DE10221765A1 - Inverter for welding devices comprises two asymmetric high bridge circuits which alternately drive two separate primary coils of a main transformer - Google Patents

Abstract

Inverter comprises two asymmetric high bridge circuits (1a, 1b) which alternately drive two separate primary coils (3a, 3b) of a main transformer (3). A current multiplier rectifier (6) is connected to the secondary coil (3c) of the main transformer. A saturated inductive resistor (5a, 5b) is connected to each primary coil of the main transformer.

Description

The invention relates to an inverter with two asymmetrical Half-bridge circuits that alternate two separate primary windings Main transformer drive, in which on the secondary winding of the Main transformer a current doubler rectifier is switched on.

The trend in inverter construction is increasingly towards smaller dimensions and lighter weights. At the same time, the requirements are increased in many aspects. The harmonic content of the mains current has to meet more and more strict legal standards. This requires considerable effort, increases the weight and volume of the entire device. It is all the more necessary to improve the efficiency of power electronics. An example of the prior art is given in the document: "Design and Experimental Analysis of a 10 kW 800 V / 48 V Dual Interleaved Two-Transistor DC / DC Forward Converter System Supplied by a VIENNA Rectifier I" by Johann Miniböck, Johann W Kolar and Hans Ertl. This document was distributed as part of a public seminar lecture at the PCIM conference in Nuremberg 2002 .

On page 10 is a basic circuit according to the preamble of this invention displayed. The text already mentions that the two inverter systems - the are connected in series here - probably influencing each other because they only work on a single transformer. Any tension in one Primary winding is fed in, is equally transferred to the other Half-bridge system and tries malfunctions there. The circuit implemented in this document from page 1 does not know these problems because they have separate transformers features. This circuit also works with a moderate switching frequency of 25 kHz and is used as a 48 V power supply for telecommunications equipment planned. However, about weight, size and cost of a second ads To save on transformers, the authors look up a circuit Page 10.

If an inverter is now required that has a significantly higher switching frequency new problems arise. High switching frequencies will be z. B. needed in pulse welding technology, because the inverter controls extremely must produce fast current patterns, e.g. B. over 1000 A / ms. At the same time an extremely fast regulation is needed because when welding completely arc shorts occur unpredictably and in chaotic sequence, so that the Output power within fractions of a millisecond around ranges of 95% of the full load can fluctuate. For such high dynamic requirements high switching frequencies are required and this is advantageous Transistors of the MOSFET type used.

Attempts have now been made to use MOSFETs in a circuit for a welding machine use. There were enormous problems related to this that MOSFET transistors have a parasitic diode inverse to the transistor. If one of the half-bridge circuits in the so-called freewheeling mode goes, this is the state in which the primary winding of the main transformer their magnetization breaks down via the freewheeling diodes, then begin in the second Inverter to conduct the inverse freewheeling diodes, then shortly afterwards a high one du / dt load of the MOSFET takes place. This is a typical situation in which one MOSFET can go into the "second break down" state of destruction and this must be prevented under all circumstances. The one described on page 10 Circuitry cannot be operated safely with MOSFETs.

In certain limit areas shortly before full control of the inverter there were further significant problems with signs of saturation in the Main transformer.

A conventional control with pulse width modulated control signals led to an oscillation of the magnetizing current in limit situations. At the same time, the PWM system was in its presence when short circuits occurred Speed too slow.

The invention has set itself the task of an inverter circuit in many Aspects to evolve so they deal with MOSFET transistors can be operated, the magnetizing currents in the main transformer clean are controllable, an extremely fast regulation without transformer saturation is achievable and that all requirements placed on a welding machine are achievable.

This object is achieved according to the invention in that with everyone Primary winding of the main transformer has a saturable inductance in series is switched.

The inverter can be divided into parallel subsystems, with the Symmetry of the power distribution is always guaranteed, a symmetry system for the capacitive center when connecting the half-bridge circuits in series can be found, the regulations of harmonics in the mains current can be met the inverter system can be implemented up to the higher power ranges is and a modular system is implemented to flexibly meet the requirements of the Market.

The weight is an outstanding size for a welding machine. With this When designing the circuit, the smoothing chokes can be kept small and for very high outputs, subsystems constructed in this way can be used Operate in parallel.

Further developments of the basic circuit are to the numerous subclaims refer to, in particular with the division of the inverter into several deal with small partial inverters and their phase-shifted operation. Also the control structure of the sub and overall system has been improved and the Effects on the supply network reduced.

When operating such an inverter system with very small currents the so-called intermittent operation begin, whereby both subsystems no longer clock alternately. When the Half-bridge circuits occur a shift in the center of the voltage supply, that can destroy the subsystems. On the other hand there is one Training a solution.

Particularly low-feedback conditions and much quieter Curves occur when in series with the output diodes of the current doubler Rectifier is connected a second saturable inductance.

A particularly simple realization arises when the first and second saturable inductors are formed by ring cores through which the current conductor leads.

It is particularly effective and thermally advantageous if the toroidal core saturable inductance made of amorphous or nanocrystalline ribbon material is.

Particularly small and inexpensive ring cores can be used if the toroidal cores of the saturable inductors are thermally conductive in bores of cooling profiles or heat transfer profiles are built in to the To significantly improve heat dissipation.

A particularly advantageous embodiment of the inverter system provides that one connection of the two primary windings together through one Current transformer is that this is a total current with changing polarity recognizes and outputs changed.

There is a significant increase in regulatory stability in borderline cases if this current transformer is a compensation current transformer with a magnetic field sensor, which can also measure the resulting DC components.

Another configuration with many advantages arises if that Inverter system has a cascade control, with a main controller Using the actual output current value of the output current or Output voltage from the output of the power section and using the setpoint of the Output current or the output voltage as required a current regulator or realized a voltage regulator and the output signal of this Main controller is fed as a command signal to a controller that acts as a Current mode controller for the primary current of the main transformer is realized.

A system with both control systems is created when the main controller is both contains a current regulator as well as a voltage regulator, which in one Transfer circuit are linked so that the controller that Receives guidance that generates the smaller guidance signal.

When designing the controller, there is also the advantageous way that the Main controller as a digital controller with the usual means of processor technology is formed and that the analog command signal via a D / A converter process is generated to use it as a current setpoint signal to the current-mode controller supply.

In order to continue to use the bipolar signal of the current transformer, in advantageously for the formation of the primary current actual value for the Currentmode controller with the primary current actual value from the compensation current transformer rectified like an amount generator.

A very simple and inexpensive structure of the common mode controller is created by an oscillator with a downstream pulse generator Control pulses generated, with the aid of which one of the flip-flop memories is assigned alternately assigned to the half-bridge inverter be set and reset and that the respective setting or resetting this flip-flop memory with the help of downstream control circuits for switching the transistors on or off Half bridge circuit leads.

In continuation, it is advantageous if the current mode controller at the input has a comparator which compares the primary current actual value with the Compares the amplitude of the command signal, and that with a larger actual value the Flip-flop memories are reset, so ultimately the two Transistors of the respectively active half-bridge circuit are switched off again.

Depending on the amount of AC power, it is good if the two asymmetrical half-bridge circuits can be fed from the same supply voltage are.

At higher mains voltages, however, there are advantages if the two asymmetrical half-bridge circuits with their supply voltages in series are switched.

A particularly stable behavior of the overall system, especially with the smallest Power consumption occurs when the Half-bridge circuits a monitoring circuit the symmetry of the capacitive Center connection in relation to the positive supply voltage and the negative Supply voltage measures and that the output signal of this Monitoring circuit shows the asymmetrical behavior with the Information of the direction of the asymmetry.

It also helps if the output signal of the monitoring circuit is used to drive the drive pulses of that half-bridge circuit block or shorten that over the smaller supply voltage until the symmetry of the supply voltages is restored.

There are two ways to build larger inverter systems: Half-bridge circuits and a main transformer (possibly provided with the first saturable inductors) and a current transformer and a Current doubler rectifier (possibly provided with the second saturable additional Inductors) can be combined to form a power section.

An even more extensive modularization arises when a power section together with a control transformer and with control circuits and with a current mode controller can be combined to form a subsystem.

Inverter systems with very high output powers can now be used realize that several subsystems are connected in parallel and that the Reference variable at the input of the current mode controller for all subsystems is identical, and from a common main controller for the entire system is generated, in which case the actual output current value is the current of the entire Systems represents.

There will be a dramatic reduction in the ripple on the output current achieved by using the oscillator with a parallel connection of several subsystems downstream pulse generator is common to all and that the setting of the Flip-flop memory for the different half-bridge circuits if possible many phase-shifted times is divided so the resulting ripple of the output current becomes minimal.

A particularly advantageous combination to comply with legal requirements Harmonic regulations on the supply network arise from the power section the terminals of the positive supply voltage and the negative Supply voltage a known step-up converter circuit and a Mains rectifier is connected up to the current consumption from the To be able to control the supply network.

For the same reasons, it is extremely advantageous that the upstream Booster circuit itself from a parallel connection of several Boost converter circuits of lower power is realized.

In order to achieve an equal current distribution, it is provided that the Setpoint signal for the input current of the individual step-up converter circuits is identical for everyone.

A particularly economical and advantageous from the point of view of EMC Solution arises when the individual step-up converter circuits in one phase-shifted clock work, so that the ripple of the input current is reduced.

A component reduction and more stable EMC conditions arise if that Clock generation system for the subsystems and clock generation for the Step-up converter circuits are synchronized with one another and result from one single common oscillator and a common pulse generator are derivable.

This inverter system can also reduce costs achieve that the four transistors of the two half-bridge circuits with be controlled by a single control transformer, which via a Primary winding and four separate secondary windings.

Very high switching frequencies can be achieved in that the Transistors of the half-bridge circuits are of the MOSFET type.

Further assembly advantages and easier spare parts inventory arise if one Power section with an upstream step-up converter circuit mechanically are combined as a module assembly, so that by direct Parallel connection of several such module assemblies high power components Total performance can be realized.

An advantageous standardization arises if each of these module assemblies has its own cooling profile.

These features are in depending on the required use of the inverter system can be combined with each other over a wide range.

In the field of welding technology, it is particularly advantageous to use many smaller ones To operate power units in phase displacement with each other, because that means that Weight of the required chokes can be greatly reduced. This is particularly important for portable machines. When operating inverters on three-phase Three-phase network of 3 × 400 V is a series connection of the half-bridge circuits very advantageous, because when using MOSFET transistors Current carrying capacity decreases drastically with increasing dielectric strength, so that More economical solutions result because transistors with half Dielectric strength can be used.

By combining most of these features it is an inverter system emerged, the high in a very small space with low weight Output power reached. Of particular note is the unprecedentedly high level Control dynamics and low ripple of an inverter of this size - and Weight class. The regulations for harmonic components are fully satisfied. The Modular system brings great economic benefits.

The invention is illustrated by means of one in the drawings Embodiment explained in more detail. Show it:

Fig. 1 shows the basic circuit of a power unit according to the invention,

Fig. 2, the control structure of an inverter system according to the invention,

Fig. 3 shows a possible parallel connection of the half-bridge modules,

Fig. 4 shows a possible series circuit of the half-bridge modules,

Fig. 5 shows an inverter system with upstream boost converter circuit and line rectifier as well

Fig. 6 shows an example of a module assembly.

In Fig. 1 you can see how a first half-bridge circuit 1 a is constructed. Two transistors 10 a and 10 b are connected together with two free-wheeling diodes 11 a and 11 b in a known manner to a so-called symmetrical half-bridge circuit. The supply is connected to a positive supply connection 33 and a negative supply connection 34 and is supported by a buffer capacitor 43 a. It can be seen that the main transformer 3 has two primary windings 3 a and 3 b. The first primary winding 3 a is now installed in the bridge diagonal of the half-bridge circuit 1 a, a saturable inductor 5 a being connected in series with the primary winding. Furthermore, the primary current flows through a current transformer 4 , which generates a primary current actual value 42 .

The second half-bridge circuit 1 b is constructed as shown in a completely analogous manner. It should only be noted that the primary winding 3 b and the current transformer 4 are connected as shown so that the magnetization of the transformer 3 and the current in the current transformer 4 is opposite in the case of conductive transistors 10 a and 10 b in the half-bridge circuit 1 a than in the case of conductive ones Transistors 10 c and 10 d in the half-bridge circuit 1 b. The current-doubler rectifier 6, which is known per se, is now connected to the secondary winding 3 c. The standard circuit consists of two smoothing chokes 9 a and 9 b, each carrying half of the output current. Two output diodes 7 a and 7 b are used for rectification. The two saturable additional inductors 8 a and 8 b are connected in series with the two output diodes. The whole arrangement is referred to as power section 2 .

In FIG. 2, the power section 2 is shown as a block. The regulation for this is now described. A main regulator 13 implements a current regulator 20 or a voltage regulator 21 , depending on the requirement. The current controller 20 is supplied with the actual output current value 16 from a known current measuring system. At the same time, it receives an output current setpoint 18 from a higher instance. The voltage regulator 21 receives the output voltage actual value 17 and an output voltage target value 19 . If both a current regulator 20 and a voltage regulator 21 are required at the same time, a detachment circuit 39 known per se and shown schematically is provided, which transfers control to the regulator which generates the smaller command signal 14 . The command signal 14 is a new current setpoint for a current mode controller 15 known per se. A very fast and precise primary current actual value 22 is required for the current mode control. For this purpose, the bipolar primary current actual value 42 from the current transformer 4 is rectified in an absolute value generator 23 . The command signal 14 and the primary current actual value amount 22 are fed to a comparator 27 in the current mode controller 15 . Each half-bridge circuit 1 a or 1 b is now assigned a flip-flop memory 26 a or 26 b, which via a drive circuit 28 a or 28 b and a drive transformer 12 to the transistors of the associated half-bridge circuit 1 a or 1 b leads. Is z. B. set the flip-flop memory 26 a, then the transistors 10 a and 10 b of the half-bridge circuit 1 a are turned on - the same applies vice versa and analogously for the other flip-flop memory 26 b in connection with the half-bridge circuit 1 b.

The switching on and off of the flip-flop memories 26 a and 26 b is provided by a pulse generator 25 , which is fed by an oscillator 24 . The two flip-flop memories 26 a and 26 b are alternately set and reset with a maximum 50% duty cycle. However, if the comparator 27 determines that the primary current actual value 22 exceeds the command signal 14 , the flip-flop memories are reset immediately without any time delay. As a result, the power flow in the main transformer 3 is interrupted immediately. The current limitation of the inverter system thus reacts without a delay due to the principle, since the primary current contains a delay-free image of the output current. When connecting several subsystems 49 in parallel, it is particularly advantageous to provide the oscillator 24 and the pulse generator 25 only once and for all subsystems 49 together, since this allows the phase position of the individual half-bridge circuits to be fanned out further and the ripple of the output current of the overall system is thus drastically reduced can be.

In Fig. 3, the parallel connection of the two half-bridge circuits 1 a and 1 b is shown. This variant is particularly suitable for the operation of inverters on a single-phase 230 V supply network.

In contrast to FIG. 3, FIG. 4 shows a series connection of the two half-bridge circuits 1 a and 1 b. This creates a capacitive center point 32 , which lies in the middle between the positive supply connection 33 and the negative supply connection 34 . In order to be able to keep the center point 32 stable in the middle at each operating point of the inverter, it is advantageous to have a monitoring circuit 29 for the symmetry of the two partial voltages 40 a and 40 b. An embodiment is shown with two resistors 30 a and 30 b and two optocouplers 31 a and 31 b. The optocoupler 31 a becomes conductive when the supply voltage 40 a is greater, the optocoupler 31 becomes correspondingly conductive when the supply voltage 40 b is greater. The current mode controller 15 is controlled with the output signals 35 in such a way that the control signals of the half-bridge circuit 1 a or 1 b which has the lower supply voltage 40 are blocked by known means.

FIG. 5 shows that a step-up converter circuit 36 known per se is connected upstream of the power section 2 between the positive supply connection 33 and the negative supply connection 34 . This in turn is supplied by a mains rectifier 37 via the positive rectifier connection 45 and the negative rectifier connection 46 . The rectifier itself feeds from the supply network 38 , which is usually a single-phase network of z. B. 230 V or as shown a three-phase network of z. B. 3 × 400 V. When several subsystems 49 are connected in parallel, it is particularly advantageous to connect the command signal 14 and the setpoint signal for the input current 41 to all subsystems 49 in parallel, so that the current distribution among the subsystems is optimal.

In FIG. 6, a module assembly 44 is shown, which consists of a power section 2 and an associated step-up converter circuit 36. Such module assemblies can now be connected in parallel with the control technology according to the above characteristics without any problems, with which inverters of very high output power can be realized.

Claims (30)

1. Inverter with two asymmetrical half-bridge circuits ( 1 a, 1 b), which alternately drive two separate primary windings ( 3 a, 3 b) of a main transformer ( 3 ), in which a current flows on the secondary winding ( 3 c) of the main transformer ( 3 ) -Doppler rectifier ( 6 ) is connected, characterized in that a saturable inductance ( 5 a, 5 b) is connected in series with each primary winding ( 3 a, 3 b) of the main transformer ( 3 ). 2. Inverter according to claim 1, characterized in that the current doubler rectifier ( 6 ) has two output diodes ( 7 a, 7 b), each of which a saturable additional inductance ( 8 a, 8 b) is connected in series. 3. Inverter according to claim 1 or 2, characterized in that the saturable inductors ( 5 a, 5 b) and additional inductors ( 8 a, 8 b) are designed as toroidal cores through which the associated current conductors are guided. 4. Inverter according to claim 3, characterized, that the toroidal cores are made of amorphous or nanocrystalline band material consist. 5. Inverter according to claim 3 or 4, characterized, that the toroidal cores are thermally conductive in shots of cooling profiles or Heat transfer bodies are installed. 6. Inverter with two asymmetrical half-bridge circuits ( 1 a, 1 b), which alternately drive two separate primary windings ( 3 a, 3 b) of a main transformer ( 3 ), in which a current flows on the secondary winding ( 3 c) of the main transformer ( 3 ) -Doppler rectifier ( 6 ) is switched on, characterized in that one connection of each of the two primary windings ( 3 a, 3 b) is guided through a current transformer ( 4 ) in such a way that it outputs a total current with alternating polarity. 7. Inverter according to claim 6, characterized in that the current transformer ( 4 ) is designed as a compensation current transformer with a magnetic field sensor and detects DC components that arise. 8. Inverter with two asymmetrical half-bridge circuits ( 1 a, 1 b), which alternately drive two separate primary windings ( 3 a, 3 b) of a main transformer ( 3 ), in which a current flows on the secondary winding ( 3 c) of the main transformer ( 3 ) -Doppler rectifier ( 6 ) is connected, characterized in that it is provided with a cascade controller, a first main controller ( 13 ) depending on the actual value ( 16 ) of the output current or the output voltage of a power unit ( 2 ) and depending on the setpoint ( 18 ) of the output current or the output voltage forms a current regulator ( 20 ) or a voltage regulator ( 21 ), the output signal of which can be fed as a guide signal of the main regulator ( 13 ) to a further regulator, which acts as a current mode regulator ( 15 ) for the primary current of the Main transformer ( 3 ) is used ( Fig. 2). 9. Inverter according to claim 8, characterized in that the main regulator ( 13 ) has both a current regulator ( 20 ) and a voltage regulator ( 21 ) which are linked in a detachment circuit ( 30 ) so that the one who takes over the leadership small guide signal ( 14 ) generated. 10. Inverter according to claim 8 or 9, characterized in that the main controller ( 13 ) is constructed as a digital controller with commercially available means of processor technology and that the analog command signal ( 14 ) emitted via a digital-to-analog converter generates the current as the current setpoint -mode controller ( 15 ) can be fed. 11. Inverter according to one of claims 8 to 10, characterized in that to form the amount ( 22 ) of the actual value of the primary current for the current mode controller ( 15 ), the actual value ( 42 ) of the primary current from the compensation current transformer ( 4 ) is rectified with an amount generator ( 23 ). 12. Inverter according to one of claims 1 to 11, characterized in
that each half-bridge circuit ( 1 a, 1 b) is assigned an oscillator ( 24 ) with a downstream pulse generator ( 25 ) in order to generate control pulses for assigned flip-flop memories ( 26 a, 26 b) which can be alternately set and reset , and
that with the setting and resetting of these flip-flop memories ( 26 a, 26 b) downstream control circuits ( 28 a, 28 b), the switching transistors ( 10 ) of the associated half-bridge circuit (1a 1b) can be switched on and off. 13. Inverter according to one of claims 8 to 12, characterized in
that a comparator ( 27 ) forms the input of the current mode controller ( 15 ),
that the comparator ( 27 ) compares the amount ( 22 ) of the actual value of the primary current with the amplitude of the command signal ( 14 ), and
that the predominant amount ( 22 ) of the actual value of the primary current resets the flip-flop memories ( 26 a, 26 b) and switches off the transistors ( 10 ) of the respectively active half-bridge circuit ( 1 a, 1 b). 14. Inverter according to one of claims 1 to 13, characterized in that a common supply voltage ( 40 ) feeds both half-bridge circuits (1a, 1b9 ( Fig. 3). 15. Inverter according to one of claims 1 to 13, characterized in
that each half-bridge circuit ( 1 a, 1 b) is assigned a separate supply voltage ( 40 a, 40 b) and
that the two supply voltages ( 40 a, 40 b) are connected in series ( Fig. 4). 16. Inverter according to claim 15, characterized in
that the series connection of the supply voltages ( 40 a, 40 b) is assigned a monitoring circuit ( 29 ) which measures the symmetry of the capacitive center connection ( 32 ) with respect to the positive supply voltage ( 33 ) and the negative supply voltage ( 34 ), and
that the output signal ( 35 ) of the monitoring circuit ( 29 ) characterizes the asymmetry and the direction thereof. 17. Inverter according to claim 16, characterized in that the output signal ( 35 ) of the monitoring circuit ( 29 ), the control pulses of that half-bridge circuit ( 1 a, 1 b), which is fed by the currently smaller supply voltage ( 40 a or 40 b), blocked or shortened until the symmetry of the supply voltages ( 40 a, 40 b) is restored. 18. Inverter with two asymmetrical half-bridge circuits ( 1 a, 1 b), which alternately drive two separate primary windings ( 3 a, 3 b) of a main transformer ( 3 ), in which a current flows on the secondary winding ( 3 c) of the main transformer ( 3 ) -Doppler rectifier ( 6 ) is connected, characterized in that two half-bridge circuits ( 1 a, 1 b) and a main transformer ( 3 ), possibly provided with the saturable inductors ( 5 a, 5 b), and a current transformer ( 4 ) and a current doubler rectifier ( 6 ), possibly provided with the saturable additional inductors ( 8 a, 8 b), are combined to form the power section ( 2 ). 19. Inverter according to claim 18, characterized in that a power unit ( 2 ) with a drive transformer ( 12 ), drive circuits ( 28 ) and a current mode controller ( 15 ) form a subsystem ( 49 ). 20. Inverter according to claim 19, characterized in
that several subsystems ( 49 ) connected in parallel are supplied together (terminals 33 and 34 ) and have a common output (terminals 47 and 48 ), and
that the reference signal (14) to the inputs of all current-mode controller (15) of the subsystems (45) is supplied, said identical pilot signal (14) from a common master controller (13) of the entire system is generated and the actual value (16) of the Output current represents the current of the overall system. 21. Inverter according to one of claims 12 to 20, characterized in that
that the oscillator ( 24 ) with a downstream pulse generator ( 25 ) is common to all subsystems ( 49 ) and
that the setting of the flip-flop memories ( 26 a, 26 b) for the different half-bridge circuits ( 1 a, 1 b) is distributed over as many phase-shifted times as possible in order to minimize the ripple of the output current. 22. Inverter according to one of claims 18 to 21, characterized in that the power section ( 2 ) on the input side (terminals 33 and 34 ) is connected upstream of a step-up converter circuit ( 36 ) known per se with a mains rectifier ( 37 ), via which the current consumption is switched off the supply network ( 38 ) is controllable. 23. Inverter according to claim 22, characterized in that the step-up converter circuit ( 36 ) of high power is formed from a plurality of step-up converter circuits ( 36 a, 36 b) of smaller power in parallel connection. 24. Inverter according to claim 23, characterized in that the partial step-up converter circuits ( 36 a, 36 b) can be supplied with a setpoint signal for the setpoint ( 41 ) of the input current, which for all partial step-up converter circuits ( 36 a, 36 b) is identical. 25. Inverter according to claim 4, characterized in that the partial step-up converter circuits ( 36 a, 36 b) can be driven out of phase in order to reduce the ripple of the input current. 26. Inverter according to one of claims 18 to 25, characterized in that the clock generation system for the power units ( 2 ) and the step-up converter circuits ( 36 a, 36 b) are synchronized with each other and from the common oscillator ( 24 ) and the common pulse generator ( 25 ) are derived. 27. Inverter according to one of claims 1 to 26, characterized in that the half-bridge circuits ( 1 a, 1 b) have four transistors ( 10 a, 10 b, 10 c, 10 d) with a single drive transformer ( 12 ) with a primary winding ( 12 a) and four separate secondary windings ( 12 b, 12 c, 12 d, 12 e) is provided. 28. Inverter according to one of claims 1 to 27, characterized in that the half-bridge circuits ( 1 a, 1 b) are constructed with transistors of the MOSFET type. 29. Inverter according to one of claims 18 to 28, characterized in
that a power unit ( 2 ) with a step-up converter circuit ( 36 ) in front forms a mechanical module assembly ( 44 ),
that several such module assemblies ( 44 ) and that these module assemblies ( 44 ) are combined in parallel on the input side (terminals 45 and 46 of the rectifier) and on the output side (terminals 47 and 48 of the output connections) to form a power component of high overall power. 30. Inverter according to claim 29, characterized in that each module assembly ( 44 ) has its own cooling profile.