CN106560991A - Pulse width modulation method for H-bridge cascading-type inverter - Google Patents

Abstract

The invention discloses a pulse width modulation method for an H-bridge cascading-type inverter, and the method comprises the following steps: setting a specific function optimization target with the minimum harmonic current, and a nonlinear constraint with the H-bridge power balance; solving an initial switching angle value of a corresponding modulation degree through employing a genetic algorithm; solving an optimal switching angle value through employing a nonlinear programming function Fmincon; carrying out the planning of switching angle values in a whole modulation ratio range, and carrying out the serialization of the switching angle values in an allowed specific function index. The method employs a multilevel synchronization optimization pulse width modulation method to effectively solve problems of energy quality at low switching frequency and the instantaneous power balance of an H-bridge module, and is successfully used in the field of AC transmission.

Description

A kind of pulse duration modulation method of H bridges cascaded inverter

Technical field

The present invention relates to a kind of modulator approach of multi-electrical level inverter, more particularly to a kind of H bridges cascaded inverter is same Step optimization pulse duration modulation method.

Background technology

Traditional Multilevel modulation technology includes phase-shifting carrier wave PWM (Carrier phase-shifted pulse-width Modulation, CPS-PWM), stacking PWM (Phase disposition pulse-width modulation, PD-PWM), Multilevel space vector PWM (Space vector pulse-width modulation, SVPWM) and many level SHEPWM (Selective harmonic elimination pulse-width modulation, SHEPWM) etc..

CPS-PWM can be automatically obtained the power equalization of H-bridge unit, but voltage utilization is relatively low.PD-PWM cannot be naturally real Existing power equalization, needs the pulse train in each power model of half period interior circulation.It is inverse that many level SVPWMs are applied to many level When becoming device, when output-voltage levels number is more than 5, voltage vector is selected and action time calculates all extremely complex.

Many level SHEPWM when each power model switch angle is calculated, simply with fundamental modulation ratio and specified Harmonics elimination For constraints, do not consider that modular power is balanced.Staircase wave method as many level SHEPWM a kind of special circumstances, Can be using active power equalization and cycle pulse power equalization method come balanced each module voltage stress and current stress.Wattful power Rate equalization needs the phase relation for considering fundamental voltage and electric current, increases power equalization constraint equation to readjust switching angle Degree.Cycle pulse power equalization method includes pulse interlacing method and pulse offsets method again, and pulse interlacing method is causing output voltage just Half cycle and negative half period lose zero point symmetry, and the even-order harmonic of individual module output voltage is significantly increased；Pulse offsets Fa Keping The voltage stress of weighing apparatus modules and devices switch loss, but the active power and reactive power of modules but phase not to the utmost Together.

Synchronous fluorimetry pulsewidth modulation (Synchronous optimal pulse-width modulation, SOPWM) is needed Specific function optimization aim is set, such as harmonic current virtual value minimum, efficiency optimization and torque pulsation is minimum, not exclusively Inverter itself, but inverter and load are considered as a whole mathematical model, solved most by function minimization Excellent switch angle.

SOPWM can efficiently solve the problems such as quality of power supply of low switching frequency, equilibrium of H-bridge unit instantaneous power；Due to SOPWM existing correlative studys in two level, three-level inverter, and being applied to many level H-bridge cascade connection type inverters can increase Switching angle computation complexity, therefore the achievement in research based on many level H-bridge cascade connection type inverters of SOPWM is actually rare.

The content of the invention

In order to overcome the shortcoming and defect of prior art, the purpose of the present invention is to meet the same of total harmonic current minimum When, propose a kind of Synchronous fluorimetry pulse duration modulation method of the H bridge cascaded inverters of energy efficient balance unit instantaneous power.

The technical solution adopted for the present invention to solve the technical problems is：A kind of pulsewidth modulation of H bridges cascaded inverter Method, comprises the following steps：

Step S10：According to control system performance requirement determine single H bridge inverters within 1/4 cycle switching angle number and Modulation ratio m is interval；

Step S20：Set up Harmonic Current Distortion rate target extremal function and H bridge power equalizations fundamental voltage it is non-linear Constraints；

Step S30：Asked by genetic algorithm in modulation ratio m interval according to the Nonlinear Constraints that step S20 is obtained Solve the initial switch angle value of corresponding modulation degree；

Step S40：Initial switch angle value is obtained according to step S30, using the Non-Linear Programming function of Matlab Fmincon solves optimized switching angle value；

Step S50：When reaching the setting cycle calculations number of times of step S30, step S40, all of harmonic current of comparison is abnormal Variability, stores the optimized switching angle value of corresponding modulation ratio m；

Step S60：Switch angle value in Integrated comparative modulation ratio m interval, all discontinuous switch angle that will be solved Value carries out continuous treatment；

Step S70：The switch angle value of serialization is stored in memory, is produced according to H bridge inverters control law Pwm signal.

Further, described step S30 is comprised the following steps：

Step S301：Nonlinear Constraints are obtained according to step S20 and sets up initial optimization object function, determine switching angle The border of angle value and linear inequality constraint condition；

Step S302：Setting initial population parameter, calculates single individual fitness value in population, is selected according to fitness Parent individuality, gene information from parent population produces new son individual, by small probability disturbance to change population in individuality Gene information and create the offspring of variation；

Step S303：When meeting optimization end condition, choice of modulation obtains corresponding initial switch angle value than m.

A kind of pulse duration modulation method of described H bridges cascaded inverter, its initial optimization object function is

Wherein N be H bridges cascade number, k be H bridges switching angle number within 1/4 cycle, specific gravity factor λ₁、λ₂More than 0, and N λ₁+ λ₂=1.

Further, described step S40 is comprised the following steps：

Step S401：Final optimization pass object function and nonlinear restriction equation are obtained according to step S20, it is determined that switch angle The border of value and linear inequality constraint condition；

Step S402：Switch angle value is solved using the Non-Linear Programming function Fmincon in constrained optimization；

Step S403：When meeting optimization end condition, choice of modulation obtains corresponding optimized switching angle value than m.

A kind of pulse duration modulation method of described H bridges cascaded inverter, final optimization pass object function is

The nonlinear restriction equation is

The present invention compared with prior art, has the advantages that：

(1) modulator approach of the invention minimizes total harmonic current of H bridge cascaded inverters balanced with modular power Combine, while total harmonic current is minimized, energy efficient balance modules power effectively improves output current ripple Shape, reduces total Harmonic Current Distortion rate.

(2) SOPWM that uses of the present invention is for CPS-PWM, PD-PWM and SVPWM, when total Harmonic Current Distortion When rate is identical, with lower switching frequency, can significantly reduce the switching loss of power device.

Description of the drawings

Fig. 1 is 2 H bridge cascaded inverter main circuit topological structures；

Fig. 2 is the calculation flow chart of the present invention；

Fig. 3 is the relation between inverter switching frequency and motor in synchrony frequency；

Fig. 4 is the relation of the switch angle that optimization is calculated when k is equal to 5 and modulation ratio；

Fig. 5 is the relation of switch angle when k is equal to 5 after continuity optimization and modulation ratio；

Fig. 6 is the relation of Harmonic Current Distortion rate and modulation ratio before and after serialization；

Fig. 7 is the relation that angle and modulation ratio are switched when k is equal to 4；

Fig. 8 is the relation that angle and modulation ratio are switched when k is equal to 3；

Fig. 9 is the relation of Harmonic Current Distortion rate and gamut internal modulation ratio；

Figure 10 is when devices switch frequency is that 300Hz, synchronous angular frequency are equal to 75Hz, using the electricity of SPWM modulator approaches Pressure, electric current and torque profile figure；

Figure 11 is when devices switch frequency is that 300Hz, synchronous angular frequency are equal to 75Hz, using SOPWM modulator approaches Voltage, electric current and torque profile figure.

Specific embodiment

The present invention is described in further detail with reference to the accompanying drawings and examples.

As shown in figure 1, considering from circuit topological structure and modulator approach complexity, five level are using more one kind Many level topological structures, the present invention just by five-electrical level inverter driving asynchronous machine as a example by, other multi-electrical level inverter analysis classes Seemingly.

The switch angle optimization computation flow process of H bridge cascaded inverter SOPWM methods is as shown in Fig. 2 including following step Suddenly：

Step S10

Single H bridge inverters switching angle number and modulation ratio m area within 1/4 cycle are determined according to control system performance requirement Between.If the maximum allowable operating frequency of switching device is f_smax, fundamental voltage frequency is f₁, for single H bridge inverters were at 1/4 week Switching angle number is in phase

Modulation ratio m meets with switching angle number k

If H bridge cascaded inverters IGBT allows peak frequency f_smaxFor 300Hz, rated output frequency f_NFor 100Hz, then Inverter switching frequency f_sWith motor in synchrony frequency f₁Design curve it is as shown in Figure 3：Can Setting pattern switch stagnant ring, to avoid Modulating mode in frequency error factor point sweeping action, as shown by the dotted line in fig. 3.When synchronizing frequency f₁During less than 50Hz, many level Inverter can also obtain less Harmonic Current Distortion rate using asynchronous SPWM；When synchronizing frequency f₁During more than 50Hz, adopt Frequency-division section SOPWM.

Step S20

Set up the target extremal function of Harmonic Current Distortion rate and the fundamental voltage nonlinear restriction bar of H bridge power equalizations Part.If U_nFor the nth harmonic voltage magnitude of inverter output voltage, f₁For fundamental frequency, L_σFor asynchronous machine rotor leakage reactance it With, the impact of negligible 3 multiple subharmonic voltage when loading with three phase electric machine, then a certain mutually total harmonic current of motor is effective Value is represented by

When the H bridges of N levels cascade adopt 180 ° of square-wave frequency modulations, if DC bus-bar voltage is U_dc, total harmonic current has Valid value is represented by

I_hWith I_{h_sq}Enter rower for base value to change, and be defined as Harmonic Current Distortion rate d.In order that total harmonic wave electricity Stream is minimized, then had

Index d is related to the THD of electric machine phase current, can weigh the size of phase current THD, directly affects motor control Energy.

In 1/4 periodic regime, switching the selection of angle value has the k free degree, and H bridge cascaded inverter output voltages are

Bring formula (6) into formula (5) Harmonic Current Distortion rate d can be obtained and be

By fundamental voltage U₁To export fundamental voltage 4U during 180 ° of square-wave frequency modulations_dc/ π enters rower and changes for base value, and defines For modulation ratio m.For balanced single H bridge inverters instantaneous output voltage, need to increase Nonlinear Constraints is

Step S30

Accordingly adjusted by genetic algorithm for solving in modulation ratio m interval according to the Nonlinear Constraints that step S20 is obtained The initial switch angle value of system.Real work step using the switch angle optimizing of genetic algorithm is as follows.

Step S301：The target function type (7) for solving as needed and formula (8), setting up initial optimization object function is

Determine border and the linear inequality constraint condition of variable.If minimum pulse width is 50 μ s, according to the most scun for allowing Wide degree switchs angle interval to determine

Then linear inequality constraints condition

Variable boundary condition

[LB UB]=[0.5 Δ α 0.5 (π-Δ α)] (12)

Step S302：Setting initial population parameter, calculates single individual fitness value in population, is selected according to fitness Parent individuality, gene information from parent population produces new son individual, by small probability disturbance to change population in individuality Gene information and create the offspring of variation；

Step S303：When meeting optimization end condition, choice of modulation obtains corresponding initial switch angle value than m；Initially Optimization object function is

Wherein N be H bridges cascade number, k be H bridges switching angle number within 1/4 cycle, specific gravity factor λ₁、λ₂More than 0, and N λ₁+ λ₂=1.

Step S40

Initial switch angle value is obtained according to step S30, is solved most using the Non-Linear Programming function Fmincon of Matlab Excellent switch angle value, comprises the following steps.

Step S401：Final optimization pass object function and nonlinear restriction equation are obtained according to step S20, it is determined that switch angle The border of value and linear inequality constraint condition.Optimization object function is set to formula (7)；The switch that initial point is obtained for genetic algorithm Angle；Linear inequality constraint condition is set to formula (11)；Variable boundary condition is set to formula (12)；Nonlinear restriction equation is set to formula (8)。

Step S402：Switch angle value is solved using the Non-Linear Programming function Fmincon in constrained optimization；

Step S403：When meeting optimization end condition, choice of modulation obtains corresponding optimized switching angle value than m；Finally Optimization object function is

The nonlinear restriction equation is

Step S50

When reaching the setting cycle calculations number of times of step S30, step S40, all of Harmonic Current Distortion rate of comparison, storage The optimized switching angle value of corresponding modulation ratio m, optimization is calculated when k is equal to 5 switch angle and relation such as Fig. 4 institutes of modulation ratio Show.

Step S60

Switch angle value in Integrated comparative modulation ratio m interval, all discontinuous switch angle value for solving is connected Continuousization process；When modulation ratio m occurs minor variations, switch angle changing value is less than as far as possible π/18, can reduce motor output Electromagnetic torque pulsation size.The step of all discontinuous switch angle value for solving is carried out into continuous treatment is as follows：

Step S601：Again planning switch angle curve, angle value is switched as the initial of discontinuity point using continuity point Value, in the case where allowing Harmonic Current Distortion rate d, plans as a whole the solution of all modulation ratios m.

Step S602：Solved using genetic algorithm optimizing, Fmincon function optimizations are calculated, re-optimization is all discontinuous Point.The switch angle that continuity optimization is calculated when k is equal to 5 is as shown in Figure 5 with the relation of modulation ratio.

The serialization of switch angle sacrifices fractional harmonic current distortion rate index, Harmonic Current Distortion rate before and after serialization With the relation of modulation ratio as shown in fig. 6, Harmonic Current Distortion rate d of the partial modulation than m even increased 100%.

Respectively as shown in Figure 7 and Figure 8, switch angle is substantially continuous for the relation of switch angle and modulation ratio when k is equal to 4 and 3, Calculation procedure and k are equal to identical when 5.

The relation of Harmonic Current Distortion rate and gamut internal modulation ratio is humorous as shown in figure 9, when modulation ratio m is less than 0.93 Ripple current distortion rate d is less than 0.2, and the inhibition of harmonic current is preferable；When modulation ratio m is more than 0.93, Harmonic Current Distortion Rate d moves closer to 180 ° of square-wave frequency modulations.

Step S70

The switch angle value of serialization is stored in memory, pwm signal is produced according to H bridge inverters control law.

When devices switch frequency is that 300Hz, synchronous angular frequency are equal to 75Hz, using the voltage of SPWM modulator approaches, electricity Stream and torque profile figure are as shown in Figure 10；When devices switch frequency is that 300Hz, synchronous angular frequency are equal to 75Hz, using SOPWM The voltage of modulator approach, electric current and torque profile figure are as shown in figure 11；Figure 10 and Figure 11 compare CPS-PWM and segmentation SOPWM Voltage, electric current and torque profile.During low switching frequency, using Stator Current Harmonic aberration rate, the torque pulsation of segmentation SOPWM Much smaller than CPS-PWM.Different from CPS-PWM, the integral multiple of IGBT switching frequencies always fundamental voltage frequency is segmented SOPWM Part sideband harmonic wave is eliminated, while low-order harmonic can be suppressed, low-order harmonic electric current, electricity when can efficiently solve low switching frequency The excessive problem of machine output torque pulsation.

Finally it should be noted that：Above example is most only to illustrate technical scheme rather than a limitation Pipe has been described in detail with reference to above-described embodiment to the present invention, it will be understood by those skilled in the art that：Still can be with The specific implementation method of the present invention is modified or equivalent, and without departing from any modification of spirit and scope of the invention Or equivalent, it all should cover in the middle of scope of the presently claimed invention.

Claims (6)

1. a kind of pulse duration modulation method of H bridges cascaded inverter, it is characterised in that comprise the following steps：

Step S10：Single H bridge inverters switching angle number and modulation within 1/4 cycle are determined according to control system performance requirement It is more interval than m；

Step S20：Set up the target extremal function of Harmonic Current Distortion rate and the fundamental voltage nonlinear restriction of H bridge power equalizations Condition；

Step S30：Pass through genetic algorithm for solving phase in modulation ratio m interval according to the Nonlinear Constraints that step S20 is obtained Answer the initial switch angle value of modulation degree；

Step S40：Initial switch angle value is obtained according to step S30, is asked using the Non-Linear Programming function Fmincon of Matlab Solution optimized switching angle value；

Step S50：When reaching the setting cycle calculations number of times of step S30, step S40, all of Harmonic Current Distortion rate of comparison, Store the optimized switching angle value of corresponding modulation ratio m；

Step S60：Switch angle value in Integrated comparative modulation ratio m interval, all discontinuous switch angle value for solving is entered Row continuous treatment；

Step S70：The switch angle value of serialization is stored in memory, PWM letters are produced according to H bridge inverters control law Number.

2. the pulse duration modulation method of a kind of H bridges cascaded inverter according to claim 1, it is characterised in that described Step S30 is comprised the following steps：

Step S301：Nonlinear Constraints are obtained according to step S20 and sets up initial optimization object function, it is determined that switch angle value Border and linear inequality constraint condition；

Step S302：Setting initial population parameter, calculates single individual fitness value in population, and according to fitness parent is selected Individuality, gene information from parent population produces new son individual, by small probability disturbance to change population in genes of individuals Information and create the offspring of variation；

Step S303：When meeting optimization end condition, choice of modulation obtains corresponding initial switch angle value than m.

3. the pulse duration modulation method of a kind of H bridges cascaded inverter according to claim 1, it is characterised in that described Step S40 is comprised the following steps：

Step S401：Final optimization pass object function and nonlinear restriction equation are obtained according to step S20, it is determined that switch angle value Border and linear inequality constraint condition；

Step S402：Switch angle value is solved using the Non-Linear Programming function Fmincon in constrained optimization；

Step S403：When meeting optimization end condition, choice of modulation obtains corresponding optimized switching angle value than m.

4. the pulse duration modulation method of a kind of H bridges cascaded inverter according to claim 1, it is characterised in that described Step S60 is comprised the following steps：

Step S601：Again planning switch angle curve, angle value is switched as the initial value of discontinuity point using continuity point；

Step S602：Solved using genetic algorithm optimizing, Fmincon function optimizations are calculated, all discontinuity poinies of re-optimization.

5. the pulse duration modulation method of a kind of H bridges cascaded inverter according to claim 2, it is characterised in that it is described just Beginning optimization object function is

$F_v={\mathrm{\λ}}_1\underset{n=1}{\overset{N}{\Σ}}{(\underset{j=1}{\overset{k}{\Σ}}{\left(-1\right)}^{j+1}{\mathrm{cos\α}}_{nj}-m)}^2+\frac{{\mathrm{\λ}}_2}{{\left(0.0463N\right)}^2}\underset{i=1}{\overset{\mathrm{\∞}}{\Σ}}{\left(\frac{1}{{(6i\±1)}^2}\underset{n=1}{\overset{N}{\Σ}}\right(\underset{j=1}{\overset{k}{\Σ}}\left({\left(-1\right)}^{j+1}cos\left(6i\±1\right){\mathrm{\α}}_{nj}\right)\left)\right)}^2,$

Wherein N is that H bridges cascade number, and k is H bridges switching angle number, specific gravity factor within 1/4 cycleλ ₁、λ ₂More than 0, and Nλ ₁+λ ₂=1。

6. the pulse duration modulation method of a kind of H bridges cascaded inverter according to claim 3, it is characterised in that it is described most Whole optimization object function is

$F_v=\frac{1}{0.0463N}\sqrt{\underset{i=1}{\overset{\mathrm{\∞}}{\Σ}}{\left(\frac{1}{{(6i+1)}^2}\underset{n=1}{\overset{N}{\Σ}}\right(\underset{j=1}{\overset{k}{\Σ}}\left({(-1)}^{j+1}cos\right(6i\±1\left){\mathrm{\α}}_{nj}\right)\left)\right)}^2};$

The nonlinear restriction equation is