DE102005024465B4 - Circuit arrangement and control method for a converter - Google Patents

Abstract

Circuit arrangement (1) for converting direct current into alternating current or from alternating current into direct current,
with at least three DC voltage connections (2, 3, 4), which include at least two DC voltage branches (17, 18) and a neutral conductor (19),
with energy buffers (6, 7) which are each connected between a DC voltage branch (17, 18) and the neutral conductor (19),
with a bridge circuit (8) arranged between the DC voltage branches (17, 18), which has two switch units (S1, S2) per phase, which are connected in series via a connection point (20) which forms a center tap of the bridge circuit (8) are and to which in each case a freewheeling diode (D1, D2) is connected in anti-parallel,
with two per phase ac voltage terminals (12, 13), one of which (13) is connected to the neutral conductor (19), while the other (12) per phase via a connecting line (21), each containing a storage inductor (L) is connected to the respective center tap (20) of the bridge circuit (8), wherein at the AC voltage terminals (12, ...

Description

The The invention relates to a converter for converting two electrical DC voltages in at least one AC voltage or for forming at least one electrical AC voltage in DC voltages.

such Inverters, also called inverters, are used in particular for feeding electrical energy in the public Power supply used when, for example, DC sources such. As photovoltaic systems, accumulators or fuel cells, for disposal stand. It applies, from one or more DC potentials to generate an alternating current with respect to the phase position and amplitude to the potential curve of the AC voltage, eg. a sinusoidal mains voltage with a frequency of 50 or 60 Hz, is to be equalized. To this Purpose are single or three-phase inverters with and without transformer known.

inverter are also used to power the AC mains sinusoidally refer to. At the same time, the power quality may be with regard to the harmonic content and / or reactive power. Such abstractions Power converters become common combined with other inverters connected on the DC side, the the energy taken from the grid into a single or multi-phase AC grid convert variable frequency in order to z. B. to drive motors.

From the DE 102 21 592 A1 For example, an inverter is known for converting a direct electrical voltage into an alternating current. The inverter has two DC voltage terminals connected to a DC voltage generator, a buffer capacitor and a bridge circuit connected in parallel to the buffer capacitor, and two AC voltage terminals connected to the 50 Hz power network. The bridge circuit is designed as a full bridge with two parallel branches, each having two series-connected switch units, to each of which a rectifier diode is connected in parallel. Each AC voltage terminal is connected via a connecting line, which includes a choke coil, with one of the parallel branches of the bridge circuit via a connection node, which is in each case between two switch units. Furthermore, two separate electrical connection paths each having a switch and a series-connected rectifier diode are provided between the connection lines. The rectifier diodes are connected in the connection paths in the opposite passage direction to each other.

in the Operation, the switch units of the full bridge depending on the polarity of the AC mains voltage clocked symmetrically. At a positive half wave of the AC mains voltage become, for example, two diagonally opposite switch units the full bridge according to one fixed clock pattern high-frequency and time-synchronous closed and opened, while the other two open stay. Furthermore a switch is closed in a first connection path. In the closed state the switch units flows the current over this to charge the inductor. When opening the switch units commutes due to the demagnetization within the reactor inductances on flowing Coil current during the so-called "freewheeling phase" over the closed switch and the associated rectifier diode in the first connection path. This prevents the coil current via diodes the full bridge back commutated into the buffer capacitor and thus leads to losses. As soon as the half-wave of the AC mains voltage is negative, the other, diagonally opposite Switch units and the switch used in the other connection path.

at The prior art inverter are charging in the coil Switching state of two lossy switch units in the current path, which are switched high frequency. This leads to switching losses, the significantly affect the efficiency of the inverter. Furthermore is the voltage swing of the switching units at each bar accomplished must be relatively high. Apart from the considerable switching losses this causes Voltage swing due to this necessary high slopes of voltage and current not insignificant electromagnetic interference.

Of the Inverter and the specified control method are not provided for the removal of energy from the network, but merely serve the energy feed into the network. Here's just a single one DC voltage generator connectable. In energy production with a solar system, for example, but several solar cells in series switched so that through these sub-generators the same current flows. If a shadow falls on one of the subgenerators, that is the total generating capacity insufficient, because only operating points with equal currents can adjust.

From the DE 102 25 020 A1 a circuit arrangement for the conversion of direct current into alternating current is known, the two series-connected DC voltage generators, two DC voltage branches, two parallel to the generators connected buffer capacitors and one connected to the two DC voltage branches NEN inverter has. The inverter is formed by a half-bridge circuit which comprises two symmetrically clocked switches arranged in series with each other, to each of which a rectifier diode is connected in parallel. A supply line connected via a choke coil with the mains voltage is tapped at the midpoint between the switch units. To avoid DC voltage components of the alternating current with unequal power of the feeding DC voltage generators power compensation means are connected upstream of the inverter. These are so effective that the power supplied to the inverter in a DC branch is equal to the power dissipated by the inverter in the other DC branch.

at This inverter is only a switch at each half-wave clocked high-frequency, which reduces the switching losses. It does, however, take place during the free-running phase, a lossy Rückkommutierung the inductor current to the buffer capacitors instead. Advantageously, although for a power compensation between the DC branches that are urgently needed, because in the enterprise also only small differences in the achievement of the DC voltage branches cause DC components in the network. Indeed will be additional, the inverter upstream means required, the effort and the Increase cost of circuit realization. A withdrawal of energy from the network is not provided.

Inverters with a circuit topology corresponding to that specified in claim 1, are in the DE 38 42 985 C2 and WO 90/01826 A1 illustrated. The associated pulse width modulation control methods are designed to better utilize the entire available voltage range of the inverter or to reduce portions of higher order vibrations in the output signal of the inverter.

outgoing It is an object of the present invention, a circuit arrangement and to create a procedure that the switching or control related Overcome disadvantages of the prior art and preferably both for the supply of energy in an alternating voltage network as are also suitable for removal of energy from the network. Especially should be a back commutation of demagnetization processes the inductor inductances originating inductor current to a buffer capacitor largely avoided and simple Building an at least partial power equalization allows.

These Task is by the circuit arrangement according to the invention the features of claim 1 and the inven tion proper method Claim 13 solved.

The inventive circuit arrangement has at least three DC voltage terminals, two of which have DC voltage branches and one connected to a neutral conductor, at least two Energy buffer, for example. Buffer capacitors, each between a DC branch and the neutral in serial Arrangement are connected to each other, a bridge circuit between the the DC voltage branches is arranged, at least two AC voltage terminals, the on the one hand with the bridge circuit connected and on the other hand connected to an AC voltage, a switch circuit, which allows a deflection of the current paths, and a control device for controlling the operation of the circuit arrangement.

The bridge circuit is according to the invention by a conventional half bridge formed, the DC voltage branch only a single switch unit needed to which a freewheeling diode is connected in antiparallel. In a Single-phase configuration are therefore only two switch units connected in series. The connection point between the Switch units forms a center tap of the bridge circuit, from there, a connecting line leading to one of the AC voltage terminals branches, in which a storage throttle is arranged. The other AC voltage connection is directly with the neutral conductor connected. Advantageously, the neutral conductor is from the DC voltage side passed to the AC side and can to the ground potential be connected.

The switch circuit is connected between the connecting line and the neutral conductor and has two switch paths, in which controlled switchable switch elements are provided, which enable or block a current flow through the switch paths, depending on the state. The controller clocks the switch units of the half-bridge circuit to convert DC to AC or AC to DC, depending on the application. In addition, the control device controls the switch circuit according to a predetermined control method such that in the freewheeling state Rückkommutierung of the demagnetization of the storage throttle current flowing to the latches is largely prevented and / or if necessary, a power compensation between the DC voltage branches is achieved. Both are accomplished by the switch elements in the turnout paths selectively closed or opened by the controller to either use the switch paths as freewheeling paths for the freewheeling currents and / or to redirect the streams to power compensation paths for selective charging of the buffer memories. Due to the advantageous, the bridge circuit downstream arrangement of the switch circuit and the sophisticated control method according to the invention, these two tasks can be accomplished with only one means, namely the switch. The circuit construction is considerably simplified.

Preferably forms the circuit arrangement according to the invention a converter constructed of semiconductor switching elements, preferably uses low-loss IGBT or Mosfet switches, and without a transformer gets along. Transformerless inverters have a higher efficiency on. However, the invention is also applicable to inverters having a voltage-adjusting and / or galvanically isolating transformer applicable.

advantageously, allows the present invention, between the DC voltage branches and the neutral conductor at least two DC voltage generator or consumer to join. This extends the scope over conventional circuits that are for only a generator or consumer are designed.

In A preferred embodiment of the invention is for feeding electrical energy, for example, used in a public power grid. The energy can z. B. won with photovoltaic generators from sunlight or by accumulators, fuel cells or the like. The AC power generated is the AC mains with the right one Amplitude, frequency and phase angle supplied. In the energy supply is during of the coil charging part of the clock in both half-waves in the current path only one switch, which is to be switched high frequency. As a result, the conduction losses are low. A Rückkommutierung of the inductor current in the two energy buffers is through the control according to the invention the switch elements effectively minimized in the turnout paths. Of the through these switch elements for every mains voltage half-wave opened Switch path allows a demagnetization of the storage choke without putting energy back into the DC circuit with the energy buffers is returned. The efficiency is increased.

In another form of application is the circuit arrangement for removal of energy from an alternating voltage network and for the supply of at least two DC consumers used. The control device according to the invention allows it to take the energy lossless and sinusoidal. To do this the switch units and switch elements are driven in such a way that the storage throttle over the sine half-wave of a voltage applied to the AC terminals Mains voltage largely using the applied voltage between mains phase and neutral is charged. Only in the range of the zero crossing of the mains voltage is for a narrow Time window of the use of energy from the the energy cache containing DC circuit required. Here is failing sufficient voltage between mains phase and neutral conductor to the conventional timing of the opposite switch to Charging the throttle resorted.

The inventive circuit arrangement can form a single-phase converter configuration or one be extended to three-phase configuration. For each phase is a half bridge with only two switch units and a switch circuit with only two turnouts required. Especially in the three-phase Configuration is in the embodiment of the invention in comparison to conventional Circuit Topologies Using a Full Bridge Circuit Having Three Bridge Branches the voltage swing at the switches lower, because the bridge circuits are connected to the neutral conductor and thus on the associated circuit branches only a reduced voltage swing is executed. The switching losses are significantly reduced. With only one switch per path are also the Pass losses smaller.

Either in the one-as well as the three-phase configuration can on at least one other inverter connected to the DC side be. This makes it possible with the circuit arrangement according to the invention the AC or AC voltage of a public network initially in to convert a DC or DC voltage to this one or afterwards by means of the further inverter in an alternating current with eg. suitable for driving a motor parameters such as amplitude, frequency and Like., to convert. The inverter can be used on conventional Way or preferably according to the invention be designed.

In a preferred, simply constructed embodiment, the points circuit per phase only two points paths, which are each associated with a half-wave. In each switch path, a switch with a pa rallel to the switch connected freewheeling diode and a rectifier diode connected in series is arranged. The rectifier diodes in the individual switch paths are in the opposite passage direction to each other switched. If a switch is closed in a switch path, a freewheeling current is released through this switch path. Each switch with the associated rectifier diode or both switch paths together can be realized in the form of a single integrated component.

The Control device can switch all according to one switch to a pre-defined clock scheme. In a preferred embodiment However, the controller detects parameters, the operating conditions to indicate the switches based on the operating parameters head for. For this purpose, it preferably has a sensor device with sensor means for detecting the energy buffers applied voltages, the currents flowing in the DC voltage branches and / or the alternating voltage applied to the AC voltage terminals on. Furthermore, the control device has logical means, which serve the captured parameters together and if necessary with predeterminable thresholds and then the Switch elements of the switch circuit to switch. Especially are the logic means set up by unlocking the Turnout paths a Rückkommutierung the storage throttle currents too To largely prevent the energy buffers and if necessary to cause a power compensation. Thus, connected DC generators or consumers essentially in their optimal operating points are operated. The control device with the logic means is preferably realized in the form of a circuit, but may also include a microprocessor, Mikrocontrol ler or the like ..

One Equalization will, if necessary, be made both in the case of Feeding energy into a grid as well as taking off Energy made from a network. In the case of energy supply will be in a selected Mains voltage half-wave corresponding to the required compensation component specifically the associated Switch path to the neutral conductor open and a demagnetization of the storage throttle via the energy storage and the freewheeling diode of the opposite DC voltage branch enforced. Through this, on the positive or negative half wave limited, controlled short-term transition on a conventional Type of Rückkommutierung is inventively without additional, The inverter upstream means energy in the respective transmitted to other DC voltage branch. The transmitted amount of energy is enough, for example, for two photovoltaic plants or fuel cells in the usual operation, due to manufacturing tolerances or shading effects Performance deviations to achieve a sufficient level of compensation. The efficiency is hardly affected after charging of the opposite one Energy caching only a fraction of only one Half wave limited is. In the other half wave is inventively in the Freewheeling phase of the corresponding switch path switched through and the current without back-commutation effects, low-loss fed into the grid.

in the Case of energy extraction is also a power balance between the two DC voltage branches without additional, the inverter upstream means possible. For this purpose, the above-described inventive method the charging of the storage choke by means of the existing voltage between mains phase and neutral and short-term use of energy from the DC circuit in the area of the zero crossing the mains voltage further developed in that exclusively in Range of the positive or negative half-wave the time window of the insert is extended by energy from the DC circuit controlled. This is done by back commutation the storage throttle current in the opposite DC voltage branch achieved a power balance to the extent necessary. As in the feed-in operation Here, too, the efficiency is negligibly affected.

The in the circuit arrangement according to the invention produce caused low voltage swings on the storage throttle an equally low current ripple in which the storage throttle current. The storage choke can because of the lower iron losses and smaller required inductance are made smaller. Since the inverted current in the reactor charging charging case always flows only through a switch unit, resulting in lower passage losses, while through the lower voltage swings reduce the switching losses. Overall, this leads to lower semiconductor losses. Consequently, you can secondary Components such. B. heatsink, smaller be dimensioned. Because, except for a wanted power compensation, Rückkommutierungseffekte can be avoided cost-effective Capacitors are used, which operate at a lower AC load are designed. Especially in the case of a three-phase arrangement Is it possible, the DC circuit without the use of electrolytic capacitors perform what enormous benefits in terms of the life and shelf life of the Inverter results.

Due to the circuit topology of the invention and the small number of active components in each case a very compact structure of the semiconductor and the components involved in the commutation and thus a reduction of the area spanned by these is possible. In addition, since the amendments conditions of the current and the voltage per unit time may be lower, causes the circuit arrangement according to the invention lower electromagnetic interference. Commonly used external filter components, such as chokes or capacitors, to suppress these electromagnetic disturbances can be omitted or at least made smaller and thus made more economical.

The possibility the DC side terminal of a pole of the DC voltage sources / sinks to the passed through the inverter neutral sure that on the connected devices no through the clocking of the inverter caused high or low frequency voltage fluctuations may occur, which could lead to leakage currents via parasitic capacitances. Thereby the electromagnetic compatibility is further improved. The considerable potential hazard by high-frequency voltage jumps On contact the isolated module surfaces, z. B. a solar generator is eliminated. For the operation of the circuit arrangement In a three-phase converter configuration, the direct connection of the motor-side inverter over the neutral conductor to a much lower insulation load of the motor with respect to the maximum amplitude of the applied voltage compared to the Potential.

The Invention allows it to realize switching power supplies, pulse rectifiers or inverters, the a particularly good efficiency and low electromagnetic repercussions have and with a simple, inexpensive construction high reliability and ensure long life.

Further Details of advantageous embodiments The invention are the subject of the drawing, the description or Dependent claims.

In The drawings are embodiments of Invention illustrated. Show it:

1 a circuit arrangement for a converter according to the invention in a single-phase configuration;

2 a schematic representation of the time course of the voltage across the storage inductor, the currents and the control signals in the circuit arrangement according to 1 in the case of energy being fed into a grid without power equalization;

3 one of the 2 similar representation in the case of a supply of energy in a network with power equalization;

4 a schematic representation of the profile of the voltage across the storage inductor, the currents and the control signals in the circuit arrangement according to 1 in the case of withdrawal of energy from a grid without compensation;

5 one of the 4 similar representation in the case of extraction of energy from a power-sharing network;

6a and 6b Further developments of the imple mentation from the invention 1 ;

7 a circuit arrangement according to the invention in a three-phase configuration and

8th a development of the converter circuit according to the invention after 7 ,

1 shows a schematic diagram of a circuit arrangement 1 an inverter according to the present invention. In the illustrated single-phase, transformerless configuration, the inverter is used 1 as an inverter for the generation and supply of an alternating current in an external network. For this purpose, the inverter 1 three DC voltage connections 2 . 3 . 4 , two energy buffers 6 . 7 , a bridge circuit 8th , a switch circuit 9 , a control device 11 and two AC voltage terminals 12 . 13 on. At the DC voltage connections 2 . 3 . 4 Here are two DC generators 14 . 16 , For example, photovoltaic generators, fuel cells, accumulators or the like., Connected in series to each other, while at the AC voltage terminals 12 . 13 an external mains voltage U _{NETZ is} created.

A first DC voltage connection 2 is with a first DC voltage branch 17 and a second DC voltage connection 4 with a second DC voltage branch 18 connected while the center DC voltage connection 3 through the entire circuit arrangement 1 passed through and a neutral conductor 19 forms. This is with the AC voltage connection 13 can be connected to the mains, eg in a control cabinet, by grounding to a defined zero potential. Optionally, in the neutral conductor 19 Filter elements for the suppression of high-frequency interference ments be included. The generators 14 . 16 are each at a DC voltage branch 17 respectively. 18 and on the neutral conductor 19 connected.

The energy caches 6 . 7 are parallel to each generator 14 . 16 , in each case between one of the DC voltage branches 17 respectively. 18 and the neutral conductor 19 arranged. They are preferred example formed by buffer capacitors C1 and C2. Parallel to the series connection of the energy buffers 6 and 7 is between the DC voltage branches 17 . 18 the bridge circuit 8th connected.

The bridge circuit 8th is formed as a conventional half-bridge having two series-connected switch units S1 and S2, which are switchable at high frequencies of up to 100 kHz. Preferably, low loss IGBT (Insulated Gate Bipolar Transistor) or MOS field effect transistor switches are used, although other switch implementations are possible. Parallel to each switch unit S1, S2, a freewheeling diode D1 or D2 is arranged in the opposite forward direction. The connection point 20 between the switch units S1 and S2 is via a connecting line 21 , which includes a storage choke L, to the AC voltage terminal 12 connected.

The switch circuit 9 serves to redirect currents flowing through the storage inductor L in a controlled manner as needed. The switch circuit 9 is here by a parallel connection of two turnout paths 22 . 23 formed downstream of the bridge circuit, between the connecting line 21 and the neutral conductor 19 run. The switch path 22 comprises a switch element S3 having a freewheeling diode D3 connected in antiparallel thereto and a rectifier diode D5 in series with the parallel arrangement of the switch element S3 and the diode D3. The forward direction of the diode D5 points from the neutral conductor 19 to the connection line 21 out. Similarly, in the switch path 23 a switch element S4 provided with an antiparallel freewheeling diode D4 and a rectifier diode D6 arranged in series therewith. The anode of the rectifier diode D6 is connected to the connecting line 21 so that the diode D6 has the opposite forward direction with respect to the rectifier diode D5.

For monitoring and controlling the operation of the circuit arrangement 1 serves the control device 11 that part of the circuit 1 forms or may be partially realized in the form of a separate integrated circuit thereof. A microprocessor or the like may also be used. In any case, the control device contains 11 two in the form of blocks 24 . 26 illustrated functional units. The block 24 denotes a sensor device which serves to operate parameters of the circuit arrangement 1 to capture and signaling signals for this purpose 27 to deliver. For this purpose, the sensor device contains 24 Suitable equipped, for example, to simplify the illustration not shown sensor means to which, for example. Voltmeter for detecting the voltage applied to the buffer capacitors C1 and C2 DC voltages U _DC1 , U _{DC2 of} the DC circuits, _ammeters for detecting the in the DC voltage _branches 17 . 18 by the half-bridge components S1, D1 and S2, D2 flowing currents I ₁ and I ₂ , a means for detecting the current flowing through the inductor L current I _L and / or means belonging to the between the terminals 12 and 13 accumulating voltage U _NETZ capture. Of course, the voltages or currents given here can also be based on generally known electrical relationships from other detectable partial voltages or partial currents in the circuit arrangement 1 be derived.

The block 26 indicates logic elements of the control device 11 which are adapted to that of the sensor device 24 supplied signals 27 to receive and process based on the switch units S1 and S2 of the half-bridge 8th as well as the switch elements S3 and S4 of the switch circuit 9 suitable to control. This is in 1 illustrated by dashed lines indicated control paths, one of which is exemplified by the reference numeral 28 is provided. The logic elements 26 In particular, comparator logic may be used to compare the measured voltages or currents with one another or with predefined or predefinable threshold values, as well as a decision logic in order to select the suitable control strategy based on the results of the comparisons.

The mode of operation of the circuit arrangement described so far 1 is below with reference to 2 and 3 described, the simplified diagrams with time histories of the most important voltages and currents and control signals in the circuit arrangement 1 for the in 1 illustrate illustrated case of feeding energy into a network. The circuit arrangement according to the invention 1 works as follows:
It is assumed that the AC voltage _{terminals have} an AC voltage U _NETZ with a peak voltage of √2 · 230 volts and a frequency of 50 Hz, as shown in the uppermost diagram in FIG 2 is visible for a period. To the direction of change of the generators 14 . 16 generated DC voltage, the switches S1 to S4 depending on the polarity of the mains voltage U _NETZ by the controller 11 closed and opened after a certain clock pattern. It should be noted that, for reasons of clarity in the diagram representation, the duty cycles of the switch units S1 and S2 are shown by way of example in respective time segments of the mains voltage half-cycle. In reality, their switching frequency is for example 16 kHz or more. Advantageously, only one switch unit S1 or S2 is connected per half-wave, which minimizes the forward losses and promotes high efficiency.

How out 2 to recognize the switch unit S1 is switched high frequency in the positive half-wave of the mains voltage U _NETZ . Further, the switch element S3 is in the switch path 22 closed, while the switches S2 and S4 remain open, so that a current flow is prevented by this. When closing the switch unit S1 of the half-bridge 8th is the voltage U _DC1 to the inductor L, whereby the current I _L increases and the inductor is magnetized.

During the coasting phase, when the switch unit S1 is opened, the reactor L is demagnetized, the positive reactor current I _L continues to flow, but its amount gradually decreases. The inductor current I _L commutates via the closed switch S3 and the rectifier diode D5 in the switch path 22 which serves as a freewheeling path. The reactor current I _L does not return to the buffer capacitor C2. The associated energy losses and efficiency deteriorations are effectively avoided.

Advantageously, the voltage U _L falls in the freewheeling phase only to the value zero. The voltage swing, which is to be executed by the switch unit S1 and the freewheeling diode D1 at each clock, is thus limited to the value of the DC clamping DC _DC1 and thus relatively low. This is because the switch paths 22 . 23 with the neutral conductor 19 connected to the generator 14 and the buffer capacitor C1 are connected.

The switch unit S1 is repeatedly clocked in the positive mains voltage half-wave, wherein the closing periods in the range of the peak value of the mains voltage U _{NETZ are} longer than in the vicinity of their zero crossings to the respective instantaneous value of the mains voltage U _NETZ in the up and down magnetization of the storage inductor L fair become. This switch operation is performed by pulse width modulation of the control device 11 supplied control signals 28 or by another suitable, the duty cycle predetermining type of modulation achieved. The generated alternating current I _L , as it results in the course of the clock average and in 2 is indicated dotted, is well adjusted with respect to the phase angle and the amplitude of the potential profile of the AC voltage U _NETZ . Compared to a conventional full bridge circuit, the voltage swings at the storage inductor L are less and cause only a small ripple or relatively small ripple in the coil current I _L. This allows a proper feed of energy into the external network.

In an analogous manner, the mains voltage U _NETZ is in the negative half-wave of the switch element S4 in the switch path 23 and opened switches S1 and S3, the switch unit S2 of the half-bridge 8th suitably controlled. The reactor current I _L flows in the closed state of the switch unit S2 of the DC branch 18 via these to the choke coil L to magnetize them while in the opening state of the switch unit S2 via the now serving as a freewheel path switch path 23 commutated with the closed switch element S4. A return of the energy in the buffer capacitor C1 is again prevented. The above statements regarding operation during the positive half cycle apply accordingly.

The control device 11 not only controls the bridge 8th and the switch device 9 in the sense of an advantageous operation of the circuit arrangement according to the invention 1 In particular, in the freewheeling state, but also provides for any required power compensation. If, for example, the generators 14 . 16 In the form of photovoltaic generators are formed, which are shaded to different degrees, or for other reasons, for example, give different benefits due to manufacturing tolerances tolerance, the fed into the network AC I _{L would} contain a DC component, which is to be prevented. The control device 11 causes in this case such an energy exchange between the generators 14 and 16 that both can be operated in their optimum operating range.

In 3 is an example of the maximum possible 50% power compensation from the upper DC branch 17 in the lower DC voltage branch 18 illustrated. The different power output of the generators 14 . 16 is, for example, by the logic means 26 the control device 11 on the basis of the with the sensor device 24 detected voltages U _DC1 , U _DC2 and / or currents I ₁ , I ₂ detected. The logic means 26 then cause switch element S3 to remain open during a certain portion of the positive half wave corresponding to the required power compensation level. In the closed state of the switch unit S1, the operation is outlined as above. In the freewheeling state, however, the inductor current I _L does not commute via the switch path 22 but via the freewheeling diode D2 back to the buffer capacitor C2, which is thereby charged accordingly. Half of the generator 14 supplied energy is from the top 17 on the lower DC voltage branch 18 transfer.

Increase during power balancing Although the voltage potential jumps at the half bridge 8th to the sum of the DC voltages U _DC1 and U _DC2 , as can be seen from the course of the voltage U _L , and the current ripple in the inductor current I _L increase. However, this only occurs during a fraction of only the positive half wave and is not very harmful to the overall efficiency. In return, however, a targeted compensation is possible.

If a lower or higher degree of power compensation is required, the entire opening duration of the switch element S3 is correspondingly shortened or lengthened in each positive half cycle. This can also be accomplished by repeatedly opening and closing the switch S3 per half-wave. If the switch S3 is closed or opened during the entire positive half-cycle, no or maximum power compensation takes place. Irrespective of the compensation _direction , the maximum power compensation _depends on the respective ratio of the DC voltages U _DC1 , U _DC2 to the peak value of the mains voltage U _NETZ . For the applications provided here, in particular energy generation and feeding by means of series-connected photovoltaic or fuel cell generators, the possible measure of the power compensation is sufficient.

A power balance from the lower DC branch 18 in the upper DC voltage branch 17 If required, the switch element S4 remains open during a part of the negative half cycle of the mains voltage U _NETZ and a back commutation of the inductor current I _L to the capacitor C1 is made possible.

The circuit arrangement according to the invention 1 forms a bi-directional inverter, which is also set up to extract energy from an external network. For this purpose, the generators 14 . 16 in 1 identify corresponding consumers. The functionality is in 4 in the event that no power equalization takes place, and in 5 illustrated for the case with power compensation.

First, consider the positive half-wave of the mains voltage U _NETZ on the assumption that all switches S1 to S4 are open. At zero crossing, the mains voltage U _NETZ reaches the neutral conductor 19 not enough to magnetize the inductor L. For this reason, the switch unit S2 is first of all driven in a high-frequency manner in order, in the closed state, to set the potential of the voltage U _L to almost the potential _{-U DC2 of} the DC voltage _branch 4 to bring about a flow of current from the inductor L via the switch unit S2. This results in a rising current I ₂ , which leads to the DC branch 18 and the capacitor C2 flows. In the opening state of the switch unit S2, a potential + U _{DC1 arises} at the connecting line 21 one and the thereby decreasing inductor current I _L flows through the freewheeling diode D1 of the half-bridge 8th on the DC branch 17 , which has a current I ₁ to charge the capacitor C1 result, see. 4 ,

As soon as the mains voltage is sufficiently high, the switch unit S2 remains open. Instead, the switching element S4 is in the switch path 23 connected. In the closed state of the switch element S4, the inductor L is charged by the mains voltage U _NETZ . The inductor current I _L flows through the switch element S4 and is dissipated via the neutral loss. In the opening state of the switch element S4, the throttle L discharges, as described above, via the freewheeling diode D1 to the capacitor C1. In this way, a consumption of energy from the energy cache 7 prevented over the entire duration of the positive half wave. In the transition region between the positive half-wave of the mains voltage U _NETZ and its negative half-wave, the switch unit S2 is driven again in the manner explained above, in the absence of a sufficient potential.

In the negative half-wave of the mains voltage U _NETZ analogously, the switch element S3 is used instead of S4, wherein in the closed state of the switch element S3, the inductor L is charged and in the open state, the freewheeling diode D2 is conductive, whereby the capacitor C2 is charged. In the region of the zero crossing is on the opposite switch unit S1 of the half-bridge 8th resorted.

In each half-wave, only one switch unit S1 or S2 of the bridge circuit 8th and, apart from the line voltage zero crossings, minimizing back commutation of the current to the opposite buffer capacitor C1 or C2. The voltage U _L jumps only between the predetermined by the DC voltages potential and the zero potential, ie between + U _DC1 and zero or between _{-U DC2} and zero. As a result, the ripple of the inductor current I _{L is} low. Consequently, a sinusoidal extraction of energy from the AC network with low losses and high efficiency is possible. However, it should be noted that in the energy extraction, the duration of the opening state of the switch elements S3 and S4 in the turnout paths 22 . 23 in the range of the peak value of the mains voltage U _NETZ is to be selected larger by appropriate control than in the vicinity of the zero crossings.

As 5 illustrated, a power compensation is achieved according to the invention, if one of the consumers 14 . 16 has a larger energy requirement. For example. During the positive half cycle of the mains voltage U _NETZ, the time window in the vicinity of the zero crossing, in which S2 is clocked, is correspondingly extended in order to amplify a discharge of the capacitor C2 by means of the current I ₂ . Depending on the duty cycle between the timing of the switch unit S2 and the subsequent clocking of the switch element S4 per half-wave, a corresponding amount of energy transfer from the lower 18 in the upper DC voltage branch 17 reached. A power balance from the upper one 17 in the lower DC voltage branch 18 can be achieved to the required extent during the negative half cycle of the mains voltage U _NETZ by appropriate determination of the duty cycle between the switches S1 and S3.

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 generator, which are then connect to a plurality of DC terminals and for each of which a temporary energy storage is provided. The bridge circuit 8th , the switch circuit 9 and the control logic 26 must be adjusted accordingly in order to start from the DC voltages at the energy buffers 6 . 7 to generate an AC voltage of the desired frequency and amplitude. Conversely, an AC voltage U _NETZ an external network can be rectified and distributed to several consumers. Also, in the connection path 21 be inserted several storage chokes L. At the AC voltage terminals 12 . 13 Filtering agents may be provided for suppression. The control method according to the invention can also be implemented in the form of firmware or software.

The Protect diodes D3, D4 the respective semiconductor switch S3, S4, can however, if necessary, be omitted. This particular, though integrated semiconductor switch with reverse blocking capability, eg self-locking IGBT switch, used if they are for high-frequency applications are suitable.

For proper operation, the voltage U _DC1 or U _DC2 in the respective DC _circuit must be greater than the peak value of the mains voltage U _NETZ . 6a and 6b show schematic diagrams of developments of the inverter according to the invention, which make it possible to use even smaller voltages U _DC1 and U _DC2 . The circuit arrangement 1 is merely in the form of a block for simplicity 1 shown.

At the in 6a The solution shown are in the DC voltage branches 17 . 18 also referred to as a DC controller boost converter 29a respectively. 29b inserted. Such boosters are known from the art in various forms, for example. As advantageous multi-string circuits, and need not be explained in detail here. Suffice it to mention that each boost converter 29a . 29b the job has the potential of the generator 14 respectively. 16 generated voltage to a suitable level for operation U _DC1 and U _DC2 . This can easily handle problems that arise when linking generators of different types or with strong partial shading. The inverter 1 can be operated in the large power range with maximum yield. The operation of the boost converter 29a . 29b is preferably controlled by a controller, which is part of the control device 11 can be. Preferably, it is also parallel to each boost converter 29a respectively. 29b a switch S5a or S5b, which can be closed to the associated boost converter 29a respectively. 29b to bridge when not in use. This minimizes losses.

In the 6b illustrated embodiment of an inverter according to the invention 1 has in place of the arranged on the DC side boost converter 29a . 29b on the AC side a blanking circuit 31 on that in to the AC voltage connection 12 leading connection line 21 is inserted. The circuit 31 is formed here by a parallel connection of two self-blocking IGBT switches S6a, S6b, which have opposite passage directions. By suitable activation of the switches S6a, S6b, the mains voltage U _NETZ can be masked out during periods in which its instantaneous _value exceeds the DC voltage U _DC1 or U _DC2 that is currently being used in order to use the DC voltages also in these periods. Of course, other circuits can be used for this purpose. For example. For example, the normally-off IGBT switches S6a, S6b can also be replaced by other types of switches with rectifier diodes each oriented in the corresponding forward direction. Advantageously, the circuit 31 a further switch S7 to bridge the switches S6a, S6b when not in use.

Further advantageous embodiments of the invention are in the 7 and 8th illustrated. As far as conformity in construction and / or function, reference is made to the above description using the same reference numerals.

7 shows in a simplified manner a circuit arrangement according to the invention 1' in the three-phase converter configuration. The circuit arrangement 1' contains three with the circuitry 1 to 1 as well as mutually identical formed circuits 1a . 1b . 1c whose components are identified by adding the indices a, b and c, respectively. The circuits 1a . 1b . 1c are common to the DC terminals 2 . 4 connected between which energy producers or consumers can be connected in series with each other and to which two intermediate energy storage 6 . 7 are arranged in parallel in the form of buffer capacitors C1 and C2. A third DC voltage connection 3 is with a neutral conductor 19 connected to all circuits 1a . 1b . 1c is assigned together and is preferably connected in operation with the earth. Parallel to the buffer capacitors are half-bridge circuits 8a . 8b . 8c arranged, of which the connecting lines 21a . 21b . 21c branch off, which via inductors L to the AC voltage connections 12a . 12b . 12c are connected. Between the connecting lines 21a . 21b . 21c and the neutral line 19 are switch circuits according to the invention 9a . 9b . 9c intended. The control device according to the invention 11 is in 7 omitted for clarity.

With regard to the exact arrangement and design of individual components of the circuits 1a . 1b . 1c , in particular the half-bridges 8a . 8b . 8c and the switch circuits 9a . 9b . 9c , as well as their operation is based on the above statements in connection with the embodiment 1 proven. It should be mentioned here only briefly that the circuit arrangement 1' both to the AC _direction to generate from the DC voltages U _DC1 and U _DC2 a three-phase AC (so-called. Three-phase), and can be used for rectification, to generate starting from a three-phase _supplied from the outside DC voltages U _DC1 and U _DC2 . In this case, the control device controls 11 the half-bridge and switch circuits 8a and 9a . 8b and 9b such as 8c and 9c according to the control method according to the invention suitable to generate either to each 120 ° phase-shifted inductor currents I _La , I _Lb and I _Lc , which are fed into the three-phase network, or to the three-phase network in an advantageous manner with respect to the phase position and the harmonic energy supply to remove the DC consumer. Advantageously, only one bridge switch S1a, S1b, S1c or S2a, S2b, S2c is switched to high-frequency per phase Ua, Ub, Uc and half-wave. Furthermore, in both cases, a Rückkommutierung the choke currents to the buffer capacitors C1 and C2 prevented in the freewheeling state and, if necessary, a power compensation between the DC voltage branches 17 and 18 be performed. In addition, it is possible to dispense with the use of electrolytic capacitors on a balancing, which is normally mandatory for a three-phase inverter with three bridge _arms , because the necessary DC voltage U _DC1 and U _DC2 only assumes values in the range of economic availability of electrolytic capacitors.

At the in 8th illustrated embodiment of the embodiment according to 7 is on the DC side of the inverter 1' another inverter 1'' connected. The by energy extraction from the three-phase network with the inverter 1' generated DC or DC voltage is by means of the inverter 1'' converted into a suitable for driving a motor three-phase current. The inverter 1'' can be configured arbitrarily, but is preferably with the inverter 1' identically formed and also has a switch circuit 9 in order to minimize losses in operation and to be able to compensate for their performance. Advantageously, the inverter 1'' connected directly to the neutral conductor, whereby the occurrence caused by the timing of the switch voltage fluctuations and associated electromagnetic interference minimized. Due to lower voltage strokes at the winding terminals of motors z. B. their insulation burden significantly reduced. The circuit arrangement 8th can also be used to power an external three-phase system by means of an alternator.

A circuit arrangement 1 for a bidirectional inverter, in a single-phase configuration, has two between DC voltage branches 17 . 18 series-connected DC voltage generators or consumers 14 . 16 on, whose connection point to a neutral conductor 19 is connected and to which parallel energy cache 6 . 7 and one between the DC voltage branches 17 . 18 arranged bridge circuit 8th are connected. The bridge circuit 8th is designed as a half-bridge with two interconnected in series switch units S1, S2, to each of which a freewheeling diode D1, D2 is connected in anti-parallel. The center tap 20 the bridge circuit 8th is via a connection line 21 comprising a storage choke L having a first AC voltage terminal 12 connected while the neutral conductor 19 with a second AC voltage connection 13 connected is. Between the connection line 21 and the neutral conductor 19 is a switch circuit 9 arranged with switch elements S3, S4. A control device 11 controls the switch circuit 9 in response to detected operating conditions or according to a fixed timing scheme to, if necessary, a commutation of the flowing in the freewheeling state through the storage inductor L current to the latches 6 . 7 to prevent and / or a power compensation between the DC voltage branches 17 . 18 to accomplish. In a further development, a three-phase Umrichterkonfigu ration created.

Claims (18)

Circuit arrangement ( 1 ) for converting direct current into alternating current or from alternating current into direct current, with at least three direct voltage connections ( 2 . 3 . 4 ), to which at least two DC voltage branches ( 17 . 18 ) and a neutral conductor ( 19 ), with energy buffers ( 6 . 7 ), each between a DC voltage branch ( 17 . 18 ) and the neutral conductor ( 19 ), with one between the DC voltage branches ( 17 . 18 ) bridge circuit ( 8th ), which has two switch units (S1, S2) per phase, which are connected via a connection point ( 20 ), which has a center tap of the bridge circuit ( 8th ) are connected in series with each other and to each of which a freewheeling diode (D1, D2) is connected in anti-parallel, with per phase two AC voltage terminals ( 12 . 13 ), one of which ( 13 ) with the neutral conductor ( 19 ), while the other ( 12 ) per phase via a connecting line ( 21 ), in each of which a storage throttle (L) is included, with the respective center tap ( 20 ) of the bridge circuit ( 8th ), wherein at the AC voltage terminals ( 12 . 13 ) an alternating voltage (U _NETZ ) with an amplitude and frequency is applied, with a switch circuit ( 9 ), the per phase between the connecting line ( 21 ) and the neutral conductor ( 19 ) connected turnout paths ( 22 . 23 ) and in the turnouts ( 22 . 23 ) provided switch elements (S3, S4), the ge controls are switchable to a current flow through the turnout paths ( 22 . 23 ) or with a control device ( 11 ) which, in the case of a conversion from direct current into alternating current, is set up to switch a switching unit (S1, S2) assigned to the respective half- _cycle during a half-wave of the alternating voltage (U _NETZ ) in a high-frequency manner, in order to switch the switching unit (S1, S2) in the closed state to magnetize the storage inductor (L), while one of the respective half-wave associated switch element (S3, S4) of the points circuit ( 9 ) is closed, in the opening state of the switch unit (S1, S2), the current through the storage choke (L) through the associated switch path ( 22 . 23 ) and commutation of the current to the energy buffers ( 6 . 7 ) substantially ( 2 ), and based on detected operating conditions (U _DC1 , U _DC2 , I ₁ , I ₂ ) a power _compensation requirement between the DC voltage _branches ( 17 . 18 ) and, if necessary, to open the closed switch element (S3, S4) during a certain time proportion of the half-wave corresponding to the required power compensation degree, in order to open the current through a freewheeling diode (D1, S1, S2) associated with the respective half-cycle in the opening state of the switch unit (S1, S2). D2) to one of the intermediate energy buffers (C1, C2) in order to charge it and thereby achieve power compensation ( 3 ), or, in the case of a conversion of alternating current into direct current, during a half-wave of the alternating voltage (U _NETZ ) substantially a switching element (S3, S4) of the point circuit ( 9 ) high-frequency switch in order to magnetize the storage inductor (L) in the closed state of the switching element (S3, S4) and the current flowing through the storage inductor (L) via the associated switch path ( 22 . 23 ), wherein in the opening state of the switch element (S3, S4), the current through one of the respective half-wave associated freewheeling diode (D1, D2) to one of the DC voltage branches ( 17 . 18 ) and the respective energy buffer ( 6 . 7 ) loads ( 4 ), and on the basis of detected operating conditions (U _DC1 , U _DC2 , I ₁ , I ₂ ) determine a power _compensation requirement and, if necessary, instead of the switch _element (S3, S4) of the point circuit ( 9 ) one of the respective half-wave associated switch unit (S1, S2) of the bridge circuit ( 8th ) during a certain time proportion of the half-wave, which corresponds to the required power compensation degree, to switch high-frequency, in the closed state of the switch unit (S1, S2) the current to the respective energy buffer ( 6 . 7 ) opposite energy buffer ( 6 . 7 ) in order to discharge it and thereby provide a power compensation between the DC voltage branches ( 17 . 18 ) ( 5 ). Circuit arrangement according to Claim 1, characterized that they have a transformerless inverter with semiconductor switching elements forms. Circuit arrangement according to claim 1 or 2, characterized in that between the DC voltage terminals ( 17 . 18 ) two DC generators ( 14 . 16 ) connected in series with one another, and the circuit arrangement ( 1 ) is used to feed energy into a network. Circuit arrangement according to claim 1 or 2, characterized in that between the DC voltage terminals ( 17 . 18 ) two DC consumers ( 14 . 16 ) connected in series with one another, and the circuit arrangement ( 1 ) is used for the removal of energy from an AC voltage network. Circuit arrangement according to claim 1, since characterized in that it forms a single-phase converter configuration. Circuit arrangement according to Claim 1, characterized that it forms a three-phase converter configuration. Circuit arrangement according to Claim 1, characterized in that in each switch path ( 22 . 23 ), a switch element (S3, S4) and a rectifier diode connected in series (D5, D6) is provided, wherein the rectifier diodes (D5, D6) are connected to each other in the opposite forward direction. Circuit arrangement according to Claim 1, characterized in that the control device ( 11 ) is adapted to detect operating conditions and to control the switch circuit depending on the detected operating conditions. Circuit arrangement according to Claim 8, characterized in that the control device ( 11 ) for detecting parameters characterizing the operating conditions, a sensor device ( 24 ), including sensor means for detecting the energy buffers ( 6 . 7 ) in the DC voltage branches ( 17 . 18 ) flowing currents and / or at the AC voltage terminals ( 12 . 13 ) applied AC voltage having. Circuit arrangement according to Claim 9, characterized in that the control device ( 11 ) a logic ( 26 ), which serves to capture the detected parameters ( 27 ) and, if appropriate, with predefinable threshold values and based on the comparison, the switch elements (S3, S4) of the point circuit ( 9 ) to switch. Circuit arrangement according to Claim 10, characterized in that the logic ( 26 ) is further arranged to cause a power compensation such that at the DC voltage terminals ( 2 . 3 . 4 ) in series with each other connected DC generators or consumers ( 14 . 16 ) are operated substantially at their optimum operating point. Circuit arrangement according to Claim 1, characterized in that it is arranged on the DC side with at least one further inverter ( 1'' ) connected is. Method for converting direct current into alternating current or from alternating current into direct current with a circuit arrangement ( 1 ), which includes: at least two DC voltage branches ( 17 . 18 ) and a neutral conductor ( 19 ), Energy cache ( 6 . 7 ), each between a DC voltage branch ( 17 . 18 ) and the neutral conductor ( 19 ), one between the DC voltage branches ( 17 . 18 ) arranged bridge circuit ( 8th ), which has two switch units (S1, S2) per phase, which are connected via a connection point ( 20 ), which has a center tap of the bridge circuit ( 8th ) are connected in series with each other and to each of which a freewheeling diode (D1, D2) is connected in antiparallel, and per phase two AC voltage terminals ( 12 . 13 ), one of which ( 13 ) with the neutral conductor ( 19 ), while the other ( 12 ) per phase via a connecting line ( 21 ), in each of which a storage throttle (L) is included, with the respective center tap ( 20 ) of the bridge circuit ( 8th ), the method comprising the steps of: providing switch paths ( 22 . 23 ) per phase between the connecting line ( 21 ) and the neutral conductor ( 19 ) in the turnout paths ( 22 . 23 ) switch elements (S3, S4), which are controlled switchable to a flow of current through the switch paths ( 22 . 23 ) to enable or prevent the acquisition of operating parameters that occur at the energy buffers ( 6 . 7 ) applied DC voltages, in the DC voltage branches ( 17 . 18 ) flowing currents and / or one of the AC voltage terminals ( 12 . 13 ) AC voltage present (U _NETZ ), and controlling the flow of electricity through the switch paths ( 22 . 23 ) in response to the detected operating conditions such that in the case of a conversion of direct current into alternating current during a half-wave of the alternating voltage (U _NETZ ) one of the respective half-wave associated switch unit (S1, S2) is switched to high frequency, in the closed state of the switch unit ( S1, S2) to magnetize the storage inductor (L), while one of the respective half-wave associated switch element (S3, S4) of the points circuit ( 9 ) is closed, in the opening state of the switch unit (S1, S2), the current through the storage choke (L) through the associated switch path ( 22 . 23 ) and commutation of the current to the energy buffers ( 6 . 7 ) substantially ( 2 ), and based on detected operating conditions (U _DC1 , U _DC2 , I ₁ , I ₂ ) a power _compensation requirement between the DC voltage _branches ( 17 . 18 ) and if necessary, the closed switch element (S3, S4) during a certain time proportion of the half-wave, which corresponds to the required Leistungskompompations degree, is opened, in the opening state of the switch unit (S1, S2) the current via a respective half-wave associated freewheeling diode (D1, D2) to one of the energy buffers (C1, C2) to charge it and thereby power between the DC chip branches ( 17 . 18 ) compensate ( 3 ), or in the case of a conversion of alternating current into direct current during a half-wave of the alternating voltage (U _NETZ ) substantially one of the respective half-wave associated switching element (S3, S4) of the point circuit ( 9 ) is switched high-frequency, in order to magnetize the storage inductor (L) in the closed state of the switch element (S3, S4) and the current flowing through the storage inductor (L) via the associated switch path ( 22 . 23 ), wherein in the opening state of the switch element (S3, S4), the current via one of the respective half-wave associated freewheeling diode (D1, D2) to one of the DC voltage branches ( 17 . 18 ) and the respective energy buffer ( 6 . 7 ) ( 4 ), and determined on the basis of detected operating conditions (U _DC1 , U _DC2 , I ₁ , I ₂ ) a power _compensation need and, if necessary, instead of the switch _element (S3, S4) of the points circuit ( 9 ) one of the respective half-wave associated switch unit (S1, S2) of the bridge circuit ( 8th ) is high-frequency switched during a certain time proportion of the half-wave, which corresponds to the required power compensation degree, in order, in the closed state of the switch unit (S1, S2), to supply the current to the respective energy buffer ( 6 . 7 ) opposite energy buffer ( 6 . 7 ) in order to discharge it, thereby reducing power between the DC voltage branches ( 17 . 18 ) compensate ( 5 ). Method according to claim 13, characterized in that between the DC voltage branches ( 17 . 18 ) and the neutral conductor ( 19 ) DC voltage sources ( 14 . 16 ) and these are each operated substantially at their optimum operating point to feed energy into a grid. Method according to claim 13, characterized in that between the DC voltage branches ( 17 . 18 ) and the neutral conductor DC voltage sinks ( 14 . 16 ) and these are each operated substantially at their optimum operating point to draw energy from a network. Method according to one of claims 13 to 15, characterized that in a time window in the range of the zero crossing of the AC voltage to a clocking while consuming energy from a DC circuit is switched. Method according to Claim 16, characterized in that, for power compensation, the duty cycle between clocked switches (S1 / S3; S2 / S4) in the half-bridge ( 8th ) and the turnouts ( 22 . 23 ) is determined suitably. Method according to claim 17, characterized in that that for power compensation, the time window in the range of the zero crossing the AC voltage is shortened or extended accordingly.