Electrical arrangement and method for operating an electrical arrangement

Abstract

An electrical arrangement (1) comprising a support capacitor (10), a bridge circuit (20), a charge circuit (30) and a control unit (40) is described herein. The electrical arrangement (1) is configured to be connected to a first bus bar (L1) and a second bus bar (L2) of a DC link. The support capacitor (10) is coupled to the first and second bus bars (L1, L2) via the bridge circuit (20) and the charge circuit (30). The control unit (40) is configured to control the bridge circuit (20) and the charge circuit (30) according to a charging mode and a discharging mode. In the charging mode, the support capacitor (10) is charged using excess energy emerging from an overvoltage in the DC link, and in the discharging mode, energy stored in the support capacitor (10) is fed into the DC link. The bridge circuit (20) comprises four transistors arranged in an H-bridge configuration. Further, a method for operating an electrical arrangement (1) is provided.

Description

[0001] Description

[0002] ELECTRICAL ARRANGEMENT AND METHOD FOR OPERATING AN ELECTRICAL ARRANGEMENT

[0003] An electrical arrangement is speci fied . Furthermore , a method for operating an electrical arrangement is speci fied .

[0004] One problem to be solved is , inter alia, to speci fy an electrical arrangement which improves a voltage stability of a Direct Current link ( short : DC link) . A further problem to be solved is , inter alia, to speci fy a method for operating an electrical arrangement in order to improve a voltage stability of a DC link . The DC link is in particular a DC microgrid . A DC link preferably comprises first and second bus bars .

[0005] These problems are solved, inter alia, by an electrical arrangement comprising the features of independent claim 1 and by a method comprising the features of independent claim 9 . Advantageous embodiments and further developments are the subj ect-matter of the respective dependent patent claims .

[0006] According to at least one embodiment , the electrical arrangement comprises a support capacitor, a bridge circuit , a charge circuit and a control unit . The electrical arrangement is configured to be connected to a first bus bar and a second bus bar of a DC link . The support capacitor is coupled to the first and second bus bars via the bridge circuit and the charge circuit . The control unit is configured to control the bridge circuit and the charge circuit according to a charging mode and a discharging mode , wherein in the charging mode , the support capacitor is charged at least using excess energy emerging from an overvoltage in the DC link, and in the discharging mode , energy stored in the support capacitor is fed into the DC link . The bridge circuit comprises four transistors arranged in an H-bridge configuration .

[0007] In other words , the control unit is configured to control the bridge circuit and the charge circuit depending on a voltage between the first and second bus bars to keep the voltage of the DC link above a minimum operating voltage and below a maximum operating voltage .

[0008] In particular, the support capacitor is configured to store short-time excess electrical energy of the DC link . For example , i f an electrical energy source , such as a photovoltaic module , is delivering energy to the DC link and all DC loads combined are using less electrical energy, there is an excess electrical energy in the DC link . Excess electrical energy can cause the operating voltage of the DC link to rise above the maximum operating voltage , which can lead to damages or unwanted ef fects in the DC link .

[0009] For example , the bridge circuit is configured to convert electrical voltage of a first voltage to a second voltage . In particular, the bridge circuit is configured as a buck-boost converter . Preferably, the bridge circuit is used to enable charging of the support capacitor with a desired voltage which can be di f ferent than the voltage of the DC link and / or to deliver a desired voltage to the DC link which can be di f ferent from the voltage stored in the support capacitor .

[0010] In particular, the charge circuit is configured to charge the support capacitor . For example , the charge circuit is able to open or close a connection between the first bus bar and the bridge circuit . Preferably, the charge circuit controls a current flow between the support capacitor and the DC link .

[0011] Particularly, the control unit is configured to stabili ze a voltage in the DC link above a minimum operating voltage of 640 V and below a maximum operating voltage of 850 V . For example , the control unit is able to control the bridge circuit and the charge circuit in order to minimi ze a fluctuation in the voltage level of the DC link .

[0012] The electrical arrangement described herein is based, inter alia, on the following technical considerations . DC links and the devices connected to them are designed for operating within the limits of a minimum operating voltage and a maximum operating voltage . In cases where a mismatch between load and generation of energy occurs , the mismatch may cause the maximum operating voltage to be temporarily exceeded in an overvoltage situation or the minimum operating voltage to be undershot in an undervoltage situation . To avoid an overvoltage in the DC link, an overvoltage protection device or resistive crowbar can be used, which dissipates excess energy as heat for example . However, the energy which is dissipated as heat is lost for the DC link and decreases an overall ef ficiency .

[0013] The electrical arrangement described herein makes use , inter alia, of the idea of storing excess energy in a support capacitor instead of dissipating it as heat . The support capacitor can advantageously support the DC link for a certain amount of time during fault events to avoid a large voltage drop below the minimum operating voltage in the DC link so that converters and breakers of devices connected to the DC link are staying online . Additionally, the energy stored in the support capacitor can also be used to black start the DC link after a longer lasting fault event , for example a short circuit event . A black start is necessary when the grid experiences a blackout and must be restarted from scratch . In particular, a black start is the ability of generating enough electrical power to restart parts of a DC link to recover from a blackout . In this process , for example , several converter units are started individually and gradually reconnected to form an interconnected system again .

[0014] According to at least one embodiment of the electrical arrangement , the support capacitor comprises a supercapacitor, in particular an electrochemical capacitor . The support capacitor is for example a high-capacity capacitor, having a much higher capacitance value than solid- state capacitors . In particular, the support capacitor uses a double-layer capacitance on one electrode and an electrochemical battery electrode as the other . For example , the support capacitor comprises a plurality of capacitors connected in parallel to increase an overall capacitance .

[0015] In particular, the bridge circuit comprises four transistors arranged in an H-bridge configuration . In particular, the bridge circuit comprises a split-pi topology . The split-pi converter is a type of DC-to-DC converter that has an output voltage magnitude either greater than or less than the input voltage magnitude . It is a switched-mode power supply with a circuit configuration similar to a boost converter followed by a buck converter . This enables the bridge circuit to accept and deliver di f ferent voltages to either charge the support capacitor with various levels of voltage delivered by the DC link or to support the DC link with a desired voltage with the support capacitor having various voltage levels .

[0016] According to at least one embodiment of the electrical arrangement , the charge circuit comprises two charge transistors connected antiparallel to each other . In particular, the charge transistor is configured to enable either a current flow from the DC link to the support capacitor in order to counteract an overvoltage in the DC link or a reverse current flow from the support capacitor to the DC link in order to counteract an undervoltage in the DC link . Both transistors can be controlled by the control circuit for example .

[0017] According to at least one embodiment of the electrical arrangement , the charge circuit comprises a charge resistor connected parallel to the charge transistors . In particular, the charge resistor is configured to allow a continuous current flow between the bridge circuit and the DC link in order to decrease a continuous overvoltage or undervoltage in the DC link . Preferably, the charge resistor is a high ohmic resistor in the kQ range . In particular, the charge resistor has a resistance of at least I kQ, preferably of at least 10 .

[0018] According to at least one embodiment of the electrical arrangement , the charge circuit comprises a charge varistor connected parallel to the charge transistors . The charge varistor is in particular configured to protect the charge transistors from short-time excess voltage peaks . In particular, the charge resistor has such a high resistance that during a switch-of f operation of the charge circuit the charge varistor acts as an overvoltage protection device to clamp the voltage .

[0019] According to at least one embodiment of the electrical arrangement , the control unit is connected to a first measurement device configured to measure a current flow between the electrical arrangement and the DC link and a second measurement device configured to measure a voltage of the DC link . The current flow between the electrical arrangement and the DC link can for example be measured by evaluating the current flow between the first bus bar and the electrical arrangement . The voltage of the DC link is the potential di f ference between the first bus bar und the second bus bar .

[0020] According to at least one embodiment of the electrical arrangement , the electrical arrangement comprises an active crowbar structure configured to limit a maximal voltage in the support capacitor . I f a voltage in the support capacitor exceeds a maximum voltage , the active crowbar structure enables dissipation of electrical energy in the form of heat . The active crowbar structure comprises a crowbar transistor and a crowbar resistor . In particular, the crowbar transistor enables a current flow over the crowbar resistor to decrease a voltage in the support capacitor .

[0021] Furthermore , a method for operating an electrical arrangement is speci fied . In particular, the method for operating an electrical arrangement is suitable for operating an electrical arrangement described herein . This means that all features disclosed for the electrical arrangement are also disclosed for the method for operating an electrical arrangement and vice versa . According to at least one embodiment of the method for operating an electrical arrangement , the method comprises the steps of charging a support capacitor in a charging mode with electrical excess energy of a first and a second bus bar of a DC link via a charge circuit i f a voltage in the DC link is above a maximum operating voltage , and discharging the support capacitor in a discharging mode and deliver electrical energy to the DC link i f the voltage in the DC link is below a minimum operating voltage . Additionally, the electrical arrangement may be operated in an idle mode wherein no electrical energy flows between the DC link and the electrical arrangement i f the voltage in the DC link is within the range of operating voltages .

[0022] According to at least one embodiment of the method, the discharging mode is stopped i f the support capacitor reaches a minimum black start voltage level . In particular, the minimum black start voltage level is chosen such that enough energy remains in the support capacitor to facilitate a black start of at least one component connected to the DC link . Preferably, the minimum black start voltage level is chosen such that enough energy remains in the support capacitor to facilitate a black start of a further energy source , such as a battery or a converter connected to a power grid .

[0023] According to at least one embodiment of the method, a charging voltage level and a discharging voltage level are adj usted by a bridge circuit arranged between the support capacitor and the DC link . In particular, the bridge circuit is configured as a buck-boost converter . Preferably, the bridge circuit accepts and delivers di f ferent voltages to either charge the support capacitor with various levels of voltage delivered by the DC link or to support the DC link with a desired voltage , wherein the support capacitor having various voltage levels acts as a source of electrical energy .

[0024] According to at least one embodiment of the method, excess electrical energy is dissipated in an active crowbar structure i f a maximum voltage in the support capacitor is reached . The maximum voltage of the support capacitor is for example determined by a maximum operating voltage of the used capacitor .

[0025] According to at least one embodiment of the method, a control unit switches the electrical arrangement between the charging mode and the discharging mode depending on a measured voltage of the DC link . In particular, the control unit comprises a plurality of output channels to control transistors of the bridge circuit and / or a charge circuit depending on a voltage measured by a second measurement device . Preferably, the control unit periodically evaluates the voltage level in the DC link .

[0026] Further advantages and advantageous embodiments and further developments of the electrical arrangement and the method for operating an electrical arrangement described herein will become apparent from the following exemplary embodiments shown in connection with schematic drawings . Identical elements , elements of the same kind or elements having the same ef fect are provided with the same reference signs in the figures . The figures and the proportions of the elements shown in the figures are not to be regarded as true to scale . Rather, individual elements may be shown exageratedly large for better representability and / or for better comprehensibility . In the figures :

[0027] Figure 1 shows a schematic circuit diagram illustrating an electrical arrangement described herein according to an exemplary embodiment ; and

[0028] Figure 2 shows a schematic circuit diagram of a DC link comprising an electrical arrangement described herein according to an exemplary embodiment .

[0029] Figure 1 shows a schematic circuit diagram illustrating an electrical arrangement 1 described herein according to an exemplary embodiment . The electrical arrangement 1 is configured to be connected to a first bus bar LI and a second bus bar L2 of a DC link and comprises a support capacitor 10 , a bridge circuit 20 , a charge circuit 30 , a control unit 40 and an active crowbar structure 50 .

[0030] The support capacitor 10 comprises a plurality of capacitors connected in parallel to each other . Preferably, the support capacitor 10 has a capacitance of at least 1 mF .

[0031] The bridge circuit 20 is built using a split-pi topology . The bridge circuit 20 comprises four bridge transistors 20T in an H-bridge configuration . For example , the bridge transistors 20T are formed as insulated-gate bipolar transistors ( short : IGBT ) .

[0032] Each bridge transistor 20T comprises an antiparallel bridge diode 20D to protect the bridge transistors 20T from reverse current flow . This enables the bridge circuit 20 to accept and deliver di f ferent voltages to either charge the support capacitor 10 with various levels of voltage delivered by the DC link or to supply the DC link with a desired voltage with the support capacitor 10 having various voltage levels . Each bridge transistor 20T is controlled by the control unit 40 .

[0033] The charge circuit 30 comprises two charge transistors 30T connected antiparallel to each other . Each charge transistor 30T has a protective charge diode 30D connected in series to them . Further, the charge circuit 30 comprises a charge resistor 30R and a charge varistor 30V . The charge resistor 30R enables a constant current flow between the DC link and the bridge circuit 20 i f the voltage level di f fers between these two elements . The charge varistor 30V protects the charge circuit 30 from short-time voltage peaks .

[0034] The active crowbar structure 50 is connected in parallel to the support capacitor 10 and comprises a crowbar transistor 50T , a crowbar resistor 50R, a first crowbar diode 50D1 and a second crowbar diode 50D2 . The crowbar transistor 50T is connected in series with the crowbar resistor 50R and can be controlled by the control unit 40 . The first crowbar diode 50D1 is connected antiparallel to the crowbar transistor 50T to protect the crowbar transistor 50T from reverse current flow .

[0035] The second crowbar diode 50D2 is connected parallel to the crowbar resistor 50R . The crowbar resistor 50R can be used to dissipate excess electrical energy in the form of heat to limit the maximum voltage of the support capacitor 10 . Energy is preferably only dissipated in the active crowbar structure 50 i f a maximum voltage in the support capacitor 10 is reached in order to avoid damaging the support capacitor 10 . The control unit 40 preferably comprises a processor, a storage , and a plurality of input channels and output channels . Each of the bridge transistors 20T , all charge transistors 30T and the crowbar transistor 50T are connected to an individual output channel of the control unit 40 . In other words , the control unit 40 can individually control each bridge transistor 20T , each charge transistor 30T and the crowbar transistor 50T .

[0036] Furthermore , a first measurement device 401 and a second measurement device 402 are connected to input channels of the control unit 40 . The first measurement device 401 is configured to measure a current flow between the DC link and the electrical arrangement 1 . The second measurement device is configured to measure a voltage between the first and second bus bars LI , L2 of the DC link .

[0037] The control unit 40 is configured to control the bridge transistors 20T , the charge transistors 30T and the crowbar transistor 50T in order to charge the support capacitor 10 in a charging mode with electrical excess energy of the first and second bus bars LI , L2 of the DC link via the charge circuit 30 i f a voltage in the DC link is above a maximum operating voltage and to discharge the support capacitor 10 in a discharging mode and deliver electrical energy to the DC link i f the voltage in the DC link is below a minimum operating voltage .

[0038] Furthermore , the electrical arrangement 1 comprises a choking coil L connected between the bridge circuit 20 and the DC link and a smoothing capacitor C connected between the first and second bus bars LI , L2 of the DC link . The choking coil L inter alia decreases a current peak in the case of a black start , and the smoothing capacitor C is configured to smooth or even out fluctuations in the current coming from the bridge circuit 20 in the discharging mode . Preferably, the choking coil L limits a current gradient to at most 10 A / ps , particularly preferably to at most 5 A / ps . Furthermore , the choking coil L is used as an inductance for the bridge circuit 20 in order to facilitate the function of the bridge circuit 20 as a buck-boost converter . Thus the choking coil L can also be used to decrease or increase a voltage going into the electrical arrangement 1 or which is provided out of the electrical arrangement 1 .

[0039] Additionally, the choking coil L can comprise an air-core short circuit choke which is particularly advantageous for use in combination with a hybrid circuit braker to limit a change of rate of the fault current in a short-circuit case .

[0040] Figure 2 shows a schematic circuit diagram of a DC link comprising an electrical arrangement 1 described herein according to an exemplary embodiment .

[0041] A storage battery B, a DC load DCL, a photovoltaic element PV, an AC load ACL, an electrical arrangement 1 and an AC power grid ACG are each connected via a converter unit CON and at least one protection device PD to the first and second bus bars LI , L2 of the DC link . A converter unit CON can for example comprise a DC to DC converter or an AC to DC converter .

[0042] Each protection device PD is configured to protect the components of the DC link during fault events , such as a short circuit for example . Each protection device PD comprises an inductor, a circuit breaker, a current measurement device and a voltage measurement device . I f the current measurement device and / or the voltage measurement device detect a current and / or voltage outside an operating range , the circuit breaker disconnects the attached device from the DC link .

[0043] In particular, the circuit breaker is a hybrid circuit breaker having a mechanical switch connected in parallel to a solid-state switch . Advantageously, the mechanical switch of a hybrid circuit breaker has a relatively low resistance compared to the solid-state switch once it is switched on, but it takes a longer time to switch compared to the solid- state switch .

[0044] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features , which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments , even i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments .

[0045] List of Reference Signs

[0046] 1 electrical arrangement

[0047] 10 support capacitor

[0048] 20 bridge circuit

[0049] 20T bridge transistor

[0050] 20D bridge diode

[0051] 30 charge circuit

[0052] 30T charge transistor

[0053] 30R charge resistor

[0054] 30V charge varistor

[0055] 30D charge diode

[0056] 40 control unit

[0057] 401 first measurement device

[0058] 402 second measurement device

[0059] 50 active crowbar structure

[0060] 50T crowbar transistor

[0061] 50R crowbar resistor

[0062] 50D1 first crowbar diode

[0063] 50D2 second crowbar diode

[0064] LI first bus bar

[0065] L2 second bus bar

[0066] L choking coil

[0067] C smoothing capacitor

[0068] RD protection device

[0069] B battery

[0070] PV photovoltaic source

[0071] DCL DC load

[0072] ACL AC load

[0073] ACG AC grid

[0074] CON converter unit

Claims

Claims1. An electrical arrangement (1) comprising:- a support capacitor (10) , a bridge circuit (20) , a charge circuit (30) and a control unit (40) , wherein- the electrical arrangement (1) is configured to be connected to a first bus bar (LI) and a second bus bar (L2) of a DC link,- the support capacitor (10) is coupled to the first and second bus bars (LI, L2) via the bridge circuit (20) and the charge circuit (30) , and- the control unit (40) is configured to control the bridge circuit (20) and the charge circuit (30) according to a charging mode and a discharging mode, wherein- in the charging mode, the support capacitor (10) is charged using excess energy emerging from an overvoltage in the DC link,- in the discharging mode, energy stored in the support capacitor (10) is fed into the DC link, and- the bridge circuit (20) comprises four transistors arranged in an H-bridge configuration.

2. The electrical arrangement (1) according to the preceding claim, wherein- the support capacitor (10) comprises an electrochemical capacitor, in particular a supercapacitor.

3. The electrical arrangement (1) according to one of the preceding claims, wherein- the charge circuit (30) comprises two charge transistors (30T) connected antiparallel to each other.

4. The electrical arrangement (1) according to the preceding claim, wherein- the charge circuit (30) comprises a charge resistor (30R) connected parallel to the charge transistors (30T) .

5. The electrical arrangement (1) according to one of preceding claims 3 and 4, wherein- the charge circuit (30) comprises a charge varistor (30V) connected parallel to the charge transistors (30T) .

6. The electrical arrangement (1) according to one of the preceding claims, wherein- the control unit (40) is connected to a first measurement device (401) configured to measure a current flow between the electrical arrangement and the DC link and a second measurement device (402) configured to measure a voltage of the DC link.

7. The electrical arrangement (1) according to one of the preceding claims, wherein- the electrical arrangement (1) comprises an active crowbar structure (50) configured to limit a maximum voltage in the support capacitor (10) .

8. Method for operating an electrical arrangement (1) , comprising the following steps:- charge a support capacitor (10) in a charging mode with electrical excess energy of a first and a second bus bar (LI, L2) of a DC link via a charge circuit (30) if a voltage in the DC link is above a maximum operating voltage,- discharge the support capacitor (10) in a discharging mode and deliver electrical energy to the DC link if the voltage in the DC link is below a minimum operating voltage.

9. Method for operating an electrical arrangement (1) according to the preceding claim, wherein- the discharging mode is stopped if the support capacitor (10) reaches a minimum black start voltage level.

10. Method for operating an electrical arrangement (1) according to one of the preceding claims, wherein- a charging voltage level and a discharging voltage level are adjusted by a bridge circuit (20) arranged between the support capacitor (10) and the DC link.

11. Method for operating an electrical arrangement (1) according to one of the preceding claims, wherein- excess electrical energy is dissipated in an active crowbar structure (50) if a maximum voltage in the support capacitor (10) is reached.

12. Method for operating an electrical arrangement (1) according to one of the preceding claims, wherein- a control unit (40) switches the electrical arrangement between the charging mode and the discharging mode depending on a measured voltage of the DC link.

Images