DE2820209C2 - - Google Patents

Description

The invention relates to a control device for a Cooling system according to the preamble of the first claim.

Cooling systems, in particular large capacity have a electrically driven compressor, usually a centrifugal compressor, a compressor or condenser and a Evaporators on, all in a closed cooling circuit connected to each other. Further, a control device provided, the parameters of the cooling system based on measured values within the system.

So it is from the preamble of claim 1 based US-PS 33 55 906 known, the engine speed the compressor as a function of the delivery pressure of the Compressor, and that of the relationship between the To set compressor suction and compressor discharge pressure, at the same time the inlet guide vanes of the compressor in Dependence of a signal to be set by the Temperature of the cooling water in the outlet pipe of the Evaporator was derived.

In particular, for the measurement of the compressor pressure expensive converters necessary. In addition, the setting is done the inlet vane after a complex function so that it can not be prevented that the compressor in the so-called pumping area occurs. This compressor can pump at certain compressor pressures occur when the Speed through the compressor is too low, or at certain velocities of the gaseous Refrigerant, where the compressor pressure is too high. At such pressure imbalances in the system, the Direction of gas flow through the compressor reversed.  

From US-PS 35 55 844 is a control device for a Cooling system known to avoid such compressor pumping shall be. After this idea, the cooling system is due to Controlled signals, the gas flow and the gas pressure in the Compressor correspond, with a bypass valve is provided, avoided with the excessive gas flow through the compressor becomes. This bypass valve is based on experience of the Controlled compressor pressures. The capacity of the compressor is by the position of the inlet baffle due to the respective Cooling condition changed. When the inlet baffles the minimum Closed position is the mentioned bypass valve opened, so that the system supplied additional gas and compressor pumps is prevented.

In a cooling system according to US-PS 37 80 532 is a cooling system described with a control circuit that the system controlled by temperatures. Here are two temperature sensors, z. B. thermistors, in the cooling water outlet line the evaporator provided, the opposite to the cooling water are different heat insulated and with which both the Temperature as well as the direction and speed of one Temperature change of the cooling water measured from the evaporator becomes. These signals are combined in a summing element, wherein the combined control signal is for, the To adjust the inlet baffle of the compressor. These can be included certain operating conditions additionally dependent on Motor current of the compressor to be adjusted.

It turns out, however, that compressor pumps obviously only then reliably prevented if both the  Engine speed of the compressor as well as the inlet baffles be adjusted to one in all conditions to achieve efficient cooling effect.

The invention is therefore based on the object, a Control device for a cooling system of the type in question indicate at the inadmissible pumping conditions of the Centrifugal compressors are reliably avoided.

This object is according to the invention by the characterizing Part of claim 1 specified features solved.

Accordingly, to control the cooling system, one out of two Temperature signals detected compressor pressure signal, the Cooling water signal and a position signal indicating the position of Indicates inlet vane used. The compressor pressure signal is going through a comparison of the measured in the capacitor Condensation temperature of the refrigerant and the temperature of the saturated refrigerant vapor in the evaporator determined. Based said control signals is the cooling system in terms Engine speed and position of the inlet vanes longitudinally a control characteristic, in which a compressor pumps reliably prevented. At the same time, the energy demand of the cooling system minimized. There may also be compressors with used smaller efficient engines of higher speed become.

The Steuereinrichtuung according to the invention can with simple Sensors are realized. Elaborate pressure sensors are not necessary.  

An advantage is that even existing cooling systems accordingly be retrofitted to the invention, so that an economical Operation is possible.

Further embodiments of the invention will become apparent from the dependent claims out.

The invention is in one embodiment with reference to the drawing explained. In this represent:

Fig. 1 is a block diagram of a cooling system with a control device according to the invention;

Figures 2, 3 and 4 are graphs for explaining the operation of a cooling system controlled according to the invention;

Fig. 5 is a block diagram of a control device present in the control circuit;

FIGS. 6A to 6C are a detailed block diagram of the control circuit;

Fig. 7 is a graph of the compressor capacity of a centrifugal compressor used in the refrigeration system as a function of the opening of intake vanes of the compressor in response to the compressor pressure;

FIGS. 8A to 8F pulse trains for controlling the position of the inlet guide vane;

Fig. 9 is a graph of compressor speed as a function of the opening of the inlet vanes for a given, fixed compressor pressure.

In Fig. 1, a cooling system is shown. This comprises a centrifugal compressor 20 for passing a refrigerant through a line 21 to a condenser 22 . Water flows into the condenser from a cooling tower via a conduit 23 and is returned via a conduit 24 to the cooling tower or to further heat exchangers when a plurality of cooling systems are coupled. The refrigerant on the outflow side of the condenser is supplied via a pipe 25 through a nozzle 26 and a pipe 27 to the inlet of an evaporator 28 . The refrigerant flows through the evaporator 28 and exits via a capacitor 20 leading to the conduit 30 in the inlet guide vane 31 (PRV) are arranged. The position of the inlet baffles is regulated by a small actuator 32 which receives electrical control signals via a multi-wire 33 . Water from a building to be cooled is supplied via a line 34 to the evaporator 28 and cooled there. The cooled water is returned via a line 35 to the building.

A motor 36 , a shaft 37 is connected to the centrifugal compressor 20 and is driven by an inverter 37 or Stromwender. The inverter receives at the input a DC voltage via a line 38 which determines the amplitude of the pulse width modulated output voltage of the inverter. A voltage regulator 40 is provided between a power supply line 41 and the line 38 . The voltage regulator may be, for example, a phased rectifier circuit which receives an input AC voltage via the line 41 and outputs via the line 38 a DC voltage in response to a signal received via a line 42 . The frequency of the inverter output voltage is regulated by the periodicity of timing or gate signals output from a logic circuit 44 and supplied to the inverter 37 via a line 43 . For this purpose, the logic circuit 44 receives a speed control signal via a line 45 and controls the frequency of the gate signals in response to this control signal.

A control circuit 50 controls not only the engine speed of the engine 36 but also the position of the intake vanes 31 . The motor speed control signal is applied to a line 51 from which lines 45 and 42 branch off to logic circuit 44 and voltage regulator 40, respectively. The position control signal for the Einlaßleitflügel 31 is guided via the line 33 to the servo motor 32 . In this embodiment, the control signal for the speed of the motor 36 is a DC signal resulting from an integrator 52 . The position control signal is either a "guide wing open" signal applied to a line 53 or a "tail gate" signal applied to another line 54 . If no signal is present, this means "stop the guide wing".

The mentioned control signals are made up of different input signals generated.

A first input signal, namely the capacitor signal, is applied to a line 55 which is connected to a temperature sensor, for. B. a thermistor 56 is connected. The thermistor 56 is disposed at the outlet of the condenser 22 and measures the temperature of the refrigerant flowing therefrom.

A second input signal, viz. The vaporizer signal, is applied to a line 57 from a second thermistor 58 which measures the temperature of the saturated refrigerant vapor exiting the vaporizer 28 in the vicinity of the duct 30 .

The two input signals are fed to a differential amplifier 59 . Its output, which is the pressure signal, is applied to a line 60 and indicates the compressor pressure and the engine speed.

A potentiometer 61 is mechanically coupled with its gripper connected to a line 62 to the inlet guide vanes 31 or to the output shaft of the servomotor 32 . The electrical signal on the line 62 shows as a third input signal, the so-called position signal, the position or position of the Einlaßleitflügel 31 continuously.

Another thermistor 63 is disposed in line 35 and measures the temperature of the cooled water flowing back from the evaporator 28 to the building. The thermistor 63 supplies as a fourth input signal, a temperature signal, the so-called cooling water signal, which is applied via a line 64 to a further differential amplifier, which also a temperature setpoint signal from a potentiometer 66 or a thermostat is supplied. The setpoint signal can be set manually or automatically by an encoder 68 . To an output line 67 of the differential amplifier 65 is then a temperature error signal corresponding to the difference of the two input-side temperature signals.

From the control circuit 50 still leads a line 70 from the logic circuit 40 , via which the cooling system can be switched off in an overload of the motor 36 . For this purpose, signals for the motor current and the motor speed of the control circuit 50 are fed back via lines 71 and 72 .

Fig. 2 is a graph showing operating characteristics of a conventional compressor, showing the compressor pressure Ω versus the capacity (R) . Parameter is the motor speed M ₀ of the motor 36 in speed units, here three speeds M ₀ = 1.5, 1.4 and 1.3. Exactly the parameter would be the so-called minimum Mach number. This is once a characteristic of the engine speed and also depends on the flow characteristics of the refrigerant used. Since these flow characteristics over the operating range of the cooling system are substantially constant, M ₀ is referred to as the engine speed. In the diagram, three ranges thus result for the same engine speed. If a change in the operating parameters in each case exceeds the upper limit of the ranges, the system becomes unstable and the compressor starts to pump. The respective upper right-hand boundary of the area represents the operation with wide-open guide vanes. The three dot-dash lines (only shown for the range with M ₀ = 1.5) indicate operation with three-quarter open, half-open or one-quarter open intake vanes. The system can be continuously adjusted for engine speed and the position of the inlet vanes.

Fig. 3 shows a characteristic map for engine speed M ₀ (left ordinate), the opening of the inlet guide vanes 31 (abscissa) and the compressor capacity R specified at selected points, all the magnitudes on the compressor pressure as a parameter represented by the characteristics shown is, are related.

Each of the various characteristics applies to a constant compressor pressure Ω and provides values for the engine speed M ₀ and the opening of the inlet vanes 31 at a given capacity. For example, the curve in the upper right part with a compressor pressure of 1.2 indicates the speed changes of the engine and the opening changes for the intake vanes 31 , which must be made to reduce the capacity at that compressor pressure. Along the arrow 75 parallel to the ordinate, the sole control of the engine speed M ₀ and full opening (WOV) of the intake baffles shows the decreasing values of the capacity R for values of the compressor pressure between 1.2 and 0.8. It can be seen that the characteristic curves starting from the position WOV of the inlet guide vanes initially have a horizontal branch (ab, be) along which the inlet guide vanes have to be closed at a constant engine speed M ₀ for reducing the capacity. For further reduction in capacity at each same compressor pressure, the engine speed must be increased on further closing the Einlaßleitflügel to avoid compressor pumps (sections bc, ef) . The points a to f are also shown in FIG .

It can be seen that a complex control function along A control characteristic is required to control both the engine speed and the opening of the inlet guide vanes to coordinate without compressor pumps occurs.  

Such a control characteristic is shown in FIG. 4 by the curve 80 . The characteristic curves of constant compressor pressure Ω according to FIG. 3 are shown in the background for the ideal control path along the control characteristic 80 .

It is assumed that the system initially operates at full capacity and with fully open inlet vanes. This is indicated by the point g . If the capacity is to be reduced, the engine speed is reduced parallel to the ordinate (path ghj) with the intake louvers still fully open. If the engine speed were further reduced while the inlet guide vanes were still fully open, the compressor would be transferred to the pumping area. Therefore, now the opening of the Einlaßleitfügel is reduced to an approximately 80% open position, while the engine speed is increased (path jk) . For further capacity reduction, the closure of the guide vanes is continued, the engine speed is thereby reduced again until the control curve 80 reaches its lowest point m . Here are the guide wings about 35% open. A further reduction in capacity is achieved by further closure of the inlet vanes while increasing the engine speed (path Mn) .

If the capacity to be increased, the cooling system between the points n and k along the described control curve 80 is controlled in the opposite direction. However, the branches kj and jh of the control characteristic 80 are not followed for a further increase in capacity. Instead, the control travel, while increasing the engine speed and the opening of the inlet vanes, leads directly from the point k to the point h and then, after the inlet vanes are fully opened, to the point g .

This control path along the control curve 80 avoids compressor pumps with very high operating efficiency. It is important that the control circuit 50 knows not only the amount of changes required, but also the direction in which the change is to be effected.

Fig. 5 shows a diagram for signal processing in the control circuit 50. The temperature error signal on line 67 is fed to a threshold network 81 and a speed logic 83 . Outputs from network 81 are routed via a line 82 to the speed logic 83 and PRV control logic 96 for the position of the inlet vanes. These output signals prevent switching commands from being given to the PRV control logic 96 during a speed control of the motor 32 when a path is taken along the characteristic curve where the position of the inlet vanes is not adjusted. The switching commands are determined on the basis of the temperature error signal and are dependent on threshold values preset in the threshold network 81 . The output signal of the speed logic 83 is passed through the integrating stage 52 , on whose output line 51 the motor speed control signal is applied. The derivation of this control signal will be discussed below.

The position signal corresponding to the position of the inlet guide vanes is given by the potentiometer 61 and its wiper line 62 to the speed logic 83 via a line 84 and to a duty cycle control 86 via a line 85 . In addition, the position signal is still fed to a matching network 87 . The derived as described above, the compressor pressure signal is passed through a branched off from the line 60 line 88 to the output of the matching network 87 and thus combined with the position signal on a line 90 . This composite signal is compared with the feedback signal via the line 72 according to the actual engine speed by subtraction, so that appears on an output line 91, a difference signal indicating that the cooling system is controlled in addition to controlling the engine speed by the setting of the Einlaßleitflügel. The current engine speed signal on line 72 is additionally compared to the engine speed corresponding compressor pressure signal on a branched line 60 from the line 89 by difference, so that on an output line 92 is present a signal indicating whether the current engine speed above or below the derived velocity M ₀ is. This signal is applied to the PRV control logic and via a branch line 99 to the speed logic 83 .

The duty cycle control 86 receives, as mentioned above, via line 85 the position signal of the inlet guide vanes and via another line 93 a signal from an overload circuit 94 . The output of the duty cycle controller 86 is provided via a line 95 to the PRV control logic 96 . The overload circuit 94 is supplied via the line 71, a signal proportional to the motor current. Its output signal is supplied via branch lines 97 and 98 from the line 93 of the PRV control logic 96 and the speed logic 83, respectively. In addition, the line 70 leads from it to the above-mentioned logic 44 for the inverter 37 . The aforementioned control logic 44, 83 and 96 thus receive a decisive for the motor current signal. In addition, the overload circuit can shut down the system in the event of an overload.

The speed logic 83 thus receives four input signals, namely
a temperature error signal via line 67 indicating whether the capacity of the refrigeration system must be increased or decreased to reach the setpoint temperature;
via the line 84, a position signal with which the current position of the Einlaßleitflügel 31 is displayed;
via the line 92, a speed error signal for the engine speed and
via the line 91, a difference signal indicating a deviation of the system from the control characteristic with respect to engine speed and position of the inlet guide vanes, with which a quick return of the system takes place on the characteristic.

On the basis of these input signals, by comparing with the control characteristic 80, the motor speed can either be fed back to this control characteristic in the event of a deviation or be guided along the control characteristic to change the capacitance.

The PRV control logic 96 receives via line 92 the speed error signal, via line 82 a message in which area on the control line the system is located, and via line 95 a duty cycle signal for pulse duration modulated adjustment of the inlet vanes. By a logical comparison of the input signals, it is determined whether the inlet vanes should be closed, opened or kept in the existing position. Accordingly, either a signal appears on the output line 54 or on the output line 53, or no signal appears on both output lines to hold the position.

FIGS. 6A to 6C show the control circuit 50 in detail. In this case, values for the operating voltages of the switching stages used are shown in a circle. The (+) sign in a circle means that the positive battery voltage of 12 volts is applied at this point. The switching components used, such as amplifiers and gates, are listed at the end of the description with reference to their reference numerals.

The cooling water temperature is measured by the thermistor 63 . Its output is given via line 64 and a 24 kilohm resistor as a cooling water signal to an input of a differential amplifier 100 . The signal of the set value potentiometer 68 is applied to the other input of the amplifier 100 via a second 24 kiloohm resistor, so that a temperature error signal is applied to its output line 67 . The cooling water and the set point signal are also combined in a second comparator 101 and passed via a line 102 to the speed logic 83 when the cooling water temperature is too low. The application of this signal and other overload signals are not shown in the diagrams; however, those skilled in the art will readily understand the application of these signals to slow down the compressor speed when the cooling water temperature is too low.

Two amplifiers 103 and 104 are connected together in a pressure compensating circuit. This network produces a phase advance at 0.007 Hz and a phase lag at 0.02 Hz. The temperature error signal on line 67 is connected to this network via a line so that the output of the network on line 105 is a compensated temperature signal applied to the network Motor speed logic 83 is forwarded.

The temperature error signal on line 67 is also passed through a comparator 106 , at the output line 107 then a logic signal is applied, which is a logical "one" or high voltage when the cooling water temperature is greater than the set temperature, and a logic "zero ", that is, a low voltage indicates when the cooling water temperature is lower than the target temperature. This signal is applied to an input of a NOR gate 108 . Two other comparators 110 and 111, which are parallel to comparator 106, produce logic outputs on lines 112 and 113 , respectively, when the difference between the set point temperature and the cooling water temperature exceeds the threshold or dead zone from which the control circuit engages the cooling system. In the illustrated embodiment, the dead zone corresponds to a temperature difference of ± 0.15 ° F (about ± 0.09 ° C) which, seen electrically, by the difference between 5.12 and 5.86 volts, the operating voltages at the two Steps 110 and 111 , is shown. For reference, a voltage of 5.5 volts is used. A NOR gate 114 and an inverter gate 115 are connected in series and output a logic signal for the motor speed logic 83 in which additional gates 116, 117, 118, 120 and 121 are included. In motor speed logic, yet another inverter 122 and gates 123, 124 and 125 are provided which control the application of signals to the integrator 52 .

A portion of the signal of the position potentiometer 61 of the inlet vanes, which is fed via the line 62 , is applied via a line 84 to an input of a comparator 130 , which receives a DC reference signal at the other input. The wiper of the potentiometer 61 is in the zero position where there is no resistance when the inlet vanes are wide open. In conjunction with the other circuit components and voltages shown in the figures, this produces a logic "one" signal on output line 131 of comparator 130 when the inlet vanes are in the wide open position. The signal becomes a logic "zero" as the vane opening is lowered from the wide open position. The signal is applied to an input of the NAND gate 120 and further inverted in an inverter stage 132 . The inverted signal passes via a line 133 to the NAND gate 117 and a NAND gate 134 , the output of which is connected to an input of another NAND gate 135 in the PRV control logic 96 .

The position signal on the line 62 is also applied to the negative inputs of comparators 136 to 140. The outputs of these comparators are respectively coupled to a gate 141 to 145. The comparators and gates are part of the matching network 87 . The output signals of the gates are summed in an amplifier 146 by generating a signal indicative of the so-called minimum Mach number speed deviation of the compressor motor based on the current leading wing position, which minimum Mach number just corresponds to a motor speed no compressor pumping occurs; see. also the curve 307 in FIG. 9.

The capacitor signal corresponding to the condensation temperature of the refrigerant measured by the thermistor 56 and the evaporator signal corresponding to the refrigerant vapor temperature measured by the thermistor 58 are combined in the aforementioned differential amplifier 59 so as to generate a signal on the lines 88 and 89 , which is related to the minimum Mach number M ₀ in wide-open guide vanes. At this point, the signal is related only to compressor pressure and does not include a factor related to the guide vane position. A portion of the vaporizer signal on line 57 is applied to another comparator 148 , which generates via the line 150 a shutdown signal for the speed logic 83 when the evaporator temperature falls below a predetermined value, this value being given by a reference voltage, the is applied to the other input of the comparator 148 .

The speed or M ₀ signal on the line 88 is combined with the output of the matching network 87 , ie a speed change signal on the line 90 , and passed to the negative input of an operational amplifier 151 . The other input of amplifier 151 receives a current engine speed indication signal via line 72 as described above. The output of amplifier 151 , which is routed to engine speed logic 83 via line 91 , thus represents the deviation from a desired speed signal when the cooling system is operating in the PRV control range in which both engine speed and vane position are regulated. to follow the control curve 80 .

Referring to Fig. 6B, the differential signal on line 91 is also applied to the positive input of another comparator 153 , which receives a reference voltage at its other input. The output of this comparator 153 is a logic signal, which is passed via a line 154 to the NAND gate 120 and indicates whether the current engine speed is above or below the predetermined engine speed for the respective operating condition. This logic signal is thus used to modify the motor speed based on the temperature errors and to obtain a faster response of the system.

The duty cycle controller 86 controls the duty cycle of the PRV control logic 96 as a function of the instantaneous position of the inlet vanes. This is an essential aspect: when the vanes are closed except for a small opening, the duty cycle control 86 prevents a "close" signal from being applied to the inlet vanes at a rate faster than the system response rate. The duty cycle controller 86 may also be considered as drive control for the PRV engine 32 , which changes the capacity of the compressor by changing the position of the inlet vanes.

The problem of known PRV controllers can be better understood in connection with FIG . The curves shown therein show changes in the compressor capacity theta as a function of the vane opening for various constant values of the compressor pressure omega. For example, the curve 300 shows the relationship between the capacity and the guide vane opening for a value of the compressor pressure of 1.2. The further curves 301, 302, 303 and 304 apply to reduced values of the compressor pressure down to an omega value of 0.8 for the curve 304 . As the compressor pressure drops to values of 1.0 and below, the slope of the right hand cam member becomes progressively smaller from a PRV orifice of about 1/2. For low values of the PRV opening, however, the slopes of the curves are almost independent of the pressure value and also relatively large. A small adjustment of the inlet vanes, therefore, when the vanes are closed or nearly closed, causes a very large change in system capacity, whereas with relatively open inlet vanes, a small adjustment results in only a small change in capacity. The system does not work linearly. For ease of control, it would be desirable for the curves shown in FIG. 7 to become more linear. The duty cycle controller 86 is directed to linearization of the system operation.

The duty cycle controller 86 , shown in FIG. 6B, essentially includes an integrator stage 156 , a NOR gate 157, and a comparator 160, and receives two different inputs. A time signal from an oscillator 155 , which in the illustrated embodiment has a frequency of 0.033 Hz, is applied as a first input via a 1.3 megohm resistor to an input of the integrator stage 156 and an input of the NOR gate 157 . This signal is shown as pulse train 201 in FIG. 8A. The NOR gate 157 produces as an output a logical "one" when both inputs are at a low potential and receive zero signals, respectively. When the oscillator signal 201 assumes a low potential, is charged by the reference voltage of 5.5 volts is applied to the other input of the integrator 156 of this from the time t ₀ and produces a corresponding in Fig. 8B output voltage 202 via a line 161 to a Input of the comparator 160 is passed. This comparator receives at its second input the position signal of the inlet vanes via the line 85th When the inlet vanes are in their closed position, the DC voltage level on line 85 , represented by line 203 in Figure 8B, is nearly 2 volts. When the rising output of the integrator 156 at the point A at time t ₁ exceeds 2 volts line, the comparator switches through 160, as this is represented by the pulse train 204 in Fig. 8C. Thus, the output of the comparator 160 is "low" in the time period between t and t ₀ and the oscillator signal 201 ( Fig. 8A) is also "low". Therefore, the output of the NOR gate 157 is "high" in this period, as shown by the initial pulse of the curve 205 in Fig. 8D. As long as the output 204 of the comparator 160 remains "high", the output of the NOR gate 154 is zero or "low". The output 204 of comparator 160 again becomes "low" when the falling edge of integrator signal 202 crosses the 2 volt line at time T ₅. At this time, however, the oscillator signal 201 is "high", and hence no output signal appears at the NOR gate 157 until the rising edge of the integrator signal 202 again exceeds the 2 volt line 203 . In this way, the control signal for the inlet guide vanes is a function of the guide vanes position.

At wide open Einlaßleitflügeln is on the line 85, a 10 volt signal; this signal is shown by line 206 in FIG. 8B. The rising edge of the integrator signal 202 exceeds the 10 volt line at point B at a time t ₃. At this time, the output of the comparator 160 becomes "high" as shown by the pulse train 207 in FIG. 8E, thereby preventing an output signal from the gate 154 . Prior to this switching of the comparator, but between times t ₀ and t ₃, the output of the NOR gate 154 was high, as shown by the pulse train 209 in Fig. 8F, because both inputs of this gate were "low". This produces a longer pulse duration in the curve 208 for driving the adjustable inlet vanes. In the illustrated embodiment, a pulse of about one second has been generated in the waveform 205 and about five seconds in the waveform 208 . Intermediate positions of the inlet vanes produce corresponding pulses with lengths lying between the indicated sides.

Of course, instead of a pulse duration modulation about an amplitude modulation can be used to the Adjust the intake baffles in accordance with to regulate their current position.

The output signal of the NOR gate 157 corresponding to a capacitance control signal is supplied to the above-mentioned NAND gate 135 and another NAND gate 162 . The modulation for opening or closing of the guide vanes is accomplished with additional gates 163-168 and 170, which are connected as shown.

For example, in the event of a logic "zero" signal from the NOR stage 165 ( Figure 6C), no drive is provided to an npn transistor which switches a light emitting diode which is powered by the battery voltage B + via a one kilohm resistor and further driving a thyristor which when generated generates a signal to close the guide vanes on the line 54 . The connection to a 0.27 microfarad capacitor, designated x , represents, like a similarly marked terminal in the "open" circuit for the guide vanes, an electrical connection for the PRV motor.

Of course, the system can also be manually switched by turning a mode selector switch 171 from the displayed automatic position to other positions. When the switch contact is brought into contact with a "hold" contact H , the vane motor remains in the current position. When the switch contact is turned to the "open" position O , the thyristor in the "open" circuit is turned on and generates a signal on line 53 to open the guide vanes. Similarly, by energizing the thyristor in the "close" circuit, a corresponding close signal is generated on line 54 as the switch is moved further to position C corresponding to "close".

The signal corresponding to the motor current, which is applied to the line 71 , is divided by means of a Dreikiloohm potentiometer, wherein a part of this signal is diverted via a line 172 to a first current limiting stage 173 . When the level of the motor current reaches a predetermined value, here referred to as 100%, the stage 173 switches and produces an output signal which is passed to both the PRV logic 96 and the motor speed logic 83 . For the motor speed control, this means that the compressor motor can not be driven faster, as long as this current level of 100% is maintained; in fact, the speed is even reduced. In addition, the operation of the PRV logic under these conditions is such that the inlet vanes can not be opened. However, when a signal indicative of a decreasing load is generated, the guide vanes may be closed to reduce the load on the system. When the current level continues to increase to a value of about 103%, another current limiting stage 174 is switched to generate a signal for the PRV logic, which then drives the guide vanes toward the closed position to reduce the load. When the current continues to increase to 106%, this signal is passed via a line 175 to a third current limiting stage 176 , thereby generating on line 70 a signal which shuts off the motor speed logic and thus the power to the motor.

Fig. 9 shows a pair of curves 307 and 308 representing the change in the engine speed of the compressor as a function of the opening of the inlet vanes for a fixed compressor pressure. Curve 307 shows a pumping curve line derived from actual data indicating that operation of the refrigeration system in an area to the left below this curve would cause compressor pumping. To avoid pumping, the curve 308 is given as a mathematical function along which the operation of the cooling system is controlled for the particular compressor pressure.

The described cooling system works extremely energy efficient. This is also because the capacity change is first controlled using the engine speed at fully open Einführleitflügeln, as this is characterized by the path gj the control characteristic of FIG. 4, before the position of the Einlaßleitflügel is changed. In addition, the present invention is based on the understanding of the compressor characteristics and the derivation of the above-mentioned minimum Mach number M ₀, which is determined by the compressor pressure and at the same time an indication of the engine speed. This use of fully open vane engine speed is consistently displayed in the control circuit to adjust the capacity of the compressor to the load requirements. Deriving the compressor pressure from two temperatures allows for accurate control with minimal sensor cost.

The following is a list of parts in which the not specified in FIGS. 6A to 6C components and components are designated.

IC type Steps ( Figures 6A-6C) MLM2902P 59, 140, 148, 149 MLM2902P 136, 137, 138, 139 MC14016BCP 141, 142, 143, 144 MLM2902P 65, 101, 103, 104 MLM2902P 106, 110, 111, 156 MLM2902P 130, 146, 151, 153 MC14016BCP 123, 124, 125, 145 CA3160S 52 MLM2902P 160, 173, 174, 176 MC14572BCP 114, 115, 116, 117, 122, 132 MC14023BCP 120, 135, 162 MC14001BCP 108, 121, 165, 167 MC14011BCP 134, 164, 166, 170 MC14001BCP 118, 157, 163, 168 MC14541BCP 155 T2310A All triacs NSL5057 All light emitting diodes 2N3415 All transistors IN914 All diodes

Claims (4)

1. Control device for a cooling system,
which has an electrically driven centrifugal compressor, a condenser and an evaporator and a temperature sensor,
which is arranged in the outlet line of the evaporator, measures the temperature of the cooling water to be cooled and emits a temperature corresponding to this cooling water signal,
which has a sensor arrangement which determines the pressure generated by the centrifugal compressor and emits a pressure signal corresponding to this pressure, the control device having a control circuit,
which determines the opening degree of the inlet vanes and the rotational speed of the centrifugal compressor to change the cooling capacity of the cooling system due to the pressure signal and the cooling water signal,
characterized by the following features
the sensor arrangement has a first temperature sensor ( 56 ) in the condenser, which measures the condensation temperature of the refrigerant in the condenser ( 23 ) and emits a condenser signal corresponding to this temperature,
and a second temperature sensor ( 58 ) in the evaporator ( 28 ) which measures the temperature of the saturated refrigerant vapor and emits an evaporating signal corresponding to that temperature;
the control circuit ( 50 ) has a comparator ( 60 ) which compares the temperature signals of the two temperature sensors ( 56, 58 ) in the condenser and evaporator and outputs the pressure signal;
a signal generator ( 61 ) which measures the position of the inlet guide vanes ( 31 ) and emits a position signal corresponding to that position of the inlet vanes ( 31 );
the control circuit ( 50 ) receives, in addition to the condenser signal, evaporator signal and cooling water signal, also the position signal of the inlet vanes and controls the Einlaßleitflügel pulse width modulated with a duty cycle, which increases continuously with increasing opening degree of the Einlaßleitflügel;
the control circuit ( 50 ) provides a control characteristic that assigns the opening degree of the Einlaßleitflügel taking into account the compressor pressure a minimum speed of the centrifugal compressor in the pumping conditions of the centrifugal compressor are just avoided, which determines the cooling capacity of the cooling system and consists of four branches, each a sense of direction for the change in cooling capacity is assigned,
wherein in order to reduce the cooling capacity, starting from the maximum cooling capacity,

• - is reduced along the first branch (gj) of the control curve only the rotational speed of the centrifugal compressor with fully opened Einlaßleitflügeln to the beginning of the second branch (jk) ,
• - Wherein on the second branch (jk) for further lowering of the cooling capacity of the opening degree of the Einlaßleitflügel while increasing the rotational speed of the centrifugal compressor until the beginning of the third branch (kn) is continuously reduced,
• - Wherein on the third branch (kn) to further reduce the cooling capacity of the opening degree of the Einlaßleitflügel is continuously reduced by first reducing the speed of the centrifugal compressor to an absolute minimum and subsequently increased again to the complete closure of the Einlaßleitflügel
  and wherein in order to increase the cooling capacity, starting from the fully closed inlet guide vanes, the third branch (kb) is completely traversed with respect to the lowering of the cooling capacity in the reverse direction,
  then, in order to further increase the cooling capacity, the fourth branch (kh) is run through, which adjoins the third branch (kn) and ends on the first branch (gj) below its beginning (g) , on this fourth branch (kh) both the opening degree of the inlet guide vanes and the number of revolutions of the centrifugal compressor are simultaneously increased.

2. Control device according to claim 1, characterized in that the signal generator ( 61 ) for the position of the Einlaßleitflügel ( 31 ) is a potentiometer. 3. Control device according to claim 1 or 2, characterized in that the control circuit ( 50 ) has a speed logic ( 83 ) for adjusting the rotational speed of the centrifugal compressor ( 20 ) having a temperature error signal corresponding to the deviation of the cooling water temperature from a target value, the position signal of Einlaßleitflügel , a speed error signal corresponding to the deviation of the current speed from a predetermined speed via the pressure signal and a speed determined by the position signal and the pressure signal signal and compared with the current speed difference signal corresponding to the deviation of the current speed of the current opening degree of Einlaßleitflügel ( 31 ) corresponding to the control characteristic associated value. 4. Control device according to claim 3, characterized in that the control circuit ( 50 ) for adjusting the position of the Einlaßleitflügel ( 31 ) has a control logic ( 96 ) which determines the speed error signal, one of the position signal in a control circuit ( 86 ) for the duty cycle Control signal and a given by the temperature error signal control signal can be supplied.