DE102015003225A1 - inverter - Google Patents

Abstract

An inverter is described, with an inverter bridge, which converts the output voltage of a DC voltage source into a three-phase AC voltage and outputs via three phase conductors and a neutral conductor, with a sinusoidal filter connected downstream of the inverter bridge, and with a choke coil arrangement connected downstream of the sinusoidal filter, each having one choke coil winding for each phase conductor and for the neutral conductor, the four inductor windings of the inductor assembly being disposed on a common inductor core, all three inductor windings connected to the phase conductors having the same winding sense, and the fourth inductor winding connected in the neutral conductor being opposite to the other three Winding coil windings is wound.

Description

The invention relates to an inverter, comprising an inverter bridge, which converts the output voltage of a DC voltage source into a three-phase AC voltage and outputs via three phase conductors and a neutral conductor, with a sinusoidal filter connected downstream of the inverter bridge, and with a choke coil assembly connected downstream of the sinusoidal filter, each having one choke coil winding for each Phase conductor and has for the neutral conductor.

Such an inverter fulfills the function of converting the output voltage of a DC voltage source into a multi-phase AC voltage, which can then be used by electrical consumers and / or fed into a local or public AC network. Such inverters are used in particular in electrical systems for the conversion of renewable energies, such as wind power or photovoltaic systems for use.

Inverters of this type have an inverter bridge, which consists of a bridge circuit of several power semiconductors, which are controlled in a clocked manner. In addition, various filter circuits consisting of inductive and capacitive components are generally provided. Commonly used is the use of a so-called sine filter, which is used to shape the output from the inverter bridge output voltage. At the same time, the sine-wave filter acts as a low-pass filter, which filters out the high clock frequencies (in the size of, for example, 18 kHz) compared to the frequency of the alternating voltage generated, which are used to drive the power semiconductors of the inverter bridge.

A problem of the filter arrangements is that they have resonance points. Especially with inverters with sine-wave filters, the impedance of the filter and, in addition, the generally unknown and varying terminal impedances may shift resonance points to the range of the AC bridge clock frequency.

From the German patent application DE 10 2005 031 372 A1 is an inverter with a trained by longitudinal throttling and capacitance sine wave filter known. Specifically described is a three-phase inverter without neutral for operating a motor, in which by the interaction of sine filter and parasitic capacitances of the motor supply a resonance problem can occur. The resonances can lead to voltage pulses and thus to overvoltages on the phase conductors. When such effects occur, it is provided to connect the inverter with a current-compensated choke as an external component in order to detune the resonant circuit and thereby eliminate the resonances and protect the motor.

Inverters with a four-wire system can cause resonance excitations on all three phase conductors, closing the circuit via the neutral conductor. With a synchronous clocking of the bridge power semiconductors, such a resonance effect can thus lead to overloading of the neutral conductor.

In order to avoid this effect, a choke coil arrangement connected downstream of a sine-wave filter is provided in an inverter produced in series by the applicant, as described in US Pat 2 outlined. Here, a separate inductor is connected in each phase conductor as well as in the neutral conductor, which consists of a choke coil core with an applied thereto inductor coil winding. The choke coils of the phase conductors form in each case a so-called T-type filter with the longitudinal choke and capacitors of the sine-wave filter. The purpose of this arrangement is to set a minimum impedance so as to keep the resonant frequencies in a non-critical range in all cases.

A disadvantage of this arrangement is that the four inductors designed as individual components require a relatively high cost and a relatively large amount of space when installed in a device housing.

It set itself the task of creating an inverter that is overall space-saving and cheaper to produce.

This object is achieved in that the four inductor windings of the inductor arrangement are arranged on a common choke coil core, that all three switched in the phase conductors inductor windings have the same sense of winding, and that the fourth inductor winding, which is connected in the neutral, in the opposite direction to the other three inductor windings is wound.

The inventively designed inverter thus has a designed as a single component throttle, which acts as a current-compensated reactor (common mode choke) for all three phase conductors and forms a differential current choke (push-pull choke) for the neutral conductor in combination with the phase conductors.

The windings of the common-mode push-pull throttle are preferably on a ring core for Storage chokes, consisting of iron powder, ferrite or a similar material, applied and form by a relatively small number of turns initially very small inductances. The phase windings of the common mode push-pull choke are thus only effective for currents flowing synchronously on all three phase conductors against the neutral as inductance and form in this case by the good coupling on the common inductor core a series circuit with the neutral conductor winding and thus a relevant inductance. As a result, the resonant circuit frequency detunes itself by the occurrence of the currents in the direction of the neutral conductor and thus eliminates disturbing or even destructive acting resonance effects.

In the following, the invention will be explained in more detail with reference to the drawing. The 1 shows an inventively designed inverter; the 2 represents for comparison a inverter according to the prior art. The 3 shows a sketch of a possible structure of a usable in an inventively designed inverter common mode push-pull throttle.

The 2 shows schematically a known by a serial device of the Applicant construction principle of an inverter 1' , whose electrical output power is preferably for feeding into a public alternating voltage network 6 is provided. With the input of the inverter 1' is a DC voltage source 5 connected, which may be formed for example by the solar generator of a photovoltaic system.

The actual inverter 1' belonging components are summarized by a dashed border. These components include an inverter bridge 2 , one of the inverter bridge 2 downstream sine filter 3 , as well as one on the sine filter 3 following inductor arrangement 7 , Also shown here is an optional EMC filter 4 ,

The structure of an inverter bridge 2 is here assumed to be fundamentally known and therefore not described in detail at this point. In a three-phase system has an inverter bridge 2 such an arrangement of three half-bridges, each consisting of two power semiconductor switches, which are controlled in clocked by an electronic control circuit also not shown here.

The relatively high clock frequencies of the drive pulses used in this case are caused by a sine-wave filter acting as a low-pass filter 3 on the output lines L1, L2, L3, N of the inverter bridge 2 filtered out. The sine filter 3 has for each phase conductor L1, L2, L3 each have a longitudinal throttle 31 and a capacitor connected to the neutral N 32 on. The sine filter 3 also influences the pulse shape of the inverter output voltage.

The sine-wave filter 3 downstream is a choke coil assembly 7 in each case one choke coil for each phase conductor L1, L2, L3 and also for the neutral conductor N. 71 having. Each choke coil 71 consists of its own choke coil core with an applied inductor winding. The inductors associated with the phase conductors L1, L2, L3 71 the choke coil assembly 7 form thereby with the longitudinal throttles 31 and capacitors 32 of the sine-wave filter 3 each a so-called T-filter. The purpose of this arrangement is to provide the inverter 1' specify a minimum impedance and thus also the frequency range for possible resonances.

Between the choke coil assembly 7 and the output of the inverter 1' is an EMC filter 4 arranged, consisting of four same-direction throttle windings 41 on a common throttle core 40 which are turned on in the three phase conductors L1, L2, L3 and in the neutral conductor N. On the output side of the choke windings 41 are first capacitors 42 between each phase conductor L1, L2, L3 and the neutral conductor N, and second capacitors 43 connected between the phase conductors L1, L2, L3 and a ground potential M. The EMC filter 4 fulfills the function of a mains filter, which generates electrical interferences between the inverter bridge 2 and the AC mains 6 in both directions.

In addition to the inductive and capacitive components of the inverter 1' also affect the electrical characteristics of the inverter 1' coupled alternating voltage network 6 or a connected consumer the resonance characteristics of the inverter 1' , By a suitable dimensioning of the choke coils 71 can the choke coil assembly 7 In doing so, be designed so that the resonant frequencies of the inverter 1' regardless of the characteristics of a connected AC voltage network 6 or consumer always far away from the clock frequencies of the inverter bridge.

However, arises in this known embodiment of an inverter 1' especially by running as individual components four inductors 71 a comparatively high cost and space requirements.

This problem is solved or reduced at least in the 1 illustrated inventive constructed inverter 1 , The sine-wave filter 3 downstream inductor coil assembly 8th According to the invention here consists only of a single throttle, which is a common mode push-pull throttle 8th formed.

The structure of this common-mode push-pull throttle 8th is in the 3 sketched. The common-mode push-pull throttle 8th has four on a common choke coil core 80 arranged inductor windings 81 . 82 on. Three of these windings 81 , one of which is connected in each of the three phase lines L1, L2, L3, are wound in the same direction and executed in each case with the same number of turns. Ideally, the phase windings exist 81 also from the same wire material, so that they are performed practically identical to each other and have identical electrical properties.

The fourth winding 82 is in the opposite direction to the first three windings 81 , executed and turned on in the neutral conductor N. The electrical properties of the neutral conductor winding 82 are usually different from those of the three phase windings 81 executed to optimally fulfill the function described below.

The common-mode push-pull throttle 8th forms together with the sine filter 3 for each phase conductor L1, L2, L3 a T-filter and acts under symmetrical load as a current-compensated choke. At a phase offset of the inverter bridge 2 and the sine-wave filter 3 generated three-phase alternating voltage of 120 °, the currents I _L1 , I _L2 , I _L3 through the phase windings lift 81 the common-mode push-pull throttle 8th in the neutral conductor winding 82 exactly on. In this case: I _N = I _L1 + I _L2 + I _L3 = 0

Thus, the current flowing through the neutral conductor N current I _N = 0 and the inductance of the neutral conductor winding 82 will not take effect.

In contrast to the currents I _L1 , I _L2 , I _{L3 of} the three alternating voltage _phases , the clock-frequency currents I _{L1_takt} , I _{L2_takt} , I _{L3_takt lift} through the phase windings 81 not on and are always available as summation current I _{N_takt} in the neutral conductor N: I _{N_takt} = I _{L1_takt} + I _{L2_takt} + I _{L3_takt} ≠ 0

In the case of a resonance between the clock frequency and the natural frequency of the components of the inverter, the clock frequency currents I _{L1_takt} , I _{L2_takt} , I _{L3_takt} through the phase windings 81 increase sharply, which would overload the neutral conductor N without further measures, the excessive total current I _{N_takt} .

mit:

L:

Induktivität

n:

Windungszahl

μ₀:

magnetische Feldkonstante

μ_r:

relative Permeabilität

A:

Querschnittsfläche des Ringkerns

r:

mittlerer Radius des Ringkerns

_According to the invention, the sum current I _{N_takt flows} through the push-pull _winding 82 the common-mode push-pull throttle 8th , For a current through the neutral conductor N are the phase windings 81 all with the neutral conductor winding 82 in row. However, the overall resulting inductance in this case is greater than a pure addition of the inductances of the individual cascaded windings 81 . 82 , Because of this through a toroidal core 80 are approximated:

With:

L:

inductance

n:

number of turns

μ ₀ :

magnetic field constant

μ _r:

relative permeability

A:

Cross sectional area of the toroidal core

r:

mean radius of the toroidal core

The number of turns n results here as the sum of the number of turns of the respective phase windings 81 and the number of turns of the neutral conductor winding 82 ,

Due to the coupling, the number of turns n becomes square in the inductance L, so the resulting inductance is significantly greater than the pure addition of two individual inductances of the same number of turns.

By the inventive use of a common mode push-pull choke 8th in a four-conductor system several advantageous effects are achieved. Thus, in a case of resonance, the current I _N flowing through the neutral conductor _{N is} strongly attenuated. In many cases, the inductance becoming active shifts the resonant frequency to less critical values. Opposite in the 2 shown T-filter structure, each with its own throttle per phase conductors L1, L2, L3 and neutral N represents the common-mode push-pull choke 8th a much smaller component, which also causes lower electrical losses and is less expensive to produce.

LIST OF REFERENCE NUMBERS

1, 1 '

inverter

2

Inverter bridge

3

sine filter

31

series choke

32

capacitor

4

EMC filters

40

reactor core

41

inductor windings

42

first capacitors

43

second capacitors

5

DC voltage source

6

AC network

7

Choke assembly

71

reactors

8th

(Common mode push-pull) choke (choke coil arrangement)

80

Choke core (toroidal core)

81

(Phase) coils

82

(Neutral) winding (fourth winding)

81, 82

Choke coil windings

L1, L2, L3

phase conductor

M

ground potential

N

neutral

L1, L2, L3, N

output lines

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 102005031372 A1 [0005]

Claims (6)

Inverter ( 1 . 1' ), - with an inverter bridge ( 2 ), which determines the output voltage of a DC voltage source ( 5 ) into a three-phase AC voltage and outputs via three phase conductors (L1, L2, L3) and a neutral conductor (N), - with one of the inverter bridge ( 2 ) downstream sine-wave filter ( 3 ), - and with a sine-wave filter ( 3 ) downstream inductor arrangement ( 7 . 8th ), each having a choke coil winding ( 71 . 81 . 82 ) for each phase conductor (L1, L2, L3) and for the neutral conductor, characterized in that - the four inductor windings ( 81 . 82 ) of the choke coil arrangement ( 8th ) on a common choke coil core ( 80 ) are arranged, - that all three in the phase conductors (L1, L2, L3) connected inductor windings ( 81 ) have the same winding sense, and that the fourth reactor coil winding ( 82 ), which is connected in the neutral conductor (N), in the opposite direction to the other three inductor windings ( 81 ) is wound. Inverter according to Claim 1, characterized in that the choke coil core ( 80 ) is designed as a ring core. Inverter according to claim 1, characterized in that an EMC filter ( 4 ) is provided, comprising a throttle winding ( 41 ) in each phase conductor (L1, L2, L3) and in the neutral conductor (N) and with the inductor windings ( 41 ) downstream first capacitors ( 42 ) between the phase conductors (L1, L2, L3) and the neutral conductor (N) and second capacitors ( 43 ) are connected by the phase conductors (L1, L2, L3) against a ground potential (M). Inverter according to claim 1, characterized in that the phase conductors (L1, L2, L3) and the neutral conductor (N) for supplying electrical energy with an AC voltage network ( 6 ) are connectable. Inverter according to claim 1, characterized in that the inverter ( 1 ) Is part of a photovoltaic system. Inverter according to claim 1, characterized in that the DC voltage source ( 5 ) is a solar generator.

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