HK1028443A - Apparatus for cooling the power electronics of a reerigeration compressor drive - Google Patents

Description

Device for cooling power electronics of a drive of a refrigeration compressor

The present invention relates to a method and apparatus for cooling the electronics of a variable frequency drive associated with a refrigeration compressor.

Compressors used in many refrigeration systems typically require tight control of the speed of the compressor's motor to maintain the system within a desired limit under varying load conditions. The compressor is therefore equipped with a Variable Frequency Drive (VFD) which contains power electronics in the form of insulated gate bipolar transistors which may overheat and therefore require cooling. A generally accepted method of providing cooling to these electronic devices is to mount the transistors on a heat sink and remove heat from the heat sink by circulating a coolant within or around the heat sink. The performance of the heat sink and cooling system is the primary factor that determines the capacity of the VFD.

The heat sink is typically in the form of a relatively large mass of material having good thermal conductivity and thermal inertia properties. A flow channel is formed in the block through which the coolant circulates, which absorbs excess heat and carries it out of the system.

Cooling VFD heat sinks with water has proven to be a satisfactory method of cooling VFD transistors, however, water cooling is difficult to control and heat sink temperatures sometimes exceed the desired operating range. This in turn can create overheating of the VFD electronics and prevent operation of the refrigeration system. Furthermore, the water cooling circuit requires additional water control components, such as water pumps, heat exchangers, and such devices that require heat transfer from the transistor to the external environment. Such cooling devices are generally complex, costly and require a large installation space.

It is therefore a primary object of the present invention to improve refrigeration systems.

This object is achieved by a closed circuit refrigeration system having a condenser, an evaporator and a compressor connected in series by refrigeration circuits, and an expander in one of the refrigeration circuits for regulating the flow of refrigerant from high pressure to low pressure between the condenser and the evaporator. A variable frequency drive is connected to the compressor and contains electronics in the form of insulated gate bipolar transistors that generate heat, which needs to be cooled. The electronic device is mounted in heat-conducting relation with a mass of material having good heat-conducting properties. The bulk material acts as a heat sink to carry heat away from the power electronics device. A flow circuit is provided to route refrigerant from the condenser of the system through the fins to the inlet of the compressor of the system. An expansion valve is mounted in the flow-through circuit and controls the expansion of the refrigerant flowing in the circuit, thereby providing cooling to the heat sink and the electronics thereon.

For a better understanding of these and other objects of the invention, reference is made to the following detailed description of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of a refrigeration system incorporating the present invention;

FIG. 2 is a schematic view similar to FIG. 1 but relating to a further embodiment of the invention;

FIG. 3 is still a schematic diagram relating to yet another embodiment of the present invention;

FIG. 4 is a schematic view of another embodiment of the present invention; and

fig. 5 is an enlarged side view of a temperature expansion control valve suitable for use in the practice of the present invention.

Referring initially to fig. 1, a refrigerant system, generally designated 10, is illustrated and utilizes a carnot refrigeration cycle having a series of refrigerant circuits 12 operatively connected to various system components. The system also has a condenser 13 connected to the outlet side of a compressor 15 by a refrigerant line 12. Which in turn is connected in series with an evaporator 17, the outlet of the evaporator 17 being connected to the inlet side of the compressor by means of a refrigeration line to complete the circuit of the system. An expander 20 is installed in a refrigeration line between the condenser and the evaporator and expands the high-pressure refrigerant from the condenser to a low temperature and a low pressure. The expander may be any of such devices, such as a throttle valve or a capillary tube, as are well known and used in the art.

The substance to be cooled flows through an evaporator in heat transfer relationship with the cryogenic refrigerant. The refrigerant, which has absorbed heat during cooling, is evaporated at a relatively low pressure, and the refrigerant vapor is then delivered to the compressor inlet for recirculation through the system.

The motor of the compressor is equipped with a Variable Frequency Drive (VFD)25 that controls the engine speed. The device is shown in dashed lines in fig. 1. As is well known in the art, VFDs typically house power electronics that require cooling to enable the drive to operate under optimum conditions within the operating range of the system. In practice, the electronic devices that need to be cooled are typically Insulated Gate Bipolar Transistors (IGBTs), schematically shown at 27 in the figure. As noted above, heretofore, the electronic device has been cooled by placing it in heat transfer relationship with a heat sink and circulating cooling water. Such cooling systems are rather complex, require large space and are difficult to control.

As shown in fig. 1, the VFD electronics are mounted directly to a heat sink 30, the heat sink 30 forming part of what is referred to herein as the VFD evaporator 29. The heat sink is constructed from a bulk material having a relatively high thermal conductivity so that heat generated by the electronic device is quickly transferred away and absorbed into the heat sink. An internal flow channel 32 is installed in the bulk material. The channels follow a tortuous path through the mass of material to provide maximum contact between the channels and the fins. In practice, the flow channel may be a length of copper tubing or the like embedded in the heat sink and having an inlet 33 and an outlet 34.

The inlet 33 of the internal flow channel is connected to the refrigerant outlet 35 of the system condenser by a supply line 36. And the outlet of the flow channel is connected to the compressor inlet via a discharge pipe 39. A control valve, indicated at 40, is received in the supply line through which the refrigerant is regulated from a higher condenser pressure to a lower pressure, thereby providing the cooling fins with a low temperature refrigerant to cool the electronic components.

The details of the control valve 40 are shown in fig. 5. The valve has a probe 42 embedded in the heat sink, the probe 42 being as close as possible to the electronics to optimally determine operating temperature. The valve may be a temperature controlled valve responsive to a temperature sensed by the probe or a temperature expansion valve responsive to a pressure change at the probe caused by a temperature change in the heat sink. In this embodiment, the valve is a thermal expansion valve having a diaphragm 43 mounted within a housing 44. The pressure of the spherical probe changes depending on the temperature of the heat sink, which sets the pressure on the upper chamber 45 of the diaphragm. The pressure in the diaphragm lower chamber 46 is determined by a predetermined adjustable spring 47 and a pressure equalisation port 49, the pressure equalisation port 49 extending between the low pressure side of the chamber and the low pressure side of the valve body 50. Pressure equalization across the diaphragm of the valve positions the valve body in the valve passage, thereby controlling the amount of cooling provided to the heat sink. Preferably, the temperature of the heat sink is controlled to be in the range of 90 ° F to 140 ° F.

It can be seen from the above disclosure that the heat sink with internal flow passages can act as a refrigerant evaporator for the VFD by utilizing a refrigeration cycle to provide closely controlled cooling to the electronics to remove heat from the VFD. It can be seen that the heat transferred to the refrigerant in the VFD evaporator is conducted by the compressor of the system to the condenser of the system, where it is rejected to the condenser cooling circuit.

FIG. 2 illustrates another embodiment of the present invention, wherein like components are identified by like reference numerals in FIG. 1. In this embodiment of the invention, the discharge line 39 of the VFD evaporator is connected to the system evaporator 17 and is combined with the refrigerant flowing through the evaporator for processing. The valve probe 42 is shown mounted on the discharge tube of the VFD evaporator rather than embedded in the heat sink. The probe feeds temperature information back to the control valve 40 and the control valve 40 sets the position of the valve body based on the sensed refrigerant temperature to maintain the temperature of the heat sink within the operating range required to cool the electronics.

Referring now to fig. 3, there is shown still another embodiment of the present invention, wherein like reference numerals are again used to designate like components from above. In this other embodiment of the invention, the control valve 40 is installed in the discharge line of the VFD evaporator 29, in which case the control valve 40 is connected directly at the compressor inlet. However, as mentioned above, the drain may also be connected directly to the system. The temperature probe 42 is embedded in the heat sink 30 of the VFD evaporator and provides the control valve with relevant temperature information. The refrigerant exiting the system condenser is typically at a temperature below 140F so that the refrigerant tapped into the VFD evaporator is well within the temperature range of the fins required to cool the electronics.

Fig. 4 shows yet another embodiment of the present invention, wherein the same reference numerals are again used to designate the same components as above. In this embodiment of the invention, a portion of the refrigerant exiting the system condenser is expanded through a thermostatic valve 40 into the VFD evaporator 29. The temperature probe 42 is again embedded in the heat sink 30 and gives the microprocessor 50 relevant temperature information, the microprocessor 50 is programmed with data processing programs and sends control signals to the control valves. Other system related information may also be sent to the microprocessor and processed by the microprocessor to achieve the desired valve settings to provide cooling to the electronics with minimal overall system performance consumption.

From the above disclosure, it is evident that the present invention is a simple and effective solution for cooling the power electronics of a variable frequency drive of a refrigeration compressor. The system eliminates the complexity of conventional water cooling systems, is easy to install, and provides greater control over the cooling process. Because of its effectiveness, the present system allows for a wider range of applications for electronic devices having greater capacity than those currently used in the compressor drives of a refrigeration system in the prior art.

Claims (16)

1. A cooling apparatus for power electronics of a variable frequency drive used to control a motor of a compressor in a refrigeration system, characterized by:

a refrigeration system further having a compressor, a condenser and an evaporator connected in series by refrigeration lines and an expander in one of said refrigeration lines to condition refrigerant flowing between the condenser and the evaporator,

a variable frequency drive connected to the motor of the compressor, said drive comprising power electronics requiring cooling,

a circuit for diverting a portion of the refrigerant from the system condenser to the compressor inlet,

a variable frequency drive evaporator mounted in said loop, said evaporator being in heat transfer relationship with the electronics of said variable frequency drive;

a control valve in the circuit for expanding refrigerant through the circuit from the pressure at the system condenser to the pressure at the compressor inlet, thereby cooling the electronics.

2. The apparatus of claim 1 wherein said variable frequency drive evaporator has a heat sink formed from a block of material having a relatively high coefficient of thermal conductivity, said flow channels passing through said block of material, and wherein said power electronics are mounted in heat transfer relation with said heat sink.

3. The apparatus of claim 1 further comprising a temperature probe, said probe providing information about the temperature of the heat sink to said valve, whereby said valve opens or closes in response to a sensed temperature.

4. The apparatus of claim 3, wherein the temperature sensing head is embedded in the heat sink.

5. The apparatus of claim 3, wherein the probing tip is mounted downstream of a heat sink in the flow-through loop.

6. The apparatus of claim 2 wherein the control valve is a temperature expansion valve and further having a temperature probe capable of providing pressure information to the valve based on the temperature of the heat sink.

7. The apparatus of claim 6, wherein the probing tips are embedded in the heat sink.

8. The apparatus of claim 2, wherein the control valve is located on an upstream side of the heat sink.

9. The apparatus of claim 2, wherein the control valve is located on a downstream side of the heat sink.

10. The apparatus of claim 3, further comprising a microprocessor configured to receive input from the probe and provide an output control signal to the valve to maintain the temperature of the heat sink within a desired temperature range.

11. A method of cooling power electronics of a Variable Frequency Drive (VFD) used to control a motor of a compressor in a refrigeration system, comprising:

the power electronics of the VFD are mounted in heat-conducting relationship to a heat sink,

the refrigerant output from the refrigeration condenser is brought into heat-conducting relationship with the heat sink,

the refrigerant output from the condenser is expanded to a reduced pressure to maintain the fin temperature within a desired range.

12. The method of claim 11, further comprising the steps of: passing the refrigerant exiting the fins into an inlet of a system compressor.

13. The method of claim 11, further comprising the steps of: and enabling the refrigerant coming out of the cooling fins to enter a system evaporator.

14. The method of claim 11, further comprising the steps of: the refrigerant is passed through a control valve to expand the refrigerant before it is brought into heat transfer relationship with the heat sink.

15. The method of claim 14, further comprising the steps of: sensing a temperature of the heat sink and positioning the control valve in accordance with the sensed temperature.

16. The method of claim 14, further comprising the steps of: sensing the temperature of the heat sink, providing the sensed temperature data to a microprocessor for processing, the microprocessor providing an output signal to the control valve to maintain the temperature of the heat sink within a desired range.