AT18523U1 - LED converter arrangement with linearized control system - Google Patents

Abstract

The invention comprises an LED converter arrangement (10) for operating at least one LED (41), comprising detection means (17) for detecting an electrical supply variable (16) of the at least one LED (41), and a control device (15) for controlling switching means (13A, 13B) of the LED converter arrangement (10) serving as an actuator as a function of the detected electrical supply variable (18) and a predetermined electrical supply variable (19) of the at least one LED (41), wherein the control device (15) comprises a control element (20) and a linearization element (21) which is designed to operate the control element (20) with a constant controller coefficient (KI) for each predetermined electrical supply variable (19) of the at least one LED (41).

Description

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Description

LED converter arrangement with linearized control system

FIELD OF THE INVENTION

[0001] The present invention relates to an LED converter arrangement for operating at least one LED, a method for operating the LED converter arrangement, and further devices with the LED converter arrangement, which can be used in particular for lighting applications.

BACKGROUND OF THE INVENTION

[0002] Known LED converter arrangements operated in a gap mode regularly have control systems with a non-linear behavior.

[0003] In such LED converters, an adjustment of the controller coefficients, which describe the transfer function of the control element used, takes place with each change in the controlled variable in order to compensate for the inevitably associated non-linear change in the manipulated variable and thus to keep a cut-off frequency and thus a time response of the control loop constant.

[0004] This means that a uniform and analytical calculation of the transfer behavior of the underlying control loop using transfer functions is not possible.

[0005] A comprehensive analysis of such a nonlinear control system is very difficult or even impossible. Statements regarding stability, for example, require the aid of numerical simulations.

SUMMARY OF THE INVENTION

[0006] There is therefore a need for devices and methods that remedy these disadvantages.

[0007] This object is achieved according to the invention by an LED converter arrangement for operating at least one LED according to claim 1, by an operating device according to claim 11 comprising the LED converter arrangement, and by a lighting device according to claim 12 comprising the operating device. The dependent claims define preferred and advantageous embodiments of the invention.

[0008] According to a first aspect, an LED converter arrangement for operating at least one LED comprises: detection means for detecting an electrical supply variable of the at least one LED; and a control device for controlling switching means of the LED converter arrangement, which serve as an actuator, as a function of the detected electrical supply variable and a predetermined electrical supply variable of the at least one LED. The control device comprises a control element and a linearization element, which is configured to operate the control element with a constant control coefficient for each predetermined electrical supply variable of the at least one LED.

[0009] Advantageously, a comprehensive linearization of a transfer function of the controlled system can be achieved with the at least one LED, so that the control element can be operated over the entire value range of the electrical supply variable with a constant controller coefficient provided for this purpose, without always requiring a linearization of the transfer function of the controlled system at the respective operating point.

[0010] An LED converter arrangement can be understood as an electronic circuit and/or assembly which is designed to convert an electrical power by means of at least one energy storage device and at least one switching means, wherein a power flow through

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the energy storage device is controllable. An LED converter arrangement within the meaning of this application can be understood as any LED converter in which a manipulated variable can be set and a controlled variable can be slowly adjusted.

[0011] Detection means can be understood as means that serve to detect electrical quantities and, for this purpose, provide detected electrical quantities derived from these quantities. For example, a measuring resistor can serve as a detection means for a current flowing through the measuring resistor. The electrical supply quantity to be detected, which is passed through the measuring resistor, results in a detected electrical supply quantity in the form of a voltage drop across the measuring resistor.

[0012] An electrical supply quantity can be understood as an electrical quantity, in particular current or voltage, which serves to supply an electrical load.

[0013] A control device can be understood as an electronic circuit and/or assembly that serves to systematically and purposefully influence the behavior of the LED converter arrangement and, for this purpose, comprises, in particular, an integrated circuit configured to provide control signals for active operating means, in particular switching means, of the LED converter arrangement as a function of input variables and the programming or wiring of the integrated circuit. Examples of such integrated circuits include microcontrollers or application-specific integrated circuits (ASICs).

[0014] A microcontroller can be understood as a programmable integrated circuit which, in addition to a processor function, can also include peripheral functions.

[0015] An application-specific integrated circuit can be understood as a non-programmable integrated circuit whose function is defined by its manufacture.

[0016] A microcontroller is advantageous for a cost structure in small series production, and an ASIC in large series production.

[0017] A control element can be understood as a means in a control loop that serves to determine a general manipulated variable from a (control) deviation between a reference variable (setpoint) and a detected and fed-back controlled variable (actual value), which influences an associated controlled system such that the control deviation is minimized in a steady-state state of the control loop. For example, a control element can output a general manipulated variable in the form of a duty cycle of a pulse-width-modulated control signal to switching means serving as an actuator.

[0018] A linearization element can be understood as an element in a control loop with a non-linear transfer function, which serves to bring about a linearization of an inherently non-linear characteristic curve of an element of the controlled system.

[0019] An actuator can be understood as a means in a control loop that serves to determine a manipulated variable from a general manipulated variable, which influences an associated controlled system in such a way that the controlled variable moves toward the reference variable in order to minimize the control deviation in a steady state of the control loop. For example, switching means serving as an actuator can output a manipulated variable in the form of a period of a periodic absence of power supply (i.e., a dead time) to the controlled system.

[0020] A switching device can be understood as an electronically actuated switch that can alternate between a closed, electrically conductive state and an open, electrically insulating state. Examples include transistors.

[0021] Controller coefficients can be understood as characteristic values of a controller, which, as constants in a transfer function of the controller, define the control behavior of the controller. Examples of coefficients of controllers with proportional, integral and/or derivative

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Proportional, integrating and/or derivative coefficients Kpr, Kı and Kp are used.

[0022] The LED converter arrangement can be designed such that average current intensities through the at least one LED serve as electrical supply variables of the at least one LED.

[0023] Advantageously, medium currents are easy to measure.

[0024] For example, a voltage drop across a measuring resistor can be recorded analogously and averaged by an analog low-pass filter or by means of digital further processing.

[0025] The control device can be configured to control switching means of the LED converter arrangement serving as an actuator in a gap operation.

[0026] Advantageously, switching losses only occur when switching means serving as actuators are switched off.

[0027] The control device can be configured to operate the at least one LED in a plurality of dimming levels with a respective associated peak current of an inductance of the LED converter arrangement.

[0028] Advantageously, the dimming capability of the LED converter assembly provides additional application possibilities in various areas. For example, the power consumption of a dimmed LED load is reduced. Furthermore, the dimming capability can also enable the LED converter assembly to be used in emergency lighting mode. Furthermore, without the dimming capability, certain lighting moods that positively influence the user's comfort cannot be created.

[0029] Dimming levels are understood to mean different brightness levels of a light source, in particular with at least one LED, which result when the light source is controlled with different power inputs per unit of time.

[0030] The control element can be designed as an integrating control element.

[0031] Advantageously, an integrating control element (i.e. an IL controller) can completely eliminate the control deviation.

[0032] The linearization element can have an inverse function for a control system of the LED converter arrangement comprising the at least one LED, wherein the inverse function allows the control element to be operated in each of the plurality of dimming stages for each predetermined electrical supply variable of the at least one LED with a constant control coefficient.

[0033] In particular, this enables a linearization of a non-linearity in the control loop of the LED converter caused by a gap operation of the LED converter.

[0034] Advantageously, such a linearization enables a uniform and analytical analysis of the transfer behavior of the underlying control loop.

[0035] Advantageously, such a linearization element can be preconfigured during manufacture or during initial commissioning of the LED converter arrangement, so that no significant delay times occur for regular commissioning in an active operation.

[0036] The control device can be configured to evaluate the inverse function in the respective one of the plurality of dimming levels using a fixed-point arithmetic, wherein an absolute error between the fixed-point arithmetic and a corresponding floating-point arithmetic is less than a predetermined error tolerance threshold.

[0037] In this case, it is advantageous to use control devices that, for reasons of cost and/or computing power and thus time, do not have dedicated floating-point arithmetic, which is generally recommended and desirable, but emulate it with fixed-point arithmetic. The integrated circuits required for this are, in principle, simpler in design and can be provided more cost-effectively.

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[0038] The detection means may comprise a measuring resistor. [0039] Advantageously, a measuring resistor is a very cost-effective analog circuit element. [0040] The switching means may comprise a transistor.

[0041] Advantageously, a transistor is a very cost-effective, precisely switchable analog circuit element that can be selected to be optimized for a particular application.

[0042] The LED converter arrangement can be designed as a step-down converter.

[0043] Advantageously, a step-down converter has a very simple and cost-effective circuit architecture, which in many cases can replace a conventional longitudinally regulated voltage stabilization.

[0044] According to a second aspect, an operating device for operating at least one LED comprises: an LED converter arrangement according to embodiments.

[0045] Advantageously, the above-mentioned device features of the LED converter arrangement with their respective advantages can be used analogously in the operating device.

[0046] An operating device can be understood as an electronic circuit and/or assembly which is designed to feed the at least one LED from an electrical energy source which is not designed to do so per se.

[0047] According to a third aspect, a lighting device comprises: an operating device according to embodiments; and at least one LED.

[0048] Advantageously, the above-mentioned device features of the LED converter arrangement or of the operating device with their respective advantages can be used analogously in the lighting device.

[0049] According to a fourth aspect, a method for operating at least one LED comprises: detecting an electrical supply variable of the at least one LED; and controlling switching means of the LED converter arrangement, which serve as an actuator, as a function of the detected electrical supply variable and a predetermined electrical supply variable of the at least one LED. The control device is configured to operate a control element of the control device with a constant control coefficient for each predetermined electrical supply variable of the at least one LED.

[0050] The method can be carried out with an LED converter arrangement according to embodiments.

[0051] The method comprises the respective corresponding features of the LED converter arrangement.

[0052] Advantageously, the above-mentioned device features of the LED converter arrangement, with their respective advantages, can be used analogously in the method. BRIEF DESCRIPTION OF THE FIGURES

[0053] The invention will be briefly explained below using preferred embodiments and with reference to the drawings, wherein like reference numerals designate like or similar elements.

[0054] Fig. 1 shows schematically a known LED converter arrangement.

[0055] Fig. 2 shows schematically a control circuit for an LED converter arrangement according to an embodiment.

[0056] Fig. 3 shows schematically an operating device with the LED converter arrangement according to an embodiment and a lighting device with the operating device.

[0057] Fig. 4 shows schematically a method for operating the LED converter arrangement

according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0058] The invention is explained in more detail below using preferred embodiments and with reference to the drawings.

[0059] A description of embodiments in specific fields of application does not imply any restriction to these fields of application.

[0060] Elements of schematic representations are not necessarily drawn to scale, but rather in such a way that their function and purpose will be understood by those skilled in the art.

[0061] Unless expressly stated otherwise, the features of the various embodiments can be combined with one another.

[0062] Fig. 1 schematically shows a known LED converter arrangement 10, which is designed as a step-down converter.

[0063] This exemplary LED converter arrangement 10 serves to operate at least one LED 41 that can be connected on the load side.

[0064] For this purpose, the LED converter arrangement 10 is designed to convert an electrical power supplied on the supply side by means of at least one energy storage device 11, 12 and at least one switching means 13A, 13B, wherein a power flow through the energy storage device 11, 12 can be controlled via a pulse-width modulated control 14A, 14B of the at least one switching means 13A, 13B.

[0065] The LED converter arrangement 10 comprises transistors that can be controlled in a push-pull manner as switching means 13A, 13B. In this way, a square-wave voltage with a specific duty cycle is generated from the electrical power supplied on the supply side.

[0066] As energy storage 11, 12, the LED converter arrangement 10 comprises an inductance 11 and a filter capacitor 12, which together form an LC low-pass filter, which averages the square-wave voltage generated by the switching means 13A, 13B from the voltage supplied on the supply side.

[0067] This results in an electrical supply variable 16, in the example case an average LED current 16, which represents the controlled variable of the control circuit 30 described in more detail below.

[0068] In general, the LED converter arrangement 10 is designed such that average current intensities through the at least one LED 41 serve as the actual electrical supply quantity 16, the detected actual electrical supply quantity 18 or the desired electrical supply quantity 19 of the at least one LED 41.

[0069] The LED converter arrangement 10 further comprises detection means 17 for detecting the electrical supply variable 16 of the at least one LED 41. In Fig. 1, the detection means 17 comprise a measuring resistor which serves to provide a detected electrical variable 18 derived from the average LED current 16, which represents the feedback variable of the control circuit 30 described in more detail below.

[0070] Specifically, the average LED current 16 to be detected flows through the measuring resistor and consequently leads to a detected electrical supply quantity 18 in the form of a voltage drop across the measuring resistor against ground, which is proportional to the average LED current 16 to be detected.

[0071] The LED converter arrangement 10 also comprises a control device 15, which is explained in more detail below in connection with Fig. 2.

[0072] Fig. 2 schematically shows a control circuit 30 for an LED converter arrangement 10 according to an embodiment.

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[0073] The controlled system to be controlled comprises, in addition to a member which expresses the non-linearity of the at least one LED 41 in a gap operation, a linearization member 21.

[0074] The control device 15, which can also be seen from the control circuit 30, serves to control the switching means 13A, 13B of the LED converter arrangement 10, which act as an actuator, as a function of the detected electrical supply variable 18 (feedback variable, which comprises the actual value of the controlled variable) and a predetermined electrical supply variable 19 (setpoint value of the controlled variable) of the at least one LED 41.

[0075] The control of the actuator takes place in a gap operation with a dead time Tpzap, which depends in particular on a duty cycle and a period of the pulse-width modulated control signal 14A and represents the manipulated variable of the control circuit 30.

[0076] The control device 15 is further configured to operate the at least one LED 41 in a plurality of dimming levels with a respective associated peak current Ip of the inductance 11.

[0077] The electrical supply size 16 of the at least one LED 41 is thus determined by

- a voltage supplied on the supply side against ground,

- a duty cycle of the pulse-width modulated control signal 14A, which is predetermined based on a desired dimming level and which determines the duty cycle of the square-wave voltage,

- a dimensioning of the inductance 11, at which a current flow with a corresponding peak current Ip is established by applying the square-wave voltage,

- a period of the pulse-width modulated control signal 14A, which is predetermined due to the gap operation and which, together with the predetermined duty cycle of the same signal, determines the dead time TpzAp (manipulated variable) between successive current flows, and

- dimensioning of the filter capacitance 12 to smooth the current intensity generated by the inductance 11.

[0078] The control device 15 comprises a control element 20, which is designed in particular as an integrating control element. An integrating control element acts on the manipulated variable by temporally integrating the control deviation with a weighting by the controller coefficient Kı = 1/Ty (with reset time T\N). The integrating controller has a transfer function G(s) in the frequency domain of:

G(s)=Kı/s.

[0079] The controlled system can be described quite generally by the controlled variable as a function f of the manipulated variable. For the control circuit 30 of Fig. 2 with the underlying LED converter arrangement 10 of Fig. 1, this means that the average LED current 16 results as a function of the dead time TpozAp of the gap operation:

[0080] lavc = ATpDpeAD)

[0081] A cutoff frequency fc of the closed control loop 30 is generally dependent on the controller coefficient Ki and on a slope of the function f describing the controlled system. Due to the non-linearity of the function f, a linearization of the function f would therefore have to be performed for each permissible value of the manipulated variable Tpead. However, in order to keep the cutoff frequency fe constant, and thus the time response of the control loop 30 constant for each permissible value of the controlled variable Iave, the controller coefficient Ki would have to be a function of the controlled variable lavc.

[0082] To avoid this, the control device 15 also comprises the linearization element 21, which is designed to operate the control element 20 with a constant control coefficient Ki for each predetermined electrical supply variable 19 of the at least one LED 41, i.e. for each average LED target current Iave.

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[0083] The linearization element 21 has an inverse or reverse function f’, which describes the manipulated variable as a function of the controlled variable:

Tpeap= f'(lave)

[0084] By concatenating the inverse function f7 implemented in the linearization element 21 and the function f describing the controlled system, each value of the controlled variable lave is mapped to itself:

HF" (Invo)) = lavc

[0085] Due to a dependence of the inverse function f' on the peak current Ip, i.e. on the specified dimming level, an optimal linearization of the control system is always carried out for each peak current Ip.

[0086] The inverse function therefore allows the control element 20 to be operated in the respective one of the plurality of dimming levels for each predetermined electrical supply variable 19 of the at least one LED 41 with a constant control coefficient Kı.

[0087] The control device 15 is configured to evaluate the inverse function in the respective one of the plurality of dimming levels using a fixed-point arithmetic, wherein an absolute error between the fixed-point arithmetic and a corresponding floating-point arithmetic is less than a predetermined error tolerance threshold.

[0088] In particular, a more precise linearization can be achieved if the peak current Ip in the inverse function f' can be varied via the dimming levels. Alternatively, it is possible to keep the peak current Ip constant in the inverse function, for example, at a maximum value of the peak current Ip.

[0089] Fig. 3 schematically shows an operating device 40 with the LED converter arrangement 10 according to an embodiment and a lighting device 50 with the operating device 40.

[0090] The operating device 40 for operating at least one LED 41 comprises an LED converter arrangement 10 and optionally further functional elements such as a rectifier, an auxiliary winding for a low-voltage power supply, etc.

[0091] The lighting device 50 comprises such an operating device 40 according to embodiments and the at least one LED 41, and is particularly suitable for "point-of-load" energy supply architectures.

[0092] Fig. 4 schematically shows a method 60 for operating the LED converter arrangement 10 according to an embodiment.

[0093] The method 60 can be carried out with an LED converter arrangement 10 according to embodiments and serves to operate at least one LED 41 with an LED converter arrangement 10 which is designed as in Fig. 1, for example, and which is included in a control circuit 30 as in Fig. 2, for example.

[0094] The method 60 comprises: detecting 61 an electrical supply variable 16 of the at least one LED 41; and controlling 61 switching means 13A, 13B of the LED converter arrangement 10 serving as an actuator as a function of the detected electrical supply variable 18 and a predetermined electrical supply variable 19 of the at least one LED 41. The control device 15 is configured to operate a control element 20 of the control device 15 for each predetermined electrical supply variable 19 of the at least one LED 41 with a constant control coefficient Ki.

[0095] Although LED converter arrangements have been described according to exemplary embodiments, various modifications can be implemented in other exemplary embodiments. For example, the features essential to the invention can be applied to any LED converter arrangement in which a manipulated variable can be set and a controlled variable can be slowly adjusted.

Claims (10)

A hes AT 18 523 U1 2025-08-15 Ss N Claims 1. An LED converter arrangement (10) for operating at least one LED (41), comprising detection means (17) for detecting an electrical supply variable (16) of the at least one LED (41), and a control device (15) for controlling switching means (13A, 13B) of the LED converter arrangement (10) serving as an actuator as a function of the detected electrical supply variable (18) and a predetermined electrical supply variable (19) of the at least one LED (41), wherein the control device (15) comprises a control element (20) and a linearization element (21) which is designed to operate the control element (20) with a constant controller coefficient (Kı) for each predetermined electrical supply variable (19) of the at least one LED (41). 2. LED converter arrangement (10) according to claim 1, wherein the LED converter arrangement (10) is designed such that average current intensities through the at least one LED (41) serve as electrical supply variables (16, 18, 19) of the at least one LED. 3. LED converter arrangement (10) according to claim 1 or claim 2, wherein the control device (15) is designed to control switching means (13A, 13B) of the LED converter arrangement (10) serving as an actuator in a gap operation. 4. LED converter arrangement (10) according to one of the preceding claims, wherein the control device (15) is configured to operate the at least one LED (41) in a plurality of dimming levels with a respective associated peak current intensity (Ip) of an inductance (11) of the LED converter arrangement (10). 5. LED converter arrangement (10) according to one of the preceding claims, wherein the control element (20) is designed as an integrating control element. 6. LED converter arrangement (10) according to claim 5, wherein the linearization element (21) has an inverse function for a control system of the LED converter arrangement (10) comprising the at least one LED (41), wherein the inverse function allows the control element (20) to be operated with a constant control coefficient (Kı) in each of the plurality of dimming stages for each predetermined electrical supply variable (19) of the at least one LED (41). 7. LED converter arrangement (10) according to claim 6, wherein the control device (15) is configured to evaluate the inverse function in the respective one of the plurality of dimming stages using fixed-point arithmetic, wherein an absolute error between the fixed-point arithmetic and a corresponding floating-point arithmetic is less than a predetermined error tolerance threshold. 8. LED converter arrangement (10) according to one of the preceding claims, wherein the detection means (17) comprise a measuring resistor. 9. LED converter arrangement (10) according to one of the preceding claims, wherein the switching means (13A, 13B) comprise a transistor. 10. LED converter arrangement (10) according to one of the preceding claims, wherein the LED converter arrangement (10) is designed as a step-down converter. 2 sheets of drawings