JP7551588B2 - Refrigeration Cycle Equipment - Google Patents

Description

The present invention relates to a refrigeration cycle device that uses a so-called open winding motor, which has multiple phase windings that are not connected to each other, as a motor for driving a compressor.

In refrigeration cycle devices such as air conditioners and heat source units, when the compressor is stopped, the refrigerant accumulates inside the compressor and liquefies, a phenomenon known as stagnation. In particular, during winter nights or in cold regions where the outside air temperature drops significantly, the cooled liquid refrigerant dissolves in the lubricating oil (also called refrigeration oil) inside the compressor, and the viscosity of the lubricating oil increases, causing excessive shaft torque when the motor that drives the compressor is started, which can cause the motor to fail to start or cause damage inside the compressor.

As a countermeasure, when the compressor is stopped, a control method is known in which a current (called a motor current) is passed from the inverter to the motor to heat the motor windings (called the motor windings), and the generated heat is used to preheat the refrigerant and lubricating oil that have accumulated in the compressor.

Japanese Unexamined Patent Publication No. 58-140571

In the above preheating control, it is necessary to suppress the motor current value to a level that does not cause the motor to start rotating. However, suppressing it too much can result in problems such as insufficient preheating or preheating taking a long time. In addition, the motor current for preheating flows to the motor windings through a specific switch element out of the multiple switch elements in the inverter. This can result in a problem in that the operating period of only that specific switch element is extended, which could shorten its lifespan.

The objective of the present embodiment is to provide a highly reliable refrigeration cycle device that can sufficiently preheat the compressor without the motor starting to rotate, and that can eliminate the problem of shortening the life of the inverter's switching elements.

The refrigeration cycle device according to an embodiment of the present invention comprises a motor for driving a compressor having multiple phase windings that are not connected to each other; a first inverter that controls the current flow to one end of each of the phase windings; a second inverter that controls the current flow to the other end of each of the phase windings; and a control means that controls the first and second inverters so that, when the motor is stopped, a zero-axis current flows from one end of each of the phase windings to the other end and a zero-axis current flows from the other end of each of the phase windings to one end alternately.

FIG. 1 is a diagram showing a configuration of an embodiment. FIG. 2 is a diagram showing a configuration of a motor drive unit and a path of a positive zero-axis current flowing through each phase winding in one embodiment. FIG. 3 is a diagram showing winding heating control conditions according to one embodiment. FIG. 4 is a flowchart showing control of a motor control unit in one embodiment. FIG. 5 is a diagram showing changes in on/off duty of each inverter during a winding heating operation in one embodiment. FIG. 6 is a diagram showing an on/off pattern of each inverter during a winding heating operation in one embodiment. FIG. 7 is a diagram showing a path of a negative zero-axis current flowing through each phase winding in one embodiment. FIG. 8 is a diagram showing waveforms of zero-axis currents flowing through respective phase windings in one embodiment. FIG. 9 is a diagram showing a relationship between the value of the AC zero-axis current flowing through each phase winding and the outside air temperature in one embodiment.

An embodiment of the present invention will be described with reference to the drawings.
As shown in Fig. 1, one end of an outdoor heat exchanger 3 is connected by piping to the discharge port of a hermetic compressor 1 incorporating a motor 1M as a drive motor via a four-way valve 2, and one end of an indoor heat exchanger 11 is connected by piping to the other end of the outdoor heat exchanger 3 via an electric expansion valve 4, which serves as a pressure reducer. The other end of the indoor heat exchanger 11 is connected by piping to the suction port of the compressor 1 via the four-way valve 2. The piping connections of these refrigeration cycle components constitute a heat pump type refrigeration cycle for an air conditioner capable of cooling and heating.

The motor 1M is a permanent magnet synchronous motor with multiple phase windings, for example an open-windings motor in which the three phase windings Lu, Lv, and Lw described below are disconnected from each other. The electric expansion valve 4 is a pulse motor valve (PWM) whose opening changes continuously according to the number of drive pulses supplied.

During cooling operation, as shown by the solid arrow in FIG. 1, the gas refrigerant discharged from the compressor 1 flows through the four-way valve 2 to the outdoor heat exchanger 3. The high-temperature gas refrigerant that flows into the outdoor heat exchanger 3 releases heat to the outside air and condenses. The liquid refrigerant that flows out of this outdoor heat exchanger (condenser) 3 flows into the indoor heat exchanger 11 in a state where it is depressurized by the electric expansion valve 4. The liquid refrigerant that flows into the indoor heat exchanger 11 evaporates by taking heat from the indoor air. The gas refrigerant that flows out of this indoor heat exchanger (evaporator) 11 is sucked into the compressor 1 through the four-way valve 2. During heating operation, the flow path of the four-way valve 2 is switched, so that the high-temperature gas refrigerant discharged from the compressor 1 flows through the four-way valve 2 to the indoor heat exchanger 11 as shown by the dashed arrow in FIG. 1. The gas refrigerant that flows into the indoor heat exchanger 11 releases heat to the indoor air and condenses. The liquid refrigerant flowing out of this indoor heat exchanger (condenser) 11 is depressurized by the electric expansion valve 4 and flows to the outdoor heat exchanger 3. The liquid refrigerant flowing into the outdoor heat exchanger 3 absorbs heat from the outside air and evaporates. The gas refrigerant flowing out of this outdoor heat exchanger (evaporator) 3 passes through the four-way valve 2 and is sucked into the compressor 1.

An outdoor fan 5 is disposed near the outdoor heat exchanger 3, and an outdoor air temperature sensor 6 that detects the outdoor air temperature To is disposed in the outdoor air intake duct of the outdoor fan 5. An indoor fan 12 is disposed near the indoor heat exchanger 11, and an indoor temperature sensor 13 that detects the indoor temperature Ta is disposed in the indoor air intake duct of the indoor fan 12.

The above-mentioned refrigeration cycle components such as the compressor 1, four-way valve 2, outdoor heat exchanger 3, motorized expansion valve 4, outdoor fan 5, and outdoor air temperature sensor 6 are housed in outdoor unit A together with the outdoor control unit 7. The above-mentioned refrigeration cycle components such as the indoor heat exchanger 11, outdoor fan 12, and indoor temperature sensor 13 are housed in indoor unit B together with the indoor control unit 14.

2, the outdoor control unit 7 includes a motor drive unit 20 that drives the compressor 1. The configuration of the motor drive unit 20 will be described.
A DC power supply circuit 22 consisting of a diode bridge circuit, a smoothing capacitor, etc. is connected to a three-phase AC power supply 10 via a noise filter 21, and an inverter (also called a first inverter or a master inverter) 30 that controls the supply of current to one end of the phase windings Lu, Lv, Lw of the motor 1M is connected between the output end of the DC power supply circuit 22 and one end of the phase windings Lu, Lv, Lw of the motor 1M. The motor 1M is housed inside the compressor 1 and drives the compression mechanism to rotate.

An inverter (also called a second inverter or slave inverter) 40 that controls the current supply to the other ends of the phase windings Lu, Lv, Lw of the motor 1M is connected between the output end of the DC power supply circuit 22 and the other ends of the phase windings Lu, Lv, Lw. This motor drive unit 20 employs a common power supply system in which the inverters 30, 40 are connected to a common DC power supply circuit 22. Instead of the common power supply system, a power supply isolation system in which the inverters 30, 40 are connected to separate DC power supply circuits may also be employed.

The inverter 30 includes as its main circuits a U-phase series circuit in which switching elements, such as IGBTs (Insulated Gate Bipolar Transistors) 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, 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, 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. Regenerative diodes (also called free-wheeling diodes) 31a to 36a are connected in inverse parallel to the IGBTs 31 to 36.

The inverter 40 includes, as main circuits, a U-phase series circuit in which IGBTs 41 and 42 are connected in series and the interconnection point of the IGBTs 41 and 42 is connected to the other end of the phase winding Lu, a V-phase series circuit in which IGBTs 43 and 44 are connected in series and the interconnection point of the IGBTs 43 and 44 is connected to the other end of the phase winding Lv, and a W-phase series circuit in which IGBTs 45 and 46 are connected in series and the interconnection point of the IGBTs 45 and 46 is connected to the other end of the phase winding Lw. Regenerative diodes 41a to 46a are connected in inverse parallel to the IGBTs 41 to 46.

The inverter 30 is a three-phase inverter, a so-called IPM (Intelligent Power Module) that houses in a single package a main circuit consisting of three sets of two switch element series circuits connected in parallel, and peripheral circuits such as a drive circuit that drives the six switch elements of the main circuit. The inverter 40 is also an IPM with the same configuration.

A normally open contact (referred to as a relay contact) 51a of a switch, for example, a relay 51, is connected between the other end of the phase winding Lu and the other end of the phase winding Lv. A normally open contact (referred to as a relay contact) 52a of a switch, for example, a relay 52, is connected between the other end of the phase winding Lv and the other end of the phase winding Lw. The relays 51 and 52 are controlled by the motor control unit 23 described below so that they are energized and deenergized in a synchronized state. When the relay contacts 51a and 52a are closed, the other ends of the phase windings Lu, Lv, and Lw are interconnected, and the phase windings Lu, Lv, and Lw are in a star-connected state. When the relay contacts 51a and 52a are opened, the phase windings Lu, Lv, and Lw are in a non-connected state (open state), and the phase windings Lu, Lv, and Lw are electrically separated from each other.

Current sensors 53u, 53v, and 53w are arranged on each current line between the inverter 30 and one end of the phase windings Lu, Lv, and Lw, and the detection signals of these current sensors 53u, 53v, and 53w are sent to the motor control unit 23. A relay drive unit 24 that energizes or deenergizes the relays 51 and 52 is connected to this motor control unit 23.

When the motor 1M is stopped (when the compressor 1 is stopped), the motor control unit 23 opens the relay contacts 51a and 52a to keep the phase windings Lu, Lv, and Lw in a disconnected state, but when the motor 1M is started, the relay contacts 51a and 52a are closed to connect the phase windings Lu, Lv, and Lw in a star-connected state and set a star-connection mode in which the inverter 30 is switched independently. Then, after starting the motor 1M by energizing the inverter 30 through forced commutation or the like, the motor control unit 23 estimates the speed (rotation speed) of the motor 1M from the detection results of the current sensors 53u, 53v, and 53w, and controls the independent switching of the inverter 30 so that the estimated speed becomes the target speed commanded by the motor control unit 23, thus executing so-called sensorless vector control. During this independent switching of the inverter 30, the inverter 40 is kept in the off state, that is, all switching elements are kept in the off state. While the target speed is low, the motor 1M is driven only by the inverter 30, and air conditioning operation continues. Next, when the target speed increases and the estimated speed of the motor 1M increases and enters a predetermined high-speed operating range, the motor control unit 23 opens the relay contacts 51a and 52a to disconnect the phase windings Lu, Lv, and Lw, sets the open winding mode in which the inverters 30 and 40 are switched in coordination with each other, and executes sensorless vector control to control the coordinated switching of the inverters 30 and 40 so that the estimated speed becomes the target speed. However, in this open winding mode, a zero-axis current is generated in a general drive waveform used in a star-connected state, etc. This zero-axis current simply becomes a loss during the operation of the motor 1M, so the switching waveforms of the inverters 30 and 40 are controlled to minimize the flow of the zero-axis current.

The target speed is determined by the outdoor control unit 7 based on the magnitude of the load on the air conditioner. The magnitude of the load is determined, for example, based on the difference between the indoor temperature Ta detected by the indoor temperature sensor 13 and a predetermined set temperature, or a change in this difference.

When the compressor 1 is stopped (the motor 1M is stopped and the phase windings Lu, Lv, Lw are disconnected), if the outside air temperature To detected by the outside air temperature sensor 6 is less than the threshold value To2 (for example, 0°C) (low outside air temperature state), the motor control unit 23 preheats the compressor 1 while the motor 1M is stopped by controlling the switch elements of the inverters 30, 40 to turn on and off so that the zero-axis currents Iu0, Iv0, Iw0 that flow from one end of the phase windings Lu, Lv, Lw to the other end with the same value and the zero-axis currents Iu0, Iv0, Iw0 that flow from the other end of the phase windings Lu, Lv, Lw to one end with the same value are alternately generated while maintaining the relays 52, 51 in the open state by the relay drive unit 24. The zero-axis currents Iu0, Iv0, Iw0 flow, and the phase windings Lu, Lv, Lw heat up. Motor 1M, including its phase windings Lu, Lv, and Lw, is housed inside compressor 1, which is a pressure vessel, together with the compression mechanism. Therefore, if the phase windings Lu, Lv, and Lw are heated, the temperature of the refrigerant inside compressor 1 and the lubricating oil for the compression mechanism will rise.

Next, the control executed by the motor control unit 23 when the compressor 1 is stopped will be explained with reference to the winding heating control conditions in FIG. 3 and the flowchart in FIG. 4. Steps S1, S2, etc. in the flowchart will be abbreviated as simply S1, S2, etc.

The motor control unit 23 determines whether the outside air temperature To is less than the threshold value To2 (S1). If the outside air temperature To is not less than the threshold value To2 (NO in S2), the motor control unit 23 determines whether the outside air temperature To is equal to or greater than the threshold value "To2+ΔT" (S3). If the outside air temperature To is not equal to or greater than the threshold value "To2+ΔT" (NO in S3), the motor control unit 23 returns to the determination in S1 above.

When the outside air temperature To falls below the threshold To2 (YES in S1), the motor control unit 23 starts the winding heating operation (S2). That is, as shown in FIG. 5, if the outside air temperature To is in a higher region close to the threshold To2, the motor control unit 23 turns on and off the IGBTs 31, 33, 35 on the upstream side of the inverter 30 and the IGBTs 32, 34, 36 on the downstream side with an on/off duty that changes in a sinusoidal manner in the range of 52% to 48% in one period T of the carrier signal, and turns on and off the IGBTs 41, 43, 45 on the upstream side of the inverter 40 and the IGBTs 42, 44, 46 on the downstream side with an on/off duty that changes in a sinusoidal manner in the range of 48% to 52% in the opposite phase to the on/off on the inverter 30 side. If the outside air temperature To is in a low region away from the threshold To2, the IGBTs 31, 33, 35 on the upstream side of the inverter 30 and the IGBTs 32, 34, 36 on the downstream side are turned on and off with an on/off duty that changes sinusoidally in a wide range from 58% to 42% in one period T of the carrier signal, and the IGBTs 41, 43, 45 on the upstream side of the inverter 40 and the IGBTs 42, 44, 46 on the downstream side are turned on and off with an on/off duty that changes sinusoidally in a range from 48% to 52% in the opposite phase to the on/off on the inverter 30 side.

When the IGBTs 31, 33, 35 on the upstream side of the inverter 30 and the IGBTs 32, 34, 36 on the downstream side are turned on and off with an on/off duty of 52%, and the IGBTs 41, 43, 45 on the upstream side of the inverter 40 and the IGBTs 42, 44, 46 on the downstream side are turned on and off with an on/off duty of 48%, as shown in FIG. 6, the center of the period during which the IGBTs 31, 33, 35 on the upstream side of the inverter 30 are turned on and the IGBTs 32, 34, 36 on the downstream side are turned off (the timing of 1/2 of one period T of the carrier signal) and the timing of the inverter The center of the period during which the IGBTs 41, 43, and 45 on the upstream side of the inverter 40 are on and the IGBTs 42, 44, and 46 on the downstream side are off (the timing of 1/2 the period T of the carrier signal) overlaps, and both sides of the period during which the IGBTs 31, 33, and 35 on the upstream side of the inverter 30 are on and the IGBTs 32, 34, and 36 on the downstream side are off are longer by Δt, determined by the duty difference, than both sides of the period during which the IGBTs 41, 43, and 45 on the upstream side of the inverter 40 are on and the IGBTs 42, 44, and 46 on the downstream side are off.

During these Δt times, as shown by the dashed arrows in FIG. 2, positive direction zero-axis currents Iu0, Iv0, Iw0 flow from one end of the phase windings Lu, Lv, Lw to the other end via a path that passes from the positive output end of the DC power supply circuit 22 through the IGBTs 31, 33, 35 of the inverter 30, and the zero-axis currents Iu0, Iv0, Iw0 that pass through the other ends of the phase windings Lu, Lv, Lw flow to the negative output end of the DC power supply circuit 22 via a path that passes through the IGBTs 42, 44, 46 of the inverter 40.

In low outside air temperatures, where the IGBTs 31, 33, 35 on the upstream side of inverter 30 and 32, 34, 36 on the downstream side are turned on and off with an on/off duty of 58%, and the IGBTs 41, 43, 45 on the upstream side of inverter 40 and 42, 44, 46 on the downstream side are turned on and off with an on/off duty of 42%, the Δt time is longer, and the values of the positive zero-axis currents Iu0, Iv0, Iw0 are correspondingly larger.

When the IGBTs 31, 33, 35 on the upstream side of inverter 30 and 32, 34, 36 on the downstream side are turned on and off with an on/off duty of 48%, and the IGBTs 41, 43, 45 on the upstream side of inverter 40 and 42, 44, 46 on the downstream side are turned on and off with an on/off duty of 52%, both sides of the period when the IGBTs 41, 43, 45 on the upstream side of inverter 40 are turned on and the IGBTs 42, 44, 46 on the downstream side are turned off are Δt longer than both sides of the period when the IGBTs 31, 33, 35 on the upstream side of inverter 30 are turned on and the IGBTs 32, 34, 36 on the downstream side are turned off. During these Δt times, as shown by the dashed arrows in FIG. 7, negative-direction zero-axis currents Iu0, Iv0, Iw0 flow from the other end to one end of the phase windings Lu, Lv, Lw through a path that passes from the positive output end of the DC power supply circuit 22 through the IGBTs 41, 43, and 45 of the inverter 40, and the zero-axis currents Iu0, Iv0, Iw0 that pass through one end of the phase windings Lu, Lv, Lw flow through the IGBTs 32, 34, and 36 of the inverter 30 to the negative output end of the DC power supply circuit 22.

In low outside air temperatures, where the IGBTs 41, 43, 45 on the upstream side of inverter 40 and 42, 44, 46 on the downstream side are turned on and off with an on/off duty of 58%, and the IGBTs 31, 33, 35 on the upstream side of inverter 30 and 32, 34, 36 on the downstream side are turned on and off with an on/off duty of 42%, the Δt time is longer, and the values of the negative zero-axis currents Iu0, Iv0, Iw0 are correspondingly larger.

In this way, the phase windings Lu, Lv, Lw are heated by the AC zero-axis current Io, which is composed of the positive zero-axis currents Iu0, Iv0, Iw0 flowing from one end of the phase windings Lu, Lv, Lw to the other end and the negative zero-axis currents Iu0, Iv0, Iw0 flowing from the other end of the phase windings Lu, Lv, Lw to one end. This heat preheats the refrigerant and lubricating oil that have been stagnating in the compressor 1. This preheating reduces the startup load on the compressor 1 when the compressor 1 is next started, allowing the compressor 1 to start up smoothly and quickly.

FIG. 8 shows examples of waveforms of the zero-axis currents Iu0, Iv0, and Iw0, and a waveform of the AC zero-axis current Io consisting of these zero-axis currents Iu0, Iv0, and Iw0.
The positive zero-axis currents Iu, Iv, Iw are all the same, the negative zero-axis currents Iu, Iv, Iw are all the same, and the winding current period of the inverter with the larger on/off duty overlaps with the winding current period of the inverter with the smaller on/off duty, so no rotational torque is generated in the motor 1M. Therefore, the phase windings Lu, Lv, Lw can be heated without rotating the motor 1M.

Because the motor 1M does not start rotating, the values of the zero-axis currents Iu0, Iv0, and Iw0 can be increased to values sufficient for preheating the compressor 1. Furthermore, because the inverters 30 and 40 are driven with an on/off duty that changes sinusoidally when generating the zero-axis currents Iu0, Iv0, and Iw0, all the IGBTs in the inverters 30 and 40 are turned on and off for equal periods of time, so there is no problem in that current flows only through a specific IGBT, shortening the lifespan of only that specific IGBT.

After starting the winding heating operation in S2 above, if the outside air temperature To is still below the threshold value To2 (YES in S1), the motor control unit 23 continues heating the windings (S2).
During the winding heating operation in S2, if the outside air temperature To rises to or exceeds the threshold value To2 (NO in S2), the motor control unit 23 determines whether the outside air temperature To is equal to or higher than the threshold value "To2+ΔT" (S3). If the outside air temperature To is not equal to or higher than the threshold value "To2+ΔT" (NO in S3), the motor control unit 23 returns to the determination in S1.

If the outside air temperature To is equal to or higher than the threshold value To2 (NO in S2) and equal to or higher than the threshold value "To2 + ΔT" (YES in S3), the motor control unit 23 ends the winding heating operation or maintains the winding heating inoperative state (S4).

Note that, as shown in FIG. 9, the values of the zero-axis currents Iu0, Iv0, and Iw0 during the winding heating operation may be controlled so that the outside air temperature To changes linearly between a threshold value To2 and a lower threshold value To1. That is, during the winding heating operation, the motor control unit 23 increases the on/off duty of each IGBT as the outside air temperature To decreases, thereby increasing the values of the zero-axis currents Iu0, Iv0, and Iw0. This makes it possible to keep the time required for preheating the compressor 1 almost constant regardless of the outside air temperature To. Furthermore, it is possible to supply a necessary and sufficient amount of heat even in extremely low outside air temperature conditions.

Furthermore, a sensor may be provided to detect the temperature inside or on the outer surface of the compressor 1, and the on/off duty of each IGBT may be changed so that the detected temperature remains constant.
During winding heating, the IGBTs serving as the switching elements of the inverters 30 and 40 were driven with on/off duty that changed in an opposite phase sinusoidal manner. From the standpoint of noise and vibration generation, it is considered preferable to drive them in a sinusoidal manner, but the on/off pattern does not have to be sinusoidal as long as a roughly equal current flows through each switching element of the inverters 30 and 40.

The above embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications may be implemented in various other forms, and various omissions, rewrites, and modifications may be made without departing from the spirit of the invention. These embodiments and modifications are included within the spirit of the invention and are included in the scope of the invention and its equivalents as set forth in the claims.

A...outdoor unit, 1...compressor, 1M...open winding motor, Lu, Lv, Lw...phase windings, 6...outdoor temperature sensor, 7...outdoor control unit, 20...motor drive unit, 23...motor control unit, 30...inverter (first inverter), 40...inverter (second inverter), 51a, 52a...relay contacts (switches).

Claims (5)

a motor for driving a compressor, the motor having a plurality of phase windings that are not connected to each other;
a first inverter for controlling energization of one end of each of the phase windings;
a second inverter that controls the energization of the other end of each of the phase windings;
a control means for controlling the first and second inverters so that, when the motor is stopped, a zero-axis current flows from one end of each of the phase windings to the other end and a zero-axis current flows from the other end of each of the phase windings to one end alternately;
A refrigeration cycle device comprising: the control means controls the first and second inverters so that the zero-axis currents are generated alternately when the motor is stopped and an outside air temperature is lower than a threshold value.
The refrigeration cycle device according to claim 1. The control means changes a value of each of the zero-axis currents in response to the outside air temperature.
The refrigeration cycle device according to claim 2. the first inverter has a plurality of first switch elements;
the second inverter has a plurality of second switch elements;
the control means controls the first switch elements and the second switch elements to be turned on and off so that, when the motor is stopped, a zero-axis current having the same value flowing from one end to the other end of each of the phase windings and a zero-axis current having the same value flowing from the other end to one end of each of the phase windings are generated alternately.
The refrigeration cycle device according to claim 1. 5. The refrigeration cycle apparatus according to claim 4, wherein the control means drives the first switch elements and the second switch elements with on/off duties that change in an opposite phase sinusoidal manner in the on/off control of the first switch elements and the second switch elements.

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