CN104467013B - Large-sized photovoltaic electric station grid connection inverter active outer loop control method and device - Google Patents

Abstract

The invention discloses a kind of large-sized photovoltaic electric station grid connection inverter active outer loop control method, the method specifically includes following steps: determine photovoltaic cell output voltage v_PVWith electric current i_PV；Determine the power P that photovoltaic cell exports_PV；Determine the slope Δ P of the output power from photovoltaic cells and voltage_PV/Δv_PV；Determine that MPPT controls ring output inverter DC side reference current i_{dc_ref}；Determine photovoltaic meritorious output reference value P_ref.The present invention is directed to the single-stage main circuit structure that large-sized photovoltaic power station is commonly used, on the basis of MPPT outer shroud and grid-connected current internal ring two ring control, propose a kind of novel meritorious outer loop control method controlling ring output inverter DC side reference current based on MPPT, this control method structure is relatively simple, it is prone to set up the mathematical model of differential form, is suitably applied the analysis large-sized photovoltaic power station impact on power system dynamic step response.

Description

Large-sized photovoltaic electric station grid connection inverter active outer loop control method and device

Technical field

The present invention relates to maximal power tracing in photovoltaic plant, be specifically related to a kind of large-sized photovoltaic electric station grid connection inverter active outer shroud Control method

Background technology

In " solar electrical energy generation development " 12 " planning " with " State Council is about the some meanings promoting that photovoltaic industry develops in a healthy way See " under Policy Background, some large-sized photovoltaic power stations in succession put into operation in NORTHWEST CHINA area or are incorporated into the power networks.In view of grid-connected Inverter control structures is to large-sized photovoltaic power station economy, the material impact of reliability service, and analyzes large-sized photovoltaic power station to electric power The needs of system dynamic characteristic impact, the research of expansion large-sized photovoltaic electric station grid connection control strategy for inverter and modeling seems and particularly must Want.

The most grid-connected have single-stage and two kinds of main circuit topologies of two-layer configuration.In two-layer configuration, prime DC/DC mainly realizes Maximal power tracing and boost function, rear class DC/AC realizes stable DC chain voltage and inversion grid connection function.Main flow based on electricity The DC/AC control circuit of potential source type is in double-loop control mode, and the current reference generated with reference to outer ring controller, through internal ring Control realization inversion grid connection.But based on efficiency, cost, the considering of system dimension, the commonly used single-stage in current large-sized photovoltaic power station Structure synchronizing mode, the grid-connected DC/AC control circuit of two-layer configuration is not directly adaptable to use the grid-connected system of single step arrangement System.

Single step arrangement photovoltaic combining inverter can be classified as two rings and the big class of three close-loop control two according to the complexity of control system.Three Ring control structure controls to add the complexity of control system and the difficulty of engineer applied compared with two rings, is unfavorable for promoting large-sized photovoltaic electricity The scale application process stood.For MPPT control ring output, mainly have DC-link voltage, grid-connected active power and Net watt current three kinds controls the way of output.Single step arrangement combining inverter controlled volume is DC voltage, simultaneously in two ring controls Structure processed is chosen DC voltage as MPPT control ring output be unsatisfactory for general control rule.Furthermore, although MPPT Control the ring grid-connected active power of output or watt current reference is capable of maximal power tracing, but inverter direct-flow side electric current is with straight The contact of stream side voltage is tightr than grid-connected active power and watt current.Finally, in combining inverter modeling of control system side Face, MPPT controls the commonly used mode in sampling instant logic-based judgement change controlled quentity controlled variable of ring and realizes controlling target, it is difficult to Set up the mathematical model of differential form.

Summary of the invention

In consideration of it, it is an object of the invention to provide a kind of large-sized photovoltaic electric station grid connection inverter active outer loop control method and device.

An object of the present invention is achieved through the following technical solutions, large-sized photovoltaic electric station grid connection inverter active outer shroud control Method processed, specifically includes following steps:

Determine photovoltaic cell output voltage v_PVWith electric current i_PV；

Determine the power P that photovoltaic cell exports_PV；

P_PV=v_PV*i_PV

Determine the slope Δ P of the output power from photovoltaic cells and voltage_PV/Δv_PV；

${\mathrm{\ΔP}}_{\mathrm{PV}}/{\mathrm{\Δv}}_{\mathrm{PV}}=\frac{P_{\mathrm{pv}}\left({\mathrm{nT}}_s\right)-P_{\mathrm{pv}}\left[(n-1)T_s\right]}{v_{\mathrm{pv}}\left({\mathrm{nT}}_s\right)-v_{\mathrm{pv}}\left[(n-1)T_s\right]}$

Wherein P_pv(nT_s) represent calculated photovoltaic output P under current sample time_PV, v_pv(nT_s) represent under current sample time The photovoltaic cell output voltage v detected_PV；P_pv[(n-1)T_s] represent calculated photovoltaic output under a upper sampling instant P_PV, v_pv[(n-1)T_s] represent the photovoltaic cell output voltage v that a upper sampling instant detects_PV。

Determine that MPPT controls ring output inverter DC side reference current i_{dc_ref}；

$i_{\mathrm{dc}\_\mathrm{ref}}\left[(n+1)T_s\right]=i_{\mathrm{dc}\_\mathrm{ref}}\left({\mathrm{nT}}_s\right)-K\·\frac{{\mathrm{\ΔP}}_{\mathrm{pv}}}{{\mathrm{\Δv}}_{\mathrm{pv}}}$

Wherein i_{dc_ref}[(n+1)T_s], i_{dc_ref}(nT_s) represent the inverter direct-flow side reference under next sampling instant, current sample time respectively Electric current i_{dc_ref}, K is step-size factor,For DC side reference current i_{dc_ref}Disturbance step-length；

Determine photovoltaic meritorious output reference value P_ref, P_ref=v_PV*i_{dc_ref},

Wherein v_PVFor photovoltaic cell output voltage, i_{dc_ref}For DC side reference current.

Further, described photovoltaic meritorious output reference value P_refBy DC side reference current i_{dc_ref}With the photovoltaic output voltage detected v_PVIt is multiplied and obtains.

Further, photovoltaic meritorious output reference value P is being determined_refAlso include after step determining reactive power reference qref Q_refWith reference electricity Stream calculation step, described reactive power reference qref Q_refIt is by combining employing burning voltage control or the control of firm power factor Obtain；Described reference current calculation procedure is: combine photovoltaic meritorious output reference value P_ref, reactive power reference qref Q_refAnd electrical network Voltage obtains grid-connected current reference value, and the calculating process of reference current is specific as follows:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]$

$\left[\begin{array}{c}{i}_{\mathrm{\α}\_\mathrm{ref}}\\ i_{\mathrm{\β}\_\mathrm{ref}}\end{array}\right]=\frac{1}{u_{\mathrm{\α}}^2+u_{\mathrm{\β}}^2}\left[\begin{array}{cc}{u}_{\mathrm{\α}}& u_{\mathrm{\β}}\\ u_{\mathrm{\β}}& -u_{\mathrm{\α}}\end{array}\right]\left[\begin{array}{c}{P}_{\mathrm{ref}}\\ Q_{\mathrm{ref}}\end{array}\right],$

Wherein u_a, u_b, u_cFor the three-phase power grid voltage detected, u_α, u_βFor under biphase rest frame represent line voltage, i_{α_ref}, i_{β_ref}For the internal ring current controller reference value under biphase rest frame.

Further, described MPPT controls ring according to present operating point photovoltaic output characteristics variable step disturbance photovoltaic inverter direct-flow side Reference current, step sizes is by Δ P_PV/Δv_PVObtain with the product of K.

The two of the purpose of the present invention are achieved through the following technical solutions: a kind of for large-sized photovoltaic electric station grid connection inverter active Outer loop control mechanism, including

For determining the device of photovoltaic cell output voltage and electric current；

For determining the device of the output power from photovoltaic cells；

For determining the device of the output power from photovoltaic cells and voltage slope；

For determining that MPPT controls the device of ring output inverter DC side reference current；

The device of reference value is exported for determining that photovoltaic is gained merit.

Further, the device for determining reactive power reference qref is also included and for determining the device of reference current, described reference The device of electric current obtains grid-connected current reference value according to photovoltaic meritorious output reference value, reactive power reference qref and line voltage, ginseng The calculating process examining electric current is specific as follows:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]$

$\left[\begin{array}{c}{i}_{\mathrm{\α}\_\mathrm{ref}}\\ i_{\mathrm{\β}\_\mathrm{ref}}\end{array}\right]=\frac{1}{u_{\mathrm{\α}}^2+u_{\mathrm{\β}}^2}\left[\begin{array}{cc}{u}_{\mathrm{\α}}& u_{\mathrm{\β}}\\ u_{\mathrm{\β}}& -u_{\mathrm{\α}}\end{array}\right]\left[\begin{array}{c}{P}_{\mathrm{ref}}\\ Q_{\mathrm{ref}}\end{array}\right],$

Wherein u_a, u_b, u_cFor the three-phase power grid voltage detected, u_α, u_βFor under biphase rest frame represent line voltage, i_{α_ref}, i_{β_ref}For the internal ring current controller reference value under biphase rest frame.

Owing to have employed technique scheme, present invention have the advantage that:

The present invention is directed to the single-stage main circuit structure that large-sized photovoltaic power station is commonly used, at MPPT outer shroud and grid-connected current internal ring two On the basis of ring controls, it is proposed that a kind of novel meritorious outer shroud controlling ring output inverter DC side reference current based on MPPT Control method, this control method structure is relatively simple, it is easy to set up the mathematical model of differential form, is suitably applied analysis large-scale The photovoltaic plant impact on power system dynamic step response.

Accompanying drawing explanation

In order to make the object, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing, the present invention is made further Describe in detail, wherein:

Fig. 1 is single-stage photovoltaic grid-connected system main circuit structure schematic diagram；

Fig. 2 be photovoltaic power station grid connected inverter gain merit outer shroud control control block diagram.

Detailed description of the invention

Below with reference to accompanying drawing, the preferred embodiments of the present invention are described in detail；Should be appreciated that preferred embodiment is only The explanation present invention rather than in order to limit the scope of the invention.

The photovoltaic array of capacity about 500kW is generally confluxed and is followed by the DC side of 500kW photovoltaic DC-to-AC converter by large-sized photovoltaic power station, Two 500kW photovoltaic DC-to-AC converters are 1MVA photovoltaic generation unit through double transformer with split windings one capacity of composition, and after warp Cross conflux, boosting finally is connected to the grid.The main circuit structure of separate unit photovoltaic combining inverter is illustrated in fig. 1 shown below.Light after confluxing Photovoltaic array is connected with inverter through DC bus capacitor, and inverter realizes grid-connected under PWM ripple controls.

Set forth herein that the photovoltaic combining inverter being illustrated in fig. 2 shown below is gained merit outer loop control method, the method specifically includes following steps:

S1. photovoltaic cell output voltage v is determined_PVWith electric current i_PV；

S2. the power P that photovoltaic cell exports is determined_PV, P_PV=v_PV*i_PV；

S3. the slope Δ P of the output power from photovoltaic cells and voltage is determined_PV/Δv_PV,

Wherein P_pv(nT_s) represent calculated photovoltaic output under current sample time Power P_PV, v_pv(nT_s) represent the photovoltaic cell output voltage v detected under current sample time_PV；P_pv[(n-1)T_s] in expression Calculated photovoltaic output P under one sampling instant_PV, v_pv[(n-1)T_s] represent the photovoltaic cell that a upper sampling instant detects Output voltage v_PV。

S4. determine that MPPT controls ring output inverter DC side reference current Wherein i_{dc_ref}[(n+1)T_s], i_{dc_ref}(nT_s) represent the inverter direct-flow side reference under next sampling instant, current sample time respectively Electric current i_{dc_ref}, K is step-size factor,For DC side reference current i_{dc_ref}Disturbance step-length；

S5. photovoltaic meritorious output reference value P is determined_ref, P_ref=v_PV*i_{dc_ref}, wherein v_PVFor photovoltaic cell output voltage, i_{dc_ref} For DC side reference current.

In Fig. 2, Δ P_PV/Δv_PVRepresent by the photovoltaic cell output voltage v detected_PVWith electric current i_PVCalculate now photovoltaic The output slope to voltage, Z^-1Representing 1 sampling period of signal lag, MPPT controls output inverter DC side reference Electric current i_{dc_ref}, then with the photovoltaic output voltage v detected_PVIt is multiplied and obtains photovoltaic meritorious output reference value P_ref, this MPPT is controlled Ring processed is according to present operating point photovoltaic output characteristics variable step disturbance photovoltaic inverter direct-flow side reference current i_{dc_ref}, and then affect inverse Become device active voltage with reference to P_ref, it is achieved maximal power tracing.

On the basis of step S5, combine and use burning voltage control or firm power factor to control the reactive power reference obtained Value Q_ref, i.e. constitute the power outer shroud control system of photovoltaic combining inverter.On this basis, calculate in conjunction with line voltage To grid-connected current reference value, grid-connected through current inner loop control realization.

The computational methods of grid-connected current reference value are:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]$

$\left[\begin{array}{c}{i}_{\mathrm{\α}\_\mathrm{ref}}\\ i_{\mathrm{\β}\_\mathrm{ref}}\end{array}\right]=\frac{1}{u_{\mathrm{\α}}^2+u_{\mathrm{\β}}^2}\left[\begin{array}{cc}{u}_{\mathrm{\α}}& u_{\mathrm{\β}}\\ u_{\mathrm{\β}}& -u_{\mathrm{\α}}\end{array}\right]\left[\begin{array}{c}{P}_{\mathrm{ref}}\\ Q_{\mathrm{ref}}\end{array}\right],$ Wherein u_a, u_b, u_cFor the three-phase power grid voltage detected, u_α, u_βFor the line voltage represented under biphase rest frame, i_{α_ref}, i_{β_ref}For the interior circular current control under biphase rest frame Device reference value processed.

According to said method, present invention also offers a kind of large-sized photovoltaic electric station grid connection inverter active outer loop control mechanism, including For determining the device of photovoltaic cell output voltage and electric current；For determining the device of the output power from photovoltaic cells；For determining light Volt cell output and the device of voltage slope；

For determining that MPPT controls the device of ring output inverter DC side reference current；Reference value is exported for determining that photovoltaic is gained merit Device.

Described meritorious outer loop control mechanism, also includes the device for determining reactive power reference qref and for determining reference current Device, the device of described reference current obtains also according to photovoltaic meritorious output reference value, reactive power reference qref and line voltage Net current reference value, the calculating process of reference current is specific as follows:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]$

$\left[\begin{array}{c}{i}_{\mathrm{\α}\_\mathrm{ref}}\\ i_{\mathrm{\β}\_\mathrm{ref}}\end{array}\right]=\frac{1}{u_{\mathrm{\α}}^2+u_{\mathrm{\β}}^2}\left[\begin{array}{cc}{u}_{\mathrm{\α}}& u_{\mathrm{\β}}\\ u_{\mathrm{\β}}& -u_{\mathrm{\α}}\end{array}\right]\left[\begin{array}{c}{P}_{\mathrm{ref}}\\ Q_{\mathrm{ref}}\end{array}\right].$

The present invention is directed to the single-stage main circuit structure that large-sized photovoltaic power station is commonly used, at MPPT outer shroud and grid-connected current internal ring two On the basis of ring controls, it is proposed that a kind of novel meritorious outer shroud controlling ring output inverter DC side reference current based on MPPT Control method, this control method structure is relatively simple, it is easy to set up the mathematical model of differential form, is suitably applied analysis large-scale The photovoltaic plant impact on power system dynamic step response.

The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, it is clear that those skilled in the art can The present invention is carried out various change and modification without departing from the spirit and scope of the present invention.So, if these of the present invention are repaiied Change and belong within the scope of the claims in the present invention and equivalent technologies thereof with modification, then the present invention is also intended to comprise these changes and become Including type.

Claims (5)

1. large-sized photovoltaic electric station grid connection inverter active outer loop control method, it is characterised in that: specifically include following steps Determine photovoltaic cell output voltage v_PVWith electric current i_PV；

Determine the power P that photovoltaic cell exports_PV；

P_PV=v_PV*i_PV

Determine the slope Δ P of the output power from photovoltaic cells and voltage_PV/Δv_PV；

${\mathrm{\ΔP}}_{PV}/{\mathrm{\Δv}}_{PV}=\frac{P_{pv}\left({\mathrm{nT}}_s\right)-P_{pv}\[(n-1)T_s\]}{v_{pv}\left({\mathrm{nT}}_s\right)-v_{pv}\[(n-1)T_s\]}$

Wherein P_pv(nT_s) represent the power P of calculated photovoltaic cell output under current sample time_PV, v_pv(nT_s) represent present sample Time inscribe the photovoltaic cell output voltage v detected_PV；P_pv[(n-1)T_s] represent calculated photovoltaic electric under a upper sampling instant The power P of pond output_PV, v_pv[(n-1)T_s] represent the photovoltaic cell output voltage v that a upper sampling instant detects_PV；

Determine that MPPT controls ring output inverter DC side reference current i_{dc_ref}；

$i_{dc\_ref}\[(n+1)T_s\]=i_{dc\_ref}\left({\mathrm{nT}}_s\right)-K\·\frac{{\mathrm{\ΔP}}_{pv}}{{\mathrm{\Δv}}_{pv}}$

Wherein i_{dc_ref}[(n+1)T_s], i_{dc_ref}(nT_s) represent the inverter direct-flow side reference under next sampling instant, current sample time respectively Electric current i_{dc_ref}, K is step-size factor,For DC side reference current i_{dc_ref}Disturbance step-length；

Determine photovoltaic meritorious output reference value P_ref, P_ref=v_PV*i_{dc_ref},

Wherein v_PVFor photovoltaic cell output voltage, i_{dc_ref}For DC side reference current.

Large-sized photovoltaic electric station grid connection inverter active outer loop control method the most according to claim 1, it is characterised in that: really Determine photovoltaic meritorious output reference value P_refAlso include after step determining reactive power reference qref Q_refWith reference current calculation procedure,

Described reactive power reference qref Q_refBe by combine employing burning voltage control or firm power factor control obtain；

Described reference current calculation procedure is: combine photovoltaic meritorious output reference value P_ref, reactive power reference qref Q_refObtain with line voltage To grid-connected current reference value, the calculating process of reference current is specific as follows:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]$

$\left[\begin{array}{c}{i}_{\mathrm{\α}\_ref}\\ i_{\mathrm{\β}\_ref}\end{array}\right]=\frac{1}{u_{\mathrm{\α}}^2+u_{\mathrm{\β}}^2}\left[\begin{array}{cc}{u}_{\mathrm{\α}}& u_{\mathrm{\β}}\\ u_{\mathrm{\β}}& -u_{\mathrm{\α}}\end{array}\right]\left[\begin{array}{c}{P}_{ref}\\ Q_{ref}\end{array}\right],$

Wherein u_a, u_b, u_cFor the three-phase power grid voltage detected, u_α, u_βFor under biphase rest frame represent line voltage, i_{α_ref}, i_{β_ref}For the internal ring current controller reference value under biphase rest frame.

Large-sized photovoltaic electric station grid connection inverter active outer loop control method the most according to claim 1, it is characterised in that: described MPPT control ring is according to present operating point photovoltaic output characteristics variable step disturbance photovoltaic inverter direct-flow side reference current, and step-length is big Little by Δ P_PV/Δv_PVObtain with the product of K.

4. one kind is used for large-sized photovoltaic electric station grid connection inverter active outer loop control mechanism, it is characterised in that: include

For determining the device of photovoltaic cell output voltage and electric current；

For determining the device of the output power from photovoltaic cells；

For determining the device of the output power from photovoltaic cells and voltage slope；

For determining that MPPT controls the device of ring output inverter DC side reference current；

Inverter direct-flow side reference current is i_{dc_ref}；

$i_{dc\_ref}\[(n+1)T_s\]=i_{dc\_ref}\left({\mathrm{nT}}_s\right)-K\·\frac{{\mathrm{\ΔP}}_{pv}}{{\mathrm{\Δv}}_{pv}}$

Wherein i_{dc_ref}[(n+1)T_s], i_{dc_ref}(nT_s) represent the inverter direct-flow side reference under next sampling instant, current sample time respectively Electric current i_{dc_ref}, K is step-size factor,For DC side reference current i_{dc_ref}Disturbance step-length；

The device of reference value is exported for determining that photovoltaic is gained merit；

Photovoltaic meritorious output reference value is P_ref, P_ref=v_PV*i_{dc_ref},

Wherein v_PVFor photovoltaic cell output voltage, i_{dc_ref}For DC side reference current.

Large-sized photovoltaic electric station grid connection inverter active outer loop control mechanism the most according to claim 4, it is characterised in that: also wrap Including the device for determining reactive power reference qref and for determining the device of reference current, the device of described reference current is according to light Volt meritorious output reference value, reactive power reference qref and line voltage obtain grid-connected current reference value, the calculating process of reference current Specific as follows:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]$

$\left[\begin{array}{c}{i}_{\mathrm{\α}\_ref}\\ i_{\mathrm{\β}\_ref}\end{array}\right]=\frac{1}{u_{\mathrm{\α}}^2+u_{\mathrm{\β}}^2}\left[\begin{array}{cc}{u}_{\mathrm{\α}}& u_{\mathrm{\β}}\\ u_{\mathrm{\β}}& -u_{\mathrm{\α}}\end{array}\right]\left[\begin{array}{c}{P}_{ref}\\ Q_{ref}\end{array}\right],$

Wherein u_a, u_b, u_cFor the three-phase power grid voltage detected, u_α, u_βFor under biphase rest frame represent line voltage, i_{α_ref}, i_{β_ref}For the internal ring current controller reference value under biphase rest frame.