Electromagnetic detection optimized bipolar SHM PWM transmission method

Abstract

The application discloses an electromagnetic detection optimized bipolar SHMPWM transmitting method, which comprises the following steps: S1, by analyzing the influence of the resistive and inductive load on the transmitting current waveform distortion and the transmitting spectrum energy loss, extending the current waveform based on the equal-area principle, compensating for the lost transmitting current spectrum energy, and calculating the current waveform extension time; S2, considering the inductive load and the dead zone effect, establishing a bipolar SHMPWM nonlinear equation set; S3, using the particle swarm algorithm to iteratively operate the bipolar SHMPWM nonlinear equation set, and obtaining the solving result of the switching angle of the half-cycle symmetric SHMPWM. The application adopts the optimized particle swarm algorithm to solve the equation set to obtain the switching angle, and realizes that the frequency domain information of the half-cycle symmetric SHMPWM frequency focusing waveform conforms to the specific harmonic amplitude set by the expectation.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic detection technology, and in particular to an optimized bipolar SHMPWM transmission method for electromagnetic detection. Background Technology

[0002] Electromagnetic detection technology is a research hotspot in the field of detection both domestically and internationally, with applications in mineral exploration, geological monitoring, and engineering site selection. Frequency-domain electromagnetic detection methods obtain geological information of specific strata by selecting appropriate transmission current frequencies. Early studies proposed multi-frequency methods that simultaneously transmit and measure the fundamental frequency and multiple accompanying spectra, aiming to improve detection efficiency. To further improve the controllability of the transmitted waveform spectrum and reduce interference between adjacent frequencies, researchers have proposed methods such as m-sequence pseudo-random and 2n pseudo-random methods. These methods enhance frequency domain coverage by uniformly distributing the transmitted waveform frequencies. However, when conducting fine-scale detection at specific target depths, traditional multi-frequency transmission methods still cannot meet the requirements, failing to obtain multiple closely spaced frequency signals, which limits the detection accuracy.

[0003] To address this issue, Selective Harmonic Elimination Pulse Width Modulation (SHMPWM) and Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) serve as improved transmission strategies. These methods utilize Fourier series expansion of the transmitted waveform to solve a system of nonlinear equations, thereby obtaining the switching angle and eliminating or retaining signals of specific frequencies. These methods effectively eliminate adjacent harmonic interference, improving the accuracy and clarity of the spectrum, and are particularly suitable for fine-grained detection of specific formations. Compared to conventional multi-frequency detection waveforms, SHMPWM and SHEPWM control methods offer the following advantages: 1) Reduced switching frequency and switching losses; 2) Improved power quality and increased system efficiency; 3) Applicability to multi-level inverter designs, expanding their application range; 4) Improved DC voltage utilization efficiency.

[0004] However, despite the effectiveness of the aforementioned methods in improving the frequency controllability and detection accuracy of the transmitted waveform, some problems remain unresolved. For example, the inductive reactance of the transmitting line is unavoidable, leading to inconsistent rates of current rise and fall during turn-off, resulting in waveform distortion and subsequent loss of spectral energy. Simultaneously, non-ideal variations in the transmitted current generate strong primary field noise, interfering with the detection signal, especially the weak signals from shallow and middle strata, which negatively impacts the time-domain forward and inverse modeling results for deep-seated detection. To address these issues, researchers have proposed optimization techniques such as piecewise current control and PWM chopping, and designed improved transmitting circuits including absorption circuits, constant voltage clamping circuits, and energy feedback circuits, achieving some success. However, due to differences in the environments of different detection sites, the adaptive capabilities of these optimization methods are insufficient, consistently affecting the accuracy and stability of electromagnetic detection. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide an optimized bipolar SHMPWM transmission method for electromagnetic detection, which enables precise control of the DC and harmonic parameters of the output waveform, while retaining only the main frequency required for transmission, thereby achieving efficient electromagnetic detection.

[0006] Technical solution: An electromagnetic detection-optimized bipolar SHMPWM transmission method, comprising the following steps:

[0007] S1. By analyzing the influence of resistive and inductive loads on the distortion of the transmitted current waveform and the influence of transmitted spectrum energy loss, the current waveform is extended based on the principle of equal area to compensate for the lost transmitted current spectrum energy and calculate the current waveform extension time.

[0008] S2, considering inductive load and dead-time effect, establish the bipolar SHMPWM nonlinear equation set;

[0009] S3. The particle swarm optimization algorithm is used to iteratively calculate the nonlinear equations of the bipolar SHMPWM to obtain the switching angle solution of the half-cycle symmetric SHMPWM.

[0010] Furthermore, the specific steps for calculating the current waveform extension time are as follows:

[0011] S11, which converts the transmitting circuit into a first-order fully-response resistive-inductive circuit;

[0012] From the first-order total response circuit, we obtain:

[0013]

[0014] The corresponding topological relationships of the resistive-inductive circuits for each variable are as follows:

[0015] f(t)=i(t)

[0016]

[0017] Assuming the current stabilizes within 5τ, the relationship between t1 and t2 is as follows:

[0018] |t1-t2|>>5τ

[0019] In the formula, f(t) is the instantaneous value of the first-order circuit current, f(∞) is the steady-state value of the first-order circuit current, and f(0) is the constant-state value of the first-order circuit current. + U is the initial value of the current in a first-order circuit. d I d Let L and R be the steady-state voltage and steady-state current, respectively; L and R be the inductance and resistance of the equivalent circuit, respectively; t1 and t2 be the switch closing and opening times, respectively; i(t) be the current during conduction; τ be the time constant; and e be the natural constant. 1+ ) is the initial value at the instant of closure at time t1;

[0020] S12, based on the principle of equal area, calculate the extension time ΔT of the actual unipolar current waveform;

[0021] The current waveform over the time interval [t1, t1+5τ] and the horizontal axis are equivalent to a graph with a width of T1 and a height of I. d The rectangle is defined, and t1 is the starting time of the current rising phase. T1 is calculated using the following formula:

[0022]

[0023] Let t1 = 0, then we get:

[0024] T1=4τ+e -5 τ≈4τ

[0025] During the current decrease time interval [t2, t3], the actual current i'(t) is:

[0026]

[0027] When the current drops to 0:

[0028]

[0029] In the formula, t2 is the starting time of the current decreasing phase, and t3 is the time when the current decreases to 0;

[0030] The current waveform over the time interval [t2, t3] and the horizontal axis are equivalent to a graph with a width of T2 and a height of I. d A rectangle; obtained from equal areas:

[0031]

[0032] Therefore, T2 is:

[0033] T2=(1+ln(1 / 2))τ

[0034] Based on the principle of equal area, the time interval from t1 to t2 is widened by ΔT, so that the corrected emission current energy is equal to the ideal emission current energy; then ΔT is:

[0035] ΔT=5τ-T1-T2=ln2·τ

[0036] Step 13: Calculate the extension time ΔT′ of the bipolar current waveform;

[0037] When the current is within the rising time interval [t′1, t′1+5τ], the algebraic sum of the missing area and the excess area is equivalent to a region with width ΔT′ and height I. d For a rectangle, solve for ΔT′ using the following formula:

[0038]

[0039] Then we have:

[0040]

[0041] Let t′1=0, then we get:

[0042] ΔT′=2ln2·τ

[0043] In the formula, t′1 and t′2 are the starting time and zero-crossing time of the rising phase of the actual bipolar current waveform, respectively;

[0044] Applying the principle of equal area, the waveform from t′1 to t′3 should be widened by ΔT′ on the original basis, so that the corrected emission current energy is equal to the ideal emission current energy. t′3 is the starting time of the falling phase of the actual bipolar current waveform.

[0045] Furthermore, the nonlinear equations for bipolar SHMPWM are as follows:

[0046]

[0047] The relationship between the limiting switching angles is as follows:

[0048] 0 < α1 < α2 < ... < α N <π

[0049] Amplitude of each harmonic A i The calculation formula is as follows:

[0050]

[0051] Where a0 is the DC component, a ib i These are the sine and cosine components, respectively, U SHM (ωt) is the instantaneous value of the inverter output voltage, U d For the inverter output DC voltage, α i Let α be the switching angle, i = 1, 2, ..., N, where N is the number of switching angles within a half-cycle; d T represents the dead zone angle occupied by the dead time within a single period. d ω is the dead time; ω is the angular velocity.

[0052] Furthermore, in step S3, the optimized particle swarm optimization algorithm is applied to solve the SHMPWM nonlinear equations, and the switching angles α1, α2, ..., α are... N It can be represented in the following form:

[0053]

[0054] fitness f i The definition is as follows:

[0055]

[0056] In the formula, ψ i () represents the switching angles α1, α2, ..., α N The function, P N These are real constants obtained from the frequency domain characteristics of a given half-cycle mirror-symmetric SHMPWM waveform;

[0057] The adaptive weight g is calculated using the following formula:

[0058]

[0059] In the formula, g max g min These are the maximum and minimum weight coefficients, respectively; The fitness of the i-th particle at the k-th iteration; Let be the average fitness of all particles at the k-th iteration; The minimum fitness of all particles at the k-th iteration;

[0060] Considering the influence of adaptive weight g, acceleration factors C1 and C2 on the particle swarm optimization algorithm, the optimized velocity formula is as follows:

[0061]

[0062] In the formula, Rand() is a random number. This represents the position of the i-th particle in the d-th dimension. This is the optimal position for the current population. The best location for all populations;

[0063] X is the contraction factor, expressed as follows:

[0064]

[0065] Where C = C1 + C2.

[0066] Compared with the prior art, the significant advantages of this invention are as follows:

[0067] 1. Applying SHMPWM technology to electromagnetic detection, considering the influence of inductive load and dead-zone effect on the transmitted waveform in actual circuits, solves the problem of ineffective energy focusing and fine distribution in electromagnetic detection due to the energy loss of the transmitted current spectrum; for the fine exploration needs of underground mineral resources, considering the influence of inductive load and dead-zone effect on harmonic distribution in actual SHMPWM transmitting circuits, a half-cycle symmetrical SHMPWM nonlinear equation set is established, and the optimized particle swarm optimization algorithm is used to solve the equation set to obtain the switching angle, so that the frequency domain information of the half-cycle symmetrical SHMPWM frequency focusing waveform meets the desired specific harmonic amplitude;

[0068] 2. This invention analyzes the impact of inductive loads on the distortion of the transmitted current waveform and the loss of spectral energy. Based on the principle of equal area, it proposes a method for extending the current waveform to compensate for the lost spectral energy of the transmitted current and provides a method for calculating the extension time. At the same time, the dead zone effect is taken into account to achieve precise control of the DC and harmonic parameters of the output waveform, while retaining only the main frequency required for transmission, thereby achieving efficient electromagnetic detection. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the transmitter circuit topology that outputs a half-cycle symmetrical SHMPWM waveform;

[0070] Figure 2 This is a flowchart of an optimized bipolar SHMPWM transmit strategy for electromagnetic detection, taking into account inductive loads and dead-time effects.

[0071] Figure 3 (a) in the figure is the waveform of bipolar SHMPWM without the addition of a symmetrical dead zone.

[0072] (b) is the output half-cycle symmetrical SHMPWM waveform after adding a symmetrical dead time;

[0073] Figure 4 This is a diagram showing the ideal emitter current waveform and the actual emitter current waveform of a unipolar SHMPWM.

[0074] Figure 5 This is a diagram showing the ideal emitter current waveform and the actual emitter current waveform of a bipolar SHMPWM.

[0075] Figure 6 (a) shows the current drop waveform of the resistive-inductive bipolar SHMPWM before optimization and compensation, and (b) shows the current drop waveform of the resistive-inductive bipolar SHMPWM after optimization and compensation.

[0076] Figure 7 (a) shows the rising current waveform of the resistive-inductive bipolar SHMPWM before optimization and compensation, and (b) shows the rising current waveform of the resistive-inductive bipolar SHMPWM after optimization and compensation.

[0077] Figure 8 This is a flowchart of the optimized particle swarm optimization algorithm.

[0078] Figure 9 This is a frequency domain information diagram of the actual half-cycle symmetrical SHMPWM current before optimization;

[0079] Figure 10 This is the frequency domain information diagram of the optimized half-cycle symmetrical SHMPWM current. Detailed Implementation

[0080] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0081] This invention utilizes Specific Harmonic Attenuation Pulse Width Modulation (SHMPWM) technology to establish a mathematical model and design a method for outputting the optimal transmission current, thereby achieving focused and precise distribution of electromagnetic detection energy.

[0082] like Figure 1 As shown, a diode-clamped three-level inverter is used as the transmitter circuit topology. The three-level inverter has lower switching transistor stress and lower losses than the two-level inverter, which can meet the high-power, high-voltage output requirements of the electromagnetic detection transmitter. The inverter includes eight power switches S1-S8, eight anti-parallel freewheeling diodes D1-D8, and four clamping diodes V... D1 -V D8 And two clamping capacitors C1 and C2. C1 and C2 are capacitors of the same specification, so that N o The point becomes the voltage midpoint of the power supply. The load terminal of the electromagnetic emission is connected to... Figure 1 Between points A and B. U e It is the power supply voltage, i o u o These are the output current and voltage, respectively. The transmitter outputs a rectangular voltage u. o A transmitting current i is generated in the earth load through the cable and grounding electrodes a and b. o At the same time, due to the rapid reversal of the polarity of the transmitted current, an induction is generated deep in the earth, and the induction signal is radiated to the ground, which is received and analyzed by the receiver to obtain the stratum information.

[0083] like Figure 2 The diagram shows a flowchart of an optimized bipolar SHMPWM transmission method for electromagnetic detection that considers inductive load and dead-time effects. The SHMPWM waveform is modulated offline using pre-stored switching angles to account for the dead-time problem. Figure 3 As shown in (a) and (b), these are the symmetrical SHMPWM waveforms of the output half-cycle before and after the addition of the symmetrical dead zone, respectively.

[0084] The specific steps of the electromagnetic detection optimized bipolar SHMPWM transmission method of the present invention, which considers inductive load and dead-time effect, are as follows:

[0085] Step 1: Extend the current waveform based on the principle of equal area and calculate the current waveform extension time;

[0086] By analyzing the effects of resistive-inductive loads on the distortion of the transmitted current waveform and the energy loss of the transmitted spectrum, the current waveform is extended based on the principle of equal area. A method for compensating for the lost transmitted current spectrum energy is used to calculate the current waveform extension time.

[0087] The specific steps are as follows:

[0088] Step 11: Equivalent the transmitting circuit to a first-order fully-response resistive-inductive circuit;

[0089] From the total response of a first-order circuit, we can obtain:

[0090]

[0091] The corresponding topological relationships of the resistive-inductive circuits for each variable are as follows:

[0092] f(t)=i(t) (2)

[0093]

[0094] The current when the circuit is on can be calculated as follows:

[0095]

[0096] Assuming the current stabilizes within a 5τ time interval, the relationships between t1 and t2 are as follows:

[0097] |t1-t2|>>5τ (6)

[0098] In the formula, f(t) is the instantaneous value of the first-order circuit current, f(∞) is the steady-state value of the first-order circuit current, and f(0) is the constant-state value of the first-order circuit current. + U is the initial value of the current in a first-order circuit. d I dLet L and R be the steady-state voltage and steady-state current, respectively; L and R be the inductance and resistance of the equivalent circuit, respectively; t1 and t2 be the switch closing and opening times, respectively; i(t) be the current during conduction; τ be the time constant; and e be the natural constant. 1+ ) is the initial value at the instant of closing at time t1.

[0099] Step 12: Based on the principle of equal area, calculate the extension time ΔT of the actual unipolar current waveform;

[0100] like Figure 4 The figure shows the waveforms of the ideal unipolar emission current and the actual emission current. The current waveform over the time interval [t1, t1+5τ] and the horizontal axis are now represented as an equivalent graph with width T1 and height I. d The rectangle is defined, and t1 is the starting time of the current rising phase. T1 is calculated using the following formula:

[0101]

[0102] Let t1 = 0, then we get:

[0103] T1=4τ+e -5 τ≈4τ (8)

[0104] During the current decrease time interval [t2, t3], the actual current i'(t) of the transmitting circuit is:

[0105]

[0106] When the current drops to 0:

[0107]

[0108] In the formula, t2 is the starting time of the current decreasing phase, and t3 is the time when the current decreases to 0.

[0109] Similarly, the current waveform over the time interval [t2, t3] and the horizontal axis can be represented as a graph with a width of T2 and a height of I. d A rectangle. Since their areas are equal, we have the following formula:

[0110]

[0111] Therefore, T2 is:

[0112] T2=(1+ln(1 / 2))τ (12)

[0113] Applying the principle of equal area, the original time interval from t1 to t2 is widened by ΔT, so that the corrected emission current energy is equal to the ideal emission current energy. Therefore, ΔT is:

[0114] ΔT=5τ-T1-T2=ln2·τ (13)

[0115] Step 13: Calculate the extension time ΔT′ of the bipolar current waveform by analogy with the calculation method for the extension time of the unipolar current waveform;

[0116] like Figure 5 For the ideal bipolar emission current waveform and the actual emission current waveform, when the current is within the rise time [t′1, t′1+5τ], the algebraic sum of the missing area and the excess area is equivalent to a waveform with width ΔT′ and height I. d For a rectangle, solve for ΔT′ using the following formula:

[0117]

[0118] Similar to the waveform of a unipolar resistive-inductive load, we have:

[0119]

[0120] Let t′1=0, then we get:

[0121] ΔT′=2ln2·τ (16)

[0122] In the formula, t′1 and t′2 are the starting time and zero-crossing time of the rising phase of the actual bipolar current waveform, respectively;

[0123] Applying the principle of equal area, the waveform from t′1 to t′3 should be widened by ΔT′ compared to the original waveform, so that the corrected emission current energy is equal to the ideal emission current energy. t′3 is the starting moment of the falling phase of the actual bipolar current waveform. The emission current waveforms before and after correction are as follows: Figure 6 As shown in (a) and (b), the black shaded area represents the portion of the actual current that needs to be compensated.

[0124] Similarly, the compensation waveform of the bipolar current in the rising segment can be obtained, and the compensation time is ΔT′. The rising current waveforms of the resistive-inductive bipolar SHMPWM before and after compensation are shown in the figure. Figure 7 As shown in (a) and (b) in the figure.

[0125] Step 2: Taking the dead zone effect into account, establish an optimized bipolar SHMPWM nonlinear equation set considering inductive load and dead zone effect.

[0126] The nonlinear equations are as follows:

[0127]

[0128] The relationship between the limiting switching angles is as follows:

[0129] 0 < α1 < α2 < ... < α N <π (18)

[0130] α d With T d The relationship is as follows:

[0131]

[0132] Amplitude of each harmonic A i The calculation formula is as follows:

[0133]

[0134] Where a0 is the DC component, a i b i These are the sine and cosine components, respectively, U SHM (ωt) is the instantaneous value of the inverter output voltage, U d For the inverter output DC voltage, α i Let α be the switching angle, i = 1, 2, ..., N, where N is the number of switching angles within half a cycle. d T represents the dead zone angle occupied by the dead time within a single period. d ω is the dead time, and ω is the angular velocity.

[0135] Step 3: Use the optimized particle swarm optimization algorithm to solve the optimal solution of the nonlinear equation system, thereby obtaining the specific switching angle of SHMPWM that meets the actual requirements;

[0136] By optimizing the particle swarm optimization algorithm, a strategy is designed to automatically exit the iterative loop when the fitness requirement is met. The flowchart is as follows. Figure 8 As shown, the specific steps are as follows:

[0137] Step 31: Initialize the maximum number of iterations Max, the count setpoint count_set, and the counter; set the function change tolerance F_tolerance, which is generally a very small positive number;

[0138] Step 32: At each iteration, calculate the best fitness f_best and calculate the absolute value of the change f_change between the best fitness of the current iteration and the best fitness of the previous iteration.

[0139] Step 33: Determine whether the absolute value of the fitness change f_change is less than the function change tolerance F_tolerance. If so, increment the counter by 1; otherwise, clear the counter to zero.

[0140] Step 34: If the current iteration count exceeds the maximum iteration count Max, then exit the loop and obtain the optimal solution; if the current iteration count does not exceed the maximum iteration count Max, and the count value is greater than the count set value count_set, it means that the optimal solution is within a certain fluctuation range, then exit the loop directly.

[0141] Step 35: Determine whether the optimal fitness f_best meets the required precision. If not, continue to loop through steps 31-34 until the required precision is met and the optimal solution is obtained, then end the calculation.

[0142] The SHMPWM nonlinear equations are solved using an optimized particle swarm optimization algorithm, with the switching angles α1, α2, ..., α... N It can be represented in the following form:

[0143]

[0144] fitness f i The definition is as follows:

[0145]

[0146] In the formula, ψ i Represents the switching angles α1, α2, ..., α N The function, P N These are real constants obtained from the frequency domain characteristics of a given half-cycle mirror-symmetric SHMPWM waveform.

[0147] In terms of computational performance, an adaptive weighting method combined with a shrinkage factor is employed. For problems requiring rapid convergence to a local optimum, the adaptive weighting can be reduced; while for problems requiring extensive searching of the global optimum, the adaptive weighting should be increased. This invention dynamically adjusts the adaptive weighting according to the search progress to balance global and local search capabilities. The formula for calculating the adaptive weighting g is as follows:

[0148]

[0149] In the formula, g max g min These are the maximum and minimum weighting coefficients, typically taken as 0.9 and 0.4 respectively. The fitness of the i-th particle at the k-th iteration; That is, the average fitness of all particles at the k-th iteration;

[0150] That is, the minimum fitness of all particles at the k-th iteration;

[0151] Considering the influence of adaptive weight g, acceleration factors C1 and C2 on the particle swarm optimization algorithm, the optimized velocity formula is as follows:

[0152]

[0153] In the formula, Rand() is a random number. This represents the position of the i-th particle in the d-th dimension. This represents the optimal position in the current population (the position of the individual that performs best among all individuals in the current population). The optimal position for all populations (referring to the position of the optimal solution found in the population so far in the entire optimization process).

[0154] A new influencing factor—the contraction factor x—is introduced into the new velocity formula, as shown below:

[0155]

[0156] Where C = C1 + C2.

[0157] In practice, it has been found that within a certain range, the higher the particle velocity, the better the performance of the particle swarm optimization (PSO) algorithm. The shrinkage factor *x* and the adaptive weight *g* have similar effects. The choice of which parameter to use depends on the problem to be solved. By setting the shrinkage factor *x* and the adaptive weight *g*, the particle velocity is controlled, thereby improving the performance of the PSO algorithm. The acceleration factors C1 and C2 are typically set to 2. In practice, to better control the convergence speed and avoid premature convergence, a value of C slightly greater than 4 is usually chosen to obtain a more suitable shrinkage factor value. In this PSO algorithm, C≈4.1 is used, at which point *x*≈0.729.

[0158] To avoid getting trapped in local optima, a tolerance for function change is set as a relevant quantity. Before each loop, the absolute value of the fitness change is calculated and compared. If the absolute value of the fitness change is consistently less than the predetermined tolerance, it indicates that the searched particle is in the optimal position, the solution is converging, and the loop can be automatically exited. Regarding the angle constraint, considering practical considerations, SHMPWM waveform emission settings are implemented to add constraints on the switching angle. If the requirements are not met, the particle swarm is repeatedly initialized and recalculated. Regarding the solution accuracy, a precision requirement is set. If the optimal solution obtained still does not meet the high-precision setting, repeated operations are necessary until a satisfactory solution is obtained. Figure 8 The flowchart for optimizing the particle swarm optimization algorithm is shown.

[0159] Based on the same inventive concept, embodiments of this application provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the aforementioned steps of an electromagnetic detection optimized bipolar SHMPWM transmission strategy that considers inductive load and dead-zone effect.

[0160] Table 1 shows the results of solving the switching angle of a half-cycle symmetrical SHMPWM considering inductive load and dead-time effect.

[0161] Table 1. Results of Half-Period Symmetrical SHMPWM Switching Angle Calculation

[0162] Switching angle <![CDATA[ α1 ]]> <![CDATA[ α2 ]]> <![CDATA[ α3 ]]> <![CDATA[ α4 ]]> <![CDATA[ α5 ]]> <![CDATA[ α6 ]]> <![CDATA[ α7 ]]> <![CDATA[ α8 ]]> <![CDATA[ α9 ]]> <![CDATA[ α10 ]]> After optimization 0.4388 0.6155 0.8361 1.0596 1.4978 1.6438 2.0820 2.3055 2.5261 2.7028

[0163] Figure 9 To optimize the frequency domain information diagram of the actual half-cycle symmetrical SHMPWM current before optimization, Figure 10 This is an optimized half-cycle symmetrical SHMPWM current frequency domain information diagram that considers the actual current waveform extension time and dead-time effect. The output fundamental frequency is set to 50Hz, the current harmonic amplitude is 0.8A, and the 1st, 5th, and 7th harmonics are retained. Figure 9 , Figure 10 Comparative analysis shows that the optimized amplitudes of the 5th and 7th harmonics are significantly compensated and are basically consistent with the ideal situation.

[0164] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. An electromagnetic detection-optimized bipolar SHMPWM transmission method, characterized in that, The steps include the following: S1. By analyzing the influence of resistive and inductive loads on the distortion of the transmitted current waveform and the influence of transmitted spectrum energy loss, the current waveform is extended based on the principle of equal area to compensate for the lost transmitted current spectrum energy and calculate the current waveform extension time. S2, considering inductive load and dead-time effect, establish the bipolar SHMPWM nonlinear equation set; S3. The particle swarm optimization algorithm is used to iteratively calculate the nonlinear equations of the bipolar SHMPWM to obtain the switching angle solution of the half-cycle symmetric SHMPWM. The specific steps for calculating the current waveform extension time are as follows: S11, which converts the transmitting circuit into a first-order fully-response resistive-inductive circuit; From the first-order total response circuit, we obtain: The corresponding topological relationships of the resistive-inductive circuits for each variable are as follows: Set current at 5 If the time interval is stable, then the relationship between t1 and t2 is as follows: In the formula, It is the instantaneous value of the current in a first-order circuit. It is the steady-state value of the current in a first-order circuit. It is the initial value of the current in a first-order circuit, U. d I d These are steady-state voltage and steady-state current, respectively. L , R t1 and t2 are the inductance and resistance of the equivalent circuit, respectively, and t1 and t2 are the closing and opening times of the switch, respectively. This is the current when the circuit is on; τ It is a time constant; e It is a natural constant. It is the initial value at the instant of closing at time t1; S12, based on the principle of equal area, calculate the extension time ΔT of the actual unipolar current waveform; The current waveform over the time interval [t1, t1+5τ] and the horizontal axis are equivalent to a graph with a width of T1 and a height of I. d The rectangle is defined, and t1 is the starting time of the current rising phase. T1 is calculated using the following formula: Let t1=0, then we get: During the current decrease time period [t2, t3], the actual current for: When the current drops to 0: In the formula, t2 is the starting time of the current decreasing phase, and t3 is the time when the current decreases to 0; The current waveform over the time interval [t2, t3] and the horizontal axis are equivalent to a graph with a width of T2 and a height of I. d A rectangle; obtained from equal areas: Therefore, T2 is: Based on the principle of equal area, the time interval from t1 to t2 is widened by ΔT, so that the corrected emission current energy is equal to the ideal emission current energy; then ΔT is: Step 13: Calculate the extension time ΔT′ of the bipolar current waveform; When the current is within the rising time interval [t′1, t′1+5τ], the algebraic sum of the missing area and the excess area is equivalent to a region with width ΔT′ and height I. d For a rectangle, solve for ΔT′ using the following formula: Then we have: Let t′1=0, then we get: In the formula, t′1 and t′2 are the starting time and zero-crossing time of the rising phase of the actual bipolar current waveform, respectively; Applying the principle of equal area, the waveform from t′1 to t′3 should be widened by ΔT′ on the original basis so that the corrected emission current energy is equal to the ideal emission current energy. t′3 is the starting time of the falling phase of the actual bipolar current waveform. The nonlinear equations for bipolar SHMPWM are as follows: The relationship between the switching angle limits is as follows: Amplitude of each harmonic The calculation formula is as follows: in, a 0 represents the DC component. a j , b j These are the sine and cosine components, respectively. α is the instantaneous value of the inverter output voltage. j For the switching angle, j =1,2,…, N , N The number of switching angles within half a cycle; α d T represents the dead zone angle occupied by the dead time within a single period. d Dead time; ω is the angular velocity.

2. The electromagnetic detection optimized bipolar SHMPWM transmission method according to claim 1, characterized in that, In step S3, the optimized particle swarm optimization algorithm is applied to solve the SHMPWM nonlinear equations, and the switching angle is adjusted. It can be represented in the following form: fitness The definition is as follows: In the formula, Indicates the switching angle The function, P N These are real constants obtained from the frequency domain characteristics of a given half-cycle mirror-symmetric SHMPWM waveform; The formula for calculating the adaptive weight g is as follows: In the formula, , These are the maximum and minimum weight coefficients, respectively; The fitness of the m-th particle in the k-th iteration; Let be the average fitness of all particles at the k-th iteration; The minimum fitness of all particles at the k-th iteration; Considering adaptive weights g The effects of acceleration factors C1 and C2 on the particle swarm optimization algorithm are shown in the optimized velocity formula below: In the formula, Rand() is a random number. This represents the position of the m-th particle in the d-th dimension. This is the optimal position for the current population. The best location for all populations; X is the contraction factor, expressed as follows: in, .

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