Electric motor drive device and air conditioner

Abstract

An electric motor drive device (50) comprises: an inverter (2) that inverts a DC voltage to three-phase AC voltages and supplies the three-phase AC voltages to an electric motor (1); a phase current detection unit (6) that detects a phase current which is a current flowing in each phase of the electric motor; a phase current peak value calculation unit (7) that calculates a phase current peak value, which is a peak value of the phase current detected by the phase current detection unit; and a command value computation unit (51) that generates, on the basis of the phase current peak value and a predetermined phase current peak limit value, a fan rotation speed command value for a blower fan operated by the electric motor, wherein the command value computation unit generates the fan rotation speed command value that reduces the fan rotation speed, which is a rotation speed of the blower fan when the phase current peak value is more than the phase current peak limit value and generates the fan rotation speed command value that increases the fan rotation speed when the phase current peak value is less than the phase current peak limit value.

Description

Electric motor drive device and air conditioner

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

[0002] Conventionally, motor drive devices including inverters and the like have controlled the power supplied to the motor to drive the motor as desired. For example, in air conditioners, a blower is used to efficiently exchange heat between a refrigerant flowing through a heat exchanger and, for example, air. In this case, the rotation speed of the fan is controlled by controlling the output voltage of an inverter that applies voltage to the motor that rotates the blower fan.

[0003] For example, in the air conditioner described in Patent Document 1, the rotation speed of the electric motor is controlled to a target rotation speed by applying a DC voltage by switching it using an inverter. Also, in the air conditioner described in Patent Document 1, the switching elements of the inverter are controlled to be turned on and off based on the magnetic pole position of the electric motor, the DC voltage applied to the inverter, and the current flowing through the inverter.

[0004] JP 2011-069551 A

[0005] In the air conditioner described in Patent Document 1, the current flowing through the inverter is detected using a circuit combining a shunt resistor and a peak-hold circuit. However, current detection using a peak-hold circuit has the problem of a larger error between the actual current value and the detected value compared to instantaneous value detection. Furthermore, if excessive current flows through the inverter, a protection function is activated to stop operation or perform other control. Therefore, when current detection is performed using a peak-hold circuit, the threshold for determining whether to activate the protection circuit must be set lower than in the case of instantaneous value detection to prevent the protection function from being activated too slowly. Therefore, when using a peak-hold circuit for current detection, the maximum operable rotation speed is expected to be lower, i.e., operating efficiency is expected to be reduced, compared to a configuration that detects current without using a peak-hold circuit.

[0006] Furthermore, existing instantaneous value detection systems do not require an external circuit and do not have a means for detecting peak current values, making it difficult to vary the rotation speed according to the peak current value, i.e., to operate the motor at the maximum rotation speed according to the load conditions.

[0007] The present disclosure has been made in view of the above, and has an object to provide an electric motor drive device that can operate at a maximum rotation speed according to the load condition of the electric motor.

[0008] In order to solve the above-mentioned problems and achieve the object, an electric motor drive device according to the present disclosure includes an inverter that converts a DC voltage into a three-phase AC voltage and supplies it to an electric motor, a phase current detection unit that detects phase currents that are currents that flow through each phase of the electric motor, a phase current peak value calculation unit that calculates a phase current peak value that is the peak value of the phase current detected by the phase current detection unit, and a command value calculation unit that generates a fan rotation speed command value for a blower fan operated by the electric motor based on the phase current peak value and a predetermined phase current peak limit value, wherein the command value calculation unit generates a fan rotation speed command value that decreases the fan rotation speed that is the rotation speed of the blower fan when the phase current peak value is greater than the phase current peak limit value, and generates a fan rotation speed command value that increases the fan rotation speed when the phase current peak value is smaller than the phase current peak limit value.

[0009] The electric motor drive device according to the present disclosure has an advantage that it can be operated at the maximum rotation speed according to the load condition of the electric motor.

[0010] FIG. 1 is a diagram showing an example of the configuration of an electric motor drive device according to embodiment 1; A flowchart showing an example of the operation of a phase current detection unit and a phase current peak value calculation unit of the electric motor drive device; A flowchart showing an example of the operation of a speed increase control unit and a rotation speed command value calculation unit of the electric motor drive device; A flowchart showing an example of a method by which the speed increase control unit and the rotation speed command value calculation unit of the electric motor drive device suppress hunting in the fan rotation speed; A diagram showing an example of the control operation of the fan rotation speed by the electric motor drive device; A flowchart showing an example of the operation by the speed increase control unit and the rotation speed command value calculation unit of the electric motor drive device to calculate a fan rotation speed command value; A diagram showing an example of the configuration of an air conditioner according to embodiment 2; A diagram showing an example of the control operation of the air conditioner according to embodiment 2;

[0011] Hereinafter, an electric motor drive device and an air conditioner according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0012] First Embodiment. Fig. 1 is a diagram showing an example of the configuration of an electric motor drive device 50 according to a first embodiment. The electric motor drive device 50 has a DC power supply 3 connected to its input side and an electric motor 1 connected to its output side. The electric motor drive device 50 converts DC voltage supplied from the DC power supply 3 into a three-phase AC voltage and supplies the AC voltage to the electric motor 1, thereby driving the electric motor 1. The electric motor drive device 50 is applied to an air conditioner, the illustration of which is omitted in Fig. 1. The electric motor 1 operates, for example, a blower fan (hereinafter also referred to as an outdoor fan) provided in an outdoor unit of the air conditioner. Note that the electric motor 1 may also be used to drive a compressor of the air conditioner.

[0013] As shown in FIG. 1 , the electric motor drive device 50 includes an inverter 2 that converts a DC voltage supplied from a DC power supply 3 into a three-phase AC voltage and supplies the converted voltage to the electric motor 1, a phase current detection unit 6 that detects instantaneous values ​​of currents (hereinafter referred to as phase currents) flowing through each phase of the electric motor 1, a phase current peak value calculation unit 7 that calculates peak values ​​of the phase currents of each phase, a speed increase control unit 9 that determines an amount of change in the rotation speed of an outdoor fan based on a predetermined phase current peak limit value 8 and the peak values ​​of the phase currents calculated by the phase current peak value calculation unit 7, and a rotation speed command value calculation unit 10 that calculates a command value for the rotation speed of the outdoor fan (hereinafter referred to as fan rotation speed command value) based on the amount of change determined by the speed increase control unit 9. The speed increase control unit 9 and the rotation speed command value calculation unit 10 constitute a command value calculation unit 51. The phase current detection unit 6, the phase current peak value calculation unit 7, the speed increase control unit 9, and the rotation speed command value calculation unit 10 are realized, for example, by a microcontroller.

[0014] The inverter 2 includes bridge-connected switching elements 4a to 4f and shunt resistors 5a to 5c. A PWM (Pulse Width Modulation) signal for PWM control, generated by an inverter control unit (not shown), is applied to the switching elements 4a to 4f. The switching elements 4a to 4f are driven in accordance with the PWM signal to generate a three-phase AC voltage to be applied to the electric motor 1. The shunt resistors 5a to 5c are respectively provided between the switching elements of each phase and the DC bus and are used by the phase current detection unit 6 to detect the instantaneous value of the phase current of each phase. That is, the phase current detection unit 6 calculates the instantaneous value of the phase current of each phase from the terminal voltages and resistance values ​​of the shunt resistors 5a to 5c. The instantaneous value of the phase current of each phase is output from the phase current detection unit 6 to a phase current peak value calculation unit 7, which then calculates the peak value of the phase current of each phase (hereinafter referred to as the phase current peak value).

[0015] FIG. 2 is a flowchart showing an example of the operation of the phase current detector 6 and the phase current peak value calculator 7 of the electric motor drive device 50, specifically, the operation of calculating the phase current peak value of each phase.

[0016] First, the phase current detector 6 detects the instantaneous value of the phase current (step S11).

[0017] Next, the phase current peak value calculation unit 7 calculates the dq-axis currents (step S12). That is, the phase current peak value calculation unit 7 performs dq conversion on the instantaneous values ​​of the phase currents detected by the phase current detection unit 6 to calculate the instantaneous values ​​of the d-axis current, which is the current on the d-axis, and the instantaneous values ​​of the q-axis current, which is the current on the q-axis. Next, the phase current peak value calculation unit 7 calculates the square 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 of the phase current effective value (step S14). The phase current peak value calculation unit 7 executes the above steps S12 to S14 for each of the three phases to determine the phase current peak value of each phase.

[0018] FIG. 3 is a diagram showing an example of the operation of the speed increase control unit 9 and the rotation speed command value calculation unit 10 of the electric motor drive device 50.

[0019] The speed-up control unit 9 calculates the difference between a preset maximum rotation speed 11 and a target rotation speed 12 of the blower fan to generate a maximum fan increase amount 13. The speed-up control unit 9 also calculates the difference between the phase current peak value calculated by the phase current peak value calculation unit 7 and a phase current peak limit value 8, and executes PI (Proportional Integral) control using this difference in a fan stall value calculation unit 14 to calculate a fan stall value 15. The phase current peak limit value 8 needs to be set equal to or less than an overcurrent interrupt value so that the electric motor drive device 50 does not fall into an overcurrent interrupt. An overcurrent interrupt is a protective action that stops the operation of the inverter 2 when the input current to the inverter 2 becomes excessive. The overcurrent interrupt value is used to determine whether to perform an overcurrent interrupt, i.e., to determine whether the input current to the inverter 2 is excessive. An overcurrent interrupt is performed when the input current to the inverter 2 exceeds the overcurrent interrupt value, for example.

[0020] The speed increase control unit 9 further calculates the difference between the maximum fan speed increase value 13 and the fan stall value 15 to generate a fan speed increase value 16 .

[0021] Here, the conditions shown in the following formulas (1) and (2) are set between the maximum rotation speed 11, the target rotation speed 12, and the fan stall value 15.

[0022] Target rotation speed 12<Maximum rotation speed 11 (1) 0≦Fan stall value 15≦Fan speed increase value 16 (2)

[0023] A rotation speed command value calculation unit 10 generates a fan rotation speed command value by adding the fan rotation speed increase value 16 generated by the speed increase control unit 9 to the target rotation speed 12. The fan rotation speed command value calculated by the rotation speed command value calculation unit 10 is passed to an inverter control unit (not shown). Based on the fan rotation speed command value, the inverter control unit generates a PWM signal to be applied to the switching elements 4 a to 4 f of the inverter 2, thereby switching the switching elements 4 a to 4 f.

[0024] In the above process in which the speed increase control unit 9 and the rotation speed command value calculation unit 10 of the electric motor drive device 50 calculate the fan rotation speed command value based on the phase current peak value and the phase current peak limit value 8, by setting the conditions shown in the above equations (1) and (2), the fan rotation speed command value fluctuates between the maximum rotation speed 11 and the target rotation speed 12.

[0025] Furthermore, the speed increase control unit 9 and rotation speed command value calculation unit 10 of the electric motor drive device 50 suppress hunting of the fan rotation speed when the electric motor 1 is driven at a value near the phase current peak limit value 8 using the methods shown in Figures 4 and 5. Figure 4 is a flowchart showing an example of a method by which the speed increase control unit 9 and rotation speed command value calculation unit 10 of the electric motor drive device 50 suppress hunting of the fan rotation speed. Figure 5 is a diagram showing an example of a control operation of the fan rotation speed by the electric motor drive device 50. In Figure 5, the horizontal axis represents time, and the vertical axis represents the fan rotation speed command value.

[0026] As shown in FIG. 4 , the speed increase control unit 9 and the rotation speed command value calculation unit 10 first calculate the fan stall value 15 (step S21) and then calculate the fan speed increase value 16 (step S22). Next, the speed increase control unit 9 compares the latest fan speed increase value 16 calculated in step S22 with the previous value of the fan speed increase value 16 (step S23). The previous value of the fan speed increase value 16 is the fan speed increase value 16 calculated in the previous execution of step S22. If the latest fan speed increase value 16 is greater than the previous value (step S23: Yes), the calculation of the fan speed command value is stopped until a certain time has elapsed in accordance with a preset time constraint. That is, after the fan rotation speed is kept constant for a certain period of time as shown in FIG. 5 (step S24), the rotation speed command value calculation unit 10 calculates the fan rotation speed command value (step S25).

[0027] On the other hand, if the latest fan speed increase value 16 is equal to or less than the previous value (step S23: No), the rotation speed command value calculation unit 10 immediately calculates the fan rotation speed command value (step S25).

[0028] In this way, when transitioning from the deceleration range, in which the fan rotation speed is reduced, to the acceleration range, in which the fan rotation speed is increased, the speed-up control unit 9 and the rotation speed command value calculation unit 10 increase the fan rotation speed after a time-restricted period in which the fan rotation speed is not changed. Furthermore, when transitioning from the acceleration range to the deceleration range, the fan rotation speed is reduced without a time-restricted period. This results in an operation in which the rate of change per unit time in the deceleration range of the fan rotation speed is greater than the rate of change per unit time in the acceleration range.

[0029] Furthermore, by setting the condition shown in the following equation (3), the occurrence of hunting when the fan rotation speed changes from the deceleration range to the acceleration range is suppressed, and the fan rotation speed control is stabilized.

[0030] Control period of the speed increase control unit 9 << Time constraint ... (3)

[0031] The control period of the speed-up control unit 9 is the period during which the command value calculation unit 51 generates a fan rotation speed command value to control the rotation speed of the outdoor fan, and the speed-up control unit 9 calculates the fan speed-up value 16 at each control period. For example, if the control period of the speed-up control unit 9 is a period of microseconds (μs), the time constraint is set to a period of seconds (s).

[0032] FIG. 6 is a flowchart showing an example of the operation of the speed increase control unit 9 and the rotation speed command value calculation unit 10 of the electric motor drive device 50 to calculate the fan rotation speed command value.

[0033] As shown in FIG. 6 , the speed increase control unit 9 and the rotation speed command value calculation unit 10 first calculate the fan stall value 15 (step S31) and check whether the calculated fan stall value 15 is zero (step S32). If the fan stall value 15 is zero (step S32: Yes), the rotation speed command value calculation unit 10 generates a fan rotation speed command value indicating a preset maximum rotation speed (step S33). If the fan stall value 15 is not zero (step S32: No), the rotation speed command value calculation unit 10 checks whether the fan stall value 15 is equal to the maximum fan increase amount 13 (step S34). If the fan stall value 15 is equal to the maximum fan increase amount 13 (step S34: Yes), the rotation speed command value calculation unit 10 generates a fan rotation speed command value indicating the target rotation speed 12 (step S35). If the fan stall value 15 and the maximum fan increase amount 13 are not the same (step S34: No), the rotation speed command value calculation unit 10 generates a fan rotation speed command value indicating the rotation speed obtained by adding the fan acceleration value 16 to the target rotation speed 12 (step S36).

[0034] As described above, the electric motor drive device 50 according to this embodiment detects the instantaneous value of each phase current flowing through the inverter 2 and calculates the peak value of each phase current from the detected instantaneous value. Furthermore, the electric motor drive device 50 reduces the rotation speed when the calculated phase current peak value is greater than the phase current peak limit value 8, and increases the rotation speed when the phase current peak value is equal to or less than the phase current peak limit value 8. The electric motor drive device 50 according to this embodiment can operate the electric motor 1 at the maximum rotation speed according to the load status of the electric motor 1, thereby achieving improved operating efficiency.

[0035] Furthermore, the motor drive device 50 controls the fan rotation speed so that the amount of change per unit time is greater in the deceleration range than in the acceleration range, thereby suppressing hunting in the fan rotation speed when the motor 1 is driven near the phase current peak limit value 8, thereby achieving stable control of the fan rotation speed.

[0036] Second Embodiment In a second embodiment, an application example of the electric motor driving device 50 described in the first embodiment will be described.

[0037] Fig. 7 is a diagram showing an example of the configuration of an air conditioner 100 according to embodiment 2. The air conditioner 100 shown in Fig. 7 is realized by applying the electric motor drive device 50 described in embodiment 1. The air conditioner 100 is an example of a refrigeration cycle device realized by applying the electric motor drive device 50.

[0038] The air conditioner 100 includes the DC power supply 3, motor drive device 50, and motor 1 described in the first embodiment, as well as a blower fan 18, a compressor 19, a four-way valve 20, an outdoor heat exchanger 21, an expansion valve 22, an indoor heat exchanger 23, and refrigerant piping 24. The motor 1 operates the blower fan 18 to send air to the outdoor heat exchanger 21 for heat exchange.

[0039] A refrigeration cycle is formed by circulating a refrigerant through 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 pipe 24.

[0040] In this way, by applying the motor drive device 50 and electric motor 1 described in the first embodiment to operate the blower fan 18 of the air conditioner 100, when frost formation on the outdoor unit of the air conditioner 100 is not advanced, that is, when the electric motor 1 is in a light load state, it is possible to use current up to the phase current peak limit value 8 and increase the rotation speed accordingly. For example, control such as that shown in Fig. 8 becomes possible, thereby improving operating efficiency.

[0041] Fig. 8 is a diagram showing an example of the control operation of the air conditioner 100 according to embodiment 2. Fig. 8 shows an example of the control operation when frost formation on the outdoor unit progresses and the load on the electric motor 1 increases accordingly. In Fig. 8, the horizontal axis represents time. The vertical axis of Fig. 8(a) represents the load state of the electric motor 1, the vertical axis of Fig. 8(b) represents the phase current, and the vertical axis of Fig. 8(c) represents the rotation speed of the blower fan 18.

[0042] That is, when frost formation is occurring as shown in Fig. 8(a), the motor drive device 50 controls the current value to be constant (constant at the phase current peak limit value 8) as shown in Fig. 8(b) within a range that does not reach the overcurrent interrupt value. This makes it possible to increase the rotation speed of the motor 1 under light load when frost formation is not progressing to the maximum rotation speed 11 as shown in Fig. 8(c), enabling more efficient heat exchange with the outdoor heat exchanger 21. In other words, it is possible to obtain an air conditioner 100 that can improve heating capacity.

[0043] Furthermore, if wind blows in the opposite direction to the airflow direction of the blower fan 18 driven by the motor drive unit 50, the load on the motor 1 increases, which can cause an increase in the current value. However, because the motor drive unit 50 controls the current value to be constant, it is possible to continue heating operation by reducing the rotation speed when wind blows in the opposite direction and increasing the rotation speed when the wind stops. This provides an air conditioner 100 that is highly reliable and capable of improving heating capacity.

[0044] Furthermore, even if the outdoor heat exchanger 21 becomes clogged due to aging or the accumulation of dust, etc., and the torque required to drive the blower fan 18 increases, the air conditioner 100 can be operated at an optimum rotation speed at which the current value remains constant. Therefore, the air conditioner 100 can be obtained with high reliability and improved heating capacity.

[0045] 7 shows an example in which the electric motor 1 operates the blower fan 18, but the electric motor 1 may also operate the compression mechanism of the compressor 19. Furthermore, the electric motor drive device 50 described in the first embodiment may be applied to both the electric motor that operates the blower fan 18 and the electric motor that operates the compression mechanism of the compressor 19, and each electric motor may be driven.

[0046] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0047] REFERENCE SIGNS LIST 1 electric motor, 2 inverter, 3 DC power supply, 4a to 4f switching elements, 5a to 5c shunt resistors, 6 phase current detection unit, 7 phase current peak value calculation unit, 8 phase current peak limit value, 9 speed increase control unit, 10 rotation speed command value calculation unit, 11 maximum rotation speed, 12 target rotation speed, 13 fan increase maximum value, 14 fan stall value calculation unit, 15 fan stall value, 16 fan speed increase value, 18 blower fan, 19 compressor, 20 four-way valve, 21 outdoor heat exchanger, 22 expansion valve, 23 indoor heat exchanger, 24 refrigerant piping, 50 electric motor drive device, 51 command value calculation unit, 100 air conditioner.

Claims

1. An inverter that converts DC voltage into three-phase AC voltage and supplies it to an electric motor; a phase current detection unit that detects a phase current that is a current flowing through each phase of the electric motor; a phase current peak value calculation unit that calculates a phase current peak value that is a peak value of the phase current detected by the phase current detection unit; a command value calculation unit that generates a fan rotation speed command value for a blower fan operated by the electric motor based on the phase current peak value and a predetermined phase current peak limit value; Equipped with the command value calculation unit generates the fan rotation speed command value to decrease a fan rotation speed, which is the rotation speed of the blower fan, when the phase current peak value is greater than the phase current peak limit value, and generates the fan rotation speed command value to increase the fan rotation speed, when the phase current peak value is smaller than the phase current peak limit value. Electric motor drive unit.

2. The phase current peak value calculation unit calculating a squared value of an effective value of the phase current from a d-axis current and a q-axis current obtained by performing a dq transform on the instantaneous value of the phase current detected by the phase current detection unit, and calculating the phase current peak value from the calculated squared value; 2. The electric motor drive device according to claim 1.

3. The command value calculation unit is A process of subtracting a target rotation speed of the blower fan from a predetermined maximum rotation speed of the blower fan to obtain a maximum fan increase amount; calculating a fan stall value based on a difference between the phase current peak value and the phase current peak limit value; determining a fan increase value by subtracting the fan stall value from the maximum fan increase value; and generating the fan rotation speed command value by adding the fan speed increase value to the target rotation speed.

3. The electric motor drive device according to claim 1 or 2.

4. The command value calculation unit is the fan speed increase value is calculated at a control period, which is a period for controlling the rotation speed of the blower fan, and when the fan speed increase value calculated is greater than the previously calculated fan speed increase value, after a predetermined time has elapsed, the fan rotation speed command value is generated using the currently calculated fan speed increase value.

4. The electric motor drive device according to claim 3.

5. An air conditioner comprising the motor drive device according to claim 1.