CN104283505A - Current equalizing control method of double BOOST circuits of two-stage photovoltaic power generation system - Google Patents

Abstract

The invention discloses a current equalizing control method of double BOOST circuits of a two-stage photovoltaic power generation system. The currents of the two BOOST circuits are sampled in real time through a system. The input current of one BOOST circuit serves as the reference, a duty ratio increment is worked out through the two BOOST input currents by means of a PI regulator, the on-off time (namely the duty ratio) of a switching device of the other BOOST circuit is corrected with the increment, and thus the currents of the two BOOST circuits are made equal. The problem that the currents of the two BOOST circuits running in parallel connection are unequal is solved, and thus the problems that the service life of a device with an overcurrent circuit becomes shorter, and an inverter is shut down due to overcurrent are avoided.

Description

The two BOOST circuit current-sharing control method of two-stage type photovoltaic generating system

Technical field

The invention belongs to technical field of photovoltaic power generation, be specifically related to the two BOOST circuit current-sharing control method of a kind of two-stage type photovoltaic generating system.

Background technology

In recent years, group string data photovoltaic DC-to-AC converter has had and has developed faster, group string inverter has multichannel MPPT (MPPT maximum power point tracking) follow-up control, each group MPPT can independently control to follow the trail of maximum power point, effectively can reduce like this and to block due to partial phantom or the inconsistent photovoltaic array caused of component characteristic cannot the impact of Maximum Power Output, compare centralized inverter, group string data photovoltaic DC-to-AC converter generating efficiency is high, MPPT voltage range is wide, large-scale application will be obtained in distributed photovoltaic power generation system, also application is to a certain degree had in some large-sized photovoltaic power stations.

Because group string data photovoltaic DC-to-AC converter direct current input side voltage is lower, therefore need BOOST booster circuit to improve input voltage, orthogonal conversion is carried out for inverter circuit, the group string data photovoltaic DC-to-AC converter having two-way MPPT to input, correspond to two-way BOOST booster circuit, but two-way circuit can make its equiva lent impedance inconsistent due to the reason such as line impedance and switching characteristic, this will cause when normally running, the electric current flowing through two-way circuit is unequal, that is not current-sharing, the road flowing through larger current for a long time can cause device to shorten useful life, and another route is little and be not fully utilized in flowing through electric current, inverter overcurrent even can be caused time serious to shut down because of not current-sharing.

Summary of the invention

The object of this invention is to provide the two BOOST circuit current-sharing control method of a kind of two-stage type photovoltaic generating system, to solve pair lifetime that BOOST circuit inequality conductance causes and overcurrent halting problem.

In order to realize above object, the technical solution adopted in the present invention is: the two BOOST circuit current-sharing control method of a kind of two-stage type photovoltaic generating system, the method comprises the steps:

(1) input current of real-time sampling two-way BOOST circuit, making the electric current of BOOST1 circuit be the electric current of reference current I_ref, BOOST2 circuit is I_fdb, calculates the difference Error of two-way electric current;

(2) using the input of current differential Error as pi regulator, in pi regulator, proportional integral computing is carried out to it;

(3) using the output valve d (k) of pi regulator as duty ratio correction duty, then using the Duty ratio control amount Duty_bst2 of the Duty ratio control amount Duty_bst1 sum of itself and current BOOST1 circuit switch device as BOOST2 circuit switch device;

(4) duty ratio Duty_bst2 is carried out sinusoidal pulse width modulation, generate the break-make that PWM ripple removes control BOOST2 circuit switch device, thus the input current value of control BOOST2 circuit is approached to the input current of BOOST1 circuit, until equal, realizes current-sharing.

The formula that pi regulator carries out proportional integral computing to current differential Error is as follows:

$d\left(t\right)=K_{\mathrm{pi}}e\left(t\right)+\frac{1}{\mathrm{\τ}}\∫e\left(t\right)\mathrm{dt}$

In above formula, e (t) is input, and d (t) is for exporting;

Turn to difference equation by discrete for above formula, kth is clapped output and is:

$\begin{array}{c}d\left(k\right)=k_{p}e\left(k\right)+k_i{T}_{\mathrm{sam}}\underset{i=1}{\overset{k}{\mathrm{\Σ}}}e\left(i\right)=k_{p}e\left(k\right)+d_i\left(k\right)\\ =k_{p}e\left(k\right)+k_i{T}_{\mathrm{sam}}e\left(k\right)+d_i(k-1)\end{array}$

Wherein T _samfor the sampling period, the deviation input that e (k) is kth time, k _p, k _ifor coefficient.

The Duty ratio control amount Duty_bst1 of current BOOST1 circuit switch device is calculated by MPPT algorithm.

The two BOOST circuit current-sharing control method of two-stage type photovoltaic generating system of the present invention is mainly adapted to the photovoltaic system that two-way BOOST inputs, utilize the electric current of system real-time sampling two-way BOOST circuit, with the input current of a wherein road BOOST circuit for benchmark, a duty ratio increment is calculated through pi regulator by two-way BOOST input current, the make-and-break time (i.e. duty ratio) revising another road BOOST circuit switch device is removed by this increment, the electric current realizing two-way BOOST circuit is equal, thus the uneven flow problem solved when two BOOST circuit in parallel runs, avoid occurring the problem that the device of current circuit shortens useful life and inverter overcurrent is shut down.

Accompanying drawing explanation

Fig. 1 is the two BOOST sharing control block diagram of two-stage type photovoltaic DC-to-AC converter of the present invention.

Embodiment

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

The structure of the two BOOST circuit of two-stage type photovoltaic generating system of the present invention as shown in the uppermost portion of fig. 1, prime BOOST circuit completes boost function, rear class inverter circuit completes invert function, in order to make the electric current flowing through BOOST1 and BOOST2 equal, need to add current-sharing control method, the latter half of Fig. 1 gives this control structure, and as seen from the figure, the method comprises the steps:

(1) input current of real-time sampling two-way BOOST circuit, making the electric current of BOOST1 circuit be the electric current of reference current I_ref, BOOST2 circuit is I_fdb, calculates the difference Error of two-way electric current;

Error＝I _ref-I _fdb

(2) using the input of current differential Error as pi regulator, in pi regulator, proportional integral computing is carried out to it;

(3) using the output valve d (k) of pi regulator as duty ratio correction duty, then using the Duty ratio control amount Duty_bst2 of the Duty ratio control amount Duty_bst1 sum of itself and current BOOST1 circuit switch device as BOOST2 circuit switch device;

Duty_bst2＝duty+Duty_bst1

(4) duty ratio Duty_bst2 is carried out sinusoidal pulse width modulation, generate the break-make that PWM ripple removes control BOOST2 circuit switch device, thus the input current value of control BOOST2 circuit is approached to the input current of BOOST1 circuit, until equal, realizes current-sharing.

The formula that in step of the present invention (2), pi regulator carries out proportional integral computing to current differential Error is as follows:

$d\left(t\right)=K_{\mathrm{pi}}e\left(t\right)+\frac{1}{\mathrm{\τ}}\∫e\left(t\right)\mathrm{dt}$

In above formula, e (t) is input, and d (t) is for exporting;

Turn to difference equation by discrete for above formula, kth is clapped output and is:

$\begin{array}{c}d\left(k\right)=k_{p}e\left(k\right)+k_i{T}_{\mathrm{sam}}\underset{i=1}{\overset{k}{\mathrm{\Σ}}}e\left(i\right)=k_{p}e\left(k\right)+d_i\left(k\right)\\ =k_{p}e\left(k\right)+k_i{T}_{\mathrm{sam}}e\left(k\right)+d_i(k-1)\end{array}$

Wherein T _samfor the sampling period, the deviation input that e (k) is kth time, k _p, k _ifor coefficient.

In the present embodiment step (3), the Duty ratio control amount Duty_bst1 of current BOOST1 circuit switch device is calculated by MPPT algorithm.

Above embodiment only understands core concept of the present invention for helping; the present invention can not be limited with this; for those skilled in the art; every according to thought of the present invention; the present invention is modified or equivalent replacement; any change done in specific embodiments and applications, all should be included within protection scope of the present invention.

Claims (3)

1. the two BOOST circuit current-sharing control method of two-stage type photovoltaic generating system, it is characterized in that, the method comprises the steps:

(1) input current of real-time sampling two-way BOOST circuit, making the electric current of BOOST1 circuit be the electric current of reference current I_ref, BOOST2 circuit is I_fdb, calculates the difference Error of two-way electric current;

(2) using the input of current differential Error as pi regulator, in pi regulator, proportional integral computing is carried out to it;

(3) using the output valve d (k) of pi regulator as duty ratio correction duty, then using the Duty ratio control amount Duty_bst2 of the Duty ratio control amount Duty_bst1 sum of itself and current BOOST1 circuit switch device as BOOST2 circuit switch device;

(4) duty ratio Duty_bst2 is carried out sinusoidal pulse width modulation, generate the break-make that PWM ripple removes control BOOST2 circuit switch device, thus the input current value of control BOOST2 circuit is approached to the input current of BOOST1 circuit, until equal, realizes current-sharing.

2. the two BOOST circuit current-sharing control method of two-stage type photovoltaic generating system according to claim 1, is characterized in that: the formula that pi regulator carries out proportional integral computing to current differential Error is as follows:

$d\left(t\right)=K_{\mathrm{pi}}e\left(t\right)+\frac{1}{\mathrm{\τ}}\∫e\left(t\right)\mathrm{dt}$

In above formula, e (t) is input, and d (t) is for exporting;

Turn to difference equation by discrete for above formula, kth is clapped output and is:

$\begin{array}{c}d\left(k\right)=k_{p}e\left(k\right)+k_i{T}_{\mathrm{sam}}\underset{i=1}{\overset{k}{\mathrm{\Σ}}}e\left(i\right)=k_{p}e\left(k\right)+d_i\left(k\right)\\ =k_{p}e\left(k\right)+k_i{T}_{\mathrm{sam}}e\left(k\right)+d_i(k-1)\end{array}$

Wherein T _samfor the sampling period, the deviation input that e (k) is kth time, k _p, k _ifor coefficient.

3. the two BOOST circuit current-sharing control method of two-stage type photovoltaic generating system according to claim 1, is characterized in that: the Duty ratio control amount Duty_bst1 of current BOOST1 circuit switch device is calculated by MPPT algorithm.