Title: Three-phase electronic ballast
Abstract: A ballast (10) for powering at least one gas discharge lamp (52) from a three-phase AC voltage source (30) comprises a three-phase rectifier circuit (200), a high frequency filter capacitor (300), and a high frequency inverter (400). Preferably, three-phase rectifier circuit (200) is implemented by a six-diode bridge, and high frequency filter capacitor (300) can be realized by a film capacitor or a ceramic capacitor. Ballast (10) provides a high power factor and low total harmonic distortion without requiring a dedicated power factor correction circuit. Other benefits of ballast (10) include enhanced efficiency, longer life, and lower inrush current.
Patent Number: 6,906,474 Issued on 06/14/2005 to Trestman, et al.
| Inventors:
|
Trestman; Grigoriy A. (Salem, MA);
Parisella; Joseph L. (Beverly, MA);
Koeppl; Richard H. (Topsfield, MA)
|
| Assignee:
|
Osram Sylvania, Inc. (Danvers, MA)
|
| Appl. No.:
|
674143 |
| Filed:
|
September 29, 2003 |
| Current U.S. Class: |
315/224; 315/251; 315/DIG.5; 363/44 |
| Intern'l Class: |
H05B 037/00 |
| Field of Search: |
315/224,251,219,DIG.5,DIG.7
363/44,89
|
References Cited [Referenced By]
U.S. Patent Documents
| 6043997 | Mar., 2000 | He et al.
| |
| 6343021 | Jan., 2002 | Williamson.
| |
| 2004/0085032 | May., 2004 | Eckert.
| |
Primary Examiner: Vu; David
Attorney, Agent or Firm: Labudda; Kenneth D.
Claims
1. A ballast for powering at least one gas discharge lamp, comprising:
a three-phase rectifier circuit operable to receive a three-phase alternating
current (AC) voltage source and to provide a rectified output voltage, wherein
the rectified output voltage has a maximum value, a minimum value, an average value,
and a ripple value, wherein the ripple value is the difference between the maximum
value and the minimum value, and the root-mean-square (RMS) value of the ripple
is no greater than about 5% of the average values;
a high frequency filter capacitor coupled to the rectifier circuit; and
a high frequency inverter coupled to the rectifier circuit and the high frequency
filter capacitor, wherein the inverter is operable to power the at least one gas
discharge lamp.
2. A ballast for powering at least one gas discharge lamp, comprising:
a three-phase rectifier circuit operable to receive a three-phase alternating
current (AC) voltage source and to provide a rectified output voltage;
a high frequency filter capacitor coupled to the rectifier circuit;
a high frequency inverter coupled to the rectifier circuit and the high frequency
filter capacitor, wherein the inverter is operable to power the at least one gas
discharge lamp; and
a three-phase electromagnetic interference (EMI) filter interposed between the
three-phase rectifier circuit and the three-phase AC voltage source, wherein the
three-phase EMI filter comprises:
a first input connection adapted to receive a first phase of the three-phase
AC voltage source;
a second input connection adapted to receive a second phase of the three-phase
AC voltage source;
a third input connection adapted to receive a third phase of the three-phase
AC voltage source;
a fourth input connection adapted to receive a ground of the three-phase AC voltage
source;
a first inductor coupled between the first input connection and the first input
terminal of the rectifier circuit;
a second inductor coupled between the second input connection and the second
input terminal of the rectifier circuit;
a third inductor coupled between the third input connection and the third input
terminal of the rectifier circuit;
a first capacitor coupled between the first and second input terminals of the
rectifier circuit;
a second capacitor coupled between the second and third input terminals of the
rectifier circuit; and
a third capacitor coupled between the fourth input connection and the second
input terminal of the rectifier circuit.
3. A ballast for powering at least one gas discharge lamp, comprising:
a rectifier circuit adapted to receive a three-phase alternating current (AC)
voltage source, the rectifier circuit comprising:
a first input terminal for receiving a first phase of the three-phase AC voltage
source;
a second input terminal for receiving a second phase of the three-phase AC voltage
source;
a third input terminal for receiving a third phase of the three-phase AC voltage
source;
first and second output terminals;
a first diode having an anode coupled to the first input terminal and a cathode
coupled to the first output terminal;
a second diode having an anode coupled to the second output terminal and a cathode
coupled to the first input terminal;
a third diode having an anode coupled to the second input terminal and a cathode
coupled to the first output terminal;
a fourth diode having an anode coupled to the second output terminal and a cathode
coupled to the second input terminal;
a fifth diode having an anode coupled to the third input terminal and a cathode
coupled to first output terminal; and
a sixth diode having an anode coupled to the second output terminal and a cathode
coupled to the third input terminal;
a high frequency filter capacitor coupled between the first and second output
terminals of the rectifier circuit;
an inverter coupled to the first and second output terminals of the rectifier
circuit, wherein the inverter is operable to power the at least one gas discharge
lamp, the inverter having an operating frequency that is greater than about 20,000
hertz; and
a three-phase electromagnetic interference (EMI) filter coupled between the three-phase
AC voltage source and the input terminals of the rectifier circuit, wherein the
three-phase EMI filter comprises:
a first input connection adapted to receive the first phase of the three-phase
AC voltage source;
a second input connection adapted to receive the second phase of the three-phase
AC voltage source;
a third input connection adapted to receive the third phase of the three-phase
AC voltage source;
a fourth input connection adapted to receive a ground of the three-phase AC voltage
source;
a first inductor coupled between the first input connection and the first input
terminal of the rectifier circuit;
a second inductor coupled between the second input connection and the second
input terminal of the rectifier circuit;
a third inductor coupled between the third input connection and the third input
terminal of the rectifier circuit;
a first capacitor coupled between the first and second input terminals of the
rectifier circuit;
a second capacitor coupled between the second and third input terminals of the
rectifier circuit; and
a third capacitor coupled between the fourth input connection and the second
input terminal of the rectifier circuit.
4. A ballast for powering at least one gas discharge lamp, comprising:
a rectifier circuit adapted to receive a three-phase alternating current (AC)
voltage source, the rectifier circuit comprising:
a first input terminal for receiving a first phase of the three-phase AC voltage
source;
a second input terminal for receiving a second phase of the three-phase AC voltage
source;
a third input terminal for receiving a third phase of the three-phase AC voltage
source;
first and second output terminals;
a first diode having an anode coupled to the first input terminal and a cathode
coupled to the first output terminal;
a second diode having an anode coupled to the second output terminal and a cathode
coupled to the first input terminal;
a third diode having an anode coupled to the second input terminal and a cathode
coupled to the first output terminal;
a fourth diode having an anode coupled to the second output terminal and a cathode
coupled to the second input terminal;
a fifth diode having an anode coupled to the third input terminal and a cathode
coupled to first output terminal; and
a sixth diode having an anode coupled to the second output terminal and a cathode
coupled to the third input terminal, wherein the rectifier circuit is operable
to provide a rectified output voltage between the first and second output terminals,
the rectified output voltage having a maximum value, a minimum value, an average
value, and a ripple value, wherein the ripple value is the difference between the
maximum value and the minimum value, and the root-mean-square (RMS) value of the
ripple is no greater than about 5% of the average value;
a high frequency filter capacitor coupled between the first and second output
terminals of the rectifier circuit; and
an inverter coupled to the first and second output terminals of the rectifier
circuit, wherein the inverter is operable to power the at least one gas discharge
lamp, the inverter having an operating frequency that is greater than about 20,000
hertz.
5. The ballast of claim 4, wherein the ballast is operable to draw a line current
from each phase of the three-phase AC voltage source, the line current drawn from
each phase of the three-phase AC voltage source having a total harmonic distortion
(THD) that is no greater than about 33%.
6. The ballast of claim 5, wherein the ballast is operable to provide a power
factor (PF) that is no less than about 0.9.
7. A ballast for powering at least one gas discharge lamp from a three-phase
alternating current (AC) voltage source, comprising:
a three-phase electromagnetic interference (EMI) filter, comprising:
a first input connection adapted for coupling to the first phase of the three-phase
AC voltage source;
a second input connection adapted for coupling to the second phase of the three-phase
AC voltage source;
a third input connection adapted for coupling to the third phase of the three-phase
AC voltage source; and
a fourth input connection adapted for coupling to a ground of the three-phase
AC voltage source;
a rectifier circuit, comprising:
first, second, and third input terminals coupled to the three-phase EMI filter;
first and second output terminals;
a first diode having an anode coupled to the first input terminal and a cathode
coupled to the first output terminal;
a second diode having an anode coupled to the second output terminal and a cathode
coupled to the first input terminal;
a third diode having an anode coupled to the second input terminal and a cathode
coupled to the first output terminal;
a fourth diode having an anode coupled to the second output terminal and a cathode
coupled to the second input terminal;
a fifth diode having an anode coupled to the third input terminal and a cathode
coupled to the first output terminal; and
a sixed diode having an anode coupled to the second output terminal and a cathode
coupled to the third input terminal;
a high frequency filter capacitor coupled between the first and second output
terminals of the rectifier circuit; and
an inverter coupled to the first and second output terminals of the rectifier
circuit, wherein the inverter is operable to power the at least one gas discharge
lamp, the inverter having an operating frequency that is greater than about 20,000
hertz.
8. The ballast of claim 7, wherein:
the high frequency filter capacitor is one of:
a film capacitor; and
a ceramic capacitor; and
the high frequency filter capacitor has a capacitance that is on the order of
about 0.1 microfarads.
9. The ballast of claim 8, wherein the three-phase EMI filter further comprises:
a first inductor coupled between the first input connection and the first input
terminal of the rectifier circuit;
a second inductor coupled between the second input connection and the second
input terminal of the rectifier circuit;
a third inductor coupled between the third input connection and the third input
terminal of the rectifier circuit;
a first capacitor coupled between the first and second input terminals of the
rectifier circuit;
a second capacitor coupled between the second and third input terminals of the
rectifier circuit; and
a third capacitor coupled between the second input terminal of the rectifier
circuit and the fourth input connection of the three-phase EMI filter.
10. The ballast of claim 9, wherein:
the rectifier circuit is operable to provide a rectified output voltage between
the first and second output terminals, the rectified output voltage having a maximum
value, a minimum value, an average value, and a ripple value, wherein the ripple
value is the difference between the maximum value and the minimum value, and the
root-mean-square (RMS) value of the ripple is no greater than about 5% of the average
value; and
the ballast is operable to:
(i) draw a line current from each phase of the three-phase AC voltage source,
wherein the line current drawn from each phase of the AC source has a total harmonic
distortion (THD) that is no greater than about 33%; and
(ii) provide a power factor (PF) that is no less than about 0.9.
Description
FIELD OF THE INVENTION
The present invention relates to the general subject of circuits for powering
discharge lamps. More particularly, the present invention relates to a three-phase
electronic ballast.
BACKGROUND OF THE INVENTION
In recent years, electronic ballasts have begun to displace traditional "core
and coil" magnetic ballasts. In comparison with magnetic ballasts, electronic ballasts
provide a host of benefits, including dramatically higher energy efficiency and
better quality of illumination (e.g., little or no visible flicker in the light
emitted by the lamp). On the other hand, magnetic ballasts are usually less expensive
and more reliable than electronic ballasts.
A typical prior art single-phase electronic ballast is described in FIG. 1.
The ballast includes a 1-phase electromagnetic interference (EMI) filter, a fullwave
diode bridge BR1, a power factor correction (PFC) circuit, an electrolytic
capacitor C1, and a high frequency inverter. The ballast receives operating
power from a single-phase alternating current (AC) voltage source. The DC bus voltage,
Vbus, across capacitor C1 is described in FIG. 2.
In the prior art ballast of FIG. 1, the PFC circuit, which is typically realized
by a controlled DC-to-DC converter such as a boost converter, is required in order
to ensure that the power factor (PF) is high enough, and that the total harmonic
distortion (THD) in the current drawn from the AC voltage source is low enough,
to meet applicable standards for power quality. Without a PFC circuit, the PF would
be much too low (e.g., about 0.5) and the THD would be much too high (e.g., about
150%). Unfortunately, a dedicated PFC circuit is materially expensive, requires
a considerable amount of physical space, and has power losses that detract from
the energy efficiency of the ballast.
In the prior art ballast of FIG. 1, the large electrolytic bulk capacitor C1
is necessary in order to ensure that the amount of ripple (ΔV in FIG. 2)
in Vbus is sufficiently small so as to prevent excessive low frequency (e.g., 120
hertz) flicker in the illumination provided by the lamp(s). Typically, the electrolytic
capacitor has a high capacitance (e.g., 47 microfarads or higher) and a high voltage
rating (e.g., 250 volts or higher), and is therefore quite large. Additionally,
a high value bulk capacitor causes correspondingly high levels of inrush current.
Perhaps the greatest disadvantage of using electrolytic bulk capacitors is encountered
in those ballasts that operate in high ambient temperature environments, in which
case the ballast's operating life is largely determined by the useful operating
life of the electrolytic capacitor (which decreases by a factor of two for every
10° C. increase in operating temperature). Thus, significant impetus exists
for developing ballast circuits that do not require electrolytic bulk capacitors.
FIG. 3 describes a typical grouping scheme that is desirable in industrial/office
buildings having lighting fixtures that employ single-phase electronic ballasts
like the ballast of FIG. 1. In order to equalize the loading on each phase
of the 3-phase AC voltage source, it is necessary that the fixtures be divided
into groups wherein each group draws about the same amount of power from the AC
voltage source. As such a grouping scheme requires that the building be wired so
that each of the three phases are distributed accordingly, it greatly complicates
the building wiring.
What is needed, therefore, is an electronic ballast that does not require a
dedicated PFC circuit or an electrolytic bulk capacitor in order to provide acceptable
power quality and illumination without noticeable flicker. A need also exists for
a ballast that does not require grouping of lighting fixtures within a building
so as to equalize the loading on each phase of the AC voltage source. Such a ballast
would offer a number of benefits over existing electronic ballasts, including lower
material cost, reduced physical size, higher energy efficiency, enhanced life,
lower inrush current, and simplified building wiring, and would thus represent
a significant advance over the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 describes a single-phase electronic ballast, in accordance with the prior art.
FIG. 2 describes the DC bus voltage provided by the single-phase electronic
ballast of FIG. 1.
FIG. 3 describes a typical grouping scheme for lighting fixtures that employ
the single-phase electronic ballast of FIG. 1.
FIG. 4 describes a three-phase electronic ballast, in accordance with a preferred
embodiment of the present invention.
FIG. 5 describes the DC bus voltage provided by the three-phase electronic ballast
described in FIG. 4, in accordance with a preferred embodiment of the present invention.
FIG. 6 describes a group of lighting fixtures that employ the threephase electronic
ballast described in FIG. 4, in accordance with a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A ballast
10 for powering at least one gas discharge lamp
52 from
a three-phase alternating current (AC) voltage source
30 is described in
FIG.
4. Ballast
10 comprises a three-phase rectifier circuit
200,
a high frequency filter capacitor
300, and a high frequency inverter
400.
Three-phase AC voltage source
30 is a conventional 60 hertz voltage source
that is provided by the electrical utility company.
In a preferred embodiment of ballast
10, three-phase rectifier circuit
200 comprises a first input terminal
202, a second input terminal
204, a third input terminal
206, a first output terminal
212,
a second output terminal
214, a first diode
220, a second diode
230,
a third diode
240, a fourth diode
250, a fifth diode
260,
and a sixth diode
270. First input terminal
202 is adapted to receive
a first phase
32 of three-phase AC voltage source
30. Second input
terminal
204 is adapted to receive a second phase
34 of source
30.
Third input terminal is adapted to receive a third phase
36 of AC source
30. First diode
220 has an anode
222 coupled to first input
terminal
202 and a cathode
224 coupled to first output terminal
212.
Second diode
230 has an anode
232 coupled to second output terminal
214 and a cathode
243 coupled to first input terminal
202.
Third diode
240 has an anode
242 coupled to second input terminal
204 and a cathode
244 coupled to first output terminal
212.
Fourth diode
250 has an anode
252 coupled to second output terminal
214 and a cathode
254 coupled to second input terminal
204.
Fifth diode
260 has an anode
262 coupled to third input terminal
206 and a cathode
264 coupled to first output terminal
212.
Sixth diode
270 has an anode
272 coupled to second output terminal
214 and a cathode
274 coupled to third input terminal
206.
During operation, rectifier circuit
200 receives the three-phase alternating
current (AC) voltage source
30 and provides a rectified output voltage.
As described in FIG. 5, the rectified output voltage, Vbus, has a maximum value,
a minimum value, an average value (Vavg), and a ripple value (ΔV). In ballast
10, the ripple value (ΔV), which is defined as the difference between
the maximum value and the minimum value, has a root-mean-square (RMS) value that
is no greater than about 5% of the average value Vavg. Advantageously, rectifier
circuit
200 utilizes all three phase
32,
34,
36 of the
AC source
30 to provide a Vbus that naturally has a small amount of 360
hertz ripple and that therefore requires no-capacitive filtering in order to provide
an acceptably low level of visible flicker in the illumination of the lamp(s).
This is in contrast with the prior art ballast of FIG. 1 where, in the absence
of a large electrolytic capacitor C
1, the 120 hertz ripple would be extremely
high, with consequent excessive flicker in the illumination of the lamp(s).
Referring to FIG. 4, high frequency filter capacitor
300 is coupled
between the first and second output terminals
212,
214 of rectifier
circuit
200. The sole function of capacitor
300 is to provide an
AC path for high frequency current drawn by inverter
400. Capacitor
300
can thus be realized by a capacitor with a relatively low capacitance value (e.g.,
0.1 microfarads when ballast
10 is designed to power four 32 watt lamps).
Consequently, capacitor
300 can be implemented by a film capacitor or a
ceramic capacitor. Advantageously, because ballast
10 does not require an
electrolytic bulk capacitor, its operating life will be substantially greater than
the prior art ballast described in FIG. 1, if the ballast is operated in a high
ambient temperature environment. Moreover, because of the relatively low capacitance
of capacitor
300, the amount of inrush current that occurs in ballast
10
will be dramatically less than what occurs in the prior art ballast described in
FIG.
1.
High frequency inverter
400 is coupled to rectifier circuit
200
and high frequency filter capacitor
300. During operation, inverter
400
powers at least one gas discharge lamp
52 and has an operating frequency
that is greater than about 20,000 hertz. In general, inverter
400 includes
a plurality of output terminals
40,
42,
44, . . . ,
48
for connection to a plurality of discharge lamps
52,
54, . . . ,
58.
Inverter
400 may be realized by any of a number of circuit arrangements
(e.g., a half-bridge inverter followed by a series resonant output circuit) that
are well known to those skilled in the art of electronic ballasts.
During operation of ballast
10, the line current that is drawn from
each phase
32,
34,
36 of AC source
30 has a total harmonic
distortion (THD) that is no greater than about 33%. Additionally, as the line current
drawn from each phase is only moderately out of phase with the voltage between
each phase and ground
38, ballast
10 provides a power factor (PF)
that is no less than about 0.9. Thus, ballast
10 is capable of approaching
or meeting applicable standards for power quality without requiring an active power
factor correction (PFC) circuit such as a boost converter. Consequently, in comparison
with the prior art electronic ballast described in FIG. 1, ballast
10 provides
the added benefits of lower material cost, smaller physical size, and enhanced
energy efficiency (e.g., 94% versus about 88% for the ballast of FIG.
1).
Preferably, as described in FIG. 4, ballast
10 further comprises
a three-phase electromagnetic interference (EMI) filter
100 that is interposed
between rectifier circuit
200 and three-phase AC voltage source
30.
During operation, three-phase EMI filter
100 attenuates any line-conducted
EMI that tends to arise due to the high frequency operation of inverter
400.
In a preferred embodiment of ballast
10, three-phase EMI filter comprises
first, second, third, and fourth input connections
22,
24,
26,
28,
first, second, and third inductors
102,
104,
106, and first,
second, and third capacitors
112,
114,
120. First input connection
22 is adapted to receive a first phase
32 of three-phase AC voltage
source
30. Second input connection is adapted to receive a second phase
of source
30. Third input connection is adapted to receive a third phase
of source
30. Fourth input connection is adapted to receive a ground
38
of source
30. A neutral
37 of source
30 has no corresponding
connection to ballast
10. First inductor
102 is coupled between first
input connection
22 and the first input terminal
202 of rectifier
circuit
200. Second inductor
104 is coupled between second input
connection
24 and the second input terminal
204 of rectifier circuit
200. Third inductor
106 is coupled between third input connection
26 and the third input terminal
206 of rectifier circuit
200.
First capacitor
112 is coupled between the first and second input terminals
202,
204 of rectifier circuit
200. Second capacitor
114
is coupled between the second and third input terminals
204,
206 of
rectifier circuit
200. Third capacitor
120 is coupled between fourth
input connection
28 and the second input terminal
204 of rectifier
circuit
200.
Turning now to FIG. 6, it can be seen that ballast
10 allows for installations
in which all of the fixtures in a building are wired to the AC source
30
in an identical manner. This is in contrast to the arrangement described in FIG.
3, where the fixtures must be segregated into three groups in order to equalize
the loading on each phase of the AC source. Thus, ballast
10 provides the
added benefit of simplifying the electrical wiring that is routed to the lighting
fixtures within a building.
Although the present invention has been described with reference to certain
preferred embodiments, numerous modifications and variations can be made by those
skilled in the art without departing from the novel spirit and scope of this invention.
*
