A method, system and device for flexible control of output power of photovoltaic power generation system

Abstract

The present invention relates to the field of photovoltaic power generation technology, and discloses a method, system, and device for flexible control of the output power of a photovoltaic power generation system. The present invention determines the value of a DC bus voltage deviation flag based on the deviation between the DC voltage on the DC bus of a grid-connected inverter and a DC bus voltage reference value; and uses an improved MPPT control algorithm to control the output power of the photovoltaic power generation system. The improved MPPT control algorithm changes the duty cycle of the switching device of the Boost circuit with a corrected step size, and the corrected step size is obtained by correcting the fixed step size in the MPPT control algorithm using the value of the DC bus voltage deviation flag as a correction coefficient. The present invention can automatically adjust the output of the photovoltaic power generation system according to the power balance situation, without the need to add additional devices, and only requires some modifications to the existing MPPT control method, so the implementation difficulty is relatively low.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to a method, system and device for flexibly controlling the output power of a photovoltaic power generation system. Background Art

[0002] Photovoltaic power generation is the main force of new energy power generation. It plays an important role in alleviating the energy crisis and reducing environmental pollution, and has huge development potential.

[0003] In order to improve the efficiency of photoelectric conversion, photovoltaic power generation systems usually operate in a maximum power point tracking (MPPT) mode. Existing MPPT methods are divided into open-loop MPPT methods and closed-loop MPPT methods based on different judgment methods and criteria. The impact of changes in external temperature, light and load on the output characteristics of photovoltaic cells shows some basic laws. For example, there is an approximate linear relationship between the maximum power point voltage of photovoltaic cells and the open-circuit voltage of photovoltaic cells. The open-loop MPPT control method performs power control based on these laws. The closed-loop MPPT method realizes MPPT through real-time measurement and closed-loop control of the output voltage and current values ​​of photovoltaic cells. The most widely used self-optimization algorithms belong to this category. Typical self-optimization MPPT algorithms include the Perturbation and Observation Method (P&O) and the Incremental Conductance (INC) method.

[0004] With the gradual increase in grid-connected photovoltaic capacity, the power balance relationship of the power system no longer requires the photovoltaic power generation system to be in a state of maximum power generation all the time, but requires the photovoltaic power generation system to output power in a more flexible manner. Therefore, it is necessary to study a more flexible and efficient output power control method for photovoltaic power generation systems. Summary of the Invention

[0005] The present invention provides a method, system and device for flexible control of the output power of a photovoltaic power generation system, which solves the technical problem that the existing photovoltaic power generation system output power control method is difficult to flexibly and stably maintain the power supply and demand balance of the photovoltaic power generation system.

[0006] A first aspect of the present invention provides a method for flexible output power control of a photovoltaic power generation system. The primary main circuit of the photovoltaic power generation system includes a photovoltaic array, a boost circuit, a grid-connected inverter, an LCL filter circuit, and an AC power grid. The photovoltaic array and the boost circuit are connected via a first capacitor, and the boost circuit and the grid-connected inverter are connected via a second capacitor. The method includes:

[0007] Determining a value of a DC bus voltage deviation flag according to a deviation between a DC voltage on a DC bus of a grid-connected inverter and a DC bus voltage reference value; when the value of the DC bus voltage deviation flag is 1, it indicates that the DC bus voltage is too low; and when the value of the DC bus voltage deviation flag is -1, it indicates that the DC bus voltage is too high;

[0008] An improved MPPT control algorithm is used to control the output power of a photovoltaic power generation system; the improved MPPT control algorithm changes the duty cycle of a switching device in a Boost circuit with a corrected step size, and the corrected step size is obtained by correcting the fixed step size in the MPPT control algorithm using the value of the DC bus voltage deviation flag as a correction coefficient.

[0009] According to an implementation of the first aspect of the present invention, determining the value of the DC bus voltage deviation flag according to the deviation between the DC voltage on the DC bus of the grid-connected inverter and the DC bus voltage reference value includes:

[0010] Multiplying the deviation between the DC voltage on the DC bus of the grid-connected inverter and the DC bus voltage reference value by -1 and then passing the result through a first-order low-pass filter to obtain a first processing result;

[0011] Performing a hysteresis comparison on the first processing result, an upper threshold value of the DC bus voltage deviation, and a lower threshold value of the DC bus voltage deviation to obtain a second processing result;

[0012] If the second processing result satisfies the upper hysteresis condition and lasts for the first preset action delay time, setting the value of the DC bus voltage deviation flag to 1;

[0013] If the second processing result satisfies the lower hysteresis condition and lasts for a second preset action delay time, the value of the DC bus voltage deviation flag is set to -1.

[0014] According to an achievable manner of the first aspect of the present invention, the values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value satisfy:

[0015]

[0016] Where U dcref is the DC bus voltage reference value, ΔU dcmin is the DC bus voltage deviation lower limit threshold, ΔU dcmax is the upper limit threshold of DC bus voltage deviation.

[0017] According to an achievable manner of the first aspect of the present invention, the fixed step size includes a first preset step size used when reducing the duty cycle and a second preset step size used when increasing the duty cycle, and the use of the improved MPPT control algorithm to control the output power of the photovoltaic power generation system includes:

[0018] Collecting electrical quantity measurement data of the primary main circuit of the photovoltaic power generation system; the electrical quantity measurement data includes the DC voltage and DC current output by the photovoltaic array;

[0019] Based on the electrical quantity measurement data, calculating a change in the DC voltage output by the photovoltaic array in a current control cycle and a previous control cycle as a first change, and calculating a change in the output power of the photovoltaic array in the current control cycle and a previous control cycle as a second change;

[0020] Calculating the product of the first variation and the second variation;

[0021] If the product of the first change amount and the second change amount is greater than 0 and the second change amount is not equal to 0, the product of the value of the DC bus voltage deviation flag and the first preset step size is used as the corrected step size to reduce the duty cycle of the switching device of the Boost circuit; if the product of the first change amount and the second change amount is not greater than 0 and the second change amount is not equal to 0, the product of the value of the DC bus voltage deviation flag bit and the second preset step size is used as the corrected step size to increase the duty cycle of the switching device of the Boost circuit.

[0022] A second aspect of the present invention provides a flexible control system for output power of a photovoltaic power generation system. The primary main circuit of the photovoltaic power generation system includes a photovoltaic array, a boost circuit, a grid-connected inverter, an LCL filter circuit, and an AC power grid. The photovoltaic array and the boost circuit are connected via a first capacitor, and the boost circuit and the grid-connected inverter are connected via a second capacitor. The system includes:

[0023] a determination module, configured to determine a value of a DC bus voltage deviation flag according to a deviation between a DC voltage on a DC bus of a grid-connected inverter and a DC bus voltage reference value; when the value of the DC bus voltage deviation flag is 1, it indicates that the DC bus voltage is too low; and when the value of the DC bus voltage deviation flag is -1, it indicates that the DC bus voltage is too high;

[0024] A control module is used to control the output power of a photovoltaic power generation system using an improved MPPT control algorithm; the improved MPPT control algorithm changes the duty cycle of a switching device in a Boost circuit with a corrected step size, and the corrected step size is obtained by correcting the fixed step size in the MPPT control algorithm using the value of the DC bus voltage deviation flag as a correction coefficient.

[0025] According to an implementation of the second aspect of the present invention, the determining module includes:

[0026] a first processing unit, configured to multiply a deviation between a DC voltage on the DC bus of the grid-connected inverter and a DC bus voltage reference value by -1 and then pass the result through a first-order low-pass filter to obtain a first processing result;

[0027] a second processing unit, configured to perform a hysteresis comparison on the first processing result, an upper threshold value of a DC bus voltage deviation, and a lower threshold value of a DC bus voltage deviation, to obtain a second processing result;

[0028] a first setting unit, configured to set the value of the DC bus voltage deviation flag to 1 if the second processing result satisfies an upper hysteresis condition and lasts for a first preset action delay time;

[0029] The second setting unit is configured to set the value of the DC bus voltage deviation flag to -1 if the second processing result satisfies a lower hysteresis condition and lasts for a second preset action delay time.

[0030] According to an implementation of the second aspect of the present invention, the values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value satisfy:

[0031]

[0032] Where U dcref is the DC bus voltage reference value, ΔU dcmin is the DC bus voltage deviation lower limit threshold, ΔU dcmax is the upper limit threshold of DC bus voltage deviation.

[0033] According to an achievable manner of the second aspect of the present invention, the fixed step size includes a first preset step size used when reducing the duty cycle and a second preset step size used when increasing the duty cycle, and the control module includes:

[0034] An acquisition unit is used to acquire electrical quantity measurement data of a primary main circuit of a photovoltaic power generation system; the electrical quantity measurement data includes a DC voltage and a DC current output by the photovoltaic array;

[0035] a first calculation unit, configured to calculate, based on the electrical quantity measurement data, a change in the DC voltage output by the photovoltaic array between a current control cycle and a previous control cycle as a first change, and calculate a change in the output power of the photovoltaic array between the current control cycle and the previous control cycle as a second change;

[0036] a second calculation unit, configured to calculate the product of the first variation and the second variation;

[0037] A control unit is configured to, if the product of the first variation and the second variation is greater than 0 and the second variation is not equal to 0, use the product of the value of the DC bus voltage deviation flag and the first preset step size as a corrected step size to reduce the duty cycle of the switching device of the Boost circuit; and if the product of the first variation and the second variation is not greater than 0 and the second variation is not equal to 0, use the product of the value of the DC bus voltage deviation flag and the second preset step size as a corrected step size to increase the duty cycle of the switching device of the Boost circuit.

[0038] A third aspect of the present invention provides a photovoltaic power generation system output power flexible control device, comprising:

[0039] A memory for storing instructions; wherein the instructions are used to implement the method for flexible output power control of a photovoltaic power generation system as described in any one of the above implementation methods;

[0040] A processor is configured to execute instructions in the memory.

[0041] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for flexible output power control of a photovoltaic power generation system as described in any of the above-mentioned implementation methods.

[0042] It can be seen from the above technical solutions that the present invention has the following advantages:

[0043] The present invention determines the value of a DC bus voltage deviation flag bit based on the deviation between the DC voltage on the DC bus of a grid-connected inverter and a DC bus voltage reference value; adopts an improved MPPT control algorithm to control the output power of a photovoltaic power generation system; wherein the improved MPPT control algorithm changes the duty cycle of a switching device of a Boost circuit with a corrected step size, and the corrected step size is obtained by using the value of the DC bus voltage deviation flag bit as a correction coefficient to correct a fixed step size in the MPPT control algorithm; the present invention can automatically adjust the output of a photovoltaic power generation system according to a power balance condition, without adding additional devices, and only requires some modifications to the existing MPPT control method, thus having relatively low implementation difficulty, and solving the technical problem that the existing photovoltaic power generation system output power control method is difficult to flexibly and stably maintain the power supply and demand balance of the photovoltaic power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 This is the circuit diagram of the primary main circuit of the photovoltaic power generation system;

[0046] Figure 2 A flowchart of a method for flexible output power control of a photovoltaic power generation system provided by an optional embodiment of the present invention;

[0047] Figure 3 A logic block diagram for determining a DC bus voltage deviation according to an optional embodiment of the present invention;

[0048] Figure 4 Schematic diagram of the current-voltage curve and power-voltage curve of the photovoltaic array;

[0049] Figure 5 This is a logic diagram of the MPPT control strategy based on the disturbance-observation method in the prior art;

[0050] Figure 6 A logic diagram for controlling the output power of a photovoltaic power generation system using an improved MPPT control algorithm provided in an optional embodiment of the present invention;

[0051] Figure 7 Schematic diagram of the PV curve of a photovoltaic array using a photovoltaic power generation system as an example;

[0052] Figure 8This is a logic block diagram for determining DC bus voltage deviation using a photovoltaic power generation system as an example.

[0053] Figure 9 This is a waveform diagram when the photovoltaic power generation system cannot operate stably;

[0054] Figure 10 This is the waveform diagram of the photovoltaic power generation system when it is operating stably;

[0055] Figure 11 This is a structural connection block diagram of a photovoltaic power generation system output power flexible control system provided by an optional embodiment of the present invention.

[0056] Reference numerals:

[0057] 01-PV array; 02-Boost circuit; 03-grid-connected inverter; 04-LCL filter circuit; 05-AC grid; 06-first capacitor; 07-second capacitor;

[0058] 1-determination module; 2-control module;

[0059] 10-subtractor; 20-multiplier; 30-first-order low-pass filter; 40-hysteresis comparator. DETAILED DESCRIPTION

[0060] The embodiments of the present invention provide a method, system and device for flexible control of the output power of a photovoltaic power generation system, which are used to solve the technical problem that the existing photovoltaic power generation system output power control method is difficult to flexibly and stably maintain the power supply and demand balance of the photovoltaic power generation system.

[0061] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0062] The present invention provides a method for flexibly controlling the output power of a photovoltaic power generation system.

[0063] Among them, such as Figure 1 As shown, the primary main circuit of the photovoltaic power generation system includes a photovoltaic array 01, a boost circuit 02, a grid-connected inverter 03, an LCL filter circuit 04 and an AC power grid 05. The photovoltaic array 01 and the boost circuit 02 are connected via a first capacitor 06, and the boost circuit 02 and the grid-connected inverter 03 are connected via a second capacitor 07.

[0064] Photovoltaic array 01 is composed of a certain number of photovoltaic modules connected in series or parallel, and a photovoltaic module is composed of a certain number of photovoltaic cells connected in series or parallel. Boost circuit 02 is a single-transistor isolated DC converter with an output voltage higher than the input voltage, commonly known as a boost chopper. Grid-connected inverter 03 is used to convert the DC power generated by photovoltaic array 01 into AC power and feed it into the grid. Grid-connected inverter 03 uses classic DC voltage and reactive power dual closed-loop control.

[0065] First capacitor 06 and second capacitor 07 are important components in a photovoltaic power generation system, located between photovoltaic array 01 and grid-connected inverter 03. They reduce ripple in the output voltage of photovoltaic array 01, thereby indirectly reducing ripple in the output power of photovoltaic array 01. Furthermore, first capacitor 06 and second capacitor 07 function as power receivers or power sources during each half-cycle, alternating between cycles and maintaining power balance on the DC bus.

[0066] The LCL filter circuit 04 is a very important part of the photovoltaic system after the inverter. Its function is to ensure that the output grid-connected voltage and the injected grid current have high power quality.

[0067] In the embodiment of the present application, a flexible control method for the output power of the photovoltaic power generation system is used to achieve maximum power point tracking of the photovoltaic array 01 and control the grid-connected transmission power and grid-connected current of the inverter, thereby balancing the maximum power output by the photovoltaic array 01 and the power transmitted to the grid.

[0068] Figure 1 Middle,U pv , I pv are the DC voltage and DC current of PV array 01 port, U dcm is the DC voltage on the DC bus of the grid-connected inverter 03.

[0069] The DC voltages at the input and output ports of the Boost circuit 02 correspond to U pv 、U dcm , and satisfy U dcm =U pv / (1-D), D is the duty cycle of the Boost circuit 02.

[0070] See also Figure 2 , Figure 2 A flow chart of a method for flexibly controlling output power of a photovoltaic power generation system provided by an embodiment of the present invention is shown.

[0071] An embodiment of the present invention provides a method for flexibly controlling the output power of a photovoltaic power generation system, comprising steps S1-S2.

[0072] Step S1, determining the value of the DC bus voltage deviation flag based on the deviation between the DC voltage on the DC bus of the grid-connected inverter 03 and the DC bus voltage reference value; when the value of the DC bus voltage deviation flag is 1, it indicates that the DC bus voltage is low, and when the value of the DC bus voltage deviation flag is -1, it indicates that the DC bus voltage is high.

[0073] In one achievable manner, determining the value of the DC bus voltage deviation flag according to the deviation between the DC voltage on the DC bus of the grid-connected inverter 03 and the DC bus voltage reference value includes:

[0074] Multiplying the deviation between the DC voltage on the DC bus of the grid-connected inverter 03 and the DC bus voltage reference value by -1 and then passing the result through a first-order low-pass filter to obtain a first processing result;

[0075] Performing a hysteresis comparison on the first processing result, an upper threshold value of the DC bus voltage deviation, and a lower threshold value of the DC bus voltage deviation to obtain a second processing result;

[0076] If the second processing result satisfies the upper hysteresis condition and lasts for the first preset action delay time, setting the value of the DC bus voltage deviation flag to 1;

[0077] If the second processing result satisfies the lower hysteresis condition and lasts for a second preset action delay time, the value of the DC bus voltage deviation flag is set to -1.

[0078] The DC bus voltage reference value is the DC voltage reference value determined when the photovoltaic power generation system is designed.

[0079] As a specific implementation method, the DC bus voltage deviation ΔU is defined as dc =U dcm -U dcref , where U dcm is the DC voltage on the DC bus of the grid-connected inverter 03, U dcref is the DC bus voltage reference value, and the variable FlagUdcBal is defined as the DC bus voltage deviation flag. FlagUdcBal=1 means the DC bus voltage is too low, and FlagUdcBal=-1 means the DC bus voltage is too high. Figure 3 As shown, the deviation ΔU between the DC voltage on the DC bus of the grid-connected inverter 03 and the DC bus voltage reference value is calculated by the subtractor 10. dc , through the multiplier to ΔU dcThe first processing result is multiplied by -1, and the result is passed through a first-order low-pass filter 30 to obtain a first processing result. The first processing result is then input into a hysteresis comparator 40 to obtain a second processing result. If the second processing result satisfies the upper hysteresis condition and lasts for a time t1, a DC bus voltage low flag is generated, i.e., FlagUdcBal=1. If the second processing result satisfies the lower hysteresis condition and lasts for a time t2, a DC bus voltage high flag is generated, i.e., FlagUdcBal=-1.

[0080] The values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value are related to the specific photovoltaic power generation system component parameters and control characteristics. In one embodiment, the values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value satisfy:

[0081]

[0082] Where U dcref is the DC bus voltage reference value, ΔU dcmin is the DC bus voltage deviation lower limit threshold, ΔU dcmax is the upper limit threshold of DC bus voltage deviation.

[0083] Step S2, using an improved MPPT control algorithm to control the output power of the photovoltaic power generation system; the improved MPPT control algorithm changes the duty cycle of the switching device of the Boost circuit 02 with a corrected step size, and the corrected step size is obtained by correcting the fixed step size in the MPPT control algorithm by using the value of the DC bus voltage deviation flag as a correction coefficient.

[0084] Take the MPPT control algorithm based on the disturbance observation method as an example. Figure 4 As shown in the figure, under normal conditions, the PU characteristic curve of the photovoltaic cell is a single-peak function with a maximum power point extreme value. This feature provides the conditions for using the perturbation observation method to find the maximum power point. The perturbation observation method actually adopts the idea of ​​step search, that is, starting from the initial state, the input signal is changed finitely each time, and then the size and direction of the output change caused by the input signal change are measured. After the direction is identified, the input of the controlled object is controlled to adjust in the required direction, thereby realizing self-optimal control. Figure 4 In the area to the left of the MPP point, P pv and U pv The change direction is the same. In the area to the right of the MPP point, P pv and U pv The change direction of P is opposite. pv is the output power of photovoltaic array 01, P pvmaxis the maximum output power of PV array 01, U pvMPP is the DC voltage output by the photovoltaic array 01 at the MPP point, I pvMPP is the DC current output by the photovoltaic array 01 at the MPP point, I-Ucurve represents the current-voltage curve of the photovoltaic array 01, P-Ucurve represents the power-voltage curve of the photovoltaic array 01, I pvmax The maximum value of the DC current output by PV array 01.

[0085] The control logic of the existing MPPT control algorithm is as follows Figure 5 The basic idea is to first perturb the output voltage (or current) of the photovoltaic cell, then observe the change in the output power of the photovoltaic cell, and continuously change the direction of the perturbation voltage (or current) according to the trend of power change, so that the photovoltaic cell finally works at the maximum power point. Figure 5 The control logic shown includes:

[0086] 1) Calculate the output DC voltage U of the photovoltaic array 01 in two adjacent control cycles pv The change in dU pv =U pv (k)-U pv (k-1), where U pv (k) represents the DC voltage output by the photovoltaic array 01 in the current control period, U pv (k-1) represents the DC voltage output by PV array 01 in the previous control cycle;

[0087] 2) Calculate the output power P of PV array 01 in two adjacent control cycles pv and its variation dPpv, where: P pv =U pv ×I pv , dP pv =P pv (k)-P pv (k-1). Among them, I pv The output DC current of photovoltaic array 01, P pv (k) represents the output power of PV array 01 in the current control period, P pv )k-1) represents the output power of PV array 01 in the last control cycle;

[0088] 3) Determine dU pv 、dP pv Whether they are in the same direction, that is: judge dU pv ×dP pv Is it greater than 0?

[0089] 4) If the result of step 3) is greater than 0, further determine dP pvIs it equal to 0? If it is equal to 0, the duty cycle of the previous control cycle is maintained unchanged; if it is not equal to 0, the duty cycle of the switching device of the Boost circuit 02 is reduced. At this time, D(k)=D(k-1)-ΔD dec , where D)k) represents the duty cycle of the switching device of the Boost circuit 02 in the current control cycle, D(k-1) represents the duty cycle of the switching device of the Boost circuit 02 in the previous control cycle, and ΔD dec The step size used to reduce the duty cycle;

[0090] 5) If the result of step 3) is less than or equal to 0, further determine dP pv Is it equal to 0? If it is equal to 0, the duty cycle of the previous control cycle is maintained unchanged; if it is not equal to 0, the duty cycle of the switching device of the Boost circuit 02 is increased, and at this time D(k)=D(k-1)+ΔD inc , where ΔD inc is the step size used when increasing the duty cycle.

[0091] In an embodiment of the present invention, a DC bus voltage deviation flag is added to the existing MPPT control algorithm to improve the MPPT control algorithm.

[0092] In one achievable manner, the fixed step size includes a first preset step size used when reducing the duty cycle and a second preset step size used when increasing the duty cycle, and the use of the improved MPPT control algorithm to control the output power of the photovoltaic power generation system includes:

[0093] Collecting electrical quantity measurement data of the primary main circuit of the photovoltaic power generation system; the electrical quantity measurement data includes the DC voltage and DC current output by the photovoltaic array 01;

[0094] Calculating, based on the electrical quantity measurement data, a change in the DC voltage output by the photovoltaic array 01 between the current control cycle and the previous control cycle as a first change, and calculating a change in the output power of the photovoltaic array 01 between the current control cycle and the previous control cycle as a second change;

[0095] Calculating the product of the first variation and the second variation;

[0096] If the product of the first change amount and the second change amount is greater than 0 and the second change amount is not equal to 0, the product of the value of the DC bus voltage deviation flag and the first preset step size is used as the corrected step size to reduce the duty cycle of the switching device of the Boost circuit 02; if the product of the first change amount and the second change amount is not greater than 0 and the second change amount is not equal to 0, the product of the value of the DC bus voltage deviation flag bit and the second preset step size is used as the corrected step size to increase the duty cycle of the switching device of the Boost circuit 02.

[0097] As a specific implementation method, the logic diagram of the embodiment of the present invention using the improved MPPT control algorithm to control the output power of the photovoltaic power generation system is as follows: Figure 6 shown. Figure 6 The control logic shown includes:

[0098] 1) Calculate the output DC voltage U of the photovoltaic array 01 in two adjacent control cycles pv The change in dU pv =U pv (k)-U pv (k-1), where U pv (k) represents the DC voltage output by the photovoltaic array 01 in the current control period, U pv (k-1) represents the DC voltage output by PV array 01 in the previous control cycle;

[0099] 2) Calculate the output power P of PV array 01 in two adjacent control cycles pv and its variation dPpv, where: P pv =U pv ×I pv , dP pv =P pv (k)-P pv (k-1). Among them, P pv (k) represents the output power of PV array 01 in the current control cycle, and Ppv(k-1) represents the output power of PV array 01 in the previous control cycle;

[0100] 3) Determine dU pv 、dP pv Whether they are in the same direction, that is: judge dU pv ×dP pv Is it greater than 0?

[0101] 4) If the result of step 3) is greater than 0, further determine dP pvIs it equal to 0? If it is equal to 0, the duty cycle of the previous control cycle is maintained unchanged; if it is not equal to 0, the duty cycle of the Boost circuit 02 switching device is reduced. At this time, D(k)=D(k-1)-FlagUdcBal×ΔD dec , where FlagUdcBal is the DC bus voltage deviation flag;

[0102] When FlagUdcBal=1, it means that the DC bus voltage is low and the power output by the photovoltaic array 01 is low. At this time, the actual power control result of the photovoltaic array 01 is to reduce the duty cycle of the Boost circuit 02, and the DC voltage U dcm Controlled by the grid-connected inverter 03, it can be considered to be basically unchanged; reducing the duty cycle will cause the photovoltaic array 01 to output a DC voltage U pv Increases, the power tracking of PV array 01 gradually approaches its maximum power point, and the output power of PV array 01 increases;

[0103] When FlagUdcBal=-1, it means that the DC bus voltage is too high and the power output by the photovoltaic array 01 is too high. At this time, the actual power control result of the photovoltaic array 01 is to increase the duty cycle of the Boost circuit 02, and the DC voltage U dcm Controlled by the grid-connected inverter 03, it can be considered to be basically unchanged; increasing the duty cycle will cause the photovoltaic array 01 to output a DC voltage U pv Decreases, the power tracking of PV array 01 gradually moves away from the maximum power point, and the output power of PV array 01 decreases;

[0104] 5) If the result of step 3) is less than or equal to 0, further determine dP pv Is it equal to 0? If it is equal to 0, the duty cycle of the previous control cycle is maintained unchanged; if it is not equal to 0, the duty cycle of the Boost circuit 02 switching device is increased, at this time D(k)=D(k-1)+FlagUdcBal×ΔD inc ;

[0105] When FlagUdcBal=1, it means that the DC bus voltage is low and the power output by the photovoltaic array 01 is low. At this time, the actual power control result of the photovoltaic array 01 is to increase the duty cycle of the Boost circuit 02. The DC voltage U dcm Controlled by the grid-connected inverter 03, it can be considered to be basically unchanged; increasing the duty cycle will cause the photovoltaic array 01 to output a DC voltage U pv decreases, the power tracking of PV array 01 gradually approaches the maximum power point, and the output power of PV array 01 increases;

[0106] When FlagUdcBal=-1, it means that the DC bus voltage is too high and the power output by the photovoltaic array 01 is too high. At this time, the actual power control result of the photovoltaic array 01 is to reduce the duty cycle of the Boost circuit 02, and the DC voltage U dcm Controlled by the grid-connected inverter 03, it can be considered to be basically unchanged; reducing the duty cycle will cause the photovoltaic array 01 to output a DC voltage U pv As the power of PV array 01 increases, the power tracking of PV array 01 gradually moves away from its maximum power point, and the output power of PV array 01 decreases.

[0107] The method of the present application is described below using a photovoltaic power generation system as an example.

[0108] The output power P corresponding to the maximum power point of the photovoltaic array 01 of the photovoltaic power generation system pv is 292.3kW, corresponding to the output DC voltage U pv The rated power of grid-connected inverter 03 is 225kW, and the rated DC voltage of DC bus is 1.37kV. The PV curve diagram of photovoltaic array 01 is as follows: Figure 7 shown.

[0109] Setting U dcref The upper and lower threshold values ​​of the DC bus voltage deviation are set to ΔU dcmax =0.05kV, ΔU dcmin =-0.05kV. So: 0.02×1.37<0.05<0.05×1.37.

[0110] According to the method of this application, Figure 8 As shown, perform the following steps:

[0111] (1) Calculate the DC bus voltage deviation ΔU dc =U dcm -U dcref , multiply the result by -1 and pass it through a first-order low-pass filter with a filtering time constant of T = 0.001s.

[0112] (2) Compare the result of step (1) with the upper limit threshold value of DC bus voltage deviation ΔU dcmax =0.05kV, lower threshold value ΔU dcmin =-0.05kV for hysteresis comparison.

[0113] (3) When the result of step (2) meets the upper hysteresis condition and lasts for 200 μs, a DC bus voltage low flag is generated, i.e., FlagUdcBal = 1.

[0114] (4) When the result of step (2) meets the lower hysteresis condition and lasts for 500 μs, a DC bus voltage high flag is generated, i.e., FlagUdcBal = -1.

[0115] (5) When the traditional MPPT strategy is used to control the duty cycle of the Boost circuit 02, the photovoltaic power generation system has no stable power operating point because the power of the photovoltaic array 01MPP point is larger than the rated power of the grid-connected inverter 03. Figure 9 shown.

[0116] (6) When the power control strategy proposed in this application is adopted, the photovoltaic array 01 can stably operate on the right side of the MPP point, such as Figure 10 When the output power of the grid-connected inverter 03 changes, the photovoltaic array 01 can flexibly and synchronously adjust the power to keep the power balanced and controllable.

[0117] The above embodiments of the present invention have at least the following unexpected technical effects:

[0118] The output of the photovoltaic power generation system can be automatically adjusted according to the power balance situation without adding additional devices. Only some changes to the existing MPPT control method are needed. It is relatively easy to implement and solves the technical problem that the existing photovoltaic power generation system output power control method is difficult to flexibly and stably maintain the power supply and demand balance of the photovoltaic power generation system.

[0119] The present invention further provides a photovoltaic power generation system output power flexible control system, which can be used to execute the photovoltaic power generation system output power flexible control method described in any of the above embodiments of the present invention.

[0120] See also Figure 11 , Figure 11 The figure shows a structural connection block diagram of a photovoltaic power generation system output power flexible control system provided by an embodiment of the present invention.

[0121] An embodiment of the present invention provides a photovoltaic power generation system output power flexible control system, comprising:

[0122] Determination module 1, for determining the value of the DC bus voltage deviation flag bit according to the deviation between the DC voltage on the DC bus of the grid-connected inverter 03 and the DC bus voltage reference value; when the value of the DC bus voltage deviation flag bit is 1, it indicates that the DC bus voltage is low, and when the value of the DC bus voltage deviation flag bit is -1, it indicates that the DC bus voltage is high;

[0123] Control module 2 is used to control the output power of the photovoltaic power generation system using an improved MPPT control algorithm; the improved MPPT control algorithm changes the duty cycle of the switching device of the Boost circuit 02 with a corrected step size, and the corrected step size is obtained by correcting the fixed step size in the MPPT control algorithm using the value of the DC bus voltage deviation flag as a correction coefficient.

[0124] In one possible implementation, the determining module 1 includes:

[0125] A first processing unit is configured to multiply the deviation between the DC voltage on the DC bus of the grid-connected inverter 03 and the DC bus voltage reference value by -1 and then pass the result through a first-order low-pass filter to obtain a first processing result;

[0126] a second processing unit, configured to perform a hysteresis comparison on the first processing result, an upper threshold value of a DC bus voltage deviation, and a lower threshold value of a DC bus voltage deviation, to obtain a second processing result;

[0127] a first setting unit, configured to set the value of the DC bus voltage deviation flag to 1 if the second processing result satisfies an upper hysteresis condition and lasts for a first preset action delay time;

[0128] The second setting unit is configured to set the value of the DC bus voltage deviation flag to -1 if the second processing result satisfies a lower hysteresis condition and lasts for a second preset action delay time.

[0129] In one achievable manner, the values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value satisfy:

[0130]

[0131] Where U dcref is the DC bus voltage reference value, ΔU dcmin is the DC bus voltage deviation lower limit threshold, ΔU dcmax is the upper limit threshold of DC bus voltage deviation.

[0132] In one implementation, the fixed step size includes a first preset step size used when reducing the duty cycle and a second preset step size used when increasing the duty cycle, and the control module 2 includes:

[0133] The acquisition unit is used to collect electrical quantity measurement data of the primary main circuit of the photovoltaic power generation system; the electrical quantity measurement data includes the DC voltage and DC current output by the photovoltaic array 01;

[0134] a first calculation unit, configured to calculate, based on the electrical quantity measurement data, a change in the DC voltage output by the photovoltaic array 01 between a current control cycle and a previous control cycle as a first change, and calculate a change in the output power of the photovoltaic array 01 between the current control cycle and the previous control cycle as a second change;

[0135] a second calculation unit, configured to calculate the product of the first variation and the second variation;

[0136] A control unit, configured to, if the product of the first change amount and the second change amount is greater than 0 and the second change amount is not equal to 0, use the product of the value of the DC bus voltage deviation flag and the first preset step size as a corrected step size to reduce the duty cycle of the switching device of the Boost circuit 02; and, if the product of the first change amount and the second change amount is not greater than 0 and the second change amount is not equal to 0, use the product of the value of the DC bus voltage deviation flag and the second preset step size as a corrected step size to increase the duty cycle of the switching device of the Boost circuit 02.

[0137] The present invention also provides a photovoltaic power generation system output power flexible control device, comprising:

[0138] A memory for storing instructions; wherein the instructions are used to implement the method for flexible output power control of a photovoltaic power generation system as described in any one of the above embodiments;

[0139] A processor is configured to execute instructions in the memory.

[0140] The present invention also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for flexible output power control of a photovoltaic power generation system as described in any one of the above embodiments is implemented.

[0141] Those skilled in the art can clearly understand that, for the convenience and conciseness of description, the specific working processes of the systems, devices, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and the specific beneficial effects of the systems, devices, modules and units described above can refer to the corresponding beneficial effects in the aforementioned method embodiments, which will not be repeated here.

[0142] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For example, the division of the modules is merely a logical function division. In actual implementation, there may be other division methods, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of systems or modules, which can be electrical, mechanical or other forms.

[0143] The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules may be selected to achieve the purpose of the present embodiment according to actual needs.

[0144] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or software functional modules.

[0145] If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0146] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for flexible output power control of a photovoltaic power generation system, wherein the primary main circuit of the photovoltaic power generation system includes a photovoltaic array, a boost circuit, a grid-connected inverter, an LCL filter circuit, and an AC power grid, wherein the photovoltaic array and the boost circuit are connected via a first capacitor, and the boost circuit and the grid-connected inverter are connected via a second capacitor, characterized in that: The method comprises: Determining a value of a DC bus voltage deviation flag according to a deviation between a DC voltage on a DC bus of a grid-connected inverter and a DC bus voltage reference value; when the value of the DC bus voltage deviation flag is 1, it indicates that the DC bus voltage is too low; and when the value of the DC bus voltage deviation flag is -1, it indicates that the DC bus voltage is too high; An improved MPPT control algorithm is used to control the output power of a photovoltaic power generation system; the improved MPPT control algorithm changes the duty cycle of a switching device in a Boost circuit with a modified step size, wherein the modified step size is obtained by modifying a fixed step size in the MPPT control algorithm using the value of the DC bus voltage deviation flag as a correction coefficient; The step of determining the value of the DC bus voltage deviation flag according to the deviation between the DC voltage on the DC bus of the grid-connected inverter and the DC bus voltage reference value includes: Multiplying the deviation between the DC voltage on the DC bus of the grid-connected inverter and the DC bus voltage reference value by -1 and then passing the result through a first-order low-pass filter to obtain a first processing result; Performing a hysteresis comparison on the first processing result, an upper threshold value of the DC bus voltage deviation, and a lower threshold value of the DC bus voltage deviation to obtain a second processing result; If the second processing result satisfies the upper hysteresis condition and lasts for the first preset action delay time, setting the value of the DC bus voltage deviation flag to 1; If the second processing result satisfies the lower hysteresis condition and lasts for a second preset action delay time, the value of the DC bus voltage deviation flag is set to -1.

2. The method for flexible control of output power of a photovoltaic power generation system according to claim 1, characterized in that: The values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value satisfy: ； Where, is the DC bus voltage reference value, is the DC bus voltage deviation lower limit threshold, is the upper limit threshold of DC bus voltage deviation.

3. The method for flexible control of output power of a photovoltaic power generation system according to claim 1, characterized in that: The fixed step size includes a first preset step size used when reducing the duty cycle and a second preset step size used when increasing the duty cycle. The improved MPPT control algorithm is used to control the output power of the photovoltaic power generation system, including: Collecting electrical quantity measurement data of the primary main circuit of the photovoltaic power generation system; the electrical quantity measurement data includes the DC voltage and DC current output by the photovoltaic array; Based on the electrical quantity measurement data, calculating a change in the DC voltage output by the photovoltaic array in a current control cycle and a previous control cycle as a first change, and calculating a change in the output power of the photovoltaic array in the current control cycle and a previous control cycle as a second change; Calculating the product of the first variation and the second variation; If the product of the first change amount and the second change amount is greater than 0 and the second change amount is not equal to 0, the product of the value of the DC bus voltage deviation flag and the first preset step size is used as the corrected step size to reduce the duty cycle of the switching device of the Boost circuit; if the product of the first change amount and the second change amount is not greater than 0 and the second change amount is not equal to 0, the product of the value of the DC bus voltage deviation flag bit and the second preset step size is used as the corrected step size to increase the duty cycle of the switching device of the Boost circuit.

4. A photovoltaic power generation system output power flexible control system, wherein the primary main circuit of the photovoltaic power generation system includes a photovoltaic array, a boost circuit, a grid-connected inverter, an LCL filter circuit, and an AC power grid, wherein the photovoltaic array and the boost circuit are connected via a first capacitor, and the boost circuit and the grid-connected inverter are connected via a second capacitor, characterized in that: The system comprises: a determination module, configured to determine a value of a DC bus voltage deviation flag according to a deviation between a DC voltage on a DC bus of a grid-connected inverter and a DC bus voltage reference value; when the value of the DC bus voltage deviation flag is 1, it indicates that the DC bus voltage is too low; and when the value of the DC bus voltage deviation flag is -1, it indicates that the DC bus voltage is too high; A control module configured to control the output power of a photovoltaic power generation system using an improved MPPT control algorithm; the improved MPPT control algorithm changes the duty cycle of a switching device in a Boost circuit using a modified step size, wherein the modified step size is obtained by modifying a fixed step size in the MPPT control algorithm using the value of the DC bus voltage deviation flag as a correction coefficient; The determination module includes: a first processing unit, configured to multiply a deviation between a DC voltage on the DC bus of the grid-connected inverter and a DC bus voltage reference value by -1 and then pass the result through a first-order low-pass filter to obtain a first processing result; a second processing unit, configured to perform a hysteresis comparison on the first processing result, an upper threshold value of a DC bus voltage deviation, and a lower threshold value of a DC bus voltage deviation, to obtain a second processing result; a first setting unit, configured to set the value of the DC bus voltage deviation flag to 1 if the second processing result satisfies an upper hysteresis condition and lasts for a first preset action delay time; The second setting unit is configured to set the value of the DC bus voltage deviation flag to -1 if the second processing result satisfies a lower hysteresis condition and lasts for a second preset action delay time.

5. The photovoltaic power generation system output power flexible control system according to claim 4, characterized in that: The values ​​of the DC bus voltage deviation upper limit threshold value and the DC bus voltage deviation lower limit threshold value satisfy: ； Where, is the DC bus voltage reference value, is the DC bus voltage deviation lower limit threshold, is the upper limit threshold of DC bus voltage deviation.

6. The photovoltaic power generation system output power flexible control system according to claim 4, characterized in that: The fixed step size includes a first preset step size used when reducing the duty cycle and a second preset step size used when increasing the duty cycle, and the control module includes: An acquisition unit is used to acquire electrical quantity measurement data of a primary main circuit of a photovoltaic power generation system; the electrical quantity measurement data includes a DC voltage and a DC current output by the photovoltaic array; a first calculation unit, configured to calculate, based on the electrical quantity measurement data, a change in the DC voltage output by the photovoltaic array between a current control cycle and a previous control cycle as a first change, and calculate a change in the output power of the photovoltaic array between the current control cycle and the previous control cycle as a second change; a second calculation unit, configured to calculate the product of the first variation and the second variation; A control unit is configured to, if the product of the first variation and the second variation is greater than 0 and the second variation is not equal to 0, use the product of the value of the DC bus voltage deviation flag and the first preset step size as a corrected step size to reduce the duty cycle of the switching device of the Boost circuit; and if the product of the first variation and the second variation is not greater than 0 and the second variation is not equal to 0, use the product of the value of the DC bus voltage deviation flag and the second preset step size as a corrected step size to increase the duty cycle of the switching device of the Boost circuit.

7. A photovoltaic power generation system output power flexible control device, characterized in that: include: A memory for storing instructions; wherein the instructions are used to implement the method for flexible output power control of a photovoltaic power generation system according to any one of claims 1 to 3; A processor is configured to execute instructions in the memory.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for flexible output power control of a photovoltaic power generation system according to any one of claims 1 to 3 is implemented.

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