A distributed power low voltage ride through circuit

Abstract

The application provides a kind of distributed power low voltage crossing circuit, wherein the circuit includes: fault type discrimination module, for according to the input fault type characterization signal, output indicating signal, wherein, in the case where indicating signal is first characterization signal, determine to collect phase voltage, in the case where indicating signal is second characterization signal, determine to collect line voltage;Low voltage crossing state discrimination module, for according to first input signal, second input signal and indicating signal output control signal, wherein, control signal is used to control whether photovoltaic needs to enter low voltage crossing function;Reference current output module, for receiving control signal, phase angle signal and the current amplitude of photovoltaic output, and according to control signal, phase angle signal and the current amplitude of photovoltaic output, output photovoltaic positive sequence current d-axis reference value and photovoltaic positive sequence current q-axis reference value.Through the above scheme, the technical effect of flexible control of the phase of output current is realized.

Description

Technical Field

[0001] This application belongs to the field of power grid control technology, and in particular relates to a distributed power source low voltage ride-through circuit. Background Technology

[0002] Currently, in the process of building new power systems, the grid connection of a large number of new energy sources places increasingly higher demands on the grid's reliable power supply, safety, stability, and economic operation. The high proportion of distributed generation connected to the distribution network leads to changes in the network's structure and characteristics. When a fault occurs in the distribution network, its fault current characteristics also change. However, existing distributed photovoltaic (PV) low-voltage ride-through models can only control the magnitude of the reactive current output by the distributed PV system, and cannot achieve free and flexible adjustment of the phase of the distributed PV output current. Summary of the Invention

[0003] The purpose of this application is to provide a distributed power supply low-voltage ride-through circuit that enables flexible control of the phase of the output current.

[0004] A distributed power source low-voltage ride-through circuit, comprising:

[0005] The fault type discrimination module is used to output an indication signal based on the input fault type characterization signal, wherein, when the indication signal is a first characterization signal, the phase voltage is determined to be collected, and when the indication signal is a second characterization signal, the line voltage is determined to be collected.

[0006] The low voltage ride-through state determination module is used to receive a first input signal, a second input signal and the indication signal, and output a control signal according to the first input signal, the second input signal and the indication signal, wherein the control signal is used to control whether the photovoltaic system needs to enter the low voltage ride-through function;

[0007] The reference current output module is used to receive the control signal, the phase angle signal and the current amplitude of the photovoltaic output, and output the d-axis reference value of the photovoltaic positive sequence current and the q-axis reference value of the photovoltaic positive sequence current according to the control signal, the phase angle signal and the current amplitude of the photovoltaic output;

[0008] Specifically, when the control signal indicates that the low voltage ride-through function needs to be entered, the amplitude of the photovoltaic output current is controlled to be a preset multiple of the rated current, and the phase is controlled by the phase angle signal. When the control signal indicates that the low voltage ride-through function is not entered, the amplitude of the photovoltaic output current is controlled to be the rated current, and the phase is 0.

[0009] In one embodiment, the fault type discrimination module includes: a first input port, a second input port, a comparison module, a first output port, and a second output port. The first input port is used to input a fault type characterization signal, the second input port is used to input a preset value, and the comparison module is used to compare the input from the first input port and the input from the second input port and output an indication signal through the first output port and the second output port.

[0010] In one embodiment, when the first output port outputs signal 1 and the second output port outputs signal 0, the indication signal is determined to be a first characterization signal; when the first output port outputs signal 0 and the second output port outputs signal 1, the indication signal is determined to be a second characterization signal.

[0011] In one embodiment, the low-voltage ride-through state discrimination module includes: a first control terminal, a second control terminal, a first multiplier, a second multiplier, a first adder, and a comparator, wherein:

[0012] The first input terminal of the first multiplier is connected to the indication signal of the fault type discrimination module, the second input terminal of the first multiplier is connected to the first input signal of the first control terminal, and the output terminal of the first multiplier is connected to the first input terminal of the first adder.

[0013] The first input terminal of the second multiplier is connected to the indication signal of the fault type discrimination module, the second input terminal of the second multiplier is connected to the second input signal of the second control terminal, and the output terminal of the second multiplier is connected to the second input terminal of the first adder.

[0014] The first input terminal of the comparator is connected to the output terminal of the first adder, the second input terminal of the comparator is connected to the control voltage, wherein the control voltage is a preset multiple of the rated voltage, and the output terminal of the comparator outputs a control signal.

[0015] The first multiplier, the second multiplier, and the first adder are used to select the first input signal and the second input signal.

[0016] In one implementation, when the first input signal is selected and the first input signal is less than the control voltage, or when the second input signal is selected and the second input signal is less than the control voltage, a control signal is generated to control the photovoltaic system from entering the low voltage ride-through function.

[0017] When the first input signal is selected and the first input signal is not less than the control voltage, or when the second input signal is selected and the second input signal is not less than the control voltage, a control signal is generated for controlling the photovoltaic system to enter the low voltage ride-through function.

[0018] In one embodiment, the control signal includes: a first node output signal and a second node output signal. When the first node output signal is 1 and the second node output signal is 0, a control signal is generated to control the photovoltaic system from not entering the low voltage ride-through function. When the first node output signal is 0 and the second node output signal is 1, a control signal is generated to control the photovoltaic system from entering the low voltage ride-through function.

[0019] In one embodiment, the first input signal is the phase voltage of the distributed photovoltaic grid-connected point, and the second input signal is the minimum line voltage of the distributed photovoltaic grid-connected point.

[0020] In one embodiment, the reference current output module includes:

[0021] The system includes a third multiplier, a fourth multiplier, a fifth multiplier, a sixth multiplier, a seventh multiplier, a second adder, a third adder, and a vector converter, where:

[0022] The first input terminal of the third multiplier is connected to the third input signal, the second input terminal of the third multiplier is connected to the current amplitude of a predetermined multiple of the rated current, the output terminal of the third multiplier is connected to the first input terminal of the fourth multiplier, the second input terminal of the fourth multiplier is connected to the first node output signal, and the output terminal of the fourth multiplier is connected to the first input terminal of the second adder.

[0023] The first input terminal of the fifth multiplier is connected to the third input signal, the second input terminal of the fifth multiplier is connected to the second node output signal, and the output terminal of the fifth multiplier is connected to the second input terminal of the second adder.

[0024] The output of the second adder is connected to the first input of the vector converter;

[0025] The first input terminal of the sixth multiplier is connected to the fourth input signal, the second input terminal of the sixth multiplier is connected to the first node output signal, and the output terminal of the sixth multiplier is connected to the first input terminal of the third adder, wherein the fourth input signal is a phase angle signal;

[0026] The first input terminal of the seventh multiplier is connected to signal 0, the second input terminal of the seventh multiplier is connected to the output signal of the second node, and the output terminal of the seventh multiplier is connected to the second input terminal of the third adder.

[0027] The output of the third adder is connected to the second input of the vector converter.

[0028] The vector converter is used to convert the input signal into a photovoltaic positive sequence current d-axis reference value and a photovoltaic positive sequence current q-axis reference value using a vector conversion formula.

[0029] In one embodiment, the photovoltaic positive sequence current d-axis reference value and the photovoltaic positive sequence current q-axis reference value are used to convert the photovoltaic terminal voltage value in the dq coordinate system and inversely transform it to obtain the output value of the photovoltaic terminal voltage ABC three phases.

[0030] In one embodiment, the third input signal is the magnitude of the photovoltaic output current, and the fourth input signal is the phase angle signal, which is the phase difference between the distributed photovoltaic output current and the terminal voltage.

[0031] The distributed power generation low-voltage ride-through circuit provided in this application may include: a fault type discrimination module, used to output an indication signal based on an input fault type characterization signal, wherein, when the indication signal is a first characterization signal, the phase voltage is determined to be collected, and when the indication signal is a second characterization signal, the line voltage is determined to be collected; a low-voltage ride-through state discrimination module, used to receive a first input signal, a second input signal, and the indication signal, and output a control signal based on the first input signal, the second input signal, and the indication signal, wherein the control signal is used to control whether the photovoltaic system needs to enter the low-voltage ride-through function; a reference current output module, used to receive the control signal, the phase angle signal, and the current amplitude output by the photovoltaic system, and output a photovoltaic positive sequence current d-axis reference value and a photovoltaic positive sequence current q-axis reference value based on the control signal, the phase angle signal, and the current amplitude output by the photovoltaic system; wherein, when the control signal indicates that the low-voltage ride-through function needs to be entered, the photovoltaic output current amplitude is controlled to be a preset multiple of the rated current, and the phase is controlled by the phase angle signal; when the control signal indicates that the low-voltage ride-through function has not been entered, the photovoltaic output current amplitude is controlled to be the rated current, and the phase is 0. By setting input ports for the first input signal, the second input signal, the fault type characterization signal, and the phase angle signal, these signals can be controlled to determine whether to enter the low-voltage ride-through function. Furthermore, in the case of entering or not entering the low-voltage ride-through function, the d-axis reference value and q-axis reference value of the photovoltaic positive-sequence current are output. This solves the technical problem that existing distributed photovoltaic low-voltage ride-through models can only control the magnitude of the reactive current output by the distributed photovoltaic system, but cannot achieve free and flexible adjustment of the phase of the distributed photovoltaic output current. This achieves the technical effect of flexible phase control of the output current. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the grid connection point voltage that can be cut off under the distributed power generation low voltage ride-through model provided in this application;

[0034] Figure 2 This is a schematic diagram of a low-voltage ride-through model for a distributed photovoltaic system with flexibly adjustable output current phase, as provided in this application.

[0035] Figure 3This is a schematic diagram of the fault type discrimination module provided in this application;

[0036] Figure 4 This is a schematic diagram of the structure of the comparison submodule provided in this application;

[0037] Figure 5 This is a schematic diagram of the low voltage ride-through state discrimination module provided in this application;

[0038] Figure 6 This is a schematic diagram of the reference current output module provided in this application;

[0039] Figure 7 This is a schematic diagram of the vector conversion module in the reference current output module provided in this application;

[0040] Figure 8 This is a schematic diagram of the distributed power supply low-voltage ride-through circuit provided in this application. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0042] The above method will be described below with reference to a specific embodiment. However, it is worth noting that this specific embodiment is only for better illustration of this application and does not constitute an improper limitation of this application.

[0043] For the low-voltage ride-through model of distributed generation, the grid connection point voltage of the distributed generation is selected (the line voltage at the grid connection point is selected for two-phase and three-phase faults, and the phase voltage at the grid connection point is selected for single-phase ground faults), such as Figure 1 As shown, distributed power sources should not be disconnected from the grid within the area of ​​the voltage profile line and above; otherwise, distributed power sources are allowed to disconnect.

[0044] Based on this, the low-voltage ride-through control strategy for distributed generation can be set as follows: According to different voltage drops on the inverter's grid side, the magnitude of the reactive current output by distributed photovoltaic power generation under distribution network fault conditions is defined as follows:

[0045] IT≥1.5×(0.9-UT)×I (0.2≤UT≤0.9)

[0046] IT ≥ 1.05 × I (UT < 0.2)

[0047] IT = 0 (UT > 0.9)

[0048] Where UT is the per-unit value of the rated voltage at the photovoltaic terminal, IT is the reactive current, and I = rated photovoltaic capacity / (1.732 × rated voltage at the grid connection point).

[0049] However, the above scheme can only control the magnitude of the reactive current output by distributed photovoltaics, and cannot achieve free and flexible adjustment of the phase of the output current of distributed photovoltaics.

[0050] Therefore, in this example, to determine the impact of the distributed photovoltaic (PV) current output phase on the current characteristics during distribution network faults, a low-voltage ride-through model was constructed that allows for flexible adjustment of the PV output current phase, focusing on the current phase factor in the PV output characteristics. This model allows for freely setting the phase of the PV output current relative to the generator terminal voltage after a fault.

[0051] like Figure 2 As shown in the example, this paper presents a low-voltage ride-through model with flexible adjustment of the phase of the distributed photovoltaic (PV) output current. The model includes a fault type discrimination module, a low-voltage ride-through state discrimination module, and a reference current output module. A, B, C, D, and In are input interfaces, and E, F, G, and H are output interfaces. Interface A collects the phase voltage of the PV grid-connected point; interface B collects the minimum line voltage of the PV grid-connected point; interface C collects the fault type; the value of interface D is the phase difference between the PV output current and the generator terminal voltage; the value of interface In is the magnitude of the PV output current; interface E outputs the d-axis reference value idref+ of the PV positive-sequence current; interface F outputs the q-axis reference value iq+ref of the positive-sequence current; interface G outputs the d-axis reference value idref- of the negative-sequence current; and interface H outputs the q-axis reference value iq-ref of the positive-sequence current.

[0052] The values ​​of input interface C and input interface D can be manually and flexibly set in the electromagnetic transient software. The value of interface D can be expressed in radians, and the value of interface In can be the photovoltaic capacity / (1.732 × grid connection point rated voltage).

[0053] The value of input interface C represents the fault type. In power system electromagnetic transient simulation software, the corresponding distribution network fault type can be represented by a number. For example, the correspondence between numbers and fault types can be shown in Table 1 below:

[0054] Table 1

[0055]

[0056]

[0057] Specifically, the low-voltage ride-through model can include the following modules:

[0058] 1) Fault type identification module:

[0059] like Figure 3 As shown, the input signal of this fault type discrimination module is C, and the output signals are phv and line_V. Signal C represents the fault type. When signal C is 0-2, it indicates a single-phase fault in the system; when signal C is 3-9, it indicates a non-single-phase fault in the system. When C≤2, it is determined that the phase voltage of the photovoltaic grid-connected point needs to be collected; when C>2, it is determined that the line voltage of the photovoltaic grid-connected point needs to be collected.

[0060] The comparison submodule can be as follows: Figure 4 As shown, for this comparison module, when input port 1 > output port 2 (which can be set to 2.1), the output is 1; when input port 1 < input port 2, the output is 0. The phv signal in the fault type discrimination module is used as the signal for acquiring phase voltage, and the line_V signal in the fault type discrimination module is used as the signal for acquiring line voltage. When C ≤ 2, signal phv = 1, line_V = 0; when C > 2, signal phv = 0, line_V = 1.

[0061] 2) Low Voltage Ride-Through Status Detection Module:

[0062] like Figure 5 The diagram shows a schematic of the low voltage ride-through state discrimination module. This module determines whether the model enters the low voltage ride-through function. The input signals of this module are A, B, line_v, and phv, and the output signals are switch and off.

[0063] When line voltage is required, the line_v signal is 1, the phv signal is 0, signal A is input to the comparator module, and signal B is set to zero; otherwise, signal B is input to the comparator module, and signal A is set to zero.

[0064] It should be noted that both line voltage and phase voltage are per-unit values. Therefore, when signal A or B is less than 0.9 (meaning the voltage is less than 0.9 times the rated value), the photovoltaic system enters the low-voltage ride-through function. In this case, the node switch will be set to 1 and the off switch to 0. Conversely, when the photovoltaic system does not need to enter the low-voltage ride-through function, the node switch will be set to 0 and the off switch to 1. Therefore, switch and off are used as signals for whether the system enters the low-voltage ride-through function.

[0065] 3) Reference current output module:

[0066] like Figure 6 The diagram shows a reference current output module. The input signals of this module are D, In, switch, and off, and the output signals are E, F, G, and H.

[0067] When the switch signal is set to 1 and the off signal is set to 0, the distributed power source enters the low-voltage ride-through function. The photovoltaic output current amplitude is set to 1.2 times the rated current, and the current phase is controlled by the phase angle input from interface D. Conversely, when the switch signal is set to 0 and the off signal is set to 1, the photovoltaic system does not enter the low-voltage ride-through function. The current output amplitude is the rated current, and the phase is 0. In this case, the photovoltaic system only generates active power.

[0068] Specifically, interfaces G and H can both be set to 0, allowing for flexible adjustment when negative sequence current is required later.

[0069] The vector conversion module in the aforementioned reference current output module can be as follows: Figure 7 As shown, for the vector transformation submodule, the transformation can be performed according to the following formula:

[0070]

[0071] Where X represents the magnitude of active current and Y represents the magnitude of reactive current.

[0072] Among them, interface E outputs the d-axis reference value idref+ of the positive sequence current, interface F outputs the q-axis reference value iq+ref of the positive sequence current, interface G outputs the d-axis reference value idref- of the negative sequence current, and interface H outputs the q-axis reference value iq-ref of the positive sequence current. Applying the above low-voltage ride-through model to the photovoltaic control strategy, signals E and F (idref+ and iqref+) are used as inputs to the current-feedforward PI control. Through the current-feedforward PI control strategy, the value of the photovoltaic terminal voltage (in the dq coordinate system) can be obtained. Then, through the Parker inverse transform, the output values ​​of the three phases (A, B, and C) of the photovoltaic terminal voltage are obtained. Finally, these values ​​are modulated with a sawtooth wave to generate PWM drive signals, which are sent to the power electronic devices of the photovoltaic inverter to control the on / off state of the power electronic devices. This enables photovoltaic grid-connected control under conditions where the phase of the distributed photovoltaic output current can be flexibly adjusted.

[0073] It is worth noting that the values ​​of 1.2 times the rated current, 0.9 times the rated value, and 1.732 × the rated voltage at the grid connection point mentioned above are only exemplary descriptions. In actual implementation, other values ​​can be selected according to actual needs and circumstances. This application does not limit them.

[0074] In the example above, this model is used to analyze the impact of the distributed photovoltaic (PV) current output phase on the fault current characteristics of the distribution network, in order to analyze the optimal phase of the PV output (the PV output current phase that has the least impact on the fault characteristics at a certain location on the distribution line after a fault occurs in the distribution network). Simultaneously, applying this low-voltage ride-through model to a practical PV controller allows for control of the PV output based on the optimal phase, thereby minimizing the impact of distributed PV access on the secondary equipment of the distribution network.

[0075] Figure 8 This is a schematic diagram of a distributed power supply low-voltage ride-through circuit provided in this application. Although this application provides the device structure shown in the following embodiments or figures, more or fewer modular units may be included in the device based on conventional or non-inventive effort. In steps or structures where there is no logically necessary causal relationship, the modular structure of these devices is not limited to the modular structure described in the embodiments and figures of this application. In practical applications of devices or end products, the modular structure can be implemented by connecting the modules according to the modular structure shown in the embodiments or figures.

[0076] Specifically, such as Figure 8 As shown, the aforementioned distributed power source low-voltage ride-through circuit may include:

[0077] The fault type discrimination module 801 is used to output an indication signal based on the input fault type characterization signal, wherein, when the indication signal is a first characterization signal, the phase voltage is determined to be collected, and when the indication signal is a second characterization signal, the line voltage is determined to be collected.

[0078] The low voltage ride-through state determination module 802 is used to receive a first input signal, a second input signal and the indication signal, and output a control signal according to the first input signal, the second input signal and the indication signal, wherein the control signal is used to control whether the photovoltaic system needs to enter the low voltage ride-through function;

[0079] The reference current output module 803 is used to receive the control signal, the phase angle signal and the current amplitude of the photovoltaic output, and output the d-axis reference value of the photovoltaic positive sequence current and the q-axis reference value of the photovoltaic positive sequence current according to the control signal, the phase angle signal and the current amplitude of the photovoltaic output;

[0080] Specifically, when the control signal indicates that the low voltage ride-through function needs to be entered, the amplitude of the photovoltaic output current is controlled to be a preset multiple of the rated current, and the phase is controlled by the phase angle signal. When the control signal indicates that the low voltage ride-through function is not entered, the amplitude of the photovoltaic output current is controlled to be the rated current, and the phase is 0.

[0081] In one embodiment, the fault type discrimination module may include: a first input port, a second input port, a comparison module, a first output port, and a second output port. The first input port is used to input a fault type characterization signal (corresponding to C above), the second input port is used to input a preset value, and the comparison module is used to compare the input of the first input port and the input of the second input port, and output the indication signal through the first output port and the second output port.

[0082] In one embodiment, when the first output port (corresponding to the above-mentioned phv) outputs signal 1 and the second output port (corresponding to the above-mentioned line_V) outputs signal 0, the indication signal is determined to be a first characterization signal; when the first output port outputs signal 0 and the second output port outputs signal 1, the indication signal is determined to be a second characterization signal.

[0083] In one embodiment, the low-voltage ride-through state discrimination module may include: a first control terminal, a second control terminal, a first multiplier, a second multiplier, a first adder, and a comparator, wherein:

[0084] The first input terminal of the first multiplier is connected to the indication signal of the fault type discrimination module, the second input terminal of the first multiplier is connected to the first input signal of the first control terminal (corresponding to the above-mentioned input signal A), and the output terminal of the first multiplier is connected to the first input terminal of the first adder.

[0085] The first input terminal of the second multiplier is connected to the indication signal of the fault type discrimination module, the second input terminal of the second multiplier is connected to the second input signal of the second control terminal (corresponding to the above-mentioned input signal B), and the output terminal of the second multiplier is connected to the second input terminal of the first adder.

[0086] The first input terminal of the comparator is connected to the output terminal of the first adder, the second input terminal of the comparator is connected to the control voltage, wherein the control voltage is a preset multiple of the rated voltage, and the output terminal of the comparator outputs a control signal.

[0087] The first multiplier, the second multiplier, and the first adder are used to select the first input signal and the second input signal.

[0088] In one implementation, when the first input signal is selected and the first input signal is less than the control voltage, or when the second input signal is selected and the second input signal is less than the control voltage, a control signal is generated to control the photovoltaic system to not need to enter the low voltage ride-through function; when the first input signal is selected and the first input signal is not less than the control voltage, or when the second input signal is selected and the second input signal is not less than the control voltage, a control signal is generated to control the photovoltaic system to enter the low voltage ride-through function.

[0089] In one embodiment, the control signal includes: a first node output signal (corresponding to the aforementioned node switch) and a second node output signal (corresponding to the aforementioned node off). When the first node output signal is 1 and the second node output signal is 0, a control signal is generated to control whether the photovoltaic system does not need to enter the low voltage ride-through function; when the first node output signal is 0 and the second node output signal is 1, a control signal is generated to control whether the photovoltaic system needs to enter the low voltage ride-through function. That is, switch and off are used as signals for whether the system enters the low voltage ride-through function.

[0090] In one embodiment, the first input signal may be the phase voltage of the distributed photovoltaic grid-connected point, and the second input signal may be the minimum line voltage of the distributed photovoltaic grid-connected point.

[0091] In one embodiment, the aforementioned reference current output module may include: a third multiplier, a fourth multiplier, a fifth multiplier, a sixth multiplier, a seventh multiplier, a second adder, a third adder, and a vector converter, wherein:

[0092] The first input terminal of the third multiplier is connected to the third input signal (corresponding to the signal In mentioned above), the second input terminal of the third multiplier is connected to the current amplitude of a predetermined multiple of the rated current, the output terminal of the third multiplier is connected to the first input terminal of the fourth multiplier, the second input terminal of the fourth multiplier is connected to the output signal of the first node, and the output terminal of the fourth multiplier is connected to the first input terminal of the second adder.

[0093] The first input terminal of the fifth multiplier is connected to the third input signal, the second input terminal of the fifth multiplier is connected to the second node output signal, and the output terminal of the fifth multiplier is connected to the second input terminal of the second adder.

[0094] The output of the second adder is connected to the first input of the vector converter;

[0095] The first input terminal of the sixth multiplier is connected to the fourth input signal (corresponding to the signal D mentioned above), the second input terminal of the sixth multiplier is connected to the output signal of the first node, and the output terminal of the sixth multiplier is connected to the first input terminal of the third adder, wherein the fourth input signal is a phase angle signal;

[0096] The first input terminal of the seventh multiplier is connected to signal 0, the second input terminal of the seventh multiplier is connected to the output signal of the second node, and the output terminal of the seventh multiplier is connected to the second input terminal of the third adder.

[0097] The output of the third adder is connected to the second input of the vector converter.

[0098] The vector converter is used to convert the input signal into a photovoltaic positive sequence current d-axis reference value and a photovoltaic positive sequence current q-axis reference value using a vector conversion formula.

[0099] In one embodiment, the aforementioned photovoltaic positive sequence current d-axis reference value and photovoltaic positive sequence current q-axis reference value can be used to convert the photovoltaic terminal voltage value in the dq coordinate system and inversely transform it to obtain the output values ​​of the three phases ABC of the photovoltaic terminal voltage.

[0100] In one embodiment, the third input signal can be the magnitude of the photovoltaic output current, and the fourth input signal can be a phase angle signal, that is, the fourth input signal can be the phase difference between the distributed photovoltaic output current and the terminal voltage.

[0101] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, hardware + program embodiments are relatively simple in description because they are fundamentally similar to method embodiments; relevant parts can be referred to the descriptions in the method embodiments.

[0102] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0103] While this application provides the method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-inventive labor. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only execution order. In actual device or client product execution, the methods shown in the embodiments or drawings can be executed sequentially or in parallel (e.g., in a parallel processor or multi-threaded processing environment).

[0104] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, a computer can be, for example, a personal computer, a laptop computer, an in-vehicle human-machine interaction device, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0105] While this specification provides method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-inventive means. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only execution order. In actual device or end product execution, the methods shown in the embodiments or drawings may be executed sequentially or in parallel (e.g., in a parallel processor or multi-threaded processing environment, or even a distributed data processing environment). The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, product, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, product, or apparatus. Without further limitations, the presence of other identical or equivalent elements in the process, method, product, or apparatus that includes said elements is not excluded.

[0106] For ease of description, the above devices are described in terms of function, divided into various modules. Of course, in implementing the embodiments of this specification, the functions of each module can be implemented in one or more software and / or hardware components, or a module that performs the same function can be implemented by a combination of multiple sub-modules or sub-units. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division; in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.

[0107] Those skilled in the art will also know that, besides implementing the controller using purely computer-readable program code, the same functions can be achieved by logically programming the method steps, making the controller function as logic gates, switches, application-specific integrated circuits (ASICs), programmable logic controllers (PLCs), and embedded microcontrollers. Therefore, such a controller can be considered a hardware component, and the devices within it used to implement various functions can also be considered structures within that hardware component. Alternatively, the devices used to implement various functions can be considered as both software modules implementing the method and structures within a hardware component.

[0108] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0109] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0110] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0111] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, system embodiments are basically similar to method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. In the description of this specification, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments in this specification. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0112] The above description is merely an embodiment of the present specification and is not intended to limit the embodiments of the present specification. For those skilled in the art, various modifications and variations can be made to the embodiments of the present specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the embodiments of the present specification should be included within the scope of the claims of the embodiments of the present specification.

Claims

1. A distributed power source low-voltage ride-through circuit, characterized in that, include: The fault type discrimination module is used to output an indication signal based on the input fault type characterization signal, wherein, when the indication signal is a first characterization signal, the phase voltage is determined to be collected, and when the indication signal is a second characterization signal, the line voltage is determined to be collected. The low voltage ride-through state determination module is used to receive a first input signal, a second input signal and the indication signal, and output a control signal according to the first input signal, the second input signal and the indication signal, wherein the control signal is used to control whether the photovoltaic system needs to enter the low voltage ride-through function; The reference current output module is used to receive the control signal, the phase angle signal and the current amplitude of the photovoltaic output, and output the d-axis reference value and the q-axis reference value of the photovoltaic positive sequence current according to the control signal, the phase angle signal and the current amplitude of the photovoltaic output; Specifically, when the control signal indicates that the low voltage ride-through function needs to be entered, the amplitude of the photovoltaic output current is controlled to be a preset multiple of the rated current, and the phase is controlled by the phase angle signal; when the control signal indicates that the low voltage ride-through function has not been entered, the amplitude of the photovoltaic output current is controlled to be the rated current, and the phase is 0. The low-voltage ride-through state discrimination module includes: a first control terminal, a second control terminal, a first multiplier, a second multiplier, a first adder, and a comparator, wherein: The first input terminal of the first multiplier is connected to the indication signal of the fault type discrimination module, the second input terminal of the first multiplier is connected to the first input signal of the first control terminal, and the output terminal of the first multiplier is connected to the first input terminal of the first adder. The first input terminal of the second multiplier is connected to the indication signal of the fault type discrimination module, the second input terminal of the second multiplier is connected to the second input signal of the second control terminal, and the output terminal of the second multiplier is connected to the second input terminal of the first adder. The first input terminal of the comparator is connected to the output terminal of the first adder, the second input terminal of the comparator is connected to the control voltage, wherein the control voltage is a preset multiple of the rated voltage, and the output terminal of the comparator outputs a control signal. The first multiplier, the second multiplier, and the first adder are used to select the first input signal and the second input signal. The control signals include: a first node output signal and a second node output signal. When the first node output signal is 1 and the second node output signal is 0, a control signal is generated to control the photovoltaic system from not entering the low voltage ride-through function. When the first node output signal is 0 and the second node output signal is 1, a control signal is generated to control the photovoltaic system from entering the low voltage ride-through function. Wherein, the first input signal is the phase voltage of the distributed photovoltaic grid-connected point, and the second input signal is the minimum line voltage of the distributed photovoltaic grid-connected point.

2. The low-voltage ride-through circuit according to claim 1, characterized in that, The fault type discrimination module includes: a first input port, a second input port, a comparison module, a first output port, and a second output port. The first input port is used to input a fault type characterization signal, the second input port is used to input a preset value, and the comparison module is used to compare the input of the first input port and the input of the second input port, and output the indication signal through the first output port and the second output port.

3. The low-voltage ride-through circuit according to claim 2, characterized in that, When the first output port outputs signal 1 and the second output port outputs signal 0, the indication signal is determined to be the first characterization signal; when the first output port outputs signal 0 and the second output port outputs signal 1, the indication signal is determined to be the second characterization signal.

4. The low-voltage ride-through circuit according to claim 1, characterized in that, When the first input signal is selected and the first input signal is less than the control voltage, or when the second input signal is selected and the second input signal is less than the control voltage, a control signal is generated to control the photovoltaic system so that it does not need to enter the low voltage ride-through function. When the first input signal is selected and the first input signal is not less than the control voltage, or when the second input signal is selected and the second input signal is not less than the control voltage, a control signal is generated to control the photovoltaic system to enter the low voltage ride-through function.

5. The low-voltage ride-through circuit according to claim 1, characterized in that, The reference current output module includes: The system includes a third multiplier, a fourth multiplier, a fifth multiplier, a sixth multiplier, a seventh multiplier, a second adder, a third adder, and a vector converter, where: The first input terminal of the third multiplier is connected to the third input signal, the second input terminal of the third multiplier is connected to the current amplitude of a predetermined multiple of the rated current, the output terminal of the third multiplier is connected to the first input terminal of the fourth multiplier, the second input terminal of the fourth multiplier is connected to the first node output signal, and the output terminal of the fourth multiplier is connected to the first input terminal of the second adder. The first input terminal of the fifth multiplier is connected to the third input signal, the second input terminal of the fifth multiplier is connected to the second node output signal, and the output terminal of the fifth multiplier is connected to the second input terminal of the second adder. The output of the second adder is connected to the first input of the vector converter; The first input terminal of the sixth multiplier is connected to the fourth input signal, the second input terminal of the sixth multiplier is connected to the first node output signal, and the output terminal of the sixth multiplier is connected to the first input terminal of the third adder, wherein the fourth input signal is a phase angle signal; The first input terminal of the seventh multiplier is connected to signal 0, the second input terminal of the seventh multiplier is connected to the output signal of the second node, and the output terminal of the seventh multiplier is connected to the second input terminal of the third adder. The output of the third adder is connected to the second input of the vector converter. The vector converter is used to convert the input signal into a photovoltaic positive sequence current d-axis reference value and a photovoltaic positive sequence current q-axis reference value using a vector conversion formula.

6. The low-voltage ride-through circuit according to claim 5, characterized in that, The d-axis reference value and q-axis reference value of the photovoltaic positive sequence current are used to convert the voltage value of the photovoltaic terminal in the dq coordinate system and then inversely transform it to obtain the output value of the three phases ABC of the photovoltaic terminal voltage.

7. The low-voltage ride-through circuit according to claim 5, characterized in that, The third input signal is the amplitude of the photovoltaic output current, and the fourth input signal is the phase angle signal, which is the phase difference between the distributed photovoltaic output current and the terminal voltage.

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