Harmonic suppression method for power distribution network and related equipment

Abstract

The invention provides a power distribution network harmonic suppression method and related equipment. The method comprises the following steps: constructing a topological structure and a mathematical model of a distributed power supply interface inverter in a target power distribution network; constructing a hybrid control mode based on the current control mode and the voltage control mode; and based on the hybrid control mode, the topological structure of the distributed power supply interface inverter and the mathematical model, different frequency domains of the distributed power supply interface inverter are respectively controlled so as to realize harmonic suppression of the target power distribution network. Compared with the prior art, the harmonic amplification and propagation phenomena of the power distribution network are effectively inhibited, so that the power quality of the power distribution network is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method for suppressing harmonics in a distribution network and related equipment. Background Art

[0002] Under the "dual carbon" goals of carbon peak and carbon neutrality, ensuring national energy supply is a major mission for deepening the energy revolution. Distributed power sources (DG, Distributed Generation) such as photovoltaics and wind power with power electronic converters as grid-connected interfaces are developing rapidly.

[0003] With the widespread access of DG and flexible loads, the distribution network is increasingly showing the "double high" characteristics of a high proportion of renewable energy and a high proportion of power electronics, which has profoundly changed the dynamic behavior of the power grid, and its operation and management are facing unprecedented challenges. Among them, the problems of broadband oscillation and high-frequency harmonics are particularly prominent, which not only seriously affects the power quality of the distribution network, but also may damage the normal operation of the power grid and user equipment. Due to the characteristics of small power, large number and dispersed location of nonlinear harmonic sources such as DG inverters and flexible loads in the "double high" distribution network, the traditional method of centrally installing power quality adjustment devices such as passive or active filters at a single node is no longer applicable, and the global harmonic suppression effect is not significant. In addition, the harmonic resonance phenomenon that may exist in the distribution network will lead to the amplification and diffusion of harmonic sources, making the cross-regional propagation of harmonic pollution and the dynamic chain evolution phenomenon significantly more serious. Therefore, the "double high" distribution network urgently needs to carry out decentralized harmonic governance research. Summary of the invention

[0004] The present invention provides a method for suppressing harmonics in a distribution network and related equipment, the purpose of which is to improve the power quality of the distribution network by suppressing the harmonics of the distribution network.

[0005] In order to achieve the above object, the present invention provides a method for suppressing harmonics in a distribution network, comprising:

[0006] Step 1, constructing the topological structure and mathematical model of the distributed power interface inverter in the target distribution network;

[0007] Step 2, constructing a hybrid control mode based on the current control mode and the voltage control mode;

[0008] Step 3: Based on the hybrid control mode, the topological structure and mathematical model of the distributed power interface inverter, different frequency domains of the distributed power interface inverter are controlled separately to achieve harmonic suppression of the target distribution network.

[0009] Specifically, the topology of the distributed power interface inverter in the target distribution network includes:

[0010] DC side bus, first bridge arm, second bridge arm, third bridge arm, LC filter, distribution network;

[0011] The positive pole of the DC side bus is respectively connected to the first end of the first bridge arm, the first end of the second bridge arm, and the first end of the third bridge arm;

[0012] The negative pole of the DC side bus is respectively connected to the second end of the first bridge arm, the second end of the second bridge arm, and the second end of the third bridge arm;

[0013] The middle point of the first bridge arm is connected to the first input end of the LC filter, and the first output end of the LC filter is connected to the first input end of the power distribution network;

[0014] The middle point of the second bridge arm is connected to the second input end of the LC filter, and the second output end of the LC filter is connected to the second input end of the power distribution network;

[0015] The middle point of the third bridge arm is connected to the third input end of the LC filter, and the third output end of the LC filter is connected to the third input end of the power distribution network.

[0016] Specifically, the mathematical model of the distributed power interface inverter in the target distribution network is:

[0017]

[0018] v=E·d

[0019] Where, L represents the inductance value in the LC filter, i represents the phase current i output by the three bridge arms a 、i b 、i c The vector form of the composition is expressed as:

[0020]

[0021] C represents the capacitance value in the LC filter, R represents the equivalent resistance value in the LC filter, and v represents the phase voltage v output at the middle point of the three bridge arms. a 、v b 、v c The vector form of the composition, v o The vector form of the LC filter phase voltage, i dg Indicates the phase current i output by the inverter dg,a 、i dg,b 、i dg,c The vector form of the composition, v pcc Indicates the phase voltage v of the input distribution network pcc,a 、v pcc,b 、v pcc,cIn vector form, E represents the DC bus voltage, and d represents the switch duty cycle of the three bridge arms.

[0022] Furthermore, different frequency domains of the distributed power interface inverter are controlled separately based on the hybrid control mode, including:

[0023] In the fundamental wave domain, the output voltage of the distributed power interface inverter is adjusted through the voltage control mode in the hybrid control mode to perform droop control on the active power and reactive power output by the distributed power interface inverter;

[0024] In the harmonic domain, the harmonic current output by the distributed power interface inverter is controlled through the current control mode in the hybrid control mode.

[0025] Further, the output voltage of the distributed power interface inverter is adjusted by the voltage control mode in the hybrid control mode to perform droop control on the active power and reactive power output by the distributed power interface inverter, including:

[0026] Get the actual value of active power P, actual value of reactive power Q, and rated value of active power P output by the distributed power interface inverter * and reactive power rating Q * ;

[0027] The active power rating P * and reactive power rating Q * , as well as the actual value of active power P and the actual value of reactive power Q, are substituted into the droop control formula The frequency reference value ω and amplitude reference value V of the output voltage are calculated, where ω * Indicates the rated frequency of the distribution network, V * Indicates the rated amplitude of the distribution network, m d represents the frequency droop coefficient, n d represents the amplitude droop coefficient;

[0028] The frequency reference value ω and the amplitude reference value V of the output voltage are input into the fundamental voltage reference synthesis module for synthesis to obtain the fundamental voltage reference value of the distributed power interface inverter;

[0029] The fundamental voltage reference value is compared with the actual fundamental voltage value and then input into the voltage controller, and the output voltage of the distributed power interface inverter is adjusted by the voltage controller.

[0030] Specifically, the harmonic current output by the distributed power interface inverter is controlled by the current control mode in the hybrid control mode, including:

[0031] Extract the harmonics of the three-phase voltage of the distribution network to obtain the harmonic voltage;

[0032] The conductance command of the distributed power interface inverter in the harmonic domain is obtained through the frequency-divided conductance-voltage distortion rate droop control strategy;

[0033] Multiply the conductance command by the harmonic voltage to obtain the harmonic reference current;

[0034] The harmonic reference current is compared with the phase current output by the inverter and then input into the current controller, and the harmonic current is controlled by the current controller.

[0035] Furthermore, the expression of the divided-frequency conductance-voltage distortion rate droop control strategy is:

[0036] G i =S p,u [G i,0 +ρ(VD i -VD i,max )]

[0037] Among them, G i It represents the conductance instruction of the distributed power interface inverter in the harmonic domain, and its value is (0≤G i ≤G max ), S p,u represents the residual power capacity per unit value of the distributed power interface inverter, ρ represents the droop gain coefficient, VD i Indicates the i-th harmonic distortion rate of the harmonic voltage, VD i,max It indicates the maximum harmonic distortion rate of the i-th harmonic voltage allowed by the distribution network standard.

[0038] To further explain, the calculation expression of harmonic reference current is:

[0039]

[0040] in, represents the harmonic reference current, Represents the i-th harmonic component of the harmonic voltage.

[0041] The present invention also provides a terminal device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the method for suppressing harmonics in a distribution network is implemented when the processor executes the computer program.

[0042] The present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the method for suppressing harmonics in a power distribution network is implemented.

[0043] The above scheme of the present invention has the following beneficial effects:

[0044] The present invention constructs a topological structure and a mathematical model of a distributed power interface inverter in a target distribution network; constructs a hybrid control mode based on a current control mode and a voltage control mode; and controls different frequency domains of the distributed power interface inverter respectively based on the hybrid control mode, the topological structure and the mathematical model of the distributed power interface inverter, so as to achieve harmonic suppression of the target distribution network. Compared with the prior art, the present invention effectively improves the power quality of the distribution network by suppressing the harmonic amplification and propagation phenomenon of the distribution network.

[0045] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of a flow chart of an embodiment of the present invention;

[0047] Figure 2 It is the topological structure diagram of the distributed power interface inverter;

[0048] Figure 3 It is a block diagram of harmonic suppression control of the power interface inverter in hybrid control mode;

[0049] Figure 4 It is a block diagram for realizing the frequency-divided conductance-voltage distortion rate droop control strategy in an embodiment of the present invention;

[0050] Figure 5 It is a schematic diagram of the droop curve of the frequency-divided conductance-voltage distortion rate;

[0051] Figure 6 It is a schematic diagram of a simulation model in which multiple distributed power interface inverters participate in harmonic suppression;

[0052] Figure 7 This is a schematic diagram of the changes in voltage and current waveforms and their harmonic distortion rates before harmonic suppression is enabled;

[0053] Figure 8 The diagram is a schematic diagram of the changes in voltage and current waveforms and their harmonic distortion rate when harmonic suppression is enabled;

[0054] Fig. 9 Schematic diagram of the structure of a terminal device in an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0057] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a locking connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0058] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0059] In view of the existing problems, the present invention provides a method for suppressing harmonics in a power distribution network and related equipment.

[0060] The embodiments of the present invention explain the professional terms mentioned as follows:

[0061] Distribution network: It is a network composed of overhead lines, cables, towers, distribution transformers, disconnectors, reactive power compensators and some ancillary facilities, which plays the role of distributing electric energy in the power system;

[0062] Inverter: a device that converts DC power into AC power, consisting of an inverter bridge, control logic and filter circuit;

[0063] Harmonics: refers to the amount of electricity contained in the current whose frequency is an integer multiple of the fundamental wave. Generally, it refers to the amount of electricity generated by the current with a frequency greater than the fundamental wave after the Fourier series decomposition of the periodic non-sinusoidal electricity.

[0064] Current control mode: By controlling the output current of the inverter to track the reference current command, the inverter can be equivalent to a controlled current source;

[0065] Voltage control mode: By controlling the output voltage of the inverter to track the reference voltage command, the inverter can be equivalent to a controlled voltage source;

[0066] Fundamental frequency domain: The frequency range is the grid fundamental frequency (50Hz in my country) and the normal small fluctuation range near the fundamental frequency;

[0067] Harmonic domain: the remaining frequency domain range after removing the fundamental domain;

[0068] Droop control: refers to the control of micro-sources based on the control target of the microgrid, using a droop curve similar to that of traditional generators, and using the frequency active droop characteristic (Droop Character) to dynamically distribute the unbalanced power of the system to each unit to ensure the uniformity of frequency and voltage in the microgrid system.

[0069] like Figure 1 As shown, an embodiment of the present invention provides a method for suppressing harmonics in a power distribution network, comprising:

[0070] Step 1, constructing the topological structure and mathematical model of the distributed power interface inverter in the target distribution network;

[0071] Step 2, constructing a hybrid control mode based on the current control mode and the voltage control mode;

[0072] Step 3: Based on the hybrid control mode, the topological structure and mathematical model of the distributed power interface inverter, different frequency domains of the distributed power interface inverter are controlled separately to achieve harmonic suppression of the target distribution network.

[0073] Most preferably, Figure 2 As shown, the topological structure of the distributed power interface inverter in the target distribution network includes:

[0074] DC side bus, first bridge arm, second bridge arm, third bridge arm, LC filter, distribution network;

[0075] The positive pole of the DC side bus is respectively connected to the first end of the first bridge arm, the first end of the second bridge arm, and the first end of the third bridge arm;

[0076] The negative pole of the DC side bus is respectively connected to the second end of the first bridge arm, the second end of the second bridge arm, and the second end of the third bridge arm;

[0077] The middle point of the first bridge arm is connected to the first input end of the LC filter, and the first output end of the LC filter is connected to the first input end of the power distribution network;

[0078] The middle point of the second bridge arm is connected to the second input end of the LC filter, and the second output end of the LC filter is connected to the second input end of the power distribution network;

[0079] The middle point of the third bridge arm is connected to the third input end of the LC filter, and the third output end of the LC filter is connected to the third input end of the power distribution network.

[0080] In the embodiment of the present invention, the first bridge arm, the second bridge arm, and the third bridge arm are all composed of two upper and lower bridge arm switches, and the bridge arm switches are all MOS tubes, which are S a , S b , S c , The drains of the upper bridge arm switches are connected to the positive pole of the DC bus, and the sources of the lower bridge arm switches are connected to the negative pole of the DC bus; the connection midpoint between the source of the upper bridge arm switch and the drain of the lower bridge arm switch in the first bridge arm is defined as the middle point, and the phase voltage output by the middle point is v a , the middle point is connected to the first input terminal of the LC filter; the connection midpoint between the source of the upper bridge arm switch and the drain of the lower bridge arm switch in the second bridge arm is the middle point, and the phase voltage output by the middle point is v b , the middle point is connected to the second input terminal of the LC filter; the connection midpoint between the source of the upper bridge arm switch and the drain of the lower bridge arm switch in the third bridge arm is the middle point, and the phase voltage output by the middle point is v c , the middle point is connected to the third input terminal of the LC filter.

[0081] In an embodiment of the present invention, the LC filter includes three inductors, three equivalent resistors and three capacitors, wherein the first end of each inductor is connected to the middle point of a group of bridge arms as an input end of the LC filter, the second end of each inductor is connected to the first end of an equivalent resistor, the second end of each equivalent resistor is connected to the first end of a capacitor, the second ends of the three capacitors are short-circuited together, and the second end of each equivalent resistor is connected to the input end of the power distribution network as an output end of the LC filter, and outputs a three-phase current i dg,a 、i dg,b 、i dg,c .

[0082] In an embodiment of the present invention, the distribution network includes three switches, three feeder impedances and three bus phase voltages, wherein the first ends of the three switches are connected to the three output ends of the LC filter in a one-to-one correspondence, the second ends of the three switches are connected to the first ends of the three feeder impedances in a one-to-one correspondence, and the second ends of the three feeder impedances are connected to the three bus phase voltages v pcc,a 、v pcc,b 、v pcc,c One-to-one connection.

[0083] Based on Figure 2 The topology shown in the figure establishes the mathematical model of the distributed power interface inverter in the target distribution network as follows:

[0084]

[0085] v=E·d

[0086] Where, L represents the inductance value in the LC filter, i represents the phase current i output by the three bridge arms a 、i b 、i c The vector form of the composition is expressed as:

[0087]

[0088] C represents the capacitance value in the LC filter, R represents the equivalent resistance value in the LC filter, and v represents the phase voltage v output at the middle point of the three bridge arms. a 、v b 、v c The vector form of the composition, v o The vector form of the LC filter phase voltage, i dg Indicates the phase current i output by the inverter dg，a 、i dg，b 、i dg，c The vector form of the composition, v pcc Indicates the phase voltage v of the input distribution network pcc，a 、v pcc，b 、v pcc，c In vector form, E represents the DC bus voltage, and d represents the switch duty cycle of the three bridge arms.

[0089] At present, most distributed power inverters use current control mode for grid-connected power generation. However, in order to provide the necessary voltage and frequency support for the distribution network, distributed power inverters use voltage control mode for grid-connected power generation, which has also been widely used. The voltage control mode generally uses droop control to simulate the frequency and voltage external characteristics of the synchronous generator, thereby improving the frequency and voltage stability of the distribution network.

[0090] The embodiment of the present invention constructs a hybrid control mode based on the respective advantages of the absorption current control mode and the voltage control mode. The hybrid control mode includes a fundamental domain control part and a harmonic domain control part. After combining the fundamental domain control result with the harmonic domain control result, the duty cycle of the MOS tubes in the first bridge arm, the second bridge arm, and the third bridge arm is adjusted through the PWM modulation module, thereby controlling the output voltage and harmonic current of the distributed power interface inverter. The specific control framework is as follows Figure 3 shown.

[0091] Specifically, different frequency domains of the distributed power interface inverter are controlled separately based on the hybrid control mode, including:

[0092] In the fundamental wave domain, the output voltage of the distributed power interface inverter is adjusted through the voltage control mode in the hybrid control mode to perform droop control on the active power and reactive power output by the distributed power interface inverter;

[0093] In the harmonic domain, the harmonic current output by the distributed power interface inverter is controlled through the current control mode in the hybrid control mode to realize the active harmonic suppression function of the distribution network.

[0094] Specifically, in the fundamental wave domain, the output voltage of the distributed power interface inverter is adjusted through the voltage control mode in the hybrid control mode to perform droop control on the active power and reactive power output by the distributed power interface inverter, including:

[0095] Obtain the actual active power value P, the actual reactive power value Q, the rated active power value P* and the rated reactive power value Q* output by the distributed power interface inverter;

[0096] If the feeder impedance in the distributed power interface inverter is inductive impedance or is transformed into inductive impedance through virtual impedance technology, the active power rating P * and reactive power rating Q * , through the droop control model The actual value of active power P and the actual value of reactive power Q are calculated respectively to obtain the frequency reference value ω and amplitude reference value V of the output voltage, where ω * Indicates the rated frequency of the distribution network, V * Indicates the rated amplitude of the distribution network, m d represents the frequency droop coefficient, n d represents the amplitude droop coefficient;

[0097] The frequency reference value ω and the amplitude reference value V of the output voltage are input into the fundamental voltage reference synthesis module for synthesis to obtain the fundamental voltage reference value of the distributed power interface inverter;

[0098] The fundamental voltage reference value is compared with the actual fundamental voltage value and then input into the voltage controller, and the output voltage of the distributed power interface inverter is adjusted by the voltage controller.

[0099] Specifically, in the harmonic domain, the harmonic current output by the distributed power interface inverter is controlled through the current control mode in the hybrid control mode, including:

[0100] Phase voltage v of the distribution network pcc Perform harmonic extraction to obtain the harmonic voltage v pcc,h ;

[0101] The conductance command of the distributed power interface inverter is obtained through the frequency-divided conductance-voltage distortion rate droop control strategy;

[0102] Multiply the conductance command by the harmonic voltage to obtain the harmonic reference current;

[0103] The harmonic reference current is compared with the phase current output by the inverter and then input into the current controller, and the harmonic current is controlled by the current controller.

[0104] Specifically, the calculation expression of harmonic reference current is:

[0105]

[0106] in, represents the harmonic reference current, Represents the i-th harmonic component of the harmonic voltage.

[0107] In such Figure 3 In the control strategy shown, the distributed power interface inverter is equivalent to a conductance instruction of G at each harmonic frequency. However, if the conductance instruction does not match the line impedance, the voltage distortion rate at the access point of the distributed power interface inverter will be reduced, but the distortion rate of some harmonic voltage components will increase at other positions of the line. In this regard, the embodiment of the present invention adopts a frequency-divided conductance-voltage distortion rate droop control strategy to avoid the "whack-a-mole" phenomenon in the harmonic suppression of a single distributed power inverter. Specifically, Figure 4 As shown, its expression is:

[0108] G i =S p，u [G i，0 +ρ(VD i -VD i，max )]

[0109] Among them, G i Indicates the conductance instruction of the distributed power interface inverter, and its value is (0≤G i ≤G max ), S p，u represents the residual power capacity per unit value of the distributed power interface inverter, ρ represents the droop gain coefficient, VD i Indicates the i-th harmonic distortion rate of the harmonic voltage, VD i.max It indicates the maximum harmonic distortion rate of the i-th harmonic voltage allowed by the distribution network standard.

[0110] The embodiment of the present invention specifically analyzes the frequency-divided conductance-voltage distortion rate droop control strategy for multiple distributed power inverters connected to the same bus, and the process is as follows:

[0111] Taking the xth distributed power interface inverter among multiple distributed power inverters as an example, let its conductance instruction corresponding to the i-th harmonic frequency be G x，i At this time, the i-th voltage distortion rate of the phase voltage of the distribution network connected to it is VD i , where VD is defined i It is the ratio of the effective value of the i-th harmonic voltage to the effective value of the fundamental positive sequence voltage, and the expression is:

[0112]

[0113] The expression of the frequency-divided conductance-voltage distortion rate droop control strategy of the xth distributed power interface inverter is:

[0114] G x，i =S p，u，x [G i，0 +ρ(VD i -VD i，max )]

[0115] Among them, G x，i It represents the conductance instruction of the xth distributed power interface inverter, and its value is (0≤G i ≤G max ), ρ represents the droop gain coefficient, and its value is ρ>0, S p，u，x It represents the per-unit value of the remaining power capacity of the xth distributed power interface inverter, which can be defined as:

[0116]

[0117] Among them, S N Indicates the reference power (kVA), S x represents the remaining capacity of the xth distributed power interface inverter, and

[0118] For a clearer expression, the embodiment of the present invention draws a droop curve according to the expression of the frequency-divided conductance-voltage distortion rate droop control strategy, such as Figure 5 As shown, when 0≤VD i ≤VD i，max -G i，0 / ρ interval, G i is zero; at VD i >VD i，max -G i，0 / ρ interval, G i With VD i There is a positive proportional relationship between them. In particular, when S p，u =1 and VD i =VD i，max When G i =G i，0 . Gi The upper limit is G i，max , used to ensure the stability of the system.

[0119] In order to verify the correctness and effectiveness of the harmonic suppression method provided in the embodiment of the present invention, a distribution network system simulation model containing four distributed power interface inverters is constructed in the Matlab / simulink software platform. Figure 6 The simulation model parameters are shown in Table 1:

[0120] Table 1

[0121] parameter symbol Numeric unit Grid rated voltage <![CDATA[v g ]]> 380 V(rms) Rated frequency of power grid f 50 Hz Grid side inductance <![CDATA[L g ]]> 0.02 mh Grid side resistance <![CDATA[R g ]]> 0.01 Ω Reactive power compensation capacitor <![CDATA[C com ]]> 80 μF Transmission Line Inductance <![CDATA[L t ]]> 0.01 mh Transmission Line Capacitance <![CDATA[C t ]]> 40 μF Transmission line resistance <![CDATA[R t ]]> 0.1 Ω Feeder Inductance <![CDATA[L dg ]]> 0.04 mh Feeder resistance <![CDATA[R dg ]]> 0.01 Ω

[0122] The rated capacities of the four distributed power interface inverters are set to S 1 =S 3 =30kVA, S 2 =S 4 =20kVA, the output rated power is set as: The parameters of the frequency-divided conductance-voltage distortion rate droop control strategy are set as: G i，0 =0.6Ω -1 , VD i，max =3% (i=5, 7, 11, 13), ρ = 200, S N =20kVA.

[0123] It should be noted that, in order to maintain generality and keep the description simple, the following simulation results only give the single-phase voltage and current waveforms of the system and their analysis results. The simulation results are as follows:

[0124] (1) Before the active harmonic suppression of the distributed generation interface inverter is enabled, in order to illustrate the harmonic distribution and content of the distribution network before harmonic suppression, the conductance instructions G of the four distributed generation interface inverters are set. i =0, the simulation results are as follows Figure 7 As shown by Figure 7 It can be seen that the harmonic distortion THD of the large power grid voltage is 0%, and due to the amplification effect of line resonance on the harmonic source, the bus voltage of the distribution network is seriously distorted, among which the bus 1# voltage v pcc1 The harmonic distortion THD is 10.54%, bus 2# voltage v pcc2 The harmonic distortion THD is 18.43%. Due to the amplification of the harmonic current source, i g and i T The harmonic content of the power supply seriously exceeded the standard, and the harmonic distortion THD was 55.41% and 37.51% respectively;

[0125] (2) After the active harmonic suppression of the distributed power interface inverter is enabled, the simulation results are as follows: Figure 8 As shown, bus 1# voltage v pcc1 The harmonic distortion THD dropped from 10.54% to 2.89%, and the bus 2# voltage v pcc2 The harmonic distortion THD of the power grid is reduced from 18.43% to 2.99%; the large grid current i g and the transmission line current i T The harmonic distortion THD of the system is reduced from 55.41% and 37.51% to 2.09% and 2.51% respectively. In summary, the simulation results verify the effectiveness of the proposed active harmonic suppression control strategy.

[0126] The embodiment of the present invention constructs a topological structure and a mathematical model of a distributed power interface inverter in a target distribution network; constructs a hybrid control mode based on a current control mode and a voltage control mode; and controls different frequency domains of the distributed power interface inverter respectively based on the hybrid control mode, the topological structure and the mathematical model of the distributed power interface inverter to achieve harmonic suppression of the target distribution network. Compared with the prior art, the embodiment of the present invention effectively improves the power quality of the distribution network by suppressing the harmonic amplification and propagation phenomenon of the distribution network.

[0127] An embodiment of the present invention further provides a terminal device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements a method for suppressing harmonics in a distribution network when executing the computer program.

[0128] like Fig. 9 As shown, the terminal device D10 provided in the embodiment of the present invention includes: at least one processor D100 ( Fig. 9 Only one processor is shown in the figure), a memory D101, and a computer program D102 stored in the memory D101 and executable on the at least one processor D100, wherein the processor D100 implements the steps in any of the above-mentioned method embodiments when executing the computer program D102. Alternatively, the processor D100 implements the functions of each module / unit in the above-mentioned device embodiments when executing the computer program D102.

[0129] The processor may be a central processing unit (CPU), or other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0130] In some embodiments, the memory may be an internal storage unit of the terminal device, such as a hard disk or memory of the terminal device. In other embodiments, the memory may also be an external storage device of the terminal device, such as a plug-in hard disk, a smart memory card (SMC, Smart Media Card), a secure digital (SD, Secure Digital) card, a flash card (Flash Card), etc. equipped on the terminal device. Further, the memory may also include both an internal storage unit of the terminal device and an external storage device. The memory is used to store an operating system, an application program, a boot loader (Boot Loader), data and other programs, such as the program code of the computer program, etc. The memory may also be used to temporarily store data that has been output or is to be output.

[0131] It should be noted that the information interaction, execution process, etc. between the above-mentioned devices / units are based on the same concept as the method embodiment of the embodiment of the present application. Their specific functions and technical effects can be found in the method embodiment part and will not be repeated here.

[0132] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the protection scope of the embodiments of the present application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0133] An embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, a method for suppressing harmonics in a power distribution network is implemented.

[0134] If the integrated module is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present application implements all or part of the process in the above method embodiment, which can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may at least include: any entity or device that can carry the computer program code to the construction device / terminal device, recording medium, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. For example, U disk, mobile hard disk, disk or optical disk, etc. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electric carrier signals and telecommunication signals.

[0135] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for suppressing harmonics in a distribution network, characterized in that: include: Step 1, constructing the topological structure and mathematical model of the distributed power interface inverter in the target distribution network; Step 2, constructing a hybrid control mode based on the current control mode and the voltage control mode; Step 3: Based on the hybrid control mode, the topological structure and the mathematical model of the distributed power interface inverter, different frequency domains of the distributed power interface inverter are controlled separately to achieve harmonic suppression of the target distribution network.

2. The method for suppressing harmonics in a distribution network according to claim 1, characterized in that: The topological structure of the distributed power interface inverter in the target distribution network includes: DC side bus, first bridge arm, second bridge arm, third bridge arm, LC filter, distribution network; The positive electrode of the DC side bus is respectively connected to the first end of the first bridge arm, the first end of the second bridge arm, and the first end of the third bridge arm; The negative electrode of the DC side bus is respectively connected to the second end of the first bridge arm, the second end of the second bridge arm, and the second end of the third bridge arm; The middle point of the first bridge arm is connected to the first input end of the LC filter, and the first output end of the LC filter is connected to the first input end of the power distribution network; The middle point of the second bridge arm is connected to the second input end of the LC filter, and the second output end of the LC filter is connected to the second input end of the power distribution network; The middle point of the third bridge arm is connected to the third input end of the LC filter, and the third output end of the LC filter is connected to the third input end of the power distribution network.

3. The method for suppressing harmonics in a distribution network according to claim 2, characterized in that: The mathematical model of the distributed power interface inverter in the target distribution network is: Where, L represents the inductance value in the LC filter, i represents the phase current i output by the three bridge arms a 、i b 、i c The vector form of the composition is expressed as: C represents the capacitance value in the LC filter, R represents the equivalent resistance value in the LC filter, and v represents the phase voltage v output at the middle point of the three bridge arms. a 、v b 、v c The vector form of the composition, v o The vector form of the LC filter phase voltage, i dg Indicates the phase current i output by the inverter dg,a 、i dg,b 、i dg,c The vector form of the composition, v pcc Indicates the phase voltage v of the input distribution network pcc,a 、v pcc,b 、v pcc,c In vector form, E represents the DC bus voltage, and d represents the switch duty cycle of the three bridge arms.

4. The method for suppressing harmonics in a distribution network according to claim 3, characterized in that: The controlling the different frequency domains of the distributed power interface inverter respectively based on the hybrid control mode includes: In the fundamental wave domain, the output voltage of the distributed power interface inverter is adjusted by the voltage control mode in the hybrid control mode to perform droop control on the active power and reactive power output by the distributed power interface inverter; In the harmonic domain, the harmonic current output by the distributed power interface inverter is controlled by the current control mode in the hybrid control mode.

5. The method for suppressing harmonics in a distribution network according to claim 4, characterized in that: In the fundamental wave domain, the output voltage of the distributed power interface inverter is adjusted by the voltage control mode in the hybrid control mode to perform droop control on the active power and reactive power output by the distributed power interface inverter, including: Obtain the actual value of active power P, the actual value of reactive power Q, and the rated value of active power P output by the distributed power interface inverter * and reactive power rating Q * ; The active power rating P * and reactive power rating Q * , and the actual value of active power P and the actual value of reactive power Q, are substituted into the droop control formula Calculate the frequency reference value ω and amplitude reference value V of the output voltage respectively, where ω * Indicates the rated frequency of the distribution network, V * Indicates the rated amplitude of the distribution network, m d represents the frequency droop coefficient, n d represents the amplitude droop coefficient; Inputting the frequency reference value ω and the amplitude reference value V of the output voltage into a fundamental voltage reference synthesis module for synthesis to obtain a fundamental voltage reference value of the distributed power interface inverter; The fundamental voltage reference value is compared with the actual fundamental voltage value and then input into a voltage controller, and the output voltage of the distributed power interface inverter is adjusted by the voltage controller.

6. The method for suppressing harmonics in a power distribution network according to claim 5, characterized in that: In the harmonic domain, the harmonic current output by the distributed power interface inverter is controlled by a current control mode in a hybrid control mode, including: Extracting harmonics from the phase voltage of the distribution network to obtain harmonic voltage; Obtaining the conductance instruction of the distributed power interface inverter in the harmonic domain through a frequency-divided conductance-voltage distortion rate droop control strategy; Multiplying the conductance command by the harmonic voltage to obtain a harmonic reference current; The harmonic reference current is compared with the phase current output by the inverter and then input into a current controller, and the harmonic current is controlled by the current controller.

7. The method for suppressing harmonics in a power distribution network according to claim 6, characterized in that: The expression of the frequency-divided conductance-voltage distortion rate droop control strategy is: G i =S p,u [G i,0 +ρ(VD i -VD i,max )] Among them, G i It represents the conductance instruction of the distributed power interface inverter in the harmonic domain, and its value is (0≤G i ≤G max ), S p,u represents the residual power capacity per unit value of the distributed power interface inverter, ρ represents the droop gain coefficient, VD i Indicates the i-th harmonic distortion rate of the harmonic voltage, VD i,max It indicates the maximum harmonic distortion rate of the i-th harmonic voltage allowed by the distribution network standard.

8. The method for suppressing harmonics in a distribution network according to claim 7, characterized in that: The calculation expression of the harmonic reference current is: in, represents the harmonic reference current, Represents the i-th harmonic component of the harmonic voltage.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method for suppressing harmonics in a power distribution network as claimed in any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for suppressing harmonics in a power distribution network as claimed in any one of claims 1 to 8 is implemented.

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