Inverter with switching device for control supply

Abstract

Inverter (1) with a switching device (10) for selectively supplying a control unit (13) of the inverter (1) via power received via AC terminals (17) or DC terminals (16) of the inverter (1), the switching device (10) comprising a first, positively guided relay (11), designed as a two-pole changeover switch, wherein the positively guided relay (11) in a first switch position assumed to be in the rest state connects the control unit to the DC terminals (16) and in a second switch position to the AC terminals (17), wherein a control coil (21) of the positively guided relay (11) is connected to the AC terminals (17) via a control circuit (2) having a signal input (3), wherein the signal input (3) is connected to the control unit (13).

Description

[0001] The invention relates to an inverter with a switching device for selectively supplying a control of the inverter via a power received via an AC connection or a DC connection of the inverter, as well as to a power generation system with such an inverter.

[0002] Inverters are an essential component of power generation systems, which, for example, feed renewable direct current power generated by PV generators into the grid in the form of alternating current. Such inverters typically have a control system that can be powered either by the grid's alternating current or by the generator's direct current. Accordingly, separate power converters are provided for both power sources, which are activated and deactivated depending on the operating conditions of the inverter and the availability of the power sources. The IEC standard IEC62109 (currently in the 2011 version) requires galvanic isolation of the two power sources while maintaining single-fault tolerance.

[0003] The object of this invention is to provide an inverter in which a switching device allows the selection of several power sources while complying with the said standard in a simple manner, in particular while avoiding separate power converters for the two said power sources.

[0004] This object is achieved by an inverter having the features of independent claim 1. Preferred embodiments of the inverter are the subject of the dependent claims.

[0005] An inverter according to the invention has a switching device for selectively supplying a controller of the inverter via power received via AC terminals or DC terminals of the inverter. The switching device comprises a positively driven relay, designed as a two-pole changeover switch, wherein the positively driven relay connects the controller to the DC terminals for supply in a first switch position assumed in the idle state and to the AC terminals in a second switch position. A control coil of the positively driven relay is connected to the AC terminals via a control circuit having a signal input, the signal input being connected to the controller.

[0006] In an advantageous embodiment, the control circuit has a second relay designed as a normally closed contact, via whose switching contacts the AC connections are connected to the control coil of the positively driven relay, wherein a control coil of the second relay is connected to the signal input for controlling the second relay via the control.

[0007] In another, particularly cost-effective embodiment, the control circuit comprises a storage device connected to the AC terminals via a rectifying charging circuit and further connected to the control coil of the positively driven relay, so that the control coil can be supplied with energy via the storage device and thus control the positively driven relay. The charging circuit further comprises an optocoupler controllable via the signal input, which can be used to switch a charge of the storage device via the AC terminals. The optocoupler can be designed as an opto-triac.

[0008] By connecting the control coil of the positively driven relay to the AC terminals via the control circuit, it is ensured that the control system is supplied via the AC terminals precisely when AC power is available there, i.e., when the AC terminals are connected to an operational grid, and that the control system does not itself switch to a supply via the DC terminals by opening the second relay by controlling the control coil of the second relay. On the other hand, in the event of a grid failure, the switching device automatically supplies the control system via the DC terminals, as the positively driven relay then falls into the first switch position assumed in the idle state. The DC terminals are preferably connected to an intermediate circuit of the inverter.

[0009] At the same time, the design of the first relay as a positive-drive relay ensures that even in the event of a fault in the first relay, such as a welded switching contact, no contact of the DC terminals can be connected to a contact of the AC terminals via the switching device or the control system. A fault in the second relay can be easily identified by appropriate voltage measurements at the relay contacts, detecting a deviation from the expected voltage values ​​when the relay is intact.

[0010] In an advantageous embodiment of the invention, a rectifier is arranged between the AC terminals and the controller to supply the controller with a DC voltage in all cases. The rectifier can be arranged between the AC terminals and the first relay or between the first relay and the controller, whereby in the first case, the first relay switches a DC voltage and in the second case, an AC voltage.

[0011] Optionally, a current-limiting element can be arranged between the first relay and the control system to reduce current peaks when the first relay switches. Current-limiting elements can also be provided at other locations in the switching device.

[0012] To adjust the voltage supplying the controller to a suitable value, a power converter can be arranged between the first relay and the controller. This can be designed, in particular, as a flyback converter with galvanic isolation between the input and output of the power converter and a buffer capacitor that ensures continuous operation of the controller in the event of a brief power interruption.

[0013] In an advantageous variant, in which the inverter should be able to freely determine the control unit's power source as needed, the control unit can be configured to cause the first relay to switch by generating a control signal via the signal input of the control circuit. The control signal can be generated, in particular, depending on the voltage stability of the current power source and can cause a switch to the other DC and AC terminals if the voltage stability threatens to be insufficient for a secure supply.

[0014] Preferably, the control coil of the positively driven relay is connected to the AC terminals via a rectifying element, particularly if the control coil is configured for DC control, in order to control the control coil with a direct current. Furthermore, the control coil can be provided with a protective circuit to suppress voltage peaks during control.

[0015] However, it is also conceivable to connect the control coil directly to the AC terminals. This is preferably used for relay types whose control coil is configured for AC control.

[0016] In a further aspect of the invention, a power generation plant comprises an inverter according to the invention.

[0017] In the following, the invention is illustrated by means of figures, of which Fig. 1 shows a first embodiment of a switching device in an inverter according to the invention, Fig. 2 shows a second embodiment of a switching device in an inverter according to the invention, Fig. 3 shows a further embodiment of a control circuit according to the invention in a switching device of an inverter, Fig. 4 a state model of a switching device in an inverter according to the invention, Fig. 5 an extended state model of a switching device in an inverter according to the invention, and Fig. 6 shows a power generation plant with an inverter according to the invention.

[0018] In Fig. Figure 1 shows a schematic structure of a switching device 10 for selectively supplying a controller 13 via DC terminals 16 or via AC terminals 17 of an inverter. The switching device 10 is intended for integration into an inverter according to the invention. The AC terminals 17 are routed, on the one hand, via an input circuit 4, which may contain, for example, a rectifier, to first switching contacts of a first, positively driven relay 11, and, on the other hand, via a control circuit 2 to terminals of a control coil 21 of the first relay 11. Furthermore, DC terminals 16 are routed to second switching contacts of the first relay 11.The first relay 11 can thus, in a first switch position, transmit power supplied via the AC terminals 17 to a controller 13 connected to the switching device 10 via a power converter 14, and, in a second switch position assumed in the idle state of the first relay 11, transmit power supplied via the DC terminals 16 to supply the controller 13. The controller 13 is also connected to a signal input 3 of the control circuit 2 for transmitting a switching signal and can thus control whether the control coil 21 of the first relay 11 is energized with power received at the AC terminals 17.

[0019] Fig. Figure 2 shows an advantageous embodiment of the switching device 10 according to the invention for selectively supplying the controller 13 via DC terminals 16 or via AC terminals 17 of an inverter. In the embodiment shown, supply lines of the controller 13 are connected via a power converter 14, here a galvanically isolating converter, and current-limiting elements 15, here implemented as resistors, to a pair of switching contacts of a first, positively driven relay 11 of the switching device 10. This pair of switching contacts can be switchably connected jointly, via a control of the control coil 21 of the first relay 11, either to a first switching contact pair connected to the DC terminals 16 or to a second switching contact pair connected to the AC terminals 17 via a rectifier 18.

[0020] For control, the control coil 21 of the first relay 11 is also connected to the AC terminals 17 via a second relay 12 designed as a normally closed contact.

[0021] If sufficient alternating voltage is applied to the AC terminals 17 and the switching contacts of the second relay 12 are closed, the first relay 11 is switched to a position in which the pair of switching contacts to which the controller 13 is connected is connected to the first pair of switching contacts. The controller 13 is then supplied with power via the AC terminals 17. If the switching contacts of the second relay 12 are open or if there is insufficient alternating voltage at the AC terminals 17, the first relay 11 is switched to a position in which the pair of switching contacts to which the controller 13 is connected is connected to the second pair of switching contacts. The controller 13 is then supplied with power via the DC terminals 16.

[0022] The AC terminals 17 are connected to the AC terminals of the inverter, while the DC terminals 16 can be connected to an intermediate circuit of the inverter. However, the DC terminals 16 can also be connected to another point in the inverter's DC power path, for example, directly to a DC input of the inverter.

[0023] In Fig. Figure 4 shows a first state model of the switching device according to the invention. Here, DC+ denotes a state in which a sufficient direct voltage is present at the DC terminals to supply the controller, and DC- denotes a state in which this is not the case. Analogously, AC+ denotes a state in which a sufficient alternating voltage is present at the AC terminals to supply the controller, and AC- denotes a state in which this is not the case. Furthermore, C:AC denotes the state in which the controller is connected to the AC terminals for power supply, and C:DC denotes the state in which the controller is connected to the DC terminals for power supply. Corresponding to this connection, C+ denotes a state in which the controller receives sufficient supply power and is thus ready for operation, and C- denotes a state in which this is not the case, and the controller is therefore not ready for operation.

[0024] In a first state S1 of the state model, there is no sufficient supply voltage available via either the AC or DC terminals (DC- / AC-). Accordingly, the controller is not ready for operation (C-), while the controller is connected to the DC terminals (C:DC).

[0025] If the AC mains returns, so that a sufficient voltage is available at the AC terminals for the operation of the control system (AC+ / DC-), a second state S2 is assumed. In the second state S2, the control system is ready for operation and is supplied via the AC terminals (C+ / C:AC). This is achieved in the switching device according to the invention by designing the second relay of the switching device as a normally closed contact, so that the returning AC voltage sets the first relay to the second switch position.

[0026] If sufficient voltage is now also present at the DC terminals (DC+ / AC+), the switching device switches to a third state, S3. In this state, the operational control system continues to be supplied via the AC terminals (C+ / C:AC).

[0027] If the AC voltage applied to the AC terminals subsequently drops to a level that is no longer sufficient to supply the controller or maintain the second switch position of the first relay (DC+ / AC-), a fourth state S4 is assumed and the first relay returns to the first switch position, in which the controller's supply lines are connected to the DC terminals. The controller's operational readiness is then maintained by the DC voltage at the DC terminals (C+ / C:DC).

[0028] If the DC voltage at the DC terminals also falls below the value required to supply the controller (DC- / AC-), the state model of the switching device changes from the fourth state S4 back to the first state S1. The controller remains connected to the DC terminals but is no longer operational (C- / C:DC).

[0029] In the opposite direction, the state model transitions from the first state S1 to the fourth state S4 when the voltage at the DC terminals returns. If the voltage at the AC terminals then also returns, the state model transitions from the fourth state S4 to the third state S3. If the voltage at the DC terminals initially fails, the state model transitions from the third state S3 to the second state S2, and then to the first state S1 if the voltage at the AC terminals, the power source for the control system, also fails.

[0030] In Fig. 5 shows a state model for a switching device according to the invention, which, compared to the state model from Fig. 4 is expanded to include a fifth state S5 and a sixth state S6. The fifth state S5 is reached when the switching device is in the second state, in which the controller is ready for operation and connected to the AC terminals (C+ / C:AC), and the AC terminals provide sufficient AC voltage for the supply, while there is insufficient DC voltage at the DC terminals (DC- / AC+). A control signal that the controller sends to the control coil of the second relay opens the relay (R-), so that when the connection between the control coil of the first relay and the AC terminals is eliminated, the first relay falls into the first switch position, in which the controller is connected to the DC terminals. The switching device is now in the fifth state S5. Since the DC terminals cannot provide sufficient power to the controller, the voltage on the control supply lines drops.If the control system is set up to monitor the voltage on the supply lines, the control system can detect the voltage drop in time before the voltage on the supply lines becomes insufficient for the control system to continue operating, and can send a closing signal to the second relay so that the control coil of the first relay returns to the second switch position and the switching device returns to the second state S2. Even if the control system is not set up to monitor a voltage drop on the supply lines, the switching device returns to the second state S2 if the control system is no longer operational due to the lack of supply via the DC connections and can no longer send the opening signal to the second relay, which is designed as a break contact, so that it closes again.

[0031] The sixth state S6 is reached in a similar way to the fifth state S5, but starting from the third state S3, in which the DC connections also provide sufficient DC voltage to operate the controller. In this case, too, the controller sends an open signal to the first relay, causing the first relay to change from the second switch position to the first switch position, and the controller is now supplied with power from the DC source. Unlike the fifth state S5, the switching device can also remain permanently in the sixth state S6 or return to the third state S3 at any time via a close signal from the controller.

[0032] By switching to the fifth state S5 or the sixth state S6, the controller can actively initiate a change of power source, for example, if the existing power source cannot provide sufficient supply reliability. The controller can also check whether the DC terminals provide a sufficient DC voltage for the controller's operation, without requiring a voltage measurement directly at the DC terminals.

[0033] Fig.6 shows a power generation system 2 comprising an inverter 1 according to the invention with a switching device 10. The inverter 1 is connected to a grid 43 at AC terminals 17, while a photovoltaic generator 44 of the power generation system 2 is connected to DC terminals 16 of the inverter 1. The switching device 10, like a converter circuit 40, is connected to both the AC terminals 17 and the DC terminals 16 of the inverter 1 and is configured to selectively supply a controller 13, which is provided for controlling the converter circuit 40. A power converter 14 is provided between the switching device 10 and the controller 13, and provides a voltage level suitable for supplying the controller 13 at its output.Optionally, a further DC / DC converter 41, for example a boost converter, can be provided between the DC terminals 16 and the converter circuit 40 with an upstream intermediate circuit 42. In this case, the switching device 10 is preferably connected between the DC / DC converter 41 and the intermediate circuit. List of reference symbols 1 inverter 2 Control circuit 3 Signal input 4 Input circuit 10 Switching device 11 relays 12 relays 13 Control 14 power converters 15 current-limiting element 16 DC connectors 17 AC connections 18 rectifiers 21 Control coil 22 Control coil 23 optocouplers 24 storage 25 Charging circuit 40 converter circuit 41 DC / DC converters 42 intermediate circuit

Claims

[1] Inverter (1) with a switching device (10) for selectively supplying a controller (13) of the inverter (1) via a power received via AC connections (17) or DC connections (16) of the inverter (1), the switching device (10) comprising a first, positively driven relay (11), designed as a two-pole changeover switch, wherein the positively driven relay (11) connects the controller for supply to the DC connections (16) in a first switch position assumed in the idle state and to the AC connections (17) in a second switch position, wherein a control coil (21) of the positively driven relay (11) is connected to the AC connections (17) via a control circuit (2) having a signal input (3), wherein the signal input (3) is connected to the controller (13). [2] Inverter (1) according to claim 1, wherein the control circuit (2) has a second relay (12) designed as a break contact, via whose switching contacts the AC terminals (17) are connected to the control coil (21) of the positively driven relay (11), wherein a control coil (22) of the second relay (12) is connected to the signal input (3) for controlling the second relay (12) via the controller (13). [3] Inverter (1) according to claim 1, wherein the control circuit (2) comprises a storage device (24) which is connected to the AC terminals (17) via a rectifying charging circuit (25) and which is connected to the control coil (21) of the positively driven relay (11), wherein the charging circuit (25) comprises an optocoupler (23) which can be controlled via the signal input and with which a charge of the storage device (24) can be switched via the AC terminals. [4] Inverter (1) according to one of the preceding claims, wherein a rectifier (18) is arranged between the AC terminals (17) and the controller (13). [5] Inverter (1) according to claim 4, wherein the rectifier (18) is arranged between the AC terminals (17) and the first relay (11). [6] Inverter (1) according to one of the preceding claims, wherein a switching converter (14) is arranged between the first relay (11) and the controller (13). [7] Inverter (1) according to one of the preceding claims, wherein the controller (13) is configured to generate a control signal at the signal input (3) of the control circuit (2) as a function of a voltage stability of the supply of the controller (13). [8] Inverter (1) according to one of the preceding claims, wherein the control coil (21) of the positively driven relay (11) is connected to the AC terminals (17) via a rectifying element. [9] Inverter (1) according to one of claims 1 to 7, wherein the control coil (21) of the positively driven relay (11) is directly connected to the AC terminals (17). [10] Inverter (1) according to one of the preceding claims, wherein the DC terminals (16) are connected to an intermediate circuit (42) of the inverter (1). [11] Power generation plant with an inverter (1) according to one of the preceding claims.

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