CN116965158A - Emergency lighting system - Google Patents

Abstract

An emergency power system (100) and an emergency lighting dimming method are disclosed. The emergency power system (100) comprises a power source (10), a tangential waveform generator (11, 13, 300, 310, 311, 400, 410, 411) coupled to the power source (10) and arranged to provide a tangential waveform (fig. 2 and 3) to a load (12). The load may be one or more emergency lighting devices. The feedback detection module (14, 201) may be used to monitor voltage and/or current data provided to the load (12) by the phase-cut waveform generator. The controller (13, 202-205) controls the phase-cut waveform generator (11, 13, 300, 310, 311, 400, 410, 411) to adjust the power level of the load (12) by modifying the phase-cut waveform based on the monitored voltage and/or current data and the reference data to achieve an appropriate dimming level.

Description

Emergency lighting system

Technical Field

The present invention relates to systems and methods for providing emergency lighting, and more particularly to an emergency lighting system including a phase-cut waveform generator that may use a dimming unit to control a lighting device using electrical load feedback from the lighting device.

Background

An emergency backup power system is required to provide temporary emergency lighting when a power outage/outage occurs. Conventional backup power systems may include an uninterruptible power supply (or UPS) to provide emergency power to a load in the event of a failure of an input power source (e.g., mains). Battery powered run times of UPSs are limited and therefore efficient use of emergency power is important. It should be noted that inverter battery backup systems are also commonly used in emergency lighting systems.

Emergency lighting refers to lighting that is activated upon a power outage. The purpose of emergency lighting is to allow occupants of a building to safely leave the building in the event of a power outage or other emergency. Within a building, emergency lighting is typically provided by emergency lighting devices (e.g., LEDs or fluorescent lights) powered by an emergency back-up power system. A battery pack may also be provided in the emergency lighting device.

Conventional emergency backup inverter systems are known to provide dimming level power to operate normal lamp drivers as well as dimming signals. The dimming signal is a separate dimmer input provided to the lamp driver to reduce the light level. Conventional types of dimmer signals include 0-10V and DALI. Signals are transmitted between 1V and 10V using 1-10V dimming techniques. 10V is the maximum (100%), 1V is the minimum (the exact percentage of dimming may vary). The light output of the luminaire is scaled such that a voltage of 10V provides 100% light output and 0V provides the minimum light output. With DALI (digital addressable lighting interface) dimming technology, each system consists of a controller and a maximum of 64 lighting components, such as ballasts. Each of these lighting components has a unique address. The controller may control these lighting components because the DALI system may transmit and receive dimming signals.

A system for dimming output power using a dimming signal is described in US2017/003598A1, which is incorporated herein by reference.

Conventional lighting devices such as DoB LEDs, screw-mount LEDs, CFLs, and (without limitation) direct AC input TLEDs are common in the lighting market. A DoB (vehicle-mounted driver) LED including a vehicle-mounted module may be used as the LED light source. The DoB LED module uses solid state electronics. Screw-mount LEDs and CFLs are LEDs or compact fluorescent lamps designed to replace incandescent bulbs and to be installed into fixtures designed for incandescent bulbs. Tubular LED lamps (TLEDs) are designed to retrofit existing fluorescent fixtures with LED lighting. Some TLED retrofit lamps have an internal driver that can accept AC input through the original fluorescent ballast or through a connection to the line voltage. Some of these retrofit LED lamps are dimmable, but they have no separate dimming signal input unless they are "intelligent LEDs".

In order to provide dimming capabilities to a lighting device that does not include a separate dimming signal input, another conventional approach may be used if the lighting device is compatible with this type of dimming. In the method, the emergency inverter comprises a programmable control unit for reducing the power supplied to the lighting device in an emergency state. When the emergency inverter is initially activated, the power level must be determined based on: (1) a rated output power of the emergency inverter, (2) a number of lighting device drivers connected to the emergency inverter, and (3) characteristics of the lighting device drivers. The programmable control unit is preset by the user to a determined power level to ensure that the total power usage of the emergency lighting device remains within the rated power of the emergency inverter/power supply. Although this method does not require a separate dimming signal input, the preset nature of the programmable control unit is inconvenient for the user. Furthermore, if the electrical load requirements change, for example if the characteristics or number of emergency lighting devices change, the preset power level in the programmable control unit has to be recalculated and reset, which increases the workload and time costs.

The conventional emergency lighting system described above has two major problem drawbacks. First, if the emergency lighting device does not include a separate dimming signal input, the 0-10V or DALI dimming control signal cannot be used to dim the emergency lighting device to save power from the emergency inverter/power supply. Second, even if the emergency inverter is equipped with a programmable control unit having a preset power level, any change to the emergency lighting system will incur additional effort and time for the user.

This document describes systems and methods that aim to address at least some of the problems discussed above and/or other problems discussed below.

Disclosure of Invention

Aspects and embodiments of the present invention address one and/or both of the above disadvantages.

One aspect of the present invention relates to an improved method of using an emergency lighting driver/inverter having dimming capabilities using a phase-cut dimming scheme.

Other aspects of the invention utilize different methods to create a wave output with a tangent waveform, including creating a tangent waveform from a wave and creating a tangent waveform from the SPWM. The wave may be, for example, a sine wave, a rectangular wave, or a triangular wave.

One embodiment of the invention relates to an emergency power system comprising a power source and a phase-cut waveform generator coupled to an output of the power source and arranged to provide a phase-cut waveform to a load. The load may be one or more emergency lighting devices. The detection module is used for monitoring the voltage and/or current provided to the load by the phase-cut waveform generator. The controller controls the phase-cut waveform generator to adjust/reduce the power level of the load by modifying the phase-cut waveform based on the monitored voltage and/or current data and the reference data.

Another embodiment of the invention relates to a method for dimming an emergency lighting device. The method comprises the following steps: measuring a load voltage and current of the emergency lighting device, comparing the reference dimming data with the measured load voltage and current, and determining a dimming control signal based on the comparison. The method further includes the step of generating a phase-cut waveform based on the control signal to reduce the load voltage and current of the emergency lighting device. The tangent waveform may be generated by the SPWM.

Yet another embodiment of the invention relates to an emergency power system comprising a power source and a phase-cut waveform generator comprising a wave generator coupled to an output of the power source and arranged to provide a phase-cut waveform to a load. The tangent waveform generator is configured with a preset power level (which is not user controllable or settable) to be provided to the load.

It is to be understood that all combinations of the above concepts and additional concepts discussed in more detail below (as long as such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are considered part of the inventive subject matter disclosed herein. It will also be understood that terms used specifically herein (which may also be present in any disclosure incorporated by reference) should be given the meanings most consistent with the specific concepts disclosed herein.

Drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. In the drawings, elements corresponding to elements already described may have the same reference numerals. In the drawings of which there are shown,

figure 1 schematically illustrates elements of an emergency lighting system according to one embodiment of the invention,

figure 2 shows a leading edge tangent waveform,

figure 3 shows a trailing edge tangent waveform,

figure 4 shows a block diagram for creating a tangent waveform from a sine wave,

figure 5 shows a block diagram of creating a tangent waveform from the SPWM,

figure 6 shows a leading edge tangent waveform created from a sine wave,

figure 7 shows a trailing edge tangent waveform created from a sine wave,

figure 8 shows a leading edge tangent waveform created from the SPWM,

figure 9 shows a trailing edge tangent waveform created from the SPWM,

fig. 10 schematically illustrates one embodiment of a dimmer controller according to another embodiment of the present invention, an

Fig. 11 is a flowchart of a dimming method according to another embodiment of the present invention.

Detailed Description

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will herein be described in detail, one or more specific embodiments, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, and is not intended to limit the invention to the specific embodiments illustrated and described.

Hereinafter, for understanding, elements of the embodiments are described in operation. However, it will be apparent that the various elements are arranged to perform the functions described as being performed by them.

As used herein for purposes of this disclosure, the term "load" refers to an electronic device that draws current from a power source. Examples of loads may include lighting devices such as resistive incandescent lamps, halogen lamps, compact fluorescent Light Emitting Diodes (LEDs), and lamp drivers.

The term "dimming" refers to reducing the power applied to a load, such as reducing the brightness of a lamp by changing/chopping the voltage waveform or reducing the current of an AC power supply applied to the load, or reducing the voltage of a DC power supply applied to the lighting.

The term "LED" should be understood to include any electroluminescent diode or other type of carrier injection/junction based system capable of generating radiation in response to an electrical signal. Thus, the term LED includes, but is not limited to, various semiconductor-based structures that emit light in response to an electrical current, light emitting polymers, organic Light Emitting Diodes (OLEDs), electroluminescent strips, and the like. In particular, the term LED refers to all types of light emitting diodes (including semiconductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the various portions of the infrared, ultraviolet, and visible spectrums (typically including radiation wavelengths from about 400 nanometers to about 700 nanometers). Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below). It should also be appreciated that LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full width half maximum or FWHM) for a given spectrum (e.g., narrow bandwidth, wide bandwidth), as well as radiation having various dominant wavelengths within a given general color classification.

It should also be understood that the term LED is not limited to the physical and/or electrical packaging type of the LED. For example, as described above, an LED may refer to a single light emitting device having multiple dies configured to emit different spectra of radiation, respectively (e.g., may or may not be individually controllable). Further, LEDs may be associated with phosphors that are considered to be an integral part of the LED (e.g., some types of white LEDs). In general, the term LED may refer to packaged LEDs, non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mounted LEDs, radial package LEDs, power package LEDs, LEDs that include some type of housing and/or optical element (e.g., a diffusing lens), and the like.

The term "light source" is understood to mean any one or more of a variety of radiation sources, including, but not limited to, LED-based light sources (including one or more LEDs as defined above), incandescent light sources (e.g., incandescent lamps, halogen lamps), fluorescent sources, phosphor light sources, high intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyrolytic light sources (e.g., flames), candle light sources (e.g., gas masks, carbon arc radiation sources), photoluminescent sources (e.g., gas discharge sources), cathode light sources using electron saturation, electric current light sources, crystal light sources, kine light sources, thermal light sources, triboluminescent sources, acoustic light sources, radioactive light sources, and luminescent polymers.

The term "lighting fixture or device" is used herein to refer to the implementation or arrangement of one or more lighting units in a particular form factor, component, or package. The term "lighting unit" is used herein to refer to a device comprising one or more light sources of the same or different types. A given lighting unit may have any one of the following: various mounting arrangements for the light source(s), housing/case arrangements and shapes, and/or electrical and mechanical connection configurations. Further, a given lighting unit may optionally be associated with (e.g., include, be coupled with, and/or be packaged with) various other components related to the operation of the light source(s) (e.g., control circuitry). "LED-based lighting unit" refers to a lighting unit comprising one or more LED-based light sources as described above, alone or in combination with other non-LED-based light sources.

The term "controller" or "module" is generally used herein to describe a structure or circuitry that can be implemented in a variety of ways (e.g., such as using dedicated hardware and/or software) to perform the various functions discussed herein. A "processor" is one example of a controller (or central component of a controller) that employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the various functions discussed herein. A controller may be implemented with or without a processor, or as a combination of dedicated hardware performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) performing other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application Specific Integrated Circuits (ASICs), and Field Programmable Gate Arrays (FPGAs).

Furthermore, the invention is not limited to the embodiments, and the invention lies in each and every novel feature or combination of features described herein or recited in mutually different dependent claims.

FIG. 1 illustrates one example of an Emergency Lighting System (ELS) 100 according to one embodiment. The ELS100 includes an emergency power supply 10. The emergency power supply 10 may be configured using various components such as an Uninterruptible Power Supply (UPS) (not shown). The UPS may be connected to an active input AC power source (not shown). Other options for the emergency power supply 10 include an engine-driven generator or inverter and a battery system. The output emergency power supply 10 is connected to an H-bridge 11. The H-bridge 11 comprises a switch (not shown) controlling the power to the load 12. In this embodiment, the load 12 is one or more emergency lighting fixtures, such as LED-based lighting units. The H-bridge 11 receives a Pulse Width Modulation (PWM) signal from a controller 13 to regulate the power provided to the load 12. The feedback loop may be created using the detection module 14. The detection module 14 monitors the power provided to the load 12 so that the power provided to the load 12 can be regulated by the controller 13.

Various embodiments relating to the control/regulation of the power provided to the load 12 will now be discussed with reference to fig. 2-9. One aspect of the present invention is to produce a sine wave output with a tangent waveform. Of course, it should be understood that other types of waves may be used, such as rectangular waves or triangular waves. The waveform may be the leading edge shown in fig. 2 or the trailing edge shown in fig. 3. The sine wave output with a tangential waveform varies the output power by varying the supply voltage. Reducing the output power provided to the load 12 creates dimming in the emergency lighting fixture. In the illustrated embodiment, chopping of the sine wave enables dimming of the AC output to load 12 so that the necessary illumination periods and outputs required for the safety outlet during emergency standby and AC power loss conditions can be maintained.

In various embodiments of the present invention, different methods may be used to create a sine wave output with a tangent waveform, including creating a tangent waveform from a sine wave and creating a tangent waveform from the SPWM.

As will be appreciated by those of ordinary skill in the art, the term SPWM means "sinusoidal pulse width modulation" and is a pulse width modulation technique used in inverters. The inverter generates an output of an AC voltage from an input of the DC with the aid of a switching circuit to reproduce a sine wave by generating one or more rectangular pulses of voltage per half period. If the size of the pulse is adjusted, the output is referred to as pulse width modulation. With this modulation, some pulses are generated every half period. The pulses near the end of the half period are always narrower than the pulses near the center of the half period so that the pulse width is comparable to the equivalent amplitude of the sine wave at that portion of the period. To vary the output voltage with high efficiency, the width of all pulses is amplified or reduced while maintaining a sinusoidal proportion. With PWM (pulse width modulation), only the on-time of the pulse is changed during the amplitude.

Conventional hardware and software requirements of the SPWM may include microcontrollers, MOSFETs, gate drivers, crystal oscillators, toggle switches, resistors, capacitors, required diodes, transformers, regulators, opto-isolators, keil compilers, and languages: an assembly or high-level language such as embedded C, python or Ruby.

Fig. 4 shows a first method, namely, generating a complete sine wave using a sine wave generator 300 and a filter 310, and then switching on and off using a switching device 311 to form a tangent waveform from the complete sine wave. To generate a complete sine wave, a sine wave generator is used, which may be an SPWM H bridge. Those skilled in the art will appreciate that other ways of generating a sine wave may be used with the switching device to turn the sine wave into a tangent wave. Fig. 6 and 7 show how a switching device 211 (such as SCR, MOSFET, TRIAC or other semiconductor device) generates two types of waveforms.

The second method uses an algorithm (which can be implemented in software or hardware by the SPWM) to create a tangent waveform in one step. This is accomplished by: the on-time step function is modulated to the SPWM signal and a PWM signal corresponding to the phase-cut waveform is created, and then the PWM is filtered to obtain the phase-cut waveform. As shown in fig. 5, a sine wave generator 400, a switching device 411, and a filter 410 may be used. Fig. 8 and 9 show how a phase-cut waveform can be created by modulating the SPWM and the on-time step function together.

Referring again to fig. 1, in some embodiments, the H-bridge 11 and the controller 13 may be used to implement the first and second methods described above.

Fig. 10 shows a block diagram of a dimmer controller 200 according to one embodiment of the present invention. The components of the dimmer controller 200 may include or replace the controller 13 and the detection module 14 as shown in fig. 1. As shown in fig. 10, a voltage and/or current sensor 201 is used to monitor one or both of the load 12 voltage and the load 12 current. The voltage and/or current sensor 201 may be implemented using various conventional discrete or integrated circuit components. The monitored voltage/current data is used by the feedback module 202. The feedback module 202 analyzes the monitored voltage/current data to determine the power or dimming level at the load 12.

The analysis may be performed in various ways. For example, the feedback module 12 may compare the monitored voltage/current data to reference phase cut signal data (or reference data). The reference data may be in the form of a look-up table for various dimming power levels, or reference waveforms, or voltage/current level thresholds. The reference data may be initially preset and then dynamically updated when the ELS100 is activated. In this regard, the feedback processing module will analyze the full power provided to the load 12 at start-up. If the reference "full power" data is unchanged from the monitored voltage/current data, the stored reference data may be used to provide appropriate dimming to the load 12. If the reference "full power" phase cut signal data is changed as compared to the monitored voltage/current data, the stored reference data may be dynamically updated to account for any changes in ELS100 configuration and/or load 12 requirements. Based on the reference "full power" data, the power of the load 12 may be reduced to an appropriate dimming level (e.g., 50%, 20%, etc. of the reference "full power").

The detection module 14 may continue to monitor the load 12 voltage/current data to allow further adjustment as needed in the presence of an emergency situation. For example, the emergency lighting requirements may change as the emergency conditions continue, or greater dimming may be provided to extend the life of the emergency power supply 10. Such dynamic changes are preset or programmed based on the duration of the emergency condition, the power level/run time remaining of the emergency power supply 10, or the temperature of the emergency power supply 10.

The feedback processing module 12 provides the analysis result to the controller 203. The controller 203 generates an adaptive data structure for creating control signals to adjust/create sine wave outputs with tangential waveforms. The PWM signal module 205 may be used to create a PWM signal that controls/regulates the sine wave output with a phase-cut waveform generator (as shown in fig. 4 and 5).

The memory 204 may be used to store data and reference data as needed.

In other embodiments, the phase-cut waveform generator is configured with a preset dimming power level to provide to the load 12. In this embodiment, the user does not need to control or set the preset dimming power level.

It should be understood that the various elements/blocks shown in fig. 10 may be combined or modified to provide the above-described functions and structures. Furthermore, a combination of hardware and software may be used for implementation. In this regard, fig. 11 illustrates a flow chart of an algorithm that may be used to implement the dimmer controller architecture illustrated in fig. 10. The numbering step shown in fig. 11 corresponds to the digital structural elements shown in fig. 10.

In addition, dimmer controller 200 may include an interface 15 for monitoring/controlling/adjusting dimming of load 12 as desired. The interface 15 may be a simple manual switch such as a rotary dial or tilt switch for manually adjusting dimming as desired. In other embodiments, the interface 15 may be a data port that allows interfacing with a monitoring device. The interface 15 may also be a wireless connection to a remote control center. For example, the wireless connection may be WiFi, wireless mesh, NFC, or the like.

Thus, the advantages of the various illustrated embodiments over existing systems are clear because a system implementing the various illustrated embodiments will operate with or above minimum required lighting during AC power loss and achieve longer periods of backup power during emergency situations. In the illustrated embodiment, the emergency backup system incorporates dimming capabilities of different types of emergency lighting systems. The device may also be used in conjunction with current full power output UPS/IPS emergency back-up and current inverter emergency back-up systems, or may be a dedicated emergency back-up device for use with LED loads installed in a single lighting fixture with and without AC LED drivers.

Although several inventive embodiments have been described and illustrated herein, various other means and/or structures for performing the functions and/or obtaining results and/or one or more advantages described herein will be apparent to those of ordinary skill in the art, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention are directed. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, other embodiments of the invention may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure relate to each individual feature, system, article, material, kit, and/or method described herein. Furthermore, if two or more such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, any combination of two or more such features, systems, articles, materials, kits, and/or methods is included within the scope of the present disclosure.

All definitions and definitions used herein should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite articles "a" and "an" as used in the specification and claims should be understood to mean "at least one" unless explicitly stated to the contrary "

The phrase "and/or" as used in the specification and claims should be understood as "one or both" of the elements so combined, i.e., elements that are in some cases combined and in other cases separated. The various elements listed as "and/or" should be interpreted in the same manner, i.e., "one or more" such elements are combined. In addition to the elements specifically identified by the "and/or" clause, other elements may optionally be present, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, in one embodiment, references to "a and/or B" when used in conjunction with an open language such as "include" may refer to a alone (optionally including elements other than B); in another embodiment, it may refer to B only (optionally including elements other than a); in yet another embodiment, it may refer to both a and B (optionally including other elements); etc.

As used in the specification and claims, "or" should be understood to have the same meaning as "and/or" defined above. For example, when separating items in a list, "or" and/or "should be construed as inclusive, i.e., including at least one but also including more than one number or list of elements, and optionally additional unlisted items. Only the opposite terms, such as "only one of … …" or "exactly one of … …", or "consisting of … …" when used in the claims, will be meant to include exactly one element of the number or list of elements. In general, the term "or" as used herein should be interpreted to mean an exclusive substitute (i.e., "one or the other, but not both") when an exclusive term is added in front, such as "either," one of … …, "" only one of … …, "or exactly one of" … …. As used in the claims, the term "consisting essentially of" shall have the ordinary meaning as used in the patent statutes.

As used herein in the specification and claims, the phrase "at least one" should be understood to refer to at least one element selected from any one or more elements in a list of elements, but not necessarily including at least one of each element specifically listed within the list of elements, and not excluding any combination of elements in the list of elements. The definition also allows that elements may optionally be present, rather than elements specifically identified in the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, in one embodiment, "at least one of a and B" (or equivalently, "at least one of a or B," or equivalently "at least one of a and/or B") may refer to at least one a, optionally including more than one a, absent B (and optionally including elements other than B); in another embodiment, it means that at least one B, optionally including more than one B, is absent a (and optionally includes elements other than a); in a further embodiment, it means at least one a, optionally comprising more than one a, and at least one B, optionally comprising more than one B (and optionally comprising other elements); etc.

It should also be understood that, in any method claimed herein that includes more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited, unless clearly indicated to the contrary.

In the claims and the above description, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "consisting of … …," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. As described in section 2111.03 of the handbook of patent review procedures of the united states patent office, only the transitional phrases "consisting of … …" and "consisting essentially of … …" are closed or semi-closed transitional phrases, respectively.

In the claims, any reference signs in parentheses are the formulas of the reference signs or embodiments in the figures indicating the exemplary embodiments, thereby increasing the understandability of the claims. These reference signs should not be construed as limiting the claims.

Claims (10)

1. An emergency power system (100), comprising:

a power supply (10),

a phase-cut waveform generator comprising a wave generator (11, 13, (300, 310, 311) or (400, 410, 411)) coupled to an output of the power supply (10) and arranged to provide a phase-cut waveform to a load (12) by modulating a turn-on time step function to a Sinusoidal Pulse Width Modulation (SPWM) signal and filtering to generate the phase-cut waveform;

-a detection module (14, 201) arranged to monitor voltage and/or current data provided to the load (12) by the phase-cut waveform generator; and

a controller (13, 202-205) arranged to control the tangential wave generator (11, 13, (300, 310, 311) or (400, 410, 411)) to adjust the power level of the load (12) by modifying the tangential wave based on the monitored voltage and/or current data and the reference data.

2. The emergency power system (100) of claim 1, wherein the tangent waveform generator (11, 13, (300, 310, 311) or (400, 410, 411)) generates the tangent waveform from a sine wave, a rectangular wave, and/or a triangular wave (fig. 2 and 3).

3. The emergency power system (100) of claim 1, wherein the reference data is in the form of a look-up table for each dimming power level, or for reference waveforms of each dimming power level, or for voltage/current level thresholds of each dimming power level.

4. The emergency power system (100) of claim 1, wherein the controller (13, 202-205) generates PWM control signals for controlling the phase-cut waveform generator (11, 13, (300, 310, 311) or (400, 410, 411)).

5. The emergency power system (100) of claim 1, wherein the detection module (14, 201) comprises a voltage and/or current sensor (201).

6. The emergency power system (100) of claim 1, wherein the controller (13, 202-205) makes the determination to dynamically update the reference data based on the voltage and/or current data monitored at full power of the load (12) at emergency lighting system start-up.

7. The emergency power system (100) of claim 5, wherein the controller (13, 202-205) generates the PWM control signal to adjust the phase-cut waveform generator (11, 13, 300, 310, 311, 400, 410, 411) based on one or more current conditions that occur when the emergency power system (100) is activated.

8. The emergency power system (100) of claim 7, wherein the one or more current conditions include: the amount of time the emergency power system (100) has been activated and/or the remaining run time of the power supply (10) and/or the temperature of the power supply (10).

9. The emergency power system (100) of claim 1, further comprising an interface (15) for allowing a user to control/adjust the power level of the load (12).

10. A method for dimming an emergency lighting device, comprising the steps of:

measuring load voltage and current of the emergency lighting device;

comparing reference dimming data with the measured load voltage and current;

determining a dimming control signal based on the comparison;

a phase-cut waveform is generated based on the control signal to reduce the load voltage and current of the emergency lighting device, wherein the phase-cut waveform is generated from a sinusoidal pulse width modulated, SPWM, signal by modulating an on-time step function to the SPWM signal and filtering to generate the phase-cut waveform.