Harmonic suppression method and system for power conversion equipment of power distribution network

Abstract

The application relates to the technical field of power conversion device control, and discloses a power distribution network power conversion equipment harmonic suppression method and system. The method comprises the following steps: collecting harmonic amplitudes to construct a state vector and a coupling matrix, predicting the control harmonic and calculating a feedback influence quantity, superimposing an inhibition quantity and a compensation quantity to generate a double-layer instruction to adjust a switching parameter, outputting a pulse width modulation signal and monitoring a residual error to update the coupling matrix. The application improves the global optimization performance of harmonic suppression and the self-adaptive ability to power grid environment changes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power conversion device control, in particular to a power conversion device harmonic suppression method and system for power distribution network. BACKGROUND

[0002] The power conversion devices such as inverters and rectifiers in the power distribution network realize power conversion through pulse width modulation technology in the operation process, but due to the nonlinear characteristics of power switching devices, the fifth, seventh, eleventh and thirteenth original harmonics will be generated in the output current, which will cause the grid voltage waveform distortion and affect the power supply quality. In order to suppress these original harmonics, the existing technology mainly adopts the method of improving the pulse width modulation control strategy, which adjusts the switching angle and the modulation degree to reduce the amplitude of specific harmonics. Common methods include space vector pulse width modulation, selective harmonic elimination pulse width modulation, repetitive control and resonance control, etc. These methods realize the suppression of original harmonics to a certain extent through the optimization of control algorithm.

[0003] However, the main deficiency of the existing technology is that when performing original harmonic suppression control, the control action itself will produce new harmonic pollution. Specifically, when adjusting the pulse width modulation duty ratio or switching angle to suppress low-order original harmonics, these control actions will generate sideband harmonics, i.e. control harmonics, near the switching frequency. The existing method considers original harmonic suppression and control harmonic suppression as two independent control tasks, and adopts a serial processing method of suppressing original harmonics first and then suppressing control harmonics, which leads to mutual interference and conflict between the two control targets. SUMMARY

[0004] The present application provides a power conversion device harmonic suppression method and system for power distribution network, which solves the problem of control action generating control harmonics and control harmonic suppression weakening the effect of original harmonic suppression in the existing power conversion device harmonic suppression method. By establishing a harmonic coupling matrix to predict control harmonics and calculating feedback influence quantity for pre-compensation, the coordinated suppression of original harmonics and control harmonics is realized, and the global optimization performance of harmonic suppression and the self-adaptive ability to the change of grid environment are improved.

[0005] In a first aspect, the present application provides a power conversion device harmonic suppression method for power distribution network, which comprises:

[0006] Step S1, collecting the amplitude of multiple harmonics of the output current of the power conversion device, constructing a harmonic state vector and a harmonic coupling matrix;

[0007] Step S2, predicting a control harmonic amplitude generated by a control action of suppressing a native harmonic at a switching frequency according to the harmonic coupling matrix, mapping the control harmonic amplitude to a fundamental frequency through the harmonic coupling matrix, and calculating a feedback influence amount of the control harmonic on the native harmonic;

[0008] Step S3, superimposing a native harmonic suppression amount and a compensation amount of the feedback influence amount to generate a double-layer suppression instruction, and adjusting a switching angle and a modulation degree according to the double-layer suppression instruction;

[0009] Step S4, outputting a corrected pulse width modulation driving signal, and monitoring a harmonic residual error to update the harmonic coupling matrix.

[0010] In a second aspect, the present application provides a power distribution network power conversion device harmonic suppression system, the power distribution network power conversion device harmonic suppression system comprising:

[0011] In the technical scheme provided by the present application, the harmonic state vector is constructed by collecting the harmonic amplitude of the output current of the power conversion device and combining the proportion weight of each harmonic in the total harmonic distortion rate, the discrete harmonic data is converted into a vector form which can be operated by a matrix, and a data foundation is laid for subsequent coupling analysis based on linear algebra theory. The construction of the harmonic coupling matrix is based on the partial differential relationship of the pulse width modulation switching angle adjustment amount on the harmonic amplitude, the sensitivity function is used to quantify the influence degree of adjusting a harmonic on other harmonics, the implicit harmonic interaction mechanism is explicitly converted into a calculable mathematical model, the control system can accurately know the coupling strength and direction between different harmonics, and the limitation of ignoring the mutual influence by independently processing each harmonic in the prior art is overcome.

[0012] The core innovation of the present application is to predict the control harmonic amplitude generated by the control action of suppressing the original harmonic at the switching frequency according to the harmonic coupling matrix, and map the control harmonic amplitude to the fundamental frequency through the harmonic coupling matrix to calculate the feedback influence amount of the original harmonic, thereby realizing the control paradigm change from post-repair to prior prevention. Through the prediction mechanism, the side effects caused by the control action are quantified before the control is executed, so that the control system has foresight, the compensation amount of the original harmonic suppression amount and the feedback influence amount is superimposed to generate a double-layer suppression instruction, both the original harmonic suppression and the control harmonic influence offset are considered in a single control action, the contradiction between the two control tasks in the traditional serial control mode is avoided, the switching angle and the modulation degree are adjusted according to the double-layer suppression instruction, and the corrected pulse width modulation driving signal is output, so that the control instruction can accurately act on the power switch device, the harmonic residual error is monitored, and the closed-loop adaptive mechanism of the harmonic coupling matrix is updated, so that the system can correct the prediction model according to the actual operation effect, when the system characteristics drift due to the change of power grid impedance or load fluctuation, the coupling matrix parameters are automatically adjusted to adapt to the new operating condition, thereby overcoming the performance degradation problem of fixed model parameters in dynamic environment, and improving the robustness and long-term stability of the harmonic suppression performance. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor based on these drawings.

[0014] Figure 1 An embodiment of the harmonic suppression method for power conversion equipment in the power distribution network in the present application is shown in the figure.

[0015] Figure 2 The structure of the harmonic coupling matrix in the embodiment of the present application is shown in the figure.

[0016] Figure 3 The figure shows the accuracy verification of the control harmonic prediction in the embodiment of the present application. DETAILED DESCRIPTION

[0017] The embodiments of the present application provide a power conversion device harmonic suppression method and system for a power distribution network. The terms "first", "second", "third", "fourth" and the like (if any) in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "comprise" or "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0018] For ease of understanding, the specific processes of the embodiments of the present application are described below. Please refer to Figure 1 One embodiment of the power conversion device harmonic suppression method for a power distribution network in the embodiments of the present application includes:

[0019] Step S1, collecting the harmonic amplitudes of the output current of the power conversion device, constructing a harmonic state vector and a harmonic coupling matrix;

[0020] Specifically, the construction of the harmonic state vector converts the discrete harmonic amplitude data into a vector form that can be processed by matrix operation. The time-domain current signal is decomposed into frequency-domain harmonic components through fast Fourier transform, and the amplitudes of specific order harmonics are extracted and arranged in order to form a column vector structure. The construction of the harmonic coupling matrix is based on partial differential sensitivity analysis. The influence of a small change in switching angle on the amplitude of each harmonic is calculated to quantify the interaction between different harmonics. Each element in the matrix represents a specific coupling strength. The diagonal elements reflect the self-regulation effect, and the non-diagonal elements reflect the cross-interference degree.

[0021] Step S2, predicting the control harmonic amplitude generated at the switching frequency by the control action for suppressing the original harmonic according to the harmonic coupling matrix, mapping the control harmonic amplitude to the fundamental frequency through the harmonic coupling matrix, and calculating the feedback influence of the control harmonic on the original harmonic;

[0022] Specifically, first, the PWM duty cycle adjustment amount is calculated according to the suppression requirement of the original harmonic, which will inevitably produce a sideband spectral component centered on the switching frequency when acting on the power switching device, which is the source of the control harmonic. Through the Fourier series expansion of the modulation theory, the time domain switching action is converted into the frequency domain sideband harmonic amplitude. Then the frequency conversion coefficient is introduced, which is based on the ratio of the switching frequency to the fundamental frequency, realizing the energy mapping of the high-frequency control harmonic to the low-frequency fundamental frequency. The equivalent control harmonic component after mapping is multiplied by the harmonic coupling matrix again to get the specific influence value of the control harmonic on each original harmonic, forming a feedback influence vector.

[0023] Step S3, superimpose the original harmonic suppression amount and the compensation amount of the feedback influence amount to generate a double-layer suppression instruction, and adjust the switching angle and the modulation degree according to the double-layer suppression instruction;

[0024] Specifically, the calculation of the basic suppression amount is based on the difference between the current harmonic amplitude and the expected target value, and the control gain matrix is used to amplify the control signal. The calculation of the pre-compensation amount is based on the feedback influence obtained in step S2, which is processed by the same control gain matrix, but the sign is opposite to realize the offset effect. The vector superposition of the two control amounts generates the final double-layer suppression instruction, which contains multiple components corresponding to the control requirements of different harmonics. When converting the vector form of the control instruction into the actual PWM parameter adjustment amount, the switching angle increment needs to be solved through the inverse Fourier transform relationship, and the modulation degree adjustment amount needs to be calculated according to the voltage modulation ratio formula, and the two types of parameters jointly act on the space vector pulse width modulation module.

[0025] Step S4, output the corrected pulse width modulation driving signal, and update the harmonic coupling matrix by monitoring the harmonic residual error.

[0026] Specifically, after the corrected PWM driving signal acts on the circuit through the power switching device, the output current is re-acquired for frequency spectrum analysis to obtain the actual harmonic amplitude. The difference between the actual value and the expected value is the original harmonic residual error and the control harmonic residual error, which reflects the deviation between the prediction model and the actual system. The coupling matrix is updated by using the least squares recursive method, and the specific process is to calculate the residual gradient, adjust the matrix element value along the gradient direction, and the adjustment amplitude is controlled by the learning rate parameter. The updated coupling matrix more accurately reflects the harmonic interaction characteristics under the current grid impedance and load state, improves the prediction accuracy of the subsequent control period, and forms a self-learning and self-optimizing control loop.

[0027] In a specific embodiment, step S1 includes:

[0028] The current signal at the output end of the power conversion device is acquired by a current sensor, and the current signal is processed by fast Fourier transform to extract the amplitude and phase information of multiple harmonics.

[0029] According to the extracted harmonic amplitude, the proportion weight of each harmonic in the total harmonic distortion rate is calculated, and the harmonic amplitude is constructed into a harmonic state vector;

[0030] Based on the partial differential relationship of the pulse width modulation switching angle adjustment amount to the harmonic amplitude, a sensitivity function is calculated, the sensitivity function is numerically calculated at the current switching angle and normalized to obtain the coupling coefficient of the harmonic coupling matrix;

[0031] According to the coupling coefficient, a harmonic coupling matrix is constructed, the diagonal elements of the harmonic coupling matrix are self-influence coefficients, and the non-diagonal elements are cross-coupling coefficients.

[0032] Specifically, the fast Fourier transform converts the time-domain continuous current signal into a frequency-domain discrete harmonic component, and the amplitude and phase angle of each harmonic are obtained through complex operation, the amplitude represents the contribution degree of the harmonic to the current waveform distortion, and the phase angle reflects the time relationship between the harmonic and the fundamental wave. The calculation of the proportion weight is based on the ratio of the square of the amplitude of each harmonic to the sum of the squares of the total harmonic amplitudes, the weight directly reflects the responsibility proportion of a specific harmonic in the overall power quality deterioration, and the greater the weight value, the more significant the influence of the harmonic on the total harmonic distortion rate. The harmonic state vector arranges a plurality of independent harmonic amplitude data in order of the number into a column vector form, so that the subsequent matrix operation can batch process the coupling relationship of multiple harmonics.

[0033] The partial differential relationship describes the response rate of the harmonic amplitude when the switching angle changes slightly, and the sensitivity function in the analytical form is obtained by taking the partial derivative of the Fourier series expression of the space vector pulse width modulation. The sensitivity value under the current working condition is obtained by substituting the numerical value of the current actual running switching angle into the sensitivity function for numerical calculation, and the normalization processing is to divide all sensitivity values by the maximum absolute value among them, so that the numerical range of the coupling coefficient is unified to between negative one and positive one, which is convenient for the numerical stability of the matrix operation. The self-influence coefficient located on the diagonal line of the matrix represents the influence of adjusting the switching angle of a harmonic on the amplitude of the harmonic itself, and the numerical value is always negative one, reflecting the negative feedback characteristic of suppression control. The cross-coupling coefficient located at the non-diagonal line position represents the incidental influence on the j-th harmonic when the i-th harmonic is adjusted, the positive value represents the enhancement effect and the negative value represents the weakening effect, and the matrix quantifies the complex interaction mechanism between multiple harmonics.

[0034] Figure 2 The figure is a schematic diagram of the harmonic coupling matrix structure in the embodiments of the present application. As shown in Figure 2As shown, the matrix is a four-row and four-column structure, the row coordinates represent the harmonic order of control, the column coordinates represent the affected harmonic order, and the matrix element values represent the coupling coefficients. The diagonal elements are all negative one, indicating the self-influence coefficient, and the diagonal line filling pattern indicates the negative feedback effect of suppressing a certain harmonic on itself. The non-diagonal elements are cross-coupling coefficients, the horizontal line filling pattern indicates a positive coupling relationship with a positive value, the diagonal line filling pattern indicates a negative coupling relationship with a negative value, and the grid filling pattern indicates a weak coupling relationship with a value close to zero. For example, the element in the first row and the second column is 0.15, indicating that when suppressing the 5th harmonic, it has a positive enhancement effect on the 7th harmonic. The element in the second row and the first column is 0.12, indicating that when suppressing the 7th harmonic, it also has a positive effect on the 5th harmonic. The element in the first row and the third column is negative 0.08, indicating that when suppressing the 5th harmonic, it has a weakening effect on the 11th harmonic. The matrix as a whole quantifies the mutual influence mechanism of different harmonics in the PWM control adjustment process.

[0035] In a specific embodiment, the step S2 of predicting the control harmonic amplitude generated at the switching frequency by the control action of suppressing the original harmonic according to the harmonic coupling matrix comprises:

[0036] determining a preliminary control quantity of each harmonic according to the proportion weight of each harmonic in the harmonic state vector, the preliminary control quantity representing the pulse width modulation duty cycle adjustment amplitude required to suppress the corresponding harmonic;

[0037] substituting the preliminary control quantity into the modulation theory formula, combining the current modulation degree and the DC side voltage parameters, and calculating the switching frequency sideband harmonic amplitude caused by the control action;

[0038] obtaining the predicted control harmonic amplitude according to the switching frequency sideband harmonic amplitude.

[0039] Specifically, the determination of the preliminary control quantity multiplies the harmonic amplitude by its weight and applies a proportional control gain, and the calculation formula is , wherein the preliminary control quantity of the nth harmonic, the proportional control gain coefficient, the amplitude of the nth harmonic, the proportion weight of the harmonic. The physical meaning of this control quantity is the pulse width modulation duty cycle amplitude that needs to be adjusted to suppress a specific harmonic. The harmonic with a larger weight is allocated more control resources, and the harmonic with a larger amplitude requires a larger adjustment amount. The proportional gain coefficient is set according to the system response characteristics and is usually valued between zero point five and three.

[0040] The modulation theory formula is based on the frequency domain characteristics of pulse width modulation, and the sideband harmonic amplitude calculation formula generated by switching action is:

[0041] , wherein ​represents the sideband harmonic amplitude near the switching frequency, is a first order Bessel function, is the current modulation degree, i.e. the ratio of the fundamental amplitude of the output voltage to the DC side voltage, is a DC side voltage parameter. The first order Bessel function describes the interaction strength between the fundamental and the switching frequency in the carrier modulation process, the modulation degree determines the modulation depth which affects the energy distribution of the sideband harmonics, and the DC side voltage as a power reference affects the absolute amplitude of the harmonics. The preliminary control quantities of all harmonics are summed and taken the absolute value, reflecting the total harmonic energy generated at the switching frequency after the superposition of multiple control actions. The calculated switching frequency sideband harmonic amplitude is directly used as the predicted control harmonic amplitude, which represents the degree of high-frequency harmonic pollution inevitably generated when performing the original harmonic suppression control.

[0042] In a specific embodiment, the control harmonic amplitude in step S2 is mapped to the fundamental frequency through the harmonic coupling matrix, including:

[0043] A frequency conversion coefficient is calculated based on the ratio of the switching frequency to the fundamental frequency, which represents the energy transfer proportion of the high-frequency control harmonic to the low-frequency original harmonic;

[0044] The control harmonic amplitude is multiplied by the frequency conversion coefficient to obtain the equivalent control harmonic component after frequency mapping;

[0045] The equivalent control harmonic component is input into the harmonic coupling matrix for matrix multiplication to obtain the coupling component vector corresponding to each original harmonic.

[0046] Specifically, the calculation of the frequency conversion coefficient uses the ratio of the switching frequency to the fundamental frequency. When the switching frequency is ten kilohertz and the fundamental frequency is fifty hertz, the conversion coefficient is two hundred. The physical meaning of this coefficient is to quantify the attenuation proportion of the energy transfer from high-frequency harmonic to low-frequency harmonic. The control harmonic is a high-frequency component near the switching frequency, while the original harmonic is a low-frequency component at an integer multiple of the fundamental frequency. The frequency difference between the two is several hundred times, and there is natural attenuation caused by the frequency interval in the energy transfer process. The conversion coefficient is a parameter that describes the degree of this attenuation. The control harmonic amplitude is multiplied by the conversion coefficient to obtain the equivalent control harmonic component, which represents the effective amplitude of the control harmonic after being equivalent to the fundamental frequency and affecting the original harmonic. It is equivalent to mapping the high-frequency energy to the low-frequency band in proportion.

[0047] The equivalent control harmonic component is constructed as a column vector with the same dimension as the harmonic state vector, and each element in the vector has the same value as the equivalent control harmonic component. When the vector is multiplied by the harmonic coupling matrix, each row of the matrix is multiplied by the corresponding elements of the vector and then summed to obtain the total coupling effect on the corresponding harmonic of the row. The result of the matrix multiplication is the coupling component vector, the first element of which represents the coupling effect of the control harmonic on the fifth original harmonic, the second element corresponds to the seventh original harmonic, and so on. The magnitude and sign of each element reflect the strength and direction of the coupling effect, respectively. The coupling component vector completely quantifies the feedback effect of the control harmonic on all original harmonics through the harmonic coupling matrix. This vector is directly used to calculate the subsequent pre-compensation amount.

[0048] In a specific embodiment, the feedback effect of the control harmonic on the original harmonic is calculated, including:

[0049] Each element of the coupling component vector is corresponded to each original harmonic in the harmonic state vector.

[0050] According to the values and signs of the elements in the coupling component vector, the enhancement or weakening effect of the control harmonic on each original harmonic is determined.

[0051] The coupling component vector is used as the feedback effect of the control harmonic on the original harmonic.

[0052] Specifically, the coupling component vector and the harmonic state vector have the same dimension structure and element arrangement order. The first element of the coupling component vector corresponds to the fifth original harmonic, the second element corresponds to the seventh original harmonic, the third element corresponds to the eleventh original harmonic, and the fourth element corresponds to the thirteenth original harmonic. This one-to-one correspondence ensures that each coupling component accurately describes the effect of the control harmonic on a specific original harmonic. The magnitude of each element reflects the strength of the effect, and the larger the value, the more significant the effect of the control harmonic on the original harmonic. The positive or negative sign of the element determines the direction of the effect. A positive value indicates that the control harmonic will increase the amplitude of the original harmonic, forming an enhancement effect, while a negative value indicates that the control harmonic will decrease the amplitude of the original harmonic, forming a weakening effect. By checking the signs and values of each element in the coupling component vector, it is clear whether the control harmonic enhances or weakens each original harmonic and how much the effect is.

[0053] The physical significance of the coupled component vector as a feedback influence quantity lies in its quantitative description of the secondary influence of the control harmonic on the primary harmonic through the harmonic coupling mechanism. This vector fully records the amplitude changes caused by the control harmonic generated at the switching frequency to each primary harmonic near the fundamental frequency after frequency mapping and coupling matrix calculation. By directly inputting the entire coupled component vector as a feedback influence quantity into the subsequent pre-compensation calculation stage, the control system can consider the side effects caused by the control action itself when generating suppression commands. These side effects are offset by superimposing pre-compensation quantities, achieving coordinated optimization control of the primary harmonic and control harmonic. This avoids the contradictory phenomenon in traditional methods where suppressing the primary harmonic exacerbates the control harmonic or suppressing the control harmonic weakens the suppression effect of the primary harmonic.

[0054] Figure 3 This is a schematic diagram illustrating the verification of controlled harmonic prediction accuracy in an embodiment of this application. Figure 3 As shown in the figure, the horizontal axis represents the control period, and the vertical axis represents the control harmonic amplitude. The solid lines marked with dots represent the control harmonic amplitudes predicted based on the harmonic coupling matrix and modulation theory formulas, while the dashed lines marked with squares represent the actual control harmonic amplitudes acquired and analyzed by Fast Fourier Transform. The gray-filled areas represent the prediction error between the predicted and actual values. The data annotations in the figure show that the predicted value for the first control period was 2.50 amps, and the actual value was 2.80 amps; the predicted value for the third control period was 2.30 amps, and the actual value was 2.35 amps; the predicted value for the fifth control period was 2.10 amps, and the actual value was 2.15 amps; the predicted value for the seventh control period was 1.90 amps, and the actual value was 1.95 amps; and the predicted value for the ninth control period was 1.82 amps, and the actual value was 1.83 amps. The prediction error gradually decreases as the control period progresses, verifying the accuracy of the control harmonic prediction using the harmonic coupling matrix and the effectiveness of the adaptive learning mechanism in this invention.

[0055] In one specific embodiment, step S3 includes:

[0056] The fundamental suppression amount of the primary harmonics is calculated based on the difference between the harmonic state vector and the set desired harmonic state vector.

[0057] The pre-compensation amount is calculated using the control gain matrix based on the feedback influence amount. The pre-compensation amount is used to offset the additional influence on the original harmonics when suppressing control harmonics.

[0058] The basic suppression amount and the pre-compensation amount are vector-superimposed to obtain the two-layer suppression command;

[0059] The switching angle adjustment and modulation adjustment for each harmonic are calculated based on the double-layer suppression command.

[0060] Specifically, the calculation of the basic suppression amount first obtains an error vector by subtracting the harmonic state vector from the expected harmonic state vector, the error vector reflecting the deviation of the current harmonic amplitudes from the target amplitudes, and then amplifies the error vector by a control gain matrix to form a basic control signal. The control gain matrix is a diagonal matrix, and the diagonal elements correspond to the control gains of different harmonics. Different harmonics have different control difficulties, so the gain coefficients are set differently. The gain coefficient of low-order harmonics is relatively small because low-order harmonics are relatively easy to suppress, and the gain coefficient of high-order harmonics is relatively large because high-order harmonics are difficult to control. The calculation formula is wherein is the basic suppression amount vector, is the control gain matrix, is the harmonic state vector, is the expected harmonic state vector, and the multiplication of the matrix and the vector obtains the basic control amount of each harmonic.

[0061] The calculation of the pre-compensation amount inputs the feedback influence amount into the control gain matrix for the same gain amplification processing, but with a negative sign to achieve the counteracting effect. The feedback influence amount reflects the additional influence of the suppression control harmonics on the original harmonics, and the role of the pre-compensation amount is to add an opposite component in the control instruction in advance, so that the negative influence of the control harmonic suppression action on the original harmonics is pre-compensated. Vector superposition is to add the corresponding elements of the basic suppression amount vector and the pre-compensation amount vector one by one to obtain a double-layer suppression instruction vector. This vector considers the suppression demand of the original harmonics and the compensation demand of the control harmonics, and realizes the coordinated optimization of the two control targets. Each element of the double-layer suppression instruction vector corresponds to the total control demand of different harmonics. Through the inverse Fourier transform relationship, the frequency domain control amount is converted into the time domain switching angle adjustment amount, and the radian value that each switching angle needs to increase or decrease is calculated. The calculation of the modulation degree adjustment amount is based on the demand of suppressing the control harmonics, and the change amount of the modulation degree is solved according to the relationship between the voltage modulation ratio and the sideband harmonic amplitude. The switching angle adjustment amount and the modulation degree adjustment amount are jointly input into the space vector pulse width modulation module to generate the corrected driving signal.

[0062] In a specific embodiment, step S4 comprises:

[0063] After outputting the corrected pulse width modulation driving signal to the power switching device, the output current signal is re-acquired and analyzed by fast Fourier transform to obtain an actual harmonic amplitude vector and an actual control harmonic amplitude;

[0064] The original harmonic residual between the actual harmonic amplitude vector and the expected harmonic state vector is calculated, and the control harmonic residual between the actual control harmonic amplitude and the target control harmonic amplitude is calculated.

[0065] The coupling coefficients of the harmonic coupling matrix are updated by using the least squares recursive method according to the original harmonic residual and the control harmonic residual.

[0066] Specifically, after the modified pulse width modulation driving signal acts on the power switching device for a complete control cycle, the current waveform at the output end of the power conversion device has changed, at this time the output current signal is re-acquired and fast Fourier transform analysis is performed to extract the actual amplitude of each harmonic component to form an actual harmonic amplitude vector, and the amplitude of the sideband harmonic near the switching frequency is extracted as the actual control harmonic amplitude. The original harmonic residual is calculated by subtracting the expected harmonic state vector from the actual harmonic amplitude vector, and each element of the residual vector represents the deviation of the actual suppression effect of each original harmonic from the target value, a positive value indicating insufficient suppression and a negative value indicating excessive suppression. The control harmonic residual is calculated by subtracting the target control harmonic amplitude from the actual control harmonic amplitude, and the residual reflects the deviation of the control harmonic suppression effect from the expectation, and the two types of residuals together reflect the matching degree of the prediction model and the actual system characteristics.

[0067] The least squares recursive method adjusts the coupling coefficients of the harmonic coupling matrix based on the residual gradient. The specific process is to calculate the correlation between the residual vector and the control command vector, determine the contribution of each coupling coefficient to the residual, and adjust the coefficient value in the direction of reducing the residual. The update law uses the gradient descent principle to obtain the new coupling coefficient by adding the learning rate to the old coupling coefficient multiplied by the residual gradient. The learning rate controls the step size of each update, and a too large value leads to oscillation and a too small value leads to slow convergence. The value is usually set between zero point one and zero point two. The updated harmonic coupling matrix more accurately reflects the harmonic interaction characteristics under the current grid impedance conditions and load state, improves the prediction accuracy of the next control cycle, gradually reduces the residual, and the system adaptively tracks the changes in the grid environment, maintains stable harmonic suppression performance, and forms a closed-loop self-learning mechanism.

[0068] The above describes the power conversion device harmonic suppression method in the embodiments of the present application. The power conversion device harmonic suppression system in the embodiments of the present application is described below. One embodiment of the power conversion device harmonic suppression system in the embodiments of the present application includes:

[0069] The acquisition module is configured to acquire the harmonic amplitudes of the output current of the power conversion device, and construct a harmonic state vector and a harmonic coupling matrix.

[0070] The calculation module is configured to predict the control harmonic amplitude generated at the switching frequency by the control action of suppressing the original harmonic according to the harmonic coupling matrix, map the control harmonic amplitude to the fundamental frequency through the harmonic coupling matrix, and calculate the feedback influence of the control harmonic on the original harmonic.

[0071] The generation module is configured to superimpose the original harmonic suppression amount and the compensation amount of the feedback influence to generate a double-layer suppression instruction, and adjust the switching angle and the modulation degree according to the double-layer suppression instruction.

[0072] a monitoring module configured to output the corrected pulse width modulation drive signal and monitor the harmonic residual to update the harmonic coupling matrix.

[0073] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit the present application; even though the present application has been described in detail with reference to the foregoing embodiments, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of harmonic suppression for power conversion equipment in an electric power distribution network, characterized by, The method comprises: Step S1, collecting the amplitude of the multiple harmonics of the output current of the power conversion device, constructing a harmonic state vector and a harmonic coupling matrix, comprising: collecting the current signal of the output end of the power conversion device through the current sensor, performing fast Fourier transform processing on the current signal, and extracting the amplitude and phase information of the multiple harmonics; calculating the proportion weight of each harmonic in the total harmonic distortion according to the extracted amplitude of each harmonic, and constructing the amplitude of each harmonic into a harmonic state vector; based on the partial differential relationship of the pulse width modulation switching angle adjustment amount to the amplitude of each harmonic, calculating the sensitivity function, and numerically calculating and normalizing the sensitivity function at the current switching angle to obtain the coupling coefficient of the harmonic coupling matrix; constructing a harmonic coupling matrix according to the coupling coefficient, the diagonal elements of the harmonic coupling matrix are self-influence coefficients, and the non-diagonal elements are cross-coupling coefficients; Step S2, according to the harmonic coupling matrix, the control action of suppressing the original harmonic generates a control harmonic amplitude at the switching frequency, the control harmonic amplitude is mapped to the fundamental frequency through the harmonic coupling matrix, and the feedback influence amount of the control harmonic on the original harmonic is calculated; Step S3, superimpose the compensation amount of the feedback influence amount and the original harmonic suppression amount to generate a double-layer suppression instruction, and adjust the switching angle and the modulation degree according to the double-layer suppression instruction, comprising: calculating the basic suppression amount of the original harmonic according to the difference between the harmonic state vector and the set expected harmonic state vector; calculating a pre-compensation amount through a control gain matrix according to the feedback influence amount, the pre-compensation amount is used to offset the additional influence on the original harmonic when suppressing the control harmonic; superimpose the basic suppression amount and the pre-compensation amount to obtain a double-layer suppression instruction; calculate the switching angle adjustment amount and the modulation degree adjustment amount corresponding to each harmonic according to the double-layer suppression instruction; Step S4, output the corrected pulse width modulation driving signal, and monitor the harmonic residual error to update the harmonic coupling matrix.

2. The power conversion equipment harmonic suppression method for a power distribution network according to claim 1, characterized by, In step S2, the control action of suppressing the original harmonic generates a control harmonic amplitude at the switching frequency according to the harmonic coupling matrix, comprising: Determine the preliminary control amount of each harmonic according to the proportion weight of each harmonic in the harmonic state vector, the preliminary control amount represents the pulse width modulation duty cycle adjustment amplitude required to suppress the corresponding harmonic; Substitute the preliminary control amount into the modulation theory formula, combine the current modulation degree and the DC side voltage parameter to calculate the switching frequency sideband harmonic amplitude caused by the control action; According to the switching frequency sideband harmonic amplitude, the predicted control harmonic amplitude is obtained.

3. The power conversion equipment harmonic suppression method for a power distribution network according to claim 2, characterized by, In step S2, the control harmonic amplitude is mapped to the fundamental frequency through the harmonic coupling matrix, comprising: Calculate the frequency conversion coefficient based on the ratio of the switching frequency to the fundamental frequency, the frequency conversion coefficient represents the energy transmission proportion of the high-frequency control harmonic to the low-frequency original harmonic; Perform multiplication operation on the control harmonic amplitude and the frequency conversion coefficient to obtain the equivalent control harmonic component after frequency mapping; The equivalent control harmonic component is input into the harmonic coupling matrix for matrix multiplication operation to obtain a coupling component vector corresponding to each order of the original harmonic.

4. The power conversion equipment harmonic suppression method for a power distribution network according to claim 3, characterized by, The step S2 of calculating the feedback influence amount of the control harmonic on the original harmonic comprises: Each element of the coupling component vector corresponds to each order of the original harmonic in the harmonic state vector. According to the numerical value and the sign of each element in the coupling component vector, the enhancing or weakening effect of the control harmonic on each order of the original harmonic is determined. The coupling component vector is taken as the feedback influence amount of the control harmonic on the original harmonic.

5. The power conversion equipment harmonic mitigation method for a power distribution network of claim 1, wherein, The step S4 comprises: After the modified pulse width modulation driving signal is output to the power switching device, the output current signal is re-acquired and fast Fourier transform analysis is performed to obtain an actual harmonic amplitude vector and an actual control harmonic amplitude; The original harmonic residual of the actual harmonic amplitude vector and the expected harmonic state vector is calculated, and the control harmonic residual of the actual control harmonic amplitude and the target control harmonic amplitude is calculated; The coupling coefficients of the harmonic coupling matrix are updated by using the least square recursive method according to the original harmonic residual and the control harmonic residual.

6. A power conversion equipment harmonic suppression system for a power distribution network, characterized by, The power distribution network power conversion device harmonic suppression system comprises: The acquisition module is configured to acquire the multiple harmonic amplitudes of the output current of the power conversion device, and construct a harmonic state vector and a harmonic coupling matrix. The calculation module is configured to predict the control harmonic amplitude generated at the switching frequency by the control action of suppressing the original harmonic according to the harmonic coupling matrix, map the control harmonic amplitude to the fundamental frequency through the harmonic coupling matrix, and calculate the feedback influence amount of the control harmonic on the original harmonic. The generation module is configured to superimpose the double-layer suppression instruction by adding the compensation amount of the feedback influence amount to the original harmonic suppression amount, and adjust the switching angle and the modulation degree according to the double-layer suppression instruction. The monitoring module is configured to output the modified pulse width modulation driving signal, and monitor the harmonic residual to update the harmonic coupling matrix.

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