AT518371A1 - Circuit arrangement for a frequency converter - Google Patents

Abstract

The invention relates to a circuit arrangement for a frequency converter consisting of a passive, network-side EMC filter and an active part. The active part has the functionality of a current source inverter (CSI) and consists of: a) three AC capacitors (C1, C2, C3) in star connection or three AC capacitors (C12, C13, C23) in delta connection at the input, b) three AC capacitors (CU , CV, CW) in a star connection or three AC capacitors (CWV, CWU, CVU) in delta connection at the output, c) a DC link reactor (D) with four terminals and d) four triple switches (S1, S2, S3, S4) corresponding to the capacitors connect to the throttle (D).

Description

The invention relates to a circuit arrangement for a frequency converter consisting of a passive, network-side EMC filter and an active part.

The state of the art includes 3-phase, passive EMC filters, which, however, are only partially connected in parallel. Active, parallel switchable EMC filters are also known, for example from US 2014/01843315 A1. In this case, it is a power supply unit of a voltage source inverter which can be connected in parallel.

There are also static frequency converters that can transform a constant line frequency or line voltage into a variable output frequency or output voltage.

For a long time, current source inverters (CSI) in thyristor technology with rectangular mains currents and voltage spikes at the output have been known, which load the motor windings. A CSI is in principle 4-quadrant capable and drives an electric machine not only by motor, but feeds, for example, when lowering loads in cranes when the machine is a generator, the resulting energy back into the supply network.

From EP 0886371 A1, as well as DE 1972616 A1 and US 6078162, it is known that a CSI can be connected in parallel by means of thyristors and gate turn-off thyristors and suitable control.

Also known are circuitry from textbooks and scientific papers that propose IGBTs (Insulated Gate Bipolar Transistors) instead of the thyristors.

A CSI has a massive DC reactor as an energy storage, which can be made lighter and cheaper, if the nonlinearity of the

Iron core exploited and the execution is provided as a saturation or Isthmus throttle.

Nevertheless, this design is difficult and expensive and has not been largely replaced by the voltage source inverter (VSI = Voltage Source Inverter). A VSI has an intermediate circuit capacitor as an energy store, wherein a lighter, cheaper electrolytic capacitor can be used. However, such a capacitor has a limited life. US Pat. No. 6,275,393 B1 discloses a VSI with a charging circuit for the DC link capacitor.

In its standard version, the VSI has a three-phase bridge on the mains side consisting of six bipolar, low-cost and low-loss components that charge the DC link capacitor. On the motor side, there are six fast-switching components, currently IGBTs, with integrated, parallel freewheeling diodes in three-phase bridge circuit, which modulates the largely constant voltage of the DC link capacitor to the motor windings in such a way that an adjustable frequency and voltage is generated there. The mains currents are also not sinusoidal and must be improved for sensitive networks by means of external EMC filters.

Very disadvantageous are the output voltages: they are rectangular, with the amplitude of the DC link voltage, and lead - especially with longer motor cables - by reflections to voltage overshoots, which can destroy the motor windings. Again, additional external motor filters are often needed. These are available in different versions on the market.

For very long motor cables, elaborate "sine-motor filters" must be used which make the rectangular output voltage quasi-sinusoidal. Although these generate a largely sinusoidal voltage between the motor phases, but not against ground potential.

In this embodiment, the VSI is not 4-quadrant capable.

If the 4-Qadrantenfähigkeit is indispensable, it usually switches instead of the bipolar three-phase bridge, a circuit with the structure of a motor inverter between the DC link capacitor and input terminals. Between these and the network, a complex, electric filter must be switched to keep the square-wave voltage from the mains. From US 2014/0184315 A1 such a circuit arrangement is known.

The object of the invention is to provide a circuit arrangement for a frequency converter, on the one hand avoids the disadvantages set out above and on the other hand, the production, with economically procurable components, a 4-quadrant capable Stromzwischenkreisumrichters in a compact unit.

The object is achieved by the invention.

The circuit arrangement according to the invention is characterized in that the active part has the functionality of a current intermediate-circuit converter (CSI) and consists of: a) three AC capacitors in star connection or three AC capacitors in delta connection at the input, b) three AC capacitors in star connection or three AC capacitors in delta connection at the output, c) a four-terminal DC reactor and d) four triple-throw switches connecting the capacitors to the reactor respectively. With the invention, it is possible for the first time to produce a compact circuit arrangement which requires in particular only about 30% of the space required in the control cabinet over equivalent circuit arrangements of the prior art and also only about 20% of the wiring effort compared to the prior art.

By way of comparison, it may again be shown that a solution according to the current state of the art would include two common voltage source inverters VSI, a heavy line filter and an equally heavy sine motor filter which generates sinusoidal voltages between the phases but not against earth potential.

With the invention, a parallel switchable circuit arrangement is thus created, which is combined in a compact arrangement. The compact arrangement is surrounded by a high-frequency-tight housing, which, as usual with EMC filters, is connected to PE (Protection Earth).

According to a development of the invention, the AC capacitors are constructed by connecting several capacitors in parallel. As a result, inexpensive, conventional components can be procured on the market, which ensure economic production.

Special and individual versions are also possible due to their cost effectiveness. It is also possible to use self-healing capacitors. The current conventional capacitors used in the prior art have only a limited life.

According to a particular feature of the invention, the DC reactor a) is composed of two magnetically coupled coils with four terminals and b) has a defined leakage inductance, which ensures a common mode rejection between input and output, c) consists of its magnetic core of medium frequency sintered metal (powder : eg Sendust, High Flux, MPP) and d) is designed as a saturation or Isthmusdrossel, where e) the windings of anodized aluminum foils are made, which also form conductors and the layer insulation. Such a throttle ensures the economic production of the frequency converter. Furthermore, the high switching frequency, for example, 100 kHz, the inductor by a factor of 330 smaller and lighter than the CSI with thyristors.

According to a further, alternative feature of the invention, a passive and a symmetrically active part is provided, wherein the circuit arrangement can be connected in parallel and the functions: a) EMC filters for sinusoidal mains currents, b) 4-quadrant frequency converters and c) sine-motor Filter for sinusoidal motor voltages between the phases and against ground potential met and is combined in a compact arrangement, which is surrounded by a high-frequency-tight housing. Due to the possibility of parallel connection according to the invention, the immense advantage is given that with only two sizes, for example 11 kW and 22 kW, an inverter series up to 110 kW can be represented. The potential of saving on development, validation and certification costs is therefore enormously high.

According to a particular, alternative feature of the invention, a passive and an asymmetric active part is provided, wherein the circuit arrangement can be connected in parallel and the functions: a) EMC filter for sinusoidal mains currents and b) 1-quadrant frequency converter with a voltage source at the output and is combined in a compact arrangement, which is surrounded by a high-frequency-tight housing. This feature combination according to the invention makes it possible to offer the most compact solar inverter on the market.

According to a development of the invention an asymmetrical active part is provided, wherein the circuit arrangement is parallel switchable and the functions: a) 1-quadrant frequency converter with a voltage source at the input and b) sine motor filter function for sinusoidal motor voltages between the phases but also met against ground potential and united in a compact arrangement. As is well known, deep hole pumps require motor cables several kilometers in length and a "true" sine motor filter. This is possible with the present invention.

According to one embodiment of the invention, depending on the polarity of the voltage source, this charged or feeds energy into the network. This further increases the savings potential.

According to a very special feature of the invention, the triple-throw switch has the following structural arrangement: a. ) in the star-connected AC capacitors, the neutral point is connected to the reference potential of the control unit and the measurement of the voltage by means of voltage dividers of resistors, which also serve to discharge the capacitors, and / or b. ) the three series circuits of Schottky diodes and J-FETs in "wide bandgap" technology, such as: silicon carbide (SiC) form the three reverse non-conductive diodes electronic switches, and / or c. ) Three mutually galvanically isolated aluminum heat sink are provided for each of the three switches, and / or d. ) the cathodes of the diodes and the drains of the J-FETs are electrically connected through their cooling surfaces through their heat sinks, and / or e. ) the supplement of conductive vanes, for example of graphite, is provided between heat sinks and diodes and J-FETs in order to improve the electrical and thermal conductivity between heat sinks and diodes and J-FETs, and / or f. ) the three J-FETs are driven via the gate signals, whereby the reactor connection is cyclically connected to the AC capacitors, so that the inductor current cyclically commutates between the AC capacitors, and / or g. ) a construction of multiple multilayer printed circuit boards, or parallel plates with insulation layers between the sheets, reduces the effective commutation inductance, and / or h. ) the galvanic isolation of the power supply of the gate driver of GND is carried out by planar transformers whose primary winding is connected to a middle frequency generator, preferably near GND, and whose secondary winding electrically supplies the gate drivers, and / or i.) the windings of the planar transformers produced by spiral tracks on and within the multilayer printed circuit board used and there are ferrite films attached to the top and bottom of the circuit board. The main advantage is that with a 4-way multilayer printed circuit board, the windings of the transformers are free.

The invention will be explained in more detail with reference to exemplary embodiments, which are illustrated in the drawing.

Show it:

1 shows a circuit arrangement for a frequency converter,

Fig. 2a shows a circuit arrangement with the energy into the network and Fig. 2b shows a circuit arrangement with the energy from the mains a voltage source is charged;

Fig. 3a shows a circuit arrangement for an e-car and

Fig. 3b shows a circuit arrangement where a motor operates in the generator mode and Fig. 4 shows a structural arrangement.

Referring to Fig. 1, there is shown a circuit arrangement which is capable of being coupled in parallel and which fulfills the functions: sinusoidal-mode EMC filter, 4-quadrant frequency converter with the functionality of a CSI and sinusoidal motor voltage sine motor filter and is combined in a compact arrangement. It is surrounded by a high-frequency-tight housing, which, as usual with EMC filters, is connected to PE (Protection Earth 6).

The passive part 1 is the network side part of a conventional EMC filter:

The passive part 1 consists of three capacitors Cx1, Cx2, CX3, in star connection and a capacitor Cy, connected to the star point of the capacitors Cxi, Cx2, Cx3, and a switch Sy, which connects the capacitor Cy to the protective conductor 6, if the Neutral of the three-phase network L1, L2, L3 is connected to the protective conductor 6. As known, is open at ungrounded networks. Furthermore, the passive consists of a three-phase inductor DL.

The active part 2 is a symmetrical arrangement with the function of a current intermediate-circuit converter (CSI) consisting of: 1.) Three input capacitors C3, C2, C1 in star connection or C12, C13, C23 in delta connection, which can also be constructed by connecting several AC capacitors in parallel , 2.) A DC intermediate circuit choke D, as energy storage, through which only currents with iD> 0 A flow.

It is composed of two magnetically coupled coils with a defined leakage inductance, which ensures common mode rejection between input and output. It therefore has four connections. - Its magnetic core consists of medium-frequency suitable sintered metal (powder: for example: Sendust, High Flux, MPP) and is designed as a saturation or Isthmusdrossel. - The winding consists of anodized aluminum foils, which also form conductors and layer insulation and make good use of the winding space of the powder core. 3.) 3 output capacitors CW, CV, CU in star connection or CWV, CWU, CVU in delta connection, whereby those can be constructed by parallel connection of several AC capacitors. 4.) A matrix of four triple switches S1, S2, S3 and S4 between the capacitors and the DC reactor. 5.) a control and regulation unit 3, where the measured values of the voltages of all capacitors and that of the inductor current iD are processed and achieved by suitable switch positions of S1, S2, S3 and S4, that: a. ) sinusoidal input currents iL1, il_2 and iL3 arise, b. ) a defined, for example, the passage power proportional current iD flows, whereby the parallel connection of devices of different rated power is ensured and c. ) sinusoidal output voltages of adjustable frequency and amplitude between U, V and W are generated.

Like the CSI with thyristors, energy can be fed back into the grid when the motor becomes a generator. The described arrangement is therefore d. ) 4-quadrant capable.

Since current is intended to flow through the DC intermediate-circuit choke D only in one direction, non-conductive components are ideal for the switches S1 to S4 backward. Thyristors had this feature and were used in conventional CSI.

However, this invention needs faster, reverse non-conductive components that are currently difficult or unavailable in the component market.

Currently, you have to make do with a series circuit of diode and backward conductive components. These are, for example, Schottky diodes and J-FETs (junction field effect transistors, normally-on) both in "wide bandgap" technology such as SiC (Silicon Carbide). This is because the switching frequency should be relatively high, for example 100 kFlz, in order to keep the capacitance values of the capacitors and the necessary inductance of the current intermediate circuit choke as small as possible.

Referring to Figures 2a and 2b, the 1-quadrant operation is shown with a passive and an asymmetric active part, the circuitry being switchable in parallel and having the functions: a) EMC filters for sinusoidal power supplies, b) 1-quadrant frequency converters and is combined in a compact arrangement surrounded by a high-frequency-tight housing and the DC reactor (D) a) is constructed of two magnetically coupled coils with four terminals and b) has a defined leakage inductance, which ensures a common mode rejection between input and output , c) their magnetic core consists of medium-frequency sintered metal (powder: eg Sendust, High Flux, MPP) and d) is designed as a saturation or Isthmusdrossel, where e) the windings of anodized aluminum foil, which form both conductors and the layer insulation ,

The circuit arrangement is self-explanatory and the reference numerals correspond to the components in FIG. 1.

If only from a voltage source, such as a battery or a solar cell energy to be fed into the grid, this is possible in 1-quadrant operation.

Fig. 2b shows an arrangement which is a voltage source, such as a battery of an electric car, which is loaded from the network. For this purpose, in contrast to Fig. 2a, the voltage source is reversed.

According to FIGS. 3a and 3b, the one-quadrant operation is shown with only one asymmetric active part being provided, wherein the circuit arrangement can be connected in parallel and the functions: a) 1-quadrant frequency converter with a voltage source at the input and b) a sine wave Motor filter function for sinusoidal motor voltages between the phases but also against ground potential fulfilled and united in a compact arrangement.

FIG. 3a shows an arrangement which drives a motor, for example in an e-car, from a voltage source, for example a rechargeable battery or a fuel cell.

Fig. 3b shows an arrangement where a motor, for example, in an electric car when braking or downhill, in generator mode energy back into a reversed voltage source, such as a battery.

Each circuit arrangement is self-explanatory and the reference numerals correspond to the components in FIG. 1.

According to Fig. 4, the structural arrangement is set forth:

4 shows, for example, one of the four triple-throw switches S1, S2, S3, S4 from FIG. 1, which are all of a similar design, with real components in their inventive, constructive arrangement:

The AC capacitors C1, C2, C3 are connected in star here; the neutral point is connected to the reference potential GND of the control and regulation unit 3.

The measurement of uC1, uC2 and uC3 is done by means of voltage dividers from resistors. These also serve to discharge the capacitors.

The measurement of the current through the DC intermediate circuit choke D by means of a current transformer outside of S1.

The three series circuits of Schottky diodes D1, D2, D3 and J-FETs F1, F2, F3 form the 3 backward non-conducting electronic switches of S1.

Three galvanically isolated heat sinks KK1, KK2, KK3 made of aluminum are provided. For each of the three switches a separate heat sink KK1, KK2, KK3 is provided.

The cathodes of the diodes and the drains of the J-FETs are electrically connected via their cooling surfaces through their heat sinks.

The supplement of guide vanes, for example of graphite, between the heat sink KK1, KK2, KK3 and the cooling surfaces of the diodes and J-FETs improves the electrical and thermal conductivity between the heat sink KK1, KK2, KK3 and diodes and J-FETs.

The root of the triple switch S1 here form the three sources of the J-FETs, which is connected to one of the four throttle ports.

The three J-FETs are driven via the gate signals G11, G12, G13, whereby the throttle terminal is cyclically connected to C1, C2, C3.

As a result, the inductor current iD commutes cyclically between C1, C2, C3.

The control is designed so that always at least one of the 3 J-FETs is switched on, so that the inductor current iD is never interrupted.

A multi-layered printed circuit board design or, for larger powers, parallel sheets with insulation layers between the sheets, reduces the effective commutation inductance, allowing for higher switching frequencies.

The control unit 3 and the gates of the 3 J-FETs are galvanically isolated. This can be done by means of available components in the gate drivers.

The power supply to the gate drivers must also be galvanically isolated from GND. This can be achieved by means of planar transformers whose primary winding is connected to a mid-frequency generator, near GND, and whose secondary winding electrically supplies the gate drivers.

The windings of the planar transformers are realized by spiral-shaped conductor tracks in and on the multilayer printed circuit board used. Above and below the spiral tracks, ferrite foils on the top and bottom of the board improve the efficiency of the planar transformers and reduce noise.

Claims (8)

claims: 1. Circuit arrangement for a frequency converter consisting of a passive, network-side EMC filter and an active part, characterized in that the active part has the functionality of a current source inverter (CSI) and consists of: a) three AC capacitors (C1, C2, C3) in Star connection or three AC capacitors (C12, C13, C23) in delta connection at the input, b) three AC capacitors (CU, CV, CW) in star connection or three AC capacitors (CWV, CWU, CVU) in delta connection at the output, c) a DC intermediate circuit choke (D ) with four connections and d) four triple switches (S1, S2, S3, S4) which connect the capacitors to the choke (D) accordingly. 2. A circuit arrangement according to claim 1, characterized in that the AC capacitors (CU, CV, CW, CWV, CWU, CVU) are constructed by parallel connection of a plurality of capacitors. 3. A circuit arrangement according to claim 1 or 2, characterized in that the DC reactor (D) a) is constructed of two magnetically coupled coils with four terminals and b) has a defined leakage inductance, which ensures a common mode rejection between input and output, c) her magnetic core of medium frequency sintered metal (powder: eg: Sendust, High Flux, MPP) exists and d) is designed as a saturation or Isthmusdrossel, where e) the windings of anodized aluminum foils, which also form conductors and the layer insulation. 4. Circuit arrangement according to at least one of claims 1 to 3, characterized in that a passive and a symmetrically active part is provided, wherein the circuit arrangement can be connected in parallel and the functions: a) EMC filter for sinusoidal mains currents, b) 4-quadrant Frequency converter and c) sine motor filter for sinusoidal motor voltages between the phases and also against earth potential and is combined in a compact arrangement, which is surrounded by a high-frequency-tight housing. 5. Circuit arrangement according to at least one of claims 1 to 3, characterized in that a passive and an asymmetric active part is provided, wherein the circuit arrangement can be connected in parallel and the functions: a) EMC filter for sinusoidal mains currents and b) 1-quadrant Frequency converter with a voltage source at the output and is combined in a compact arrangement, which is surrounded by a high-frequency-tight housing. 6. Circuit arrangement according to at least one of claims 1 to 5, characterized in that an asymmetric active part is provided, wherein the circuit arrangement can be connected in parallel and the functions: a) 1-quadrant frequency converter with a voltage source at the input and b) sinusoidal motor Filter function for sinusoidal motor voltages between the phases but also against ground potential and is combined in a compact arrangement. 7. Circuit arrangement according to at least one of claims 1 to 6, characterized in that, depending on the polarity of the voltage source, this is charged or feeds energy into the network. 8. Circuit arrangement according to at least one of claims 1 to 7, characterized in that the triple-throw switch (S1, S2, S3, S4) has the following constructive arrangement: a. ) is connected in the star connected AC capacitors (C1, C2, C3), the neutral point to the reference potential (GND) of the control unit and the measurement of the voltage (? as indicated) (uC1, uC2 and uC3) by means of voltage dividers of resistors takes place, these also serve to discharge the capacitors, and / or b. ) the three series circuits of Schottky diodes (D1, D2, D3 and J-FETs F1, F2, F3) in "wide bandgap" technology such as: silicon carbide (SiC) forming the three reverse non-conducting diode electronic switches, and / or c. ) are provided from each other galvanically isolated aluminum heat sink (KK1, KK2, KK3) for each of the three switches, and / or d. ) the cathodes of the diodes and the drains of the J-FETs are electrically connected via their cooling surfaces through their heat sinks, and / or e. ) the supplement of conductive vanes, for example made of graphite, between the heat sink and diodes and J-FETs is provided to improve the electrical and thermal conductivity between the heat sink and diodes and J-FETs, and / or f. ) the three J-FETs are driven via the gate signals (G11, G12, G13), whereby the choke connection is cyclically connected to the AC capacitors (C1, C2, C3), so that the choke current (iD) cyclically between the AC capacitors (C1, C2) C2, C3) commutes, and / or g. ) a construction of multiple multilayer printed circuit boards, or for larger power parallel sheets with insulating layers between the sheets, which reduces effective Kommutierungsinduktivität, and / or h. ), the galvanic isolation of the power supply of the gate driver of GND is performed by means of planar transformers whose primary winding is connected to a middle frequency generator, preferably near GND, and whose secondary winding electrically supplies the gate drivers, and / or i. ) The windings of the planar transformers are produced by spiral-shaped conductor tracks on and within the multilayer printed circuit board used and there are ferrite foils attached to the top and bottom of the circuit board.