CN102355151A - Multi-functional grid-connected inverter and grid-connected inverter control method - Google Patents

Abstract

The invention belongs to the field of electrical engineering, distributed power generation and power quality control, and aims to provide a multi-functional grid-connected inverter and a grid-connected inverter control method. The grid-connected inverter comprises a direct-current bus bar with a capacitor and three sets of single-phase full-bridge inverter circuits sharing the direct-current bus bar, the direct-current output ends of a distributed power supply or a grid-connected energy-storing generating set are connected to both ends of the capacitor of the direct-current bus bar, the output of each set of single-phase full-bridge inverter circuit is connected to a filter, and the output ends of each filter are connected with a distribution network of the 380V voltage class through a single-phase step-up isolation transformer. According to the invention, the grid-connected inverter equipment is effectively utilized to carry out effective control on the power quality of points of interconnection, so that the grid-connected inverter is multi-purpose and multi-functional, the cost performance of the grid-connected inverter is enhanced, the investment, operation and maintenance cost of a system can be reduced, and the reliability of the system can be enhanced. The principle of the provided control scheme is clear, and the control scheme is highly operable and reliable in operation.

Description

A kind of combining inverter and parallel network reverse control method with complex function

Technical field

The present invention relates to a kind of combining inverter and parallel network reverse control method, belong to electrical engineering, distributed power generation and power quality controlling field with complex function.

Background technology

Since distributed generation system not still regenerative resource insert the important tie of electrical network, and can also improve the stability of traditional electrical network to a certain extent, therefore obtained increasing attention.Because regenerative resources such as wind energy, photovoltaic have intermittence, randomicity characteristics, are typical uncontrollable sources.How better uncontrollable regenerative resource to be inserted electrical network, be a research focus for a long time.In order to address this problem, there is the scholar to propose the notion of little electrical network.Little electrical network has caused recently widely and has paid close attention to as a kind of integrated local power system of multiple regenerative resource, energy storage and load.Along with the fast development of distributed generation system and little electric power network technique, combining inverter is with a wide range of applications as critical component wherein.

It is worthy of note, in distributed generation system and little electrical network, contain a large amount of electronic power convertors and brought no small influence for its quality of power supply.Simultaneously, the quality of power supply that non-linear, idle and asymmetric load also can further worsen and the site is located in distributed generation system and the little electrical network.This contaminated electric energy not only can influence the operate as normal of local sensitive load and combining inverter, even may involve the normal operation of loading in the power distribution network that is attached thereto.On the other hand, along with the development of electricity market, fixing price according to quality of electric energy will be the trend of distributed power generation and little power network development.And the quality of the site quality of power supply is directly connected to the height of rate for incorporation into the power network.Therefore, the improvement to itself and the site quality of power supply has crucial meaning.

The major measure of existing power quality controlling promptly and the site source or equipment such as passive filter and reactive power compensator are installed.Yet this not only can the increase system invest and operation and maintenance cost, but also has reduced the reliability of system.Obviously, combining inverter is as one of vitals in distributed generation system and the little electrical network, if the quality of power supply that it when the conventional combining inverter of completion is incorporated into the power networks power tracking, can also be administered and the site is located has great importance undoubtedly.The combining inverter that existing this type has complex function mainly adopts single-phase full bridge or three phase full bridge power electronics topology; The complex function that it had is mainly harmonic current managing, can administer simultaneously and site place harmonic wave, complex function combining inverter idle and unsymmetrical current also rare.In addition, existing combining inverter with complex function DC bus-bar voltage is often had relatively high expectations needs a plurality of DC power supplys (photovoltaic cell, energy-storage battery etc.) module could insert its dc bus through series connection or through the prime DC/DC converter that boosts.

Summary of the invention

Patent of the present invention is the deficiency that overcomes prior art, has proposed a kind of combining inverter topology and control method thereof with complex function.The present invention administers when can realize uneven, the idle harmonic electric current in distributed generation system and little electrical network and place, site.

In order to reach above purpose, the main technical schemes that the present invention adopts is:

A kind of combining inverter with complex function is provided, comprises the dc bus of capacitor, the generate electricity by way of merging two or more grid systems dc output end of device of various distributed power sources or energy storage is connected to the dc-link capacitance two ends; This combining inverter also comprises three groups of single-phase full bridge inverter circuits of dc bus altogether, and the output of each group single-phase full bridge inverter circuit all is connected to filter, and the output of filter all inserts the power distribution network of 380V electric pressure through the single-phase step-up isolating transformer.Because dc bus can effectively reduce the possibility that circulation occurs altogether.Simultaneously, each circuitry phase is separated lotus root fully with control, is with the very competent of unbalanced load, and can realizes functions such as phase-splitting control, N+1 redundancy, online insertion and removal easily, improves the reliability of system.

Among the present invention, the generate electricity by way of merging two or more grid systems dc output end of device of said distributed power source or energy storage is meant: the output of the rectification output end of the output of photovoltaic, direct-drive aerogenerator/flywheel or miniature gas turbine, super capacitor/superconduction or battery energy storage device.

Among the present invention, outlet side adopts the LC filter, can effectively eliminate the influence of high order harmonic component to system, simultaneously the LC filter also and isolating transformer leakage inductance thereafter constitute the LCL filter together equivalently, better to the inhibition ability of high order harmonic component.Certainly, output filter also can adopt L or LCL filter, but L mode filter high frequency attenuation speed is not high, often needs bigger inductance value just can reach desirable filter effect, has increased system bulk and cost; In addition, if adopt the LCL filter, then can not make full use of the isolating transformer leakage inductance and reach the advantage that reduces system's investment and volume.

Among the present invention, there is resonant tank between said LC filter and the isolating transformer, is in series with damping resistance with damped harmonic oscillation at its filter capacitor branch road.

Among the present invention, said dc bus is the dc bus of 400V, adopts the 400V DC bus-bar voltage, can reduce the requirement to DC power supply, sometimes even can save prime DC/DC converter.The no-load voltage ratio of said single-phase step-up isolating transformer is 150V: 220V; Adopt the isolating transformer that boosts of 150V: 220V, can effectively reduce pressure DC bus-bar voltage, and effectively isolated inverter side direct current and high order harmonic component to netting the influence of side.

As a kind of technical scheme of remodeling, can also be to be that 1: 1 isolating transformer substitutes said single-phase step-up isolating transformer with no-load voltage ratio.

The present invention also provides a kind of combining inverter system that comprises aforementioned combining inverter, and this grid-connected inverting system also has a controller that is used to control single-phase full bridge inverter circuit trigger impulse; And at least also comprise: measure the voltage sensor of combining inverter set end voltage, and the current sensor of measuring combining inverter output current, filter inductance electric current and current on line side.

The invention provides the parallel network reverse control method of a kind of aforementioned combining inverter system, may further comprise the steps:

(1) controller is sampled to combining inverter set end voltage transducer and its output current, filter inductance electric current and current on line side signal of sensor;

(2) obtain the required power tracking current command signal i of combining inverter based on instantaneous reactive power theory _Gabc

(3) for compound to its also improvement of place, the site quality of power supply on the basis of conventional combining inverter, obtain the offset current component i of required input _Habc

(4) output current signal of combining inverter and its instruction current i _Refabc=i _Gabc+ i _HabcPoor, through after pi regulator and the output violent change link, the required trigger impulse of power device in the generation combining inverter under the triangular carrier modulating action is with the completion transformation of electrical energy.

Offset current component i in the step of the present invention (3) _HabcAcquisition process may further comprise the steps:

Utilize current on line side i _SabcWith isolating transformer high voltage side current i _OabcThe equivalent load current i that indirect calculation is total _Abc

Utilize no phase-locked loop current detection technology equivalent load current and combining inverter set end voltage u _SabcDetect, with the load current i under the abc coordinate system _AbcAlong the arbitrary initial angular position theta ₀The projection of dq coordinate system, obtain its current component i under the dq coordinate system _dAnd i _pSimultaneously, the combining inverter set end voltage also along this dq coordinate system projection, is obtained corresponding component of voltage u _dAnd u _q

The positive sequence fundamental active current component that utilizes instantaneous reactive power theory to detect obtains the value i under this dq coordinate system _PdAnd i _PqBe tied to the anti-Park conversion of abc coordinate system by this dq coordinate, obtain the expression formula i of positive sequence first-harmonic real component under the abc coordinate system _PabcThen, by total load current i _AbcDeduct i _PabcCan obtain idle, the harmonic wave and the negative sequence component i of required compensation _Habc

The present invention also comprises the depression of order to plant model: with the combining inverter equivalence of three-phase is three complete separate single-phase inverters, and then obtains the filter inductance current i _LWith isolating transformer primary current i _pTo inverter output voltage u _oBetween transfer function model; Utilize the weighted current feedback method, realize the depression of order of high-order model, 5 complete rank models are reduced to 1 rank, realize PI control to utilize this reduced-order model.

Beneficial effect of the present invention is mainly reflected in:

1, the present invention can effectively utilize requisite combining inverter equipment in distributed generation system and the little electrical network realize to and effective improvement of the site quality of power supply; Make combining inverter have the function of the many duties of a machine; Realize compoundization and the multifunction of its function; Improve its cost performance, reduce the cost of investment and the operation and maintenance cost of system, improve system reliability.

2, put forward the controlling schemes clear principle, workable, reliable, can effectively accomplish and in the power tracking that is incorporated into the power networks, accomplish the also improvement of the site quality of power supply.In addition, because the employing of no phase-locked loop current technique can reduce unnecessary hardware phase-locked-loop circuit or software locks phase program, can effectively overcome conventional phase locked loops inaccurate mutually disadvantage of lock under line voltage distortion or uneven condition.This controlling schemes is applicable to that simultaneously other have the control of the similar topology of function of the present invention.

3, adopt reduced-order model to realize depression of order, simplified the design process of controller greatly high-order model.

Description of drawings

Fig. 1 has the circuit topology that complex function combining inverter and machine end load thereof are constituted.

Fig. 2 is the control algolithm block diagram with complex function combining inverter.

Fig. 3 is the voltage and current vector under the dq coordinate system.

The one phase equivalent circuit of Fig. 4 complex function combining inverter.

The abbreviation result of Fig. 5 one phase equivalent circuit middle impedance network.

The Diagram Model of Fig. 6 complex function combining inverter.

Fig. 7 is based on the complex function combining inverter Diagram Model abbreviation result of reduced-order model.

Fig. 8 complex function combining inverter system and control strategy theory diagram.

Fig. 9 complex function combining inverter is being administered and the idle output current during with unsymmetrical current in place, site.

Figure 10 complex function combining inverter is being administered and the idle net side power during with unsymmetrical current in place, site.

The output current of Figure 11 complex function combining inverter when improvement and place, site harmonic current.

The net side power of Figure 12 complex function combining inverter when improvement and place, site harmonic current.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is further described.

Shown in Figure 1 a kind ofly have the combining inverter of complex function and the system of composition comprises: the 400V dc bus; Three groups of single-phase full bridge inverter circuits that are total to dc bus; Output LC filter is damped harmonic oscillation, and the filter capacitor branch road is in series with damping resistance; The isolating transformer that boosts, no-load voltage ratio is N ₁: N ₂=150V: 220V; The controller that constitutes by TI company's T MS320F2812; Point of common coupling PCC (Point of Common Coupling) is incorporated into the power networks; Nonlinear-load and mechanical switch thereof, uncompensated load and mechanical switch thereof.Wherein, the control method of the combining inverter of complex function comprises: controller to the voltage and current sensor output signal sample, the power tracking current-order generates, the extraction of offset current, FEEDBACK CONTROL and trigger impulse generation.At first, controller is sampled to the output of voltage and current transducer, obtains the required various voltage and current signals of controller.Secondly, obtain the required power tracking current command signal i of combining inverter based on instantaneous reactive power theory _GabcOnce more, for compound to its also improvement of place, the site quality of power supply on the basis of conventional combining inverter, need obtain the offset current component i of required input _HabcAt last, the output current signal of combining inverter and its instruction current i _Refabc=i _Gabc+ i _HabcPoor, through after pi regulator and the output violent change link, the required trigger impulse of power device in the generation combining inverter under the triangular carrier modulating action is with the completion transformation of electrical energy.It is worthy of note,, also high-order model has been carried out depression of order in order to reduce the complexity of PI design of Controller.

The calculating of power tracking electric current

In order to realize the tracking of combining inverter to the power that is incorporated into the power networks, the present invention has adopted a kind of based on direct method of current, can eliminate the conventional power outer shroud, reduces the complexity of control algolithm.If being incorporated into the power networks of combining inverter is meritorious, the reactive power set-point is respectively P and Q, can know by instantaneous reactive power theory so: the as a result i of grid-connected current command value under the dq coordinate system _DrefAnd i _QrefShould satisfy

$\left\{\begin{array}{c}P=u_d{i}_{d,\mathrm{ref}}+u_q{i}_{q,\mathrm{ref}}\\ Q=u_q{i}_{d,\mathrm{ref}}-u_d{i}_{q,\mathrm{ref}}\end{array}\right.---\left(1\right)$

Can know by formula (3)

$\left\{\begin{array}{c}{i}_{\mathrm{dref}}=(u_{d}P+u_{q}Q)/(u_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">d</figure-callout>}}^2+u_q^2)\\ i_{\mathrm{qref}}=(u_{q}P-u_{d}Q)/(u_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">d</figure-callout>}}^2+u_q^2)\end{array}\right.---\left(2\right)$

Formula (4) is the conversion T shown in Fig. 2 among Fig. 2.By i _DrefAnd i _QrefPass through anti-Park conversion respectively, the value i of power tracking electric current under the abc coordinate system can obtain being incorporated into the power networks _Gabc

The extraction of offset current component

Control algolithm block diagram as shown in Figure 2, the controller of complex function combining inverter is through the on high-tension side output current i of sampling isolating transformer _OabcWith current on line side i _Sabc,, can know total equivalent load current i by reference current direction shown in Figure 1 _AbcCan be by i _SabcWith i _OabcSum replaces.

Adopt the no phase-locked loop current detection technology, select permanent power P ark conversion

$C_{\mathrm{abc}/\mathrm{dq}}=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}\cos \left(\mathrm{\&theta;}\right)& \cos (\mathrm{\&theta;}-2\mathrm{\&pi;}/3)& \cos (\mathrm{\&theta;}+2\mathrm{\&pi;}/3)\\ -\sin \left(\mathrm{\&theta;}\right)& -\sin (\mathrm{\&theta;}-2\mathrm{\&pi;}/3)& -\sin (\mathrm{\&theta;}+2\mathrm{\&pi;}/3)\\ 1/\sqrt{2}& 1/\sqrt{2}& 1/\sqrt{2}\end{array}\right]---\left(3\right)$

Wherein, θ=∫ ω dt=∫ 2 π fdt+ θ ₀, θ ₀Being initial phase, also is the angle between dq coordinate system d axle and the abc coordinate system a axle, can be arbitrary value.C _Abc/dqInverse transformation satisfy:

Utilize Park conversion shown in the formula (1), can obtain current i _AbcI as a result in selected dq coordinate system _dAnd i _q, can obtain its DC component through low pass filter

With

Similarly, can utilize the voltage u at this Park transfer pair PCC place _SabcCarry out conversion, obtain u _dAnd u _qAnd through the value behind the low pass filter

With

By the relation of electric current and voltage shown in Figure 3 under the dq coordinate, utilize

With With

Can obtain the as a result i of positive sequence first-harmonic real component under the dq coordinate system of load current _PdAnd i _Pq

$\left\{\begin{array}{c}{i}_{\mathrm{pd}}=\frac{{\stackrel{\&OverBar;}{u}}_d\stackrel{\&OverBar;}{i_d}+{\stackrel{\&OverBar;}{u}}_q\stackrel{\&OverBar;}{i_q}}{{\stackrel{\&OverBar;}{u}}_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">d</figure-callout>}}^2+{\stackrel{\&OverBar;}{u}}_q^2}{\stackrel{\&OverBar;}{u}}_d\\ i_{\mathrm{pq}}=\frac{{\stackrel{\&OverBar;}{u}}_d\stackrel{\&OverBar;}{i_d}+{\stackrel{\&OverBar;}{u}}_q\stackrel{\&OverBar;}{i_q}}{{\stackrel{\&OverBar;}{u}}_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">d</figure-callout>}}^2+{\stackrel{\&OverBar;}{u}}_q^2}{\stackrel{\&OverBar;}{u}}_q\end{array}\right.---\left(4\right)$

The C of conversion shown in Fig. 2 _PqBe formula (2), by i _PdAnd i _PqUtilize the Park inverse transformation can obtain its i as a result under the abc coordinate system _PabcAt last, by i _AbcDeduct i _PabcBe the negative phase-sequence, harmonic wave and the idle component i that need compensation in the total load electric current _HabcFinally, by i _HabcAnd i _GabcSum has constituted the instruction current value i of complex function combining inverter jointly _Refabc

The depression of order of high-order model

Fig. 2 gives the control algolithm of combining inverter, can be known by combining inverter topology shown in Figure 1, and entire circuit topology three-phase is separated lotus root, can be used as 3 single-phase inverters and treat, and certain single-phase equivalent electric circuit is as shown in Figure 4.Knowledge by Circuit theory can be known, but the part of the impedance network among Fig. 4 abbreviation is as shown in Figure 5, wherein each impedance Z ₁, Z ₂And Z ₃Be respectively

${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HDA0000095648070000021.png,HDA0000095648070000023.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1=\frac{s^{3}L(L_{1}C+L_{m}C)+s(L+L_1)}{s^2(L_{1}C+L_{m}C)+1}---\left(5\right)$

${\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2=s{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+\frac{s^3{L}_1{L}_{m}C}{s^2(L_{1}C+L_{m}C)+1}---\left(6\right)$

$Z_3=\frac{{\mathrm{sL}}_m}{s^2(L_{1}C+L_{m}C)+1}---\left(7\right)$

Principle of stacking in the application circuit theory can get its input voltage u _oTo the filter inductance current i _LWith isolating transformer primary current i _PsBetween transfer function do

$G_{u_o\&RightArrow;i_{\mathrm{ps}}}=\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HDA0000095648070000021.png,HDA0000095648070000023.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2//Z_3}g\frac{Z_3}{{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_3}=\frac{Z_3}{Z_1{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_1{Z}_3+Z_2{Z}_3}---\left(8\right)$

$G_{u_o\&RightArrow;i_L}=\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HDA0000095648070000021.png,HDA0000095648070000023.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2//Z_3}=\frac{{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_3}{Z_1{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_1{Z}_3+Z_2{Z}_3}---\left(9\right)$

Can be known that by Fig. 4 there are 5 energy storage original papers in system, model order is high, is not easy to controlling Design.Use for reference (Shen Guoqiao such as Shen Guoqiao; The split capacitor method Current Control [J] of Xu De letter .LCL filtering combining inverter. Proceedings of the CSEE .2008; 28 (18): the weighted current feedback that 36-41.) proposes, come the depression of order of implementation model, definition weighted current feedback quantity:

i＝αi _ps+(1-α)i _L (10)

So, system is to input voltage u _oTo the transfer function between the current i do

$G_{u_o\&RightArrow;i}=\mathrm{\&alpha;}{G}_{u_o\&RightArrow;i_{\mathrm{ps}}}+(1-\mathrm{\&alpha;})G_{u_o\&RightArrow;i_L}=\frac{(1-\mathrm{\&alpha;}){\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_3}{Z_1{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_1{Z}_3+Z_2{Z}_3}---\left(11\right)$

Bring analytical expression (1)-(3) of impedance into, abbreviation

has:

$G_{u_o\&RightArrow;i}=\frac{(1-\mathrm{\&alpha;})(L_1{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+L_2{L}_m+L_1{L}_m){\mathrm{<figure-callout\; id="2"\; label="Cs"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">Cs</figure-callout>}}^2+(1-\mathrm{\&alpha;}){\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+L_m}{s[({\mathrm{LL}}_1{L}_{m}C+{\mathrm{LL}}_1{L}_{2}C+{\mathrm{LL}}_m{L}_{2}C)s^2+(L_2{L}_m+{\mathrm{LL}}_m+L_1{L}_m+{\mathrm{<figure-callout\; id="2"\; label="LL"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">LL</figure-callout>}}_2+L_2{L}_1)]}---\left(12\right)$

Here, if get:

$\mathrm{\&alpha;}=\frac{L_2{L}_m+L_1{L}_m+L_1{L}_2}{L_2{L}_m+{\mathrm{LL}}_m+L_1{L}_m+L_1{L}_2}---\left(13\right)$

Because the magnetizing inductance of transformer is much larger than the leakage inductance of former secondary, i.e. L ₁≈ L ₂=L _mSo:

$\mathrm{\&alpha;}\&ap;\frac{{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+L_1}{L+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000095648070000011.png,HDA0000095648070000031.png"\; state="\{\{state\}\}">L</figure-callout>}}_2+L_1}---\left(14\right)$

Formula (12) can be reduced to so

$G_{u_o\&RightArrow;i}=\frac{1}{(L+{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000095648070000021.png,HDA0000095648070000023.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)s}---\left(15\right)$

It is thus clear that the modular form behind the depression of order (15) is one 1 rank system, and only determine by the inductance parameters in the system.Can utilize the PI controller of the design of reduced-order model shown in the formula (15) complex function combining inverter very easily.

FEEDBACK CONTROL and trigger impulse generate

By the analysis of front, can obtain the Diagram Model of said complex function combining inverter under the PI controller, as shown in Figure 6.Wherein, K _PwmBe the amplification coefficient of inverter, for the single-phase full-bridge inverter of bipolarity modulation, K _Pwm=V _DcFig. 7 has provided the design of Controller block diagram based on reduced-order model, and visible under the effect of reduced-order model, the design object of PI controller is reduced to simple first-order system, has simplified the design process of PI controller greatly.Fig. 8 has provided the control strategy block diagram that designs resulting said complex function combining inverter based on above analysis.At first, inductive current i _LabcWith isolating transformer primary current i _PsabcUnder formula (10) and formula (14) effect, produce weighted current i _AbcThen, this weighted current and instruction current value i _RefabcBetween error send into pi regulator.At last, the output that PI transfers machine generates the required trigger impulse of each power device in the complex function combining inverter by the triangular carrier modulation system after through the amplitude limit link, makes the output current i of complex function combining inverter _OabcTrace command value i _RefabcThereby, in the power tracking that is incorporated into the power networks, realize improvement to the PCC place quality of power supply.

Embodiment 1:

Select each phase parameter of uncompensated load to be: a is 70 Ω ohmic loads mutually, and b is 40 Ω resistance and the load of 118uF capacitances in series mutually, and c is 50 Ω ohmic loads mutually.Fig. 9 has provided nonlinear-load switch S 1 and has broken off, during uncompensated load switch S 2 closures, and when the complex function combining inverter is P=15kW, Q=0var at the power instruction that is incorporated into the power networks, the current on line side i before and after the combining inverter complex function drops into _SbAnd i _ScExperimental waveform, Figure 10 have provided meritorious, the reactive power experimental waveform of its corresponding net side.Can find from Fig. 9, Figure 10: because the existence of uneven and load or burden without work, before complex function combining inverter input compensation function, the current on line side three-phase occurs significantly uneven, and fluctuates with 2 frequencys multiplication at the off line side power of the effect of unsymmetrical current.Simultaneously, reactive current makes net side reactive power waveform contain a bigger DC component.After the complex function of combining inverter drops into idle and imbalance compensation function; Current on line side three-phase imbalance and reactive current have obtained good restraining; Eliminated the 2 frequencys multiplication fluctuation of net side power, and the DC component of reactive power has also obtained tangible improvement.

Embodiment 2:

Select nonlinear-load for not controlling the rectification load, its DC load resistance is 50 Ω.Still keep P=15kW, Q=0var, Figure 11 has provided uneven combination switch S2 and has broken off, during nonlinear-load switch S 1 closure, and voltage on line side u before and after the combining inverter complex function drops into _SaWith current on line side i _SaExperimental waveform, Figure 12 has provided that corresponding with it net side is meritorious, the reactive power experimental waveform.Be not difficult to find from Figure 11 and Figure 12: since nonlinear-load be the DC side strip resistance do not control the rectification load; Before the complex function of combining inverter comes into operation; Current on line side is the stack of the output current of nonlinear-load electric current and combining inverter, under the effect of nonlinear-load electric current, demonstrates bigger harmonic distortion.Simultaneously, the net side is meritorious pulses with 6 frequencys multiplication with the reactive power waveform.After the complex function of combining inverter drops into the harmonic compensation function, can obviously improve and the harmonic current at place, site, and suppress the net side power pulsations that causes by nonlinear-load.It is pointed out that the harmonic wave of line voltage and make net side reactive power spike occur owing to produce current spikes constantly in commutation, and imperfect straight line.

Be not difficult to find out that from embodiment 1 and embodiment 2 the present invention can effectively compensate also imbalance, the idle harmonic electric current at place, site when power tracking is incorporated into the power networks in completion, eliminate net side power fluctuation, improves the also quality of power supply of site, has application promise in clinical practice.

Claims (10)

1. combining inverter with complex function comprises that the generate electricity by way of merging two or more grid systems dc output end of device of the dc bus of capacitor, distributed power source or energy storage is connected to the dc-link capacitance two ends; It is characterized in that; This combining inverter also comprises three groups of single-phase full bridge inverter circuits of dc bus altogether; The output of each group single-phase full bridge inverter circuit all is connected to filter, and the output of filter all inserts the power distribution network of 380V electric pressure through the single-phase step-up isolating transformer.

2. combining inverter according to claim 1; It is characterized in that the generate electricity by way of merging two or more grid systems dc output end of device of said distributed power source or energy storage is meant: the output of the rectification output end of the output of photovoltaic, direct-drive aerogenerator/flywheel or miniature gas turbine, super capacitor/superconduction or battery energy storage device.

3. combining inverter according to claim 1 is characterized in that, said filter is LC filter or L, LCL filter.

4. combining inverter according to claim 3 is characterized in that, has resonant tank between said LC filter and the isolating transformer, is in series with damping resistance at its filter capacitor branch road and is used for damped harmonic oscillation.

5. combining inverter according to claim 1 is characterized in that, said dc bus is the dc bus of 400V, and the no-load voltage ratio of said single-phase step-up isolating transformer is 150V: 220V.

6. combining inverter according to claim 1 is characterized in that, is to be that 1: 1 isolating transformer substitutes said single-phase step-up isolating transformer with no-load voltage ratio.

7. a combining inverter system that comprises the said combining inverter of claim 1 is characterized in that, this grid-connected inverting system also has a controller that is used to control single-phase full bridge inverter circuit trigger impulse; And at least also comprise: measure the voltage sensor of combining inverter set end voltage, and the current sensor of measuring combining inverter output current, filter inductance electric current and current on line side.

8. the parallel network reverse control method based on the said combining inverter of claim 7 system is characterized in that, may further comprise the steps:

(1) controller is sampled to combining inverter set end voltage transducer and its output current, filter inductance electric current and current on line side signal of sensor;

(2) obtain the required power tracking current command signal i of combining inverter based on instantaneous reactive power theory _Gabc

(3) for compound to its also improvement of place, the site quality of power supply on the basis of conventional combining inverter, obtain the offset current component i of required input _Habc

(4) output current signal of combining inverter and its instruction current i _Refabc=i _Gabc+ i _HabcPoor, through after pi regulator and the output violent change link, the required trigger impulse of power device in the generation combining inverter under the triangular carrier modulating action is with the completion transformation of electrical energy.

9. parallel network reverse control method according to claim 8 is characterized in that, offset current component i in the step (3) _HabcAcquisition process may further comprise the steps:

Utilize current on line side i _SabcWith isolating transformer high voltage side current i _OabcThe equivalent load current i that indirect calculation is total _Abc

Utilize no phase-locked loop current detection technology equivalent load current and combining inverter set end voltage u _SabcDetect, with the load current i under the abc coordinate system _AbcAlong the arbitrary initial angular position theta ₀The projection of dq coordinate system, obtain its current component i under the dq coordinate system _dAnd i _qSimultaneously, the combining inverter set end voltage also along this dq coordinate system projection, is obtained corresponding component of voltage u _dAnd u _q

The positive sequence fundamental active current component that utilizes instantaneous reactive power theory to detect obtains the value i under this dq coordinate system _PdAnd i _PqBe tied to the anti-Park conversion of abc coordinate system by this dq coordinate, obtain the expression formula i of positive sequence first-harmonic real component under the abc coordinate system _PabcThen, by total load current i _AbcDeduct i _PabcCan obtain idle, the harmonic wave and the negative sequence component i of required compensation _Pabc

10. parallel network reverse control method according to claim 8 is characterized in that, this method also comprises the depression of order to plant model: with the combining inverter equivalence of three-phase is three complete separate single-phase inverters, and then obtains the filter inductance current i _LWith isolating transformer primary current i _pTo inverter output voltage u _oBetween transfer function model; Utilize the weighted current feedback method, realize the depression of order of high-order model, 5 complete rank models are reduced to 1 rank, realize PI control to utilize this reduced-order model.

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