WO2009107130A1

WO2009107130A1 - Power system for air conditioning systems

Info

Publication number: WO2009107130A1
Application number: PCT/IL2009/000213
Authority: WO
Inventors: Shimon Limor
Original assignee: Power Electronics Systems (2006) Ltd.
Priority date: 2008-02-25
Filing date: 2009-02-25
Publication date: 2009-09-03

Abstract

A method for providing an operating voltage to an air conditioner, including: measuring an input line voltage; comparing the measured input line voltage to an desired operating voltage of the air conditioner; and transforming the input line voltage to an output voltage that is nearer the desired operating voltage than is the input voltage.

Description

POWER SYSTEM FOR AIR CONDITIONING SYSTEMS

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, is concerned with improving the performance of air conditioners, example for, by providing them with variable voltages. In some embodiments of the invention, the invention provides apparatus for stabilizing an output voltage as compared with an input voltage. Each country has its own electrical infrastructure, which provides a specific line voltage at electrical outlets. Furthermore, these specific line voltages can vary between upper limits and lower limits, which also differ from country to country. Lastly, short, large, and unexpected drops in line voltage, such as the California effect, are known to be experienced in some electrical infrastructures. When voltage drops enough, the current drawn by air conditioners rises sharply and in some cases, the air conditioners "stall" raising the current even more. This causes a further drop in voltage. The effects can cascade and cause substantial problems.

Air conditioning systems are built to operate at specific ranges of input voltages. If voltages outside these specific ranges are provided to air conditioners, the latter may stall, perform at low efficiency, or break down. Furthermore, air conditioners have specific voltages (which from now on will be called optimal operating voltages) at which performance is optimal. Above and below optimal voltages, air conditioners experience a decline in performance.

Air conditioners are built so that the input voltage ranges at which they work include the specific voltages provided by different countries. However, their optimal voltages usually do not match the line voltage, causing the air conditioners to work under non-optimal conditions. Also, sharp and unexpected line voltage drops can fall outside the voltage ranges at which air conditioners work, causing them to stall.

A number of solutions have been proposed and are in use for providing variable voltages to induction motors. One method is the "star-delta" configuration in which the motor is fed from a three phase transformer and the windings of the motor are switched from a star connection to the power line to a delta connection as the motor speeds up. This provides two levels of voltage for starting the motor. A second method utilizes a tapped autotransformer to vary the voltage. In this method, the voltage to the motor is supplied via a step-down autotransformer having multiple taps. The motor is first connected to the lowest tap and, as the motor speeds up, the input of the motor is transferred to successively higher voltages by changing the tap supplying the voltage. A third method uses phase control to vary the voltage. In this method thyristors are used to control the voltage and the phase of firing of the thyristors is used to vary the voltage delivered to an output. This method does not deliver a sinusoidal voltage and its inefficiencies in starting motors are well known. In particular, there is an intrinsic phase delay, especially during start-up and power robbing transients when the thyristor fires. Furthermore, it is generally not possible to use capacitors for improvement of power factor with phase control.

Israel patent application ILl 999000133307 filed December 5, 1999, and published May 29, 2003, the disclosure of which is incorporated here by reference, describes a system for lighting control in which a transformer primary is placed across the input (between "line" and "return" connections) and the secondary is in series between the load and the line. The secondary is wound and attached to oppose (and thus reduce) the line voltage supplied to the load. This provides a reduced voltage at the load. When the full voltage is needed, the transformer input is disconnected from the return and short circuited, forcing the voltage on the secondary to zero. The secondary can then be short circuited.

Multiple transformer stages can be supplied to provide a greater variation in load voltages. PCT publication WO 2008/010213, describes a system in which a three phase transformer is used to provide a varying voltage to a load, such as a motor on start-up. In this system, the primaries of the transformer are connected between the lines and the secondaries are selectively placed in series with the same or other phases.

The disclosures of each of the above references is incorporated herein by reference. SUMMARY OF THE INVENTION

The present invention, in some embodiments thereof, is concerned with improving the performance of air conditioners or other loads, for example, by providing them with variable voltages. . There is thus provided, in accordance with an embodiment of the invention a method for providing an operating voltage to an air conditioner, including: measuring an input line voltage; comparing the measured input line voltage to a desired operating voltage of the air conditioner; and transforming the input line voltage to an output voltage that is nearer the desired operating voltage than is the input voltage.

In some embodiments of the invention, the input voltage is a nominal line voltage having an allowed variation. In some embodiments, the desired voltage is below the nominal line voltage. In some embodiments, the desired voltage is outside the range of allowed voltage variation. In some embodiments of the invention, if the nominal voltage input to the air conditioner were set to the desired value, then the allowed variation would cause the air conditioner to stall.

In some embodiments of the invention, the allowed variation in line voltage is ±10%. Optionally, the desired operating voltage is lower than 90% of the nominal line voltage. Optionally, the desired operating voltage is greater than 75% of the nominal line voltage.

Optionally, the method includes includes controlling the output voltage such that its percentage variation is less than 50% or 30% of the allowed variation in the input voltage when the input voltage is allowed to vary over its entire allowed range. In an embodiment of the invention, the air conditioner has a higher power factor at the desired voltage than at a nominal input voltage. Optionally, the improvement in power factor results in a reduction in VAR of greater than 25%, 50% 60% or 70%.

In an embodiment of the invention wherein the air conditioner has a higher efficiency at the desired voltage than at the input line voltage. Optionally, the improvement in power factor results in an improvement in efficiency of 5% or 10%. In an embodiment of the invention when the voltage drops abruptly, the input line voltage is transformed to a higher voltage. There is further provided, in accordance with an embodiment of the invention apparatus for controlling the voltage supplied to a load, comprising: a multi-phase transformer having a primary and a secondary winding for each phase, each secondary being connected in series between an input line and an output connected to the load; the primary is configurable by switches such that the phase of the voltage of the secondary is different from the line to which it is connected by a phase different from 0 and 180 degrees; and a controller that monitors the input line voltage and controls the switches to maintain the voltage to the load such that its percentage variation is less than the voltage variation of the input when the input varies over an allowed voltage variation around its nominal value.

Optionally, the apparatus includes: a plurality of switches, switchable to switch the input of each of the primaries such that they are selectively connected in more than one of a plurality of configurations including at least one configuration in which the various primaries are connected between :

(a) the input phase to which its secondary is connected and another input phase;

(b) the input phase to which its secondary is connected and a neutral or virtual neutral;

(c) two phases different from the input phase to which its secondary is connected; and

(d) a phase different from the input phase to which its secondary is connected and a neutral or virtual neutral.

Optionally, the plurality of switches is also capable of (e) shorting the primaries. Optionally, for (e) the respective secondary is also short circuited.

Optionally, the primaries and secondaries are configured such that voltage at the output is lower than the line voltage for each of (a) through (d). Optionally, the connection of the primaries can be inverted such that the voltages output is higher than the line voltage for each of (a) through (d).

Optionally, the primaries and secondaries are configured such that the voltage output is higher than the line voltage for each of (a) through (d). Optionally, the plurality of switches is switchable to switch the input of each of the primaries such that they are selectively connectable between two or more of (a) to (d).

Optionally, the plurality of switches is switchable to switch the input of each of the primaries such that that they are selectively connectable between three or more of (a) to (d).

Optionally, switching for (a) to (d) takes place only with respect to the primaries of the transformers.

Optionally, for switching between any of (a) to (d) no switching is necessary in the lines between the input and the load.

Optionally, wherein the voltage at the output is higher than the line voltage for at least one configuration of the switches.

Optionally, the switches are capable of inverting the polarity of at least one of the connections.

Optionally, the multi-phase transformer is a three phase transformer and wherein the input is a three phase voltage source.

In an embodiment of the invention, the primary windings are connected directly across the line inputs and the secondary windings are series connected to the lines, on the load side of the parallel connection.

In an embodiment of the invention, the secondary windings are connected in series with the line inputs and the primary windings are connected in parallel to the lines on the load side of the secondary windings.

Optionally, the secondary windings are connected in series with the line inputs and one side of each primary is connected at the line side of the secondary windings and the other of the primary winding is connected at the load side of the secondary windings.

Optionally, the apparatus includes a transfonner that transforms the input line voltage by a constant ratio to change the nominal output voltage by the same ratio.

There is further provided, in accordance with an embodiment of the invention, air conditioning apparatus comprising: an air conditioner; a controller operative to: measure an input line voltage; compare the measured input line voltage to a desired operating voltage of the air conditioner; and voltage transforming apparatus that transforms the input line voltage to an output voltage that is nearer the desired operating voltage than is the input voltage, responsive to the comparison.

Optionally, the controller and voltage transforming apparatus are comprised in apparatus for controlling the voltage supplied to a load according to an embodiment of the invention.

Optionally, the controller carries out the method of any of claims 1-11. Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced. In the drawings:

FIG. 1 is a schematic circuit drawing of a drive system powering an air conditioner, in accordance with an exemplary embodiment of the invention;

FIG. 2 is a circuit drawing of a transformer and associated switches in the drive system of the power unit, in accordance with an embodiment of the invention;

FIG. 3 is a phasor diagram of line and phase voltages in a three phase system; FIGs. 4A and 4B are respectively the connections of the circuit of FIG. 2 and a phasor diagram for a first configuration in which a lowest voltage is achieved; FIGs. 5 A and 5B are respectively the connections of the circuit of FIG. 2 and a phasor diagram for a second configuration in which a first higher voltage is achieved;

FIGs. 6A and 6B are respectively the connections of the circuit of FIG. 2 and a phasor diagram for a third configuration in which a second higher voltage is achieved; FIG. 7 shows the connections of the circuit of FIG. 2 for a fourth configuration in which the line voltage is delivered to the motor;

FIG. 8 shows voltage output as a function of voltage input for a system according to an embodiment of the invention;

FIG. 9 is a circuit drawing of a transformer and associated switches in the drive system, in accordance with an embodiment of the invention;

FIG. 10 is a circuit drawing of a transformer and associated switches in the drive system, in accordance with yet another embodiment of the invention;

FIG. 11 is a flow chart of a methodology of control of the line voltage, in order to match the line voltage to the optimal operating voltage of an air conditioner; and FIG. 12 is a schematic circuit drawing of a system for powering an air conditioner including input voltage transformation, in accordance with an embodiment of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION According to an aspect of some embodiments of the present invention, an apparatus is provided for stabilizing the voltage to a load under varying line voltages. In the example shown input variations of ±10% can be reduced to about ±2.6%.

According to an aspect of some embodiments of the present invention, an apparatus is provided for improving the performance of an air conditioner by varying the voltage supplied to an air conditioner such that the voltage supplied is nearer to an optimal voltage of the air conditioner than the line voltage.

The present inventor has found that air conditioners designed for a particular nominal line voltage are not designed for this voltage to be the optimal operating voltage for the air conditioner. The reason for this is that the actual voltage may vary plus or minus 10% around the line voltage. In general, the efficiency (and current) increases as the voltage drops below the line voltage to reach an optimum efficiency at a voltage several percentage points below the line voltage. However, when the voltage drops further, the efficiency drops fairly quickly and the current rises substantially. Thus, were the air conditioner to be designed to be optimal at the nominal line voltage, it would operate poorly at the low end of the allowable variation in voltage and might even stall. For this reason, air conditioners are generally designed to operate at a voltage above their optimum efficiency. In many instances, air conditioners are designed to operate over a range of nominal line voltages. Thus an air conditioner may be sold for operation in regions in which the line voltage is 220 V as well as in regions in which the line voltage is 230 V. This only exacerbates the problem.

In accordance with some embodiments of the invention, a variable voltage transformation unit is provided to set the voltage to a voltage nearer the efficiency optimum for the transformer than the line voltage. Preferably the line voltage is measured and the transformation unit changes the voltage such that it is closer to the optimum than the current line voltage.

In some embodiments of the invention, the transformation unit is configured to overcome the California effect. In these systems the range of voltages is high enough so that the voltage to the air conditioner can be raised quickly to avoid the precipitate rise in current and stalling. Optionally, a circuit breaker can then be opened to take the air conditioner off-line without damage to the electrical system.

Fig. 1 is a schematic circuit drawing of apparatus 90, in which a power unit (variable voltage transformation unit) 100 powers a motor 102 of an air conditioning unit 101, in accordance with an exemplary embodiment of the invention. As shown, power unit 100 receives three phase power at phases Ll, L2 and L3 at a first voltage and delivers power to motor 102 at a variable output voltage at phases U, V and W. The motor drives a load 104. A neutral N may be supplied to the motor. A measuring unit 106 measures the input line voltage to power unit 100, and sends the measured values to a computing and processing unit 108. Computing and processing unit 108 compares the line voltage to the optimal operating voltage of air conditioning unit 101, decides whether and how the voltage to the motor is to be changed, and sends instructions to a control unit 110. Control unit 110 controls power unit 100, so that power unit 100 changes the voltage that enters air conditioning unit 101, according to the instructions of computing and processing unit 108. As indicated above, the voltage to the air conditioner is set to a voltage nearer the optimum voltage of the air conditioner than is the line voltage. It is noted that this system and methodology can improve the efficiency of the air conditioner at a line voltage that is near or at nominal.

Fig. 2 shows some details of circuitry of power unit 100, in an exemplary embodiment of the invention. In its simplest form the power controller comprises a three phase transformer having first windings designated as Pl, P2 and P3 and secondary windings Sl, S2 and S3. The secondary windings are connected in series between the line inputs and the load. In addition, the power controller includes a plurality of three phase switches Kl, K2, K3 and K4, which are effective to connect the primary windings across the line inputs in different ways. Additionally, an optional three phase switch K6 is used to short circuit the secondary windings under certain circumstances as described below.

The main configurations of the switches are illustrated in the following figures.

Fig. 3 shows the relationship between the phase to phase and phase to neutral voltages for a three phase 400 V line to line input. For simplicity of presentation, the input line to line voltage is not shown in the following phasor drawings.

Figs. 4A and 4B are respectively the connections of the circuit of Fig. 2 and a vector diagram for a first configuration in which a lowest voltage is delivered to the load.

Fig. 4 A shows the circuit of Fig. 2 when switches Kl and K3 are closed and the other switches are open. In this configuration, Pl is connected between line phases 1 and 2, P2 is connected between line phases 2 and 3 and P3 is connected between line phases 3 and 1.

Since the phase of the voltage applied to the primaries is 30° out of phase with the line to which the secondary is connected, the phase diagram shown in Fig. 4B results. By way of illustration, and without limiting the invention, a primary secondary ratio of 400/43 is assumed and the input voltage is assumed to be the nominal 400 volts.

On Figs. 4A, 5A and 6A, the primary input phase to phase voltages are shown by short dashed lines, the secondary voltages are shown as solid lines, the output phase to phase voltage is shown as a line of long dashes and the output line to line voltage is shown as a dot-dashed line. For nominal line to line voltage input voltage, the output line to line voltage is 346 V or 0.865 of nominal input. Thus if this configuration is used for an input voltage that is 10% higher than nominal, the output voltage will be

1.1*0.86=95.15 of nominal.

Figs. 5A and 5B are respectively the connections of the circuit of Fig. 2 and a phasor diagram for a second configuration in which a next higher voltage is delivered to the load.

Fig. 5 A shows the circuit of Fig. 2 when switches Kl and K4 are closed and the other switches are open. In this configuration, each of Pl, P2 and P3 is connected between its own phase and neutral. Optionally, the connection can be to an actual neutral or to a virtual neutral N' formed by the connection of one end of the transformers to a same point.

Since the phase of the voltage applied to the primaries is in phase with the line to which the secondary is connected, the phase diagram shown in Fig. 4B results, for the same assumed input as in Figs. 4A and 4B. Since the voltage on each of the P windings is 230 volts, the secondary voltages are 24.8 volts, out of phase with the input line voltages. The phase to phase voltages U, V, W are then 365 V or .09125 of nominal input. Thus if this configuration is used for an input voltage that is 5% higher than nominal, the output voltage will be 1.05*0.9125=0.9585 of nominal.

Figs. 6A and 6B are respectively the connections of the circuit of Fig. 2 and a phasor diagram for a third configuration in which a next higher voltage is delivered to the load.

Fig. 6A shows the circuit of Fig. 2 when switches K2 and K3 are closed and the other switches are open. In this configuration, each of Pl, P2 and P3 is connected between another phase and neutral.

Since the phase of the voltage applied to the respective primaries is 60° out of phase with the line to which the secondary is connected, the phase diagram shown in

Fig. 6B results for the same assumed input as in Figs. 4A and 4B. Since the voltage on each of the P windings is 230 volts, the secondary voltages are 24.8 volts. The phase to phase voltages U, V, W are then are then 380 V or .095 of nominal input. Thus if this configuration is used for an input voltage that is nominal, the output voltage will be 0.95 of nominal.

Fig. 7 shows the connections of the circuit of Fig. 2 in which the input line voltage is delivered to the load. The phasor diagram is the same as Fig. 3 since there is no voltage on the secondaries. In Fig. 7, switches K2 and K4 of Fig. 2 are closed and the other switches are open, except that K6 is optionally closed. In this configuration, each of Pl, P2 and Ps are disconnected from the line and shorted and the secondaries are optionally shorted as well. Thus, no substantial voltage opposes the input line voltage and that voltage, is applied directly to the motor. Thus if the line voltage is 5% below nominal, the output will be 0.95 of nominal.

It is to be understood that shorting the secondaries is not absolutely necessary. However, they are preferably shorted to avoid core and/or conduction losses in the transformer. It is noted that for the described configuration, when the line voltage falls to

90% of nominal, the output will be 90% for the configuration of Fig. 7. Since it desirable to have a lower output voltage for the configuration of Fig. 7 so that all of the connection modes can be used effectively. Using all of the connection modes minimizes the swing of voltage during switching. Thus, if it is desirable to keep the output voltage between about 81% and 86% of nominal, the line voltage is optionally reduced, as for example by placing a transformer having a 0.9 voltage reduction ratio before or after the circuitry shown in Figs 2-7. With this configuration, the voltage variations of the output shown in Fig. 7 result. The switching points between various configurations are shown as the vertical lines between the linearly varying voltages for each of Figs. 4-7.

It is noted that the total range of output voltages for an input voltage of ±10% is about 2.7%. If a wider spread is desired, then a larger transformer ratio is used for the switched transformers. If a higher minimum voltage is desired, then a lower common transformer ratio is used. Thus, the output characteristics can be tailored to a great extend depending on the line voltage variations expected, the actual optimal point of the transformer and the sensitivity of the load air conditioner to changes in voltage. Fig. 12 shows a system 90' including a common transformer 800. The common transformer is suitable for use in all the embodiments of the invention.

It is noted that when switching (break before make, is desirable) between the configurations of Figs. 4A, 5A, 6A and 7, the current to the motor is not interrupted, although the secondary windings momentarily provide a high impedance, since the primary is open circuited. Optionally, a snubber or other spike reducing circuitry is placed across the primaries. While other methodologies for voltage switching can be used (such as those described in the background of the invention), the method and apparatus described above is especially suited for switching a motor load.

If fewer voltage steps are required, then the number of switches on the primary side can be reduced. For example, if K3 and K4 are replaced by short circuits, closing Kl, while keeping K2 and K6 open will result in the configuration of Fig. 4 A and will supply a voltage of 253 volts to the load. Opening Kl and shorting K2 and optionally K6 will result the configuration of Fig. 7 and will deliver the input line voltage to the load. The present invention has thus far been described in the context of providing voltages below or equal to that of the line voltage to the load, as for example, for optimizing the voltage to an air conditioner under conditions of normal line voltage variation. However, a similar configuration can be used to provide one or more higher than line voltages to the load, if the windings on the transformer (or the primary or secondary connections) are reversed, for example to overcome a large drop in the line voltage and avoid the California effect.

In a preferred embodiment of the invention, both decreases and increases are combined in a single unit to both optimize the input voltage to the air conditioner and to compensate for a large momentary drop in the line voltage. For example, when an increase in voltage is desired, the primary can be inverted, such that the output of the secondary increases the line voltage rather than decreases it.

Similarly, further intermediate voltages can be achieved by switching the primaries in different ways, for example, by connecting the primaries between a different phase from the secondary. It is noted however, that in the preferred embodiments shown, all switching is in the low current side and there are no switches in the main current path.

In the embodiment (90) described above and shown in Figs. 1-6, the primaries are connected directly across the input lines and the secondary windings are series connected on the load side of the parallel connection of the primaries. In alternative embodiments of the invention, the secondary windings are series connected to the line side and the parallel connection of the primaries is on the load side, after the secondary windings. Fig. 9 shows such a connection, for a power unit 200, in which each of the references for the windings and the switches is the same as in Fig. 2. The operation of power unit 200 is analogous to that of power unit 100 and the same switching results in the same voltages as described above. In some embodiments of the invention, power unit 200 replaces power unit 100 in Fig. 1.

In yet another alternative embodiment of the invention, one side of each primary is connected at the line side of the secondary windings and the other of the primary winding is connected at the load side of the secondary windings.

Fig. 10 shows such a connection, for a power unit 300, in which each of the references for the windings and the switches is the same as in Fig. 2. The operation of power controller 300 is analogous to that of power unit 100 and the same switching results in the same voltages as described above. In some embodiments of the invention, power unit 300 replaces power unit 100 in Fig. 2.

Further variations on the preferred embodiment of voltage control for the present invention as shown in PCT publication WO 2008/010213 mentioned above.

Fig. 11 is a flow chart of a methodology 700 for providing the air conditioner with a voltage that is close to the air conditioner's optimal operating. At 702, the line voltage is measured. At 704, the line voltage is compared to the air conditioner's optimal operating voltage. As mentioned above, the line voltage is usually higher than the optimal operating voltage, and therefore needs to be reduced. At 706, a fitting transformation is chosen, so that the line voltage is transformed to a voltage close to the air conditioner's optimal operating voltage. In a non-limiting example, the fitting transformation is chosen among the transformations of Figures 2-9, or possible transformations of power units 200 and 300 of Figures 9 and 10, respectively. At 708, the chosen fitting transformation is applied, for example by opening and closing the appropriate switches of power unit 100 of Figure 2, power unit 200 of Figure 9, or power unit 300 of Figure 10. As a result of the transformation, an operative voltage closer to the optimal operating voltage than the line voltage is applied to the air conditioner, at 710. The line voltage is constantly monitored during this process, as shown by the connector between steps 710 and 702. The constant monitoring of the line voltage is necessary, because line voltage is known to vary between a lower bound and a higher bound, and if the air conditioner is to operate efficiently, the line voltage must be reduced instantaneously to an operative voltage close to the optimal operating voltage. Though the transformations of Figures 2-9 bring about reductions of the line voltage, method 700 is not limited to voltage reduction alone. Method 700 can also be applied to cases in which line voltage needs to be raised in order to be closer to the optimal operating voltage. Such a case is the California Effect, a sudden, large, and unexpected drop in line voltage. In such an instance, in step 706 a transformation is chosen to raise the line voltage, in 708 the transformation is applied, and in 710 a raised voltage is provided to the air conditioner, both to increase its efficiency and to prevent it from stalling. Furthermore, while the above embodiments have been described in the context of a control of an air-conditioner, similar methodologies can be used to provide voltage stabilization for large loads under varying line conditions. For example if a ±2.5% output voltage is desired for input variations of ±10%, the circuit and values shown for the above embodiments can be used with an input transformer having a 0.975 voltage reduction instead of the 0.9 suggested above for air conditioning. It should be understood that by varying the common transformer ratio the nominal regulated output voltage can be set to substantially any value.

It will be appreciated that the above described methods may be varied in many ways, including, changing the order of steps, and/or performing a plurality of steps concurrently. It should also be appreciated that the above described description of methods and apparatus are to be interpreted as including apparatus for carrying out the methods, and methods of using the apparatus. The present invention has been described using non-limiting detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. It should be understood that features and/or steps described with respect to one embodiment may be used with other embodiments and that not all embodiments of the invention have ail of the features and/or steps shown in a particular figure or described with respect to one of the embodiments. Variations of embodiments described will occur to persons of the art. Furthermore, the terms "comprise," "include," "have" and their conjugates, shall mean, when used in the claims, "including but not necessarily limited to."

It is noted that some of the above described embodiments may describe the best mode contemplated by the inventors and therefore may include structure, acts or details W

15 of structures and acts that may not be essential to the invention and which are described as examples. Structure and acts described herein are replaceable by equivalents which perform the same function, even if the structure or acts are different, as known in the art. Therefore, the scope of the invention is limited only by the elements and limitations as used in the claims.

Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following example.

EXAMPLE Reference is now made to the following example, which together with the above descriptions illustrates some embodiments of the invention in a non limiting fashion. An Electra type ELW20 residential air conditioner was tested. While the embodiment described above was for a three phase system, in which a greater range of voltages is available, the same principle holds for one phase systems as well, for example using a variation of the system described in application IL1999000133307 or one of the other voltage variation methods known in the art. The line voltage was 240 V. Various properties of the air conditioner were measured in two instances:

1. Line voltage of 240 V was supplied to the air conditioner;

2. The air conditioner was provided with 204 V. 3. The conditions of testing were the same for both settings and were in accordance withISO 5151 and ENl 4511 STD. The results of the test are shown in table 1 :

TABLE 1

As shown the performance of the air conditioner is greatly improved: Voltage is reduced by 15%, Current is reduced by 23%, Power is reduced by 13.9%, Power Factor is increased by 11.2%, Reactive Voltage (VAR) is reduced by 70%, and Actual Voltage

(VA) is reduced by 23 %. In particular, it is noted that the VARs are significantly reduced, which is a large saving for the power company.

In various embodiments of the invention, depending on the actual air conditioner being controlled, the VARs can be reduced by 20%, 50%, 60%, 70% or more. In various embodiments of the invention the efficiency can be increased by 5%, 10%, 15% or more.

While it is possible to find an optimum value for voltage to the air conditioner

(depending on which parameter is being optimized), in practice some intermediate value may be chosen which has an improved power factor, efficiency or other characteristics or some balance of these factors. This voltage is referred to herein as a "desired operating voltage."

Claims

WHAT IS CLAIMED IS:

1. A method for providing an operating voltage to an air conditioner, including: measuring an input line voltage; comparing the measured input line voltage to an desired operating voltage of the air conditioner; and transforming the input line voltage to an output voltage that is nearer the desired operating voltage than is the input voltage.

2. A method according to claim 1 wherein the input voltage is a nominal line voltage having an allowed variation.

3. A method according to claim 2 wherein the desired voltage is below the nominal line voltage.

4. A method according to claim 2 or claim 3 wherein the desired voltage is outside the range of allowed voltage variation.

5. A method according to claim 2 or claim 3 wherein if the nominal voltage input to the air conditioner were set to the desired value, then the allowed variation would cause the air conditioner to stall.

6. A method according to any of claims 2-5 wherein the allowed variation in line voltage is ±10%.

7. A method according to claim 6 wherein the desired operating voltage is lower than 90% of the nominal line voltage.

8. A method according to claim 7 wherein the desired operating voltage is greater than 75% of the nominal line voltage.

9. A method according to any of claims 1-8 and including controlling the output voltage such that its percentage variation is less than 50% of the allowed variation in the input voltage when the input voltage is allowed to vary over its entire allowed range.

10. A method according to claim 9 and including controlling the output voltage such that its percentage variation is less than 30% of the allowed variation in the input voltage when the input is voltage is allowed to vary over its entire allowed range.

11. A method according to any of claims 2-10 wherein the air conditioner has a higher power factor at the desired voltage than at a nominal input voltage.

12. A method according to claim 11 wherein the power factor is improved by a reduction of the VAR drawn from the line.

13. A method according to claim 12 wherein the VAR is reduced by over 25%.

14. A method according to claim 13 wherein the VAR is reduced by over 50%.

15. A method according to any of claims 2-14 wherein the air conditioner has a higher efficiency at the desired voltage than at the input line voltage.

16. A method according to any of the preceding claims wherein when the voltage drops abruptly, the input line voltage is transformed to a higher voltage.

17. Apparatus for controlling the voltage supplied to a load, comprising: a multi-phase transformer having a primary and a secondary winding for each phase, each secondary being connected in series between an input line and an output connected to the load; the primary is configurable by switches such that the phase of the voltage of the secondary is different from the line to which it is connected by a phase different from 0 and 180 degrees; and a controller that monitors the input line voltage and controls the switches to maintain the voltage to the load such that its percentage variation is less than the voltage variation of the input when the input varies over an allowed voltage variation around its nominal value.

18. Apparatus according to claim 17 wherein the switches comprises: a plurality of switches, switchable to switch the input of each of the primaries such that they are selectively connected in more than one of a plurality of configurations including at least one configuration in which the various primaries are connected between :

19. Apparatus according to claim 18 wherein the plurality of switches is also capable of (e) shorting the primaries.

20. Apparatus according to claim 19 wherein for (e) the respective secondary is also short circuited.

21. Apparatus according to any of claims 18-20 wherein the primaries and secondaries are configured such that voltage at the output is lower than the line voltage for each of (a) through (d).

22. Apparatus according to claim 21 wherein the connection of the primaries can be inverted such that the voltages output is higher than the line voltage for each of (a) through (d).

23. Apparatus according to any of claims 18-20 wherein the primaries and secondaries are configured such that the voltage output is higher than the line voltage for each of (a) through (d).

24. Apparatus according to any of claims 18-23 wherein the plurality of switches is switchable to switch the input of each of the primaries such that they are selectively connectable between two or more of (a) to (d).

25. Apparatus according to any of claims 18-24 wherein the plurality of switches is switchable to switch the input of each of the primaries such that that they are selectively connectable between three or more of (a) to (d).

26. Apparatus according to any of claims 18-25 wherein switching for (a) to (d) takes place only with respect to the primaries of the transformers.

27. Apparatus according any of the claims 17-26 wherein for switching between any of (a) to (d) no switching is necessary in the lines between the input and the load.

28. Apparatus according to any of claim 17-23 wherein the voltage at the output is higher than the line voltage for at least one configuration of the switches.

29. Apparatus according to any of claims 17-28 wherein the switches are capable of inverting the polarity of at least one of the connections.

30. Apparatus according to any of claims 17-29 wherein the multi-phase transformer is a three phase transformer and wherein the input is a three phase voltage source.

31. Apparatus according to any of claims 17-30 wherein the primary windings are connected directly across the line inputs and the secondary windings are series connected to the lines, on the load side of the parallel connection.

32. Apparatus according to any of claims 17-30, wherein the secondary windings are connected in series with the line inputs and the primary windings are connected in parallel to the lines on the load side of the secondary windings.

33. Apparatus according to any of claims 17-30, wherein the secondary windings are connected in series with the line inputs and one side of each primary is connected at the line side of the secondary windings and the other of the primary winding is connected at the load side of the secondary windings.

34. Air conditioning apparatus comprising: an air conditioner; a controller operative to: measure an input line voltage; compare the measured input line voltage to a desired operating voltage of the air conditioner; and voltage transforming apparatus that transforms the input line voltage to an output voltage that is nearer the desired operating voltage than is the input voltage, responsive to the comparison.

35. Apparatus according to any of claims 17-34 and including a transformer that transforms the input line voltage by a constant ratio to change the nominal output voltage by the same ratio.

36. Air conditioning apparatus according to claim 34 or claim 35 wherein the controller and voltage transforming apparatus are comprised in an apparatus according to any of claims 17-33.

37. Air conditioning apparatus according to any of claims 17-36 wherein the controller carries out the method of any of claims 1-16.