Selective harmonic elimination method for MPUC inverter based on multiverse optimization

Abstract

The present invention provides a method for selective harmonic elimination of an MPUC inverter based on multiverse optimization, and relates to the technical field of pulse width modulation of an MPUC inverter. The method first uses different power supply voltage amplitudes and different modulation controls to produce different output voltage waveforms, and uses five states to trigger the MPUC inverter; then the torque pulsation characteristics of the induction motor powered by the three-phase five-level MPUC inverter are analyzed, and the selective elimination of the influence of different power supply harmonics on the motor torque pulsation is compared and analyzed; finally, the multiverse optimization algorithm is used to search and detect the space through the two processes of exploration and mining to solve the switching angle of the selective harmonic elimination pulse width modulation SHEPWM, thereby realizing the selective harmonic elimination of the three-phase five-level MPUC inverter. The method can effectively suppress the corresponding torque pulsation in the induction motor by selectively eliminating specific time harmonics in the inverter power supply, thereby improving the working stability of the motor.

Description

Technical Field

[0001] The invention relates to the technical field of MPUC inverter pulse width modulation, and in particular to a method for selective harmonic elimination of an MPUC inverter based on multiverse optimization. Background Art

[0002] At present, the methods to reduce the electromagnetic noise and torque pulsation of the motor from the perspective of controlling the inverter harmonics include: software and hardware filters, increasing the switching frequency, dynamically adjusting the switching frequency, random PWM strategy, improving the inverter topology, and eliminating specific time harmonics. The document "Random PWM Control Strategy for Reducing Vibration and Noise of Induction Motors for Electric Vehicles" achieves selective control of harmonics in a specific frequency band by adding a bandpass digital filter to the control algorithm, but the calculation amount of the digital filter is relatively large. The paper "Acoustic noise in induction motors: causes and solutions" proves that increasing the switching frequency of the converter can effectively reduce the operating noise of the motor, but too high a switching frequency will cause negative effects such as increased losses and stress of the power switching devices; the paper "Audible noise and losses invariable speed induction motor drives with IGBT inverters-influence of the squirrel cage design and the switching frequency" reduces the vibration of the motor system in different operating states by dynamically changing the switching frequency; the paper "Characterization and Selection of Probability Statistical Parameters in Random Slope PWM Based on Uniform Distribution" effectively reduces the electromagnetic noise near the integer multiples of the switching frequency in the AC motor by random switching frequency, but in the process of random spectrum spreading, it is possible that the harmonic content near the original harmonic peak will increase, thereby generating new electromagnetic vibration and electromagnetic noise;

[0003] The Single-Phase Step-Up Switched-Capacitor-Based Multilevel Inverter Topology With SHEPWM strategy is an effective method to eliminate low-order time harmonics of the inverter and adapt to low switching frequency. Common methods for solving SHEPWM nonlinear transcendental equations include numerical methods, algebraic methods and intelligent algorithms. In recent years, some new intelligent algorithms have been applied to SHEPWM strategies. The reference "Real-coded Genetic Simulated Annealing Algorithm SHEPWM Control Technology" uses genetic algorithms, but the selection of population size, mutation probability, mating probability, evolutionary algebra and population initialization may lead to the loss of population evolution ability, reduced diversity, premature population, or non-convergence. The reference "Research on PWM Modulation Strategy of T-type Three-level Inverter" uses particle swarm optimization algorithm, whose performance and convergence are directly affected by parameters, and the setting of parameters still depends on experience to a large extent. The paper "Application of the Bee Algorithm for Selective Harmonic Elimination Strategy in Multilevel Inverters" applies the bee colony algorithm to the calculation of the SHEPWM equation group, which has the advantages of high accuracy, but slow convergence speed and easy premature maturity; the paper "Application of Chaotic Ant Colony Algorithm in Three-Level Inverter SHEPWM Strategy" gives an ant colony optimization algorithm, but at the beginning, pheromone is scarce, the global convergence is poor, and the efficiency is low. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for selective harmonic elimination of an MPUC inverter based on multiverse optimization in view of the deficiencies of the above-mentioned prior art, so as to selectively eliminate the harmonics of a five-level MPUC inverter.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for selective harmonic elimination of an MPUC inverter based on multiverse optimization, comprising the following steps:

[0006] Step 1, analyze the switching state of the three-phase five-level MPUC inverter, use different power supply voltage amplitudes and different modulation controls to generate different output voltage waveforms, and use states 1, 3, 5, 7, and 8 to trigger the MPUC inverter;

[0007] Step 2: Analyze the torque ripple characteristics of the induction motor powered by the three-phase five-level MPUC inverter; compare and analyze the selective elimination of the influence of different power supply harmonics on the motor torque ripple;

[0008] Step 2.1, determining the asynchronous torque of the induction motor powered by the three-phase five-level MPUC inverter;

[0009] When the air gap harmonic flux and rotor harmonic current order of the induction motor powered by the three-phase five-level MPUC inverter are the same, the induction motor will generate asynchronous torque due to the mutual influence of electromagnetic action, as shown in the following formula:

[0010] T n,1 =C T φ n I 2n cosψ 2n (1)

[0011] Among them, T n,1 To supply the asynchronous torque generated by the induction motor, is the torque constant, m1 is the number of motor phases, p is the number of motor pole pairs, N2 is the number of rotor turns per phase, k w2 is the fundamental rotor winding coefficient; φ n is the stator flux generated by the nth time harmonic; ψ 2n Because φ n The generated electromotive force and rotor harmonic current I 2n The phase difference;

[0012] The direction of the asynchronous torque depends on the number of high-order time harmonics. When the harmonic number n = 6k+1, k is a natural number, and the direction of the asynchronous torque is the same as the speed; when n = 6k′-1, k′ is a natural number not equal to 0, and the direction of the asynchronous torque is opposite to the speed;

[0013] Step 2.2, determining the pulsating torque of the induction motor powered by the three-phase five-level MPUC inverter;

[0014] The pulsating torque of the motor is generated by the interaction of currents and magnetic fluxes of different frequencies in the air gap of the motor; due to the uncertainty of the harmonic order, the pulsating torque generated by each group of currents and magnetic fluxes is also different. The most important pulsating torque is generated by the stator fundamental magnetic flux and the rotor harmonic current, as shown in the following formula:

[0015] T n =2C T φI 2n cos[(n±1)ωt-ψ 1,2n ] (2)

[0016] Among them, T n is the pulsating torque generated by the stator fundamental flux and the nth harmonic current of the rotor, φ is the fundamental flux, ψ 1,2n is the phase difference between the fundamental electromotive force and the rotor current, ω is the angular frequency of the rotor current, and t is the time;

[0017] According to formula (2), in the induction motor powered by the three-phase five-level MPUC inverter, the frequency of the pulsating torque generated by the 5th and 7th harmonics is 6f, where f is the fundamental frequency output by the three-phase five-level MPUC inverter, and the directions are opposite, that is, f-(-5f)=6f and f-7f=-6f; similarly, the frequency of the pulsating torque generated by the 11th and 13th harmonics is 12f, that is, f-(-11f)=12f and f-13f=-12f; and then the pulsating torque generated by the rotor harmonic current of any order and the fundamental magnetic flux field is obtained, that is, the main pulsating torque source is 6 times the fundamental frequency, so the instantaneous pulsating torque of the motor is shown in the following formula:

[0018] T (em) (t) = T0 + T6cos6ωt + T 12 cos12ωt……T 6n cos6nωt (3)

[0019] Among them, T (em) (t) is the instantaneous pulsating torque of the motor, T0 is the instantaneous pulsating torque fundamental amplitude, T 6n It is the pulsating torque generated by the 6nth harmonic, where n is not equal to 0;

[0020] Step 3: Use the multiverse optimization algorithm to search and detect the space through two processes of exploration and mining to solve the switching angle of the selective harmonic elimination pulse width modulation SHEPWM, so as to achieve the selective harmonic elimination of the three-phase five-level MPUC inverter;

[0021] Step 3.1: According to the output voltage waveform amplitude and waveform symmetry characteristics of the five-level MPUC inverter, the nonlinear SHEPWM equation group of the five-level MPUC inverter output is expressed as:

[0022]

[0023] Where M is the amplitude modulation ratio, n=6k′-1 is the high order harmonic to be eliminated, α s is the sth switching angle in (0, π / 2), S is the total number of switching angles, and p k is the position coefficient. When the inverter output level increases, p k is 1, the output level decreases when p k is -1;

[0024] Step 3.2, transform the nonlinear SHEPWM equations output by the five-level MPUC inverter into a multi-objective optimization problem;

[0025] Each sub-equation in formula (4) is regarded as an optimization objective function, denoted as f (1) 、f (2) 、f (3),……,f (m) , m is the number of equations; the multi-objective function of formula (4) is transformed into a single objective function, as shown in the following formula:

[0026]

[0027] Step 3.3: Use the single objective function minF as the fitness function of the multiverse optimization algorithm, minimize the fitness function value, and obtain the optimal switching angle of SHEPWM.

[0028] In the SHEPWM solution problem, the switching angle is regarded as a transmission of particles from a white hole to a black hole. The particles select a black hole from the white hole according to WEP and TDR. Then, WEP and TDR are continuously updated according to the fitness value to continuously find the optimal solution. Specifically, the following steps are included:

[0029] Step 3.3.1, initialize the number of iterations I, the number of switch angles S, the number of universe groups U, and calculate the value of minF; when the number of iterations is less than I, proceed to the next step;

[0030] Step 3.3.2, the particle selects a black hole from the white hole according to WEP and TDR, and calculates the fitness value;

[0031] Step 3.3.3, randomly place u universes in s angles;

[0032] Step 3.3.4, based on the standard expansion rate, white holes are generated by the roulette rule, and particles from white holes choose black holes according to WEP and TDR; then, WEP and TDR are continuously updated according to the fitness value, so as to continuously search for the most universe;

[0033] Step 3.3.5, calculate each switch angle after iteration, and record the optimal value and the optimal point;

[0034] Step 3.3.6, update the calculated switch angles; if the updated optimal universe is better than the current optimal universe, replace the current switch angles with the updated switch angles and update the optimal universe, otherwise keep the current switch angles and the current optimal universe;

[0035] Step 3.3.7, record the optimal value and the best point;

[0036] Step 3.3.8, add 1 to the number of iterations. If the number of iterations is less than the specified number, return to step 2;

[0037] Step 3.3.9, end.

[0038] The beneficial effect of adopting the above technical solution is that: the MPUC inverter selective harmonic elimination method based on multiverse optimization provided by the present invention uses the multiverse optimization algorithm to calculate the switching angle required for SHEPWM, thereby realizing selective harmonic elimination without the need for initial conditions. The method can effectively suppress the corresponding sub-torque pulsation in the induction motor by selectively eliminating specific sub-time harmonics in the inverter power supply, thereby improving the working stability of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flow chart of a method for selective harmonic elimination of an MPUC inverter based on multiverse optimization provided by an embodiment of the present invention;

[0040] Figure 2 A topological structure diagram of a three-phase five-level MPUC inverter provided in an embodiment of the present invention;

[0041] Figure 3 The output voltage level and current direction diagram of the MPUC inverter provided in the embodiment of the present invention under different switching states, wherein (a) is a single-phase MPUC topology diagram, (b) is the current direction when the output voltage of the single-phase MPUC inverter is 2E, (c) is the current direction when the output voltage of the single-phase MPUC inverter is E, (d) is the current direction when the output voltage of the single-phase MPUC inverter is 0, (e) is the current direction when the output voltage of the single-phase MPUC inverter is -E, (f) is the current direction when the output voltage of the single-phase MPUC inverter is -2E;

[0042] Figure 4 A five-level phase voltage waveform diagram provided by an embodiment of the present invention;

[0043] Figure 5 A graph showing the relationship between the objective function and the number of iterations provided by an embodiment of the present invention;

[0044] Figure 6 The inverter phase voltage and its FFT experimental waveform diagram provided by the embodiment of the present invention;

[0045] Figure 7 The inverter line voltage and its FFT experimental waveform diagram provided by the embodiment of the present invention;

[0046] Figure 8 A diagram of the harmonic content of the inverter line voltage under different modulation degrees provided by an embodiment of the present invention;

[0047] Fig. 9 The inverter phase voltage u provided in the embodiment of the present invention is AN And its FFT experimental waveform;

[0048] Fig.10The inverter line voltage u provided in the embodiment of the present invention is AB And its FFT experimental waveform;

[0049] Fig.11 The torque waveform diagram within 0.46-0.48s provided by the embodiment of the present invention;

[0050] Fig.12 A torque FFT comparison diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0052] In this embodiment, the MPUC inverter selective harmonic elimination method based on multiverse optimization is as follows: Figure 1 As shown, the following steps are included:

[0053] Step 1: Analyze the switching state of the three-phase five-level MPUC inverter, and use different power supply voltage amplitudes and different modulation controls to generate different output voltage waveforms. In order to reduce power loss, only 1, 3, 5, 7, and 8 states are used to trigger the MPUC inverter;

[0054] The three-phase five-level MPUC (Modified Packed U-Cells) inverter topology is as follows: Figure 2 As shown in the figure, the structure consists of three groups of identical MPUC inverters. Taking the single-phase MPUC five-level inverter as an example, Figure 3 (a) is the topology of the structure. The structure consists of two independent DC power supplies and six groups of power switching devices.

[0055] The switching states of the inverter are shown in Table 1. The switch tubes T1 and T4, T2 and T5, T3 and T6 are complementary states during the conduction process. From Table 1, it can be concluded that 3 groups of switch devices can produce a total of 8 switching states. Different power supply voltage amplitudes combined with different modulation controls will produce different output voltage waveforms. Since it is not necessary to use all redundant switching states, only states 1, 3, 5, 7, and 8 are used to trigger the PUC inverter, thereby further reducing power loss. In this embodiment, under the working conditions of Table 1, the flow direction of the voltage and current of the MPUC inverter is as shown in Figure 3 As shown in (b)-(f).

[0056] Table 1 MPUC inverter switch status table

[0057]

[0058] Among them, u ANis the output phase voltage of the single-phase MPUC inverter, and E is the DC power supply voltage;

[0059] Step 2: Analyze the torque ripple characteristics of the induction motor powered by the three-phase five-level MPUC inverter; compare and analyze the selective elimination of the influence of different power supply harmonics on the motor torque ripple;

[0060] The harmonic components in the input current of the induction motor will lead to the generation of harmonic electromagnetic torque. When the motor is driven by a PWM converter, its stator current is non-sinusoidal, which causes the magnetic flux density to change, causing the magnetic potential to generate harmonics in time and space in the air gap, thereby generating unnecessary harmonic torque. Harmonic torque can generally be divided into asynchronous torque and pulsating torque.

[0061] Step 2.1, determining the asynchronous torque of the induction motor powered by the three-phase five-level MPUC inverter;

[0062] When the air gap harmonic flux and rotor harmonic current order of the induction motor powered by the three-phase five-level MPUC inverter are the same, the induction motor will generate asynchronous torque due to the mutual influence of electromagnetic action, as shown in the following formula:

[0063] T n,1 =C T φ n I 2n cosψ 2n (1)

[0064] Among them, T n,1 To supply the asynchronous torque generated by the induction motor, is the torque constant, m1 is the number of motor phases, p is the number of motor pole pairs, N2 is the number of rotor turns per phase, k w2 is the fundamental rotor winding coefficient; φ n is the stator flux generated by the nth time harmonic; ψ 2n Because φ n The generated electromotive force and rotor harmonic current I 2n The phase difference;

[0065] The direction of the asynchronous torque depends on the number of high-order time harmonics. When the harmonic number n=6k+1 (i.e. n=1, 7, 13…), k is a natural number, and the direction of the asynchronous torque is the same as the speed; when n=6k′-1 (i.e. n=5, 11, 17,…), k′ is a natural number not equal to 0, and the direction of the asynchronous torque is opposite to the speed; the asynchronous torque generated by the harmonic current is small, and the harmonic torques of opposite directions can be offset each other, so the impact on the motor is not significant and can be ignored in actual operation;

[0066] Step 2.2, determining the pulsating torque of the induction motor powered by the three-phase five-level MPUC inverter;

[0067] The pulsating torque of the motor is generated by the interaction of currents and magnetic fluxes of different frequencies in the air gap of the motor; due to the uncertainty of the harmonic order, the pulsating torque generated by each group of currents and magnetic fluxes is also different. The most important pulsating torque is generated by the stator fundamental magnetic flux and the rotor harmonic current, as shown in the following formula:

[0068] T n =2C T φI 2n cos[(n±1)ωt-ψ 1,2n ] (2)

[0069] Among them, T n is the pulsating torque generated by the stator fundamental flux and the nth harmonic current of the rotor, φ is the fundamental flux, ψ 1,2n is the phase difference between the fundamental electromotive force and the rotor current, ω is the angular frequency of the rotor current, and t is the time;

[0070] For the induction motor powered by a three-phase five-level MPUC inverter, the current harmonic order corresponding to n-1 is 6k+1, k is a natural number, and the current harmonic order corresponding to n+1 is 6k′-1; since the amplitudes of the 5th, 7th, 11th, and 13th harmonic currents are affected by the harmonic magnetic field, they will decrease with the increase of the harmonic order; therefore, it is necessary to consider the pulsating harmonic torque caused by the interaction between the fundamental magnetic field and each harmonic current;

[0071] According to formula (2), in the induction motor powered by the three-phase five-level MPUC inverter, the frequency of the pulsating torque generated by the 5th and 7th harmonics is 6f, where f is the fundamental frequency output by the three-phase five-level MPUC inverter, and the directions are opposite, that is, f-(-5f)=6f and f-7f=-6f; similarly, the frequency of the pulsating torque generated by the 11th and 13th harmonics is 12f, that is, f-(-11f)=12f and f-13f=-12f; and then the pulsating torque generated by the rotor harmonic current of any order and the fundamental magnetic flux field is obtained, that is, the main pulsating torque source is 6 times the fundamental frequency, so the instantaneous pulsating torque of the motor is shown in the following formula:

[0072] T (em) (t) = T0 + T6cos6ωt + T 12 cos12ωt……T 6n cos6nωt (3)

[0073] Among them, T (em) (t) is the instantaneous pulsating torque of the motor, T0 is the base amplitude of the instantaneous pulsating torque, T 6n It is the pulsating torque generated by the 6nth harmonic, where n is not equal to 0;

[0074] Harmonic torque is an excitation source that cannot be ignored during the operation of the motor, causing the motor torque to change periodically, resulting in speed oscillation, and affecting the vibration of the mechanical device through magneto-solid coupling. Therefore, the pulsating harmonic torque must be suppressed to prevent the resonance from affecting the system when the harmonic torque frequency is consistent with the resonant frequency of the motor mechanical device.

[0075] Step 3: Use the multiverse optimization algorithm to search and detect the space through two processes of exploration and mining to solve the switching angle of the selective harmonic elimination pulse width modulation SHEPWM, so as to achieve the selective harmonic elimination of the three-phase five-level MPUC inverter, and analyze the selective harmonic elimination effect of the method and the suppression effect on the torque pulsation of the induction motor;

[0076] Step 3.1: According to the output voltage waveform amplitude and waveform symmetry characteristics of the five-level MPUC inverter, the nonlinear SHEPWM equation group of the five-level MPUC inverter output is expressed as:

[0077]

[0078] Where M is the amplitude modulation ratio, n=6k′-1 is the high order harmonic to be eliminated, α s is the sth switching angle in (0, π / 2), S is the total number of switching angles, and p k is the position coefficient. When the inverter output level increases, p k is 1, the output level decreases when p k is -1;

[0079] The phase voltage waveform of the five-level MPUC inverter is as follows: Figure 4 As shown, within half a cycle, the voltage wave forms a 1 / 4 even symmetry, with S switching points. m , α S …is the switching angle. In a three-phase system, due to the symmetry of the load, after eliminating certain harmonics in the phase voltage, the line voltage does not contain the harmonics of the phase voltage, nor does it contain the third harmonic and its multiple harmonics.

[0080] Step 3.2, transform the nonlinear SHEPWM equations output by the five-level MPUC inverter into a multi-objective optimization problem;

[0081] Each sub-equation in formula (4) is regarded as an optimization objective function, denoted as f (1) 、f (2) 、f (3) ,……,f (m) , m is the number of equations; the multi-objective function of formula (4) is transformed into a single objective function, as shown in the following formula:

[0082]

[0083] Step 3.3: Use the single objective function minF as the fitness function of the multiverse optimization algorithm, minimize the fitness function value, and obtain the optimal switching angle of SHEPWM.

[0084] In the multiverse optimization algorithm (MVO), the universe with a high expansion rate tends to transmit matter particles from the white hole to the black hole of the universe with a low expansion rate through wormholes.

[0085] In the SHEPWM solution problem, the switching angle is regarded as a transmission of particles from a white hole to a black hole. The particles select a black hole from the white hole according to WEP and TDR. Then, WEP and TDR are continuously updated according to the fitness value to continuously find the optimal solution. Specifically, the following steps are included:

[0086] Step 3.3.1, initialize the number of iterations I, the number of switch angles S, the number of universe groups U, and calculate the value of minF; when the number of iterations is less than I, proceed to the next step;

[0087] Step 3.3.2, the particle selects a black hole from the white hole according to WEP and TDR, and calculates the fitness value;

[0088] Step 3.3.3, randomly place u universes in s angles;

[0089] Step 3.3.4, based on the standard expansion rate, white holes are generated by the roulette rule, and particles from white holes choose black holes according to WEP and TDR; then, WEP and TDR are continuously updated according to the fitness value, so as to continuously search for the most universe;

[0090] Step 3.3.5, calculate each switch angle after iteration, and record the optimal value and the optimal point;

[0091] Step 3.3.6, update the calculated switch angles; if the updated optimal universe is better than the current optimal universe, replace the current switch angles with the updated switch angles and update the optimal universe, otherwise keep the current switch angles and the current optimal universe;

[0092] Step 3.3.7, record the optimal value and the best point;

[0093] Step 3.3.8, add 1 to the number of iterations. If the number of iterations is less than the specified number, return to step 2;

[0094] Step 3.3.9, end.

[0095] The Multi-Verse Optimizer (MVO) is an algorithm based on simulating the process of material exchange in the universe; different universes have different expansion rates (Normalized Inflation Rate, NI); according to the different expansion rates, matter is transferred from white holes with high expansion rates to black holes with low expansion rates. This process is simulated in a roulette way:

[0096]

[0097] Where: and are the jth variable of the i-th universe and the variable selected by the roulette mechanism; NI(U i ) is the standard expansion rate of the ith universe; r1 is a random number between 0 and 1;

[0098] Matter is not only transferred through white and black holes, but also exchanged through wormholes; assuming that the wormhole tunnel is always established between the universe and the optimal universe, this wormhole establishment mechanism is expressed by the formula:

[0099]

[0100] Where: x j is the jth variable of the current optimal universe; ub j and lb j For variable x j The upper and lower limits of r2, r3, and r4 are all random numbers between 0 and 1;

[0101] WEP (Wormhole Existence Probability) and TDR (Travelling Distance Rate) are the wormhole existence probability coefficient and the travel distance rate, respectively, as shown in the following formula:

[0102]

[0103] TDR = 1-(l / L) 1 / p (9)

[0104] Where l and L are the current and maximum iterations, respectively; min is the minimum WEP value; max is the maximum WEP value; and p defines the detection speed that changes with the number of iterations. The higher the p value, the faster the local detection speed and the shorter the time.

[0105] From formulas (7) and (8), it can be seen that TDR decreases exponentially and WEP increases linearly. Before TDR and WEP intersect, TDR is greater than WEP, which is beneficial to prevent the occurrence of local optimal solutions. After the intersection, as TDR decreases and WEP increases, the iterative process improves the accurate evaluation of the optimal global result. This mechanism is a mechanism to improve the search accuracy in the iterative process.

[0106] The multiverse optimization MVO algorithm is used to solve the SHEPWM nonlinear equations of the five-level MPUC inverter, and the specific subharmonics in the inverter power supply that have a greater impact on the torque pulsation of the induction motor can be selectively eliminated, which can effectively suppress the motor torque pulsation and improve the motor working quality.

[0107] In this embodiment, first, the effect of SHEPWM selective detuning is verified by taking the three-phase MPUC inverter with inductive load as an example. The simulation parameters are as follows: the reactor at the output end of the inverter is 15mH, the resistance is 5Ω; the DC side reference voltage is 24V. The harmonics to be eliminated are the 5th, 7th, 9th, 11th, and 17th harmonics. The modulation index range is 0.7 to 1. This embodiment takes the modulation index of 0.8 as an example and uses the MVO algorithm to solve the required switching angle. Figure 5 The curve drawn is the relationship between the objective function and the number of iterations. Figures 6-7 Based on the above, the three-phase inverter outputs phase voltage and line voltage waveforms, as well as the corresponding FFT waveforms. The other modulation line voltage FFTs are as follows: Figure 7 shown.

[0108] Depend on Figure 6 (a) and Figure 7 (a) It can be seen that the inverter output phase voltage is five-level and the line voltage is seven-level; Figure 6 (b) and Figure 7 (b) It can be seen that the phase voltage does not contain the 5th, 7th, 11th, 13th, and 17th harmonics. At the same time, due to the symmetry of the three-phase circuit, the output line voltage does not contain the above-mentioned eliminated harmonics and harmonics of multiples of 3. Figure 8 The following is the distribution diagram of each harmonic of line voltage at different modulation degrees.

[0109] Consistent with the above simulation parameters, a physical simulation system of a three-phase MPUC inverter with resistive inductive load was built. The system main control chip uses 32-bit DSPTMS320F28335; the inverter main circuit uses IGBTBSM50GB120DN2 as the power switch device; the oscilloscope model in the experiment is DS1052E. Figures 9-10 Based on the simulation, the three-phase inverter output voltage phase voltage and line voltage experimental waveforms, as well as the corresponding FFT waveforms.

[0110] Depend on Fig. 9As shown in the figure, the phase voltage changes in five levels, and the harmonics to be eliminated in its FFT waveform are effectively suppressed. Fig.10 The line voltage waveform shown in the figure does not contain the eliminated harmonics except for the number of levels. The experiment verifies the effectiveness of the selective harmonic elimination method of the three-phase MPUC five-level inverter based on the MVO algorithm.

[0111] In this embodiment, based on the above method, MATLAB is used to simulate the induction motor with variable frequency power supply; and Maxwell simulation software is used to simulate the torque of the three-phase AC induction motor. The motor parameters are shown in Table 2.

[0112] Table 2 Motor parameters

[0113] parameter Numeric Rated power (kW) 6.6 Rated voltage(V) 380 Winding connection method Y Number of poles 4 Rated speed (rpm) 1450 Rated frequency(Hz) 50

[0114] The rated voltage signal generated by the inverter is imported into the finite element model of the three-phase induction motor. Under the same condition of modulation index of 0.8, the first group of SHEPWM control methods eliminates the 5th, 7th, 11th, 13th, and 17th harmonics; the second group of SHEPWM control methods eliminates the 17th, 19th, 23rd, 25th, and 29th harmonics; the simulation time is 0.5s. Fig.11 As shown in the figure, the stabilized torque waveform is selected as the analysis object. After the intercepted torque is subjected to FFT, the torque spectrum obtained by normalization is as follows: Fig.11 shown.

[0115] Depend on Figure 11-12 It can be seen that as the harmonic order increases, the impact on the motor torque pulsation gradually decreases, that is, the motor torque is mainly low-order pulsation. Fig.12 The simulation results of torque pulsation in the figure show that the first group of SHEPWM eliminates the 5th, 7th, 11th, 13th, and 17th harmonics in the inverter power supply, and the percentages of the 6th and 12th torque harmonics of the motor are reduced to 0.17% and 0.05% respectively, which are effectively suppressed; the 18th harmonic torque still has a significant content, because only the 17th harmonic is eliminated in the phase voltage, and the 19th harmonic is not eliminated. In contrast, the second group of SHEPWM eliminates the 17th, 19th, 23rd, 25th, and 29th harmonics in the phase voltage. Under its influence, the percentages of the 18th and 24th torque harmonics of the corresponding motor are reduced to 0.03%. In contrast, because the 5th, 7th, 11th, and 13th harmonics are not eliminated in the second group of SHEPWM, the percentages of the 6th and 12th torque harmonics of the motor are as high as 16.33% and 1.27%, and the low-order torque pulsation is relatively strong.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for selective harmonic elimination of MPUC inverter based on multiverse optimization, characterized in that: The following steps are involved: Step 1, analyze the switching state of the three-phase five-level MPUC inverter, use different power supply voltage amplitudes and different modulation controls to generate different output voltage waveforms, and use states 1, 3, 5, 7, and 8 to trigger the MPUC inverter; Step 2: Analyze the torque ripple characteristics of the induction motor powered by the three-phase five-level MPUC inverter; compare and analyze the selective elimination of the influence of different power supply harmonics on the motor torque ripple; Step 3: Use the multiverse optimization algorithm to search and detect the space through two processes of exploration and mining to solve the switching angle of the selective harmonic elimination pulse width modulation SHEPWM, so as to achieve the selective harmonic elimination of the three-phase five-level MPUC inverter; Step 3.1: According to the output voltage waveform amplitude and waveform symmetry characteristics of the five-level MPUC inverter, the nonlinear SHEPWM equation group of the five-level MPUC inverter output is expressed as: Where M is the amplitude modulation ratio, n=6k′-1 is the high order harmonic to be eliminated, α s is the sth switching angle in (0, π / 2), S is the total number of switching angles, and p k is the position coefficient. When the inverter output level increases, p k is 1, the output level decreases when p k is -1; Step 3.2, transform the nonlinear SHEPWM equations output by the five-level MPUC inverter into a multi-objective optimization problem; Each sub-equation in formula (4) is regarded as an optimization objective function, denoted as f (1) 、f (2) 、f (3) ,……,f (m) , m is the number of equations; the multi-objective function of formula (4) is transformed into a single objective function, as shown in the following formula: Step 3.3: Use the single objective function minF as the fitness function of the multiverse optimization algorithm, minimize the fitness function value, and obtain the optimal switching angle of SHEPWM.

2. The method for selective harmonic elimination of MPUC inverter based on multiverse optimization according to claim 1, characterized in that: The step 2 comprises the following steps: Step 2.1, determining the asynchronous torque of the induction motor powered by the three-phase five-level MPUC inverter; When the air gap harmonic flux and rotor harmonic current order of the induction motor powered by the three-phase five-level MPUC inverter are the same, the induction motor will generate asynchronous torque due to the mutual influence of electromagnetic action, as shown in the following formula: T n,1 =C T f n I 2n cosψ 2n (1) Among them, T n,1 To supply the asynchronous torque generated by the induction motor, is the torque constant, m1 is the number of motor phases, p is the number of motor pole pairs, N2 is the number of rotor turns per phase, k w2 is the fundamental rotor winding coefficient; φ n is the stator flux generated by the nth time harmonic; ψ 2n Because φ n The generated electromotive force and rotor harmonic current I 2n The phase difference; The direction of the asynchronous torque depends on the number of high-order time harmonics. When the harmonic number n = 6k+1, k is a natural number, and the direction of the asynchronous torque is the same as the speed; when n = 6k′-1, k′ is a natural number not equal to 0, and the direction of the asynchronous torque is opposite to the speed; Step 2.2, determining the pulsating torque of the induction motor powered by the three-phase five-level MPUC inverter; The pulsating torque of the motor is generated by the interaction of currents and magnetic fluxes of different frequencies in the air gap of the motor; due to the uncertainty of the harmonic order, the pulsating torque generated by each group of currents and magnetic fluxes is also different. The most important pulsating torque is generated by the stator fundamental magnetic flux and the rotor harmonic current, as shown in the following formula: T n =2C T φI 2n cos[(n±1)ωt-ψ 1,2n ] (2) Among them, T n is the pulsating torque generated by the stator fundamental flux and the nth harmonic current of the rotor, φ is the fundamental flux, ψ 1,2n is the phase difference between the fundamental electromotive force and the rotor current, ω is the angular frequency of the rotor current, and t is the time; According to formula (2), in the induction motor powered by the three-phase five-level MPUC inverter, the frequency of the pulsating torque generated by the 5th and 7th harmonics is 6f, where f is the fundamental frequency output by the three-phase five-level MPUC inverter, and the directions are opposite, that is, f-(-5f)=6f and f-7f=-6f; similarly, the frequency of the pulsating torque generated by the 11th and 13th harmonics is 12f, that is, f-(-11f)=12f and f-13f=-12f; and then the pulsating torque generated by the rotor harmonic current of any order and the fundamental magnetic flux field is obtained, that is, the main pulsating torque source is 6 times the fundamental frequency, so the instantaneous pulsating torque of the motor is shown in the following formula: T (em) (t)=T0+T6cos6ωt+T 12 cos12ωt……T 6n cos6nωt (3) Among them, T (em) (t) is the instantaneous pulsating torque of the motor, T0 is the base amplitude of the instantaneous pulsating torque, T 6n It is the pulsating torque generated by the 6nth harmonic, where n is not equal to 0.

3. The method for selective harmonic elimination of MPUC inverter based on multiverse optimization according to claim 2, characterized in that: The step 3.3 comprises the following steps: Step 3.3.1, initialize the number of iterations I, the number of switch angles S, the number of universe groups U, and calculate the value of minF; when the number of iterations is less than I, proceed to the next step; Step 3.3.2, the particle selects a black hole from the white hole according to WEP and TDR, and calculates the fitness value; Step 3.3.3, randomly place u universes in s angles; Step 3.3.4, based on the standard expansion rate, white holes are generated by the roulette rule, and particles from white holes choose black holes according to WEP and TDR; then, WEP and TDR are continuously updated according to the fitness value, so as to continuously search for the most universe; Step 3.3.5, calculate each switch angle after iteration, and record the optimal value and the optimal point; Step 3.3.6, update the calculated switch angles; if the updated optimal universe is better than the current optimal universe, replace the current switch angles with the updated switch angles and update the optimal universe, otherwise keep the current switch angles and the current optimal universe; Step 3.3.7, record the optimal value and the best point; Step 3.3.8, add 1 to the number of iterations. If the number of iterations is less than the specified number, return to step 2; Step 3.3.9, end.

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