CN100508327C - A fast and stable photovoltaic three-phase grid-connected control method for maximum power tracking - Google Patents

Abstract

The present invention relates to a photovoltaic three phase synchronization control method realizing maximum power tracking swiftly and stably, which belongs to the technical field photovoltaic power generating control. The method includes the steps as follows: judging the DeltaP/DeltaV value according to the power difference DeltaP between the current time k and the previous time and the voltage difference DeltaV; working out the Iref(k) when the photovoltaic array produces the maximum power; using the Iref(k) to adjust the uq* under the coordinates in vectorial synchronous rotation with the electric network voltage; acquiring six ways of space vectorial SVPWM impulse series according to the rotation angle degree Theta of the three phase electric network voltage, with the aim to control the inverter in order to ensure that the output current of the photovoltaic inverter has the same phase position as that of the mains voltage while ensuring the photovoltaic array is realizing the maximum power output tracking. The power factor is 1. The present invention also can adjust the Idref(k) according to local load requirements, therefore achieving adjustment to the power factor, with low synchronization current harmonic wave distortion factor.

Description

A kind of fast and stable is realized the photovoltaic three-phase grid control method of maximal power tracing

Technical field

The present invention relates to a kind of fast and stable and realize the photovoltaic three-phase grid control method of photovoltaic array maximal power tracing, belong to photovoltaic generating system control technology application.

Background technology

The solar energy that development and utilization is abundant, wide does not produce and lack environment and produces pollution, is the additional energy of recent urgent need, also is the basis of future source of energy structure.Therefore how research realizes that MPPT maximum power point tracking control (MPPT) algorithm combines with grid-connected control technology organic facies, make photovoltaic array under the environment of illumination difference, variations in temperature, grid-connected photovoltaic system both can track the maximum power working point of photovoltaic array fast, and system is stable, make the grid-connected current of inverter output can satisfy international standard IEEE requirement simultaneously, and can not cause harmonic pollution to have very important significance line voltage.

The photovoltaic three-phase grid power-generating control system does not need the energy storage link, power inverter by one two level three-phase bridge, the direct current that photovoltaic array is sent by control mode is converted to alternating current, three-phase output end by power inverter links to each other with civil power, directly export electric energy to electrical network, as same distributed power generation station.Traditional control mode is complicated; usually need dual-loop control circuit; wherein interior ring is realized parallel networking type photovoltaic inverter output current and line voltage for electric current loop and is exported synchronously; outer shroud is that Voltage loop realizes that by the output voltage track reference voltage of regulating photovoltaic array photovoltaic array is incorporated into the power networks; influence each other because certainly existing between these two control rings; be difficult to the accurately maximum power operating point of locking photovoltaic array; thereby will inevitably cause the loss of many power because of the disturbance of power; traditional in addition grid-connected control technology all is to interrupt sampling at each PWM carrier cycle end; data according to sampling are carried out the duty ratio that series of computation obtains next carrier cycle; certainly will cause the control hysteresis time is a carrier cycle, affects will for like this grid-connected current and grid-connected protection scheme.

Its electric output characteristic of solar energy photovoltaic array has very strong nonlinear characteristic, and its output voltage electric current is influenced by intensity of illumination, ambient temperature and loading condition.Fig. 1 has clearly show a 300W _pPhotovoltaic array changes along with intensity of illumination and the one group of output voltage and the power relation curve that change, the figure illustrates the maximum power tracing process simultaneously, and existing non-pressure process, single order climbing method and electricity are led MPPT maximum power point tracking control technologys such as modulator approach, all be difficult to accomplish fast, follow the tracks of photovoltaic battery array maximum power working point (MPP) smoothly, these methods mostly are applied to independently photovoltaic generating system, charge in batteries control system for example, though non-pressure process can be applied to grid-connected control system, can satisfy the photovoltaic parallel in system stability requirement, implement maximal power tracing but be difficult to be implemented under the different intensities of illumination, thereby can cause extra power loss.

Have following relational expression in the time of near photovoltaic array is operated in maximum power point:

$\frac{\mathrm{dP}}{\mathrm{dV}}=\mathrm{BI}-C---\left(1\right)$

B wherein, C is:

$B=(1+\frac{q}{\mathrm{AKT}}V),C=\frac{q}{\mathrm{AKT}}(I_{\mathrm{sc}}+I_o)\·V---\left(2\right)$

I in the following formula _oFor flowing through the diode reverse drain saturation current in the photovoltaic cell model, I _ScShort circuit current when being zero for photovoltaic cell model load both end voltage, q is the quantity of electric charge 1.6 * 10 ^-19C, K are Boltzmann constant 1.38 * 10 ^-23J/K, T are the working temperature of photovoltaic array, and unit is K, and A is the desirable constant of diode;

When dP/d V=0, illustrate that photovoltaic array is operated in maximum power point.

Summary of the invention

The purpose of this invention is to provide simple and direct effective MPPT maximum power point tracking control algolithm (the Maximum PowerPoint Tracking of a kind of optimization, MPPT) make photovoltaic array Maximum Power Output under the condition of different illumination and variations in temperature, improve the conversion efficiency of photovoltaic array, reduce system cost indirectly; Application of synchronized current phasor PI control method realizes the grid-connected current closed-loop control, inverter output and the synchronous electric current (power factor is 1) of line voltage can be realized, the problem that the grid-connected current of photovoltaic grid-connected generating control system is impacted electrical network can be solved again; Adopt the dual timer scheme, the control hysteresis cycle is narrowed down in 5 microseconds, both improved the dynamic protection response speed, reduce the percent harmonic distortion of grid-connected current again.

Characteristics of the present invention are: adopt high speed digital signal processor; use the dynamic fixed-point algorithm of C language; make when having realized the photovoltaic array maximal power tracing grid-connected electric current fully and line voltage synchronous; power factor is 1, can implement closed-loop control fully to grid-connected current, can not cause any impact to electrical network; improved the dynamic protection response speed; safe and reliable to operation, pollution-free to line voltage, the grid-connected current percent harmonic distortion is lower than 4%.This method contains following steps successively:

Step (1), DSP gathers a, b two phase voltages of utility grid and u by formula _α=u _α, $u_{\mathrm{\β}}=({2u}_b+u_a)/\sqrt{3}$ Carry out Clarke Clark conversion, obtain line voltage vector anglec of rotation θ;

Step (2), DSP gathers the current signal of inverter output end A, B two-phase, and the method for (1) is carried out Clarke Clark conversion and is obtained i set by step _α, i _β, the line voltage vector anglec of rotation θ that utilizes step (1) to obtain again, by formula i _d=i _αCos θ+i _βSin θ, i _q=-i _αSin θ+i _βCos θ carries out the Park conversion, obtains the direct current composition i under the synchronous rotating frame _d, i _q

Step (3), in implementation step (1) and step (2), gather photovoltaic array VD, current signal, and try to achieve the power output of the photovoltaic array of current time k according to voltage, current signal, calculate the photovoltaic array power output of current time k and the difference Δ P of last sampling instant power output, calculate the photovoltaic array output voltage of current time k and the difference DELTA V of last sampling instant voltage again, calculate Δ P/ Δ V value;

Step (4), according to the different Δ P/ Δ V values that step (3) obtains, put the value of identification Directional Sign Sign:

If, Δ P/ Δ V〉and 0, then discern Directional Sign Sign and put-1,

If Δ P/ Δ V＜0 is then discerned Directional Sign Sign and is put 1,

If Δ P/ Δ V=0 then discerns Directional Sign Sign and puts 0;

Step (5), the value of the Sign that obtains according to step (4) is calculated as follows the reference current I of the photovoltaic array output current of current time k _Ref(k), wherein, I _Qref(k) be I _Ref(k) q axle component, I _Dref(k) be I _Ref(k) d axle component:

I _ref(k)＝I _ref(k-1)+α×Sign

The step value of α for setting, span is 10 ^-3To 10 ^-5Between;

Step (6), the direct current composition i that utilizes step (2) to obtain according to the following steps _qRegulate q axle reference voltage

:

Step (6.1) is calculated Δ i _q=I _Qref(k)-i _q

Step (6.2), the Δ i that step (6.1) is obtained _qBe input to first pi regulator, scale parameter P scope is between 0.01 to 0.3, and integral parameter obtains q axle reference voltage under the synchronous rotating frame between 0.0001 to 0.016

Step (7), I _Dref(k) can be used for regulating the photovoltaic DC-to-AC converter output power factor, work as I _Dref(k) be set at 0 o'clock, photovoltaic DC-to-AC converter output current and line voltage same-phase, the direct current composition i that utilizes step (2) to obtain according to the following steps _dRegulate d axle reference voltage :

Step (7.1) is calculated Δ i _d=I _Dref(k)-i _d

Step (7.2), the Δ i that step (7.1) is obtained _dBe input to second pi regulator, scale parameter P scope is between 0.01 to 0.3, and integral parameter obtains d axle reference voltage under the synchronous rotating frame between 0.0001 to 0.016

Step (8) is utilized line voltage vector anglec of rotation θ that step (1) obtains, step (6) is obtained And step (7) obtains

Carry out the Park inverse transformation, its formula is $u_{\mathrm{\α}}^{*}=u_d^{*}\cos \mathrm{\θ}-u_q^{*}\sin \mathrm{\θ},$ $u_{\mathrm{\β}}^{*}=u_d^{*}\sin \mathrm{\θ}+u_q^{*}\cos \mathrm{\θ},$ Obtain under the two-phase rest frame

Step (9) utilizes step (8) to obtain

Adopt space vector SVPWM algorithm, handle forming 6 road pwm pulses through DSP, drive the corresponding electronic power switch device of three brachium pontis of inverter, be transported in the utility grid thereby the maximum power that photovoltaic array sends is converted to interchange by interface circuit.

Two timers of TMS320F2812 have been used in the above step, one of them timer is used for carrying out the suitable space vector duty ratio of three brachium pontis that AD sampling and data processing obtain two level, and the another one timer is with generating PWM carrier cycle formation space vector pulse modulated wave (SVPWM).

This method is regulated the active current i of photovoltaic combining inverter output by the compensating action of PI under synchronous coordinate system _qReal-time tracking is through the given reference current I of MPPT algorithm _RefSo that the photovoltaic array steady operation is in maximum power point, make the complete and line voltage synchronous (power factor is 1) of the output current that is incorporated into the power networks, certainly also can realize no-power compensation function according to the requirement of local load, because this scheme has been carried out closed-loop control to grid-connected current, when being incorporated into the power networks electrical network there is not shock effect.Adopt the dual timer scheme both to improve dynamic response protection speed, improved the waveform of grid-connected current again.

Description of drawings

Fig. 1. photovoltaic array P-V changes and the maximal power tracing curve with solar illumination, 1-maximal power tracing curve, 2-photovoltaic array P-V curve, intensity of illumination is 700W/m ², 3-photovoltaic array P-V curve, intensity of illumination is 1000W/m ²

Fig. 2. photovoltaic array grid-connection control system structural topology figure;

Fig. 3 .ADC sampling period and PWM carrier cycle schematic diagram, 4-PWM carrier cycle, 5-AD changes sampling time, 6-control hysteresis time;

Fig. 4. the maximal power tracing algorithm flow chart;

Fig. 5. use the three-phase photovoltaic grid-connected experimental waveform figure that this invention has realized, 7-line voltage, 8-power network current, 9-photovoltaic array output voltage, 10-photovoltaic array output current.

Embodiment

This method realizes according to following steps in digital signal processor DSP:

Step (1). utilize digital signal processor to gather a, b two-phase mains voltage signal, utilize formula u _α=u _α, $u_{\mathrm{\β}}=({2u}_b+u_a)/\sqrt{3}$ It is carried out the Clark conversion, try to achieve line voltage anglec of rotation θ.

Step (2). utilize digital signal processor to gather inverter output a, b two-phase grid-connected current signal, it is carried out the Clark conversion, and then the electrical network angle θ that utilizes step (1) to try to achieve, utilize formula i _d=i _αCos θ+i _βSin θ, i _q=-i _αSin θ+i _βCos θ carries out the Park conversion, with the current signal of α, β phase be transformed into the synchronous dq axis coordinate system of line voltage under direct current composition i _d, i _q

Step (3). in implementation step (1), (2), gather photovoltaic array VD, current signal, and try to achieve the power output of current time photovoltaic array according to voltage, current signal, further try to achieve the difference DELTA P of current time photovoltaic array power output and previous moment power output, calculate the difference DELTA V of current time photovoltaic array output voltage and last sampling instant voltage then, calculate Δ P/ Δ V value.

Step (4). judge according to step (3) result calculated:

If, Δ P/ Δ V〉and 0, then discern Directional Sign Sign and put-1;

If Δ P/ Δ V＜0 is then discerned Directional Sign Sign and is put 1;

If Δ P/ Δ V=0 then discerns Directional Sign Sign and puts 0;

Step (5). according to the judged result of step (4), calculate the I of current time according to the following equation _Ref(k):

I _ref(k)＝I _ref(k-1)+α×Sign

Wherein α is the fixed step size value, and the size of this value rationally is provided with according to the scope of digital processor processes word length and the AD sample rate of setting, and general span is 1e-3 to 5e-5.

Step (6). utilize step (5) to calculate I _Ref(k) regulate meritorious, with I _Ref(k) deduct i _qValue, through pi regulator output obtain with the line voltage synchronous rotating reference frame under synchronous rotational voltage vector

Composition is simultaneously in order to make inverter output current and line voltage phase place identical (power factor is 1), with i _DrefValue is set to 0 i that deducts feedback _dValue (i _DrefAlso can different values be set reactive power compensation is carried out in local electric power system according to system's needs), through another pi regulator output obtain with the line voltage synchronous rotating frame under synchronous rotational voltage vector

Composition.

Step (7). utilize the resulting electrical network angle of step (1) θ and utilize step (6) to obtain through two pi regulator outputs

Through the Park inverse transformation, formula is $u_{\mathrm{\α}}^{*}=u_d^{*}\cos \mathrm{\θ}-u_q^{*}\sin \mathrm{\θ},$ $u_{\mathrm{\β}}^{*}=u_d^{*}\sin \mathrm{\θ}+u_q^{*}\cos \mathrm{\θ},$ Obtain under the two-phase rest frame

Step (8). utilize step (7) resultant

Form the three-phase space voltage vector

Utilize the digital signal processor TMS320F2812 incident A processing module of TI company to export 6 road pwm pulses,, thereby the power conversion that photovoltaic array sends is transported to electrical network for exchanging through driving interface drives two-level inversion device.

Three-phase photovoltaic grid-connected control system with maximum power point tracking of the present invention is that example describes with Fig. 2 specific design:

1) solar-energy photo-voltaic cell array: the solar-energy photo-voltaic cell array is the input of three-phase photovoltaic grid-connected system, provides electric energy for whole system comprises control circuit.Under the illumination condition, solar battery array is an electric energy with the transform light energy that is received by day, through two level power converters direct current is converted to interchange, power delivery is arrived electrical network, after the darkness, whole system quits work automatically, utilizes relay to make output automatic disconnection off-grid.

2) dc bus input capacitance: mainly play certain filter action.

3) two level three-phase bridge type converters: play very key effect as the transformation of electrical energy link, corresponding 6 IGBT by formed 6 road space vector PWM drive waveform three-phase inverters of control circuit, realize the output of photovoltaic array maximum power when making the alternating current that photovoltaic DC-to-AC converter is exported and line voltage is synchronous, improved the conversion efficiency of whole photovoltaic system.

4) filter inductance: the inverter output current is carried out filtering.

5) collecting sensor signal circuit board: adopt 3 Hall type voltage sensors to gather the photovoltaic array output voltage respectively, electrical network A, B two-phase voltage signal, adopt 3 Hall type current sensors to gather A, the B two-phase current signal of photovoltaic array output current, inverter output respectively, used these signals all need it is nursed one's health between the 0-3V, and it is the AD sample circuit interface of control core plate that this signal is inputed to the TMS320F2812 chip.

6) master control circuit board: the control acp chip is TMS320F2812, utilize the signal that the AD module is carried into the process sensor circuit board in its sheet to sample, then signal is restored, calculate suitable SVPWM modulation waveform according to step process illustrated in the summary of the invention, generate duty ratio and form pwm pulse, access to corresponding IGBT gate drive circuit by the driving interface circuit by PWM module in the TMS320F2812 sheet.

Claims (1)

1. A photovoltaic three-phase grid-connected control method that realizes maximum power point tracking quickly and stably, is characterized in that the method is implemented in the digital signal processor DSP according to the following steps: In step (1), the DSP collects the a and b two-phase voltages of the mains power grid and according to the formula u _α =u _a , $u_{\mathrm{\&beta;}}=(2u_b+u_a)/\sqrt{3}$ Carry out the Clark transformation to obtain the grid voltage vector rotation angle θ; In step (2), the DSP collects the current signals of the two phases A and B of the inverter output terminals, performs Clark transformation according to the method in step (1) to obtain i _α , i _β , and then uses the grid voltage vector obtained in step (1) For the rotation angle θ, perform Park transformation according to the formula i _d =i _α cosθ+i _β sinθ, i _q =-i _α sinθ+i _β cosθ to obtain the DC current components i _d and i _q in the synchronous rotating coordinate system; Step (3), while implementing steps (1) and (2), collect the DC output voltage and current signals of the photovoltaic array, and obtain the output power of the photovoltaic array at the current time k according to the voltage and current signals, and calculate the current time The difference ΔP between the output power of the photovoltaic array at k and the output power at the previous sampling moment, and then calculate the difference ΔV between the output voltage of the photovoltaic array at the current moment k and the voltage at the previous sampling moment, and calculate the value of ΔP/ΔV; Step (4), according to the different ΔP/ΔV values obtained in step (3), set the value of the identification direction sign Sign: If ΔP/ΔV>0, the identification direction sign Sign is set to -1, If ΔP/ΔV<0, the identification direction flag Sign is set to 1, If ΔP/ΔV=0, the identification direction sign Sign is set to 0; Step (5), according to the value of Sign that step (4) obtains, calculate the reference current I _ref (k) of the photovoltaic array output current of current moment k according to the following formula, wherein, I _qref (k) is I _ref (k) The q-axis component of I _dref (k) is the d-axis component of I _ref (k): I _ref (k)=I _ref (k-1)+α×Sign α is the set step value, and the value range is between 10 ^-3 and 10 ^-5 ; Step (6), use the DC current component i _q obtained in step (2) to adjust the q-axis reference voltage according to the following steps

Step (6.1), calculating Δi _q =I _qref (k)-i _q ; In step (6.2), input the Δi _q obtained in step (6.1) to the first PI regulator, the proportional parameter P ranges from 0.01 to 0.3, and the integral parameter ranges from 0.0001 to 0.016, to obtain q in the synchronous rotating coordinate system Axis reference voltage

In step (7), I _dref (k) can be used to adjust the output power factor of the photovoltaic inverter. When I _dref (k) is set to 0, the output current of the photovoltaic inverter is in phase with the grid voltage. Use the following steps (2) The obtained DC current component i _d adjusts the d-axis reference voltage

Step (7.1), calculating Δi _d =I _dref (k)-i _d ; In step (7.2), input the Δi _d obtained in step (7.1) to the second PI regulator, the proportional parameter P ranges from 0.01 to 0.3, and the integral parameter ranges from 0.0001 to 0.016, to obtain d in the synchronous rotating coordinate system Axis reference voltage Step (8), use the grid voltage vector rotation angle θ obtained in step (1) to obtain

and step (7) obtained

Carry out Park inverse transformation, its formula is $u_{\mathrm{\&alpha;}}^{*}=u_d^{*}\cos \mathrm{\&theta;}-u_q^{*}\sin \mathrm{\&theta;},$ $u_{\mathrm{\&beta;}}^{*}=u_d^{*}\sin \mathrm{\&theta;}+u_q^{*}\cos \mathrm{\&theta;},$ In the two-phase stationary coordinate system, the

Step (9), utilize step (8) to obtain

Using the space vector SVPWM algorithm, 6 channels of PWM pulses are formed by DSP processing, and the corresponding power electronic switching devices of the three bridge arms of the inverter are driven through the interface circuit, so as to convert the maximum power emitted by the photovoltaic array into AC and transmit it to the mains grid .

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