Photovoltaic maximum power point tracking strategy under high energy consumption production line pulsating bus voltage

Abstract

The application provides a photovoltaic maximum power point tracking strategy under high-energy-consumption production line pulsating bus voltage, and relates to the technical field of light storage power supply.The application is applied to the access point of the power supply system of the high-energy-consumption production line load to the light storage, and the access point is the bus with voltage pulsation after the rectification of the multi-pulse thyristor.The first DC / DC converter of the photovoltaic array is connected to the bus with pulsating voltage through a control algorithm.At the same time, the MPPT control of the photovoltaic array under the pulsating bus voltage is realized through the closed-loop control of the current waveform injected into the bus by the first DC / DC converter.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic and energy storage technology, specifically to a photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines. Background Technology

[0002] In high-energy-consuming industrial production lines such as those for electrolytic copper foil production and MnO2 production, the industrial three-phase AC power from the power grid is transformed by a phase-shifting adjustable voltage transformer, and then rectified by a three-phase multi-pulse thyristor rectifier to output a pulsating bus voltage, which is then supplied to the electrolytic cells for the electrolytic reaction. According to existing technical solutions, after integrating photovoltaic power generation and energy storage, the power system adopts an AC bus voltage architecture, such as... Figure 1 As shown. At the current time k, when such high-energy-consuming production lines are connected to photovoltaic power generation and energy storage systems, there are two mainstream technical solutions, but both have clear applicable conditions and limitations:

[0003] The first type mentioned above Figure 1 The AC bus voltage architecture shown is a solution already used in the prior art, suitable for specific power system configurations; however, in this power system, electrical energy is transmitted from the DC side to the AC side, and then from the AC side back to the DC side, resulting in an excessively long transmission path and too many transformation steps for the electrical energy.

[0004] The second type is the DC bus architecture, such as Figure 2 As shown, this architecture is common in existing distributed photovoltaic and energy storage access industrial and commercial power systems, but it relies on a constant DC bus voltage architecture, that is, the DC bus voltage needs to be stably maintained at 750V, which cannot adapt to voltage fluctuation scenarios.

[0005] However, the actual power supply scenario for high-energy-consuming production lines contradicts the requirements of the two architectures mentioned above in the following way: As mentioned earlier, the bus voltage obtained after the power grid of high-energy-consuming production lines is processed by phase-shifting voltage regulating transformers and multi-pulse thyristor rectifiers naturally has pulsating characteristics; while the output voltage of traditional photovoltaic arrays in MPPT (maximum power point tracking) control mode is always a constant DC voltage. The voltage characteristics of the two are fundamentally conflicting, making the MPPT control strategy completely unsuitable. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a photovoltaic maximum power point tracking (MPPT) strategy under pulsating bus voltage in high-energy-consuming production lines, thus overcoming the incompatibility of existing MPPT control strategies with high-energy-consuming production lines.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a photovoltaic maximum power point tracking (MPPT) strategy under pulsating bus voltage in a high-energy-consuming production line. The MPPT strategy controls a first DC / DC converter connected to a photovoltaic array in the pulsating bus voltage architecture of a photovoltaic-storage power system in a high-energy-consuming production line. The pulsating bus voltage architecture also includes a high-energy-consuming production line load, a three-phase transformer, and a multi-pulse thyristor rectifier. The power grid supplies power to the high-energy-consuming production line load via the three-phase transformer and the multi-pulse thyristor, and a bus with pulsating voltage is drawn from the output terminal of the multi-pulse thyristor. The photovoltaic array is connected to the bus via the first DC / DC converter. The photovoltaic MPPT strategy includes:

[0011] S1. High-frequency sampling obtains the photovoltaic array port voltage U. pv (k) Port current I pv (k) Output port voltage u of the first DC / DC converter dc (k), Output port current i dc (k);

[0012] S2. The sampled data points U are controlled by the MPPT frequency. pv (k) and I pv (k) Calculate the average to obtain U pva (k) and I pva (k), according to U pva (k) and I pva (k) Calculate the output power P of the photovoltaic array at the current time k. pv (k);

[0013] S3. Determine the output power P of the photovoltaic array at the current time k. pv Is (k) equal to P calculated at the previous time k-1? pv If (k-1) is true, then the expected maximum power P m (k)=P m (k-1); otherwise, further determine P. m Is (k) greater than P? m If (k-1) is true, then the expected maximum power value P is... m (k)=P m (k-1)+ΔP, otherwise P m (k)=P m (k-1)-ΔP; where ΔP is the step size for power adjustment;

[0014] S4, according to i dcR =P m (k) / u dc (k) Calculate the reference value i of the reverse current that the first DC / DC converter needs to inject into the bus.dcR ; using i error (k)=i dcR -i dc (k), to obtain the current error i error (k); i error (k) is fed into the output current PI controller to obtain the control duty cycle d of the first DC / DC converter; S1~S4 are cycled to realize the photovoltaic maximum power point tracking strategy.

[0015] Preferably, the pulsating bus voltage architecture further includes an energy storage battery and a second DC / DC converter;

[0016] The energy storage battery is connected to the bus by injecting a pulsating current that is opposite to the voltage pulsation direction of the bus through a second DC / DC converter.

[0017] Preferably, the three-phase transformer includes an adjustable phase-shifting transformer.

[0018] Preferably, the multi-pulse thyristor rectifier includes a twelve-pulse thyristor rectifier.

[0019] Preferably, the first DC / DC converter includes a Boost converter.

[0020] Preferably, the second DC / DC converter is a bidirectional converter.

[0021] Preferably, the bidirectional converter includes a fully controlled Boost converter.

[0022] Preferably, the energy storage battery includes a lithium battery, a fuel cell, or a supercapacitor.

[0023] Preferably, the load of the high-energy-consuming production line includes an electrolytic cell.

[0024] Preferably, the electrolytic cell is used for electrolytic production of copper foil or MnO2.

[0025] (III) Beneficial Effects

[0026] This invention provides a photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines. Compared with existing technologies, it has the following advantages:

[0027] This invention addresses the scenario where, in a high-energy-consumption production line, the power system's connection point to the photovoltaic (PV) and energy storage systems is a bus with pulsating voltage after rectification by a multi-pulse thyristor. Through a control algorithm, it enables the photovoltaic array to connect a first DC / DC converter in parallel to the bus with pulsating voltage. Simultaneously, by using the first DC / DC converter to implement closed-loop control of the current waveform injected into the bus, MPPT control of the photovoltaic array under pulsating bus voltage is achieved. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 Design architecture diagram for integrating photovoltaic and energy storage into existing power systems used in industries such as industrial electrolysis for copper foil production and MnO2 production;

[0030] Figure 2 A schematic diagram of a constant DC bus voltage architecture for existing industrial and commercial power supply systems after connecting distributed photovoltaic energy storage;

[0031] Figure 3 This is a schematic diagram of the pulsating bus voltage architecture of the high-energy-consumption production line photovoltaic-storage power system according to an embodiment of the present invention;

[0032] Figure 4 A flowchart of the photovoltaic maximum power point tracking strategy under pulsating bus voltage in a high-energy-consuming production line;

[0033] Figure 5 for Figure 3 In the pulsating bus voltage architecture shown, when the multi-pulse thyristor rectifier is a twelve-pulse thyristor rectifier, the output waveform of the pulsating thyristor rectifier is as follows:

[0034] Figure 6 For what Figure 3 The photovoltaic array in the middle outputs a constant maximum power P m At the same time, the output port is connected in parallel. Figure 5 The pulsating voltage u shown dc The output port current of the DC / DC converter connected to the photovoltaic array needs to be controlled to P. m / u dc That is, the current i that pulsates in the opposite direction to the pulsating bus voltage. dc A waveform diagram. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This application provides a photovoltaic maximum power point tracking (MPPT) strategy for high-energy-consuming production lines under pulsating bus voltage. This overcomes the incompatibility of existing MPPT control strategies with high-energy-consuming production lines. When the power system of the high-energy-consuming production line load is connected to the photovoltaic and energy storage system at the pulsating bus voltage after rectification by multi-pulse thyristors, a photovoltaic MPPT strategy suitable for pulsating bus voltage is proposed. This allows the photovoltaic array to track the pulsating bus voltage through the output of the DC-DC converter, while achieving maximum power output.

[0037] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0038] In existing technologies employing an AC bus voltage architecture, electrical energy is transmitted from the DC side to the AC side and then back to the DC side. This results in an excessively long transmission path and numerous energy conversion stages, leading to unnecessary construction costs and losses in the power system. Conversely, with a DC bus voltage architecture, traditional photovoltaic arrays output a constant DC voltage after MPPT control. This does not account for voltage ripples after rectification by the grid voltage via a phase-shifting transformer and a multi-pulse thyristor rectifier, rendering the traditional MPPT control algorithm inapplicable.

[0039] This invention proposes a photovoltaic maximum power point tracking (MPPT) strategy under pulsating bus voltage in high-energy-consuming production lines. It addresses the technical problem of incompatibility between pulsating bus voltage in high-energy-consuming production lines and traditional photovoltaic MPPT control. In high-energy-consuming production lines 7 such as electrolytic copper foil production and electrolytic MnO2 production, the pulsating bus voltage formed after rectification by a phase-shifting voltage regulator transformer and multi-pulse thyristors from the grid enables photovoltaics to achieve maximum power output.

[0040] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0041] This invention provides a photovoltaic maximum power point tracking (MPPT) strategy under pulsating bus voltage in high-energy-consuming production lines. This PPT strategy is applied in situations such as... Figure 3 The illustrated pulsating bus voltage architecture includes a high-energy-consuming production line load, a photovoltaic array, an energy storage battery, a three-phase transformer, a multi-pulse thyristor rectifier, a first DC / DC converter, and a second DC / DC converter. The power grid supplies power to the high-energy-consuming production line load via the three-phase transformer and the multi-pulse thyristor. A bus with a pulsating voltage is drawn from the output of the multi-pulse thyristor. The photovoltaic array is connected to the bus via the first DC / DC converter. The first DC / DC converter achieves MPPT (Multi-Pulse Test) and tracks the bus voltage by injecting a pulsating current in the opposite direction to the voltage pulsation of the bus. The energy storage battery is connected to the bus via the second DC / DC converter by injecting a pulsating current in the opposite direction to the voltage pulsation of the bus.

[0042] like Figure 4 As shown, the photovoltaic maximum power point tracking strategy includes:

[0043] S1. High-frequency sampling obtains the photovoltaic array port voltage U. pv (k) Port current I pv (k) Output port voltage u of the first DC / DC converter dc (k), Output port current i dc (k);

[0044] S2. The sampled data points U are controlled by the MPPT frequency. pv (k) and I pv (k) Calculate the average to obtain U pva (k) and I pva (k), by averaging U pva (k) and I pva (k) Calculate the output power P of the photovoltaic array at the current time k. pv (k);

[0045] S3. Determine the output power P of the photovoltaic array at the current time k. pv Is (k) equal to P calculated at the previous time step? pv If (k-1) is true, then the expected maximum power P m (k)=P m (k-1); otherwise, further determine P. m Is (k) greater than P? m If (k-1) is true, then the expected maximum power P m (k)=P m (k-1)+ΔP, otherwise P m (k)=P m (k-1)-ΔP; where ΔP is the step size for power adjustment.

[0046] S4, according to i dcR =P m (k) / u dc (k) Calculate the reference value i of the reverse current that the first DC / DC converter needs to inject into the bus. dcR and using i error (k)=i dcR -i dc (k), to obtain the current error i error (k); i error (k) is fed into the output current PI controller to obtain the control duty cycle d of the first DC / DC converter; S1~S4 are cycled to realize the photovoltaic maximum power point tracking strategy.

[0047] It should be noted that, in Figure 3 In this context, high-energy-consuming production line loads are exemplified by electrolytic cells, which can be used for electrolytic production of copper foil, MnO2, and hydrogen. High-energy-consuming production line loads can also include coal chemical production line loads, ceramic production line loads, and fertilizer production line loads. Furthermore, it should be noted that although the embodiments in this application describe a "photovoltaic maximum power point tracking strategy," in practice, this maximum power point tracking strategy is also applicable to other fluctuating DC power sources, such as wind power generation.

[0048] The following section provides a detailed explanation of each component in the pulsating bus voltage architecture and the photovoltaic maximum power point tracking strategy:

[0049] The three-phase transformer can be an adjustable phase-shifting transformer, and the multi-pulse thyristor rectifier can be a twelve-pulse thyristor rectifier. The first DC / DC converter connected to the photovoltaic array can be a Boost converter that injects reverse pulsating current into the pulsating bus voltage to achieve MPPT and track the pulsating bus voltage. The second DC / DC converter connected to the energy storage battery can be a Boost converter that replaces the traditional Boost diode with a fully controlled switch to inject reverse pulsating current into the pulsating bus voltage to achieve tracking of the pulsating bus voltage and bidirectional energy flow at the connection point. The energy storage battery can take various forms, such as lithium batteries, fuel cells, and supercapacitors.

[0050] like Figure 3 As shown, when the power system for electrolytic copper foil production and electrolytic MnO2 production is connected to the photovoltaic energy storage system at the pulsating bus voltage after rectification by a multi-pulse thyristor, the photovoltaic array, after being regulated by the first DC / DC converter, can be connected to the pulsating bus voltage and operate at its maximum power point. The photovoltaic array outputs maximum power at this point, which can be considered a constant power source. That is, the input port power of the first DC / DC converter is constant at the maximum power P of the photovoltaic array. m According to the law of power conservation, ignoring converter losses, the output port power of the first DC / DC converter should also be P. m And by Figure 3 It can be seen that the output port voltage of the first DC / DC converter, i.e., the DC bus voltage, is clamped by the pulsating voltage output from the multi-pulse rectifier. Furthermore, assuming the power grid is a strong grid, the pulsating voltage after voltage regulation by the phase-shifting transformer and rectification by the multi-pulse rectifier will not be affected by the injected current on the bus, and will always be equivalent to being clamped by the three-phase grid voltage into a multi-pulse fluctuating voltage waveform u. dc Taking the output waveform of a twelve-pulse thyristor rectifier as an example, such as Figure 5 As shown.

[0051] Therefore, to ensure that the photovoltaic array outputs a constant maximum power P m At the same time, the output port is connected in parallel. Figure 5The pulsating voltage u shown dc The output port current of the DC / DC converter connected to the photovoltaic array needs to be controlled to P. m / u dc That is, the current i that pulsates in the opposite direction to the pulsating bus voltage. dc ,like Figure 6 As shown. Therefore, after incorporating the pulsating bus voltage, the control strategy for the DC / DC converter connected to the photovoltaic array includes: obtaining the photovoltaic array port voltage U through high-frequency sampling. pv (k) Port current I pv (k) DC / DC converter output port voltage u dc (k), Output port current i dc (k). Then, the sampled data points U are processed using the control frequency of MPPT. pv (k) and I pv (k) Calculate the average to obtain U pva (k) and I pva (k). The average U is obtained by... pva (k) and I pva (k) Calculate the output power P of the photovoltaic array at the current time k. pv (k). Then, the output power P of the photovoltaic array at the current time k is... pv (k) and P calculated at the previous time step pv Compare (k-1) and if they are equal, then the maximum expected power value P is... m (k) compared to P m If (k-1) remains constant, and is increased, then the maximum power expectation value P will be... m (k) compared to P m (k-1) Increase ΔP; if it decreases, then the maximum power expectation value P will be... m (k) compared to P m (k-1) Decrease ΔP. ΔP is the step size for power regulation, a control parameter selected based on actual conditions such as system power and regulation speed. It can be a constant value or dynamically changing. This yields the maximum expected power value P at that moment. m (k) after which, according to i dcR =P m (k) / u dc (k) The reference value i of the reverse current that the DC / DC converter needs to inject into the bus can be calculated. dcR And compared with the actual output port current i obtained by high-frequency sampling dc (k) Compare to obtain the current error i error (k) can be fed into the output current PI controller to obtain the control duty cycle d of the DC / DC converter as a feedback control quantity, and then the cycle will return to the beginning to perform the next round of sampling and control.

[0052] In summary, compared with existing technologies, it has the following beneficial effects:

[0053] 1. When the power system of a high-energy-consuming production line load is connected to a bus with pulsating voltage after rectification by a multi-pulse thyristor at the access point of the photovoltaic energy storage, a control algorithm is used to connect the photovoltaic array to the bus with pulsating voltage via the first DC / DC converter. Simultaneously, closed-loop control of the current waveform injected into the bus by the first DC / DC converter enables MPPT control of the photovoltaic array under pulsating bus voltage.

[0054] 2. When connecting the power system of the load of the high-energy-consuming production line to the photovoltaic energy storage system, a reverse pulsating current is injected, thereby changing the original AC bus to a bus with voltage pulsation at the connection point, so as to realize the effective connection of the photovoltaic energy storage power supply to the power system of industrial and commercial electricity.

[0055] 3. The electrical energy from photovoltaic arrays and energy storage batteries does not need to go through the original multiple sets of AC transformers, inverters and rectifiers for conversion, and does not go through AC lines for transmission. This reduces the losses in the power conversion and transmission links, improves the efficiency of the power system, and reduces the waste of electrical energy.

[0056] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photovoltaic maximum power point tracking strategy under pulsating bus voltage in a high-energy-consuming production line, characterized in that, The photovoltaic maximum power point tracking strategy is used to control the first DC / DC converter connected to the photovoltaic array in the pulsating bus voltage architecture of the photovoltaic-storage power system of a high-energy-consuming production line. The pulsating bus voltage architecture also includes a high-energy-consuming production line load, a three-phase transformer, and a multi-pulse thyristor rectifier. The power grid supplies power to the high-energy-consuming production line load via the three-phase transformer and the multi-pulse thyristor, and a bus with a pulsating voltage is drawn from the output terminal of the multi-pulse thyristor. The photovoltaic array is connected to the bus via the first DC / DC converter. The photovoltaic maximum power point tracking strategy includes: S1. High-frequency sampling obtains the photovoltaic array port voltage. U pv (k) Port Current I pv (k) Voltage at the output port of the first DC / DC converter u dc (k) Output port current i dc (k); S2. The sampled data points are processed using the control frequency of MPPT. U pv (k) and I pv (k) Calculate the average to obtain U pva (k) and I pva (k), according to U pva (k) and I pva (k) Calculate the output power of the photovoltaic array at the current time k. P pv (k); S3. Determine the output power of the photovoltaic array at the current time k. P pv Is (k) equal to the value calculated at time k-1 in the previous time step? P pv If (k-1) is true, then the expected value of the maximum power is... P m (k)= P m (k-1); otherwise, further judgment. P m Is (k) greater than P m If (k-1) is true, then the expected value of the maximum power will be... P m (k)= P m (k-1)+ ΔP, otherwise P m (k)= P m (k-1)- ΔP ;in, ΔP This is the step size for power adjustment; S4, according to i dcR = P m (k) / u dc (k) Calculate the reference value of the reverse current that the first DC / DC converter needs to inject into the bus. i dcR ;use i error (k)= i dcR - i dc (k) yields the current error. i error (k); will i error (k) is fed into the output current PI controller to obtain the control duty cycle of the first DC / DC converter. d This causes the photovoltaic output current to pulsate in the opposite direction to the bus voltage; by cycling through S1~S4, the photovoltaic maximum power point tracking strategy is realized.

2. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 1, characterized in that, The pulsating bus voltage architecture also includes an energy storage battery and a second DC / DC converter; The energy storage battery is connected to the bus by injecting a pulsating current that is opposite to the voltage pulsation direction of the bus through a second DC / DC converter.

3. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 1, characterized in that, The three-phase transformer includes an adjustable phase-shifting transformer.

4. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 1, characterized in that, The multi-pulse thyristor rectifier includes a twelve-pulse thyristor rectifier.

5. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 1, characterized in that, The first DC / DC converter includes a Boost converter.

6. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 2, characterized in that, The second DC / DC converter is a bidirectional converter.

7. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 6, characterized in that, The bidirectional converter includes a fully controlled Boost converter.

8. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 2, characterized in that, The energy storage battery includes a lithium battery, a fuel cell, or a supercapacitor.

9. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in any one of claims 1 to 8, characterized in that, The high-energy-consuming production line load includes an electrolytic cell.

10. The photovoltaic maximum power point tracking strategy under pulsating bus voltage in high-energy-consuming production lines as described in claim 9, characterized in that, The electrolytic cell is used to electrolyze copper foil or to electrolyze MnO2.

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