HK1149793B - Suction valve pulse width modulation control based on evaporator or condenser pressure - Google Patents

Description

Pulse width modulation control of suction valve based on evaporator or condenser pressure

Technical Field

The present application relates to a pulse width modulation control for a suction pulse width modulation valve that allows a refrigerant system to provide either continuous capacity or precise stepped capacity, wherein the system pressure is monitored to determine an optimal duty cycle for pulse width modulation.

Background

Refrigerant systems are used in many applications such as conditioning environments. Air conditioners and heat pumps are used to cool and/or heat air entering an environment. The cooling or heating load on the environment may vary with ambient conditions and may change as the temperature and/or humidity levels demanded by the occupant of the environment change. Obviously, the operation and control of the refrigeration system must adequately reflect these changes to maintain stable temperature and humidity conditions within the environment.

One method known in the art for assisting in regulating the capacity of a refrigerant system is to use pulse width modulation control. It is known in the art to utilize pulse width modulation control to rapidly cycle valves for controlling the flow of refrigerant through a refrigeration system and thereby regulate capacity. By limiting the flow of refrigerant through the system, the capacity can be reduced below the full capacity at which the system operates.

One challenge presented by the use of pulse width modulation control in the prior art is that while this technique does provide good control of capacity, the system pressure on the refrigerant system can have undesirably large fluctuations between the open/closed positions of the suction pulse width modulation valve. If the valve is opened or closed over a longer period of time, the pressure on, for example, the condenser and evaporator may fluctuate considerably. Such pressure fluctuations are undesirable, may make it difficult to control the operation of the expansion valve, may make it more difficult to maintain a constant temperature within the environment to be cooled, and may become less efficient in overall system operation.

On the other hand, if the valve cycles too frequently to reduce pressure fluctuations, there are additional losses associated with system changeover from the valve being in the open position to the valve being in the closed position. Furthermore, the chance of valve failure will increase due to the large number of cycles.

In another proposed control for an HVAC system, pulse width modulated control for pulse width modulation of rolling elements is provided by separating the elements and restoring the separated elements to contact one another in a pulse width modulated manner. This control will monitor the pressure and temperature on the suction (low pressure) side and adjust the duty cycle of the pulse width modulation. However, the disclosed control does not specifically seek to minimize surge, does not control the suction pulse width modulation valve, and also does not monitor the condition on the discharge (high pressure) side of the system.

Disclosure of Invention

In a disclosed embodiment of the invention, a pulse width modulation control is provided for selectively varying the flow of refrigerant from the evaporator downwardly to the compressor. By controlling the flow of refrigerant through the suction pulse width modulation valve, the capacity provided by the refrigerant system can be varied. The control monitors a signal indicative of at least one system pressure and ensures that the pressure does not fluctuate beyond specified limits. The duty cycle of the suction pulse width modulation valve may be selected to ensure that the pressure fluctuations remain within these limits. In the disclosed embodiments, system pressure is monitored at the condenser or evaporator, or both. If the pressure fluctuations are close to a limit, the cycle rate of the suction pulse width modulation valve is adjusted to remain within the specified limit. On the other hand, the cycle rate of the regulator valve may not be required as long as the pressure fluctuations are within the limits. One of the most effective methods for reducing pressure fluctuations is to increase the cycling rate of the valve. However, other parameters, such as, for example, the opening and closing times of the valves, may be varied to achieve the desired results.

The circulation rate may be adjusted based on the following factors: operating conditions, the degree to which temperature and humidity parameters are maintained within the environment to be cooled, reliability limitations of the solenoid valves, efficiency objectives, system thermal inertia, stability factors, and the like. Alternatively, some adaptive control may be used, where the control "learns" how changes in the duty cycle will result in changes in the detected pressure. Those skilled in the art will understand how to provide such control.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Drawings

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

FIG. 2 is a graph of pulse width modulation controlled time VS pressure, including system pressure over time.

Detailed Description

A refrigeration system 20 having a compressor 22 that compresses a refrigerant and delivers the refrigerant downwardly to a condenser 24 is shown in fig. 1. The pressure sensor 26 detects the pressure near the condenser 24 or at the condenser 24. The refrigerant passes down an expansion valve 28 and then to an evaporator 30. The pressure sensor 32 detects the refrigerant pressure near the evaporator 30 or at the evaporator 30. A suction pulse width modulation valve 34 is located downstream of the evaporator 30. The controller 35 controls the opening of the suction pulse width modulation valve. A pressure sensor 36 senses the pressure in the suction line leading from the suction pulse width modulation valve 34 back to the compressor 22.

The pressure associated with condenser 24 (as sensed by sensor 26) and the pressure associated with evaporator 30 (as sensed by sensor 32) are both communicated to controller 35. The controller 35 is programmable to achieve the advantages described below.

As shown in fig. 2, the suction pulse width modulation valve 34 is controlled by pulse width modulation. The pulse width modulation control will result in a peak P and a valley V when the suction pulse width modulation valve 34 is cycled open and closed. In the disclosed embodiment, the suction pulse width modulation valve 34 is a solenoid valve capable of rapid cycling. The present invention varies the duty cycle or the time at which the peaks P and valleys V exist.

Fig. 2 also shows the system pressure, which may be the pressure monitored by sensor 26 or pressure sensor 32. In the disclosed embodiment, two pressures may be monitored, and thus the controls disclosed below may be used for both. Set the upper limit U_LAnd a lower limit L_L. The pressure is kept within the boundary set by these two limits. The boundary is likely to be different at the high side (sensor 26) than at the low side (sensor 32). Thus, the controller 35 monitors the pressure and ensures that the pressure is between the limits. As long as the pressure is between the limits, the valve cycles at a slower rate and still achieves the desired capacity. As the pressure fluctuations approach the limit, the suction pulse width modulation valve 34 cycles at a higher rate, which will reduce the pressure fluctuations.

It will be appreciated from FIG. 2 that within region X on the system pressure chart, one of the pressures approaches the limit U_LAnd L_L. The duty cycle or the time during which the peaks P and valleys V exist when the valve is open and closed is relatively long. However, when the controller 35 detects that the pressure fluctuations become too large (as shown above region X), the duty cycle is reduced so that the peaks and troughs remain for a shorter period of time. By shortening the time period for which the valve is opened and closed, the pressure fluctuation becomes small as shown downstream of the region X. The present invention thus enables suction pulse width modulation valve control with pulse width modulation and solves the above-mentioned problem of pressure fluctuations. In addition, the present invention also monitors the pressure on the high side or the pressure of the refrigerant at the location being compressed. The prior art generally focuses only on suction pressure and therefore does not provide the control capability of the present invention.

In another feature, the control may be an adaptive control that "remembers" changes in the duty cycle provided in the past and the resulting changes in system pressure. Thus, the control may "learn" to better control the pressure fluctuations and achieve a system pressure at a desired level. The control may also find the best way to cycle the pulse width modulation valve by trying different cycling rates to determine which will produce the best results within the constraints imposed (e.g., the maximum cycling rate of the valve).

Furthermore, it must be noted that the pulse width modulated suction valve may not necessarily have an open state and a closed state corresponding to a fully open position and a fully closed position, which provides additional flexibility in system control and operation.

Pulse width modulation control is known, and valves operated by pulse width modulation signals are also known. The present invention utilizes these known techniques in a unique manner to achieve the above objects and advantages.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (10)

1. A refrigeration system, comprising:

a compressor, a condenser downstream of the compressor, an expansion device downstream of the condenser, and an evaporator downstream of the expansion device;

a suction pulse width modulation valve located between the evaporator and the compressor; and

a controller for selectively operating the suction pulse width modulation valve to deliver refrigerant to the compressor, the controller being operable to operate the suction pulse width modulation valve with a pulse width modulation signal, and a duty cycle of the pulse width modulation signal being controlled to control fluctuations in the sensed system pressure,

wherein an upper limit and a lower limit are set for the system pressure, a controller monitors the system pressure to ensure that the system pressure remains within the upper and lower limits, the controller adjusts the duty cycle of the suction pulse width modulation valve to ensure that the system pressure remains between the upper and lower limits,

wherein if the system pressure approaches one of the upper limit and the lower limit, the duty cycle is changed so that the valve remains open and closed for a shorter period of time.

2. The refrigerant system as set forth in claim 1, wherein said system pressure is associated with said compressor.

3. The refrigerant system as set forth in claim 2, wherein said system pressure is further associated with said evaporator.

4. The refrigerant system as set forth in claim 1, wherein said system pressure is associated with said evaporator.

5. The refrigerant system as set forth in claim 1, wherein said suction pulse width modulation valve is openable between a fully open position and a fully closed position and further movable to an intermediate position.

6. A method of controlling a refrigeration system, comprising the steps of:

providing a compressor, a condenser downstream of said compressor, an expansion device downstream of said condenser, an evaporator downstream of said expansion device, and a suction pulse width modulation valve between said evaporator and said compressor; and

selectively operating the suction pulse width modulation valve to deliver refrigerant to the compressor, controlling a duty cycle of the pulse width modulation signal by utilizing a pulse width modulation signal to operate the suction pulse width modulation valve and in conjunction with the sensed system pressure to ensure that the sensed system pressure does not exceed a fluctuation limit,

wherein upper and lower limits are set for the system pressure, the system pressure is monitored to ensure that the system pressure remains within the upper and lower limits, and the adjusting the duty cycle of the suction pulse width modulation valve is performed to ensure that the system pressure remains between the upper and lower limits,

wherein if the system pressure approaches one of the limits, the duty cycle is reduced such that the valve remains open and closed for a shorter period of time.

7. The method of claim 6, wherein the system pressure is associated with the condenser.

8. The method of claim 7, wherein the system pressure is further associated with the evaporator.

9. The method of claim 6, wherein the system pressure is associated with the evaporator.

10. The refrigerant system as set forth in claim 6, wherein said suction pulse width modulation valve is openable between a fully open position and a fully closed position and further movable to an intermediate position.