DC varaiable speed compressor control method and control system

The present disclosure relates to the field of air conditioning technology. In particular, it involves a control method and control device based on a DC variable speed AC compressor.

The present application is a national stage of PCT/US16/59871, filed on Nov. 1, 2016, with its specification incorporated by reference, but otherwise the same. The disclosure below will assume common knowledge of air conditioning and heat pump as well as their heat exchange principle in terms of achieving cooling and heating as well as DC inverter technology in varying compressor speed. Therefore, when discussing particular AC inner working, it is applied to heat pump collectively. The discussion will also treat compressor speed and compressor RPS (rotation per second) interchangeably as well.

BACKGROUND OF THE DISCLOSURE

With the development of air-conditioning technology, DC variable speed air conditioner is becoming mainstream product because it is energy efficient, low noise and good thermostatic, etc. DC variable speed AC can adjust the speed freely, therefore lower the number of on/off cycle, and achieve comfort and energy saving. But the variable speed AC in the current market provides their implementation only based on the basic matching principle—i.e. matching the current output to the current load, in order to lower the number of on/off cycle. When DC variable speed AC is concerned, a duration is defined as from starting the compressor at starting temperature, until stopping the compressor at stopping temperature. Within this duration time, as the temperature changes from the starting temperature to the stopping temperature, the temperature curve changes depending on how the speed control is implemented. Even assuming that the same starting temperature, stopping temperature and duration means the same cooling/heating experience to users, but in terms of energy consumption, each temperature curve represent a different profile. As indicated, the current variable speed AC implementation does not factor in energy consumption. Much missing particularly is a method to estimate the energy consumption in temperature curve profiles so to choose a speed control strategy based on matching a particular profile.

In considering the energy consumption calculation model, there are a lot of factors come into play. For example, how the future temperature changes in the environment is one factor, and so is the building heat gain coefficient, etc. This consideration would require the speed control method to have self-learning characteristic, in order to choose a best matching cooling/heating temperature curve profile.

SUMMARY OF THE DISCLOSURE

Based on the above deficiencies, an objective of the disclosure is to provide a new speed control method implementation, so that this new implementation will be able to estimate energy consumption in order to change to an optimal control policy. Another aspect of the new implementation is to change the speed control strategy in respond to peak energy consumption period, so that the energy consumption during peak period will be lowered, which leads to lowest energy consumption.

To achieve the above technical objectives, the present disclosure provides a control system for DC speed control AC compressor, comprises of: a speed control calculation unit, a data storage unit, an information acquisition unit, a network communication module and a speed control output unit.

As the speed control calculation unit, it is for calculating targeted saturation pressure/temperature, and based on the targeted saturation pressure/temperature, calculating the total output under high output mode and low output mode, as well as the duration under the high output mode and the low output mode.

As the data storage unit, it is for storing data used by the speed control calculation unit, including lookup table n for the load coefficient values with their corresponding outdoor temperatures, for the time duration.

As the information acquisition unit, it is for collecting sensor data generated by the outdoor unit, including the outdoor temperature, outdoor unit liquid outlet temperature, compressor return inlet temperature, compressor high pressure and compressor low pressure.

As the network communication module, it is for receiving from remote server the weather forecast, obtain temperature curve for the environment.

As the speed control output unit, it is for setting the AC speed based on the calculated values from the speed control calculation unit, namely the total output under high output mode and low output mode, as well as the duration under the high output mode and the low output mode. This control method would coincide the low output duration with peak environment temperature timing which is within the compressor on duration.

To achieve the aforementioned technical objectives, a new DC variable speed control method in the present disclosure comprises:a. calculating total the indoor cool/heating load N;b. calculating the total cooling/heating output capacity Q;c. determining median value for targeted saturation pressure/temperature by comparing the relationship between total capacity Q, product of total load N and its upper limit coefficient, as well as product of total load and its lower limit coefficient—if Q>the product of N and its upper limit coefficient, or Q<the product of N and its lower limit coefficient, then reset target saturation pressure temperature median value—but if Q<the product of N and its upper limit coefficient, and Q>the product of N and its lower limit coefficient, then use the current saturation pressure temperature value as the target saturation pressure temperature median value;d. based on the target saturation pressure temperature median value, setting target saturation pressure temperature for high output mode and low output mode, then calculating the corresponding total output QH (high) and QL (low), as well as duration thigh(high) and tlow(low);e. arranging duration distribution for thighand tlowwithin the timeframe of time2(within which the peak environment temperature occurs while running the AC), in order to coincide the tlowwith the peak environment temperature timing during time2—then during the high output mode duration thigh, perform high output mode compressor control based on total needed QH—and during the low output mode duration tlow, perform low output mode compressor control based on total needed QL.

Definition

FIG. 1shows an AC compressor operation cycle in this disclosure, defining Tonas the room temperature at the time of the on signal is given by the indoor unit or the thermostat. Also defined is Toff, which is the room temperature at the time of the off signal given by the indoor unit or the thermostat. Continuing on, t0is defined as the time when the prior AC compressor off signal is given, t1is defined as the starting time of this AC compressor cycle and t2is defined as the stopping time of this AC compressor cycle. Continuing on, period from t0to t2is the defined as time0(i.e. a DC variable speed compressor operation cycle), from t0to t1is the defined as time1(i.e. compressor off duration), from t1to t2is the defined as time2(i.e. duration for compressor to be on). If time2is shorter, it means greater the load to handle, and greater the corresponding output. Negatively, the electrical consumption is also greater. Therefore, setting of time2period can be set according to user's cooling/heating performance demand or energy-saving preference. But it can also be set by a remote server. The present disclosure assumes that time2has been known by the time to perform speed control.

FIG. 2shows a diagram of the disclosed AC system, including AC compressor sensors control unit, where G is defined as the system refrigerant circulation flow rate (in kg/s). This flow rate data is obtained from this compressor regression model:
G=f(PL,PH,Ts,RPS).

wherein, PL is AC compressor low pressure obtained by low-pressure sensor, and PH is AC compressor high pressure obtained by high-pressure sensor, Ts is return air temperature sensor value obtained, RPS for the AC compressor speed. These parameter data are real time data from operation, so their values can be corresponding to function of t. Therefore, the circulating refrigerant flow of G can also be obtained in real time by calculation.

From cooling thermodynamic, Houtis defined as fluid outlet enthalpy, where its value can be obtained from the refrigerant's properties table:
Hout=f(PH,Tout).

This is possible because temperature can be obtained from fluid outlet temperature sensor, and the PH value can be obtained from the high pressure sensor.

Similarly, Hinis defined as fluid inlet enthalpy, where its value can be obtained from the refrigerant's properties table:
Hin=f(PL,Ts).

This is also possible because temperature can be obtained from fluid inlet temperature sensor, and the PL value can be obtained from the low pressure sensor.

The system cooling capacity q can be expressed as a function of:
q=G×(Hout−Hin).

Correspondingly, in heating, Hdisis defined as compressor discharge outlet enthalpy, where its value can be obtained from the refrigerant's properties table:
Hdis=f(PH,Td).

Same as cooling, this is possible because Td can be obtained from compressor outlet temperature sensor, and the PH value can be obtained from the high pressure sensor. Therefore, in heating, heating capacity q can be expressed as a function of:
q=G×(Hdis−Hout).

From the above, when q(t) is integrated from t1to t2, that value will be the total cooling/heating output Q for the time interval:
∫t1t2q(t)dt.

Further, N is defined as total indoor load from the t0to t2time interval. Due to the fact that the cooling load increases when heat gain coefficient n increases, which corresponding outdoor temperature increases (or in the case of heating load increases when heat loss coefficient n increases, which corresponding outdoor temperature decreases), we can see that the indoor load coefficient n (heat gain/heat loss per unit of time) is a function of the outdoor air temperature, where:
n=f(Ta).

In the present disclosure, the functional relationship of n-Tavalues can be stored in numeric format within the lookup database.

Therefore, the total indoor load from t0to t2is N, where N is a formula of:
∫t0t2n(t)dt,
thereinafter, called Formula N.

FromFIG. 1, when the compressor operating in one cycle, if the starting room temperature Toffis the same as the ending room temperature Toff, then that means the total cooling/heating load from t0to t2is equal t0total cooling/heating output from t1to t2. Therefore, the indoor load coefficient can be observed from the output as:

From this relationship, every time when the AC system runs one interval from start to end under various outdoor temperatures, the indoor load coefficient can be observed and stored in the data storage unit. Therefore, by retrieving the corresponding indoor load coefficient n, one can get the total indoor load N from t0to t2. Extending this t0to t2as an operating period of general AC consumption, the total load of N can be compared with the accumulated total output Q from t1to t2. Therefore, with an accumulated lookup table based on self-learning, a new indoor load coefficient is obtained each time the AC system runs an interval. This makes it possible for a given outdoor temperature, an indoor load coefficient n can be filtered from the lookup table to match the heat gain/heat loss characteristics.

Selecting Load Coefficient n

Because it is possible for the user to stop the AC before the temperature setting is reached—not a complete cycle, therefore, data points from these instances would not give accurate relationship between n and average outdoor temperature Ta.

If there is communication between outdoor unit and indoor unit/thermostat, one can determine the reliability of load coefficient n from knowing whether the indoor temperature has reached to the temperature setting.

If there are only on-off signals between outdoor unit and indoor unit/thermostat, a technical solution can be found taking an average value from the multiple data points for a given temperature to account for the effect of such occurrences, or set a reliability threshold to filter out the unreliable data points.

Compressor Output Speed Expression

In terms of DC variable speed AC compressor, the compressor speed F, compressor target saturation pressure and target saturation temperature are correlated—knowing one would get to the other two. Based on targeted saturation temperature, the present disclosure of performing compressor PID (proportional, integral, and derivative) control is for adjusting the DC variable speed AC compressor operation speed F.

Selecting the Best Energy Saving Temperature Curve

The present disclosure configures the DC variable speed AC compressor such that the cooling/heating output mode is either high—QH, or low—QL, with the corresponding high output duration and low output duration in time2operation cycle.

Further, the implementation should obtain temperature curve forecast on the environment and adjust the running mode so that at the peak temperature timing, it would be within the low output operating cycle of the DC variable speed AC compressor. Doing so, would lower the electricity consumption.

DETAILED DESCRIPTION OF THE DISCLOSURE

First Embodiment

FIG. 3is the variable speed AC control system configuration diagram of the first embodiment, comprises: speed control calculation unit10, database unit20, operation data acquisition unit30, network communication module40and output speed control unit50, wherein

the speed control calculation unit10is for calculating the indoor load coefficient n, total indoor load N, system capacity q and total system output Q, and based on comparing (1) the product of the total load N and its upper limit coefficient, (2) the product of the total load N and its lower limit coefficient, as well as (3) the total cooling output Q, determining a temperature Tson target saturation pressure, and based on Ts, calculating the high/low output mode total output QH/QL and output duration thigh/tlow; and

database unit20, for storing and providing the indoor load coefficient n/outdoor temperature lookup data, as well as the compressor timing of the operating cycle time2, which are needed by the speed control calculation unit10; and

the operation data acquisition unit30, for acquiring sensor data generated by the outdoor unit, including outdoor air temperature T, outdoor unit liquid outlet temperature Tout, compressor return inlet temperature Tin, compressor discharge temperature Tdis, the value of the compressor high pressure PH and the low pressure PL; and

the network communication unit40is used to get weather forecasts results from a remote server, used to obtain in advance the ambient temperature for the operation period; and

the output speed control unit50for utilizing the output from the speed control calculation unit10, including the high/low output mode total output QH/QL and output duration thigh/tlow, control the speed of compressor during operation, so that the low output operating cycle tlowwould coincide with the duration time2(within which the peak temperature timing occurs); and

the speed control calculation unit10includes an indoor unit110to calculate the total load, and an output unit120for calculating total cooling/heating output capacity; and

the indoor unit110for calculating the total load of N from the t0to t2period; and

the output unit120for calculating total cooling/heating output capacity Q from the t1to t2period.

Total Indoor Load Calculation

In this embodiment, the variable speed AC compressor control method uses the results of weather forecast to calculate the total indoor load N. The logic of this calculation depends on at least knowing the future t1to t2outdoor temperature change, before starting the AC compressor. As shown inFIG. 4, the steps for calculation of indoor total load are:a. on AC compressor starting time t1, retrieving the timing from the prior stopping time t0to the new starting time t1;b. calculating the average outdoor temperature of t0to t1as Ta1;c. from the n-Talookup table, determining the total indoor load of N1from t0to t1;d. from the weather forecast, receiving the outdoor temperature change information between t1to t2period;e. calculating the average outdoor temperature;f. from the n-Talookup table, determine the total indoor load of N2from t1to t2;g. calculate the total indoor load of N=N1+N2from t0to t2;

Cooling Mode DC Speed Control Method

First, the calculation for speed control is based on current compressor operation parameters, assuming the output is Q between t1and t2.

By comparing the total output Q and indoor total load N, next the method would perform high output mode and low output mode profiling. If Q is greater than N×110%, then adjust the speed control so that the target low saturation pressure temperature Teswould be moving the upward by a predetermined value, for example, Tes+1° C., then repeat the comparison of total output Q and indoor total load N. Similarly, if Q is less than N×90%, then adjust the speed control so that Teswould be moving the downward by a predetermined value, for example, Tes−1° C.

After satisfying N×90%<Q<N×110% in the profiling process, the method would set the Tesmedian value for the target low saturation pressure temperature, and define Tes−ΔT as the target low saturation pressure temperature for high output mode, for example, Tes−2° C. Similarly, the method would define Tes+ΔT as the target low saturation pressure temperature for low output mode, for example, Tes+2° C. Because the target low saturation pressure temperature Tesis related to compressor low pressure value PL, therefore, by taking the operation parameters, and plugging them in formula:
Q=∫t1t2f(Tes−ΔT,PL,Ts,RPS)×(Hout−Hin)dt,

one can obtain the total cooling output QH under the high output mode. Similarly, from formula:
Q=∫t1t2f(Tes+ΔT,PL,Ts,RPS)×(Hout−Hin)dt,

one can also obtain the total cooling output QL under the low output mode. Therefore, by solving:
QH×th+QL×t1=Nandth+t1=time2,

one can obtain the duration for high output mode thighand the duration for low output tlow.

Next, the system would be run under the target low saturation pressure temperature Tes−ΔT for the duration thighin high output mode, and run under the target low saturation pressure temperature Tes+ΔT for the duration tlowin low output mode. At the same time, the system would be run so that the midpoint of the low output duration tlowwould coincide with the timing of the peak outside temperature that would occur within the compressor on cycle, based on how distribution of the predetermined high output duration thighand low output duration tlowis within the compressor on time2cycle.

Heating Mode DC Speed Control Method

First, the calculation for speed control is based on current compressor operation parameters, assuming the output is Q between t1and t2.

By comparing the total output Q and indoor total load N, next the method would perform high output mode and low output mode profiling. If Q is greater than N×110%, then adjust the speed control so that the target high saturation pressure temperature Tcs would be moving downward by a predetermined value, for example, Tcs−1° C., then repeat the comparison of total output Q and indoor total load N. Similarly, if Q is less than N×90%, then adjust the speed control so that Tcs would be moving upward by a predetermined value, for example, Tcs+1° C.

After satisfying N×90%<Q<N×110% in the profiling process, the method would set the Tcs median value for the target high saturation pressure temperature, and define Tcs+ΔT as the target high saturation pressure temperature for high output mode, for example, Tcs+2° C. Similarly, the method would define Tcs−ΔT as the target high saturation pressure temperature for low output mode, for example, Tcs+2° C. Because the target high saturation pressure temperature Tcs is related to compressor high pressure value PH, therefore, by taking the operation parameters, and plugging them in formula:
Q=∫t1t2f(Tcs+ΔT,PH,Ts,RPS)×(Hdis−Hout)dt,

one can obtain the total heating output QH under the high output mode. Similarly, from formula:
Q=∫t1t2f(Tcs−ΔT,PH,Ts,RPS)×(Hdis−Hout)dt,

one can also obtain the total heating output QL under the low output mode. Therefore, by solving:
QH×th+QL×t1=Nandth+t1=time2,

one can obtain the duration for high output mode thighand the duration for low output tlow.

Next, the system would be run under the target high saturation pressure temperature Tcs+ΔT for the duration thighin high output mode, and run under the target high saturation pressure temperature Tcs−ΔT for the duration tlowin low output mode. At the same time, the system would be run so that the midpoint of the low output duration tlowwould coincide with the timing of the lowest outside temperature that would occur within the compressor on cycle, based on how distribution of the predetermined high output duration thighand low output duration tlowis within the compressor on time2cycle.

In this embodiment, the DC speed control compressor system should perform profiling of the system within a few cycle of after being turned on, first finding out the target saturation pressure temperature setting, and after determining the target saturation pressure temperature, based on how distribution of the high output duration and low output duration is, adjust speed control strategy. The temperature increment for testing saturation pressure temperature can be set based on actual operation situation determined by the user or a cloud server. Similarly, the coefficient multiplier for total load N also can be set based on actual operation situation determined by the user or a cloud server. Also can be set by the user or a cloud server is the ΔT value, which can be adjusted based on the user's temperature change sensitivity.

Second Embodiment

The variable speed AC control system of the second embodiment comprises: speed control calculation unit10, database unit20, operation data acquisition unit30, network communication module40and output speed control unit50, wherein

the speed control calculation unit10is for calculating the indoor load coefficient n, total indoor load N, system capacity q and total system output Q, and based on comparing (1) the product of the total load N and its upper limit coefficient, (2) the product of the total load N and its lower limit coefficient, as well as (3) the total cooling output Q, determining a temperature Tson target saturation pressure, and based on Ts, calculating the high/low output mode total output QH/QL and output duration thigh/tlow; and

database unit20, for storing and providing the indoor load coefficient n/outdoor temperature lookup data, as well as the compressor timing of the operating cycle time2, which are needed by the speed control calculation unit10; and

the operation data acquisition unit30, for acquiring sensor data generated by the outdoor unit, including outdoor air temperature T, outdoor unit liquid outlet temperature Tout, compressor return inlet temperature Tin, compressor discharge temperature Tdis, the value of the compressor high pressure PH and the low pressure PL; and

the network communication unit40is used to get weather forecasts results from a remote server, used to obtain in advance the ambient temperature for the operation period; and

the output speed control unit50for utilizing the output from the speed control calculation unit10, including the high/low output mode total output QH/QL and output duration thigh/tlow, control the speed of compressor during operation, so that the low output operating cycle tlowwould coincide with the duration time2(within which the peak temperature timing occurs); and

the speed control calculation unit10includes an indoor unit110to calculate the total load, and an output unit120for calculating total cooling/heating output capacity; and

the indoor unit110for calculating the total load of N from the t0to t2period; and

the output unit120for calculating total cooling/heating output capacity Q from the t1to t2period.

Total Indoor Load Calculation

In this embodiment, the variable speed AC compressor control method uses the results of weather forecast to calculate the total indoor load N. The logic of this calculation depends on at least knowing the future t1to t2outdoor temperature change, before starting the AC compressor. As shown inFIG. 6, the steps for calculation of indoor total load are:a. on AC compressor starting time t1, retrieving the n values from the prior stopping time t0to the new starting time t1based on the varied temperature values;b. by method of accumulation, determining the total indoor load of N1from t0to t1;c. using the calculated average temperature at t1, from the lookup n−Tatable, obtaining the corresponding load coefficient n(Ta), further calculating the total load N2from t1to t2period;d. calculating the total load as N=N1+N2;e. determining whether the stop signal is received—if not, then go to step f—if yes, then stop;f. determining whether the outdoor temperature has changed—if not, go back to step e—if yes, then go to step g;g. assuming the load coefficient n(Tax) at txwhen the temperature is changed is different from the prior n(Ta), using n(Tax) for calculating the total load for the rest of period from txto t2, and updating the resulting new N2before returning to step d.

Cooling Mode DC Speed Control Method

First, the calculation for speed control is based on current compressor operation parameters, assuming the output is Q between t1and t2.

By comparing the total output Q and indoor total load N, next the method would perform high output mode and low output mode profiling. If Q is greater than N×120%, then adjust the speed control so that the target low saturation pressure temperature Teswould be moving the upward by a predetermined value, for example, Tes+1° C., then repeat the comparison of total output Q and indoor total load N. Similarly, if Q is less than N×80%, then adjust the speed control so that Teswould be moving the downward by a predetermined value, for example, Tes−1° C.

After satisfying N×80%<Q<N×120% in the profiling process, the method would set the Tesmedian value for the target low saturation pressure temperature, and define Tes−ΔT as the target low saturation pressure temperature for high output mode, for example, Tes−2° C. Similarly, the method would define Tes+ΔT as the target low saturation pressure temperature for low output mode, for example, Tes+2° C. Because the target low saturation pressure temperature Tesis related to compressor low pressure value PL, therefore, by taking the operation parameters, and plugging them in formula:
Q=∫t1t2f(Tes−ΔT,PL,Ts,RPS)×(Hout−Hin)dt,

one can obtain the total cooling output QH under the high output mode. Similarly, from formula:
Q=∫t1t2f(Tes+ΔT,PL,Ts,RPS)×(Hout−Hin)dt,

one can also obtain the total cooling output QL under the low output mode. Therefore, by solving:
QH×th+QL×t1=Nandth+t1=time2,

one can obtain the duration for high output mode thighand the duration for low output tlow.

Next, the system would be run under the target low saturation pressure temperature Tes−ΔT for the duration thighin high output mode, and run under the target low saturation pressure temperature Tes+ΔT for the duration tlowin low output mode. At the same time, the system would be run so that the midpoint of the low output duration tlowwould coincide with the timing of the peak outside temperature that would occur within the compressor on cycle, based on how distribution of the predetermined high output duration thighand low output duration tlowis within the compressor on time2cycle.

Heating Mode DC Speed Control Method

First, the calculation for speed control is based on current compressor operation parameters, assuming the output is Q between t1and t2.

By comparing the total output Q and indoor total load N, next the method would perform high output mode and low output mode profiling. If Q is greater than N×120%, then adjust the speed control so that the target high saturation pressure temperature Tcs would be moving downward by a predetermined value, for example, Tcs−1° C., then repeat the comparison of total output Q and indoor total load N. Similarly, if Q is less than N×80%, then adjust the speed control so that Tcs would be moving upward by a predetermined value, for example, Tcs+1° C.

After satisfying N×80%<Q<N×120% in the profiling process, the method would set the Tcs median value for the target high saturation pressure temperature, and define Tcs+ΔT as the target high saturation pressure temperature for high output mode, for example, Tcs+2° C. Similarly, the method would define Tcs−ΔT as the target high saturation pressure temperature for low output mode, for example, Tcs+2° C. Because the target high saturation pressure temperature Tcs is related to compressor high pressure value PH, therefore, by taking the operation parameters, and plugging them in formula:
Q=∫t1t2f(Tcs+ΔT,PH,Ts,RPS)×(Hdis−Hout)dt,

one can obtain the total heating output QH under the high output mode. Similarly, from formula:
Q=∫t1t2f(Tcs−ΔT,PH,Ts,RPS)×(Hdis−Hout)dt,

one can also obtain the total heating output QL under the low output mode. Therefore, by solving:
QH×th+QL×t1=Nandth+t1=time2,

one can obtain the duration for high output mode thighand the duration for low output tlow.

Next, the system would be run under the target high saturation pressure temperature Tcs+ΔT for the duration thighin high output mode, and run under the target high saturation pressure temperature Tcs−ΔT for the duration tlowin low output mode. At the same time, the system would be run so that the midpoint of the low output duration tlowwould coincide with the timing of the lowest outside temperature that would occur within the compressor on cycle, based on how distribution of the predetermined high output duration thighand low output duration now is within the compressor on time2cycle.

In this embodiment, the DC speed control compressor system should perform profiling of the system within a few cycle of after being turned on, first finding out the target saturation pressure temperature setting, and after determining the target saturation pressure temperature, based on how distribution of the high output duration and low output duration is, adjust speed control strategy. The temperature increment for testing saturation pressure temperature can be set based on actual operation situation determined by the user or a cloud server. Similarly, the coefficient multiplier for total load N also can be set based on actual operation situation determined by the user or a cloud server. Also can be set by the user or a cloud server is the ΔT value, which can be adjusted based on the user's temperature change sensitivity.