A DC port control system for a network-forming converter to improve power angle stability

Abstract

The present invention discloses a DC port control system for a network-forming converter to enhance power angle stability, which relates to the technical field of power system applications. Aiming at the power angle stability problem faced by new energy fields with network-forming converters under grid fault conditions, by real-time predicting the interaction energy between the DC port and the network-forming converter during the transient process, quickly calculating the power and energy differences of the network-forming converter in potential transient instability based on the notch energy function, and adjusting the dynamic characteristics and control parameters of the DC port system at the transient scale, the instantaneous storage and interaction of energy at the DC port of the network-forming converter during the transient process are realized, avoiding the occurrence of power angle instability problems and DC voltage over-limit. The present invention does not affect the control structure and performance of the original network-forming strategy. Only by adding a DC port compensation link on the basis of the original control system, it is convenient to implement, enabling the improvement of the power angle stability of the network-forming converter without changing its active support and other operating characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of power system applications, and specifically to a DC port control system for a grid-forming converter that improves power angle stability. Background Art

[0002] Under the dual pressures of fossil energy depletion and the climate environment, countries around the world have taken measures to improve energy utilization efficiency, vigorously develop clean and renewable energy to improve the energy structure, aiming to achieve sustainable energy supply and harmonious development of the economic society. The 19th National Congress of the Communist Party of China in our country has placed ecological civilization construction in a prominent position, requiring efforts to promote green development, circular development, and low-carbon development, and actively respond to climate change together with the international community; and controlling greenhouse gas emissions and achieving green and low-carbon development are also the internal requirements for our country to transform the development mode, break through the bottleneck constraints of resources and the environment, and enhance international competitiveness.

[0003] With the vigorous development of new energy power generation technology, new energy such as photovoltaic and wind power is connected to the same AC power grid through power electronic devices, and these new energy sources and the AC power grid together constitute a multi-new energy feed-in system. The grid connection of new energy through converters has significantly changed the dynamic characteristics of modern power grids, bringing challenges to the safety and stability of the power grids. On the one hand, the strong randomness and uncertainty of new energy output have an impact on the voltage quality of the power grid; on the other hand, with the increase in the proportion of new energy, the power grid shows low inertia characteristics, and the zero-inertia dynamic response of the grid-following control converter makes the power system frequency fluctuate greatly, thus bringing new power system operation safety risks.

[0004] To address the above challenges, grid-forming control technology has gradually received attention. Different from the grid-following control converter, the grid-forming control converter presents a voltage source characteristic, and the use of the virtual synchronous machine power synchronization control strategy enables it to provide virtual inertia support for the system compared with the phase-locked loop, optimizing the frequency response characteristics. The synchronization method that does not rely on external transmission phase information enables it to work in both island and grid-connected modes; however, when a grid fault occurs and the voltage drops, the DC side power of the grid-forming converter will overflow the AC side output power, resulting in the risk of transient power angle instability. Summary of the Invention

[0005] To solve the deficiencies mentioned in the above background art, the purpose of the present invention is to provide a DC port control system for a grid-forming converter that improves power angle stability, which can effectively solve the transient stability problem of the grid-forming control converter when the grid voltage drops.

[0006] In the first aspect, the purpose of the present invention can be achieved through the following technical solutions: A DC port control system for a grid-forming converter that improves power angle stability, comprising:

[0007] A power calculation module, configured to receive the voltage and current at the point of common coupling of the grid-forming converter, calculate the active power and reactive power output by the grid-forming converter, and input the active power and reactive power output by the grid-forming converter into the power synchronization module;

[0008] A DC voltage control module, configured to receive the voltage value of the DC port capacitor, compare it with a preset voltage reference value, generate an active power reference value, and input the active power reference value into the power synchronization module;

[0009] A power synchronization module, configured to calculate the amplitude and phase of the converter output voltage according to the active power value and the active power reference value output by the grid-forming converter, and input the amplitude and phase of the converter output voltage into the voltage reference value synthesis module;

[0010] A voltage reference value synthesis module, configured to generate a converter output voltage reference value according to the amplitude and phase of the converter output voltage, and input the converter output voltage reference value into the voltage control module;

[0011] A voltage control module, configured to compare the converter output voltage reference value with the actual value to generate a current reference value, and input the current reference value into the current control module;

[0012] A current control module, configured to compare the current reference value with the actual value to generate a voltage reference value before the filtering device, and input the voltage reference value before the filtering device into the pulse width modulation module;

[0013] A pulse width modulation module, configured to generate a converter drive signal according to the voltage reference value before the filtering device.

[0014] Combined with the first aspect, in some implementation manners of the first aspect, the system further includes: the DC voltage control module includes: a steady-state DC voltage control module, a notch energy prediction module, and a transient voltage additional control module.

[0015] Combined with the first aspect, in some implementation manners of the first aspect, the system further includes: the steady-state DC voltage control module receives the energy mapping value of the converter DC port voltage, subtracts it from a preset reference value, and inputs it into a transient voltage two-way deadbeat regulator to output a compensation reference value for the active power on the AC side of the converter.

[0016] In combination with the first aspect, in certain implementation manners of the first aspect, the system further includes: the notch energy prediction module is composed of a notch filter and a hysteresis comparator. The notch filter receives the difference between the measured value and the reference value of the output power of the converter, filters out interference signals of specific frequencies, and then outputs an energy difference. The energy difference is input to the hysteresis comparator and compared with the stable power threshold derived by the equal-area method of kinetic and potential energy, and then the energy interaction prediction result between the DC port and the AC side of the converter is output. The energy interaction prediction types include two working condition types: no instability risk and presence of instability risk. When the output of the hysteresis comparator is positive, the prediction result is that there is a risk of transient power angle instability; when the output of the hysteresis comparator is negative, the prediction result is that there is no risk of transient power angle instability.

[0017] In combination with the first aspect, in certain implementation manners of the first aspect, the system further includes: the transient voltage additional control module is composed of a transient voltage two-channel zero-static regulator and a voltage superposition device; the transient voltage additional control module receives the energy difference output by the notch energy prediction module, obtains the adjustment result of the DC voltage under the transient scale through the transient voltage two-channel zero-static regulator, and obtains the DC voltage reference value for the AC-DC power balance under the grid fault condition through the superposition device with the DC voltage reference value under the steady state condition.

[0018] In combination with the first aspect, in certain implementation manners of the first aspect, the system further includes: the power synchronization module performs power control, droop control, and virtual synchronous machine control, and generates the reference values of the output voltage power angle and amplitude through the adjustment process of different control methods by receiving the offset between the output power of the AC side of the converter and its reference value.

[0019] In combination with the first aspect, in certain implementation manners of the first aspect, the system further includes: under the normal operation state of the grid, the energy difference between the DC side and the AC side of the converter is approximately zero, the DC side capacitor does not perform charge and discharge operations, the energy difference of the notch energy prediction module does not exceed the comparator threshold, and the prediction result is that there is no potential instability risk; the output of the transient voltage additional module is set to zero, the grid-forming converter operates according to the preset active power command, and the DC voltage control module does not affect the normal operation and dynamic characteristics of the grid-forming strategy.

[0020] In combination with the first aspect, in certain implementations of the first aspect, the system further includes: when a grid voltage dip fault occurs, the active power output by the grid-forming converter drops instantaneously during the fault, and a large power difference is generated between the DC side and the AC side of the converter; at this time, when the energy difference received by the notch energy prediction module exceeds the threshold, the hysteresis comparator outputs a prediction result that the converter has a risk of instability, and the transient voltage additional control module starts to work. The energy difference passes through the transient voltage dual-path zero-static regulator to obtain the adjustment result of the DC voltage in the transient scale, raises the DC voltage reference value in the transient fault state, changes the dynamic characteristics of the DC port, so that the DC port transiently stores and compensates for the power difference of the converter; the unbalanced power of the converter reduced via the DC port reduces the power angle overshoot, thereby limiting and protecting the DC voltage.

[0021] In another aspect of the present invention, in order to achieve the above object, a terminal device is disclosed, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores a computer program capable of running on the processor. When the processor loads and executes the computer program, it adopts a grid-forming converter DC port control system for improving power angle stability as described above.

[0022] In another aspect of the present invention, in order to achieve the above object, a computer-readable storage medium is disclosed. The computer-readable storage medium stores a computer program. When the computer program is loaded and executed by the processor, it adopts a grid-forming converter DC port control system for improving power angle stability as described above.

[0023] Advantages of the present invention:

[0024] The control structure of the present invention is simple, parameter adjustment is easy, it does not affect the reference power of the converter under the normal operation state of the grid, does not require mode switching between the normal operation state and the fault state of the grid, can adaptively control the DC port of the grid-forming converter to temporarily store transient energy at the moment of a large-signal disturbance fault in the grid, provides instant transient power angle stability support for the grid-forming converter, can shorten the transient process of the system in the case of a large-signal disturbance fault in the grid, enables the system to restore the stable operation state in a short time, reduces the overshoot of the DC capacitor voltage, alleviates the overvoltage risk of the DC port, only uses the active power reference value and the actual output value in the control of the grid-forming converter as feedback quantities, does not depend on time-varying system information such as voltage drop degree and line impedance, avoids the deviation of the transient energy stored in the DC port caused by communication delay, improves the rapidity of power angle stability support, and reduces the complexity and implementation difficulty of the control strategy. Description of the Drawings

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0026] Figure 1 This is the control block diagram of the grid-forming converter virtual synchronous machine with an adaptive transient support loop introduced in the embodiment of the present invention;

[0027] Figure 2 This is the typical system structure and control block diagram of the grid-forming converter in the embodiment of the present invention;

[0028] Figure 3 This is the schematic diagram of the control effect of the present invention.

[0029] In the figure:

[0030] 1. Infinite bus; 2. Filtering equipment; 3. Grid-forming converter; 4. DC port; 4-1. DC port capacitor; 5. Power calculation module; 6. DC voltage control module; 6-1. Steady-state DC voltage control module; 6-2. Notch energy prediction module; 6-3 Transient voltage additional control module; 7. Power synchronization control module; 7-1. Power droop synchronization control module; 7-2. Virtual synchronous machine control module; 8. Voltage reference value synthesis module; 9. Voltage control module; 10; Current control module; 11. Pulse width modulation module. Specific implementation mode

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] Embodiment 1:

[0033] As Figure 1 shown, a DC port control system of a grid-forming converter for improving power angle stability, characterized by including:

[0034] A power calculation module 5, configured to receive the voltage and current of the grid-forming converter at the point of common coupling, calculate the active power and reactive power output by the grid-forming converter, and input the active power and reactive power output by the grid-forming converter to the power synchronization module 7;

[0035] The DC voltage control module 6 is used to receive the voltage value of the DC port capacitor. After comparing it with the preset voltage reference value, it generates an active power reference value and inputs the active power reference value into the power synchronization module 7;

[0036] The DC voltage control module 6 includes: a steady-state DC voltage control module 6-1, a notch energy prediction module 6-2, and a transient voltage additional control module 6-3;

[0037] The steady-state DC voltage control module 6-1 receives the energy mapping value of the converter DC port voltage. After taking the difference with the reference value, it inputs the compensated reference value of the active power on the AC side of the converter to the transient voltage two-way deadbeat regulator.

[0038] The notch energy prediction module 6-2 is composed of a notch filter and a hysteresis comparator. The notch filter receives the difference between the measured value and the reference value of the converter output power, filters out the interference signals of specific frequencies, and then outputs the energy difference. The energy difference is input to the hysteresis comparator and compared with the stable power threshold derived by the equal area method of kinetic and potential energy, and then outputs the energy interaction prediction result between the DC port and the AC side of the converter. The energy interaction prediction types include two working condition types: no instability risk and instability risk. When the output of the hysteresis comparator is positive, the prediction result is that there is a risk of transient power angle instability; when the output of the hysteresis comparator is negative, the prediction result is that there is no risk of transient power angle instability.

[0039] The transient voltage additional control module 6-3 is composed of a transient voltage two-way deadbeat regulator and a voltage superposition device; the transient voltage additional control module receives the energy difference output by the notch energy prediction module, obtains the regulation result of the DC voltage under the transient scale through the transient voltage two-way deadbeat regulator, and obtains the DC voltage reference value for the AC-DC power balance under the grid fault condition through the superposition device with the DC voltage reference value under the steady-state condition, realizing the transient storage and compensation of the energy difference between the DC side and the AC side of the converter at the DC port under the transient fault condition, and realizing the regulation of the DC voltage under the fault condition to avoid the DC voltage exceeding the limit.

[0040] The power synchronization module 7 is used to calculate the amplitude and phase of the converter output voltage according to the active power value and the active power reference value output by the network-forming converter, and input the amplitude and phase of the converter output voltage into the voltage reference value synthesis module 8;

[0041] The power synchronization module 7 performs power control, droop control, and virtual synchronous machine control. By receiving the offset between the output power of the converter AC side and its reference value, it generates the reference values of the output voltage power angle and amplitude through the adjustment process of different control methods.

[0042] The voltage reference value synthesis module 8 is used to generate the converter output voltage reference value according to the amplitude and phase of the converter output voltage, and input the converter output voltage reference value into the voltage control module 9;

[0043] The voltage control module 9 is used to compare the converter output voltage reference value with the actual value to generate the current reference value, and input the current reference value into the current control module 10;

[0044] The current control module 10 is used to compare the current reference value with the actual value to generate the voltage reference value before the filter device, and input the voltage reference value before the filter device into the pulse width modulation module 11;

[0045] The pulse width modulation module 11 is used to generate the converter drive signal according to the voltage reference value before the filter device.

[0046] When the power grid is operating normally, as Figure 2 shown, the notch energy prediction module 6-2 receives the power values of the DC side and the AC side of the converter, filters out the interference signals of specific frequencies through the notch filter 6-2-1, inputs them into the hysteresis comparator 6-2-2, compares with the power threshold value, and outputs the energy interaction prediction results of the converter DC port and the AC side. When the power grid is operating normally, the energy difference between the DC port and the AC side is 0, and the notch energy prediction module outputs a prediction result that there is no potential instability risk; the transient voltage addition module 6-3 outputs the regulator 6-3-2 to be set to zero, and the grid-forming converter operates according to the active power command calculated by the steady-state DC voltage control module 6-1;

[0047] When a voltage dip fault occurs in the power grid, the active power output by the grid-forming converter 3 drops instantaneously at the moment of the fault, and a large power difference is generated between the DC side and the AC side of the converter; at this time, the energy difference received by the notch energy prediction module 6-2 exceeds its threshold value, and the hysteresis comparator outputs a prediction result that the converter has an instability risk. The transient voltage addition control module 6-3 starts to work. The energy difference passes through the transient voltage two-way zero-static regulator 6-3-1 to obtain the regulation result of the DC voltage under the transient scale, and is superimposed with the voltage reference value under the steady-state condition through the voltage adder 6-3-3 to raise the DC voltage reference value under the transient fault state, realizing the transient storage and compensation of the converter power difference at the DC port; the unbalanced power of the converter reduced through the DC port can reduce its power angle overshoot and avoid the potential transient power angle instability risk of the converter.

[0048] The control effect of a DC control method for a grid-forming converter for improving power angle stability proposed in this patent is as Figure 3As shown, at the moment when the grid voltage fault occurs, the DC voltage reference value is superimposed with the adjustment result of the transient voltage additional control module 6-3 to control the rapid rise of the DC capacitor voltage and temporarily store the unbalanced power of the converter under the fault, thereby improving the transient power angle stability of the converter. Figure 3 The left and right respectively show the effects of traditional DC control and improved DC control, indicating that introducing the DC control proposed in the present invention can enable the grid-forming converter to remain synchronized with the grid under transient faults, avoiding the risk of transient instability. The control method that does not require mode switching does not affect the operating point of the converter under steady state and can trigger control at the moment when the fault occurs, avoiding the instability risk caused by communication delay. This control method accelerates the transient process of the converter, shortens the overshoot of the DC capacitor voltage, and avoids the overvoltage risk at the DC port.

[0049] Based on the same inventive concept, the present invention also provides a computer device, which includes: one or more processors, and a memory for storing one or more computer programs; the program includes program instructions, and the processor is used to execute the program instructions stored in the memory. The processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is used to implement one or more instructions. Specifically, it is used to load and execute one or more instructions in the computer storage medium to implement the above method.

[0050] It should be further noted that, based on the same inventive concept, the present invention also provides a computer storage medium, on which a computer program is stored. When the computer program is run by a processor, the above-mentioned method is executed. The storage medium can be any combination of one or more computer-readable media. The computer-readable media can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present invention, the computer-readable storage medium can be any tangible medium that contains or stores a program, and this program can be used by or combined with an instruction execution system, apparatus, or device.

[0051] In the description of this specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0052] The above shows and describes the basic principles, main features, and advantages of the present disclosure. Those skilled in the art should understand that the present disclosure is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present disclosure. Without departing from the spirit and scope of the present disclosure, the present disclosure will have various changes and improvements, and these changes and improvements all fall within the scope of the present disclosure claimed.

Claims

1. A DC port control system for a network-forming converter to improve power angle stability, characterized in that Including: A power calculation module, configured to receive the voltage and current of the grid-forming converter at the point of common coupling, calculate the active power and reactive power output by the grid-forming converter, and input the active power and reactive power output by the grid-forming converter into the power synchronization module; A DC voltage control module, configured to receive the voltage value of the DC port capacitor, generate an active power reference value after comparing it with a preset voltage reference value, and input the active power reference value into the power synchronization module; The DC voltage control module includes: a steady-state DC voltage control module, a notch energy prediction module, and a transient voltage additional control module; The steady-state DC voltage control module receives the energy mapping value of the converter DC port voltage, subtracts it from the preset reference value, and inputs it to the transient voltage two-way deadbeat regulator to output the compensation reference value of the active power on the AC side of the converter; The notch energy prediction module is composed of a notch filter and a hysteresis comparator. The notch filter receives the difference between the measured value and the reference value of the converter output power, filters out the interference signals of specific frequencies, and outputs the energy difference. The energy difference is input to the hysteresis comparator and compared with the stable power threshold deduced by the equal area method of kinetic and potential energy to output the energy interaction prediction result between the DC port and the AC side of the converter. The energy interaction prediction types include: two working condition types of no instability risk and existence of instability risk. When the output of the hysteresis comparator is positive, the prediction result is that there is a risk of transient power angle instability; when the output of the hysteresis comparator is negative, the prediction result is that there is no risk of transient power angle instability; The transient voltage additional control module consists of a transient voltage two-way deadbeat regulator and a voltage adder; the transient voltage additional control module receives the energy difference output by the notch energy prediction module, obtains the regulation result of the DC voltage under the transient scale through the transient voltage two-way deadbeat regulator, and obtains the DC voltage reference value for the AC-DC power balance under the grid fault condition through the adder with the DC voltage reference value in the steady state; A power synchronization module, configured to calculate the amplitude and phase of the converter output voltage according to the active power value and the active power reference value output by the grid-forming converter, and input the amplitude and phase of the converter output voltage into the voltage reference value synthesis module; A voltage reference value synthesis module, configured to generate a converter output voltage reference value according to the amplitude and phase of the converter output voltage, and input the converter output voltage reference value into the voltage control module; A voltage control module, configured to compare the converter output voltage reference value with the actual value to generate a current reference value, and input the current reference value into the current control module; A current control module, configured to compare the current reference value with the actual value to generate a voltage reference value before the filter device, and input the voltage reference value before the filter device into the pulse width modulation module; A pulse width modulation module, configured to generate a converter drive signal according to the voltage reference value before the filter device.

2. The DC port control system of a network-forming converter for enhancing power angle stability according to claim 1, wherein, Under the normal operation state of the power grid, the energy difference between the DC side and the AC side of the converter is zero, the DC side capacitor does not charge or discharge, the energy difference of the notch energy prediction module does not exceed the comparator threshold, and the prediction result is that there is no potential instability risk; the output of the transient voltage addition module is set to zero, the grid-forming converter operates according to the preset active power command, and the DC voltage control module does not affect the normal operation and dynamic characteristics of the grid-forming strategy.

3. The DC port control system of a network-forming converter for enhancing power angle stability according to claim 2, characterized in that When a voltage dip fault occurs in the power grid, the active power output by the grid-forming converter drops instantaneously at the moment of the fault, and a large power difference is generated between the DC side and the AC side of the converter; at this time, the energy difference received by the notch energy prediction module exceeds the threshold, and the hysteresis comparator outputs a prediction result that the converter has an instability risk. The transient voltage addition control module starts to work. The energy difference passes through the transient voltage two-way deadbeat regulator to obtain the adjustment result of the DC voltage under the transient scale, raises the DC voltage reference value under the transient fault state, changes the dynamic characteristics of the DC port, and enables the DC port to transiently store and compensate for the power difference of the converter; the unbalanced power of the converter reduced via the DC port reduces the power angle overshoot, avoids the potential transient power angle instability risk of the converter, and at the same time limits and protects the DC voltage.

4. The DC port control system of a network-forming converter for improving power angle stability according to claim 1, wherein, The power synchronization module performs power control, droop control, and virtual synchronous machine control. By receiving the offset between the output power of the converter's AC side and its reference value, it generates the reference values of the output voltage power angle and amplitude through the adjustment process of different control methods.

5. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, The memory stores a computer program that can run on a processor. When the processor loads and executes the computer program, it adopts a DC port control system for a grid-forming converter that improves power angle stability according to any one of claims 1 to 4.

6. A computer-readable storage medium storing a computer program therein, characterized in that, When the computer program is loaded and executed by the processor, it adopts a DC port control system for a grid-forming converter that improves power angle stability according to any one of claims 1 to 4.

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