DE102008057874A1 - Switch circuit for a photo-voltaic assembly, at a current circuit, has a mechanical switch and a second electronic switch - Google Patents

Abstract

The circuit (7) to connect/disconnect a photo-voltaic assembly (1) at a current circuit (l) has a relay (15) to operate a mechanical switch (9). A second, electronic switch (11) is in parallel to the first switch, i.e. an insulated gate bipolar transistor (IGBT). Both switches use a switch voltage (U1,U2) with the voltage to the second switch passing through a condenser (15) to earth.

Description

The The invention relates to a switching arrangement for connection and disconnection a photovoltaic system to or from a circuit with a Relay for actuating a mechanically closing and opening first switching element. The invention further relates to an operating method to operate the Switching arrangement.

The Switch off photovoltaic systems from a load, such as an inverter or a DC motor / alternator machine set, transform the energy generated by the PV modules into a public one Feed supply network, is for the switching elements used Technically sophisticated. Idle is on the output side a PV system about 1000 volts, which in operation to about 700 volts fall off. In operation means in the case of large facilities considered here of up to several megawatts of power a DC generated between 500 amps and 1000 amps. When switching off such Direct current at 700 volts voltage become the mechanical contacts heavily loaded. The switching elements must be checked regularly because sticking or improper switching of the contacts to an uncontrolled Short circuit would. Similar to in an electric welding machine would a welding of immense size in progress set, which would lead to destruction of the adjacent components.

The Shutdown by means of an electronic switch, such. B. one IGBT, is safe and maintenance-free, but has the disadvantage that permanently a Voltage of 0.5 volts to 1 volt is above the IGBT, causing too unwanted, leads to electrical losses.

present Invention is based on the object, the respective disadvantages of conventional and the electronic switch to work around.

These Task is solved by means of the switching arrangement in that parallel to the first switching element, a second, electronically operating switching element, In particular, an IGBT is provided. An advantageous embodiment The invention provides that both switching elements each to a switching voltage can be applied, of which the voltage applied to the second switching element Switching voltage at the same time a capacitor is connected to earth. Alternatively, it may be useful that both switching elements each can be applied to switching voltages from a signal generator generated offset in time.

Regarding the Operating method is the task in the capacitor variant thereby solved, that a) when connecting first the switching voltage is applied to the relay, causing the first Switching element is closed, that b) before the process step c) the switching voltage (U2) to the electronic, second switching element is placed, and that c) to disconnect the circuit, the first and the second switching voltage (U1, U2) simultaneously from the relay, or be taken from the electronic second switching element. This measure causes, when removing the switching voltage, the relay immediately drops and the first switching element opened becomes. The electronic second switching element is still through the Capacitor voltage held closed for a short period of time, until it has discharged to earth, then then, so after the first switching element also to break the circuit. As a consequence, the current flow when opening the first switch diverted into the path with the second switching element to go over the electronic second switch, first to flow, and then after the discharge of the capacitor to the circuit finally separate. The voltage at the first switching element corresponds to the switching operation Voltage drop over the electronic switching element, usually between the said 0.5 volts and 1 volt. So there will be an opening of the mechanical switch achieved only at a low switching voltage occurs at a low residual current, the residual current only during the Redistribution on the flow of electricity over the Parallel path with the second switching element is present and none Cause switching sparks can.

A Embodiment provides steps a) and b) together. The current flow is predominantly on the closed two switching elements on the first switching element flow, because it has almost no electrical resistance. The parallel current over the second switching element is so small that it is not worth mentioning Power loss leads. Thus, the design of a simplified switching sequence for the two Switching achieved, the only one switch-on accordingly the concern of the switching voltages and a turn-off accordingly includes the absence of switching voltages.

Regarding the Operating procedure, the task is still through a variant with solved a signal generator, by the i) when connecting first the switching voltage (U1) is applied to the relay, whereby the first Switching element is closed, ii) before disconnecting the circuit the second switching voltage (U2) to the electronic, second switching element iii) subsequently the first switching voltage is taken away from the relay, and iv) after all the second switching voltage from the electronic, second switching element is taken away.

at two variants of the method provides an advantageous embodiment before that before the first step a) or i) the second switching voltage is placed on the electronic, second switching element. hereby is a mild or soft connection of the photovoltaic system reached the load. The circuit is first via the electronic, second Switch closed, resulting in no wear. Then only the first switching element is closed, which in turn only in the low voltage of 0.5 volts to 1 volt happens and it finds the redistribution of the current flow from the parallel path to the IGBT to the parallel path with the mechanical switch instead.

Further Advantages and embodiments of the invention will become apparent from the Description of an embodiment based on the figures. Show it:

1 a symbolic circuit diagram of a first embodiment with signal generator, and

2 a symbolic circuit diagram of a second embodiment with capacitor.

A photovoltaic system 1 consists of a variety of photovoltaic modules, which are usually interconnected to a variety of strands. Each module in turn has a plurality of series-connected photovoltaic cells, which each provide an output voltage of about 1.5 volts when exposed to sunlight. Overall, in a large-scale system of the type considered here, the voltages of the individual cells add up to an open circuit voltage of approximately 1000 volts, which drops to approximately 700 volts in the event of operation. The supplied currents are several 100 amperes up to 1000 amperes. This photovoltaically generated power is available as DC / DC voltage at terminals 3.5 of the module fields. The energy is supplied via a circuit I to a load L, which may be an electronic inverter or a machine set in which a DC motor drives a three-phase generator, the output side of which is connected to a supply network (not shown). For connecting the photovoltaic system 1 to the load L and to the separation of the photovoltaic system 1 from the load L in the circuit I is a switching arrangement 7 provided, the two parallel switching elements 9 and 11 having.

The switching element 9 includes a mechanically actuated contact 13 that by means of a relay coil 15 closed or opened. Closing the contact 13 is relatively uncritical, since a very fast electrical connection between the line parts is made. When opening, however, forms an arc at the DC considered here 17 which leads to wear, in particular to erosion of the contacting areas.

Parallel to the mechanical switching element 9 is an electronic switching element 11 , in particular an IGBT provided. On the electronic switching element 11 A voltage between 0.5 volts and 1 volts drops continuously, which in continuous operation leads to a heating of the component accompanied by a significant loss of electrical power.

A signal generator 19 generates a first output voltage U1 for actuating and holding the relay 15 and a second output voltage U2 connected to a control input 12 the electronic second switching element 11 is laid. In operation of the switching arrangement 7 When switching on in the morning, the switching voltage U1 is first applied to the relay 15 placed, whereby the first switching element 9 is closed. This switching process is not critical and does not lead to premature wear of the contacts.

If the photovoltaic system 1 is to be separated from the load L, before opening the mechanical switching element 9 first the electronic switching element 11 activated, ie by applying the switching voltage U2 to the control input 12 closed. The current circulating in circuit I will continue to flow through the mechanical switch 9 flow, because it has no internal electrical resistance and provides the smallest obstacle for the current. If the separation process is subsequently initiated, first the first switching voltage U1 is withdrawn, so that in consequence the relay 15 falls off and the mechanical contact 13 opens. When opening, the resistor, which was not previously present when the line is closed, rises and the current becomes the electronic switching element 11 diverted. In this phase lies above the mechanical switching contact 13 the voltage at the IGBT of about 1 volt. To complete the separation process then the second switching voltage U2 is last from the control input 12 the electronic, second switching element 11 taken away and the circuit I is interrupted.

The simplified version after 2 provides that the signal generator 19 falls away and by a simple operating part 21 is replaced. In addition, the control input 12 of the second electronic switching element 11 (ie in the practice of the IGBT) via a capacitor C to ground. When closing the circuit I is then simultaneously a common control signal Ust both to the control input 12 of the second switching element 11 as well as to the relay coil 15 of the first switching element 9 placed. Both switching elements 9 . 11 Close and the circulating current is almost out finally via the mechanical switching contact 13 flow, because its resistance is negligible.

When opening the circuit I, the operating part is operated again and the control signal Ust is from both the first and the second switching element 9 , respectively. 11 taken away. During the opening process of the first switching element 9 increases the resistance when releasing the mechanical contact 13 from its mating contact piece due to the resulting air gap. Since the second switching element 11 is still conducting (the capacitor C discharges slowly and provides a delayed response at the control input 12 of the IGBT), the current is redistributed to the parallel current path with the second switching element 11 ie with the IGBT. Only when the capacitor is sufficiently discharged that the required switching potential at the IGBT is no longer applied, also switches the electronic, second switching element 11 ,

1

photovoltaic system

3, 5

terminal pair

7

switching arrangement

9

mechanical switching element

11

electronic switching element

13

mechanical Contact

15

Relay (coil)

17

Electric arc

19

signaler

21

actuating member

I

circuit

L

load

U1

switching voltage mechanical switching element

U2

switching voltage electronic switching element

Ust

control signal

Claims (7)

Switching arrangement ( 7 ) for connecting and disconnecting a photovoltaic system ( 1 ) to or from a circuit (I) with a relay ( 15 ) for actuating a mechanically closing and opening first switching element ( 9 ), characterized in that parallel to the first switching element ( 9 ) a second, electronically operating switching element ( 11 ), in particular an IGBT is provided. Switching arrangement according to Claim 1, characterized in that both switching elements ( 9 . 11 ) can each be applied to a switching voltage (U1, U2), of which the to the second switching element ( 11 ) applied switching voltage (U2) via a capacitor (C) is guided to ground. Switching arrangement according to Claim 1, characterized in that both switching elements ( 9 . 11 ) in each case to a switching voltage (U1, U2) can be applied, by a signal generator ( 19 ) can be generated at different times. Method for operating a switching arrangement according to Claim 2, characterized in that a) when switching on, first the switching voltage (U1) to the relay ( 15 ), whereby the first switching element ( 9 ), b) before the method step c) the switching voltage (U2) to the electronic, second switching element ( 11 ) and c) that for disconnecting the circuit (I) the first and the second switching voltage (U1, U2) are simultaneously applied by the relay ( 15 ), or by the electronic second switching element ( 11 ). Method for operating a switching arrangement according to claim 3, characterized in that i) when switching on, first the switching voltage (U1) to the relay ( 15 ), whereby the first switching element ( 9 ) is closed, ii) that before disconnecting the circuit (I), the second switching voltage (U2) to the electronic, second switching element ( 11 iii) that subsequently the first switching voltage (U1) from the relay ( 15 ) and iv) that finally the second switching voltage (U2) from the electronic second switching element ( 11 ) is taken away. Method according to claim 4, characterized in that steps a) and b) are carried out simultaneously. A method according to claim 4 or 5, characterized in that before the first step a), the second switching voltage (U2) to the electronic, second switching element ( 11 ) is placed.