Patent Description:
HVAC&R systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature and humidity, for occupants of the respective environments. In some cases, the HVAC&R system may include a vapor compression system, which circulates a working fluid along a refrigerant loop. The working fluid is configured to change phases between vapor, liquid, and combinations thereof in response to being subj ected to different temperatures and pressures associated with operation of the vapor compression system. For example, the vapor compression system utilizes a compressor to circulate the working fluid to a heat exchanger which may transfer heat between the refrigerant and another fluid flowing through the heat exchanger. In some cases, the compressor is driven by a motor, which receives power from a variable speed drive. Existing variable speed drives for HVAC&R systems may incur switching losses because of relatively slow switching times of insulated-gate bipolar transistors (IGBTs) between an open and a closed position during operation of the variable speed drive. An example of HVAC&R system is disclosed in <CIT>.

In one embodiment a heating, ventilating, air conditioning, and refrigeration (HVAC&R) system includes the features of claiim <NUM>.

In another embodiment a method includes the features of claim <NUM>.

Embodiments of the present disclosure are directed towards a heating, ventilating, air conditioning, and refrigeration (HVAC&R) system that uses a variable speed drive having a silicon carbide transistor. Variable speed drives may be coupled to a motor that drives a compressor of the HVAC&R system. More specifically, variable speed drives may be utilized to adjust a speed of the motor. Typically, HVAC&R systems utilize significant amounts of power. Accordingly, enhancing the efficiency of such systems may reduce operating costs by reducing an amount of energy consumed and/or reducing energy loss incurred during operation.

Variable speed drives may incur losses during operation due to conduction losses and/or switching losses. For example, conduction losses may occur when components of the variable speed drive conduct current (e.g., an insulated-gate bipolar transistor (IGBT) conducts current when in a closed state). Additionally, switching losses may occur when components of the variable speed drive (e.g., an insulated-gate bipolar transistor (IGBT)) switch between an open and a closed state during operation of the variable speed drive. Typically, switching components of the variable speed drive, such as an IGBT module, which also includes a silicon diode. Silicon diodes may be relatively inexpensive, but also have relatively slow switching times. Accordingly, an efficiency of the variable speed drive may be reduced as a result of the switching time for the silicon diode to switch between an open and a closed position.

Embodiments of the present disclosure relate to variable speed drives that include a silicon carbide transistor in lieu of an IGBT. The silicon carbide transistor may reduce switching losses because the silicon carbide transistor includes a more efficient (e.g., faster) switching time when compared to IGBTs. Incorporating the silicon carbide transistor into variable speed drives may enhance an efficiency of the variable speed drive, and thus, increase the efficiency of the overall HVAC&R system.

Turning now to the drawings, <FIG> is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system <NUM> in a building <NUM> for a typical commercial setting. The HVAC&R system <NUM> may include a vapor compression system <NUM> that supplies a chilled liquid, which may be used to cool the building <NUM>. The HVAC&R system <NUM> may also include a boiler <NUM> to supply warm liquid to heat the building <NUM> and an air distribution system which circulates air through the building <NUM>. The air distribution system can also include an air return duct <NUM>, an air supply duct <NUM>, and/or an air handler <NUM>. In some embodiments, the air handler <NUM> may include a heat exchanger that is connected to the boiler <NUM> and the vapor compression system <NUM> by conduits <NUM>. The heat exchanger in the air handler <NUM> may receive either heated liquid from the boiler <NUM> or chilled liquid from the vapor compression system <NUM>, depending on the mode of operation of the HVAC&R system <NUM>. The HVAC&R system <NUM> is shown with a separate air handler on each floor of building <NUM>, but in other embodiments, the HVAC&R system <NUM> may include air handlers <NUM> and/or other components that may be shared between or among floors.

<FIG> and <FIG> are embodiments of the vapor compression system <NUM> that can be used in the HVAC&R system <NUM>. The vapor compression system <NUM> may circulate a refrigerant through a circuit starting with a compressor <NUM>. The circuit may also include a condenser <NUM>, an expansion valve(s) or device(s) <NUM>, and a liquid chiller or an evaporator <NUM>. The vapor compression system <NUM> may further include a control panel <NUM> that has an analog to digital (A/D) converter <NUM>, a microprocessor <NUM>, a non-volatile memory <NUM>, and/or an interface board <NUM>.

Some examples of fluids that may be used as refrigerants in the vapor compression system <NUM> are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-<NUM>, R-134a, hydrofluoro olefin (HFO), "natural" refrigerants like ammonia (NH<NUM>), R-<NUM>, carbon dioxide (CO<NUM>), R-<NUM>, or hydrocarbon based refrigerants, water vapor, or any other suitable refrigerant. In some embodiments, the vapor compression system <NUM> may be configured to efficiently utilize refrigerants having a normal boiling point of about <NUM> degrees Celsius (<NUM> degrees Fahrenheit) at one atmosphere of pressure, also referred to as low pressure refrigerants, versus a medium pressure refrigerant, such as R-134a. As used herein, "normal boiling point" may refer to a boiling point temperature measured at one atmosphere of pressure.

In some embodiments, the vapor compression system <NUM> may use one or more of a variable speed drive (VSDs) <NUM>, a motor <NUM>, the compressor <NUM>, the condenser <NUM>, the expansion valve or device <NUM>, and/or the evaporator <NUM>. The motor <NUM> may drive the compressor <NUM> and may be powered by a variable speed drive (VSD) <NUM>. The VSD <NUM> receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor <NUM>. In other embodiments, the motor <NUM> may be powered directly from an AC or direct current (DC) power source. The motor <NUM> may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor <NUM> compresses a refrigerant vapor and delivers the vapor to the condenser <NUM> through a discharge passage. In some embodiments, the compressor <NUM> may be a centrifugal compressor. The refrigerant vapor delivered by the compressor <NUM> to the condenser <NUM> may transfer heat to a cooling fluid (e.g., water or air) in the condenser <NUM>. The refrigerant vapor may condense to a refrigerant liquid in the condenser <NUM> as a result of thermal heat transfer with the cooling fluid. The liquid refrigerant from the condenser <NUM> may flow through the expansion device <NUM> to the evaporator <NUM>. In the illustrated embodiment of <FIG>, the condenser <NUM> is water cooled and includes a tube bundle <NUM> connected to a cooling tower <NUM>, which supplies the cooling fluid to the condenser.

The liquid refrigerant delivered to the evaporator <NUM> may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser <NUM>. The liquid refrigerant in the evaporator <NUM> may undergo a phase change from the liquid refrigerant to a refrigerant vapor. As shown in the illustrated embodiment of <FIG>, the evaporator <NUM> may include a tube bundle <NUM> having a supply line <NUM> and a return line 60R connected to a cooling load <NUM>. The cooling fluid of the evaporator <NUM> (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator <NUM> via return line 60R and exits the evaporator <NUM> via supply line <NUM>. The evaporator <NUM> may reduce the temperature of the cooling fluid in the tube bundle <NUM> via thermal heat transfer with the refrigerant. The tube bundle <NUM> in the evaporator <NUM> can include a plurality of tubes and/or a plurality of tube bundles. In any case, the vapor refrigerant exits the evaporator <NUM> and returns to the compressor <NUM> by a suction line to complete the cycle.

<FIG> is a schematic of the vapor compression system <NUM> with an intermediate circuit <NUM> incorporated between condenser <NUM> and the expansion device <NUM>. The intermediate circuit <NUM> may have an inlet line <NUM> that is directly fluidly connected to the condenser <NUM>. In other embodiments, the inlet line <NUM> may be indirectly fluidly coupled to the condenser <NUM>. As shown in the illustrated embodiment of <FIG>, the inlet line <NUM> includes a first expansion device <NUM> positioned upstream of an intermediate vessel <NUM>. In some embodiments, the intermediate vessel <NUM> may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel <NUM> may be configured as a heat exchanger or a "surface economizer. " In the illustrated embodiment of <FIG>, the intermediate vessel <NUM> is used as a flash tank, and the first expansion device <NUM> is configured to lower the pressure of (e.g., expand) the liquid refrigerant received from the condenser <NUM>. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel <NUM> may be used to separate the vapor from the liquid received from the first expansion device <NUM>. Additionally, the intermediate vessel <NUM> may provide for further expansion of the liquid refrigerant because of a pressure drop experienced by the liquid refrigerant when entering the intermediate vessel <NUM> (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel <NUM>). The vapor in the intermediate vessel <NUM> may be drawn by the compressor <NUM> through a suction line <NUM> of the compressor <NUM>. In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor <NUM> (e.g., not the suction stage). The liquid that collects in the intermediate vessel <NUM> may be at a lower enthalpy than the liquid refrigerant exiting the condenser <NUM> because of the expansion in the expansion device <NUM> and/or the intermediate vessel <NUM>. The liquid from intermediate vessel <NUM> may then flow in line <NUM> through a second expansion device <NUM> to the evaporator <NUM>.

As noted above, variable speed drives may incur conduction losses and/or switching losses during operation, which leads to a reduction in an efficiency of the variable speed drive. Conduction losses occur when a component of a variable speed drive is conducting electrical current (e.g., when an IGBT is in a closed state). As such, energy input to the variable speed drive is lost in the form of thermal energy (e.g., heat). Additionally, switching losses occur when a component of a variable speed drive transitions between open and closed states (e.g., to adjust an amount or voltage or frequency of power supplied to the motor). For example, a transistor of the variable speed drive may be adjusted between an open and a closed state to adjust a voltage and/or frequency of power ultimately output to the motor. Existing variable speed drives include insulated-gate bipolar transistors (IGBTs), which may include relatively slow switching speeds. Accordingly, an efficiency of the variable speed drive is reduced as a result of the switching speeds of the IGBTs. Embodiments of the present disclosure relate to variable speed drives that have a silicon carbide transistor. The silicon carbide transistor includes quicker switching speeds when compared to IGBTs of existing variable speed drives. Accordingly, including silicon carbide transistors in the variable speed drive may enhance an efficiency of the variable speed drive, and thus, increase an overall efficiency of a HVAC&R system.

For example, <FIG> is a schematic of the variable speed drive <NUM> that includes a silicon carbide transistor <NUM>. As shown in the illustrated embodiment of <FIG>, the variable speed drive <NUM> includes a rectifier <NUM>, a DC bus <NUM>, and an inverter <NUM>. The rectifier <NUM> receives alternating current (AC) power at a constant voltage and frequency and converts the AC power into direct current (DC) power. For example, the rectifier <NUM> may receive the AC power from an AC power source <NUM>, which may supply three-phase AC power to the variable speed drive <NUM>. The DC bus <NUM> may then filter and/or stabilize the DC power, such that the DC power is suitable for use by the inverter <NUM>. The inverter <NUM> may then transfer the DC power back to AC power that includes a variable voltage and frequency. The AC power from the inverter <NUM> is utilized to power the motor <NUM>, which drives the compressor <NUM> of the vapor compression system <NUM>.

As shown in the illustrated embodiment of <FIG>, the silicon carbide transistor <NUM> is included in the rectifier <NUM> and the inverter <NUM>. As such, the silicon carbide transistor <NUM> may be utilized to adjust an amount of voltage and/or frequency of the power that is directed to the DC bus <NUM> and/or the motor <NUM>. The voltage and/or frequency of the power is based on discharge pressure of the compressor <NUM>. In some embodiments, the voltage and/or frequency of the power is further based on a voltage of the AC power from the AC power source <NUM>, a voltage of the DC power at the DC bus <NUM>, a speed of the motor <NUM>, or a combination thereof. In any case, the silicon carbide transistor <NUM> includes a reduced switching speed when compared to existing IGBTs. As such, the variable speed drive efficiency is enhanced and the overall efficiency of the vapor compression system <NUM> may also increase.

<FIG> is a circuit diagram of an embodiment of the silicon carbide transistor <NUM> that may be included in the variable speed drive <NUM> of the vapor compression system <NUM>. In some embodiments, an IGBT having a silicon diode may be replaced with the silicon carbide transistor <NUM> (e.g., a metal-oxide-semiconductor field-effect transistor (MOSFET)). In some embodiments, a circuit board of the variable speed drive <NUM> may be modified in order to include the silicon carbide transistor <NUM> into the variable speed drive <NUM> and improve the efficiency of the variable speed drive <NUM>. Specifically, a circuit board and/or a gate driver board of the variable speed drive <NUM> may be modified to implement the silicon carbide transistor <NUM>. Additionally, electromagnetic filters and/or other magnetic filters may be included in the circuit board or other suitable locations in the variable speed drive <NUM> to accommodate the silicon carbide transistor <NUM>. A cooling system of the variable speed drive <NUM> may also be modified as a result of less thermal energy being created by the silicon carbide transistor <NUM> when compared to IGBTs. In any case, the silicon carbide transistor <NUM> may reduce switching losses, thereby increasing an efficiency of the variable speed drive <NUM>.

As discussed above, losses incurred by the variable speed drive <NUM> with the silicon carbide transistor <NUM> are significantly less than those incurred by the variable speed drive with the typical IGBT with a silicon diode. As such, the variable speed drive <NUM> that includes the silicon carbide transistor <NUM> achieves an improved efficiency over the variable speed drives that include a typical IGBT with a silicon diode. For example, the variable speed drive <NUM> may improve an efficiency of the vapor compression system <NUM> between <NUM>% and <NUM>%, between <NUM>% and <NUM>%, or between <NUM>% and <NUM>%. As is understood, the vapor compression system <NUM> may consume relatively large amounts of power. As such, improvements in efficiency that are between <NUM>% and <NUM>% may significantly reduce an amount of power consumption by the vapor compression system <NUM>, and thus, reduce operating costs of the vapor compression system <NUM>. Accordingly, incorporating the silicon carbide transistor <NUM> into the variable speed drive <NUM> may improve the efficiency of the vapor compression system <NUM>, and thus, reduce operating costs of the vapor compression system <NUM>.

<FIG> is a block diagram of an embodiment of a process <NUM> for operating the vapor compression system <NUM> having the variable speed drive <NUM> with the silicon carbide transistor <NUM>. For example at block <NUM>, the compressor <NUM> circulates refrigerant through the refrigerant loop of the vapor compression system <NUM>. Additionally, at block <NUM>, the variable speed drive <NUM> supplies power to the motor <NUM> to drive the compressor <NUM>. As discussed above, the variable speed drive <NUM> includes the silicon carbide transistor <NUM>, which reduces power losses (e.g., switching losses and/or conduction losses) and increases an efficiency of the vapor compression system <NUM>.

Claim 1:
A heating, ventilating, air conditioning, and refrigeration, HVAC&R, system (<NUM>), comprising:
- a variable speed drive (<NUM>) configured to provide power to a motor (<NUM>) configured to drive a compressor (<NUM>) of the HVAC&R system (<NUM>), the variable speed drive comprising:
- a rectifier (<NUM>) configured to receive alternating current, AC, power from an AC power source (<NUM>) and convert the AC power to direct current, DC, power, wherein the AC power comprises a constant voltage and a constant frequency, the rectifier (<NUM>) comprising a first silicon carbide transistor (<NUM>) configured to adjust a voltage, or a frequency, or both, of power flowing through the variable speed drive (<NUM>);
- a DC bus (<NUM>) configured to receive the DC power from the rectifier (<NUM>); and
- an inverter (<NUM>) configured to receive the DC power from the DC bus (<NUM>) and to convert the DC power to AC power having a variable voltage and a variable frequency, the inverter comprising a second silicon carbide transistor (<NUM>) configured to adjust a voltage, or a frequency, or both, of power flowing through the variable speed drive (<NUM>); and
- a controller coupled to each silicon carbide transistor (<NUM>) and configured to adjust a state of the first and second silicon carbide transistors (<NUM>) based on a discharge pressure of the compressor (<NUM>).