JP2014017986A - Motor control unit and refrigerator having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor control unit and a refrigerator having the same, capable of performing a stable motor control with an inexpensive motor circuit.SOLUTION: A motor control unit includes: a converter part for converting AC voltage of a commercial power supply into DC voltage; and an inverter part for outputting three-phase AC voltage from the DC voltage to rotate a motor. The electric current in d-axis direction is increased, if any one of the following is seen: the motor rotation frequency is equal to or lower than a specified rotation number; the electric power supply voltage is equal to or higher than a specified value; or it is in the specified time when ringing is expected to be generated by the switching of three-phase AC current.

Description

  The present invention relates to a motor control device and a refrigerator including the motor control device.

  Motor control devices for household appliances used in refrigerators, etc. require motor control software that can operate at high efficiency and a wide range of rotation speeds even with inexpensive motors and board specifications in order to realize power saving and cost reduction. Become.

  For example, it is possible to reduce the cost by using an inexpensive magnet material for the rotor which is a motor component and an inexpensive wire material for the stator.

  However, using an inexpensive material makes control difficult due to a decrease in inductance, an increase in resistance, a deterioration in temperature characteristics, and a decrease in motor torque. Further, when the commercial power supply voltage is used as it is, it is difficult to operate at a high rotational speed due to insufficient voltage. Also, the voltage is too high, and the PWM on-time required for current detection cannot be secured at a low rotational speed, making control difficult.

  This is because the voltage required for motor control decreases in the low rotation speed range, and the on time of PWM for applying the voltage to the motor decreases, making current detection impossible. In order to detect the current, it takes a certain time to apply the voltage.

  Conventionally, the PWM frequency is lowered to secure the current detection time. However, when the PWM frequency is lowered, the current ripple becomes large and problems such as increased vibration occur.

  As described above, various factors are related to the operation of the motor control, and the number of rotations that becomes the limit of control varies depending on each factor.

  Conventionally, the control disclosed in Patent Document 1 is known as a means for solving the problem of excessive voltage undervoltage.

  In Patent Document 1, in a power conversion circuit having a function of converting alternating current to direct current and increasing a direct current voltage, and a control device having a weak flux control function by vector control of a synchronous motor, adjustment of the power conversion circuit and the weak flux control is performed. Realizes high-efficiency control from low to high speeds.

JP 2004-101151 A

  However, in patent document 1, the cost for the power converter circuit which has the function to raise DC voltage rises. In addition, the necessary space for the substrate is increased.

  In order to solve the above problems, an object of the present invention is to provide a motor control device that realizes a stable motor control operation with an inexpensive motor circuit configuration, and a refrigerator including the motor control device.

  In order to solve the above problems, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above problems. For example, a converter unit that converts commercial power AC voltage into DC voltage, and outputs a three-phase AC voltage from the DC voltage to rotate the motor. And a motor control device comprising: an inverter unit for causing the motor rotation speed to be lower than a predetermined rotation speed, a power supply voltage to be higher than a predetermined value, or a predetermined time when ringing occurs due to switching of a three-phase alternating current In this case, the current in the d-axis direction is increased.

  According to the present invention, a stable motor control operation can be performed with an inexpensive motor circuit configuration.

1 is a block diagram illustrating an embodiment of a motor control device according to the present invention. The figure which illustrates the relationship between the rotation speed of a motor, and the ON time of the voltage signal of PWM. The figure which illustrates the relationship between a power supply voltage and the ON time of the voltage signal of PWM. The figure which illustrates the motor current information when the flow of PWM output and current detection are normal. The figure which illustrates motor current information when current detection cannot be performed normally. The flowchart which illustrates the algorithm of d-axis current increase processing. The figure which illustrates motor current information when d axis current is increased. The figure which illustrates the relationship between d-axis current and the minimum controllable rotation speed.

  Hereinafter, as an example of the present invention, an embodiment of a motor control device using a permanent magnet synchronous motor will be described.

  FIG. 1 is a block diagram showing an embodiment of a motor control device according to the present invention. This motor control device converts the AC voltage of the commercial power source 1 into a DC voltage by the converter unit 2.

  The inverter unit 3 outputs a three-phase AC voltage based on the drive signal 4 output from the microcomputer, and rotates the motor 5.

  The current capturing unit 6 in the microcomputer calculates and obtains the motor current from the motor current information 8 generated in the shunt resistor 7.

  The dq conversion unit 10 performs dq conversion on the calculated motor current 9. The rotation speed command unit 12 outputs a rotation speed command value 13 for turning the motor 5.

  The d-axis current command unit 14 calculates a current required for startup, a field weakening, a current necessary for phase adjustment and current detection, and outputs a d-axis current command value 15.

  The output voltage calculation unit 16 calculates a motor voltage value to be output from the dq-converted current information 11, the rotation speed command value 13, and the d-axis current command value 15, and outputs a motor command voltage 17.

  The dq converter 18 performs dq reverse conversion on the motor command voltage 17 and outputs a drive signal 4.

  Next, FIG. 2 shows the relationship between the rotational speed of the motor and the ON time of the PWM voltage signal that is the drive signal. Since the necessary voltage decreases as the rotational speed decreases, the PWM on-time is shortened, and when the time required for current detection is less than 20, current detection is impossible 21. The time required for current detection is determined by the ringing time, the dead time, and the sampling required time of the A / D converter.

  Next, FIG. 3 shows the relationship between the power supply voltage and the ON time of the PWM voltage signal that is the drive signal. As the power supply voltage becomes higher, the required on-time becomes shorter, so the PWM on-time becomes shorter, and when the time 23 necessary for current detection is cut, current detection becomes impossible 24.

  Next, FIG. 4 shows motor current information 8 generated in the shunt resistor 7 when the PWM output flow and current detection can be normally performed. The voltage maximum phase, intermediate phase, and minimum phase are compared with the carrier signal to generate signals for the upper and lower arms, and the PWM signal is generated. Note that ringing 25 occurs in the motor current when switching occurs. Therefore, it is necessary to read the normal current after the ringing has stabilized 26.

  Next, FIG. 5 shows motor current information 8 generated in the shunt resistor 7 when current detection cannot be performed normally. If the on-time 19 of the PWM voltage signal is shortened, it is turned off 27 before the ringing is stabilized, and current detection becomes impossible.

  Next, FIG. 6 is a flowchart illustrating an algorithm of the d-axis current increase process. When the number of revolutions of the motor 5 is 28 or less (the number of revolutions of the motor is less than a predetermined number of revolutions) at which the time required for current detection cannot be secured, 29 (power supply) Either when the voltage is greater than or equal to a predetermined value), or when starting at 30 (predetermined time when ringing occurs due to switching of the three-phase alternating current), which requires a long current detection time due to unstable control. As the d-axis current, a d-axis current increase value 31 is used. If none of the above applies, a value 32 that does not increase the d-axis current is used.

  FIG. 7 shows motor current information when the d-axis current is increased in a state where the current generated in the shunt resistor cannot be normally detected. By increasing the d-axis current not related to torque generation, the on-time 33 of the PWM voltage signal can be lengthened without changing the motor rotation speed, and current detection can be made possible.

  FIG. 8 shows the relationship between the d-axis current and the minimum controllable rotational speed. By increasing the d-axis current, the minimum usable rotational speed can be reduced, and a wide range of rotational speeds can be used.

  From the above, by applying the motor control device of the present embodiment to the refrigerator, the current detection accuracy can be improved by changing the program at a low cost, saving the board space, and improving the stability of the control. The controllable rotation speed range can be expanded.

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Converter part 3 Inverter part 4 Drive signal 5 Motor 6 Current taking-in part 7 Shunt resistance 8 Motor current information 9 Calculated motor current 10, 18 dq conversion part 11 Dq-converted current information 12 Rotation speed command part 13 Rotational speed command value 14 d-axis current command section 15 d-axis current command value 16 Output voltage calculation section 17 Motor command voltage 19 Voltage signal ON time 20 Time required for current detection (for rotational speed)
21 Current detection not possible (for rotation speed)
23 Time required for current detection (for power supply voltage)
24 Current detection not possible (for power supply voltage)
25 Ringing 26 Ringing is stable 27 Off 28 Less than the numerical value at which the required time cannot be secured 29 More than the power supply voltage value at which the required time cannot be secured 30 Start-up 31 d-axis current increase value 32 d-axis current increase value 33 PWM voltage signal value On time

Claims (2)

In a motor control device comprising: a converter unit that converts an AC voltage of a commercial power source into a DC voltage; and an inverter unit that outputs a three-phase AC voltage from the DC voltage and rotates the motor.
The current in the d-axis direction is increased when the rotational speed of the motor is equal to or lower than a predetermined rotational speed, the power supply voltage is equal to or higher than a predetermined value, or a predetermined time during which ringing occurs due to switching of a three-phase alternating current. A motor control device.   A refrigerator comprising the motor control device according to claim 1.