CN109921466B - Two-stage photovoltaic power generation system load shedding operation control method based on slope power - Google Patents
Two-stage photovoltaic power generation system load shedding operation control method based on slope power Download PDFInfo
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Abstract
A two-stage photovoltaic power generation system load shedding operation control method based on slope power is characterized in that a fast maximum power tracking algorithm is used for obtaining the maximum available power of a system under the conditions of current illumination and temperature, the voltage value of a photovoltaic array port corresponding to the maximum available power is determined, and the voltage is used as the voltage outer ring reference value of a DC/DC converter; the voltage reference value is gradually reduced by a fixed step length, and the output power of the photovoltaic power generation system is reduced under the influence of the reduction of the voltage of the photovoltaic array port. And when the output power of the photovoltaic power generation system reaches 2 times of the given load shedding rate power, the reference value of the DC/DC outer ring voltage stops being reduced. The above process is repeated continuously. The power of the direct current side of the photovoltaic array is fluctuating slope power, and the average value of the fluctuating slope power is equal to the given load shedding rate power. The grid-connected side converter adopts an improved direct-current voltage tracking control algorithm, allows the direct-current capacitor voltage to fluctuate within a certain range through a power compensation algorithm, and maintains the grid-connected power approximately constant.
Description
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a load shedding operation control method of a two-stage photovoltaic power generation system based on slope power.
Background
Solar energy has received wide attention because of its advantages of being clean, pollution-free and renewable. In recent years, the development of solar power generation technology is continuously advanced, and the penetration level of a photovoltaic power generation system in a power system is gradually increased. Because the traditional thermal generator set has inertia and certain frequency response capability, the primary frequency modulation task of the power system is mainly borne by the thermal generator set, and the photovoltaic power generation system does not have the characteristics, so the power system with high photovoltaic permeability cannot well react to load change.
In order to solve the problem of frequency modulation of a high photovoltaic permeability power system and enable a photovoltaic power generation system to participate in frequency adjustment, the prior art has two methods, one method is to use a storage battery in the photovoltaic power generation system to cope with load change in the system, the method has high efficiency, photovoltaic power generation power does not need to be lost, but the cost of energy storage construction and operation maintenance is high; the other method is to make the photovoltaic system actively carry out load shedding operation, and reserve a certain power margin to participate in the frequency adjustment of the power grid, but the photovoltaic load shedding control method usually needs illumination, a temperature sensor and photovoltaic panel parameters to estimate the power of the maximum power point, the algorithm is complex to realize, the cost of the sensor is high, and the method is easily influenced by inaccurate photovoltaic panel parameters.
Disclosure of Invention
The purpose of the invention is: the method is scientific and reasonable, high in applicability, high in use value, good in effect, easy to implement in engineering, free of photovoltaic array model parameters, free of illumination and temperature sensors and capable of quickly responding to illumination changes, and the load shedding operation control method of the two-stage photovoltaic power generation system based on the slope power is provided, so that the photovoltaic power generation system can work at a given load shedding rate level and actively participate in power grid frequency modulation.
The technical scheme adopted for realizing the purpose is as follows: a two-stage photovoltaic power generation system load shedding operation control method based on slope power is characterized by comprising the following steps:
1) DC/DC converter control
The DC/DC converter is used for carrying out maximum power estimation and active load reduction control, the DC/DC converter adopts a control mode of combining voltage outer loop control and current inner loop control, a power reference value is generated by multiplying an external given load reduction rate by the maximum available power under the current condition, and the maximum power under the current environment condition is obtained by adopting a constant-voltage maximum power tracking algorithm; an improved disturbance observation method with a fixed voltage step length is adopted, the DC/DC converter is changed to output power, and photovoltaic active load shedding control is achieved;
firstly, a constant-voltage maximum power tracking algorithm is adopted, and for a photovoltaic array, the voltage corresponding to the maximum power point can be output and is approximate to a certain proportion of open-circuit voltage, as follows: vmpp≈KocVoc
The voltage V at the maximum power point can be approximately obtained by a constant-voltage maximum power tracking algorithmmppThen, the estimated maximum power point voltage is used as a reference value of the voltage outer loop of the DC/DC circuit to make the system operate at the estimated maximum power point, thereby obtaining the power P of the estimated maximum power pointmpp；
Wherein, VmppMaximum power point voltage, V, estimated for a certain illumination and temperature conditionocIs the open circuit voltage, K, of the photovoltaic arrayocAn experimental coefficient of 0.78-0.92 is usually taken, and it is necessary to pay attention to the open-circuit voltage VocThe influence of temperature is large, and when only the change of illumination intensity is considered and the influence of temperature change is ignored, the open-circuit voltage V can be approximately consideredocThe voltage is kept constant, so that the maximum power point voltage can be approximately estimated;
secondly, implementing photovoltaic active load shedding control by adopting an improved disturbance observation method with fixed voltage step length, and gradually reducing the voltage outer ring reference value of the DC/DC circuit to carry out power tracking control until the output power of the photovoltaic array is reduced to the given power P of the photovoltaic systemrefWhen the voltage is higher than the reference value, stopping reducing the voltage outer ring reference value;
thirdly, the reference value of the voltage outer ring is set as the maximum power point voltage V againmppRepeating the first step and the second step;
fourthly photovoltaic arrayThe DC output power of the column is periodic and approximately ramp-shaped, with an average value of (1-epsilon%) P for a given load shedding ratio output powermppThe active load reduction control load reduction rate epsilon% is given by an external frequency control link, and the load reduction rate is reduced by 1 and multiplied by the maximum power PmppGiven power P as a photovoltaic systemref(ii) a Multiplying the retention epsilon% of the photovoltaic system by P according to the P-V characteristic curve of the photovoltaic cellmaxThe standby power of (2) participating in the primary frequency of the power system; wherein ε is between 0 and 100;
2) DC bus voltage fluctuation and capacity calculation
Because the input power of the DC/DC converter is the fluctuating triangular slope power, in order to ensure constant grid-connected power, the direct current bus capacitor needs to temporarily store fluctuating photovoltaic energy, part of energy of voltage fluctuation of the direct current bus is cached, the capacitance value of the direct current capacitor needs to be improved, the capacitance value is set according to the fluctuation period of the input power of the DC/DC converter, the fluctuation power and the allowable fluctuation capacitor voltage range, and the capacitance value can be reduced by reducing the power fluctuation period of the direct current side;
3) grid-connected inverter control strategy
The grid-connected inverter has the functions of stabilizing direct-current side voltage and controlling grid-connected current, in order to avoid grid-connected side power fluctuation, the fluctuation of direct-current capacitor voltage is allowed to absorb photovoltaic side fluctuation power, the current given value of an alternating current control loop of the grid-connected inverter is not a constant value, a power compensation algorithm is adopted, namely, a double-loop control is taken as a basis, the difference value between ideal power and actual grid-connected average power is used as power compensation after being multiplied by a coefficient, the difference value and the direct-current voltage outer loop output determine the amplitude of the grid-connected current together, so that the grid-connected average power tends to be smooth, the purpose of compensating fluctuation power is achieved, and the power compensation algorithm allows the direct-current bus voltage to have certain fluctuation so as to ensure that the grid-connected power is approximately constant.
The invention provides a method for controlling the load shedding operation of a two-stage photovoltaic power generation system based on slope power in order to overcome the defects of the prior art, which is characterized by comprising the following steps of direct maximum power tracking, DC/DC converter slope power control, determination of the size of a direct current bus side capacitor, improvement of direct current voltage control of a grid-connected inverter and the like: the slope power setting is adopted to replace the conventional constant power setting, and the direct current capacitor is used as a buffer memory, so that the output power of the final grid-connected inverter is ensured to be approximately constant. The photovoltaic active load shedding control has the advantages of simple engineering realization, capability of quickly tracking illumination change, no influence of photovoltaic array parameters, easiness in engineering realization and no need of additional illumination and temperature sensors. The method is scientific and reasonable, and has strong applicability, high use value and good effect.
Drawings
FIG. 1 is a schematic diagram of a P-V characteristic curve of a photovoltaic cell at 25 ℃ with different illumination intensities;
FIG. 2 is a schematic view of a photovoltaic load shedding control process;
FIG. 3 is a schematic diagram of a photovoltaic cell output power waveform when the proposed load shedding method is employed;
FIG. 4 is a schematic diagram of a two-stage photovoltaic grid-connected main circuit;
FIG. 5 is a DCDC circuit control strategy;
FIG. 6 is a three-phase grid-connected inverter control strategy;
FIG. 7 is a graph showing the variation of a given illumination intensity;
FIG. 8 is a waveform of the photovoltaic array output power;
FIG. 9 is a partial waveform of the output power of the photovoltaic array;
FIG. 10 is a partial waveform of the DC bus capacitor voltage;
FIG. 11 is a waveform of the throughput power of the DC bus capacitor;
FIG. 12 is a graph of a local throughput power waveform for the DC bus capacitor;
FIG. 13 is a waveform of the grid-connected power of the photovoltaic power generation system;
fig. 14 is a partial waveform diagram of a-phase ac grid-connected side current.
Detailed Description
The following will further describe a two-stage photovoltaic power generation system load shedding operation control method based on ramp power by using the accompanying drawings and embodiments.
The invention relates to a slope power-based two-stage photovoltaic power generation system load shedding operation control method, which comprises the following steps of:
1) DC/DC converter control
A two-stage photovoltaic grid-connected system is adopted, and the main circuit of the two-stage photovoltaic grid-connected system is shown in figure 4. The direct current DCDC converter adopts a traditional double closed loop structure, and the control structure diagram of the direct current DCDC converter is shown in figure 5, wherein fNFor a nominal system frequency of 50Hz, f is the acquired system frequency, PmppIs the maximum power of the photovoltaic array under a certain condition, PrefIs a power reference value, VpvAnd IpvRespectively, the output voltage and the output current of the photovoltaic array. The two-stage photovoltaic grid-connected system control mainly comprises two parts, wherein one part is grid-connected inversion control, and the other part is photovoltaic active load shedding control.
The voltage corresponding to the maximum available power under certain illumination intensity and temperature condition can be approximately obtained by adopting a constant-voltage maximum power tracking algorithm, and for a photovoltaic array, the voltage corresponding to the maximum power point can be approximately a certain proportion open-circuit voltage, as follows:
Vmpp≈KocVoc
wherein, VmppMaximum power point voltage, V, estimated for a certain lighting and temperature conditionocIs the open circuit voltage, K, of the photovoltaic arrayocAs an experimental coefficient, it is generally 0.78-0.92.
The P-V characteristic curve of the photovoltaic cell at different illumination intensities and an external temperature of 25 ℃ is shown in figure 1. The maximum power point voltage V can be approximately obtained by a constant voltage methodmppThen, the estimated maximum power point voltage is used as a reference value of a DC/DC circuit voltage outer ring, so that the system operates at the estimated maximum power point, and the power P of the estimated maximum power point can be obtained at the momentmpp。
And an improved disturbance observation method with fixed voltage step length is adopted to carry out photovoltaic active load shedding control. The process is as follows: gradually reducing the outer ring reference value of the DC/DC circuit voltage for power tracking control until the output power of the photovoltaic array is reduced to PrefTime-stop voltage reduction outer loop parameterTaking into account the voltage outer loop reference value to be reset as the estimated maximum power point voltage Vmpp. Given power value PrefCalculated as follows:
Pref＝(1-2ε％)Pmpp
wherein the load shedding rate epsilon% is the load shedding rate and is given by an external frequency control link. The control block diagram of the improved disturbance observation method is shown in FIG. 2, and the basic control strategy is as follows:
a. if Δ P is less than 0, Δ V is greater than 0 or Δ P is greater than 0, Δ V is less than 0, voltage outer ring reference value VrefDecrease;
b. if P ispvGreater than (1-epsilon%) PmppReference value V of voltage outer looprefDecrease;
c. if P ispvLess than or equal to (1-epsilon%) PmppReference value V of the voltage outer looprefReset to Vmpp；
And repeatedly executing a constant-voltage maximum power tracking algorithm and an improved disturbance observation method, wherein the direct-current output power of the photovoltaic array is in a periodic approximate slope shape, the shape of an output waveform is shown in figure 3, and the average value of the output waveform is the output power at a given load shedding rate.
By executing two steps of a constant-voltage maximum power tracking algorithm and an improved disturbance observation method, the output power of the photovoltaic array fluctuates and changes according to the rule of approximate triangular waves, and the average value of the output power is (1-epsilon%) PmppAnd the active load shedding control of the load shedding rate epsilon% is realized.
According to the photovoltaic cell P-V characteristic curve, the linearization degree of the left part of the maximum power point is higher, and the linearization degree of the right part of the maximum power point is poorer, so that the waveform of the output power of the photovoltaic array is closer to the shape of a slope when the photovoltaic array operates on the left side of the maximum power point by adopting a fixed step length improved disturbance observation method than the waveform when the photovoltaic array operates on the right side of the maximum power point, and the power average value is closer to the target power value of load shedding control. Therefore, the photovoltaic active load shedding control selects the left maximum power pointSide mode of operation. Maximum available power P under certain lighting and temperature conditionsaviI.e. a power P equal to the maximum power point under the conditionmpp。
In the method provided by the invention, the photovoltaic cell is enabled to retain about (1-epsilon%) PmppThe power margin of the power system is used for participating in primary frequency regulation of the power system, and load shedding operation with the load shedding rate of epsilon% is realized.
2) DC bus voltage fluctuation and capacity calculation
Because the input power of the DC/DC converter is fluctuating triangular slope power, and the energy of the photovoltaic cell needs to be temporarily stored by the direct current bus capacitor in order to ensure that the grid-connected power is constant, in order to achieve the purpose, the method provided by the invention allows the direct current bus voltage to have certain ripples. Because the input fluctuation power period of the DC/DC converter is very small, the fluctuation energy required to be stored by the capacitor is very small. The proper size of the direct current bus side capacitor is selected to enable the direct current bus voltage to keep a certain ripple level so as to absorb fluctuating power and maintain the power input into the power grid to be basically constant. The specific method is as follows
t1And t2Respectively as the starting time and the ending time in a period; ppvAs a function of the output power of the photovoltaic array with respect to time t; epsilon% is the load shedding rate; paviThe maximum available power under a certain illumination and temperature condition; c is a direct current bus capacitor; u shapedcThe peak value of the voltage of the direct current bus (containing ripples); u shapedc0Is the target value of the DC bus voltage (ideal DC bus voltage). Since the waveform of the output power of the photovoltaic array changing along with the time is a triangular wave, the above formula can be rewritten as
Therefore, the capacitance of the DC bus can be selected according to the following formula
Next, the selection of the capacitance value will be described by taking a photovoltaic grid-connected system of 2kW as an example. Direct-current bus voltage reference value U of photovoltaic grid-connected systemdcWhen the allowable ripple voltage peak value is 20V at 500V, the actual DC bus voltage peak value U is obtaineddcp520V, minimum value of ripple voltage Udc0480V; period of fluctuation t2-t1The maximum power of the photovoltaic array is 2kW under the standard condition and the load reduction rate epsilon% is 20% after 0.1s is taken. The above parameters are substituted into the above formula to obtain
The capacitance value range of the direct current bus capacitor selected by the conventional 2kW photovoltaic grid-connected system is generally between 800 muF and 1100 muF, and the direct current bus capacitor C with a large capacitance value is selected to be 2000 muF through the formula because the fluctuation power required to be absorbed by the method is large, so that the capacitance value of the direct current bus capacitor is increased by about one time compared with the capacitance value of the direct current bus selected by the conventional 2kW system. Therefore, the direct current ripple voltage can be well limited and the fluctuation power can be well absorbed by reasonably selecting the direct current bus capacitor.
3) Grid-connected inverter control strategy
The grid-connected inverter has the functions of stabilizing direct-current side voltage and controlling grid-connected current, and the traditional grid-connected inverter generally adopts a double closed loop strategy of a direct-current voltage outer loop and a grid current inner loop, and keeps the constant of direct-current side capacitance voltage by controlling a given value of a voltage outer loop. In order to avoid grid-connected side power fluctuation, the method allows direct current capacitor voltage fluctuation to absorb photovoltaic side fluctuation power, the current given value of an alternating current control loop of the grid-connected inverter is not a constant value, and certain fluctuation is allowed through a power compensation algorithm to ensure that the grid-connected power is approximately constant. The control strategy of the three-phase grid-connected inverter is shown in figure 6, wherein VdcAnd Vdc *Respectively, the DC bus capacitor voltage and its reference value, PacAnd Pac *Respectively a reference value, i, of the AC side grid-connected power stageG，abcThree-phase instantaneous current at the alternating current side; i.e. iGdAnd iGqThe direct and quadrature components of the grid voltage, EGdAnd EGqThe grid voltage direct and quadrature components, thetaGAnd omegaGRespectively the initial phase and angular frequency of the grid voltage.
The grid-connected inverter control strategy used by the invention introduces power compensation on the basis of the traditional control strategy. The ideal power and the actual grid-connected average power are subtracted, and after the difference value is multiplied by a coefficient, the difference value and the output of the direct-current voltage outer ring jointly determine the amplitude of the grid-connected current, so that the grid-connected average power tends to be smooth, and the purpose of compensating the fluctuating power is achieved. Compared with the traditional control strategy, the method adopted by the invention has faster and better response performance.
Example the calculation conditions are as follows:
(1) the illumination intensity condition is that G is 1000W/m2Slowly reducing to G-800W/m2Then slowly increasing to G-800W/m2As shown in fig. 7, the temperature conditions were always maintained at T ═ 25 ℃;
(2) taking an empirical coefficient KocIs 0.85;
(3) the single photovoltaic cell panel m is 66, and n is 5;
(4) open circuit voltage V of photovoltaic cell under standard conditionoc321V, short-circuit current Isc393.36A, maximum power Pmpp100.7kW, maximum power point voltage Vmpp＝273.5V；
(5) The target load shedding rate epsilon% is 20%;
(6) DC bus voltage reference value Udc0The allowable peak value of the ripple voltage of the direct current bus is 25V, and the fluctuation period t is 500V2-t1Taking 0.006 s;
according to the calculation conditions (1) to (6) of the embodiment, the MATLAB/simulink simulation verification result of the two-stage inversion grid-connected system is analyzed by applying the slope power-based two-stage photovoltaic power generation system load shedding operation control method disclosed by the invention as follows:
1) maximum obtainable power and estimation of its corresponding voltage
When the empirical coefficient KocWhen equal to 0.85, is represented by formula Vmpp≈KocVocMaximum power point voltage V under standard condition can be obtainedmpp272.85V, close to the actual maximum power point voltage 273.5V; when the temperature condition is not changed, the illumination condition is changed to G1200W/m2When the maximum power point voltage is 273.6V, it can be seen that the maximum power point voltage is approximately regarded as being constant when the illuminance is changed while the temperature is kept constant.
2) Capacitance value calculation of compensation capacitor and fluctuation voltage
According to the embodiment calculation condition (6), the maximum value 525V and the minimum value 475V of the fluctuation voltage can be obtained by the direct current bus voltage reference value and the allowable voltage ripple peak value. Substituting the above conditions into the formula
The capacitance C is selected to be 9600 μ F, so that the ripple power output by the DC/DC converter can be compensated well.
3) Analysis of derated operating results
When the external illumination condition is G-1000W/m2And the external temperature condition is that T is 25 ℃, the actual output power of the photovoltaic array is 80.5kW, and the actual load shedding rate is 20.05%. When the external illumination condition is G ═ 1200W/m2Maximum power P when the external temperature is T-25 deg.Cmpp120.2kW, maximum power point voltage Vmpp273.6V, the actual output power of the photovoltaic array is 96.7kW, and the actual load shedding rate is 19.55%. Therefore, the load shedding rate kept by the photovoltaic load shedding control performed according to the method provided by the invention is basically consistent with the target load shedding rate of 20%, and relatively accurate load shedding control can be realized. Simulation result verification shows that under the condition of illumination intensity variation, the method can ensure that the photovoltaic power generation system can keep a certain constant load shedding rate to operate so as to reserve a certain load shedding rateIs adjusted with the frequency of the participating grid.
The simulation results at 20% load shedding are shown in fig. 8 to 14. FIGS. 8 and 9 show the overall and local output power waveforms of the photovoltaic array within 1-14 s, respectively, where PpvOutputting power for the photovoltaic array; FIG. 10 shows the DC bus voltage waveform within 1-14 s, where VdcIs a dc bus voltage; FIGS. 11 and 12 show the whole and local absorbed power fluctuation power waveforms of the direct current bus capacitor within 1-14 s respectively, wherein PCThe fluctuating power absorbed by the direct current bus capacitor; FIG. 13 shows the AC side grid-tied average power waveform, where PacThe grid-connected power is the alternating current side grid-connected power. As can be seen from fig. 13, the grid-connected power is almost constant under different illumination conditions, which fully illustrates the effectiveness and feasibility of the proposed method; FIG. 14 shows the grid-connected current waveform of the a-phase on the AC side, where iaIs a-phase grid-connected current.
The computing conditions, diagrams and the like in the embodiments of the present invention are used for further description, are not exhaustive, and do not limit the scope of the claims, and those skilled in the art can conceive other substantially equivalent alternatives without inventive step in light of the teachings of the embodiments of the present invention, which are within the scope of the present invention.
Claims (1)
1. A two-stage photovoltaic power generation system load shedding operation control method based on slope power is characterized by comprising the following steps:
1) DC/DC converter control
The DC/DC converter is used for carrying out maximum power estimation and active load reduction control, the DC/DC converter adopts a control mode of combining voltage outer loop control and current inner loop control, a power reference value is generated by multiplying an external given load reduction rate by the maximum available power under the current condition, and the maximum power under the current environment condition is obtained by adopting a constant-voltage maximum power tracking algorithm; an improved disturbance observation method with a fixed voltage step length is adopted, the DC/DC converter is changed to output power, and photovoltaic active load shedding control is achieved;
firstly, a constant-voltage maximum power tracking algorithm is adopted, and for a photovoltaic array, the voltage corresponding to the maximum power point can be output and is approximate to a certain proportion of open-circuit voltage, as follows:
Vmpp≈KocVoc
the voltage V at the maximum power point can be approximately obtained by a constant-voltage maximum power tracking algorithmmppThen, the estimated maximum power point voltage is used as a reference value of the voltage outer loop of the DC/DC circuit to make the system operate at the estimated maximum power point, thereby obtaining the power P of the estimated maximum power pointmpp；
Wherein, VmppMaximum power point voltage, V, estimated for a certain lighting and temperature conditionocIs the open circuit voltage, K, of the photovoltaic arrayocTaking 0.78-0.92 as an experimental coefficient, it is necessary to pay attention to the open-circuit voltage VocWhen the influence of temperature is ignored while only the change of illumination intensity is considered, the open-circuit voltage V can be approximately consideredocThe voltage is kept constant, so that the maximum power point voltage can be approximately estimated;
secondly, implementing photovoltaic active load shedding control by adopting an improved disturbance observation method with fixed voltage step length, and gradually reducing the voltage outer ring reference value of the DC/DC circuit to carry out power tracking control until the output power of the photovoltaic array is reduced to the given power P of the photovoltaic systemrefWhen the voltage is higher than the reference value, stopping reducing the voltage outer ring reference value; resetting the voltage outer loop reference value to the estimated maximum power point voltage VmppGiven value of power PrefCalculated as follows:
Pref＝(1-2ε％)Pmpp
wherein the load shedding rate epsilon% is the load shedding rate and is given by an external frequency control link;
a. if Δ P is less than 0, Δ V is greater than 0 or Δ P is greater than 0, Δ V is less than 0, voltage outer ring reference value VrefDecrease;
b. if P ispvGreater than PrefReference value V of the voltage outer looprefDecreasing;
c. if P ispvIs less than or equal to PrefReference value V of the voltage outer looprefReset to Vmpp；
Thirdly, the reference value of the voltage outer ring is set as the maximum power point voltage V againmppRepeating the first step and the second step;
the direct current output power of the photovoltaic array is in a periodic approximate slope shape, the average value of the direct current output power is the output power of a given load shedding rate and is (1-epsilon%) PmppThe active load reduction control load reduction rate epsilon% is given by an external frequency control link, and the load reduction rate is reduced by 1 and multiplied by the maximum power PmppGiven power P as a photovoltaic systemref(ii) a Multiplying the retention epsilon% of the photovoltaic system by P according to the P-V characteristic curve of the photovoltaic cellmppThe standby power of (2) participating in the primary frequency of the power system; wherein ε is between 0 and 100;
2) DC bus voltage fluctuation and capacity calculation
Because the input power of the DC/DC converter is the fluctuating triangular slope power, in order to ensure constant grid-connected power, the direct current bus capacitor needs to temporarily store fluctuating photovoltaic energy, part of energy of voltage fluctuation of the direct current bus is cached, the capacitance value of the direct current capacitor needs to be improved, the capacitance value is set according to the fluctuation period of the input power of the DC/DC converter, the fluctuation power and the allowable fluctuation capacitor voltage range, and the capacitance value can be reduced by reducing the power fluctuation period of the direct current side; 3) grid-connected inverter control strategy
The grid-connected inverter has the functions of stabilizing direct-current side voltage and controlling grid-connected current, in order to avoid grid-connected side power fluctuation, the fluctuation of direct-current capacitor voltage is allowed to absorb photovoltaic side fluctuation power, the current given value of an alternating current control loop of the grid-connected inverter is not a constant value, a power compensation algorithm is adopted, namely, a double-loop control is taken as a basis, the difference value between ideal power and actual grid-connected average power is used as power compensation after being multiplied by a coefficient, the difference value and the direct-current voltage outer loop output determine the amplitude of the grid-connected current together, so that the grid-connected average power tends to be smooth, the purpose of compensating fluctuation power is achieved, and the power compensation algorithm allows the direct-current bus voltage to have certain fluctuation so as to ensure that the grid-connected power is approximately constant.
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