High-efficiency power control method for multi-path MPPT (Maximum Power Point Tracking) of photovoltaic inverter

Abstract

The invention discloses an efficient power control method for multi-path MPPT of a photovoltaic inverter, and the method comprises the steps: detecting the no-load voltage of a PV path, extracting an MPPT path with the highest voltage, and judging whether the no-load voltage V of the MPPT path with the highest voltage exceeds a no-load voltage threshold VocA or not; when V < time > is larger than a no-load voltage threshold VocA, the maximum MPPV path power is subjected to total power load limit tracking until the no-load voltage V < time > is smaller than the no-load voltage threshold VocB, and power tracking control is carried out on the other MPPT paths at the moment; when V < time > is less than or equal to a no-load voltage threshold VocA, the total power is not limited, and simultaneous tracking power control of all MPPT paths is carried out; and the steady-state voltage difference value between the MPPT path with the highest voltage and the MPPT path with the lowest voltage is controlled to be smaller than the steady-state voltage difference Vmppt. The method is suitable for various MPPT differentiated configuration complex working conditions, and the power control strategy effectively solves the problems of high tube stress and large loss under the voltage difference condition. And the risk of machine explosion caused by high-low configuration of the PV road is reduced, and the operation efficiency is improved. The equipment operation safety is guaranteed for a long time, and the energy income is improved.

Description

Technical Field

[0001] The invention relates to a high-efficiency power control method of a multi-channel MPPT of a photovoltaic inverter, belonging to the technical field of photovoltaic system control. Background Art

[0002] As the core component of the photovoltaic system, the photovoltaic inverter plays a key role in converting green energy. It converts the direct current generated by the photovoltaic panel into alternating current and sends it to the grid. The photovoltaic inverter uses the MPPT algorithm to track the PV panels to ensure maximum conversion efficiency. In industrial and commercial photovoltaic grid-connected inverters, the number of MPPTs is mostly more than 6. When the number of photovoltaic strings equipped with different MPPTs is inconsistent, the actual operating voltage of each PV will be inconsistent. If some roads are over-equipped, the PV voltage of the road will be very high, and if some roads are under-equipped, the PV voltage of the road will be very low, and there will be high and low matching conditions.

[0003] The complex working conditions of high and low configurations mainly have the following problems: Because the output of each MPPT is connected in parallel, the PV string with the highest PV voltage determines the inverter BUS voltage. If this line does not follow the MPPT curve, the voltage spike of the switch tube at the time of shutdown will be very high, and there is a risk of explosion if the load is not limited. In addition, the voltage boost ratio borne by the line with the lowest PV voltage is very large, resulting in large losses and reduced efficiency of the MPPT switch tube of this line. In addition, when the inverter needs to reduce the load due to over-distribution, over-temperature or high BUS voltage, if the power cannot be distributed evenly among multiple MPPTs, the electrical and thermal stress of individual lines will be relatively large, and the reliability and efficiency of the inverter will be seriously affected. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art, and to propose an efficient power control method for multi-channel MPPT of photovoltaic inverter in view of the problems that the traditional load limiting and load reduction of traditional multi-channel MPPT are unbalanced, resulting in low conversion efficiency and easy operation risks.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A high-efficiency power control method for a photovoltaic inverter with multiple MPPT paths, wherein the photovoltaic inverter comprises at least three MPPT paths connected in parallel, and any MPPT path is connected to a PV path. The high-efficiency power control method comprises: Setting a no-load voltage threshold VocA, a no-load voltage threshold VocB, and a steady-state voltage difference △Vmppt, wherein the no-load voltage threshold VocA is greater than the no-load voltage threshold VocB; Detect the no-load voltage of the PV circuit, extract the MPPT circuit with the highest voltage, and determine the no-load voltage V of the MPPT circuit with the highest voltage. 时 Whether it exceeds the no-load voltage threshold VocA; When V 时 > no-load voltage threshold VocA, the total power is limited to the highest MPPV path power to the no-load voltage V 时 < no-load voltage threshold VocB, at this time, the remaining MPPT paths are subjected to power tracking control, and the steady-state voltage difference between the highest voltage MPPT path and the lowest voltage MPPT path is controlled to be less than the steady-state voltage difference △Vmppt; When V 时 ≤ no-load voltage threshold VocA, the total power is not load-limited, and all MPPT paths are simultaneously controlled to track power, and the steady-state voltage difference between the highest voltage MPPT path and the lowest voltage MPPT path is controlled to be less than the steady-state voltage difference △Vmppt.

[0006] Preferably, an overload limit setting is performed for any MPPT circuit to limit the maximum output current and rated maximum power of the MPPT circuit.

[0007] Preferably, a steady-state voltage difference △VmpptA and a steady-state voltage difference △VmpptB are set, and the steady-state voltage difference △VmpptA is greater than the steady-state voltage difference △VmpptB; Carry out overload limiting or full load reduction control, and limit the load according to the rated maximum power and maximum output current; Detect the no-load voltage of the PV circuit, extract the MPPT circuit with the lowest voltage, and reduce the load on the MPPT circuit with the lowest voltage until the steady-state voltage difference between the MPPT circuit with the highest voltage and the MPPT circuit with the lowest voltage is less than the steady-state voltage difference △VmpptB. At this time, load reduction by power balancing control is performed on the remaining MPPT circuits. During the load shedding process, the steady-state voltage difference between the MPPT circuit with the highest voltage and the MPPT circuit with the lowest voltage is monitored. When the steady-state voltage difference is greater than the steady-state voltage difference △VmpptA, the load shedding of the MPPT circuit with the highest voltage is stopped, and the load shedding of the remaining MPPT circuits is performed by load shedding power balancing control. This cycle is repeated until the load shedding power demand is met.

[0008] The beneficial effects of the present invention are mainly reflected in: 1. Suitable for various MPPT differentiated configuration and complex working conditions. The power control strategy effectively solves the problems of high tube stress and large loss under voltage difference conditions.

[0009] 2. The risk of machine explosion caused by high or low configuration of PV circuit is reduced, and the operating efficiency is improved.

[0010] 3. It ensures the safe operation of equipment in the long term and improves the effective energy benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 It is a schematic diagram of the flow structure of efficient power control for startup and grid connection in a high-efficiency power control method for multi-channel MPPT of a photovoltaic inverter of the present invention.

[0012] Figure 2 It is a schematic diagram of the flow structure of overload limiting or full load load reduction control in a high-efficiency power control method of a photovoltaic inverter multi-channel MPPT of the present invention. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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 described embodiments are 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 creative work are within the scope of protection of the present invention.

[0014] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the inventions. It should also be noted that, for ease of description, only the parts related to the relevant inventions are shown in the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0015] The present invention provides a high-efficiency power control method for multi-channel MPPT of a photovoltaic inverter, wherein the photovoltaic inverter comprises at least three MPPT channels connected in parallel, and any MPPT channel is connected to a PV channel. The above MPPT channel and PV channel input structure belong to the prior art of the photovoltaic inverter, and its structure and output are not described in detail here.

[0016] The efficient power control method of this case, such as Figure 1 As shown, the following steps are included: A no-load voltage threshold VocA, a no-load voltage threshold VocB, and a steady-state voltage difference ΔVmppt are set, wherein the no-load voltage threshold VocA is greater than the no-load voltage threshold VocB.

[0017] Detect the no-load voltage of the PV circuit, extract the MPPT circuit with the highest voltage, and determine the no-load voltage V of the MPPT circuit with the highest voltage. 时Whether it exceeds the no-load voltage threshold VocA.

[0018] When V 时 > no-load voltage threshold VocA, the total power is limited to the highest MPPV path power to the no-load voltage V 时 < no-load voltage threshold VocB, at this time, the remaining MPPT paths are subjected to power tracking control, and the steady-state voltage difference between the MPPT path with the highest voltage and the MPPT path with the lowest voltage is controlled to be less than the steady-state voltage difference △Vmppt.

[0019] When V 时 ≤ no-load voltage threshold VocA, the total power is not load-limited, and all MPPT paths are simultaneously controlled to track power, and the steady-state voltage difference between the highest voltage MPPT path and the lowest voltage MPPT path is controlled to be less than the steady-state voltage difference △Vmppt.

[0020] Specific implementation process and principle description: Generally speaking, MPPT circuits have differentiated configurations, especially in cases of light differences or old construction, there are differences in over- and under-configuration of MPPT circuits, so the power balance between multiple MPPT circuits is poor, especially the BUS bus is determined by the highest photovoltaic string, so the loss of the lowest voltage MPPT circuit will be larger and the efficiency will be lower.

[0021] In this case, take the configuration of three MPPT lines as an example, including MPPT1~MPPT3, among which MPPT1 is 140% over-configured, MPPT2 is 100% standard, and MPPT3 is 75% under-configured. The power and voltage are MPPT1> MPPT2> MPPT3, and the no-load voltage is Voc1> Voc2> Voc3. The FF factor is generally 0.85.

[0022] When the inverter is connected to the grid, it detects the voltages of the three PVs, extracts the MPPT1 with the highest voltage, and determines the no-load voltage Voc1 of the line, which is V 时 Is it greater than 950V of VocA? If it is greater than 950V, MPPT1 will be chased first, and the total power will be limited. The rest of the paths will wait until MPPT1 catches up to below 850V of VocB before starting to chase, and the steady-state voltage difference between MPPT3 and MPPT1 shall not exceed 300V; if Voc1 is not greater than 950V, power chasing will start at the same time, and no load limitation will be performed. The steady-state voltage difference △Vmppt≤300V will also be controlled; if the steady-state voltage difference exceeds the limit, the load limitation will not continue to chase downward.

[0023] In a specific embodiment, an overload limit setting is performed for any MPPT circuit to limit the maximum output current and rated maximum power of the MPPT circuit.

[0024] Specifically, when the inverter is overloaded, each line will limit the maximum input current and the rated maximum power to prevent the power of a single line from exceeding the limit when the PV input voltage is high. That is, during the configuration process, overload monitoring is set, which makes the operation safer and more reliable.

[0025] In a specific embodiment, Figure 2 As shown, a steady-state voltage difference △VmpptA and a steady-state voltage difference △VmpptB are set, and the steady-state voltage difference △VmpptA is greater than the steady-state voltage difference △VmpptB.

[0026] Perform overload limiting or full load reduction control, and limit the load according to the rated maximum power and maximum output current.

[0027] Detect the no-load voltage of the PV circuit, extract the MPPT circuit with the lowest voltage, and reduce the load on the MPPT circuit with the lowest voltage until the steady-state voltage difference between the MPPT circuit with the highest voltage and the MPPT circuit with the lowest voltage is less than the steady-state voltage difference △VmpptB. At this time, load reduction by power balancing control is performed on the remaining MPPT circuits.

[0028] During the load shedding process, the steady-state voltage difference between the MPPT circuit with the highest voltage and the MPPT circuit with the lowest voltage is monitored. When the steady-state voltage difference is greater than the steady-state voltage difference △VmpptA, the load shedding of the MPPT circuit with the highest voltage is stopped, and the load shedding of the remaining MPPT circuits is performed by load shedding power balancing control. This cycle is repeated until the load shedding power demand is met.

[0029] At the time of overload or full load reduction, the power is limited according to the rated maximum power and the maximum output current, and then the voltage of the three PVs is detected, and the MPPT3 with the lowest voltage is extracted. The load of the third road is reduced first, and the MPPT3 voltage after load reduction is compared with the MPPT1 voltage. When the steady-state voltage difference is less than △VmpptB, △VmpptB can be 200V, and the load reduction of MPPT1 and MPPT2 is carried out by load reduction power balance control, and it stops when the load reduction power demand is met. In the load reduction process, when the highest and lowest steady-state voltage differences between the MPPT roads exceed △VmpptA, △VmpptA can be 300V, then the load reduction of the highest voltage road is stopped, and the load reduction of the remaining roads is carried out by load reduction power balance control, and the cycle stops when the load reduction power demand is met, so as to avoid excessive or insufficient load reduction of a certain road. When reducing the load, when the power balance and voltage difference conflict, the power balance is given priority.

[0030] From the above description, it can be found that it is suitable for various MPPT differentiated configuration and complex working conditions. The power control strategy effectively solves the problem of high tube stress and large loss under voltage difference. It reduces the risk of machine explosion caused by high and low configuration of PV circuit, and improves the operation efficiency. It ensures the safety of equipment operation in the long term and increases the effective energy income.

[0031] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus / device.

[0032] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A high-efficiency power control method for multi-channel MPPT of a photovoltaic inverter, wherein the photovoltaic inverter comprises at least three MPPT channels connected in parallel, any MPPT channel being connected to a PV channel, characterized in that The high-efficiency power control method comprises: Setting a no-load voltage threshold VocA, a no-load voltage threshold VocB, and a steady-state voltage difference △Vmppt, wherein the no-load voltage threshold VocA is greater than the no-load voltage threshold VocB; Detect the no-load voltage of the PV circuit, extract the MPPT circuit with the highest voltage, and determine the no-load voltage V of the MPPT circuit with the highest voltage. 时 Whether it exceeds the no-load voltage threshold VocA; When V 时 > no-load voltage threshold VocA, the total power is limited to the highest MPPV path power to the no-load voltage V 时 < no-load voltage threshold VocB, at this time, the remaining MPPT paths are subjected to power tracking control, and the steady-state voltage difference between the highest voltage MPPT path and the lowest voltage MPPT path is controlled to be less than the steady-state voltage difference △Vmppt; When V 时 ≤ no-load voltage threshold VocA, the total power is not load-limited, and all MPPT paths are simultaneously controlled to track power, and the steady-state voltage difference between the highest voltage MPPT path and the lowest voltage MPPT path is controlled to be less than the steady-state voltage difference △Vmppt.

2. According to claim 1, a high-efficiency power control method for multi-channel MPPT of photovoltaic inverter is characterized by: Set the overload limit for any MPPT circuit to limit the maximum output current and rated maximum power of the MPPT circuit.

3. According to claim 2, a high-efficiency power control method for multi-channel MPPT of photovoltaic inverter is characterized in that: Setting a steady-state voltage difference △VmpptA and a steady-state voltage difference △VmpptB, wherein the steady-state voltage difference △VmpptA is greater than the steady-state voltage difference △VmpptB; Carry out overload limiting or full load reduction control, and limit the load according to the rated maximum power and maximum output current; Detect the no-load voltage of the PV circuit, extract the MPPT circuit with the lowest voltage, and reduce the load on the MPPT circuit with the lowest voltage until the steady-state voltage difference between the MPPT circuit with the highest voltage and the MPPT circuit with the lowest voltage is less than the steady-state voltage difference △VmpptB. At this time, load reduction by power balancing control is performed on the remaining MPPT circuits. During the load shedding process, the steady-state voltage difference between the MPPT circuit with the highest voltage and the MPPT circuit with the lowest voltage is monitored. When the steady-state voltage difference is greater than the steady-state voltage difference △VmpptA, the load shedding of the MPPT circuit with the highest voltage is stopped, and the load shedding of the remaining MPPT circuits is performed by load shedding power balancing control. This cycle is repeated until the load shedding power demand is met.

Images