CN102931685A - Converter device used for wind generator system - Google Patents

Abstract

The invention discloses a converter device used for a wind generator system. The converter device comprises a filter, a first converter, a second converter, a first capacitor and a second capacitor, wherein the filter is connected to a wind-driven generator of the wind generator system; the first converter is connected to the filter; the second converter is connected to a voltage transformer on the power network side; and the first capacitor and the second capacitor are connected in series between a positive direct-current bus and a negative direct-current bus which are used for connecting the first converter and the second converter, neutral points of the positive direct-current bus and the negative direct-current bus are connected, and nodes of the first capacitor and the second capacitor are grounded.

Description

The convertor assembly that is used for wind generator system

Technical field

The present invention relates to the convertor assembly of wind generator system, more particularly, relate to a kind of convertor assembly that can reduce the current transformer common-mode voltage of wind turbine generator.

Background technology

At present in MW class dual feedback wind power generation system and the directly-driving wind power generation system general as depicted in figs. 1 and 2 the back-to-back pair of PWM current transformer of adopting as electrical energy transformer, this converter using electronic power switch device.

In wind generator system illustrated in figures 1 and 2, filter 10 (for example, the du/dt filter) for reducing generating pusher side common mode and differential mode voltage, the current transformer 20 of generating pusher side has the function that AC excitation is provided to double-fed generator (DFIG) or permanent magnet generator (PMSG), the grading resistor 30a and the 30b that are connected in series between the dc bus have the effect that the two ends execution of support capacitor 40 is all pressed, and support capacitor 40 is used for the stable DC busbar voltage and the switching transient electric current is provided; The current transformer 50 of grid side has rectification function and can control DC bus-bar voltage stable.

But, have in the wind generator system of said structure, because the HF switch process will cause motor terminal voltage to have zero-sequence component, that is, and common-mode voltage.

In existing wind generator system as illustrated in fig. 1 and 2, current transformer dc bus neutral point (that is, O point) voltage (that is, the common-mode voltage of grid side) relatively is:

$V_{\mathrm{ON}2}=\frac{V_{\mathrm{PN}2}+V_{\mathrm{NN}2}}{2}=V_{{\mathrm{CM}}_{\mathrm{grid}}}---\left(1\right)$

Wherein, V _ON2For the dc bus neutral point O with respect to place N ₂Voltage, V _PN2And V _NN2Be respectively dc bus just (that is, P point)/dc bus negative (that is, N point) with respect to place N ₂Voltage, V _CMgridCommon-mode voltage for the grid side of current transformer.

Generator neutral point voltage (that is, the common-mode voltage of motor side) is:

$V_{N1O}=\frac{V_{N1P}+V_{N1N}}{2}=V_{{\mathrm{CM}}_{\mathrm{gen}}}---\left(2\right)$

Wherein, V _N1OBe generator neutral point N ₁With respect to the voltage of dc bus neutral point O,, V _N1PAnd V _N1NBe respectively generator neutral point N1 with respect to the dc bus voltage of (that is, the P point)/dc bus negative (that is, the N point) just, V _CMgenCommon-mode voltage for the current transformer motor side.

By above-mentioned equation (1) and (2), can determine generator neutral point over the ground total common-mode voltage be:

$V_{N1N2}=V_{N1O}+V_{\mathrm{ON}2}=V_{{\mathrm{CM}}_{\mathrm{grid}}}+V_{{\mathrm{CM}}_{\mathrm{grid}}}+V_{{\mathrm{CM}}_{\mathrm{gen}}}=V_{\mathrm{CM}}---\left(3\right)$

Wherein, V _N1N2Be generator neutral point N ₁With respect to place N ₂Voltage.

Therefore, the A of generator point is with respect to place N ₂Voltage then be:

V _AN2＝V _AN1+V _N1N2＝V _AN1+V _CM (4)

Wherein, V _AN2Phase voltage V for motor _AN1With V _N1N2Sum.Motor phase voltage peak value is in higher level, the easier phenomenons such as bloom, the lost of life of occurring in the insulation of motor winding.

Suppose that DC bus-bar voltage is 1200V, then the voltage waveform of the relative transformer neutral point N2 of dc bus neutral point O as shown in Figure 3, the voltage waveform of the relative dc bus neutral point O of the interchange of the rectifier of motor side as shown in Figure 4, the AC phase voltage peak value of the current transformer of motor side (namely, VAN2) as shown in Figure 5, this voltage peak can reach 1200V, and generator will operate in the higher voltage levvl of peak value.

That is, in having the existing wind generator system of said structure, the electric stress that higher common-mode voltage will make motor bear greatly increases, thereby the probability that the motor winding insulation lost efficacy is greatly increased.For double-fed generator, high common-mode voltage can produce shaft voltage and shaft current by the coupling capacitance between stator and the rotor, causes damage of bearings, reduces the useful life of motor.In addition, high frequency common mode voltage also can produce the high frequency Ground leakage current by parasitic capacitance, causes producing electromagnetic interference (EMI), affects the normal operation of other electric equipment of system.

Summary of the invention

In order to solve the above-mentioned problems in the prior art, the invention provides the convertor assembly that is used for wind generator system that reduces the common-mode voltage of generating pusher side by the dc bus neutral ground with current transformer.

A kind of convertor assembly for wind generator system according to exemplary embodiment of the present invention comprises: filter is connected to the wind-driven generator of described wind generator system; The first current transformer is connected to described filter; The second current transformer is connected to the transformer of grid side; Be connected in series in the positive direct-current bus and the first capacitor between the negative dc bus and the second capacitor that connect the first current transformer and the second current transformer,

Wherein, as connection first capacitor of described positive direct-current bus and the neutral point of being connected dc bus and the node ground connection of the second capacitor.

In addition, described filter comprises resistance capaciting absorpting circuit and series reactor.

In addition, the neutral ground of the resistance capaciting absorpting circuit of described filter.

In addition, the neutral ground of the transformer of described grid side.

In addition, described wind generator system is dual feedback wind power generation system or directly-driving wind power generation system.

According to aforesaid according to the converter system for wind generator system of the present invention, because the dc bus neutral ground of current transformer, the common-mode voltage of pusher side reduces the dynamo bearing electric current simultaneously so can suppress to generate electricity, and has improved the life-span of wind-driven generator.

Description of drawings

By the description of embodiment being carried out below in conjunction with accompanying drawing, these and/or other aspect of the present invention and advantage will become clear and be easier to and understand, wherein:

Fig. 1 is the diagram that illustrates according to the convertor assembly that is used for dual feedback wind power generation system of prior art;

Fig. 2 is the diagram that illustrates according to the convertor assembly that is used for directly-driving wind power generation system of prior art;

Fig. 3 to Fig. 5 is respectively the diagram of phase voltage of the rectifier AC of the voltage of AC of rectifier of the voltage that illustrates according to the dc bus centerline of prior art, generating pusher side and generating pusher side;

Fig. 6 illustrates the diagram that is used for according to an embodiment of the invention the convertor assembly of dual feedback wind power generation system;

Fig. 7 illustrates the diagram that is used for according to an embodiment of the invention the convertor assembly of directly-driving wind power generation system;

Fig. 8 is the diagram that the phase voltage waveform of the generator when using convertor assembly according to an embodiment of the invention is shown;

Fig. 9 is the illustrating of phase voltage waveform that the generator of actual measurement under the neutral ground condition of dc bus is shown;

Figure 10 is the diagram that the convertor assembly that is used for dual feedback wind power generation system according to another embodiment of the present invention is shown;

Figure 11 is the diagram that the convertor assembly that is used for directly-driving wind power generation system according to another embodiment of the present invention is shown.

Embodiment

Now the embodiment of the invention is described in detail, its example shown in the accompanying drawings, wherein, identical label represents same parts all the time.Below with reference to the accompanying drawings embodiment is described to explain the present invention.

Fig. 6 and Fig. 7 illustrate respectively the convertor assembly that is used for according to an embodiment of the invention dual feedback wind power generation system and directly-driving wind power generation system.

Shown in Fig. 6 and 7, described convertor assembly for wind generator system comprises: filter 110 is connected to the wind-driven generator of described wind generator system; The current transformer 120 (below be called " the first current transformer ") of generating pusher side is connected to described filter 110; The current transformer 140 of grid side (below be called " the second current transformer ") is connected to the transformer of grid side; The first capacitor 130a has the first end that is connected to the positive direct-current bus that connects the first current transformer 120 and the second current transformer 140 and the second end that is connected to ground; The second capacitor 130b has the first end of the second end that is connected to the first capacitor 130a and is connected the second end of the negative dc bus that connects the first current transformer 120 and the second current transformer 140.

Here, the node (corresponding to the second end of the first capacitor and the first end of the second capacitor) that connects the first capacitor and the second capacitor is the neutral point of described positive direct-current bus and negative dc bus, that is, the first capacitor is preferably identical capacitor with the second capacitor.

Therefore the performed functional similarity of the current transformer of above-mentioned filter 110, the first current transformer 120 and the second current transformer 140 and filter illustrated in figures 1 and 2 and the pusher side that generates electricity and the generating pusher side of grid side will omit further describing it.

Here, as shown in Figure 6 and Figure 7, described filter 110 preferably adopts the du/dt filter, and is comprised of series reactor and resistance capaciting absorpting circuit.For example, shown in Fig. 6 and 7, each can comprise inductor and resistance capaciting absorpting circuit in parallel mutually, and resistance capaciting absorpting circuit comprises resistor and the capacitor of series connection.

In Fig. 6 and convertor assembly shown in Figure 7, V _ON2=0, that is,

So can obtain:

$V_{N1N2}=V_{N1O}=\frac{V_{N1P}+V_{N1N}}{2}=V_{{\mathrm{CM}}_{\mathrm{gen}}}$

Compare with the wind generator system of as depicted in figs. 1 and 2 the existing convertor assembly of employing, the common-mode voltage that has lacked the current transformer of grid side in the voltage of generator neutral point with respect to ground, therefore, generator neutral point reduces with respect to the voltage on ground, generator reduces with respect to the voltage on ground, and the shaft current of generator also reduces corresponding simultaneously.

Fig. 8 is the diagram that the phase voltage waveform of the generator when using convertor assembly according to an embodiment of the invention is shown.As shown in Figure 8, when DC bus-bar voltage be ± during 600V, generator (taking from the rectifier (not shown) AC of generating pusher side) is ± 600V with respect to the voltage on ground.Compare with existing technical scheme, the peak reduction of phase voltage 50%, and owing to the current potential of dc bus is fixed, any switch motion of the inverter of grid side will can not form impact to the common-mode voltage of generating pusher side, consider the generally higher switching frequency of inverter of grid side, this means that the high-frequency current by bearing reduces by 50% to the major general.

Fig. 9 is the illustrating of phase voltage waveform that the generator of actual measurement under the neutral ground condition of dc bus is shown.In Fig. 9, because it is slightly higher than simulation waveform voltage to be subjected to long cable to affect this waveform.

Figure 10 and Figure 11 illustrate respectively the convertor assembly that is used for double-fed and directly-driving wind power generation system according to another embodiment of the present invention.

Shown in Figure 10,11, except the neutral point with the resistance capaciting absorpting circuit of du/dt filter 110 is connected to the dc bus neutral point O, Figure 10 and convertor assembly shown in Figure 11 and Fig. 6 and convertor assembly shown in Figure 7 are identical, therefore will omit the description to repeating part.

In convertor assembly as shown in FIG. 10 and 11, because the neutral point of the resistance capaciting absorpting circuit of du/dt filter 110 is connected to the dc bus neutral point O, so can better bring into play the du/dt filter to the decay of high frequency common mode voltage, general crest voltage can be controlled at below 1.2 times of direct voltage.

According to aforesaid according to the converter system for wind generator system of the present invention, because the dc bus neutral ground of current transformer, the common-mode voltage of pusher side reduces the dynamo bearing electric current simultaneously so can suppress to generate electricity, and has improved the life-span of wind-driven generator.

Although represented and described some embodiments of the present invention, it should be appreciated by those skilled in the art that in the situation that does not break away from the principle of the present invention that limited its scope by claim and equivalent thereof and spirit, can make amendment to these embodiment.

Claims (5)

1. convertor assembly that is used for wind generator system comprises:

Filter is connected to the wind-driven generator of described wind generator system;

The first current transformer is connected to described filter;

The second current transformer is connected to the transformer of grid side;

Be connected in series in the positive direct-current bus and the first capacitor between the negative dc bus and the second capacitor that connect the first current transformer and the second current transformer,

Wherein, as connection first capacitor of described positive direct-current bus and the neutral point of being connected dc bus and the node ground connection of the second capacitor.

2. convertor assembly according to claim 1 is characterized in that, described filter is for comprising resistance capaciting absorpting circuit and series reactor.

3. convertor assembly according to claim 2 is characterized in that, the neutral ground of the resistance capaciting absorpting circuit of described filter.

4. convertor assembly according to claim 1 is characterized in that, the neutral ground of the transformer of described grid side.

5. convertor assembly according to claim 1 is characterized in that, described wind generator system is dual feedback wind power generation system or directly-driving wind power generation system.

Images