CN105449709A - Grid-connected control method for photovoltaic power generation system - Google Patents

Abstract

The invention relates to a grid-connected control method for a photovoltaic power generation system. An active power is injected into a grid-connected point; and a harmonic wave, a reactive power of a load and an unbalanced three-phase current of the grid-connected point are compensated. The grid-connected control method has the beneficial effects that (1) an essential grid-connected inverter in photovoltaic power generation is adopted, so that the inverter simultaneously achieves injection of the active power into a distributed power grid and compensation on the harmonic wave, the reactive power of the load and the unbalanced three-phase current of the grid-connected point; hardware resources of the inverter are utilized to the maximal extent; hardware investment and equipment volume are reduced; and the cost performance is improved; (2) a phase-locked loop-free technology is adopted; an extra hardware phase-locked element or a complicated software phase locking procedure is reduced; and influences caused by voltage waveform distortion, network voltage change, frequency offset and the like are reduced; and (3) a weighted current feedback-based hysteresis current control strategy is adopted; a control system is reduced to the first order from the fifth order; and design of the control system is simplified.

Description

A kind of photovoltaic generating system grid-connected control method

Technical field

The present invention relates to a kind of parallel network power generation technology, particularly a kind of photovoltaic generating system grid-connected control method.

Background technology

Parallel network power generation technology becomes the effective way solving mankind's energy scarcity and environmental pollution Double jeopardy day by day with its advantage such as inexhaustible property and environment-friendly advantage.But photovoltaic generation has the feature such as randomness, intermittence, belong to typical uncontrollable source.And distributed power grid is as the important way of distributed power source access electrical network, but it self also exists a large amount of power electronic equipment, thus produces a large amount of harmonic wave.And there is non-linear, uneven and idle characteristic in the localised load of distributed power grid, this all can worsen the quality of power supply at micro-capacitance sensor points of common connection (pointofcommoncoupling, PCC) place.The quality of power supply quality at PCC point place, will affect the economic benefit of electrical network.Therefore, to and the improvement of the site quality of power supply be of great significance.

The current main method to power quality controlling be and reactive power compensator and passive or Active Power Filter-APF are installed in site.But these measures not only can increase extra equipment investment, also can the stability of influential system.

Summary of the invention

The present invention be directed to grid-connected method Problems existing, propose a kind of photovoltaic generating system grid-connected control method, to and site be injected with merit power and to and site place harmonic wave, load is idle, three phase unbalance current compensates.

Technical scheme of the present invention is: a kind of photovoltaic generating system grid-connected control method, specifically comprises the steps:

1) three-phase photovoltaic power generation system with quality of power supply regulatory function is set up: connect photovoltaic array successively, DC/DC converter, three groups of single-phase full-bridge inverters, LCL filter, distributed power grid, DC/AC inverter adopts parallel active filter type three groups of single-phase full bridge formula inverters, LCL filtering part adopts LCL tri-rank filter, MPPT maximum power point tracking MPPT controller gathers photovoltaic array output voltage, electric current and DC/AC inverter output dc voltage, MPPT controller outputs signal DC/DC converter and TMS320F2812 controller, TMS320F2812 controller gathers the voltage and current of distributed power grid input, TMS320F2812 controller outputs a control signal to DC/AC inverter,

2) MPPT controller current inner loop controls the maximum power point that duty ratio realizes following the tracks of photovoltaic battery array, and it is constant that outer voltage control DC/DC converter exports DC voltage;

3) TMS320F2812 controller obtains grid-connected follow current i from MPPT controller _gabcwith harmonic wave, idle, unsymmetrical current component i _habc, i _habcbe offset current, using biphase current sum as reference current i _ref=i _habc+ i _gabc, then with the filter inductance L in the filter of LCL tri-rank ₁, L ₂electric current be multiplied by weight coefficient respectively after obtain feedback current and compare, comparison value is after pi regulator output violent change link, the trigger impulse needed for power device in three groups of single-phase full bridge formula inverters is generated, to complete transformation of electrical energy under carried-based PWM effect.

Described step 3) middle filter inductance L ₁, L ₂the weight coefficient of electric current be respectively α, β, alpha+beta=1, α=L ₁/ (L ₁+ L ₂), L ₁, L ₂for two inductance value in the filter of LCL tri-rank.

Beneficial effect of the present invention is: photovoltaic generating system grid-connected control method of the present invention, one utilizes requisite combining inverter in photovoltaic generation, make inverter realize simultaneously to distributed power grid inject active power and to and site place harmonic wave, load is idle, three phase unbalance current compensates, at utmost utilize the hardware resource of inverter, reduce hardware to drop into and equipment volume, improve its cost performance; Two have employed no phase-locked loop technology, decrease extra hardware phase lock high precision element or the software phlase locking program of complexity, reduce and affect by voltage waveform distortion, line voltage variation, frequency shift (FS) etc.; Three, have employed a kind of hysteretic loop current control strategy based on weighted current feedback, control system is reduced to 1 rank from 5 rank, simplifies the design of control system.

Accompanying drawing explanation

Fig. 1 is the three-phase photovoltaic power generation system figure that the present invention has quality of power supply regulatory function;

Fig. 2 is the instruction current generating principle figure of parallel network power generation of the present invention;

Fig. 3 is positive sequence fundamental voltage under d-q coordinate of the present invention and current phasor figure;

Fig. 4 is that LCL weighted current of the present invention controls schematic diagram;

Fig. 5 is the hysteretic loop current control schematic diagram of weighted current of the present invention feedback;

Fig. 6 is the grid-connected power of the present invention;

Fig. 7 is the grid-connected current curve diagram of the present invention;

Fig. 8 is the present invention and harmonic content variation diagram in network process;

Fig. 9 is the present invention and the variation diagram of power factor (PF) in network process.

Embodiment

Figure 1 shows that the three-phase photovoltaic power generation system figure with quality of power supply regulatory function, comprise connect successively photovoltaic array, DC/DC converter, three groups of single-phase full-bridge inverters, LCL filter, distributed power grids, and TMS320F2812 controller.

DC/DC converter mainly completes photovoltaic battery array maximal power tracing, and utilizes High Frequency Link technology the direct current that low pressure fluctuates to be converted to the stable high voltage direct current of combining inverter needs.This converter utilizes phase-shift full bridge soft switch circuit topology, improves efficiency and the power density of system.System inner ring (current regulator) realizes following the tracks of the maximum power point of photovoltaic battery array by changing duty ratio, outer voltage ensures that the DC voltage of rear class active inverter is constant.

DC/AC inverter have employed parallel active filter type three groups of single-phase full bridge formula inverters, due to common DC bus, reduces the possibility occurring circulation.Each circuitry phase and control separate lotus root completely, are with the very competent of unbalanced load, and can realize the functions such as individual-phase control, N+1 redundancy, online insertion and removal easily, improve the reliability of system.

LCL filtering part have employed filter effect better LCL tri-rank filter.Adopt LCL structural rate LC structure to have better attenuation characteristic, be high-impedance state to high fdrequency component, suppress current harmonics, and its inductance L with line series can also play the effect suppressing impulse current.The total inductance amount of LCL filter is more much smaller than other two kinds of filters that will reach identical filter effect.

Control method comprises: MPPT maximum power point tracking MPPT controller gathers photovoltaic array output voltage, electric current and DC/AC inverter output dc voltage, and MPPT controller is carried out maximum tracking power, the generation of offset current, the extraction of grid-connected power tracking electric current, FEEDBACK CONTROL and trigger impulse and generated.First, the voltage and current transducer of controller to distributed power grid input is sampled, and obtains the various voltage and current signals needed for TMS320F2812 controller.Then, grid-connected follow current i is obtained _gabcwith the current i that need compensate _habc.Reference current is i _ref=i _habc+ i _gabc, after pi regulator output violent change link, under carried-based PWM effect, generate the trigger impulse needed for power device in three groups of single-phase full bridge formula inverters, to complete transformation of electrical energy.

The extraction of offset current: in order to realize harmonic current managing, load is idle and three-phase imbalance compensates, the power-factor of load corrects, and therefore needs the instantaneous value detecting offset current.

The instruction current generating principle figure of parallel network power generation as shown in Figure 2, in figure, u _sabcfor and the voltage of site (with the tie point of distributed power grid in Fig. 1), i _sabcfor distributed electrical current on line side, i _oabcfor the output current of grid-connected DC/AC inverter, i _labc=i _oabc-i _sabcfor the load current of broad sense, i _pabcfor the real component of positive sequence first-harmonic, i _habcfor harmonic wave, idle and unsymmetrical current component, i _gabcfor grid-connected follow current, i _refbe reference current, by the ω (rotary variable) in default dq transformation matrix of coordinates, thus do not need phase-locked loop circuit can accurately detect fundamental active, fundamental wave reactive power and harmonic current.Then by obtaining grid-connected follow current based on instantaneous reactive power.

Adopt no phase-locked loop technology, choose invariable power Park and convert:

$C_{abc/dq}=\sqrt{\frac{2}{3}}\×\left[\begin{array}{ccc}\cos \mathrm{\θ}& \cos (\mathrm{\θ}-2\mathrm{\π}/3)& \cos (\mathrm{\θ}+2\mathrm{\π}/3)\\ -\sin \mathrm{\θ}& -\sin (\mathrm{\θ}-2\mathrm{\π}/3)& -\sin (\mathrm{\θ}+2\mathrm{\π}/3)\\ \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}\end{array}\right]---\left(1\right)$

θ=ω t+ θ in formula ₀, θ ₀for the angle between dq coordinate system d axle and abc coordinate system a axle, θ=ω t, ω=2 π f, f refers to mains frequency, and Coordinate Conversion herein changes into rotational coordinates dq from static coordinate abc, and the angle in changing is θ.

Positive sequence fundamental voltage as shown in Figure 3 under d-q coordinate and current phasor figure, positive sequence fundamental current i _zjproject on voltage vector u, obtain positive sequence fundamental active current component I _fp; Project to accordingly in u normal direction and obtain fundamental positive sequence reactive current component I _fq.Dq axle component after low pass filter the sine value between i and u and cosine value can be represented, C _pqfor following formula (2), i _pdand i _pqfor positive sequence fundamental active current weight under dq coordinate system:

$\left[\begin{array}{c}{i}_{Pd}\\ i_{Pq}\end{array}\right]=\left[\begin{array}{cc}v& 0\\ 0& v\end{array}\right]\left[\begin{array}{c}{\stackrel{\‾}{u}}_d\\ {\stackrel{\‾}{u}}_q\end{array}\right]---\left(2\right)$

$v=\frac{{\stackrel{\‾}{u}}_d{\stackrel{\‾}{i}}_d+{\stackrel{\‾}{u}}_q{\stackrel{\‾}{i}}_q}{{{\stackrel{\‾}{u}}_d}^2+{{\stackrel{\‾}{u}}_q}^2}---\left(3\right)$

Positive sequence fundamental active component i is obtained again by Park anti-change _pabc, the offset current needed then just can be obtained with the difference of Generalized Negative charged current.

The generation of grid-connected power tracking electric current: in order to realize the tracing control of grid-connected current amplitude, phase place, provides a kind of grid-connected current track algorithm based on no phase-locked loop technology here equally.

If P and Q is the meritorious of DC/AC inverter and idle output:

U _m, I _mbe respectively the amplitude of voltage, electric current, be respectively each self-corresponding phase place, u _d, i _d, u _q, i _qbe respectively the dq axle component that low pass filter exports.

Again by formula (4), grid-connected follow current can be written as:

$\left\{\begin{array}{c}{i}_{dref}=\frac{(u_{d}P+u_{q}Q)}{u_d^2+u_q^2}\\ i_{qref}=\frac{(u_{d}P+u_{d}Q)}{u_d^2+u_q^2}\end{array}\right.---\left(5\right)$

I _labcc-i _pabcbe in total load electric current the negative phase-sequence, harmonic wave and the idle component i that need to compensate _habc, last i _habc+ i _gabcconstitute instruction current i _ref.

The depression of order of model:

LCL weighted current controls schematic diagram as shown in Figure 4, adopts a kind of hysteretic loop current control strategy based on weighted current feedback, filter inductance L ₁current i ₁, filter inductance L ₂current i ₂.

Inverter output voltage and weighted current i ₂transfer function be:

$G_s=\frac{i_2\left(s\right)}{u_o\left(s\right)}=\frac{{\mathrm{\αL}}_2{\mathrm{Cs}}^2+\mathrm{\α}+\mathrm{\β}}{L_1{L}_2{\mathrm{Cs}}^3+(L_1+L_2)s}---\left(6\right)$

L ₁, L ₂, Cs is respectively inductance, the capacitance parameter of LCL filter in Fig. 1, and α, β are selected parameter, and its value can be obtained by formula (7).

In order to eliminate the not enough problem of stability margin because limit resonance peak brings, the proportional gain that PI is regulated the large value of selection and comparison can reduce systematic steady state error and improves dynamic property, suitable α, β value can be selected, make the counteracting or close of the zero pole point of above-mentioned transfer function, and make control system become single order from three rank.

When formula (7) is updated to (6), now control system is simplified to first-order system:

$G_s=\frac{1}{(L_1+L_2)s}---\left(8\right)$

Formula (7) and (8) show when meeting alpha+beta=1, α=L ₁/ (L ₁+ L ₂) time, now system meets pole-zero cancellation, and final system reduces to single order from three rank, makes the design of pi regulator no longer by the restriction of limit peak gain.

The formation of trigger impulse:

The hysteretic loop current control schematic diagram of weighted current feedback as shown in Figure 5: filter inductance L ₁, L ₂electric current be multiplied by weight coefficient respectively after obtain weighted current i _weighting, namely feedback current, then with reference current i _refrelatively, the trigger impulse of this phase single-phase full bridge is comparatively produced by stagnant chain rate.

Implement example: grid line voltage is 380VAC, and switching frequency is 8kHz, filter inductance L ₁=2mH, filter capacitor C=10 μ f, filter inductance L ₂=1mH, damping is 4 Ω, and DC side voltage of converter is 400V, and grid-connected input power is 15kw.

Only generate electricity by way of merging two or more grid systems before inverter 0.1s, 0.1-0.15s starts to carry out harmonic component, the power curve of grid-connected side and current curve are as shown in Figure 6,7, can find out from figure, before adjustment harmonic wave, owing to there is non-linear and uncompensated load, grid-connected survey electric current contains larger harmonic wave and unbalanced component, along with the distortion of electric current, and grid-connected side power vibrates.When after compensation harmonic, current waveform basic row becomes sinusoidal wave, but because of containing idle and unsymmetrical current, power curve is with 2 double-frequency fluctuation, and due to the existence of capacitive reactive power load, reactive power exists a negative DC component.0.15-0.2s compensates unbalanced component again, and three-phase current keeps symmetrical and substantially undistorted, and active power vibration in grid-connected side is eliminated, and because the existence of idle component, load or burden without work is still from net side absorbing reactive power.Drop into reactive power compensation after 0.2s, net side reactive power is close to 0, and the amplitude of current waveform reduces and phase place also changes a lot.

Fig. 8,9 gives and harmonic content in network process and the change of power factor (PF), and harmonic content THD content is finally about 2.5%, meet the requirement of regulation, and power factor (PF) is by after final full remuneration, close to 1, well meets Grid-connection standards.

Be not difficult to find out from enforcement example, the present invention, can effective compensation the imbalance at site place, idle and harmonic current while completing grid-connected power tracking, eliminates net side power fluctuation, improves and the quality of power supply of site, have good application prospect.

Claims (2)

1. a photovoltaic generating system grid-connected control method, is characterized in that, specifically comprises the steps:

1) three-phase photovoltaic power generation system with quality of power supply regulatory function is set up: connect photovoltaic array successively, DC/DC converter, three groups of single-phase full-bridge inverters, LCL filter, distributed power grid, DC/AC inverter adopts parallel active filter type three groups of single-phase full bridge formula inverters, LCL filtering part adopts LCL tri-rank filter, MPPT maximum power point tracking MPPT controller gathers photovoltaic array output voltage, electric current and DC/AC inverter output dc voltage, MPPT controller outputs signal DC/DC converter and TMS320F2812 controller, TMS320F2812 controller gathers the voltage and current of distributed power grid input, TMS320F2812 controller outputs a control signal to DC/AC inverter,

2) MPPT controller current inner loop controls the maximum power point that duty ratio realizes following the tracks of photovoltaic battery array, and it is constant that outer voltage control DC/DC converter exports DC voltage;

3) TMS320F2812 controller obtains grid-connected follow current i from MPPT controller _gabcwith harmonic wave, idle, unsymmetrical current component i _habc, i _habcbe offset current, using biphase current sum as reference current i _ref=i _habc+ i _gabc, then with the filter inductance L in the filter of LCL tri-rank ₁, L ₂electric current be multiplied by weight coefficient respectively after obtain feedback current and compare, comparison value is after pi regulator output violent change link, the trigger impulse needed for power device in three groups of single-phase full bridge formula inverters is generated, to complete transformation of electrical energy under carried-based PWM effect.

2. photovoltaic generating system grid-connected control method according to claim 1, is characterized in that, described step 3) in filter inductance L ₁, L ₂the weight coefficient of electric current be respectively a, β, a+b=1, α=L ₁/ (L ₁+ L ₂), L ₁, L ₂for two inductance value in the filter of LCL tri-rank.