DE102013018247A1 - Half-controlled bridge circuit useful for supplying a resistance welding device with electric current, comprises a first bridging arm and a second bridging arm - Google Patents

Abstract

Half-controlled bridge circuit (10) for supplying a resistance welding device with electric current, comprises a first bridging arm (11) and a second bridging arm (12). Both bridging arms are arranged parallel to each other such that the bridging arms are arranged in a common input voltage. Each bridging arm has at least two series-connected and similar electrical components (13, 14, 15, 16). The first component of the first bridging arm is a semi-conductor switch. The second component of the second bridging arm is a capacitive acting electrical component, preferably a capacitor. Half-controlled bridge circuit (10) for supplying a resistance welding device with electric current, comprises a first bridging arm (11) and a second bridging arm (12). Both bridging arms are arranged parallel to each other such that the bridging arms are arranged in a common input voltage. Each bridging arm has at least two series-connected and similar electrical components (13, 14, 15, 16). The first component of the first bridging arm is a semi-conductor switch. The second component of the second bridging arm is a capacitive acting electrical component, preferably a capacitor. A connection for the primary coil (18) of a welding transformer for the bridging arm is provided between a contact point of the series circuit of the first bridging arm, and between the contact point of the series circuit of the second bridging arm. Independent claims are also included for: (1) a device for electrical supply of a welding gun of the resistance welding device with current comprising the welding transformer, preferably a medium-frequency transformer and the bridge circuit, where the primary coil of the welding transformer forms the bridging arm of the bridge circuit; (2) an inverter, preferably medium-frequency inverter for the resistance welding device with connection means for alternating voltage, the bridge rectifier for rectification of connectable alternating voltage, a direct voltage intermediate circuit for transmission of the rectified alternating voltage to the half-controlled bridge circuit, which is provided at the inverter, for changing the direction of the direct voltage into an alternating voltage with variable frequency; and (3) the resistance welding device comprising the inverter, where the primary coil of the welding transformer is arranged as bridging branch of the half-controlled bridge circuit.

Description

The invention relates to a half-controlled bridge circuit for use in resistance welding and various other components in the field of welding technology, which include such a bridge circuit.

Resistance welding with direct current requires very high currents, which can be in the range of several kiloamperes. To generate these currents transformers are usually used, which are controlled on the primary side by means of a so-called full bridge with at least 4 circuit breakers and which provide the secondary side by means of a downstream rectifier, the welding current available.

The DE 696 18 212 T2 . DE 43 30 916 A1 and US 4,903,189 A describe such known from the prior art solutions.

The use of the full bridge has the disadvantage that due to the number of power semiconductors, the power loss of the arrangement is relatively high. The space must be chosen to be large, so that appropriate cooling measures can be taken.

The object of the invention is now to develop a solution by means of which these disadvantages can be avoided.

To achieve the object, a half-controlled bridge has been developed which completely replaces the full bridge known from the prior art. For generating the welding current, a welding transformer is now used, which is controlled on the primary side by means of the half-bridge according to the invention and supplies the secondary current by means of a downstream diode rectifier, the current flow.

The term "semi-controlled bridge circuit" results from the fact that, in contrast to the known full bridge, only one bridge arm of the bridge circuit according to the invention comprises active power semiconductors, and thus only this bridge arm can be activated actively.

In detail, the bridge circuit according to the invention comprises a first and a second bridge arm, wherein both bridge arms are arranged parallel to each other, so that they can be arranged on a common input DC voltage. Each bridge arm comprises two series-connected and substantially similar electrical components. The bridge arms thus represent in principle two voltage dividers connected in parallel.

The components of the first bridge arm are active semiconductor switches. The second bridge arm comprises predominantly capacitive passive electrical components and is therefore not actively electrically controlled. The components of the second bridge arm are, for example, components from the group of capacitors (eg, electrolytic capacitors).

Between the contact point of the component series connection of the first bridge arm and between the contact point of the component series connection of the second bridge arm a connection for the primary winding of a welding transformer for the realization of the bridge arm is provided in each case. A contact point corresponds in principle to the tap of a voltage divider.

The available for a transformer primary voltage is halved in this arrangement due to the capacitive connection. To compensate for this effect, the transmission ratio of the transformer is compared with the transmission ratio at full bridges adjusted accordingly. For this purpose, for example, the windings could be modified as such that a higher current carrying capacity is ensured.

Compared to the full bridge with power semiconductors to be actively controlled in both bridge arms, only power semiconductors in one of the bridge arms are active in the new concept according to the invention.

The reduced number of power semiconductors compared to full bridges advantageously leads to a reduced power loss in the bridge arms and thus also results in a reduced cooling effort. The reduced power loss is partly due to lower switching losses.

The control of the power semiconductors can be done by a current control. It is additionally recommended, for example by means of a comparator (eg comparator, window comparator) and a reference, to monitor the electrical voltage in the second bridge arm (series connection of capacitors) for a deviation from the desired medium voltage.

It would also be conceivable to use a subordinate voltage regulation, which operates at maximum load depending and / or controlled by the determined deviation with a variable and preferably increased switching frequency. This would make it possible to better utilize the connected welding transformer and protect it from saturation during operation.

The invention also extends to a device for the electrical supply of the welding tongs of a resistance welding device with welding current. Such a device comprises a welding transformer, preferably a medium-frequency transformer, and the half-controlled bridge circuit according to the invention. The primary winding of the welding transformer forms the bridge branch of the bridge circuit.

The inventive concept is suitable regardless of the welding technique for all types of applications in which an alternating direction of voltages is required and the efficiency or efficiency should be increased. Specifically, however, the invention is particularly well suited for use in resistance welding, because very high currents are used here and accordingly high power losses occur, which can be reduced due to the inventive concept. Due to the smaller number of active power semiconductors, the mechanical structure is also more compact.

Due to reduced inductances in the system, there are also fields of application with higher switching frequencies, for example the middle frequency range, as will be explained in detail later.

Preferably, the welding transformer used comprises a first and a second secondary winding coupled together and a preferably symmetrically arranged center tap.

In addition, a rectifier is preferably included, wherein the rectifier consists of a first and a second rectifier branch. The rectifier branches are arranged on the secondary winding such that they can be controlled by means of the first and / or the second secondary winding. Advantageously, both the components of the first and the second rectifier branch are formed symmetrically, wherein the connection of the rectifier to the two-part secondary circuit is realized by means of the center tap. The control of the first and the second rectifier branch by means of substantially symmetrical pulses.

Signal-based and circuit symmetries prevent saturation in the transformer during operation of the device. The symmetrical designs also allow for uniform magnetization, which has an advantageous effect on energy transfer and system performance.

In each rectifier branch of the rectifier, a semiconductor element is provided, which is suitable for controlling the current flow in the rectifier branch (eg thyristor, field effect transistor and the like).

Preferably, a current measurement is also included, which is operated by means of the current in the primary circuit of the primary winding and / or the current in the secondary circuit of the secondary winding for controlling the rectifier.

The control of the rectifier branches by means of the secondary windings preferably in the middle frequency range of 1 kHz to 20 kHz, in particular in the range between 1 kHz to 10 kHz. Especially in the medium-frequency range, the advantages mentioned above in terms of power loss and size are particularly important.

In order to meet the requirements of the customers with regard to the increasingly compact systems, it is proposed to combine components of the aforementioned device, in particular the welding transformer, the rectifier and preferably the bridge circuit, as a structural unit. The device could thus be offered for existing systems, for example as a retrofit kit.

For further improvement, a magnetic field sensor could be arranged on the transformer, the signals of which are evaluated, the semiconductor switching elements also being switched using this evaluation result. This opens up further possibilities for optimizing low-loss operation of the arrangement, because, for example, by evaluating the sensor signals, a supersaturation of the magnetic core of the transformer during operation can be proactively prevented.

Since the invention can be used inter alia to convert a DC voltage into an AC voltage, the protected area also includes an inverter.

This inverter is, in particular, a medium-frequency inverter, which is designed in particular for a resistance welding device.

This inverter includes, among other things, connection means for connecting an AC voltage (eg 3-phase 50/60 Hz power connection) to the inverter. Additionally included is a bridge rectifier for rectifying the AC voltage to provide an intermediate circuit voltage (eg, by means of multi-pulse rectification). This DC intermediate circuit is used to forward the rectified AC voltage to the invention also encompassed by the inverter half-controlled bridge circuit, which ultimately is used to change direction of the DC link voltage and can provide an AC voltage with a variable frequency range for feeding a shitty transformer.

This inverter can be realized compact and with reduced power loss compared to known inverters due to the advantages of the semi-controlled bridge circuit according to the invention.

In particular, even at higher switching frequencies, such as in the mid-frequency range, there are fewer losses than in the conversion compared to known from the prior art full bridges using the same frequency ranges.

Preferably, the invention is used to implement a resistance welding device comprising an inverter as described above, wherein the bridge branch of the semi-controlled bridge circuit, the primary winding of a welding transformer, preferably a medium-frequency welding transformer, with downstream rectifier, preferably synchronous rectifier is arranged.

1 shows a half-taxed bridge with transformer and rectifier.

2 shows components of a resistance welder.

In the 1 shown half taxed bridge 10 includes a first 11 and a second 12 Bridge arm. Both bridge arms 11 . 12 are by means of electrical components 13 . 14 ; 15 . 16 realized as a voltage divider and arranged parallel to each other, wherein these are applied to a DC link voltage L (+), L (-).

With the components 13 . 14 of the first 11 Brückenarmes are semiconductor switch Q1, Q2 belonging to the group of field effect transistors, preferably field effect transistors with freewheeling diode.

For the components 15 . 16 of the second 12 Brückenarmes are mainly capacitive acting electrical components, here in particular capacitors C1, C2.

Between the contact point of the series circuit Q1, Q2 of the first 11 Bridge arm and between the contact point of the series circuit C1, C2 of the second 12 Bridge arm or at the tap of each represented by means of the bridge arms voltage divider is at a specially provided for this purpose and encompassed by the invention semi-controlled bridge connection the primary winding 18 a welding transformer 17 arranged for the realization of the bridge branch.

The welding transformer 17 includes a first 19 and a second 20 coupled to each other secondary winding, which are arranged such that a substantially symmetrical center tap 21 is realized.

In addition, there is a rectifier 22 provided, the rectifier 22 a first 23 and a second 24 Rectifier branch includes. The rectifier branches 23 . 24 are at the secondary windings 19 . 20 arranged so that these by means of the secondary windings 19 . 20 are controllable, wherein in each rectifier branch 22 . 24 of the rectifier 22 a semiconductor element Q5, Q6 is provided which is suitable for the current flow in the rectifier branch 22 . 24 to control.

Advantageously, the semiconductor switching elements Q5, Q6 are controllable switching elements from the group of field effect transistors, in particular the field effect transistors with freewheeling diode.

The determination of the switching time of the semiconductor switching element Q5, Q6 can be determined, for example, taking into account the negative free-wheeling diode voltage. Quasi in real time, the switching times can thus be detected and further processed to refine the electrical control of the arrangement for the purpose of further increasing the efficiency and optimize.

At the center tap 21 is a first welding electrode of a welding gun 25 connected, which may have an electrical potential during the welding process, depending on how the control is done.

The second welding electrode of the welding gun 25 is connected to the contact point of both semiconductor switching elements Q5, Q6, so that this welding electrode can be energized by the semiconductor switching elements Q5, Q6. A current can thus occur between the first welding electrode and the second welding electrode once both welding electrodes of the gun 25 abut simultaneously on a conductive workpiece (not shown).

The semiconductor switching elements Q5, Q6 serve to drive the second welding electrode of the welding gun 25 which is done by means of preferably symmetrical drive pulse trains φ1 and φ2 (not shown).

In comparison to the known full bridge with 4 semiconductor switching elements only 2 semiconductor switching elements are in the new concept in use. Laboratory tests have shown that at higher switching frequencies less losses in the conversion result than in known circuits.

Due to a lower number of power semiconductor components, the mechanical structure of the device requires a smaller size with reduced inductance, which allows the device to be suitable even for higher switching frequencies.

2 shows the resistance welding device according to the invention with inverter 21 and a combination of welding transformer and rectifier 22 , In addition, a control part 23 shown to control the overall arrangement. The welding gun is not shown.

The inverter 21 supplies by means of the inventive half-controlled bridge circuit (transistor inverter) of the primary winding of the welding transformer a drive voltage with a frequency of, for example, 1000 Hz. Various drivers, power supplies and controllers are used to ensure proper operation of the inverter 21 ,

The DC intermediate circuit, which serves to feed the half-controlled bridge circuit according to the invention, is supplied by a 6-pulse bridge rectification, which draws its energy from the 3-phase power network L1-L3 at 50/60 Hz.

In order to influence the resulting power in the secondary circuit of the welding transformer, for example, the pulse width of the driving voltage could be changed. In the rectifier 22 For example, the secondary side rectification of the welding current to supply the welding electrodes of the welding gun (not shown) takes place.

At the secondary windings of the welding transformer also various sensors, inter alia, for temperature monitoring are provided and in the rectifier branch a tap for a constant current control and a secondary voltage attack is provided to monitor the assembly during operation on the secondary side.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 69618212 T2 [0003]
• DE 4330916 A1 [0003]
• US 4,903,189 A [0003]

Claims (14)

Semi-controlled bridge circuit for supplying a resistance welding device with electric current, wherein the bridge circuit ( 10 ) a first ( 11 ) and a second ( 12 ) Bridge arm, both bridge arms ( 11 . 12 ) are arranged parallel to each other, so that they can be arranged on a common input voltage (L +, L-) and wherein each bridge arm ( 11 . 12 ) at least two series-connected and substantially similar electrical components ( 13 . 14 ; 15 . 16 ), where the components ( 13 . 14 ) of the first ( 11 ) Is low-bridge semiconductor switch (Q1, Q2) and characterized in that it is in the components ( 15 . 16 ) of the second ( 12 ) Are low-arm capacitive capacitive elements, in particular capacitors (C1, C2), wherein between the contact point of the series circuit (Q1, Q2) of the first ( 11 ) Bridge arm and between the contact point of the series circuit (C1, C2) of the second ( 12 ) Brückenarmes one connection for the primary winding ( 18 ) of a welding transformer ( 17 ) is provided for the realization of the bridge branch. Semi-controlled bridge circuit according to claim 1, wherein a drive circuit for the semiconductor switches (Q1, Q2) is provided, which is based on a current regulation and wherein preferably a comparison means is provided, by means of which the electrical voltage in the second ( 12 ) Bridge arm can be monitored for a deviation from a reference voltage. Semi-controlled bridge circuit according to claim 2, wherein additionally or alternatively, a voltage regulation is provided, which is realized such that it operates load-dependent and / or using the deviation. Device for the electrical supply of the welding tongs ( 25 ) of a resistance welding device with power, comprising a welding transformer ( 17 ), preferably a medium frequency transformer ( 17 ), and a bridge circuit ( 10 ) according to one of claims 1 to 3, wherein the primary winding ( 18 ) of the welding transformer ( 17 ) the bridge branch of the bridge circuit ( 10 ). Device according to claim 4, wherein the welding transformer ( 17 ) a first ( 19 ) and a second ( 20 ) coupled to each other secondary winding and a preferably symmetrical center tap ( 21 ). Device according to claim 4 or 5, wherein additionally a rectifier ( 22 ), the rectifier ( 22 ) a first ( 23 ) and a second ( 24 ) Rectifier branch, wherein the rectifier branches ( 23 . 24 ) at the secondary winding ( 19 . 20 ) are arranged so that they are replaced by the first ( 19 ) and / or the second ( 20 ) Secondary winding can be controlled. Device according to claim 6, wherein in each rectifier branch ( 22 . 24 ) of the rectifier ( 22 ) at least one semiconductor element (Q5, Q6) is provided, which is suitable for the current flow in the rectifier branch ( 22 . 24 ) to control. Device according to claim 7, wherein the semiconductor element (Q5, Q6) is preferably a semiconductor switching element (Q5, Q6), in particular a semiconductor switching element (Q5, Q6) with freewheeling diode, and wherein means are preferably provided by which the switching instant of the semiconductor switching elements (Q5, Q6), in particular taking into account the free-wheeling diode voltage, can be determined. Device according to one of claims 4 to 8, wherein a current measurement is included, which by means of the current in the primary circuit of the primary winding ( 18 ) and / or the current in the secondary circuit of the secondary winding ( 19 . 21 ) for controlling the rectifier ( 22 ) can be operated. Device according to one of claims 6 to 9, wherein the drive of the rectifier branches ( 22 . 24 ) by means of the secondary windings ( 19 . 20 ) takes place with a frequency in the frequency range from 1 kHz to 20 kHz, in particular in the frequency range between 1 kHz to 10 kHz. Device according to one of claims 4 to 10, wherein at least the welding transformer ( 12 ) and the rectifier ( 22 ) are summarized as a structural unit. Device according to one of claims 4 to 11, wherein at the welding transformer ( 17 ) additionally a magnetic field sensor ( 26 ) is arranged. Inverter, in particular medium-frequency inverter, for a resistance welding device, with connection means for an AC voltage, with bridge rectifier for rectifying the connectable AC voltage, with DC intermediate circuit for forwarding the rectified AC voltage to a likewise comprised of the inverter semi-controlled bridge circuit ( 10 ) according to one of claims 1 to 3 for the purpose of reversing the DC voltage into an AC voltage having a variable frequency. Resistance welding device preferably comprising an inverter according to claim 13, wherein as a bridge branch of the semi-controlled Bridge circuit ( 10 ) the primary winding of a welding transformer ( 17 ) is arranged.

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