the rotational speed are reduced, and more stable synchronous driving is possible.

The refrigerant compressed by the compressor 17 passes through the condenser 18, the decompressor 19, and the evaporator 20 in this order, and returns to the compressor 17 again. Such a refrigeration cycle is configured. At this time, the condenser 18 radiates heat and the evaporator 20 absorbs heat, so that cooling and heating can be performed. A refrigerator 21 is configured with this refrigeration cycle. Here, as another example of the electric device, there is a blower, and specifically, there is a blower including a fan driven by the brushless DC motor 4.

Next, the operation of the motor drive device 22 configured as described above will be described. First, the determination of the drive signal and the phase (arm) for PWM output will be described. FIG. 2 is a timing chart showing the waveform of the drive signal to the inverter 3 in the present embodiment for one electrical angle cycle.

2, each waveform is a drive signal for turning on / off the

switching elements

3a, 3c, 3e, 3b, 3d, and 3f. The switching elements 3a to 3f are active high elements that turn on the switching elements when the drive signal is high. As shown in FIG. 2, the switching arm determination unit 10 has a table in advance so as to switch the arm on the PWM output side every 60 degrees with 30 degrees as a reference. The phase at which the upper arm performs PWM output is 30 to 90 deg, 150 to 210 deg, 270 to 330 deg, and the lower arm performs PWM output at other phases. The arm on the side where PWM output is not performed is set to be ON output during that time. A waveform indicating the timing of energization is determined by the waveform generator 11. In other words, in the present embodiment, the waveform generator 11 is energized by shifting the

switching elements

3a, 3c, and 3e of the upper arm by 120 deg using a 120 deg rectangular wave. Similarly, the lower arm is also shifted by 120 degrees to energize the

switching elements

3b, 3d, and 3f. The

switching elements

3a and 3b, 3c and 3d, 3e and 3f each have an off period of 60 degrees between the energization periods. Whether the arm outputs PWM or turns on depends on the determination of the switching arm determination unit 10, and the switching of the arm to be energized and the switching of the upper or lower arm to output the PWM are performed simultaneously. .

Note that although 120 deg energization is described in the present embodiment, driving at a wide angle such as 150 deg is also possible. At this time, similar to the control at 120 deg, it can be easily realized by simply turning on the arm opposite to the off arm. In addition to lowering the current peak by setting the wide angle, the cogging component of the current is reduced, so that the power supply harmonics of the frequency component that appears due to the product of the driving speed and the number of poles are alleviated.

Next, the waveform of the drive signal and the current flow when the energized phase of the brushless DC motor 4 is switched will be described. FIG. 3 is a diagram showing drive signal and current waveforms in the present embodiment in which the timing at which the energized phase is switched is enlarged. FIG. 4 is a diagram showing a current path in the present embodiment.

The V-phase current in FIG. 3 is a current flowing through the winding (V phase) of the stator 4b connected to the

switching elements

3c and 3d. The bus current in FIG. 3 indicates the current flowing from the smoothing capacitor 2e to the inverter 3.

The phase when the energization pattern (energization phase) switches from time (4) to time (5) in FIG. 3 is 90 degrees in FIG. At time (1) and time (3) in FIG. 3, the V-phase current passes through the same current path. Specifically, as shown in FIG. 4A, the current passes from the smoothing capacitor 2e through the switching element 3a and the switching element 3d of the inverter 3 to the smoothing capacitor 2e again.

In addition, the V-phase current passes through the same current path at time (2) and time (4) in FIG. Specifically, as shown in FIG. 4B, there is no current path from the smoothing capacitor 2e, and the current flowing through the switching element 3a passes through the return current diode 3h and becomes a return current.

In this state, when time (4) in FIG. 3 shifts to time (5) and the energized phase is switched, the current path shown in FIG. 4 (c) is obtained. Since the phase is 90 deg, the energized phase is switched, and at the same time, the arm for PWM output is switched from the upper arm (switching element 3a) to the lower arm (switching element 3f). As a result, the switching element 3a starts ON output, and the switching element 3f starts PWM output. In other words, simultaneously with the switching of the energized phase, the arm (upper arm (switching element 3a)) opposite to the arm (lower arm (switching element 3d)) that has finished the ON output was turned on (the on output was started). It becomes. In addition, when the output is started next on the arm (lower arm) on which the ON output has been completed, the output becomes the PWM output, and the control by the PWM output can be continued. However, at time (5) in FIG. 3, the PWM is not turned on immediately because the PWM is off timing.

Thus, since the ON output of the switching element 3a as the upper arm is started at the same time as the ON output of the switching element 3d as the lower arm is completed, the V-phase current passes through the return current diode 3i. A loop is formed in which a current flows through the switching element 3a to the brushless DC motor 4 ((c) in FIG. 4). Since the switching element 3a is kept on for 60 degrees, the switching element 3a continues to be turned on until the V-phase current becomes 0, so that a current path to the smoothing capacitor 2e is not generated and the bus voltage rises. There is nothing. That is, the on-output of the opposite arm is started simultaneously with the end of the on-output in one arm, and the current flowing in the arm that has finished the on-output is at least during the period in which the switching element of the opposite arm continues the on output. Until the value falls below a predetermined value.

Although the V-phase current is flowing at time (6) in FIG. 3 (FIG. 3), the switching element 3a is on, so that the V-phase current is applied to the smoothing capacitor 2e as in time (5) in FIG. There is no return path. At this time, since the switching element 3f is turned on for the first time after switching the energized phase, current starts to flow through the current path shown in FIG. Since the V-phase current is 0 at time (7) in FIG. 3 (FIG. 3), the current path is only the current path in (d) of FIG. At time (8) in FIG. 3, the current path during PWM OFF as shown in FIG. 4 (e) is the same as that in the prior art, and the current path to the smoothing capacitor 2e does not occur in the same way, and the bus voltage does not increase. .

FIG. 5A shows a conventional bus voltage waveform when the energized phase is switched, and FIG. 5B shows a bus voltage waveform when the energized phase of the present embodiment is switched. In the conventional method, there is a current path in which energy is charged in the smoothing capacitor 2e when the energized phase is switched. Therefore, as shown by the waveform 35 in FIG. Yes. On the other hand, in the present embodiment, since there is no current path for charging the smoothing capacitor 2e when the energized phase is switched, as shown in the bus voltage waveform in FIG. Stable and smooth drive is possible without any occurrence.

Next, the structure of the brushless DC motor 4 of this embodiment will be described. FIG. 6 is a cross-sectional view showing a cross section perpendicular to the rotation axis of the rotor 4a of the brushless DC motor 4 in the present embodiment.

The rotor 4a is composed of an iron core 4g and four magnets (permanent magnets) 4c to 4f. The iron core 4g is formed by stacking punched thin steel sheets of about 0.35 to 0.5 mm. The magnets 4c to 4f are arc-shaped ferrite permanent magnets, and are arranged symmetrically about the center so that the arc-shaped recesses face outward as shown in the figure. In the case where rare earth permanent magnets such as neodymium are used as the magnets 4c to 4f, a flat plate shape may be used.

In the rotor 4a having such a structure, the axis going from the center of the rotor 4a toward the center of one magnet (eg, magnet 4f) is defined as a d-axis, and one magnet (eg, magnet) from the center of the rotor 4a. The axis that goes between 4f) and the adjacent magnet (for example, magnet 4c) is defined as the q axis. Here, the inductance Ld in the d-axis direction and the inductance Lq in the q-axis direction have opposite saliency and are different. That is, this means that the motor can effectively use torque (reluctance torque) using reverse saliency other than torque (magnet torque) due to magnetic flux of the magnet. Therefore, torque can be used more effectively as a motor. As a result, a highly efficient motor is obtained as the present embodiment.

In the present embodiment, since the capacity of the smoothing capacitor 2e is reduced, pulsation occurs in the bus voltage, and the output torque decreases in a section where the bus voltage falls. However, it is possible to control the waveform generation unit 11 to increase the advance amount in accordance with the drop in the bus voltage detected by the voltage detection unit 6, thereby suppressing a decrease in output torque and enabling stable driving. .

Further, the brushless DC motor 4 of the present embodiment has a rotor 4a in which magnets 4c to 4f are embedded in an iron core 4g and has saliency. In addition to the magnet torque of the magnets 4c to 4f, reluctance torque due to saliency is used. This not only improves efficiency at low speeds, but also improves high-speed drive performance. Also, if a rare earth magnet such as neodymium is used for the magnets 4c to 4f to increase the ratio of the magnet torque, or the difference between the inductances Ld and Lq is increased to increase the ratio of the reluctance torque, the optimum conduction angle is obtained. The efficiency can be increased by changing.

Next, the case where the compressor 17 is driven using the motor drive device 22 of the present embodiment for the refrigerator 21 and the air conditioner will be described. In the conventional motor drive device, a smoothing capacitor and a reactor are large, and a large space is required for incorporation into the system. However, in the present embodiment, it is possible to reduce the smoothing capacitor 2e, which conventionally required about 400 μF, to several μF, and to 1/3 or less in volume. In addition, if the driving is performed at a low load like the refrigerator 21, the reactor 2f that is conventionally several millimeters H can be covered with the inductance component of the filter (general common mode filter). The motor drive device 22 can be greatly reduced in size and cost.

Also, in a compressor control system that drives only at a constant speed, a conventional motor drive device capable of variable speed drive has a small space in the system, and the motor drive device cannot be easily incorporated into the system. However, in this embodiment, since the motor drive device can be made very small, restrictions on installation space are eased, and a motor drive device capable of variable speed drive can be incorporated into a compressor system that drives only at a constant speed. It becomes easy. If the speed is variable, the system efficiency of the refrigerator can be improved, and a more energy-saving refrigerator can be provided.

As described above, the motor drive device 22 in the present embodiment is connected to the AC power source 1 and is motor driven to rotate the brushless DC motor 4 by switching the energized phase of the brushless DC motor 4 having a plurality of windings. A rectifier circuit (rectifier diodes 2a to 2d) for rectifying AC power input from the AC power source 1, and a smoothing capacitor 2e having a value determined to have a resonance frequency higher than 40 times the frequency of AC power; The upper arm and the lower arm are connected in series when the smoothing unit 2g that smoothes the output from the rectifier circuit, and the circuit that includes the switching element and the return current diode are configured as one arm. An input which has a plurality of connected legs, converts DC power obtained from the smoothing unit 2g into AC power and supplies the AC power to the brushless DC motor 4. And over motor 3, and a control unit 30 for outputting a drive signal inverter 3 instructs the power supply timing of supplying the brushless DC motor 4 to the inverter 3. Here, the drive signal is a plurality of arms whose upper and lower sides are opposite to each other in a period in which the switching element of one of the arms performs PWM output that repeats ON and OFF based on pulse width modulation. This is a signal for controlling the inverter 3 so that the switching element of one of the arms is turned on so that the switching element is always turned on. Then, when the energized phase of the brushless DC motor 4 is switched, the control unit 30 outputs a drive signal so that the switching element of the arm on the opposite side to the arm on which the ON output is completed starts the ON output. Thereby, even if the energized phase of the brushless DC motor 4 is switched, there is always a path in the inverter 3 for the energy accumulated in the energized phase that has been turned off to return to the brushless DC motor 4, and the energy returns to the small-capacity smoothing capacitor 2e. Therefore, a rapid increase in the bus voltage is suppressed, so that a small and inexpensive motor driving device that can stably and smoothly drive the brushless DC motor 4 can be provided.

Further, since the rectifying and smoothing circuit 2 is constituted by the smoothing capacitor 2e and the reactor 2f whose values are determined so as to have a resonance frequency higher than 40 times the frequency of the AC power supply 1, the current flowing through the resonance is regulated by the harmonic power supply regulation. Since it is out of range, the harmonic current can be reduced.

Further, since the rectifying and smoothing circuit 2 is constituted by the smoothing capacitor 2e and the reactor 2f whose values are determined so as to have a resonance frequency higher than 40 times the frequency of the AC power supply 1, the smoothing capacitor has a small capacity and an inrush current peak is generated. The harmonic current can be reduced because of lowering.

In the present embodiment, the control unit 30 further turns on output until the bus voltage, which is the voltage output from the smoothing unit 2g, rises to a predetermined voltage when the energized phase of the brushless DC motor 4 is switched. The on-output of the switching element of the arm on the opposite side to the arm that has finished is started. As a result, the bus voltage can be suppressed to a voltage increase value that does not cause an influence such as overvoltage and drive rattling, which are problems due to the rise of the bus voltage, and a stable motor driving device can be provided.

Further, in the present embodiment, the period during which the switching element of the arm on the opposite side to the arm on which the on-output has ended continues the on-output until at least the current flowing in the arm on which the on-output has ended is equal to or less than a predetermined value. . As a result, the current below the current value that does not cause a problem due to the rise of the bus voltage flows into the smoothing capacitor 2e, and more stable driving is possible.

Further, in the present embodiment, the period during which the switching element of the arm on the opposite side to the arm on which the on-output is completed continues the on-output until the energized phase of the brushless DC motor 4 is switched to the next. This facilitates the setting of the energization pattern and simplifies the software and system for driving, thereby improving maintainability and quality.

In the present embodiment, the rotor 4a of the brushless DC motor 4 is configured by embedding magnets (permanent magnets) 4c to 4f in the iron core 4g, and has saliency. Thereby, in driving the brushless DC motor 4, since the reluctance torque due to the saliency can be effectively used together with the magnet torque due to the permanent magnet, the waveform generator 11 takes a larger advance angle as the bus voltage drops, By reducing the reduction in output torque, more stable driving is possible.

In the present embodiment, the brushless DC motor 4 drives the compressor 17. The drive control of the compressor 17 does not require high-accuracy rotational speed control or acceleration control as in the industrial servo motor control, and the compressor 17 is a load having a relatively large inertia. Speed fluctuations are very light loads. Therefore, even when the bus voltage is lowered, the speed fluctuation is small and more stable driving is possible.

In the present embodiment, the compressor 17 is a reciprocating compressor. As a result, the reciprocating type that performs reciprocating motion has a very large inertia and is operated more stably when the voltage drops because the rotor is connected to a crankshaft and piston that are metallic and heavy in weight. be able to.

Further, in the present embodiment, the refrigerant used in the compressor 17 is R600a. As a result, the cylinder volume and the inertia are increased in order to obtain the refrigerating capacity, and further, stable driving that is hardly affected by fluctuations in the applied torque becomes possible.

In addition, when used in the refrigerator 21 as an electrical device using the motor drive device 22 of the present embodiment, the motor drive device can be reduced in size, so that it can be stored in a small space in a refrigerator that is driven at a constant speed. The more efficient refrigerator 21 can be provided at low cost.

Also, when used as a blower as an electrical device, the blower has a very large inertia, so that it is possible to realize a small blower that can be driven stably and is easy to carry.

As mentioned above, although the motor drive device concerning this invention and the electric equipment using the same were demonstrated based on embodiment, this invention is not limited to such embodiment. Forms obtained by subjecting various embodiments to various modifications conceived by those skilled in the art and forms obtained by arbitrarily combining the constituent elements of the embodiments are within the scope of the present invention without departing from the spirit of the present invention. included.

The motor drive device of the present invention reduces the capacity of the smoothing capacitor, and enables a small, stable and smooth drive. Thereby, the motor drive device of the present invention can be applied not only to a refrigerator and a blower but also to a compressor in a vending machine, a showcase, and a heat pump water heater. In addition, the motor driving device of the present invention can be applied to miniaturization of electrical equipment using a brushless DC motor such as a washing machine, a vacuum cleaner, and a pump.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectification smoothing circuit 2a, 2b, 2c, 2d Rectifier diode

2e Smoothing capacitor

2g Smoothing part 2g
2f Reactor 3

Inverter

3a, 3b, 3c, 3d, 3e,

3f Switching element

3g, 3h, 3i, 3j, 3k, 3l Reflux current diode 4 Brushless DC motor 4a

Rotor 4b Stator

4c, 4d, 4e, 4f Magnet (permanent magnet)
4 g Iron core 5 Position detection unit 6 Voltage detection unit 7 Speed estimation unit 8 Switching unit 9 Position estimation unit 10 Switching arm determination unit 11 Waveform generation unit 12 Drive unit 17 Compressor 18 Condenser 19 Decompressor 20 Evaporator 21 Refrigerator (electric equipment) )
22 Motor drive device 30 Control unit

Claims

A motor drive device that is connected to an AC power source and that rotates the brushless DC motor by switching the energization phase of the brushless DC motor having a plurality of windings,
A rectifier circuit for rectifying AC power input from the AC power source;
A smoothing unit configured by a capacitor and a reactor whose values are determined to be a resonance frequency higher than 40 times the frequency of the AC power, and smoothing the output from the rectifier circuit;
When a circuit composed of a switching element and a return current diode is used as one arm, the upper arm and the lower arm have a plurality of legs connected in series, and the DC power obtained from the smoothing unit is AC power. An inverter that converts the power into the brushless DC motor and
A control unit that outputs to the inverter a drive signal that instructs the supply timing of power supplied to the brushless DC motor by the inverter;
The drive signal includes a plurality of arms whose upper and lower sides are opposite to each other in a period in which a switching element of one of the plurality of arms outputs a PWM signal that repeatedly turns on and off based on pulse width modulation. Is a signal that controls the inverter so that the switching element of one of the arms is turned on at all times,
The control unit outputs the drive signal so that when the energized phase of the brushless DC motor is switched, the switching element of the arm on the opposite side to the arm on which the on-output is finished starts the on-output. .
The control unit further includes a side opposite to the arm on which the ON output has been completed before the bus voltage, which is a voltage output from the smoothing unit, rises to a predetermined voltage when the energized phase of the brushless DC motor is switched. The motor drive device according to claim 1, wherein the on-output of the switching element of the arm is started.
The period during which the switching element of the arm on the opposite side to the arm on which the ON output has ended continues the ON output is at least until the current flowing through the arm on which the ON output has ended becomes equal to or less than a predetermined value. The motor drive device described.
The period during which the switching element of the arm on the opposite side to the arm on which the ON output has been completed continues the ON output is until the energized phase of the brushless DC motor is next switched. The motor drive device described.
The motor driving device according to any one of claims 1 to 4, wherein the rotor of the brushless DC motor is configured by embedding a permanent magnet in an iron core, and further has a saliency.
The motor driving apparatus according to any one of claims 1 to 5, wherein the brushless DC motor drives a compressor.
The motor driving device according to claim 6, wherein the compressor is a reciprocating compressor.
The motor drive device according to claim 7, wherein the refrigerant used in the compressor is R600a.
A motor driving device according to any one of claims 1 to 5;
An electric device comprising: a brushless DC motor driven by the motor driving device.