Electric motor drive systems and air conditioners

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

Technical Field

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

Background Art

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

[0003] For example, in the air conditioner described in Patent Document 1, the rotational speed of the motor is controlled to a target rotational speed by switching and applying a DC voltage with an inverter. Further, in the air conditioner described in Patent Document 1, on-off control of the switching element of the inverter is performed based on the magnetic pole position of the motor, the DC voltage applied to the inverter, and the current flowing through the inverter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the air conditioner described in Patent Document 1, the current flowing through the inverter is detected by 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. In addition, if an excessive current flows through the inverter, a protection function is activated to stop operation. Therefore, when using a peak hold circuit for current detection, the threshold for determining whether or not to activate the protection circuit must be set lower than in the case of instantaneous value detection in order to prevent the protection function from activating too late. Consequently, in a configuration that uses a peak hold circuit, it is expected that the maximum operating speed will be lower, i.e., the operating efficiency will decrease, compared to a configuration that detects current without using a peak hold circuit.

[0006] Furthermore, existing instantaneous value detection systems do not have an external circuit and lack a means for detecting the current peak value. As a result, it was difficult to vary the rotational speed according to the current peak value, that is, to operate the motor at the maximum rotational speed according to the load conditions.

[0007] This disclosure has been made in view of the above, and aims to provide an electric motor drive device that can operate at the maximum rotational speed according to the load conditions of the electric motor. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, the motor drive device according to this disclosure comprises: an inverter that converts a DC voltage into a three-phase AC voltage and supplies it to a motor; a phase current detection unit that detects the phase currents that flow through each phase of the motor; a phase current peak value calculation unit that calculates the phase current peak value, which is the peak value of the phase currents 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 motor based on the phase current peak value and a predetermined phase current peak limit value, wherein the command value calculation unit The following processes are executed: subtracting the target rotation speed of the blower fan from the predetermined maximum rotation speed of the blower fan to determine the maximum fan speed increase; calculating the fan stall value based on the difference between the phase current peak value and the phase current peak limit value; subtracting the fan stall value from the maximum fan speed increase to determine the fan speed increase value; and adding the fan speed increase value to the target rotation speed to generate a fan speed command value. do. [Effects of the Invention]

[0009] The electric motor drive system described herein has the effect of being able to operate at the maximum rotational speed corresponding to the load conditions of the electric motor. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the configuration of an electric motor drive device according to Embodiment 1. [Figure 2] A flowchart illustrating an example of the operation of the phase current detection unit and the phase current peak value calculation unit of an electric motor drive system. [Figure 3] This diagram shows an example of the operation of the speed-increasing control unit and the rotational speed command value calculation unit of the electric motor drive system. [Figure 4] A flowchart illustrating an example of how the speed-increasing control unit and rotation speed command value calculation unit of an electric motor drive unit suppress fan speed hunting. [Figure 5] This diagram shows an example of fan speed control operation using an electric motor drive device. [Figure 6] A flowchart illustrating an example of how the speed-increasing control unit and rotation speed command value calculation unit of the electric motor drive unit calculate the fan rotation speed command value. [Figure 7] A diagram showing an example configuration of an air conditioner according to Embodiment 2. [Figure 8] A diagram showing an example of the control operation of an air conditioner according to Embodiment 2. [Modes for carrying out the invention]

[0011] The electric motor drive unit and air conditioner according to embodiments of this disclosure will be described in detail below with reference to the drawings.

[0012] Embodiment 1. Figure 1 shows an example configuration of an electric motor drive device 50 according to Embodiment 1. The electric motor drive device 50 has a DC power supply 3 connected to the input side and an electric motor 1 connected to the output side. The electric motor drive device 50 drives the electric motor 1 by converting the DC voltage supplied from the DC power supply 3 into a three-phase AC voltage and supplying it to the electric motor 1. The electric motor drive device 50 is applied to an air conditioner, which is not shown in Figure 1. The electric motor 1 operates, for example, a blower fan (hereinafter sometimes referred to as an outdoor fan) installed on the outdoor unit of the air conditioner. The electric motor 1 may also be used to drive the compressor of the air conditioner.

[0013] As shown in Figure 1, the motor drive unit 50 includes an inverter 2 that converts the DC voltage supplied from the DC power supply 3 into a three-phase AC voltage and supplies it to the motor 1; a phase current detection unit 6 that detects the instantaneous value of the current flowing through each phase of the motor 1 (hereinafter referred to as phase current); a phase current peak value calculation unit 7 that calculates the peak value of each phase current; a speed increase control unit 9 that determines the amount of change in the rotation speed of the outdoor fan based on a predetermined phase current peak limit value 8 and the peak value of the phase current 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 the 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 implemented, for example, by a microcontroller.

[0014] The inverter 2 includes switching elements 4a to 4f connected in a bridge configuration and shunt resistors 5a to 5c. PWM (Pulse Width Modulation) signals for PWM control generated by an inverter control unit (not shown) are applied to the switching elements 4a to 4f. The switching elements 4a to 4f generate a three-phase alternating voltage applied to the electric motor 1 by being driven according to the PWM signals. The shunt resistors 5a to 5c are provided between the switching elements of each phase and the DC bus, respectively, and are used for detecting the instantaneous value of the phase current of each phase by the phase current detection unit 6. That is, the phase current detection unit 6 calculates the instantaneous value of the phase current of each phase from the terminal voltage and resistance value 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 the phase current peak value calculation unit 7, and the phase current peak value calculation unit 7 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 operations of the phase current detection unit 6 and the phase current peak value calculation unit 7 of the electric motor drive device 50, specifically, the operation of calculating the peak value of the phase current of each phase.

[0016] First, the phase current detection unit 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 calculates the instantaneous value of the d-axis current, which is the current on the d-axis, and the instantaneous value of the q-axis current, which is the current on the q-axis, by performing a dq transformation on the instantaneous value of the phase current detected by the phase current detection unit 6. Next, the phase current peak value calculation unit 7 calculates the squared 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 squared value 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 obtain the phase current peak value of each phase.

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

[0019] The speed increase control unit 9 calculates the difference between the preset maximum rotation speed 11 and the target rotation speed 12 of the blower fan to generate the maximum fan increase value 13. Further, the speed increase control unit 9 calculates the difference between the phase current peak value calculated by the phase current peak value calculation unit 7 and the phase current peak limit value 8, and executes PI (Proportional Integral) control using this difference in the fan stall value calculation unit 14 to calculate the fan stall value 15. Note that the phase current peak limit value 8 needs to be set below the overcurrent cutoff value so that the motor drive device 50 does not enter overcurrent cutoff. Overcurrent cutoff is a protection operation that stops the operation of the inverter 2 when the input current to the inverter 2 becomes excessive. The overcurrent cutoff value is used to determine whether to perform overcurrent cutoff, that is, to determine whether the input current to the inverter 2 is excessive, and overcurrent cutoff is executed when the input current to the inverter 2 exceeds the overcurrent cutoff value, for example.

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

[0021] Here, between the above maximum rotation speed 11 and eyes rated rotation speed 12 and During the fan stall value 15, Fan speed increase value 16 and the following conditions shown in equations (1) and (2) are provided.

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

[0023] The rotation speed command value calculation unit 10 adds the fan speed increase value 16 generated by the speed increase control unit 9 to the target rotation speed 12 to generate a fan rotation speed command value. Note that 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). The inverter control unit generates a PWM signal applied to the switching elements 4a to 4f of the inverter 2 based on the fan rotation speed command value and switches the switching elements 4a to 4f.

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

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

[0026] As shown in Figure 4, the speed-increasing 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-increasing 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 previously executed step S22. If the latest fan speed increase value 16 is greater than the previous value (step S23: Yes), the calculation of the fan rotation speed command value is stopped until a certain period of time has elapsed according to a preset time constraint, that is, after the fan rotation speed has been kept constant for a certain period of time as shown in Figure 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 less than or equal to 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] Thus, when the speed-increasing control unit 9 and the rotation speed command value calculation unit 10 transition from a deceleration zone where the fan rotation speed is reduced to a speed-increasing zone where the fan rotation speed is increased, they increase the fan rotation speed only after a time-constrained period during which the fan rotation speed remains unchanged. Furthermore, when transitioning from the speed-increasing zone to a deceleration zone, they decrease the fan rotation speed without going through a time-constrained period. As a result, the amount of change per unit time in the fan rotation speed in the deceleration zone becomes greater than the amount of change per unit time in the speed-increasing zone.

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

[0030] Control cycle of the speed-increasing control unit 9 ≪ Time constraint … (3)

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

[0032] Figure 6 is a flowchart showing an example of the operation in which the speed-increasing control unit 9 and the rotation speed command value calculation unit 10 of the electric motor drive unit 50 calculate the fan rotation speed command value.

[0033] As shown in Figure 6, the speed-increasing 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 (0) or not (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 that indicates the preset maximum rotation speed (step S33). If the fan stall value 15 is not zero (step S32: No), check whether the fan stall value 15 and the maximum fan increase amount 13 are the same (step S34). If the fan stall value 15 and the maximum fan increase amount 13 are the same (step S34: Yes), the rotation speed command value calculation unit 10 generates a fan rotation speed command value that indicates the target rotation speed 12 (step S35). If the fan stall value 15 and the maximum fan speed increase value 13 are not the same (step S34: No), the rotation speed command value calculation unit 10 generates a fan speed command value that indicates the rotation speed obtained by adding the fan speed increase value 16 to the target rotation speed 12 (step S36).

[0034] As described above, the 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 values. Furthermore, if the calculated phase current peak value is greater than the phase current peak limit value 8, the motor drive device 50 reduces the rotational speed, and if the phase current peak value is 8 or less, it increases the rotational speed. The motor drive device 50 according to this embodiment can operate the motor 1 at the maximum rotational speed corresponding to the load conditions of the motor 1, thereby improving operating efficiency.

[0035] Furthermore, the motor drive unit 50 controls the fan speed so that the rate of change per unit time is greater in the deceleration range than in the acceleration range. This suppresses the occurrence of fan speed hunting when the motor 1 is driven near the phase current peak limit value 8, thereby stabilizing the control of the fan speed.

[0036] Embodiment 2. Embodiment 2 describes an example of the application of the electric motor drive device 50 described in Embodiment 1.

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

[0038] The air conditioner 100 includes the DC power supply 3, motor drive unit 50 and motor 1 described in Embodiment 1, 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 blow air to the outdoor heat exchanger 21 and perform heat exchange.

[0039] The refrigeration cycle is formed by the circulation of refrigerant through the compressor 19, four-way valve 20, outdoor heat exchanger 21, expansion valve 22, indoor heat exchanger 23, and refrigerant piping 24.

[0040] As described above, by applying the motor drive device 50 and motor 1 described in Embodiment 1 to operate the blower fan 18 of the air conditioner 100, when frost has not yet formed on the outdoor unit of the air conditioner 100, that is, when the motor 1 is under light load, it is possible to use current up to the phase current peak limit value 8 and increase the rotational speed accordingly. For example, control as shown in Figure 8 becomes possible, and the operating efficiency can be improved.

[0041] Figure 8 shows an example of the control operation of the air conditioner 100 according to Embodiment 2. Figure 8 shows an example of the control operation when frost buildup progresses on the outdoor unit and the load on the motor 1 increases accordingly. In Figure 8, the horizontal axis represents time. The vertical axis in Figure 8(a) represents the load state of the motor 1, the vertical axis in Figure 8(b) represents the phase current, and the vertical axis in Figure 8(c) represents the rotational speed of the blower fan 18.

[0042] In other words, when the frost formation image shown in Figure 8(a) occurs, the motor drive unit 50 controls the current value to remain constant (constant at the phase current peak limit value of 8) as shown in Figure 8(b), within a range that does not reach the overcurrent cutoff value. As a result, as shown in Figure 8(c), it becomes possible to increase the rotational speed of the motor 1, which is not yet frosted, to the maximum rotational speed 11 under light load, enabling efficient heat exchange by the outdoor heat exchanger 21. In other words, an air conditioner 100 capable of improving heating capacity can be obtained.

[0043] Furthermore, if wind blows in the opposite direction to the airflow direction in the blower fan 18 driven by the motor drive unit 50, the load on the motor 1 may increase, and the current value may increase. However, since the motor drive unit 50 is controlled to keep the current value constant, it is possible to reduce the rotation speed when wind blows in the opposite direction and increase the rotation speed when the wind stops, thereby continuing the heating operation. Thus, it is possible to obtain 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, increasing the torque required to drive the blower fan 18, it can still operate at an optimal rotational speed that maintains a constant current. Therefore, a highly reliable air conditioner 100 with improved heating capacity can be obtained.

[0045] Although Figure 7 shows an example in which the motor 1 operates the blower fan 18, the configuration may also be such that the motor 1 operates the compression mechanism of the compressor 19. Alternatively, the motor drive device 50 described in Embodiment 1 may be applied to both the motor that operates the blower fan 18 and the motor that operates the compression mechanism of the compressor 19, thereby driving each motor.

[0046] The configurations shown in the above embodiments are merely examples, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention. [Explanation of Symbols]

[0047] 1. Electric motor, 2. Inverter, 3. DC power supply, 4a~4f. Switching elements, 5a~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. Maximum fan increase amount, 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 unit, 51. Command value calculation unit, 100. Air conditioner.

Claims

1. An inverter that converts DC voltage to three-phase AC voltage and supplies it to the motor, A phase current detection unit for detecting the phase current, which is the current flowing through each phase of the aforementioned electric motor, A phase current peak value calculation unit calculates a phase current peak value, which is the peak value of the phase current detected by the phase current detection unit. A command value calculation unit that generates a fan 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 is: A process to determine the maximum fan speed increase by subtracting the target rotation speed of the blower fan from the predetermined maximum rotation speed of the blower fan, A process for calculating the fan stall value based on the difference between the phase current peak value and the phase current peak limit value, The process of obtaining the fan speed increase value by subtracting the fan stall value from the maximum fan speed increase value, The process of adding the aforementioned fan speed increase value to the aforementioned target rotation speed to generate the aforementioned fan rotation speed command value is executed. Electric motor drive system.

2. The phase current peak value calculation unit is: The instantaneous value of the phase current detected by the phase current detection unit is converted to dq-axis current and q-axis current to obtain the squared effective value of the phase current, and the peak value of the phase current is calculated from the calculated squared value. The electric motor drive device according to claim 1.

3. The command value calculation unit is: The fan speed increase value is calculated in a control cycle, which is the period for controlling the rotation speed of the blower fan. If the calculated fan speed increase value is greater than the previously calculated fan speed increase value, after a predetermined period of time has elapsed, the fan rotation speed command value is generated using the fan speed increase value calculated this time. The electric motor drive device according to claim 1 or 2.

4. An air conditioner equipped with an electric motor drive device as described in claim 1.

Images