DE102008018497A1 - Inverter i.e. solar inverter, for feeding multi-phase line current into mixing point of power network, has downstream line filter that is active line filter connected parallel to output of inverter - Google Patents

Abstract

The inverter (1) has an input-sided direct current/direct current converter (3) i.e. boost converter, and a network-guided, controlled static converter (4) with a commutation filter (5) and a downstream line filter for reducing static converter-sided produced harmonic current. A control device (6) controls a disconnectable power semiconductor circuit (42) by control signals (T1-T6) and detects present phase voltages (uR, uS, uT) of a power network (N). The downstream line filter is an active line filter (7') connected parallel to an output of the inverter.

Description

The The invention relates to an inverter, in particular a solar inverter, for feeding a multiphase mains current into a connection point a power supply network, the inverter having an input side DC / DC converter, a line-commutated, controlled power converter with a subsequent commutation filter and a downstream line filter to reduce harmonic currents generated on the power converter side having. It is each a turn-off power semiconductor switch with antiparallel diode connected as a converter valve one provided each phase of the power converter. The inverter points a control device for driving the power semiconductor switches by means of control signals and for detecting the pending phase voltages of the power supply network.

From the German patent application DE 10 2006 016 502 A1 is an inverter, in particular a solar inverter, known. It has a boost converter, a network-controlled controlled converter and a filter, wherein the filter with AC-side terminals and the boost converter output side are connected to DC side terminals of the grid-connected, controlled power converter. In each case, a turn-off power semiconductor switch with antiparallel-connected diode is provided as the converter valve of each phase of the line-commutated, controlled power converter. These turn-off power semiconductor switches are linked on the control side with a control device, at the inputs of which determined phase voltages of a network are pending.

From the technical essay "Active Line Filters to Improve Power Quality" by Gustav H. Vaupel, Hamburg University of Applied Sciences, Department of Electrical Engineering and Computer Science, pages 22 to 27 , The construction and operation of a three-phase active network filter based on a pulse inverter is disclosed.

The input-side DC voltage source can, for. B. a solar module or a solar panel with a plurality of such solar modules. It can be a fuel cell or even a generator of a wind turbine or a biogas plant.

Of the Inverter is preferably a three-phase inverter, in particular for feeding into a 3-phase 50 Hz / 400 V power supply network or in a 60 Hz / 460 V power supply network such. B. a power company.

The z. B. generated by a solar field or DC output voltage is from the current solar radiation as well as in particular from its electrical load dependent. Usually the controller of the inverter controls the power semiconductor switch clocked in the DC / DC converter such that the feed power in the electrical network is maximum. This credit point will also referred to as MPP (Maximum Power Point).

Preferably is the DC / DC converter, a boost converter for raising the input-side Input voltage at the level of the line-side voltage values, that is to a voltage of about 560 V at the 50 Hz / 400 V power supply network. Alternatively, the DC / DC converter can be a buck converter be the field or output DC voltage generated by a solar field if these voltages exceed 560V should.

at the inverter disclosed in the cited document, which is also referred to in the art as F3E inverter (F3E for Fundamental Frequency Front End), the antiparallel connected to the rectifier diodes power semiconductor switch switched depending on the mains voltage. On the The upper half of the bridge is always the respective power semiconductor switch turned on, whose emitter potential is higher than that the other two phases. On the lower bridge half this is analogous with the lowest collector potential as well. It is therefore a grid-controlled operation with switching from one phase to the next. A switching operation between upper and lower power semiconductor switch of one phase does not occur. Therefore, as diodes rectifier diodes be used with minimized forward voltage, facing each other Freewheeling diodes with optimized switching properties by considerably distinguish lower passage losses. The switching losses are therefore almost negligible due to the operation at mains frequency. To ensure the current commutation in the respective phases such a F3E converter is necessarily a commutation filter downstream. Such an inverter has in comparison to conventional inverters with a high-clocking Pulse inverter and with an efficiency of typically about 96% higher efficiency of 98% and better on.

The switching operations in the F3E inverter lead to mains harmonics in the mains current, in particular in the case of the odd ordinal numbers, such as 5th, 7th, 11th, 13th order and so on. The respective harmonic currents generated on the inverter side typically decrease with increasing atomic number. To national or inter In order to comply with national requirements for the grid connection of power generation plants in a public power grid, appropriate line filters are required. For example, the maximum permissible harmonic currents are in the European standard, at least for the territory of the European Union EN 61000-3-2 or EN 61000-3-12 regulated. The maximum permissible by the respective Ordnungszahl harmonic currents are dependent on the maximum short-circuit power of the electrical network at the respective node of the public power grid.

adversely in the aforementioned inverter is that the line filter for effectively filtering the comparatively low-frequency harmonic components extremely is voluminous. Such line filters usually have Capacities, inductances and / or damping resistors on. The latter also worsen the efficiency of such Line filter.

One Another disadvantage is the complexity and possible Vibration tendencies of the line filter when using a higher Filter order to specifically dominant harmonic components, such as z. B. the 5th or 7th order to dampen.

outgoing From the above-mentioned prior art, it is an object the invention to provide an inverter in which the previously mentioned disadvantages are avoided.

The The object of the invention is achieved with the features of the claim 1 solved. Advantageous embodiments are mentioned in the dependent claims 2 to 10.

According to the invention the line filter is an active parallel to the inverter output Mains filter. The particular advantage is that such a line filter only for a fraction, such as. B. 10%, the electrical Overall performance needs to be designed to be the power converter side largely compensate for generated harmonic currents. Such an active line filter can be realized compact accordingly become. The active line filter is designed to be one of the harmonic currents of the respective opposite order, that is, opposite phase, Compensation current in the common output of the inverter feed. As a result, the inverter according to the invention in the network-side connection point also a predetermined, predetermined harmonic spectrum.

To In one embodiment, the active line filter has a Pulse inverter with a multiple compared to the mains frequency higher switching frequency for extensive compensation of the on the converter side generated harmonic currents. Preferably the switching frequency is at least 100 times the mains frequency. The switching frequency is at a 50 Hz / 400 V power supply network consequently at least 5000 Hz, such as. B. 8 kHz. This is through the multiple "oversampling" in relation on the mains frequency a targeted antiphase harmonic compensation possible up to high atomic numbers of the harmonic components. Preferably, the pulse inverter of the active network filter a DC link with a capacitor. It serves as energy storage for short-term recording and back feeding of electrical Energy. Such an active line filter has a particularly high Efficiency of about 95%. However, since the active network filter only designed for about 10% of the total electrical power too is needed, the overall efficiency of the invention deteriorates Inverter only by about 0.5%.

one According to another embodiment, the active network filter at least one current detection unit for detecting a multiphase mains current, Frequency analysis means for determining the harmonic currents, such as B. a current measuring unit with downstream FFT analysis unit, and control means for controlled control of the pulse inverter on.

A Such analysis unit preferably has means for carrying out an FFT Frequency Analysis (FFT for Fast Fourier Transformation) a respective inverter-side network power. From the arithmetically determined harmonic spectrum can then be the pulse inverter controlled by Kom pensationsansteuermittel so controlled be that the harmonic currents in the node of the power supply network are largely compensated. Preferably This active mains filter has current measuring units, in particular Current transformer, for detecting the multiphase mains current.

Preferably In the three-phase case, the active line filter has two current measuring units for detecting the respective phase current. The remaining one Phase current can be directly measured from the two Determine phase currents.

According to a further embodiment, the inverter has at least one current measuring unit and one voltage measuring unit for detecting a DC input current and a DC input voltage at the input of the DC / DC converter. The control device also has imaging means for imaging a corresponding current electrical power in an expected, current-dependent upper oscillation spectrum. Furthermore, the control device has control means for the controlled control of the pulse-controlled inverter by means of PWR drive signals.

Out the determined current electrical power can by means of the control device, the respective network-side phase currents and whose current-dependent harmonic content are determined. The particular advantage is that the two measuring units anyway are required to set the maximum power point for to continuously determine the feed into the electrical network.

The Imaging agent may, for. B. an electronically stored table which depends on the current electrical power or depending on the respective determined phase current the expected harmonic currents of the respective order include. Based on this, a drive means may be the pulse inverter to control such that the frequenzabhän dependent harmonic currents in the connection point of the network in turn largely compensated are.

Preferably the previous means are software routines and memory tables, which is preferably the processor-based control device executes or reads out.

alternative can be used to determine the current electrical power also the respective phase currents detected by measurement become.

To another embodiment, preferably as Step-up converter trained DC / DC converter a turn-off another Power semiconductor switch, a decoupling diode, a storage choke and a filter capacitor. The control device has means to clocked control of the other power semiconductor switch via a control signal, so that the inverter at the maximum power point is operable. This maximizes the yield of the DC power source.

one According to another embodiment, the active line filter another passive mini mesh filter to dampen the harmonic currents be followed in particular from the 25th order. Such a thing Filter can filter out any existing high-frequency harmonic components, if required by national or international standards. In the simplest case, this filter is a compact low-pass filter with a corner frequency of approx. 1 kHz.

Especially is the considered inverter according to the invention designed for a feed-in capacity of at least 25 kW.

Preferably the inverter is a solar inverter to the input side Connecting to a solar module or to a solar panel.

The Invention and advantageous embodiments of the invention will be explained in more detail below with reference to the following figures described. Show it

1 the construction of a F3E inverter according to the prior art,

2 the structure of an exemplary inverter according to the invention,

3 an exemplary harmonic spectrum of a F3E inverter with registered limits for feeding into a power grid and

4 an advantageous embodiment of the inverter according to the invention.

1 shows the structure of an F3E inverter 1 According to the state of the art. In the shown inverter 1 it is a solar inverter for feeding a three-phase mains current iL1-iL3 into a connection point SK of a power supply network N. It is typically designed for a feed-in power of at least 25 kW. With the reference number 2 is a DC voltage source representative of a feeding source, such. For example, a solar module, a solar panel, a fuel cell, a wind power generator or the like referred to. The DC voltage source 2 is with the input side of a DC / DC converter 3 connected. Preferably, this is as in 1 shown, a boost converter 3 or a "boost converter" according to the English language usage. The known boost converter 3 has a turn-off another power semiconductor switch 32 , a decoupling diode 33 , a storage choke 31 and a filter capacitor 34 on. The additional power semiconductor switch 32 is doing about a processor-based control device 6 of the solar inverter 1 controlled by a control signal S to the solar inverter 1 at least almost in its maximum power point (MPP) to operate.

At the output of the boost converter 3 is a power converter input voltage uZ on. With iZ, the corresponding input current is for a subsequent line-commutated, controlled power converter 4 designated. The latter carries in the professional world the more common name F3E converter or F3E converter. With R, S, T are the three phases of the power converter 4 designated. He has the according to the German patent application DE 10 2006 016 502 A1 the known components such as rectifier Dio de 33 , Power semiconductor switch 32 , in particular IGBT, storage choke 31 and optionally a filter capacitor 34 on. The control of the control electrode, in particular of the gate, the respective IGBTs by means of control signals T1-T6, which the control device 6 from the detected phase voltages uR, uS, uT of the power supply network N forms. With fN, the derived network frequency, such. B. 50 Hz, referred to with iL1'-iL3 'the output side, harmonic-prone power converter currents.

To ensure the current commutation in phases R, S, T is the F3E converter 4 a passive commutation filter 5 downstream. By way of example, it has a star connection of three series circuits each consisting of a filter resistor 51 and a filter capacitor 52 on.

In the left part of the 1 is a current measuring unit 8th for detecting a DC input current iDC present. IDC is the corresponding measured current value. It is used inter alia to set the maximum power point by the controller 6 ,

2 shows the structure of an exemplary inverter 1 according to the invention. Compared to the execution according to 2 indicates the inverter shown 1 now instead of a passive network filter 7 one parallel to the output of the inverter 1 Switched active line filter 7 ' on. With "active" is an electronically controlled possible change in the filter characteristic of the line filter 7 ' meant. Furthermore, the active network filter 7 ' Frequency analysis means 71 as well as drive means 72 on. The frequency analysis means 71 serve to determine the harmonic currents iν, which are superimposed on the converter currents iL1'-iL3 '. The driving means 72 are designed to set a to the respective, ordnungszahlabhängigen harmonic currents iν equal antiphase compensation current iC1-iC3, so that the frequency-dependent harmonic currents iν in the node SK of the power supply network N can be largely compensated. For this purpose, the drive means controls 72 one in the 2 Pulse inverter not shown in the active line filter 7 ' at. In this case, the pulse inverter in comparison to the grid-driven, controlled converter 4 a much higher switching frequency fT of z. B. 8 kHz.

The control unit 6 gives the active network filter 7 ' depending on the current operating point, such. B. partial load or full load, the F3E inverter, how much the individual harmonic components must be damped. The controller generates a corresponding desired value SP 6 z. B. from a table.

In the example of 2 is the active network filter 7 ' an optional passive net mesh filter 7 '' downstream of the damping of the harmonic currents iν in particular from the 25th order. Such a small mesh filter 7 '' may be required for higher frequencies if required by the relevant standard for feed-in operation.

3 shows an exemplary harmonic spectrum Sν of a F3E inverter 1 with registered limit values G1.5, G4.5, G9 for feeding into a power supply network N. The converter output-side harmonic currents iν are plotted against the relevant odd atomic numbers at the mains frequency of 50 Hz and above the corresponding frequency f. Furthermore, harmonic currents iν are plotted as a function of, for example, six feed line values P1-P6. The exemplary power values P1-P6 for the inverter 1 are 35 kW, 30 kW, 20 kW, 10 kW, 5 kW and 1 kW. With G1.5, G4.5 and G9, the limits of the current harmonics are designated for an inverter with 30 kW rated power in a connection point SK with a system short-circuit power of 1.5 MVA, 4.5 MVA and 9 MVA.

As the present diagram shows, on the one hand take the harmonic currents iν with increasing atomic number and at the same time with decreasing Feed-in power P1-P6 from. The diagram also shows that the registered and the type of node SK dependent limits G1.5, G4.5, G9 not in every case be respected.

Furthermore, the harmonic spectrum Sν of the line-commutated controlled converter shows 4 caused by the compared in the conventional pulse inverter network synchronous phase switching pronounced and thus also predetermined harmonic harmonic components.

4 shows an advantageous embodiment of the inverter according to the invention 1 , The illustration shows the structure of the active network filter 7 ' in detail. It has a pulse inverter 74 in three-phase bridge circuit with IGBTs. The common connections of the respective phase-related bridges are each via a longitudinal choke 73 parallel to the output of the converter 4 connected. With the reference number 75 is a DC link capacitor referred to, via which a DC link voltage uK is applied. By targeted clocked control of IGBTs of the pulse inverter not further described 74 is thus a virtually lossless impressing of compensation currents iC1-iC3, that is, of reactive currents, possible, so that the sum currents iL1-iL3 of the respective converter currents iL1'-iL3 'and the respective Kom compensation currents iC1-iC3 are almost harmonic-free.

Furthermore, in the example of 4 for regulation two current measuring units 9 provided for detecting the phase currents iL1-iL3. The current power of the DC / DC converter 3 becomes an imaging agent 61 the control device 6 supplied on the basis of this power to determine the expected, current-dependent harmonic spectrum Sν. The current electrical power is calculated from a currently detected DC input current value iDC and a current input voltage value uE. Preferably, each power value is assigned a series of expected harmonic-dependent harmonic current values from the active line filter 7 '' to compensate. The corresponding data are preferably electronically in a memory of the control device 6 deposited. These data are then read out and subsequent activation means 62 supplied, which in real time suitable PWR control signals K1-K6 for clocked control of the pulse inverter 74 generate, so that the frequency-dependent harmonic currents iν in the node SK of the power supply network N are largely compensated.

Alternatively, the imaging agents 61 describe a mathematical model, which depends on the current performance of the DC / DC converter 3 simulates the expected harmonic-dependent harmonic current values.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102006016502 A1 [0002, 0034]

Cited non-patent literature

• - "Active Line Filters to Improve Power Quality" by Gustav H. Vaupel, Hamburg University of Applied Sciences, Department of Electrical Engineering and Computer Science, pages 22 to 27 [0003]
• - EN 61000-3-2 [0009]
• - EN 61000-3-12 [0009]

Claims (10)

Inverter, in particular solar inverter, for feeding a multiphase mains current (iL1-iL3) into a connection point (SK) of a power supply network (N), the inverter having an input-side DC / DC converter ( 3 ), a line-commutated, controlled power converter ( 4 ) with a subsequent commutation filter ( 5 ) and a downstream line filter ( 7 ) for reducing harmonic currents generated on the converter side (iν), wherein in each case a turn-off power semiconductor switch ( 42 ) with antiparallel-connected diode ( 41 ) as converter valves of each phase (R, S, T) of the converter ( 4 ) and wherein a control device ( 6 ) for driving the power semiconductor switches ( 42 ) by means of control signals (T1-T6) and for detecting the pending phase voltages (uR, uS, uT) of the power supply network (N), characterized in that the line filter ( 7 ) an active line filter connected in parallel with the output of the inverter ( 7 ' ). Inverter according to claim 1, characterized in that the active line filter ( 7 ' ) a pulse inverter ( 74 ) with a compared to the mains frequency (fN) often higher switching frequency (fT) for extensive compensation of the harmonic currents generated on the converter side (iν). Inverter according to claim 2, characterized in that the active line filter ( 7 ) at least one current detection unit ( 9 ) for detecting a multiphase mains current (iL1-iL3), frequency analysis means ( 71 ) for determining the harmonic currents (iν) and driving means ( 72 ) for the controlled control of the pulse inverter ( 74 ) having. Inverter according to Claim 2, characterized in that the inverter has at least one current measuring unit ( 8th ) and a voltage measuring unit for detecting an input direct current (iDC) and a DC input voltage (uE) at the input of the DC / DC converter ( 3 ), that the control device ( 6 ) Imaging agent ( 61 ) for mapping a corresponding current electrical power into an expected, current-dependent harmonic spectrum (Sν) and that the control device ( 6 ) Driving means ( 62 ) for the controlled control of the pulse inverter ( 74 ) by means of PWR drive signals (K1-K6). Inverter according to claim 3 or 4, characterized in that the pulse inverter ( 74 ) is designed for a switching frequency (fT) of at least 100 times the line frequency (fT). Inverter according to one of the preceding claims, characterized in that the power converter ( 4 ) is a F3E converter. Inverter according to one of the preceding claims, characterized in that the DC / DC converter ( 3 ) is a boost converter or a buck converter. Inverter according to one of the preceding claims, characterized in that the boost converter ( 3 ) a turn-off further power semiconductor switch ( 32 ), a decoupling diode ( 33 ), a storage choke ( 31 ) and a filter capacitor ( 34 ) and that the control device ( 6 ) Means for clocked control of the further power semiconductor switch ( 32 ) via a control signal (S), so that the inverter is operable at least almost in its maximum power point (MPP). Inverter according to one of the preceding claims, characterized in that the active line filter ( 7 ) a passive small mesh filter ( 7 '' ) for damping the harmonic currents (iν) is followed in particular from the 25th order. Inverter according to one of the preceding claims, characterized in that the inverter for a Feed-in power of at least 25 kW is designed.