阅读说明：本技术 电流纹波法下基于svpwm调制策略的三电平设计方法 (Three-level design method based on SVPWM (space vector pulse width modulation) strategy under current ripple method ) 是由 李先允 袁宇 唐昕杰 张宇 王书征 于 2020-05-22 设计创作，主要内容包括：本发明公开一种电流纹波法下基于SVPWM调制策略的三电平设计方法,包括步骤：采用电流纹波法求出基于不同SVPWM调制策略下,三电平系统的关于调制比和电压相角的电流纹波方程；依据电流纹波方程,根据工作指标选择SVPWM调制策略；依据电流纹波方程周期内最大值,设计出三电平系统的滤波电感参数；依据电流纹波方程,设计开关器件的电流参数。本发明计算出已确定工作情况的三电平系统下的电流纹波,以此来指导调制策略的选择,指导滤波电感以及开关器件的选择,能够在满足设计指标的情况下降低系统的整体体积、工作损耗和制作成本。(The invention discloses a three-level design method based on an SVPWM (space vector pulse width modulation) strategy under a current ripple method, which comprises the following steps of: solving a current ripple equation of a three-level system about a modulation ratio and a voltage phase angle under different SVPWM (space vector pulse width modulation) strategies by adopting a current ripple method; selecting an SVPWM (space vector pulse width modulation) strategy according to a working index according to a current ripple equation; designing filter inductance parameters of a three-level system according to the maximum value in the current ripple equation period; and designing the current parameters of the switching device according to a current ripple equation. The invention calculates the current ripple under the three-level system with determined working condition, so as to guide the selection of the modulation strategy and the selection of the filter inductor and the switching device, and can reduce the overall volume, the working loss and the manufacturing cost of the system under the condition of meeting the design index.)

1. A three-level design method based on an SVPWM (space vector pulse width modulation) strategy under a current ripple method is characterized by comprising the following steps: the method comprises the following steps:

s1, solving a current ripple equation of the three-level system about the modulation ratio and the voltage phase angle under different SVPWM modulation strategies by adopting a current ripple method;

s2, selecting an SVPWM (space vector pulse width modulation) strategy according to the working index according to a current ripple equation;

s3, designing filter inductance parameters of a three-level system according to the maximum value in the current ripple equation period;

and S4, designing the current parameters of the switching device according to the current ripple equation.

2. The three-level design method based on the SVPWM modulation strategy under the current ripple method according to claim 1, wherein: in step S1, the current ripple equation is:

wherein L is filter inductance value, Ts is switch sampling period of three-level system, and V is_dcThe voltage is the direct current side voltage of a three-level system; m is the modulation ratio of the three-level system; omega is the angular speed of the alternating voltage of the three-level system; theta represents the initial phase angle of each phase; Δ i represents a theoretical current change amount in one sampling period; f represents the modulation ratio m and the voltage phase angle ω t under the SVPWM modulation strategyA current ripple factor of + θ.

3. The three-level design method based on the SVPWM modulation strategy under the current ripple method according to claim 1, wherein: the step of selecting the SVPWM modulation strategy in step S2 is as follows:

s21, according to the work index of the three-level system, the DC side voltage V_dcAc side voltage e and switch sampling period T_sCalculating a system modulation ratio m;

s22, calculating the maximum value f of the current ripple coefficient f of different SVPWM modulation strategies in each period under the modulation ratio m_max1、f_max2、f_max3、…、f_maxnN is the number of the types of the SVPWM modulation strategies;

s23, modulating f under different SVPWM_max1、f_max2、f_max3、…、f_maxnMultiplying by a switching frequency weight coefficient lambda to obtain lambda₁f_max1、λ₂f_max2、λ₃f_max3、…、λ₃f_maxn；

S24, comparison of λ f_maxSize, wherein λ f is selected_maxThe minimum corresponding modulation strategy is used as the modulation strategy of the three-level system.

4. The method according to claim 3, wherein in step S3, after the SVPWM modulation strategy is selected, the filter inductance parameter L is calculated according to the requirement of the three-level system index on the current ripple size, and the calculation formula is as follows:

wherein L is the filter inductance value, Ts is the system switch sampling period, V_dcIs the DC side voltage of a three-level system, △ i represents the theoretical current variation in one sampling period, f_maxRepresenting the maximum value of the current ripple factor f in each cycle.

5. The method according to claim 4, wherein in step S4, the theoretical maximum on-current of the switching device is calculated according to the selected SVPWM strategy and the designed filter inductance parameter L and the system index to obtain the theoretical maximum on-current I_maxThe calculation equation of (a) is:

wherein, I is the effective value of the conduction current of the three-level system; theta' is a corresponding phase angle when the current peak value is obtained; and selecting the current parameter of the switching device according to the calculated maximum conduction current value.

6. The three-level design method based on the SVPWM modulation strategy under the current ripple method according to any of claims 1-5, characterized by: the different SVPWM modulation strategies in step S1 adopt a four-region SVPWM modulation strategy, a six-region SVPWM modulation strategy, and a nine-segment SVPWM modulation strategy.

Technical Field

The invention belongs to the technical field of power electronic converters, and particularly relates to a three-level design method based on an SVPWM (space vector pulse width modulation) strategy under a current ripple method.

Background

In order to be matched with the new energy automobile for use, a series of electric automobile matching facilities are researched, developed and built. The direct current charging pile becomes the development direction of charging equipment by virtue of the rapid charging capability, and the T-shaped three-level system is used as a main high-power AC-DC converter system and is very important for the design and optimization of the three-level system.

The selection of the SVPWM modulation strategy in the traditional three-level system lacks of quantitative reference indexes, the design of the filter inductor is mainly based on an empirical formula, and the current-tolerant voltage-withstanding value of a switching device is determined by selecting margin. SVPWM is an abbreviation of Space Vector Pulse Width Modulation (Space Vector Pulse Width Modulation).

According to the traditional selection method of the SVPWM modulation strategy, when the transmission power of the converter is low, the influence of the inductance value and the parameter selection of the switching device on the system is small, but with the increase of the transmission power, the larger inductance means the larger volume and the loss of the filter, and the higher manufacturing cost is achieved by selecting the switching device with larger voltage resistance and current resistance. Therefore, according to the design index of the system, the system design can be quantified under the condition of meeting the requirements according to the current ripple method, and the product volume and the cost are reduced.

Disclosure of Invention

The technical purpose is as follows: in view of the above technical problems, the present invention provides a three-level design method based on an SVPWM modulation strategy under a current ripple method, which calculates current ripples under a three-level system with a determined working condition, so as to guide selection of a modulation strategy and selection of a filter inductor and a switching device, and can reduce the overall volume, working loss, and manufacturing cost of the system under the condition of meeting design indexes.

The technical scheme is as follows: in order to achieve the technical purpose, the invention adopts the following technical scheme:

a three-level design method based on an SVPWM (space vector pulse width modulation) strategy under a current ripple method is characterized by comprising the following steps: the method comprises the following steps:

s1, solving a current ripple equation of the three-level system about the modulation ratio and the voltage phase angle under different SVPWM modulation strategies by adopting a current ripple method;

s2, selecting an SVPWM (space vector pulse width modulation) strategy according to the working index according to a current ripple equation;

s3, designing filter inductance parameters of a three-level system according to the maximum value in the current ripple equation period;

and S4, designing the current parameters of the switching device according to the current ripple equation.

Preferably, in step S1, the current ripple equation is:

wherein L is filter inductance value, Ts is switch sampling period of three-level system, and V is_dcThe method comprises the steps of obtaining a direct current side voltage of a three-level system, obtaining a modulation ratio of the three-level system, obtaining an alternating current voltage angular velocity of the three-level system, representing initial phase angles of all phases by theta, representing theoretical current variation in one sampling period by △ i, and obtaining a direct current side voltage of the three-level system by f, representing modulation ratio m and voltage phase angle of the three-level system under the SVPWM modulation strategyCurrent ripple factor of (2).

Preferably, the step of selecting the SVPWM modulation scheme in step S2 is as follows:

s21, according to the work index of the three-level system, the DC side voltage V_dcAc side voltage e and switch sampling period T_sCalculating a system modulation ratio m;

s22, calculating the maximum value f of the current ripple coefficient f of different SVPWM modulation strategies in each period under the modulation ratio m_max1、f_max2、f_max3、…、f_maxnN is the number of the types of the SVPWM modulation strategies;

s23, modulating f under different SVPWM_max1、f_max2、f_max3、…、f_maxnMultiplying by a switching frequency weight coefficient lambda to obtain lambda₁f_max1、λ₂f_max2、λ₃f_max3、…、λ₃f_maxn；

S24, comparison of λ f_maxSize, wherein λ f is selected_maxThe minimum corresponding modulation strategy is used as the modulation strategy of the three-level system.

Preferably, in step S3, after the SVPWM modulation strategy is selected, the filter inductance parameter L is calculated according to the requirement of the three-level system index on the current ripple size, and the calculation formula is as follows:

wherein L is the filter inductance value, Ts is the system switch sampling period, V_dcIs the DC side voltage of a three-level system, △ i represents the theoretical current variation in one sampling period, f_maxRepresenting the maximum value of the current ripple factor f in each cycle.

Preferably, in step S4, according to the selected SVPWM modulation strategy and the designed filter inductance parameter L, the theoretical maximum on-current borne by the switching device is calculated according to the system index to obtain the theoretical maximum on-current I_maxThe calculation equation of (a) is:

wherein, I is the effective value of the conduction current of the three-level system;corresponding phase angle when the current is at the peak value; and selecting the current parameter of the switching device according to the calculated maximum conduction current value.

Preferably, the different SVPWM modulation strategies in step S1 adopt a four-region SVPWM modulation strategy, a six-region SVPWM modulation strategy and a nine-segment SVPWM modulation strategy.

Has the advantages that: due to the adoption of the technical scheme, the invention has the following technical effects:

(1) compared with the traditional design method, the system design is carried out according to the actual working condition of the three-level system, and the designed device parameters are more in line with the actual requirements;

(2) the invention can very conveniently and directly guide the design of the three-level system, and reduce the whole volume, the working loss and the manufacturing cost of the system under the condition of meeting the design index;

(3) the invention can quantitatively calculate the current ripple under the three-level system with the determined working condition so as to guide the selection of the modulation strategy and the selection of the filter inductor and the switching device;

(4) the method can be used for calculating the relevant parameters of the three-level system with the determined working index and can also be used for guiding the design of the working index of the three-level system in a reverse way.

Drawings

FIG. 1 is a table of the operation index of the T-type three-level system of the present invention;

FIG. 2 is a diagram of a T-type three-level system according to an embodiment of the present invention;

FIG. 3 is a graph comparing variation curves of the maximum value of the current ripple coefficient in one period with respect to the modulation ratio under different SVPWM modulation ratios according to the embodiment of the present invention;

fig. 4 is a graph of variation of current ripple coefficient function f with respect to ω t under the modulation of the conventional six-region SVPWM and nine-segment SVPWM at the modulation ratio of 0.78 according to the embodiment of the present invention;

FIG. 5 is a graph of current ripple factor versus modulation ratio at current set points and zero crossings according to an embodiment of the present invention;

fig. 6 shows a is a six-region SVPWM of the embodiment of the present invention, and b is a comparison graph of current ripples of nine-segment SVPWM modulation under the same parameters.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

The invention discloses a novel three-level design method based on an SVPWM (space vector pulse width modulation) strategy under a current ripple method, which comprises the following steps of:

s1, solving a current ripple equation of the three-level system about the modulation ratio and the voltage phase angle under different SVPWM modulation strategies by adopting a current ripple method;

s2, selecting an SVPWM (space vector pulse width modulation) strategy according to the working index according to a current ripple equation;

s3, designing filter inductance parameters of a three-level system according to the maximum value in the current ripple equation period;

and S4, designing parameters of the switching device according to the current ripple equation.

As shown in fig. 2, a T-type three-level system is taken as a specific embodiment, a topology structure of the three-level system includes three-phase bridge arms connected in parallel, each phase of bridge arm includes two IGBT tubes connected in series, one side of a midpoint of each phase of bridge arm is connected to one end of each of the two IGBT tubes connected in series in different directions, the other side of each phase of bridge arm is connected to a power grid through a filter inductor, two capacitors are connected in series between dc buses, the midpoint of each capacitor is connected to the other end of each of the two IGBT tubes connected in series in different directions, and a positive dc bus and a negative dc bus are taken as a dc side of the.

The different SVPWM modulation strategies in step S1 adopt a four-region SVPWM modulation strategy, a six-region SVPWM modulation strategy, a nine-segment SVPWM modulation strategy, and the like. Taking the four-region SVPWM current ripple modulation strategy as an example, the process of calculating the current ripple equation is as follows:

s1.1, defining the voltage variation as △ v (t) as the instantaneous voltage v (t) and the average voltageA difference of (i.e.In an ideal situation, the resistance of the inductor is very small, and since the switching frequency is much greater than the fundamental frequency, the average voltage of the grid voltage is very close to the instantaneous voltage, so the current variation is mainly related to △ v (t), i.e.Wherein Ts is a switch sampling period of a three-level system, t is time, i is alternating current side current of the three-level system, △ i is theoretical current variation in one sampling period, namely the theoretical current variation in one sampling period;

s1.2, according to the definition of the current ripple, the current ripple can be obtainedThe expression is as follows:

where L represents the filter inductance value,representing the current equivalent value in the sampling period;

defining the peak value of current ripple within a sampling periodIs composed of

For phase a, the voltage v (t) is expressed as a three-level switching function:wherein S_a、S_bAnd S_cIs a three-phase switching variable; v_dcThe voltage is the direct current side voltage of a three-level system;

s1.3, according to the SVPWM modulation strategy, referring to a voltage V_refAnd the phase voltages may be expressed as follows:

the average voltage of phase a can be expressed as a dc voltage:

m is a modulation ratio, and the value range is 0 to 1.155;

s1.4, to facilitate region partitioning, the variables are transformed to αβ coordinate system, namely:

representing the initial phase angle of each phase;

the current ripple i (t) expression can be translated into:

the current ripple peak-to-peak value can be defined according to a three-level modulation strategy as a function f (m, ω t) related to the modulation ratio and the voltage phase angle, and the vector action time coefficient is four times the corresponding k value, so the equation of the current ripple peak-to-peak value with respect to the modulation ratio and the voltage phase angle is expressed as:

referring to fig. 3 to 6, taking phase a as an example, the operating parameters of the three-level system in table 1 show that the phase voltage of the system a is e_a311cos ω tV, the voltage phase angle is ω t, the commonly used traditional four-region SVPWM modulation strategy, six-region SVPWM modulation strategy and nine-segment SVPWM modulation strategy are respectively selected, and the corresponding three-level system global current ripple equation under the three SVPWM modulation methods according to the current ripple method is

Maximum value f of current ripple coefficient f under three SVPWM (space vector pulse width modulation) in one period_maxThe curve for the modulation ratio is shown in fig. 4. The DC side voltage is 800V, and the modulation ratio can be calculated to be equal to 0.78, at which time, as can be seen from FIG. 3, the four-region SVPWM modulation f_max10.27 six-region SVPWM modulation strategy f_max20.22 nine-segment SVPWM modulation strategy f_max3＝0.143；

And multiplying the current ripple by a switching frequency weight coefficient lambda respectively, namely comparing the current ripple size under the same switching frequency. λ is related to the number of switching actions in one sampling period. Taking the modulation strategy with the lowest switching action times as reference, and taking the lambda as the seven-segment expression, wherein the switching times of the four-region and six-region actions in the three modulation strategies are 7 times as the lowest, and₁＝1、λ₂the number of switching operations in one sampling period is 9 as 1, i.e. nine stages, so λ₃9/7. The following can be obtained: lambda [ alpha ]₁f_max1＝1×0.27＝0.27、λ₂f_max2＝1×0.22＝0.22、λ₃f_max3× 0.143.143 (9/7) ═ 0.1838, and comparison shows λ₃f_max3And the minimum value is needed, so the adjustment strategy selects nine-segment SVPWM.

According to the requirement of working parameters of a three-level system, the theoretical calculation value of the inductance value under the nine-segment SVPWM modulation strategy is as follows:

under the nine-segment SVPWM modulation strategy, the A-phase current reaches the maximum value when ω t is 0, and the current ripple coefficient f is 0.09 at the moment, so that the maximum on-state current of the switching device in the working theory is as follows:

and then, selecting parameters of a switching device such as an IGBT (insulated gate bipolar transistor) tube according to the calculated maximum conduction current, so that the finally determined parameters of the switching device meet the actual requirements, the design efficiency is improved, the debugging cost is reduced and the like.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.