Photovoltaic inverter and grid voltage active support device

Abstract

The application is suitable for the field of new energy power generation technology, and provides a photovoltaic inverter and a power grid voltage active support device. The photovoltaic inverter comprises: a Boost type DC / DC converter, an inverter and a filter connected in sequence. The other end of the Boost type DC / DC converter is used for being connected with a photovoltaic array, and the other end of the filter is used for being connected with a power grid and a load. The Boost type DC / DC converter is used for outputting the photovoltaic output power output by the photovoltaic array according to preset power control. The inverter is used for inverting the direct-current voltage generated by the photovoltaic array into alternating-current voltage, and keeping the direct-current side voltage in the inverter stable. The filter is used for filtering out the spur in the alternating-current voltage output by the inverter, and stabilizing the alternating-current voltage sent to the power grid and the load. The application can realize more stable active support for the power grid voltage when the power grid voltage fluctuates.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy power generation, and particularly relates to a photovoltaic inverter and a grid voltage active support device. BACKGROUND

[0002] New energy power sources represented by photovoltaic and wind power have the characteristics of volatility, intermittence and randomness, and new energy equipment does not have the primary frequency modulation capability of traditional power supply equipment. When new energy equipment is connected to a power grid in a large scale, it will have a great impact on the operation of the distribution network. Therefore, it is necessary to study the operation control method of new energy connected to the power grid, fully utilize the flexible and controllable characteristics of power electronic devices, realize the active support of distributed energy to the distribution network, ensure the stable operation of the distribution network, improve the power quality, and improve the utilization rate of new energy.

[0003] Traditional photovoltaic inverters usually change the power instruction of the inverter based on a linear active / voltage control curve to provide voltage support, and the economy and support effect are poor. SUMMARY

[0004] Embodiments of the application provide a photovoltaic inverter and a grid voltage active support device to realize more stable active support of the grid voltage.

[0005] The application is achieved by the following technical solutions:

[0006] In a first aspect, the embodiments of the application provide a photovoltaic inverter, comprising: a Boost type DC / DC converter, an inverter and a filter connected in sequence; the other end of the Boost type DC / DC converter is used to be connected with a photovoltaic array, and the other end of the filter is used to be connected with a power grid and a load.

[0007] The Boost type DC / DC converter is used to output the photovoltaic output power output by the photovoltaic array according to a preset power control; the inverter is used to invert the direct current voltage generated by the photovoltaic array into alternating current voltage, and keep the direct current voltage in the inverter stable; and the filter is used to filter out the spur in the alternating current voltage output by the inverter, and stabilize the alternating current voltage sent to the power grid and the load.

[0008] In combination with the first aspect, in some possible implementation manners, the Boost type DC / DC converter comprises: a first capacitor, a first inductor, a first diode and a first triode unit, wherein the first triode unit comprises a first triode and a second diode.

[0009] The positive electrode of the first triode unit is connected to one end of the cathode of the second diode and the collector of the first triode, and the negative electrode of the first triode unit is connected to one end of the anode of the second diode and the emitter of the first triode; the first end of the first capacitor is connected to the anode of the photovoltaic array, the second end of the first capacitor is connected to the cathode of the photovoltaic array, the first end of the first inductor is connected to the anode of the photovoltaic array, the second end of the first inductor is connected to the anode of the first diode, the second end of the first inductor is connected to the positive electrode of the first triode unit, and the negative electrode of the first triode unit is connected to the cathode of the photovoltaic array.

[0010] In combination with the first aspect, in some possible implementation manners, the inverter comprises: a second capacitor, a second triode unit, a third triode unit, a fourth triode unit, a fifth triode unit, a sixth triode unit, and a seventh triode unit, wherein the internal structures and connection modes of the second triode unit, the third triode unit, the fourth triode unit, the fifth triode unit, the sixth triode unit, and the seventh triode unit are the same as those of the first triode unit.

[0011] The first end of the second capacitor is connected to the cathode of the first diode, the positive electrode of the second triode unit, the positive electrode of the third triode unit, and the positive electrode of the fourth triode unit, the second end of the second capacitor is connected to the cathode of the photovoltaic array, the negative electrode of the fifth triode unit, the negative electrode of the sixth triode unit, and the negative electrode of the seventh triode unit, the negative electrode of the second triode unit is connected to the positive electrode of the fifth triode unit, the negative electrode of the third triode unit is connected to the positive electrode of the sixth triode unit, and the negative electrode of the fourth triode unit is connected to the positive electrode of the seventh triode unit.

[0012] In combination with the first aspect, in some possible implementation manners, the filter comprises: a second inductor, a third inductor, a fourth inductor, a fifth inductor, a sixth inductor, a seventh inductor, a third capacitor, a fourth capacitor, a fifth capacitor, a first resistor, a second resistor, and a third resistor.

[0013] The first end of the second inductor is connected to the negative electrode of the second triode unit, the second end of the second inductor is connected to the first end of the third inductor, the second end of the third inductor is connected to the power grid and the load, the first end of the fourth inductor is connected to the negative electrode of the third triode unit, the second end of the fourth inductor is connected to the first end of the fifth inductor, the second end of the fifth inductor is connected to the power grid and the load, the first end of the sixth inductor is connected to the negative electrode of the fourth triode unit, the second end of the sixth inductor is connected to the first end of the seventh inductor, and the second end of the seventh inductor is connected to the power grid and the load.

[0014] The first end of the first resistor is connected with the second end of the second inductor, the second end of the first resistor is connected with the first end of the third capacitor, the second end of the third capacitor is grounded, the first end of the second resistor is connected with the second end of the fourth inductor, the second end of the second resistor is connected with the first end of the fourth capacitor, the second end of the fourth capacitor is grounded, the first end of the third resistor is connected with the second end of the sixth inductor, the second end of the third resistor is connected with the first end of the fifth capacitor, and the second end of the fifth capacitor is grounded.

[0015] With reference to the first aspect, in some possible implementation manners, the photovoltaic inverter further includes a segmented active voltage control unit; the segmented active voltage control unit includes: a first abc / dq conversion module and a power instruction calculation module connected in sequence.

[0016] The first abc / dq conversion module is configured to convert three-phase output voltage of the inverter into voltage values in a dq coordinate system; and the power instruction calculation module is configured to obtain an instruction value of photovoltaic output power based on the voltage values of the inverter in the dq coordinate system.

[0017] With reference to the first aspect, in some possible implementation manners, the photovoltaic inverter further includes a first control module, and the first control module includes: a photovoltaic voltage instruction calculation module, a photovoltaic voltage outer loop control module and a photovoltaic current inner loop control module connected in sequence.

[0018] The photovoltaic voltage instruction calculation module is configured to obtain maximum power point information of a photovoltaic array, construct a linear approximation photovoltaic characteristic curve based on the maximum power point information, and obtain a photovoltaic port voltage instruction value of an instruction value of photovoltaic output power based on the linear approximation curve; the photovoltaic voltage outer loop control module is configured to generate an instruction value of the current inner loop control module based on the photovoltaic port voltage instruction value; and the photovoltaic current inner loop control module is configured to generate a Boost modulation signal to control photovoltaic output power to be output based on the instruction value of the current inner loop control module.

[0019] With reference to the first aspect, in some possible implementation manners, the photovoltaic inverter further includes a second control module, and the second control module includes: a second abc / dq conversion module, an inverter current control module and a dq / abc conversion module connected in sequence, and the second control module further includes a direct-current voltage control module connected with the other end of the inverter current control module.

[0020] The second abc / dq conversion module is used to convert the three-phase output current of the inverter into current values ​​in the dq coordinate system; the DC voltage control module is used to generate the d-axis command value of the inverter output current based on the DC side voltage of the inverter; the inverter current control module is used to generate the inverter modulation signal based on the inverter current value in the dq coordinate system, the d-axis command value of the inverter output current, and the q-axis command value of the inverter output current; the dq / abc conversion module is used to convert the modulation amounts of the d-axis and q-axis in the inverter modulation signal into the modulation amounts of the three-phase voltage to maintain the stability of the DC side voltage.

[0021] In conjunction with the first aspect, among some possible implementations, the expression for the linear approximation of the photovoltaic characteristic curve is as follows: Among them, P pv k represents the output power of the photovoltaic module. pv P is the slope of the linear approximation photovoltaic characteristic curve. mppt U represents the maximum output power of the photovoltaic module. mppt U is the output voltage of the photovoltaic module corresponding to the maximum output power point. pv This refers to the output voltage of the photovoltaic module.

[0022] In conjunction with the first aspect, in some possible implementations, the expression for the photovoltaic port voltage command value is as follows: Among them, P pv_ref k is the output power command value of the photovoltaic inverter. pv U is the slope of the linear approximation photovoltaic characteristic curve. pv_ref This is the photovoltaic port voltage command value for the Boost DC / DC converter.

[0023] Secondly, embodiments of this application provide a grid voltage active support device, including the photovoltaic inverter described in any one of the first aspects.

[0024] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0025] The beneficial effects of the embodiments of this application compared with the prior art are:

[0026] This application uses a Boost-type DC / DC converter, an inverter, and a filter connected in sequence to convert the fluctuating, intermittent, and random voltage generated by the photovoltaic array into a stable AC voltage that can be connected to the power grid. This ensures the stable operation of the distribution network, improves power quality, and increases the utilization rate of new energy sources, thus achieving more stable active support for the grid voltage.

[0027] It should be understood that the above general description and the following detailed description are only exemplary and explanatory and are not restrictive of the present specification. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] Figure 1 is a schematic diagram of the photovoltaic inverter provided by an embodiment of the present application in grid-connected operation;

[0030] Figure 2 is a schematic diagram of the segmented active / voltage control unit, the first control module and the second control module provided by an embodiment of the present application;

[0031] Figure 3 is a segmented active / voltage control curve provided by an embodiment of the present application;

[0032] Figure 4 is a linear approximation photovoltaic characteristic curve provided by an embodiment of the present application;

[0033] Figure 5 is an active / voltage control block diagram of the Boost type DC / DC converter provided by an embodiment of the present application;

[0034] Figure 6 is a direct-current voltage stabilizing current control block diagram of the inverter provided by an embodiment of the present application;

[0035] Figure 7 is an output power waveform diagram of the photovoltaic inverter using the traditional linear active / voltage control curve when the grid voltage fluctuates, provided by an embodiment of the present application;

[0036] Figure 8 is a grid-connected point voltage and current waveform diagram of the photovoltaic inverter using the traditional linear active / voltage control curve, provided by an embodiment of the present application;

[0037] Figure 9 is an output power waveform diagram of the photovoltaic inverter when the grid voltage is greater than the rated value, provided by an embodiment of the present application;

[0038] Figure 10 is a grid-connected point voltage and current waveform diagram of the photovoltaic inverter when the grid voltage is greater than the rated value, provided by an embodiment of the present application;

[0039] Figure 11is a power waveform diagram of the photovoltaic inverter output when the grid voltage is less than the rated value, provided by an embodiment of the present application;

[0040] Figure 12 is a grid-connected point voltage and current waveform diagram of the photovoltaic inverter when the grid voltage is less than the rated value, provided by an embodiment of the present application. DETAILED DESCRIPTION

[0041] In the following description, for the purposes of explanation and not limitation, specific details are set forth, such as particular system configurations, techniques, etc., in order to provide a thorough understanding of the embodiments of the application. However, it will be apparent to those skilled in the art that the application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the application with unnecessary detail.

[0042] It should be understood that the term "comprises" when used in this specification and the appended claims, specifies the presence of stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0043] It should also be understood that the term "and / or" when used in this specification and the appended claims, means any one or more of the associated listed items can be present, and includes multiples of any one or more of the associated listed items.

[0044] As used in this specification and the appended claims, the term "if" can be interpreted as meaning "when," or "once," or "in response to determining," or "in response to detecting," depending on the context. Similarly, the phrase "if it is determined" or "if [a described condition or event] is detected" can be interpreted as meaning "once it is determined" or "in response to determining" or "once [the described condition or event] is detected" or "in response to detecting [the described condition or event]," depending on the context.

[0045] In addition, in the description and the appended claims of the application, the terms "first", "second", "third", etc. are used only to distinguish descriptions, and cannot be understood as indicating or implying relative importance.

[0046] Reference within the specification of this application to "one embodiment" or "some embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," or other similar phrases in the specification are not necessarily all referring to the same embodiment, but are meant to include one or more embodiments of the application, unless otherwise indicated by the context.

[0047] Figure 1 is a schematic diagram of a photovoltaic inverter provided by an embodiment of the application in grid-connected operation, referring to Figure 2 , the detailed description of the photovoltaic inverter is as follows:

[0048] The photovoltaic inverter comprises a Boost-type DC / DC converter, an inverter and a filter connected in sequence; the other end of the Boost-type DC / DC converter is used for connecting with a photovoltaic array, and the other end of the filter is used for connecting with a power grid and a load.

[0049] The Boost-type DC / DC converter is used for outputting according to a preset power control photovoltaic output power output by the photovoltaic array; the inverter is used for inverting a direct current voltage generated by the photovoltaic array into an alternating current voltage and keeping the direct current side voltage in the inverter stable; and the filter is used for filtering out a spur in the alternating current voltage output by the inverter, and stabilizing the alternating current voltage sent to the power grid and the load.

[0050] Exemplarily, the Boost-type DC / DC converter comprises a first capacitor C1, a first inductor L1, a first diode B1 and a first triode unit A1, wherein the first triode unit A1 comprises a first triode M1 and a second diode B2.

[0051] The positive pole of the first triode unit A1 is connected to one end of the cathode of the second diode B2 and the collector of the first triode M1, and the negative pole of the first triode unit A1 is connected to one end of the anode of the second diode B2 and the emitter of the first triode M1; the first end of the first capacitor C1 is connected with the anode of the photovoltaic array, the second end of the first capacitor C2 is connected with the cathode of the photovoltaic array, the first end of the first inductor L1 is connected with the anode of the photovoltaic array, the second end of the first inductor L2 is connected with the anode of the first diode B1, the second end of the first inductor L1 is connected with the positive pole of the first triode unit A1, and the negative pole of the first triode unit A2 is connected with the cathode of the photovoltaic array.

[0052] The inverter comprises a second capacitor C2, a second triode unit A2, a third triode unit A3, a fourth triode unit A4, a fifth triode unit A5, a sixth triode unit A6 and a seventh triode unit A7. The internal structures and connection modes of the second triode unit A2, the third triode unit A3, the fourth triode unit A4, the fifth triode unit A5, the sixth triode unit A6 and the seventh triode unit A7 are the same as those of the first triode unit A1.

[0053] The first end of the second capacitor C2 is connected with the cathode B1 of the first diode, the anode A2 of the second triode unit, the anode of the third triode unit A3 and the anode of the fourth triode unit A4, the second end of the second capacitor C2 is connected with the cathode of the photovoltaic array, the cathode of the fifth triode unit A5, the cathode of the sixth triode unit A6 and the cathode of the seventh triode unit A7, the anode of the second triode unit A2 is connected with the anode of the fifth triode unit A5, the cathode of the third triode unit A3 is connected with the anode of the sixth triode unit A6, and the cathode of the fourth triode unit A4 is connected with the anode of the seventh triode unit A7.

[0054] Specifically, the DC side voltage of the inverter is the voltage between the two sides of the second capacitor C2.

[0055] The filter comprises a second inductor L2, a third inductor L3, a fourth inductor L4, a fifth inductor L5, a sixth inductor L6, a seventh inductor L7, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a first resistor R1, a second resistor R2 and a third resistor R3.

[0056] The first end of the second inductor L2 is connected with the cathode of the second triode unit A2, the second end of the second inductor L2 is connected with the first end of the third inductor L3, the second end of the third inductor L3 is connected with the power grid and the load, the first end of the fourth inductor L4 is connected with the cathode of the third triode unit A3, the second end of the fourth inductor L4 is connected with the first end of the fifth inductor L5, the second end of the fifth inductor L5 is connected with the power grid and the load, the first end of the sixth inductor L6 is connected with the cathode of the fourth triode unit A4, the second end of the sixth inductor L6 is connected with the first end of the seventh inductor L7, and the second end of the seventh inductor L7 is connected with the power grid and the load.

[0057] The first end of the first resistor R1 is connected with the second end of the second inductor L2, the second end of the first resistor R1 is connected with the first end of the third capacitor C3, the second end of the third capacitor C3 is grounded, the first end of the second resistor R2 is connected with the second end of the fourth inductor L4, the second end of the second resistor R2 is connected with the first end of the fourth capacitor C4, the second end of the fourth capacitor C4 is grounded, the first end of the third resistor R3 is connected with the second end of the sixth inductor L6, the second end of the third resistor R3 is connected with the first end of the fifth capacitor C5, and the second end of the fifth capacitor C5 is grounded.

[0058] The photovoltaic inverter further comprises a segmented active / voltage control unit, as shown in Figure 2 The segmented active / voltage control unit comprises a first abc / dq conversion module and a power instruction calculation module connected in sequence.

[0059] The first abc / dq conversion module is configured to convert the three-phase output voltage of the inverter into a voltage value in the dq coordinate system.

[0060] The conversion expression is as follows: Wherein, u a , u b , and u c are the three-phase output voltage of the inverter, u d and u q are the values of the three-phase voltage in the dq synchronous rotating coordinate system, and θ1 is the included angle between the d-axis and the phase reference axis.

[0061] The power instruction calculation module is configured to obtain the instruction value of the photovoltaic output power based on the voltage value of the inverter in the dq coordinate system.

[0062] The expression of the instruction value of the photovoltaic output power is as follows: P pv_ref =P pv_n -k p (U d -U d_n ), wherein P pv_n is the rated output power of the photovoltaic inverter, P pv_ref is the output power instruction value of the photovoltaic inverter, k p is the active / voltage control droop coefficient, U d is the value of the three-phase output voltage of the inverter on the d-axis, and U d_n is the rated d-axis voltage of the inverter.

[0063] Specifically, the active / voltage control droop coefficient k p changes with U d , as shown in Figure 3 When the voltage is higher than 1.05U d , the photovoltaic active output is reduced, and the droop coefficient kp increasing; when the voltage is lower than 0.95U d , the photovoltaic maintains the maximum power output.

[0064] The photovoltaic inverter further comprises a first control module, as shown in the figure. Figure 2 The first control module comprises, in sequence, a photovoltaic voltage instruction calculation module, a photovoltaic voltage outer loop control module, and a photovoltaic current inner loop control module.

[0065] The photovoltaic voltage instruction calculation module is configured to acquire maximum power point information of the photovoltaic module, i.e. power and voltage information of the MPPT point, construct a linear approximation photovoltaic characteristic curve based on the maximum power point information, and obtain a photovoltaic port voltage instruction value corresponding to an instruction value of the photovoltaic output power based on the linear approximation curve. Figure 4

[0066] The expression of the linear approximation photovoltaic characteristic curve is as follows: wherein P pv is the output power of the photovoltaic module, k pv is the slope of the linear approximation photovoltaic characteristic curve, P m is the maximum output power of the photovoltaic module, U m is the output voltage of the photovoltaic module corresponding to the maximum output power point of the photovoltaic module, and U pv is the output voltage of the photovoltaic module.

[0067] The expression of the photovoltaic port voltage instruction value is as follows: wherein P pv_ref is the output power instruction value of the photovoltaic inverter, k pv is the slope of the linear approximation photovoltaic characteristic curve, and U pv_ref is the photovoltaic port voltage instruction value of the Boost type DC / DC converter.

[0068] The photovoltaic voltage outer loop control module is configured to generate an instruction value of the current inner loop control module based on the photovoltaic port voltage instruction value.

[0069] The expression of the instruction value of the current inner loop control module is as follows: wherein k p_pvu is the value of the proportional controller of the Boost voltage outer loop PI regulator, k i_pvu is the value of the integral controller of the Boost voltage outer loop PI regulator, and s is the parameter value of the PI regulator.

[0070] The photovoltaic current inner loop control module is configured to generate a Boost modulation signal based on the instruction value of the current inner loop control module to control the photovoltaic output power for output.

[0071] ​For example, the calculation formula of the segmented active / voltage control unit and the first control module is shown in the following formula (1) and formula (2). Figure 5 The active / voltage control block diagram of the Boost type DC / DC converter shown in the figure can obtain a Boost modulation signal, and the expression of the Boost modulation signal is as follows: Wherein, m boost is the modulation signal of the Boost converter, k p_pvi is the value of the proportional controller of the Boost current inner loop PI regulator, k i_pvi is the value of the integral controller of the Boost current inner loop PI regulator, i pv is the output port current of the photovoltaic module, and s is the parameter value of the PI regulator.

[0072] For example, the photovoltaic inverter further comprises a second control module, as shown in the following formula (3) and formula (4). Figure 2 The second control module comprises, in sequence, a second abc / dq conversion module, an inverter current control module and a dq / abc conversion module, and further comprises a direct current voltage control module connected with the other end of the inverter current control module.

[0073] The second abc / dq conversion module is used for converting the three-phase output current of the inverter into current values in the dq coordinate system.

[0074] For example, the conversion formula is as follows: Wherein, i a , i b , i c are the three-phase output currents of the inverter, i d , i q are the values of the three-phase currents in the dq coordinate system, and θ1 is the included angle between the d axis and the phase reference axis.

[0075] The direct current voltage control module is used for generating the d-axis instruction value of the inverter output current based on the inverter direct current side voltage.

[0076] For example, the expression of the d-axis instruction value of the inverter output current is as follows: Wherein, i d_ref is the d-axis instruction value of the inverter output current, k p_dcv is the value of the proportional controller of the inverter direct current voltage control loop PI regulator, k i_dcv is the value of the integral controller of the inverter direct current voltage control loop PI regulator, U dc_ref is the inverter direct current voltage instruction value, U dc is the inverter direct current side voltage, and s is the parameter value of the PI regulator.

[0077] The inverter current control module is configured to generate an inverter modulation signal based on a current value of the inverter in a dq coordinate system, a d-axis instruction value of an inverter output current, and a q-axis instruction value of the inverter output current.

[0078] An exemplary expression of the inverter modulation signal is: wherein m d is a d-axis modulation amount of the inverter modulation signal, m q is a q-axis modulation amount of the inverter modulation signal, k p_di is a value of a proportional controller of a d-axis current loop PI regulator, k i_di is a value of an integral controller of the d-axis current loop PI regulator, k p_qi is a value of a proportional controller of a q-axis current loop PI regulator, k i_qi is a value of an integral controller of the q-axis current loop PI regulator, i d_ref is a d-axis instruction value of the inverter current loop, i q_ref is a q-axis instruction value of the inverter current loop, i q_ref = 0, i d is a value of the inverter output three-phase current in the d-axis, i q is a value of the inverter output three-phase current in the q-axis.

[0079] The dq / abc conversion module is configured to convert the modulation amounts of the d-axis and the q-axis in the inverter modulation signal into modulation amounts of three-phase voltages, and maintain stability of a direct-current side voltage.

[0080] An exemplary expression of the modulation amounts of the three-phase voltages of the inverter modulation signal can be obtained by combining the calculation formula of the second control module and the inverter direct-current voltage stabilization current control block diagram shown in Figure 6 , and the expression of the modulation amounts of the three-phase voltages of the inverter modulation signal is: wherein m a , m b , and m c are modulation amounts of the inverter output voltages in an abc three-phase coordinate system, m d is the d-axis modulation amount of the inverter modulation signal, m q is the q-axis modulation amount of the inverter modulation signal, and θ1 is an included angle between the d-axis and a phase reference axis.

[0081] It can be seen from Figure 7 and Figure 8 that when the power grid fluctuates and the grid point voltage significantly increases, the output power of the photovoltaic inverter using the traditional linear active voltage control curve changes little, the support effect is poor, the voltage deviation is still large, the power quality decreases, and the normal operation of equipment in the power grid is affected.

[0082] From Figure 9 , Figure 10 ,Figure 11 and Figure 12 It can be seen that, through the control of the application, when the power grid fluctuates, the photovoltaic inverter calculates the power instruction value according to the segmented active power / voltage control curve, quickly changes the port output voltage through the linear approximation curve, realizes the power output tracking instruction, when the voltage amplitude is large, the photovoltaic output power drops more, and the grid point voltage amplitude fluctuates less, when the voltage amplitude is small, the photovoltaic inverter outputs the maximum power, which guarantees the power quality of the load voltage while improving the efficiency, improves the stability of the power grid operation and the economy of the photovoltaic operation.

[0083] In the above embodiments, the description of each embodiment has its own focus, and the parts not described or recorded in a certain embodiment can be referred to the related description of other embodiments.

[0084] Those skilled in the art can appreciate that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. Professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0085] In the embodiments provided in the present application, it should be understood that the disclosed apparatus / network device and method can be implemented in other ways. For example, the apparatus / network device embodiments described above are only schematic, for example, the division of the modules or units is only a logical function division, and there can be another division manner in actual implementation, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual coupling or direct coupling or communication connection between each of them can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or other forms.

[0086] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, that is, they can be located in one place, or they can be distributed on a plurality of network units. According to actual needs, part or all of the units can be selected to achieve the purpose of the embodiment.

[0087] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A photovoltaic inverter, characterized in that The photovoltaic inverter comprises a Boost type DC / DC converter, an inverter and a filter connected in sequence; the other end of the Boost type DC / DC converter is used for being connected with a photovoltaic array; the other end of the filter is used for being connected with a power grid and a load; The Boost type DC / DC converter is used for outputting a photovoltaic output power output by the photovoltaic array according to a preset power control; The inverter is used for inverting a direct current voltage generated by the photovoltaic array into an alternating current voltage and keeping a direct current side voltage in the inverter stable; The filter is used for filtering out a spur in the alternating current voltage output by the inverter and stabilizing the alternating current voltage sent to the power grid and the load; The photovoltaic inverter further comprises a segmented active voltage control unit; the segmented active voltage control unit comprises a first abc / dq conversion module and a power instruction calculation module connected in sequence; The first abc / dq conversion module is used for converting a three-phase output voltage of the inverter into a voltage value in a dq coordinate system; The power instruction calculation module is used for obtaining an instruction value of the photovoltaic output power based on the voltage value of the inverter in the dq coordinate system; The photovoltaic inverter further comprises a first control module; the first control module comprises a photovoltaic voltage instruction calculation module, a photovoltaic voltage outer loop control module and a photovoltaic current inner loop control module connected in sequence; The photovoltaic voltage instruction calculation module is used for obtaining maximum power point information of a photovoltaic module, constructing a linear approximation photovoltaic characteristic curve based on the maximum power point information and obtaining a photovoltaic port voltage instruction value corresponding to the instruction value of the photovoltaic output power based on the linear approximation curve; The photovoltaic voltage outer loop control module is used for generating an instruction value of the current inner loop control module based on the photovoltaic port voltage instruction value; The photovoltaic current inner loop control module is used for generating a Boost modulation signal to control the photovoltaic output power to output based on the instruction value of the current inner loop control module. The Boost type DC / DC converter comprises a first capacitor, a first inductor, a first diode and a first triode unit; the first triode unit comprises a first triode and a second diode; 2. The photovoltaic inverter of claim 1, wherein, The positive pole of the first triode unit is connected to one end of the cathode of the second diode and the collector of the first triode; the negative pole of the first triode unit is connected to one end of the anode of the second diode and the emitter of the first triode; the first end of the first capacitor is connected with the anode of the photovoltaic array; the second end of the first capacitor is connected with the cathode of the photovoltaic array; the first end of the first inductor is connected with the anode of the photovoltaic array; the second end of the first inductor is connected with the anode of the first diode; the second end of the first inductor is connected with the positive pole of the first triode unit; and the negative pole of the first triode unit is connected with the cathode of the photovoltaic array. ​ 3. The photovoltaic inverter of claim 2, wherein, The inverter comprises a second capacitor, a second triode unit, a third triode unit, a fourth triode unit, a fifth triode unit, a sixth triode unit and a seventh triode unit, wherein the internal structure and connection mode of the second triode unit, the third triode unit, the fourth triode unit, the fifth triode unit, the sixth triode unit and the seventh triode unit are the same as those of the first triode unit; The first end of the second capacitor is connected with the cathode of the first diode, the positive electrode of the second triode unit, the positive electrode of the third triode unit and the positive electrode of the fourth triode unit, the second end of the second capacitor is connected with the cathode of the photovoltaic array, the negative electrode of the fifth triode unit, the negative electrode of the sixth triode unit and the negative electrode of the seventh triode unit, the negative electrode of the second triode unit is connected with the positive electrode of the fifth triode unit, the negative electrode of the third triode unit is connected with the positive electrode of the sixth triode unit, and the negative electrode of the fourth triode unit is connected with the positive electrode of the seventh triode unit.

4. The photovoltaic inverter of claim 3, wherein, The filter comprises a second inductor, a third inductor, a fourth inductor, a fifth inductor, a sixth inductor, a seventh inductor, a third capacitor, a fourth capacitor, a fifth capacitor, a first resistor, a second resistor and a third resistor; The first end of the second inductor is connected with the negative electrode of the second triode unit, the second end of the second inductor is connected with the first end of the third inductor, the second end of the third inductor is connected with the power grid and the load, the first end of the fourth inductor is connected with the negative electrode of the third triode unit, the second end of the fourth inductor is connected with the first end of the fifth inductor, the second end of the fifth inductor is connected with the power grid and the load, the first end of the sixth inductor is connected with the negative electrode of the fourth triode unit, the second end of the sixth inductor is connected with the first end of the seventh inductor, and the second end of the seventh inductor is connected with the power grid and the load; The first end of the first resistor is connected with the second end of the second inductor, the second end of the first resistor is connected with the first end of the third capacitor, the second end of the third capacitor is grounded, the first end of the second resistor is connected with the second end of the fourth inductor, the second end of the second resistor is connected with the first end of the fourth capacitor, the second end of the fourth capacitor is grounded, and the first end of the third resistor is connected with the second end of the sixth inductor, the second end of the third resistor is connected with the first end of the fifth capacitor, and the second end of the fifth capacitor is grounded.

5. The photovoltaic inverter of claim 1, wherein, The photovoltaic inverter further comprises a second control module, the second control module comprises a second abc / dq conversion module, an inverter current control module and a dq / abc conversion module connected in sequence, and further comprises a direct-current voltage control module connected with the other end of the inverter current control module; The second abc / dq conversion module is used for converting the three-phase output current of the inverter into current values in the dq coordinate system. The direct-current voltage control module is configured to generate a d-axis instruction value of an inverter output current based on a direct-current side voltage of the inverter. The inverter current control module is configured to generate an inverter modulation signal based on a current value of the inverter in a dq coordinate system, the d-axis instruction value of the inverter output current, and a q-axis instruction value of the inverter output current. The dq / abc conversion module is configured to convert modulation amounts of the d-axis and the q-axis in the inverter modulation signal into modulation amounts of three-phase voltages, and keep the direct-current side voltage stable.

6. The photovoltaic inverter of claim 1, wherein, The expression of the linearly approximated photovoltaic characteristic curve is: wherein, P pv P is the photovoltaic module output power, k pv is the linearly approximated photovoltaic characteristic curve slope, P mppt Pmax is the photovoltaic module maximum output power, U mppt Vmax is the photovoltaic module output voltage corresponding to the photovoltaic module maximum output power point, U pv V is the photovoltaic module output voltage.

7. The photovoltaic inverter of claim 1, wherein, The expression of the photovoltaic port voltage instruction value is: wherein, is a photovoltaic inverter output power instruction value, k pv is a linear approximation photovoltaic characteristic curve slope, is a Boost type DC / DC converter photovoltaic port voltage instruction value.

8. An active grid voltage support device, characterized by A photovoltaic inverter comprising any one of claims 1-7.

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