JP6450938B2 - Motor drive device, compressor drive device using the same, and refrigerator - Google Patents

Description

  The present invention relates to a motor driving device for driving a brushless DC motor, a driving device for a compressor using the same, and a refrigerator.

  In a refrigerator that is cooled using a conventional motor drive device, a four-way valve is provided in the refrigeration cycle, and a normal refrigeration cycle is configured when the compressor is operating, and high and low pressures are separated on the cycle when the compressor is stopped. The high-pressure refrigerant is passed from the compressor to the compressor, and the four-way valve is switched so as to reduce the pressure difference between the compressor suction and discharge. Thereby, when the compressor is stopped, the refrigerant on the high-pressure side does not flow into the evaporator, the temperature of the evaporator is kept low, and the internal temperature is not increased, so that energy saving of the refrigerator is achieved (for example, Patent Document 1). reference).

  In general, at the time of starting, a predetermined voltage pattern applied to the motor is switched in order at a predetermined cycle to start up, and when the set rotational speed is reached, the applied voltage pattern to the motor is changed to the magnetic pole of the motor. Driving is switched to control based on position detection such as position detection (see, for example, Patent Document 2).

  FIG. 9 shows a refrigerator using a conventional motor driving device described in Patent Document 1. As shown in FIG. As shown in FIG. 9, a refrigeration cycle is formed in the order of a low-pressure shell compressor 101, a condenser (condenser) 102, a dryer 103, a capillary tube 104, and an evaporator 105, and the refrigerant passes through the refrigeration cycle from the compressor 101 to the condenser. It is flowing toward 105. The four-way valve 106 connects the inlet A to the dryer 103, the outlet B to the capillary 104, the inlet C to the evaporator 105, and the outlet D to the compressor 101. During operation of the compressor 101, the inlet A and outlet B, and the inlet C and outlet D of the four-way valve 106 are communicated. During stoppage, the inlet A and outlet D and the inlet C and outlet B of the four-way valve 106 are communicated. Thus, when the compressor is stopped, a closed circuit in the high pressure region provided with the compressor 101, the condenser 102 and the dryer 103 and a closed circuit in the low pressure region provided with the capillary 104 and the evaporator 105 are configured. A normal refrigeration cycle is formed during the refrigeration cycle operation, and a normal cooling operation can be performed. Also, when the refrigeration cycle is stopped, the high and low pressures are separated on the cycle, and the high pressure refrigerant is passed from the dryer to the compressor, the pressure difference between the compressor suction and discharge is reduced, and the engine can be started with a small load torque fluctuation. it can. With these configurations, when the refrigeration cycle is stopped, the refrigerant on the high pressure side does not flow into the evaporator 105, the temperature of the evaporator 105 does not rise, and the loss of the refrigeration cycle can be reduced.

JP-A-10-028395 JP 2008-104337 A

  However, the above-described conventional configuration cannot cope with a large load torque fluctuation at the time of starting the motor and the vibration increases and the reliability of the compressor decreases. Therefore, in order to start the compressor 101 stably, the compressor When stopping 101, it is necessary to balance the suction and discharge pressures of the compressor 101 by using the four-way valve 106. Therefore, there is a problem that the system becomes complicated and the cost increases.

SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a motor drive device that can be stably started even when a load torque fluctuation is large.

  In order to solve the above-described conventional problems, a motor driving device according to the present invention includes a brushless DC motor that drives a load that fluctuates during one rotation, a drive unit that applies voltage to the brushless DC motor and drives the brushless DC motor, and the brushless A speed accelerating unit is provided that determines a voltage applied by the drive unit so that the speed after one rotation from the start of the DC motor is accelerated so that the speed change rate of the next one rotation is within a predetermined value.

  As a result, the speed change of the brushless DC motor due to the load fluctuation is reduced, and the vibration can be suppressed and started up.

  The motor drive device of the present invention can be stably started even when the load torque fluctuation is large.

1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. (A) Transition diagram for one rotation of load torque when the discharge pressure and suction pressure of the compressor are balanced, (B) With a conventional starting method when the discharge pressure and suction pressure of the compressor are balanced Transition diagram of speed for one rotation (A) Transition diagram for one rotation of load torque when differential pressure is applied to compressor discharge pressure and suction pressure, (B) Conventional startup when differential pressure is applied to compressor discharge pressure and suction pressure Transition diagram of speed for one rotation (A) Transition diagram for one rotation of the load torque when a differential pressure is present between the compressor discharge pressure and the suction pressure, (B) This implementation when the differential pressure is present between the compressor discharge pressure and the suction pressure Transition diagram of the speed for one rotation with the initial speed as the target speed in the start-up method in form 1 Graph showing the relationship between the speed and the speed change rate is constant The flowchart which showed the starting method in this Embodiment 1. Refrigeration cycle diagram of a conventional refrigerator

  According to a first aspect of the present invention, a brushless DC motor that drives a load that fluctuates during one rotation, a drive unit that applies a voltage to the brushless DC motor to drive, and a speed after one rotation from the start of the brushless DC motor are as follows: By providing a speed accelerating unit that determines the voltage applied by the drive unit so that the speed change rate of one rotation of the rotation is kept below a predetermined value, the speed has a square effect on the load. The speed change in the brushless DC motor can be suppressed with a small increase in speed with respect to the increase in frequency, and the vibration of the brushless DC motor is reduced. As a result, even when the load torque fluctuation is large, it is possible to start up stably.

  In a second aspect based on the first aspect, the speed accelerating unit calculates a speed within one revolution from the start of the brushless DC motor, and a speed change rate of the next one revolution is calculated from a maximum change during one revolution. By accelerating the load so that it falls below a predetermined value, the load driven by the brushless DC motor can be started under the most difficult conditions and can be stably started under all required conditions.

According to a third invention, in the first or second invention, a position detection unit that detects a magnetic pole position of the brushless DC motor is provided, and the drive unit supplies a current to a specific phase of the brushless DC motor before starting. Positioning is performed, and after the predetermined time has passed, the position information of the position detection unit is acquired and the drive is started in a state in which a current is passed through a phase advanced by 90 degrees or more from the positioning phase, so as to respond to the magnetic pole position of the brushless DC motor. Therefore, stable driving can be performed even when the load varies during one rotation and the speed changes greatly.

  4th invention is a compressor using the motor drive device in any one of 1st to 3rd invention, and can provide the compressor which can be started stably.

  A fifth invention is a refrigerator including the compressor of the fourth invention and started up with a pressure difference between the suction side and the discharge side of the compressor remaining, and there is a pressure difference between suction and discharge of the compressor. Therefore, it is possible to provide a refrigerator that can reduce the loss of the refrigeration cycle without increasing the temperature of the evaporator at a low cost with a simple system configuration.

  According to a sixth invention, in the fifth invention, the pressure difference between the suction side and the discharge side of the compressor is at least larger than 0.05 MPa, the acceleration of deterioration due to an increase in vibration is reduced, and the compressor Thus, it is possible to provide a refrigerator capable of reducing the loss of the refrigeration cycle while maintaining the reliability.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(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 30 is connected to the AC power source 1 and drives the brushless DC motor 5. Hereinafter, the motor drive device 30 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 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 position detector 6 detects the magnetic pole position of the stator 5a from the induced voltage generated in the three-phase winding of the stator 5b, the current flowing through the three-phase winding of the stator 5b and the applied voltage, and the like. In the present embodiment, the terminal voltage of the brushless DC motor 5 is acquired, and the relative magnetic pole position of the rotor 5a of the brushless DC motor 5 is detected. Specifically, the position detector 6 detects the relative rotational position of the rotor 5a based on the induced voltage generated in the three-phase winding of the stator 5b. Specifically, the induced voltage is compared with a reference voltage to detect a zero cross. As a reference voltage for the zero cross of 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. The method of detecting from the induced voltage has a simple configuration and can be configured at a lower cost.

  The speed detector 7 calculates the current driving speed of the brushless DC motor 5 from the position information detected by the position detector 6. In the present embodiment, the time from the zero cross detection of the induced voltage is measured, and the current speed is calculated from this time.

  The speed acceleration unit 8 calculates a voltage to be applied to the brushless DC motor 5 based on the current speed detected by the speed detection unit 7. The calculation of the voltage to be applied by the speed accelerating unit 8 may be proportional control in which the magnitude of the applied voltage is changed according to the current difference from the target speed that increases with time, and the load change is the largest. The applied voltage may be determined at a voltage change rate that is determined in advance so that the target speed can be reached under conditions where acceleration is difficult. When performing proportional control, the target speed is determined from the acceleration. For example, the first target speed and voltage application are fixed, and the target speed is determined according to the magnitude of speed information detected by the speed detector 7 as a result of applying the voltage. The target speed is decreased as the result of the speed detector 7 is larger, and the target speed is increased as the result of the speed detector 7 is smaller. As a result, the larger the load, the higher the average speed after one rotation, and the speed change of the next one rotation can be suppressed to a level at which vibration does not cause a problem, thereby suppressing the vibration. The level at which the speed change does not become a problem is assumed to be the same as the speed change rate at the maximum when the pressure difference between the suction and discharge of the compressor is balanced. Also, the speed change rate is defined as the minimum speed when one revolution is made from a certain point of time divided by the initial speed of one revolution. For example, if the speed at a certain point is 3r / s and the minimum speed after one rotation is 2.7r / s, the speed change rate is 0.9, which is the result of dividing 2.7 by 3. .

  In this embodiment, the voltage change rate is determined in advance by determining the voltage change rate and determining the applied voltage. Since this method is possible with a very simple configuration, a system can be constructed at a lower cost.

  Further, the speed acceleration unit 8 receives a speed command input from the outside and starts outputting an applied voltage command for starting.

  Based on the position of the brushless DC motor rotor 5a detected by the position detection unit 6, the drive unit 9 determines the supply timing of the power supplied from the inverter 4 to the three-phase winding of the brushless DC motor 5 and the drive signal for PWM control. 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. The driving waveform includes a rectangular wave and a sine wave.

  The drive unit 9 calculates and outputs a PWM duty width based on the applied voltage set by the speed acceleration unit 8.

  Further, which phase is energized is determined by the drive unit 9 based on information from the position detection unit 6, and in this embodiment is performed by a 120-degree rectangular wave, the switching element of the upper arm 4a, 4c and 4e are energized while being shifted by 120 degrees each. 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 addition, the drive unit 9 energizes at least two arbitrary phases of the brushless DC motor 5 at the time of start-up, for example, for 1 second so that the position of the rotor 5a comes to a specific magnetic pole position, and then the energized phase. The phase is advanced by 90 to 150 degrees from the current, and it waits for the position detector 6 to detect the position of the rotor of the brushless DC motor 5. Then, when the position detection unit 6 detects the position and a position detection signal is input to the drive unit 9, the state shifts to a normal driving state in which the energization phase is switched to the next phase. In the first energization period of at least two phases, the energization is performed until the 90 deg phase is delayed from the energized phase after the brushless DC motor 5 is normally driven. As a result, the start-up phase can be reliably fixed, and the phase to be energized next is advanced by 90 to 150 degrees, so that the same energization phase state as in the normal drive state is obtained, so the output torque of the brushless DC motor 5 The start-up vibration due to the phase delay can be reduced.

  Next, a refrigeration apparatus and a refrigerator using the motor drive device 30 in the present embodiment will be described.

  Although the compressor 17 is mounted in the refrigerator 22, 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.

  The refrigerant compressed by the compressor 17 constitutes a refrigeration cycle that passes through the two-way valve 18, the condenser 19, the decompressor 20, and the evaporator 21 in this order and returns to the compressor 17 again. At this time, since the condenser 19 radiates heat and the evaporator 21 absorbs heat, cooling and heating can be performed. A refrigerator 22 is configured with this refrigeration cycle.

  The two-way valve 18 includes an electromagnetic valve that can be opened and closed by energization, and a valve is used in the present embodiment. The two-way valve 18 is opened while the compressor 17 is in operation, the compressor 17 and the condenser 19 are communicated, and the refrigerant flows. On the other hand, while the compressor 17 is stopped, the two-way valve 18 is closed to close the space between the compressor 17 and the condenser 19 so that the refrigerant does not flow.

  The operation of the motor drive device 30 configured as described above will be described with reference to FIGS.

  2 to 4, the horizontal axis represents the phase of the magnetic pole position of the rotor 5a of the brushless DC motor 5, the vertical axis of A in FIGS. 2 to 4 represents the load torque driven by the brushless DC motor 5, The vertical axis of B in FIGS. 2 to 4 indicates the driving speed of the brushless DC motor 5.

  Further, as shown in FIGS. 2 to 4, the load torque and the speed of the brushless DC motor 5 vary greatly, but the increase in the load torque and the timing at which the speed of the brushless DC motor 5 is minimized do not coincide with each other. On the other hand, there is a response delay in the speed of the brushless DC motor 5.

  First, the speed change under the starting condition of the conventional compressor will be described with reference to FIG.

FIG. 2A shows a change in load torque applied to the brushless DC motor 5 in one rotation when the pressure difference between the suction and discharge of the compressor 17 is 0.5 MPa. 0.5 MPa is the maximum pressure difference that can be regarded as balanced by the pressure difference between the conventional suction and discharge, and is the maximum allowable pressure difference. That is, the speed change rate at the maximum pressure difference allowed at the time of startup at which the speed change rate becomes the maximum is the maximum speed change rate allowed. The change in the speed of the brushless DC motor at the maximum pressure difference that can be regarded as balanced is shown in FIG. The initial speed represents 3r / s, which is the speed of the conventional synchronous operation, and represents a speed change when the engine rotates once at the initial speed. That is, the compressor 17 only allows the speed change rate shown in FIG.

  Next, with reference to FIG. 3, a description will be given of a change in the starting speed when the load torque fluctuation is large in the conventional starting method.

  FIG. 3A shows a change in load torque of one rotation under the condition that the pressure difference between the suction and discharge of the compressor 17 is 2.5 MPa and the load applied to the brushless DC motor 5 is increased about five times compared with A of FIG. Is shown. This pressure difference of 2.5 MPa is the maximum pressure difference in the present system, and the maximum load change is made while the load driven by the brushless DC motor 5 rotates once. A change in speed of one rotation of the brushless DC motor at this time is shown in FIG. The initial speed is 3r / s, which is the conventional synchronous operation speed, as in B of FIG. 2, and the speed change at this time is larger than that in B of FIG. Increase significantly.

  Next, with reference to FIG. 4, a description will be given of a change in the starting speed when the load torque fluctuation is large in the present embodiment.

  4A shows the load torque applied to the brushless DC motor 5 when the pressure difference between the suction and discharge of the compressor 17 is 2.5 MPa, as in FIG. 3A. FIG. 4B shows a speed change when the initial speed is set as the target speed that is reached within one rotation in the starting method according to the present embodiment. FIG. 4A shows the change in speed when the initial speed is about 6.71 r / s obtained by multiplying the square root of 5 of the conventional starting speed under the load torque condition of FIG. 4A, and the target speed is 6.71 r. / S. The speed change rate of B in FIG. 4 is the same as the conventional one.

  The speed change rate is proportional to the square of the speed with respect to the load. Therefore, when the load becomes five times, the speed change under the load condition and driving speed shown in FIG. Can be the same as the rate.

  FIG. 5 shows that the load changes when the rotational speed is 3 r / s and the load at 0.5 MPa, which is the maximum pressure difference between the suction and discharge pressures of the compressor 17, is 1. It shows how much speed is needed. From this, it can be seen that, for example, if the load is quadrupled, the speed may be 6r / s, which is 3r / s, which is twice the square root of 4.

  That is, the square root of the ratio of the load change at the maximum pressure difference between the suction and discharge of the compressor 17 required for the system at the start-up with respect to the maximum load change treated as a state where the suction and discharge pressures of the compressor 17 are balanced. The vibration of the compressor can be suppressed by reaching the doubled speed within one rotation.

  As for the speed change that occurs within one rotation from the start, the subject whose reliability is a problem, such as the compressor 17 affected by the speed change, applies a force to the state that is not vibrating. It is hardly affected by the inertial force of the affected substance such as the compressor 17 and does not cause a problem. If the speed change continues, it will have a big impact.

  A detailed control method will be described with reference to FIG. FIG. 6 is called when the compressor 17 is stopped and ends when the activation is completed.

First, in STEP 201, the speed accelerating unit 8 determines whether or not there is a speed command for instructing the speed for driving the compressor 17. If there is a speed command, the process proceeds to STEP 201 again, and if there is a speed command, the process proceeds to STEP 202. Here, it is assumed that there is no speed command yet, and the process proceeds to STEP 201.

  When the process proceeds to STEP 201 again, it is determined again whether there is a speed command. That is, it waits in STEP201 until a speed command is input from the outside. Here, the process proceeds to STEP 202 on the assumption that a speed command has been input from the outside.

  In STEP 202, the drive unit 9 energizes any two phases of the brushless DC motor 5 in order to prepare for activation, starts to flow current, resets and starts the timer A. At this time, the speed accelerating unit 8 adjusts the applied voltage so that the current is less than the current that demagnetizes the permanent magnet of the rotor 5a of the brushless DC motor and less than the current that the inverter 4 does not break. Then, the process proceeds to STEP 203.

  In STEP 203, the drive unit 9 determines whether the timer A is equal to or longer than the predetermined time A. If it is not less than the predetermined time A, the process proceeds to STEP 204, and if it is less than the predetermined time A, the process proceeds to STEP 203. Here, it is assumed that the predetermined time A has not elapsed, and the process proceeds to STEP 203 again.

  Again, in STEP 203, the value of the timer A and the predetermined time A are compared and determined. That is, until energization of the brushless DC motor 5 is started and a predetermined time A elapses, the process waits in STEP 203, and current continues to flow in the two phases of the brushless DC motor 5, and the phase is fixed. The predetermined time A may be a time for which the phase is sufficiently fixed, and is 1 second in the present embodiment. Here, assuming that the value of the timer A is equal to or longer than the predetermined time A, the process proceeds to STEP 204.

  In STEP 204, after the drive unit 9 starts energizing to a phase advanced by 120 degrees from the phase determined from any two phases energized in STEP 202, the timer B and the timer C are reset and started. Assuming that the energization of STEP 202 is the switching element 4a and the switching element 4d, in STEP 204, the energization is performed to the switching element 4c and the switching element 4f. Then, the process proceeds to STEP 205.

  In STEP 205, the drive unit 9 determines whether the timer B is equal to or longer than the predetermined time B. If it is not less than the predetermined time B, the process proceeds to STEP 208, and if it is less than the predetermined time B, the process proceeds to STEP 206. Here, since energization in STEP 204 has just started, the process proceeds to STEP 206 with less than the predetermined time B.

  In STEP 206, it is determined whether or not the position detection unit 6 has detected the position of the brushless DC motor 5. If the position can be detected, the process proceeds to STEP 210. If the position cannot be detected, the process proceeds to STEP 207. Here, since energization in STEP 204 has just started and position detection has not been performed, the process proceeds to STEP 207.

  In STEP 207, it is determined whether or not the speed detected by the speed detector 7 has reached a speed necessary for the next one rotation so that the speed change rate becomes a predetermined value or less. If the target speed has been reached, the process is terminated, and if not, the process proceeds to STEP 205 again. The target speed is obtained from the case of starting at the conventional speed with the maximum load that is considered to be balanced. If the conventional speed is 3 r / s and the load increases five times, the target speed is about 6.71 r / s. Here, since single-view detection has not been performed yet, the process proceeds to STEP 205 again.

Assuming the transition to STEP 205 again, it is determined whether or not the timer B is equal to or longer than the predetermined time B. Here, a series of processing is performed, and it proceeds to STEP 208 assuming that a predetermined time B has elapsed.

  In STEP 208, in order to increase and accelerate the voltage applied from the drive unit 9 to the brushless DC motor 5, the applied voltage command value is added to the current value by a certain value. Here, as the value to be added, a value that can reach the target drive speed within one rotation under the maximum load condition in the present embodiment is determined in advance by experiment or simulation. Then, the process proceeds to STEP 209.

  In STEP 209, the timer B is reset and restarted in order to increase the next applied voltage, and the process proceeds to STEP 206.

  In STEP 206, position detection occurs after a certain period of time from the start of energization in STEP 204, and the process proceeds to STEP 210.

  In STEP 210, the value of timer C is acquired and restarted after resetting. Timer C is the time that the current applied voltage pattern continues. Then, the process proceeds to STEP 211.

  In STEP 211, the speed is calculated by taking the reciprocal of the acquisition result of the timer C, and the process proceeds to STEP 212.

  In STEP 212, an energization pattern that is advanced by 60 deg from the current energization phase is applied, and the process proceeds to STEP 207.

  By repeating the path from STEP 205 to STEP 207, the brushless DC motor 5 is accelerated and reaches the target speed. Then, as a result of reaching the target speed in STEP 207, the processing is terminated.

  By performing the process until the call activation is completed while the above flow is stopped, the compressor 17 can be activated without great vibration even under a load condition greater than 0.05 MPa for suction and discharge of the compressor 17.

  In the compressor 17, in the state where the differential pressure between suction and discharge is greater than 0.05 MPa, the applied voltage is not changed according to the speed in one rotation, but is monotonously increased for acceleration. Since the load torque greatly varies due to the pressure and the speed variation increases, the vibration increases and the possibility of failure due to wear of parts of the compressor 17 increases. However, in this embodiment, the conventional application method is used. Compared with, reliability can be greatly improved.

  Next, the case where the motor drive device 30 of the present embodiment is applied to the compressor 17 and mounted on the refrigerator 22 will be described.

Simultaneously with the start of the compressor 17, the two-way valve 18 is opened, and the discharge of the compressor 17 and the condenser 19 are communicated. Although the two-way valve 18 is opened at the same time as the compressor 17 is started, there is no problem even if the time is slightly changed. If the drive of the compressor 17 is continued, the condenser 19 becomes high pressure, the pressure is reduced by the pressure reducer 20, and the evaporator 21 becomes low pressure. At this time, the discharge connected to the condenser 19 of the compressor 17 becomes high pressure, and the suction connected to the evaporator 21 becomes low pressure. Here, it is assumed that the internal temperature of the refrigerator 22 is lowered and the compressor 17 is stopped. When the two-way valve 18 remains open, the pressures of the condenser 19 and the evaporator 21 are gradually balanced. Depending on the refrigerator system, it takes about 10 minutes until the pressure difference between the suction and discharge of the compressor 17 reaches a balanced state of 0.05 MPa or less. When the two-way valve 18 is shifted from the open state to the closed state simultaneously with the stop of the compressor 17, the pressure difference between the condenser 19 and the evaporator 21 is substantially maintained, and a pressure difference remains between discharge and suction of the compressor 17. When the internal temperature of the refrigerator 22 rises and the compressor 17 is started again, when the compressor 17 is stopped, the two-way valve 18 is closed and the pressure difference is maintained, and the pressure is balanced. When the two-way valve 18 is closed and the pressure difference is maintained, the electric power for providing the pressure difference again between the condenser 19 and the evaporator 21 is reduced, so that energy is saved. Even when the two-way valve 18 is left open even when the compressor 17 is stopped, or even when the two-way valve 18 is not provided, the internal temperature is 10 minutes before the pressure balances from the stop. Even when the pressure rises, it was possible to start only when the pressure difference was 0.05 MPa or less in the prior art, and it was waiting for 10 minutes to elapse. On the other hand, in the present embodiment, since it is possible to start even with a differential pressure greater than 0.05 MPa, the internal temperature rises, and the compressor 17 can be started when it is necessary to operate, so that the balance is maintained. In comparison, the power for providing a pressure difference between the condenser 19 and the evaporator 21 is reduced, so that energy saving is possible.

  The two-way valve 18 can have a simpler system than the three-way valve or the four-way valve, and can maintain the pressure difference between the suction and discharge of the compressor 17.

  As described above, in the present embodiment, the brushless DC motor 5 that drives a load that fluctuates during one rotation, the drive unit 9 that drives the brushless DC motor 5 by applying a voltage, and the startup of the brushless DC motor 5. By providing the speed accelerating unit 8 that determines the voltage applied by the drive unit 9 so that the speed within one rotation is accelerated so that the rate of change in the speed of the next one rotation is kept below a predetermined value, the speed with respect to the load is reduced. Because of the square effect, the speed change in the brushless DC motor 5 can be suppressed with a small increase in speed with respect to the increase in load, and the vibration of the brushless DC motor 5 is reduced. Can be started.

  In the present embodiment, the speed accelerating unit 8 has a speed within one revolution from the start of the brushless DC motor 5 and a load calculated from the maximum speed change rate during the next one revolution. By accelerating so as to be within the range, it is possible to start under the condition where the start of the load driven by the brushless DC motor 5 is most difficult, and it is possible to start stably under all the required conditions.

  Further, in the present embodiment, the position detection unit 6 that detects the magnetic pole position of the brushless DC motor 5 is provided, and the drive unit 9 performs positioning so that a current flows in a specific phase of the brushless DC motor 5 before starting, for a predetermined time. After the elapse of time, the position information of the position detection unit 6 is acquired and the drive is started in a state where the current is passed through the phase advanced by 90 degrees or more from the positioning phase, so that the drive corresponding to the magnetic pole position of the brushless DC motor 5 is performed. Therefore, stable driving can be performed even when there is a load fluctuation in one rotation and the speed changes greatly.

Further, the motor drive device 30 drives the compressor 17 of the refrigeration cycle connected in the order of the compressor 17, the condenser 19, the decompressor 20, the evaporator 21, and the compressor 17, and the suction side and the discharge side of the compressor 17. Since the refrigerator 22 is started in a state where the pressure difference remains, it can be started even in a state where there is a pressure difference between the suction and discharge of the compressor 17, and the evaporator 21 can be inexpensively configured with a simple system configuration. It is possible to reduce the loss of the refrigeration cycle without increasing the temperature. Further, since the pressure difference of the compressor 17 is at least larger than 0.05 MPa, the vibration increases even if the pressure difference increases normally. It is possible to reduce the loss of the refrigeration cycle while maintaining the reliability of the compressor 17 by reducing the acceleration of deterioration due to the above.

The motor drive device of the present invention can be started even when the load torque fluctuates during startup. Thereby, it can apply not only to a refrigerator but to the compressor in an air-conditioner, a vending machine, a showcase, and a heat pump water heater.

DESCRIPTION OF SYMBOLS 5 Brushless DC motor 8 Speed acceleration part 9 Drive part 17 Compressor 19 Condenser 20 Decompressor 21 Evaporator 22 Refrigerator 30 Motor drive device

Claims (6)

A brushless DC motor that drives a load that fluctuates during one rotation, a drive unit that drives by applying a voltage to the brushless DC motor, and a speed change within one rotation from the start of the brushless DC motor A motor driving device comprising a speed accelerating unit that determines a voltage applied by the drive unit so as to accelerate so that a rate falls below a predetermined value. The speed accelerating unit accelerates the speed within one rotation from the start of the brushless DC motor so that the speed change rate of the next one rotation is within a predetermined value under a condition that the load change during one rotation is maximum. Item 2. The motor drive device according to Item 1. A position detection unit for detecting the magnetic pole position of the brushless DC motor is provided, and the drive unit performs positioning for supplying a current to a specific phase of the brushless DC motor before activation, and advances by 90 degrees or more from the positioning phase after a predetermined time has elapsed. The motor drive device according to claim 1 or 2, wherein the position information of the position detection unit is acquired and driving is started in a state where a current is passed through the phase. The drive device of the compressor using the motor drive device as described in any one of Claim 1 to 3. A refrigerator comprising the compressor driving device according to claim 4 and started in a state where a pressure difference between the suction side and the discharge side of the compressor remains. The refrigerator according to claim 5, wherein the pressure difference between the suction side and the discharge side of the compressor is greater than at least 0.05 MPa.

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