JP7308389B2 - Motor drive device and refrigerator using the same - Google Patents

Description

The present disclosure relates to a motor drive device for driving a brushless DC motor and a refrigerator using the same.

Conventionally, in this type of motor drive device, the motor is driven by PWM control (pulse width modulation control). In PWM control, by changing the ON width in PWM control, the PWM ON ratio is increased or decreased to control the voltage applied to the motor. Therefore, the smaller the current motor rotation speed, the lower the PWM ON ratio, and the higher the current motor rotation speed, the higher the PWM ON ratio. Also, the lighter the load, the lower the PWM ON ratio, and the heavier the load, the higher the PWM ON ratio.

In particular, when driving a motor that emphasizes efficiency at low loads, field-weakening control is performed to operate in the field-weakening region in order to increase output in the high-load region. overmodulation control is performed to increase the (see Patent Document 1, for example).

PWM control includes asynchronous PWM control and synchronous PWM control. Asynchronous PWM control is a method of operating without synchronization between the drive frequency of the motor and the carrier frequency of PWM. Synchronous PWM control is a method of synchronizing the PWM carrier frequency with an integral multiple of the motor driving frequency.

Synchronous PWM control is used at times of high load, high-speed driving, etc., such as suppression of temperature rise in the inverter circuit (see, for example, Patent Document 2). In addition, as a position detection method in synchronous PWM control, in addition to a sensor such as a resolver or Hall element, a method using an offset of the current value flowing in the motor (for example, see Patent Document 3), and a method of detecting the current value Then, there is a method of estimating using dq coordinate transformation or the like (for example, see Patent Document 4).

FIG. 7 shows a conventional motor driving device described in Patent Document 3. In FIG. As shown in FIG. 7 , the motor drive device has a brushless DC motor 101 and an inverter 102 configured with a plurality of switching elements for driving the brushless DC motor 101 . Further, the motor driving device includes an angle detection unit 103 for detecting the angle of the brushless DC motor 101, a current detection unit 104 for detecting the current flowing through the brushless DC motor 101, the angle of the brushless DC motor detected by the angle detection unit 103, Also, a current offset amount calculation unit 105 that calculates a current offset amount representing a deviation from the target current from the current value detected by the current detection unit 104, a drive signal generation unit 106 that performs PWM control of the brushless DC motor 101, and a current It has a phase signal correction unit 107 that corrects the drive signal generated by the drive signal generation unit 106 from the current offset amount calculated by the offset calculation unit 105 and performs switching of the inverter 102 .

Drive signal generator 106 generates an appropriate drive signal according to the phase angle of brushless DC motor 101 detected by angle detector 103 . A phase signal correction unit 107 corrects the phase angle deviation output from the angle detection unit 103 and drives the inverter 102 . Thereby, a voltage suitable for the phase angle of the brushless DC motor is applied, and the brushless DC motor 101 can be stably driven.

However, the motor drive device disclosed in Patent Document 1 requires a high-performance microcontroller for performing complicated calculations and a high-speed current detection circuit for accurately detecting the current for each carrier. . Therefore, there is a problem that the cost is high.

Further, the motor driving device disclosed in Patent Document 2 requires switching between asynchronous PWM control and driving that synchronizes the motor phase and the rectangular wave output. Therefore, there is a problem that an expensive configuration such as current detection is required.

Further, in Patent Document 3, the phase information of the motor is detected using an angle sensor such as a resolver. Therefore, there is a problem that the cost is high.

Further, Patent Document 4 discloses sensorless control that does not use a sensor. However, there is a problem that a current detector for current detection and a processor for performing advanced calculations are required, resulting in high cost.

JP 2010-288359 A JP 2016-134950 A JP-A-2001-298992 JP 2012-110079 A

The present disclosure provides a motor drive device capable of stably driving the motor at high speed and high load while detecting phase angle information of a brushless DC motor with an inexpensive configuration.

A motor drive device according to the present disclosure includes an inverter that has a switching unit, switches input power by the switching unit and supplies the input power to a brushless DC motor, and a control unit that controls the inverter by PWM control. The control unit is configured to generate a PWM drive signal for driving the switching unit and to switch the switching unit based on the PWM drive signal, and the switching unit has a duty ratio of 100 for PWM control based on the PWM drive signal. % to over 100%.

FIG. 1 is a block diagram of an overall configuration including a motor drive device according to an embodiment of the present disclosure. FIG. 2 is a waveform diagram showing the PWM drive signal and the current and terminal voltage of the brushless DC motor when the ON ratio is 100% or less. FIG. 3 is a waveform diagram showing the PWM drive signal and the current and terminal voltage of the brushless DC motor when the ON ratio exceeds 100%. FIG. 4 is a waveform diagram of a PWM drive signal (when the ON ratio is 100% or less) when changing the switching section in PWM control. FIG. 5 is a waveform diagram of a PWM drive signal (when the ON ratio exceeds 100%) when changing the switching section in PWM control. FIG. 6 is a flow chart for speed control of a brushless DC motor. FIG. 7 is a block diagram showing a conventional motor drive device.

A motor drive device according to an aspect of the present disclosure includes an inverter that has a switching unit, switches input power by the switching unit and supplies the input power to a brushless DC motor, and a control unit that controls the inverter by PWM control. . The control unit is configured to generate a PWM drive signal for driving the switching unit and to switch the switching unit based on the PWM drive signal, and the switching unit has a duty ratio of 100 for PWM control based on the PWM drive signal. % to over 100%.

With such a configuration, the average applied voltage applied to each phase of the brushless DC motor can be increased by increasing the duty ratio of the PWM to more than 100%. Therefore, it is possible to increase the speed and output of the motor with an inexpensive configuration. Therefore, for example, by using a motor that is highly efficient at low speeds, it is possible to increase the speed and output of the motor while saving energy at low speeds.

In the motor drive device according to another aspect of the present disclosure, the carrier period of each carrier in PWM control may be synchronized with the switching interval of the energized phases of the brushless DC motor.

Such an arrangement simplifies the calculations required to detect the rotational position of a brushless DC motor. Therefore, an inexpensive configuration can be realized. Also, the number of switching times for driving the brushless DC motor is reduced. Therefore, switching loss can be reduced. Moreover, power consumption can be effectively reduced by being used in a low-speed region where switching loss is dominant in overall loss.

A motor drive device according to still another aspect of the present disclosure includes a brushless DC motor having a rotor and a stator, and a control unit obtaining rotation position information of the rotor based on an induced voltage of the brushless DC motor. may be configured to obtain

With such a configuration, the switching section can be turned on at the timing when the zero crossing of the induced voltage, which is the reference for each phase of the brushless DC motor, appears, so it is possible to accurately detect the position of the brushless DC motor. becomes. Moreover, since the position can be detected without a sensor, the brushless DC motor can be driven even when a sensor cannot be arranged, such as inside a compressor.

In the motor drive device according to still another aspect of the present disclosure, the switching unit may be turned on based on the PWM drive signal in a range where the duty ratio of PWM control is 50% or more and 150% or less.

With such a configuration, it is possible to reliably detect the position information of the brushless DC motor 5 .

In a motor drive device according to still another aspect of the present disclosure, the switching unit is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and the carrier that is controlled to be ON is controlled to be one before the carrier. It may be configured to be controlled to be on continuously during the interval of the carrier or the next carrier.

With such a configuration, the calculation of the timing for the part where the energization rate exceeds 100% becomes very simple, so that a less expensive microcontroller can be used and the cost can be reduced.

In the motor drive device according to still another aspect of the present disclosure, the switching unit is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and the carrier that is one before the carrier that is controlled to be ON When the switching unit is continuously controlled to be on during the period of and the duty ratio of the PWM control is in a range exceeding 100%, the control unit determines the ON end timing of the switching unit based on the PWM drive signal, It may be configured to delay the switching timing of the energized phase of the brushless DC motor.

Such a configuration increases the time margin from the timing of detecting the rotational position of the brushless DC motor to the switching timing of the energized phase. Therefore, even a less expensive microcontroller with low computational performance can stably drive the brushless DC motor, thus making it possible to reduce costs.

In a motor drive device according to still another aspect of the present disclosure, the switching unit is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and the carrier one after the carrier that is controlled to be ON When the switching unit is controlled to be turned on continuously during the period of and the duty ratio of the PWM control is in a range exceeding 100%, the control unit determines the start timing of turning on the switching unit based on the PWM drive signal, It may be configured to be earlier than the switching timing of the energized phase of the brushless DC motor.

With such a configuration, the time margin from the switching timing of the energized phase of the brushless DC motor to the position detection timing is increased. Therefore, it is possible to widen the range in which changes in the driving speed of the motor due to load fluctuations can be accommodated.

In a motor drive device according to still another aspect of the present disclosure, the brushless DC motor may be a motor that drives the compressor.

With such a configuration, even in a brushless DC motor that drives a compressor, which is a high-temperature closed space, position detection can be performed without a sensor, so the motor drive device can be configured at a low cost.

A refrigerator according to an aspect of the present disclosure includes a refrigeration cycle circuit configured by connecting a compressor having a brushless DC motor, a condenser, a pressure reducer, and an evaporator, and the brushless DC motor drives any of the motors described above. Driven by the device.

With such a configuration, it is possible to effectively reduce power consumption in a refrigerator in which the compressor has a high operating rate at low speed.

Embodiments for carrying out the present disclosure will be described below with reference to the drawings.

(Embodiment)
[1. overall structure]
FIG. 1 is a block diagram of the overall configuration including a motor drive device according to an embodiment of the present invention.

As shown in FIG. 1 , the motor driving device 13 has an inverter 4 and a control section 8 that controls the inverter 4 .

The inverter 4 has switching units 4a to 4f. The inverter switches the input electric power by switching units 4a to 4f and supplies it to the brushless DC motor 5. FIG.

A more detailed description will be given below.

The AC power supply 1 shown in FIG. 1 is a general commercial power supply. For example, in Japan, the power supply has an effective value of 100 V and a frequency of 50 Hz or 60 Hz.

AC power from the AC power supply 1 is input to the rectifier circuit 2 . The rectifier circuit 2 rectifies the input AC power into DC power. The rectifier circuit 2 is composed of four bridge-connected rectifier diodes 2a to 2d.

The smoothing unit 3 is connected to the output side of the rectifier circuit 2 and smoothes the output of the rectifier circuit 2 . The smoothing section 3 is composed of a smoothing capacitor and a reactor. Note that the smoothing unit 3 may be composed only of a smoothing capacitor, as shown in FIG. 1, in order to simplify the circuit configuration.

If a reactor is used, it may be inserted between the AC power supply 1 and the capacitor. Also, the reactors may be inserted before and after the rectifier diodes 2a to 2d, that is, on either the input side or the output side of the rectifier circuit 2. FIG. In addition, when a reactor is used and a common mode filter that constitutes high frequency elimination means is provided in the circuit, the combined component of the reactor and the reactance component of the high frequency elimination means is taken into consideration.

In this embodiment, the inverter 4 converts the DC power from the smoothing unit 3 into AC power. The inverter 4 has six switching elements 4a to 4f, which are switching units, and these switching elements 4a to 4f are connected in a three-phase bridge. In addition, in the present embodiment, the six return current diodes 4g to 4l are connected to the corresponding switching elements 4a to 4f so that the direction of conduction is opposite to that of the corresponding switching elements 4a to 4f. connected in parallel.

The brushless DC motor 5 has a rotor 5a with permanent magnets and a stator 5b with three-phase windings. The three-phase alternating current generated by the inverter 4 flows through the three-phase windings of the stator 5b of the brushless DC motor 5, thereby rotating the rotor 5a. Also, the number of poles of the brushless DC motor 5 is determined according to the required characteristics. The number of poles of the brushless DC motor 5 is four in this embodiment, but is not limited to this and may be other than four.

The control unit 8 includes, for example, a storage unit (not shown) that stores a control program, and an arithmetic processing unit (not shown) that executes the control program. The control unit 8 may be configured by a microcontroller. The control unit 8 controls the inverter 4 by PWM control as described later.

In the present embodiment, the control unit 8 intermittently acquires position information, which is information on the phase angle of rotation of the brushless DC motor 5 .

The position detector 6 detects the magnetic pole position of the rotor 5a as the positional information of the brushless DC motor. In this embodiment, the position detector 6 detects the magnetic pole position of the rotor 5a based on the induced voltage generated in the three-phase windings of the stator 5b. More specifically, the position detector 6 acquires the value of the terminal voltage of the brushless DC motor 5 and thereby detects the relative position of the magnetic poles of the rotor 5a of the brushless DC motor 5 . Note that the position detection unit 6 may be configured to continuously detect the value of the terminal voltage of the brushless DC motor 5, or may be configured to continuously detect the value of the terminal voltage of the brushless DC motor 5. It may be configured to detect the value of the terminal voltage during the period.

In the present embodiment, the position detection unit 6 compares the induced voltage generated in the three-phase winding of the stator 5b with a reference voltage (reference voltage) to detect a zero cross, A relative rotational position of 5a is detected.

Here, the reference voltage to be compared with the zero crossing of the induced voltage may be defined by the virtual midpoint of the terminal voltages for the three phases, or may be defined by a value obtained by dividing the DC bus voltage. Alternatively, the reference voltage may be defined by a value calculated from the obtained voltage value obtained by obtaining the DC bus voltage with a microcontroller. In this embodiment, the value of the virtual midpoint is used as the reference voltage. When the method of detecting the position of the brushless DC motor 5 based on the induced voltage is used as in this embodiment, the configuration is simple because there is no need to use a Hall element or the like. Therefore, it becomes possible to configure the motor drive device at a lower cost.

A speed detector 7 detects the rotational speed of the brushless DC motor 5 . In the present embodiment, the speed detection unit 7 detects the current driving speed (rotational speed) and the average speed (rotational speed) of the past one rotation of the brushless DC motor 5 from the position information detected by the position detection unit 6. to calculate Specifically, the current velocity is calculated by measuring the time of the zero-crossing detection interval of the induced voltage and calculating from this time. Further, the average speed of one past rotation is calculated from the sum of the times of the detection intervals for one rotation of the brushless DC motor 5, which is obtained by recording the time of the zero-cross detection interval of the induced voltage for one rotation. These calculations are performed each time the position detector 6 detects a zero crossing of the induced voltage.

The PWM generation unit 10 sets an energization rate (on rate) in PWM control and generates a PWM signal. Here, the ON ratio in PWM control is the ratio of the ON period in the carrier cycle of one carrier. A PWM signal is a square wave having carrier period and on-ratio information.

In this embodiment, each time the position detector 6 detects a zero crossing of the induced voltage, the PWM generator 10 generates the average speed of one rotation detected by the speed detector 7 and the externally input target speed. compare. Then, when the target speed is higher than the average speed for one rotation, the PWM generator 10 sets the ON ratio of PWM control so as to increase the voltage applied to the brushless DC motor 5 . On the other hand, when the target speed is slower than the average speed of one rotation, the PWM generator 10 sets the ON ratio of PWM control so as to lower the voltage applied to the brushless DC motor 5 . Further, when the target speed and the average speed for one rotation match, the PWM generator 10 sets the ON ratio of PWM control so as to maintain the voltage applied to the brushless DC motor 5 . Thereby, the average speed of one rotation of the brushless DC motor 5 is controlled. The details of motor speed control will be described later.

Further, the PWM generator 10 generates a waveform (motor drive waveform) for generating a rotating magnetic field for driving the brushless DC motor 5 . In this embodiment, the motor drive waveform is a rectangular wave. This simplifies the calculations required to detect the rotational position of the brushless DC motor 5, and the motor drive device 13 can be constructed at a low cost.

In the present embodiment, the motor drive waveform is a rectangular waveform with an electrical angle of 120 degrees (hereinafter referred to as an electrical angle unless otherwise specified).

The PWM generation unit 10 calculates the energization switching timing from the position detection timing detected by the position detection unit 6 and the current drive speed calculated by the speed detection unit 7 . Then, a motor drive waveform is generated so as to switch the energized phases between the phases.

In this embodiment, the brushless DC motor 5 is a three-phase motor, so the combination of energized phases changes every 60 degrees. In the energization period of one phase, energization of 120 electrical degrees and subsequent 60 degrees off are basically repeated.

The switching elements 4a, 4c, and 4e are sequentially energized so that they are shifted by 120 electrical degrees. Similarly, the switching elements 4b, 4d, and 4f are sequentially energized so that they are shifted by an electrical angle of 120 degrees. In addition, the switching element 4a and the switching element 4b are energized with an electrical angle difference of 180 degrees. Similarly, the switching elements 4c and 4d start energizing with an electrical angle difference of 180 degrees, and the switching elements 4e and 4f start energizing with an electrical angle difference of 180 degrees. A rotating magnetic field is formed by this, and the rotor 5a of the brushless DC motor 5 rotates.

However, the PWM drive signal output by the PWM generator 10 is obtained by superimposing a PWM signal for speed control on a rectangular wave (motor drive waveform) for generating a rotating magnetic field. Therefore, the actual energization section does not coincide with 120 degrees. Further, the PWM signal is superimposed only on either the first half 60 degrees or the latter half 60 degrees of the 120 degrees of the rectangular wave.

When the switching elements 4a to 4f are turned off by PWM control, the current flowing through each of the switching elements 4a to 4f is routed to the smoothing section 3 or the windings of the stator 5b of the brushless DC motor 5. Similarly, it flows through the return path between each of the return current diodes 4g to 4l of the inverter 4. As shown in FIG. Therefore, the current waveform and terminal voltage waveform of each phase of the brushless DC motor 5 exhibit stable waveforms. Therefore, the performance of position detection by the position detection unit 6 can be made more stable.

Also, the PWM generator 10 calculates the frequency (carrier frequency) of the PWM signal. A carrier frequency is calculated from the current drive speed of the brushless DC motor 5 .

Then, the PWM generator 10 generates the PWM drive signal by synthesizing the motor drive waveform and the PWM signal as described above. Note that the PWM drive signal may be a rectangular wave.

In this embodiment, the start timing of the PWM cycle (carrier cycle) is synchronized with the switching timing of the energized phases of the brushless DC motor 5 . That is, the carrier cycle of each carrier in PWM control is synchronized with the switching interval of the energized phases of the brushless DC motor. In the present embodiment, each carrier section of continuous carriers is synchronized with a section every 60 electrical degrees with reference to the electrical angle of 0 degrees when the brushless DC motor 5 is driven. That is, the PWM period is the reciprocal of the product (frequency) of the speed of the brushless DC motor 5, the number of poles, and the number of phases. In this embodiment, the brushless DC motor 5 is a 3-phase, 4-pole motor, so the carrier period is the reciprocal of 12 times the speed.

Further, the PWM output to the switching section 4a is turned on at least until the position detecting section 6 first detects the induced voltage zero crossing. That is, the switching unit 4a is turned on for each predetermined number of carriers based on the PWM drive signal, and the switching unit 4a is controlled to be turned on from the start of the predetermined carrier to at least the time when the position information is first acquired. is turned on for a period of Similarly, each of the switching units 4b to 4f is turned on for each predetermined number of carriers based on the PWM drive signal, and the switching unit is turned on at least at the first position from the start of the predetermined carrier. It is turned on until the time when the information is obtained. This makes it possible to reliably detect the position information of the brushless DC motor 5 .

In this embodiment, the lower limit of the ON ratio of PWM is set to 50%. This makes it possible to reliably detect the position information of the brushless DC motor 5 .

Generally, in PWM control, motor control is performed in a range where the ON ratio of PWM is 100% or less. However, in the present embodiment, motor control is performed in a range from 100% or less to over 100% of the ON ratio of PWM. In this embodiment, the upper limit of the ON ratio is set to 150%. Further, in the present embodiment, the lower limit of the ON ratio is set to 50% as described above.

When the PWM signal is superimposed on the first half 60 degrees of the rectangular wave of 120 degrees of the motor drive waveform, the energization of the portion exceeding 100% of the ON ratio is started before the energization start timing of the first half 60 degrees, The remaining 100% of the ON ratio is energized in the first half 60 degrees section. Further, when the PWM signal is superimposed on the latter half of 60 degrees of the rectangular wave of 120 degrees of the motor drive waveform, 100% of the ON ratio is energized in the latter half 60 degrees section, and after the energization is completed, the ON ratio 100% of the current is energized.

The drive unit 12 turns on or off (hereinafter referred to as on/off) the switching elements 4a to 4f of the inverter 4 based on the PWM drive signal. More specifically, the drive section 12 generates a drive signal based on the PWM drive signal generated by the PWM generation section 10, and inputs the drive signal to the control terminals of the switching elements 4a to 4f.

Motor drive device 13 may include rectifier circuit 2 and smoothing section 3 in addition to inverter 4 . Then, the motor driving device 13 may be connected to the AC power supply 1 . Further, the motor drive device 13 may be configured including the position detection section 6 , the speed detection section 7 , the PWM generation section 10 , and the drive section 12 as the control section 8 . The motor drive device 13 configured in this manner drives the brushless DC motor 5 .

In the example shown in FIG. 1 , brushless DC motor 5 drives compressor 20 provided in refrigerator 30 .

As the compressor 20, any compression system (mechanism) such as rotary type or scroll type is used. For example, in this embodiment, the compressor 20 is of a reciprocating type.

A crankshaft (not shown) connected to the rotor 5a of the brushless DC motor 5 converts the rotary motion of the rotor 5a into reciprocating motion. A piston (not shown), which is a compression element connected to the crankshaft, reciprocates within a cylinder (not shown). This compresses the refrigerant in the cylinder.

Note that the reciprocating compressor has little leakage of refrigerant during compression, and has high efficiency especially at low speed. On the other hand, in the reciprocating compressor, load torque pulsation generated during compression is large, and speed pulsation of the brushless DC motor 5 in the compressor 20 is generated particularly at low speed.

The refrigerant compressed by the compressor 20 passes through the condenser 21, the pressure reducer 22, and the evaporator 23 in order, and returns to the compressor 20 again. A refrigerant, which is a medium constituting a refrigerating cycle, radiates heat in the condenser 21 and absorbs heat in the evaporator 23 . Therefore, cooling and heating can be performed by heat exchange with the refrigerant.

The refrigerator 30 has a refrigeration cycle circuit composed of a compressor 20, a condenser 21, a pressure reducer 22, and an evaporator 23, and the air cooled by the evaporator 23 is sent to the refrigerator compartment and the freezer compartment to cool the housing. Cools the inside of the body.

[2. Motor drive device]
Next, the motor driving device 13 will be described in detail with reference to the drawings.

First, using FIG. 2, changes in the PWM drive signal, the current between the brushless DC motor 5 and the switching element 4a of the inverter 4, and the terminal voltage when the duty ratio in the PWM control is 100% or less. will be explained.

FIG. 2(a) shows a drive signal from the drive section 12 that is input to the switching element 4a, FIG. 2(b) shows a drive signal from the drive section 12 that is input to the switching element 4b, and FIG. c) shows the drive signal from the drive section 12 input to the switching element 4c. Further, (d) in FIG. 2 is a drive signal from the drive section 12 input to the switching element 4d, and (e) in FIG. 2 is a drive signal from the drive section 12 to be input to the switching element 4e. (f) indicates the drive signal from the drive unit 12 input to the switching element 4f. Further, (g) of FIG. 2 shows the current flowing between the switching element 4a and the brushless DC motor 5. As shown in FIG. (h) in FIG. 2 represents the terminal voltage between the switching element 4 a and the brushless DC motor 5 . As for the direction of the current in FIG. 2(g), the direction from the switching element 4a to the brushless DC motor 5 is positive.

On the horizontal axis of FIG. 2, sections from T1 to T2, from T2 to T3, from T3 to T4, from T4 to T5, from T5 to T6, and from T6 to T7 each represent a carrier period of one carrier in PWM control. At least one of the three phases is switched in each of these intervals.

Specifically, in the section from T1 to T2, the switching element 4b is switching. Similarly, the switching element 4e performs switching in the section from T2 to T3, and the switching element 4d performs switching in the section from T3 to T4. The switching element 4a performs switching in the section from T4 to T5, the switching element 4f performs switching in the section from T5 to T6, and the switching element 4c performs switching in the section from T6 to T7. ing.

Each of the switching elements 4a to 4f is turned on in the first half and turned off in the second half of a predetermined carrier period (carrier cycle) for switching. For example, the predetermined carrier for the switching element 4a is a carrier corresponding to the section from T4 to T5. Similarly, predetermined carriers for each of the switching elements 4b to 4f are carriers corresponding to sections T1 to T2, T6 to T7, T3 to T4, T2 to T3, and T5 to T6, respectively. Each of the switching elements 4a to 4f may be driven by high active. Then, it is continuously turned on in the section of the carrier next to the predetermined carrier that has been switched. That is, in the section of the next carrier, the switching elements 4a to 4f are non-PWM controlled, and are turned on and energized for one carrier period in the PWM control. As a result, when the switching elements 4a to 4f are off, the motor current circulates, and the balance between the on-time and off-time currents is improved, and efficient motor drive control is performed.

Six carrier cycles from T1 to T7 correspond to one electrical angle cycle of the brushless DC motor 5 . Of the switching elements 4a to 4f, the switching elements 4a, 4c, and 4e, which are the upper switching elements of the inverter 4, are switched based on waveforms shifted by 120 electrical degrees from each other. Likewise, each of the switching elements 4b, 4d, and 4f on the lower side of the inverter 4 is similarly switched based on waveforms shifted from each other by an electrical angle of 120 degrees. Thereby, a rotating magnetic field is generated, and the brushless DC motor 5 can be rotated. Further, since the brushless DC motor 5 of the present embodiment has three phases and four poles, two electrical angle cycles correspond to one rotation of the brushless DC motor 5 . By repeating the energization pattern in one cycle of the electrical angle, the brushless DC motor 5 is continuously rotated.

In the present embodiment, in the interval from T4 to T5, the switching element 4a is turned on during the period from T4 to T8. At this time, as shown in FIG. 2(g), the current monotonically increases during the period from T4 to T8. During the period from T8 to T5, the switching element 4a is turned off and the current monotonously decreases.

In the section from T5 to T6, the switching element 4a is continuously turned on for the entire period of one PWM cycle, but the current increases and decreases because the switching element 4f is switching.

Further, since the switching element 4a is turned off during the period from T6 to T7, the current converges to 0 during the period from T6 to T9, as shown in FIG. 2(g). Until the current becomes 0 (period from T6 to T9), the current shown in (g) of FIG. 2 flows to the brushless DC motor 5 through the return current diode 4h. Therefore, the potential difference between the terminal voltage between the switching element 4a and the brushless DC motor 5 shown in (h) of FIG. 2 and the ground is only the potential difference of the return current diode 4h. Therefore, the terminal voltage stays close to 0 V, and no induced voltage appears in the terminal voltage.

In the interval from T6 to T7, the current flowing from the switching element 4a to the brushless DC motor 5 is 0 during the period from T9 to T10, as shown in FIG. 2(g). Also, as shown in (h) of FIG. 2, the switching element 4c and the switching element 4f are on, but the terminal voltage is not connected. Therefore, the intersection (T10) between the midpoint of the voltage between the DC bus lines of the inverter 4 (one-dot chain line shown in (h) of FIG. 2) and the induced voltage is detected as the induced voltage zero cross.

In the present embodiment, during the period from T9 to T10, the switching element 4c is turned on by PWM control until at least the induced voltage zero cross is detected. Then, the ON width in the PWM control is increased or decreased according to the difference between the target speed of the brushless DC motor 5 and the average speed of one rotation. This makes it possible to reliably perform position detection.

In FIG. 2, at T10, the switching element 4c is turned off by PWM control simultaneously with the zero crossing of the induced voltage. In this case, the ON ratio of PWM control is 50%. In this embodiment, since the neutral point is used as the reference voltage, the ON ratio is 50%. By changing it, the ON ratio of PWM control can be lowered below 50%.

Next, referring to FIG. 3, changes in the PWM drive signal, the current between the brushless DC motor 5 and the switching element 4a of the inverter 4, and the terminal voltage when the duty ratio in the PWM control exceeds 100%. explain.

(a) to (f) of FIG. 3 respectively show drive signals from the drive section 12 that are input to the switching elements 4a to 4f of the inverter 4, similarly to FIG. Also, (g) and (h) of FIG. 3 represent the phase current and voltage of the brushless DC motor 5, respectively, similarly to FIG. As for the direction of the current, the direction from the switching element 4a to the brushless DC motor 5 is assumed to be positive, as in FIG.

On the horizontal axis of FIG. 3, sections from T101 to T102, from T102 to T103, from T103 to T104, from T104 to T105, from T105 to T106, and from T106 to T107 each represent a carrier cycle of one carrier in PWM control. In each of these intervals, two of the three phases of the brushless DC motor 5 are superimposed rectangular waves of PWM signals. The remaining one phase outputs a non-PWM controlled waveform on which no PWM signal is superimposed.

In FIG. 3, the first half 60 degrees of the 120 degrees of the rectangular wave is a waveform by PWM control, that is, a waveform in which a PWM signal is superimposed on a motor driving waveform. Specifically, in the section from T103 to T104, (a) and (d) of FIG. 3 are waveforms by PWM control, and (e) of FIG. 3 is an output by non-PWM control.

In FIG. 3, since the energization rate (ON ratio) of PWM control exceeds 100%, the ON output period in PWM control is longer than one carrier period of PWM. Specifically, in the interval from T103 to T104, (d) in FIG. 3 is the phase for which ON is output in PWM control even when the duty ratio of PWM is less than 100%. A portion of the on-ratio exceeding 100% is normally turned on in a section that is not turned on when the on-ratio is 100% or less. Specifically, in the section from T102 to T103, which is the carrier section immediately before T103 to T104, the on ratio is turned on corresponding to the portion exceeding 100%.

Similarly, from T101 to T102 (e) of FIG. 3, from T102 to T103 (d) of FIG. 3, from T103 to T104 (a) of FIG. 3, from T104 to T105 (f) of FIG. FIG. 3(c) and T106 to T107 in FIG. 3(b) respectively output ON corresponding to the portion exceeding 100% of the ON ratio of 100% or more.

In the 120-degree energization, the first half of 60 degrees is a waveform by PWM control, and the latter half of 60 degrees is a waveform by non-PWM control. Therefore, in the carrier section preceding the first half 60-degree section, which is a section that is continuous with the first half 60-degree section controlled by PWM control and that is not turned on when the on-ratio is 100% or less, the on-ratio An ON portion corresponding to a portion exceeding 100% of the output is output. This makes it possible to easily perform PWM control even when the ON ratio exceeds 100%.

In the case shown in FIG. 3, each of the switching units (4a to 4f) is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and the carrier one after the carrier to be controlled to be ON. It is controlled to be ON continuously during the interval (non-PWM control). The timing to start turning on the switching units (4a to 4f) based on the PWM drive signal is set earlier than the switching timing of the energized phases of the brushless DC motor 5. FIG.

When the on-ratio exceeds 100%, the controllable on-ratio range of the brushless DC motor 5 is as follows. First, the possible timing for turning on the switching unit is after the occurrence of the induced voltage zero cross appearing in the terminal voltage of the brushless DC motor 5 by the position detection unit 6 . Therefore, the range of the excess portion when the ON ratio exceeds 100% is up to 50%, which corresponds to 30 degrees, which is half of 60 degrees. That is, the maximum value of the on-ratio range is 150%.

Thus, in this embodiment, switching is performed once per position detection, and the switching loss is extremely small. Therefore, it is possible to increase the detection accuracy of the magnetic pole position of the brushless DC motor 5, reduce the loss, and perform the drive at an arbitrary speed according to the load.

Further, after the position detection is performed, based on the result of the position detection, the off start timing in the current PWM carrier section is determined, and the on timing in the next PWM carrier is determined. Therefore, control with high speed responsiveness can be performed.

Next, the difference in switching intervals when the ON ratio of PWM control is 100% or less will be described with reference to FIGS. 2 and 4. FIG.

FIG. 4 is a waveform diagram of a PWM drive signal (when the ON ratio is 100% or less) when changing the switching section in PWM control. Similar to FIG. 2, (a) to (f) of FIG. 4 show drive signals for the switching elements 4a to 4f, respectively. 4(g) shows the current flowing from the switching element 4a to the brushless DC motor 5, and FIG. 4(h) shows the terminal voltage between the switching element 4a and the brushless DC motor 5. .

As described above, in FIG. 2, the switching element 4a switches in the first half 60-degree section (T4 to T5) of the 120-degree conduction section, and switches to 100 degrees in the latter half 60-degree section (T5 to T6). % energized. On the other hand, in FIG. 4, the switching element 4a is turned on by non-PWM control in the first 60-degree section (T204 to T205) of the 120-degree conduction section, and is switched in the latter 60-degree section (T205 to T206). be. That is, in the 60-degree switching section (T205 to T206), like T4 to T8 in FIG.

In this manner, in the 120-degree section from T204 to T206, the switching is turned on and off once each, so the switching loss of the inverter 4 is further reduced.

Also, the terminal voltage shown in (h) of FIG. 2 and the terminal voltage shown in (h) of FIG. 4 are different. However, in the interval from T9 to T10 in FIG. 2 and the interval from T209 to T210 in FIG. 4, which are both intervals for position detection, the waveforms of the terminal voltages are similar to each other. Therefore, even in the case shown in FIG. 4, position detection can be performed accurately as in the case shown in FIG. As for the current, the waveform shown in (g) of FIG. 2 and the waveform shown in (g) of FIG. 4 are almost the same waveform, and the same torque as in the case shown in FIG. 2 can be obtained. can.

Next, the difference in the intervals in which PWM control is performed when the ON ratio of PWM control exceeds 100% will be described with reference to FIGS. 3 and 5. FIG.

FIG. 5 is a waveform diagram of a PWM drive signal (when the ON ratio exceeds 100%) when changing the switching section in PWM control.

In FIG. 5, the switching element 4a is energized with a rectangular wave in a 120-degree section corresponding to T304 to T306, as shown in FIG. 5(a). In the case shown in FIG. 5, the section in which PWM control is performed is the latter half of 60 degrees out of 120 degrees. Therefore, the section from T305 to T306 is a section in which PWM control is performed. Further, in the case shown in FIG. 5, the ON ratio of PWM control exceeds 100%. Therefore, the interval from T306 to T307, which is the interval following the interval from T305 to T306 where the PWM control is performed and which is off when the ON ratio is 100% or less, is the interval from T306 to T307. , an ON portion corresponding to a portion exceeding 100% of the ON ratio is output.

In other words, in the case shown in FIG. 5, each of the switching units (4a to 4f) is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and is controlled to be ON one before the carrier. is continuously controlled to be ON (non-PWM control) during the carrier section of . The ON end timing of the switching units (4a to 4f) based on the PWM drive signal is set earlier than the switching timing of the energized phases of the brushless DC motor 5. FIG.

Also, regarding the terminal voltages shown in (h) of FIG. 3 and (h) of FIG. , the case shown in FIG. 3(h) is more advanced.

As shown in FIG. 3, when the PWM control is performed in the first half 60 degrees of the 120-degree energization, the advance of the terminal voltage increases. Therefore, it is possible to ensure a wide range in which the position detection unit 6 can detect the position without changing the start timing of 120 degrees. Therefore, the magnetic pole position of the rotor 5a of the brushless DC motor 5 can be stably detected by simple control.

On the other hand, as shown in FIG. 5, when PWM control is performed in the latter half of 60 degrees of the 120-degree energization, the energization time is extended on the delayed side. For this reason, there is a margin of time until the energized phase is actually switched after the reference induced voltage zero cross is detected by the position detector 6 . Therefore, even if a microcontroller with low performance is used, appropriate control can be performed. Further, when the interval in which position detection can be performed by the position detection unit 6 becomes narrow, the position detection can be stably performed by advancing the start timing of 120 degrees by an electrical angle.

[3. Motor speed control]
Next, the speed control of the brushless DC motor 5 by PWM control will be described in detail with reference to FIG.

FIG. 6 is a flow chart for speed control of a brushless DC motor.

First, it is determined whether or not the induced voltage zero cross, which is the reference of the magnetic pole position of the brushless DC motor 5, has been detected (STEP 101). As a result of the determination, if the induced voltage zero cross is not detected, the process proceeds to STEP101 again, and the determination is performed again (STEP101, No). For example, the position detector 6 detects the induced voltage zero crossing, and the speed detector 7 makes the determination.

On the other hand, if the induced voltage zero cross is detected, the process proceeds to STEP 102 (STEP 101, Yes).

Next, the current driving speed of the brushless DC motor 5 is calculated from the detection interval of the induced voltage zero cross (STEP 102). Since the brushless DC motor 5 is a 3-phase 4-pole motor, the induced voltage zero cross occurs 12 times during one rotation of the motor. That is, the control unit 8 intermittently acquires the position information of the brushless DC motor 5 . By dividing 1 second by 12 times the zero-cross position detection interval, the current drive speed, which is the number of rotations of the brushless DC motor 5 per second, can be calculated. At this time, the average speed for one rotation is also calculated. The average speed for one rotation can be calculated by summing up 12 position detection intervals, which are the number of position detections during one rotation, and taking the reciprocal. Dividing 1 second by the total location interval gives the average speed of one revolution per second. For example, in this embodiment, the speed detector 7 calculates the current drive speed of the brushless DC motor 5 . After the calculation is completed, the process proceeds to STEP103.

Next, it is determined whether or not the average speed for one rotation calculated in STEP 102 is faster than the target speed input from the outside (STEP 103). The target speed is input from the outside, and is determined by the temperature inside the refrigerator 30 in the refrigerator 30, for example. In particular, the target speed is set high when the inside of the refrigerator 30 is not cooled, such as when the refrigerator 30 is powered on. Then, if the internal temperature of the refrigerator 30 is higher than the target temperature determined in advance as the temperature suitable for food storage (STPE 103, No), a high target speed is set to improve the cooling capacity. On the other hand, if the internal temperature of the refrigerator 30 is lower than the target temperature (STPE 103, Yes), a low target speed is set to reduce the cooling capacity. If the current average speed of one rotation is faster than the target speed (STEP103, Yes), the process proceeds to STEP104.

In STEP 104, the ON ratio of PWM control generated by the PWM generator 10 is excessive, so the ON ratio of PWM control is decreased (STEP 104). The amount of decrease in the ON ratio may be uniform, or may be determined by calculation from the difference from the target speed. In the present embodiment, the reduction amount of the ON ratio is uniformly set to 1% for simpler control. That is, if the on-ratio of PWM control before the reduction is 111%, the on-ratio after the reduction is 110%, which is 111% minus 1%. Then, the process proceeds to STEP105.

In STEP105, the start timing of the 120-degree rectangular wave is calculated from the current driving speed calculated in STEP102. Since the brushless DC motor 5 is a three-phase motor, the 120-degree energization start timing occurs every 60 degrees, and occurs six times in one cycle of the electrical angle. In addition, since the brushless DC motor 5 has four poles, one rotation of the mechanical angle generates 12 energization start timings of 120 degrees, which is twice the number of times in one cycle of the electrical angle.

For example, assume that the current drive speed calculated in STEP 102 is 20 Hz. In this case, the period of one rotation in mechanical angle is 50 ms. Dividing this by the number of occurrences of the 120-degree start timing during one rotation of the mechanical angle (12 times, which is the number of times of position detection during one rotation) gives 12.5/3 ms. That is, if the current driving speed is 20 Hz, the period of the next PWM carrier interval is 12.5/3 ms. Therefore, the energization phase is adjusted so that the timing from the end of the PWM cycle in the current carrier section to the start timing of 120 degrees of the next rectangular wave corresponding to 60 degrees in electrical angle is 12.5/3 ms. Switching timing is calculated. Then, the process proceeds to STEP106.

In STEP 106, it is determined whether or not the ON ratio in PWM control exceeds 100%. For example, when the current ON ratio of PWM is 110%, the ON ratio exceeds 100% (STEP106, Yes), so the process proceeds to STEP107.

In STEP 107, the portion of the ON ratio in PWM control that exceeds 100% is converted into time. As a method of converting the on-ratio to time, the ratio of the portion exceeding 100% of the on-ratio in PWM control during the time corresponding to 60 degrees in electrical angle at the current drive speed calculated in STEP 105 can be calculated by multiplying Here, the ON ratio of PWM control is 110%, and 10% is a portion exceeding 100%. Therefore, 1.25/3 ms is stored as the excess time for 12.5/3 ms, which is the period of the carrier interval corresponding to the next 60 degrees calculated in STEP105. Then, the process proceeds to STEP108.

If the ON ratio in PWM control is 110%, it exceeds 100%, so the excess time is calculated in STEP 107 as described above. Then, in STEP 108, the phase to be energized in the section corresponding to the next 60 degrees starts energization earlier than the end timing of the current PWM cycle corresponding to 60 degrees by the calculated excess time. , the energization start timing is calculated and set. Then, the process proceeds to STEP109.

In STEP 109, the end timing of the current energized phase is set. When the on-ratio is 110%, the on-ratio excluding the excess over 100% is 100%. Therefore, the energization of the phase whose energization ends in the section corresponding to the next 60 degrees continues until the timing when the carrier period of the PWM control ends. That is, when the ON ratio in PWM control exceeds 100%, there is a period during which the three phases are energized simultaneously. Then the process ends.

On the other hand, for example, if the average speed for one rotation calculated in STEP 102 is 20 Hz and the target speed input from the outside is 25 Hz, the average speed for one rotation is less than or equal to the target speed (STEP 103, No). , to STEP110.

Also, in this case, since the average speed for one rotation is lower than the target speed (STEP110, Yes), the process proceeds to STEP111.

In STEP 111, since the average speed for one rotation is insufficient, the ON ratio of PWM control is increased to increase the speed. In this embodiment, the amount of increase in the ON ratio of PWM control is set to a fixed value of 1%, as in STEP 104 . That is, for example, when the ON ratio of PWM control is 79%, the ON ratio is increased by 1%, and 80% after the increase is stored as a new PWM ON ratio. Then, the process proceeds to STEP105.

In STEP 105, a time corresponding to an electrical angle of 60 degrees, that is, a PWM cycle, is calculated, which corresponds to a section from the next 120-degree switching timing to the next 120-degree switching timing. For example, if the current drive speed is 20 Hz, the timing 12.5/3 ms after the next 120-degree switching timing is calculated as the next 120-degree switching timing. Then, the process proceeds to STEP106.

In STEP 106, it is determined whether or not the PWM ON ratio exceeds 100%. Here, since the current ON ratio of PWM control is 80%, ie, 100% or less (STEP 106, No), the process proceeds to STEP 112.

In STEP112, the ON ratio of PWM control is 80%, and there is no portion exceeding 100%, so 0 is stored as the overtime, and the process proceeds to STEP108.

In STEP 108, the excess time is 0, so a value is set so that the switching timing of 120 degrees is the same as the energization start timing of the phase to be energized next, and the process proceeds to STEP 109.

Here, since the on-ratio of PWM control is 80%, energization of a phase whose energization ends due to energization switching of 120 degrees ends when a time corresponding to 80% of the PWM cycle has elapsed. Further, the carrier period of PWM control coincides with the time corresponding to 60 degrees, which is the switching interval of energization of 120 degrees. Therefore, in STEP 109, in the next 60-degree section, energization is terminated when 10/3 ms, which corresponds to 80% of the 12.5/3 ms calculated in STEP 105, has elapsed. Timing is set. Then the process ends.

On the other hand, in STEP110, when the average speed of one rotation is 20 Hz and the target speed is 20 Hz (STEP110, No), the process proceeds to STEP105. The processes from STEP 105 to STEP 109 are the same as those described above. Then the process ends.

By repeating these processes, the PWM generator 10 can accelerate the brushless DC motor 5 when the speed of one rotation is insufficient for the target speed and acceleration is required. Further, when the speed of one rotation of the brushless DC motor 5 is excessive with respect to the target speed and deceleration is necessary, deceleration can be performed. Also, if the speed of one rotation of the brushless DC motor 5 matches the target speed, the average speed of one rotation can be maintained.

Further, the PWM generator 10 switches the energized phase every 60 electrical degrees. Thereby, a rotating magnetic field for rotating the brushless DC motor 5 is generated.

It should be noted that before the processing of the flow shown in FIG. 6 is performed, a pattern (motor drive waveform) for switching the energized phases is generated. Then, how much voltage is applied to each energized phase and at what timing the energized phase is switched is determined according to the flow of FIG.

Further, even when the on-ratio of PWM control exceeds 100%, speed control can be performed in the same manner as when the on-ratio is 100% or less. Therefore, the brushless DC motor 5 can be stably controlled even in high-speed or high-load regions where the ON ratio is greater than 100%.

[4. Compressor]
Next, a case where the motor driving device 13 is applied to the compressor 20 will be described.

In the compressor 20, the brushless DC motor 5 is placed in a high-temperature atmosphere, a refrigerant atmosphere, and an oil atmosphere. Therefore, attaching a position sensor to the brushless DC motor 5 is extremely difficult. Therefore, in many cases, a sensorless technology that can detect the magnetic pole position for motor driving without using a sensor is essential.

Here, the motor driving device 13 detects the magnetic pole position of the rotor 5a of the brushless DC motor 5 housed inside the compressor 20 by means of the induced voltage of the brushless DC motor 5 that can be detected outside the compressor 20. , can be obtained. Specifically, in the present embodiment, the position detector 6 detects the magnetic pole position of the rotor 5a.

Further, the switching section is turned on by PWM control at least until the position detection section 6 detects the induced voltage zero cross. As a result, the position detector 6 can reliably detect the induced voltage zero crossing. Therefore, even without a sensor, the brushless DC motor 5 can be driven with high accuracy.

Further, in this embodiment, the compressor 20 employs a reciprocating compression system. Therefore, it is very efficient in a system such as a refrigerator that is driven at low speed for a long time. However, in the reciprocating compression system, since the compression process and the intake process are performed separately, a large torque pulsation occurs periodically. Therefore, when the responsiveness of the control is poor, the energization of the stator 5b and the position of the rotor 5a deviate, resulting in deterioration of efficiency. Therefore, in the motor driving device 13 of the present embodiment, the current driving speed of the brushless DC motor 5 is detected in order to improve control responsiveness. Specifically, the speed detection unit 7 detects the current drive speed based on the induced voltage zero-cross detection interval for each induced voltage zero-crossing detected by the position detection unit 6, as shown in FIG. By changing the on-time and carrier frequency of the PWM control by the PWM generator 10, it is possible to instantaneously respond to periodic changes in torque and changes in speed.

[5. refrigerator]
Next, refrigerator 30 using compressor 20 described above will be described. As shown in FIG. 1 , compressor 20 of refrigerator 30 is driven by motor drive device 13 .

The required load of the refrigerator 30 fluctuates greatly depending on the load inside the refrigerator, the outside air temperature, and the like. Among the operating states of the refrigerator 30, the operating state in which the load in the refrigerator, such as food, is sufficiently cooled takes up the largest proportion of time. In such an operating state, the compression load of the compressor 20 is reduced, and the brushless DC motor 5 is operated at low speed and low load. As the speed and load decrease, the conduction loss of the inverter 4 decreases, and the ratio of the switching loss to the total loss of the inverter 4 increases.

In this embodiment, the magnetic pole position of the brushless DC motor 5 is detected with high accuracy, and the brushless DC motor 5 is driven with a period in which the energized phase of the brushless DC motor 5 is switched as one carrier. Therefore, the brushless DC motor 5 can be driven with a very small number of switching times. Therefore, the energy saving performance of the refrigerator 30 to which the motor drive device 13 is applied can be greatly improved particularly in the low speed or low load region where the ratio of the switching loss of the inverter 4 is large.

Although FIG. 1 shows an example in which motor drive device 13 is provided separately from refrigerator 30 , motor drive device 13 may be provided integrally with refrigerator 30 .

As described above, in the present embodiment, the motor drive device 13 includes the control unit 8 that generates a waveform for PWM-controlling the brushless DC motor 5, and the PWM on-rate increases from 100% or less to 100%. The brushless DC motor 5 is controlled within the range exceeding. As a result, it becomes possible to increase the average applied voltage applied to each phase of the brushless DC motor by increasing the on-rate of the PWM control to more than 100%. Therefore, by selecting a low-speed, high-efficiency motor, it is possible to achieve high-speed and high-output using an inexpensive drive method while saving energy at low speed.

Also, in the control unit 8, the waveform generated by the PWM generation unit 10 may be a rectangular wave. Then, the period of PWM and the switching interval of the energized phases of the brushless DC motor 5 may be synchronized.

This simplifies the calculations required to detect the magnetic pole position of the brushless DC motor 5, enabling an inexpensive configuration.

In addition, since the number of times of switching for driving the brushless DC motor 5 is small, power consumption can be reduced particularly in a low speed range where switching loss is dominant.

The brushless DC motor 5 may have a rotor 5a and a stator 5b, and the controller 8 may have a position detector that detects the position of the rotor 5a from the induced voltage of the brushless DC motor 5. FIG. As a result, the switching can be kept on by PWM control at the timing at which the zero cross of the induced voltage, which is the reference of each phase of the brushless DC motor 5, appears, and the position of the brushless DC motor 5 can be detected with high accuracy. .

In addition, since position detection is performed without a sensor, the brushless DC motor can be driven even in a high-temperature closed space where a sensor cannot be placed.

Further, the PWM generator 10 outputs a waveform so that the non-PWM output section is followed by the PWM output section, and the energization end timing by the PWM control is not synchronized with the switching timing of the energization phase of the brushless DC motor 5. good too. This increases the time margin from the timing of detecting the position of the rotor 5a of the brushless DC motor 5 to the timing of switching the energized phase, and enables stable driving even with a less expensive microcontroller with low computational performance. Become.

In addition, the PWM generation unit 10 outputs a waveform so that a non-PWM output section follows a PWM output section, and the energization start timing by PWM control is not synchronized with the switching timing of the energization phase of the brushless DC motor 5. good too. As a result, the time margin from the switching timing of the energized phase of the brushless DC motor 5 to the detection timing of the rotor 5a position is increased, and the range that can cope with the change in the driving speed of the motor due to the load fluctuation or the like can be expanded. .

Also, the load driven by the brushless DC motor 5 may be the compression element of the compressor 20 . As a result, the position can be detected without a sensor even in the inside of the compressor, which is a high-temperature sealed space, so that the motor driving device 13 and the compressor can be constructed at low cost.

It also has a refrigeration cycle in which a compressor 20, a condenser 21, a pressure reducer 22, an evaporator 23, and the compressor 20 are connected in this order, and a brushless DC motor 5 incorporated in the compressor 20 is driven by a motor drive device 13. By using the refrigerator 30, the power consumption of a refrigerator having a high operation rate at low speed can be reduced, and the power consumption of the refrigerator can be reduced inexpensively.

The motor drive device of the present disclosure can reduce the loss of the inverter circuit especially during low speed operation. Therefore, it can be applied not only to refrigerators but also to motors that drive compressors in air conditioners, vending machines, showcases, heat pump water heaters, and the like.

1 AC power supply 2 Rectifier circuit 3 Smoothing unit 4 Inverter 5 Brushless DC motor 6 Position detection unit 7 Speed detection unit 8 Control unit 10 PWM generation unit 12 Drive unit 13 Motor drive device 20 Compressor 21 Condenser 22 Pressure reducer 23 Evaporator 30 refrigerator

Claims (8)

an inverter having a switching unit for switching input power by the switching unit and supplying the input power to a brushless DC motor;
a control unit that controls the inverter by PWM control;
with
The control unit
generating a PWM drive signal for driving the switching unit;
configured to switch the switching unit based on the PWM drive signal, the switching unit comprising:
Based on the PWM drive signal , the start of the carrier cycle of each carrier in the PWM control synchronizes the switching interval of the energized phases of the brushless DC motor,
The speed information of the brushless DC motor is acquired from the start to the end of one carrier period of the PWM control, the energization rate of the one carrier period and the end timing of the one carrier period are determined, and the energization rate is determined. is controlled to be ON in the range of 100% or less to 100% or more, and when it is 100% or less, the switching is controlled to be ON and OFF once per switching section of the energized phase;
motor drive. The brushless DC motor has a rotor and a stator,
The control unit acquires rotation position information of the rotor based on the induced voltage of the brushless DC motor.
The motor drive device according to claim 1 . The switching unit is controlled to be ON based on the PWM drive signal in a range where the duty ratio of PWM control is 50% or more and 150% or less.
3. A motor driving device according to claim 1 or 2 . The switching unit
controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and
Controlled on continuously during the section of the carrier that is one before or one after the carrier that is controlled to be on,
A motor driving device according to any one of claims 1 to 3 . The switching unit is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and is continuously controlled to be ON during the interval of the carrier immediately preceding the carrier that is controlled to be ON. When the energization rate of the PWM control is in a range exceeding 100%, the control unit determines the ON end timing of the switching unit based on the PWM drive signal by switching the energization phase of the brushless DC motor. later than the timing
5. A motor driving device according to claim 4 . The switching unit is controlled to be ON for each predetermined number of carriers based on the PWM drive signal, and is controlled to be ON continuously during the interval of the carrier one after the carrier that is controlled to be ON. When the energization rate of the PWM control is in a range exceeding 100%, the control unit determines the start timing of turning on the switching unit based on the PWM drive signal by switching the energization phase of the brushless DC motor. ahead of time,
5. A motor driving device according to claim 4 . The brushless DC motor is a motor that drives a compressor,
A motor driving device according to any one of claims 1 to 6 . A refrigeration cycle circuit configured by connecting a compressor having a brushless DC motor, a condenser, a pressure reducer and an evaporator,
The brushless DC motor is driven by the motor driving device according to any one of claims 1 to 7 ,
refrigerator.

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