CN102222937B - Photovoltaic grid-connected inverter and grid-connected control method thereof - Google Patents
Photovoltaic grid-connected inverter and grid-connected control method thereof Download PDFInfo
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- CN102222937B CN102222937B CN2011101693969A CN201110169396A CN102222937B CN 102222937 B CN102222937 B CN 102222937B CN 2011101693969 A CN2011101693969 A CN 2011101693969A CN 201110169396 A CN201110169396 A CN 201110169396A CN 102222937 B CN102222937 B CN 102222937B
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Abstract
The invention discloses a photovoltaic grid-connected inverter, which comprises a direct current (DC) signal detection module, an inversion module, a transformer, an alternating current (AC) contactor, an AC signal detection module and a control circuit, wherein the control circuit comprises a current loop PI regulator consisting of a d-axis current regulator and a q-axis current regulator, a space vector pulse width modulation (SVPWM) space vector module, a Clark/Park conversion module, a Clark/Park inverse transform module and an excitation command operating module; and the excitation command operating module can output an output quantity serving as a reference signal of the q-axis current regulator and control the inversion module to output a reactive component to pre-excite the transformer. The invention also discloses a grid-connected control method for the photovoltaic grid-connected inverter. Compared with the prior art, the invention has the advantages that: an inverter can be connected to a grid seamlessly, overcurrent impact is prevented, the system loss is reduced, and the reliability and stability of the system are improved.
Description
Technical field
The present invention relates to a kind of photovoltaic combining inverter, relate in particular to a kind of photovoltaic combining inverter and the grid-connected control method thereof of outlet side with isolating transformer that exchange.
Background technology
Photovoltaic generation has from net and grid-connected two kinds of working methods, grid type has proposed higher requirement to inverter, the grid-connected security needs of one side, the electric power of feedback grid must meet the electrical network set quota on the other hand, can not cause harmonic pollution to electrical network, therefore general domestic grid type inverter exchanges outlet side and all is with isolating transformer.Therefore also bring the problem of following two aspects: on the one hand, photovoltaic combining inverter transformer outlet side is directly incorporated into electrical network and can causes the problems such as overcurrent, shock oscillation.For this problem traditional control method, be: the switch access electrical network of charging resistor is first arranged by a closure one road string, transformer is carried out to pre-excitation; Again by another way switch switching access electrical network, as shown in Figure 1.Impact when this control mode can prevent from accessing the electrical network process to a certain extent, but also can have certain rush of current and increase system cost, the access electrical network that the inverter outlet side can not be very desirable in this switching access electrical network process.On the other hand, when the energy shortage of direct current input, particularly in the morning with the situation of rainy weather under, the control mode of this direct grid-connected, can easily cause the frequent switching on and shutting down of system, output side switch or contactor be break-make repeatedly, shorten switch or contactor useful life, reduced system reliability.
Summary of the invention
Technical problem to be solved by this invention is to overcome the frequent switching on and shutting down of the existing system of prior art and the A.C. contactor technical problem of break-make repeatedly, a kind of photovoltaic combining inverter and grid-connected control method thereof are provided, the present invention can realize that inverter is seamless grid-connected, and prevent that overcurrent from impacting, reduce system loss, improve system reliability, stability.
Thinking of the present invention is before grid-connected inverters, utilizes an excitation ordering calculation module controls inversion module output idle component to carry out pre-excitation to the isolating transformer of outlet side, grid-connected again after pre-excitation completes.Particularly, the present invention is by the following technical solutions:
A kind of photovoltaic combining inverter comprises:
The direct current signal detection module, for detection of the DC voltage/current of input side;
Inversion module, be converted to alternating current for the direct current by input;
Transformer, for the ac output end by inverter module and electrical network isolation;
A.C. contactor, be used to switch photovoltaic combining inverter from net net state;
The alternating current signal detection module, for detection of output current and the line voltage of photovoltaic combining inverter;
Control circuit, control for the operation to photovoltaic combining inverter;
Described control circuit comprises electric current loop pi regulator, the SVPWM space vector module be comprised of d shaft current adjuster, q shaft current adjuster, Clark/Park conversion module, Clark/Park inverse transform module, and excitation ordering calculation module, the exportable output variable of described excitation ordering calculation module, as the reference signal of q shaft current adjuster, is controlled inversion module output idle component to the transformer pre-excitation, grid-connected front first the carrying out from the net independent operating of photovoltaic combining inverter, in running, the alternating current signal detection module detects inversion module output current and line voltage, the inversion module output current that detection obtains is through Clark, after the Park conversion, obtain d shaft current adjuster, the feedback signal of q shaft current adjuster, described feedback signal respectively with d shaft current adjuster, the reference signal of q shaft current adjuster compares, the electric current comparison value obtained is output after the electric current loop pi regulator is regulated, output variable after adjusting is done computing with the line voltage through the Clark conversion that the alternating current signal detection module obtains after the Park inverse transformation, again after the Clark inverse transformation, by SVPWM space vector module, carry out PWM pulse width modulation controlled inversion module output voltage transformer is carried out to excitation, after the transformer pre-excitation completed, photovoltaic combining inverter was connected to the grid and generates electricity by way of merging two or more grid systems again.
A kind of grid-connected control method of photovoltaic combining inverter as mentioned above comprises the following steps:
Step 2,, the output variable of the excitation ordering calculation module of usining output, as the reference signal of q shaft current adjuster, is controlled inversion module output idle component transformer is carried out to pre-excitation;
After step 3, pre-excitation completed, photovoltaic combining inverter was connected to the grid.
Further, described excitation ordering calculation module comprises at least one input variable, and the output variable of described excitation ordering calculation module is that input variable is obtained through a monotonically increasing function computing with upper limit.
As a preferred version, the input variable of described excitation ordering calculation module is the no-load current of described transformer.
As another preferred version, the input variable of described excitation ordering calculation module is the no-load current of described transformer, and the mould of line voltage vector.
Described pre-excitation completes, and refers to that specifically following condition all is met:
The exciting current of transformer reaches its no-load current value;
In the whole DC bus-bar voltage detected from direct current signal detection module in net independent operating process, maintain all the time on minimum operation DC bus-bar voltage point and keep one section predefined time t.
Compared to existing technology, the present invention has following beneficial effect:
During the no-load transformer operation, exciting current is mainly idle component, and in transformer steady operation time institute not sudden change of making alive situation, the switching impulse current can be very not large, grid-connected front first the carrying out of photovoltaic combining inverter set up pre-excitation from the net independent operating to transformer, after the transformer pre-excitation completed, its output voltage was consistent with mains voltage signal, DC bus-bar voltage maintains on the minimum operation electrical voltage point, at this moment inverter access electrical network is more steady, can be good at realizing the seamless link of photovoltaic DC-to-AC converter and electrical network, prevented overcurrent impact failure equipment, and can avoid the frequent switching on and shutting down of system and AC contactor break-make problem repeatedly, improved system reliability, reduced system cost.
The accompanying drawing explanation
Fig. 1 is the circuit topological structure schematic diagram of existing photovoltaic combining inverter;
Fig. 2 is the control principle schematic diagram of photovoltaic combining inverter of the present invention;
Fig. 3 is the principle schematic of excitation ordering calculation module of the present invention;
Fig. 4 is the principle schematic of the excitation ordering calculation module when the mould of the no-load current that is input as transformer and line voltage vector;
Fig. 5 is the electrical block diagram of photovoltaic combining inverter of the present invention;
Fig. 6 is the control flow schematic diagram of photovoltaic combining inverter of the present invention.
Embodiment
In order to make the public can fully understand technical spirit of the present invention and beneficial effect; the applicant will describe in detail the specific embodiment of the present invention below by reference to the accompanying drawings; but the applicant is not the restriction to technical scheme to the description of embodiment, anyly according to the present invention design, changes in the form rather than substance all and should be considered as protection scope of the present invention.
Photovoltaic combining inverter of the present invention as shown in Figure 5, comprising: direct current signal detection module 10, for detection of the DC voltage/current of input side; Inversion module 6, be converted to alternating current for the direct current by input; Transformer 9, for the ac output end by inverter module and electrical network isolation; A.C. contactor 12, be used to switch photovoltaic combining inverter from net net state; Alternating current signal detection module 8, for detection of output current and the line voltage of photovoltaic combining inverter; Control circuit 11, control for the operation to photovoltaic combining inverter.
Wherein control circuit 11(is referring to Fig. 2) comprise the electric current loop pi regulator formed by d shaft current adjuster 3, q shaft current adjuster 2, SVPWM space vector module 5, Clark/Park conversion module 4, Clark/Park inverse transform module 7, and an excitation ordering calculation module M.Grid-connected front first the carrying out from the net independent operating of photovoltaic combining inverter, in running, as shown in Figure 2, output variable M_out of excitation ordering calculation module M output, as the reference signal of q shaft current adjuster 2, controls photovoltaic DC-to-AC converter output idle component to transformer 9 excitations.When transformer 9 exciting currents arrive transformer 9 no-load current values, the photovoltaic DC-to-AC converter output voltage signal is consistent with electrical network, and maintain all the time on minimum operation DC bus-bar voltage point after a period of time t in the whole DC bus-bar voltage that direct current signal detection module 10 detects in net independent operating process, control A.C. contactor 12 adhesives, realize accurately being connected to the grid of safety of photovoltaic combining inverter.
As Fig. 2, shown in Figure 5, when photovoltaic combining inverter carries out from the net independent operating before grid-connected, excitation ordering calculation module M output variable M_out is as the reference signal Iq_ref of q shaft current adjuster 2, now the reference signal Id_ref of d shaft current adjuster 3 is made as 0, the input variable M_in1 of excitation ordering calculation module M is through a monotonically increasing function with upper limit, ramp function y=k*x shown in Figure 3 for example, computing output M_out, through the electric current loop pi regulator, regulate, control inversion module 6 output idle components.The input variable M_in1(of wherein said excitation ordering calculation module M is the x in ramp function) be the no-load current Iom of transformer.The input variable M_in1 of described excitation ordering calculation module M also can as shown in Figure 4, adopt the mould of three phase network voltage vector and the no-load current of transformer 9.
Grid-connected control procedure of the present invention as shown in Figure 6, 8 pairs of inversion module 6 output currents of alternating current signal detection module and line voltage detect, the inversion module 6 output current Ia-IPM that detection obtains, Ib-IPM, Ic-IPM obtains d shaft current adjuster 3 under rotational coordinates after 7 conversion of Clark/Park conversion module, the feedback signal Id-feedback of q shaft current adjuster 2, Iq-feedback, with reference to signal Id_ref, Iq_ref and feedback signal Id-feedback, Iq-feedback compares, obtain electric current comparison value △ Id, △ Iq, electric current comparison value △ Id, the output variable Id_out of △ Iq after the electric current loop pi regulator is regulated, Iq_out respectively with the decoupling zero amount-
,
as vector, obtain the decoupling zero control that Ud_ref, Uq_ref realize d shaft current loop, q shaft current loop, through Park inverse transform module 4, obtain the set-point Uout1 of inversion module 6 output voltages, Uout1 and alternating current signal detection module 8 detect the line voltage Unet through the Clark conversion obtained and make vector, vector Uout passes through the Clark inverse transformation again, then by SVPWM space vector module 5, carry out the PWM pulse-width modulation, output pwm signal, control inversion module 6 output AC voltages to transformer 9 excitations.Wherein Clark and Park transformation for mula are as follows:
The Clark transformation for mula:
The Park transformation for mula:
。
In above-mentioned transformer pre-excitation control procedure, the output current of controlling inversion module increases gradually from 0, the output voltage of photovoltaic combining inverter increases from 0 gradually along with corresponding exciting current increases also, and phase place remains consistent with electric network voltage phase, progressively transformer is carried out to pre-excitation, when the inversion module output current exciting current that is transformer increases to the amplitudes such as no-load transformer electric current, inverter output voltage also reaches consistent with electrical network, now keeps constant this output voltage signal output of inverter; Until remain on minimum operation DC bus-bar voltage point and maintenance a period of time t in the whole DC bus-bar voltage detected from direct current signal detection module in net independent operating process, t=5s for example, controlling A.C. contactor 12 adhesives is connected to the grid, if during the DC side energy shortage, there will be DC bus-bar voltage to fall lower than minimum operation DC bus-bar voltage point, stop from the net independent operating, and again detect inverter startup, repeat above-mentioned independent operating process.
The phase angle of using when wherein said electric network voltage phase and inverter output voltage and electric current Park conversion, inverse transformation
Have in the prior art a variety of methods to obtain, wherein two kinds preferably method be: the one, line voltage carries out the Clark conversion, under static rotational coordinates by right
With
Arctan function, and ask and obtain electrical network vector voltage phase angle through the filter filtering designed
The 2nd, adopt three-phase phase-locked loop to obtain phase angle
.
The present invention is owing to adopting technique scheme, during the no-load transformer operation, exciting current is mainly idle component, and in transformer steady operation time institute not sudden change of making alive situation, the switching impulse current can be very not large, grid-connected front first the carrying out of photovoltaic combining inverter set up excitation from the net independent operating to transformer, after the transformer pre-excitation completed, its output voltage was consistent with mains voltage signal, DC bus-bar voltage maintains on the minimum operation electrical voltage point, at this moment inverter access electrical network is more steady, can be good at realizing the seamless link of photovoltaic DC-to-AC converter and electrical network, prevented overcurrent impact failure equipment, and can avoid the frequent switching on and shutting down of system and AC contactor break-make problem repeatedly, improved system reliability, reduced system cost.
Claims (8)
1. photovoltaic combining inverter comprises:
The direct current signal detection module, for detection of the DC voltage/current of input side;
Inversion module, be converted to alternating current for the direct current by input;
Transformer, for the ac output end by inverter module and electrical network isolation;
A.C. contactor, be used to switch photovoltaic combining inverter from net net state;
The alternating current signal detection module, for detection of output current and the line voltage of photovoltaic combining inverter;
Control circuit, control for the operation to photovoltaic combining inverter;
It is characterized in that,
Described control circuit comprises electric current loop pi regulator, the SVPWM space vector module be comprised of d shaft current adjuster, q shaft current adjuster, Clark/Park conversion module, Clark/Park inverse transform module, and excitation ordering calculation module, the exportable output variable of described excitation ordering calculation module, as the reference signal of q shaft current adjuster, is controlled inversion module output idle component to the transformer pre-excitation, grid-connected front first the carrying out from the net independent operating of photovoltaic combining inverter, in running, the alternating current signal detection module detects inversion module output current and line voltage, the inversion module output current that detection obtains is through Clark, after the Park conversion, obtain d shaft current adjuster, the feedback signal of q shaft current adjuster, described feedback signal respectively with d shaft current adjuster, the reference signal of q shaft current adjuster compares, the electric current comparison value obtained is output after the electric current loop pi regulator is regulated, output variable after adjusting is done computing with the line voltage through the Clark conversion that the alternating current signal detection module obtains after the Park inverse transformation, again after the Clark inverse transformation, by SVPWM space vector module, carry out PWM pulse width modulation controlled inversion module output voltage transformer is carried out to excitation, after the transformer pre-excitation completed, photovoltaic combining inverter was connected to the grid and generates electricity by way of merging two or more grid systems again, described excitation ordering calculation module comprises at least one input variable, and the output variable of described excitation ordering calculation module is that input variable is obtained through a monotonically increasing function computing with upper limit.
2. photovoltaic combining inverter as claimed in claim 1, is characterized in that, the input variable of described excitation ordering calculation module is the no-load current of described transformer.
3. photovoltaic combining inverter as claimed in claim 1, is characterized in that, the input variable of described excitation ordering calculation module is the no-load current of described transformer, and the mould of line voltage vector.
4. the grid-connected control method of photovoltaic combining inverter as claimed in claim 1, is characterized in that, comprises the following steps:
Step 1, grid-connected front first the carrying out from the net independent operating of photovoltaic combining inverter;
The output variable of step 2, the excitation ordering calculation module of usining output, as the reference signal of q shaft current adjuster, is controlled inversion module output idle component transformer is carried out to pre-excitation; Described excitation ordering calculation module comprises at least one input variable, and the output variable of described excitation ordering calculation module is that input variable is obtained through a monotonically increasing function computing with upper limit;
After step 3, pre-excitation completed, photovoltaic combining inverter was connected to the grid.
5. the grid-connected control method of photovoltaic combining inverter as claimed in claim 4, is characterized in that, the input variable of described excitation ordering calculation module is the no-load current of described transformer.
6. the grid-connected control method of photovoltaic combining inverter as claimed in claim 4, is characterized in that, the input variable of described excitation ordering calculation module is the no-load current of described transformer, and the mould of line voltage vector.
7. as the grid-connected control method of photovoltaic combining inverter as described in claim 4-6 any one, it is characterized in that, described pre-excitation completes, and refers to that specifically following condition all is met:
The exciting current of transformer reaches its no-load current value;
In the whole DC bus-bar voltage detected from direct current signal detection module in net independent operating process, maintain all the time on minimum operation DC bus-bar voltage point and keep one section predefined time t.
8. the grid-connected control method of photovoltaic combining inverter as claimed in claim 7, is characterized in that, described predefined time t is 5 seconds.
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