DE102017220109A1 - power converters - Google Patents

Abstract

Power converter (1), which is designed to drive an electrical load (2), wherein the power converter (1) comprises:
- A number of inverter half-bridges (3, 4, 5) each having at least two switching means (6, 7, 8, 9, 10, 11), wherein the inverter half-bridges (3, 4, 5) each having a first state in which an output (12, 13, 14) of the respective inverter half-bridge (3, 4, 5) is connected to a positive intermediate circuit potential (UZK_P) and each have a second state, during which an output (12, 13, 14) of the respective inverter half-bridge (3, 4, 5) is connected to a negative intermediate circuit potential (UZK_N), wherein an output (12, 13, 14) of the respective inverter half-bridge (3, 4, 5) with an associated terminal (u, v, w) of the electrical load (2) is connected,
- A first filter half-bridge (15) having at least two switching means (16, 17), wherein the first filter half-bridge (15) has a first state, during which an output (18) of the first filter half-bridge (15) with the positive DC link potential (UZK_P) is connected, and has a second state, during which the output (18) of the first filter half-bridge (15) is connected to the negative DC link potential (UZK_N),
- A first capacitive filter element (19), which is looped between the output (18) of the first filter half-bridge (15) and a ground potential, and
- A control unit (20) adapted to adjust the state of the first filter half-bridge (15) in dependence on the states of the inverter half-bridges (3, 4, 5).

Description

The invention relates to a power converter.

Conventional power converters, for example in the form of inverters or frequency converters, typically use a B6 bridge circuit (designed in a wide power range as IGBT module with 6 switches and 6 freewheeling diodes) for the voltage and frequency position on the connected three-phase motors.

Due to the odd number of inverter branches, a sum of the inverter output voltages is generally not equal to zero. The existing total voltage drives a ground current that closes across the grid. The earth leakage current causes faults and triggers fault current (RCD) circuit breakers.

The invention has for its object to provide a power converter available that causes the least possible interference, in particular causes the lowest possible fault currents.

The invention solves this problem by a power converter according to claim 1.

The power converter according to the invention, for example in the form of a frequency converter, is designed to drive an electrical load, for example in the form of a three-phase motor.

The power converter conventionally has a number, for example three, of inverter half-bridges each having at least two switching means. The switching means are typically semiconductor switching means, for example IGBTs. In that regard, reference is also made to the relevant specialist literature.

The inverter half-bridges each have a first (switching) state, during which an output of the respective inverter half-bridge is connected to a positive intermediate circuit potential. The inverter half-bridges each have a second state, during which an output of the respective inverter half-bridge is connected to a negative DC link potential. In that regard, reference is also made to the relevant specialist literature.

An output of the respective inverter half-bridge is connected to a respectively associated terminal of the electrical load.

The power converter further has a first filter half-bridge with at least two switching means, for example in the form of semiconductor switching means. The first filter half-bridge has a first state, during which an output of the first filter half-bridge is connected to the positive intermediate circuit potential, and has a second state, during which the output of the first filter half-bridge is connected to the negative intermediate circuit potential.

The power converter further includes a first capacitive filter element connected between the output of the first filter half-bridge and ground potential (ground).

The power converter further comprises a control unit, for example in the form of a microprocessor and associated program memory, which is adapted to set the state of the first filter half-bridge in dependence on the states of the inverter half-bridges.

In one embodiment, the control unit is configured to set the first state of the first filter half-bridge when one of the inverter half-bridges has the first state, and to set the second state of the first filter half-bridge when one of the inverter half-bridges the second state having.

In one embodiment, an impedance of the capacitive filter element corresponds to an impedance between an output of one of the inverter half-bridges and ground potential.

In one embodiment, the power converter is a frequency converter.

In one embodiment, the electrical load is a three-phase electric motor, wherein the power converter has three, in particular exactly three, inverter half-bridges, wherein an output of the first inverter half-bridge is connected to a first phase terminal of the electric motor, an output of the second inverter half-bridge a second phase terminal of the electric motor is connected, and an output of the third inverter half-bridge is connected to a third phase terminal of the electric motor.

In one embodiment, the power converter further comprises a second filter half-bridge with at least two switching means, wherein the second filter half-bridge has a first state, during which an output of the second filter half-bridge is connected to the positive DC link potential, and has a second state during which the output of the second filter half-bridge is connected to the negative DC link potential. The power converter further comprises a second capacitive filter element connected between the output of the second filter half-bridge and the ground potential is looped. The power converter further has a third filter half-bridge with at least two switching means, the third filter half-bridge having a first state, during which an output of the third filter half-bridge is connected to the positive DC link potential, and has a second state, during the the output of the third filter half-bridge is connected to the negative DC link potential. The power converter further comprises a third capacitive filter element connected between the output of the third filter half-bridge and the ground potential. For this embodiment, the control unit is configured to set a state of the first filter half-bridge, the second filter half-bridge and the third filter half-bridge depending on the states of the inverter half-bridges.

In one embodiment, the power converter further comprises a rectifier, which generates a DC voltage from an AC line voltage, and a DC / DC converter, which is adapted to generate from the DC voltage an adjustable DC link voltage, wherein the DC link voltage of a potential difference between the positive and the negative DC link potential. In this embodiment, the control unit is designed to control the switching means of the inverter half-bridges in block timing. With regard to the known per se block timing is also referred to the relevant literature.

According to the invention, an even number of inverter branches is created by means of at least one additional inverter branch or at least one filter branch. The at least one filter half-bridge is controlled in such a way that the resulting sum voltage results in zero over all output voltages of the conventional inverter half-bridges and the output voltage of the at least one filter half-bridge at any time. If this at least one filter branch drives a filter capacitor having the same capacitance as the parasitic coupling capacitance, then an earth coupling current across the network is completely avoided. An interference emission due to earth leakage currents in the network and false tripping of the residual current circuit breaker no longer occur.

• 1 eine erste Ausführungsform eines erfindungsgemäßen Stromrichters in Form eines Frequenzumrichters und
• 2 eine weitere Ausführungsform eines erfindungsgemäßen Stromrichters in Form eines Frequenzumrichters.

The invention will be described in detail below with reference to the drawings. Hereby show:

• 1 a first embodiment of a power converter according to the invention in the form of a frequency converter and
• 2 a further embodiment of a power converter according to the invention in the form of a frequency converter.

1 shows a first embodiment of a power converter according to the invention 1 in the form of a frequency converter.

The power converter 1 is for driving an electrical consumer 2 formed in the form of a three-phase electric motor.

The power converter 1 has a rectifier 31 which conventionally generates a DC voltage UG from a three-phase alternating mains voltage by means of rectification.

The power converter 1 further includes a DC / DC converter 32 on, which is adapted to the DC voltage UG an intermediate circuit voltage UDC to generate with adjustable voltage level. The DC link voltage UDC corresponds to a potential difference between a positive DC link potential UZK_P and a negative DC link potential UZK_N ,

The DC link voltage UDC is by means of a DC link capacitor 33 buffered.

The power converter 1 further includes a number of three inverter half-bridges 3 . 4 . 5 on, in a conventional manner, a conventional inverter 34 form. The first inverter half-bridge 3 of the three inverter half-bridges 3 . 4 . 5 has conventionally two semiconductor switching means 6 and 7 on. Accordingly, the second inverter half-bridge 4 of the three inverter half-bridges 3 . 4 . 5 two semiconductor switching means 8th and 9 on and the third inverter half-bridge 5 of the three inverter half-bridges 3 . 4 . 5 has two semiconductor switching means 10 and 11 on. The inverter half-bridges 3 . 4 . 5 are each with the DC link voltage UDC applied.

The inverter half-bridges 3 . 4 . 5 each have a first state during which an output 12 . 13 or. 14 the respective inverter half-bridge 3 . 4 or. 5 with the positive DC link potential UZK_P is connected, and each have a second state, during which an output 12 . 13 or. 14 the respective inverter half-bridge 3 . 4 or. 5 is connected to the negative DC link potential UZK_N.

An exit 12 the first inverter half-bridge 3 is with an associated connection u of the electric motor 2 connected, an exit 13 the second inverter half-bridge 4 is connected to an associated terminal v of the electric motor 2 connected and an exit 14 the third inverter half bridge 5 is with an associated terminal w of the electric motor 2 connected.

Far right is a branch with a diode 36 and a semiconductor switching means 37 shown, the operating state-dependent a braking resistor 38 fed. In that regard, reference is also made to the relevant specialist literature.

The power converter 1 further has a filter half-bridge 15 with a first semiconductor switching means 16 and a second semiconductor switching means 17 on. The filter half-bridge 15 has a first state during which an output 18 the filter half-bridge 15 with the positive DC link potential UZK_P and a second state during which the output is connected 18 the filter half-bridge 15 with the negative DC link potential UZK_N connected is. A capacitive filter element 19 is between the exit 18 the filter half-bridge 15 and a ground potential (earth) looped. The filter half-bridge 15 in connection with the capacitive filter element 19 forms an active ground current filter.

The power converter 1 further has a control unit 20 which is adapted to the state of the filter half-bridge 15 depending on the states of the inverter half-bridges 3 . 4 . 5 adjust.

In principle, the semiconductor switch 16 closed and the the semiconductor switch 17 open while across all inverter half-bridges 3 . 4 . 5 Overall, only a single one of the top switches 6 . 8th or. 10 closed is. Accordingly, the semiconductor switch 16 opened and the semiconductor switch 17 closed while across all inverter half-bridges 3 . 4 . 5 All in all, only a single lower switch 7 . 9 or. 11 closed is. In total, this always two upper and two lower semiconductor switches are driven.

Control signals for the semiconductor switches 16 . 17 can directly from the states or switching patterns of the semiconductor switches 6 to 11 be derived. Earth current compensation intervenes before any disturbances occur. In other words, forms the filter half-bridge 15 in connection with the capacitive filter element 19 an active ground current filter, for example, in the power converter 1 can be integrated and the leakage currents compensated directly.

To the outside, there are no problems caused by leakage currents, such as the tripping of Fl circuit breakers or inadmissible EMC faults.

The semiconductor switches 16 and 17 are considerably smaller in terms of switchable electrical power than the semiconductor switches 6 to 11 , However, they should be the same voltage class as the semiconductor switches 6 to 11 (1200 V for 3-phase devices). However, current peaks only occur for a short time, resulting in extremely low power loss (which may allow direct installation in / on a printed circuit board).

The capacitive filter element 19 or the filter capacitor 19 is representative of a predominantly capacitive filter. The impedance of the capacitive filter element 19 ideally corresponds exactly to the impedance, the inverter formed from the inverter half-bridges 3 . 4 . 5 sees at its (active) exit to earth. In this case, essentially coupling capacitances of a motor line and a motor winding play a role.

A possibly present in conventional converters Y-capacitor can be omitted, since its function by the means of the semiconductor switch 16 . 17 switched capacitive filter element 19 is taken over.

The capacitive filter element 19 is initially only suitable for an assigned motor cable. Other constellations, however, can be achieved by modular design of the capacitive filter element 19 or an adapted control pattern in the filter branch are taken into account.

Power converters with three current transformers in the output can detect the leakage current and the appropriate control pattern for the semiconductor switches 16 . 17 calculate in the filter branch "automatically".

The active outlet filter 16 . 17 . 19 itself can be executed as an option module, which can be integrated if necessary in the power converter or separately from the converter and can be coupled to the power converter.

The described earth current filter topology with the filter branch 16 . 17 and the single capacitive filter element 19 is preferably used when the inverter 34 comprising the inverter bridges 3 . 4 . 5 (always) in Vollaussteuerung or Blocktaktung is operated. This is advantageous if and only if the voltage position over the before the actual inverter 34 switched fast DC / DC converter 32 he follows. In this case, the inverter can 34 the fundamental wave in the form of a sine wave modulation or by means of block timing (block control) switch to its output. A zero voltage does not occur in the switching pattern, so that the earth leakage currents with the help of the described, directly the inverter 34 assigned arrangement can be fully compensated.

In the 1 illustrated embodiment with a single additional filter branch can only fully compensate the leakage current when an external conductor voltage is switched. If the power converter 1 is not operated in block timing, arises during the times in which a zero voltage is switched in the PWM cycle, ie all upper semiconductor switches 6 . 8th . 10 are closed (switching pattern [1, 1, 1]) or all lower switches 7 . 9 . 11 are closed (switching pattern [0, 0, 0]), furthermore an imbalance between upper and lower switches.

2 shows a further embodiment of a power converter according to the invention 1 in the form of a frequency converter, which avoids leakage currents even at zero voltages in the PWM cycle.

The power converter 1 indicates this in addition to the in 1 shown power converter, a second filter half-bridge 21 with two semiconductor switching means 22 . 23 on, with the second filter half-bridge 21 has a first state during which an output 24 the second filter half-bridge 21 with the positive DC link potential UZK_P is connected, and has a second state during which the output 24 the second filter half-bridge 21 with the negative DC link potential UZK_N connected is. A second capacitive filter element 25 is between the exit 24 the second filter half-bridge 21 and the earth potential is looped in.

Next is a third filter half-bridge 26 with two semiconductor switching means 27 . 28 provided, the third filter half-bridge 26 has a first state during which an output 29 the third filter half bridge 26 with the positive DC link potential UZK_P is connected, and has a second state during which the output 29 the third filter half bridge 26 with the negative DC link potential UZK_N connected is. A third capacitive filter element 30 is between the exit 29 the third filter half bridge 26 and the earth potential is looped in.

The control unit 20 is adapted to a state of the first filter half-bridge 15 , the second filter half-bridge 21 and the third filter half-bridge 26 depending on the states of the inverter half-bridges 3 . 4 . 5 adjust.

At the in 2 In the embodiment shown, a total of three filter branches are used for ground current compensation. The control of these filter branches is done as described according to the output switching pattern of the inverter half-bridges 3 . 4 . 5 in the inverter 34 , At zero voltage in the inverter 34 All 3 additional upper or all 3 additional lower semiconductor switches are activated.

A tripping of a residual current circuit breaker 35 due to a zero-voltage switching pattern can therefore be reliably avoided.

Parasitic coupling capacitances are through discrete capacitors 39 . 40 and 41 displayed.

Claims (7)

Power converter (1), which is designed to drive an electrical load (2), wherein the power converter (1) comprises: - a number of inverter half-bridges (3, 4, 5) each having at least two switching means (6, 7; , 9, 10, 11), - wherein the inverter half-bridges (3, 4, 5) each have a first state, during which an output (12, 13, 14) of the respective inverter half-bridge (3, 4, 5) is connected to a positive intermediate circuit potential (UZK_P), and in each case have a second state, during which an output (12, 13, 14) of the respective inverter half-bridge (3, 4, 5) is connected to a negative intermediate circuit potential (UZK_N), and - wherein an output (12, 13, 14) of the respective inverter half-bridge (3, 4, 5) with an associated terminal (u, v, w) of the electrical load (2) is connected, characterized in that - Power converter (1) further comprises - a first filter half-bridge (15) with at least two Switching means (16, 17), wherein the first filter half-bridge (15) has a first state, during which an output (18) of the first filter half-bridge (15) is connected to the positive intermediate circuit potential (UZK_P), and a second state during which the output (18) of the first filter half-bridge (15) is connected to the negative intermediate circuit potential (UZK_N), - a first capacitive filter element (19) connected between the output (18) of the first filter half-bridge (15 ) and a ground potential is connected, and - a control unit (20) which is adapted to adjust the state of the first filter half-bridge (15) in dependence on the states of the inverter half-bridges (3, 4, 5). Power converter (1) to Claim 1 characterized in that - the control unit (20) is adapted to set the first state of the first filter half bridge (15) when one of the inverter half bridges (3, 4, 5) has the first state and the second state the first filter half-bridge (15) set when one of the inverter half-bridges (3, 4, 5) has the second state. Power converter (1) to Claim 1 or 2 , characterized in that - an impedance of the capacitive filter element (19) of an impedance between an output (12, 13, 14) corresponds to one of the inverter half-bridges (3, 4, 5) and ground potential. Power converter (1) according to one of the preceding claims, characterized in that - the power converter (1) is a frequency converter. Power converter (1) according to one of the preceding claims, characterized in that - the electrical load (2) is a three-phase electric motor, wherein the power converter (1) has three inverter half-bridges (3, 4, 5), wherein an output (12 ) of the first inverter half-bridge (3) is connected to a first phase connection (u) of the electric motor (2), an output (13) of the second inverter half-bridge (4) is connected to a second phase connection (v) of the electric motor (2) and an output (14) of the third inverter half bridge (5) is connected to a third phase terminal (w) of the electric motor (2). Power converter (1) according to one of the preceding claims, characterized in that - the power converter (1) further comprises: - a second filter half-bridge (21) with at least two switching means (22, 23), wherein the second filter half-bridge (21 ) has a first state during which an output (24) of the second filter half-bridge (21) is connected to the positive intermediate circuit potential (UZK_P) and has a second state during which the output (24) of the second filter half-bridge ( 21) is connected to the negative DC link potential (UZK_N), - a second capacitive filter element (25), which is looped between the output (24) of the second filter half-bridge (21) and the ground potential, - a third filter half-bridge (26 ) with at least two switching means (27, 28), wherein the third filter half-bridge (26) has a first state, during which an output (29) of the third filter half-bridge (26) with the positive intermediate circuit potential (UZK_P) is connected, and has a second state during which the output (29) of the third filter half-bridge (26) is connected to the negative DC link potential (UZK_N), and - a third capacitive filter element (30) connected between the output (29 ) of the third filter half-bridge (26) and the ground potential is looped in, - wherein the control unit (20) is adapted to a state of the first filter half-bridge (15), the second filter half-bridge (21) and the third filter Half-bridge (26) depending on the states of the inverter half-bridges (3, 4, 5) to set. Power converter (1) according to one of the preceding claims, characterized in that - the power converter (1) further comprises: - a rectifier (31) which generates a DC voltage (UG) from an AC line voltage, and - a DC / DC converter ( 32), which is designed to generate from the DC voltage (UG) an intermediate circuit voltage (UZK), - wherein the control unit (20) is adapted to the switching means (6, 7; 8, 9; 10, 11) of the inverters -Helbbrücken (3, 4, 5) in block timing to control.

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