EP1400696B1 - Method for controlling a set of compressors and/or ventilators - Google Patents

Abstract

The regulation method has a defined maximum number of switching times per hour for the compressors or ventilators used for calculation of the switching-in delay time, the cycle time and the switching-in blocking time, with calculation of the base switching-in time using a formula which includes a proportionality factor for regulator amplification or attenuation and the number of compressors or ventilators switched in during the cycle time.

Description

The invention relates to a method for controlling a compressor set or a fan set, comprising one or more compressors or one or more fans.

In generic method, which are used in refrigeration systems or machines, the regulation of the suction pressure is done by switching on or off one or more compressors. The regulation of the high pressure is done by switching on or off one or more fan levels.

To achieve the required power and to avoid too high a switching frequency - this would disproportionately burden the compressors or the fans - the individual power stages are switched on and off with a time delay. Here, the time delay t _{g is} composed of a base switch-on time t _b - which is assumed to be constant - and a variable switching time t _v dependent on the control deviation.

wobei für t_v gilt: $${\mathrm{t}}_{\mathrm{v}}={\mathrm{t}}_{\mathrm{v\_max}}-\left({\mathrm{t}}_{\mathrm{v\_max}}*\mathrm{d}\mathrm{t}\right)/\mathrm{d}{\mathrm{t}}_{\max }$$

Hierbei sind:

• t_v = variable Schaltzeit
• t_{v_max} = maximale variable Schaltzeit
• dt = Regelabweichung
• dt_max = maximale Regelabweichung
  wobei sofern dt > dt_max, dann gilt dt = dt_max.

The time delay t _g is determined according to the following formula: $${\mathrm{t}}_{\mathrm{G}}={\mathrm{t}}_{\mathrm{b}}+{\mathrm{t}}_{\mathrm{v}}$$

wherein for t _v: $${\mathrm{t}}_{\mathrm{v}}={\mathrm{t}}_{\mathrm{v\_max}}-\left({\mathrm{t}}_{\mathrm{v\_max}}*\mathrm{d}\mathrm{t}\right)/\mathrm{d}{\mathrm{t}}_{\mathrm{Max}}$$

Here are:

• t _v = variable switching time
• t _{v_max} = maximum variable switching time
• dt = control deviation
• dt _max = maximum control deviation
  where dt> dt _max , then dt = dt _max .

From the above formula, it can be seen that the time delay t _{g is} inversely proportional to the control deviation dt.

Too long switching times lead to comparatively high control deviations. On the other hand, switching times that are too short cause the permissible switching frequency of the compressor or fan to be exceeded. Although the switching times are set at the time of commissioning of a refrigeration system or machine, but these are to be regarded as optimal only for the system state prevailing at startup.

If the power requirement changes - for example, in night mode when the individual consumer is covered and / or switched off - and / or the plant's ambient conditions change - for example, if the outside temperature and / or the temperature in the sales room changes - the current figures will be different Switching times from the optimum values set at the time of commissioning.

DE 35 00 636 A1 describes a method for controlling the operation of a number of compressors, each of which is equipped with a capacity regulator which can gradually change the output of the compressor to provide a total output which meets the power requirements which is currently changing. In this method, the control system is divided into a power control loop for responding to a relatively small load change and a compressor control loop for responding to a relatively large load change. The compressors and the power regulators are started sequentially, measuring the periods of operation of the compressors and the power regulators. The power control loop is further divided into a sub-loop for power controllers of a compressor that has worked the longest and is to be stopped first, and a sub-loop for the power controllers of the other compressors. The no-load operation preferably starts at the lower loop for the power controllers of the first-to-stop compressor, while the load operation is first performed at the lower loop for the power controllers of the other compressors.

No. 5,231,846 A describes a method for the stepwise operation of compressors for a refrigeration system with a plurality of compressors, wherein the method comprises the following stages: a first operating state is calculated for each compressor, and a second operating state for each compressor. Furthermore, the status of each compressor is determined, thereby creating a first list of circuits with compressors that are available to be turned on and creating a second list of circuits with compressors that are available to be turned off. For the control of the compressors with the aid of the created lists, a distinction is made according to whether the cooling capacity is to be increased or reduced on the other hand.

Object of the present invention is to provide a generic method, which makes it possible to adjust the switching times of the compressor or fan to the respective current environmental conditions and / or to the respective required power requirements.

This is achieved by a method according to the characterizing part of claim 1.

According to the invention, the maximum number of switching operations per hour per compressor or per fan is initially set to limit the switching frequency of the compressor or fan. By means of this parameter, it is determined in which minimum intervals a compressor or fan can or may be switched on.

If, for example, the maximum switching frequency is 10 switching operations per hour, a compressor or fan can therefore be switched on again every 6 minutes at the earliest; The prerequisite for this is, of course, that the compressor or fan was previously switched off.

In the case of cooling or heat demand, the switching on and off of compressors or fans takes place as a function of the deviation from a preset setpoint value. This results in a demand cycle time t _az ; this is defined as a time interval between the switching on of a compressor or fan and the next time, to which there is again a cold or heat demand and delayed a compressor or fan is switched on.

The connection of one or more compressors or fans takes place after a delay time t _{V_IN} , the switching off of one or more compressors or fans after a delay time t _{V_AUS} .

To comply with the required maximum switching frequency, a renewed connection of one or more compressors or fans is possible only after expiry of the switch-on delay time t _E. The switch-on delay time t _E is calculated by means of the maximum predetermined switching per hour; thus:
t _E = 60 minutes / maximum number of operations per hour

Due to the switch-on _delay time t _E , a switch-on _blocking time t _{S_ON} results for each compressor or fan. This switch-on blocking time is calculated as follows: $${\mathrm{t}}_{\mathrm{BE}}={\mathrm{t}}_{\mathrm{e}}-{\mathrm{t}}_{\mathrm{BZ}}-{\mathrm{t}}_{\mathrm{V\_EIN}}$$

If the on and off delay times are too long, the result is negative and positive if the times are too short. In the case of several compressors or fans, as a rule, different switch-on blocking times result; in the following calculation, only the shortest switch-on blocking time is used.

In order to avoid the switch-on _blocking time, the on and off _{delay times} t _{V_IN} and t _{V_AUS are recalculated} per compressor or fan respectively for the next demand _cycle .

As described above, the on and off delay times are composed of a basic on-time t _b and a variable switching delay or switching time t _v . The (shortest) switch-on _blocking time t _{S_ON} is distributed as a percentage to both delay _times .
P _{V_ON} = Percentage of the variable ON _delay
(eg 0.8 = 80% of the deviation on switch-on delay, 20% on switch-off delay)
P _{B_ ON} = Percentage of the basic switch-on delay
(eg 0.5 = 50% of the deviation on the basic switch-on delay, 50% on the variable)

wobei P ein Proportionalitätsfaktor ist, mittels dessen eine Verstärkung oder Dämpfung des Reglers erfolgen kann.Calculation of the new basic _{switch-on time} t _{V_EIN_B} : $${\mathrm{t}}_{\mathrm{V\_EIN\_B}}={\mathrm{t}}_{\mathrm{V\_Ein\_B}}+\left({\mathrm{t}}_{\mathrm{BE}}*{\mathrm{P}}_{\mathrm{V\_EIN}}*{\mathrm{P}}_{\mathrm{LEG}}\right)*\mathrm{P}$$

where P is a proportionality factor by means of which a gain or attenuation of the controller can take place.

Calculation of the new variable switch-on time t _{V_EIN_V} . $${\mathrm{t}}_{\mathrm{V\_EIN\_V}}={\mathrm{t}}_{\mathrm{V\_Ein\_V}}+\left({\mathrm{t}}_{\mathrm{BE}}*{\mathrm{P}}_{\mathrm{V\_EIN}}*\left(1-{\mathrm{P}}_{\mathrm{LEG}}\right)\right)*\mathrm{P}$$

Calculation of the new basic _{switch-off time} t _{V_AUS_B} : $${\mathrm{t}}_{\mathrm{V\_AUS\_B}}={\mathrm{t}}_{\mathrm{V\_AUS\_B}}+\left({\mathrm{t}}_{\mathrm{BE}}*\left(1-{\mathrm{P}}_{\mathrm{V\_EIN}}\right)*{\mathrm{P}}_{\mathrm{LEG}}\right)*\mathrm{P}$$

Calculation of the new variable switch-off time t _{V_AUS_V} : $${\mathrm{t}}_{\mathrm{V\_AUS\_V}}={\mathrm{t}}_{\mathrm{V\_AUS\_V}}+\left({\mathrm{t}}_{\mathrm{BE}}*\left(1-{\mathrm{P}}_{\mathrm{V\_EIN}}\right)*\left(1-{\mathrm{P}}_{\mathrm{LEG}}\right)\right)*\mathrm{P}$$

$${\mathrm{t}}_{\mathrm{V\_EIN\_V}}={\mathrm{t}}_{\mathrm{V\_Ein\_V}}+\left({\mathrm{t}}_{\mathrm{S\_EIN}}\ast {\mathrm{P}}_{\mathrm{V\_EIN}}\ast \left(1-{\mathrm{P}}_{\mathrm{B\_EIN}}\right)/\mathrm{N}\right)\ast \mathrm{P}$$

$${\mathrm{t}}_{\mathrm{V\_AUS\_B}}={\mathrm{t}}_{\mathrm{V\_AUS\_B}}+\left({\mathrm{t}}_{\mathrm{S\_EIN}}\ast \left(1-{\mathrm{P}}_{\mathrm{V\_EIN}}\right)\ast {\mathrm{P}}_{\mathrm{B\_EIN}}/\mathrm{N}\right)\ast \mathrm{P}$$

$${\mathrm{t}}_{\mathrm{V\_AUS\_V}}={\mathrm{t}}_{\mathrm{V\_AUS\_V}}+\left({\mathrm{t}}_{\mathrm{S\_EIN}}\ast \left(1-{\mathrm{P}}_{\mathrm{V\_EIN}}\right)\ast \left(1-{\mathrm{P}}_{\mathrm{B\_EIN}}\right)/\mathrm{N}\right)\ast \mathrm{P}$$

However, the four formulas listed apply only if only one compressor or fan is provided. If several compressors or fans are used, the products listed in the brackets must be divided by a factor N, where N stands for the number of compressors or fans that are switched on during a demand cycle time. The four aforementioned formulas are then: $${\mathrm{t}}_{\mathrm{V\_EIN\_B}}={\mathrm{t}}_{\mathrm{V\_Ein\_B}}+\left({\mathrm{t}}_{\mathrm{BE}}*{\mathrm{P}}_{\mathrm{V\_EIN}}*{\mathrm{P}}_{\mathrm{LEG}}/\mathrm{N}\right)*\mathrm{P}$$

$${\mathrm{t}}_{\mathrm{V\_EIN\_V}}={\mathrm{t}}_{\mathrm{V\_Ein\_V}}+\left({\mathrm{t}}_{\mathrm{BE}}*{\mathrm{P}}_{\mathrm{V\_EIN}}*\left(1-{\mathrm{P}}_{\mathrm{LEG}}\right)/\mathrm{N}\right)*\mathrm{P}$$

$${\mathrm{t}}_{\mathrm{V\_AUS\_B}}={\mathrm{t}}_{\mathrm{V\_AUS\_B}}+\left({\mathrm{t}}_{\mathrm{BE}}*\left(1-{\mathrm{P}}_{\mathrm{V\_EIN}}\right)*{\mathrm{P}}_{\mathrm{LEG}}/\mathrm{N}\right)*\mathrm{P}$$

$${\mathrm{t}}_{\mathrm{V\_AUS\_V}}={\mathrm{t}}_{\mathrm{V\_AUS\_V}}+\left({\mathrm{t}}_{\mathrm{BE}}*\left(1-{\mathrm{P}}_{\mathrm{V\_EIN}}\right)*\left(1-{\mathrm{P}}_{\mathrm{LEG}}\right)/\mathrm{N}\right)*\mathrm{P}$$

According to the already mentioned formula t _g = t _b + t _v for the time delay, the time delay t _{g_ON} , with which a compressor or fan is switched on, can now be determined according to the following formula: t _{g_EIN} = t _{V_EIN_B} + t _{V_EIN_V} .

The time delay t _{g_AUS} , with which a compressor or fan is switched off, is calculated according to the following formula: t _{g_AUS} = t _{V_AUS_B} + t _{V_AUS_V}

The inventive method for controlling a compressor set or a fan set allows optimization of the switching times of the compressor and fan of a compressor or fan set. A manual optimization of the switching times - as is done so far - is unnecessary thanks to the method according to the invention.

The optimization of the switching times of the compressors and fans of a compressor or fan set has the consequence that the life of the compressor and fan increases.

Claims (1)

1. A method for controlling a set of compressors or blowers comprising one or a plurality of compressors or one or a plurality of blowers, respectively, characterised in that,

   a) the maximum number of switching operations per hour for the compressors or blowers, respectively, is given and the switch-on delay time is calculated therefrom, wherein: t_E = 60 minutes / maximum number of switching operations per hour;

   b) the demand cycle time t_BZ, is determined which is defined as time interval between switching on a compressor or blower, respectively, and the following point in time at which there is a new demand for refrigeration or heating and a compressor or blower, respectively, is additionally switched on with time delay;

   c) a switch-on blocking time t_{S_ON} is calculated for each compressor or blower, respectively, wherein: t_{S_ON} = t_E -t_BZ -t_{V_ON} and the delay time t_{V_ON} with which a compressor or blower, respectively, is additionally switched on is given;

   d) a new basal switch-on time t_{V_ON_B} is calculated, wherein: $${\mathrm{t}}_{\mathrm{V\_ON\_B}}={\mathrm{t}}_{\mathrm{V\_ON\_B}}+\left({\mathrm{t}}_{\mathrm{S\_ON}}\ast {\mathrm{P}}_{\mathrm{V\_ON}}\ast {\mathrm{P}}_{\mathrm{B\_ON}}/\mathrm{N}\right)\ast \mathrm{P},$$

   

   
   wherein P is a proportionality factor with which an amplification or attenuation of the controller can be achieved, N represents the number of compressors or blowers, respectively, which can be switched on during a demand cycle time, and the calculated switch-on blocking time t_{S_ON} is distributed proportionally to the basal switch-on delay and the variable switch-on delay, wherein P_{V_ON} is a percentage of the variable switch-on delay and P_{B_ON} is a percentage of the basal switch-on delay;

   e) a new variable switch-on time t_{V_ON_V} is calculated, wherein: $${\mathrm{t}}_{\mathrm{V\_ON\_V}}={\mathrm{t}}_{\mathrm{V\_ON\_V}}+\left({\mathrm{t}}_{\mathrm{S\_ON}}\ast {\mathrm{P}}_{\mathrm{V\_ON}}\ast \left(1-{\mathrm{P}}_{\mathrm{B\_ON}}\right)/\mathrm{N}\right)\ast \mathrm{P}$$

   

   f) a new basal switch-off time t_{V_OFF_B} is calculated, wherein: $${\mathrm{t}}_{\mathrm{V\_OFF\_B}}={\mathrm{t}}_{\mathrm{V\_OFF\_B}}+\left({\mathrm{t}}_{\mathrm{S\_ON}}\ast \left(1-{\mathrm{P}}_{\mathrm{V\_ON}}\right)\ast {\mathrm{P}}_{\mathrm{B\_ON}}/\mathrm{N}\right)\ast \mathrm{P}$$

   

   g) a new variable switch-off time t_{V_OFF_V} is calculated, wherein: $${\mathrm{t}}_{\mathrm{V\_OFF\_V}}={\mathrm{t}}_{\mathrm{V\_OFF\_V}}+\left({\mathrm{t}}_{\mathrm{S\_ON}}\ast \left(1-{\mathrm{P}}_{\mathrm{V\_ON}}\right)\ast \left(1-{\mathrm{P}}_{\mathrm{B\_ON}}\right)/\mathrm{N}\right)\ast \mathrm{P}$$

   

   h) the time delay t_{g_ON}, with which a compressor or blower, respectively, is additionally switched on, is calculated according to the following formula: t_{g_ON} = t_{V_ON_B} + t_{V_ON_V} and

   i) the time delay t_{g_OFF}, with which a compressor or blower, respectively, is switched off, is calculated according to the following formula: t_{g_OFF} = T_{V_OFF_B} + t_{V_OFF_V}