JP2015171206A - Motor driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor driver capable of solving a problem that precise position detection is prevented due to a fluctuation in spike voltage width which prevents detection of induction voltage zero-cross.SOLUTION: A terminal voltage detection section 6 detects disappearance of a spike voltage, and after detecting the disappearance, detects the rotor position based on an induction voltage. Since the position detection is made after the spike voltage has reliably completed, even when the current changes sharply, the position detection is discriminate from the spike voltage. With this, a delay of motor phase or the spike voltage can be discriminated from the induction voltage. Thus, precise position detect is ensured and a motor is driven with a stable current waveform.

Description

  The present invention relates to a motor drive device that drives a brushless DC motor.

  Conventionally, in this type of motor drive device, as disclosed in Patent Document 1, for example, when a spike voltage generated by the return current is detected in order to prevent the position detection from being accurately performed due to the return current of the motor. A mask signal is generated and driven while detecting a position after being released after a predetermined time.

  FIG. 9 shows a block diagram of a second conventional motor driving apparatus for setting the mask period of the spike voltage according to a predetermined time. As shown in FIG. 9, the AC power supply 301 is rectified by 302 (a) to 302 (d) of the rectifying and smoothing unit 302. Thereafter, the signal is smoothed by 302e and input to the inverter 303. The inverter 303 is configured by connecting six switching elements in a three-phase bridge. The inverter 303 converts DC power into AC power having a predetermined frequency and inputs the AC power to the brushless DC motor 304. The position detection unit 305 detects one-phase current among the three-phase currents flowing through the brushless DC motor, and the position detection mask time setting unit 306 sets the position detection mask time according to the detected current value.

  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. However, information on the induced voltage is not acquired until the mask time set by the position detection mask time setting unit 306 is completed. The energization winding switching unit 307 switches the energization phase based on the relative position detected by the position detection unit 305, and the drive unit 308 switches the switching elements 304 a to 304 f of the invar 303 based on the energization phase determined by the energization winding switching unit 307. Drive.

JP-A-10-028395

  However, since the mask period is determined by time in the above-described conventional configuration, the spike width fluctuates when the motor current changes abruptly. Therefore, it is not possible to cope with the preset mask period, and position detection is inaccurate. As a result, the current is disturbed and the motor efficiency is reduced.

  The present invention solves the above-described conventional problems, and provides a motor drive device that is driven with a stable current waveform even when a motor current suddenly changes, and enables high-efficiency operation.

A motor driving device according to the present invention includes an AC power source, a rectifier circuit that rectifies AC input from the AC power source into DC, a smoothing unit that smoothes output from the rectifier circuit, a switching element, and a diode for return current. An inverter configured to convert direct current obtained from the smoothing unit into alternating current, a brushless DC motor that receives the alternating current obtained from the inverter as input and drives a load, and a terminal voltage while current flows through the return current diode A terminal voltage detection unit that detects a spike voltage generated at a terminal and detects a rotational position of a rotor from an induced voltage that appears in a terminal voltage of the brushless DC motor; and a supply timing of power that the inverter supplies to the brushless DC motor. A rectangular wave with a conduction angle of 120 ° to 150 ° based on information from the terminal voltage detector or a wave equivalent thereto In a drive unit that outputs to the inverter, the terminal voltage detecting section detects that the spike voltage is lost, the position detection of the rotor from the induced voltage after the loss detection.

  According to such a configuration, since the position detection is performed after the spike voltage has been reliably completed, the induced voltage and the spike voltage can be separated even when the current changes suddenly, and a motor phase delay or spike voltage is induced. Driving is performed with a stable current waveform by performing accurate position detection without erroneously detecting that the voltage exceeds the threshold value.

  The motor driving device of the present invention can provide a motor driving device that can detect a position accurately and drive with a stable current waveform even when a sudden change in current occurs, enabling high-efficiency operation. .

1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. Timing chart showing drive signal waveforms in the same embodiment Waveform diagram showing relationship between drive signal and current waveform in the same embodiment Path diagram showing current path in the same embodiment Waveform diagram showing the bus voltage waveform of a conventional motor drive device Waveform diagram showing the bus voltage waveform in the same embodiment Waveform diagram showing a terminal voltage waveform capable of detecting an induced voltage zero cross in the same embodiment Waveform diagram showing a terminal voltage waveform in which an induced voltage zero cross cannot be detected in the same embodiment Sectional drawing of the principal part of the brushless DC motor in the same embodiment Block diagram of a conventional motor drive device

  An AC power source, a rectifying circuit that rectifies AC input from the AC power source into DC, a smoothing unit that smoothes the output from the rectifying circuit, a switching element and a return current diode, and is obtained from the smoothing unit An inverter that converts direct current to alternating current, a brushless DC motor that uses the alternating current obtained from the inverter as an input to drive a load, and a spike voltage that occurs in the terminal voltage while the current flows through the return current diode is detected. Based on the information of the terminal voltage detector, the terminal voltage detector that detects the rotational position of the rotor from the induced voltage that appears in the terminal voltage of the brushless DC motor, and the supply timing of the power that the inverter supplies to the brushless DC motor. Output to the inverter as a rectangular wave with a conduction angle of 120 degrees or more and 150 degrees or less or a waveform conforming thereto. The terminal voltage detector detects that the spike voltage has disappeared, and detects the position of the rotor from the induced voltage after the disappearance is detected. As a result, position detection and spike voltage can be separated even for sudden changes in current, and stable by accurate position detection without erroneously detecting motor phase delay or spike voltage as induced voltage. Therefore, even when a sudden change in current occurs, a motor drive device capable of high-efficiency operation by accurately detecting the position and driving with a stable current waveform can be provided. .

In the second aspect of the invention, in particular, the drive unit of the first aspect of the invention sets a threshold value during a period in which the spike voltage is generated, and if the spike voltage is generated longer than the threshold value, the drive unit depends on the operation state such as the operation speed. By outputting the waveform based on the determined time, the spike voltage
Even in a large load state in which the induced voltage is hidden, commutation can be performed at an appropriate timing, and stable driving can be performed.

  According to a third aspect of the invention, in particular, the smoothing section of the first or second aspect of the invention comprises a small-capacitance capacitor and a reactor whose value is determined to be a resonance frequency higher than 40 times the frequency of the AC power supply. As a result, the motor drive device is reduced in size, and even if the current flowing through the motor pulsates and the spike voltage width fluctuates greatly with a period approximately twice that of the AC power supply, the disappearance of the spike voltage is detected. In addition, since accurate position detection is possible, a small motor driving device that can be driven stably can be provided.

  In the fourth aspect of the invention, the brushless DC motor according to any one of the first to third aspects of the invention is a power for driving the reciprocating compressor. The reciprocating type that performs reciprocating motion has a large load difference between the refrigerant compression process and the suction process, and the current and speed fluctuate accordingly.However, the position of the compressor is reduced by detecting the position after the spike voltage disappears. In addition, the position of the rotor of the brushless DC motor can be appropriately detected even in the suction process.

(Embodiment 1)
FIG. 1 is a block diagram of a motor drive device according to Embodiment 1 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 5. Hereinafter, the motor drive device 22 will be described.

  The rectifier circuit 2 rectifies AC power into DC power with the AC power supply 1 as an input, and is composed of four rectifier diodes 2a to 2d that are bridge-connected.

  The smoothing unit 3 is connected to the output side of the rectifier circuit 2 and smoothes the output of the rectifier circuit 2. It comprises a smoothing capacitor 3e and a reactor 3f. The output from the smoothing unit 3 is input to the inverter 4.

  The smoothing capacitor 3e and the reactor 3f are set so that the resonance frequency is higher than 40 times the AC power supply frequency. As a result, the current due to the resonance frequency falls outside the range of the power supply harmonic regulation, and the harmonic current can be reduced. Further, by setting the smoothing capacitor 3e to such a value, the bus voltage includes a large ripple component, and the current flowing from the AC power supply 1 to the smoothing capacitor 3e is also a current close to the frequency component of the AC power supply 1, so that the harmonic current Can be reduced.

  Since the reactor 3f is inserted between the AC power supply 1 and the smoothing capacitor 3e, it may be either before or after the rectifier diodes 2a to 2d. Furthermore, when the common mode filter that constitutes the high frequency removing means is provided in the circuit, the reactor 3f takes into consideration a composite component with the reactance component of the high frequency removing means.

  The inverter 4 converts the DC power containing a large ripple component into the voltage from the smoothing unit 3 at a cycle twice the power cycle of the AC power source 1 into AC power. The inverter 4 is configured by connecting six switching elements 4a to 4f in a three-phase bridge. The six return current diodes 4g to 4l are connected to the switching elements 4a to 4f in the reverse direction.

  The brushless DC motor 5 includes a rotor 5a having a permanent magnet and a stator 5b having a three-phase winding. The brushless DC motor 5 rotates the rotor 5a when the three-phase alternating current generated by the inverter 4 flows in the three-phase winding of the stator 5b.

  The terminal voltage detection unit 6 acquires the terminal voltage of the brushless DC motor 5 in the present embodiment. While the return current is flowing, the terminal voltage is attached with a potential difference corresponding to the voltage drop of the P side or N side of the DC bus voltage of the inverter 4 and the return current diodes 4g to 4l. When 6 acquires the terminal voltage, it is possible to detect the presence or absence of the spike voltage in the state where the reflux current is flowing. On the other hand, the magnetic pole relative position of the rotor 5a of the brushless DC motor 5 is detected. Specifically, the position detector detects the relative rotational position of the rotor 5a based on the induced voltage generated in the three-phase winding of the stator 5b.

  In addition, as a reference voltage for the zero cross of the spike voltage and the induced voltage, a virtual midpoint may be created from the terminal voltages for three phases, or a DC bus voltage may be obtained and used as the voltage. In this embodiment, it is a virtual midpoint.

  In the drive unit 7, the spike voltage disappears from the information detected by the terminal voltage detection unit 6, and based on the position of the rotor 5 a of the brushless DC motor detected from the induced voltage, the inverter 4 performs the three-phase winding of the brushless DC motor 5. Supply timing of power supplied to the line and a drive signal for PWM control are output. Specifically, the drive signal turns on or off the switching elements 4a to 4f of the inverter 4 (hereinafter referred to as on / off). As a result, optimum AC power is applied to the stator 5b, the rotor 5a rotates, and the brushless DC motor 5 is driven.

  Further, the drive unit 7 estimates the drive speed of the brushless DC motor from the position change speed detected by the terminal voltage detection unit 6. If the disappearance of the spike voltage is not detected even after the elapse of a predetermined time after the spike voltage is generated based on this estimated speed or the specific position of the predetermined induced voltage is detected, the position is detected. The inverter 4 outputs a drive signal that indicates the supply timing of the power supplied to the three-phase winding of the brushless DC motor 5. The PWM duty width is determined from the difference between the speed information calculated from the position information and the target speed.

  Next, an electric device using the motor driving 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 21 is mounted in the refrigerator 21, the rotational motion of the rotor 5a of the brushless DC motor 5 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 comprised by the brushless DC motor 5, a crankshaft, a piston, and a cylinder.

  As a 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. The reciprocating compressor 17 has a large torque fluctuation in the suction and compression processes, and the speed and current value fluctuate greatly. Therefore, it is difficult to uniformly estimate the spike width based on the speed and the current before commutation. .

  The refrigerant compressed by the compressor 17 constitutes a refrigeration cycle in which the refrigerant passes through the condenser 18, the decompressor 19, and the evaporator 20 in this order and returns to the compressor 17 again. At this time, since the condenser 18 radiates heat and the evaporator 20 absorbs heat, 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, which includes a fan of a blower driven by the brushless DC motor 5.

The operation of the motor drive device 22 configured as described above will be described. First, determination of a drive signal and a phase for PWM output will be described. FIG. 2 is a timing chart showing a drive signal waveform of the inverter 4 in the present embodiment for one electrical angle cycle.

  In FIG. 2, the respective waveforms are drive signals for turning on / off the switching elements 4a, 4c, 4e, 4b, 4d, and 4f, and the switching elements 4a to 4f turn on the switching elements when the drive signal is high. It is an active high element. 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 deg with 30 deg as a reference. The phase at which the upper arm outputs PWM 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. Which phase is energized is performed by the waveform generator 11 and is performed by a 120 deg rectangular wave in the present embodiment. Therefore, the upper arm switching elements 4a, 4c, and 4e are energized while being shifted by 120 deg. . Similarly, the lower arm is also shifted by 120 degrees to energize the switching elements 4b, 4d, and 4f. The switching elements 4a and 4b, 4c and 4d, 4e and 4f each have an off period of 60 degrees between the energization periods.

  In this embodiment, 120 deg energization is described. However, driving at a wide angle such as 150 deg is possible, and this can be easily realized by simply turning on the arm opposite to the energized phase that is turned off as in the case of 120 deg control. Is possible. The wide angle reduces the current peak and reduces the cogging component of the current, so that the power supply harmonic of the frequency component that appears due to the product of the driving speed and the number of poles is alleviated.

  Next, a drive signal waveform and a current flow when the energized phase of the brushless DC motor is switched will be described with reference to FIGS. 3 and 4. FIG. 3 is a diagram showing the relationship between the drive signal and the current waveform 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.

  In FIG. 3, the V-phase current is a current that flows through the winding of the stator 5b connected to the switching elements 4c and 4d, and the bus current is a current that flows from the smoothing capacitor 3e to the inverter 4.

  The phase when the energization pattern is switched from (4) to (5) in FIG. 3 is 90 deg in FIG. 3 (1) and (3) pass through the same current path, and as shown in (a) of FIG. 4, a current path returns from the smoothing capacitor 3e to the smoothing capacitor 3e again through the switching elements 4a and 4j of the inverter 4. Pass through.

  3 (2) and (4) pass through the same current path, and as shown in FIG. 4 (b), there is no current path from the smoothing capacitor 3e, and the current flowing through the switching element 4a is returned. It passes through the current diode 4h and becomes a reflux current.

  In this state, when the process moves from (4) to (5) in FIG. 3 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 phase for PWM output is switched from the upper arm to the lower arm. As a result, the switching element 4a is turned on, and the switching element 4f starts PWM output. That is, simultaneously with the switching of the energized phase, the energized phase of the arm (upper arm) on the opposite side to the energized phase (lower arm) that stopped output was turned on. The energized phase that starts output next in the energized phase side arm (lower arm) where output is stopped becomes PWM output, and control by PWM output can be continued. However, in the section (5) in FIG. 3, the PWM is not turned on immediately because the PWM is in the off timing.

  As described above, since the output of the switching element 4d as the lower arm is stopped and the switching element 4a is turned on at the same time, the V-phase current passes through the switching current diode 4i and then passes through the switching element 4a to be a brushless DC motor. A loop through which current flows to 5 is formed. Since the switching element 4a is kept on for 60 degrees, the switching element 4a continues to be turned on until the V-phase current becomes 0, so that no current path to the smoothing capacitor 3e is generated and the bus voltage rises. There is nothing.

  On the other hand, in the conventional general PWM control, either the upper side or the lower side is switched. Therefore, if the upper side is always switched, the current flows at the timing when the PWM is turned off when the energized phase is switched at 90 degrees. Since there is no current path for the phase that was flowing, regeneration occurs, energy is returned to the smoothing capacitor 3e, and the bus voltage rises.

  Further, although the V-phase current flows in the section (6) of FIG. 3, since the switching element 4a is on, the V-phase current flows to the smoothing capacitor 3e as in the section (5) of FIG. There is no return path. At this time, since the switching element 4f is turned on for the first time after the energized phase is switched, the current of (d) in FIG. 4 starts to flow and the bus current starts to flow. In the section (7) in FIG. 3, the V-phase current is 0, so only the current path in (d) in FIG. 4 is provided. In the section (8) of FIG. 3, the current path when PWM is turned off as shown in FIG. 4 (e) is the same as that in the prior art, and the path to the smoothing capacitor 3e does not occur in the same manner 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 path through which energy is charged in the smoothing capacitor 3e. Therefore, in the small-capacity smoothing capacitor 3e, the bus voltage rapidly increases as shown in FIG. 5A. On the other hand, in the bus voltage waveform of FIG. 5B of the present embodiment, the bus voltage does not increase and stable and smooth driving is possible.

  Next, the operation of the terminal voltage detector 6 will be described with reference to FIGS. 4, 6, and 7. FIG. 6 is a diagram showing terminal voltage waveforms in which zero crossing of the induced voltage can be detected in the same embodiment. FIG. 7 is a diagram showing a terminal voltage waveform in which an induced voltage zero cross cannot be detected in the same embodiment.

  First, in FIG. 6, at the timing of 90 deg, the switching element 4a is switched from PWM to ON output, the switching element 4d is switched from ON to OFF, and the switching element 4f is switched to PWM output. At this time, as shown in FIG. 4C, the current flowing through the output terminal connected to the switching elements 4c and 4d passes through the return current diode 4i, and a spike voltage appears in the terminal voltage connected to the switching elements 4c and 4d. In FIG. 6, the spike voltage is generated until the timing of (1). The terminal voltage detector 6 detects that the voltage is lower than the bus voltage ÷ 2, and grasps that the spike voltage has disappeared. Next, since an induced voltage zero cross occurs at a timing of 120 deg, the terminal voltage detector 6 detects that the terminal voltage has exceeded the bus voltage ÷ 2, and detects that position detection has occurred. When position detection occurs, the time from the timing processed as the previous position detection to the current position detection is recorded, and the speed is calculated based on this time.

On the other hand, in FIG. 7, the switching element 4a is switched from PWM to ON output at the timing of 90 deg as in FIG. 6, the switching element 4d is switched from ON to OFF, and the switching element 4f is switched to PWM output. At this time, as shown in FIG. 4C, the current flowing through the output terminal connected to the switching elements 4c and 4d passes through the return current diode 4i, and a spike voltage appears in the terminal voltage connected to the switching elements 4c and 4d. In FIG. 7, the spike voltage is generated until the timing (2). Since the timing at which the spike voltage disappears occurs after 120 deg, which is the induced voltage 0 cross, the terminal voltage detection unit 6 cannot detect that the terminal voltage has fallen below the bus voltage ÷ 2, and the spike voltage disappears. It cannot be detected.

  However, in the present embodiment, the drive unit 7 starts the timer at the timing of 90 deg commutation, and if the time equivalent to 60 deg calculated from the speed has elapsed, it is considered that position detection has occurred at the time equivalent to 30 deg. , And commutation is performed at a timing equivalent to 60 deg. Thereby, even when the spike voltage hides the induced voltage 0 cross, commutation at an appropriate timing is possible. Further, since the end of the spike voltage is detected, even if the brushless DC motor 5 is in a lagging phase such as load fluctuation or bus voltage fluctuation and a position detection timing occurs immediately after commutation, a predetermined mask period Therefore, accurate position detection can be performed. Further, in this embodiment, the time for determining that the disappearance of the spike voltage cannot be confirmed is equivalent to 60 deg. However, if the time is set to be short, the advance angle becomes large, and position detection occurs from commutation in the next position detection. The time until the time becomes longer, and the position can be detected by the induced voltage 0 cross. Further, if the time for determining that the disappearance of the spike voltage cannot be confirmed is set longer than 60 deg, it is possible to deal with a wider range of speed fluctuations and current fluctuations. However, the time when it is determined that the disappearance of the next spike voltage cannot be confirmed is shorter than 60 deg, and the advance angle is changed to the advance side with respect to the possibility of the delayed phase.

  Next, the structure of the brushless DC motor 5 of the present embodiment will be described. FIG. 6 is a cross-sectional view showing a cross section perpendicular to the rotation axis of the rotor of the brushless DC motor 5 in the present embodiment.

  The rotor 5a includes an iron core 5g and four magnets 5c to 5f. The iron core 5g is configured by stacking punched thin steel sheets of about 0.35 to 0.5 mm. As the magnets 5c to 5f, arc-shaped ferrite permanent magnets are often used, and as illustrated, the magnets 5c to 5f are arranged symmetrically with the arc-shaped concave portion facing outward. On the other hand, when rare earth permanent magnets such as neodymium are used as the magnets 5c to 5f, they may be flat.

  In the rotor 5a having such a structure, an axis extending from the center of the rotor 5a toward the center of one magnet (for example, 5f) is defined as a d-axis, and one magnet (for example, 5f) is connected to the center of the rotor 5a. The axis that goes to the adjacent magnet (for example, 5c) is the q axis. 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 can effectively use torque (reluctance torque) using reverse saliency as well as 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.

  Also, if a rare earth magnet such as neodymium is used as the permanent magnet to increase the ratio of magnet torque, or the difference between inductances Ld and Lq is increased to increase the ratio of reluctance torque, the optimum conduction angle can be changed. Can increase efficiency.

  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, a smoothing capacitor that requires about 400 μF can be reduced to several μF, and the volume can be reduced to 1/3 or less. In addition, if the driving is performed at a low load like the refrigerator 21, it is possible to cover the reactor with several millimeters H by the inductance component of the filter, and it is possible to greatly reduce the size and cost.

  In a compressor control system that drives only at a constant speed, a conventional motor driving device capable of variable speed driving has a small space and cannot be easily incorporated. However, since the present embodiment can be made very compact, restrictions on installation space are eased, and it becomes easy to incorporate a motor drive device capable of variable speed drive into a compressor system that is driven only at a constant speed. 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, in the present embodiment, the AC power source 1, the rectifier circuit 2 that rectifies the AC input from the AC power source 1 into DC, the smoothing unit 3 that smoothes the output from the rectifier circuit 2, and the switching element 4a to 4f and freewheeling current diodes 4g to 4l, which are configured to convert the direct current obtained from the smoothing unit 3 into alternating current, the brushless DC motor 5 that drives the load using the alternating current obtained from the inverter 4 as an input, A terminal voltage detection unit 6 for detecting a spike voltage generated in the terminal voltage while a current flows through the current diodes 4g to 4l and detecting a rotational position of the rotor from an induced voltage appearing in the terminal voltage of the brushless DC motor 5; The conduction angle is 120 degrees or more based on the information detected by the terminal voltage detector 6 about the supply timing of the power supplied from the inverter 4 to the brushless DC motor 5. The drive unit 7 outputs to the inverter 4 with a rectangular wave of 50 degrees or less or a waveform conforming thereto, and the terminal voltage detection unit 6 detects the disappearance of the spike voltage, and detects the rotor position from the induced voltage after the disappearance is detected. Since position detection is performed after the spike voltage has been reliably completed, position detection and spike voltage can be separated from sudden changes in current, inducing motor phase delay and spike voltage. By accurately detecting the position without detecting it as a voltage, it is possible to drive with a stable current waveform. Even when a sudden change in current occurs, the position is detected accurately and the current waveform is stable. It is possible to provide a motor drive device that can be driven with high efficiency and can be operated efficiently.

  In addition, the drive unit 7 according to the present embodiment sets a threshold value during a period in which the spike voltage is generated, and when the spike voltage is generated longer than the threshold value, the drive unit 7 waits for a period of time determined according to the operation state such as the operation speed. Based on the output of the waveform, even when the load is large such that the induced voltage is hidden by the spike voltage, commutation can be performed at an appropriate timing, and stable driving can be performed. .

  Further, the smoothing unit 3 of the present embodiment is constituted by a small-capacity smoothing capacitor 3e and a reactor 3f whose values are determined so as to have a resonance frequency higher than 40 times the frequency of the AC power supply 1, thereby driving the motor. The device 22 is small in size, and even if the current flowing through the motor pulsates and the spike voltage width fluctuates greatly with a period approximately twice that of the AC power source 1, it is detected that the spike voltage disappears and is accurate. Since the position can be detected, a small motor driving device that can be driven stably can be provided.

  Further, the brushless DC motor 5 of the present embodiment uses power for driving the reciprocating compressor 17. In the reciprocating type that performs reciprocating motion, the load differs greatly between the refrigerant compression process and the suction process, and the current and speed fluctuate accordingly. However, by detecting the position after the spike voltage disappears, The position of the rotor of the brushless DC motor 5 can be appropriately detected even in the compression and suction processes.

  The motor driving device of the present invention enables stable driving regardless of the occurrence of spike voltage. Thereby, it can be applied not only to refrigerators and blowers but also to compressors in vending machines, showcases, and heat pump water heaters. In addition, the present invention can also be applied to stable driving of electric devices using brushless DC motors such as washing machines, vacuum cleaners, and pumps.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectification circuit 3e Smoothing capacitor 3f Reactor 4 Inverter 5 Brushless DC motor 5a Rotor 5b Stator 6 Terminal voltage detection part 7 Drive part 17 Compressor 21 Refrigerator 22 Motor drive device

Claims (4)

An AC power source, a rectifying circuit that rectifies AC input from the AC power source into DC, a smoothing unit that smoothes the output from the rectifying circuit, a switching element and a return current diode, and is obtained from the smoothing unit An inverter that converts direct current to alternating current, a brushless DC motor that uses the alternating current obtained from the inverter as an input to drive a load, and a spike voltage that occurs in the terminal voltage while the current flows through the return current diode is detected. Based on the information of the terminal voltage detector, the terminal voltage detector that detects the rotational position of the rotor from the induced voltage that appears in the terminal voltage of the brushless DC motor, and the supply timing of the power that the inverter supplies to the brushless DC motor. Output to the inverter as a rectangular wave with a conduction angle of 120 degrees or more and 150 degrees or less or a waveform conforming thereto. Has a drive unit, the terminal voltage detecting section detects that the spike voltage is lost, loss detection motor drive apparatus to detect the position of the rotor from the induced voltage after. The drive unit determines a threshold value during a period in which a spike voltage is generated, and outputs a waveform based on the passage of time determined according to an operation state such as an operation speed when the spike voltage is generated longer than the threshold value. The motor drive device according to 1. 3. The motor driving device according to claim 1, wherein the smoothing unit includes a small-capacitance capacitor and a reactor whose values are determined so as to have a resonance frequency higher than 40 times the frequency of the AC power supply. The motor driving apparatus according to claim 1, wherein the brushless DC motor drives a reciprocating compressor.

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