Design method of direct current optimizer in distributed photovoltaic power station

Abstract

This invention discloses a design method for a DC optimizer within a distributed photovoltaic (PV) power plant, belonging to the field of new energy stability and control technology. The method includes: analyzing the dynamic characteristics of different topology DC optimization units (DCOs) when facing severe mismatch disturbances within the PV power plant, and deriving the improvement goals for Boost-type and Buck-type DC optimizers: the Boost-type DC optimizer needs to solve the "hot spot" problem and the integrator saturation problem in the control loop; the Buck-type DC optimizer needs to solve the integrator saturation problem in the control loop. Based on these design goals, Boost-type and Buck-type DC optimizers are designed to ensure stable operation of the PV power plant during severe mismatch disturbances caused by partial shading and subsequent recovery processes, avoiding phenomena such as "hot spots," thereby solving the technical problem of poor stability of PV power plants when facing severe mismatch disturbances.

Description

Technical Field

[0001] This invention belongs to the field of new energy stabilization and control technology, and more specifically, relates to a design method for a DC optimizer in a distributed photovoltaic power station. Background Technology

[0002] Solar energy, as one of the main clean energy sources, is characterized by its sustainability and wide range of applications, and has experienced rapid development in the power generation sector in recent years. According to statistics from the National Energy Administration, from 2013 to 2021, the cumulative installed capacity of photovoltaic power generation nationwide has increased more than tenfold. In the future, the photovoltaic sector will continue to maintain rapid development.

[0003] Due to the inherent working principle of photovoltaic (PV) power plants, they are highly susceptible to environmental influences. Surrounding buildings, trees, cloud cover, and dust accumulation on the panels can cause localized shading, leading to mismatch issues. However, centralized GMPPT-controlled PV power plants experience a significant decrease in power efficiency when mismatch occurs. Therefore, large-scale distributed PV power plants will become an important component of future power system development. These plants typically deploy panel-level DC optimizers (DCOs) within the PV array, resulting in a large number of power electronic devices whose impact on the transient stability of the PV system cannot be ignored.

[0004] When a distributed photovoltaic power station faces severe internal mismatch disturbances, the existing photovoltaic panel-level DCO may exhibit a "hot spot" phenomenon, which seriously affects the normal and stable operation of the photovoltaic system. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a design method for a DC optimizer within a distributed photovoltaic (PV) power station. The aim is to analyze the dynamic characteristics of different topology DC optimizers (DCOs) when facing severe mismatch disturbances within the PV power station, and to derive improvement targets for Boost-type and Buck-type DC optimizers. Based on these improvement targets, a DC optimizer is designed to ensure stable operation of the PV power station during severe mismatch disturbances caused by partial shading and subsequent recovery processes, avoiding phenomena such as "hot spots." This solves the technical problem of poor stability in PV power stations when facing severe mismatch disturbances.

[0006] To achieve the above objectives, according to one aspect of the present invention, a design method for a DC optimizer within a distributed photovoltaic power station is provided. The DC optimizer is suitable for scenarios where severe mismatch disturbances occur within the distributed photovoltaic power station. The design method includes:

[0007] S1: Based on different topologies, the DC optimizers to be designed are divided into Boost-type DC optimizers or Buck-type DC optimizers;

[0008] S2: Determine the design objectives for the Boost DC optimizer and the Buck DC optimizer respectively;

[0009] S3: When the DC optimizer to be designed is the Boost-type DC optimizer, the following operations are performed according to its design objectives:

[0010] Connect a reverse diode in parallel to the output port; when the reverse diode is conducting, connect a power-dissipating resistor in parallel to the input port; when the output voltage v of the Boost DC optimizer... dc Less than threshold V min When the photovoltaic string to which the Boost-type DC optimizer belongs is determined to be in a state of severe shading, the IGBT of this unit is actively limited to be turned off so that the system works at the forced equilibrium point. At the same time, the maximum power point tracking (MPPT) control is exited, thereby disconnecting the integrator input of the control loop.

[0011] S4: When the DC optimizer to be designed is the Buck-type DC optimizer, perform the following operations according to its design objectives:

[0012] When its output voltage v dc Greater than threshold V max When the photovoltaic string to which the Buck-type DC optimizer belongs is determined to be in a state of severe shading, the IGBT of this unit is actively restricted from conducting so that the system operates at the forced equilibrium point. At the same time, the MPPT control is exited, thereby disconnecting the integrator input of the control loop.

[0013] In one embodiment, S3 further includes: when facing severe mismatch disturbances and severe shading of the Boost topology photovoltaic string, the corresponding unit of the Boost topology photovoltaic string always operates on the left side of the photovoltaic panel MPP; the theoretical maximum output power of the Boost topology photovoltaic string is the output power corresponding to its forced equilibrium point.

[0014] In one embodiment, S3 further includes: when the system is operating at a forced equilibrium point, the IGBT is continuously turned off.

[0015] In one embodiment, the energy-consuming resistor R connected in parallel in S3 d Whether to activate is determined by the logic switch SW1 connected in series with it;

[0016] When the reverse diode D BW When the circuit is on, SW1 closes to allow the parallel resistor R to... d Input circuit;

[0017] When the reverse diode D BW When not conducting, SW1 is disconnected to allow the parallel resistor R to... d quit.

[0018] In one embodiment, S4 further includes: when the output voltage v of the Buck-type DC optimizer... dc Greater than V max If it is determined that the photovoltaic strings of other units are severely shaded, the IGBT of this unit is actively turned on to make the system work at the forced equilibrium point, the MPPT control is exited, and the integrator input of the control loop is disconnected.

[0019] In one embodiment, S4 further includes: when facing a severe mismatch disturbance and the Buck topology photovoltaic string experiences severe local shading, the corresponding unit of the Buck topology photovoltaic string operates at the MPP operating point, and the remaining units operate to the right of the MPP; the theoretical maximum output power is the output power corresponding to the forced equilibrium point.

[0020] In one embodiment, S4 further includes: when the unit is operating at the forced equilibrium point, the IGBT remains on, and the unit operating at the forced equilibrium point exits MPPT control, thereby disconnecting its control loop integrator input.

[0021] In one embodiment, S2 includes:

[0022] The design objectives are determined based on the dynamic characteristics of the Boost-type DC optimizer when facing severe mismatch disturbances.

[0023] The design objectives are determined based on the dynamic characteristics of the Buck-type DC optimizer when facing severe mismatch disturbances.

[0024] In one embodiment, the design goal of the Boost-type DC optimizer is to prevent the output voltage of the DC optimizer from reversing polarity and to prevent the integrator of the control loop from saturating.

[0025] In one embodiment, the Buck-type DC optimizer is designed to prevent saturation of the control loop integrator.

[0026] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0027] (1) This invention analyzes the dynamic characteristics of different topology DCOs when facing severe mismatch disturbances within a photovoltaic power station, and derives the improvement goals for Boost-type DC optimizers and Buck-type DC optimizers respectively: Boost-type DC optimizers need to solve the "hot spot" problem and the integrator saturation problem in the control loop; Buck-type DC optimizers need to solve the integrator saturation problem in the control loop. Based on the above design goals, Boost-type DC optimizers and Buck-type DC optimizers are designed to ensure that the photovoltaic power station can maintain stable operation and avoid phenomena such as "hot spots" when facing severe mismatch disturbances caused by partial shading and during the subsequent recovery process, thereby solving the technical problem of poor stability of photovoltaic power stations when facing severe mismatch disturbances. The improved scheme provided by this invention can well achieve the improvement design goals, enhance the ability of distributed photovoltaic power stations to operate stably when facing severe mismatch disturbances, and has strong engineering practicality.

[0028] (2) This invention designs a reverse diode at the output of the Boost DC optimizer, which successfully avoids the "hot spot" problem; designs a parallel energy-consuming resistor, which successfully suppresses the resonance problem caused by the diode connection; and designs an optimization scheme for the control loop, which successfully avoids the saturation of the integrator.

[0029] (3) This invention provides an optimization scheme for the control loop of the Buck-type DC optimizer, which successfully avoids integrator saturation. Attached Figure Description

[0030] Figure 1 A flowchart of an improved DC optimizer design for severe mismatch disturbances within a distributed photovoltaic power station, provided as an embodiment of the present invention;

[0031] Figure 2 The topology is an M×N-DMPPT large-scale distributed photovoltaic grid-connected system.

[0032] Figure 3 These are diagrams of two DCO topologies in this invention;

[0033] Figure 4 This is a diagram of the internal structure of the DCO control system.

[0034] Figure 5 The graph shows the changes in MPP and operating point of the Boost-type DC optimizer during the mismatch process.

[0035] Figure 6 The graph shows the changes in MPP and operating point of the Buck-type DC optimizer during the mismatch process.

[0036] Figure 7 A schematic diagram of the improved Boost-type DC optimizer topology designed for this invention;

[0037] Figure 8 A schematic diagram of the improved Boost-type DC optimizer controller topology designed for this invention;

[0038] Figure 9 A schematic diagram of the improved Buck-type DC optimizer controller topology designed for this invention;

[0039] Figure 10a , Figure 10b , Figure 10c This is a schematic diagram of the simulation results of Scheme 1 in one embodiment of the present invention;

[0040] Figure 11a , Figure 11b , Figure 11c This is a schematic diagram comparing the simulation results of Scheme 2 and Scheme 1 in one embodiment of the present invention;

[0041] Figure 12 This is a schematic diagram comparing the simulation results of Scheme 3 and Scheme 1 in one embodiment of the present invention;

[0042] Figure 13 This is a schematic diagram comparing the simulation results of Scheme 2 and Scheme 1 in another embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] This invention provides a design method for a DC optimizer within a distributed photovoltaic (PV) power station. The DC optimizer is suitable for scenarios involving severe mismatch disturbances within the distributed PV power station. The design method includes:

[0045] S1: Based on different topologies, the DC optimizers to be designed are divided into Boost-type DC optimizers or Buck-type DC optimizers;

[0046] S2: Determine the design objectives for the Boost DC optimizer and the Buck DC optimizer respectively;

[0047] S3: When the DC optimizer to be designed is a Boost DC optimizer, perform the following operations according to its design goals: connect a reverse diode in parallel to the output port; when the reverse diode is conducting, connect a power-dissipating resistor in parallel to the input port; when the output voltage v of the Boost DC optimizer is... dc Less than threshold V minWhen the photovoltaic string belonging to the Boost DC optimizer is determined to be in a state of severe shading, the IGBT of this unit is actively limited to be turned off so that the system operates at the forced equilibrium point. At the same time, the maximum power point tracking (MPPT) control is exited, thereby disconnecting the integrator input of the control loop.

[0048] S4: When the DC optimizer to be designed is a Buck-type DC optimizer, perform the following operations according to its design objectives: when its output voltage v dc Greater than threshold V max When the photovoltaic string belonging to the Buck-type DC optimizer is determined to be in a state of severe shading, the IGBT conduction of this unit is actively limited to make the system work at the forced equilibrium point. At the same time, the MPPT control is exited, thereby disconnecting the integrator input of the control loop.

[0049] Specifically, step S2 includes:

[0050] S21: Determine the dynamic characteristics of the Boost-type DC optimizer when faced with severe mismatch disturbances;

[0051] S22: Determine the design objectives for improving the Boost-type DC optimizer based on the dynamic characteristics conclusions;

[0052] S23: Determine the dynamic characteristics of the Buck-type DC optimizer when faced with severe mismatch disturbances;

[0053] S24: Determine the design objectives for the improved Buck-type DC optimizer based on the conclusions of S21;

[0054] Furthermore, in step S21, under the Boost topology, all photovoltaic power generation units in the photovoltaic string should satisfy the following relationship at any time (where i is the index of the photovoltaic power generation unit):

[0055] Furthermore, in step S21, when the degree of local shading of the photovoltaic string is relatively severe (for ease of description, we assume PV2 is severely shaded here), the maximum power point (MPP) current value I of the shaded photovoltaic panel is... pvm The intensity of light will decrease significantly with the substantial decrease in ambient light intensity. Assuming that each photovoltaic unit can still operate stably in MPPT mode after the disturbance, the following inequality relationship holds: Where P pvm,i For each photovoltaic panel's MPP power, V DC I is the rated value of the DC bus voltage. DC *This represents the steady-state value of the ideal output DC current of the photovoltaic string when all n photovoltaic panels are operating in MPPT mode. Considering the DCO is a Boost topology, i D,2 and i DC The steady-state values ​​are equal, and since the output current i of the photovoltaic string in steady state is... DC It cannot exceed the DCO input current i pv,2 Therefore, this inequality does not hold. Consequently, severely obstructed cells will always operate to the left of the MPP and will be unable to reach the perturbed MPPT operating point.

[0056] Further, in step S21, the input differential signal (v) of the disturbed unit DCO controller pv,2 -v pvm,2 It always remains less than 0. Figure 4 As shown, the integrator in the control loop (COMP) will continuously integrate negatively, causing the IGBT duty cycle signal d output by the control system to decrease to its lower limit of 0. The IGBT in the DCO circuit will then continuously operate in the blocking state (forced operating point). Under these circumstances, the DCO control system will be unable to regulate the photovoltaic panel operating voltage v. pv v pv and v dc After being forced to synchronize and drop to the same voltage value and remain stable to the left of MPP, this state is set as the forced operating point, such as... Figure 5 As shown.

[0057] Furthermore, in step S21, when an extreme mismatch occurs among the power generation units in the photovoltaic string, the photovoltaic string outputs current i DC It may be greater than the minimum short-circuit current among all the photovoltaic panels shaded by shadow (min I). sc,c (For the photovoltaic panel with the lowest ambient light intensity), the DCO output voltage will be negative, causing the photovoltaic panel with the lowest short-circuit current to have the opposite polarity of its operating voltage. This will eventually cause the photovoltaic unit to change from a power source to a load, thus triggering the "hot spot" phenomenon.

[0058] Furthermore, in step S21, the integrator in the control loop will continue to integrate negatively, which will lead to saturation and make it difficult for the system to resume normal operation after the occlusion is removed.

[0059] Furthermore, in step S22, the design goals for the Boost-type DC optimizer improvement are determined as follows: to prevent reverse polarity of the DCO output voltage; and to prevent saturation of the integrator in the control loop.

[0060] Furthermore, in step S23, under the Buck topology, all photovoltaic power generation units in the photovoltaic string should satisfy the following relationship at any time (where i is the index of the photovoltaic power generation unit):

[0061] Furthermore, in step S23, when the degree of local shading of the photovoltaic string is relatively severe (for ease of description, it is assumed here that PV2 is severely shaded, while the others (PVk) operate normally), the MPP power P of each unit in the entire photovoltaic string... pvm,i The sum will decrease significantly. Assuming that each photovoltaic unit can still stabilize at its own MPPT operating point after the disturbance, the MPP current I of the normal unit will be significantly reduced. pvm,k The following inequality relationship will be satisfied:

[0062] Where P pvm,i For each photovoltaic panel's MPP power, V DC I is the rated value of the DC bus voltage. DC * This represents the steady-state value of the ideal output DC current of the photovoltaic string when all n photovoltaic panels are operating in MPPT mode. Considering the DCO is a Buck topology, i L,k and i DC The steady-state values ​​are equal, and the output current i of the photovoltaic string in steady state is equal. DC It should be greater than the DCO input current i pv,k However, this contradicts the aforementioned inequality. Therefore, the normal cell will always operate on the right side of MPP and will be unable to reach the perturbed MPPT operating point.

[0063] Further, in step S23, the input differential signal (v) of the disturbed unit DCO controller pv,k -v pvm,k The IGBT duty cycle signal d remains greater than 0. The integrator in the control loop (COMP) will continuously integrate positively, causing the IGBT duty cycle signal d output by the control system to increase to its upper limit of 1. The IGBT in the DCO circuit will continue to operate in a continuously on state (forced operating point). Under these circumstances, the DCO control system will be unable to regulate the photovoltaic panel operating voltage v. pv v pv and v dc After being forced to synchronize and drop to the same voltage value and remain stable to the right of MPP, this state is set as the forced operating point, such as... Figure 6 .

[0064] Furthermore, in step S23, the integrator in the control loop will continue to integrate in the positive direction, which will lead to saturation and make it difficult for the system to resume normal operation after the occlusion is removed.

[0065] Furthermore, in step S24, the design goal of the Buck-type DC optimizer improvement is determined to be: to prevent the integrator in the control loop from saturating.

[0066] Step S3 designs an improved Boost-type DC optimizer for severe mismatch disturbances within distributed photovoltaic power plants, including the following design:

[0067] D1: Parallel reverse diode D at the output port BW ;

[0068] D2: Parallel power dissipation resistor R at the DCO input port d The resistor is controlled by its series logic switch SW1 to determine whether it is engaged or disengaged. Figure 7 ;

[0069] D3: Design threshold V min DC optimizer output voltage v dc Less than V min When the photovoltaic string to which the unit belongs is determined to be in a state of severe shading, the IGBT is actively restricted to turn off, the system operates at the forced equilibrium point, MPPT control is exited, and the integrator input of the control loop is disconnected.

[0070] Furthermore, in the design of D1, the reverse diode D... BW The output voltage v of the photovoltaic power generation unit dc It turns on when crossing zero, controlling v dc The decline does not continue, thus avoiding v dc When polarity is reversed, "hot spots" appear in the photovoltaic unit.

[0071] Furthermore, in the design of D1, the reverse diode D... BW When the circuit is turned on, parallel resonance may occur in the DCO circuit, requiring further design.

[0072] Furthermore, in the design of D2, when diode D is detected... BW When turned off, the logic switch is turned on, and the energy-consuming resistor is connected to the circuit to dissipate excess energy, increase system damping, and suppress the aforementioned parallel oscillation phenomenon. When diode D is detected... BW When the circuit is turned on, the logic switch is turned off, and the energy-consuming resistor is removed from the circuit, which does not affect the normal operation of the DCO.

[0073] Furthermore, in the design of D3, the output voltage v is obtained through the DC optimizer. dc Compared with a threshold, it quickly determines whether the photovoltaic string is under severe shading. When severe shading occurs, it actively limits IGBT turn-off, accelerating the circuit to operate at the forced equilibrium point. To address the DCO control's integrator saturation problem, it removes the MPPT control and integral input of the severely shaded unit, such as... Figure 8 .

[0074] Step S4 designs an improved Buck DC optimizer for severe mismatch disturbances within distributed photovoltaic power plants, including the following design:

[0075] Set threshold V max DC optimizer output voltage vdc Greater than V max If it is determined that other photovoltaic strings in other units are severely shaded, the system actively controls the IGBTs of this unit to turn on, the system operates at the forced equilibrium point, MPPT control is exited, and the integrator input of the control loop is disconnected. Figure 9 .

[0076] Similar to a Boost DC optimizer, the output voltage v of the DC optimizer... dc With threshold V max In comparison, the system quickly determines whether the photovoltaic string is under severe shading. If severe shading occurs, it actively restricts IGBT turn-off, accelerating the circuit to operate at the forced equilibrium point. To address the DCO control's integrator saturation issue, the MPPT control and integral input of the severely shaded unit are disabled.

[0077] In one embodiment, an improved Boost DC optimizer design is provided for handling severe mismatch disturbances within a distributed photovoltaic power station, such as... Figure 1 As shown, compared with the original Boost-type DC optimizer, in order to solve the output power reduction and "hot spot" problem caused by voltage polarity reversal that may occur under severe mismatch disturbances inside the photovoltaic power station, a reverse diode (D) is connected in parallel at its output port. BW );

[0078] To further suppress the parallel resonance problem that may occur in the aforementioned Boost-type DC optimizer during severe mismatch, a parallel energy-dissipating resistor (R) is added. d and logic switch SW1;

[0079] To prevent the integrator in the DC optimizer's DCO control loop from remaining in a saturated state for an extended period, threshold values ​​V are designed for the Boost-type DC optimizer. min When the system detects the operating voltage v of the photovoltaic unit pv Less than V min When the photovoltaic panel of the unit is determined to be under severe shading, the duty cycle signal output by the DCO control system is set to zero, its Boost circuit is actively controlled to operate in IGBT blocking mode, the MPPT stage is exited, and the control system integrator is stopped to avoid integrator saturation due to reverse integration; when the severe mismatch disturbance of the photovoltaic string is recovered, the parallel energy dissipation resistor R is removed. d The MPPT process and control system integrator are then implemented.

[0080] To verify the technical effectiveness of the control method provided by this invention, simulation experiments were conducted to compare the design before and after the improvement under specific working conditions. The model is as follows: Figure 2As shown, an electromagnetic transient simulation model of a distributed photovoltaic (PV) power station connected to an AC power grid based on DCO-DMPPT was established using the Matlab / Simulink simulation platform. The PV power station consists of a power generation system containing one distributed PV string. The number of PV-DCO power generation units connected in series in the PV string is set to 10. The parameters of the PV array, DCO and its control system, and PV inverter and its control system are shown in Tables 1 and 2.

[0081] Table 1 Photovoltaic Array Parameters

[0082]

[0083] Table 2 DCO and VSC parameters (including control system)

[0084]

[0085]

[0086] Since the design of the control loop, including the MPPT and integrator, is similar in concept and effect to the Buck-type DC optimizer in Example 2, this example will not verify the effect of this part.

[0087] Comparison of three DCO schemes:

[0088] Option 1: Use the original Boost DC optimizer, such as Figure 3 As shown in (a);

[0089] Option 2: Based on Option 1, add a reverse diode D to the DCO output port of this invention. BW ;

[0090] Option 3: Based on Option 2, add a parallel energy-dissipating resistor R to the DCO input port in this invention design. d ;

[0091] The simulation environment is as follows, comparing the system response under three Boost-type DC optimizer design schemes when facing severe mismatch disturbances within the photovoltaic power plant:

[0092] During initial operation, the ambient light intensity and temperature of each photovoltaic panel in the photovoltaic string were set to values ​​under standard test conditions (STC). All photovoltaic power generation units operated in MPPT mode, and the rated output power of the photovoltaic string was 2500W. At t=1s, PV4 and PV5 were set to generate -450W / m 2 and -700W / m 2 The light intensity step disturbance is used to simulate the extreme mismatch scenario of a photovoltaic power station.

[0093] Simulations were performed using the DCO from scheme 1 under the aforementioned environment, and the operating voltage v of each photovoltaic panel was measured. pv DCO output voltage v dc MPPT stage output signal v pvm The DCO controller outputs the duty cycle signal d, and the photovoltaic string output current i. DC and the total output power P of the photovoltaic string out like Figure 10a , Figure 10b , Figure 10c As shown (PV1 is used as the representative of a photovoltaic unit under normal illumination, and the oscillation from 0 to 1s in the simulation waveform is the initialization process of the electromagnetic transient model),

[0094] When some photovoltaic strings are severely shaded, resulting in extreme mismatch in the photovoltaic power station, although the unshaded photovoltaic units still operate in MPPT mode, the DCO output voltage and photovoltaic panel operating voltage (V) of the PV5 with the most severe shading will be significantly affected. dc,5 and v pv,5 The value will drop to a negative value and continue to decrease synchronously thereafter. At this point, PV5 changes from a power supply attribute to a load attribute, i.e., the photovoltaic string "hot spot" phenomenon occurs. In order to maintain a constant DC bus voltage, the DCO output voltage (V) of a normal unit... dc,1 The output current and power (i) of the entire photovoltaic string will continue to rise. Furthermore, since PV5 consumes the energy output from other photovoltaic power generation units, the output current and power (i) of the entire photovoltaic string will also increase. DC and P out The efficiency of photovoltaic power plants will gradually decrease, leading to a reduction in their capacity efficiency and causing serious abnormalities.

[0095] Simulations were performed using the DCO from scheme 2 under the aforementioned environment, and the operating voltage v of each photovoltaic panel was measured. pv DCO output voltage v dc MPPT stage output signal v pvm Photovoltaic string output current i DC and the total output power P of the photovoltaic string out like Figure 11a , Figure 11b , Figure 11c As shown (PV1 is used as the representative of a photovoltaic unit under normal illumination, and the oscillation from 0 to 1s in the simulation waveform is the initialization process of the electromagnetic transient model),

[0096] and Figure 10a , Figure 10b , Figure 10c In comparison, after extreme mismatch disturbances, the DCO output voltage (V) of PV5, which suffers the most severe shadow occlusion, is lower. dc,5 The voltage drops rapidly and stabilizes near 0V. Therefore, the reverse diode D in the Boost-type DC optimizer designed in this invention... BWThis effectively avoids the polarity reversal of the Boost-type DC optimizer output voltage when severe mismatch disturbances occur within a distributed photovoltaic power station, successfully preventing the "hot spot" phenomenon. However, at the same time, due to D BW When the circuit is turned on, the DCO of the PV5 power generation unit exhibits parallel resonance, and the output voltage of the PV5 power generation unit v... pv,5 Significant oscillations occurred.

[0097] Simulations were performed using the DCO from scheme 3 under the aforementioned environment. The system's determination diode D was tested in the event of an extreme mismatch disturbance. BW When the circuit is turned on, logic switch SW1 activates, engaging the energy-dissipating resistor. This converts the output voltage v of the PV5 generator unit. pv,5 Compared to using Option 2, such as Figure 12 As shown (the oscillation from 0 to 1s in the simulation waveform is the initialization process of the electromagnetic transient model).

[0098] The comparison shows that after an extreme mismatch disturbance, the DCO of the PV5 power generation unit exhibits parallel resonance when using Scheme 2; under Scheme 3, this oscillation decays rapidly, v pv,5 It stabilizes at 0V. Therefore, the parallel energy-consuming resistor in the Boost-type DC optimizer designed in this invention effectively suppresses D... BW Parallel resonance that occurs when the circuit is turned on.

[0099] The comparison of the three DCO design schemes above shows that the Boost-type DC optimizer designed in this invention can effectively avoid the "hot spot" phenomenon and suppress parallel resonance when extreme mismatch disturbances occur inside the distributed photovoltaic power station.

[0100] In one embodiment, an improved Buck-type DC optimizer design for severe mismatch disturbances within a distributed photovoltaic power station includes:

[0101] To prevent the integrator in the DC optimizer's DCO control loop from remaining in a saturated state for an extended period, threshold values ​​V are designed for the Buck-type DC optimizer. max When the system detects the operating voltage v of the photovoltaic unit pv Greater than V max When it is determined that the photovoltaic panels of other units are severely shaded, the duty cycle signal output by the DCO control system of this unit is set to one, and its Boost circuit is actively controlled to work in the IGBT continuous conduction state. The MPPT stage is exited and the control system integrator is stopped to avoid the integrator from saturating in reverse integration. When the severe mismatch disturbance of the photovoltaic string is recovered, the MPPT stage and the control system integrator are put into operation.

[0102] To verify the technical effectiveness of the control method provided by this invention, simulation experiments were conducted to compare the design before and after the improvement under specific operating conditions. Since the design of the MPPT and integrator in the control loop is similar in concept and effect to the Buck-type DC optimizer in Example 2, the effectiveness of these components will not be verified in this example.

[0103] Comparison of the two DCO schemes:

[0104] Option 1: Use the original Buck-type DC optimizer, such as Figure 3 As shown in (b);

[0105] Option 2: Based on Option 1, add an optimized design to the DCO control loop of this invention, that is, identify the output voltage v of the Buck-type DC optimizer. dc Greater than V max When it is determined that there are other units whose photovoltaic strings are severely shaded, the IGBT of this unit is actively controlled to turn on, the system operates at the forced equilibrium point, MPPT control is exited, and the integrator input of the control loop is disconnected;

[0106] The simulation environment is as follows, comparing the system response under two DCO design schemes when faced with severe mismatch disturbances within the photovoltaic power plant:

[0107] During initial operation, the ambient light intensity and temperature of each photovoltaic panel in the photovoltaic string were set to values ​​under standard test conditions (STC). All photovoltaic power generation units operated in MPPT mode, and the rated output power of the photovoltaic string was 2500W. At t = 1.5s, PV4 and PV5 were set to generate -600W / m². 2 PV6 and PV7 generate -500W / m 2 The light intensity step disturbance was cleared at t=3s, and the total output power P of the photovoltaic system before and after the controller improvement design was compared. out Waveform as Figure 13 As shown.

[0108] As can be seen from the above comparison, the improved DCO control scheme designed in this invention results in a shorter time for the photovoltaic power generation system to recover to the MPPT working mode, and a smaller oscillation amplitude during the process, proving the effectiveness of the improved DCO control scheme designed in this invention.

[0109] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a DC optimizer in a distributed photovoltaic power station, characterized in that, The DC optimizer is suitable for scenarios where severe mismatch disturbances occur within a distributed photovoltaic power station, and the design method includes: S1: Based on different topologies, the DC optimizers to be designed are divided into Boost-type DC optimizers or Buck-type DC optimizers; S2: Determine the design objectives for the Boost DC optimizer and the Buck DC optimizer respectively; S3: When the DC optimizer to be designed is the Boost-type DC optimizer, perform the following operations according to its design objectives: parallel reverse diode; when the reverse diode is turned on, parallel energy consumption resistor is connected to the input port; when the output voltage v dc of the Boost type direct current optimizer is less than the threshold value V min , it is determined that the photovoltaic string to which the Boost type direct current optimizer belongs is in serious shadow shielding condition, the IGBT of the unit is actively limited to be turned off, so that the system works at a forced balance point, and the maximum power point tracking (MPPT) control is exited to disconnect the integrator input of the control link. S4: When the DC optimizer to be designed is the Buck-type DC optimizer, perform the following operations according to its design objectives: When its output voltage v dc is greater than threshold value V max , it is determined that the photovoltaic string to which the Buck-type direct-current optimizer belongs is in a serious shadowing situation, and the IGBT of the unit is actively limited to be turned on, so that the system works at a forced balance point, and the MPPT control is exited to disconnect the integrator input of the control link.

2. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 1, characterized in that, S3 further includes: when facing severe mismatch disturbances and severe shading of the Boost topology photovoltaic string, the corresponding unit of the Boost topology photovoltaic string always operates on the left side of the photovoltaic panel MPP; the theoretical maximum output power of the Boost topology photovoltaic string is the output power corresponding to its forced equilibrium point.

3. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 2, characterized in that, The S3 further includes: when the system is operating at a forced equilibrium point, the IGBT is continuously turned off.

4. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 2, characterized in that, S3 in parallel with the energy dissipation resistance R d Decided by the logic switch SW1 in series with whether to invest; When the reverse diode D BW When the circuit is on, SW1 closes to allow the parallel resistor R to... d Input circuit; When the reverse diode D BW When not conducting, SW1 is disconnected to allow the parallel resistor R to... d quit.

5. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 1, characterized in that, The S4 further includes: when the output voltage v of the Buck-type DC optimizer dc Greater than V max If it is determined that the photovoltaic strings of other units are severely shaded, the system will actively control the IGBTs of this unit to turn on so that the system operates at the forced equilibrium point, exit MPPT control, and disconnect the integrator input of the control loop.

6. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 5, characterized in that, S4 further includes: when facing severe mismatch disturbances and severe local shading of the Buck topology photovoltaic string, the corresponding unit of the Buck topology photovoltaic string operates at the maximum power point (MPP), and the remaining units operate on the right side of the MPP; the theoretical maximum output power is the output power corresponding to its forced equilibrium point.

7. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 5, characterized in that, The S4 further includes: when the unit is working at the forced equilibrium point, the IGBT is continuously turned on, and the unit working at the forced equilibrium point exits the MPPT control, thereby disconnecting the integrator input of its control loop.

8. The design method for a DC optimizer in a distributed photovoltaic power station as described in any one of claims 1-7, characterized in that, S2 includes: The design objectives are determined based on the dynamic characteristics of the Boost-type DC optimizer when facing severe mismatch disturbances. The design objectives are determined based on the dynamic characteristics of the Buck-type DC optimizer when facing severe mismatch disturbances.

9. The design method for a DC optimizer in a distributed photovoltaic power station as described in claim 8, characterized in that, The design goal of the Boost-type DC optimizer is to prevent the output voltage of the DC optimizer from reversing polarity and to prevent the integrator in the control loop from saturating.

10. The design method of the DC optimizer in a distributed photovoltaic power station as described in any one of claims 1-7, characterized in that, The design goal of the Buck-type DC optimizer is to prevent the integrator in the control loop from saturating.

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