Off-grid operation control method of converter and photovoltaic system

Abstract

The invention discloses an off-grid operation control method for a converter, and the method comprises the steps: executing bus voltage loop control, taking a bus voltage reference value as a given signal, and taking an actual bus voltage as a feedback signal; the output of the bus voltage loop is subjected to amplitude limiting processing and output to a linear distribution link, and a photovoltaic voltage reference value is generated; photovoltaic voltage loop control is executed, the photovoltaic voltage reference value is a given signal, and the actual voltage of the photovoltaic array is a feedback signal; photovoltaic current loop control is executed, the smaller value in bus voltage loop output and photovoltaic voltage loop output is taken as a given signal, and the actual current of the photovoltaic array is taken as a feedback signal; generating a PWM control signal of the converter based on the output of the photovoltaic current loop; in the linear distribution link, linear power distribution is carried out based on the open-circuit voltage proportion of each path of photovoltaic array, and a photovoltaic voltage reference value is generated. According to the invention, the generation power of each path of photovoltaic array can be linearly distributed along with different loads when the multi-path photovoltaic array operates in an off-grid manner.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to an off-grid operation control method of a converter and a photovoltaic system. Background Art

[0002] In a photovoltaic hybrid energy storage inverter, when the energy storage battery is discharged or not connected, only photovoltaic power is connected to the hybrid inverter. At the same time, the grid is out of power, and pure photovoltaic power is needed to provide power for off-grid operation to maintain the power supply of the load. Generally, photovoltaic power will have multiple accesses. In the prior art, due to the uncertain relationship between the load power and the maximum power point power of each photovoltaic power, the bus voltage will fluctuate frequently. In severe cases, the bus voltage may even be undervoltage and shut down. There is also a situation where the bus voltage is pulled down, thereby triggering the bus undervoltage protection. Summary of the invention

[0003] In order to solve the deficiencies of the prior art, this application adopts the following technical solutions: In a first aspect, the present application provides an off-grid operation control method of a converter, which is applied to a photovoltaic system, wherein the photovoltaic system includes an inverter, a plurality of photovoltaic arrays and a converter, wherein the converter is arranged between the photovoltaic array and the inverter, and the control method includes: Execute bus voltage loop control, use bus voltage reference value as given signal of bus voltage loop, and use actual bus voltage as feedback signal of bus voltage loop; The output of the bus voltage loop is subjected to a limiting process and outputted to a linear distribution link to generate a photovoltaic voltage reference value for each photovoltaic array; Performing photovoltaic voltage loop control on each photovoltaic array, taking the photovoltaic voltage reference value of the Nth photovoltaic array as a given signal of the Nth photovoltaic voltage loop, and taking the actual voltage of the Nth photovoltaic array as a feedback signal of the Nth photovoltaic voltage loop; Performing photovoltaic current loop control on each photovoltaic array, taking the smaller value between the bus voltage loop output and the photovoltaic voltage loop output of the Nth photovoltaic array as the given signal of the photovoltaic current loop of the Nth photovoltaic array, and taking the actual current of the Nth photovoltaic array as the feedback signal of the photovoltaic current loop of the Nth photovoltaic array; Generate a PWM control signal for the Nth converter based on the output of the Nth photovoltaic current loop; The linear distribution link performs linear power distribution based on the open-circuit voltage ratio of each photovoltaic array to generate the photovoltaic voltage reference value of each photovoltaic array.

[0004] In summary, the off-grid operation control method of a converter provided in the present application adopts a three-loop control structure. According to the different open-circuit voltages of each photovoltaic array, the linear distribution of the power generation of each photovoltaic array when multiple photovoltaic arrays are operated off-grid is realized, and the power generation of each photovoltaic array is adjusted to better support the load, thereby reducing the occurrence of photovoltaic panel short circuit and undervoltage faults.

[0005] Furthermore, the control method further includes: A light-load operating range and a heavy-load operating range are set based on the output characteristic curve of each photovoltaic array, and a limiting range of the output of the bus voltage loop is set based on the voltage range of the light-load operating range and / or the heavy-load operating range, so that the output voltage of the photovoltaic array when operating in the light-load operating range is less than or greater than the output voltage when operating in the heavy-load operating range.

[0006] Furthermore, the control method further includes: The voltage range of the heavy-load working interval is greater than or equal to the first voltage and less than or equal to the second voltage, and the voltage range of the light-load working interval is greater than or equal to the third voltage and less than or equal to the fourth voltage; Among them, the first voltage is the lowest operating voltage allowed by the photovoltaic array, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the first voltage and the second voltage; the third voltage satisfies: on the output characteristic curve, the power corresponding to the third voltage is equal to the power corresponding to the first voltage; the fourth voltage is the maximum open-circuit voltage of the photovoltaic array.

[0007] Further, The output of the bus voltage loop is limited to be greater than or equal to the first voltage and less than or equal to the second voltage; the converter includes a control device, and the control device includes a selection module; the control method also includes: The signal of the bus voltage loop after the limiting process is used as the first round input signal of the selection module; the output of the bus voltage loop is multiplied by a preset voltage coefficient, and the deviation between the result of multiplying the output of the bus voltage loop by the preset voltage coefficient and the maximum open circuit voltage is calculated, and the deviation is used as the second round input signal of the selection module; In response to the output of the bus voltage loop being greater than or equal to the first voltage, the selection module selects the first signal to be output to the linear distribution link, In response to the output of the bus voltage loop being less than the first voltage, the selection module selects a second signal to be output to the linear distribution link.

[0008] Furthermore, the preset voltage coefficient is calculated by the following formula: ; Wherein, A represents the preset voltage coefficient, V open is the actual open circuit voltage of the photovoltaic array, V m is the voltage corresponding to the theoretical maximum power point of the photovoltaic array.

[0009] Furthermore, the control method further includes: The voltage range of the heavy-load working interval is greater than or equal to the first voltage and less than or equal to the second voltage, and the voltage range of the light-load working interval is greater than or equal to 0 and less than the first voltage; Among them, the first voltage is less than the second voltage, the second voltage is the voltage corresponding to a preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the first voltage and the second voltage; the output of the bus voltage loop is limited to be greater than 0 and less than the second voltage.

[0010] Furthermore, the control method further includes: The voltage range of the heavy-load working interval is greater than or equal to the second voltage and less than or equal to the third voltage, and the voltage range of the light-load working interval is greater than the third voltage and less than or equal to the fourth voltage; Among them, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the second voltage and the third voltage; the third voltage satisfies: on the output characteristic curve, the power corresponding to the third voltage is equal to the power corresponding to the minimum operating voltage allowed by the photovoltaic array; the fourth voltage is the maximum open-circuit voltage of the photovoltaic array.

[0011] Further, the output of the bus voltage loop is limited to be greater than 0 and less than the fifth voltage, and the fifth voltage is the difference between the maximum open-circuit voltage of the photovoltaic array and the second voltage; The control method also includes: using the maximum open-circuit voltage of the photovoltaic array, converting the limiting processing result output by the bus voltage loop to a range greater than or equal to the second voltage and less than or equal to the fourth voltage, and outputting the conversion result to the linear distribution link.

[0012] Furthermore, the open circuit voltage ratio of the photovoltaic array is expressed by the following formula: ; In the formula, Indicatesi The actual open circuit voltage of the photovoltaic array, Indicates the maximum open circuit voltage of the photovoltaic array.

[0013] In a second aspect, the present application further provides a photovoltaic system, which includes an inverter, a plurality of photovoltaic arrays and a converter, wherein the converter is arranged between the photovoltaic array and the inverter, and the photovoltaic system applies the off-grid operation control method of the converter as described above.

[0014] A photovoltaic system provided in the present application can realize linear distribution of the power generated by each photovoltaic array when multiple photovoltaic arrays are operated off-grid according to the different open-circuit voltages of each photovoltaic array, adjust the power generated by each photovoltaic array to better support the load, and reduce the occurrence of short circuit and undervoltage faults in the photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of an off-grid operation control method of a converter provided by an embodiment of the present application applied to a photovoltaic system; Figure 2 A flowchart of the steps of a method for controlling off-grid operation of a converter provided in one embodiment of the present application; Figure 3 A control flow chart of a method for controlling off-grid operation of a converter provided in an embodiment of the present application; Figure 4 A schematic diagram of the division of the light-load working range and the heavy-load working range in the off-grid operation control method of the converter provided in the first embodiment of the present application; Figure 5 For this application and Figure 4 A control flow chart of the corresponding off-grid operation control method of the converter applying the selection module; Figure 6 A schematic diagram of the division of a light-load working interval and a heavy-load working interval in the off-grid operation control method of a converter according to the second embodiment of the present application; Figure 7 For this application and Figure 6 A control flow chart of a corresponding off-grid operation control method of a converter; Figure 8 A schematic diagram of the division of a light-load working interval and a heavy-load working interval in an off-grid operation control method of a converter according to a third embodiment of the present application; Fig. 9 For this application and Figure 8 A control flow chart of a corresponding off-grid operation control method of a converter; Fig.10 A schematic diagram of an off-grid operation control method for a photovoltaic system with two photovoltaic arrays using a converter provided in an embodiment of the present application; Fig.11 A schematic diagram of the division of a light-load working interval and a heavy-load working interval in an off-grid operation control method of a converter according to a fourth embodiment of the present application; Fig.12 For this application and Fig.11 The control flow chart of the off-grid operation control method of the corresponding converter. DETAILED DESCRIPTION

[0016] The present application will be described in detail below in conjunction with the specific implementation modes shown in the accompanying drawings, but these implementation modes do not limit the present application. Structural, methodological, or functional changes made by ordinary technicians in the field based on these implementation modes are included in the protection scope of the present application.

[0017] In order to solve the deficiencies of the prior art, in the first aspect, the present application provides a method for controlling off-grid operation of a converter, which is applied to a photovoltaic system, such as Figure 1 As shown, the photovoltaic system includes an inverter, a plurality of photovoltaic arrays and a converter, and the converter is arranged between the photovoltaic array and the inverter. Figure 2 As shown, the control method includes: Step S11, executing bus voltage loop control, specifically, taking the bus voltage reference value as the given signal of the bus voltage loop, and taking the actual bus voltage as the feedback signal of the bus voltage loop; Step S12, limiting the output of the bus voltage loop and outputting it to the linear distribution link to generate a photovoltaic voltage reference value for each photovoltaic array; Step S13, performing photovoltaic voltage loop control on each photovoltaic array, specifically, taking the photovoltaic voltage reference value of the Nth photovoltaic array as a given signal of the Nth photovoltaic voltage loop, and taking the actual voltage of the Nth photovoltaic array as a feedback signal of the Nth photovoltaic voltage loop; Step S14, performing photovoltaic current loop control on each photovoltaic array, specifically, taking the smaller value between the bus voltage loop output and the photovoltaic voltage loop output of the Nth path as the given signal of the photovoltaic current loop of the Nth path, and taking the actual current of the photovoltaic array of the Nth path as the feedback signal of the photovoltaic current loop of the Nth path; Step S15, generating a PWM control signal for the Nth converter based on the output of the Nth photovoltaic current loop; Among them, the linear distribution link performs linear power distribution based on the open-circuit voltage ratio of each photovoltaic array to generate a photovoltaic voltage reference value for each photovoltaic array.

[0018] like Figure 3 As shown in Figure 1, the converter includes three loop control structures. The outermost loop is the bus voltage loop, denoted as GV bus ; The middle ring is the photovoltaic voltage ring, denoted as GV pv , Figure 3 China GV pv1 Indicates the first photovoltaic voltage loop, Figure 3 China GV pvN Represents the Nth photovoltaic voltage loop; the inner loop is the photovoltaic current loop, denoted as GI pv , Figure 3 Medium GI pv1 Represents the first photovoltaic current loop, Figure 3 Medium GI pvN Represents the Nth photovoltaic current loop; each photovoltaic array has a corresponding photovoltaic voltage loop and photovoltaic current loop.

[0019] Provide bus voltage reference value as bus voltage loop GV bus For the sake of convenience, the bus voltage loop GV bus The given signal is recorded as VBR; the actual voltage value of the bus is collected and the actual voltage value of the bus is used as the bus voltage loop GV bus For the convenience of explanation, the bus voltage loop GV bus The feedback signal is recorded as VB. Based on the given signal VBR, the bus voltage loop GV bus Calculate the error of the feedback signal VB, and then the bus voltage loop GV bus Based on the error result, a demand signal is output. For ease of explanation, the bus voltage loop GV bus The output signal is x0.

[0020] In step S12, firstly, the bus voltage loop GV bus The output signal x0 is limited so that it works within the set working range. The limiter outputs the output signal x0 after the limiting process to the linear distribution link. Based on the open circuit voltage ratio K of each photovoltaic array, the linear distribution link performs linear power distribution on each photovoltaic array. The output signal x0 after the limiting process is multiplied by the open circuit voltage ratio K to generate the photovoltaic voltage reference value of each photovoltaic array, thereby optimizing the allocated power of each photovoltaic array to support the load. Among them, the open circuit voltage ratio Kn represents the ratio of the open circuit voltage of the nth photovoltaic array to the maximum open circuit voltage of the photovoltaic system. For the convenience of explanation, the photovoltaic voltage reference value is recorded as Vpr, Figure 3 Where Vpr1 represents the photovoltaic voltage reference value of the first photovoltaic array. Figure 3 Where VprN represents the photovoltaic voltage reference value of the Nth photovoltaic array.

[0021] In step S13, the photovoltaic voltage reference value Vpr of the Nth path is used as the photovoltaic voltage loop GV pvN The given signal is used to collect the actual voltage value of the N-th photovoltaic array, and the actual voltage value of the N-th photovoltaic array is used as the voltage loop GV of the N-th photovoltaic array. pvNFor ease of explanation, the photovoltaic voltage loop GV pv The feedback signal is recorded as Vpv, Figure 3 Where Vpv1 represents the feedback signal of the first photovoltaic array. Figure 3 Where VpvN represents the feedback signal of the Nth photovoltaic array.

[0022] Based on the input given signal Vpr and feedback signal Vpv, the photovoltaic voltage loop GV pv Output regulation signal, which is related to bus voltage loop GV bus The output signal x0 is compared with the bus voltage loop GV bus With photovoltaic voltage ring GV pv The output competition between the two is taken as the photovoltaic current loop GI corresponding to the photovoltaic array. pv To facilitate explanation, the photovoltaic current loop GI pv The given signal is denoted as Ipr, Figure 3 Ipr1 represents the photovoltaic current loop GI in the first photovoltaic array pv1 The given signal, Figure 3 IprN represents the photovoltaic current loop GI in the Nth photovoltaic array. pvN of the given signal.

[0023] Collect the actual current value of the Nth photovoltaic array and use the actual current value of the Nth photovoltaic array as the Nth photovoltaic current loop GI pvN For ease of explanation, the photovoltaic current loop GI pv The feedback signal is recorded as Ipv, Figure 3 Ipv1 represents the photovoltaic current loop GI in the first photovoltaic array pv1 The feedback signal, Figure 3 IpvN represents the photovoltaic current loop GI in the Nth photovoltaic array. pvN feedback signal.

[0024] Based on the given signal Ipr and the feedback signal Ipv, the photovoltaic current loop GI pv Output regulation signal. Based on photovoltaic current loop GI pvN The output regulation signal generates the PWM control signal of the Nth converter to realize power control of multiple photovoltaic arrays.

[0025] According to the above description, the off-grid operation control method of a converter provided in the present application adopts a three-loop control structure. According to the different open-circuit voltages of each photovoltaic array, the linear distribution of the power generation of each photovoltaic array when multiple photovoltaic arrays are operated off-grid is realized, and the power generation of each photovoltaic array is adjusted to better support the load, thereby reducing the occurrence of photovoltaic panel short circuit and undervoltage faults.

[0026] As an implementation method, the open circuit voltage ratio of the photovoltaic array is expressed by the following formula: ; In the formula, represents the actual open-circuit voltage of the ith photovoltaic array, Indicates the maximum open circuit voltage of the photovoltaic array.

[0027] K i is the ratio between the actual open-circuit voltage of the ith photovoltaic array and the maximum open-circuit voltage of the photovoltaic array, K i It is used to reflect the boost ratio of the i-th photovoltaic array. In step S12, based on the open-circuit voltage ratio K of each photovoltaic array, the linear distribution link performs linear power distribution on each photovoltaic array according to the photovoltaic capacity, and the output signal x0 after the limit processing is multiplied by the open-circuit voltage ratio K to generate the photovoltaic voltage reference value of each photovoltaic array, thereby optimizing the allocated power of each photovoltaic array.

[0028] As an implementation method, the control method further includes: setting a light load working range and a heavy load working range based on the output characteristic curve of each photovoltaic array, and setting a limit range of the output of the bus voltage loop based on the voltage range of the light load working range and / or the heavy load working range, and the output voltage of the photovoltaic array when working in the light load working range is less than or greater than the output voltage when working in the heavy load working range. The following is a detailed description of embodiments 1, 2, and 3.

[0029] Embodiment 1 As an implementation, the control method further includes: the voltage range of the heavy load working interval is greater than or equal to the first voltage and less than or equal to the second voltage, and the voltage range of the light load working interval is greater than or equal to 0 and less than the first voltage; Among them, the first voltage is less than the second voltage, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the first voltage and the second voltage; the output of the bus voltage loop is limited to be greater than 0 and less than the second voltage.

[0030] like Figure 4 As shown, the voltage point Vm is the voltage corresponding to the maximum power point Pm of the photovoltaic array, and the second voltage V2 is the voltage corresponding to the preset range near the maximum power point Pm of the photovoltaic array. In the embodiment of the present application, the light load working interval is set to 0 to the first voltage V1, and the heavy load working interval is set to the first voltage V1 to the second voltage V2.

[0031] Based on the voltage range of the above light load working range and heavy load working range, Figure 5 Middle bus voltage ring GVbus The limiting range of the output signal x0 is greater than 0 and less than the second voltage V2. The light load working range and the heavy load working range are set based on the output characteristic curve of each photovoltaic array, and the linear distribution of the power generated by each photovoltaic array when multiple photovoltaic arrays are off-grid is adjusted to better support the load according to the difference in the open-circuit voltage of each photovoltaic array.

[0032] Embodiment 2 As an implementation, the control method further includes: the voltage range of the heavy load working interval is greater than or equal to the second voltage and less than or equal to the third voltage, and the voltage range of the light load working interval is greater than the third voltage and less than or equal to the fourth voltage; Among them, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the second voltage and the third voltage; the third voltage satisfies: on the output characteristic curve, the power corresponding to the third voltage is equal to the power corresponding to the minimum operating voltage allowed by the photovoltaic array; the fourth voltage is the maximum open-circuit voltage of the photovoltaic array.

[0033] like Figure 6 As shown in the figure, the power point of the photovoltaic array corresponding to the first voltage V1 is recorded as P1; the voltage Vm corresponding to the maximum power point Pm of the photovoltaic array, and the second voltage is the voltage corresponding to the preset range near the voltage Vm, and the second voltage is recorded as V2. Taking the voltage Vm corresponding to the maximum power point Pm of the photovoltaic array as the boundary, Figure 6 The output characteristic curve is divided into a left half and a right half, the third voltage Vx is the voltage corresponding to the power P1 in the right half of the output characteristic curve, and the voltage Vm corresponding to the maximum power point Pm of the photovoltaic array is between the second voltage V2 and the third voltage Vx. The fourth voltage is the maximum open-circuit voltage of the photovoltaic array, and the fourth voltage is recorded as Vmax. In the embodiment of the present application, the heavy-load working interval is set to the second voltage V2 to the third voltage Vx, and the light-load working interval is set to the third voltage Vx to the fourth voltage Vmax.

[0034] Furthermore, as an implementation method, the output of the bus voltage loop is limited to be greater than 0 and less than a fifth voltage, and the fifth voltage is the difference between the actual open-circuit voltage of the photovoltaic array and the second voltage; the control method also includes: using the maximum open-circuit voltage of the photovoltaic array, converting the limiting processing result of the bus voltage loop output to a range greater than or equal to the second voltage and less than or equal to the fourth voltage, and outputting the conversion result to the linear distribution link.

[0035] like Figure 7 As shown, based on the heavy load working interval being set to the second voltage V2 to the third voltage Vx, and the light load working interval being set to the third voltage Vx to the fourth voltage Vmax, Figure 7 Middle bus voltage ring GV bus The limiting range of the output signal x0 is greater than 0 and less than the fifth voltage, and the fifth voltage is the difference between the fourth voltage Vmax of the photovoltaic array and the second voltage V2.

[0036] The maximum open-circuit voltage of each photovoltaic array is Vmax, and the bus voltage loop GV after limiting is bus The output signal x0 is subtracted from the maximum open-circuit voltage Vmax of the photovoltaic array to convert the bus voltage loop GV bus The output limit processing result is converted to a range greater than or equal to the second voltage V2 and less than or equal to the fourth voltage Vmax, and the conversion result is output to the linear distribution link. Through the above settings, when the bus voltage is raised and the photovoltaic array operating voltage is greater than the inverter rectifier voltage, the power of each photovoltaic array can be linearly distributed to adjust the load of each photovoltaic array; and the light load working range of the photovoltaic array is designed in the right half of the output characteristic curve of the photovoltaic array, reducing the occurrence of photovoltaic array undervoltage and photovoltaic array short circuit, and improving the reliability of the power circuit operation.

[0037] It should be noted that the actual open circuit voltage of the photovoltaic array V open Greater than the inverter's allowable open circuit voltage V max When V open =V max , if it is less than, record V open The actual open circuit voltage Vopen between the photovoltaic arrays is equal or unequal.

[0038] Embodiment 3 As an implementation, the control method further includes: the voltage range of the heavy load working interval is greater than or equal to the first voltage and less than or equal to the second voltage, and the voltage range of the light load working interval is greater than or equal to the third voltage and less than or equal to the fourth voltage; Among them, the first voltage is the lowest operating voltage allowed by the photovoltaic array, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the first voltage and the second voltage; the third voltage satisfies: on the output characteristic curve, the power corresponding to the third voltage is equal to the power corresponding to the first voltage; the fourth voltage is the maximum open-circuit voltage of the photovoltaic array.

[0039] like Figure 8As shown, in the embodiment of the present application, the lowest operating voltage allowed by the inverter is recorded as the first voltage V1, and the power point corresponding to the first voltage V1 is recorded as P1; the voltage corresponding to the maximum power point Pm of the photovoltaic array is Vm, and the second voltage is the voltage corresponding to the preset range near the voltage Vm, and the voltage Vm is between the first voltage V1 and the second voltage, and the second voltage is recorded as V2. Taking the voltage Vm corresponding to the maximum power point Pm of the photovoltaic array as the boundary, Figure 8 The PV curve diagram is divided into a left half and a right half, the third voltage is the voltage corresponding to the power P1 in the right half of the output characteristic curve, and the third voltage is recorded as Vx. The fourth voltage is the maximum open circuit voltage of the photovoltaic array, and is recorded as Vmax.

[0040] The light-load working range and heavy-load working range are set based on the output characteristic curve of each photovoltaic array. The heavy-load working range of the photovoltaic array is designed to be in the left half of the output characteristic curve of the photovoltaic array. When the photovoltaic array is in the heavy-load working range and the photovoltaic array operating voltage is greater than the inverter rectifier voltage, the bus operating voltage is reduced to reduce the stress of the switch tube and reduce the switching loss; the light-load working range of the photovoltaic array is designed to be in the right half of the output characteristic curve of the photovoltaic array to reduce the occurrence of photovoltaic array undervoltage and photovoltaic array short circuit, thereby improving the reliability of the power circuit operation.

[0041] As an implementation manner, the control method further includes: the output of the bus voltage loop is limited to be greater than or equal to the first voltage and less than or equal to the second voltage.

[0042] As an optional implementation, the converter includes a control device, and the control device includes a selection module. The control method also includes: using the signal of the bus voltage loop after the limit processing as the first input of the selection module; multiplying the output of the bus voltage loop by a preset voltage coefficient, calculating the deviation between the result of multiplying the output of the bus voltage loop by the preset voltage coefficient and the maximum open circuit voltage, and using the deviation as the second input signal of the selection module.

[0043] In response to the output of the bus voltage loop being greater than or equal to the first voltage, the selection module selects the first signal to be output to the linear distribution link; in response to the output of the bus voltage loop being less than the first voltage, the selection module selects the second signal to be output to the linear distribution link.

[0044] like Fig. 9 As shown, the limiting range of the limiter is set to the first voltage V1 to the second voltage V2, and the bus voltage loop GV bus The output signal x0 is limited to be greater than or equal to the first voltage V1 and less than or equal to the second voltage V2, and the output signal x0 after the limiting process is used as the first input of the selection module. busThe output signal x0 is multiplied by a preset voltage coefficient A of the photovoltaic array, and the deviation between the result of multiplying the output of the bus voltage loop by a preset voltage coefficient and the maximum open circuit voltage is calculated. In the embodiment of the present application, the maximum open circuit voltage Vmax is subtracted from the result of multiplying the output of the bus voltage loop by a preset voltage coefficient to obtain the deviation, and the deviation is used as the second input signal of the selection module.

[0045] The selection module can be configured to determine the output of the two-choice switch according to the switching condition. When the signal x0 is greater than or equal to the first voltage V1, the two-choice switch is switched to "1", and the selection module outputs the output signal x0 after the limiting process; when the output signal x0 is less than the first voltage V1, the two-choice switch is switched to "0", and the selection module outputs the bus voltage loop GV bus The output signal x0 of the selection module is multiplied by the preset voltage coefficient A of the photovoltaic array. The output of the selection module is multiplied by the open circuit voltage ratio K of each photovoltaic array to generate the photovoltaic voltage loop GV pv The given signal is linearly distributed according to the power size of each photovoltaic array.

[0046] Further, as an implementation method, the preset voltage coefficient is calculated by the following formula: ; Where A represents the preset voltage coefficient, Vopen is the actual open-circuit voltage of the photovoltaic array, and Vm is the voltage corresponding to the theoretical maximum power point of the photovoltaic array.

[0047] Bus voltage ring GV bus The output signal x0 of the bus voltage loop GV is multiplied by the preset voltage coefficient A, and the multiplication result is between 0 and the first voltage V1. The maximum open circuit voltage Vmax is subtracted from the multiplication result, and the difference result is between the third voltage Vx and the actual open circuit voltage Vopen, thereby bus The output signal x0 is converted to the light load operating range.

[0048] For example, based on the above description, Fig.10 As shown in the figure, a photovoltaic system is set up. The photovoltaic system has two photovoltaic arrays. The maximum current of each photovoltaic array is 10A, and the maximum open circuit voltage Vmax of each photovoltaic array is 1000V. The actual open circuit voltage Vopen of the first photovoltaic array is 800V, and the actual open circuit voltage Vopen of the second photovoltaic array is 500V. The light load and heavy load working ranges are divided as follows Fig.11 As shown in FIG. 1 , the heavy load working range is divided into 200V to 850V, the light load working range is divided into 956V to 1000V, and the voltage corresponding to the maximum power point of the photovoltaic array is 820V. The off-grid operation control method of the photovoltaic system converter is as follows: Fig.12 As shown. According to the above preset voltage system calculation formula, the preset voltage coefficient A is 0.21951; the limiter processing range is 200V to 850V; according to the above open circuit voltage ratio calculation formula, according to the maximum photovoltaic array open circuit voltage 1000V that the inverter can receive, the open circuit voltage ratio of the first photovoltaic array is 0.8, and the open circuit voltage ratio of the second photovoltaic array is 0.5. The off-grid operation control process of the photovoltaic system converter is consistent with the above description and will not be repeated here.

[0049] According to the above description, the off-grid operation control method of a converter provided in the present application adopts a three-loop control structure, and according to the different open-circuit voltages of each photovoltaic array, realizes the linear distribution of the power generation of each photovoltaic array when multiple photovoltaic arrays are off-grid, adjusts the power generation of each photovoltaic array to better support the load, and reduces the occurrence of photovoltaic panel short circuit and undervoltage faults; and, based on the output characteristic curve of each photovoltaic array, sets the light load working range and the heavy load working range, and designs the heavy load working range of the photovoltaic array in the left half of the output characteristic curve of the photovoltaic array. When the photovoltaic array is in the heavy load working range and the photovoltaic array operating voltage is greater than the inverter rectifier voltage, the bus working voltage is reduced to reduce the stress of the switch tube and reduce the switching loss; the light load working range of the photovoltaic array is designed in the right half of the output characteristic curve of the photovoltaic array to reduce the occurrence of photovoltaic array undervoltage and photovoltaic array short circuit, and improve the reliability of the power circuit operation.

[0050] On the second aspect, the present application also provides a photovoltaic system, which includes an inverter, a plurality of photovoltaic arrays and a converter. The converter is arranged between the photovoltaic array and the inverter. The photovoltaic system applies the off-grid operation control method of the converter in the above description, which can realize linear distribution of the power generated by each photovoltaic array with loads of different sizes when multiple photovoltaic arrays are off-grid, thereby improving the reliability of the power circuit operation.

[0051] It will be appreciated that the word "exemplary" as used herein means "serving as an example, instance, or illustration". Any embodiment described as "exemplary" is not necessarily preferred or superior to other embodiments and / or does not exclude the combination of features of other embodiments. It will be appreciated that certain features of the present application described in the context of separate embodiments for the sake of clarity may also be provided in a single embodiment by combination. Conversely, various features of the present application described in the context of a single embodiment for the sake of clarity may also be provided individually or in any suitable combination or as any other described embodiment of the present application.

[0052] The above disclosure is only the preferred embodiment of the present application, but it is not intended to limit the scope of rights of the present application. A person of ordinary skill in the art can understand that without departing from the spirit and scope of the present application and the appended claims, changes, modifications, substitutions, combinations, and simplifications should all be equivalent replacement methods and still fall within the scope of the invention.

Claims

1. A method for controlling off-grid operation of a converter, applied to a photovoltaic system, wherein the photovoltaic system comprises an inverter, a plurality of photovoltaic arrays and a converter, wherein the converter is arranged between the photovoltaic array and the inverter, and wherein: The control method comprises: Execute bus voltage loop control, use bus voltage reference value as given signal of bus voltage loop, and use actual bus voltage as feedback signal of bus voltage loop; The output of the bus voltage loop is subjected to a limiting process and outputted to a linear distribution link to generate a photovoltaic voltage reference value for each photovoltaic array; Performing photovoltaic voltage loop control on each photovoltaic array, taking the photovoltaic voltage reference value of the Nth photovoltaic array as a given signal of the Nth photovoltaic voltage loop, and taking the actual voltage of the Nth photovoltaic array as a feedback signal of the Nth photovoltaic voltage loop; Performing photovoltaic current loop control on each photovoltaic array, taking the smaller value between the bus voltage loop output and the photovoltaic voltage loop output of the Nth photovoltaic array as the given signal of the photovoltaic current loop of the Nth photovoltaic array, and taking the actual current of the Nth photovoltaic array as the feedback signal of the photovoltaic current loop of the Nth photovoltaic array; Generate a PWM control signal for the Nth converter based on the output of the Nth photovoltaic current loop; The linear distribution link performs linear power distribution based on the open-circuit voltage ratio of each photovoltaic array to generate the photovoltaic voltage reference value of each photovoltaic array.

2. The off-grid operation control method of the converter according to claim 1, characterized in that: The control method further comprises: A light-load operating range and a heavy-load operating range are set based on the output characteristic curve of each photovoltaic array, and a limiting range of the output of the bus voltage loop is set based on the voltage range of the light-load operating range and / or the heavy-load operating range, so that the output voltage of the photovoltaic array when operating in the light-load operating range is less than or greater than the output voltage when operating in the heavy-load operating range.

3. The off-grid operation control method of the converter according to claim 2, characterized in that: The control method further comprises: The voltage range of the heavy-load working interval is greater than or equal to the first voltage and less than or equal to the second voltage, and the voltage range of the light-load working interval is greater than or equal to the third voltage and less than or equal to the fourth voltage; Among them, the first voltage is the lowest operating voltage allowed by the photovoltaic array, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the first voltage and the second voltage; the third voltage satisfies: on the output characteristic curve, the power corresponding to the third voltage is equal to the power corresponding to the first voltage; the fourth voltage is the maximum open-circuit voltage of the photovoltaic array.

4. The off-grid operation control method of the converter according to claim 3, characterized in that: The output of the bus voltage loop is limited to be greater than or equal to the first voltage and less than or equal to the second voltage; the converter includes a control device, and the control device includes a selection module; The control method further comprises: The signal of the bus voltage loop after the limiting process is used as the first input of the selection module; the output of the bus voltage loop is multiplied by a preset voltage coefficient, and the deviation between the result of multiplying the output of the bus voltage loop by the preset voltage coefficient and the maximum open circuit voltage is calculated, and the deviation is used as the second input signal of the selection module; In response to the output of the bus voltage loop being greater than or equal to the first voltage, the selection module selects a first signal to be output to the linear distribution link, In response to the output of the bus voltage loop being less than the first voltage, the selection module selects a second signal to be output to the linear distribution link.

5. The off-grid operation control method of the converter according to claim 4, characterized in that: The preset voltage coefficient is calculated by the following formula: ； In the formula, A represents the preset voltage coefficient, Vopen is the actual open-circuit voltage of the photovoltaic array, and Vm is the voltage corresponding to the theoretical maximum power point of the photovoltaic array.

6. The off-grid operation control method of the converter according to claim 2, characterized in that: The control method further comprises: The voltage range of the heavy-load working interval is greater than or equal to the first voltage and less than or equal to the second voltage, and the voltage range of the light-load working interval is greater than or equal to 0 and less than the first voltage; Among them, the first voltage is less than the second voltage, the second voltage is the voltage corresponding to a preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the first voltage and the second voltage; the output of the bus voltage loop is limited to be greater than 0 and less than the second voltage.

7. The off-grid operation control method of the converter according to claim 2, characterized in that: The control method further comprises: The voltage range of the heavy-load working interval is greater than or equal to the second voltage and less than or equal to the third voltage, and the voltage range of the light-load working interval is greater than the third voltage and less than or equal to the fourth voltage; Among them, the second voltage is the voltage corresponding to the preset range near the maximum power point of the photovoltaic array, and the voltage corresponding to the maximum power point of the photovoltaic array is between the second voltage and the third voltage; the third voltage satisfies: on the output characteristic curve, the power corresponding to the third voltage is equal to the power corresponding to the minimum operating voltage allowed by the photovoltaic array; the fourth voltage is the maximum open-circuit voltage of the photovoltaic array.

8. The off-grid operation control method of the converter according to claim 7, characterized in that: The output of the bus voltage loop is limited to be greater than 0 and less than the fifth voltage, and the fifth voltage is the difference between the maximum open-circuit voltage of the photovoltaic array and the second voltage; The control method also includes: using the maximum open-circuit voltage of the photovoltaic array, converting the limiting processing result output by the bus voltage loop to a range greater than or equal to the second voltage and less than or equal to the fourth voltage, and outputting the conversion result to the linear distribution link.

9. The off-grid operation control method of the converter according to claim 1, characterized in that: The open circuit voltage ratio of the photovoltaic array is expressed by the following formula: ； In the formula, represents the actual open-circuit voltage of the ith photovoltaic array, Indicates the maximum open circuit voltage of the photovoltaic array.

10. A photovoltaic system, comprising an inverter, a plurality of photovoltaic arrays and a converter, wherein the converter is arranged between the photovoltaic array and the inverter, characterized in that: The photovoltaic system applies the off-grid operation control method of the converter according to any one of claims 1 to 9.

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