CN104037800B - A kind of photovoltaic combining inverter current control method - Google Patents

Abstract

The invention discloses a kind of photovoltaic combining inverter current loop control method of improvement, it comprises the following steps to belong to solar photovoltaic technology field: step 1, by line voltage feedforward obtain voltage feedforward control amount u1; Step 2, obtain current error Δ i by outer voltage control structure; Step 3, carry out segmentation to current error Δ i, form multiple current error section, each current error section adopts different gains, after adopting the current inner loop control structure of P controller, obtains current equivalence voltage duty cycle controlled quentity controlled variable u ₂; The command value u_order of step 4, acquisition switch comparand register.Control method of the present invention realizes simple, not needing complicated integration and differentiation coefficient to adjust, without the need to introducing virtual orthographic signal, avoiding dp coordinate transform consuming time, effectively can reduce output current distortion simultaneously, strengthen the resistivity of harmonious wave interference that electrical network distorted.

Description

A kind of photovoltaic combining inverter current control method

Technical field

The present invention relates to the optimal control of photovoltaic combining inverter, propose a kind of photovoltaic combining inverter current control method of improvement, belong to solar energy power generating field.

Background technology

Solar energy be the most clean, the most real on our times, large-scale develop and utilize one of the most promising regenerative resource.Solar photovoltaic grid-connection generating is the main trend of solar energy photovoltaic utilization, will be developed fast.Photovoltaic combining inverter is the core of photovoltaic generating system, is the interface circuit between generation of electricity by new energy, micro-capacitance sensor etc. and bulk power grid, and its grid current quality control is one of key technology.Photovoltaic combining inverter generally includes based on the L/LC/LCL low pass filter of the PWM inversion topological of HF switch, grid-connected connection, voltage and current signal testing circuit, inversion control ring and drive circuit.The object of Current Control is exactly make inverter carry the electric current of high power factor, low THD value to electrical network.At present, conventional inverter current ring control method has current hysteresis-band control, PID control parameter (PID), ratio resonance to control (PR), Repetitive controller (RC), current model PREDICTIVE CONTROL (CMPC) etc.This several control method respectively has quality, also has research that different control methods is combined formation co-operated control, achieves good Current Control performance.

It is most widely used control method in feedback control system that PID controls, and it calculates controlled quentity controlled variable by obtaining error, and control thought is simple.Parameter designing adopts the method such as frequency analysis, POLE PLACEMENT USING.In single-phase grid-connected inverter Current Control, controlled variable is AC signal, and PID controls to realize DAZ gene to AC signal, differential controls very responsive to disturbance, also need to introduce virtual orthographic signal, use PID controller after doing dq conversion, realize the astatic effect of grid-connected current.For ensureing system stability, the gain of PID adjuster is restricted, and system is less in the open-loop gain of low-frequency range, and the rejection ability of system to output current steady-state error and harmonic wave is not good.Meanwhile, this method is also subject to line voltage and distorts the impact of harmonious wave interference.

Summary of the invention

The object of the invention is to the deficiency overcoming traditional PI D Current Control Technology, propose a kind of photovoltaic combining inverter current control method adopting current error signal segmentation scales to control.The method, based on traditional PID Current Control, removes the differential component to interference signal sensitivity, removes the quadrature components that cannot realize AC signal zero static difference.The present invention is simple to operate, reduces the steady-state error of output current under the control overflow meeting system stability, enhances the resistivity of the harmonious wave interference that to distort to electrical network, reduces output current THD value to less than 5%.

For realizing above object, the technical scheme that the present invention takes is:

A kind of photovoltaic combining inverter current control method, described photovoltaic combining inverter current control method adopts the double-closed-loop control structure of voltage feed-forward control and outer voltage and current inner loop, and it comprises the following steps:

Step 1, by line voltage feedforward obtain voltage feedforward control amount u ₁;

Step 2, by adopting the outer voltage control structure of PI controller to obtain current error Δ i, described current error Δ i is grid-connected current effective value instruction I ^*be multiplied by sin show, then with grid-connected current sampled value i _ndifference relatively;

Step 3, segmentation is carried out to current error Δ i, form multiple current error section, each current error section adopts different gains, in guarantee Current Control amount continuous print situation, after adopting the current inner loop control structure of P controller, obtain current equivalence voltage duty cycle controlled quentity controlled variable u ₂;

The command value u_order of step 4, acquisition switch comparand register, this command value u_order=u ₁+ u ₂.

Voltage feedforward control amount u is obtained in described step 1 ₁method be: the feedforward of line voltage that mains voltage sensor measurement is obtained, under HF switch effect, inversion link is considered as the little inertial element of high-gain, by line voltage sampled value divided by busbar voltage sampled value, be multiplied by the value of PWM module period register again, to obtain voltage feedforward control amount u ₁.

Grid-connected current effective value instruction I in described step 2 ^*for busbar voltage regulation loop PI controlled quentity controlled variable exports.

Described PI controlled quentity controlled variable is that the voltage error value of busbar voltage being sampled between effective value and busbar voltage voltage stabilizing value controls to obtain through PI controller.

In described step 3, current equivalence voltage duty cycle controlled quentity controlled variable u ₂for the P controller through different gains, the product of the Current Control amount m obtained and the value of PWM module period register.

Described step 3 comprises:

Step 31, obtain the error segmented node of multiple current error section, be designated as c ₁, c ₂c _n, wherein, n is the number of error segmented node, and an xth error segmented node is designated as c _x, n>=2, x≤n, c _n-1<c _n; Each error segmented node correspondence arranges corresponding proportional gain, is designated as kp respectively ₁, kp ₂kp _n, an xth error segmented node c _xa corresponding xth proportional gain kp _x, wherein, kp _n-1>kp _n;

Step 32, calculating current controlled quentity controlled variable m, its computational methods are:

When | Δ i|<c ₁time, m=0;

Work as c _n-1≤ Δ i<c _ntime, $m={\mathrm{kp}}_{n-1}*(\mathrm{\&Delta;i}-c_{n-1})+\underset{x=3}{\overset{n}{\mathrm{\&Sigma;}}}[{\mathrm{kp}}_{x-2}*(c_{x-1}-c_{x-2})];$

As Δ i>=c _ntime, $m={\mathrm{kp}}_n*(\mathrm{\&Delta;i}-c_n)+\underset{x=2}{\overset{n}{\mathrm{\&Sigma;}}}[{\mathrm{kp}}_{x-1}*(c_x-c_{x-1})];$

As-c _n< Δ i≤-c _n-1time, $m={\mathrm{kp}}_{n-1}*(\mathrm{\&Delta;i}+c_{n-1})+\underset{x=3}{\overset{n}{\mathrm{\&Sigma;}}}[{\mathrm{kp}}_{x-2}*({-c}_{x-1}+c_{x-2})];$

As Δ i≤-c _ntime, $m={\mathrm{kp}}_n*(\mathrm{\&Delta;i}+c_n)+\underset{x=2}{\overset{n}{\mathrm{\&Sigma;}}}[{\mathrm{kp}}_{x-1}*(-c_x+c_{x-1})];$

Step 33, obtain current equivalence voltage duty cycle controlled quentity controlled variable u ₂.

In described step 31, to error segmented node c _xand the proportional gain kp of correspondence _xadjust.

Described method of adjusting is: first current inner loop adopts and determines gain scale control, then increases proportionality coefficient gradually, when adjusting to output current to certain threshold value, records proportionality coefficient threshold value kp this moment and electric current steady-state error maximum absolute value value | Δ i _max|, make kp ₁=kp, ${\mathrm{kp}}_x=\frac{\mathrm{kp}}{2^{x-1}};c_1=0,c_x=(x-1)*\frac{\left|{\mathrm{\&Delta;i}}_{\max }\right|}{n}.$

Described certain threshold value is the critical value of output current between the non-overshoot of hyperharmonic.

Compared with prior art, Advantages found of the present invention exists:

1, realize simply, not needing complicated integration and differentiation coefficient to adjust, without the need to introducing virtual orthographic signal, avoiding dp coordinate transform consuming time.

2, determine gain scale and control to there is static difference, excessive proportional gain can make the stability of a system decline.The present invention is according to current error size, and big error selects large gain, and little error selects little gain, electric current THD value can be controlled in the scope required.

3, by improving output current quality, improve the rejection ability of system to humorous wave interference.

Accompanying drawing explanation

Fig. 1 is typical photovoltaic combining inverter topology and control chart;

Fig. 2 is the flow chart of a kind of photovoltaic combining inverter current control method of the present invention;

Fig. 3 is inverter current ring control block diagram;

Fig. 4 is electric current loop Discrete control flow chart;

Fig. 5 is kp _xand c _xsetting method.

Embodiment

Below in conjunction with the drawings and specific embodiments, content of the present invention is described in further details.

Embodiment

Fig. 1 gives topological structure and the control chart of typical single-phase bipolar formula non-isolated photovoltaic grid-connected inverter.Prime Boost circuit is charged to bus capacitor, realizes the MPPT controlling functions of DC bus boosting and photovoltaic module.Rear class Converting Unit adopts double-loop control to realize power conversion.Double-loop control refers to outer voltage for the purpose of bus capacitor voltage stabilizing and current inner loop for the purpose of power stage.U _{b_ref}choose with actual needs according to bus capacitor is withstand voltage, be generally 400V.Outer voltage bus regulator adopts PI to control, and it can realize U _{b_ref}dAZ gene; Current feedback signal is sinusoidal quantity, and current inner loop then adopts P to control.

Please refer to shown in Fig. 2, photovoltaic combining inverter current control method, it comprises the following steps:

S10, line voltage feedover, under HF switch effect, inversion link is considered as the little inertial element of high-gain, by line voltage sampled value rel_UAC divided by busbar voltage sampled value rel_Ubus, be multiplied by the value of PWM module period register again, obtain electric voltage feed forward Duty ratio control amount u ₁, inversion generation and civil power, with the voltage frequently with identical width, eliminate the interference of civil power distortion to grid-connected current.

Before S20, outer voltage refer to inversion, the PI voltage stabilizing of bus DC side controls, and requires that bus is stabilized in Ub, and busbar voltage sampling effective value Ub_rms and Ub makes difference and obtain error delta U, controls, obtain grid-connected current effective value instruction I through PI ^*.This command value is multiplied by sin show, then with grid-connected current sampled value i _nrelatively, current error Δ i is obtained.

S30, to current error segmentation, different error band adopts different gains, and ensures that Current Control amount is continuous, through P controller, obtains Current Control amount m, then is multiplied by the value of PWM module period register, obtain current equivalence voltage duty cycle controlled quentity controlled variable u ₂.

The principle adopting current error signal segmentation scales to control please refer to shown in Fig. 3.Fig. 3 is inversion control block diagram.I* is the Setting signal of grid-connected current; G1 (s) is current regulator; Ignore the non-linear effects of power device pressure drop and Dead Time, bridge type inverse link under SPWM control mode can be considered the little inertial element of a high-gain, this link can represent with G2 (s)=K/ (Ts+1), and K is open-loop gain, and T is time constant; G3 (s)=1/ (Ls+R) is the filtering link of AC inductance L and circuit impedance R composition; Gf (s) is the feedback element of grid-connected current; Gn (s) is the voltage feed-forward control link adopted in Systematical control, eliminates line voltage to the interference of electric current loop.

Make Gf (s)=1, then unity negative feedback ssystem transfer function

$\frac{I_n}{I^{*}}=\mathrm{\&phi;}\left(s\right)=\frac{G_1\left(s\right)K}{{\mathrm{TLs}}^2+(\mathrm{TR}+L)s+G_1\left(s\right)K+R},$ Typical second-order system.

G1 (s) herein=kp, to determine gain coefficient analysis.Be Taylor to φ (s) to launch,

G (s)=a ₁s+a ₂s ²+ a ₃s ³+ a ₄s ⁴+ ..., a _nfor Taylor coefficients.

Make r (t)=sin (ω t), ω is frequency.

Then system exports and is $C\left(s\right)=\frac{\mathrm{\&omega;}}{s^2+{\mathrm{\&omega;}}^2}\&CenterDot;(a_{1}s+a_2{s}^2+a_3{s}^3+a_4{s}^4+......)$

Time-domain response is c (t)=f ₁δ (t)+f ₂sin (ω t)+f ₃cos (ω t), f _nthe coefficient function irrelevant with t.As time goes on, system cannot eliminate steady-state error, thus proposes the demand that kp adjusts.

The kp that the present invention proposes adjusts general principle.Inversion link G2 (the s)=K/ (Ts+1) of high frequency is approximated to proportional component G2 (s)=K, then open-loop transfer function analyze the dynamic process of switch.Some switch periods t ₁moment, before switch motion, if input current is r (t ₁₀), sampling exports as c (t ₁₀), error e (t ₁₀), then the output of proportional controller is k _pe (t ₁₀); After switch motion, input current is r (t ₁₁), sampling output is error tradition determines gain P controller, is difficult to meet electric current THD and drops to less than 5%, as long as reduce e (t) as far as possible, just can reach control overflow.R (t before and after switch ₁₁)=r (t ₁₀), e (t ₁₁) only and k _pe (t ₁₀) size relevant, when not overshoot, k _pe (t ₁₀) larger, e (t ₁₁) less, so, at e (t ₁₀) large time by little equivalent gain (controlled quentity controlled variable/error), ensure k _pe (t ₁₀) increase

Fig. 4 is the electric current loop Discrete control method flow diagram that the present invention proposes.The present invention is for three error segmented node, and in figure, Δ i is current error signal, c ₁, c ₂, c ₃for error segmented node, kp ₁, kp ₂, kp ₃for the proportional gain that corresponding error band is selected, c ₁<c ₂<c ₃, kp ₁>kp ₂>kp ₃.This control method is specially:

If | Δ i|<c1, then m=0;

If c1<=Δ i<c2, then m=kp1* (Δ i-c1);

If c2<=Δ i<c3, then m=kp2* (Δ i-c2)+kp1* (c2-c1);

If Δ i>=c3, then m=kp3* (Δ i-c3)+kp2* (c3-c2)+kp1* (c2-c1);

If-c2< Δ i<=-c1, then m=kp1* (Δ i+c1);

If-c3< Δ i<=-c2, then m=kp2* (Δ i+c2)+kp1* (-c2+c1);

If Δ i<=-c3, then m=kp3* (Δ i+c3)+kp2* (-c3+c2)+kp1* (-c2+c1).

Fig. 5 is kp _xand c _xlogic of adjusting.Initial, electric current loop adopts determine gain scale control, and proportionality coefficient kp, increases kp gradually, and steady-state error is more and more less, when adjust to output current by overshoot but also non-overshoot time, record kp and steady-state error maximum absolute value value this moment | Δ i _max|, make kp ₁=kp, kp ₂=kp/2, kp ₃=kp/4; c ₁get relative to | Δ i _max| a small amount of or 0, c ₂=| Δ i _max|/3, c ₃=2*| Δ i _max|/3.In practical operation, can arrange some nodes, current error is divided into some sections according to actual conditions, each section is got with different proportional gain kp _x.

The command value u_order of S40, acquisition switch comparand register, this command value u_order=u ₁+ u ₂, for controlling photovoltaic combining inverter electric current.

Although the present invention is described by specific embodiment, it will be appreciated by those skilled in the art that, without departing from the present invention, various conversion can also be carried out and be equal to substituting to the present invention.In addition, for particular condition or application, various amendment can be made to the present invention, and not depart from the scope of the present invention.Therefore, the present invention is not limited to disclosed specific embodiment, and should comprise the whole execution modes fallen within the scope of the claims in the present invention.

Claims (7)

1. a photovoltaic combining inverter current control method, described photovoltaic combining inverter current control method adopts the double-closed-loop control structure of voltage feed-forward control and outer voltage and current inner loop, and it is characterized in that, it comprises the following steps:

Step 1, by line voltage feedforward obtain voltage feedforward control amount u ₁;

Step 2, by adopting the outer voltage control structure of PI controller to obtain current error △ i, described current error △ i is grid-connected current effective value instruction I ^*be multiplied by table, then with grid-connected current sampled value i _ndifference relatively;

Step 3, segmentation is carried out to current error △ i, form multiple current error section, each current error section adopts different gains, in guarantee Current Control amount continuous print situation, after adopting the current inner loop control structure of P controller, obtain current equivalence voltage duty cycle controlled quentity controlled variable u ₂;

In described step 3, current equivalence voltage duty cycle controlled quentity controlled variable u ₂for the P controller through different gains, the product of the Current Control amount m obtained and the value of PWM module period register;

Described step 3 comprises:

Step 31, obtain the error segmented node of multiple current error section, be designated as c ₁, c ₂c _n, wherein, n is the number of error segmented node, and an xth error segmented node is designated as c _x, n>=2, x≤n, c _n-1<c _n; Each error segmented node correspondence arranges corresponding proportional gain, is designated as kp respectively ₁, kp ₂kp _n, an xth error segmented node c _xa corresponding xth proportional gain kp _x, wherein, kp _n-1>kp _n;

Step 32, calculating current controlled quentity controlled variable m, its computational methods are:

When | △ i|<c ₁time, m=0;

Work as c _n-1≤ △ i<c _ntime, $m={\mathrm{kp}}_{n-1}*(\mathrm{\&Delta;}i-c_{n-1})+\underset{x=3}{\overset{n}{\&Sigma;}}\&lsqb;{\mathrm{kp}}_{x-2}*(c_{x-1}-c_{x-2})\&rsqb;;$

As △ i>=c _ntime, $m={\mathrm{kp}}_n*(\mathrm{\&Delta;}i-c_n)+\underset{x=2}{\overset{n}{\&Sigma;}}\&lsqb;{\mathrm{kp}}_{x-1}*(c_x-c_{x-1})\&rsqb;;$

As-c _n< △ i≤-c _n-1time, $m={\mathrm{kp}}_{n-1}*(\mathrm{\&Delta;}i+c_{n-1})+\underset{x=3}{\overset{n}{\&Sigma;}}\&lsqb;{\mathrm{kp}}_{x-2}*(-c_{x-1}+c_{x-2})\&rsqb;;$

As △ i≤-c _ntime, $m={\mathrm{kp}}_n*(\mathrm{\&Delta;}i+c_n)+\underset{x=2}{\overset{n}{\&Sigma;}}\&lsqb;{\mathrm{kp}}_{x-1}*(-c_x+c_{x-1})\&rsqb;;$

Step 33, obtain current equivalence voltage duty cycle controlled quentity controlled variable u ₂;

The command value u_order of step 4, acquisition switch comparand register, this command value u_order=u ₁+ u ₂.

2. photovoltaic combining inverter current control method according to claim 1, is characterized in that, obtains voltage feedforward control amount u in described step 1 ₁method be: the feedforward of line voltage that mains voltage sensor measurement is obtained, under HF switch effect, inversion link is considered as the little inertial element of high-gain, by line voltage sampled value divided by busbar voltage sampled value, be multiplied by the value of PWM module period register again, to obtain voltage feedforward control amount u ₁.

3. photovoltaic combining inverter current control method according to claim 1, is characterized in that, grid-connected current effective value instruction I in described step 2 ^*for busbar voltage regulation loop PI controlled quentity controlled variable exports.

4. photovoltaic combining inverter current control method according to claim 3, is characterized in that, described PI controlled quentity controlled variable is that the voltage error value of busbar voltage being sampled between effective value and busbar voltage voltage stabilizing value controls to obtain through PI controller.

5. photovoltaic combining inverter current control method according to claim 1, is characterized in that, in described step 31, to error segmented node c _xand the proportional gain kp of correspondence _xadjust.

6. photovoltaic combining inverter current control method according to claim 5, it is characterized in that, described method of adjusting is: first current inner loop adopts and determines gain scale control, then proportionality coefficient is increased gradually, when adjusting to output current to certain threshold value, record proportionality coefficient threshold value kp this moment and electric current steady-state error maximum absolute value value | △ i _max|, make kp ₁=kp, c ₁=0,

7. photovoltaic combining inverter current control method according to claim 6, is characterized in that, described certain threshold value is the critical value of output current between the non-overshoot of hyperharmonic.