Abstract: A surge detection system for use in a fluid system having a load driven by a centrifugal compressor, the compressor being driven by an electric motor. The surge detection system comprises a means for sensing a differential pressure developed across the compressor and a means for sensing a current representing input power to the motor. The surge detection system further comprises a first computing means responsive to the differential pressure developed across the compressor for indicating when a valid surge is occurring in the compressor, and a second computing means responsive to the variable speed drive current for indicating when a valid surge is occurring in the compressor.

Abstract: A vapor compression system with set point optimization generates a set of thermodynamic operating parameters such that the system operates with optimum energy efficiency. Based on environmental conditions such as indoor and outdoor temperature as well as thermal load, the set of parameters for steady-state set point is generated. The system also monitors actual system properties in real-time and provides them as feedback to the set point computation module. Based on these actual real-time measurements, a new steady-state set point can be generated to enable the system to continue operating at maximum coefficient of performance upon change in environmental or thermal load requirements.

Abstract: A drive circuit 12 for driving an electric compressor 10 is connected with a DC power source 14. Arranged between the DC power source 14 and the drive circuit 12 is a switch 16 which, when turned on, supplies an electric current therethrough the drive circuit 12. Also a capacitor 22 is connected parallel to a drive circuit 12 and a switch 16 is connected parallel to a resistance 26. When starting, the control circuit 30 activates the drive circuit 12 to drive the compressor 10. Subsequently, the control circuit 30 turns the switch 16 on so that the current is supplied from the DC power source 14 to the drive circuit 12.

Abstract: In the cooling operation, it is determined whether supplied electric current (IDC) supplied to an electric motor for driving a compressor is less than a predetermined value or not, that is, whether consumed electric power of the electric motor is less than a predetermined value or not. In the cool-down control, the determination may be "NO", however, in this case an inverter is controlled so that the IDC is set to the predetermined value. Thus, in the present invention, since IDC is always the predetermined value a1 or less and the consumed electric power of the electric motor is always the predetermined value or less, coefficiency of performance (COP) of the refrigerating cycle can be maintained to a predetermined magnitude.

Abstract: According to the present invention, when the inside air circulation mode is determined, the blower for blowing air to the heat exchanger is operated with the regular blower voltage. When the outside air introduction mode is determined, the blower is operated with the lower blower voltage lower than the regular blower voltage. As a result, consumed electric power of a compressor in the outside air introduction mode can be controlled and the deterioration of the efficiency of the refrigerating cycle in the inside air circulation mode can be prevented.

Abstract: A flexible process controller for coordinating the operations of various equipment is disclosed. Briefly stated, in the preferred embodiment of the present invention, various parameters of the sub-systems in a HVAC system are monitored and made alterable or changeable. These parameters are transmitted to and controlled by a flexible process controller which thereafter cooperates with a motor drive controller. Logic incident to and resident in the flexible process controller consider the various parameters monitored and allow the user or the system to minimize power consumption amongst one or more of the sub-systems while maximizing efficiency and operability.

Abstract: An electronic refrigeration and defrost control unit includes a compressor relay, a defrost relay, and a fan relay. The compressor relay includes two hot terminals and one neutral terminal, the defrost relay includes three hot terminals and one neutral terminal, and the fan relay includes three hot terminals and one neutral terminal. The terminals are preferably quick connect terminals which eliminate the need for splicing neutral wires together. The electronic refrigeration and defrost control unit preferably includes a processor control circuit for driving an LED display and driving the defrost relay, fan relay and compressor relay. The control circuit is coupled to a power input which includes a super capacitor for storing power in the event of a brown-out or power shortage condition.

Abstract: Apparatus for heating and cooling an enclosed operator space in an off-road vehicle controlling evaporator fan speed, compressor clutch and condenser fan operation, and having sensors for detecting operator space temperature and an evaporator freezing condition, the condenser fan motor fuse condition, and under or over pressure conditions in the compressor; the apparatus also controls the operation of a heat source such as a heat valve in a coolant path or an electric resistance heater. The evaporator fan speed is controlled by pulse-width modulating power to the fan motor and speed is displayed by a bar graph; a digital display of temperature and system diagnostics is also provided. Operation of the clutch is inhibited when the evaporator freezes.

Abstract: A refrigeration unit of the type having an economizer cycle driven by a prime mover cooled by a liquid coolant. Electrical control configures refrigerant flow paths of the unit to provide heating and cooling cycles, as required to control the temperature of a conditioned space to a predetermined set point temperature. Heat from the liquid coolant is used to enhance the heating cycle. A heating cycle is initiated immediately, when required, when the temperature of the liquid coolant is above a predetermined temperature. A heating cycle is delayed by a special refrigeration cycle which increases the load on the prime mover, when the temperature of the liquid coolant is not above the predetermined temperature.

Abstract: When an air-conditioner operation mode signal AM representative of a confirmation to permit the starting of a motor-driven compressor is supplied from an air-conditioner control unit to a battery management unit, the battery management unit detects power supply conditions including a voltage, a ground fault, a wire disconnection, etc. of a high-voltage battery, and supplies a start permission signal AUX2 indicative of a permission to start the motor-driven compressor to the air-conditioner control unit depending on the detected power supply conditions. After having received the start permission signal AUX2, the air-conditioner control unit turns on an air-conditioner inverter drive signal DAI to operate the motor-driven compressor.

Abstract: An external heat exchanger of a heat pump air-conditioner on an electric vehicle is determined as being frosted based on signals from temperature sensors. If the external heat exchanger is frosted, then a frosting flag is set and the air-conditioner is operated in a cooling mode to radiate heat from the external heat exchanger for thereby defrosting the external heat exchanger while the air-conditioner is in a pre-air-conditioning mode before the driver enters the electric vehicle or while the battery on the electric vehicle is being charged. While the battery is being charged, the external heat exchanger is defrosted by the electric energy supplied from an external power supply to charge the battery.

Abstract: A method of controlling refrigerant pressure during elevated ambient temperature conditions in a refrigeration unit having a refrigerant compressor driven by a prime mover, and controllable suction line modulation. The method includes the steps of detecting the actual load PML on the prime mover, sensing the ambient temperature AA, and providing a dynamic load limit DLL as a function of the ambient temperature AA. The actual load PML is compared with the dynamic load limit DLL, and the suction line modulation is changed as a function of the comparison step to cause the actual load PML to follow the changing dynamic load limit DLL. The invention also includes a method of preventing excessive on-off cycling of a refrigeration unit during low ambient temperature conditions, with the refrigeration unit operating in a cycling start-stop mode to control the temperature of a conditioned space to a selected set point temperature SP.

Abstract: An air conditioner includes a means for detecting a frequency for controlling an AC motor of a compressor, a means for determining whether the frequency during operation converges to within a predetermined range, of the frequency required to maintain the designated temperature, and a means for shifting the designated temperature by a predetermined temperature when the frequency converges to the predetermined range. The temperature is shifted when the frequency decreases and converges to the predetermined range while the air conditioner operation causes the room temperature to approach the designated temperature. Thus, even if the body temperature of a user decreases because, for example, he is sleeping, the stable state of the operation can be accurately determined and thereby a comfortable temperature is maintained.

Abstract: A compressor motor of an air conditioner is powered by A.C. power from an invertor. In a first mode of operation, the power comprises a combination of a commercial A.C. power source and a solar battery. In a second mode of operation, i.e., a cost-efficiency mode, the frequency of power supplied to the motor is varied to ensure that the motor is powered solely by power derived from the solar battery when such power is above a reference value.

Abstract: Methods and apparatus for extending engine operating time, with a given amount of fuel, of an internal combustion engine connected to drive a compressor of a transport refrigeration unit. A fuel level signal is provided in response to the amount of fuel in a fuel tank associated with the internal combustion engine. The operation of the transport refrigeration unit is modified in different predetermined ways at predetermined different values of the fuel level signal, as fuel is consumed, to reduce the rate at which engine fuel is used after each modification. The time that a space being conditioned by the transport refrigeration unit for a given fuel supply is thus extended, maintaining temperature control of the conditioned space over this extended time while sacrificing non-load threatening, incremental degrees of control precision.

Abstract: A refrigeration unit, and method of operating same, having a compressor driven by a prime mover. The prime mover is selectively operable in either a continuous mode which includes heating and cooling cycles, or in start-stop cycling mode which includes cooling and null cycles, to control the temperature of a conditioned space relative to a predetermined set point temperature. In one embodiment, the cycle mode is operable only when the set point temperature is in a predetermined temperature range, the limits of which are selectable. The prime mover is operated in the continuous mode, notwithstanding the selection of the cycle mode, when the set point temperature is not within the temperature range authorized for cycle operation.

Abstract: An air conditioning system that can operate an air conditioner of an electric vehicle without interfering with the charging process, which utilizes a secondary battery. When operation of the vehicle is terminated and the control system determines that a frosting judgment decision is positive, the control system judges whether the charging current has dropped to a specified level or less. As soon as the charging current has dropped to or below the specified level, the excess charging current may be used for a defrosting operation. When the operation of the vehicle is stopped and the control system determines that a frosting judgment decision is negative, the control system judges whether a preliminary air conditioning switch is on. If the preliminary air conditioning switch is on, it is judged whether charging of the secondary battery is in progress. If charging is progressing, the control system determines whether the charging current has dropped to or below a specified level.

Abstract: The electric motor vehicle of this invention is an electric motor vehicle which is provided with a drive motor (13) driven by electric power from a storage battery (11), an air conditioner (1), and a regenerative brake means which temporarily uses the motor (13) as a generator when decelerating the vehicle to generate regenerative electric power and to charge the storage battery (11). It is further provided with an excess regenerative electric power judging means (18) for judging excess regenerative electrical energy based on regenerative electrical energy by the regenerative brake and allowable regenerative electrical energy of the storage battery at that time, and an electric power distribution means (14) for distributing the excess regenerative electric power based on the excess regenerative electrical energy.

Abstract: A compressor of a refrigeration cycle is normally driven by a commercial power source. During a power failure, the compressor is driven by an auxiliary solar power source, wherein the compressor is initially driven at a minimum frequency for a delay period and is thereafter driven at a higher frequency.

Abstract: In air conditioner having a power-variable compressor, an inverter for varying the driving frequency of the compressor through V/f control, a controller for supplying a variable-frequency control instruction in accordance with the air conditioning load to the inverter, and an input voltage detector for detecting a source voltage input to the inverter, the controller includes reference means for beforehand storing V/f value data corresponding to plural voltage sections to which a predetermined range of the input voltage to the inverter is divided at a predetermined voltage interval, and selects data representing the ratio (V/f) of the output voltage (V) corresponding to the detected input voltage and the driving frequency (f) from the reference means to output the variable frequency control instruction to the inverter so that an air conditioning operation is carried out in accordance with the air conditioning load.

Abstract: A system which drives a compressor of a refrigeration system at one or more speeds. The system includes a motor having a stationary assembly and a rotatable assembly. The stationary assembly includes windings adapted to be commutated in at least one preselected sequence. The rotatable assembly is in magnetic coupling relation to the stationary assembly and in driving relation to the compressor. The motor drives the compressor at a desired speed corresponding to a speed select signal representative of one of the speeds. The system further includes an application specific integrated circuit (ASIC) connected to the motor. The ASIC receives the speed select signal and is responsive to it for generating a commutation reference signal. The commutation reference signal in combination with the commutation signal generates a peak current demand signal and thereby cause the motor to operate at the desired speed.

Abstract: Apparatus for heating and cooling an enclosed operator space in an off-road vehicle controlling evaporator fan speed, compressor clutch and condenser fan operation, and having sensors for detecting operator space temperature and an evaporator freezing condition, the condenser fan motor fuse condition, and under or over pressure conditions in the compressor; the apparatus also controls the operation of a heat source such as a heat valve in a coolant path or an electric resistance heater. The evaporator fan speed is controlled by pulse-width modulating power to the fan motor and speed is displayed by a bar graph; a digital display of temperature and system diagnostics is also provided. Operation of the clutch is inhibited when the evaporator freezes.

Abstract: Control circuit for a refrigerating system, used in hermetic compressors, comprising first and second temperature sensors (61,62) and a current sensor (63) for the current drawn by the motor, said control circuit including a central processing unit (30), which instructs at least the selective closing of first and second driving switches (40,50), which are respectively connected with a main winding (11) and with a starting winding (12) of an electric motor (10), when the first temperature sensor (61) detects a temperature inside the refrigerating cabinet corresponding to a maximum value of an ideal temperature interval, previously informed to the central processing unit (30), the temperature of the motor (10) and the current drawn by said motor (10) being within their respective ideal operative values, previously informed to said central processing unit (30).

Abstract: A back-up switching system for a refrigeration unit in a trailer wherein the refrigeration unit includes a compressor and diesel engine normally operative and connected to the compressor. A standby electric motor is alternately operatively connected to the compressor and actuated by A/C power line for running the compressor instead of the diesel engine. The invention provides a back-up switching relay system connected to the A/C voltage for selectively applying the voltage to the standby motor. The backup switching system is responsive to a first signal from the A/C voltage if there is a power failure or to a second signal when there is a standby motor failure to generate a signal to close the diesel relays and operate the diesel engine. Upon reactivation of the previously failed A/C voltage source or standby motor a relay off signal is provided to the diesel relay system and the refrigeration unit is then again operated by line voltage to the standby motor.

Abstract: The present invention involves an inductively activated silicon switch for a control and protection circuit for motors and compressors. The circuit includes a logic gate for combining both motor control and protection functions. The logic gate has inputs from a thermostat, a compressor shell temperature circuit, a fan overheat detection circuit, a motor start relay circuit, and motor load sensing circuits. The logic gate output is connected to an oscillator for inductively activating the power output stage, as well as a start relay, a compressor shell temperature hysteresis circuit, and a fan timer circuit connected to the fan control circuit. The control circuitry further includes an over-ride circuit for manually allowing a limited number of immediate restart attempts.

Abstract: Methods and apparatus for monitoring conditions which may cause shut down of a refrigeration unit. When a condition of the refrigeration unit is detected which requires shut down, a shut down counter is incremented and the shut down is made with the provision for automatic restart of the refrigeration unit in response to predetermined parameters of the refrigeration unit. When the predetermined parameters initiate automatic re-start of the refrigeration unit, a timer is started. If the refrigeration unit operates for a predetermined period of time without shut down, the counting means is reset. A shut down before expiration of the predetermined timing period again increments the shut down counter. In one embodiment, when a predetermined condition which may cause shut down approaches a predetermined shut down value, the methods and apparatus modify the operation of the refrigeration unit one or more times in an attempt to prevent shut down.

Abstract: The microprocessor-based HVAC control system detects sensor faults by comparing thermistor readings with predetermined extreme values, indicative of sensor fault. The system automatically selects the appropriate combination of automatic/preset modes of operating key system components such as the expansion valve, the demand defrost system and the indoor fan speed control system. With a view towards minimizing any negative impact on system performance and reliability in the event of sensor malfunction.

Abstract: An electric car air-conditioning apparatus, which is small in size and capable of preventing abnormal heating upon occurrence of a failure and preventing damage when a capacitor is connected with its polarity reversed, provided with a current-conduction detecting device for detecting the operation of current conduction of a current conducting device for charging the capacitor with a current from a battery, and a power breaking device for breaking a current from the battery, wherein a control section actuates the power breaking device to break the current from the battery in the case where the current-conduction detecting device detects the operation of current conduction for a period longer than a predetermined time when the control section is not outputting a control signal for closing a switching device through which power is supplied from the battery to drive a motor-driven compressor, and in the case where the current-conduction detecting device detects the operation of current conduction when the control

Abstract: A refrigeration system of the type having an economizer cycle is provided with a null cycle, in addition to heating and cooling cycles, without shutting a compressor prime mover down, to preserve air flow in a conditioned space. First, second and third controllable valves respectively: (1) select main and auxiliary condensers, (2) open and close a liquid line, and (3) open and close a line which provides a warm liquid to an economizer heat exchanger. The valves are controlled in at least one predetermined open/close pattern during a null cycle, and preferably in a plurality of selectable predetermined open/close patterns, to provide a null cycle at any instant which substantially matches the net heat gain or loss taking place in the conditioned space. Thus, the temperature of the served space will be more apt to remain in a null temperature range close to set point, providing smoother and more accurate control over the temperature of the conditioned space for longer shelf life of perishables stored therein.

Abstract: An electric-vehicle air-conditioning apparatus small in size, simple in construction and high in reliability, which can be used for many types of vehicles, includes a battery, a conducting device connected in series with the battery, a switching device connected in parallel to the conducting device, a capacitor charged from the battery through the conducting device, a device supplied with power from the battery through the switching device for driving an electrically-operated air-conditioning compressor. The conducting device is adapted to charge the capacitor with a constant current.

Abstract: An air condition control unit is provided with an EEPROM previously memorizing respectively different specific numbers of indoor control units and power supply means. Further provided thereto are power supply judging means for judging whether a remote controller receives the power from another indoor control unit by monitoring power source lines, and power not-supply determining means for determining the unit of its own to be a unit which does not supply the power to the remote controller when the power supply judging means judges the remote controller receives the power.

Abstract: A DC power supply bus is used to connect a solar cell to an outdoor unit of air conditioners. The output voltage of each outdoor unit is controlled so as to maximize the power generation efficiency of the solar cell and the DC power supplied to the air conditioner is regulated to a predetermined value.

Abstract: An air conditioning system suitable for use in an electric vehicle. In the air conditioning system, a refrigerant gas circulatory system of the heat pump type for selectively effecting cooling and heating is disposed inside the electric vehicle and comprises lines which interconnect three heat exchangers, a directional control valve, a compressor and an expansion valve to one another. A control device is provided so as to activate and inactivate the heat exchanger, the directional control valve and the compressor. Before the expected running of the vehicle, at least a portion of the refrigerant gas circulatory system can be operated by the control device using a drive source different from the drive source used for running the vehicle. Accordingly, a comfortable room environment can be established for the expected time on riding by activating the air conditioning system in an unmanned state.

Abstract: Methods and apparatus for monitoring and controlling the operation of a refrigeration unit in a manner which eliminates the need for circuit breakers and fuses in control circuits which are instrumental in selecting and changing the operational mode of the refrigeration unit. When a need to change to a different operating mode is detected, a controller energizes a control device associated with the different operating mode and quickly determines if the current draw is within an acceptable range. If the current draw is within an acceptable range or window, the controller initiates the requested different operating mode. If the current draw is not within the acceptable range, the controller generates an appropriate alarm and different courses of action are decided upon which depend upon whether the current draw is above or below the limits of the acceptable range, the nature of the requested operating mode, and the desired temperature of a space conditioned by the refrigeration unit.

Abstract: An automotive air conditioning system equipped with an electrical compressor uses a single-shaft, dual output generator to provide a low voltage output to drive existing 12-V or 24-V automotive electrical equipment and a high voltage output to drive the air conditioning motor-driven compressor, and a control device to control the electrical compressor.

Abstract: The present invention is a cold control for refrigerators. The cold control circuit includes temperature sensitive resistances disposed within the cold box portion of the refrigerator. The cold control circuit senses the temperature of the cold box portion by a NTC thermistor which is disposed in the cold box portion and connected to the control circuit. When the temperature rises above the turn-on set point, the NTC thermistor has a relatively small resistance and activates a transistor. The transistor is connected to a latching circuit which maintains activation of the refrigerator until the thermistor falls below the turn-off point. Another solid state switch of the control circuit activates the refrigerator compressor, such as a transistor turning on an inverter in a DC powered refrigerator and a triac directly supplying current in an AC powered refrigerator.

Abstract: A method of detecting conditions during the operation of a transport refrigeration unit (20) which may cause shutdown, and then modifying the operation of the unit in an attempt to find an operating condition that will keep the unit operating safely. The unit includes a compressor (26) driven by an engine (30) operable at low and high speeds. Upon detecting (264) an over-temperature condition of the engine a first modification (282) is initiated, including switching the engine to low speed. If the engine temperature does not drop to a safe value (288, 292), a second modification (296) is initiated. If the engine was in low speed (280) when the over-temperature condition was detected, the second modification is initiated immediately. Upon detecting (314) a low oil pressure condition, the engine is switched (316) to high speed. If the oil pressure rises to a safe level, engine operation is continued at high speed. Appropriate alarms (326) accompany the modified operating conditions.

Abstract: A control for a multiple chiller refrigeration system whereby a chiller can be stopped at a predetermined load in order that the remaining building load can be picked up by the remaining running chillers without exceeding set load capacities of the running chillers.

Abstract: An apparatus can prevent a voltage drop a the power supply that would occur when AC power is supplied to a large number of air conditioners from the same power supply simultaneously as when recovering from a power failing. The timing of applying the reset signal to a microprocessor in the apparatus is set arbitrarily by a time setting circuit. A time setting switch is used to set to an arbitrary value for the time elapsed from the generation of the reset signal to the start of an air conditioner compressor. According to the setting of this switch, the microprocessor performs a control to change the delay time for the start of the air conditioner. When the power is restored after a power failure, it is possible to prevent the air conditioners from restarting simultaneously and therefore reduce the voltage drop in the power supply.

Abstract: A current control method and apparatus for use in an air conditioning apparatus is disclosed. A total current detection portion is mounted at the AC power supply portion and a peak current detection device is mounted between the conversion portion and the inverter. The total current detection portion detects a maximum current applied to the air conditioning apparatus and the peak current detection portion detects a peak current generated in the inverter. The limitation of the detected total current value is particularly preset in the heating and in the cooling operations. When the detected value surpasses the preset limitation, the inverter motor is stopped.

Abstract: There is disclosed a current control apparatus comprising first controllers adapted for detecting an overall or total load current to calculate distribution values for distributing a current margin with respect to an overall or total current limit value to respective air-conditioners; and second controllers adapted for respectively controlling air-conditioners so as not to exceed individual current limit values, and for carrying out an incremental correction of individual current limit values in accordance with distribution values calculated by the first controllers.

Abstract: A method of detecting conditions during the operation of a transport refrigeration unit which may cause shutdown, and then modifying the operation of the unit in an attempt to find an operating condition that will keep the unit operating safely. The unit includes a compressor driven by an engine operable at low and high speeds. Upon detecting an over-temperature condition of the engine a first modification is initiated, including switching the engine to low speed. If the engine temperature does not drop to a safe value, a second modification is initiated. If the engine was in low speed when the over-temperature condition was detected, the second modification is initiated immediately. Upon detecting a low oil pressure condition, the engine is switched to high speed. If the oil pressure rises to a safe level, engine operation is continued at high speed. Appropriate alarms accompany the modified operating conditions.

Abstract: A rapid voltage drop due to generator output saturation is prevented by providing a generator output saturation detection means that extracts a generator output saturation detection signal from the collector terminal of the field transistor controlling the excitation current of the automotive generator and measures the duty ratio of the field transistor in the control device to detect saturation of the generator output, and a compressor control means for reducing the speed of the electrical compressor when saturation is detected.

Abstract: A method and control system for operating a chiller system having a lead compressor and a lag compressor in which the load on the compressors is balanced by limiting the % KW demand on the lag compressor from exceeding the 90 KW of the lead compressor while forcing the lag compressor to supply chilled water at a temperature lower than the lead compressor chilled water.

Abstract: This invention provides an inverter controlled air conditioner capable of employing a rush current preventing relay having a small capacitance, thereby decreasing the cost. An inverter circuit includes a rectifying circuit connected to an AC power supply, a smoothing capacitor connected to the output terminals of the rectifying circuit, and a switching circuit, connected to the two terminals of the capacitor, for outputting a voltage having a predetermined frequency upon performing switching. An auxiliary power supply circuit has a rectifying circuit connected to the AC power supply. A control section drives the switching circuit with an output from the rectifying circuit as the operation voltage. Relay drive circuits for receiving the output from the rectifying circuit as the operation voltage are connected to an electromagnetic contactor and a relay. When the air conditioner is started, the control section energizes the relay for a predetermined period of time t.sub.

Abstract: An air conditioning system comprises an inverter that inverts commercial power into a variable-frequency AC and supplies it to a compressor; a DC power circuit for converting the commercial power into DC current; a unit for detecting an analog value of current supplied from the commercial power; and a control unit to control inverted digital data by compensating the digital current data discrepancy due to scattering of the DC control voltage, when there is A/D conversion after an actual power supplied to the inverter has been detected via the detector.

Abstract: An integrated heat pump and hot water system provides heating or cooling of a comfort zone, as required, and also provides water heating. As a power management feature, the speed of a variable speed compressor is reduced to a predetermined fraction, e.g. 80%, of its normal operating speed, in response to a demand limit signal provided from the electric power utility during times of peak electrical load. A reference compressor speed is computed based on the current compressor speed, indoor temperature, outdoor temperature, and zero-load temperature difference. If the system is between operating cycles when the demand limit signal is received, a stored speed is used which corresponds to the compressor speed at a predetermined outdoor-indoor temperature difference. This system produces graceful reduction in comfort cooling during demand limit periods.

Abstract: A circuit for controlling a free-piston engine, particularly of a refrigerator compressor, includes a bridge circuit part (1) of H configuration, in the sides (4, 5, 6, 7) of which there are positioned electronically controlled switching elements (8). The part of H configuration (1) is connected to an engine (10). A microprocessor (17) is provided to control the opening and closure of the electronic switching elements in accordance with the measurement of the mains power absorbed by the engine. The circuit provides elements (23, 25) for measuring the absorbed mains current traversing the diagonals (4, 7; 5, 6) of the H part (1), said current being proportional to the mains power absorbed by the engine (10). The elements (25) feeds a signal to the microprocessor which, on the basis of this signal, generates a further signal which, by comparison with a value equal to the current actually absorbed by the engine, enables the electronic switching elements (8) to be controlled.

Abstract: This invention provides a multi-staged refrigeration system which includes a method for optimizing the energy used by measuring the energy used by the compressors and increasing the intermediate pressure if the energy decreases when increasing the pressure and decreasing the pressure if the energy increases when increasing the pressure.

Abstract: An air-conditioning apparatus includes a control circuit adapted to detect, from among first to third line voltages of a three-phase AC power supply, the second or third line voltage not synchronizing with a serial signal. The control circuit detects a difference between a phase angle of the detected line voltage and that of the serial signal, compares the difference with set values and determines, by that comparison, whether the three-phase AC power supply is in a positive-phase sequence or in a negative-phase sequence. The operation of a compressor is inhibited when the negative-phase sequence is determined by the control circuit.