Abstract
A new lighting fixture electronics design is disclosed that is particularly useful for lighting fixtures to utilize energy either directly from the traditional AC power grid or from locally generated renewable DC power sources. The invention entails improvement to the traditional LED driver or lighting ballast design to be able to additionally accept local DC microgrid power directly, without the need to pass the DC power through an external inverter to create an AC voltage. In this way, building construction can be commenced with a single lighting fixture that is capable to operate in multiple input modes, receiving power either from the AC grid or a DC grid, without the need for additional expense required to update the circuitry of the lighting fixtures in the building when the building is upfit at a future date with local renewable energy generating devices.
Claims
1. An electronic power conditioning device for lighting, comprising: a circuit for converting the AC input voltage to an intermediate DC voltage, a power factor correction (PFC) circuit of the wattage draw to the AC mains, and a circuit converting the intermediate DC voltage to an appropriate DC voltage for a light source, wherein the conversion from AC input voltage to an intermediate DC voltage consists of four diodes, and wherein at least two of the diodes in the circuit for converting the AC input voltage to an intermediate DC voltage are rated for current in excess of the total input wattage draw divided by the minimum rated root-mean-square voltage.
2. The electronic power conditioning device for lighting in claim 1, wherein the circuit for converting the AC input voltage to an intermediate DC voltage comprises four diodes arranged in an electrical bridge design.
3. The electronic power conditioning device for lighting in claim 1, wherein the output voltage of the circuit is DC voltage to drive the forward voltage of an LED array.
4. The electronic power conditioning device for lighting, defined in claim 1, wherein the light source is a light emitting diode (LED) array that are electrically in series-parallel configuration.
5. The electronic power conditioning device for lighting, defined in claim 1, wherein the rated AC input voltage range includes voltages in the 120 VAC-240 VAC range and for the same input circuit the rated DC input range includes any voltages in the 375 VDC to 600 VDC range.
6. The electronic power conditioning device for lighting in claim 1, wherein the input voltage to the device may be either from an alternating current or direct current source.
7. An electronic power conditioning device for lighting, comprising: a rectifier circuit for converting AC input voltage to an intermediate DC voltage, a power factor correction (PFC) circuit of the wattage draw to the AC mains, and a circuit converting the intermediate DC voltage to an appropriate DC voltage to drive the light source, and a sense circuit that detects the DC input, wherein the sense circuit connects to the input of the power factor correction circuit to provide an electrical connection when DC input voltage is present on the input connection.
8. The electronic power conditioning device for lighting in claim 7, wherein the sense circuit monitors the input leads for voltage oscillation to detect the input voltage mode.
9. The electronic power conditioning device for lighting in claim 7, wherein the sense circuit monitors the input leads for stable voltage to detect the input voltage mode.
10. The electronic power conditioning device for lighting in claim 9, wherein the sense circuit comprises a relay to electrically bypass the input rectifiers.
11. The electronic power conditioning device for lighting in claim 9, wherein the sense circuit comprises a switch to electrically bypass the input rectifiers.
12. The electronic power conditioning device for lighting in claim 7, wherein the input voltage to the device may be either from an alternating current or direct current source.
13. An electronic power conditioning device for lighting, comprising: a rectifier circuit converting AC input voltage to an intermediate DC voltage, a power factor correction (PFC) circuit of the wattage draw to the AC mains, a circuit converting the intermediate DC voltage to an appropriate DC voltage to driver the forward voltage of an LED array, a sense circuit that detects the DC input, and wherein the sense circuit electrical connects to the input of circuit converting the intermediate DC voltage to an appropriate output voltage to drive the light source, to provide the DC input detected on the input leads directly into the circuit converting the intermediate DC voltage to an appropriate DC voltage for the output.
14. The electronic power conditioning device for lighting in claim 13, wherein the output voltage of the circuit is DC voltage to drive the forward voltage of an LED array.
15. The electronic power conditioning device for lighting in claim 13, wherein the input voltage to the lighting fixture is provided from a regulated DC bus.
16. The electronic power conditioning device for lighting in claim 13, wherein the input voltage to the lighting fixture is provided from a storage battery as the source of energy.
17. The electronic power conditioning device for lighting in claim 13, wherein the circuit converting the intermediate DC voltage to an appropriate output voltage to drive the light source is electrically isolated from the input voltage.
18. The electronic power conditioning device for lighting in claim 13, wherein the input voltage to the device may be either from an alternating current or direct current source.
19. The electronic power conditioning device for lighting in claim 13, wherein the sense circuit monitors the input leads for stable voltage to detect the input voltage mode.
20. The electronic power conditioning device for lighting in claim 19, wherein the sense circuit comprises a relay to electrically bypass the input rectifiers.
21. The electronic power conditioning device for lighting in claim 19, wherein the sense circuit comprises a switch to electrically bypass the input rectifiers.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is an example of a block diagram of the electrical operation of a typical LED driver that is prior art for power conversion from AC input to DC output.
[0026] FIG. 2 is a decision tree that can be used to calculate the increased current rating required for the input diodes within the rectification circuit on the input of the driver to allow for high voltage DC input operation.
[0027] FIG. 3 is a decision tree that can be used to calculate the increased reverse voltage rating required for the input diodes within the rectification circuit on the input of the driver to allow for high voltage DC input operation.
[0028] FIG. 4 is a block diagram of an example of a sense circuit that detects the DC input and then uses a pair of relays or switches to bypass the input voltage rectifier circuit.
[0029] FIG. 5. is a block diagram of an LED driver with input capability to bypass not only the rectification circuit but the entire PFC section if the input DC sensed is from a stable source such as a battery or regulated DC bus.
DETAILED DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is an example of the electrical operation of most LED drivers that are manufactured within the lighting industry. LED drivers are used to convert the mains AC input voltage into a well-regulated DC voltage that is useful to drive LED arrays. The LEDs may be arranged electrically in series, parallel, or series parallel configurations to achieve a wide range of LED driver output voltages. The mains AC input is received by the driver by electrically connecting the line voltage (2) and the neutral wire (1) of the AC branch circuit in the building used to power the lighting fixture. The AC power is converted to a DC input through use of a rectifier that comprises a diode bridge formed such that electrons will only flow one way into the Power Factor Correction (PFC) circuit (4). Typically, there is a capacitor (5) electrically tied across the DC input leads to the PFC circuit that acts as a filter to smooth the DC voltage.
[0031] The output of the PFC circuit is called the DC Bus (6) that is a regulated DC input into the switched-mode-power-supply (SMPS) (7). The DC Bus (6) is typically in hundreds of volts DC, as it is derived from the PFC (4) conditioning the AC mains input voltage. The SMPS (7) reduces the higher voltage of the DC Bus to the appropriate voltage needed by the LEDs (8) electrically in a series, parallel, or series parallel configuration.
[0032] This invention includes the design calculation used to determine the current carrying requirement for the diodes that are needed within the diode bridge rectification circuit (3) so that the appropriate diodes may be selected for an LED driver design that can receive either high voltage AC mains input (in the range between 90 VAC and 480 VAC nominal input) or DC voltage input (120 VDC to 600 VDC). The limit for the DC input current should not be construed as to be limited to 600 VDC for this invention, as this circuit will work with thousands of volts input. However common commercial jacketed wiring used within commercial buildings for the AC mains was manufactured with a rating and testing to only 600 V. Therefore, until wiring for DC microgrids become specifically prevalent, the standard for max VDC transmission within buildings will most likely stay at 600 VDC or below.
[0033] The calculations for diode sizing need to be carried out for both AC input, and separately performed for DC input requirements. FIG. 2 illustrates the calculation requires to size the current carrying capacity of the diodes properly for the AC and DC input to the same LED driver. First, the minimum AC voltage input expected for the LED driver (10) is defined. It should be noted that this value is for the nominal AC voltage which is a root-mean-squared (RMS) value of the AC voltage. Further, the input ratings for LED drivers and electronic ballasts often account for power grid line quality variation, adding +/- 10 percent to all nominal values. Therefore, if the VAC minimum is intended to be 110 Vrms, the true value used for design is 99 Vrms. Next, the total input wattage draw of the LED driver is calculated (11) considering the conversion efficiency of the driver and the wattage required on the output of the driver by the LED array or light source. Next, to determine the current capacity that will be required of the diodes (12) the wattage draw is divided by the minimum input AC voltage, and then further divided by a factor of two. The division in half is due to the presence of two diodes conducting current for AC input voltage within the diode rectification bridge, although both diodes are only conducting for half the time. Then the minimum DC voltage that may be applied as input to the LED driver is selected (13). For example, if portions of the solar array are down for maintenance, the voltage stack-up of the array may not stay constant within the system over time. There may also be variability in the voltage output of the solar array by site due to physical configuration changes, so the intent of the LED driver design may be to accommodate a wider range of DC inputs. The max wattage draw of the driver with a DC input is determined (14) by dividing the output wattage required for the LED array by the driver efficiency to calculate the input wattage draw requirement. Then the current carrying capacity calculation of the diodes in the DC input mode (15) is the wattage draw divided by the lowest input DC voltage anticipated from the DC microgrid. After calculating the AC input amp draw (12) and the DC input amp draw (15) the two values are compared (16) to determine the highest number. The highest number between either the AC or DC operation mode is used (17) to specify the current rating of the diode needed for the single diode rectification circuit employed for both AC and DC input modes.
[0034] FIG. 3 is a demonstration of the calculation used to determine the Reverse Peak-Voltage rating of at least 2 of the 4 diodes employed within the diode rectification circuit. For diodes, the reverse peak voltage is a rating to denote the amount of voltage that the diode will need to withstand when experiencing a reverse bias in the circuit. While on might assume this only applies to the circuit when in AC input mode, this is a concern for DC input mode as well, as the installer may accidentally flip polarity on the input leads for the DC input. Without the proper rating, this could damage the diodes if not rated with a high enough reverse voltage peak. For sizing the AC reverse voltage peak, first it is needed to select the maximum mains input (40) from the input voltage range expected for the lighting fixture. If the maximum voltage selected in a nominal voltage, then to account for variation on the power grid an adder of 10% may also be added to the value. Then, as these AC voltages are commonly expressed in RMS voltage terms, the peak value is calculated by multiplying by the square-root of 2. For example, if a light fixture intends to have the top of the nominal AC input range as 277 VAC, then accounting for power grid variation gives a design value of 305 VAC. To convert 305 AC to a peak value requires multiplying by 1.414, which gives a voltage peak value of 431 V. For DC input mode, the maximum VDC anticipated for the LED driver (43) should be selected. Typically, this could be up to 600 VDC if employing common commercial building wiring infrastructure, although with usage of bus bars or other techniques could be at thousands of volts. The maximum input volts anticipated from the local DC microgrid is equivalent to the voltage peak value anticipated (44) for peak reverse voltage calculation. Next, comparing the two calculated voltage peak values (45) is performed to select the highest peak voltage (47) to set the minimum reverse voltage rating for at least 2 of the 4 diodes in the rectification bridge circuit.
[0035] FIG. 4 is a of an example of an updated diode rectification bridge, using the calculations from FIG. 2 and FIG. 3 to size the diodes (21,22) appropriately to be able to accommodate either AC voltage mains input or a high voltage DC microgrid input. FIG. 4 also illustrates a sensing circuit (20) that detects the DC input and then uses a pair of relays or switches to bypass the input voltage rectifier circuit. The two voltage input lines (23,24) are used for dual mode input, either AC or DC voltage into the circuit. In AC input mode the AC line (23) and the AC neutral (24) are connected electrically to the driver. When operating in DC mode, one of the input lines (23,24) may be connected to high voltage DC (positive polarity) and the other to high voltage DC (negative polarity). The bridge bypass circuit (20) functions to monitor the voltage across the input AC line (26) and the input AC neutral connection (33) for the presence of oscillating voltage. If the bypass sense circuit (20) senses voltage without oscillation, the circuit will direct the voltage directly into the PFC circuit (4) and the filter capacitor (27). This bypass then increases the efficiency by bypassing the losses of the rectification diode bridge (3).
[0036] FIG. 5 is an alternate embodiment where the bridge-and-PFC bypass circuit (35) is connected to the input leads (23,24) of the LED driver circuit, to monitor voltage at prior to input into the rectification to monitor the voltage across the input AC line (26) and the input AC neutral connection (33) for the presence of oscillating voltage. If the bridge-and-PFC bypass circuit (35) senses voltage without oscillation, the circuit will determine the voltage is coming directly from the local DC microgrid as a well-regulated DC source and connect electrically directly to the internal DC bus (36) of the driver across the positive and negative DC connections (34,35) out of the PFC circuit. In this way, the local DC microgrid voltage becomes the internal DC bus (36) voltage and is fed directly into the SMPS circuit (7).
