Method and device for improving power generation efficiency of multi-group string type photovoltaic inverter

Abstract

The invention discloses a method and a device for improving the power generation efficiency of a multi-group string type photovoltaic inverter, and solves the problem that the power generation efficiency is reduced when a solar cell array is in a local shadow shielding condition and the string type photovoltaic inverter operates at a local maximum power point in a maximum power point tracking process. The method comprises the following steps: 1, acquiring an open-circuit voltage Voc, a rated voltage Vmp and a short-circuit current Isc of a single PV panel, the number M of PV panels forming a string and the number N of strings from an external device; 2, detecting an input voltage V (k) and an input current I (k) of the MPPT device; 3, comparing the input power P (k) of the current MPPT device with the past input power P (k-1); 4, if the P (k) is different from the P (k-1), determining whether the P (k) is greater than the P (k-1); 5, if the P (k) is greater than the P (k-1), further comparing the current input voltage V (k) with the past input voltage V (k-1), otherwise, returning to the data acquisition stage; and 6, adjusting the working point voltage Vref of the MPPT device according to the comparison result. Through the method, even if the PV array part is covered by shadow, the system can operate at the global maximum power point (GMPP), so that the power generation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to a method and a device for improving the power generation efficiency of a multi-string photovoltaic inverter, belonging to the technical field of new energy grid-connected consumption equipment. Background Technique

[0002] The principle of solar power generation is that when sunlight shines on a p-n junction solar panel formed by n-type doping on a silicon crystal, electricity is generated through the photovoltaic effect. For this purpose, solar cells (Solar Cell) for concentrating sunlight, a photovoltaic panel (PhotovoltaicPanel) which is an aggregate of solar cells, and a solar array (Solar Array) which is an aggregate of photovoltaic panels are required. Different from traditional energy sources such as fossil fuels, solar energy is a clean energy that does not pose risks such as greenhouse gas emissions, noise, and environmental damage caused by global warming, and there is no need to worry about depletion. In addition, different from wind energy and water energy, solar power generation equipment can be installed freely and has low maintenance costs. In solar power generation equipment, the current and voltage when the solar cell generates the maximum power are called the maximum power point (MPP: Maximum Power Point). The maximum power point can be detected by detecting the current and voltage, and the technology of making the solar power generation equipment generate the maximum power by tracking the change of the maximum power point caused by temperature is called MPPT (Maximum PowerPoint Tracking) technology. Using MPPT technology can improve the electrical energy efficiency of solar power generation equipment, so it is widely used in solar power generation equipment to prevent the output power from decreasing due to temperature drop. In a solar photovoltaic system, a photovoltaic array usually consists of multiple PV modules connected in series or in parallel. The output characteristics of the PV array are affected by factors such as sunlight intensity, temperature, and load changes. In order to make the most of solar energy resources under various conditions, the maximum power point tracking technology is usually adopted. At the same time, in order to ensure the operation efficiency of the power generation system, the influence of the surrounding environment is considered during the design and installation of the photovoltaic array: it is required that there are no tall buildings, trees and other obstacles affecting the sunlight irradiation on the photovoltaic cell panel. However, with the increase in the penetration rate of distributed photovoltaics, a large number of photovoltaics between buildings are put into use, and it is inevitable that there will be a situation where sunlight is blocked. Therefore, the situation of partial shading needs to be considered at this time. The main impact of partial shading on the photovoltaic array is to reduce the global maximum power (GMMP), and secondly, the interference of the local maximum power (LMMP) on the control, especially in a centralized control system. Currently, the main means to reduce the impact of partial shading are as follows: 1. Change the structure of the photovoltaic array, change the centralized type to the string type or the multi-string type, but the number of conversion controllers in the system increases significantly, resulting in more complex system control, rising costs and reduced reliability. 2. Retain the centralized structure and solve the problem of local peak interference by improving the maximum power point tracking technology (MPPT) for global peak determination. However, most current studies only analyze specific situations and have low universality of application.Common MPPT algorithms include the constant voltage method, the perturbation and observation method, the incremental conductance method, the fuzzy control method, etc. Usually, the incremental conductance method is adopted to achieve the maximum power point tracking function by comparing the instantaneous conductance of the photovoltaic cell with the change in conductance, which is commonly used. It is represented that when the change in output conductance is equal to the negative value of the output conductance, the photovoltaic cell operates at the maximum power point. Therefore, by appropriately setting the tracking step size, the changes in temperature and light can be quickly tracked, which is suitable for occasions with rapid light changes. However, in the process of tracking the maximum power point, the MPPT device in the existing technology may get stuck at a local peak point, resulting in the control system being unable to track the true global maximum power point (GMPP), thereby reducing the output power of the photovoltaic system. In addition, the existing MPPT algorithms may require frequent parameter adjustments under different environmental conditions, increasing the complexity and computational burden of the system. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and device for improving the power generation efficiency of a multi-string photovoltaic inverter. Through real-time detection and calculation of multiple parameters, the MPPT algorithm is optimized, the working voltage and current are dynamically adjusted, local peak traps are avoided, and the tracking efficiency of the global maximum power point (Global Maximum Power Point, GMPP) is improved to ensure efficient energy conversion under various environmental conditions. The present invention can achieve GMPP tracking even when part of the PV array is shaded, thereby improving the power generation efficiency of the multi-string inverter.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A method for improving the power generation efficiency of a multi-string photovoltaic inverter includes the following steps:

[0006] Step 1: Collect the input voltage V(k) of the MPPT device, the input current I(k) of the MPPT device, the open-circuit voltage Voc of a single PV panel, the rated voltage Vmp of a single PV panel, the short-circuit current Isc of a single PV panel, the number M of PV panels connected in series, and the number of series N;

[0007] Step 2: Compare whether the input power P(k) of the MPPT device at the current moment is different from the input power P(k - 1) of the MPPT device at the past moment;

[0008] Step 3: If P(k) is different from P(k - 1) in Step 2, then compare whether P(k) is greater than P(k - 1); if P(k) is the same as P(k - 1) in Step 2, then return to Step 1;

[0009] Step 4: If P(k) in Step 3 is greater than P(k - 1), then determine whether V(k) is greater than V(k - 1), and then execute Step 5.1;

[0010] If P(k) in Step 3 is less than or equal to P(k - 1), then determine whether V(k) is greater than V(k - 1), and then execute Step 5.2;

[0011] Step 5.1:

[0012] If V(k) in Step 4 is greater than V(k - 1), then increase the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0013] If V(k) in Step 4 is less than or equal to V(k - 1), then decrease the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0014] Step 5.2:

[0015] If V(k) in Step 4 is less than or equal to V(k - 1), then increase the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0016] If V(k) in Step 4 is greater than V(k - 1), then decrease the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0017] Step 6: Recalculate the MPPT value;

[0018] Step 7: Determine whether the difference between the maximum value and the minimum value of Vref is less than the error set value;

[0019] Step 8: If the difference between the maximum value and the minimum value of Vref in Step 7 is less than the error set value, then confirm the global maximum power point GMPP and output the global maximum power point GMPP;

[0020] Step 9: If GMPP is not confirmed in Step 8 and continue the optimization, then compare the input current I(k) with the set value and magnitude of the number of N - 1 in series, and set Vref to the set value according to the comparison result;

[0021] Step 9 includes: Determine whether I(k) is greater than the first set value, that is, the photovoltaic output current set value I(K) N-1 , I(K) N-1 is the output current of the photovoltaic battery pack calculated after subtracting 1 from the current number of connected photovoltaic battery strings. If I(k) is greater than the first set value, then determine Vref as the value determined by the following formula (1);

[0022] If I(k) is less than or equal to the first set value, then it is determined whether I(k) is greater than the second set value, that is, the PV output current set value I(K). N-2 , I(K) N-2 ; It is the output current of the PV battery pack calculated after subtracting 2 from the number of currently connected PV battery strings. If I(k) is greater than the second set value, then Vref is determined to be the value determined by the following formula (2);

[0023] If I(k) is less than the first set value and less than the second set value, then Vref is determined to be the value determined by the following formula (3):

[0024] V ref = V mp *M / (N - 2) (1)

[0025] V ref = V mp *M / (N - 1) (2)

[0026] V ref = V mp *M / N (3).

[0027] A control device for improving the power generation efficiency of a multi-string PV inverter, comprising: a processor, a memory, and an acquisition unit. The acquisition unit is used to acquire the input voltage V(k) of the MPPT device, the input current I(k) of the MPPT device, the open-circuit voltage Voc of a single PV panel, the rated voltage Vmp of a single PV panel, the short-circuit current Isc of a single PV panel, the number M of PV panels forming a series, and the number of series N; the processor is respectively communicatively connected to the memory and the acquisition unit, the memory is communicatively connected to the acquisition unit, the memory is used to store the executable instructions of the processor and the data acquired by the acquisition unit, and the processor is configured to execute the above method for improving the power generation efficiency of a multi-string PV inverter by executing the executable instructions.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] By adopting the technical solution of the present invention, it is possible to effectively overcome the local peak trap problem existing in the prior art, significantly improve the tracking efficiency of GMPP, and thus improve the overall output power of the PV system. At the same time, the complexity of the MPPT algorithm is simplified, the operation burden of the system is reduced, and the stability and reliability of the system are improved. The present invention can achieve global maximum power point tracking even when part of the PV array is shaded, thereby improving the power generation efficiency of the multi-string inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural diagram of the working principle of a PV array;

[0031] Figure 2 It is the working principle diagram of the MPPT input voltage sensing unit and current sensing unit in the present invention;

[0032] Figure 3 It is the flowchart of the GMPP tracking process in an embodiment of the present invention. Specific Embodiments

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. As Figure 1 shown is the structural diagram of the working principle of the photovoltaic array of the present invention.

[0034] The control device for improving the power generation efficiency of a multi-string photovoltaic inverter of the present invention includes: a processor, a memory, and a collection unit. The collection unit is used to collect the input voltage V(k) of the MPPT device, the input current I(k) of the MPPT device, the open-circuit voltage Voc of a single PV panel, the rated voltage Vmp of a single PV panel, the short-circuit current Isc of a single PV panel, the number M of PV panels forming a series, and the number of series N; the processor is communicatively connected to the memory and the collection unit respectively, and the memory is communicatively connected to the collection unit. The memory is used to store the executable instructions of the processor and the data collected by the collection unit. The processor is configured to execute a method for improving the power generation efficiency of a multi-string photovoltaic inverter by executing the executable instructions.

[0035] In this embodiment, the processor is the MPPT operating point voltage determination unit, and the collection unit includes an MPPT input voltage detection unit and an MPPT input current detection unit. As Figure 2 shown is the working principle diagram of the MPPT input voltage sensing unit and current sensing unit in the present invention.

[0036] The following method steps are executed in the control device for improving the power generation efficiency of a multi-string photovoltaic inverter:

[0037] Step 1: The MPPT operating point voltage determination unit receives the input voltage [V(k)] of the MPPT device and the input current [I(k)] of the MPPT device from the MPPT input voltage detection unit and the MPPT input current detection unit, and collects the open-circuit voltage (Voc) of a single photovoltaic panel, the rated voltage (Vmp) of the photovoltaic panel, the short-circuit current (Isc) of the photovoltaic panel, the number (M) of photovoltaic panels forming a series, and the number of series (N) from an external device;

[0038] Step 2: The MPPT operating point voltage determination unit determines whether the input power [P(k)] of the MPPT device at the current moment is different from the input power [P(k-1)] of the MPPT device at the past moment;

[0039] Step 3: If P(k) is different from P(k - 1) in Step 2, then compare whether P(k) is greater than P(k - 1); if P(k) is the same as P(k - 1) in Step 2, then return to Step 1;

[0040] Step 4: If P(k) is greater than P(k - 1) in Step 3, then determine whether V(k) is greater than V(k - 1), and then execute Step 5.1;

[0041] If P(k) is less than or equal to P(k - 1) in Step 3, then determine whether V(k) is greater than V(k - 1), and then execute Step 5.2;

[0042] Step 5.1:

[0043] If V(k) is greater than V(k - 1) in Step 4, then increase the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0044] If V(k) is less than or equal to V(k - 1) in Step 4, then decrease the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0045] Step 5.2:

[0046] If V(k) is less than or equal to V(k - 1) in Step 4, then increase the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0047] If V(k) is greater than V(k - 1) in Step 4, then decrease the operating point voltage Vref of the MPPT device by the set voltage change value ΔV;

[0048] Step 6: Recalculate the MPPT value;

[0049] Step 7: The MPPT operating point voltage determination unit determines whether the difference between the maximum value and the minimum value of Vref is less than the error setting value (this error setting value is a variable precision and can be adjusted according to the actual engineering application needs, generally taking 0.1 - 0.01);

[0050] Step 8: If the difference between the maximum value and the minimum value of Vref in Step 7 is less than the error setting value, then confirm the global maximum power point GMPP and output the global maximum power point GMPP;

[0051] Step 9: If the GMPP is not confirmed in Step 8, then the current working mode will continue to optimize, and the MPPT operating point voltage determination unit will compare the value of the current photovoltaic output current I(k) with the photovoltaic output current setting value I(K) N-1Compare their sizes, where N is the number of PV accesses (assuming that when a solar cell array is composed of 3 PV battery packs connected in series, and at this time 3 batteries are accessed simultaneously, N = 3; the set value of the PV output current is I(K) N-1 is the output current of the PV battery pack calculated by subtracting 1 from the current number of PV battery strings accessed, and the set value can be calculated in advance according to Equation (1) above. Similarly, the set value of the PV output current 2 is I(K) N-2 , and according to the comparison result, set V ref to the set value; Step 9 specifically includes: The MPPT operating point voltage determination unit determines whether I(k) is greater than the first set value, that is, the set value of the PV output current I(K) N-1 ; if I(k) is greater than the first set value, the MPPT operating point voltage determination unit sets V ref to the value determined by the following Equation (4); if I(k) is less than or equal to the first set value, the MPPT operating point voltage determination unit determines whether I(k) is greater than the second set value; if I(k) is greater than the second set value, that is, the set value of the PV output current I(K) N-2 , the MPPT operating point voltage determination unit sets V ref to the value determined by the following Equation (5). If I(k) is less than the first set value and less than the second set value, the MPPT operating point voltage determination unit sets V ref to be determined by Equation (6).

[0052] V ref = V mp *M / (N - 2) (4)

[0053] V ref = V mp *M / (N - 1) (5)

[0054] V ref = V mp *M / N (6).

[0055] In addition to the above embodiments, the present invention may also have other embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A method for improving the power generation efficiency of a multi-string photovoltaic inverter, characterized in that, Comprising the following steps: Step 1: Collect the input voltage V(k) of the MPPT device, the input current I(k) of the MPPT device, the open-circuit voltage Voc of a single PV panel, the rated voltage Vmp of a single PV panel, the short-circuit current Isc of a single PV panel, the number M of PV panels forming a series, and the series number N; Step 2: Compare whether the input power P(k) of the MPPT device at the current moment is different from the input power P(k-1) of the MPPT device at the past moment; Step 3: If P(k) is different from P(k-1) in Step 2, then compare whether P(k) is greater than P(k-1); if P(k) is the same as P(k-1) in Step 2, then return to Step 1; Step 4: If P(k) is greater than P(k-1) in Step 3, then determine whether V(k) is greater than V(k-1), and then execute Step 5.1; If P(k) is less than or equal to P(k-1) in Step 3, then determine whether V(k) is greater than V(k-1), and then execute Step 5.2; Step 5.1: If V(k) is greater than V(k-1) in Step 4, then increase the operating point voltage Vref of the MPPT device by the set voltage change value ΔV; If V(k) is less than or equal to V(k-1) in Step 4, then decrease the operating point voltage Vref of the MPPT device by the set voltage change value ΔV; Step 5.2: If V(k) is less than or equal to V(k-1) in Step 4, then increase the operating point voltage Vref of the MPPT device by the set voltage change value ΔV; If V(k) is greater than V(k-1) in Step 4, then decrease the operating point voltage Vref of the MPPT device by the set voltage change value ΔV; Step 6: Recalculate the MPPT value; Step 7: Determine whether the difference between the maximum value and the minimum value of Vref is less than the error set value; Step 8: If the difference between the maximum value and the minimum value of Vref in Step 7 is less than the error set value, then confirm the global maximum power point GMPP and output the global maximum power point GMPP; Step 9: If GMPP is not confirmed in Step 8 and continue to optimize, then compare the input current I(k) with the set value and magnitude of the number of N minus 1 in series, and set Vref to the set value according to the comparison result; Step 9 includes: determining whether I(k) is greater than a first set value, i.e., the photovoltaic output current set value I(K) N-1 , I(K) N-1 is the output current of the photovoltaic battery pack calculated after subtracting 1 from the current number of connected photovoltaic battery strings. If I(k) is greater than the first set value, then Vref is determined to be the value determined by the following formula (1); If I(k) is less than or equal to the first set value, then determine whether I(k) is greater than the second set value, i.e., the photovoltaic output current set value I(K) N-2 , I(K) N-2 ; is the output current of the photovoltaic battery pack calculated after subtracting 2 from the current number of connected photovoltaic battery strings. If I(k) is greater than the second set value, then determine Vref as the value determined by the following formula (2); If I(k) is less than the first set value and less than the second set value, then determine Vref as the value determined by the following formula (3): V ref = V mp * M / (N - 2) (1) V ref = V mp * M / (N - 1) (2) V ref = V mp * M / N (3).

2. A control device for improving the power generation efficiency of a multi-string photovoltaic inverter, characterized in that, Including: A processor, a memory, and a collection unit. The collection unit is used to collect the input voltage V(k) of the MPPT device, the input current I(k) of the MPPT device, the open-circuit voltage Voc of a single PV panel, the rated voltage Vmp of a single PV panel, the short-circuit current Isc of a single PV panel, the number M of PV panels forming a series, and the series number N; the processor is communicatively connected to the memory and the collection unit respectively, the memory is communicatively connected to the collection unit, the memory is used to store the executable instructions of the processor and the data collected by the collection unit, and the processor is configured to execute the method for improving the power generation efficiency of a multi-string photovoltaic inverter according to Claim 1 by executing the executable instructions.

Images