GB2038571A - System for energising and dimming gas discharge lamps - Google Patents

Abstract

An illumination control system for gas discharge lamps (44, 45) is provided with a central inverter (22) which produces an output voltage at a high frequency e.g. 23 kHz. The amplitude of the inverter output is adjustable to dim the lamps. A transmission line (30, 31, 36) consisting of spaced wires having respective thick insulation sheaths distributes the high frequency power to remotely located assemblies of ballasts (42, 43) and lamps (44, 45). The ballasts consist of passive linear components. A high power factor rectifier network (21) provides a d-c input to the inverter from the 50/60 Hz mains. <IMAGE>

Description

SPECIFICATION System for energising and dimming gas discharge lamps This invention relates to the energization of gas discharge lamps, and more specifically relates to novel energy conservation circuits for energizing and controlling the illumination output of gas-filled lamps and high intensity discharge lamps.

To conserve energy in lighting applications using gas discharge lamps, it is known that the lamps should be energized from a relatively high frequency source, and that the lamps should be dimmed if their output light is greater than needed under a given situation. For fluorescent lamps, the use of a frequency of about 20 kHz will reduce energy consumption by more than about 20%, as compared to energization at 60 Hz. For high intensity discharge lamps, such as those using mercury vapor, metal halide and sodium, the saving in energy exists but is somewhat less than for a fluorescent lamp. Numerous publications deal with the desirability of high frequency energization of gas discharge lamps, including, for example: Federal Construction Council, High-Frequency Lighting, Technical Report No. 53, National Academy of Sciences Publication No.

1610, 1968, p. 6-30; Campbell, J.H., New Parameters for High Frequency Lighting Systems. Illuminating Engineering, V. 55, May 1960, p. 247-254; discussion, p. 254-256; Campbell, J. H., Schultz, H.E., and Schlick, J. A., A New 3000-Cycle Fluorescent-Lighting System. IEEE Transactions on Industry and General Applications, Vol. IGA-1, Jan.-Feb.

1965, p. 19-24; Campbell, J. H. Schultz, H. E. and Schlick, J. A., Characteristics of a New 3000-CPS System for Industrial and Commercial Use.

Illuminating Engineering, V. 60, March 1965, p. 148-152; Dobras, Q. D., Status of High Frequency Lighting. General Electric Architects and Engineers Conference, April 1963, p. 17-24; Northern Illinois Gas Company, High Frequency Lighting at our General Office, June 1970; and Wolfframm, B. M., Solid State Ballasting of Fluorescent and Mercury Lamps. IEEE Conference Record of 4th Annual Meeting of the Industry 8 General Applications Group, October 12-16, 1969, p. 381-386.

Energy saved by dimming gas discharge lamps depends on the degree of dimming which is permitted in a given situation. The light output of a lamp is roughly proportional to the power expended. Thus, at 50% light output, only about 50% of the full rated power is expended.

Many applications exist where it is acceptable or desirable to decrease the amount of light from a lamp. For example, light in a building might be decreased uniformly or locally in the presence of sunlight coming through a window to maintain a constant or acceptable illumination at a work surface.

Thus, during a normal work day, an energy saving of about 50% may be experienced.

Light might also be decreased during nonworking hours and maintained at a low level for security purposes. Light output might also be decreased, either from local controls or from signals from a generating station during periods of overload on the utility lines.

Energy savings may also be obtained by dimming lamp output when the lamps are new and have a light output much higher at a given input power than at the end of their life.

Such a lighted area must be properly illuminated at the end of lamp life, energy can be saved by dimming the lamps when they are new, and then reducing the dimming as the lamps age. Energy savings of 15% for fluorescent lamps and 20% to 30% for high intensity discharge lamps can be obtained in this fashion.

One system used at the present time to obtain the benefits of high frequency energization of gas discharge lamps distributes power at low frequency (60 Hz) to each of the fixtures of a lighting system. Each fixture could commonly contain several lamps in parallel or series connection. Each fixture is also provided with an inverter to produce the high frequency energizing power and contains the necessary ballast circuits for the lamp. Circuits used in the individual fixture for the above type circuit are typically shown in United States Patents 3,422,309, 3,619,716; 3,731,142; and 3,824,428, each in the names of Spira and Licata; and 3,919,592 in the name of Gray, each of which is assigned to the assignee of the present invention. Systems of this type are available from the Lutron Electronics Co., Inc. of Coopersburg, Pennsylvania under the trademark Hi-Lume.

While the above arrangement performs well, a complete inverter circuit and controls therefor must be placed in each fixture. Thus, the system is costly and the reliability problem is repeated for each fixture. Since each fixture receives the complete inverter circuit, designers and users are hesitant to use complex and expensive circuits and control schemes because of cost and reliability. Furthermore, each circuit exists in the relatively hot environment of the lamp fixture. The schens also requires that four leads go to each fixture; two for power and two for the dimming signal. A further problem is that it is difficult to provide a good 50 Hz to 60 Hz power factor in each fixture since the power factor correction devices are bulky and expensive.

In another known system, a single source of high frequency is used and provides energy for a relatively short distance over relatively short power lines. Dimming is obtained by changing the inverter frequency to a capacitive ballast. An arrangement of this is shown in the publication Federal Construction Council, High-Frequency Lighting, Washington, D.C.; National Academy of Sciences, 1968, referred to above.

This arrangement has several disadvantages. First it provides relatively poor dimming. The lamps used in the system require seqarate filament transformers since, if high frequency is used to power the filaments, it is difficult to keep the filament voltage constant with variable frequency. The separate filament transformers are costly and further complicate the system. It is also difficult to change the inverter frequency and requires costly and complex controls. A further problem of these systems is that the load on the inverter is capacitive so that the high frequency power factor is poor. Thus, excessive current flows in the wires between the inverter and ballast, creating additional energy loss.

Other arrangements are known in which 50 Hz to 60 Hz power is supplied from a local source directly to the lamps and their ballasts, and dimming is obtained by changing the current amplitude through the use of an autotransformer or thyristor control circuit. While this system obviously does not have the advantage of high frequency excitation for the lamps, it is also true that bulky components are needed in this fixture and a good 50/60 Hz power factor is hard to obtain.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, a novel arrangement is provided wherein a central high frequency inverter is provided to energize a plurality of remote ballasts and associated gas discharge lamps with an a-c output wave form which may or may not be symmetrical. Circuits of any desired sophistication are provided for control of the central inverter and dimming is obtained by varying the amplitude of the inverter output. The connection from the inverter to the ballasts and lamps and remote fixtures is preferably by a novel low-loss transmission line consisting of a pair of spaced conductors which are each insulated by a very thick insulating sheath which minimizes their capacitive coupling to one another and to the grounded conduit in which they are located.It also minimizes magnetic field coupling to an iron or ferrous material conduit, and thus the iron losses in the conduit. Moreover, the structure permits use of a ferrous metal conduit. Furthermore, magnetic coupling proximity effect losses are minimized by the novel heavily insulated transmission line.

The ballasts used with the lamps are those which preferably use passive and linear components, but they could be active and/or nonlinear. A passive ballast is defined herein as one using only resistors, inductors, transformers and capacitors. An active ballast is one using amplifier components such as transistors, thyristors, magnetic amplifiers, and the like. A linear component is one having a fairly linear relationship between input and output.

The output current wave shape of the inverter of the invention is preferably sinusoidal but, in general, it is a substantially continuous periodic wave form. By a substantially continuous periodic wave form is meant a wave form which has an alternating component and may or may not have a d-c component. By substantially continuous wave form is also meant one which has no significant interval of "zero" current during each cycle of the high frequency output, as is present in some pulsed sources or in a phase controlled thyristor circuit. However, a continuous wave form shall include wave forms such as sinusoids; triangular wave forms; square or rectangular wave forms, each with or without d-c components.The output amplitude of the inverter may be controlled by: (a) Phase control; (b) Puise width modulation with a filtering ballast; or (c) D-c input voltage.

In each of the above, there will always be continuously flowing current. By pulse width modulator above is meant fixed frequency an variable pulse width or fixed pulse width and variable frequency, or combinations thereof.

In order to maintain a high power factor, the rectifier network used in converting the frequency at the mains (50 Hz to 60 Hz) to a d-c input for the high frequency inverter has a novel structure. Moreover, the ballast circuits used in the fixtures have a novel configuration. Finally, while any desired high frequency inverter circuit can be used, a novel preferred inverter to be described is particularly useful with this invention.

With the inverter of this invention, the use of the single inverter permits it to be designed with many features with high reliability at low cost. Thus, all complexity is confined to a single unit rather than being repeated over many fixtures. The single inverter can be located to enjoy full air circulation and may be easily cooled. When dimming with a single inverter, all lamps track in intensity. Since dimming is obtained by inverter output amplitude control, simple, low cost and highly reliable equipment can be used in the fixture.

Thus, the fixture for lamp and ballast has only a small number of small, low loss, highly reliable capacitive and inductive and transformer components.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram showing the essential components of the present invention.

Figure 2 is a cross-sectional view of a preferred transmission line for connecting the output of the inverter to the ballasts and lamps in Fig. 1.

Figure 3 is a circuit diagram of a preferred inverter which can be used in the diagram of Fig. 1.

Figure 4 is a circuit diagram of a ballast and lamp structure which can be used in the block diagram of Fig. 1.

Figure 5 is a circuit diagram of a power supply rectifier which can be used with the present invention.

Figure 6 is a block diagram of a novel inverter circuit arrangement which can be used in the present invention.

DETAILED DESCRIPTION OF THE DRAW INGS Referring first to Fig. 1, there is shown a relatively low frequency (for example, from 25 to 60 Hz) source 20 which is connected to a rectifier network 21 which produces rectified output.power for a single central inverter 22.

Source 20 and network 21 can be replaced by any appropriate d-c supply or can be driven from the d-c battery of an emergency battery which is charged or energized from a power line. In addition, although the use of a d-c supply powering an inverter is most suitable, it is also possible to use a frequency converter in a manner similar to that shown in U.S. Patent 3,731,142 dated May 1, 1973, in the names of Joel Spira and Joseph Licata where, for example, a-c voltage or an unfiltered rectified d-c voltage is fed directly to a frequency converter. Rectifier network 21 may be of the type shown in Fig. 5 which will be later described, and which has high power factor characteristics. Inverter 22 will be later described in connection with Fig. 3 and produces a sinusoidal a-c output wave shape at a frequency of about 23 kHz.The output of inverter 22 is preferably higher than about 20 kHz to be above the audio range, and can be as high as permitted by semiconductor switching losses, component losses, and the like which increase with higher frequencies. Note that if the apparatus is installed in an area where audio noise is not important, the inverter output need be higher than only about an order of magnitude greater than the input line frequency.

An inverter output amplitude control circuit 23 is connected to inverter 22 and, under the influence of a signal from dimming signal control device 24, will increase or reduce the amplitude of the wave shape of the high frequency output of inverter 22. The control device 24 can be a manual control or can be derived from such devices as photocell controls, time clocks, and the like which apply some desired condition responsive and/or temporal responsive control to inverter 22.

The output of inverter 22 is then connected to two leads 30 and 31 of a transmission line which is particularly well adapted to distribute the high frequency power output of inverter 22 over relatively long distances with relatively low loss. By way of example, the lines 30 and 31 could have a length of about 100 feet, and could supply power to about twentyfive discrete spaced fixtures which each might contain two lamps. In this use, 1850 watts must be provided to the system with a power factor of about 0.9.

Note that this installation could consist of fifty 40-watt fluorescent lamps which require 2500 watts at 60 Hz. Only 1850 watts are needed at the higher frequency and with the novel system of the invention for the same light output.

Note further that only two wires are needed to carry power to lamp fixtures with the present invention as contrasted to the need for four wires in fixtures which locally contain inverter circuits and are connected to easily transmitted low frequency (50/60 Hz) power.

Fig. 2 shows a preferred form of the novel transmission line of the invention for distribution of high frequency high power energy, as contrasted to well known arrangements for the distribution of high frequency, low power signalling voltages. In Fig. 2, lines 30 and 31 are formed of respective central conductors 32 and 33, respectively, which each consist of nineteen strands of copper wire having diameters of 0.014 inch. The outer diameter of the bundle of strands is about 0.070 inch.

Each of conductors 32 and 33 are covered with dielectric sheaths 34 and 35, respectively, which may be of any suitable conventional insulation. Each of sheaths 34 and 35 have diameters of 0.235 inch and are preferably at least about three times the diameter of their respective central conductor. Strands 30 and 31 are then contained in a grounded steel conduit 36 which may be a so-called 3/4 inch conduit which has an inner diameter of about 0.825 inch and an outside diameter of about 0.925 inch. The transmission lines 30 and 31 are confined in conduit 36 for a major portion of their lengths, as needed by the particular installation.

Note that the dimensions given above are only typical and that other dimensions could be selected. By using relatively thick insulation sheaths 34 and 35, the capacitive coupling and thus losses between conductors 32 and 33 and from the conductors 32 and 33 to conduit 36 are minimized. Thus the transmission line will have low loss qualities, even if it extends long distances. Note that any desired connection can be used if the distance from inverter 22 to its loads is short.

By using maximum thickness insulation sheaths 34 and 35 which can still be conveniently drawn through conduit 36, the electric field intensity is reduced, thereby to reduce bulk loss resistivity. In the past, it was be lieved necessary to use a mini-mum dielectric thickness to minimiteEdielèctric-tii~me and thus ielectric loss.Xhe present inv;e--ntion de pa-rtsofrom this con.wntional-appro-a-ch in order to reduce the shunt capacitive losses between the wires and from the wires to the conduit.

The relatively thick insulation sheaths 34 and 35-also minimize magnetic field losses incurred by coupling with the ferrous metal conduit. The-lower magnétic loss is due to the greater distawnce of the conductors 32 and 33 from the ferr.oùs metal conduit. The magnetic field varies inversely as the distance from a conductor. Energy losses due to the presence off ferrous metal in a magnetic field vary directly ås-a square of the magnetic field intensity. Therefore, it-is seen --that these losses vary inversely as the square of the distance between the conductors and the fer -rous metal conduit.This permits -use of -fer rous conduits, rather than aluminum or other non-ferrous materials. Preferably, the ctiarác- teristic impedance of the transmission line should be matched to that of the load to reduce the VAR loss and variation in voltage along the line.

Tfre transmission line conductors 30 and 31 extend through a building or along a roadway, -or the like, and are connected to one-ar more remote fixtures. Two fixtures 40 and 41 are shown for illustration -purposes, but any number can be used. Fixtures 40 and 41 each contain ballasts 42-and-43, respectively, and associated gas discharge lamps 44 and 45, respectively. A typical ballast and lamp assembly will be later described in con -nection with Fig. 4. Lamps 44 and 45 may be fluorescent or high intensity gas-discharge lamps or any other desired type of gas discharge lamp. Ballasts 42 and 43 preferably use passive linear components such as reactors (of relatively small size because of the relatively high frequency applied to the bal last) and capacitors which are reliable and inexpensive.Note that in a prior high efficiency 60 Hz ballast, there was a ballast loss of -about 12 watts in the fixture so that the fixture is quite hot. With the present invention, the ballast loss in the fixture is less than 1 watt. Thus the components in the ballast are not subject to high temperature.

In operation, high frequency power (above about 20 kHz) is transmitted from-inverter 22 over the transmission lines 30-31 with relatively low loss and -is distributed -to the plural ity of remotely '-lo-c--ated and simple bond reliable ballasts 42 and 43 and their associated lamps 44 and 45, respectively.

In order to dim the output of all the lamps 44 and 45 in an identical manner, a signal from signal source 24 (which can be a manual control, a clock control, a control from the electric utility to control utility loading, a sunlight intensity responsive control, tor the like) causes the inverter output amplitude control circuit to reduce the output amplitude of the a-c output of inverter 22. The light output of lamps 44 and 45 will then decrease roughly proportionally to the reduction in power from inverter 22.

Any desired inverter circuit having a variable a-c output can be used for the inverter .22. Fig. 3 shows-a novel inverter circuit which can be used with the present invention.

A circuit similar to that of Fig. 3 is Shown in the-pulication-An Improved Method of Resonant Current Pulse Modulation for Power Convergers, Francisc C. Schwarz, IEEE Transactions, Vol. IEC 1-23, No. 2, May, 1976; and are also shown in U.S. Patent 3;663,940 to -Francisc Schwárz. That circuit, however, does not obtain variable amplitude adjustment with constant frequency as is the case of Fig. 3.

In Fig. 3, the d-c output of rectifier 21 is -applied between d--c positive bus 50 and the negative or ground bus 51 which are con nected across series-connected, high speed thyristors 52 an-d-53.~Thyristors 52 and 53 have-turn-on speeds of less than about 1 microsec'dnd and turn-off speeds of about 2 to 3 microseconds. The junction between thyristors 52 and 53 is connected to series-con nected -capacitor 54, inductor 55, the primary winding 56 of a step-up transformer 57 and the ground bus 51. Transformer 57 has a high voltage secondary winding 58 which delivers a high frequency sinusoidal output voltage of about 255 volts a-c for a d-c input vbltage bf about 320 volts.

Suitable bypass diodes 59 and 60 may be connected across thyristors 52 and 53, respectively. Capacitor 54 and inductor 55 have values chosen to be resonant at about 23 kHz. Thus, capacitor 54 may have a value of 0.33 microfarads and inductor 55 may have a value of about 130 microhenrys.

Amplitude control circuit 23 provides timed output gate pulses to thyristors 52 and 53 to control their operation, and these pulses are phase-controlled by the dimming signal.

In operation, and to start the inverter, consider that both thyristors 5-2 and 53 are off. A gate pulse from control 23 first turns on thyristor 52 to create a current path through -components 50, 52, 54, 55, 56 and 51. The gate pulse to thyristor 52 is removed after a few microseconds and when conduction of thyristor 52 is fully established. Since capacitor 54 and inductor 55 are resonant at about 23 kHz, the current in the above circuit goes through a half cycle at the resonant frequency and, when it comes close to zero, thyristor 52 is commutated off, and the current reverses and flows through the path 51, 56, 55, 54, 59 and 50.

At this point, a pulse from control 23 turns on thyristor 53 so that the resonant current (and energy stored in the resonant circuit) can nOw reverS6 and flow through the circuit including components 53, 56, 55 and 54 in a resonant half cycle. The triggering pulse from circuit 23 is removed after conduction is established in thyristor 53. Thus, when the current at the end of this negative half cycle approaches zero, the thyristor 53 is commutated off and the current reverses into the positive half cycle and flows through components 60, 54, 55, and 56. The next pulse from control 23 turns on thyristor 52 as the resonant current swings into its positive half cycle to complete a full cycle of operation.

Obviously, a high output voltage is induced into output winding 58 during this operation which is subsequently applied to the transmission line consisting of conductors 30 and 31.

Amplitude variation is obtained by delaying the application of the firing signal to thyristors 52 and 53 and thus varying the duty cycle of the inverter. Thus, the conduction time of the thyristors, during the half cycle, is reduced and less voltage is applied to the primary winding 56. However, the vo!tage to winding 56 is sinusoidal due to the resonance of capacitor 54 and inductor 55. Thus the voltage fed to ballasts 42 and 43 (Fig. 1) is also sinusoidal. Amplitude variation may be obtained by variable delay of the firing signal to either or both thyristor switches.

As will be later described, the ballasts 42 and 43 are tuned to the output frequency of inverter 22. The sinusoidal wave form reduces inefficiency due to harmonics and also reduces production of electromagnetic interference. However, as mentioned previously, nonsinusoidal wave forms can also be used with the invention.

Note that any desired inverter circuit and control could be used in place of inverter 22 including arrangements for varying the voltage at bus 50; pulse width modulation techniques; transistorized circuits; and the use of a high frequency variable ratio transformer, or other circuits using similar controllably conductive devices.

While some aspects of the particular inverter circuit of Fig. 3 are known, it was never previously used for gas discharge lamp control purposes. This is because in ordinary lamp applications, the lamps would go out if the voltage input is reduced. However, in the present invention, the lamps stay on and dim as input voltage amplitude is decreased because the lamps are operated at high frequency and are provided with a special and suitable passive linear ballast.

A novel ballast arrangement such as that shown in Fig. 4 is provided for each of ballasts 42 and 43. The ballast of Fig. 4 is used for two series lamps 70 and 71 (equivalent to lamps 44 in fixture 40 of Fig. 1), where lamps 70 and 71 are rapid-start fluorescent lamps which are very suitable for dimming. Other gas discharge lamps could have been used.

The ballast circuit for the lamps 70 and 71 includes capacitors 72 and 73, transformer 75 and inductor 76. A winding tap 77 is connected to filament 78 of tube 70. A winding tap 79 is connected to filaments 80 and 81 of tubes 70 and 71, respectively. A winding 82 is connected to filament 83 of tube 71. Transformer 75 has a primary winding of about 235 turns. Taps 77 and 79 and winding 82 may be about 9.5 turns. A conventional thermally responsive switch 84 which opens, for example, at 105"C is in series with capacitor 72.

The values of capacitors 72 and 73 and inductor 76 are chosen to be resonant at about 32 kHz while capacitor 72 and inductor 76 resonate close to about 1 2 kHz. Therefore, the reactive impedance of inductor 76 is greater than that of capacitor 72 at 23 kHz.

By way of example, capacitor 72 is 0.033 microfarad; capacitor 73 is about 0.0047 microfarad; and inductor 76 is about 5.1 millihenrys.

An important feature of the ballasts of the invention is that they only need to provide filament heater power. Moreover, the ballast inductors and capacitors can be contained in the same can or housing, thus contributing to small size and economy for the ballast. The use of a common housing also simplifies the installation of the ballast since it is not necessary to handle many separate parts.

The ballast circuit described above has the following desirable characteristics: 1. It will not be damaged by accidental application of 50 Hz to 60 Hz power.

2. The inverter 22 will not be shorted if any one ballast component fails. Thus, the short circuit can be located more easily since the lamps in unshorted fixtures are still on.

3. The circuit exhibits a good power factor to the inverter 22 and transmission lines 30-31.

4. There is a relatively constant filament voltage over the dimming range to avoid damage to lamps.

5. The starting voltage is sufficiently high to strike the lamps under specified conditions but is not so high that the lamps can be damaged.

6. The ballast is small and efficient because the ballast transformer only handles the filament power of the lamps.

The operation of the circuit of Fig. 4 is as follows: When a-c power is applied to lines 30 and 31, the 23 kHz power causes components 72, 73 and 76 to partially resonate at their resonant frequency of 32 kHz. The increase in current flow due to this partial resonance causes the voltage on capacitor 73 to rise high enough to start lamps 20 and 21.

The partial resonance is important since it affords sufficient but not excessive starting voltage which might damage lamps 70 and 71. Once lamp 71 starts, capacitor 73 is essentially shorted so that capacitor 72 and -inductor 76 are resonant below the inverter frequency.

During operation, capacitor 72 blocks low frequency voltage of from 50 Hz to 60 Hz, if that voltage is accidentally applied to lines 30 and 31. Thus, accidental destruction of the ballast by low frequency power is prevented.

Also, since impedance components including capacitors 72 and 73, transformer 75 and inductor 76 are connected in series, the fail ure of any one component will not appear as a short on the inverter 22. Thus, all lamps of all fixtures are not extinguished and the faulty component can be easily located.

Good power factor is obtained with the circuit of Fig. 4 by making the impedance of capacitor 72 close to that of inductor 76 at 23 kHz. Since the reactive impedances of components 72 and 76 subtract, the resultant is small compared to the series resistance of lamps 70 and 71. Thus, the reactive component of the load is small so that good power factor is obtained.

A relatively constant filament voltage for filaments 78, 80, 81 and 83 is assured since the primary winding of transformer 75 is connected across lamp 70. The voltage drop across this lamp is relatively constant even as the lamp is dimmed. Thus, the filament voltages remain approximately constant. Note, however, that as the amplitude of the input voltage from lines 30 and 31 is varied, the current in lamps 70 and 71 varies and the light output of the lamps varies.

The conductor 76, in addition to being a component of the power factor network, has a larger reactive impedance than capaitor 72, and thus acts as a ballasting impedance to limit current in lamps 70 and 71.

Although the arrangement of Fig. 4 shows the invention in connection with fluorescent lamps, it should be understood that the invention can be applied to the energization and dimming of any gas discharge lamp. Indeed, the invention can be used to operate and dim incandescent lamps if desired to give a user of the circuit flexibility of application. If one or more incandescent lamps are used in place of lamps 70 and 71, the ballast circuit can, of course, be eliminated.

Lamps 70 and 71 in Fig. 4 could be replaced by conventional high intensity discharge lamps, such as mercury vapor, metal halide, and high and low pressure sodium lamps. These lamps do not have filaments and are relatively immune to damage from too high a striking voltage. Thus, the ballast of Fig. 4 can be modified to remove the transformer 75 and its filament heater windings when applied to a high intensity discharge lamp.

The circuit of Fig. 4 can also be modified to place the inductor 76 across the lamp terminals in a well known circuit arrangement.

With the transformer 75 removed, the capacitor 72 is designed to block 60 Hz power and to prevent shut-down of the system in case of a shorted component. Resonance is established between the inductor 76 and the capacitors in series therewith near the driving frequency of the inverter 22. Thus, before the H.l.D. lamp strikes, the circuit has a high Q and a large voltage builds up across the lamp.

This provides sufficient voltage to strike the lamp arc, and the lamp becomes a lower impedance, more nearly matched to the ballast. The ballast then regulates the lamp are current as a function of the ballast input voltage.

Any suitable ballast circuit could be used with the H.l.D. lamp where, however, the ballast is subject to an energy-conserving dimming operation.

Fig. 5 shows a rectifier network circuit 21 which can be used with the present invention, and which has the advantage of having a high power factor so as not to place an unnecessarily high current drain on the 50/60 Hz wiring leading to the rectifier network 21.

The circuit consists of a resonant circuit including inductor 90 and capacitor 91 connected between the input low frequency a-c source and the single phase, bridge-connected rectifier 92. The d-c output of rectifier 92 is then connected to an output capacitor 93, which may be an electrolytic capacitor, and to the positive bus 50 and ground bus 51. The values of inductor 90 and capacitor 91 are critical and are 30 millihenrys and 10 microfarads, respectively.

In operation, the LC circuit 90-91 in front of rectifier 92 causes the current drawn from the 50/60 Hz input to flow for a longer time during each half cycle and to have a better phase relationship with the voltage. The inductor 90 and capacitor 91 are resonant at a period of about one-fourth of the period of the input circuit frequency (usually 50 Hz to 60 Hz). At one point in the cycle, the voltage on capacitor 93 exceeds the voltage on capacitor 91. This back-biases rectifier 92 so that line current will surge into capacitor 91 rather than cutting-off. The surging of current into capacitor 91 during reverse-biasing of rectifier 92 causes inductor 90 and capacitor 91 to resonate, thereby causing more uniform current flow from the a-c mains over each half cycle, and thereby substantially improving power factor.

It is understood that the system shown herein can also be realized with inverter 22 as a multi-phase inverter s.uch as a three-phase inverter. In this case, the high frequency power will be distributed to ballasts and lamps by means of multi-conductor transmission line, e.g. three conductors for three-phase power. The ballasts and lamps would be connected eonductor-to-conductor, or conductor to neutral, if a neutral is provided. Likewise, the low frequency 50/60 Hz supply 20 in Fig. 1 can be a multi-phase supply, e.g. three phase.

An important feature of this invention is the use of a single central inverter transformer 57 to supply the proper starting voltage to the lamps. This feature improves the efficiency of the system. In the conventional system, a transformer is contained in each fixture to supply proper starting voltage. It is well known to transformer designers that for a given voltampere size, one large transformer is moce efficient than a number of smaller transformers.

The inverter transformer 57 supplies the proper starting voltage and the transformers 75 in the fixture ballasts (Fig. 4) does not have to carry full lamp power, but only carries filament power. All lamp power is supplied from the single inverter transformer 57 of Fig.

3 which is more efficient than an aggregate of smaller transformers for each ballast and for the same total volt amperes rating. Thus higher system efficiency is obtained.

Furthermore, since the ballast transformers 75 only carry filament power, the fixture ballasts are smaller, cooler, lighter, more efficient, less complex and thus more reliable than ballast transformers which must carry the full lamp power.

The ballast will generate approximately an order of magnitude less heat than those in which lamp volt amperes must be handled by the ballast transformer. Therefore the fixture temperature is considerably lower. When fluorescent lamps are run at this resultant cooler temperature, their light output for a given input power (efficacy) increases. This effect can save an approximate additional 5% in power in a given system.

In addition to the gain in efficiency by the use of a central transformer 57, the heat produced by the lamp power volt-amperes is dissipated in the central inverter transformer 57 rather than in the individual fixtures. The central inverter transformer 57 can be efficiently cooled since it will be in a convenient and accessible location, and any desired cooling can be used.

One inverter or converter structure which generally follows the concepts of the arrangement shown in Fig. 3 is shown in block diagram form in Fig. 6. In Fig. 6 controls are provided for the circuit of Fig. 3 which enable the circuit to be uniquely applicable to a variable power output type of system such as a lamp dimming system where the inverter is the central high frequency supply for a plurality of lamp loads which are connected to the supply over a transmission line or the like.

The inverter to be described in Fig. 6 will satisfy the following criteria: 1. The converter output will be a sine wave which is believed to be the best for the lowest transmission line loss.

2. The output amplitude of the sine wave output of the converter is variable in order to obtain dimming.

3. The inverter operates with high efficiency, thereby to save energy.

4. The output frequency of the inverter can be greater than about 20 kHz and above the audio range so that the converter will not generate annoying audible noise when used in an environment susceptible to an audio noise problem.

5. The converter can be reliably started up and turned off with the switching devices of the inverter being immediately operated in order to insure proper converter operation and to insure proper lamp striking.

6. The inverter sine wave output has low distortion even though there is a relatively large change in the load current due, for example, to dimming or a change in the number of lamps in the system which are conducting load current.

7. The converter is protected against fault load current and is turned off and requires an intentional operation by the user to turn it back on if a load fault is developed.

8. The converter is internally protected with automatically reset means for temporarily turning off the converter upon the occurrence of an internal converter fault and then automatically returning the converter to duty.

In Fig. 6, input power at lines 50-51 are connected to the block 52-53 labeled CON VERTER POWER SWITCHING ELEMENTS.

These power switching elements could be the thyristor switching devices 52 and 53 of Fig.

3 (and their associated diodes 59 and 60, respectively) or could be any other desired type of switching element including transistors and the like.

The circuit including switching elements 52 to 53 contains a converter fault detector circuit 100 which is operable to produce an output signal in response to a fault within the converter. By way of example the fault detector 100 could consist of a current transformer whose output winding is connected to a load resistor which produces a suitable output to a shut-down circuit system 103.

The main current carrying circuit next contains the sine wave filter 54-55 consisting of previously described components 54 and 55 and which insures that the square wave input from the converter power switching elements 52 and 53 is converted to a sine wave with low distortion. This is obtained because, at the fundamental frequency, the sum of the impedances of inductor 55 and of capacitor 54 is zero, so that the fundamental frequency of the square wave is unattenuated. However, the total impedance of the tuned circuit 54-55 is different from zero for other frequency components which form the input square wave and these frequency components are greatly attenuated. Consequently, a relatively low distortion sine wave output is produced by the converter circuit in view of the tuned circuit including capacitor 54 and inductor 55.Moreover, the frequency of this circuit is chosen above the audible range and preferably is greater than 20 kHz so that both criterion 1 and 4 above are met.

The load circuit in Fig. 6 is next connected through a phase-sensitive zero crossing detector circuit 110 which is operable to time the operation of a synchronizing circuit 111. The phase-sensitive zero crossing detector can consist of any desired type of circuit. The circuit could consist of a saturable core transformer which is saturated during most of the positive and negative half cycles and is unsaturated only for a short time during each current zero interval. Thus, an output voltage pulse is produced on a secondary winding and across a load resistor each time the main converter current passes through zero.

The main load current circuit also includes a load fault detector circuit 1 20 which may include a load current transformer having a secondary winding which has an output connected to a suitable shut-down circuit system 123.

The main load circuit next includes a load buffer network 1 30 which can consist of a voltage transformer and a capacitor which tends to overpower large values of resistance which might appear due to a very light load, and preserves the sine wave configuration of the output. Thus, in the circuit of Fig. 3, which does not contain the above-mentioned capacitor, if the load resistance becomes too large, the circuit becomes over-damped and the voltage across the load is no longer a sine wave and the resonance of members 54 and 55 ceases. The load buffer capacitor presents an added resonating component which is in parallel with the load and is used to preserve criteria 7 listed above.

The block diagram of Fig. 6 contains considerable control circuitry which can be conveniently constructed and adjusted for use with a single central inverter and which would be very expensive to reproduce at each fixture of a fluorescent lamp system. Thus, the circuit of Fig. 6 includes a variable amplitude control circuit 140, which receives an input from the synchronizing circuit 111. The variable amplitude control circuit is used to change the switching point of the power switching elements 52 and 53 (to obtain phase control) and is controlled from several inputs. These include the shut-down circuit 103 which is operated from the converter fault detector and the shut-down circuit 1 23 which is operated from the load fault detector 1 20. Circuit 140 is also controlled by a lamp striking sequence circuit 1 50 or from a manual control input 151 which operates through the lamp striking sequence circuit 1 50. A start-up and shutdown sequence control circuit 1 52 is also provided.

Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

Claims (32)

1. An energy-conserving illumination control system consisting of: a plurality of passive linear ballasts and respective gas discharge lamps therefor; a single high frequency power source which is connected to a power input line and which has an output frequency of greater than about 20 kHz; said high frequency power source output being connected to each of said plurality of passive linear ballasts and lamps; the output wave shape of said high frequency power source being a substantially continuous periodic wave form; and control circuit means connected to said high frequency power source for varying the amplitude of at least one of the current or voltage wave shapes of the output of said high frequency power source, thereby to vary the light intensity of each of said lamps; the energy consumed by said illumination control system being functionally related to the output light intensity from said plurality of lamps.

2. The system as set forth in claim 1 wherein said wave shape is at least approximately sinusoidal.

3. The system substantially as set forth in claim 1 or 2 which includes a high frequency power transmission line for coupling the output of said high frequency power source to each of said plurality of passive linear ballasts.

4. The system substantially as set forth in claim 3 wherein said transmission line includes first and second elongated conductors for coupling the output of said high frequency power source to each of said plurality of passive linear ballasts; each of said first and second conductors being covered with an insulation sheath of substantial thickness.

5. The system substantially as set forth in claim 4 wherein said first and second conductors are disposed within a ferrous metal conduit for at least a portion of their length.

6. The system as set forth in claim 4 wherein the diameter of said insulation sheath for each of said conductors is at least three times the diameter of their respective conductor.

7. The system of claim 1 wherein said high frequency power source includes a series inverter comprising first and second seriesconnected controllably conductive devices each poled in the same direction and rectifier means for connecting rectified power from said relatively low frequency power source to said series-connected controllably conductive devices; said first controllably conductive device being connected in closed circuit relation with a capacitor, an inductor and transformer means; said capacitor and inductor being resonant at about the frequency of said high power source; and inverter output amplitude control means coupled to the resonant current of said capacitor and inductor for switching said first and second controllably conductive devices on in synchronism with said resonant frequency of said capacitor and inductor; said transformer means being connected to said ballasts.

8. The system of claim 7 which further includes control means to control the firing point of at least one of said first and second controllably conductive devices in each cycle to obtain control of the output amplitude of said inverter.

9. The illumination control system of claim 1 wherein said high frequency power source includes a d-c converter for rectifying the input from said power input line and producing a d-c output, and an a-c converter for converting said d-c output into a high frequency output in exess of about 20 kHz.

1 0. The system of claim 9 wherein said d-c converter circuit includes: a tuned circuit comprising an inductor and capacitor having respective values which are tuned to resonate at a frequency which is higher by less than about one order of magnitude than said relatively low a-c frequency; coupling means for connecting said a-c supply circuit to said tuned circuit; a rectifier means having a-c input means connected to said tuned circuit and having a d-c output circuit means; said inductor being connected in series with said rectifier means; said capacitor being connected in shunt with said rectifier means and having one terminal connected to the junction between said inductor and said rectifier means; and an output capacitor connected to said d-c output circuit means.

11. The system of claim 10 wherein said rectifier means comprises a single phase, fullwave bridge-connected rectifier; and wherein said coupling means includes connection wires for connecting said a-c supply circuit to said inductor and capacitor respectively.

1 2. The system of claim 10 wherein said tuned circuit has a resonant frequency of about 3 to 6 times that of said power input line frequency.

13. The system of claim 10, 11 or 12 wherein said coupling means includes a second rectifier means.

14. The system of claim 10, 11, 12 or 13 wherein the current wave shape of the current drawn from said a-c supply circuit is approximately in phase with the voltage thereof, and wherein said current has a long duty cycle which approximates a sinusoid.

1 5. The energy-conserving illumination control system of claim 1, 2 or 3 wherein each of said ballasts contains a single ballast transformer for providing only filament power to its respective lamps.

1 6. The energy-conserving illumination system of claim 1 5 wherein said single high frequency power source includes a main ballast transformer for said lamps and for handling the volt amperes of all of said ballasts and lamps in said system.

1 7. The energy-conserving illumination system of claim 1 6 wherein said transformer means provides the start-up voltage of each of said lamps in said system.

1 8. The system of claim 1 wherein said high frequency power source includes a series inverter comprising at least one controllably conductive device and a diode connected in anti-parallel relationship with said at least one controllably conductive device; a capacitor and an inductor connected to one another and forming a resonant circuit which is resonant at about the frequency of said high power source; said at least one controllably conductive device connected in closed circuit relation with said capacitor and said inductor; transformer means connected in circuit relation with said resonant circuit; discharge circuit means connected to said capacitor; and inverter output amplitude control means for switching said at least one controllably conductive device on in synchronism with said resonant frequency of said capacitor and inductor; said transformer means being connected to said ballasts.

1 9. A high frequency converter comprising, in combination: a d-c input source; power switching means including control electrode means for turning on said power switching means at high speed, and producing a square wave output wave form; sine wave filter means connected in series with power switching means for producing a sinusoidal wave shape from said square wave output wave form; a load buffer network connected to said sine wave filter for connection to a load and maintaining a sinusoidal wave form over a large range of load current; a zero crossing detector circuit for producing a output pulse each time the output current of said sine wave filter goes through zero; a synchronizing circuit connected to said zero crossing detector and producing an output pulse train at the frequency of the output current of said sine wave filter means; ; a variable amplitude control circuit coupled to said control electrode means and connected to said synchronizing circuit and producing output pulses to said control electrode means at said frequency of said output current of said sine wave filter means; and control circuit means connected to said variable amplitude control circuit for control lably delaying the phasing of said output pulses of said variable amplitude control circuit relative to the current zero time of said output current of said sine wave filter means.

20. The converter of claim 1 9 wherein said control circuit means includes lamp strik ing sequence circuit means for relatively slowly increasing the output voltage of said converter when said converter is turned on.

21. - The converter of claim 1 9 wherein said control circuit means further includes converter start-up and shut-down circuit means for enabling reliable turn-on and turnoff of said converter by delaying the application of firing pulses to said control electrode means until control voltages are properly established.

22. The converter of claim 1 9 which further includes first fault detector circuit means for detecting a fault in said converter, and shut-down circuit means connected between said first fault detector circuit means and said variable amplitude control circuit for shutting down said converter in response to a fault in said converter.

23. The converter of claim 22 which further includes second fault detecter circuit means for detecting a fault in said output current of sine wave filter means and in the load circuit of said converter; and shut-down circuit means connected between said second fault detector circuit means and said variable amplitude control circuit for shutting down said converter in response to a fault in the load circuit of said converter; and manually operable reset means for resetting said converter following the operation of said second fault detector circuit means.

24. An energy conserving illumination control circuit comprising, in combination: a ballast circuit having first and second input leads; a source of input energy having a frequency in excess of about 600 Hz connected to said first and second input leads; gas-filled lamp means to be energized from said source with the current through said lamps being limited by said ballast circuit; said ballast circuit consisting of at least one capacitor and at least one inductor connected in series relationship with one another; said one capacitor and said one inductor being resonant at a frequency close to the frequency of said source and connected in circuit relation with said gas-filled lamp means; said source having a substantially continuous wave form and having a variable amplitude; said ballast circuit permitting dimming of said lamp means to less than 50% of the full lamp intensity and exhibiting a power factor of greater than about 0.8 under all dimming conditions.

25. The control circuit of claim 24 wherein said one capacitor and said one inductor are contained in a common metal container.

26. A gas discharge lamp ballast circuit comprising, in combination: a source of input a-c voltage having a relatively high frequency, first and second series-connected gas discharge lamps energized from said source of voltage; a series-connected capacitor and inductor connected in closed series relationship with said source of input a-c voltage; said capacitor connected in parallel with said at least one of said first and second gas discharge lamps; a filter capacitor connected in series with said source of input a-c voltage and said lamps; said filter capacitor having a value which substantially prevents the application of relatively low frequency power to said ballast circuit; said filter capacitor and said inductor being resonant at a frequency lower than the frequency of said source of input a-c voltage; said capacitor, said filter capacitor and said inductor being resonant at a frequency sugstantially higher than the frequency of said input a-c voltage.

27. A conjugate ballast circuit comprising, in combination: a source of input a-c voltage at a relatively high frequency; first and second series-connected gas discharge lamps; first reactive impedance means connected in parallel with said series-connected lamps; second reactive impedance means connected in series with said a-c source and with said seriesconnected lamps; a filter capacitor connected.

in series with said a-c source and said first impedance means for preventing application of relatively low frequency a-c power to said ballast; one of said first or second reactive impedances being a capacitor and the other being an inductor; said filter capacitor, said first reactive impedance and said second reactive impedance being resonant at said relatively high frequency.

28. A ballast having a T network for a first and second series-connected lamp comprising, in combination: an a-c source having a relatively high output frequency; inductor means and first and second capacitors; said first and second capacitors being connected in series with one another and in series with said a-c source and said first and second lamps; said inductor means being connected in closed series relation with said second capacitor and said series-connected lamps; said first capacitor comprising a low frequency blocking capacitor; said inductor means and said first and second capacitors being resonant at said relatively high frequency.

29. An energy-conserving illumination control system substantially as herein described with reference to, and as shown in, the accompanying drawings.

30. A high frequency converter substantially as herein described with reference to, and as shown in, the acompanying drawings.

31. A gas discharge lamp ballast circuit substantially as herein described with refer ence to, and as shown in, the accompanying drawings.

32. A conjugate ballast circuit substantially as herein described with reference to, and as shown in, the accompanying drawings.