A method and system for suppressing grid-connected current harmonics of an inverter

Abstract

The application discloses an inverter grid-connected current harmonic suppression method and system, collects inverter bridge arm current and grid-connected point voltage, carries out operation on the inverter bridge arm current and the grid-connected point voltage to obtain grid-connected current, carries out harmonic suppression on the grid-connected current through a harmonic suppression ring to obtain harmonic suppression ring output value, obtains feedforward value of the grid-connected point voltage and fundamental wave current loop control output value, takes a negative value of the harmonic suppression ring output value and superimposes the feedforward value of the grid-connected point voltage and the fundamental wave current loop control output value, obtains modulation voltage of the inverter, carries out PWM modulation on components of the modulation voltage to generate a switching signal for driving the grid-connected inverter to work. The application estimates the grid-connected current, suppresses specific harmonics in the grid-connected current, makes the grid-connected current harmonic suppression effect better, adopts feedforward on the grid-connected point voltage, makes the inverter have better dynamic performance and stability under strong grid or weak grid, and reduces the grid-connected current harmonic suppression difficulty.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of grid-connected power generation, and more particularly to a method and system for suppressing grid-connected current harmonics of an inverter. BACKGROUND

[0002] As a core interface device between new energy power generation equipment and the power grid, the inverter shoulders the key tasks of power conversion and power quality management. According to relevant standards, the grid-connected current harmonics of the inverter should meet certain requirements, such as the standard NB / T32004-2018 stipulates that the total harmonic distortion rate of the grid-connected current of the inverter when operating in grid-connected mode should not be higher than 5%, and each harmonic should also be lower than a certain content requirement, therefore, the inverter needs to have certain grid-connected current harmonic suppression capability.

[0003] The grid-connected current harmonics mainly include low-order harmonics and high-order harmonics, among which the high-order harmonics are generally filtered out by the grid-connected filter, and the low-order harmonics are generally suppressed by the control algorithm of the inverter. For the low-order harmonics of the grid-connected current, the harmonic sources mainly consist of two parts, one is the low-order harmonic voltage generated by the inverter itself, and the other is the low-order harmonic voltage contained in the power grid, therefore, in addition to suppressing the low-order harmonic voltage generated by the inverter itself, the control algorithm of the inverter also needs to cope with the influence of the low-order harmonic voltage of the power grid on the grid-connected current. Moreover, since the sampled current of the inverter is generally the bridge arm current, it cannot directly control the grid-connected current, which leads to great difficulty in suppressing the grid-connected current harmonics of the inverter. In addition, due to the high proportion of new energy power generation access, the power grid presents a weak grid form with increasingly large impedance, which further increases the difficulty of suppressing the grid-connected current harmonics of the inverter. SUMMARY

[0004] Therefore, the present application discloses a method and system for suppressing grid-connected current harmonics of an inverter to reduce the difficulty of suppressing grid-connected current harmonics.

[0005] A method for suppressing grid-connected current harmonics of an inverter, comprising:

[0006] acquiring the bridge arm current of the inverter and the grid point voltage;

[0007] operating the bridge arm current of the inverter and the grid point voltage to obtain a grid-connected current, suppressing the grid-connected current by a harmonic suppression loop to obtain a harmonic suppression loop output value;

[0008] obtaining a feedforward value of the grid point voltage and a fundamental current loop control output value;

[0009] taking a negative value of the harmonic suppression loop output value and superimposing it with the feedforward value of the grid point voltage and the fundamental current loop control output value to obtain a modulation voltage of the inverter;

[0010] The components of the modulation voltage are PWM modulated to generate a switching signal for driving the grid-connected inverter to operate.

[0011] Optionally, the operation on the inverter bridge arm current and the grid-connected point voltage to obtain the grid-connected current comprises:

[0012] The grid-connected point voltage is differentiated and multiplied by a grid-connected filter capacitance value to obtain a grid-connected filter capacitance current estimation value;

[0013] The grid-connected current is obtained based on the grid-connected filter capacitance current estimation value and the inverter bridge arm current.

[0014] Optionally, the harmonic suppression on the grid-connected current by the harmonic suppression loop to obtain a harmonic suppression loop output value comprises:

[0015] The harmonic suppression loop comprises at least one harmonic suppression loop submodule, and the grid-connected current is input to each harmonic suppression loop submodule for harmonic suppression to obtain a corresponding submodule output value;

[0016] The harmonic suppression loop output value is obtained by adding the submodule output values.

[0017] Optionally, the input of the grid-connected current to each harmonic suppression loop submodule for harmonic suppression to obtain a corresponding submodule output value comprises:

[0018] The grid-connected current is converted from a two-phase static coordinate system to a two-phase rotating coordinate system according to different input stage coordinate transformation angles to obtain a target grid-connected current;

[0019] The target grid-connected current is filtered by a low-pass filter to obtain dq direct current components of each harmonic;

[0020] The dq direct current components of each harmonic are respectively input to an adjuster to obtain adjuster output components;

[0021] The adjuster output components are respectively converted from the two-phase rotating coordinate system to the two-phase static coordinate system according to different output stage coordinate transformation angles to obtain the submodule output values.

[0022] Optionally, when the harmonic suppression is based on grid-connected current dq components, the input stage coordinate transformation angles are-3kθ and 3kθ;

[0023] When the harmonic suppression is based on grid-connected current αβ components, the input stage coordinate transformation angles are-(3k-1)θ and (3k+1)θ;

[0024] In the absence of phase compensation, the output stage coordinate transformation angle adopts -3kθ and 3kθ, and in the presence of phase compensation, the output stage coordinate transformation angle adopts and

[0025] wherein, and is a phase compensation value of each harmonic suppression loop sub-module, θ is a grid phase angle, k represents a harmonic order index coefficient, and k is a positive integer.

[0026] Optionally, the phase compensation value of each harmonic suppression loop sub-module is obtained by using an optimization method according to a system open-loop Bode diagram, and specifically includes the following steps.

[0027] A frequency domain model of an inverter control system is established based on a control loop of the inverter, and a system open-loop Bode diagram is established according to the frequency domain model;

[0028] A phase margin value at each harmonic frequency is determined based on the system open-loop Bode diagram;

[0029] The phase compensation value at the each harmonic frequency is determined so that the phase margin value meets a corresponding set phase margin value under different grid short-circuit ratios;

[0030] The phase compensation value at the each harmonic frequency is the phase compensation value of each harmonic suppression loop sub-module.

[0031] Optionally, the grid-connected current is input to each harmonic suppression loop sub-module for harmonic suppression to obtain a corresponding sub-module output value, including:

[0032] The harmonic suppression loop sub-module is implemented based on a quasi-proportional-resonant regulator:

[0033] The grid-connected current is input to each quasi-proportional-resonant regulator for processing to obtain the sub-module output value.

[0034] Optionally, the quasi-proportional-resonant regulator includes a phase compensation factor.

[0035] Optionally, the acquisition of the feedforward value of the grid-connected point voltage and the fundamental current loop control output value includes:

[0036] A bridge arm current instruction is acquired.

[0037] A current loop control equation is used to operate the bridge arm current and the bridge arm current instruction to obtain the fundamental current loop control output value.

[0038] A grid voltage feedforward amount calculation equation is used to operate the grid-connected point voltage to obtain the feedforward value of the grid-connected point voltage.

[0039] Optionally, the feedforward value is a weighted feedforward value.

[0040] A system for suppressing grid-connected current harmonics of an inverter, comprising:

[0041] a collection unit configured to collect an inverter bridge arm current and a grid-connected point voltage;

[0042] a harmonic suppression unit configured to operate the inverter bridge arm current and the grid-connected point voltage to obtain a grid-connected current, suppress harmonics of the grid-connected current through a harmonic suppression loop, and obtain a harmonic suppression loop output value;

[0043] an acquisition unit configured to acquire a feedforward value of the grid-connected point voltage and a fundamental current loop control output value;

[0044] a modulation unit determination unit configured to take a negative value of the harmonic suppression loop output value, and superimpose the negative value with the feedforward value of the grid-connected point voltage and the fundamental current loop control output value to obtain a modulation voltage of the inverter;

[0045] a modulation unit configured to perform PWM modulation on components of the modulation voltage to generate a switching signal for driving the grid-connected inverter to work.

[0046] Optionally, the harmonic suppression unit comprises:

[0047] a current estimator unit configured to perform differential operation on the grid-connected point voltage, multiply the grid-connected point voltage by a grid-connected filter capacitance value, and obtain a grid-connected filter capacitance current estimation value;

[0048] a grid-connected current determination subunit configured to operate the grid-connected filter capacitance current estimation value and the inverter bridge arm current to obtain the grid-connected current.

[0049] Optionally, the harmonic suppression unit further comprises:

[0050] a harmonic suppression subunit configured to, when the harmonic suppression loop comprises at least one harmonic suppression loop submodule, input the grid-connected current into each of the harmonic suppression loop submodules to perform harmonic suppression and obtain a corresponding submodule output value of each of the harmonic suppression loop submodules;

[0051] a suppression loop output value determination subunit configured to add the submodule output values of each of the harmonic suppression loop submodules to obtain the harmonic suppression loop output value.

[0052] Optionally, the harmonic suppression subunit is specifically configured to:

[0053] transform the grid-connected current from a two-phase static coordinate system to a two-phase rotating coordinate system according to different input level coordinate transformation angles to obtain a target grid-connected current;

[0054] The target grid-connected current passes through a low-pass filter to obtain dq direct current components of each harmonic;

[0055] The dq direct current components of each harmonic pass through a regulator respectively to obtain regulator output components;

[0056] The regulator output components are respectively transformed from the two-phase rotating coordinate system to the two-phase stationary coordinate system according to different output stage coordinate transformation angles to obtain the output values of each sub-module.

[0057] Optionally, when the harmonic suppression is based on the grid-connected current dq components, the input stage coordinate transformation angles are-3kθ and 3kθ;

[0058] When the harmonic suppression is based on the grid-connected current αβ components, the input stage coordinate transformation angles are-(3k-1)θ and (3k+1)θ;

[0059] When there is no phase compensation, the output stage coordinate transformation angles are-3kθ and 3kθ, and when there is phase compensation, the output stage coordinate transformation angles are and

[0060] wherein, and is a phase compensation value of each harmonic suppression loop sub-module, θ is a grid phase angle, k represents a harmonic order index coefficient, and k is a positive integer.

[0061] Optionally, the method further comprises:

[0062] a phase compensation value determination unit configured to obtain the phase compensation value of each harmonic suppression loop sub-module by using an optimization method according to a system open-loop Bode diagram:

[0063] The phase compensation value determination unit is specifically configured to:

[0064] establish a frequency domain model of an inverter control system based on a control loop of the inverter, and establish a system open-loop Bode diagram according to the frequency domain model;

[0065] determine a phase margin value at each harmonic frequency based on the system open-loop Bode diagram;

[0066] determine the phase compensation value at each harmonic frequency so that the phase margin value meets a corresponding set phase margin value under different grid short-circuit ratios;

[0067] The phase compensation value at each harmonic frequency is the phase compensation value of each harmonic suppression loop sub-module.

[0068] Optionally, the harmonic suppression sub-unit is specifically configured to:

[0069] When the harmonic suppression loop submodule is implemented based on a quasi-proportional resonant regulator, the grid-connected current is input to each of the quasi-proportional resonant regulators for processing to obtain the output value of each submodule.

[0070] Optionally, the acquisition unit is specifically used for:

[0071] Get bridge arm current command;

[0072] The fundamental current loop control output value is obtained by performing current loop control equations on the bridge arm current and the bridge arm current command.

[0073] The feedforward value of the grid connection point voltage is obtained by using the grid voltage feedforward calculation equation.

[0074] As can be seen from the above technical solution, this invention discloses a method and system for suppressing harmonics in inverter grid-connected current. The method involves collecting the inverter arm current and grid-connected point voltage, calculating the grid-connected current from these data, suppressing harmonics in the grid-connected current using a harmonic suppression loop to obtain the output value of the harmonic suppression loop, acquiring the feedforward value of the grid-connected point voltage and the control output value of the fundamental current loop, taking the negative value of the harmonic suppression loop output value, and superimposing it with the feedforward value of the grid-connected point voltage and the control output value of the fundamental current loop to obtain the modulation voltage of the inverter. The component of the modulation voltage is then subjected to PWM modulation to generate a switching signal that drives the grid-connected inverter. This invention, by estimating the grid-connected current, can suppress specific harmonics in the grid-connected current, resulting in better harmonic suppression. By using feedforward on the grid-connected point voltage, the inverter can possess better dynamics and stability under both strong and weak grid conditions, and the difficulty of suppressing grid-connected current harmonics is reduced. Attached Figure Description

[0075] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the published drawings without creative effort.

[0076] Figure 1 This is a flowchart of a method for suppressing grid-connected current harmonics in an inverter, as disclosed in an embodiment of the present invention.

[0077] Figure 2 This is a schematic diagram of a grid-connected current harmonic suppression control system disclosed in an embodiment of the present invention;

[0078] Figure 3 This is a schematic diagram of a power grid voltage feedforward module disclosed in an embodiment of the present invention;

[0079] Figure 4 This is a schematic diagram of a current harmonic suppression module disclosed in an embodiment of the present invention;

[0080] Figure 5 This is a schematic diagram of a current harmonic suppression module disclosed in an embodiment of the present invention;

[0081] Figure 6 This is a schematic diagram of another current harmonic suppression module disclosed in an embodiment of the present invention;

[0082] Figure 7 This is a schematic diagram of another current harmonic suppression module disclosed in an embodiment of the present invention;

[0083] Figure 8 This is a schematic diagram of another current harmonic suppression module disclosed in an embodiment of the present invention;

[0084] Figure 9 This is a schematic diagram of another current harmonic suppression module disclosed in an embodiment of the present invention;

[0085] Figure 10 This is a schematic diagram of another current harmonic suppression module disclosed in an embodiment of the present invention;

[0086] Figure 11 This is a schematic diagram of another current harmonic suppression module disclosed in an embodiment of the present invention;

[0087] Figure 12 This is a simulation waveform diagram of the bridge arm current and grid-connected current when using the grid voltage feedforward method according to an embodiment of the present invention;

[0088] Figure 13 This is a simulation waveform diagram of bridge arm power and grid-connected current under strong grid conditions using a bridge arm current regulator suppression method, as disclosed in an embodiment of the present invention.

[0089] Figure 14 This is a simulation waveform diagram of bridge arm current and grid-connected current under weak grid conditions using a bridge arm current regulator suppression method, as disclosed in an embodiment of the present invention.

[0090] Figure 15 This is a simulation waveform diagram of the bridge arm current and grid-connected current under weak network conditions when using the scheme proposed in this invention, as disclosed in an embodiment of the invention;

[0091] Figure 16 This is a schematic diagram of the structure of an inverter grid-connected current harmonic suppression system disclosed in an embodiment of the present invention. Detailed Implementation

[0092] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0093] This invention discloses a method and system for suppressing harmonics in inverter grid-connected current. The method involves collecting the inverter arm current and grid-connected voltage, calculating the grid-connected current from these data, and using a harmonic suppression loop to suppress harmonics in the grid-connected current. The method also includes obtaining the feedforward value of the grid-connected voltage and the control output value of the fundamental current loop. The harmonic suppression loop output value is then negatively evaluated and superimposed with these values ​​to obtain the inverter's modulation voltage. The modulation voltage component is then PWM-modulated to generate a switching signal that drives the grid-connected inverter. This invention, by estimating the grid-connected current, can suppress specific harmonics in the grid-connected current, resulting in better harmonic suppression. Furthermore, by using feedforward on the grid-connected voltage, the inverter exhibits good dynamics and stability under both strong and weak grid conditions, and the difficulty of suppressing grid-connected current harmonics is reduced.

[0094] See Figure 1 The present invention discloses a flowchart of a method for suppressing harmonics in inverter grid-connected current, the method comprising:

[0095] Step S101: Collect inverter arm current and grid connection point voltage;

[0096] For details, see Figure 2 The schematic diagram of the grid-connected current harmonic suppression control system shown in this embodiment indicates that the inverter arm current (inductor current / reactor current) collected in this embodiment is i. L_abc (i L_a i L_b i L_c The collected grid-connected voltage is v. g_abc (v g_a v g_b v g_ c) A DC / AC converter is used to convert a DC source (direct current power supply) into an AC source.

[0097] To facilitate subsequent calculations, this invention uses the inverter bridge arm current i L_abc And the grid connection voltage is v g_abc The coordinate transformation was performed, as follows:

[0098] The inverter bridge arm current i is calculated using formula (1). L_abc (i L_ai L_b i L_c Transforming from a three-phase stationary coordinate system to a two-phase stationary coordinate system yields the αβ components of the bridge arm currents. L_αβ (i L_α i L_β Formula (1) is as follows:

[0099]

[0100] Formula (2) is used to calculate the grid connection point voltage v. g_abc (v g_a v g_b v g_c Transforming from a three-phase stationary coordinate system to a two-phase stationary coordinate system yields the αβ components v of the grid-connected point voltage. g_αβ (v g_α v g_β Formula (2) is as follows:

[0101]

[0102] The grid phase angle θ is obtained based on the phase-locked loop (PLL). Based on the grid phase angle θ and formula (3), the αβ component i of the bridge arm current in formula (1) is obtained. L_αβ The dq component i of the bridge arm current is obtained by transforming from a two-phase stationary coordinate system to a two-phase rotating coordinate system. L_dq (i L_d i L_q Formula (3) is as follows:

[0103]

[0104] Based on the grid phase angle θ and formula (4), the αβ component v of the grid connection point voltage in formula (2) is... g_αβ By transforming from a two-phase stationary coordinate system to a two-phase rotating coordinate system, the dq component v of the grid-connected point voltage is obtained. g_dq (v g_d v g_q Formula (4) is as follows:

[0105]

[0106] It should be noted that, for details please refer to [link / reference]. Figure 2 In this invention, the current harmonic suppression module is based on the input grid phase angle θ and the dq component i of the bridge arm current. L_dq (i L_d i L_q And the dq component v of the grid connection point voltage. g_ dq(v g_ d, v g_qThis is used to suppress harmonics in the inverter's grid-connected current and outputs the harmonic suppression loop value u. harm_out .

[0107] Step S102: Calculate the grid-connected current by the inverter arm current and the grid connection point voltage, and suppress the harmonics of the grid-connected current by the harmonic suppression loop to obtain the output value of the harmonic suppression loop;

[0108] It should be noted that the harmonic suppression loop in this embodiment includes various harmonic suppression loops, and each harmonic suppression loop has a phase compensation function. The phase compensation values ​​of each harmonic suppression loop can be the same or different, depending on the actual needs, and this invention does not limit this. By adding a phase compensation function to the harmonic suppression loop, this invention improves the phase margin of the control system, thereby maintaining system stability while suppressing grid-connected current harmonics.

[0109] Step S103: Obtain the feedforward value of the grid connection point voltage and the fundamental current loop control output value;

[0110] Specifically, for the dq component v of the grid connection point voltage g_dq The feedforward value u of the grid connection point voltage is obtained using the grid voltage feedforward scheme. feed_dq The grid voltage feedforward scheme used in this embodiment can effectively address the resonance problem under weak grid conditions and improve the dynamic response speed of the inverter under weak grid conditions. See details... Figure 3 The schematic diagram of the grid voltage feedforward module shown is as follows, in which, Figure 3 The grid voltage feedforward module in the middle is also known as Figure 2 The grid voltage feedforward module is shown in the figure.

[0111] Feedforward value u of grid connection point voltage feed_dq The calculation equation is shown in formula (5), and formula (5) is as follows:

[0112] u feed_dq =K feed u g_dq +(1-K feed LPF g *u g_dq (5);

[0113] In the formula, K feed The direct feedforward coefficient of the grid voltage (with a value between 0 and 1), LPF g For a low-pass filter, its transfer function is given by formula (6) or formula (7), as follows:

[0114]

[0115]

[0116] In the formula, ω cg This represents the cutoff frequency of the low-pass filter, and γ represents the damping coefficient of the second-order low-pass filter, with a typical value of [value missing].

[0117] In practical applications, the feedforward value in this embodiment is preferably a weighted feedforward value.

[0118] Step S104: Take the negative value of the harmonic suppression loop output value and superimpose it with the feedforward value of the grid connection point voltage and the control output value of the fundamental current loop to obtain the modulation voltage of the inverter.

[0119] In this embodiment, the modulation voltage of the inverter is the dq component u of the inverter modulation voltage in practical applications. m_dq Inverter modulation voltage dq component u m_dq The calculation formula is shown in formula (8), and formula (8) is as follows:

[0120] u m_dq =u dq_out +u feed_dq -u harm_out (8);

[0121] In the formula, u feed_dq u is the feedforward value of the grid connection point voltage. dq_out The output value of the fundamental current loop control, u harm_out This is the output value of the harmonic suppression loop.

[0122] Step S105: PWM modulate the components of the modulation voltage to generate a switching signal that drives the grid-connected inverter.

[0123] In this embodiment, the component of the modulation voltage is the dq component u of the inverter modulation voltage. m_dq .

[0124] Specifically, (1) the dq component u of the inverter modulation voltage m_dq After transforming from a two-phase rotating coordinate system to a three-phase stationary coordinate system, the abc component u of the inverter modulation voltage is obtained. m_abc (u m_a u m_b u m_c The transformation formula from the two-phase rotating coordinate system to the three-phase stationary coordinate system is shown in formula (9), which is as follows:

[0125]

[0126] In the formula, θ is the phase angle of the power grid.

[0127] (2) The abc component of the inverter modulation voltage u m_abcPWM modulation is performed to generate the switching signal that drives the grid-connected inverter.

[0128] In this embodiment, driving the grid-connected inverter to work actually means driving the switching devices of the grid-connected inverter to work. The switching devices of the grid-connected inverter are such as IGBT (Insulated Gate Bipolar Transistor) or MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

[0129] PWM stands for Pulse Width Modulation. It's an analog control method that modulates the bias of the base of a transistor or the gate of a MOSFET based on changes in the load, thereby altering the on-time of the transistor or MOSFET and ultimately changing the output of a switching power supply.

[0130] This invention discloses a method for suppressing harmonics in inverter grid-connected current. The method involves collecting the inverter arm current and grid-connected point voltage, calculating the grid-connected current from these data, and then using a harmonic suppression loop to suppress harmonics in the grid-connected current, obtaining the output value of the harmonic suppression loop. The method also involves acquiring the feedforward value of the grid-connected point voltage and the control output value of the fundamental current loop, negatively assigning the harmonic suppression loop output value to these values, and superimposing them to obtain the modulation voltage of the inverter. The modulated voltage component is then subjected to PWM modulation to generate a switching signal that drives the grid-connected inverter. This invention, by estimating the grid-connected current, can suppress specific harmonics in the grid-connected current, resulting in better harmonic suppression. Furthermore, by using feedforward on the grid-connected point voltage, the inverter exhibits better dynamics and stability under both strong and weak grid conditions, and the difficulty of suppressing grid-connected current harmonics is reduced.

[0131] To further optimize the above embodiment, the process of calculating the grid-connected current from the inverter arm current and the grid connection point voltage in step S102 specifically includes:

[0132] (1) Perform a differential operation on the grid connection point voltage and multiply it with the grid connection filter capacitor value to obtain the estimated value of the grid connection filter capacitor current.

[0133] (2) The grid-connected current is calculated based on the estimated value of the grid-connected filter capacitor current and the inverter bridge arm current.

[0134] In this embodiment, the estimated value of the grid-connected filter capacitor current specifically refers to the dq component of the estimated value of the grid-connected filter capacitor current, the inverter arm current specifically refers to the dq component of the inverter arm current, and the grid-connected current specifically refers to the dq component of the estimated value of the grid-connected current.

[0135] For details, see Figure 4 The current harmonic suppression module scheme diagram shown below illustrates the grid-connected current estimation process:

[0136] ① The dq component of the grid connection point voltage v g_dq via differentiator G diff Then multiply by the value of the AC filter capacitor to obtain the estimated value of the grid-connected filter capacitor current dq component i. c_est_dq .

[0137] Among them, the differentiator G diff The implementation method is not limited in this invention, and the differentiator G diff A typical transfer function is shown in Equation (10), which is as follows:

[0138]

[0139] In the formula, ξ represents the differentiator operator, with a value between 0 and 1, z represents the discrete-domain transfer function operator, and T s This indicates the calculation cycle of the differentiator.

[0140] ② The estimated value of the grid-connected filter capacitor current dq component i c_est_dq and the dq component of the inverter bridge arm current i L_dq The estimated value of the grid-connected current dq component i is obtained by subtraction. g_est_dq .

[0141] To further optimize the above embodiment, step S102, which involves suppressing harmonics in the grid-connected current using a harmonic suppression loop to obtain the output value of the harmonic suppression loop, includes:

[0142] (1) The harmonic suppression ring includes at least one harmonic suppression ring sub-module. The grid-connected current is input to each harmonic suppression ring sub-module for harmonic suppression, and the corresponding output value of each sub-module is obtained.

[0143] (2) The output values ​​of each submodule are added together to obtain the output value of the harmonic suppression loop.

[0144] The process of inputting grid-connected current into each harmonic suppression loop submodule for harmonic suppression and obtaining the corresponding output value of each submodule includes, but is not limited to, the following two methods:

[0145] (I) The first method for inputting grid-connected current into each harmonic suppression loop submodule for harmonic suppression and obtaining the corresponding output value of each submodule is as follows:

[0146] (1) Transform the grid-connected current from the two-phase stationary coordinate system to the two-phase rotating coordinate system according to the coordinate transformation angle of different input stages to obtain the target grid-connected current;

[0147] (2) Pass the target grid-connected current through a low-pass filter to obtain the dq DC components of each harmonic;

[0148] (3) The DC components of each harmonic are passed through a regulator to obtain the regulator output components;

[0149] (4) The output components of the regulator are transformed from the two-phase rotating coordinate system to the two-phase stationary coordinate system according to different output level coordinate transformation angles to obtain the output values ​​of each sub-module.

[0150] For details, see Figure 4 The diagram of the current harmonic suppression module shown illustrates the process for determining the output value of the harmonic suppression loop:

[0151] The estimated value of the grid-connected current dq component i g_est_dq The components are transformed from a two-phase stationary coordinate system to a two-phase rotating coordinate system using transformation angles of -3θ, 3θ…-3kθ, 3kθ (where k represents the harmonic order index coefficient, k = 1, 2, 3…, the same below), and then passed through a low-pass filter (LPF). m The dq DC components of the 2nd, 4th...3k-1th and 3k+1th harmonics are obtained respectively, and then passed through PI regulators. m Then the obtained regulator output is processed by... The transformation from a two-phase rotating coordinate system to a two-phase stationary coordinate system involves changing the angles, and then the output values ​​of each transformation are summed to obtain the output value u of the harmonic suppression loop. harm_out , The phase compensation value is used for each harmonic suppression circuit to compensate for the phase lag in the control circuit caused by sampling, loading, modulation delays, and grid voltage feedforward, especially in weak grid conditions where the feedforward of the grid connection point voltage can cause significant phase lag. The phase compensation value improves the phase margin of the control system, thus maintaining system stability while suppressing harmonics.

[0152] Among them, the low-pass filter LPF m The transfer function can be Equation (11) or Equation (12), as follows:

[0153]

[0154] or

[0155]

[0156] In the formula, m represents the harmonic order, m = 2, 4...3k-1, 3k+1, ω cm Here, λ is the cutoff frequency of the low-pass filter, and λ is the damping coefficient of the second-order low-pass filter, with a typical value of [value missing].

[0157] PI regulator PI m The transfer function is shown in equation (13), as follows:

[0158]

[0159] In the formula, m represents the harmonic order, m = 2, 4...3k-1, 3k+1, K p_m K is the proportional coefficient of the PI controller. i_m is the integral coefficient of the PI controller, and s is the Laplace operator.

[0160] It should be noted that various implementation schemes can be used for harmonic suppression, as illustrated below:

[0161] When performing harmonic suppression based on the grid-connected current dq component, the input stage coordinate transformation angles are -3kθ and 3kθ.

[0162] When harmonic suppression is performed based on the αβ component of the grid-connected current, the input stage coordinate transformation angles are -(3k-1)θ and (3k+1)θ.

[0163] Without phase compensation, the output stage coordinate transformation angles are -3kθ and 3kθ. With phase compensation, the output stage coordinate transformation angles are... and

[0164] in, and θ represents the phase compensation value of each harmonic suppression loop submodule, θ is the power grid phase angle, k represents the harmonic order index coefficient, and k is a positive integer.

[0165] Specifically, harmonic suppression schemes can be divided into two main categories based on whether the harmonic suppression is based on a PI controller or a quasi-proportional resonant controller.

[0166] The first category, based on PI regulators, employs various implementation schemes depending on whether the harmonic suppression module for the grid connection point voltage bridge arm current input current is an abc component, an αβ component, or a dq quantity, and the different coordinate transformation methods used in the subsequent stages. These schemes are detailed below:

[0167] For implementation of Option 1, please refer to [link / reference]. Figure 5When both the grid connection point voltage and the bridge arm current input are abc components, the grid connection current abc component is estimated. This abc component is then transformed into a dq component, and harmonic suppression is performed based on this dq component. In this case, the input stage coordinate transformation angle for the harmonic suppression stage is -3kθ, 3kθ, and the output stage coordinate transformation angle is [missing information].

[0168] in, and θ represents the phase compensation angle of the harmonic suppression loop, θ is the power grid phase angle, and k represents the harmonic order index coefficient, where k is a positive integer.

[0169] For implementation scheme two, see [link / reference] Figure 6 When both the grid connection point voltage and the bridge arm current input are αβ components, the grid connection current αβ component is estimated. This αβ component is then transformed into a grid connection current dq component, and harmonic suppression is performed based on this dq component. In this case, the input stage coordinate transformation angle for the harmonic suppression stage is -3kθ, 3kθ, and the output stage coordinate transformation angle is [missing information].

[0170] in, and θ represents the phase compensation angle of the harmonic suppression loop, θ is the power grid phase angle, and k represents the harmonic order index coefficient, where k is a positive integer.

[0171] For implementation of Option 3, please refer to [link / reference]. Figure 7 The grid connection point voltage and bridge arm current input are both abc components, and the grid connection current abc component is estimated. The grid connection current abc component is transformed into a grid connection current αβ component, and harmonic suppression is performed based on the grid connection current αβ component. At this time, the coordinate transformation angles of the input stage of the harmonic suppression stage are -(3k-1)θ and (3k+1)θ, and the coordinate transformation angles of the output stage are...

[0172] in, and θ represents the phase compensation angle of the harmonic suppression loop, θ is the power grid phase angle, and k represents the harmonic order index coefficient, where k is a positive integer.

[0173] Implementation plan four, see [link / reference] Figure 8 The grid connection point voltage and bridge arm current input are both αβ components, and harmonic suppression is performed based on the αβ component of the grid connection current. At this time, the coordinate transformation angles of the input stage of the harmonic suppression stage are -(3k-1)θ and (3k+1)θ, and the coordinate transformation angles of the output stage are...

[0174] in, and θ represents the phase compensation angle of the harmonic suppression loop, θ is the power grid phase angle, and k represents the harmonic order index coefficient, where k is a positive integer.

[0175] The second category, based on a quasi-proportional resonant regulator, determines various implementation schemes according to the grid connection point voltage and the bridge arm current input current harmonic suppression module, which consists of abc components, αβ components, or dq quantities. The details are as follows:

[0176] First, it should be noted that the harmonic suppression module determined based on the quasi-proportional resonant regulator has the following structure:

[0177] The estimated value of the grid-connected current dq component i g_est_dq Each is connected to a quasi-proportional resonant regulator qKR with phase compensation function. _m The resulting outputs are processed and then summed to obtain the current harmonic suppression output u. harm_out .

[0178] Quasi-proportional resonant regulator qKR _m The s-domain transfer function is shown in Equation (14), which is as follows:

[0179]

[0180] In the formula, m represents the harmonic order, m = 2, 4...3k-1, 3k+1, K p_m For qKR _m The proportional coefficient of the regulator, K r_m For qKR _m The resonant coefficient of the regulator, ω c_m For qKR _m The cutoff frequency of the regulator, ω r_m For qKR _m The resonant frequency of the regulator, For qKR _m The phase compensation angle of the regulator. ω r_m The value of is m times the power grid frequency. Used to address delays in sampling, loading, and modulation in the control loop, as well as phase lag in the control loop caused by grid voltage feedforward, s is the Laplace operator.

[0181] For implementation of Option 1, please refer to [link / reference]. Figure 9 When both the grid connection point voltage and the bridge arm current input are abc components, the grid connection current abc component is estimated; the grid connection current abc component is transformed into the grid connection current dq component, and harmonic suppression is performed based on the grid connection current dq component.

[0182] For implementation scheme two, see [link / reference] Figure 10When both the grid connection point voltage and the bridge arm current input are αβ components, the grid connection current αβ component is estimated based on the αβ component; the grid connection current αβ component is transformed into the grid connection current dq component, and harmonic suppression is performed based on the grid connection current dq component.

[0183] For implementation of Option 3, please refer to [link / reference]. Figure 11 When both the grid connection point voltage and the bridge arm current input are dq components, the dq components are used directly for harmonic suppression.

[0184] It should be noted that the present invention improves the phase margin of the control system by adding phase compensation (i.e., the phase compensation value of each harmonic suppression ring submodule) in the harmonic suppression ring, thereby maintaining the stability of the system while suppressing grid current harmonics.

[0185] In this invention, the phase compensation values ​​of each harmonic suppression loop submodule are obtained using an optimization method based on the system's open-loop Bode plot, specifically including:

[0186] A frequency domain model of the inverter control system is established based on the control loop of the inverter, and an open-loop Bode plot of the system is established based on the frequency domain model.

[0187] The phase margin value at each harmonic frequency is determined based on the open-loop Bode plot of the system.

[0188] Determine the phase compensation value at each harmonic frequency so that the phase margin value meets the corresponding set phase margin value under different grid short-circuit ratios;

[0189] The phase compensation value at each harmonic frequency is the phase compensation value of each harmonic suppression loop submodule.

[0190] (II) Another method for inputting the grid-connected current into each harmonic suppression ring submodule for harmonic suppression and obtaining the corresponding output value of each submodule is as follows:

[0191] The harmonic suppression loop submodule is implemented based on a quasi-proportional resonant regulator:

[0192] The grid-connected current is input to each quasi-proportional resonant regulator for processing, and the output value of each submodule is obtained.

[0193] In this embodiment, the quasi-proportional resonant regulator includes a phase compensation factor.

[0194] To further optimize the above embodiments, step S103 may specifically include:

[0195] (1) Obtain the bridge arm current command;

[0196] (2) The bridge arm current and bridge arm current command are calculated using the current loop control equation to obtain the fundamental current loop control output value;

[0197] (3) The feedforward value of the grid connection point voltage is obtained by using the grid voltage feedforward calculation equation.

[0198] Specifically, assuming the bridge arm current command is i L_dq_ref (Active instruction i) L_d_ref and reactive power instruction i L_q_ref ), i L_dq_ref The source of the input is either the internal voltage loop output, the power loop output, or an externally given command input; this invention does not limit the source.

[0199] According to the bridge arm current command i L_dq_ref and the bridge arm current dq component i L_dq The fundamental current loop control output value u is obtained by calculating the current loop control equation. dq_out The expression is shown in formula (15), and formula (15) is as follows:

[0200]

[0201] In the formula, K p_i K is the proportional coefficient of the current loop PI regulator. i_i is the integral coefficient of the current loop PI regulator, and s is the Laplace operator.

[0202] In summary, this invention can suppress specific harmonics in the grid-connected current by estimating the grid-connected current, resulting in better grid-connected current harmonic suppression. By adding phase compensation in the harmonic suppression loop, the phase margin of the control system is improved, thereby maintaining system stability while suppressing grid-connected current harmonics. By using weighted feedforward on the grid-connected point voltage, the grid-connected inverter can have better dynamics and stability regardless of whether it is in a strong or weak grid, and the difficulty of grid-connected current harmonic suppression is reduced.

[0203] To further demonstrate that the inverter grid-connected current harmonic suppression method disclosed in this invention represents a significant improvement over traditional solutions, simulation experiments were also conducted, as detailed below:

[0204] The simulation conditions are set as follows:

[0205] The power grid contains 5th, 7th, 11th and 13th harmonics. The grid current harmonic suppression effects under the power grid voltage feedforward method, the bridge arm current regulator suppression method and the suppression method disclosed in this invention are simulated respectively. Among them, the regulator suppression method only adds suppression for the 5th, 7th, 11th and 13th harmonics.

[0206] When using the grid voltage feedforward method, the simulated waveforms of the grid-connected current and bridge arm current are as follows:Figure 12 As shown in the figure, there is obvious distortion in the grid-connected current, which means that the grid voltage feedforward method cannot effectively suppress the harmonics of the grid-connected current.

[0207] When the arm current regulator suppression method is used, and the power grid is in a strong grid state (SCR=20), the simulated waveforms of the grid-connected current and arm current are as follows: Figure 13 As shown in the figure, the harmonics in the bridge arm current are suppressed and the current is relatively smooth, but the grid-connected current has obvious distortion. When the bridge arm current regulator suppression method is used, and the grid is in a weak grid state (SCR=8), the simulated waveforms of the grid-connected current and bridge arm current are as follows. Figure 14 As shown in the figure, both the bridge arm current and the grid-connected current exhibit significant resonance. This means that the bridge arm current regulator suppression method cannot effectively suppress grid-connected current harmonics.

[0208] When the harmonic suppression scheme provided by this invention is adopted, and the power grid is in a weak grid state (SCR=8), the simulated waveforms of the grid-connected current and the bridge arm current are as follows: Figure 15 As shown in the figure, the grid-connected current harmonic situation is significantly improved, indicating that the harmonic suppression scheme provided by this invention has a good harmonic suppression effect and is also applicable under weak grid conditions.

[0209] Therefore, the advantages of the present invention over existing solutions are as follows:

[0210] 1) Compared with the grid voltage feedforward method and the bridge arm current regulator suppression method, this invention can clearly suppress specific harmonics in the grid current by estimating the grid current, and the grid current harmonic suppression effect is better.

[0211] 2) Compared with the traditional grid-connected current regulator suppression method, the present invention saves the use of grid-connected current sensors and reduces costs.

[0212] 3) The present invention adds phase compensation to the harmonic suppression loop, which improves the phase margin of the control system and can maintain the stability of the system while suppressing harmonics.

[0213] 4) When combined with the grid voltage weighted feedforward scheme, this invention has better grid adaptability. The suppression method disclosed in this invention can be applied to both strong and weak grids.

[0214] Corresponding to the above method embodiments, the present invention discloses a system for suppressing inverter grid-connected current harmonics.

[0215] See Figure 16 The present invention discloses a schematic diagram of a system for suppressing grid-connected current harmonics in an inverter. The system includes:

[0216] Acquisition unit 201 is used to acquire inverter arm current and grid connection point voltage;

[0217] The harmonic suppression unit 202 is used to calculate the grid-connected current by the inverter arm current and the grid-connected point voltage, and to suppress the harmonics of the grid-connected current by the harmonic suppression loop to obtain the output value of the harmonic suppression loop.

[0218] It should be noted that the harmonic suppression loop in this embodiment includes various harmonic suppression loops, and each harmonic suppression loop has a phase compensation function. The phase compensation values ​​of each harmonic suppression loop can be the same or different, depending on the actual needs, and this invention does not limit this. By adding a phase compensation function to the harmonic suppression loop, this invention improves the phase margin of the control system, thereby maintaining system stability while suppressing grid-connected current harmonics.

[0219] Acquisition unit 203 is used to acquire the feedforward value of the grid connection point voltage and the fundamental current loop control output value;

[0220] Specifically, for the dq component v of the grid connection point voltage g_dq The feedforward value u of the grid connection point voltage is obtained using the grid voltage feedforward scheme. feed_dq The grid voltage feedforward scheme used in this embodiment can effectively address the resonance problem under weak grid conditions and improve the dynamic response speed of the inverter under weak grid conditions. See details... Figure 3 The schematic diagram of the grid voltage feedforward module shown is as follows, in which, Figure 3 The grid voltage feedforward module in the middle is also known as Figure 2 The grid voltage feedforward module is shown in the figure.

[0221] The modulation unit determination unit 204 is used to take the negative value of the harmonic suppression loop output value and superimpose it with the feedforward value of the grid connection point voltage and the control output value of the fundamental current loop to obtain the modulation voltage of the inverter.

[0222] The modulation unit 205 is used to perform PWM modulation on the components of the modulation voltage to generate a switching signal that drives the grid-connected inverter.

[0223] In this embodiment, the component of the modulation voltage is the dq component u of the inverter modulation voltage. m_dq .

[0224] This invention discloses a system for suppressing harmonics in inverter grid-connected current. The system collects the inverter arm current and grid-connected point voltage, calculates the grid-connected current from these data, and uses a harmonic suppression loop to suppress harmonics in the grid-connected current, obtaining the output value of the harmonic suppression loop. It also acquires the feedforward value of the grid-connected point voltage and the control output value of the fundamental current loop. The output value of the harmonic suppression loop is then negatively evaluated and superimposed with these values ​​to obtain the modulation voltage of the inverter. The modulated voltage component is then subjected to PWM modulation to generate a switching signal that drives the grid-connected inverter. This invention, by estimating the grid-connected current, can suppress specific harmonics in the grid-connected current, resulting in better harmonic suppression. Furthermore, by using feedforward on the grid-connected point voltage, the inverter exhibits better dynamics and stability under both strong and weak grid conditions, and the difficulty of suppressing grid-connected current harmonics is reduced.

[0225] To further optimize the above embodiments, the harmonic suppression unit 202 may include:

[0226] The current estimation subunit is used to perform differential calculation on the grid connection point voltage and multiply it with the grid connection filter capacitor value to obtain the grid connection filter capacitor current estimation value.

[0227] The grid-connected current determination subunit is used to calculate the grid-connected current based on the estimated value of the grid-connected filter capacitor current and the inverter bridge arm current.

[0228] To further optimize the above embodiments, the harmonic suppression unit 202 may further include:

[0229] The harmonic suppression subunit is used to input the grid-connected current to each of the harmonic suppression ring submodules for harmonic suppression when the harmonic suppression ring includes at least one harmonic suppression ring submodule, and obtain the corresponding output value of each submodule.

[0230] The suppression loop output value determination subunit is used to add the output values ​​of each submodule to obtain the harmonic suppression loop output value.

[0231] In this embodiment, the harmonic suppression subunit is specifically used for:

[0232] The grid-connected current is transformed from a two-phase stationary coordinate system to a two-phase rotating coordinate system by different input stage coordinate transformation angles to obtain the target grid-connected current.

[0233] The target grid-connected current is passed through a low-pass filter to obtain the dq DC components of each harmonic.

[0234] The dq DC components of each harmonic are passed through a regulator to obtain the regulator output components.

[0235] The output components of the regulator are transformed from the two-phase rotating coordinate system to the two-phase stationary coordinate system by different output level coordinate transformation angles to obtain the output values ​​of each sub-module.

[0236] It should be noted that when harmonic suppression is performed based on the dq component of the grid-connected current, the input stage coordinate transformation angles are -3kθ and 3kθ.

[0237] When harmonic suppression is performed based on the αβ component of the grid-connected current, the input stage coordinate transformation angles are -(3k-1)θ and (3k+1)θ.

[0238] Without phase compensation, the output stage coordinate transformation angles are -3kθ and 3kθ. With phase compensation, the output stage coordinate transformation angles are... and

[0239] in, and θ represents the phase compensation value of each harmonic suppression loop submodule, θ is the power grid phase angle, k represents the harmonic order index coefficient, and k is a positive integer.

[0240] The inhibition system may also include:

[0241] The phase compensation value determination unit is used to obtain the phase compensation values ​​of each harmonic suppression loop submodule based on the system's open-loop Bode plot using an optimization method.

[0242] The phase compensation value determination unit is specifically used for:

[0243] A frequency domain model of the inverter control system is established based on the control loop of the inverter, and an open-loop Bode plot of the system is established based on the frequency domain model.

[0244] The phase margin value at each harmonic frequency is determined based on the open-loop Bode plot of the system.

[0245] Determine the phase compensation value at each harmonic frequency so that the phase margin value meets the corresponding set phase margin value under different grid short-circuit ratios;

[0246] The phase compensation value at each harmonic frequency is the phase compensation value of each harmonic suppression loop submodule.

[0247] In the above embodiments, the harmonic suppression subunit can also be used for:

[0248] When the harmonic suppression loop submodule is implemented based on a quasi-proportional resonant regulator, the grid-connected current is input to each of the quasi-proportional resonant regulators for processing to obtain the output value of each submodule.

[0249] To further optimize the above embodiments, the acquisition unit 203 may specifically be used for:

[0250] Get bridge arm current command;

[0251] The fundamental current loop control output value is obtained by performing current loop control equations on the bridge arm current and the bridge arm current command.

[0252] The feedforward value of the grid connection point voltage is obtained by using the grid voltage feedforward calculation equation.

[0253] It should be noted that the specific working principles of each component in the inverter grid-connected current harmonic suppression system are detailed in the corresponding sections of the method embodiments, and will not be repeated here.

[0254] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0255] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0256] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for suppressing harmonics in inverter grid-connected current, characterized in that, include: Collect inverter arm current and grid connection point voltage; The grid-connected current is obtained by calculating the inverter arm current and the grid connection point voltage. Harmonic suppression is performed on the grid-connected current through a harmonic suppression loop to obtain the output value of the harmonic suppression loop. The harmonic suppression ring has a phase compensation function; Obtain the feedforward value of the grid connection point voltage and the fundamental current loop control output value; The output value of the harmonic suppression loop is negative, and then superimposed with the feedforward value of the grid connection point voltage and the control output value of the fundamental current loop to obtain the modulation voltage of the inverter. The components of the modulation voltage are PWM modulated to generate a switching signal that drives the inverter.

2. The suppression method according to claim 1, characterized in that, The step of calculating the grid-connected current from the inverter arm current and the grid connection point voltage includes: The grid connection point voltage is differentiated and multiplied with the grid connection filter capacitor value to obtain the estimated value of the grid connection filter capacitor current. The grid-connected current is calculated based on the estimated value of the grid-connected filter capacitor current and the inverter bridge arm current.

3. The suppression method according to claim 1, characterized in that, The process of suppressing harmonics in the grid-connected current using a harmonic suppression loop to obtain the output value of the harmonic suppression loop includes: The harmonic suppression ring includes at least one harmonic suppression ring submodule. The grid-connected current is input to each of the harmonic suppression ring submodules for harmonic suppression, and the corresponding output values ​​of each submodule are obtained. The output values ​​of each submodule are summed to obtain the output value of the harmonic suppression loop.

4. The suppression method according to claim 3, characterized in that, The step of inputting the grid-connected current to each of the harmonic suppression loop submodules for harmonic suppression, and obtaining the corresponding output values ​​of each submodule, includes: The grid-connected current is transformed from a two-phase stationary coordinate system to a two-phase rotating coordinate system by different input stage coordinate transformation angles to obtain the target grid-connected current. The target grid-connected current is passed through a low-pass filter to obtain the dq DC components of each harmonic. The dq DC components of each harmonic are passed through a regulator to obtain the regulator output components. The output components of the regulator are transformed from the two-phase rotating coordinate system to the two-phase stationary coordinate system by different output level coordinate transformation angles to obtain the output values ​​of each sub-module.

5. The suppression method according to claim 4, characterized in that, When performing harmonic suppression based on the grid-connected current dq component, the input stage coordinate transformation angles are -3kθ and 3kθ. When harmonic suppression is performed based on the αβ component of the grid-connected current, the input stage coordinate transformation angles are -(3k-1)θ and (3k+1)θ. Without phase compensation, the output stage coordinate transformation angles are -3kθ and 3kθ; with phase compensation, the output stage coordinate transformation angles are -φ. 3k-1 -3kθ and φ 3k+1 +3kθ; Where, φ 3k-1 and φ 3k+1 θ represents the phase compensation value of each harmonic suppression loop submodule, θ is the power grid phase angle, k represents the harmonic order index coefficient, and k is a positive integer.

6. The suppression method according to claim 5, characterized in that, The phase compensation values ​​of each harmonic suppression loop submodule are obtained by an optimization method based on the system's open-loop Bode plot, specifically including: A frequency domain model of the inverter control system is established based on the control loop of the inverter, and an open-loop Bode plot of the system is established based on the frequency domain model. The phase margin value at each harmonic frequency is determined based on the open-loop Bode plot of the system. Determine the phase compensation value at each harmonic frequency so that the phase margin value meets the corresponding set phase margin value under different grid short-circuit ratios; The phase compensation value at each harmonic frequency is the phase compensation value of each harmonic suppression loop submodule.

7. The suppression method according to claim 3, characterized in that, The step of inputting the grid-connected current to each of the harmonic suppression loop submodules for harmonic suppression, and obtaining the corresponding output values ​​of each submodule, includes: The harmonic suppression loop submodule is implemented based on a quasi-proportional resonant regulator: The grid-connected current is input to each of the quasi-proportional resonant regulators for processing to obtain the output value of each submodule.

8. The suppression method according to claim 7, characterized in that, The quasi-proportional resonant regulator includes a phase compensation factor.

9. The suppression method according to claim 1, characterized in that, The process of obtaining the feedforward value of the grid connection point voltage and the fundamental current loop control output value includes: Get bridge arm current command; The fundamental current loop control output value is obtained by performing current loop control equations on the bridge arm current and the bridge arm current command. The feedforward value of the grid connection point voltage is obtained by using the grid voltage feedforward calculation equation.

10. The suppression method according to claim 1, characterized in that, The feedforward value is a weighted feedforward value.

11. A system for suppressing harmonics in inverter grid-connected current, characterized in that, include: The acquisition unit is used to acquire the inverter arm current and grid connection point voltage; The harmonic suppression unit is used to calculate the grid-connected current from the inverter arm current and the grid-connected point voltage, and to suppress the harmonics of the grid-connected current through the harmonic suppression loop to obtain the output value of the harmonic suppression loop. The harmonic suppression ring has a phase compensation function; The acquisition unit is used to acquire the feedforward value of the grid connection point voltage and the fundamental current loop control output value; The modulation unit determination unit is used to take the negative value of the harmonic suppression loop output value and superimpose it with the feedforward value of the grid connection point voltage and the control output value of the fundamental current loop to obtain the modulation voltage of the inverter. The modulation unit is used to perform PWM modulation on the components of the modulation voltage to generate a switching signal that drives the inverter.

12. The suppression system according to claim 11, characterized in that, The harmonic suppression unit includes: The current estimation subunit is used to perform differential calculation on the grid connection point voltage and multiply it with the grid connection filter capacitor value to obtain the grid connection filter capacitor current estimation value. The grid-connected current determination subunit is used to calculate the grid-connected current based on the estimated value of the grid-connected filter capacitor current and the inverter bridge arm current.

13. The suppression system according to claim 11, characterized in that, The harmonic suppression unit further includes: The harmonic suppression subunit is used to input the grid-connected current to each of the harmonic suppression ring submodules for harmonic suppression when the harmonic suppression ring includes at least one harmonic suppression ring submodule, and obtain the corresponding output value of each submodule. The suppression loop output value determination subunit is used to add the output values ​​of each submodule to obtain the harmonic suppression loop output value.

14. The suppression system according to claim 13, characterized in that, The harmonic suppression subunit is specifically used for: The grid-connected current is transformed from a two-phase stationary coordinate system to a two-phase rotating coordinate system by different input stage coordinate transformation angles to obtain the target grid-connected current. The target grid-connected current is passed through a low-pass filter to obtain the dq DC components of each harmonic. The dq DC components of each harmonic are passed through a regulator to obtain the regulator output components. The output components of the regulator are transformed from the two-phase rotating coordinate system to the two-phase stationary coordinate system by different output level coordinate transformation angles to obtain the output values ​​of each sub-module.

15. The suppression system according to claim 14, characterized in that, When performing harmonic suppression based on the grid-connected current dq component, the input stage coordinate transformation angles are -3kθ and 3kθ. When harmonic suppression is performed based on the αβ component of the grid-connected current, the input stage coordinate transformation angles are -(3k-1)θ and (3k+1)θ. Without phase compensation, the output stage coordinate transformation angles are -3kθ and 3kθ; with phase compensation, the output stage coordinate transformation angles are -φ. 3k-1 -3kθ and φ 3k+1 +3kθ; Where, φ 3k-1 and φ 3k+1 θ represents the phase compensation value of each harmonic suppression loop submodule, θ is the power grid phase angle, k represents the harmonic order index coefficient, and k is a positive integer.

16. The suppression system according to claim 15, characterized in that, Also includes: The phase compensation value determination unit is used to obtain the phase compensation values ​​of each harmonic suppression loop submodule based on the system's open-loop Bode plot using an optimization method. The phase compensation value determination unit is specifically used for: A frequency domain model of the inverter control system is established based on the control loop of the inverter, and an open-loop Bode plot of the system is established based on the frequency domain model. The phase margin value at each harmonic frequency is determined based on the open-loop Bode plot of the system. Determine the phase compensation value at each harmonic frequency so that the phase margin value meets the corresponding set phase margin value under different grid short-circuit ratios; The phase compensation value at each harmonic frequency is the phase compensation value of each harmonic suppression loop submodule.

17. The suppression system according to claim 13, characterized in that, The harmonic suppression subunit is also specifically used for: When the harmonic suppression loop submodule is implemented based on a quasi-proportional resonant regulator, the grid-connected current is input to each of the quasi-proportional resonant regulators for processing to obtain the output value of each submodule.

18. The suppression system according to claim 11, characterized in that, The acquisition unit is specifically used for: Get bridge arm current command; The fundamental current loop control output value is obtained by performing current loop control equations on the bridge arm current and the bridge arm current command. The feedforward value of the grid connection point voltage is obtained by using the grid voltage feedforward calculation equation.

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