Method for operating a converter, control unit for controlling a converter and converter

Abstract

The present disclosure relates to a method for operating a converter. The converter comprises a first, second, third and fourth terminal for receiving DC voltages; a first and second capacitor; and a series connection of a first, second, third and fourth semiconductor switch unit. The first terminal of the converter is connected via a first inductor with the first semiconductor switch unit. The fourth terminal of the converter is electrically connected via a second inductor with the fourth semiconductor switch unit. The first capacitor is connected with the first and second semiconductor switch unit. The second capacitor is connected with the third and fourth semiconductor switch unit. The method comprises monitoring a current through the first and second inductor; and switching the first or fourth semiconductor switch unit to the conducting state in response to detecting an over current through the first or second inductor, respectively.

Description

[0001] METHOD FOR OPERATING A CONVERTER, CONTROL UNIT FOR CONTROLLING A CONVERTER AND CONVERTER

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method for operating a converter, a control unit for controlling a converter and a converter.

[0004] BACKGROUND

[0005] Solar energy may be translated into electrical energy by solar photovoltaic (PV) panels, e.g. PV arrays. The electrical energy translated from solar energy is in the form of direct current (DC) energy. Eventually, the DC electric energy is delivered to alternating current (AC) power systems by means of power electronic conversion systems. Consumption and loads may use the electrical energy in the form of AC energy. Examples of loads may comprise home appliances, industry motors, etc.

[0006] SUMMARY

[0007] A power converter system for converting DC power to AC power may comprise two stages. A first stage may comprise or be a DC-to-DC power converter stage. That is, one level of DC voltage or current may be converted to a lower or greater level of DC voltage or current. For example, a DC voltage or current may be converted to a lower or greater DC voltage or current (i.e. voltage or current of lower or higher level), respectively. The second stage may comprise or be a DC-to-AC power converter stage, which may be referred to as inverter stage. That is, DC power may be converted to AC power. For example, a DC voltage or current may be converted to an AC voltage or current, respectively. Optionally, the power converter system may be bidirectional. In this case, the second stage may be configured to be an AC-to-DC power converter stage. That is, AC power may be converted to DC power.

[0008] In case a PV system, such as a PV array or PV panel, are electrically connected to a DC-to-DC power converter stage, the DC- to-DC converter stage may be configured to boost an input DC voltage provided by the PV array or panel to a value higher at the output of the DC-to-DC converter stage. The terms “solar PV” and, thus, “solar PV system” may be used as synonyms for the terms “PV” and “PV system”, respectively.

[0009] Depending on the regions of the world there are variations of grounding systems used in the various national grids. Examples of grounding system comprise TN-C system, TN-S system, TN-C-S system, TT system and IT system. These grounding systems are well known and, thus, a detail description of them is omitted. When connecting an electrical source (voltage source), such as a photo voltaic (PV) system, via a converter to the grid, the electrical source may be electrical grounded according to one of the aforementioned systems. Examples of PV system comprise PV array(s), PV string(s) etc. During operation ground faults may occur. The term “ground failure” may be used as a synonym for the term “ground fault”. The term ground fault means that electricity, such as a current, takes an unplanned path to ground, e.g. due to an unwanted short circuit occurring. A converter for connecting the electrical source, e.g. PV system, to the grid should be configured to sustain such a ground fault. That is, such a converter should be able to prevent an unwanted current flow due to such ground fault, because such an unwanted current flow may damage the converter, e.g. components of the converter, and / or a load connected to the converter, such as the grid or another converter stage in case the grid is connected via the other converter stage to the converter.

[0010] In view of the above, this disclosure aims to provide a converter for a DC-to-DC conversion that allows to tolerate a ground fault. An objective of this disclosure is to provide such a converter that allows tolerating a first ground fault and a second consequent ground fault as well. Especially an objective of this disclosure is to provide a converter for a DC-to-DC conversion that allows tolerating a first and second ground fault in TN grids (e.g. grid using a TN-S ground system, TN-C ground system or TN-C-S ground system) or IT grids (e.g. grid using an IT ground system).

[0011] These and other objectives are achieved by the solution of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0012] Herein, the terms “electrically connect” and “connect” are used as synonyms. A semiconductor switch may comprise a control terminal. Herein, a semiconductor switch may be a transistor, a thyristor, triac etc. The semiconductor switch may be controlled via a control terminal to switch between the conducting state (i.e. on-state) and the non-conducting state (off-state). The term “controllable semiconductor switch” may be used as a synonym for the term “semiconductor switch”. Herein, semiconductor switches may be power semiconductor transistors, such as an insulated-gate bipolar transistors (IGBTs) or metal-oxide-semi- conductor field-effect transistors (MOSFETs). Using MOSFET instead of IGBTS for the semiconductor switches has the following advantages: The operation speed of a MOSFET is faster than the operation speed of a similar rated IGBT. Power losses of a MOSFET are lower than power losses of a similar rated IGBT. IGBTs and MOSFETs allow to switch high current and voltages.

[0013] Herein, semiconductor switches may be transistors. A semiconductor switch being a transistor may be an insulated-gate bipolar transistor (IGBT), a field-effect transistor (FET), a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction transistors (BJT) or a junction gate field-effect transistor (JFET). Optionally, a semiconductor switch may be a semiconductor switch with a diode associated to it. For example, a semiconductor switch may be a transistor, such as a IGBT, with a diode connected in anti-parallel to the transistor. That is, in case a semiconductor switch is a transistor, optionally a diode is connected in anti-parallel to the transistor. For example, a semiconductor switch may be a transistor, such as a MOSFET, comprising an intrinsic body diode.

[0014] A first aspect of this disclosure provides a method for operating a converter. The converter comprises a first, second, third and fourth terminal for receiving DC voltages. The converter comprises a series connection of a first semiconductor switch unit, a second semiconductor switch unit, a third semiconductor switch unit and a fourth semiconductor switch unit. The converter comprises a first capacitor and second capacitor. The first terminal of the converter is electrically connected via a series connection of a first diode and a first inductor with a first terminal of the first semiconductor switch unit. A second terminal of the first semiconductor switch unit is electrically connected with a first terminal of the second semiconductor switch unit and the second terminal of the converter. A second terminal of the second semiconductor switch unit is electrically connected with a first terminal of the third semiconductor switch unit. A second terminal of the third semiconductor switch unit is electrically connected with a first terminal of the fourth semiconductor switch unit and the third terminal of the converter. The fourth terminal of the converter is electrically connected via a series connection of a second diode and a second inductor with a second terminal of the fourth semiconductor switch unit. A first terminal and a second terminal of the first capacitor is electrically connected with the first terminal of the first semiconductor switch unit and the second terminal of the second semiconductor switch unit, respectively. A first terminal and a second terminal of the second capacitor is electrically connected with the first terminal of the third semiconductor switch unit and the second terminal of the fourth semiconductor switch unit, respectively. The method comprises monitoring a current through the first inductor and second inductor. The method comprises switching the first semiconductor switch unit or the fourth semiconductor switch unit to the conducting state in response to detecting an over current through the first inductor or second inductor, respectively.

[0015] In case a single ground fault occurs at any one of the first, second, third and fourth terminal of the converter (i.e. any one of the first, second, third and fourth terminal is grounded), either the first diode or the second diode may prevent an unwanted current flow via the converter caused by the ground fault. Thus, the converter allows to tolerate a ground fault. In case a first and second ground fault occurs at any one of the pair of the first and second terminal of the converter (i.e. first and second terminal of converter are grounded), the pair of the first and third terminal of the converter (i.e. first and third terminal of converter are grounded), the pair of the first and fourth terminal of the converter (i.e. first and fourth terminal of converter are grounded), the pair of the second and fourth terminal of the converter (i.e. second and fourth terminal of converter are grounded) and the pair of the third and fourth terminal of the converter (i.e. third and fourth terminal of converter are grounded) the first diode and / or the second diode may prevent an unwanted current flow via the converter caused by the double ground fault. Thus, the converter allows to tolerate a first and second ground fault (i.e. a double ground fault). In case a first and second ground fault occurs at the second and third terminal of the converter the method of the first aspect allows to prevent an unwanted current flow via the converter caused by the double ground fault. Thus, the method allows to tolerate a first and second ground fault (i.e. a double ground fault) in all conditions. In light of the above, the converter and the method of the first aspect allows preventing an unwanted current flow caused by any possible single ground fault or double ground fault at the first, second, third and fourth terminal of the converter.

[0016] In other words, the converter comprises a series connection of the first semiconductor switch unit, second semiconductor switch unit, third semiconductor switch unit and fourth semiconductor switch unit, wherein an end of the aforementioned series connection is connected via the first diode and first inductor to the first terminal of the converter and the other end of the aforementioned series connection is connected via the second diode and second inductor to the fourth terminal of the converter. The second terminal of the converter is connected to a node between the first and second semiconductor switch unit, and the third terminal of the converter is connected to a node between the third and fourth semiconductor switch unit. The converter comprises a series connection of the first capacitor and second capacitor, the series connection of the first capacitor and second capacitor being connected in parallel with the series connection of the semiconductor switch units, wherein a node between the second and third semiconductor switch unit is connected with a node between the first and second capacitor.

[0017] The first and third terminal may be configured to be electrically connected with a first voltage source and the second and fourth terminal may be configured to be electrically connected with a second voltage source. The first and second voltage source may be a first and second PV system. The PV system comprising or being one or more PV panels and / or PV arrays. The first and second voltage sources may be a first and second battery, optional rechargeable batteries. The term “battery energy storage (BES)” may be used as a synonym for the term “battery”. The converter operated by the method of the first aspect allows providing a low loss maximum power point tracking (MPPT) operation. This allows an increase of an extraction of energy from energy sources, e.g. solar PV energy from PV systems, that may be connected to the first, second, third and fourth terminals of the converter.

[0018] The first and second capacitor split a voltage across them into two voltages of lower voltages. In addition, the series connection of the first and second semiconductor switch units being parallel to the first capacitor distribute the voltage of the first capacitor among them, and the series connection of the third and fourth semiconductor switch units being parallel to the second capacitor distribute the voltage of the second capacitor among them. As a result, low voltage and / or low current semiconductor devices may be used for implementing the semiconductor switch units. This allows reducing costs and size of the converter.

[0019] The converter may be a DC-to-DC converter. Optionally, the converter may be a DC-to-DC converter stage that feeds an DC- to-AC converter stage (i.e. an inverter stage). The converter may be configured to boost DC voltage(s) received at the first, second, third and fourth terminals of the converter, i.e. convert a received DC voltage to a voltage of higher level. The converter operated by the method of the first aspect being a DC-to-DC converter stage and a DC-to-AC converter stage being fed by the converter may interface a PV system and a grid. That is, they may be used to convert the DC voltage / direct current provided by the PV system to an AC voltage / altemating current for the grid. The first and second capacitor may be referred to as “first DC link capacitor” and “second DC link capacitor”, respectively. The converter allows, due to its structure a partial power processing for power conversion. In a partial power processing, a majority of the power from the source (feeding the converter) is directed to the load side (which provides power to a load when the load is connected to the converter) without any switching, while a small portion of the power is processed by means of the semiconductor switch units of the converter. The converter can maintain the voltage at the first and second capacitor at a predefined level as well as maintain the MPPT point of an input to the first, second, third and fourth terminals of the converter. At all input variations of voltage sources connectable to the first, second, third and fourth terminal of the converter, the semiconductor switch units operate a smaller portion of the total power, and therefore, may be implemented using low voltage and / or low current semiconductor devices, such as low voltage and / or low current semiconductor switches. Such low voltage and / or low current semiconductor devices are lower in costs compared to semiconductor devices rated for higher voltage and / or higher current. Low voltage and / or low current semiconductor devices can be switched faster and at high frequencies compared to semiconductor devices rated for higher voltage and / or higher current. Therefore, size of passive elements (such as inductors and capacitors) used in the converter can be reduced considerably. These devices dissipate lower losses resulting lower cooling and heatsink requirements. As a result, the converter operated by the method of the first aspect is improved with regard to costs and size. In addition, the converter is improved with regard to losses of semiconductor switches used in the converter for controlling the converter. Thus, the converter allows a scalability for higher voltage applications without comprising efficiency and cost. The converter may be referred to as “partial power converter” or “partially rated power converter”. The first inductor and second inductor support limiting a fault current. At normal conditions the first and second inductor are used for the conversion operation, e.g. boost operation, of the converter.

[0020] The method may comprise controlling the semiconductor switch units of the converter by performing a maximum power point tracking (MPPT) algorithm. Herein, controlling the semiconductor switch units means controlling switching of the semiconductor switch units.

[0021] Performing the MPPT algorithm for controlling the semiconductor switch units of the converter allows harvesting a maximum energy from electrical sources, e.g. voltage sources, that may be connected to the first, second, third and fourth terminal of the converter. Such electrical sources may be PV systems, such as PV panels or PV arrays. For example, the first, second, third and fourth terminal of the converter may be connected to PV systems, such as PV panels or PV arrays. In this case, performing the MPPT algorithm for controlling the semiconductor switch units allows ensuring that the PV systems produce the maximum available energy. The present disclosure is not limited to a specific type of MPPT algorithm. Thus, any known MPPT algorithm may be used.

[0022] The converter may be a MPPT-DC-to-DC converter. The method may comprise performing a MPPT algorithm to draw the most power possible from a photovoltaic (PV) system. Thus, the converter may be configured to employ a MPPT algorithm to draw the most power possible from a photovoltaic (PV) system. The maximum power point (MPP) is the voltage at which a PV system may generate its maximum power.

[0023] The terms “converter circuit”, “converter device” or “converter module” may be used as a synonym for the term “converter”. The components of the converter may be arranged in a housing of the converter. The term “on-state” may be used as a synonym for the term “conducting state”.

[0024] In an implementation form of the first aspect, the first terminal of the converter is electrically connected via a first switch with the series connection of the first diode and the first inductor. The second terminal of the converter may be electrically connected via a second switch with the second terminal of the first semiconductor switch unit. The third terminal the converter may be electrically connected via a third switch with the second terminal of the third semiconductor switch unit. The fourth terminal of the converter may be electrically connected via a fourth switch with the series connection of the second diode and the second inductor. The method may comprise switching all conducting semiconductor switch units of the first, second, third and fourth semiconductor switch unit and the first, second, third and fourth switch to the non-conducting state after lapse of a time period that starts with switching the first semiconductor switch unit or the fourth semiconductor switch unit to the conducting state in response to detecting an over current through the first inductor or second inductor, respectively.

[0025] Optionally, the method comprises switching the first, second, third and fourth switch to the non-conducting state after lapse of a time period that starts with switching the first semiconductor switch unit or the fourth semiconductor switch unit to the conducting state in response to detecting an over current through the first inductor or second inductor, respectively.

[0026] At least one, optionally each, of the first switch, second switch, third switch and fourth switch may be a switch that is configured to physically and electrically isolate using mechanical / electro mechanical means. For example, such a switch is configured to provide a gap between two electrical connections when the switch is in the non-conducting state (i.e. off-state). The term “mechanical breaker” or “mechanical switch” may be used to refer to such a switch. The first, second, third and fourth switch allow protecting the load side of the converter because they disconnect the load side of the converter from the side of the first, second, third and fourth terminal of the converter (i.e. the source side of the converter) when they are switched to the nonconducting state.

[0027] In an implementation form of the first aspect, each of the first, second, third and fourth semiconductor switch unit comprises or is a semiconductor switch. Switching the first semiconductor switch unit or the fourth semiconductor switch unit to the conducting state may comprise switching the semiconductor switch of the first semiconductor switch unit or the fourth semiconductor switch unit, respectively, to the conducting state.

[0028] In an implementation form of the first aspect, each of the first and second semiconductor switch unit comprises or is a series connection of two or more semiconductor switches. The converter may comprise one or more capacitors, the number of the one or more capacitors equals one less than the number of semiconductor switches of each of the first and second semiconductor switch unit. Each of the one or more capacitors may electrically connect a first node between two switches of the series connection of two or more semiconductor switches of the first semiconductor switch unit and a second node between two switches of the second series connection of two or more semiconductor switches of the second semiconductor switch unit with each other. The number of nodes between the first node and the first terminal of the first semiconductor switch unit and the number of nodes between the second node and the second terminal of the second semiconductor switch unit are equal to each other. Switching the first semiconductor switch unit to the conducting state may comprise switching the two or more semiconductor switches of the first semiconductor switch unit to the conducting state.

[0029] The one or more capacitors may be referred to as “flying capacitor(s)”. Thus, the first and second semiconductor switch units may form with the first inductor and the one or more capacitors a 3-level flying capacitor boost converter or higher-level flying capacitor boost converter.

[0030] In an implementation form of the first aspect, each of the third and fourth semiconductor switch unit comprises or is a series connection of two or more semiconductor switches. The converter may comprise one or more capacitors, the number of the one or more capacitors equals one less than the number of semiconductor switches of each of the third and fourth semiconductor switch unit. Each of the one or more capacitors may electrically connect a first node between two switches of the series connection of two or more semiconductor switches of the third semiconductor switch unit and a second node between two switches of the second series connection of two or more semiconductor switches of the fourth semiconductor switch unit with each other. The number of nodes between the first node and the first terminal of the third semiconductor switch unit and the number of nodes between the second node and the second terminal of the fourth semiconductor switch unit are equal to each other. Switching the fourth semiconductor switch unit to the conducting state may comprise switching the two or more semiconductor switches of the fourth semiconductor switch unit to the conducting state.

[0031] The one or more capacitors may be referred to as “flying capacitor(s)”. Thus, the third and fourth semiconductor switch units may form with the second inductor and the one or more capacitors a 3-level flying capacitor boost converter or higher-level flying capacitor boost converter.

[0032] In an implementation form of the first aspect, the first diode is arranged such that the anode and the cathode are directed in the direction of the first terminal of the converter and the first terminal of the first semiconductor switch unit, respectively. The second diode may be arranged such that the anode and the cathode are directed to the second terminal of the fourth semiconductor switch unit and the fourth terminal of the converter, respectively.

[0033] Alternatively, the first diode may be arranged such that the cathode and the anode are directed in the direction of the first terminal of the converter and the first terminal of the first semiconductor switch unit, respectively. The second diode may be arranged such that the cathode and the anode are directed to the second terminal of the fourth semiconductor switch unit and the fourth terminal of the converter, respectively.

[0034] The converter may be unidirectional and each of the first, second, third and fourth terminal of the converter is an input terminal, or the converter may be bidirectional.

[0035] In case the converter is bidirectional, rechargeable batteries may be connected to the converter. For example, a first rechargeable battery may be connected to the first and third terminal of the converter and a second rechargeable battery may be connected to the second and fourth terminal of the converter. This allows converting by the converter a DC voltage provided by the first and second battery to a voltage of lower or higher level and charging by the converter the first and second rechargeable battery.

[0036] The converter may comprise a fifth and sixth terminal that are configured to be electrically connected with an electrical load, the fifth terminal is electrically connected with the first terminal of the first capacitor, and the sixth terminal is electrically connected with the second terminal of the second capacitor.

[0037] The electrical load may be for example a converter stage, such as a DC-to-AC converter stage. The electrical load may be an electrical equipment that is configured to be electrically supplied with DC power, e.g. DC voltage or DC current.

[0038] The converter may comprise a DC-to-AC converter, wherein a first terminal and second terminal of the DC-to-AC converter are electrically connected with the first terminal of the first capacitor and the second terminal of the second capacitor, respectively. This allows the converter to convert DC power to AC power, e.g. connecting a PV system to the grid or AC load.

[0039] In order to achieve the method according to the first aspect of this disclosure, some or all of the implementation forms and optional features of the first aspect, as described above, may be combined with each other.

[0040] A second aspect of the disclosure provides a control unit for controlling a converter. The converter comprises a first, second, third and fourth terminal for receiving DC voltages. The converter comprises a series connection of a first semiconductor switch unit, a second semiconductor switch unit, a third semiconductor switch unit and a fourth semiconductor switch unit. The converter comprises a first capacitor and second capacitor. The first terminal of the converter is electrically connected via a series connection of a first diode and a first inductor with a first terminal of the first semiconductor switch unit. A second terminal of the first semiconductor switch unit is electrically connected with a first terminal of the second semiconductor switch unit and the second terminal of the converter. A second terminal of the second semiconductor switch unit is electrically connected with a first terminal of the third semiconductor switch unit. A second terminal of the third semiconductor switch unit is electrically connected with a first terminal of the fourth semiconductor switch unit and the third terminal of the converter. The fourth terminal of the converter is electrically connected via a series connection of a second diode and a second inductor with a second terminal of the fourth semiconductor switch unit. A first terminal and a second terminal of the first capacitor is electrically connected with the first terminal of the first semiconductor switch unit and the second terminal of the second semiconductor switch unit, respectively. A first terminal and a second terminal of the second capacitor is electrically connected with the first terminal of the third semiconductor switch unit and the second terminal of the fourth semiconductor switch unit, respectively. The control unit is configured to monitor a current through the first inductor and second inductor. The control unit is configured to control the first semiconductor switch unit or the fourth semiconductor switch unit to switch to the conducting state in response to detecting an over current through the first inductor or second inductor, respectively.

[0041] The term “control device” may be used as a synonym for the term “control unit”.

[0042] The first and third terminal of the converter may be configured to be electrically connected with a first voltage source and the second and fourth terminal of the converter may be configured to be electrically connected with a second voltage source.

[0043] The above description of the method according to the first aspect is correspondingly valid for the control unit of the second aspect. The control unit of the second aspect may be configured to perform the method of the first aspect.

[0044] The control unit of the second aspect and its implementation forms and optional features achieve the same advantages as the method of the first aspect and its respective implementation forms and respective optional features.

[0045] In order to achieve the control unit according to the second aspect of this disclosure, some or all of the implementation forms and optional features of the second aspect, as described above, may be combined with each other.

[0046] A third aspect of the disclosure provides a converter. The converter comprises a first, second, third and fourth terminal for receiving DC voltages. The converter comprises a series connection of a first semiconductor switch unit, a second semiconductor switch unit, a third semiconductor switch unit and a fourth semiconductor switch unit. The converter comprises a first capacitor and second capacitor. The first terminal of the converter is electrically connected via a series connection of a first diode and a first inductor with a first terminal of the first semiconductor switch unit. A second terminal of the first semiconductor switch unit is electrically connected with a first terminal of the second semiconductor switch unit and the second terminal of the converter. A second terminal of the second semiconductor switch unit is electrically connected with a first terminal of the third semiconductor switch unit. A second terminal of the third semiconductor switch unit is electrically connected with a first terminal of the fourth semiconductor switch unit and the third terminal of the converter. The fourth terminal of the converter is electrically connected via a series connection of a second diode and a second inductor with a second terminal of the fourth semiconductor switch unit. A first terminal and a second terminal of the first capacitor is electrically connected with the first terminal of the first semiconductor switch unit and the second terminal of the second semiconductor switch unit, respectively. A first terminal and a second terminal of the second capacitor is electrically connected with the first terminal of the third semiconductor switch unit and the second terminal of the fourth semiconductor switch unit, respectively. The converter further comprises a measuring circuit configured to measure a current through the first inductor and second inductor. The converter further comprises a control unit configured to obtain the measured current through the first inductor and second inductor and detect an over current through the first inductor and second inductor by monitoring the obtained measured current through the first inductor and second inductor. The control unit is configured to control the first semiconductor switch unit or the fourth semiconductor switch unit to switch to the conducting state in response to detecting the over current through the first inductor or second inductor, respectively.

[0047] The first and third terminal of the converter may be configured to be electrically connected with a first voltage source and the second and fourth terminal of the converter may be configured to be electrically connected with a second voltage source

[0048] The above description of the method according to the first aspect is correspondingly valid for the converter of the third aspect. The control unit of the converter of the third aspect may be configured to perform the method of the first aspect.

[0049] The converter of the third aspect and its implementation forms and optional features achieve the same advantages as the method of the first aspect and its respective implementation forms and respective optional features.

[0050] In an implementation form of the third aspect, the first terminal of the converter is electrically connected via a first switch with the series connection of the first diode and the first inductor. The second terminal of the converter may be electrically connected via a second switch with the second terminal of the first semiconductor switch unit. The third terminal of the converter may be electrically connected via a third switch with the second terminal of the third semiconductor switch unit. The fourth terminal of the converter may be electrically connected via a fourth switch with the series connection of the second diode and the second inductor. The control unit may be configured to control all conducting semiconductor switch units of the first, second, third and fourth semiconductor switch unit and the first, second, third and fourth switch to switch to the non-conducting state after lapse of a time period that starts with controlling, in response to detecting an over current through the first inductor or second inductor, the first semiconductor switch unit or the fourth semiconductor switch unit, respectively, to switch to the conducting state.

[0051] Optionally, the control unit may be configured to control the first, second, third and fourth switch to switch to the non-conducting state after lapse of a time period that starts with switching the first semiconductor switch unit or the fourth semiconductor switch unit to the conducting state in response to detecting an over current through the first inductor or second inductor, respectively.

[0052] In an implementation form of the third aspect, each of the first, second, third and fourth semiconductor switch unit comprises or is a semiconductor switch. The control unit may be configured to control the first semiconductor switch unit or the fourth semiconductor switch unit to switch to the conducting state by controlling the semiconductor switch of the first semiconductor switch unit or the fourth semiconductor switch unit, respectively, to switch to the conducting state.

[0053] In an implementation form of the third aspect, each of the first and second semiconductor switch unit comprises or is a series connection of two or more semiconductor switches. The converter may comprise one or more capacitors, the number of the one or more capacitors equals one less than the number of semiconductor switches of each of the first and second semiconductor switch unit. Each of the one or more capacitors may electrically connect a first node between two switches of the series connection of two or more semiconductor switches of the first semiconductor switch unit and a second node between two switches of the second series connection of two or more semiconductor switches of the second semiconductor switch unit with each other. The number of nodes between the first node and the first terminal of the first semiconductor switch unit and the number of nodes between the second node and the second terminal of the second semiconductor switch unit are equal to each other. The control unit may be configured to switch the first semiconductor switch unit to the conducting state by controlling the two or more semiconductor switches of the first semiconductor switch unit to switch to the conducting state. In an implementation form of the third aspect, each of the third and fourth semiconductor switch unit comprises or is a series connection of two or more semiconductor switches. The converter may comprise one or more capacitors, the number of the one or more capacitors equals one less than the number of semiconductor switches of each of the third and fourth semiconductor switch unit. Each of the one or more capacitors may electrically connect a first node between two switches of the series connection of two or more semiconductor switches of the third semiconductor switch unit and a second node between two switches of the second series connection of two or more semiconductor switches of the fourth semiconductor switch unit with each other. The number of nodes between the first node and the first terminal of the third semiconductor switch unit and the number of nodes between the second node and the second terminal of the fourth semiconductor switch unit are equal to each other. The control unit may be configured to switch the fourth semiconductor switch unit to switch to the conducting state by controlling the two or more semiconductor switches of the fourth semiconductor switch unit to switch to the conducting state.

[0054] In an implementation form of the third aspect, the first diode is arranged such that the anode and the cathode are directed in the direction of the first terminal of the converter and the first terminal of the first semiconductor switch unit, respectively. The second diode may be arranged such that the anode and the cathode are directed to the second terminal of the fourth semiconductor switch unit and the fourth terminal of the converter, respectively.

[0055] Alternatively, the first diode may be arranged such that the cathode and the anode are directed in the direction of the first terminal of the converter and the first terminal of the first semiconductor switch unit, respectively. The second diode may be arranged such that the cathode and the anode are directed to the second terminal of the fourth semiconductor switch unit and the fourth terminal of the converter, respectively.

[0056] In an implementation form of the third aspect, the converter is unidirectional and each of the first, second, third and fourth terminal of the converter is an input terminal. Alternatively, the converter may be bidirectional.

[0057] In an implementation form of the third aspect, the converter comprises a fifth and sixth terminal that are configured to be electrically connected with an electrical load. The fifth terminal is electrically connected with the first terminal of the first capacitor, and the sixth terminal is electrically connected with the second terminal of the second capacitor.

[0058] The converter may comprise a DC-to-AC converter, wherein a first terminal and second terminal of the DC-to-AC converter are electrically connected with the first terminal of the first capacitor and the second terminal of the second capacitor, respectively.

[0059] In order to achieve the converter according to the third aspect of this disclosure, some or all of the implementation forms and optional features of the third aspect, as described above, may be combined with each other.

[0060] The converter described with regard to the method of the first aspect, the converter described with regard to the control unit of the second aspect and the converter of the third aspect correspond to each other. The method of the first aspect, control unit of the second aspect and converter of the third aspect allow a low cost MPPT DC-to-DC conversion and a protection against ground faults. With regard to string inverters for interfacing a PV system (e.g. a PV array) to a grid, each string inverter comprising the converter described with regard to the first aspect or second aspect or the converter of the third aspect as a DC- to-DC converter stage and an DC-to-AC converter stage, the method of the first aspect, control unit of the second aspect and converter of the third aspect enable having a string level optimization, rather than multiple strings to be maintained at one MPPT. The method of the first aspect, the converter described with regard to the control unit of the second aspect and the converter of the third aspect allows extension of PV strings, BES integration or any combination of both. With the method of the first aspect, control unit of the second aspect and the converter of the third aspect, it is possible to improve the efficiency, power density and the cost of a MPPT DC / DC converter, e.g. when used for PV systems. Moreover, a high electrical efficiency can be achieved as lower voltage semiconductor devices can be used and by means of the integration of control and driving circuits in close proximity to switching power cells thereby minimizing delays and latencies in the control loop.

[0061] All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0062] BRIEF DESCRIPTION OF DRAWINGS

[0063] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0064] FIG. 1 shows an example of a converter according to this disclosure and an example of a control unit according to this disclosure for controlling a converter.

[0065] FIG. 2 shows an example of a state of the converter of FIG. 1 , in which two ground faults occur at terminals of the converter.

[0066] FIG. 3 shows an example of an implementation form of the converter of FIG. 1.

[0067] FIG. 4 shows an example of an implementation form of the converter of FIG. 1.

[0068] FIG. 5 shows an example of an implementation form of the converter of FIG. 1.

[0069] FIG. 6 shows an example of an implementation form of the converter of FIG. 1.

[0070] FIG. 7 shows an example of a method according to this disclosure for operating a converter according to this disclosure.

[0071] Same elements shown in the Figures (FIGs) are labeled with the same reference sign, and may be implemented likewise.

[0072] DETAILED DESCRIPTION OF EMBODIMENTS

[0073] FIG. 1 shows an example of a converter according to this disclosure and an example of a control unit according to this disclosure for controlling a converter. The converter of FIG. 1 is an example of the converter of the third aspect. Thus, the description of the converter of the third aspect is correspondingly valid for the converter of FIG. 1. The control unit of FIG. 1 is an example of the control unit of the second aspect. Thus, the description of the control unit of the second aspect is correspondingly valid for the control unit of FIG. 1. The converter 1 of FIG. 1 comprises a first terminal Tl, second terminal T2, third terminal T3 and fourth terminal T3 for receiving DC voltages. As shown in FIG. 1, the first and third terminal Tl, T3 may be configured to be electrically connected with a first voltage source 100 and the second and fourth terminal T2, T4 may be configured to be electrically connected with a second voltage source 200. The converter 1 comprises a series connection of a first semiconductor switch unit SU1, a second semiconductor switch unit SU2, a third semiconductor switch unit SU3 and a fourth semiconductor switch unit SU4. The converter 1 comprises a first capacitor Cl and second capacitor C2. The first terminal Tl of the converter 1 is electrically connected via a series connection of a first diode DI and a first inductor LI with a first terminal of the first semiconductor switch unit SU 1. A second terminal of the first semiconductor switch unit SU 1 is electrically connected with a first terminal of the second semiconductor switch unit SU2 and the second terminal T2 of the converter 1. A second terminal of the second semiconductor switch unit SU2 is electrically connected with a first terminal of the third semiconductor switch unit SU3. A second terminal of the third semiconductor switch unit SU3 is electrically connected with a first terminal of the fourth semiconductor switch unit SU4 and the third terminal T3 of the converter 1. The fourth terminal T4 of the converter 1 is electrically connected via a series connection of a second diode D2 and a second inductor L2 with a second terminal of the fourth semiconductor switch unit SU4. A first terminal and a second terminal of the first capacitor Cl is electrically connected with the first terminal of the first semiconductor switch unit SU1 and the second terminal of the second semiconductor switch unit SU2, respectively. A first terminal and a second terminal of the second capacitor C2 is electrically connected with the first terminal of the third semiconductor switch unit SU3 and the second terminal of the fourth semiconductor switch unit SU4, respectively.

[0074] The converter further comprises a measuring circuit 2 configured to measure a current (flowing) through the first inductor LI and a current (flowing) through the second inductor L2. The converter 1 further comprises a control unit 3 configured to obtain the measured current (flowing) through the first inductor LI and the measured current (flowing) through the second inductor L2. The control unit 3 is configured to detect an over current (flowing) through the first inductor and an overcurrent (flowing) through second inductor by monitoring the obtained measured current (flowing) through the first inductor LI and the obtained measured current (flowing) through the second inductor L2. The control unit 3 is configured to control the first semiconductor switch unit SU1 to switch to the conducting state in response to detecting the over current (flowing) through the first inductor LI . The control unit 3 is configured to control the fourth semiconductor switch unit SU4 to switch to the conducting state in response to detecting the over current (flowing) through the second inductor L2. The control unit 3 may comprise or correspond to a processor, microprocessor, controller, microcontroller, field programmable gate array (FPGA), application specific integrated circuit (ASIC) or any combination of the aforementioned components. The control unit 3 may provide control signals to the first semiconductor switch unit SU1, the second semiconductor switch unit SU2, the third semiconductor switch unit SU3 and the fourth semiconductor switch unit SU4, especially to control terminals of one or more semiconductor switches (such as one or more transistors) of the semiconductor switch units. The control unit 3 may be configured to control the semiconductor switch units SU1, SU2, SU3, SU4 of the converter 1 by performing a maximum power point tracking (MPPT) algorithm. The present disclosure is not limited to a specific type of MPPT algorithm. Thus, any known MPPT algorithm may be used.

[0075] For example, the measuring circuit 2 may comprise for each of the first inductor LI and second inductor L2 a resistor, e.g. shunt resistor, that is connected in series with the respective inductor for measuring the current (flowing) through the respective inductor (not shown in FIG. 1). The present disclosure is not limited to a specific way of measuring currents. Thus, the measuring circuit 2 for measuring currents may be implemented in any known way.

[0076] The box “1” may represent a housing of the converter 1. The control unit 3 may be part of the converter 1 (as shown in FIG. 1 ) or be an external unit to the converter 1. The converter 1 may be a partial power converter. The converter 1 may be unidirectional and each of the first, second, third and fourth terminal Tl, T2, T3, T4 of the converter 1 may be an input terminal. As shown in FIG. 1, the converter 1 may comprise a fifth terminal T5 and sixth terminal T6 that are configured to be electrically connected with an electrical load 300. The fifth terminal T5 is electrically connected with the first terminal of the first capacitor Cl and, thus, with the first terminal Tl of the converter 1. The sixth terminal T6 is electrically connected with the second terminal of the second capacitor C2 and, thus, with the fourth terminal T4 of the converter 1.

[0077] For example, the converter 1 may be a DC-to-DC converter and the load 300 may be an DC-to-AC converter, as shown in FIG. 1. The DC-to-AC converter may feed a grid 400. In this case, the first and second voltage sources 100, 200 may be PV systems, such as PV panel(s) and / or PV array(s). Optionally, the sources 100, 200 may be two close strings in a PV park that are designed to generate similar DC power. The converter 1 being a DC-to-DC converter and the load 300 being a DC-to-AC converter may be used for converting DC power, e.g. DC voltage and / or direct current, provided by the first and second voltage sources 100, 200, e.g. PV systems, to AC power, e.g. AC voltage and / or alternating current, and provide the AC power to the grid 400. Optionally, the load 300 may be a DC load (not shown in FIG. 1).

[0078] Alternatively, the converter 1 may be bidirectional. In this case, the first and second voltage sources 100, 200 may be rechargeable battery energy storages (BES) and the load 300 may be configured to use electrical energy from the BES 100, 200 (power flow from the terminals Tl, T2, T3, T4 to the terminals T5, T6 of the converter 1) and charge the BES 100, 200 with electrical energy (power flow from the terminals T5, T6 to the terminals Tl, T2, T3, T4 of the converter 1). Thus, the converter 1 being bidirectional supports discharging and charging of BES 100, 200.

[0079] As shown in FIG. 1 , the first diode DI is arranged such that the anode and the cathode of the first diode DI are directed in the direction of the first terminal Tl of the converter 1 and the first terminal of the first semiconductor switch unit SU1, respectively. The second diode D2 may be arranged such that the anode and the cathode of the second diode D2 are directed to the second terminal of the fourth semiconductor switch unit SU4 and the fourth terminal T4 of the converter 1, respectively. Alternatively (not shown in the FIGs), the first diode DI may be arranged such that the cathode and the anode of the first diode are directed in the direction of the first terminal Tl of the converter 1 and the first terminal of the first semiconductor switch unit SU 1 , respectively . The second diode D2 may be arranged such that the cathode and the anode of the second diode D2 are directed to the second terminal of the fourth semiconductor switch unit SU4 and the fourth terminal T4 of the converter 1 , respectively (not shown in the FIGs).

[0080] For further information on the converter 1 reference is made to FIGs 2, 3, 4, 5 and 6.

[0081] FIG. 2 shows an example of a state of the converter of FIG. 1 , in which two ground faults occur at terminals of the converter. The description of FIG. 1 is correspondingly valid for the converter 1 and control unit 3 of FIG. 2.

[0082] As shown in FIG. 2, when a ground fault (“GND fault”), may be referred to as first ground fault, occurs at the second terminal T2 of the converter 1 and a ground fault (“GND fault”), may be referred to as second ground fault, occurs at the third terminal T3 of the converter 1 an unwanted current flow may occur between the first terminal Tl of the converter 1 and the fourth terminal T4 of the converter 1 (indicated by the dashed arrows in FIG. 2). Especially, as shown in FIG. 2, due to the double ground fault the first voltage source 100 and second voltage source 200 connected to the converter 1 may be connected in series causing an over current flowing through the first inductor LI and the second inductor L2 and, thus, an overvoltage across the series connection of the first capacitor Cl and second capacitor (e.g. across a DC link formed by the first and second capacitor Cl, C2). Thus, detecting such an over current flowing through the first inductor LI or the second inductor L2 and switching the first semiconductor switch unit SU1 or fourth semiconductor switch unit SU4 to the non-conducting state in response to detecting the over current through the first inductor LI or second inductor L2, respectively, allows preventing, especially interrupting, the aforementioned unwanted current flow caused by the double ground fault. Namely, the first semiconductor switch unit SU1 or fourth semiconductor switch unit SU4 provide in the conducting state a path for short circuiting the voltage source 100 or 200, respectively, when the double ground fault occurs. In other words, this allows short circuiting one of the voltage sources 100, 200 that are connected in series due to the ground failure and, thus, preventing flow of an over current and occurrence of an over voltage at the converter 1.

[0083] Therefore, a voltage across the series connection of the first and second capacitor may be limited to the voltage provide by one of the two voltage sources 100, 200 when the double ground fault occurs. As a result, such control method of the first and fourth semiconductor switch unit SU1, SU4 by the control unit 3 allows tolerating the double ground fault shown in FIG. 2. In the cases of a single ground fault at any one of the first, second, third and fourth terminal Tl, T2, T3, T4 of the converter 1 or a different double ground fault at any two different terminals of the first, second, third and fourth terminal Tl, T2, T3, T4 of the converter 1 , the structure of the converter 1 , especially the first diode DI and second diode D2 of the converter 1 , prevents an unwanted current flow and, thus, unwanted over current and allows tolerating such ground fault(s).

[0084] FIG. 3 shows an example of an implementation form of the converter of FIG. 1. The converter of FIG. 3 corresponds to the converter of FIG. 1. Thus, the description of the converter of FIG. 1 is correspondingly valid for the converter of FIG. 3 and in the following mainly an optional feature(s) of the converter of FIG. 3 is described.

[0085] As shown in FIG. 3, the first terminal Tl of the converter 1 may be electrically connected via a first switch 10 with the series connection of the first diode DI and the first inductor LI. The second terminal T2 of the converter 1 may be electrically connected via a second switch 20 with the second terminal of the first semiconductor switch unit SUL The third terminal T3 of the converter 1 may be electrically connected via a third switch 30 with the second terminal of the third semiconductor switch unit SU3. The fourth terminal T4 of the converter may be electrically connected via a fourth switch 40 with the series connection of the second diode D2 and the second inductor LI . The control unit 3 may be configured to control all conducting semiconductor switch units of the first, second, third and fourth semiconductor switch units SU1, SU2, SU3, SU4 and the first, second, third and fourth switch 10, 20, 30, 40 to switch to the non-conducting state after lapse of a time period that starts with controlling, in response to detecting an over current through the first inductor LI or second inductor L2, the first semiconductor switch unit SU1 or the fourth semiconductor switch unit SU4, respectively, to switch to the conducting state.

[0086] Optionally, the control unit 3 is configured to control the first, second, third and fourth switch 10, 20, 30, 40 to the nonconducting state after lapse of a time period that starts with switching the first semiconductor switch unit SU 1 or the fourth semiconductor switch unit SU4 to the conducting state in response to detecting an over current through the first inductor LI or second inductor L2, respectively.

[0087] At least one, optionally each, of the first switch 10, second switch 20, third switch 30 and fourth switch 40 may be a switch that is configured to physically and electrically isolate using mechanical / electro mechanical means. For example, such a switch is configured to provide a gap between two electrical connections when the switch is in the non-conducting state (i.e. off-state). The first, second, third and fourth switch 10, 20, 30, 40 allow protecting the load side 300 of the converter 1 because they disconnect the load side 300 of the converter 1 from the side of the first, second, third and fourth terminal Tl, T2, T3, T4 of the converter 1 (i.e. the source side 100, 200 of the converter 1) when they are switched to the non-conducting state.

[0088] FIG. 4 shows an example of an implementation form of the converter of FIG. 1. The converter of FIG. 4 corresponds to the converter of FIG. 3. Thus, the description of the converter of FIG. 3 is correspondingly valid for the converter of FIG. 4 and in the following mainly an optional feature(s) of the converter of FIG. 4 is described. As shown in FIG. 4, the converter 1 may comprise the DC-to-AC converter 300, wherein a first terminal and second terminal of the DC-to-AC converter300 are electrically connected with the first terminal of the first capacitor C 1 and the second terminal of the second capacitor C2, respectively. That is, the DC-to-AC converter 300 may be connected in parallel with the series connection of the first capacitor Cl and second capacitor C2. In this case, the converter 1 is an DC-to-AC converter comprising a DC-to-DC converter stage comprising the inductors LI, L2 and the semiconductor switch units SU1, SU2, SU3, SU4 and a DC-to-AC converter stage in the form of the DC-to-AC converter 300. As shown in FIG. 4, the converter 1 may comprise a fifth terminal T5, a sixth terminal T6 and a seventh terminal T7 that are configured to be electrically connected with an electrical load, e.g. an AC load, (not shown in FIG. 4) or the grid 400. The fifth terminal T5, sixth terminal T6 and seventh terminal T7 of the converter 1 are connected to the DC-to-AC converter 300, especially an output of the DC-to-AC converter 300.

[0089] Optionally, the converter of FIG. 4 does not comprise the optional switches 10, 20, 30 and 40. The optional feature of the converter 1 of FIG. 4, i.e. the converter 1 comprising the DC-to-AC converter 300, may be implemented in any one of the converters of FIGs 5 and 6.

[0090] FIG. 5 shows an example of an implementation form of the converter of FIG. 1. The converter of FIG. 5 corresponds to the converter of FIG. 3. Thus, the description of the converter of FIGs 1, 2 and 3 is correspondingly valid for the converter of FIG.

[0091] 5 and in the following mainly an optional feature(s) of the converter of FIG. 5 is described.

[0092] As shown in FIG. 5, each of the first, second, third and fourth semiconductor switch unit SU1, SU2, SU3, SU4 may comprise or be a semiconductor switch SI, such as a transistor. The control unit 3 may be configured to control the first semiconductor switch unit SU 1 or the fourth semiconductor switch unit SU4 to switch to the conducting state by controlling the semiconductor switch SI of the first semiconductor switch unit SU1 or the semiconductor switch SI of the fourth semiconductor switch unit SU2, respectively, to switch to the conducting state.

[0093] The control unit 3 may be configured to control any one of the first, second, third and fourth semiconductor switch unit SU 1 , SU2, SU3, SU4 by controlling the semiconductor switch (e.g. transistor) of the respective semiconductor switch unit, especially providing a control signal to the control terminal of the semiconductor switch (e.g. transistor).

[0094] As shown in FIG. 5, the semiconductor switches of the first, second, third and fourth semiconductor switch unit SU1, SU2, SU3, SU4 may be IGBTs, wherein a diode is connected in antiparallel to each IGBT. This is only by way of example and, thus, any other type of semiconductor switch, e.g. any other type of transistor may be used.

[0095] Optionally, the converter 1 of FIG. 5 does not comprise the optional switches 10, 20, 30 and 40.

[0096] FIG. 6 shows an example of an implementation form of the converter of FIG. 1. The converter of FIG. 6 corresponds to the converter of FIG. 3. Thus, the description of the converter of FIGs 1 , 2 and 3 is correspondingly valid for the converter of FIG.

[0097] 6 and in the following mainly an optional feature(s) of the converter of FIG. 6 is described.

[0098] As shown in FIG. 6, each of the first and second semiconductor switch unit SU 1 , SU2 may comprise or be a series connection of two or more semiconductor switches SI, S2 (in FIG. 6 exemplarily two semiconductor switches SI, S2 are shown). The converter 1 may comprise one or more capacitors Cl 1 (in FIG. 6 exemplarily one capacitor Cl 1 is shown), the number of the one or more capacitors C 11 equals one less than the number of semiconductor switches S 1 , S2 of each of the first and second semiconductor switch unit SU1, SU2. Each of the one or more capacitors Cl 1 may electrically connect a first node N1 between two switches SI, S2 of the series connection of two or more semiconductor switches SI, S2 of the first semiconductor switch unit SU1 and a second node N2 between two switches SI, S2 of the second series connection of two or more semiconductor switches SI, S2 of the second semiconductor switch unit SU2 with each other. The number of nodes between the first node N1 and the first terminal of the first semiconductor switch unit SU1 and the number of nodes between the second node N2 and the second terminal of the second semiconductor switch unit SU2 are equal to each other. The control unit 3 may be configured to switch the first semiconductor switch unit SU1 to the conducting state by controlling the two or more semiconductor switches SI, S2 of the first semiconductor switch unit SU1 to switch to the conducting state.

[0099] As shown in FIG. 6, each of the third and fourth semiconductor switch unit SU3, SU4 may comprise or be a series connection of two or more semiconductor switches SI, S2 (in FIG. 6 exemplarily two semiconductor switches SI, S2 are shown). The converter 1 may comprise one or more capacitors C21 (in FIG. 6 exemplarily one capacitor C21 is shown), the number of the one or more capacitors C21 equals one less than the number of semiconductor switches SI, S2 of each of the third and fourth semiconductor switch unit SU3, SU4. Each of the one or more capacitors C12 may electrically connect a first node N1 between two switches S 1 , S2 of the series connection of two or more semiconductor switches S 1 , S2 of the third semiconductor switch unit SU3 and a second node N2 between two switches SI, S2 of the second series connection of two or more semiconductor switches S 1 , S2 of the fourth semiconductor switch unit SU4 with each other. The number of nodes between the first node N1 and the first terminal of the third semiconductor switch unit SU4 and the number of nodes between the second node N2 and the second terminal of the fourth semiconductor switch unit SU4 are equal to each other. The control unit 4 may be configured to switch the fourth semiconductor switch unit SU4 to switch to the conducting state by controlling the two or more semiconductor switches SI , S2 of the fourth semiconductor switch unit SU4 to switch to the conducting state.

[0100] The control unit 3 may be configured to control any one of the first, second, third and fourth semiconductor switch unit SU1, SU2, SU3, SU4 by controlling the semiconductor switches (e.g. transistors) of the respective semiconductor switch unit, especially providing a control signal to the control terminal of the semiconductor switches (e.g. transistors).

[0101] As shown in FIG. 6, the semiconductor switches of the first, second, third and fourth semiconductor switch unit SU1, SU2, SU3, SU4 may be IGBTs, wherein a diode is connected in antiparallel to each IGBT. This is only by way of example and, thus, any other type of semiconductor switch, e.g. any other type of transistor may be used.

[0102] Optionally, the converter 1 of FIG. 6 does not comprise the optional switches 10, 20, 30 and 40.

[0103] FIG. 7 shows an example of a method according to this disclosure for operating a converter according to this disclosure, such as the converter according to any one FIGs 1, 2, 3, 4, 5 and 6. The method of FIG. 7 is an example of the method of the first aspect. Thus, the description of the method of the first aspect is correspondingly valid for the method of FIG. 7.

[0104] As shown in FIG. 7, the method comprises a step 1000 of monitoring the current through the first inductor LI and second inductor L2 of the converter 1. The method comprises a step 2000 of switching the first semiconductor switch unit SU 1 or the fourth semiconductor switch unit SU4 to the conducting state in response to detecting an over current through the first inductor LI or second inductor L2, respectively. The steps 1000 and 2000 may occur simultaneously. For further information on the method of FIG. 7 reference is made to the description of the method of the first aspect and the description of FIGs 1, 2, 3, 4, 5 and 6.

[0105] The converter of any one of FIGs 1, 2, 3, 4, 5 and 6, the control unit 3 of any one of FIGs 1, 2, 3, 4, 5 and 6, and the method of FIG. 7 may be extended with regard to using the converter for discharging and charging battery energy storages 100, 200 (BES) in order to achieve the state of charge (SOC) of the BES 100, 200, where the desired current may be determined by a SOC algorithm. The converter and control unit according to this disclosure, such as the converter and control unit according to any one FIGs 1, 2, 3, 4, 5 and 6, is configured to perform the method according to this disclosure, such as the method according to FIG. 7.

[0106] The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A method for operating a converter (1 ), wherein the converter (1) comprises: a first, second, third and fourth terminal (T1 , T2, T3, T4) for receiving DC voltages, a series connection of a first semiconductor switch unit (SU1), a second semiconductor switch unit (SU2), a third semiconductor switch unit (SU3) and a fourth semiconductor switch unit (SU4), a first capacitor (Cl) and second capacitor (C2), wherein the first terminal (T 1 ) of the converter ( 1 ) is electrically connected via a series connection of a first diode (DI) and a first inductor (LI) with a first terminal of the first semiconductor switch unit (SU1), a second terminal of the first semiconductor switch unit (SU 1 ) is electrically connected with a first terminal of the second semiconductor switch unit (SU2) and the second terminal (T2) of the converter (1 ), a second terminal of the second semiconductor switch unit (SU2) is electrically connected with a first terminal of the third semiconductor switch unit (SU3), a second terminal of the third semiconductor switch unit (SU3) is electrically connected with a first terminal of the fourth semiconductor switch unit (SU4) and the third terminal (T3) of the converter (1 ), the fourth terminal (T4) of the converter (1 ) is electrically connected via a series connection of a second diode (D2) and a second inductor (L2) with a second terminal of the fourth semiconductor switch unit (SU4), a first terminal and a second terminal of the first capacitor (C 1 ) is electrically connected with the first terminal of the first semiconductor switch unit (SU1) and the second terminal of the second semiconductor switch unit (SU2), respectively, and a first terminal and a second terminal of the second capacitor (C2) is electrically connected with the first terminal of the third semiconductor switch unit (SU3) and the second terminal of the fourth semiconductor switch unit (SU4), respectively, wherein the method comprises: monitoring a current through the first inductor (LI) and second inductor (L2), and switching the first semiconductor switch unit (SU 1 ) or the fourth semiconductor switch unit (SU4) to the conducting state in response to detecting an over current through the first inductor (LI) or second inductor (L2), respectively.

2. The method according to claim 1 , wherein the first terminal (Tl) of the converter (1) is electrically connected via a first switch (10) with the series connection of the first diode (DI) and the first inductor (LI), the second terminal (T2) of the converter (1 ) is electrically connected via a second switch (20) with the second terminal of the first semiconductor switch unit (SU1), the third terminal (T3) the converter (1 ) is electrically connected via a third switch (30) with the second terminal of the third semiconductor switch unit (SU3), and the fourth terminal (T4) of the converter (1) is electrically connected via a fourth switch (40) with the series connection of the second diode (D2) and the second inductor (L2), wherein the method comprises: switching all conducting semiconductor switch units of the first, second, third and fourth semiconductor switch unit (SU1, SU2, SU3, SU4) and the first, second, third and fourth switch (10, 20, 30, 40) to the non-conducting state after lapse of a time period that starts with switching the first semiconductor switch unit (SU1) or the fourth semiconductor switch unit (SU4) to the conducting state in response to detecting an over current through the first inductor (LI) or second inductor (L2), respectively.

3. The method according to claim 1 or 2, wherein each of the first, second, third and fourth semiconductor switch unit (SU1, SU2, SU3, SU4) comprises or is a semiconductor switch (SI), and switching the first semiconductor switch unit (SU 1 ) or the fourth semiconductor switch unit (SU4) to the conducting state comprises switching the semiconductor switch (SI) of the first semiconductor switch unit (SU1) or the fourth semiconductor switch unit (SU4), respectively, to the conducting state.

4. The method according to claim 1 or 2, wherein each of the first and second semiconductor switch unit (SU1, SU2) comprises or is a series connection of two or more semiconductor switches (SI, S2), the converter (1) comprises one or more capacitors (Cl l), the number of the one or more capacitors (Cl l) equals one less than the number of semiconductor switches (SI, S2) of each of the first and second semiconductor switch unit (SU1, SU2), and each of the one or more capacitors (Cl l) electrically connects a first node (Nl) between two switches of the series connection of two or more semiconductor switches (S 1 , S2) of the first semiconductor switch unit (SU 1 ) and a second node (N2) between two switches of the second series connection of two or more semiconductor switches (S 1 , S2) of the second semiconductor switch unit (SU2) with each other, wherein the number of nodes between the first node (Nl ) and the first terminal of the first semiconductor switch unit (SU 1 ) and the number of nodes between the second node (N2) and the second terminal of the second semiconductor switch unit (SU2) are equal to each other, wherein switching the first semiconductor switch unit (SU 1 ) to the conducting state comprises switching the two or more semiconductor switches (SI, S2) of the first semiconductor switch unit (SU1) to the conducting state.

5. The method according to any one of claims 1 , 2 and 4, wherein each of the third and fourth semiconductor switch unit (SU3, SU4) comprises or is a series connection of two or more semiconductor switches (SI, S2), the converter (1) comprises one or more capacitors (C21), the number of the one or more capacitors (C21) equals one less than the number of semiconductor switches (SI, S2) of each of the third and fourth semiconductor switch unit (SU3, SU4), and each of the one or more capacitors (C21) electrically connects a first node (Nl) between two switches of the series connection of two or more semiconductor switches (SI, S2) of the third semiconductor switch unit (SU3) and a second node (N2) between two switches of the second series connection of two or more semiconductor switches (SI, S2) of the fourth semiconductor switch unit (Su4) with each other, wherein the number of nodes between the first node (Nl) and the first terminal of the third semiconductor switch unit (SU3) and the number of nodes between the second node (N2) and the second terminal of the fourth semiconductor switch unit (SU4) are equal to each other, wherein switching the fourth semiconductor switch unit (SU4) to the conducting state comprises switching the two or more semiconductor switches (SI, S2) of the fourth semiconductor switch unit (SU4) to the conducting state.

6. The method according to any one of the previous claims, wherein the first diode (DI) is arranged such that the anode and the cathode are directed in the direction of the first terminal (Tl) of the converter and the first terminal of the first semiconductor switch unit (SU1), respectively, and the second diode (D2) is arranged such that the anode and the cathode are directed to the second terminal of the fourth semiconductor switch unit (SU4) and the fourth terminal (T4) of the converter (1 ), respectively.

7. A control unit (3) for controlling a converter (1 ), wherein the converter (1) comprises: a first, second, third and fourth terminal (T1 , T2, T3, T4) for receiving DC voltages, a series connection of a first semiconductor switch unit (SU1), a second semiconductor switch unit (SU2), a third semiconductor switch unit (SU3) and a fourth semiconductor switch unit (SU4), a first capacitor (Cl) and second capacitor (C2), wherein the first terminal (T1 ) of the converter (1 ) is electrically connected via a series connection of a first diode (DI ) and a first inductor (LI) with a first terminal of the first semiconductor switch unit (SU 1 ), a second terminal of the first semiconductor switch unit (SU 1 ) is electrically connected with a first terminal of the second semiconductor switch unit (SU2) and the second terminal (T2) of the converter ( 1 ), a second terminal of the second semiconductor switch unit (SU2) is electrically connected with a first terminal of the third semiconductor switch unit (SU3), a second terminal of the third semiconductor switch unit (SU3) is electrically connected with a first terminal of the fourth semiconductor switch unit (SU4) and the third terminal (T3) of the converter (1), the fourth terminal (T4) of the converter (1 ) is electrically connected via a series connection of a second diode (D2) and a second inductor (L2) with a second terminal of the fourth semiconductor switch unit (SU4), a first terminal and a second terminal of the first capacitor (C 1 ) is electrically connected with the first terminal of the first semiconductor switch unit (SU1) and the second terminal of the second semiconductor switch unit (SU2), respectively, and a first terminal and a second terminal of the second capacitor (C2) is electrically connected with the first terminal of the third semiconductor switch unit (SU3) and the second terminal of the fourth semiconductor switch unit (SU4), respectively, wherein the control unit (3) is configured to: monitor a current through the first inductor (LI) and second inductor (L2), and control the first semiconductor switch unit (SU1) or the fourth semiconductor switch unit (SU4) to switch to the conducting state in response to detecting an over current through the first inductor (LI) or second inductor (L2), respectively.

8. A converter ( 1 ) comprising : a first, second, third and fourth terminal (T1 , T2, T3, T4) for receiving DC voltages, a series connection of a first semiconductor switch unit (SU1), a second semiconductor switch unit (SU2), a third semiconductor switch unit (SU3) and a fourth semiconductor switch unit (SU4), a first capacitor (Cl) and second capacitor (C2), wherein the first terminal (T 1 ) of the converter ( 1 ) is electrically connected via a series connection of a first diode (DI) and a first inductor (LI) with a first terminal of the first semiconductor switch unit (SU 1 ), a second terminal of the first semiconductor switch unit (SU 1 ) is electrically connected with a first terminal of the second semiconductor switch unit (SU2) and the second terminal (T2) of the converter (1), a second terminal of the second semiconductor switch unit (SU2) is electrically connected with a first terminal of the third semiconductor switch unit (SU3), a second terminal of the third semiconductor switch unit (SU3) is electrically connected with a first terminal of the fourth semiconductor switch unit (SU4) and the third terminal (T3) of the converter (1), the fourth terminal (T4) of the converter ( 1 ) is electrically connected via a series connection of a second diode (D2) and a second inductor (L2) with a second terminal of the fourth semiconductor switch unit (SU4),a first terminal and a second terminal of the first capacitor (C 1 ) is electrically connected with the first terminal of the first semiconductor switch unit (SU1) and the second terminal of the second semiconductor switch unit (SU2), respectively, and a first terminal and a second terminal of the second capacitor (C2) is electrically connected with the first terminal of the third semiconductor switch unit (SU3) and the second terminal of the fourth semiconductor switch unit (SU4), respectively, wherein the converter (1) further comprises: a measuring circuit (2) configured to measure a current through the first inductor (LI) and second inductor (L2), a control unit (3) configured to obtain the measured current through the first inductor (LI) and second inductor (L2) and detect an over current through the first inductor (LI) and second inductor (L2) by monitoring the obtained measured current through the first inductor (LI) and second inductor (L2), wherein the control unit (3 ) is configured to control the first semiconductor switch unit (SU 1 ) or the fourth semiconductor switch unit (SU4) to switch to the conducting state in response to detecting the over current through the first inductor (LI) or second inductor (L2), respectively.

9. The converter (1) according to claim 8, wherein the first terminal (Tl) of the converter (1) is electrically connected via a first switch (10) with the series connection of the first diode (DI) and the first inductor (LI), the second terminal (T2) of the converter (1 ) is electrically connected via a second switch (20) with the second terminal of the first semiconductor switch unit (SU1), the third terminal (T3) the converter ( 1 ) is electrically connected via a third switch (30) with the second terminal of the third semiconductor switch unit (SU3), and the fourth terminal (T4) of the converter (1) is electrically connected via a fourth switch (40) with the series connection of the second diode (D2) and the second inductor (L2), wherein the control unit (3) is configured to control all conducting semiconductor switch units of the first, second, third and fourth semiconductor switch unit (SU1, SU2, SU3, SU4) and the first, second, third and fourth switch (10, 20, 30, 40) to switch to the non-conducting state after lapse of a time period that starts with controlling, in response to detecting an over current through the first inductor (LI) or second inductor (L2), the first semiconductor switch unit (SU 1 ) or the fourth semiconductor switch unit (SU4), respectively, to switch to the conducting state.

10. The converter (1) according to claim 8 or 9, wherein each of the first, second, third and fourth semiconductor switch unit (SU 1 , SU2, SU3, SU4) comprises or is a semiconductor switch (1), and the control unit (3 ) is configured to control the first semiconductor switch unit (SU 1 ) or the fourth semiconductor switch unit (SU4) to switch to the conducting state by controlling the semiconductor switch (S 1 ) of the first semiconductor switch unit (SU1) or the fourth semiconductor switch unit (SU4), respectively, to switch to the conducting state.

11. The converter (1) according to claim 8 or 9, wherein each of the first and second semiconductor switch unit (SU 1 , SU2) comprises or is a series connection of two or more semiconductor switches (SI, S2),the converter (1) comprises one or more capacitors (Cl 1), the number of the one or more capacitors (Cl 1) equals one less than the number of semiconductor switches (SI, S2) of each of the first and second semiconductor switch unit (SU1, SU2), and each of the one or more capacitors (Cl 1) electrically connects a first node (Nl) between two switches of the series connection of two or more semiconductor switches (S 1 , S2) of the first semiconductor switch unit (SU 1 ) and a second node (N2) between two switches of the second series connection of two or more semiconductor switches (S 1 , S2) of the second semiconductor switch unit (SU2) with each other, wherein the number of nodes between the first node (Nl ) and the first terminal of the first semiconductor switch unit (SU 1 ) and the number of nodes between the second node (N2) and the second terminal of the second semiconductor switch unit (SU2) are equal to each other, wherein the control unit (3) is configured to switch the first semiconductor switch unit (SU1) to the conducting state by controlling the two or more semiconductor switches (SI, S2) of the first semiconductor switch unit (SU1) to switch to the conducting state.

12. The converter (1) according to any one of claims 8, 9 and 11, wherein each of the third and fourth semiconductor switch unit (SU3, SU4) comprises or is a series connection of two or more semiconductor switches (SI, S2), the converter (1) comprises one or more capacitors (C21), the number of the one or more capacitors (C21) equals one less than the number of semiconductor switches (SI, S2) of each of the third and fourth semiconductor switch unit (SU3, SU4), and each of the one or more capacitors (C21) electrically connects a first node (Nl) between two switches of the series connection of two or more semiconductor switches (SI, S2) of the third semiconductor switch unit (SU3) and a second node (N2) between two switches of the second series connection of two or more semiconductor switches (SI, S2) of the fourth semiconductor switch unit (Su4) with each other, wherein the number of nodes between the first node (Nl) and the first terminal of the third semiconductor switch unit (SU3) and the number of nodes between the second node (N2) and the second terminal of the fourth semiconductor switch unit (SU4) are equal to each other, wherein the control unit (3) is configured to switch the fourth semiconductor switch unit (SU4) to switch to the conducting state by controlling the two or more semiconductor switches (SI, S2) of the fourth semiconductor switch unit (SU4) to switch to the conducting state.

13. The converter (1) according to any one of claims 8 to 12, wherein the first diode (DI) is arranged such that the anode and the cathode are directed in the direction of the first terminal (T1 ) of the converter and the first terminal of the first semiconductor switch unit (SU 1 ), respectively, and the second diode (D2) is arranged such that the anode and the cathode are directed to the second terminal of the fourth semiconductor switch unit (SU4) and the fourth terminal (T4) of the converter (1), respectively.

14. The converter (1 ) according to any one of claims 8 to 13, wherein the converter (1) is unidirectional and each of the first, second, third and fourth terminal (Tl, T2, T3, T4) of the converter (1 ) is an input terminal, or the converter (1 ) is bidirectional.

15. The converter (1) according to any one of claims 8 to 14, wherein the converter (1 ) comprises a fifth and sixth terminal (T5, T6) that are configured to be electrically connected with an electrical load (300), the fifth terminal (T5) is electrically connected with the first terminal of the first capacitor (Cl), and - the sixth terminal (T6) is electrically connected with the second terminal of the second capacitor (C2).

Images