Motor driving device and refrigeration cycle device

Abstract

A motor drive unit (9) includes a motor (lM) including a plurality of phase windings (Lu, Lv, Lw) in a mutually unconnected state, a first inverter (30) which controls application of electric power to one ends of the phase windings (Lu, Lv, Lw), a second inverter (40) which controls application of electric power to the other ends of the phase windings (Lu, Lv, Lw), relays each of which includes a make / break contact connected between the other ends of the phase windings (Lu, Lv, Lw), and a controller (9b) which switches, according to a value of a current flowing through the motor (1M), between an open-windings mode and a star-connection mode.

Description

Motor drive device and refrigeration cycle device

[0001] The present invention relates to a motor drive device that drives a motor having a plurality of phase windings that are not connected to each other, and to a refrigeration cycle apparatus that includes the motor drive device.

[0002] A permanent magnet synchronous motor having multiple phase windings is used as a drive motor for a compressor mounted in a refrigeration cycle device such as an air conditioner. One known example of a permanent magnet synchronous motor (also called a DC brushless motor) is an open-winding motor, in which the multiple phase windings are disconnected from one another.

[0003] The motor drive device for driving this open-winding motor (abbreviated as "motor") includes a first inverter that controls the energization of one end of each phase winding of the motor, a second inverter that controls the energization of the other end of each phase winding of the motor, and a switch connected between the other ends of the phase windings. The motor drive device selectively selects between a star-connection mode in which the phase windings are star-connected (also called a star-shaped connection) and the first inverter is switched independently by closing the switch, and an open-winding mode in which the phase windings are disconnected and the first and second inverters are switched in conjunction with each other by opening the switch. Setting the open-winding mode allows the motor to be driven at high rotation speeds, while setting the star-connection mode at low rotation speeds allows the motor to be driven with high efficiency, thereby enabling the motor to be driven as efficiently as possible over a wide operating range, from high to low rotation speeds. This achieves both an expanded operating range of the motor and improved efficiency of the motor drive device.

[0004] Patent No. 4906836

[0005] A mechanical relay with mechanical switching contacts is used as a switch to switch between star connection mode and open winding mode. To ensure proper operation, this relay has an upper limit for the current that flows through the switching contacts. This upper limit is generally called the rated current or rated contact current (hereinafter referred to as the rated current). If an overcurrent exceeding this rated current continues to flow through the switching contacts of the relay, the relay may fail. Furthermore, a mechanical relay has a lifespan that is determined by the number of times it operates. This lifespan becomes shorter the more frequently it switches between star connection mode and open winding mode.

[0006] An object of an embodiment of the present invention is to provide a refrigeration cycle device that can prevent the malfunction of overcurrent flowing through the switching contacts of a relay, and can minimize the number of times the relay operates, thereby improving the life of the relay.

[0007] The motor drive device of claim 1 comprises: a motor having a plurality of phase windings that are disconnected from one another; a first inverter that controls the supply of current to one end of each of the phase windings; a second inverter that controls the supply of current to the other end of each of the phase windings; a relay having an open / close contact connected between the other ends of the phase windings; and a controller that switches, in accordance with the value of current flowing through the motor, between an open winding mode in which the other ends of the phase windings are disconnected by opening the relay and the first and second inverters are linked together for switching, and a star connection mode in which the other ends of the phase windings are connected together by closing the relay and the first inverter is switched.

[0008] A block diagram showing the configuration of a refrigeration cycle apparatus including a motor drive device of an embodiment. A block diagram showing the configuration of a motor drive device of an embodiment. A diagram showing the relationship between motor rotation speed and motor current in a motor drive device of an embodiment, for each mode of star connection and open winding. A diagram showing the relationship between motor rotation speed and efficiency in a motor drive device of an embodiment, for each mode of star connection and open winding. A diagram showing mode switching conditions in a motor drive device of an embodiment. A flowchart showing control of a motor drive device of an embodiment. A diagram showing an example of changes in motor rotation speed from defrost preparation to the start of defrosting and the end of defrosting in a refrigeration cycle apparatus according to an embodiment.

[0009] Hereinafter, a refrigeration cycle apparatus according to one embodiment will be described with reference to the drawings. As an example of the refrigeration cycle apparatus, a so-called multi-type air conditioner in which multiple outdoor units and multiple indoor units are connected in parallel will be described. The present invention is not limited to air conditioners, and can also be applied to other refrigeration cycle apparatuses such as heat pump chiller units and refrigerators.

[0010] As shown in Fig. 1, for example, two indoor units B1 and B2 are connected in parallel to an outdoor unit A via a liquid-side pipe C1 and a gas-side pipe C2. A signal line E for data transmission and control is connected between the outdoor unit A and the indoor units B1 and B2. This connection between the outdoor unit A and the indoor units B1 and B2 constitutes a multi-type refrigeration cycle system that performs heating and cooling. In this refrigeration cycle system, the outdoor unit A functions as a parent unit for overall control, and the indoor units B1 and B2 function as child units that operate in accordance with instructions from the parent unit.

[0011] The outdoor unit A includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, an expansion valve (pressure reducer) 4, an accumulator 5, an outdoor fan 6, an outdoor temperature sensor 7, a heat exchanger temperature sensor Te, an outdoor controller 8, and a motor drive device 9 of this embodiment. During cooling operation, as indicated by solid arrows, gas refrigerant flowing from the indoor units B1, B2 to the gas side pipe C2 passes through the four-way valve 2 and the accumulator 5 and is sucked into the compressor 1. The gas refrigerant compressed and discharged by the compressor 1 passes through the four-way valve 2 to the outdoor heat exchanger 3 (condenser). The refrigerant condenses after exchanging heat with outside air in the outdoor heat exchanger 3 and flows through the expansion valve 4 and the liquid side pipe C1 to the indoor units B1, B2. During heating operation, the flow path of the four-way valve 2 is switched, so that the liquid refrigerant flowing from the indoor units B1, B2 to the liquid side pipe C1 passes through the expansion valve 4 and flows to the outdoor heat exchanger 3 (evaporator), where the refrigerant exchanges heat with the outside air and vaporizes, passing through the four-way valve 2 and accumulator 5 and being sucked into the compressor 1, and the gas refrigerant compressed and discharged by the compressor 1 passes through the four-way valve 2 and gas side pipe C2 and flows to the indoor units B1, B2.

[0012] During heating operation, frost gradually forms on the surface of the outdoor heat exchanger 3, which functions as an evaporator. If this continues, the heat exchange rate of the outdoor heat exchanger 3 will decrease. As a countermeasure, the outdoor controller 8 detects the temperature of the outdoor heat exchanger 3 using the heat exchanger temperature sensor Te and monitors the amount of frost on the outdoor heat exchanger 3 based on the detected temperature. If the amount of frost increases, the outdoor controller 8 determines that defrosting of the outdoor heat exchanger 3 is necessary and starts defrost preparation by lowering the motor rotation speed N. When the motor rotation speed N drops to a predetermined value, the outdoor controller 8 switches the flow path of the four-way valve 2 to defrosting mode and starts defrosting operation by increasing the motor rotation speed N to a high rotation speed range, thereby removing the frost on the outdoor heat exchanger 3 using the heat of the refrigerant. The outdoor controller 8 then monitors the frost state of the outdoor heat exchanger 3 based on the temperature detected by the heat exchanger temperature sensor Te. When the frost disappears, the outdoor controller 8 lowers the motor rotation speed N. When the motor rotation speed N drops to the predetermined value, the outdoor controller 8 returns the flow path of the four-way valve 2 to heating mode and ends the defrosting operation. In addition, the outdoor controller 8 notifies the motor drive unit 9 of the need for defrosting when it determines that defrosting is necessary, and upon receiving this notification, begins preparations for defrosting, and notifies the motor drive unit 9 of the completion of the defrosting operation.

[0013] Each of the indoor units B1 and B2 includes a flow control valve 11, an indoor heat exchanger 12, an indoor fan 13, an indoor temperature sensor 14, and an indoor controller 15. During cooling operation, as indicated by the solid arrows, liquid refrigerant flowing from the outdoor unit A through the liquid-side pipe C1 passes through the flow control valve 11 and flows to the indoor heat exchanger (evaporator) 12. The refrigerant exchanges heat with the indoor air in the indoor heat exchanger 12 and vaporizes. The refrigerant then returns to the outdoor unit A through the gas-side pipe C2. During heating operation, gas refrigerant flowing from the outdoor unit A through the gas-side pipe C2 passes to the indoor heat exchanger (condenser) 12. The refrigerant then exchanges heat with the indoor air in the indoor heat exchanger 12 and condenses. The refrigerant then returns to the outdoor unit A through the liquid-side pipe C1. The flow control valve 11 is a pulse motor valve (PMV) whose opening angle changes continuously from fully closed to fully open depending on the number of drive voltage pulses supplied. The indoor fan 13 draws in indoor air and sends it to the indoor heat exchanger 12. The indoor temperature sensor 14 is disposed in the flow path of the indoor air drawn in by the indoor fan 13, and detects the temperature Ta of the indoor air. The indoor controller 15 detects the difference ΔTa between the temperature Ta detected by the indoor temperature sensor 14 and a preset indoor temperature Ts as the air conditioning load, controls the opening of the flow rate adjustment valve 11 in accordance with the air conditioning load ΔTa, and notifies the outdoor controller 8 of the air conditioning load ΔTa via a signal line E.

[0014] The outdoor controller 8 controls the rotation speed of the compressor 1 and the outdoor fan 6 so that the outdoor unit A can exhibit the capacity corresponding to the total load of the air conditioning load ΔTa notified from the indoor units B1, B2.

[0015] The compressor 1 is a hermetic compressor in which a motor 1M shown in Fig. 2 is used as a drive motor and housed in a sealed case together with a compression unit. The motor 1M is a three-phase permanent magnet synchronous motor, a so-called open-winding motor, having multiple phase windings Lu, Lv, and Lw that are not connected to one another. The phase windings Lu, Lv, and Lw are formed by winding a large number of thin copper wires at a high density to improve efficiency in the low rotation speed range (also referred to as the low- to medium-rotation speed range).

[0016] The motor drive device 9 of each of the outdoor units A1 to A3 includes a drive circuit 9a and a controller 9b shown in Fig. 2. The drive circuit 9a includes a DC power supply unit 55 that full-wave rectifies and smoothes the AC voltage of a three-phase AC power supply 50 and outputs the resulting voltage, an inverter (also referred to as a first inverter or master inverter) 30 that controls the energization between the output terminal of the DC power supply unit 55 and one end of the phase windings Lu, Lv, and Lw of the open-winding motor 1M, and an inverter (also referred to as a second inverter or slave inverter) 40 that controls the energization between the output terminal of the DC power supply unit 55 and the other end of the phase windings Lu, Lv, and Lw of the open-winding motor 1M. A common power supply system is adopted in which the DC power supply 55 serves as a common DC power supply for the inverters 30 and 40.

[0017] The inverter 30 includes a U-phase series circuit in which switching elements such as IGBTs 31 and 32 are connected in series and the interconnection point of the IGBTs 31 and 32 is connected to one end of a phase winding Lu of the open-winding motor 1M, a V-phase series circuit in which IGBTs 33 and 34 are connected in series and the interconnection point of the IGBTs 33 and 34 is connected to one end of a phase winding Lv of the open-winding motor 1M, and a W-phase series circuit in which IGBTs 35 and 36 are connected in series and the interconnection point of the IGBTs 35 and 36 is connected to one end of a phase winding Lw of the open-winding motor 1M, and controls the supply of electricity from the positive output terminal of a DC power supply 55 to one end of the phase windings Lu, Lv, Lw and from one end of the phase windings Lu, Lv, Lw to the negative output terminal of the DC power supply 55 by switching of the IGBTs 31 to 36. Regenerative diodes (also called freewheel diodes) 31a to 36a are connected in anti-parallel to the IGBTs 31 to 36.

[0018] Inverter 40 has a U-phase series circuit in which IGBTs 41, 42 are connected in series and the interconnection point of the IGBTs 41, 42 is connected to the other end of phase winding Lu of open-winding motor 1M, a V-phase series circuit in which IGBTs 43, 44 are connected in series and the interconnection point of the IGBTs 43, 44 is connected to the other end of phase winding Lv of motor 1M, and a W-phase series circuit in which IGBTs 45, 46 are connected in series and the interconnection point of the IGBTs 45, 46 is connected to the other end of phase winding Lw of open-winding motor 1M. The inverter controls the supply of current from the positive output terminal of DC power supply 55 to the other ends of phase windings Lu, Lv, Lw and from the other ends of phase windings Lu, Lv, Lw to the negative output terminal of DC power supply 55 by switching IGBTs 41 to 46. Regenerative diodes 41a to 46a are connected in anti-parallel to the IGBTs 41 to 46.

[0019] In fact, inverter 30 is a module, known as an IPM (Intelligent Power Module), in which a main circuit formed by connecting the three series circuits of U, V, and W phases in parallel with each other, and peripheral circuits such as a drive circuit for driving IGBTs 31 to 36 of this main circuit are housed in a single package. An IPM with a similar configuration is also used for inverter 40.

[0020] A normally open switching contact (referred to as a relay contact) 51a of a mechanical relay 51 is connected between the other end of the phase winding Lu and the other end of the phase winding Lv of the motor 1M. A normally open switching contact (referred to as a relay contact) 52a of a mechanical relay 52 is connected between the other end of the phase winding Lv and the other end of the phase winding Lw of the motor 1M. The relays 51 and 52 are controlled by a controller 9b to be energized (powered on) and deenergized (powered off) in a synchronized state. When the relays 51 and 52 are energized, the relay contacts 51a and 52a are closed, and the other ends of the phase windings Lu, Lv, and Lw are interconnected, resulting in a star-connected state for the phase windings Lu, Lv, and Lw. When the relays 51 and 52 are deenergized, the relay contacts 51a and 52a are opened, resulting in a disconnected state for the phase windings Lu, Lv, and Lw, i.e., an electrically isolated open winding state.

[0021] To ensure proper operation, the relays 51 and 52 have an upper limit, or so-called rated current, for the current that flows through the relay contacts 51a and 52a. If an overcurrent exceeding the rated current flows through the relay contacts 51a and 52a, the relays 51 and 52 are likely to fail. Relays 51 and 52 with a high rated current are large and expensive, so it is desirable to use relays with a low rated current. Furthermore, the number of times the relay contacts 51a and 52a are opened and closed significantly affects the lifespan of the relays 51 and 52. In other words, if the number of times the relay contacts 51a and 52a are opened and closed increases, the relays 51 and 52 will reach the end of their lifespan and fail.

[0022] Current sensors 53u, 53v, and 53w are arranged on three current lines between the inverter 30 and one ends of the phase windings Lu, Lv, and Lw, and output signals from these current sensors 53u, 53v, and 53w are sent to the controller 9b. The current sensors 53u, 53v, and 53w detect currents Iu, Iv, and Iw (referred to as motor currents) flowing through the phase windings Lu, Lv, and Lw.

[0023] In the star-connection mode (described later), the controller 9b estimates the rotation speed of the motor 1M from the motor current I and executes sensorless vector control, controlling the independent switching of the inverter 30 so that the estimated rotation speed becomes the target rotation speed in response to a command from the outdoor controller 8. In the open-winding mode (described later), the controller 9b executes sensorless vector control, controlling the switching of the inverters 30, 40 so that the estimated rotation speed becomes the target rotation speed. The controller 9b includes a main control unit 60, a current detection unit 61, a relay drive unit 62, a display unit 63, and relays 51, 52, which form the core of the control. The current detection unit 61 detects the instantaneous values ​​of the motor currents Iu, Iv, and Iw detected by the current sensors 53u, 53v, and 53w. These instantaneous values ​​of the motor currents Iu, Iv, and Iw are referred to as the motor current I. The relay drive unit 62 energizes and deenergizes the relays 51, 52 in response to commands from the main control unit 60. The main control unit 60 is composed of a microcomputer and its peripheral circuits, and controls the opening and closing of the relay contacts 51 a, 52 a and the switching of the inverters 30, 40 in response to commands from the outdoor controller 8 and the detection results of the current detection unit 62, etc.

[0024] In particular, the main control unit 60 switches between an open winding mode in which the other ends of the phase windings Lu, Lv, Lw are disconnected by opening the relay contacts 51 a, 52 a, thereby interconnecting and switching the inverters 30, 40, and a star connection mode in which the other ends of the phase windings Lu, Lv, Lw are interconnected by closing the relay contacts 51 a, 52 a, thereby switching the inverter 30 independently, in accordance with at least the value of the motor current I. The main functions related to this switching include a rotation speed detection unit 60 a and first, second, and third control units 60 b to 60 d.

[0025] The rotation speed detection unit 60a detects (estimates) the rotation speed (speed) N of the motor 1M based on the switching states of the inverters 30 and 40 and the motor current I of one of the phase windings Lu, Lv, and Lw. Hereinafter, the rotation speed N of the motor 1M will be referred to as the motor rotation speed N.

[0026] When starting the motor 1M, the first control unit 60b sets the motor 1M to open winding mode and controls the switching of the inverters 30, 40 so that the motor rotation speed N increases to a predetermined value in the high rotation speed range. Once the motor rotation speed N has increased to the predetermined value, the first control unit 60b controls the switching of the inverters 30, 40 so that the motor rotation speed N is maintained at the predetermined value for a predetermined time of about one minute in order to ensure stability of the oil level of the lubricating oil in the compressor 1.

[0027] Following the control of the first control unit 60b, the second control unit 60c controls the switching of the inverters 30, 40 in the open winding mode so that the motor rotation speed N becomes the target rotation speed (target speed) Nt corresponding to the capacity instructed by the outdoor controller 8. In particular, the second control unit 60c stores in its internal memory a second threshold value I2 that is the same as or slightly smaller than the rated current flowing through the relays 51, 52, and a first threshold value I1 that is smaller than the second threshold value I2, and executes the following controls (1) to (3) based on these threshold values ​​I1 and I2.

[0028] (1) In star connection mode, if the peak value of motor current I rises to second threshold value I2, relay contacts 51a, 52a are immediately opened to switch to open winding mode while continuing motor drive, regardless of motor rotation speed N, and when switching is complete, switching of inverters 30, 40 is controlled so that motor rotation speed N becomes target rotation speed Nt. In other words, if the star connection mode remains in the state where relay contacts 51a, 52a are closed when the peak value of motor current I rises to threshold value I2, an overcurrent may flow through relay contacts 51a, 52a, so the mode is immediately switched to open winding mode regardless of motor rotation speed N. In open winding mode, where relay contacts 51a, 52a are opened, no current flows through relay contacts 51a, 52a in the first place, so it is possible to prevent relays 51, 52 from breaking down due to an overcurrent while continuing to drive motor 1M.

[0029] (2) In the star connection mode, if the peak value of the motor current I is lower than the second threshold value I2, the motor rotation speed N rises to a high speed range equal to or greater than the second set value N2, and this state continues for a second predetermined time t2s (e.g., one minute), the relay contacts 51a and 52a are immediately opened while the motor continues to be driven, and the mode is switched to the open winding mode, controlling the switching of the inverters 30, 40 so that the motor rotation speed N reaches the target rotation speed Nt. That is, when the motor rotation speed N is in a high speed range equal to or greater than the second set value N2, the open winding mode, which operates the two inverters 30, 40, is switched to because the open winding mode provides a high level of voltage necessary for motor drive and is more efficient. However, because the motor rotation speed N and the motor current I may fluctuate frequently due to fluctuations in the air conditioning load, etc., the mode is configured to wait at least the second predetermined time t2s required for the fluctuations in the motor rotation speed N and the motor current I to converge, even if there are fluctuations. This makes it possible to prevent the relay contacts 51a and 52a from being frequently opened and closed, thereby reducing the number of times the relay contacts 51a and 52a are opened and closed, thereby extending the life of the relays 51 and 52.

[0030] (3) In the open winding mode, if the state in which the peak value of the motor current I is equal to or less than the first threshold value I1 continues for a first predetermined time t1s (e.g., 20 minutes), the relay contacts 51a and 52a are closed to switch to the star connection mode while continuing to drive the motor, and when the switch is completed, the switching of the inverter 30 is controlled so that the motor rotation speed N becomes the target rotation speed Nt (the switching of the inverter 40 is stopped). Specifically, in the open winding mode, if the state in which the peak value of the motor current I is equal to or less than the first threshold value I1 and the motor rotation speed N is in a low rotation speed range equal to or less than a first set value that is lower than the second set value N2 continues for the first predetermined time t1s, the relay contacts 51a and 52a are closed to switch to the star connection mode while continuing to drive the motor, and the switching of the inverter 30 is controlled so that the motor rotation speed N becomes the target rotation speed Nt. That is, if the peak value of the motor current I remains below the first threshold value I1 for at least the first predetermined time t1s, there is no need to worry about an overcurrent flowing through the relay contacts 51a, 52a even if the star connection mode in which the relay contacts 51a, 52a are closed is set. Also, if the motor rotation speed N remains within a low rotation speed range below the first set value N1 for the first predetermined time t1s, a voltage level sufficient for driving the motor can be obtained even in the highly efficient star connection mode in which only one inverter 30 is operating. Based on these considerations, the mode is switched to star connection mode.

[0031] The first threshold I1, which is the criterion for determining whether to switch from the open winding mode to the star connection mode, is set lower than the second threshold I2, which is the criterion for determining whether to switch from the star connection mode to the open winding mode. This is to address the problem that, when switching from the open winding mode to the star connection mode, the motor current I is larger in the star connection mode than in the open winding mode, even when driven at the same motor rotation speed N, due to factors such as the magnitude of the field component current (d-axis current) converted to the field axis (d-axis) coordinate on the rotor shaft of the motor 1M. In other words, by setting the first threshold I1 lower than the second threshold I2, it is possible to prevent a malfunction in which the peak value of the motor current I immediately rises to the second threshold I2 after switching from the open winding mode to the star connection mode, resulting in a switch from the star connection mode to the open winding mode. This also reduces the number of times the relay contacts 51a and 52a are opened and closed.

[0032] Figure 3 shows the relationship between motor rotation speed N and power supply current Is for star connection mode and open winding mode. When motor rotation speed N is low, power supply current Is in star connection mode is slightly lower than power supply current Is in open winding mode, making star connection mode more efficient. As motor rotation speed N increases, power supply current Is in star connection mode increases rapidly, while power supply current Is in open winding mode increases slowly. In this case, in star connection mode, motor current I becomes high and the back electromotive force of motor 1M increases, making it impossible to drive motor 1M at higher rotation speeds. Figure 4 shows the relationship between motor rotation speed N and efficiency for star connection mode and open winding mode. When motor rotation speed N is low, star connection mode is more efficient than open winding mode, but as motor rotation speed N increases, open winding mode becomes more efficient than star connection mode.

[0033] Taking into consideration the characteristics of the motor 1M shown in FIGS. 3 and 4, the mode switching conditions shown in FIG. 5 are stored in the second control unit 60c of the controller 9b in order to obtain the highest possible efficiency within the range in which the motor current I does not exceed the rated current flowing through the relays 51 and 52.

[0034] When the defrosting operation is performed by the outdoor controller 8, the third control unit 60d sets the open winding mode regardless of the motor current I before the start of the defrosting operation and maintains this set state until the defrosting operation is completed. Specifically, when the third control unit 60d receives a notice from the outdoor controller 8 that defrosting is necessary, that is, at the time of defrost preparation before the flow path of the four-way valve 2 is switched and the defrosting operation is started, the third control unit 60d sets the open winding mode regardless of the motor current I, controls the switching of the inverters 30, 40 so that the motor rotation speed N becomes the target rotation speed Nt for the defrosting operation in accordance with the command from the outdoor controller 8, and maintains this set state of the open winding mode regardless of the motor current I until it receives a notice of the end of the defrosting operation from the outdoor controller 8.

[0035] Next, the control executed by the controller 9b will be described with reference to the flowchart of Fig. 6. Steps S1, S2, etc. in the flowchart will be abbreviated as simply S1, S2, etc.

[0036] [When starting the motor 1M] When an operation start command is received from the outdoor controller 8 (YES in S1), the controller 9b initializes the time counts t1 and t2 to "0" (S2), and sets the open winding mode (S3) in which the other ends of the phase windings Lu, Lv, and Lw are disconnected by opening the relay contacts 51a and 52a, thereby switching the inverters 30 and 40. When the motor 1M is stopped, the normally open relay contacts 51a and 52a are originally open due to the de-energization (power off) of the relays 51 and 52, and the phase windings Lu, Lv, and Lw are disconnected from one another, so the open winding mode can be set without activating the relay contacts 51a and 52a.

[0037] In response to the setting of this open winding mode, the controller 9b sets a target rotation speed Nt that corresponds to the capacity instructed by the outdoor controller 8 (S4), and controls the switching of the inverters 30, 40 so that the motor rotation speed N becomes the target rotation speed Nt (S5). This starts the motor 1M. The setting of the target rotation speed Nt and the switching control at this start-up include control to increase the motor rotation speed N to a predetermined value in the high rotation speed range and maintain that state for a predetermined time of about one minute.

[0038] A portion of the current path formed in the open winding mode is shown by dashed lines in Fig. 2. First, IGBT 31 of inverter 30 is turned on, causing IGBT 42 of inverter 40 to repeatedly turn on and off, and IGBTs 43 and 45 of inverter 40 are both turned on, causing IGBTs 34 and 36 of inverter 30 to repeatedly turn on and off in synchronization with each other. As a result, as shown by the dashed arrows, current flows from the positive output terminal of DC power supply 55 through IGBT 31 to phase winding Lu, and the current passing through phase winding Lu flows through IGBT 42 to the negative output terminal of DC power supply 55. Current also flows from the positive output terminal of DC power supply 55 through IGBTs 43 and 45 to phase windings Lv and Lw, and the current passing through phase windings Lv and Lw flows through IGBTs 34 and 36 to the negative output terminal of DC power supply 55. Next, IGBT 33 of inverter 30 is turned on, causing IGBT 44 of inverter 40 to repeatedly turn on and off, and IGBTs 41 and 45 of inverter 40 are both turned on, causing IGBTs 32 and 36 of inverter 30 to repeatedly turn on and off in synchronization with each other. As a result, a current flows from the positive output terminal of DC power supply 55 through IGBT 33 to phase winding Lv, and the current passing through phase winding Lv flows through IGBT 44 to the negative output terminal of DC power supply 55. A current also flows from the positive output terminal of DC power supply 55 through IGBTs 41 and 45 to phase windings Lu and Lw, and the current passing through phase windings Lu and Lw flows through IGBTs 32 and 36 to the negative output terminal of DC power supply 55. Next, IGBT 35 of inverter 30 is turned on, causing IGBT 46 of inverter 40 to repeatedly turn on and off, and IGBTs 41 and 43 of inverter 40 are both turned on, causing IGBTs 32 and 34 of inverter 30 to repeatedly turn on and off in synchronization with each other. As a result, current flows from the positive output terminal of DC power supply 55 through IGBT 35 to phase winding Lw, and the current passing through phase winding Lw flows through IGBT 46 to the negative output terminal of DC power supply 55. Current also flows from the positive output terminal of DC power supply 55 through IGBTs 41 and 43 to phase windings Lu and Lv, and the current passing through phase windings Lu and Lv flows through IGBTs 32 and 34 to the negative output terminal of DC power supply 55. The rotor of motor 1M rotates as these three current paths are switched in sequence.

[0039] By setting this open winding mode, a voltage approximately √3 times that of the star connection mode can be applied to the phase windings Lu, Lv, and Lw, making it possible to efficiently increase the motor rotation speed N to a high rotation speed range that corresponds to the high air conditioning load at the start of operation. In particular, when the air conditioner starts up, not only is the air conditioning load high, but the indoor fan 13 has just started operating, so fresh indoor air does not flow well to the indoor temperature sensor 14, making indoor temperature detection unstable and making it difficult to accurately grasp the air conditioning load. In such a situation at the start of operation, setting the open winding mode from the beginning, in which the relays 51, 52 are not energized and the relay contacts 51 a, 52 a are left open, and increasing the rotation speed N of the motor 1M to a high rotation speed range ensures that the number of times the relay contacts 51 a, 52 a operate is reduced by at least one compared to setting the star connection mode, in which the relays 51, 52 are energized and the relay contacts 51 a, 52 a are closed, in the low rotation speed range and then switching to the open winding mode in the high rotation speed range. In other words, it is possible to demonstrate sufficient air conditioning capacity to handle unstable high air conditioning loads while keeping the number of times the relay contacts 51 a, 52 a operate low.

[0040] [After Start of Motor 1M] Following start of motor 1M in the open winding mode, the controller 9b checks whether there is a defrosting requirement notification from the outdoor controller 8 (S6). If there is no defrosting requirement notification (NO in S6), the controller 9b currently has the open winding mode set (YES in S10), and if the peak value of motor current I is equal to or less than the first threshold value I1 (YES in S11) and the motor rotation speed N has fallen to or less than the set value N1 (YES in S12), the controller 9b starts counting time t1 (S13) and compares the counted time t1 with a predetermined time (20 minutes) t1s (S15).

[0041] While the time count t1 is less than the predetermined time t1s (NO in S15), the controller 9b checks for an operation stop command from the outdoor controller 8 (S25). If there is no operation stop command (NO in S25), the controller 9b returns to S4 above and sets the target rotation speed Nt (S4), and controls the switching of the inverters 30, 40 so that the motor rotation speed N becomes the target rotation speed Nt (S5). Subsequently, if there is no notification that defrosting is required (NO in S6), the controller 9b repeats the determination from S10 above.

[0042] If the judgment in S11 above shows that the peak value of the motor current I has risen from a region below the first threshold value I1 to a region above the first threshold value I1 (NO in S11), or if the judgment in S11 above shows that the motor rotation speed N has risen from a region below the set value N1 to a region above the set value N1 (NO in S12), the controller 9b clears the time count t1 to "0" (S14) and compares the time count t1 with a predetermined time t1s (S15).

[0043] If the determination in S11 above shows that the peak value of motor current I remains below first threshold value I1 (YES in S11), and the determination in S12 above shows that motor rotation speed N remains below set value N1 (YES in S12), and the time count t1 continues and reaches a predetermined time t1s (YES in S13 and S15), the controller 9b switches from the open winding mode to the star connection mode (S16) and clears time count t1 to "0" (S17). If there is no operation stop command (NO in S25), the controller 9b returns to S4 above, sets a target rotation speed Nt (S4), and controls the switching of the inverter 30 so that the motor rotation speed N becomes the target rotation speed Nt (S5).

[0044] Next, if there is no notification that defrosting is required (NO in S6), the controller 9b determines whether the motor rotation speed N is equal to or greater than a set value N2 (S19) on the assumption that the peak value of the motor current I is less than the second threshold value I2 (NO in S18) since the currently set mode is the star connection mode (NO in S10). If the motor rotation speed N is equal to or greater than the set value N2 (YES in S19), the controller 9b starts counting time t2 (S20) and compares the counted time t2 with a predetermined time (one minute) t2s (S22).

[0045] While the time count t1 is less than the predetermined time t1s (NO in S22), if there is no operation stop command (NO in S25), the controller 9b returns to S4 above and sets the target rotation speed Nt (S4), and controls the switching of the inverter 30 so that the motor rotation speed N becomes the target rotation speed Nt (S5). Subsequently, if there is no notification that defrosting is required (NO in S6), the controller 9b repeats the determination from S10 above.

[0046] If the condition in S18 remains true (NO in S18), the motor rotation speed N remains equal to or greater than the set value N2 (YES in S19), and the time count t2 continues until it reaches a predetermined time t2s (YES in S20 and S22), the controller 9b switches from the star connection mode to the open winding mode (S23) and clears the time count t2 to "0" (S24). If there is no operation stop command (NO in S25), the controller 9b returns to S4, sets the target rotation speed Nt (S4), and controls the switching of the inverters 30 and 40 so that the motor rotation speed N becomes the target rotation speed Nt (S5). If there is no notification of the need for defrosting (NO in S6), the controller 9b repeats the determination from S10.

[0047] Even if the precondition that the peak value of the motor current I is less than the second threshold value I2 remains satisfied in the judgment of S18 above (NO in S18), if the judgment of S19 above shows that the motor rotation speed N has fallen into an area less than the set value N2 (NO in S19), the controller 9b clears the time count t1 to "0" (S21) and compares the time count t1 with a predetermined time t1s (S22).

[0048] However, if the peak value of the motor current I rises to the second threshold value I2 in the determination in S18 above (YES in S18), there is a possibility that an overcurrent exceeding the rated current may continue to flow through the relay contacts 51a, 52a, so the controller 9b immediately switches from the star connection mode to the open winding mode (S23). In the open winding mode, in which the relay contacts 51a, 52a are open, no current flows through the relay contacts 51a, 52a in the first place, so it is possible to avoid adverse effects of an overcurrent on the relays 51, 52.

[0049] If the determination in S6 above indicates that defrosting is required (YES in S6), the controller 9b forcibly sets the open winding mode regardless of the motor current I (S7), and controls the switching of the inverters 30, 40 so that the motor rotation speed N becomes the target rotation speed Nt for the defrosting operation in accordance with the command from the outdoor controller 8 (S8).The controller 9b then checks whether the outdoor controller 8 has not notified the end of the defrosting operation (S9).If there is no end notification (NO in S9), the controller 9b repeats the switching control in S8 above (S8).

[0050] An example of the change in the motor rotation speed N from the start of defrost preparation in response to a notification that defrosting is required until the defrosting operation is completed is shown in Fig. 7. Since the motor rotation speed N reaches a high rotation speed range during defrosting operation when the load is large, setting the open winding mode in advance before the start of defrosting operation enables stable and reliable defrosting operation.

[0051] [Summary] In short, in open winding mode, if the peak value of motor current I remains below first threshold value I1, which is smaller than the rated current flowing through relays 51 and 52, for a predetermined time t1s, then switching to star connection mode will not cause an overcurrent to flow through relay contacts 51a and 52a, and if motor rotation speed N remains within a low rotation speed range below set value N1 for a predetermined time t1s, then switching to star connection mode will provide a voltage level sufficient to drive the motor, even if switching to the highly efficient star connection mode in which only one inverter 30 is operated.

[0052] In the star connection mode, under the assumption that the peak value of the motor current I is less than the second threshold value I2, if the motor rotation speed N remains in a high rotation speed range equal to or greater than the set value N2 for a predetermined time t2s or more, the open winding mode in which the two inverters 30, 40 are operated is switched to, since this mode provides higher efficiency.

[0053] However, in the star connection mode, if the peak value of the motor current I rises to the second threshold value I2, the mode is immediately switched to the open winding mode in which no current flows through the relay contacts 51a and 52a, in order to prioritize prevention of overcurrent at the relay contacts 51a and 52a over efficiency.

[0054] Therefore, the motor can be driven as efficiently as possible while preventing the problem of overcurrent flowing through the relay contacts 51 a and 52 a. Since overcurrent does not flow through the relay contacts 51 a and 52 a, the life of the relay contacts 51 and 52 can be improved.

[0055] Since switching between the open winding mode and the star connection mode is not repeated frequently, the number of times the relays 51 and 52 are operated can be minimized, which also improves the life of the relay contacts 51 and 52.

[0056] [Modification] In the above embodiment, switching between the open winding mode and the star connection mode is performed using the peak value of the instantaneous value as the motor current value I. However, switching between the open winding mode and the star connection mode may also be performed using the effective value Ia instead of the peak value of the instantaneous value.

[0057] Furthermore, in the above embodiment, switching between the open winding mode and the star connection mode is performed in accordance with the rotation speed of the motor. However, the d-axis current value, which is the amount of field weakening that is considered to be equivalent to the rotation speed of the motor, the PWM voltage output duty of the inverter, the modulation rate, or the like can be used instead of the rotation speed of the motor.

[0058] In the above embodiment, a common power supply system is employed in which the inverters 30, 40 are connected to the same DC power supply 55, but the present invention can also be implemented in a power supply isolation system in which the inverters 30, 40 are connected to separate DC power supplies.

[0059] Furthermore, the above-described embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications can be embodied in various other forms, and various omissions, rewritings, and modifications can be made without departing from the spirit of the invention. These embodiments and modifications are included within the spirit of the invention, and are also included in the scope of the inventions and their equivalents as defined in the claims.

[0060] REFERENCE SIGNS LIST 1...Compressor, 1M...Open winding motor, Lu, Lv, Lw...Phase winding, 2...Four-way valve, 3...Outdoor heat exchanger, 4...Expansion valve, 8...Outdoor controller, 9...Motor drive device, 9a...Drive circuit, 9b...Controller, 12...Indoor heat exchanger, 15...Indoor controller, 50...Three-phase AC power supply, 55...DC power supply unit, 30...Inverter (first inverter), 40...Inverter (second inverter), 51, 52...Relay (switch), 51a, 52a...Normally open contact, 53u, 53v, 53w...Current sensor, 60...Main control unit, 60a...Rotation speed detection unit, 60b to 60d...First, second, third control units, 61...Current detection unit, 62...Relay drive unit

Claims

1. A motor drive device comprising: a motor having a plurality of phase windings that are disconnected from one another; a first inverter that controls the supply of current to one end of each of the phase windings; a second inverter that controls the supply of current to the other end of each of the phase windings; a relay having an open / close contact connected between the other ends of the phase windings; and a controller that switches between an open winding mode in which the other ends of the phase windings are disconnected when the relay is opened and the first and second inverters are linked together for switching, and a star connection mode in which the other ends of the phase windings are connected to one another and the first inverter is switched on when the relay is closed, depending on the value of the current flowing through the motor.

2. The motor drive device according to claim 1, wherein the controller switches to the open winding mode when, in the star connection mode, the current flowing through the motor rises to a second threshold value that is equal to or smaller than the rated energization current of the relay.

3. The motor drive device according to claim 2, wherein the controller switches to the star connection mode when, in the open winding mode, the current flowing through the motor remains equal to or less than a first threshold value that is smaller than the second threshold value for a predetermined period of time.

4. The motor drive device according to claim 1, wherein the controller switches to the open winding mode when, in the star connection mode, the current flowing through the motor rises to a second threshold value that is equal to or smaller than the rated energization current of the relay, and when the rotation speed of the motor rises to or exceeds a second set value and remains in that state for a predetermined period of time.

5. The motor drive device according to claim 4, wherein the controller switches to the star connection mode when, in the open winding mode, the current flowing through the motor remains below a first threshold value that is smaller than the second threshold value and the rotation speed of the motor remains below a first set value that is lower than the second set value for a predetermined period of time.

6. The motor drive device according to any one of claims 1 to 5, wherein the controller sets the open winding mode when starting the motor.

7. A refrigeration cycle device equipped with a motor drive device according to any one of claims 1 to 6, wherein the controller, when executing a defrosting operation of the refrigeration cycle device, sets the open winding mode regardless of the current flowing through the motor before the start of the defrosting operation, and maintains this setting state until the defrosting operation is completed.