Motor drive device and air conditioner

Abstract

A motor drive device (50) is provided with: an inverter (2) that converts a DC voltage into a three-phase AC voltage and supplies the three-phase AC voltage to a motor (1); a phase current detection unit (6) that detects a phase current, which is a current flowing in each phase of the motor; a phase current peak value calculation unit (7) that calculates a phase current peak value, which is the peak value of the phase current detected by the phase current detection unit; and a command value calculation unit (51) that generates a fan rotational speed command value for the blower fan operated by the motor on the basis of the phase current peak value and a preset phase current peak value limit value, and that calculates the rotational speed of the blower fan when the phase current peak value is greater than the phase current peak value limit value. When the phase current peak value is less than the phase current peak value limit value, a fan rotational speed command value for reducing the fan rotational speed, which is the rotational speed of the blower fan, is generated, and when the phase current peak value is less than the phase current peak value limit value, a fan rotational speed command value for increasing the fan rotational speed is generated.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a motor drive device and an air conditioner. BACKGROUND

[0002] Conventionally, a motor drive device having an inverter or the like controls power supplied to a motor to cause the motor to perform desired driving. For example, in an air conditioner, a blower fan efficiently performs heat exchange between refrigerant flowing in a heat exchanger and, for example, air. At this time, the rotational speed of the fan is controlled by controlling the output voltage of the inverter that applies a voltage to a motor that rotates the fan of the blower fan.

[0003] For example, in the air conditioner described in Patent Literature 1, the rotational speed of the motor is controlled to a target rotational speed by switching with an inverter and applying a direct current voltage. In addition, in the air conditioner described in Patent Literature 1, based on the magnetic pole position of the motor, the direct current voltage applied to the inverter, and the current flowing in the inverter, the switching elements of the inverter are controlled to be turned on and off.

[0004] Patent Literature 1: Japanese Patent Application Publication No. 2011-069551

[0005] Although in the air conditioner described in Patent Literature 1, the current flowing in the inverter is detected with a circuit that combines a shunt resistor and a peak holding circuit, there is a problem that the error between the actual current value and the detected value is large in current detection using the peak holding circuit compared to instantaneous value detection. In addition, in the case where excessive current flows in the inverter, control to stop the operation or the like is performed by a protection function. Therefore, in the case where current detection is performed using the peak holding circuit, in order to prevent the protection function from operating slowly, it is necessary to set the threshold value for determining whether to operate the protection circuit lower than in the case of instantaneous value detection. Therefore, in the case of a structure using the peak holding circuit, compared to a structure in which current detection is performed without using the peak holding circuit, it is expected that the maximum rotational speed at which the motor can operate becomes lower, that is, the operation efficiency decreases.

[0006] In addition, in the case of existing instantaneous value detection, since no external circuit is provided and there is no detection unit of the current peak value, it is difficult to perform the change in the rotational speed corresponding to the current peak value, that is, the operation at the maximum rotational speed corresponding to the load condition of the motor. SUMMARY

[0007] The present disclosure is made in view of the above circumstances, and aims to obtain a motor drive device capable of performing operation at a maximum rotational speed corresponding to the load condition of a motor.

[0008] To solve the above problem and achieve the object, the motor drive device of the present disclosure has an inverter that converts a direct-current voltage into a three-phase alternating-current voltage and supplies it to a motor; a phase current detection section that detects a current flowing in each phase of the motor, that is, a phase current; a phase current peak value calculation section that calculates a peak value of the phase current detected by the phase current detection section, that is, a phase current peak value; and a command value operation section that generates a fan rotational speed command value for a blower fan that operates by the motor based on the phase current peak value and a phase current peak value limit value set in advance, the command value operation section generating a fan rotational speed command value that reduces the fan rotational speed, which is the rotational speed of the blower fan, when the phase current peak value is greater than the phase current peak value limit value, and generating a fan rotational speed command value that increases the fan rotational speed when the phase current peak value is less than the phase current peak value limit value.

[0009] The motor drive device of the present disclosure exerts an effect of being able to operate at the maximum rotational speed corresponding to the load condition of the motor. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a diagram showing a configuration example of the motor drive device of Embodiment 1

[0011] Figure 2 is a flowchart showing one example of the operation of the phase current detection section and the phase current peak value calculation section of the motor drive device.

[0012] Figure 3 is a diagram showing one example of the operation of the speed-up control section and the rotational speed command value calculation section of the motor drive device.

[0013] Figure 4 is a flowchart showing one example of the method of the speed-up control section and the rotational speed command value calculation section of the motor drive device for suppressing oscillation of the fan rotational speed.

[0014] Figure 5 is a diagram showing one example of the control operation of the fan rotational speed by the motor drive device.

[0015] Figure 6 is a flowchart showing one example of the operation of the speed-up control section and the rotational speed command value calculation section of the motor drive device for calculating the fan rotational speed command value.

[0016] Figure 7 is a diagram showing a configuration example of the air conditioner of Embodiment 2.

[0017] Figure 8 is a diagram showing one example of the control operation of the air conditioner of Embodiment 2. DETAILED DESCRIPTION

[0018] Hereinafter, the motor drive device and the air conditioner according to the embodiment of the present disclosure will be described in detail based on the drawings.

[0019] Embodiment 1

[0020] Figure 1 is a diagram showing a configuration example of the motor drive device 50 according to Embodiment 1. In the motor drive device 50, a DC power supply 3 is connected on the input side, and a motor 1 is connected on the output side. The motor drive device 50 drives the motor 1 by converting a DC voltage supplied from the DC power supply 3 into a three-phase AC voltage and supplying the three-phase AC voltage to the motor 1. The motor drive device 50 is applied to an air conditioner in which the description of the air conditioner in Figure 1 is omitted. The motor 1, for example, causes a blow fan (hereinafter, sometimes referred to as an outdoor fan) provided to an outdoor unit of the air conditioner to operate. In addition, the motor 1 can also be used for driving a compressor of the air conditioner.

[0021] As shown in Figure 1 , the motor drive device 50 includes an inverter 2 that converts a DC voltage supplied from the DC power supply 3 into a three-phase AC voltage and supplies the three-phase AC voltage to the motor 1, a phase current detection section 6 that detects instantaneous values of currents (hereinafter, referred to as phase currents) flowing in each phase of the motor 1, a phase current peak value calculation section 7 that calculates peak values of the phase currents of each phase, a speed-up control section 9 that decides an amount of change in a rotational speed of the outdoor fan based on a pre-set phase current peak value limit value 8 and the peak values of the phase currents calculated by the phase current peak value calculation section 7, and a rotational speed command value calculation section 10 that calculates a command value (hereinafter, referred to as a fan rotational speed command value) of the rotational speed of the outdoor fan based on the amount of change decided by the speed-up control section 9. The speed-up control section 9 and the rotational speed command value calculation section 10 constitute a command value operation section 51. In addition, the phase current detection section 6, the phase current peak value calculation section 7, the speed-up control section 9, and the rotational speed command value calculation section 10 are realized by, for example, a microcontroller.

[0022] The inverter 2 has bridge-connected switching elements 4a to 4f and shunt resistors 5a to 5c. The switching elements 4a to 4f are supplied with PWM (Pulse Width Modulation) signals for PWM control generated by an inverter control section (not shown). The switching elements 4a to 4f generate three-phase AC voltage applied to the motor 1 by being driven in accordance with the PWM signals. The shunt resistors 5a to 5c are respectively provided between the switching elements of each phase and a DC bus, for instantaneous value detection of the phase current of each phase by a phase current detection section 6. That is, the phase current detection section 6 calculates the instantaneous value of the phase current of each phase from the terminal voltage of the shunt resistors 5a to 5c and the resistance value. The instantaneous value of the phase current of each phase is output from the phase current detection section 6 to a phase current peak value calculation section 7, which calculates the peak value (hereinafter referred to as the phase current peak value) of the phase current of each phase.

[0023] Figure 2 is a flowchart showing one example of the operation of the phase current detection section 6 and the phase current peak value calculation section 7 of the motor drive device 50, specifically, the operation of calculating the phase current peak value of each phase.

[0024] First, the phase current detection section 6 detects the instantaneous value of the phase current (step Sll).

[0025] Next, the phase current peak value calculation section 7 calculates the dq-axis currents (step S12). That is, the phase current peak value calculation section 7 calculates the instantaneous value of the d-axis current as the current on the d-axis and the instantaneous value of the q-axis current as the current on the q-axis by dq-converting the instantaneous value of the phase current detected by the phase current detection section 6. Next, the phase current peak value calculation section 7 calculates the square value of the phase current effective value from the d-axis current and the q-axis current (step S13), and calculates the phase current peak value from the square value of the phase current effective value (step S14). The phase current peak value calculation section 7 performs the above steps S12 to S14 on the three phases respectively, to find the phase current peak value of each phase.

[0026] Figure 3 is a diagram showing one example of the operation of the step-up control section 9 and the rotational speed command value calculation section 10 of the motor drive device 50.

[0027] The increase control section 9 calculates a difference between the maximum rotational speed 11 set in advance and the target rotational speed 12 of the blower fan to generate a blower fan increase amount maximum value 13. In addition, the increase control section 9 calculates a difference between the phase current peak value calculated by the phase current peak value calculation section 7 and the phase current peak value limit value 8, and calculates a blower fan stall speed value 15 by performing PI (Proportional Integral) control using the difference by the blower fan stall speed value calculation section 14. Further, the phase current peak value limit value 8 needs to be set to be below an overcurrent cutoff value to avoid the motor drive device 50 from falling into overcurrent cutoff. The overcurrent cutoff is a protective action that stops the operation of the inverter 2 in a case where the input current to the inverter 2 is excessively large. The overcurrent cutoff value is used for determination of whether or not to perform overcurrent cutoff, that is, determination of whether or not the input current to the inverter 2 is excessively large, and overcurrent cutoff is performed in a case where the input current to the inverter 2 exceeds the overcurrent cutoff value, for example.

[0028] The increase control section 9 further calculates a difference between the blower fan increase amount maximum value 13 and the blower fan stall speed value 15 to generate a blower fan increase speed value 16.

[0029] Here, among the maximum rotational speed 11, the target rotational speed 12, and the blower fan stall speed value 15 described above, conditions expressed by the following formula (1) and formula (2) are set.

[0030] Target rotational speed 12 < Maximum rotational speed 11... (1)

[0031] 0 ≤ Blower fan stall speed value 15 ≤ Blower fan increase speed value 16... (2)

[0032] The rotational speed command value calculation section 10 adds the blower fan increase speed value 16 generated by the increase control section 9 to the target rotational speed 12 to generate a blower fan rotational speed command value. Further, the blower fan rotational speed command value calculated by the rotational speed command value calculation section 10 is transmitted to an inverter control section, which is omitted from illustration. The inverter control section generates a PWM signal applied to the switching elements 4a to 4f of the inverter 2 based on the blower fan rotational speed command value to switch the switching elements 4a to 4f.

[0033] The above-described processing in which the increase control section 9 and the rotational speed command value calculation section 10 of the motor drive device 50 calculate the blower fan rotational speed command value based on the phase current peak value and the phase current peak value limit value 8 is performed by setting the conditions expressed by the above-described formula (1) and formula (2), and thus the blower fan rotational speed command value is varied between the maximum rotational speed 11 and the target rotational speed 12.

[0034] In addition, the increase control section 9 and the rotational speed command value calculation section 10 of the motor drive device 50 suppress oscillation of the blower fan rotational speed when the motor 1 is driven at a value around the phase current peak value limit value 8 by the methods shown in Figure 4 and Figure 5 Figure 4 ​is a flowchart showing one example of a method in which the step-up control section 9 and the rotational speed command value calculation section 10 of the motor drive device 50 suppress oscillation of the fan rotational speed. Figure 5 is a graph showing one example of a control action of the fan rotational speed by the motor drive device 50. In Figure 5 , the horizontal axis represents time, and the vertical axis represents the fan rotational speed command value.

[0035] As shown in Figure 4 , the step-up control section 9 and the rotational speed command value calculation section 10 first calculate the fan stall speed value 15 by the step-up control section 9 (step S21), and calculate the fan step-up speed value 16 (step S22). Next, the step-up control section 9 compares the latest fan step-up speed value 16 calculated in step S22 and the last value of the fan step-up speed value 16 (step S23). The last value of the fan step-up speed value 16 refers to the fan step-up speed value 16 that has been calculated in the last time step S22 was executed. In the case where the latest fan step-up speed value 16 is greater than the last value (step S23: YES), the calculation of the fan rotational speed command value is stopped until a certain time elapses in accordance with a time limit set in advance, and then, as shown in Figure 5 , the fan rotational speed is maintained for a certain period after the fan rotational speed is kept constant (step S24), and the rotational speed command value calculation section 10 calculates the fan rotational speed command value (step S25).

[0036] On the other hand, in the case where the latest fan step-up speed value 16 is below the last value (step S23: NO), the rotational speed command value calculation section 10 immediately calculates the fan rotational speed command value (step S25).

[0037] In this way, the step-up control section 9 and the rotational speed command value calculation section 10 increase the fan rotational speed after a period in which the fan rotational speed is not changed elapses when moving from the step-down region in which the fan rotational speed is decreased to the step-up region in which the fan rotational speed is increased. In addition, the fan rotational speed is decreased without elapsing a period when moving from the step-up region to the step-down region. Thereby, an action in which the amount of change per unit time in the step-down region of the fan rotational speed is greater than the amount of change per unit time in the step-up region is made.

[0038] Further, by setting a condition shown in the following equation (3), generation of oscillation when the fan rotational speed changes from the step-down region to the step-up region is suppressed, and the fan rotational speed control is stabilized.

[0039] Control period of step-up control section 9 << time limit … (3)

[0040] The control period of the increase speed control section 9 refers to a period in which the command value calculation section 51 generates the fan rotational speed command value and controls the rotational speed of the outdoor fan, and the increase speed control section 9 calculates the fan increase speed value 16 in the control period. For example, in a case where the control period of the increase speed control section 9 is a period of microseconds (μβ), the time limit is set to a period of seconds (s).

[0041] Figure 6 is a flowchart showing one example of the operation of the increase speed control section 9 and the rotational speed command value calculation section 10 of the motor drive device 50 to calculate the fan rotational speed command value.

[0042] As shown in Figure 6 , the increase speed control section 9 and the rotational speed command value calculation section 10 first calculate the fan stall speed value 15 by the increase speed control section 9 (step S31), and determine whether the calculated fan stall speed value 15 is zero (0) (step S32). In a case where the fan stall speed value 15 is zero (step S32: YES), the rotational speed command value calculation section 10 generates the fan rotational speed command value indicating the maximum rotational speed set in advance (step S33). In a case where the fan stall speed value 15 is not zero (step S32: NO), it is confirmed whether the fan stall speed value 15 and the fan increase amount maximum value 13 are the same (step S34). In a case where the fan stall speed value 15 and the fan increase amount maximum value 13 are the same (step S34: YES), the rotational speed command value calculation section 10 generates the fan rotational speed command value indicating the target rotational speed 12 (step S35). In a case where the fan stall speed value 15 and the fan increase amount maximum value 13 are not the same (step S34: NO), the rotational speed command value calculation section 10 generates the fan rotational speed command value indicating the rotational speed after adding the fan increase speed value 16 to the target rotational speed 12 (step S36).

[0043] As described above, the motor drive device 50 of the present embodiment detects the instantaneous values of the respective phase currents flowing in the inverter 2, and calculates the peak values of the respective phase currents on the basis of the detected instantaneous values. In addition, the motor drive device 50 decreases the rotational speed in a case where the calculated peak values of the phase currents are greater than the phase current peak value limit value 8, and increases the rotational speed in a case where the peak values of the phase currents are equal to or less than the phase current peak value limit value 8. The motor drive device 50 of the present embodiment can operate the motor 1 at the maximum rotational speed corresponding to the load condition of the motor 1, and can achieve an improvement in operating efficiency.

[0044] In addition, the motor drive device 50 performs control so that the amount of change per unit time of the fan rotational speed is greater in the decrease speed region than in the increase speed region, and thus can suppress the generation of oscillation of the fan rotational speed when the motor 1 is driven near the phase current peak value limit value 8, and can achieve stabilization of the control of the fan rotational speed.

[0045] Embodiment 2.

[0046] In Embodiment 2, an application example of the motor drive device 50 explained in Embodiment 1 will be explained.

[0047] Figure 7 is a view showing a configuration example of the air conditioner 100 of Embodiment 2. The air conditioner 100 shown in Figure 7 is realized by applying the motor drive device 50 explained in Embodiment 1. The air conditioner 100 is one example of a refrigeration cycle device realized by applying the motor drive device 50.

[0048] The air conditioner 100 is provided with the direct-current power supply 3, the motor drive device 50, and the motor 1, the supply fan 18, the compressor 19, the four-way valve 20, the outdoor heat exchanger 21, the expansion valve 22, the indoor heat exchanger 23, and the refrigerant piping 24 explained in Embodiment 1. The motor 1 is used to operate the supply fan 18 that supplies air to the outdoor heat exchanger 21 to perform heat exchange.

[0049] A refrigeration cycle is configured by circulating a refrigerant in the compressor 19, the four-way valve 20, the outdoor heat exchanger 21, the expansion valve 22, the indoor heat exchanger 23, and the refrigerant piping 24.

[0050] Thus, by applying the motor drive device 50 and the motor 1 explained in Embodiment 1 to operate the supply fan 18 of the air conditioner 100, in a state where frosting of the outdoor unit of the air conditioner 100 is not intensified, that is, in a case where the motor 1 is in a light load state, it is possible to use the current up to the phase current peak limit value 8, and accordingly, to increase the rotational speed. For example, it is possible to perform Figure 8 the control shown in

[0051] Figure 8 is a view showing one example of the control operation of the air conditioner 100 of Embodiment 2. Figure 8 An example of the control operation in a case where frosting of the outdoor unit is intensified, and the load of the motor 1 is increased will be shown. In Figure 8 , the horizontal axis represents time. In addition, Figure 8 the vertical axis of (a) of Figure 8 represents the state of the load of the motor 1, Figure 8 the vertical axis of (b) represents the phase current,

[0052] That is, the motor drive device 50, in a case where the frosting image shown in (a) of Figure 8 , performs control to make the current value constant (to make the phase current peak limit value 8 constant) in a range where the overcurrent cutoff value is not reached, as shown in (b) of Figure 8 . Thus, as shown in (c) of Figure 8As shown in (c), the rotation speed of the motor 1 during light load, at which the frost is not aggravated, is increased to the maximum rotation speed 11, and heat exchange is efficiently performed by the outdoor heat exchanger 21. In other words, the air conditioner 100 that can improve the heating capacity is obtained.

[0053] In addition, if the air blowing fan 18 driven by the motor driving device 50 blows air in the opposite direction to the air blowing direction, the load of the motor 1 is sometimes increased, and the current value is increased. However, the motor driving device 50 controls the current value to be constant, and thus the rotation speed is decreased in the case where the air in the opposite direction is generated, and the rotation speed is continued to the heating operation in the case where the air is stopped. Therefore, the air conditioner 100 that is highly reliable and can improve the heating capacity is obtained.

[0054] Further, the outdoor heat exchanger 21 becomes a clogged state due to aging, accumulation of dust, or the like, and thus even in the case where the torque required to drive the air blowing fan 18 is increased, the rotation is performed at the optimal rotation speed with the constant current value. Therefore, the air conditioner 100 that is highly reliable and can improve the heating capacity is obtained.

[0055] Further, although an example in which the motor 1 drives the air blowing fan 18 is shown in Figure 7 Further, although an example in which the motor 1 drives the air blowing fan 18 is shown in

[0056] The structure shown in the above embodiments represents one example, and can be combined with other known techniques, can be combined with each other, and can omit or change a part of the structure within the range not departing from the gist.

[0057] Explanation of Reference Numerals

[0058] 1... motor; 2... inverter; 3... DC power supply; 4a-4f... switching elements; 5a-5c... shunt resistors; 6... phase current detection section; 7... phase current peak value calculation section; 8... phase current peak value limit value; 9... speed-up control section; 10... rotational speed command value calculation section; 11... maximum rotational speed; 12... target rotational speed; 13... maximum fan increase amount; 14... fan stall value calculation section; 15... fan stall value; 16... fan speed-up value; 18... air supply fan; 19... compressor; 20... four-way valve; 21... outdoor heat exchanger; 22... expansion valve; 23... indoor heat exchanger; 24... refrigerant piping; 50... motor drive device; 51... command value calculation section; 100... air conditioner.

Claims

1. An electric motor drive apparatus, characterized by comprising: Possessing: an inverter that converts a direct-current voltage into a three-phase alternating-current voltage and supplies it to a motor; a phase current detection section that detects a current flowing in each phase of the motor, that is, a phase current; a phase current peak value calculation section that calculates a peak value of the phase current detected by the phase current detection section, that is, a phase current peak value; and an instruction value operation section that generates a fan rotational speed instruction value for a blower fan that operates by the motor, based on the phase current peak value and a phase current peak value limit value set in advance, the instruction value operation section generates the fan rotational speed instruction value that reduces a fan rotational speed that is a rotational speed of the blower fan, in a case where the phase current peak value is greater than the phase current peak value limit value, and generates the fan rotational speed instruction value that increases the fan rotational speed, in a case where the phase current peak value is less than the phase current peak value limit value.

2. The motor drive device according to claim 1, characterized in that the phase current peak value calculation section calculates a square value of a root mean square value of the phase current, based on a d-axis current and a q-axis current obtained by dq-converting an instantaneous value of the phase current detected by the phase current detection section, and calculates the phase current peak value based on the calculated square value.

3. The motor drive device according to claim 1 or 2, characterized in that the instruction value operation section performs the following processing: processing of subtracting a target rotational speed of the blower fan from a maximum rotational speed of the blower fan set in advance, to obtain a fan increase amount maximum value; processing of calculating a fan stall speed value based on a difference between the phase current peak value and the phase current peak value limit value; processing of subtracting the fan stall speed value from the fan increase amount maximum value, to obtain a fan speed-up value; and processing of adding the fan speed-up value to the target rotational speed, to generate the fan rotational speed instruction value.

4. The motor drive device according to claim 3, characterized in that the instruction value operation section calculates the fan speed-up value with a period of controlling the rotational speed of the blower fan, that is, a control period, and in a case where the fan speed-up value greater than a fan speed-up value calculated last time is calculated, generates the fan rotational speed instruction value using the fan speed-up value calculated this time, after a certain time set in advance elapses.

5. An air conditioner, characterized by possessing the motor drive device according to any one of claims 1 to 4. ​

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