EP3908084A1 - Schaltwandler - Google Patents

Schaltwandler Download PDF

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Publication number
EP3908084A1
EP3908084A1 EP20173164.3A EP20173164A EP3908084A1 EP 3908084 A1 EP3908084 A1 EP 3908084A1 EP 20173164 A EP20173164 A EP 20173164A EP 3908084 A1 EP3908084 A1 EP 3908084A1
Authority
EP
European Patent Office
Prior art keywords
converter
load current
block
ffc
ripple
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20173164.3A
Other languages
English (en)
French (fr)
Inventor
Harald Netzer
Blazej Szyler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tridonic GmbH and Co KG
Original Assignee
Tridonic GmbH and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tridonic GmbH and Co KG filed Critical Tridonic GmbH and Co KG
Priority to EP20173164.3A priority Critical patent/EP3908084A1/de
Priority to EP21718610.5A priority patent/EP4129010A1/de
Priority to PCT/EP2021/060151 priority patent/WO2021223998A1/en
Publication of EP3908084A1 publication Critical patent/EP3908084A1/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • H05B45/3725—Switched mode power supply [SMPS]
    • H05B45/39—Circuits containing inverter bridges

Definitions

  • the invention relates to a switched converter which supplies an LED load.
  • the invention further relates to an LED lighting module comprising such switched converter.
  • the invention generally, relates to the output current (LED current) feedback control in a switched converter, such as, for example, an LLC converter.
  • One example is the 100 Hz ripple in the DC supply voltage or, for example, 400 VDC of the switched converter. This 100 Hz ripple should not be present in the output current.
  • the converter may also be used for a power supply for other gear, such as, for example, by acting as a DALI bus power supply. If this other gear supplied by the converter draws power in a certain frequency, this may lead to a ripple in the output current not fully compensated by the PI controller feedback loop.
  • FIG. 1 A topology of LED gears which may be used in the invention is shown in Fig. 1 .
  • the mains voltage is rectified (not shown) and then filtered by the block electromagnetic interference (EMI) filter.
  • a boost converter (block boost PFC) is used for power factor correction and to produce a DC bus voltage (pV_bus) of about 400 V.
  • This bus voltage is the input voltage of a half bridge LLC converter (block HB-LLC) which either provides the galvanically isolated input voltage for a third DC/DC block (e.g. a buck converter) or directly provides an output voltage / current to drive LED loads.
  • a half bridge LLC converter block HB-LLC
  • a third DC/DC block e.g. a buck converter
  • the DC bus voltage may be used to produce a low voltage power of e.g. 12V for a first control circuitry (e.g. ASIC).
  • the ASIC may communicate with a second control circuitry (e.g. a microcontroller).
  • the Microcontroller may be in charge of a communication interface (e.g. DALI, via an optocoupler).
  • the microcontroller may have a further interface e.g. for inputting nominal values for the output current.
  • the first control circuitry may be supplied with a signal ILED representing the current on the secondary side of the galvanic isolation.
  • the first control circuitry may control the switching of the switched converter via a signal HB-CTRL.
  • the DC bus voltage pV_bus is usually subject to the 100 Hz ripple. If the half bridge LLC circuit is operated at a constant frequency, which is not the case, the full ripple will be present in the LED current and, therefore, in the light. As the half bridge frequency is set by a controller that controls the average LED current, part of the 100 Hz ripple is suppressed by the controller.
  • the output current depends on the half bridge frequency, the component values of the LLC converter (magnetizing inductance, resonance inductance, resonance capacitance), the LED voltage, the bus voltage, etc. So, if optimal feed forward gain values are determined with one gear (or actually one gain per LED voltage), these values are not optimal with another gear.
  • the invention relates to a switched converter, supplied with a DC voltage originating from an AC voltage, preferably mains voltage.
  • the switched converter comprises output terminals for supplying a LED load, a feed-back loop controller configured to generate an output signal setting a switching frequency of at least one switch of the converter for controlling a load current on a nominal value, based on a signal indicating the load current and supplied to the feedback loop controller and a feed-forward control, FFC, block, wherein a response time of the FFC block is faster than a response time of the feed-back loop controller.
  • the FFC block is configured to analyze in time increments said load current sensing signal and/or the DC signal as to a ripple present in said signals and to add a ripple compensation signal to said output signal of the feed-back loop controller.
  • the controller may be optimized for slower transients and a FFC is added to the controller output in order to reject the 100 Hz ripple.
  • Feed forward means that, based on the actual difference between the nominal or average bus voltage and the currently measured bus voltage, the half bridge frequency is either increased or decreased in order to compensate this deviation of the HB-LLC input voltage (pV_bus) .
  • This gain can be determined during the design of the LED gear.
  • one gain value does not fit for all working points in which the HB-LLC circuit operates.
  • different gain values are required for different output voltages (LED voltages) because the characteristic of the HB-LLC circuit is steeper (steeper V_out to half bridge frequency relationship implies that only a low change of half bridge frequency is required to see an effect in the LED current) at high LED voltages and it is flatter (flatter V_out to half bridge frequency relationship implies that a higher change of half bridge frequency is required to see an effect in the LED current) at low LED voltages.
  • Fig. 2 visualizes this behavior. It can be seen that at high output voltages, such as 300V the curve is very steep, whereas at low output voltages, such as 120 V, it is very flat.
  • the output current depends on the half bridge frequency, the component values of the LLC converter (magnetizing inductance, resonance inductance, resonance capacitance), the LED voltage, the bus voltage, etc. So, if optimal feed forward gain values are determined with one gear (or actually one gain per LED voltage), these values are not optimal with another gear.
  • the switched converter further comprises a sensing unit configured to directly or indirectly detect the load current and to forward the load current sensing signal based on the detected load current to the FFC block.
  • the FFC block is configured to evaluate an actual ripple value in the load current and to adjust the compensation signal at least partially on the basis of the actual ripple value.
  • the FFC block is further configured to adjust a gain of the FFC block on the basis of the actual ripple value.
  • the FFC block further comprises a self-learning, in particular artificial intelligence, block, which is configured to further adjust the compensation signal based on a learned algorithm taking into account at least one operation condition of the converter, in particular a value of a bus voltage, a temperature and/or a load characteristic.
  • a self-learning, in particular artificial intelligence, block which is configured to further adjust the compensation signal based on a learned algorithm taking into account at least one operation condition of the converter, in particular a value of a bus voltage, a temperature and/or a load characteristic.
  • the FFC block is configured to measure in discrete time periods a mains period and to adjust the compensation signal on the basis of the mains period.
  • the converter comprises a microcontroller, wherein the microcontroller comprises the FFC block, wherein the microcontroller is further configured to measure a frequency of the mains and to generate the compensation signal based on said frequency.
  • the switched converter is supplied with a DC bus voltage
  • the FFC block is configured to receive a nominal or average value of the DC bus voltage and an actual value of the DC bus voltage
  • the FFC block is configured to set the compensation signal based on the nominal or average value of the DC bus voltage and on the actual value of the DC bus voltage.
  • the switched converter is an LLC converter.
  • the invention relates to a LED lighting module having at least one converter according to any of the preceding claims and at least one LED load.
  • the invention relates to a method for supplying a LED load, comprising: generating an output signal setting a switching frequency of at least one switch of a converter for controlling a load current on a nominal value, based on a signal indicating a load current and supplied to a feedback loop controller, and analyzing in time increments of said load current sensing signal and/or a DC signal as to a ripple present in said signals and to add a ripple compensation signal to said output signal of the feedback loop controller.
  • the method further comprises directly or indirectly detecting the load current, and forwarding the load current sensing signal based on the detected load current to the FFC block.
  • the aspect of the present invention might contain integrated circuits that are readily manufacturable using conventional semiconductor technologies, such as complementary metal-oxide semiconductor technology, short "CMOS".
  • CMOS complementary metal-oxide semiconductor technology
  • the aspects of the present invention may be implemented with other manufacturing processes for making optical as well as electrical devices.
  • FIG. 3 a system 300 comprising a switched converter 302 according to an embodiment is shown.
  • the switched converter 302 supplied with a DC voltage 301 originating from an AC voltage, preferably mains voltage, comprises:
  • the FFC block 302b is configured to analyze in time increments of said load current sensing signal and/or the DC signal 301 as to a ripple present in said signals and to add a ripple compensation signal to said output signal of the feed-back loop controller 302a.
  • the feed forward gain can be determined online (so during runtime of the gear) automatically.
  • the optimal feed forward gain value is found by the gear autonomously.
  • Fig. 4 shows the system 300 comprising the switched converter 302 according to an embodiment.
  • the converter 302 comprises a mains frequency detection block 401, a microcontroller 400 and an LED driver 404.
  • the microcontroller 400 comprises a frequency analyzer and anti-phase signal generator block 402, a logic block or FFC block 302b, the controller 302a, an LED current demand block 403 and a signal combination block 405.
  • a smart software algorithm allows the LED current controller 302a to cancel the low frequency ripple created by the first stage of the driver.
  • the driver is a flyback driver.
  • the first stage of the driver would "mirror" the mains frequency on to the secondary side and create a 100 Hz - 120 Hz low frequency, LF, ripple on the bus. Then, the LED current source supplied from this rail would transfer this 100 Hz - 120 Hz ripple on to the LED current.
  • Low cost LED drivers can be configured to use only simple filters to limit the amount of ripple present on the V_bus, hence limiting the LED current ripple.
  • the controller 302a based on the microcontroller 400 can superimpose the generated sinusoidal signal to counteract the LF ripple.
  • the LF ripple is monitored continuously, which requires real time system, with minimal delay time between taking samples and adjusting the controller 302a.
  • the logic block 302b includes an algorithm comprising the following instructions:
  • the microcontroller 400 can reduce the LF ripple in the LED current, while doing all other tasks as designated.
  • the smart algorithm decides the frequency and amplitude of the ripple cancelling signal based on very few samples, and assumes that they are fixed throughout the operation of the driver. This limits the amount of hardware and software resources needed to actively cancel the LF ripple in the LED current
  • low limits of the LF ripple can be achieved without additional circuits and without large storage elements, i.e. electrolytic capacitors.
  • Fig. 5 shows a switched converter 302 according to an embodiment.
  • the output current (LED current) is monitored, as explained in the following.
  • the average output current is measured anyway, because it is the required feedback signal for the feedback loop controller 302a, e.g. a HB-LLC control loop, only a measurement (tracking) of the output current peak value should be added.
  • the peak value can be found by a peak tracking block within the microcontroller 400, e.g. an ASIC.
  • a peak tracking block within the microcontroller 400, e.g. an ASIC.
  • the difference between peak value and average value will be almost zero (in ideal case it is zero) .
  • the difference between peak and average will be larger.
  • the feed forward control block 302b does not only receive the average (or nominal) bus voltage V_bus_avg and the currently measured bus voltage V_bus, but also information about the average and actual (or peak) LED current. Based on the current information the feed forward gain can be optimized (or controlled) until the difference between ILED_pk and ILED_avg is at a minimum.
  • the DC/DC switched converter 302 that is used to supply LED loads is a buck converter or flyback converter.
  • the switched converter 302 only provides a fixed output voltage, which is then the input voltage for a further stage that then supplies the LED load.
  • the feed forward gain is determined by comparison of the average output voltage and the peak output voltage.
  • Fig. 6 shows exemplary waveforms of the LED current with different feed forward gains.
  • a feed forward control block 302b which has a shorter (faster) response time than the response time of the PI controller 302a.
  • the feed forward control block 302b is supplied with the LED current sensing signal, and adds a compensation/correction value to the output signal of the feedback loop controller 302a, in order to reduce any ripple, which might occur in the output current, and not fully compensated by the relatively slow PI controller 302a.
  • the feed-forward control block 302b evaluates/measures any ripple in the LED current and adjusts its gain depending on the actual ripple value.
  • the feed forward control may start with a low gain and increase it until the gain has an optimum value, in which the ripple is essentially compensated.
  • the feed-forward control 302b may comprise a self-learning (artificial intelligence) block, which learns as how to adjust the gain depending on the operation conditions (value of the bus voltage, temperature, load characteristics, etc.).
  • the feed forward control block 302b may be supplied with a nominal value for the DC bus voltage as well as an actual value of the bus voltage, wherein these supplied signals are taken into account for adjusting the gain of the feed forward control block.
  • one of the signals supplied to the feed forward control block may not be the nominal value of the bus voltage (which may vary from device to device), but the average value of the measured bus voltage.
  • the mains-induced low frequency current ripple is compensated by a "smart algorithm", measuring in discrete time periods the mains period and, then, generating a compensation signal to reduce the forecast ripple between the measurement of the mains frequency and the next frequency measuring step.
  • an adaptive, self-learning and also feed forward approach is used in the sense that, dependent on measurements, a compensation is performed until the next measurement is carried out.
  • the smart algorithm produces a compensation signal, which is super-imposed in a feed forward manner onto the output signal of the feedback controlled loop.
  • the microcontroller 400 is used for measuring the frequency of the mains and to generate the compensation signal.
  • the computation effort and the resources required are relatively low, as the measurement of the mains frequency is only done in discrete steps and the compensation signal is then used for a given time period.
  • the microcontroller 400 already used for other purposes can also be used for this task.
  • One application for this invention is the area of so-called maintained LED drivers, which are drivers which may charge a battery from mains and then in an emergency case operate emergency lighting means of the battery, and at the same time, drive other or the same lighting means of the mains supply.
  • Fig. 7 shows an HB-LLC circuit 501 according to an embodiment.
  • the HB-LLC circuit comprises two switches M40 and M41, moreover the capacitor C51 is connected to a primary side winding L51d, which is coupled to two windings L51a and L51b.
  • diodes D50a and D50b are provided on the secondary side as well as a capacitor C52, which is connected to the LED load.
  • Fig. 8 shows a method 800 for supplying a LED load 303 according to an embodiment.
  • the method 800 comprises the following steps:

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  • Dc-Dc Converters (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)
EP20173164.3A 2020-05-06 2020-05-06 Schaltwandler Withdrawn EP3908084A1 (de)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP20173164.3A EP3908084A1 (de) 2020-05-06 2020-05-06 Schaltwandler
EP21718610.5A EP4129010A1 (de) 2020-05-06 2021-04-20 Schaltwandler
PCT/EP2021/060151 WO2021223998A1 (en) 2020-05-06 2021-04-20 A switched converter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20173164.3A EP3908084A1 (de) 2020-05-06 2020-05-06 Schaltwandler

Publications (1)

Publication Number Publication Date
EP3908084A1 true EP3908084A1 (de) 2021-11-10

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EP20173164.3A Withdrawn EP3908084A1 (de) 2020-05-06 2020-05-06 Schaltwandler
EP21718610.5A Pending EP4129010A1 (de) 2020-05-06 2021-04-20 Schaltwandler

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EP (2) EP3908084A1 (de)
WO (1) WO2021223998A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP4358647A1 (de) * 2022-10-19 2024-04-24 Tridonic GmbH & Co KG Synchron-sperrwandler mit rückkopplungsgesteuertem sekundärseitigem schalter

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080012502A1 (en) * 2004-03-15 2008-01-17 Color Kinetics Incorporated Led power control methods and apparatus
US20080051942A1 (en) * 2004-07-29 2008-02-28 Anorad Corporation Damping and stabilization for linear motor stage
WO2008112820A2 (en) * 2007-03-12 2008-09-18 Cirrus Logic, Inc. Power control system for current regulated light sources
US20130169172A1 (en) * 2011-12-28 2013-07-04 Iwatt Inc, Predictive Control of Power Converter for LED Driver
US20180092179A1 (en) * 2015-04-23 2018-03-29 Versitech Limited Ac-dc single-inductor multiple-output led drivers

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080012502A1 (en) * 2004-03-15 2008-01-17 Color Kinetics Incorporated Led power control methods and apparatus
US20080051942A1 (en) * 2004-07-29 2008-02-28 Anorad Corporation Damping and stabilization for linear motor stage
WO2008112820A2 (en) * 2007-03-12 2008-09-18 Cirrus Logic, Inc. Power control system for current regulated light sources
US20130169172A1 (en) * 2011-12-28 2013-07-04 Iwatt Inc, Predictive Control of Power Converter for LED Driver
US20180092179A1 (en) * 2015-04-23 2018-03-29 Versitech Limited Ac-dc single-inductor multiple-output led drivers

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP4358647A1 (de) * 2022-10-19 2024-04-24 Tridonic GmbH & Co KG Synchron-sperrwandler mit rückkopplungsgesteuertem sekundärseitigem schalter

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Publication number Publication date
EP4129010A1 (de) 2023-02-08
WO2021223998A1 (en) 2021-11-11

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