WO2007003241A1

WO2007003241A1 - Circuit arrangement and method for controlling a converter

Info

Publication number: WO2007003241A1
Application number: PCT/EP2006/004178
Authority: WO
Inventors: Jochen Hantschel
Original assignee: Jochen Hantschel
Priority date: 2005-05-24
Filing date: 2006-05-04
Publication date: 2007-01-11
Also published as: DE102005024465A1; DE102005024465B4

Abstract

The invention relates to a one phase circuit arrangement (1) for two-directional converter comprising two direct voltage generators or consumers (14, 16), which are in series interconnected between two direct voltage branches (17, 18), whose connection bridge is connected to a neutral line (19) and to which two energy storage units (6, 7) and a half-bridge (8) positioned between the two direct voltage branches (17, 18) are in parallel connected. The central tap (20) of the bridge circuit (8) is connected to the first alternating current connection (12) by means of a connecting line (21) comprising a storage choke (L), whereas the neutral line (19) is connected to a second alternating current connection (13). A switch circuit (9) provided with switching elements (S3, S4) is located between the connecting line (21) and the neutral line (19). A control device (11) is used for controlling the switch circuit (9) in such a way that it makes it possible to prevent, when necessary, switching of a neutral flowing current through the storage choke (L) in the direction of the energy storage units (6, 7) and/or to carry out a power compensation between the direct voltage branches (17, 18). An improved embodiment of a three-phase converter is also disclosed.

Description

Schaltunσsanordntmg and control method for a converter

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

Such inverters, also called inverters, are used in particular for feeding electrical energy into the public power grid, if, for example, DC voltage sources, such as e.g. Photovoltaic systems, accumulators or fuel cells are available. In this case, it is necessary to generate an alternating current from one or more direct voltage potentials, which is to be adjusted in relation to the phase position and amplitude to the potential curve of the alternating voltage, for example a sinusoidal mains voltage having a frequency of 50 or 60 Hz

- i - is. For this purpose, single or three-phase inverters with and without transformer are known.

Inverters are also used to draw sinusoidal current from the AC mains. At the same time, the power quality with regard to the harmonic content and / or the reactive power must not be impaired. Such extracting converters are often combined with other DC-side connected inverters which convert the power drawn from the grid into a single or multi-phase AC variable frequency network, e.g. To drive motors.

From DE 102 21 592 Al an inverter for converting a DC electrical voltage into an AC is known. 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 connection is connected via a connecting line, which contains a choke coil, with one of the parallel branches of the bridge circuit via a connection node, which lies 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 to each other in the direction VexbjijT ^ ujnjgjipfjLC ^^. During operation, the switch units of the full bridge are clocked symmetrically as a function of the polarity of the mains alternating voltage. In a positive half wave of the AC mains voltage, for example, two diagonally opposite switch units of the full bridge according to a fixed clock pattern high-frequency and time-synchronously closed and opened, while the other two remain open. In addition, a switch is closed in a first connection path. In the closed state of the switch units, the current flows through them to charge the choke coil. When the switch units are opened, the coil current which continues to flow due to the demagnetization within the inductance inductors commutates via the closed switch and the associated rectifier diode in the first connection path during the so-called "freewheeling phase." This prevents the coil current from returning across full-bridge diodes As soon as the half-wave of the mains AC voltage is negative, the other, diagonally opposite switch units and the switch are inserted in the other connection path.

In the prior art inverter located in the coil charging switching state, two lossy switch units in the current path, which are switched high frequency. This leads to switching losses that significantly affect the efficiency of the inverter. In addition, the voltage swing that must be performed by the switching units at each cycle is relatively high. Apart from the ^¬ he heblichen switching losses this voltage swing caused considerable electromagnetic interference because of the required high rates of rise of voltage and current not.

The inverter and the specified control method

_ O _ are not intended to extract energy from the grid, but merely serve to feed energy into the grid. In this case, only a single DC voltage generator can be connected. In the power generation with a solar system, for example, but several solar cells are connected in series, so that flows through these sub-generators, the same stream. If a shadow falls on one of the subgenerators, the overall generative power is insufficient because only operating points with the same currents can be set.

From DE 102 25 020 Al a anordnungchaltungsanordnung for the conversion of direct current into alternating current is known, comprising two series-arranged DC voltage generators, two DC voltage branches, two parallel to the generators buffer capacitors and connected to the two DC voltage branches inverter. 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.

In this Wechsej-ri.chte_r_wird_jDei _^ j ^ d ^ r__H_a_lbwe_lJ, e_le_di_g ^ lent a switch clocked at high frequency, whereby the switching losses reduce. However, it takes place during the free run phase lossy Rückkommutierung the reactor current to the buffer capacitors instead. Advantageously, although provided for a power compensation between the DC voltage branches, which is urgently needed, because in operation even small differences in the performance of the DC branches cause DC components in the network. However, this additional, the inverter upstream means are required, which increase the complexity and cost of the circuit realization. An extraction of energy from the network is not provided.

On this basis, it is an object of the present invention to provide a circuit arrangement and a method which overcome the circuit-related disadvantages of the prior art and are preferably suitable both for feeding energy into an alternating voltage network and for removing energy from the network. In particular, a Rückkommutierung of deriving from Abmagnetisierungsvorgängen the inductor inductor inductor current to a buffer capacitor should be largely avoided and with a simple structure, an at least partial power compensation may be possible.

This object is achieved by the circuit arrangement according to the invention with the features of claim 1 and the inventive method according to claim 13.

The circuit arrangement according to the invention comprises at least three DC terminals, two of which ^¬ voltage branches with equal tension and is connected to a neutral conductor, at least two intermediate energy storage, for example. Pufferkondensa ^¬ gates, each connected between a direct voltage branch and the neutral conductor, serially arranged to one another, a bridge circuit between the DC voltage is arranged branches, at least two AC voltage terminals, which are connected on the one hand to the bridge circuit and on the other hand connected to an AC voltage, a point 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 formed according to the invention by a conventional half-bridge, which requires only a single switch unit per DC branch, to which a freewheeling diode is connected in anti-parallel. In a single-phase configuration, therefore, only two switch units are connected in series. The connection point between the switch units forms a center tap of the bridge circuit, from which branches off a leading to one of the AC voltage leads connecting line in which a storage inductor is arranged. The other AC voltage connection is directly connected to the neutral conductor. Advantageously, the neutral conductor is passed from the DC side to the AC side and can be connected to the ground potential.

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 point circuit according to a predetermined control method such that in the freewheeling state, a Rückkommutierung of the demagnetization of the memory Throttle flowing current 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 are selectively closed or opened in the turnout paths by the controller to either use the turnout paths as freewheeling paths for the freewheeling currents and / or redirect the streams on Leistungsungskompensationspfade for targeted charging of the buffer. 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, the circuit arrangement according to the invention forms a converter, which is constructed from semiconductor switching elements, preferably uses low-loss IGBT or Mosfet switch, and manages without a transformer. Transformerless converters have a higher efficiency. However, the invention is also applicable to converters having a voltage-adapting and / or galvanic-separating transformer.

Advantageously, the present invention makes it possible to connect at least two DC voltage generators or consumers between the DC voltage branches and the neutral conductor. This extends the scope of application over conventional circuits designed for only one generator or consumer.

In a preferred embodiment, the invention for feeding electrical energy, for example. In a public Electricity network used. The energy can be obtained, for example, with photovoltaic generators from sunlight or by accumulators, fuel cells or the like. to be delivered. The generated alternating current is fed to the Wechselstrorαnetz with the correct amplitude, frequency and phase. In the power supply is located during 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 the inductor current in the two intermediate energy storage is effectively minimized by the inventive control of the switch elements in the turnout paths. The switch path opened by these switch elements for each mains voltage half-wave enables a demagnetization of the storage choke, without energy being fed back into the DC circuit with the energy buffers. The efficiency is increased.

In another embodiment, the circuit arrangement for removing energy from an AC voltage network and for supplying at least two DC consumers is used. The control device according to the invention makes it possible to remove the energy with low loss and sinusoidal. For this, the switch units and switch elements are controlled such that the storage choke on the half sine wave of voltage applied to the AC voltage connections mains voltage largely using the applied tension ^¬ is charged between mains phase and neutral. Le ^¬ is diglich in the area of the zero crossing of the line voltage for a narrow window of time, the use of energy from the energy buffer containing DC circuit erfor ^¬ sary. Here, in the absence of a sufficient voltage between mains phase and neutral conductor to the conventional clocking of the opposite switch for charging the Choke used.

The circuit arrangement according to the invention can form a single-phase converter configuration or be extended to a three-phase configuration. For each phase, a half-bridge with only two switch units and a switch circuit with only two switch paths is required. In particular, in the three-phase configuration is in the embodiment of the invention compared to conventional circuit topologies using a full bridge circuit with three bridge arms, the voltage swing at the switches lower because the bridge circuits are connected to the neutral and thus perform on the associated circuit branches only a reduced voltage swing is. The switching losses are significantly reduced. With only one switch per path, the forward losses are also smaller.

Both in the one-and three-phase configuration, at least one other inverter can be connected on the DC side. This makes it possible with the circuit arrangement according to the invention, the AC o- of the AC voltage of a public network first to convert a DC or DC voltage to this or these then by means of another inverter in an alternating current with, for example. For driving a motor suitable parameters such as amplitude, frequency and the like. to transform. The inverter may be configured in a conventional manner or preferably according to the invention.

In a preferred, simply constructed embodiment, the di_e Wei_chenschaltung per phase has only two turnout paths, which are each associated with a half-wave. In each ^¬ the switch path is a switch with a switch to the switch Rallel connected freewheeling diode and a rectifier diode connected in series. The rectifier diodes in the individual switch paths are connected to one another in the opposite forward direction. If a switch is closed in a switch path, a freewheeling flow 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 controller may switch all switches according to a predetermined timing scheme. In a preferred embodiment, however, the controller detects parameters that characterize operating conditions to drive the switches based on the operating parameters. For this purpose, it preferably has a sensor device with sensor means for detecting the voltages applied to the intermediate energy stores, the currents flowing in the DC voltage branches and / or the alternating voltage applied to the AC voltage terminals. Furthermore, the control device has logic means which serve to compare the detected parameters with each other and optionally with predefinable threshold values and then to switch the switch elements of the point circuit. In particular, the logic means are adapted to largely prevent a back-commutation of the storage throttle currents to the energy buffers by enabling the switch paths and, if necessary, to cause a power compensation. Thus, connected DC generators or consumers can be operated substantially at their optimum operating points. The control device with the logic means is preferably realized in the form of a circuit, but can also be a microprocessor, microcontroller or the like.

Power balancing, when needed, is done both when feeding energy into a grid and when drawing power from a grid. In the case of energy supply, the associated switch path to the neutral conductor is selectively opened in a selected mains voltage half-wave corresponding to the required compensation component and a demagnetization of the storage inductor is forced via the energy store and the freewheeling diode of the opposite direct-voltage branch. By this, limited to the positive or negative half wave, controlled short-term transition to a conventional way of Rückkommutierung invention is transferred without additional, the inverter upstream means energy in the other DC voltage branch. The amount of energy transferred is sufficient, for example, to achieve a sufficient degree of compensation for two photovoltaic systems or fuel cells in the operation usually occurring due to manufacturing tolerances or shading effects deviations in performance. The efficiency is hardly affected after the charging of the respective opposite energy buffer is limited to a fraction of only one half-wave. In the other half wave according to the invention in the freewheeling phase, the corresponding switch path is turned on and the current without Rückkommutierungseffekte, low-loss fed into the network.

In the case of energy extraction is also a power ^¬ compensation between the two DC voltage branches without additional, the inverter "upstream means possible. For this purpose, the above-described method of charging the storage choke according to the invention by means of the existing NEN voltage between the mains phase and neutral and the short-term use of energy from the DC circuit in the range of the zero crossing of the mains voltage further characterized in that only in the positive or negative half wave the time window of the use of energy from the DC circuit is controlled expanded. This achieves a power compensation to the required extent by Rückkommutierung the storage throttle current in the opposite DC voltage branch. As in the feed-in operation, the efficiency is negligibly affected here as well.

The caused in the circuit arrangement according to the invention low voltage swings on the storage choke generate an equally low current ripple in which the storage throttle current. The storage choke can be made smaller because of the resulting lower iron losses and lower inductance required. Since the inverted current in the operating case charging the throttle always flows only through one switch unit, lower forward losses occur, while the lower voltage swings reduce the switching losses. Overall, this leads to lower semiconductor losses. As a result, secondary components such as heat sinks can be made smaller. Because back commutation effects are avoided, apart from a desired power compensation, lower cost capacitors designed for lower AC load can be used. Especially in the case of a dreiphasi ^¬ gen arrangement, it is possible to make the DC circuit without the use of electrolytic capacitors, resulting in huge advantages in terms of durability and storability of the Umrichte_r.

By the circuit topology according to the invention and the small number of active components in this is a very compact design of the semiconductor and the components involved in the commutation and thus a reduction of the area spanned by this possible. In addition, since the changes of the current and the voltage per unit time can be smaller, the circuit arrangement according to the invention causes less 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 of DC-side connection of one pole of the DC voltage sources / sinks to the neutral conductor passed through the inverter ensures that no high-frequency or low-frequency voltage fluctuations due to the clocking of the inverter can occur at the connected devices, which leads to leakage currents via parasitic capacitances could lead. As a result, the electromagnetic compatibility is further improved. The considerable hazard potential due to high-frequency voltage jumps when touching the isolated module surfaces, e.g. a solar generator is eliminated. For the operation of the circuit arrangement in a three-phase Ümrichterkonfiguration the direct connection of the motor-side inverter via the neutral leads to a much lower isolation load of the motor with respect to the maximum amplitude of the applied voltage to the ground potential.

The invention makes it possible to realis_ie_ren switching power supplies, pulse DC ^¬ rectifiers or inverters, which have _ ^¬ effects a particularly good efficiency and low electromagnetic return and with a simple, inexpensive structure ensure high reliability and long life.

Further details of advantageous embodiments of the invention are the subject of the drawing, the description or subclaims.

In the drawings, embodiments of the invention are illustrated. Show it:

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

Figure 2 is a schematic representation of the time course of the voltage across the storage inductor, the currents and the control signals in the Schaltungsanorndung of Figure 1 in the case of an injection of energy into a network without power compensation.

Figure 3 is a representation similar to Figure 2 in the case of a supply of energy in a network with power compensation.

Figure 4 is a schematic representation of the profile of the voltage across the storage inductor, the currents and the control signals in the Schaltungsanorndung of Figure 1 in the case of removal of energy from a network without power compensation.

Figure 5 is a view similar to Figure 4 tung compensating for the case of a removal of energy from a network with ^¬ Leis.

6a and 6b further developments of the invention guide mold according to Fig. 1;

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

8 shows a development of the converter circuit according to the invention according to FIG. 7.

Fig. 1 shows a schematic diagram of a circuit arrangement 1 of an inverter according to the present invention. In the illustrated single-phase, transformerless configuration, the inverter 1 serves as an inverter for generating and supplying an alternating current to an external network. For this purpose, the inverter 1 has three DC voltage terminals 2, 3, 4, two intermediate energy stores 6, 7, a bridge circuit 8, a point circuit 9, a control device 11 and two AC voltage terminals 12, 13. At the DC voltage terminals 2, 3, 4 are here two DC voltage 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 _N E _{TZ is} applied.

A first DC voltage terminal 2 is connected to a first DC voltage branch 17 and a second DC voltage terminal 4 is connected to a second DC voltage branch 18, while the central DC voltage terminal 3 is passed through the entire circuit arrangement 1 and forms a neutral conductor 19. This is connected to the AC voltage connection 13 and can be connected to the ground, 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 disturbances be included. The generators 14, 16 are each connected to a DC voltage branch 17 and 18 and to the neutral conductor 19.

The intermediate energy storage 6, 7 are arranged parallel to each generator 14, 16, between one of the DC voltage branches 17 and 18 and the neutral conductor ^'19th They are preferably formed by buffer capacitors Cl and C2. Parallel to the series connection of the intermediate energy stores 6 and 7, the bridge circuit 8 is connected between the DC voltage branches 17, 18.

The bridge circuit 8 is formed as a conventional half-bridge having two series-connected switch units Sl 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 Sl, S2, a freewheeling diode Dl or D2 is arranged in the opposite forward direction. The connection point 20 between the switch units Sl and S2 is connected via a connecting line 21, which contains a storage inductor L, to the AC voltage terminal 12.

The switch circuit 9 serves to redirect currents flowing through the storage inductor L as required in a controlled manner. The switch circuit 9 is formed here by a parallel connection of two switch paths 22, 23, which are connected downstream of the bridge circuit, run between the connecting line 21 and the neutral conductor, 1.9. The switch path 22 has a switch element S3 with a conventionally antiparallel connected freewheeling diode D3 and a Rectifier diode D5, which is connected to the parallel arrangement of the switch element S3 and the diode D3 in series. The forward direction of the diode D3 points from the neutral conductor 19 to the connecting line 21. Similarly, in the switch path 23, a switch element S4 are provided with an antiparallel freewheeling diode D4 and arranged in series thereto rectifier diode D6. The anode of the rectifier diode D6 is connected to the connection 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, the control device 11, which forms part of the circuit 1 or may be partially realized in the form of a separate integrated circuit is used. It may also be a microprocessor or the like. be used. In any case, the control device 11 contains two functional units in the form of blocks 24, 26. The block 24 identifies a sensor device which serves to detect operating parameters of the circuit arrangement 1 and to supply signals 27 indicative thereof. For this purpose the Ξensoreinrichtung contains suitable furnished sensor means, not shown here for simplicity of illustration 24, for example, to which. Voltmeter for detecting the buffer capacitors Cl and C2 applied DC voltages U _DC I _Λ U _DC2 of equal circuits, current meter for detecting the DC voltage branches 17, 18 flows through the half-bridge components Sl, Dl or S2, D2 currents Ii 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 resulting voltage _^ _U _NE τz_ capture. Natuer ^¬ Lich the voltages or currents given here can by generally known electro-technical relations also other detectable partial voltages or partial currents in the circuit 1 are derived.

The block 26 identifies logic elements of the control device 11 which are adapted to receive and process the signals 27 supplied by the sensor device 24 in order to suitably control the switch units S1 and S2 of the half-bridge 8 as well as the switch elements S3 and S4 of the switch circuit 9 based thereon , This is illustrated in Fig. 1 by dashed lines indicated driving paths, one of which is exemplified by the reference numeral 28. In particular, the logic elements 26 may include comparator logic to compare the measured voltages or currents with each other or to predetermined or predeterminable thresholds, as well as decision logic to select the appropriate driving strategy based on the results of the comparisons.

The operation of the inventive circuit arrangement 1 described so far is described below with reference to FIGS. 2 and 3, the simplified diagrams with time histories of the most important voltages and currents and control signals in the circuit arrangement 1 for the illustrated in Fig. 1 case of the supply of energy into a network illustrate. The circuit arrangement 1 according to the invention functions as follows:

It is assumed that there is an AC voltage U _NETZ with a peak voltage of Λ / 2-230 V and a frequency of 50 Hz at the AC voltage terminals, as shown in the uppermost diagram in Frg. ^~ 2 for one period - can be seen. For the direction of change of the DC voltage generated by the generators 14, 16, the switches Sl to S4 as a function of the polarity of the mains voltage U _NET z closed and opened by the controller 11 according to a specific clock pattern. It should be noted that for reasons of clarity in the diagram representation of the duty cycles of the switch units Sl and S2 are shown in each time segments of the mains voltage half-wave by way of example. In reality, their switching frequency is, for example, 16 kHz or more. Advantageously, only one switch unit Sl or S2 is switched per half-wave, which minimizes the forward losses and promotes high efficiency.

As can be seen from FIG. 2, in the positive half-wave of the mains voltage U _NETZ, the switch unit S1 is switched to high-frequency. Further, the switch element S3 is closed in the switch path 22, while the switches S2 and S4 remain open, so that a current flow is prevented by this. When closing the switch unit Sl of the half-bridge 8, the voltage U _DC i is applied to the choke coil L, whereby the current I _L increases and the choke coil is magnetized.

During the freewheeling phase, when the switch unit S1 is opened, the choke coil L is demagnetized, wherein the positive choke 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 deterioration in efficiency 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 carried out by the switch unit S1 and the freewheeling diode D1 at each cycle is thus based on the value of the DC voltage. limited to _DC i and therefore relatively low. This is because the switch paths 22, 23 are connected to the neutral conductor 19 to which also the generator 14 and the buffer capacitor Cl are connected.

The switch unit S1 is repeatedly clocked in the positive mains voltage half-wave, wherein the closing times 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 _NE τz in the magnetization and demagnetization of the storage inductor L to meet. This switch operation is achieved by pulse width modulation of the control signals supplied by the controller 11 28 or by another suitable, the duty cycle predetermining type of modulation. The generated alternating current I _L , as it results in the course of the clock average and is indicated in dotted lines in Fig. 2, with respect to the phase angle and the amplitude to the potential curve of the AC voltage U _NE τz adapted well. 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 a manner analogous to the mains voltage U _NE τz closed switch element S4 is in the course path 23, and open switches Sl and S3, the scarf ^¬ tereinheit S2 of the half-bridge 8 is suitably driven in the negative half-wave. The choke coil current I _L flows in the closed state of the switch unit S2 of the DC branch 18 via this to the inductor L _um_ they aufzumagnetisieren while in the opening state of the switch unit S2 via the now serving as a freewheel path switch path 23 with the closed switch element S4 commutes. A return of the energy in the buffer capacitor Cl is again prevented. The above statements regarding operation during the positive half cycle apply accordingly.

The control device 11 controls not only the bridge 8 and the switch device 9 in the sense of an advantageous operation of the circuit arrangement 1 according to the invention, in particular in the freewheeling state, but also ensures an optionally required power compensation. If, for example, the generators 14, 16 are designed in the form of photovoltaic generators, which are shaded to different degrees, or for other reasons, for example, give different powers due to tolerances due to manufacturing tolerances, the alternating current I _L fed into the network would become one DC component to be prevented. The controller 11 causes in this case, such an energy exchange between the generators 14 and 16 that can be operated at ^¬ de in their optimal operating range.

FIG. 3 illustrates by way of example a maximum possible 50% power compensation from the upper DC voltage branch 17 into the lower DC voltage branch 18. The different power output of the generators 14, 16 is determined, for example, by the logic means 26 of the control device 11 on the basis of the voltages U _D ci / U _DC ₂ detected by the sensor device 24 and / or currents Ii, I ₂ . The logic means 26 then causes the switch element S3 to remain open during a certain time portion of the positive half cycle corresponding to the required power compensation level. In the closed state of the switch unit Sl the operation is outlined as above. However, in the freewheel state, the inductor current I _L does not commutate the switch path 22, but via the freewheeling diode D2 back to the buffer capacitor C2, which is thereby charged accordingly. Half of the energy supplied by the generator 14 is transferred from the upper 17 to the lower DC branch 18.

During power equalization, although the voltage potential jumps at the half-bridge 8 increase to the sum of the DC voltages U _D ci and U _DC 2, 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 occurs only during a fraction of only the positive half-wave and is little 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. Regardless of the compensation direction, the maximum power compensation of the respective ratio of the DC voltages U _D ci _? U _DC2 depends on 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 to the upper DC branch 17 is required accomplished accordingly by the switch element S4 remains open during a part of the negative half cycle of the mains voltage U _NETZ and a Rückkommutierung of the inductor current I _{L is made possible} to the capacitor Cl targeted.

The circuit arrangement 1 according to the invention forms a bidirectional converter which is also set up for the extraction of energy from an external network. For this purpose, the generators 14, 16 in Fig. 1 indicate corresponding consumers. The operation is illustrated in FIG. 4 for the case where no power compensation takes place, and in FIG. 5 for the case with power compensation.

First of all, the positive half-wave of the mains voltage U _{NETZ should be considered} under the assumption that all switches S1 to S4 are open. At zero crossing, the mains voltage U _NET against the neutral conductor 19 is insufficient to magnetize the inductor L. Therefore, the switch unit S2 is firstly driven in a high-frequency manner so as to bring the potential of the voltage U _L to almost the potential -UD _{C2 of} the DC voltage branch 4 in the closed state in order to allow a current flow from the choke coil L via the switch unit S2. This results in a rising current I ₂ flowing to the DC branch 18 and the capacitor C2. In the open state of the switch unit S2, a potential + U _DC i adjusts itself to the connecting line 21 and the thereby decreasing inductor current I ₁ , flows via the freewheeling diode Dl of the half-bridge 8 to the DC voltage branch 17, resulting in a current Ii for charging the capacitor Cl has, cf. Fig. 4.

As soon as the mains voltage is sufficiently high, the switch unit S2 remains open. Instead, the switching element ment S4 switched in the switch path 23. In the closed state of the switch element S4, the inductor L is charged by the mains voltage ÜNETZ. 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 Dl to the capacitor Cl. In this way, a consumption of energy from the energy buffer 7 over the entire duration of the positive half-wave is prevented. 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 described above in the absence of a sufficient potential.

In the negative half wave of the mains voltage U _NE τz the switch element Ξ3 instead of S4 is used analogously, 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, the opposite switching unit S1 of the half bridge 8 is used.

In each half-wave only one switch unit Sl or S2 of the bridge circuit 8 is switched and, apart from the mains voltage zero crossings, a Rückkommutierung the current to the opposite buffer capacitor Cl and C2 minimized. The voltage U _L jumps only between the potentials given by the DC voltages and the zero potential, ie between + U _D ci and zero or between -U _D c2 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. But it should be noted that at 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 to choose greater by appropriate control than in the vicinity of the zero crossings.

As illustrated in FIG. 5, a power compensation is achieved according to the invention if one of the consumers 14, 16 has a greater energy requirement. For example. During the positive half cycle of the mains voltage U _NE χz, 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 ratio between the timing of the switch unit S2 and the subsequent clocking of the switch element S4 a corresponding amount of energy transfer from the lower 18 to the upper DC voltage branch 17 is achieved per half-wave. A power compensation from the upper 17 in the lower DC voltage branch 18 can be achieved to the extent necessary during the negative half cycle of the mains voltage U _NE τz by appropriate determination of the duty cycle between the switches Sl and S3.

Numerous modifications are possible within the scope of the invention. For example. For example, the circuit arrangement 1 can be extended to use more than two DC voltage generators connected in series, which are then to be connected to a plurality of DC voltage terminals and for each of which an energy buffer is to be provided. The bridge circuit 8, the switch circuit 9 and the control logic 26 must be adjusted accordingly to start from the. DC voltages at the intermediate energy stores 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. In addition, a plurality of storage chokes L may be inserted in the connection path 21. At the AC voltage terminals 12, 13 filter means may be provided for suppression. The control method according to the invention can also be implemented in the form of firmware or software.

The diodes D3, D4 protect the respective semiconductor switch S3, S4, but may be omitted if necessary. This is particularly the case when integrated semiconductor switches with reverse blocking capability, for example self-blocking IGBT switches, are used, provided that they are suitable for high-frequency applications.

For proper operation, the voltage U _DC i or U _D c ₂ in the respective DC circuit must be greater than the peak value of the mains voltage U _NE τz. 6a and 6b show schematic diagrams of developments of the converter according to the invention, which make it possible to use even smaller voltages U _DC i and U _D c ₂ . The circuit arrangement 1 is shown therein for simplicity only in the form of a block 1.

In the solution shown in FIG. 6a, boost converters 29a and 29b, which are also referred to as DC regulators, are inserted in the DC voltage branches 17, 18. Such Hochsetz- plates are known from the art in different forms, for example. As an advantageous multi-string circuits, and need not be further explained here. Suffice it to say that each step-up converter 29a, 29b has the task of raising the potential of the voltage generated by the generator 14 or 16_ to a level U _DC i or U _D c2 suitable for operation. This can be used to solve problems that arise when generators of different types or in the case of severe partial shading can be effortlessly mastered. The inverter 1 can be operated in the large power range with maximum yield. The operation of the boost converters 29a, 29b is preferably controlled by a regulator, which may be part of the control device 11. Preferably, a switch S5a or S5b is further arranged parallel to each boost converter 29a or 29b, which can be closed in order to bridge the associated boost converter 29a or 29b when not in use. This minimizes losses.

The illustrated in Fig. 6b embodiment of an inverter 1 according to the invention has instead of the arranged on the Gleispannungsseite boost converter 29a, 29b on the AC side of a blanking circuit 31, which is inserted in the leading to the AC voltage connection 12 connecting line 21. The circuit 31 is formed here by a parallel connection of two self-blocking IGBT switches Sβa, S6b, which have opposite passage directions. By suitable activation of the switches Sβa, S6b, the mains voltage U _NE τz can be masked out during periods in which its instantaneous value exceeds the DC voltage U _DC i or U _DC 2 that is currently being used in order to use the DC voltages also during these periods. Of course, other circuits can be used for this purpose. For example. For example, the normally-off IGBT switches Sβa, Sβb can also be replaced by other types of switches with rectifier diodes each oriented in the respective forward direction. Advantageously, the circuit 31 may include another switch S7 to bypass the switches Sβa, Sβb when not in use.

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

FIG. 7 shows, in a simplified manner, a circuit arrangement 1 'according to the invention in the three-phase converter configuration. The circuit arrangement 1 'contains three circuits Ia, Ib, Ic which are identical to the circuit arrangement 1 according to FIG. 1 as well as to one another and whose components are identified by adding the indices a, b or c. The circuits Ia, Ib, Ic are connected in common to the DC voltage terminals 2, 4, 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 Cl and C2. A third DC voltage terminal 3 is connected to a neutral conductor 19, which is assigned to all the circuits Ia, Ib, Ic together and is preferably connected in operation to the ground. Half bridge circuits 8a, 8b, 8c are arranged parallel to the buffer capacitors, of which the connecting lines 21a, 21b, 21c branch off, which are connected via choke coils L to the AC voltage terminals 12a, 12b, 12c. Between the connecting lines 21a, 21b, 21c and the neutral line 19 turnouts 9a, 9b, 9c according to the invention are provided. The control device 11 according to the invention is omitted in Fig. 7 for reasons of Übersichtlichkeits ^¬.

As to the precise arrangement and configuration of individual components of the circuits Ia, Ib, Ic, in particular the -Halbbrücken 8a - 8b, and the -8C _Weichenschaltungen 9a, 9b, 9c, and their operation is limited to the above Ausführun ^¬ gene linked to the Ausführungsfqrm according to Fig. 1 grasslands. It should be briefly mentioned here that the circuit arrangement 1 'can be used both for the alternating direction in order to generate a three-phase alternating current (so-called three-phase current) from the direct voltages U _DC i and U _D c2, and also for rectification in order to start from a three-phase current fed from the outside to generate the DC voltages U _D ci and U _DC2 . In this case, the control device 11 controls the half-bridge and switch circuits 8a and 9a, 8b and 9b and 8c and 9c suitably according to the control method according to the invention to either to each 120 ° phase-shifted inductor currents I _La / ILb and I _Lc to produce in the Are fed three-phase network, or to take the three-phase network in an advantageous manner with respect to the phase position and the harmonic content of energy to supply the DC consumers. Advantageously, only one bridge switch SIa, SIb, Sic or S2a, S2b, S2c is switched to high-frequency per phase Ua, Ub, Uc and half-wave. Further, in both cases, a Rückkommutierung the reactor currents to the buffer capacitors Cl and C2 prevented in the freewheeling state and, if necessary, a power compensation between the DC voltage branches 17 and 18 are 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 _DC i and U _DC2 only assumes values in the range of economic availability of electrolytic capacitors ,

In the embodiment of FIG. 7 illustrated in FIG. 8, a further inyerter 1 "is connected to the DC voltage side of the converter 1 '. The direct current generated by energy extraction from the three-phase network with the inverter 1 'or the DC voltage is by means of of the inverter 1 '' converted into a suitable for driving a motor three-phase current. The inverter 1 '' can be configured as desired, but is preferably identical to the inverter 1 'and also has a switch circuit 9 in order to minimize losses during operation and to compensate for power. Advantageously, the inverter 1 "is connected directly to the neutral conductor, whereby the occurrence of voltage fluctuations caused by the timing of the switches and the associated electromagnetic interference signals are minimized. Lower voltage swings at the winding terminals of motors, for example, their insulation load is significantly reduced. The circuit arrangement according to FIG. 8 can also be used to supply an external three-phase network by means of an alternator.

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

Claims

Claims:

1. Circuit arrangement (1), in particular for converting direct current into alternating current or from alternating current into direct current,

with at least three DC voltage connections (2, 3, A), 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) connected in series via a connection point (20) which forms a center tap of the bridge circuit (8) and to each of which a freewheeling diode (D1, D2) is connected in antiparallel,

with at least two AC voltage terminals (12, 13), one of which (13) is connected to the neutral conductor (19), while at least one other (12) is contained via a connecting line (21) in which at least one storage choke (L) is contained, is connected to the center tap (20) of the bridge circuit (8),

comprising a switch circuit (9) which has switch paths (22, 23) connected between the connecting line (21) and the neutral conductor (19) and switch elements (S3, S4) provided in the switch paths (22, 23), which can be switched controlled; a current flow through the switch paths (22, 23) to enable or prevent, and

with a control device (11) which is adapted ^'to control the switching circuit (9) so as to, if required, to substantially prevent and / or commutation of the current flowing through the storage choke (L) current to the intermediate memories (6, 7) Power compensation between the DC voltage branches (17, 18) to accomplish.

2. Circuit arrangement according to claim 1, characterized in that it forms a transformerless converter with semiconductor switching elements.

3. A circuit arrangement according to claim 1 or 2, characterized in that between the DC voltage terminals (17, 18) two DC voltage generators (14, 16) are connected, which are connected in series with each other, and the circuit arrangement (1) for feeding energy into Network is used.

4. Circuit arrangement according to claim 1 or 2, characterized in that between the DC voltage terminals

(17, 18) two DC voltage consumers (14, 16) are connected, which are connected in series with each other, and the circuit arrangement (1) for removing energy from an AC voltage network is used.

5. Circuit arrangement according to claim 1, characterized marked ^¬ characterized in that it forms a single-phase converter configuration.

6. Circuit arrangement according to claim 1, characterized marked ^¬ characterized in that it has a three-phase converter configuration forms.

7. Circuit arrangement according to claim 1, characterized in that in each switch path (22, 23), a switch element (S3, S4) and a series-connected rectifier diode

(D5, D6) is provided, wherein the rectifier diodes (D5, D6) are connected to each other in the opposite forward direction.

8. 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 in dependence on the detected operating conditions.

9. Circuit arrangement according to claim 8, characterized in that the control device (11) for detecting operating conditions characterizing parameters sensor means (24), including sensor means for detecting the voltage at the intermediate energy stores (6, 7) voltages applied in the DC voltage branches ( 17, 18) flowing currents and / or at the AC voltage terminals

(12, 13) applied AC voltage having.

10. The circuit arrangement according to claim 9, characterized in that the control device (11) comprises logic (26), which serves the detected parameters (27) mitein ^¬ other and to compare optionally with predetermined threshold values and based on the comparison, the switch elements (S3, S4) of the switch circuit (9) to switch.

11. Circuit arrangement according to claim 10, characterized in that the logic (26) further adapted thereto is to cause a power compensation such that at the DC terminals (2, 3, 4) connected in series DC generators or consumers (14, 16) are operated substantially at its optimum operating point.

12. Circuit arrangement according to claim 1, characterized in that it is connected on the DC side with at least one further inverter (1 '').

13. A method for converting direct current into alternating current or from alternating current into direct current with a circuit arrangement (1), comprising: at least two DC voltage branches (17, 18) and a neutral conductor (19), energy buffer (6, 7) are each connected between a DC voltage branch (17, 18) and the neutral conductor (19), a bridge circuit (8) arranged between the DC voltage branches (17, 18) and comprising two switch units (S1, S2) which are connected via a connection point (20). , which forms a center tap of the bridge circuit (8), are connected in series with each other and to each of which a freewheeling diode (Dl, D2) is connected in anti-parallel, and at least two AC voltage terminals (12, 13), one of which (13) the neutral conductor (19) is connected, while at least one other (12) via a connecting line (21) in which at least one storage choke (L) is included, with the center tap (20) of the bridges circuit (8), the method comprising the steps of:

Providing switch paths (22, 23) between the connection line (-21) and the neutral conductor (19) with switch elements (S3, S4) contained in the switch paths (22, 23), which are controllably switchable for current flow through the To enable or prevent turnouts (22, 23)

Detecting operating parameters indicative of DC voltages applied to the intermediate energy stores (6, 7), currents flowing in the DC voltage branches (17, 18), and / or AC voltage applied to the AC voltage terminals (12, 13), and

Controlling the flow of current through the switch paths (22, 23) as a function of the detected operating conditions such that a Rückkommutierung of the current flowing through the storage inductor (L) current to the energy buffers (6, 7) substantially prevented and, if necessary, power between the DC voltage branches (17 , 18) is compensated.

14. The 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) connected ^¬ sen and these are each operated substantially at its optimum operating point to energy in a To feed mains.

15. The method according to claim 13, characterized in that between the DC voltage branches (17, 18) and the neutral conductor DC voltage sinks (14, 16) connected and these are each operated substantially at its optimum operating point to remove energy from a network.

16. The method according to any one of claims 13 to 15, characterized in that at each half-wave at the AC voltage terminals (12, 13) connected AC voltage only one switch unit (Sl, S2) is hochfreguent and in the freewheeling state, the current through the Dros- Seispule (L) via an associated switch path (22, 23) is redirected.

17. The method according to any one of claims 13 to 16, characterized in that in a time window in the region of the zero crossing of the AC voltage is switched to a clocking while consuming energy from a DC circuit.

18. Method according to claim 17, characterized in that the duty cycle between clocked switches (S1 / S3; S2 / S4; S2 / S4; S1 / S3) in the half-bridge (8) and the switch paths (22, 23) is suitable for power compensation is determined.

19. The method according to claim 18, characterized in that for power compensation, the time window in the region of the zero crossing of the AC voltage is shortened or extended accordingly.