DE102008018497B4 - Inverter, in particular solar inverter, with an active line filter - Google Patents

Abstract

Inverter, in particular solar inverter, for feeding a polyphase mains current (iL1-iL3) into a connection point (SK) of a power supply network (N), the inverter comprising an input-side DC / DC converter (3), a line-commutated, controlled F3E converter (4 ) with a subsequent commutation filter (5) and a downstream line filter (7) for reducing harmonic currents generated on the converter side (iv), wherein in each case a turn-off power semiconductor switch (42) with antiparallel connected diode (41) as a converter valve of each phase (R, S , T) of the power converter (4) is provided and wherein the inverter comprises a control device (6) for driving the power semiconductor switch (42) by means of control signals (T1-T6) and for detecting the upcoming phase voltages (uR, uS, uT) of the power supply network (N ) having,
characterized,
- that the line filter (7) is a parallel to the output of the inverter switched active line filter (7 '),
- That the active line filter (7 ') a pulse inverter (74) with a compared to the mains frequency (fN) often higher switching frequency (fT) for the substantial compensation of the harmonic currents generated on the converter side (iv) ...

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 net-guided, controlled F3E converter with a subsequent commutation filter and a downstream line filter to reduce the power converter side generated harmonic currents 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 general term forming, 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 European patent application EP 0 685 919 A1 For example, there is known an electric current harmonic compensator for a power supply network comprising a capacitor, a self-commutated power converter and a choke coil, wherein a current impressed in the choke coil corresponds to an inverted sum of the current harmonics of a harmonic generating means. For generating the impressed current, means for forming a desired current are provided which have a first band-pass device connected to the supply network for generating a harmonic-free alternating voltage. There are further provided means for generating a desired value for the inverted sum of the current harmonics having a tuned to the line frequency, second bandpass device with downstream inverter.

Out the technical essay "Active Line filter to improve the power quality "by Gustav H. Vaupel, University of Applied Sciences Hamburg, Department of Electrical Engineering and Computer Science, page 22 bis 27, is the structure and operation of a three-phase active line filter disclosed on the basis of a pulse inverter.

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 control device controls of the inverter clocked the power semiconductor switch in the DC / DC converter such indicates that the feed-in power into the electrical grid is maximum. This power point is also known as MPP (Maximum Power Point).

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

In 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 switches are switched in response to the mains voltage. On the upper bridge half always the respective power semiconductor switch is turned on, whose emitter potential is higher than that of the other two phases. On the lower bridge half this is analogous with the lowest collector potential as well. It is therefore a network-controlled operation with switching from one phase to the next. A switching operation between upper and lower power semiconductor switch of a phase does not occur. Therefore can be used as diodes rectifier diodes with minimized forward voltage, compared to free-wheeling diodes with optimized Schaltalteigen characterized by significantly lower transmission losses. The switching losses are therefore almost negligible because of the operation at mains frequency. To ensure current commutation in the respective phases, such a F3E converter is necessarily followed by a commutation filter. Such an inverter has a higher efficiency of 98% and better compared to conventional inverters with a high-clock pulse inverter and with an efficiency of typically about 96%.

The switchover in the F3E inverter to mains harmonics in the mains, especially in the odd-numbered Ordinal numbers such as 5th, 7th, 11th, 13th order and so on. The take respective harmonic currents generated on the inverter side typically with increasing atomic number. To national or also international requirements for grid connection of power generation plants in a public To meet the power grid, Corresponding line filters are required. So are the maximum permissible Harmonics for example, at least for the territory of the European Union in the European Standard EN 61000-3-2 or EN 61000-3-12 regulated. The of the respective Ordinal maximum permissible Harmonics are dependent on it from the maximum short circuit power of the electric network at respective connection point of public Power supply network.

adversely in the aforementioned inverter is that the line filter is extremely bulky for effective filtering of the comparatively low-frequency harmonic components. such Line filters usually have Capacities, inductances and / or Damping resistors on. Latter also worsen the efficiency of such a network filter.

One Another disadvantage is the complexity and possible vibration tendencies of the mains filter when using a higher filter order to targeted dominant harmonic components, such. B. the 5th or 7th order, to dampen.

outgoing From the above-mentioned prior art, it is an object The invention, suits an inverter ben, 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 in the dependent claims 2 to 8 called.

This is according to the invention Line filter an active parallel to the output of the inverter switched Mains filter. The active line filter has a pulse inverter with a much higher switching frequency compared to the mains frequency for extensive compensation of the harmonic currents generated on the power converter side. 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 has imaging means for mapping a corresponding current electrical Power in an expected, current-dependent harmonic spectrum on. The control device has control means for controlled activation of the pulse-controlled inverter by PWR drive signals in such a way, that the frequency dependent Harmonics in the connection point of the power supply network are largely compensated.

Of the special advantage is that such a network filter only for one Fraction, such as B. 10%, the total electrical power designed needs to be to the power converter side generated harmonic currents largely to compensate. Such an active line filter can be correspondingly compact will be realized. The active line filter is designed to have a opposite to the harmonic current of the respective order, this means antiphase, compensation current in the common output of the Inverter feed. As a result, the inverter according to the invention in the network connection point as well a predetermined, predetermined harmonic spectrum.

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 leaves determine directly from the two measured phase currents.

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

The imaging agent may, for. Example, be an electronically stored table, which depending on the current electrical power or depending on the respective determined phase current include the expected harmonic currents of the respective order. Based on this, a drive means can control the pulse-controlled inverter in such a way that the frequency-dependent harmonic currents at the point of connection of the network, such as are largely compensated.

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

alternative can to determine the current electrical power and the respective phase currents be detected metrologically.

To a further embodiment has the preferably designed as a boost converter DC / DC converter a turn-off another power semiconductor switch, a decoupling diode, a Storage choke and a filter capacitor on. The control device has means for clocked activation of the further power semiconductor switch over Control signal on, so that the inverter at the maximum power point is operable. This maximizes the yield of the DC power source.

one another embodiment According to the active net filter can still passively a small mesh filter for damping 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 for a feed of at least 25 kW.

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

The Invention as well as advantageous embodiments of the invention further described below with reference to the following figures. Show it

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

2 the construction of an exemplary,

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 supplying a three-phase mains current iL1-1L3 to 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 to be able to operate at least almost in its maximum power point (MPP).

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 known components such as rectifier diode 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 are derived from te 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. He serves under derem for setting the maximum power point by the controller 6 ,

2 shows the structure of an exemplary inverter 1 , Compared to the execution according to 1 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 iv, which are superimposed on the converter currents iL1'-iL3 '. The driving means 72 are designed to set a to the respective ordnungszahlabhängigen harmonic currents iv equal-phase antiphase compensation current iC1-iC3, so that the frequency-dependent harmonic currents iv 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 attenuation of the harmonic currents iv 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 Sv of a F3E inverter 1 with registered limit values G1.5, G4.5, G9 for feeding into a power supply network N. The rectifier output-side harmonic currents iv are plotted against the relevant odd ordinal numbers at the mains frequency of 50 Hz and above the corresponding frequency f. Furthermore, harmonic currents iv 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 nominal 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 iv with increasing Ordnungszahl and at the same time with decreasing feed-in power P1-P6. The diagram also shows that the registered and the type of node SK dependent Limit values G1.5, G4.5, G9 are not observed in every case.

Furthermore, the harmonic spectrum Sv of the grid-controlled 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 power converter currents iL1'-iL3 'and the respective compensation currents iC1-iC3 are almost free of harmonics.

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 Sv. 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 iv 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.

Claims (8)

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-driven, controlled F3E power converter ( 4 ) with a subsequent commutation filter ( 5 ) and a downstream line filter ( 7 ) for the reduction of harmonic currents generated on the power converter side (iv), wherein in each case a turn-off power semiconductor switch ( 42 ) with antiparallel-connected diode ( 41 ) as a converter valve of each phase (R, S, T) of the power converter ( 4 ) and wherein the inverter comprises 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 ' ), that - the active line filter ( 7 ' ) a pulse inverter ( 74 ) with a switching frequency (fT) that is many times higher than the line frequency (fN) for substantially compensating the harmonic currents (iv) generated on the converter side, - 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 (Sv), 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) such that the frequency-dependent harmonic currents (iv) are largely compensated in a linking point (SK) of the power supply network (N). Inverter according to Claim 1, characterized in that the imaging means ( 61 ) is an electronically stored table, which depending on the current electrical power include the expected harmonic currents (iv) of the respective order. Inverter according to Claim 1 or 2, characterized in that the preceding means ( 61 . 62 ) Software routines and memory tables are, which are executable or readable on the processor-based control device. Inverter according to one of the preceding claims, 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 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 activation 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 (iv) is followed in particular from the 25th order. Inverter according to one of the preceding claims, characterized characterized in that the inverter for a feed-in of at least 25 kW is designed.