The invention relates to an inverter and a method of conversion
an electrical DC voltage in an AC voltage of a
be z. B. used when electrical energy from DC sources,
such as photovoltaic systems, fuel cells or the like. In the public
Supply network is to feed. Such inverters are z.
B. capable of one or more DC potentials
one to the potential curve of a sinusoidal mains voltage with a
Frequency equal to 50 or 60 Hz.
DE 102 21 592 A1
describes a transformerless inverter with two DC terminals, one arranged between the DC terminals storage capacitor, a H-shaped full bridge circuit having four semiconductor switches, and with storage chokes, which are arranged in the leading to the AC voltage terminals branches of the bridge halves. To generate the desired AC voltage from an applied DC voltage certain switches of the full bridge depending on the polarity of the AC voltage with a high clock frequency pulse width modulated to provide in the closed state of the switch, the so-called. Aufmagnetisierungsphase, a current for charging the choke coils. When opening the high-frequency clocked switch, the so-called freewheeling phase, the coil current that continues to flow within the chokes due to the demagnetization commutes via separate freewheeling paths that are provided between the branches of the bridge halves. Each freewheeling path has a switch and a series-connected rectifier diode, wherein the rectifier diodes are connected in the freewheeling paths in opposite passage directions to each other. The free-wheeling paths prevent lossy back-commutation of the inductor current via full-bridge diodes back to the storage capacitors.
From the DE 102 25 020 A1
an inverter circuit is known, the two DC voltage branches, between which two photovoltaic generators and two storage capacitors are each arranged in series, a half-bridge circuit having two switches arranged in series and two AC voltage terminals, one of which via a storage choke containing connecting line to the center tap of the half-bridge connected is. In each half cycle of the alternating voltage, one of the switches of the half bridge is switched high frequent while the other remains open. In the Aufmagnetisierungsphasen the inductor, a current is supplied, resulting from the associated storage capacitor or DC generator. In the open state of the clocked switch commutes a freewheeling current back to the opposite storage capacitor. A power compensation circuit inserted between the DC branches ensures, with different output of the photovoltaic generators, that the power supplied to the half-bridge in the one DC branch is equal to that dissipated by the half-bridge in the other DC branch.
Another inverter circuit arrangement is in DE 10 2005 024 465 A1
described. The circuit arrangement is likewise based on the half-bridge circuit, which requires only a single switch per DC branch, which is to be clocked at high frequency. Between the AC voltage terminals a switch circuit is provided with further switch units and rectifier diodes, which allows a deflection of the current paths. A controller controls the half bridge and the switch circuit to generate an alternating current, wherein a freewheeling current is passed through the switch circuit, so that a Rückkommutierung on DC side storage capacitors is prevented. The control device further has logic to control the switches of the half-bridge and the point circuit as needed for power equalization between the DC voltage branches.
WO 90/01826 A1
describes a half-bridge inverter circuit with center tap in a three-phase configuration.
The known inverter circuits have proven themselves in the supply of energy in a network in practice. However, the DC voltages applied to the DC side must at least have the magnitude of the peak value of the mains voltage. Otherwise, the voltage for magnetizing the choke coil and thus for generating the desired alternating current or the desired AC voltage is not sufficient. However, the amount of DC voltage supplied is especially when connecting renewable energy sources, eg. As photovoltaic generators, not guaranteed at each operating point. A photovoltaic generator is constructed from a plurality of modules, each having a series circuit of a plurality of generator cells with a rated voltage of, for example, 0.7 to 0.8 volts. The voltage supplied by the cells varies considerably in terms of production and operation, in particular as a function of the temperature and due to shadowing effects. The bigger the whole span variance of the modules and generators. Any increase in the number of generator modules to achieve a generator voltage that is sufficient for most operating points is not possible due to the limited dielectric strength of the input-side storage capacitors and makes little sense for cost reasons.
It is therefore known to connect energy sources whose DC voltage level is below the mains peak value at certain operating points, usually via a so-called DC-DC controller to an inverter circuit, cf. z. B. DE 38 30 460 A1
, A DC-DC step-up converter, which is also referred to as a DC-DC converter or clocked voltage converter, is an electronic circuit that converts an input-side DC voltage into a larger output voltage. Step-up converters are well known in various embodiments. In an inductive converter, for example, a coil is used for energy storage, which is charged via a closable switch. When the switch is open, the coil discharges through a diode connected in series to deliver energy stored in the coil's magnetic field to a consumer.
Boost converters are used in an inverter circuit,
to a deterioration of the efficiency. This one is even worse
the bigger the
Step-up converter is dimensioned and the higher the load, so the
from the boost converter output current, the losses
are proportional to the second power of the current. The high voltage level
at the output of the boost converter has in an inverter circuit
high losses result. At the output of the bridge circuit high potential jumps arise
successive magnetization and freewheeling phases
the result of high switching losses and large Rippelströme and Ummagnetisierungsverluste
within the storage throttle. There are also heavily dimensioned boost converters
DE 100 20 537 A1
describes a full bridge inverter that feeds energy from a photovoltaic cell into an AC grid. At a DC voltage source which is connected between a first and a second input terminal, an H-shaped full-bridge circuit is connected, which has four parallel-connected transistors as switch elements, each of which a diode is connected in anti-parallel. Between the second input terminal and a connection point at the input of the full bridge an additional diode is provided. In one embodiment, a boost converter is used to generate from the DC input voltage, if necessary, a higher output potential. The boost converter is arranged together with an additional switch at its output in a voltage converter branch, which leads from the second input terminal to the input of the full bridge.
the potential of the voltage source is greater than the instantaneous AC mains voltage takes place
the feeding by known clocking of the transistors of the full bridge circuit. exceeds
the instantaneous mains AC voltage the potential of the voltage source,
become in an extended mode of operation, the polarity-dependent associated transistors
switched through while the
Switch takes place in the voltage converter branch. Thus, the higher voltage potential
applied at the output of the boost converter to the input of the full bridge. It
but then a relatively high current through both the switch in the
Voltage converter branch as well as by two of the transistors
the full bridge.
this leads to
to relatively high passage losses, which the overall efficiency
It is the object of the invention to provide an inverter circuit
and a method of converting a DC voltage to an AC voltage
to create a specific frequency that makes it possible
even with insufficient input DC voltage values, in particular below
the peak value of the AC mains voltage, energy with high efficiency
to feed into a network. It should in particular. switching losses
as well as reversal losses and ripple currents in the storage throttle largely
The object of the present invention is achieved by the method according to the invention
with the features of claim 1 and the inverter according to the invention
solved according to claim 14.
According to one aspect of the present invention, there is provided a method of converting a DC electrical voltage into an AC voltage by means of a circuit comprising a half-bridge circuit having switch elements and freewheeling elements and at least one storage inductor at the output of the bridge circuit connected to an AC voltage terminal connected to an AC voltage can be connected with a certain frequency. The switch elements are switched in dependence on the polarity of the AC voltage with a fixed clock pattern, wherein individual switch elements are driven synchronously with the frequency of the AC voltage and other switches with a high clock frequency. In the closed state of the high-frequency clocked switch, ie in Aufmagnetisierungsphasen, a Aufmagnetisierungsstrom for magnetizing the at least one Spei cholesterol provided. In the open state of these switch elements, the freewheeling phases, a freewheeling current flows through selected freewheeling elements, which enables a demagnetization of the storage inductor.
According to the invention
The current operating conditions are recorded and it is on the basis of this
determined whether the throttle (L) when using the clock pattern in
the magnetization phases is sufficiently magnetized. In
The result of this determination becomes the operating mode for driving
the switch elements suitably chosen. If it is determined
that the storage choke in the Aufmagnetisierungsphasen sufficient
can be magnetized according to a normal operating mode
the DC potential even in the Aufmagnetisierungsphasen
for providing the current for magnetizing the storage choke
used, d. H. with appropriate closure of at least one high frequency
clocked switch element of the half-bridge circuit to the storage choke
coupled. In the freewheeling phase of normal operation, if that
Switch element opened
is com mutated due to the demagnetization within the storage choke
continuing to flow
Freewheeling current on a separate freewheeling path.
it is determined that the storage choke in the Aufmagnetisierungsphasen
is not or insufficiently magnetized, is an extended
Operating mode fixed. In this mode, the input DC potential becomes
in an amount higher potential
converted by the appropriate timing at least one switch element
in the Aufmagnetisierungsphasen as Aufmagnetisierungspotential
used to provide the charging current for the storage choke
or is coupled to the storage choke. In the freewheeling phases
but not the freewheel path used in normal operating mode,
but the magnetizing path used in the normal operating mode
used to provide the freewheeling current, so that the DC potential itself
is coupled to the storage inductor and the freewheeling potential
Invention is particularly suitable for use for the feed
of energy in a network, eg public
Supply network, by means of a photovoltaic system. This can be a
or two or even more photovoltaic generators in particular
in series connection at the input of the circuit arrangement according to the invention
be provided. It can
Other DC sources that provide a variable DC potential,
such as fuel cells or accumulators are used.
Voltage variances based on manufacturing tolerances or
due to temperature drift or shading effects during operation,
be compensated by the invention readily by, for example.
Potential for a desired
Level is adjusted. There may be a wide range of variable DC potentials at the
Input can be used, the DC voltage also significantly
below the peak value of the AC voltage, for example the peak value
of about √2 x 230 volts
or √2 · 120 volts one
AC mains voltage with a frequency of 50 or 60 Hertz, lie
can. It has been found that with a DC amplitude
at least about one third of the peak value of the mains voltage
an effective operation possible
is. Thus, the invention is a wide input voltage range
The invention makes it possible, even with insufficient generator voltages to feed energy with high efficiency in a network, including several measures are provided. For example. the use of the increased voltage potential is limited only to periods of half-wave in which the DC voltage of a generator does not provide sufficient magnetization potential. In the other periods, the lower DC voltage of a generator is used to magnetize the storage choke. Due to the lower potential level of the generator voltage, the switching losses, Rippelströme and iron losses in the storage inductor and electromagnetic interference compared to a mode in which always from the increased potential, for example. The output potential of a boost converter, would be clocked off significantly reduced. Furthermore, the efficiency is improved by the fact that in the periods in which the DC voltage of a generator is not sufficient and in the extended operating mode, the increased potential is coupled to the input of the storage inductor, the DC voltage of the generator specifies the free-running potential. The freewheeling current is supplied to the storage inductor from a DC branch to which the generator is connected. This has in comparison to a freewheel z. B. from a neutral conductor or even an opposite DC voltage branch a smaller voltage swing on the connected to the bridge circuit input of the storage throttle result. The voltage swing corresponds only approximately to the voltage difference between the output potential of the boost converter and the potential of the DC input voltage. Due to the higher freewheeling potential, the demagnetization of the storage inductor takes place much more slowly, whereby energy is advantageously fed into the grid even in the freewheeling phase. In addition ripple currents and Ummagnetisierungsverluste within the storage throttle as well as EMC interference are drastically reduced. Due to the low voltage Jumps, which a switch element of the bridge circuit, which is provided in the amount of potential increase serving voltage converter branch to generate the pulse pattern must perform at its high-frequency clocking fall in this as well as in the DC branch freewheeling diode only low switching losses. Further, the Leitenddauer the high-frequency clocked switch element can be effectively reduced in the range of the peak value of the half-wave of the AC voltage, so that passes through this a smaller amount of energy into the network and the switch as well as a possibly this upstream boost converter can be made much smaller. In any case, additional costs can be saved.
a preferred embodiment
The invention is used to determine whether the throttle in the Aufmagnetisierungsphasen
is sufficiently magnetized, the current inductor current
detected and required for magnetizing the storage throttle
Set current. Further, a desired average voltage at
Input of the storage choke determined and with a reference value
comparing the choice of the appropriate operating mode and the appropriate
Driving strategy allows.
In particular, the reference value is suitably chosen to be a decision
if the input DC voltage is possibly taking into account
appropriate safety reserves to achieve the desired
middle bridge output
or throttle input voltage is sufficient.
an advantageous embodiment
the reference value is a variable, depending on current operating conditions
customizable or adjustable value. Preferably, the reference value
formed by the amount of the current DC voltage value or
for example, voltage drops in the magnetizing path
and certain tolerances are taken into account.
If the desired
Mean throttle input voltage in terms of magnitude below the DC potential
is located, the magnetization of the storage throttle is carried out according to the normal
Operating mode from the DC circuit, while the freewheel preferably via a
Freewheel path takes place, the commutation of the freewheeling current on
the opposite one
DC branch or the neutral or the like. Prevented. If
the amount of the desired
mean throttle input voltage value above the DC voltage
is located, the invention is extended
Operating mode with magnetization from the voltage transformer branch
and freewheeling from the DC voltage circuit via a DC voltage branch
set. In order to make this possible,
are switch elements and freewheeling elements, for example freewheeling diodes,
the half bridge
both in the DC voltage branch and in the voltage converter branch
According to one
Another aspect of the present invention is an inverter
for converting a DC voltage into an AC voltage, in particular
an alternating mains voltage with a frequency of 50 or 60 hertz,
created, wherein the inverter for carrying out the method according to the invention
is set up. The inverter has a DC voltage circuit
at least one DC voltage branch to which a DC voltage source
is that provides a DC input voltage, an AC circuit
with an alternating voltage branch to which an alternating voltage is applied
can be and contains a storage choke, and a half-bridge circuit
on, the switch elements and freewheeling elements, for example. Freewheeling diodes,
for converting a DC voltage into an AC voltage,
and whose tap is connected to the input of the storage choke
is. The inverter further has a DC voltage branch
connected voltage converter branch with a voltage converter device
to increase the input DC voltage to an absolute higher output potential on.
A control device is provided, the switch elements
the bridge circuit
according to one
to control specified clock pattern to accomplish the direction of change.
The control device has an evaluation device, which
a detection device detected signals, the operating conditions
and processes these signals, and a driver
on which the switch elements of the bridge circuit with a specific
Clock pattern drives. The evaluation device according to the invention has
a suitable logic and is set up, starting from
determine the detected signals, whether the choke when using the
Clock pattern sufficiently magnetized in magnetization phases
will, and depending on
This finding the appropriate of the aforementioned operating modes of the method according to the invention
thus formed inverter according to the invention comprises in the
In connection with the method according to the invention the advantages mentioned above
on. Likewise, the above-described modifications
and further developments of the method according to the invention, which
accordingly also applicable to the inverter according to the invention
Preferably, the detected input signals include a signal that the current flowing through the storage inductor current or a da with related size. The control device then advantageously has a current controller logic which regulates the actual value of the current flowing through the storage inductor to a desired average value.
For the determination
of the suitable operating mode, the evaluation device can use a determination logic,
from the input signals, a desired average voltage at
Input of the choke and containing a comparator logic,
the desired one
mean voltage value with a reference value, z. B. a the
Input voltage characteristic reference value compares how this
According to the invention
the DC branch of one of the switching elements of the bridge circuit
and a rectifier diode arranged in series with the switch element. This
Switch element is clocked high frequency in normal operating mode,
to magnetize the storage choke. In extended operating mode
this switch element is closed, and the rectifier diode
serves as a freewheeling diode, via
the freewheeling current flows.
Voltage converter branch according to the invention is parallel to the series circuit
from the switch element and the rectifier diode of the DC voltage branch
arranged and has a voltage converter means, preferably
a DC-DC boost converter,
in particular an inductive voltage converter, and a storage capacitor
and a series connected to the voltage converter means
Switch element of the bridge circuit
on. This switch element is used in extended operating mode
Magnetization of the storage choke high frequency clocked and
is open in normal operating mode. Advantageously, the
Voltage lift, this switch and the freewheeling diode in the
DC voltage branch in extended operating mode, relatively low.
is a half-bridge, according to the invention
the only one switch element clocked high frequency per half-wave
inverter according to the invention
may further comprise power compensation means, if necessary
enable power equalization between the DC voltage branches. This
can, for example, at different shading two connected in series
Photovoltaic generators may be needed to prevent
the total output of the plant due to the solar cell characteristic
is lowered. The power compensation can, for example, accomplished by
be that for certain
the freewheeling current is enabled
on the opposite
Voltage transformer branch back
to commute, causing energy over
transmit the voltage converter means to the respective DC voltage branch
is or fed by the boost converter less energy
must become. By the control device and certain switch elements
and freewheeling elements of the bridge circuit
thus formed power compensation means allow both generators
at its optimum operating point according to the solar cell characteristic
to be able to operate.
In the same way you can
Storage capacitors of the voltage converter device in certain freewheeling phases
be specifically charged to produce the increased potential
without where necessary, a DC-DC boost converter required
Details of advantageous embodiments
The invention are the subject of the drawing, the description or
The drawings are embodiments of
Invention illustrated. Show it:
1 a circuit arrangement of an inverter according to the invention with a half-bridge in a single-phase configuration;
2a and 2 B schematic representations of the time courses of the bridge voltage, the currents and the control signals in the circuit arrangement according to 1 ,
In 1 is a circuit diagram in a slightly schematic way 1 of an inverter according to the invention in a single-phase, transformerless configuration. The illustrated inverter 1 is used to generate and supply an alternating current to an external network. For this purpose, the inverter points 1 a DC voltage circuit 2 , which is also referred to as an intermediate circuit and specifies the input DC voltage, here designed as a half-bridge transformerless bridge circuit 3 , a voltage converter circuit 4 for an increase in the magnitude of the potential of the DC input voltage and an AC voltage circuit 6 on.
The DC voltage circuit has three DC voltage connections 7 . 8th . 9 on where DC generators 11 . 12 , For example. Photovoltaic generators, fuel cells, batteries or the like., Are connected in series with each other. Here is a first DC voltage generator 11 between the DC voltage connections 7 and 8th while a second DC generator 12 between the DC voltage connections 8th and 9 is arranged. For reasons of simplification, it is assumed that the Gleichspannungsgenerato Ren provide the same DC input voltage or intermediate circuit voltage U ZK1 , although in operation, the supplied voltage values , for example, due to shading or tolerances may differ from each other.
From the DC voltage connections 7 . 8th . 9 lead DC voltage branches 13 . 14 . 15 away, of which the DC voltage branch located in the middle 14 through the entire circuit arrangement 1 passed through to form a neutral conductor. Between the DC voltage branches 7 and 8th respectively. 8th and 9 Storage capacitors C 1 and C 2 are each parallel to the DC voltage generators 11 and 12 connected.
Parallel to the series connection of the capacitors C 1 , C 2 is the half-bridge circuit 3 arranged, the two in series interconnected switch elements S 1 and S 2 , which in one with the respective DC voltage branch 13 respectively. 15 connected magnetization and freewheeling path 16 respectively. 17 are arranged. The switch elements S 1 and S 2 are, like other switch elements also, preferably formed as a semiconductor switch in the form of IGBT (Insulated Gate Bipolar Transistor) or MOS field effect transistor switches or other low-loss switches connected at high frequencies of up to 100 kilohertz can be. Parallel to the switch elements S 1 and S 2 , a free-wheeling diode D 1 and D 2 is provided in each case, which are arranged in the opposite direction of passage to the switch elements S 1 , S 2 , to protect them against reverse currents. The freewheeling diodes D 1 and D 2 are here only optional and can also be omitted. In series with the respective switch units S 1 and S 2 , rectifier diodes D 10 and D 20 are provided, which are arranged in the same forward direction as the switch elements S 1 and S 2 . In the illustrated embodiment, the diode D 10 is located between the switch element S 1 and a center tap 18 the half bridge 13 while the diode D 20 between the center tap 18 and the switch element S 2 is arranged. However, viewed from the DC side, the rectifier diodes D 10 and D 20 can also be arranged in front of the switch elements S 1 and S 2 .
The half bridge 3 has two further switch elements S 3 , S 4 , which are provided with parallel to these and in the opposite forward direction arranged freewheeling diodes D 3 and D 4 and in voltage converter branches 19 . 20 arranged to the voltage converter circuit 4 belong.
The voltage transformer branch 19 is arranged parallel to the series arrangement of switch element S 1 and rectifier diode D 10 and here advantageously has a DC-DC boost converter 21 on, which is preferably designed in the form of a voltage-increasing inductive converter. Such boosters or voltage transformers are well known in the art and need not be further explained here. Their function is to increase the potential of an input voltage, here the voltage U ZK1 , to a higher potential, which is designated here by U ZK2 . The boost converter 21 is with its input to the DC branch 13 connected while its output is connected to the switch element S 3 , which in turn to the center tap 18 the half bridge 3 connected. Further, at the output of the boost converter 21 a buffer capacitor C 3 is connected, whose other connection to the neutral conductor 8th connected is.
In a similar manner and in a symmetrical configuration, the voltage converter branch provided parallel to the series arrangement of switch element S 2 and rectifier diode D 20 20 here a DC-DC boost converter 22 on, on the DC branch 15 between the DC voltage connection 9 and the switch element S 2 is connected and the output of which is connected both to the switch unit S 4 , D 4 and to a buffer capacitor C 4 connected between the voltage converter branch 20 and the neutral conductor 14 is inserted.
The circuit arrangement according to the invention 1 also includes two freewheel paths 23 . 24 parallel to each other between the center tap 18 the half bridge 3 and the neutral conductor. Every freewheel path 23 . 24 has a switch element S 5 and S 6 with an optionally at this anti-parallel freewheeling diode D 5 and D 6 and a on in series to this on-level rectifier diode D 50 and D 60 having the same forward direction as the associated switching element S 5 or S 6 has. Incidentally, the rectifier diodes D 50 and D 60 in the individual freewheeling paths 23 . 24 switched to each other in the opposite direction of passage.
The center tap 18 the half bridge 3 is via a connection line 26 in which a storage inductor L is provided to from the half-bridge 3 to buffer supplied energy and deliver it to an AC voltage network, with an AC voltage connection 27 of the AC voltage circuit 6 connected. At the AC voltage connection 27 and another AC voltage connection 28 , which is connected to the neutral conductor, an external AC voltage U NETZ is connected. Furthermore, the AC circuit contains 6 a smoothing capacitor C 5 , between the connecting line 26 and the neutral is inserted to high frequency voltage components between the center tap 18 and the neutral conductor 14 resulting bridge voltage U BR ago filter out.
How out 1 further, it is apparent to monitor and control the operation of the circuitry 1 a control device 29 intended. The control device 29 receives input signals at its input 31 , which come from various sensor means, such as current and voltage sensors, not shown here. In particular, input signals which are the intermediate circuit voltages U ZK1 or the increased intermediate circuit voltages U ZK2 , the inductor current I L flowing through the storage inductor, the mains voltage U NETZ and optionally further state variables in the circuit arrangement 1 be identified, recorded and taken into account. The control device 29 takes the detected input signals 31 and processes them according to predetermined logical rules to output signals at their output 32 to spend on the control of the switch elements S 1 to S 6 output. The input signals 31 can the controller 29 be supplied in analog or digital form, so that the control device 29 contain analog and / or digital logic elements or may be implemented in the form of running on a microprocessor control program in which the corresponding logic rules are implemented.
Regardless of its implementation, the controller includes 29 an evaluation device or logic 33 , which is adapted to at least one of the state variables, as by one of the input signals 31 be characterized, to determine therefrom further variables and to compare with a reference value, and a driving device or logic 34 that with the evaluation device 33 is connected and instructed by this to choose a suitable drive strategy to the switch elements S 1 to S 6 via the output signals 32 in a suitable way.
In 2a are to illustrate the operation of the circuit arrangement according to the invention 1 simplified diagrams with time profiles of different partial voltages and currents and control signals in the circuit arrangement 1 in the case of a positive half wave of the mains voltage U NETZ illustrated. Corresponding diagrams for the case of the negative half wave of the mains voltage U NETZ are in 2 B shown. It should be noted that the switching frequency during operation is several, for example. 16 kilohertz, while in the drawing, for complexity reasons, only a few clock cycles per half-wave are shown, by way of example, the basic operation of the circuit 1 to clarify. The circuit arrangement 1 works as follows:
The circuit arrangement 1 is preferably used to feed energy into a network, in particular a public utility grid. It should be under the assumption that at the AC voltage connections 27 . 28 a sinusoidal mains voltage U NETZ with a peak voltage of √2 · 230 volts and a frequency of 50 or 60 Hz is applied, as shown in the top diagram representations of 2a and 2 B is illustrated for the respective half-wave, from the intermediate circuit voltages U ZK1 the DC voltage generators 11 . 12 at the output of the inverter 1 An AC current can be generated, which matches the phase position and amplitude of the AC voltage U NETZ . For this purpose, the control device controls 29 after a certain clock pattern, the switch elements S 1 to S 6 suitable to close and open them. In this case, switches S 1 to S 4 by suitable modulation, for example. Pulse width modulation of the drive signals 32 operated high-frequency, while the switch elements S 5 and S 6 are closed and opened in synchronism with the mains frequency.
How out 2a shows, in the case of a positive half-wave and a low voltage level of the mains voltage U NETZ according to a normal operating mode, the switch S 1 is switched to high frequency, while the switch S 5 remains closed during almost the entire positive half cycle. The remaining switch elements S 2 to S 4 and S 6 are open. At each closure of the switch element S 1 , hereinafter referred to as the magnetization phase, a magnetizing current I S1 flows out of the DC voltage circuit 2 , in particular the storage capacitor C 1 , over the branch 16 with the switch element S 1 and the rectifier diode D 10 to the storage inductor L, to charge them energetically or magnetically. The bridge voltage U BR corresponds to neglecting the voltage drops in the branch 16 the intermediate circuit voltage U ZK1 . The inductor current I L increases steadily in each charging phase. With increasing mains voltage U NETZ , the closing time of the switch S 1 is greater ßer. If the switch element S 1 is opened at each clocking, which is referred to as free-running phase, the bridge voltage U BR drops substantially to the value zero, so that there is a demagnetization of the inductor L and a drop of the inductor current I L in each freewheeling phase. In this case, the freewheeling current I S5 flows from the neutral conductor via the freewheeling path 23 with the rectifier diode D 50 and the switch S 5 to the connecting line 26 with the storage choke L. Like out 2a To recognize, the coil current I L gradually increases with the formation of small ripples, which are referred to as current ripple, and follows on average the course of the mains voltage U NETZ .
As soon as the intermediate circuit voltage U ZK1 for a sufficient charging of the choke coil L is insufficient, an extended operating mode is initiated. This case is handled by the evaluation device 33 detected by the received input signal (s) 31 a currently desired average voltage Ū BR at the throttle input 26 , which allows sufficient magnetization of the storage inductor L, determined and compares this average voltage value Ū BR with a reference value REF. More specifically, and in a preferred embodiment, the driver includes 33 a current controller logic, not shown here, which controls the mean current Î L of the current flowing through the inductor current I L according to a desired value that matches the AC mains voltage U NETZ . Depending on the setpoint and actual values of the inductor current I L , the actuation device determines the respectively required mean inductance input voltage BR and compares this with the reference value REF. Although it is possible to predetermine the reference value in advance, for example, as a function of a known value of U ZK1 , in the preferred embodiment of the invention the reference value is determined with the aid of the currently detected value of U ZK1 , whereby voltage drops in the magnetizing path are taken into account accordingly. If the value Ū BR is greater in magnitude than the reference value REF, the driver supplies 33 to the control logic 34 a signal 36 indicating that the extended operating mode should be initiated.
In the extended mode of operation, the driver causes 34 in that the switch element S 1 remains closed, while now the switch element S 3 is switched high-frequency. The switch element S 5 in the path 23 can be closed or opened. In the subsequent Aufmagnetisierungsphasen is thus through the boost converter 21 increased DC link voltage U ZK2 used to magnetize the storage inductor L. This is then in the Aufmagnetisierungsphasen at the center tap 18 the bridge 3 at. The charging current I S3 flows in the closed state of the switch S 3 from the output of the boost converter 21 over the voltage transformer branch 19 and the switch element S 3 to the center tap 18 and further via the connection line 26 to the input of the inductor L. In the open state of the switch S 3 , a freewheeling current I S1 flows from the DC voltage circuit 2 , So the storage capacitor C 1 , via the now serving as a freewheeling branch 16 including the switch element S 1 and the rectifier diode D 10 to the coil L.
Advantageously, the bridge voltage U BR varies only between the value of the increased intermediate circuit voltage U ZK2 in the magnetization phase and approximately the lower value of the input voltage U ZK1 , which defines the freewheeling potential in the freewheeling phase . The voltage jumps of the bridge voltage U BR are relatively low, in any case, significantly lower than in the case when the freewheel of the neutral conductor or even the opposite DC voltage branch 15 would be done. As a result, the electromagnetic compatibility is improved, so that external filters, such as chokes, capacitors or the like., Smaller dimensioned for electromagnetic interference and thus run more economical or even can be omitted. In addition, the demagnetization of the storage throttle L is significantly slowed by the low voltage swings of the bridge voltage U BR . This in turn has extremely low Rippelströme and Ummagnetisierungsverluste within the storage inductor L result. Furthermore fall in the switch element S 3 and the freewheeling diode D 10 , which carry out the voltage jumps, only very low switching losses. After always only one switch element of the bridge 3 is conductive, the forward losses are low. Overall, a very high efficiency can be achieved.
Advantageously, even in the freewheeling phase, energy of the storage inductor L and downstream is supplied to the network. Thus, how can 2a can be clearly seen, the duration during which the switch S 3 is turned on in the upper region of the sine wave, respectively, be significantly reduced. This passes through the switch S 3, a smaller amount of energy into the network. The switch S 3 and the boost converter 21 can be much smaller designed or executed.
When the mains voltage U NETZ drops again after the vertex and the reference voltage level REF falls below, as indicated by the signal 36 the evaluation device 33 is displayed, the drive logic switches 34 again in the above-mentioned normal operation mode in which it opens the switch element S 3 and the switching element S 1 clocked high-frequency. The magnetization is again via the switch element S 1 and the diode D 10 starting from the potential U ZK1 , while the freewheel on the freewheeling path 23 he follows.
In the negative half-wave of the mains voltage U NETZ the switch elements S 1 , S 3 and S 5 remain open, while in an analogous manner, the switch elements S 2 , S 4 and S 6 are suitably controlled. In this case, in the normal operating mode, when the desired average voltage Ū BR is greater than the potential at the DC voltage branch 15 , the negative DC link voltage -U ZK1 , the switch element S 2 is switched to high-frequency with the switch element S 6 and the switch element S 4 open. In the Aufmagnetisierungsphasen the bridge voltage U BR is given by the intermediate circuit potential -U ZK1 , and there is a magnetizing current I S2 flows through the rectifier diode D 20th and the switch element S 2 to magnetize the storage inductor L. In freewheeling phases, when the switch element S 2 is opened, the freewheeling path leads 24 with the closed switch element S 6 and the rectifier diode D 60, the freewheeling current. The bridge voltage U BR jumps between the potential -U ZK1 and zero.
In the period in which the actual value of the AC voltage U NETZ the potential -U ZK1 below or, more precisely, the amount of the currently desired average voltage Ū BR at the input of the storage inductor L is greater than the reference voltage value, for. B. the amount of DC voltage U ZK1 plus reserve, the controller switches 29 in the extended or modified operating mode, in which the on the DC branch 16 applied potential -U ZK1 through the boost converter 22 is converted to a magnitude higher potential -U ZK2 , which now specifies the magnetization potential in the Aufmagnetisierungsphasen. The switch element S 4 is now switched to high frequency, while the switch element S 2 remains closed. The switch element S 6 can be opened or remain closed. Currents for magnetizing the choke coil L now flow through the switch element S 4 , while the freewheel on the rectifier diode D 20 and the switch element S 2 in the now as freewheeling path the nenden branch 17 he follows. The bridge voltage U BR fluctuates between the increased DC link potential -U ZK2 and the DC link potential -U ZK1 . The voltage swing is low, which results in low switch losses and re-magnetization losses and high efficiency.
The control device 29 also contains logic rules for power compensation between the DC voltage branches 13 and 15 , Is, for example due to shading the power output of the lower solar generator 12 reduces, which can be determined by detection and comparison of the voltages U ZK1 of the generators and the currents fed by these, causes the control logic 34 if necessary, that the switch S 5 in the freewheeling path 23 in the positive half-wave of the mains voltage U NETZ is opened for a short duration. As a result, the inductor current I L in freewheeling phases can commutate via the free-wheeling diode D 4 of the switch element S 4 to the buffer capacitor C 4 , which is thereby charged. Thus, a portion of the generator 11 supplied energy to the lower voltage converter branch 20 and over the boost converter 22 on the lower DC voltage branch 15 transfer. This proportion and thus the degree of power compensation is determined by the ratio of the total opening time to the closing time of the switch element S 5 .
A reverse power compensation from the lower one 15 to the upper DC branch 13 is achieved by temporally proportionate opening of the switch element S 6 in the negative half-wave and Rückkommutierung the inductor current I L via the freewheeling diode D 3 to the buffer capacitor C 3 . Thus, the freewheeling diodes D 3 and D 4 and the switch elements S 5 and S 6 together with the power compensation logic of the control device 29 Power compensation means according to the invention.
Numerous modifications are possible within the scope of the invention. For example. can the circuitry 1 be extended to use more than two series-connected DC voltage generators. The neutral conductor 14 can be connected to the ground, eg in a control cabinet, by grounding to a defined zero potential. In the neutral conductor and / or the connecting line 26 For example, filter elements for suppressing high-frequency interfering signals can be inserted, such elements being included in FIG 1 not illustrated. The indicated inverter 1 can also be easily extended to a three-phase configuration when a three-phase alternating current is to be generated from the DC voltages U ZK1 .
Furthermore, another suitable criterion for determining whether or not the input voltage U ZK1 is sufficient for magnetizing the storage choke can also be set up. Such a criterion can, for example, be based on a comparison of the magnitude of the current value of the mains alternating voltage U NETZ with a suitable voltage reference value, for example a reference value dependent on the input voltage. It is also to be noted that state quantities in the circuit can be derived from other quantities by means of general electrotechnical relationships or used instead of those for the criterion.
In addition, the inverter according to the invention in a particular embodiment without the boost converter 21 . 22 be educated. The voltage converter device is then solely by the buffer capacitors C 1 , C 2 and a special drive logic 34 formed, which works similar to the power compensation logic. By a targeted charging of the buffer capacitors C 1 , C 2 in certain freewheeling phases can ei ne sufficient voltage increase in the voltage converter branches for an input voltage range of certain minimum size 19 . 20 be achieved.
The circuit arrangement according to the invention 1 results in low potential jumps of the bridge voltage U BR both in the normal operating mode and in the extended operating mode and thus low switching losses and Ummagnetisie rungsverluste in the coil, so that a high efficiency is ensured. This is advantageously achieved because of a branch 16 (respectively. 18 ) is provided with a switch element S 1 (or S 2 ) and a rectifier diode D 10 (or D 20 ), which in the normal operating mode as a magnetizing path and in the extended operating mode, in which the input voltage is converted to a higher potential, as a freewheeling path is used. Advantageously, only a single switch S 1 or S 2 or S 3 or S 4 is switched high-frequency pulse width modulated, whereby the switching losses are further reduced.