Low-voltage ride-through control method and device for network-forming inverter

Abstract

The invention relates to the technical field of power electronics, and discloses a low-voltage ride-through control method and device for a network-forming inverter, and the method comprises the steps: monitoring the voltage drop degree of a network side; and adjusting a proportional control coefficient and an integral control coefficient of a proportional-integral controller in the grid-forming inverter according to the grid-side voltage drop degree. By adaptively adjusting the reactive power-voltage loop PI parameter, the stability of the inverter is ensured, and the reactive current response speed of the network-forming inverter during low voltage ride through is greatly improved at the same time.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a low voltage ride-through control method and device for a grid-connected inverter. Background Art

[0002] With the rapid increase in the penetration rate of new energy, the strength of the power grid continues to weaken, and traditional grid-following photovoltaic / energy storage inverters cannot provide fast and reliable support for the strength of the power grid. Therefore, the grid-building inverter designed based on the characteristics of synchronous generators has received more and more attention for its inherent inertia support capability, frequency regulation capability and voltage support capability, and will be widely used in future new power systems. However, the current grid-building technology is far from mature. Compared with the grid-building inverter, it is not adaptable enough to grid faults, and it is more difficult to control during low voltage crossing. At present, for the low voltage crossing of the grid-building type, generally only the stability during the crossing process is considered, and there is no in-depth study on the performance during the crossing process, resulting in a slow reactive current support speed when the grid is short-circuited, which is not conducive to the rapid recovery of the grid. Summary of the invention

[0003] In view of this, the present invention provides a low voltage ride through control method and device for a grid-type inverter to solve the problem of slow reactive current response speed of the grid-type inverter during low voltage ride through.

[0004] In a first aspect, the present invention provides a low voltage ride-through control method for a grid-connected inverter, the method comprising:

[0005] Monitor the voltage drop degree on the grid side;

[0006] The proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-connected inverter are adjusted according to the degree of grid-side voltage drop.

[0007] The present invention provides a low voltage ride-through control method for a grid-type inverter, which greatly improves the reactive current response speed of the grid-type inverter during low voltage ride-through while ensuring the stability of the inverter by adaptively adjusting the reactive-voltage loop PI parameters.

[0008] In an optional implementation manner, monitoring the grid-side voltage drop degree includes:

[0009] Get the electrical status value of the grid-connected inverter during operation;

[0010] Determining whether a power grid fault occurs according to the electrical status value;

[0011] When a grid fault occurs, the grid-side voltage drop is calculated based on the grid-side voltage and the rated voltage.

[0012] In an optional implementation manner, adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-type inverter according to the grid-side voltage drop degree includes:

[0013] Substitute the grid-side voltage drop degree into the adaptive coefficient calculation formula to obtain the adaptive coefficient of the proportional-integral controller;

[0014] The proportional control coefficient and the integral control coefficient of the proportional-integral controller are adjusted according to the adaptive coefficient.

[0015] In an optional implementation, the adaptive coefficient calculation formula is:

[0016] N=A*Ut+B

[0017] Among them, N is the adaptive coefficient, Ut is the voltage drop degree on the grid side, and A and B are constants.

[0018] In an optional implementation, adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller according to the adaptive coefficient includes:

[0019] Obtain the proportional control coefficient and the integral control coefficient of the proportional-integral controller when the grid-connected inverter is in normal operation;

[0020] The proportional control coefficient and the adaptive coefficient are adjusted and multiplied to obtain the proportional control coefficient of the proportional-integral controller during low voltage ride-through;

[0021] The integral control coefficient and the adaptive coefficient are adjusted and multiplied to obtain the integral control coefficient of the proportional-integral controller during low voltage ride-through.

[0022] In a second aspect, the present invention provides a low voltage ride through control device for a grid-type inverter, the device comprising:

[0023] Monitoring module, used to monitor the voltage drop degree on the grid side;

[0024] The regulating module is used to adjust the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-type inverter according to the degree of grid-side voltage drop.

[0025] The present invention provides a low voltage ride-through control device for a grid-type inverter, which adaptively adjusts the reactive-voltage loop PI parameters to ensure the stability of the inverter while greatly improving the reactive current response speed of the grid-type inverter during low voltage ride-through.

[0026] In an optional implementation, the monitoring module includes:

[0027] An acquisition unit, used to acquire the electrical state value of the grid-connected inverter when it is running;

[0028] A judgment unit, used for judging whether a fault occurs in the power grid according to the electrical state value;

[0029] The calculation unit is used to calculate the grid-side voltage drop degree according to the grid-side voltage and the rated voltage when a grid fault occurs.

[0030] In an optional implementation, the adjustment module includes:

[0031] A processing unit, used for bringing the grid-side voltage drop degree into the adaptive coefficient calculation formula to obtain the adaptive coefficient of the proportional-integral controller;

[0032] A setting unit is used to adjust the proportional control coefficient and the integral control coefficient of the proportional-integral controller according to the adaptive coefficient.

[0033] In a third aspect, the present invention provides a computer device, comprising: a memory and a processor, the memory and the processor are communicatively connected to each other, computer instructions are stored in the memory, and the processor executes the low voltage ride-through control method of the grid-connected inverter of the first aspect or any corresponding embodiment thereof by executing the computer instructions.

[0034] In a fourth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the low voltage ride-through control method for a grid-type inverter of the first aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 is a flow chart of a low voltage ride-through control method for a grid-connected inverter according to an embodiment of the present invention;

[0037] Figure 2 is a control schematic diagram of a reactive power-voltage loop of a grid-type inverter according to an embodiment of the present invention;

[0038] Figure 3 is a schematic diagram of inverter output simulation under fixed parameters according to an embodiment of the present invention;

[0039] Figure 4 is a schematic diagram of inverter output simulation under parameter adaptation according to an embodiment of the present invention;

[0040] Figure 5 is a structural block diagram of a low voltage ride through control device for a grid-type inverter according to an embodiment of the present invention;

[0041] Figure 6 It is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0043] For the low voltage ride-through of the inverter, on the one hand, the stability of the ride-through process must be ensured, that is, the inverter must not be disconnected from the grid during the ride-through process. Another very important aspect is to examine the response speed of its reactive current. The traditional grid-following inverter is connected to the grid as a current source, and its control speed can be designed to be very fast to ensure its fast tracking capability in the event of a grid failure. The grid-building inverter is connected to the grid as a voltage source, which determines that its control speed cannot be very fast, otherwise it will cause oscillation and disconnection from the grid. This results in the reactive loop of the grid-building inverter responding very slowly when a short circuit occurs in the grid, and it cannot quickly emit reactive current, which cannot meet the grid's demand for the grid-building inverter to quickly emit reactive current to support the grid.

[0044] In order to solve the problem of slow reactive current response speed of a grid-type inverter during low voltage crossing, an embodiment of the present invention provides a low voltage crossing control method for a grid-type inverter. By adaptively adjusting the reactive-voltage loop PI parameters, the reactive current response speed of the grid-type inverter during low voltage crossing is greatly improved while ensuring the stability of the inverter.

[0045] According to an embodiment of the present invention, an embodiment of a low voltage ride-through control method for a grid-type inverter is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0046] In this embodiment, a low voltage ride-through control method for a grid-type inverter is provided, which can be used for a grid-type inverter. Figure 1 is a flow chart of a low voltage ride through control method of a grid-connected inverter according to an embodiment of the present invention. Figure 1 As shown, the process includes the following steps:

[0047] Step S11, monitoring the voltage drop degree on the grid side.

[0048] Specifically, the control of the reactive power-voltage loop of the grid-type inverter is as follows: Figure 2 As shown, Qref is the reactive power given value, Q is the reactive power feedback value, △Q is the feedback error, and PI control is a proportional-integral controller, whose output is △U, which is added to the rated voltage Un to obtain the inverter port voltage given value Uref. The PI controller is used to control Q to track Qref, and it has two control parameters, namely the proportional control coefficient Kp and the integral control coefficient Ki.

[0049] According to regulatory requirements, when the grid-side voltage Us is detected to be less than 0.9Un, it is considered that a short-circuit fault occurs in the grid, and the grid-connected inverter enters the low voltage ride-through state. The value of the required output reactive current increment △Iq is calculated according to the degree of grid voltage drop. The calculation formula is:

[0050] △Iq= K(0.9 - Ut)* In (0≤Ut≤0.9) (1)

[0051] Among them, △Iq is the reactive current increment of the grid-connected inverter output; K is the proportional coefficient, which is generally between 1.5 and 3; Ut is the ratio of Us to Un; In is the rated current.

[0052] Because the grid-connected inverter cannot directly control the reactive current, it is necessary to convert the reactive current into reactive power for control. According to △Iq and Us, △Qref can be calculated as:

[0053] △Qref= 3 * Us * △Iq (2)

[0054] Then we get Qref=Q0+ΔQref, where Q0 is the Qref value before the low breakout.

[0055] According to formula (2), it can be seen that the reactive power that the grid-type inverter needs to output will vary greatly under different drop depths. In the existing technology, the PI control parameter is a fixed value. In the experiment, it was found that the control effect of the fixed parameter under different grid voltage drop degrees varies greatly. As the grid voltage decreases, the response speed of the reactive current control also decreases. Under the condition of lower grid voltage, it cannot meet the requirements of existing regulations for reactive current response speed.

[0056] Step S12, adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-connected inverter according to the grid-side voltage drop degree.

[0057] Specifically, to solve the problem in step S11, the embodiment of the present invention adaptively adjusts the PI parameters according to the depth of the grid voltage drop to improve the stability of the inverter and the rapidity of the response.

[0058] The present invention provides a low voltage ride-through control method for a grid-type inverter, comprising: monitoring the voltage drop degree on the grid side; adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-type inverter according to the voltage drop degree on the grid side. By adaptively adjusting the reactive-voltage loop PI parameters, the reactive current response speed of the grid-type inverter during low voltage ride-through is greatly improved while ensuring the stability of the inverter.

[0059] In an optional implementation, step S11 includes:

[0060] Step S111, obtaining the electrical state value of the grid-connected inverter during operation.

[0061] Step S112, judging whether a power grid fault occurs according to the electrical status value.

[0062] Step S113, when a grid fault occurs, the grid-side voltage drop degree is calculated according to the grid-side voltage and the rated voltage.

[0063] Specifically, the real-time electrical status value of the grid-connected inverter is obtained, and whether the grid fails is determined based on the electrical status value. When Us is less than 0.9Un, the grid is determined to have failed. When the grid is determined to have failed, the grid-connected inverter is switched to low voltage ride-through, and the ratio of the grid-side voltage to the rated voltage is calculated, and the ratio is used to characterize the degree of grid-side voltage drop.

[0064] In an optional implementation, step S12 includes:

[0065] Step S121, the grid-side voltage drop degree is substituted into the adaptive coefficient calculation formula to obtain the adaptive coefficient of the proportional-integral controller.

[0066] Specifically, the adaptive coefficient calculation formula is:

[0067] N= A * Ut + B (3)

[0068] Among them, N is the adaptive coefficient, Ut is the voltage drop degree on the grid side, and A and B are constants.

[0069] In an embodiment of the present invention, A and B are adjusted according to the system performance requirements. A 40kW three-phase inverter is taken as an example to illustrate the specific design method of adaptive parameters. When the grid-side voltage drops more deeply, a larger N is required to increase the response speed. For example, when Ut=0.4, N=10 is set. When the grid-side voltage drops less, a smaller N is required to avoid a sudden increase in reactive power, which causes Ut to be instantaneously greater than 0.9, and the inverter exits the low-through mode, causing the inverter to frequently enter and exit the low-through mode, causing the grid-side voltage to oscillate violently. Therefore, when Ut=0.9, N=1 is designed. Substituting the two Ut values ​​and N values ​​into formula (3) respectively, we get A=-18 and B=17.2. That is, N=-18*Ut+17.2.

[0070] Step S122, adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller according to the adaptive coefficient.

[0071] Specifically, step S122 includes:

[0072] Step S1221, obtaining a proportional control coefficient and an integral control coefficient of a proportional-integral controller when the grid-connected inverter operates normally.

[0073] Step S1222, multiplying the proportional control coefficient and the adaptive coefficient adjustment to obtain the proportional control coefficient of the proportional-integral controller during low voltage ride-through.

[0074] Step S1223, multiplying the integral control coefficient and the adaptive coefficient adjustment to obtain the integral control coefficient of the proportional-integral controller during low voltage ride-through.

[0075] In the embodiment of the present invention, the proportional control coefficient adjustment formula is as follows:

[0076] Kp1= N * Kp (4)

[0077] Among them, Kp is the PI parameter during normal operation, Kp1 is the PI control parameter during low voltage ride-through, and N is the adaptive coefficient.

[0078] The integral control coefficient adjustment formula is as follows:

[0079] Ki1= N * Ki (5)

[0080] Among them, Ki is the PI parameter during normal operation, Ki1 is the PI control parameter during low voltage ride-through, and N is the adaptive coefficient.

[0081] In an optional implementation, the advantages of the present application scheme over the existing scheme are verified by using a Simulink simulation model. A 40kW grid-type inverter and a grid model are built in Simulink, and the reactive loop PI parameters are Kp = 0.0001 and Ki = 0.00005. First, the working condition where the grid voltage drops to 0.2Un is simulated. Figure 3 and Figure 4 shown. Figure 3 The reactive power output by the inverter under fixed parameters, where the grid fault occurs in 2s and the reactive power response time is about 500ms. Figure 4 The simulation results of the parameter adaptive scheme under the same working conditions show that the reactive power response time is about 20ms, which is much shorter than the response time under fixed parameters, verifying the effectiveness of the proposed technical scheme.

[0082] In this embodiment, a low voltage ride-through control device for a grid-type inverter is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and will not be repeated for those that have been described. As used below, the term "module" can implement a combination of software and / or hardware for a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0083] This embodiment provides a low voltage ride through control device for a grid-type inverter, such as Figure 5 As shown, including:

[0084] The monitoring module 51 is used to monitor the voltage drop degree on the grid side.

[0085] The regulating module 52 is used to regulate the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-connected inverter according to the grid-side voltage drop degree.

[0086] The present invention provides a low voltage ride-through control device for a grid-type inverter, which adaptively adjusts the reactive-voltage loop PI parameters to ensure the stability of the inverter while greatly improving the reactive current response speed of the grid-type inverter during low voltage ride-through.

[0087] In an optional embodiment, the monitoring module 51 includes:

[0088] The acquisition unit 511 is used to acquire the electrical state value of the grid-connected inverter during operation.

[0089] The judgment unit 512 is used to judge whether a fault occurs in the power grid according to the electrical state value.

[0090] The calculation unit 513 is used to calculate the grid-side voltage drop degree according to the grid-side voltage and the rated voltage when a grid fault occurs.

[0091] In an optional embodiment, the adjustment module 52 includes:

[0092] The processing unit 521 is used to bring the grid-side voltage drop degree into the adaptive coefficient calculation formula to obtain the adaptive coefficient of the proportional-integral controller.

[0093] The tuning unit 522 is used to adjust the proportional control coefficient and the integral control coefficient of the proportional-integral controller according to the adaptive coefficient.

[0094] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0095] The low voltage ride-through control device of the grid-type inverter in this embodiment is presented in the form of a functional unit, where the unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that executes one or more software or fixed programs, and / or other devices that can provide the above functions.

[0096] The embodiment of the present invention also provides a computer device having the above Figure 5 The low voltage ride through control device of the grid-type inverter is shown.

[0097] See also Figure 6 , Figure 6 is a schematic diagram of the structure of a computer device provided by an optional embodiment of the present invention, such as Figure 6 As shown, the computer device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple computer devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 6 A processor 10 is taken as an example.

[0098] The processor 10 may be a central processing unit, a network processor or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0099] The memory 20 stores instructions executable by at least one processor 10, so that the at least one processor 10 executes the method shown in the above embodiment.

[0100] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created according to the use of the computer device, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely arranged relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0101] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid state drive; the memory 20 may also include a combination of the above types of memory.

[0102] The computer device further comprises a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0103] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0104] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A low voltage ride through control method for a grid-connected inverter, characterized in that: The method comprises: Monitor the voltage drop degree on the grid side; The proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-type inverter are adjusted according to the degree of grid-side voltage drop.

2. The low voltage ride through control method of the grid-connected inverter according to claim 1, characterized in that: The monitoring of the voltage drop degree on the grid side includes: Get the electrical status value of the grid-connected inverter during operation; Determining whether a power grid fault occurs according to the electrical status value; When a grid fault occurs, the grid-side voltage drop is calculated based on the grid-side voltage and the rated voltage.

3. The low voltage ride through control method of a grid-connected inverter according to claim 1, characterized in that: The method of adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-type inverter according to the grid-side voltage drop degree includes: Substitute the grid-side voltage drop degree into the adaptive coefficient calculation formula to obtain the adaptive coefficient of the proportional-integral controller; The proportional control coefficient and the integral control coefficient of the proportional-integral controller are adjusted according to the adaptive coefficient.

4. The low voltage ride through control method of the grid-connected inverter according to claim 3, characterized in that: The adaptive coefficient calculation formula is: N=A*Ut+B Among them, N is the adaptive coefficient, Ut is the voltage drop degree on the grid side, and A and B are constants.

5. The low voltage ride through control method of a grid-connected inverter according to claim 3, characterized in that: The step of adjusting the proportional control coefficient and the integral control coefficient of the proportional-integral controller according to the adaptive coefficient comprises: Obtain the proportional control coefficient and the integral control coefficient of the proportional-integral controller when the grid-connected inverter is in normal operation; The proportional control coefficient and the adaptive coefficient are adjusted and multiplied to obtain the proportional control coefficient of the proportional-integral controller during low voltage ride-through; The integral control coefficient and the adaptive coefficient are adjusted and multiplied to obtain the integral control coefficient of the proportional-integral controller during low voltage ride-through.

6. A low voltage ride through control device for a grid-type inverter, characterized in that: The device comprises: Monitoring module, used to monitor the voltage drop degree on the grid side; The regulating module is used to adjust the proportional control coefficient and the integral control coefficient of the proportional-integral controller in the grid-type inverter according to the degree of grid-side voltage drop.

7. The low voltage ride through control device of the grid-type inverter according to claim 6, characterized in that: The monitoring module comprises: An acquisition unit, used to acquire the electrical state value of the grid-connected inverter when it is running; A judgment unit, used for judging whether a fault occurs in the power grid according to the electrical state value; The calculation unit is used to calculate the grid-side voltage drop degree according to the grid-side voltage and the rated voltage when a grid fault occurs.

8. The low voltage ride through control device of a grid-type inverter according to claim 6, characterized in that: The adjustment module comprises: A processing unit, used for bringing the grid-side voltage drop degree into the adaptive coefficient calculation formula to obtain the adaptive coefficient of the proportional-integral controller; A setting unit is used to adjust the proportional control coefficient and the integral control coefficient of the proportional-integral controller according to the adaptive coefficient.

9. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the low voltage ride-through control method of the grid-connected inverter according to any one of claims 1 to 5 by executing the computer instructions.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a computer to execute the low voltage ride-through control method for a grid-type inverter according to any one of claims 1 to 5.

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