Buck converter

Abstract

This invention relates to a buck converter, comprising a controller that controls a first switch and a second switch, and is arranged to operate the buck converter in a first mode and a second mode. In the first mode, an output connection is formed between an output node and a second output terminal of a rectifier circuit, the first switch is arranged to operate as a buck converter switch, and the second switch is arranged to operate as a synchronous freewheeling switch. In the second mode, an output connection is formed between a first output terminal of the rectifier circuit and an output node, the first switch is arranged to operate as a synchronous freewheeling switch, the second switch is arranged to operate as a buck converter switch, and wherein the controller is arranged to receive a mode control signal for operating the buck converter in either the first or second mode.

Description

TECHNICAL FIELD

[0001] The present invention relates to a step-down converter. The present invention also relates to a lighting system. The present invention also relates to a method for controlling a step-down converter. BACKGROUND

[0002] Installers of the electrical infrastructure of public lighting and their customers aim to use a DC power microgrid to supply public road lighting. Figure 1 Such a DC microgrid is shown. The electrical energy consumed by the lighting devices connected to the DC microgrid comes first from rectified 400V, 3-phase AC mains and secondly from a photovoltaic solar power system which is a DC power source.

[0003] As Figure 1 shown, two step-down converters are used to convert the input power into the desired output power. Two different types of step-down converters are needed because one step-down converter operates in a first position, (i.e. in the high side), and the other step-down converter operates in a second position (i.e. in the low side).

[0004] It is an object of the present invention to provide a step-down converter which is able to operate in different configurations so that it can operate in a high side position as well as in a low side position. SUMMARY

[0005] It is an object of the present invention to provide a step-down converter which can operate in different configurations.

[0006] To overcome this problem, in a first aspect of the present invention, there is provided a step-down converter comprising:

[0007] an input for receiving an input voltage;

[0008] an output node for providing an output voltage to a load;

[0009] a rectifier circuit coupled to the input;

[0010] a first switch coupled between a first output of the rectifier circuit and a switching node;

[0011] a second switch coupled between the switching node and a second output of the rectifier circuit;

[0012] an inductor coupled between the switching node and the output;

[0013] a first capacitor coupled between the first output of the rectifier and the output;

[0014] a second capacitor coupled between the output and the second output of the rectifier; and

[0015] a controller for controlling the first switch and the second switch and arranged to operate the buck converter in a first mode and a second mode,

[0016] wherein in the first mode;

[0017] an output connection is formed between the output node and a second output terminal of the rectifier circuit;

[0018] the first switch is arranged to operate as a buck converter switch;

[0019] the second switch is arranged to operate as a synchronous rectifier switch;

[0020] and wherein in the second mode;

[0021] an output connection is formed between a first output terminal of the rectifier circuit and the output node;

[0022] the first switch is arranged to operate as a synchronous rectifier switch;

[0023] the second switch is arranged to operate as a buck converter switch;

[0024] and wherein the controller is arranged to receive a mode control signal for operating the buck converter in the first mode or the second mode.

[0025] The buck converter according to this aspect can be configured to operate as a buck converter with a low-side output in the first mode. By changing the operation of the buck converter in the second mode, the buck converter has a high-side output (i.e. a floating output). This change of mode can be done without any significant hardware modifications, as the output capacitor is divided between the high-side output and the low-side output of the buck converter.

[0026] In another example, the buck converter has a rectifier circuit arranged to receive a three-phase input voltage.

[0027] In case high power is required, a three-phase input is required to allow a large power to be provided to the buck converter.

[0028] In another example, the mode control signal is provided via one of a wireless control signal, a mechanical switch or a voltage provided to an input of the controller.

[0029] The provision of the mode control signal allows the step-down converter to operate in the first mode or the second mode or to change the mode of operation. The wireless control signal can be provided by an installer via a hand-held device that allows for a simple configuration of the step-down converter. There can be a mechanical switch in the socket in which the step-down converter is installed. By installing the step-down converter in a high-side socket, the mechanical switch can be configured such that the step-down converter is automatically configured as a high-side step-down converter. The same applies to a low-side socket, in which the mechanical switch is configured such that the step-down converter is configured as a low-side step-down converter upon insertion of the step-down converter into the low-side socket. The step-down converter can be arranged such that it can receive signals from two different mechanical switches, such that the mechanical switch in a high-side socket can be positioned differently compared to the mechanical switch in a low-side socket.

[0030] In another example, the step-down converter comprises a power factor corrector between the rectifier circuit and the first switch and the second switch.

[0031] When a lamp or luminaire is operated at the rated power, more than 25 Watts are being consumed by the load and the step-down converter, then a power correction according to the regulations is required.

[0032] In another example, the third switch is coupled in series with the first capacitor and the fourth switch is coupled in series with the second capacitor, wherein the third switch and the fourth switch are arranged to limit the inrush current during start-up of the step-down converter.

[0033] This allows the capacitors of the high-side and the low-side to be connected or disconnected from the rest of the circuit. When the third switch is open, the first capacitor is disconnected from the rest of the circuit (i.e. no current can flow through the capacitor anymore). This can be done in case the step-down converter is operated in the first (low-side) mode, wherein the first capacitor will not be active. Thus, when the fourth switch is open, the second capacitor is disconnected from the rest of the circuit. This can be done in case the step-down converter is operated in the second (high-side) mode, wherein the second capacitor will not be active. In addition, the switches can be used to prevent the generation of an excessive inrush current. When one of the switches is open during start-up of the step-down converter or when the step-down converter is provided with power from the input voltage, the capacitors cannot charge and an excessive inrush current is prevented. In addition, by preventing the capacitors connected to the output of the step-down converter from charging, an undesired voltage build-up at the output can be prevented, which can otherwise lead to an undesired or uncontrolled activation of the load.

[0034] In another example, the third switch and the fourth switch are arranged to limit the inrush current by closing the third switch and the fourth switch in a linear operation. Operating the switches in a linear operation allows the capacitors to charge with a predefined current. This allows the inrush current to be limited to a defined value and also allows the capacitors to charge such that the output voltage is controllably increased.

[0035] In another example, during start-up of the buck converter and in the first mode, the fourth switch is arranged to be closed, and wherein during start-up of the buck converter and in the second mode, the third switch is arranged to be closed. This allows limiting the inrush current during operation in the first mode and during operation in the second mode.

[0036] In another example, a driver is provided, comprising:

[0037] a first buck converter according to any of the preceding examples and arranged to operate in a first mode,

[0038] a second buck converter according to any of the preceding examples and arranged to operate in a second mode,

[0039] wherein a second output of the rectifier circuit of the first buck converter is coupled to a first output of the rectifier circuit of the second buck converter,

[0040] wherein an output of the lighting system is between the output node of the first buck converter and the output node of the second buck converter.

[0041] The driver is capable of providing a positive and a negative output voltage. Depending on how the load is connected, a single high voltage load can be connected to both output nodes, or two different loads can be connected between the output nodes with a return path to the connection between the first and second buck converter, which in this example is the second output of the rectifier circuit of the first buck converter.

[0042] In another example, a lighting system is provided, wherein the lighting system comprises:

[0043] a driver; and

[0044] a load, which is a single load or a dual load;

[0045] wherein the single load is coupled to the driver between the output node of the first buck converter and the output node of the second buck converter; and

[0046] wherein the dual load is coupled to the driver between the output node of the first buck converter and the second output of the rectifier circuit of the first buck converter and between the output node of the second buck converter and the second output of the rectifier circuit of the first buck converter.

[0047] The driver can be used to provide power to a lighting load, wherein the lighting load can be configured as a single lighting load or a dual lighting load.

[0048] In another example, the lighting load is an LED load.

[0049] According to another example, there is provided a method for controlling a buck converter, the buck converter comprising:

[0050] an output node for providing an output voltage to a load;

[0051] a rectifier circuit coupled to the input;

[0052] a first switch coupled between a first output of the rectifier circuit and a switching node;

[0053] a second switch coupled between the switching node and a second output of the rectifier circuit;

[0054] an inductor coupled between the switching node and the output;

[0055] a first capacitor coupled between the first output of the rectifier and the output;

[0056] a second capacitor coupled between the output and the second output of the rectifier; and

[0057] a controller;

[0058] and wherein the method comprises:

[0059] operating the buck converter in a first mode, wherein in the first mode:

[0060] an output connection is made between the output node and the second output of the rectifier circuit;

[0061] the first switch is arranged to operate as a buck converter switch;

[0062] the second switch is arranged to operate as a synchronous freewheeling switch;

[0063] operating the buck converter in a second mode, wherein in the second mode:

[0064] an output connection is made between the first output of the rectifier circuit and the output node;

[0065] the first switch is arranged to operate as the synchronous freewheeling switch;

[0066] the second switch is arranged to operate as a buck converter switch. BRIEF DESCRIPTION OF DRAWINGS

[0067] Examples of the application will now be described with reference to the accompanying drawings, in which:

[0068] Figure 1 An example of a current system with two different buck converters is shown.

[0069] Figure 2 An example of a known buck converter is shown, which has an output voltage relative to the negative of the input voltage.

[0070] Figure 3 An example of a known buck converter is shown, which has an output voltage as the difference between the positive of the input voltage and the output.

[0071] Figure 4 An embodiment of a buck converter according to the invention is shown.

[0072] Figure 5 Another embodiment of a buck converter according to the invention is shown.

[0073] Figure 6 Another different embodiment of a buck converter according to the invention is shown.

[0074] Figure 7 Another different embodiment of a buck converter according to the invention is shown.

[0075] Figure 8 An embodiment of a system according to the invention is shown. DETAILED DESCRIPTION

[0076] The present invention will be described with reference to the accompanying drawings.

[0077] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of apparatuses, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the present invention. These and other features, aspects, and advantages of the apparatuses, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the drawings are diagrammatic and schematic only, and are not drawn to scale. It should also be understood that the same reference numerals will be used throughout the figures to indicate the same or similar components.

[0078] Figure 1 A known system is shown with a first three-phase AC power system, a second three-phase power system and a third three-phase AC power system. The first three-phase AC power system with conductors L1, L2, L3 and N is characterized by a starting point of the transformer winding with a ground connection and which is connected to a not shown generator. The second three-phase AC power system is characterized by an isolation from ground provided by the winding of power transformer A. The third three-phase AC power system is characterized by an isolation from ground provided by the winding of power transformer B.

[0079] An isolated second three-phase AC power system is connected to the input of a first three-phase bridge rectifier that generates a DC bus voltage A. The DC bus voltage A is the input voltage of a buck converter A. The buck converter A operates in a first mode (Mode A) that has an output voltage that is negative with respect to the input voltage's negative terminal, as will be discussed in Figure 2

[0080] An isolated third three-phase AC power system is connected to the input of a second three-phase bridge rectifier that generates a DC bus voltage B. The DC bus voltage B is the input voltage of a buck converter B. The buck converter B operates in a second mode (Mode B) that has an output voltage that is the difference between the positive terminal of the input voltage and the output terminal, as will be discussed in Figure 3

[0081] The ground reference of the first buck converter (i.e. the low potential of the rectifier bridge of the first buck converter) is connected to the high potential of the rectifier bridge of the second buck converter. This allows both buck converters to generate positive and negative voltages with respect to a midpoint line "M". The first converter generates a positive voltage with respect to the midpoint M and the second buck converter generates a negative voltage with respect to the midpoint M. The midpoint M line can also be connected to ground to have a protective earth (PE) conductor used in a Terre Neutral Separated (TN-S) earthing system. A first load can be connected between the output of the first buck converter and the midpoint M. A second load can be connected between the midpoint and the output of the second buck converter.

[0082] Both buck converters are dedicated to their location. This means that due to their hardware design, the buck converters cannot be interchanged between each other.

[0083] Figure 2 A buck converter is shown that has an output voltage on a capacitor CI between the output of the input voltage and the ground reference of the input voltage. Switch Ql allows the inductor LI to build an inductor current when the switch is closed. When the switch is open, the inductor current discharges through the freewheeling diode DI to the load and the capacitor CI. In case the load is connected to the L terminal, the current returns through the freewheeling diode through the L conductor. In case the load is connected between the two output terminals of the buck converter (i.e. without a midpoint conductor), the current returns through the diode DI and the inductor LI of the second buck converter.

[0084] Figure 3 ​​A buck converter is shown which is characterized by having an output voltage which is the difference between a positive input voltage L+ and the output on a capacitor Cl. When the switch is closed, the switch Ql allows the inductor LI to build up an inductor current. When the switch is open, the inductor current discharges through the freewheeling diode Dl to the load and capacitor Cl. In the case where the load is connected to the L+ terminal, the current flows through the L+ terminal to the load and back to the inductor LI. In the case where the load is connected between the two output terminals of the buck converter (i.e. without a midpoint conductor), the current flows back through the inductor LI and diode Dl of the first buck converter.

[0085] Figure 4 An embodiment of a buck converter according to the invention is shown. The buck converter receives an input voltage which can be a DC voltage or a rectified AC voltage. If required, a power factor correction circuit can be introduced between the supply voltage and the input terminals L+ and L-. L+ and L- can also be derived from a three-phase input voltage. A suitable rectifier can be used for the rectification of the three-phase voltage. In addition, a power factor correction circuit can be introduced after the rectifier. The buck converter also has two switches coupled in series between the input terminals L+ and L-. A first switch Ql is coupled between the input voltage bus L+ and a switching node HB. A second switch Q2 is coupled between the switching node HB and the ground reference L-. An inductor LI is coupled between the switching node HB and an output node (output). A first capacitor Cl is coupled between the input voltage bus L+ and the output node (output). A second capacitor C2 is coupled between the output node (output) and the ground reference L-. A controller is used to control the first switch Ql and the second switch Q2 so that a desired power can be delivered to the output node (output). In this example, the output voltage is used as a feedback signal, but the skilled person understands that there can be more ways to control the buck converter, for example, output current control or feed forward control modes.

[0086] A mode control signal is provided to the controller. This allows the controller to be configured so that the buck converter operates in a first mode or a second mode. The control signal can be provided in many different ways, for example, by a wireless signal, a mechanical switch or a controlled voltage applied to the mode control input. The buck converter can be configured so that the output voltage for connecting a load can be positive or negative with respect to the ground reference potential. In the first mode, in order to provide a positive voltage V DC.3 , the buck converter is controlled to control the second switch Q2 as a freewheeling diode and the first switch Ql as a switch for controlling the current built up in the inductor LI. Although only the second capacitor C2 is in parallel with the output voltage V DC.3 , both the first capacitor Cl and the second capacitor C2 contribute to the filtering and stabilization of the output voltage.

[0087] When the buck converter is operated in the second mode, by providing a different mode control signal, the first switch Q1 is a freewheeling diode and the second switch Q2 is controlled as a switch for controlling the current build-up in the inductor LI. Although only the capacitor CI is in parallel with the output voltage V DC.2 but both the first capacitor CI and the second capacitor C2 contribute to the filtering and stabilizing of the output voltage.

[0088] In Figure 5 , an example of a buck converter according to the invention is provided. Figure 5 The buck converter of Figure 4 shows the same technical features as the buck converter described in Figure 5 . The buck converter now further comprises a third switch Q3 coupled in series with the first capacitor CI. Because the first capacitor CI and the second capacitor C2 are coupled in series between the input terminals, this can cause a large inrush current to flow when the buck converter is powered up. To prevent too large inrush currents from occurring, a switch can be placed in series with one of the first capacitor CI and the second capacitor C2. In Figure 5 , the third switch Q3 is in series with the first capacitor CI. This means that the series combination of the first capacitor CI and the third switch Q3 is placed at the output node (output) of the buck converter, i.e. this series combination is used for stabilizing the output voltage. The third switch Q3 can be open when the buck converter is powered up. This can be the moment when the input voltage is provided to the buck converter by switching on a switch between the input voltage and the buck converter. Because the third switch Q3 is open, no current flows through the series connection of the first capacitor CI and the second capacitor C2, because the series path is interrupted by the third switch Q3. When the start-up period has passed, the third switch Q3 can be closed with a defined conduction, so that the first capacitor CI can be charged with a controlled inrush current through the third switch Q3, the inductor LI and the second switch Q2. After this period, the buck converter increases and controls the output voltage V DC.3 and operates in the first mode.

[0089] In Figure 6 , another example of a buck converter according to the invention is described. Figure 6 The buck converter of Figure 4 shows the same technical features as the buck converter described in Figure 5the function of the third switch Q3 in the first mode. At least during the power-up of the buck converter, the series path between the first capacitor CI and the second capacitor C2 is interrupted, thus preventing an excessive inrush current. When the start-up period has passed, the third switch Q3 can be closed with a defined conductivity, so that the second capacitor C2 can be charged with a controlled inrush current through Q1, LI and Q3. After this period, the buck converter increases and controls the output voltage V DC.2 and operates in the second mode.

[0090] In Figure 7 a preferred example of a buck converter according to the present application is disclosed. Figure 7 The buck converter of Figure 4 shows the same technical features as the buck converter described in Figure 5 and Figure 6 by opening at least one of the third switch Q3 and the fourth switch Q4.

[0091] By having two switches Q3 and Q4, it is possible to configure which one of the third switch Q3 and the fourth switch Q4 will be open based on the selected mode of operation of the buck converter, i.e. the first mode or the second mode. For example, if the buck converter is configured to operate in the first mode, the second switch Q2 is configured to operate as a freewheeling diode and the first switch Q1 is controlled as a switch for controlling the current established in the inductor LI. The third switch Q3 is arranged to be closed after the power-up of the buck converter is arranged to be constantly closed. If the buck converter operates in the second mode, the second switch Q2 is configured to operate as a switch for controlling the current established in the inductor LI and the first switch Q1 is controlled as a freewheeling diode. The fourth switch Q4 is arranged to be closed after the power-up of the buck converter and the third switch Q3 is arranged to be constantly closed.

[0092] Alternatively, in the first mode, the third switch Q3 can remain open and in the second mode, the fourth switch Q4 can remain open.

[0093] Figure 8 A power system with two similar buck converters is shown. The first buck converter is configured to operate in the first mode via a mode control signal and is placed on the high side of the power system. The second buck converter is configured to operate in the second mode via a control mode signal and is placed on the low side of the power system.

[0094] In this example, two step-down converters receive galvanically isolated three-phase input voltages from two three-phase AC busbars. These input voltages are rectified by two three-phase rectifier circuits and are individually provided to the two step-down converters. The connection from the second output of the rectifier circuit A of the first step-down converter A to the first output of the rectifier circuit B of the second step-down converter B is implemented in such a way that the two step-down converters generate individual voltages with respect to the midpoint M.

[0095] The connection of the load depends on the requirements of the load, when a load with a high voltage requirement is connected to the power system, the load is connected between the outputs of the two step-down converters. In this example, the load will receive a voltage of +350 V and -350 V, thus a total of 700 V.

[0096] When a load with a lower voltage requirement is used, two different loads can be connected between the outputs of the step-down converters. In this case, a midpoint connection is required. Both loads are connected to the midpoint connection M. Due to the Terre neutral protection, the midpoint and the protective earth connection are connected to each other. Due to the connection between the first step-down converter and the second step-down converter with respect to the protective earth, the first step-down converter A generates a positive voltage and the second step-down converter B generates a negative voltage. In this example, a positive voltage of 350 V is provided by the first step-down converter and a negative voltage of -350 V is generated by the second step-down converter. Two loads requiring 350 V can be connected to the two step-down converters.

[0097] With regard to the above examples of the invention, the controller can be implemented in many different ways, such as but not limited to a microcontroller, an FPGA, a dedicated chip or an analog control circuit.

[0098] The load connected to the step-down converter can be any type of load, such as but not limited to a motor, a lighting load, preferably an LED lighting load.

[0099] In order to improve the power factor of the system comprising the step-down converter, a power factor correction circuit can be placed between the rectifier circuit and the step-down converter. The coupling of the first switch and the second switch is then done via the power factor correction circuit. An example of a power factor correction circuit can be a boost converter.

[0100] Further modifications of the disclosed embodiments in addition to those described herein will become apparent to those skilled in the art from the disclosure, and it is intended to fall within the scope of the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A buck converter comprising: an input for receiving an input voltage; an output node for providing an output voltage to a load; a rectifier circuit coupled to the input; a first switch (Ql) coupled between a first output of the rectifier circuit and a switching node; a second switch (Q2) coupled between the switching node and a second output of the rectifier circuit; an inductor (LI) coupled between the switching node and the output node; a first capacitor (Cl) coupled between the first output of the rectifier and the output node; a second capacitor (C2) coupled between the output node and the second output of the rectifier; and a controller for controlling the first switch (Ql) and the second switch (Q2) and arranged to operate the buck converter in a first mode and a second mode, wherein in the first mode: an output connection is formed between the output node and the second output of the rectifier circuit; the first switch (Ql) is arranged to operate as a buck converter switch; the second switch (Q2) is arranged to operate as a synchronous freewheeling switch; and wherein in the second mode: an output connection is formed between the first output of the rectifier circuit and the output node; the first switch (Ql) is arranged to operate as the synchronous freewheeling switch; the second switch (Q2) is arranged to operate as a buck converter switch; and wherein the controller is arranged to receive a mode control signal for operating the buck converter in the first mode or the second mode.

2. The buck converter of claim 1, wherein the rectifier circuit is arranged to receive a three-phase input voltage.

3. The buck converter of claim 1, wherein the mode control signal is provided via one of a wireless control signal, a mechanical switch, or a voltage provided to an input of the controller.

4. The buck converter of claim 1, further comprising a power factor circuit between the rectifier circuit and a series combination of the first switch (Ql) and the second switch (Q2).

5. The buck converter of claim 1, wherein a third switch (Q3) is coupled in series with the first capacitor (Cl) and a fourth switch (Q4) is coupled in series with the second capacitor (C2).

6. The buck converter of claim 5, wherein the third switch (Q3) and the fourth switch (Q4) are arranged to limit inrush current by closing the third switch (Q3) and the fourth switch (Q4) in linear operation.

7. The buck converter of claim 5, wherein during start-up of the buck converter and in the first mode, the fourth switch (Q4) is arranged to be closed, and wherein during start-up of the buck converter and in the second mode, the third switch (Q3) is arranged to be closed. ​ 8. A driver comprising: a first buck converter according to the preceding claim 1 and arranged to operate in the first mode, a second buck converter according to the preceding claim 1 and arranged to operate in the second mode, wherein the second output of the rectifier circuit of the first buck converter is coupled to the first output of the rectifier circuit of the second buck converter, wherein an output of the driver is between the output node of the first buck converter and the output node of the second buck converter.

9. A lighting system comprising: a driver according to claim 8; and a load, the load being a single lighting load or a dual lighting load; wherein the single lighting load is coupled to the driver between the output node of the first buck converter and the output node of the second buck converter; and wherein the dual lighting load is coupled to the driver between the output node of the first buck converter and the second output of the rectifier circuit of the first buck converter and between the output node of the second buck converter and the second output of the rectifier circuit of the first buck converter.

10. The lighting system according to claim 9, wherein the lighting load is an LED load.

11. A method for controlling a buck converter, the buck converter comprising: an input for receiving an input voltage; an output node for providing an output voltage to a load; a rectifier circuit coupled to the input; a first switch (Q1) coupled between a first output of the rectifier circuit and a switching node; a second switch (Q2) coupled between the switching node and a second output of the rectifier circuit; an inductor (LI) coupled between the switching node and the output node; a first capacitor (CI) coupled between the first output of the rectifier and the output node; a second capacitor (C2) coupled between the output node and the second output of the rectifier; and a controller; wherein the method comprises: operating the buck converter in a first mode, wherein in the first mode: an output connection is formed between the output node and the second output of the rectifier circuit; the first switch (Q1) is arranged to operate as a buck converter switch; the second switch (Q2) is arranged to operate as a synchronous freewheeling switch; operating the buck converter in a second mode, wherein in the second mode: an output connection is formed between the first output of the rectifier circuit and the output node; the first switch (Q1) is arranged to operate as the synchronous freewheeling switch; the second switch (Q2) is arranged to operate as a buck converter switch.

Images