CN202395646U - Active damping circuit of LCL grid-connected inverter system - Google Patents

Abstract

The utility model relates to an active damping circuit of an LCL grid-connected inverter system. The grid-connected inverter system includes an inverter and an LCL network access filter. The active damping circuit is characterized in that a controller is arranged, and the controller includes a proportion resonance regulator, a differential regulator, substracters, and a PWM generating circuit. A current sensor transmits a network access current which is captured from the grid side of the LCL network access filter to a first subtracter, and a reference value of the network access current is also input into the first subtracter. The first subtracter outputs to the proportion resonance regulator. The proportion resonance regulator outputs to a second subtracter. A voltage sensor transmits a grid side inductance voltage which is captured from the LCL network access filter to a second subtracter via the differential regulator. The second subtracter outputs to the PWM generation circuit. The PWM generation circuit outputs to the inverter via an isolating drive circuit. In such a manner, an active damping circuit in a parallel structure is formed.

Description

The active damping circuit of a kind of LCL combining inverter system

Technical field

The utility model relates to the active damping circuit of a kind of LCL combining inverter system, belongs to the control technology field of grid converter.

Background technology

The voltage-source type combining inverter is the interface that current flourish new forms of energy get into electrical network; Be used for various distributed grid-connected systems (like photovoltaic generating system, direct-driving type wind power generation system, fuel cell system etc.), exchange the interface of dc bus and electrical network in inverse type interface and the direct current microgrid of microgrid etc., demand is huge.

In order to alleviate and to limit their pollutions to electrical network, international standards such as IEEE Std 929-2000, UL1741 have been done strict index restriction to the network access electric current of combining inverter, comprise total harmonic distortion and single harmonic component content.In conjunction with the realization technology of combining inverter, reach the switching frequency harmonic current and suppress index difficulty the most, relate to the selection of network access filter.The network access filter construction has L, LC and three kinds of forms of LCL, and the existing document of their filtering performance and control characteristic is discussed.From present stage commercial Application situation; The general L mode filter that adopts in the small-power combining inverter; In, the general LCL mode filter that adopts LC mode filter or band damping resistance in the powerful SPWM combining inverter; And academia receive much concern have the source damping (Active Damping, AD) the LCL filter of link is more rare in practical application, present stage is used from scale about the active damping Study on Technology of LCL filter and still has a segment distance.

Compare the L mode filter, the LCL mode filter is a pair of conjugation resonance limit for the combining inverter system introduces, its damping ratio be zero and frequency of oscillation higher, threaten the stability of combining inverter control system.The thought of active damping technology is to introduce and is attracted to conjugation resonance limit in the stability region independent zero point and leaves certain margin of safety, or introduces conjugation and offset conjugation resonance limit zero point.Existing a large amount of document is studied the active damping method: Dahono is through the effect of research damping resistance in LCL type combining inverter ssystem transfer function; Utilize the signal flow graph conversion that in esse resistive element is transferred in the controller architecture; The notion of virtual resistance (Virtual resistor) has been proposed, introduced 4 kinds with damping resistance mode corresponding virtual resistance implementation commonly used.The another kind of mode that increases system damping is to feed back and realize through increasing the filter status variable: have document propose to adopt series connection leading-the active damping method of the filter capacitor Voltage Feedback of (Lead-Lag) module that lags behind; Also have document to propose active damping method based on the filter capacitor current feedback of proportional component; The method that also has document to propose employing feedback fraction network access electric current and capacitance current is reduced to single order with three rank LCL and is reached elimination resonance.

Above-mentioned active damping circuit all can be realized the effective damping of LCL filter resonance limit, but limited to the raising effect of network access current waveform quality, particularly receives the influence of Voltage Harmonic and distortion disturbance easily.

Summary of the invention

The purpose of the utility model provides the active damping circuit of a kind of LCL combining inverter system, on the basis of prior art network access current controller (ratio resonance adjuster), introduces net side inductive drop u ₂Feedback realize the resonance damping of LCL filter, improving network access current waveform quality to the inhibitory action of Voltage Harmonic influence.

For realizing above-mentioned purpose; The utility model adopts following technical scheme: the realization principle of the utility model is: through conjugation zero point or independent zero point are set; Offset conjugation resonance limit that the LCL filter produces or conjugation resonance limit is attracted in the stability region in the combining inverter system; Adopt net side inductor current feedback and the state variable of introducing in the LCL filter to carry out the method realization of feedback compensation, the state variable system net side inductive drop in the said introducing LCL filter is through carrying out feedback compensation to net side inductive drop; Control the resonance damping of LCL filter, and then the network access current waveform and the amplitude of combining inverter system are controlled.On the basis of above-mentioned principle, parallel connection is arranged or connects two kinds of active damping circuit:

The active damping circuit of a kind of LCL combining inverter system; The combining inverter system comprises inverter and LCL type network access filter; It is characterized in that: a controller is set, and this controller comprises that ratio resonance adjuster, differential regulator, subtracter and PWM produce circuit, and the network access electric current that obtains in LCL type network access filter net side through current sensor inputs to first subtracter; Network access current reference value also inputs to first subtracter; First subtracter exports ratio resonance adjuster to, and ratio resonance adjuster exports second subtracter to, and the net side inductive drop that in LCL type network access filter, obtains through voltage sensor is through behind the differential regulator; Also input to second subtracter; The PWM that exports to of second subtracter produces circuit, and PWM produces the output of circuit and delivers to inverter through isolated drive circuit, constitutes the active damping circuit of parallel-connection structure.

The active damping circuit of a kind of LCL combining inverter system; The combining inverter system comprises inverter and LCL type network access filter; It is characterized in that: a controller is set, and this controller comprises that ratio resonance adjuster, differential regulator, subtracter and PWM produce circuit, and the network access electric current that obtains in LCL type network access filter net side through current sensor inputs to first subtracter; Network access current reference value also inputs to first subtracter; First subtracter exports ratio resonance adjuster to, and ratio resonance adjuster exports second subtracter to, and the net side inductive drop that in LCL type network access filter, obtains through voltage sensor also inputs to second subtracter; Second subtracter export differential regulator to; The PWM that exports to of differential regulator produces circuit, and PWM produces the output of circuit and delivers to inverter through isolated drive circuit, constitutes the active damping circuit of cascaded structure.

The advantage of the utility model and showing effect: the utility model is introduced net side inductive drop u on the basis of prior art network access current controller (ratio resonance adjuster) ₂Feedback realize the resonance damping of LCL filter, network access current i ₂The ratio resonant controller realize the network access Current Control.Net side inductive drop u ₂When feedback realizes the damping of LCL filter resonance, can also effectively suppress the influence of Voltage Harmonic to the network access electric current.

Description of drawings

Fig. 1 is the parallel connection type structure of the utility model, (a) parallel connection type circuit diagram; (b) parallel connection type control block diagram;

Fig. 2 is the tandem type structural circuit figure of the utility model;

Fig. 3 is the utility model net side inductive drop u ₂Derivative Feedback and existing capacitance voltage u _CDerivative Feedback and capacitance current i _CController characteristic curve under three kinds of active damping methods of Proportional Feedback, wherein: (a) network access open current loop transfer function Bode figure; (b) line voltage suppresses admittance I ₂/ U _g, be used for weighing the inhibition ability of controller to the line voltage disturbance;

Fig. 4 is network access electric current, a line voltage experimental waveform under three kinds of active damping circuit of Fig. 3, wherein: (a) the utility model net side inductive drop u ₂Derivative Feedback; (b) existing capacitance voltage u _CDerivative Feedback; (c) existing capacitance current i _CProportional Feedback.

Embodiment

Below in conjunction with accompanying drawing and embodiment the utility model is elaborated.

The symbol of accompanying drawing and label declaration: U _PV---the inverter input voltage; S ₁～S ₄---power switch pipe; u _g---line voltage; L ₁, L ₂---the network access filter inductance; i ₁, I ₁, u ₁, U ₁, r ₁---filter inductance L ₁Electric current, voltage and internal resistance; i ₂, I ₂, u ₂, U ₂, r ₂---filter inductance L ₂Electric current, voltage and internal resistance; C ₁---filter capacitor; i _C, I _C, u _CU _C,---filter capacitor C ₁Electric current and voltage; u _Inv---output voltage between the inverter brachium pontis; I _2ref---the network access current reference; K---inverter equivalence proportional component; G ₂(s)---the network access current controller; k ₁---the Derivative Feedback coefficient.

The utility model is introduced net side inductance L on the basis of prior art network access current controller (ratio resonance adjuster) ₂Voltage u ₂Feedback realize the resonance damping of LCL filter.The concrete circuit of realizing has two kinds in the active damping circuit diagram 2 (a) of active damping circuit diagram 1 (a) and the cascaded structure of parallel-connection structure.Among Fig. 1 (a), inverter 1, LCL type network access filter 2 and isolated drive circuit 5 are known circuit.Controller 3 is set, produces circuit comprising ratio resonance adjuster, differential regulator 4, subtracter and PWM, they are known module.The network access electric current that obtains in LCL type network access filter net side through current sensor inputs to first subtracter; Network access current reference value also inputs to first subtracter; First subtracter exports ratio resonance adjuster to; Ratio resonance adjuster exports second subtracter to, and the net side inductive drop that in LCL type network access filter, obtains through voltage sensor also inputs to second subtracter through behind the differential regulator; The PWM that exports to of second subtracter produces circuit, and PWM produces the output of circuit and delivers to inverter through isolated drive circuit.Among Fig. 2 (a); The network access electric current that obtains in LCL type network access filter net side through current sensor inputs to first subtracter; Network access current reference value also inputs to first subtracter, and first subtracter exports ratio resonance adjuster to, and ratio resonance adjuster exports second subtracter to; The net side inductive drop that in LCL type network access filter, obtains through voltage sensor also inputs to second subtracter; Second subtracter export differential regulator to, the PWM that exports to of differential regulator produces circuit, PWM produces the output of circuit and delivers to inverter through isolated drive circuit.

The network access Current Control block diagram of single-phase photovoltaic grid-connected inverter for the ease of analyzing, is approximately a gain link K with the PWM inversion unit shown in accompanying drawing 1 (b).In accompanying drawing 1 (b), I _2refBe network access current reference, G ₂(s) be network access current controller transfer function, can make inverter import electric energy to electrical network with the power factor of setting through the control inverter output current.Technology such as the at present normal PI of the employing control of the Current Control of single-phase grid-connected inverter, the ring control that stagnates, PI control have algorithm simple with characteristics such as reliability height, therefore be widely used, can't realize the floating tracking but conventional PI controls the offset of sinusoidal reference current; Hysteresis current control has characteristics such as realize simple and dynamic corresponding is fast, but switching frequency, loss and control precision receive the influence of hysteresis band.Ratio resonance (PR) control is made up of proportional controller resonant adjuster; Gain is infinitely great at the fundamental frequency place; Thereby the zero steady-state error that can realize the sinusoidal fundamental wave electric current is followed the tracks of, and this joint compares several kinds of active damping methods under the prerequisite of selecting the PR controller in advance for use.The PR controller transfer function is suc as formula shown in (1)

$G_2\left(s\right)=k_p+\frac{2k_{r}s}{s^2+{\mathrm{\ω}}_g^2}---\left(1\right)$

1. according to adopting net side filter inductance voltage u ₂The active damping circuit (being the parallel-connection structure of the utility model) of feedback is inverter network access Current Control block diagram down, and the transfer function that can derive combining inverter network access electric current does

$I_2\left(u_2\right)=\frac{{\mathrm{KG}}_2\left(s\right)}{s^3\&CenterDot;L_1{L}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s^2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KL}}_2+s\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+K{G}_2\left(s\right)}\&times;I_{2\mathrm{ref}}$

(2)

$-\frac{s^2\&CenterDot;L_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+}{{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="HDA0000109842810000011.png"\; state="\{\{state\}\}">s</figure-callout>}}^3\&CenterDot;L_1{L}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s^2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KL}}_2+s\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+{\mathrm{KG}}_2\left(s\right)}\&times;U_g$

2. according to existing employing filter capacitor voltage u _CInverter network access Current Control block diagram under the active damping circuit of feedback, the transfer function that can derive combining inverter network access electric current does

$I_2\left(u_C\right)=\frac{{\mathrm{KG}}_2\left(s\right)}{s^3\&CenterDot;L_1{L}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s^2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KL}}_2+s\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+{\mathrm{KG}}_2\left(s\right)}\&times;I_{2\mathrm{ref}}$

(4)

$-\frac{s^2\&CenterDot;L_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s\&CenterDot;k_{1}K+1}{{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="HDA0000109842810000011.png"\; state="\{\{state\}\}">s</figure-callout>}}^3\&CenterDot;L_1{L}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s^2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KL}}_2+s\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+K{G}_2\left(s\right)}\&times;U_g$

3. according to existing employing filter capacitor current i _CInverter network access Current Control block diagram under the active damping circuit of feedback, the transfer function that can derive combining inverter network access electric current does

$I_2\left(i_C\right)=\frac{{\mathrm{KG}}_2\left(s\right)}{{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="HDA0000109842810000011.png"\; state="\{\{state\}\}">s</figure-callout>}}^3\&CenterDot;L_1{L}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s^2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KL}}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+{\mathrm{KG}}_2\left(s\right)}\&times;I_{2\mathrm{ref}}$

(5)

$-\frac{s^2\&CenterDot;L_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KC}}_1+1}{{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="HDA0000109842810000011.png"\; state="\{\{state\}\}">s</figure-callout>}}^3\&CenterDot;L_1{L}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s^2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\mathrm{KL}}_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+s\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000109842810000011.png,HDA0000109842810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+{\mathrm{KG}}_2\left(s\right)}\&times;U_g$

For comprehensive more above-mentioned three kinds of antihunt circuits, select unified filter parameter group L ₁=1.0mH, C ₁=10.0 μ F, L ₂=1.0mH and f _SW=10kHz supposes K=1, realizes that calculating the damping feedback factor under the condition of system damping than ζ=0.707 is respectively 1.36 * 10 ^-4, 1.36 * 10 ^-4With 10.60, and primary election k _p=4, k _r=100.

Fig. 3 (a) is the open-loop transfer function Bode figure of network access electric current to reference, can find out, three kinds of damping structures can reach same network access Current Control performance down, with accord with theoretical analysis.In the closed loop transfer function, of network access electric current, also contain the disturbing influence of line voltage, its influence can be used ' admittance function I ₂/ U _g' weigh, accompanying drawing 3 (b) is the Bode figure of three kinds of line voltage admittance inhibition functions under the damping structure.Can find out; They are consistent in the inhibition ability of fundamental frequency section; But the harmonic pollution that contains abundant harmonic voltage, particularly medium and low frequency owing to line voltage is more serious; In order to suppress the influence of these harmonic voltages to the network access electric current, many documents have proposed to add the influence that a plurality of PR controllers suppress Voltage Harmonic.But the bandwidth that is limited to the network access current regulator, the adding limited amount of PR controller, otherwise can cause system unstable.(b) can find out significantly from accompanying drawing 3, net side inductive drop u ₂The damping structure of feedback has bigger net to press harmonic wave to suppress ability in the medium and low frequency section, and this is other two kinds of good characteristics that damping structure did not have, and can improve the quality of network access electric current.

Validity for the active damping circuit of the employing net side inductive drop Derivative Feedback of the correctness of the further above-mentioned analysis of checking and the utility model; Build a 3kW single-phase full bridge combining inverter; Dc voltage 350V, line voltage 220V/50Hz, the LCL filter parameter is: L ₁=1.066mH, L ₂=1.022mH, C ₁=10 μ F, f _SW=10kHz.Under the active damping scheme that adopts net side inductive drop, filter capacitor voltage and current feedback thereof, combining inverter network access electric current and grid voltage waveform keep network access electric current outer loop parameter constant like Fig. 4 (a) and (b) with (c) in the experiment.

As can be seen from Figure 4; Three kinds of active damping circuit have all been realized effective resonance damping; Contrast accompanying drawing 4 (a) with (b) in the network access current waveform can find out, net side inductive drop Derivative Feedback and can effectively reduce of the influence of line voltage low-frequency harmonics the network access electric current.

Claims (2)

1. the active damping circuit of a LCL combining inverter system; The combining inverter system comprises inverter and LCL type network access filter; It is characterized in that: a controller is set, and this controller comprises that ratio resonance adjuster, differential regulator, subtracter and PWM produce circuit, and the network access electric current that obtains in LCL type network access filter net side through current sensor inputs to first subtracter; Network access current reference value also inputs to first subtracter; First subtracter exports ratio resonance adjuster to, and ratio resonance adjuster exports second subtracter to, and the net side inductive drop that in LCL type network access filter, obtains through voltage sensor is through behind the differential regulator; Also input to second subtracter; The PWM that exports to of second subtracter produces circuit, and PWM produces the output of circuit and delivers to inverter through isolated drive circuit, constitutes the active damping circuit of parallel-connection structure.

2. the active damping circuit of a LCL combining inverter system; The combining inverter system comprises inverter and LCL type network access filter; It is characterized in that: a controller is set, and this controller comprises that ratio resonance adjuster, differential regulator, subtracter and PWM produce circuit, and the network access electric current that obtains in LCL type network access filter net side through current sensor inputs to first subtracter; Network access current reference value also inputs to first subtracter; First subtracter exports ratio resonance adjuster to, and ratio resonance adjuster exports second subtracter to, and the net side inductive drop that in LCL type network access filter, obtains through voltage sensor also inputs to second subtracter; Second subtracter export differential regulator to; The PWM that exports to of differential regulator produces circuit, and PWM produces the output of circuit and delivers to inverter through isolated drive circuit, constitutes the active damping circuit of cascaded structure.

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