UPS devices with passive balancing

Abstract

A UPS device with passive balancing. The invention relates to a converter (100, 200), the converter (100, 200) comprising a DC splitting link (130) having a positive line (120), a floating midpoint (122) and a negative DC line (121), a first DC capacitor (108) arranged between the positive line and the floating midpoint, a second DC capacitor (109) arranged between the negative line (121) and the floating midpoint (122), a first resistor (111) arranged in parallel with the first DC capacitor (108), and a second resistor (112) arranged in parallel with the second DC capacitor (109). The first resistor (111) and the second resistor (112) are configured to be engaged during a pre-charging phase of the converter (100, 200).

Description

Technical Field

[0001] The present invention relates to a converter, an uninterruptible power supply (UPS) device, a controller for an uninterruptible power supply device, the use of a switchable resistor to provide DC voltage balancing, and a method for balancing the voltage of a DC splitting link in a converter. Background Art

[0002] In a UPS with an AC / DC booster, the DC link needs to be precharged. For example, the converter in the UPS device may include a precharge circuit that is connected to the AC line and the DC line of the converter so that the capacitor is precharged when the converter starts to avoid high currents for loading the capacitor when the circuit is turned on. In particular, voltage balance may be a problem on units with split DC links. This is not the case in a 4-wire system because the midpoint voltage is fixed by bonding, but this may become a problem in a 3-wire distribution where the midpoint is floating. Typically, precharging can be accomplished by an AC precharge circuit that includes a switch, a current limiting resistor, and a diode for each phase. However, such a circuit may suffer from unbalanced voltages and currents and a lack of ability to resist faults. Summary of the invention

[0003] It may therefore be an object of the present invention to provide a circuit for an improved converter.

[0004] This problem is solved by the subject matter of the independent claims. Embodiments are provided by the dependent claims, the following description and the drawings.

[0005] The described embodiments similarly relate to a converter, an uninterruptible power supply (UPS) device, a controller for an uninterruptible power supply device, the use of a switchable resistor to provide DC voltage balancing, and a method for balancing the voltage of a DC split link in a converter. Although it may not be described in detail, different combinations of the embodiments may produce synergistic effects.

[0006] In addition, it should be noted that all embodiments of the present invention regarding the method can be performed in the order of the steps described, but this is not necessarily the only and basic order of the steps of the method. Without departing from the corresponding method embodiment, the method proposed herein can be performed in another order of the disclosed steps, unless explicitly mentioned to the contrary below.

[0007] Technical terms are used in their common sense. If a specific meaning of certain terms is conveyed, the definitions of the terms are given below in the context in which they are used.

[0008] According to a first aspect, a converter is provided, the converter comprising a DC splitting link having a positive line, a floating midpoint and a negative DC line, a first DC capacitor arranged between the positive line and the midpoint, a second DC capacitor arranged between the negative line and the midpoint, a first resistor arranged in parallel with the first DC capacitor and a second resistor arranged in parallel with the second DC capacitor. The first resistor and the second resistor are configured to be engaged at least during a pre-charging phase of the converter.

[0009] The midpoint is floating and therefore not grounded. Without the resistor, the voltage between the positive and negative lines could be split in any ratio, resulting in an undesirable imbalance. The resistor enables the voltage in the split DC link to be balanced, i.e., the voltage of the positive line and the midpoint relative to the voltage between the midpoint and the negative line, in particular during the pre-charging of the capacitor immediately after the converter is turned on. Since the resistor circuit is passive, the balance is safe and is performed by a simple arrangement without switching delays, or without delays in cases where, for example, the control of the active elements is unavailable or unavailable at this time. That is, the passive balance can particularly provide balance when the active balancing circuit is not working or has not yet worked, for example, in the pre-charging phase of the converter when starting the converter, or for supporting the active balancing device. Therefore, the engagement of the passive DC voltage balancing device is also provided to facilitate the active converter to balance according to the needs of the operating conditions. Therefore, the resistor can remain turned on or re-connected after the pre-charging phase. This may be the case under certain operating conditions, for example, where active balancing is unstable, for supporting active balancing, or for discharging DC capacitors during, for example, short power interruptions or shutdown of a converter or UPS.

[0010] In this disclosure, the two resistor arrangement is designated as a “resistor circuit.” It may be implemented as a supplement to an AC pre-charge circuit, which may typically be arranged as a three-phase diode bridge with series current limiting resistors and an AC input engagement relay.

[0011] Furthermore, “capacitance” or “capacitor” refers to the DC capacitance or DC capacitor of the DC splitting link throughout the present disclosure.

[0012] According to one embodiment, the converter further comprises a first switchable contact arranged in series with the first resistor and a second switchable contact arranged in series with the second resistor. In other words, the first resistor and the first switchable contact are arranged in series between the positive line and the floating midpoint, such that they are connected in parallel with the first capacitance. Thus, the second resistor and the second switchable contact are arranged in series between the floating midpoint and the negative line, such that they are connected in parallel with the second capacitance. The contacts allow engaging or disengaging the resistors and thus allow passive balancing performed by the resistors.

[0013] According to one embodiment, the first switchable contact and the second switchable contact are configured to be switched simultaneously. This can ensure that no imbalance occurs if, for example, only one resistor is engaged accidentally.

[0014] According to one embodiment, the first contact and the second contact are parts of a single switch. In other words, the contacts are contacts of the same switch, so only one control signal is needed to switch them simultaneously.

[0015] According to one embodiment, the switchable contacts are of the "normal-on" type. That is, if no control signal is available, the contacts are closed so that they conduct the current between the positive or negative line through the resistor to the midpoint.

[0016] According to one embodiment, the switch is an electromechanical relay. The electromechanical relay may be of the "normally open" type, such that the switch closes without an activation signal and provides coupling without losses, thereby not introducing any difference or imbalance between the two paths.

[0017] According to one embodiment, when pre-charging is complete, the switch (i.e., the contacts of the switch) is disconnected. In this case, the passive balancing of the resistors stops. For example, pre-charging can be defined as complete when the active balancing circuit is operational or when a voltage threshold at the capacitor is reached. Another point in time may be when the pre-charging circuit is disengaged. However, this point in time does not necessarily coincide with the point in time when the switch is disconnected.

[0018] In this way, a passive DC voltage balancing device is provided, which is engaged in a split DC link topology from the beginning of the DC link pre-charging phase until the start-up of the active converter. By closing the switch, i.e. opening e.g. a relay, when pre-charging is completed, the subsequent isolation of the above passive balancing during normal converter operation is obtained by the switching device (e.g. a relay).

[0019] According to one embodiment, the converter is a rectifier. In this case, the pre-charging circuit is a so-called AC pre-charging circuit. However, according to another embodiment, the converter may also be a DC-DC converter. In this case, a 2-pole active converter powered by a DC power source (such as a battery) may be used in a similar manner for pre-charging.

[0020] According to one embodiment, the first resistor and the second resistor are equal in value. Having the same value is a prerequisite for balance.

[0021] According to one embodiment, the first DC capacitance and the second DC capacitance are each realized by at least one capacitor.The DC split link comprises a parallel connection of, for example, electrolytic capacitors in the positive part of the DC split link and correspondingly in the negative part of the DC split link, the electrolytic capacitors being connected at a floating midpoint.

[0022] According to another aspect, a controller for a converter as described herein is provided, the controller being configured to switch a first switchable contact and a second switchable contact. As described above, when precharging is complete, the contacts can be turned off, i.e., switched from a closed state to an open state. For example, when the precharging circuit is disengaged, or when the capacitor has a predefined threshold voltage, or when the active balancing circuit is operating, the controller can switch the contacts simultaneously. The controller can also be configured to switch, i.e., engage and disengage the precharging circuit. The controller can be an analog or digital circuit and can include logic elements. The logic elements can include hard-wired and / or programmable logic. The logic elements can be included in a microprocessor, a CPLD, an FPGA, or other programmable electronic device. Instructions can be stored in a memory device such as EEPROMS, other memories, etc.

[0023] According to another aspect, there is provided an uninterruptible power supply device comprising a converter and a controller as described herein.

[0024] According to another aspect, there is provided a use of a switchable resistor arranged in parallel with a DC capacitor of a DC split link in an uninterruptible power supply device to provide DC voltage balance. The switchable resistor may be a resistor in series with a switch. The resistor may be engaged during and / or after a pre-charge phase. For a split DC link, there is a positive path and a negative path. Therefore, the switchable resistor may be located in the positive path and the negative path to provide DC voltage balance.

[0025] Therefore, a switchable passive balancing device is proposed, which ensures that the voltage of the split DC link is balanced during the pre-charging of the DC capacitors of the split DC link. The preferred embodiment of the invention is in the context of a UPS, but it can be used for any combination of systems employing a split DC link connected to a DC power source, such as photovoltaic devices, battery energy storage systems (BESS), etc.

[0026] According to another aspect, a method for balancing the voltage of a DC split link having a positive line, a floating midpoint and a negative DC line in a converter is provided, wherein a first DC capacitor is arranged between the positive line and the floating midpoint, a second DC capacitor is arranged between the negative line and the floating midpoint, and wherein a first resistor is arranged in parallel with the first DC capacitor and a second resistor is arranged in parallel with the second DC capacitor. The method comprises the following steps: starting the converter, starting precharging the capacitors, and at least during the precharging of the capacitors, engaging the resistors and balancing the voltages at the first capacitor and the second capacitor. Starting the converter means supplying power to the converter or, in general, to the UPS. As described above, due to resistors, for example of the "always on" type, precharging starts immediately before the active precharging unit is operational.

[0027] The method may include other steps. For example, when nominal operation is available, a voltage threshold is reached, or pre-charge is disengaged, the other step may be to disengage the resistor.

[0028] These and other features, aspects and advantages of the present invention will be better understood with reference to the accompanying drawings and the following description.In principle identical or equivalent elements have the same reference numerals. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A diagram showing an AC / DC converter with a resistor circuit according to an embodiment;

[0030] Figure 2 A diagram showing a DC / DC converter with a resistor circuit according to an embodiment;

[0031] Figure 3 A block diagram showing an uninterruptible power supply device according to an embodiment; and

[0032] Figure 4 A diagram showing a method according to an embodiment is shown. DETAILED DESCRIPTION

[0033] Figure 1 A diagram of an AC / DC converter 100 according to an embodiment is shown. More complex, Figure 1 The split DC link 130 is shown to include a DC capacitor 108 comprising three electrolytic capacitors connected in parallel between a positive line 120 and a flow midpoint 122 and a DC capacitor 109 correspondingly comprising three electrolytic capacitors connected in parallel between a negative line 121 and a flow midpoint 122 . Figure 1 Further shown is an AC pre-charge circuit 140, which includes a three-phase diode bridge 106, 107 with a series current limiting resistor 104 and an AC input engagement contact or relay 102. In addition, Figure 1 A resistor circuit 110 is shown, comprising a resistor 111 and a contact 113 in series and parallel with the capacitor 108, and a resistor 112 and a contact 114 in series and parallel with the capacitor 109. The two contacts 113, 114 drawn may be two contacts of the same switch 115 to prevent accidental insertion of parallel resistors on a single bank, thereby causing an imbalance. In addition, it may be a normally closed relay 115 to ensure that passive balancing is always inserted even in the event of a component failure.

[0034] Figure 2 A diagram of a converter 200 according to an embodiment is shown. Figure 1In the converter 100 shown, the capacitors 108 , 109 are pre-charged; however, the pre-charging is performed using a 2-pole active converter 202 , which is ultimately powered by a DC power source such as a battery 204 .

[0035] Figure 3 A block diagram of an uninterruptible power supply (UPS) device 300 according to an embodiment is shown. The UPS includes the above-mentioned converter 100 or 200, DC split links 108, 109, a resistor circuit 110 having contacts, and a controller 150.

[0036] Figure 4 A diagram of a method 400 according to an embodiment is shown. The method may be performed, for example, by a controller 150 of a converter 100, 200 in a UPS 300 and comprises the following steps:

[0037] In a first step 402, the converter is started, i.e., powered on. In a second step 404, the DC capacitors 108, 109 are precharged. The precharging may be done, for example, by an AC 140 or DC / DC 202 precharging unit. In a next step 406, the resistors are engaged to obtain a balance of the voltages of the capacitors 108, 109. To this end, the contacts 113, 114 of the switch 115 with contacts are closed. The contacts may be closed by default, so that this step 406 may not be an active step. This step 406 and the previous step 404 may be performed simultaneously or in reverse order. After performing these steps, the DC capacitors 108, 109 are precharged in a balanced manner. In a next step 408, when the precharging is complete, the voltage has reached a predefined threshold, or active balancing is available, the contacts 113, 114 are turned off, i.e., disconnected, so that the resistors 111, 112 are disengaged. With respect to step 408, if operating conditions require, the contacts 113, 114 may also remain in the on state to support active balancing, or they may be turned on again.

[0038] Controllers may be analog, digital, or mixed circuits and may include logic elements.

[0039] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement other changes to the disclosed embodiments when practicing the claimed invention. 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. A single processor or other unit can implement the functions of multiple items or steps recited in the claims. The fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used advantageously. A computer program can be implemented to provide logic. The computer program can be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium provided with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any figure mark in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A converter (100, 200), comprising: A DC split link (130) having a positive line (120), a floating midpoint (122) and a negative DC line (121); a first DC capacitor (108) disposed between the positive line and the floating midpoint; a second DC capacitor (109) arranged between the negative DC line (121) and the floating midpoint (122); A first resistor (111) arranged in parallel with the first DC capacitor (108); a second resistor (112) arranged in parallel with the second DC capacitor (109); a first switchable contact (113), the first switchable contact (113) being arranged in series with the first resistor (111); a second switchable contact (114), the second switchable contact (114) being arranged in series with the second resistor (112); wherein the first resistor (111) and the second resistor (112) are configured to be engaged at least during a pre-charge phase of the converter (100, 200), and The first switchable contact (113) and the second switchable contact (114) are of the "normally open" type.

2. The converter (100, 200) according to claim 1, wherein the first switchable contact (113) and the second switchable contact (114) are configured to be switched simultaneously.

3. The converter (100, 200) according to claim 1, wherein the first switchable contact (113) and the second switchable contact (114) are parts of a single switch (115).

4. The converter (100, 200) of claim 3, wherein the single switch (115) is an electromechanical relay.

5. The converter (100, 200) according to claim 3 or 4, wherein the single switch (115) is configured to be opened when the pre-charging is completed.

6. The converter (100, 200) according to any one of claims 1-4, wherein the converter is a rectifier.

7. The converter (100, 200) according to any one of claims 1-4, wherein the converter is a DC-DC converter.

8. The converter (100, 200) according to any one of claims 1-4, wherein the first resistor (111) and the second resistor (112) are of equal value.

9. The converter (100, 200) according to any one of claims 1-4, wherein the first DC capacitance (108) and the second DC capacitance (109) are each implemented by at least one capacitor.

10. A controller (150) for a converter (100) according to any one of claims 1 to 9, configured to switch the first switchable contact (113) and the second switchable contact (114).

11. An uninterruptible power supply device (300), comprising the converter (100, 200) according to any one of claims 1 to 9 and the controller according to claim 10.

12. Use of a switchable resistor (111, 112) arranged in parallel with a DC capacitor (108, 109) of a DC splitting link (130) to provide DC voltage balancing in an uninterruptible power supply device according to claim 11.

13. A method (400) for balancing the voltage of a DC splitting link (130) having a positive line (120), a floating midpoint (122) and a negative DC line (121) in a converter (100, 200), wherein a first DC capacitor (108) is arranged between the positive line (120) and the floating midpoint (122), and a second DC capacitor (109) is arranged between the negative DC line (121) and the floating midpoint (122); wherein a first resistor (111) ) is arranged in parallel with the first DC capacitor (108), and a second resistor (112) is arranged in parallel with the second DC capacitor (109); wherein a first switchable contact (113) is arranged in series with the first resistor (111); a second switchable contact (114) is arranged in series with the second resistor (112); and wherein the first switchable contact (113) and the second switchable contact (114) are of the "normally on" type; and wherein the method (400) comprises the following steps: Starting (402) the converter (100, 200); Starting (404) precharging the first DC capacitor (108) and the second DC capacitor (109); The resistors (111, 112) are engaged (406) and the voltages at the first DC capacitor (108) and the second DC capacitor (109) are balanced at least during pre-charging of the DC capacitors (108, 109).

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