JP2010515007A - Standby type variable frequency compressor drive unit - Google Patents

Abstract

  A transport refrigeration system is provided that includes a variable speed compressor that operates only in the low capacity perishable range. Line voltage and line frequency power can be used during high capacity operation, and for variable speed operation, a relatively small inverter can be used to provide variable voltage and variable frequency. it can. This variable voltage and variable frequency can also be supplied to a variable speed condenser motor to increase the capacity of the condenser during economizer operation. This variable voltage and variable frequency can also be used to supply a DC voltage to the compressor for heating purposes.

Description

  The present invention relates to refrigeration systems, and more particularly to selectively using a variable speed drive of a compressor during operation in an unload mode.

  The transport refrigeration system includes a cargo space to be cooled and a refrigeration system that provides heat exchange capability to maintain a controlled temperature range within the cargo space. A temperature sensor and controller are operatively connected to the cooling circuit to adjust the output from the cooling circuit to maintain a desired temperature level.

  The cooling circuit is designed to have sufficient capacity to absorb the maximum heat loss that flows into and through the transportable cooling device, and this loss is directly related to the external environmental temperature. It is proportional.

  Under refrigeration conditions, the control device adjusts the cooling circuit by switching the cooling circuit ON and OFF in response to the detected temperature in the cargo space. That is, the cooling circuit switches to OFF when the detected temperature reaches the set point on the low temperature side, and switches to ON when the detected temperature reaches the set point on the high temperature side. When the temperature of the ambient air is close to the temperature of the transport volume chamber (ie when it is part load so-called chilled conditions), the cooling circuit will have a larger capacity than required, so such chilled conditions In, the system shortage is substantially reduced. That is, under such chilled conditions, the cooling circuit is too large in capacity, but needs to operate continuously to maintain temperature control of the transport volume chamber.

  ON / OFF mode operation for refrigeration conditions (ie, pull-down conditions, refrigeration conditions, and chilled conditions at full load) is estimated to account for approximately 60% of market demand, whereas chilled conditions or parts Load conditions are estimated to account for about 40% of market demand. Thus, using the current method of adjusting suction pressure, or throttling, to reduce capacity while operating the compressor motor at full speed, substantially reduces efficiency. On the other hand, if the variable speed compressor is always used, power consumption becomes excessive due to drive loss during operation in the ON / OFF mode and pull-down mode.

  Briefly, according to one aspect of the invention, the compressor is operable at a variable speed when the system is operating at chilled conditions. Thus, continuous operation can be maintained while maximizing power efficiency.

  According to another aspect of the present invention, power to the compressor is reduced by conventional methods until the variable speed is in a range where it can be used effectively and efficiently through a relatively small inverter.

  According to yet another aspect of the present invention, an inverter is provided during operation under partial load conditions, the inverter being selectively applied to supply a variable voltage and variable frequency to the compressor drive motor, As a result, the compressor drive motor can continue to operate at a selective variable speed, thereby achieving high operating efficiency.

  According to another aspect of the present invention, an evaporator flow control device is further applied if the system capacity remains higher than the load demand during variable speed operation.

  According to another aspect of the present invention, during operation under chilled conditions, the system operates using line voltage and line frequency until the temperature demand stabilizes, at which point the power supply is stable. Switches from line voltage and line frequency to variable voltage and variable frequency.

  Various modifications and other configurations can be applied without departing from the spirit and scope of the present invention.

1 is a schematic diagram of a vapor compression system according to the prior art. 1 is a schematic diagram of an improved vapor compression system according to the present invention. The graph which shows the result of the driving | operation according to the mode of this invention.

  FIG. 1 shows a vapor compression system 10 according to the prior art. The vapor compression system 10 includes a main vapor compression circuit comprising a compressor 12, a condenser 14, an expander 16 and an evaporator 18. These components are connected in series by a main refrigerant line, which passes from the discharge port 13 of the compressor 12 through the line 20 to the condenser 14 and from the condenser 14 through the line 22. Providing a refrigeration flow from the expander 16 through the line 24 to the evaporator 18 and from the evaporator 18 through the line 26 to the intake port 15 of the compressor 12.

  Further, an economizer circuit is connected between the condenser 14 and at least one of the intermediate pressure port 28 and the suction port 15 of the compressor 12. This circuit is preferably in the form of an economizer refrigerant line 40 leading from the condenser 14 to the auxiliary expander 42 and further leading from the auxiliary expander 42 through the economizer refrigerant line 44 to the heat exchanger 32. In the typical mode of operation of the economizer circuit, the economizer circuit extends from the heat exchanger 32 via line 38 to the intermediate pressure port 28 of the compressor 12.

  Further, in order to selectively connect or block the flow passing through the economizer circuit, an economizer cutoff valve 46 can be advantageously disposed in the economizer refrigerant line, for example, in the line 40. Alternatively, if the expander 42 is an electronic expansion valve, the valve 46 is not necessary.

  Further according to the prior art, the system 10 further includes a bypass circuit connected between the intermediate pressure port 28 of the compressor 12 and the suction port 15. This bypass circuit allows the compressor 12 to be unloaded. The bypass circuit is appropriately configured for the flow through the economizer heat exchanger 32 so as to supercool the main refrigerant flow using the flow from the bypass circuit, and thus the economizer heat exchanger. 32 is used to improve the efficiency in unloading operation. Thus, the bypass refrigerant line 38 advantageously extends to the economizer heat exchanger 32 and back from the heat exchanger 32 through line 36 to the intake port 15 of the compressor 12. In order to selectively connect or shut off the flow through the bypass circuit, a bypass shutoff valve 34 is advantageously provided in the bypass line 36 extending from the heat exchanger 32 to the suction port 15.

  It should be noted that references throughout this specification have been made to block flow through a particular circuit or component. As used herein, the term is used to describe a flow in which the circuit in question is substantially inactive, that is, a substantial portion of the flow through the circuit is interrupted. Is substantially cut off.

  The main refrigerant line 22 flows in the economizer heat exchanger 32 and exchanges heat with the flow of the line 38 in the heat exchanger 32. Accordingly, the heat exchanger 32 is configured to receive the first flow from the main refrigerant line 22 and the second flow from at least one of the economizer circuit and the bypass circuit, and operates in the full load economizer mode. Or, preferably, heat transfer occurs during operation in the partial load mode.

  Using this configuration, when the compressor 12 is to be operated in an unloaded condition, the valve 34 opens to allow a portion of the refrigerant to flow through the intermediate pressure port 28 and allow a portion of the refrigerant flowing through the compressor 12 to flow. Compress to intermediate pressure, thereby reducing the load on the compressor 12.

  In operation in the unload mode, the flow of the main refrigerant is subcooled in the economizer heat exchanger 32, improving the system performance in operation in this mode. In this regard, depending on the position of the intermediate pressure port 28, the intermediate pressure of the flow exiting from this port is relatively close to the suction pressure, which contributes to the heat exchange action in the economizer heat exchanger 32. The temperature difference that can be utilized increases.

  In addition, a control member 48 is advantageously provided that is operably associated with the shut-off valves 34, 46 (or electronically controlled expander 42) to improve system performance. For full load economizer mode or unload mode where the heat exchanger 32 is still operating and functioning for the purpose, the valves 34 and 46 are placed between the open and closed positions to operate the system 10 as required. Selectively with. Of course, the system 10 can also be operated in full load non-economizer mode with both valves 34, 46 closed.

  In lieu of or in addition to the bypass circuit portion used for unloading operation, the evaporator flow control device 49 can be used in response to a reduction in system load. The evaporator flow control device 49 may have various types of valves such as suction pressure adjustment valves or pulse width adjustment valves, the purpose of which is to reduce the flow of refrigerant to the compressor. Yes, by extension, balancing compressor capacity and load to avoid operation at low coil temperatures. Further, the evaporator flow control device can be a PWM (pulse width modulation) compressor, and the PWM compressor uses a pulse width modulation request signal for engaging and disengaging the mutually engaged scroll wraps. It is one of the scroll type compressors used with the load reduction system which performs. The load on the compressor is reduced by separating / raising the fixed scroll set from the orbiting scroll set. This separation is controlled via a fluid bypass PWM solenoid valve. Capacity adjustment is ultimately controlled by pulsing this solenoid valve that switches the compressor from high capacity operation to low capacity operation.

  Referring to FIG. 2, the compressor 12 of FIG. 1 is replaced with a compressor 51 that can be selectively operated in both the fixed speed operation mode and the variable speed operation mode. The compressor 51 may be a reciprocating compressor, but may be another type of compressor such as a scroll compressor or a rotary compressor.

  The compressor 51 is connected to the control device 52 through a plurality of power connectors 53 so as to be directly energized. The compressor 51 is further connected to an inverter 56 through a plurality of power connectors 54 so that the inverter 56 is connected to the control device 52 through a connector 57. Control of the inverter 56 is performed by the controller 52 via the connector 58. Line power is supplied to controller 52 via line 59.

  Using the illustrated apparatus, the compressor 51 is selectively operated by operating the switch 61 and the switch 62 so as to supply the compressor 51 with either a line voltage and a line frequency or a variable voltage and a variable frequency. Can be operated. That is, when the switch 61 is closed and the switch 62 is open, the line voltage is supplied to the compressor via the connector 53. Alternatively, when the switch 62 is closed and the switch 61 is open, the line voltage and line frequency are supplied to the inverter 56, and the inverter 56 supplies the variable voltage and variable frequency to the compressor 51 via the connector 54. To do.

  In the embodiment shown in FIG. 2, the adjustment valve 49 is provided as in FIG. 1, but the bypass circuit shown in FIG. 1 is omitted. Accordingly, the present invention will be described with respect to the case where a regulating valve is provided but no bypass circuit is provided. However, it should be understood that the present invention may be equally useful in systems that include a bypass circuit.

  FIG. 3 is a typical graph showing the change over time in both cargo temperature and supply temperature when system operation transitions to operation under unload conditions. As can be seen in the figure, over time, the cargo temperature gradually approaches the supply temperature and eventually reaches a set point.

  The lower part of FIG. 3 shows changes in various operation modes when operating under partial load conditions and unload conditions. These operating modes directly correspond to the temperature conditions shown at the top of the figure. That is, under the partial load condition where the difference between the cargo temperature and the supply temperature is substantially constant, the compressor 51 operates in the economizer mode using the line voltage and the line frequency. This is indicated by the solid line FE.

  When the difference between the cargo temperature and the supply temperature begins to decrease, the compressor is disconnected from the economizer mode and switched to standard mode operation using line voltage and line frequency. This mode is used when the load is pulled down to the perishable range. Operation in this mode is indicated by ED in FIG.

  When operating in refrigeration conditions and when operating in mode 2 used when the chilled load is pulled down to the perishable range, the compressor operates in unload mode using line voltage, At this time, the above-described evaporator flow control device 49 is used.

  Thus, in the operation in each operation mode 2, 3 and 4, the speed of the compressor is kept constant. However, it should be noted that the power consumption of the compressor is substantially reduced when going from the economizer mode to the standard mode and further to the unload mode using the evaporator flow control device. As a result, for the operation mode 1 indicated by the solid line CBA, when the inverter 56 is connected via the switch 62, the required power is reduced, and the size required for the inverter 56 is smaller than the normal size. Substantially smaller. For example, the inverter is sized for 5 kilowatts instead of the size for operation at 10-11 kilowatts. That is, the drive can be much smaller in size than would be used in mode 1 alone. The reason for this is that in a steam pressurized closed circuit cooling system, the power for compression in the system is approximately linear with respect to the inherent intake gas density change with a substantially lower room temperature in the perishable range. It is because it decreases. By reducing the density and mass flow of the suction gas after pull-down, it is possible to use a variable speed drive with a fairly small size near the set point.

  When the system has a capacity greater than that required for fresh products, operation in mode 1 is performed. Fresh products require tight temperature control, which is best achieved by operating the system continuously.

  In mode 1, the system operates in unload compressor mode using line voltage and line frequency, and the evaporator flow controller 49 is used until the temperature demand is stable. At a certain point from when the regulating valve starts to close until it is completely closed, the control device 52 determines switching of the switches 61 and 62, cuts off the line voltage and the line frequency, and switches to the variable voltage and the variable frequency. The compressor 51 is operated at a variable speed. In this mode, the controller 52 precisely controls the compressor speed to provide the exact temperature of the transport load for all perishable conditions. Run at this variable speed to the optimum minimum speed, and then if the system capacity remains higher than the transport load requirement, operate the evaporator flow controller 49 until stable temperature control is obtained. . Conversely, in the unload mode of operation, when the optimum maximum speed is reached and more cooling power is required, the system switches switches 61 and 62 to operate at a fixed speed at line voltage and line frequency. To resume.

  The variable speed drive is not used in the compressor under high capacity conditions, so this variable speed drive is switched to the condenser fan motor and used to increase the condenser fan speed, It would be advantageous to improve the performance of the condenser fan when capacity is limited. This allows the system to be more effective under high temperature pull-down conditions while keeping the size of the condenser to a minimum, thereby reducing costs and reducing the discharge temperature and pressure. In addition, the reliability of the compressor can be improved, and further, important components that are not used can be used.

  Applying the variable speed drive only in mode 1 is advantageous because it can provide a redundant system. That is, if this drive fails during transportation for some reason, the system can operate without using a variable speed drive and eliminates load loss by using the current control scheme. be able to. Furthermore, since it operates on the conditions of light load, the reliability of a drive device improves.

  This variable speed drive is also used to heat a compressor motor by applying a small DC voltage to a compressor for trailer applications that have a separately purchased crankcase heater. be able to. Variable speed drives can be used in place of these heaters and can be offered to all consumers as a standard package that provides cost savings and reliability. This allows the refrigeration system of the present invention to function in any region of the world without any special changes or selections.

Claims (18)

A method of operating a transport refrigeration system of the type having a compressor and associated vapor compression circuit, economizer circuit, and evaporator flow control device, comprising:
The above compressor can be operated at a variable speed,
The compressor is provided with an inverter that selectively supplies one of line voltage and line frequency power, or variable voltage and variable frequency power,
During high capacity operation that pulls down the load to the perishable range, the compressor is operated at a fixed speed,
An operation method characterized by operating the compressor at a variable speed during operation at a low capacity in a fresh product range.   2. The operation method according to claim 1, wherein the vapor compression circuit is used in combination with the economizer circuit during operation at a fixed speed.   The operation method according to claim 1, wherein the vapor compression circuit is used without using the economizer circuit during operation at a fixed speed.   The operation method according to claim 1, wherein the vapor compression circuit is used in combination with the evaporator flow control device during operation at a fixed speed.   The operation method according to claim 1, wherein power of a line voltage and a line frequency is supplied to the compressor during operation at a low capacity.   The operation method according to claim 5, wherein the evaporator flow control device is used until the temperature demand is stabilized.   When the valve of the evaporator flow control device begins to close, the line voltage and line frequency power is switched to variable voltage and variable frequency power, and the compressor is driven at a variable speed. Item 7. The driving method according to Item 6.   The operation method according to claim 1, wherein a variable speed condenser fan motor is provided and, when operating with the economizer, a variable voltage and variable frequency power is selectively applied to the fan motor. .   2. The operating method according to claim 1, wherein a variable voltage and variable frequency power is used to supply a DC voltage to the compressor for the purpose of heating. A vapor compression circuit including an economizer, an evaporator flow control device, and a compressor that receives power from the power source through the control device, and is configured to operate when the compressor is in a partial load condition A method of operating a transport refrigeration system,
An inverter that receives fixed voltage and fixed frequency power from the power source and converts it to a variable voltage and variable frequency output is provided.
A compressor that can operate in either fixed speed operation or variable speed operation is provided.
In order to supply any one of a fixed voltage and a fixed frequency or a variable voltage and a variable frequency to the variable speed compressor, a switch for selectively connecting or disconnecting the inverter to the circuit is provided,
A driving method characterized in that a variable voltage and a variable frequency are used only when the driving condition is a partial load.   The operation method according to claim 10, wherein the vapor compression circuit is used in combination with the economizer circuit during operation at a fixed speed.   The operation method according to claim 10, wherein the vapor compression circuit is used without using the economizer circuit during operation at a fixed speed.   11. The operating method according to claim 10, wherein the vapor compression circuit is used in combination with the evaporator flow control device during operation at a fixed speed.   The operation method according to claim 10, wherein a power having a fixed voltage and a fixed frequency is supplied to the compressor during operation at a low capacity. 15. The method of operation according to claim 14, wherein the evaporator flow control device is used until the temperature demand is stabilized.   When the valve of the evaporator flow control device begins to close, the line voltage and line frequency power is switched to variable voltage and variable frequency power, and the compressor is driven at a variable speed. Item 16. The driving method according to Item 15.   11. The operating method according to claim 10, wherein a variable speed condenser fan motor is provided and, when operating with the economizer, a variable voltage and variable frequency power is selectively applied to the fan motor. .   11. The operating method according to claim 10, wherein a variable voltage and variable frequency power is used to supply a DC voltage to the compressor for the purpose of heating.

Images