CN104113225A - SVPWM realization method for proportion-variable factor neutral-point balance control strategy - Google Patents

Abstract

The invention discloses an SVPWM realization method for a proportion-variable factor neutral-point balance control strategy. The method comprises steps that: step 1, positive and negative attributes of a small vector are determined according to a current direction; step 2, a proportion factor rou is calculated; step 3, positive small vector action time t+ and negative small vector action time t- are calculated according to the proportion factor rou acquired in the step 2; step 4, Tcmp1 of a triangular carrier wave at the first comparison time point during comparison is calculated; step 5, Tcmp2 and Tcmp3 of triangular carrier waves respectively at the second comparison time point and the third comparison time point are calculated according to a symmetric seven segment type vector modulation algorithm; and step 6, the triangular carrier waves at different comparison point times are compared to acquire a driving pulse of a three-level PWM rectifier switch tube. The method can effectively control a neutral-point voltage of a three-level PWM rectifier, so neutral-point voltage balance in dynamic processes of load switching and power source voltage fluctuation are maintained, and the three-level PWM rectifier is enabled to operate more stably and higher efficient.

Description

The SVPWM implementation method of control with changed scale factor neutral balance control strategy

Technical field

The present invention relates to operation and the control field of three-level pwm current transformer, be specifically related to the SVPWM implementation method of control with changed scale factor neutral balance control strategy.

Background technology

Diode clamp formula three-level PWM rectifier is applicable to the occasion that AC voltage is higher, capacity is larger, its each brachium pontis consists of four power switchs, therefore the voltage peak that each master power switch bears only has half of two level PWM rectifiers, can significantly improve the voltage withstand class of rectifier.And three-level PWM rectifier has 27 switching vector selectors, so it is not that very high situation also can guarantee the current waveform that net side is good at switching frequency, and its harmonic wave and aberration rate will be significantly smaller than two level PWM rectifiers.Yet, three-level converter circuit topological structure but has intrinsic mid point fluctuation problem, three-level PWM rectifier is when actual motion, because selection, action time or the power supply of switching vector selector, fluctuation of load etc. all can cause the fluctuation of mid-point voltage, when fluctuation surpasses permissible value, can worsen waveform quality and even damage device, therefore need alignment voltage to control to maintain balance.

As shown in Figure 1, traditional mid-point voltage control method generally adopts passive mid-point voltage control method to the topology of three-level PWM rectifier.At complex plane definition AC voltage vector, have

$V^{*}=\sqrt{\frac{2}{3}}(V_a+V_b{e}^{j\frac{2}{3}\mathrm{\π}}+V_c{e}^{-j\frac{2}{3}\mathrm{\π}})---\left(1\right)$

So can access 27 kinds of voltage vectors, as shown in Figure 2, according to the size of vector length, voltage vector is divided into 3 kinds of large vector, middle vector and small vectors.From accompanying drawing 2, whole space is divided into 6 large sectors by large vector, can be further subdivided into 6 little sectors, as shown in Figure 3 to each large sector again.

Traditional passive mid-point voltage control method can be divided into following 3 steps and complete:

The action time of the 1st step calculating voltage space vector;

In the time of in reference voltage vector drops on some sectors, there are 3 space vector of voltage to synthesize this reference voltage vector, are respectively t1, t2, t3 the action time that can obtain these 3 synthesized voltage vectors by the SVPWM algorithm of three level.

The 2nd step is calculated the comparison point time of triangular carrier comparison;

Drive pulse waveform is produced and adopts symmetrical seven segmentation Vector Modulation algorithms, and whole sector is divided into 7 sections action time, and be respectively the 1st period to the 7th period action time action time Central Symmetry.For the ease of follow-up triangular carrier comparison, the comparison point time of definition triangular carrier comparison is Tcmp1, Tcmp2, Tcmp3

$\left\{\begin{array}{c}\mathrm{Tcmp}1=\frac{1}{4}t1\\ \mathrm{Tcmp}2=\mathrm{Tcmp}1+\frac{1}{2}t2\\ \mathrm{Tcmp}3=\mathrm{Tcmp}2+\frac{1}{2}t3\end{array}\right..$

The 3rd step triangular carrier relatively produces driving pulse;

By comparison point time T cmp1, Tcmp2, Tcmp3, with the cycle, be Ts, the triangular wave that peak-to-peak value is Ts/2 compares, and finally obtains the driving pulse of three-level PWM rectifier switching tube, and schematic diagram relatively as shown in Figure 4.

By analyzing knownly on affecting the mid point fluctuating factor of three-level PWM rectifier, can affect neutral point voltage balance the action time of small vector, and each small vector is to there being 2 kinds of switching configurations, and definition makes u _dc1increase, u _dc2the small vector reducing is positive small vector, makes u _dc1reduce, u _dc2the small vector increasing is negative small vector, and the positive and negative attribute of small vector is determined by current on line side direction.In symmetrical seven segmentation Vector Modulation algorithms, 1 switching configuration that the voltage vector of the 1st section and the 7th section effect is a certain small vector, another switching configuration that the voltage vector of the 4th section of effect is this small vector, these of two switching configurations are positive small vector, another is negative small vector.Hence one can see that, and passive mid-point voltage control method has been fixed the action time of positive and negative small vector, do not accomplish dynamically to adjust according to mid-point voltage actual conditions, therefore can produce mid-point voltage unbalance.

Control with changed scale factor control method is according to the voltage extent of upper and lower two electric capacity of DC side, distributes in real time positive and negative small vector action time, thereby reaches the control object of DC side neutral balance.Scale factor calculation formula is

$\mathrm{\ρ}=\frac{u_{\mathrm{dc}1}-u_{\mathrm{dc}2}}{V}=\frac{\mathrm{\ΔV}}{V}---\left(3\right)$

Wherein, V is the maximum difference of DC side two electric capacity that obtain of expectation, when ρ is greater than 1, ρ is composed into 1, when ρ is less than-1, ρ is composed into-1, thereby just ρ has been limited in to [1,1].If the time of positive small vector effect is t _just, the time of negative small vector effect is t _negative, have

According to current mid-point voltage situation, can calculate scale factor ρ like this, then adjust the action time of positive and negative small vector according to formula (4), thereby reach the effect of controlling neutral point voltage balance.

Summary of the invention

In order to solve the deficiencies in the prior art, the present invention has designed the concrete methods of realizing that control with changed scale factor neutral balance control strategy is applied to three level SVPWM algorithms, can effectively control the mid-point voltage of three-level PWM rectifier, and in the dynamic processes such as load switching, mains fluctuations, can keep neutral point voltage balance, thereby make three-level PWM rectifier stable and high effective operation more.

Technical scheme of the present invention is: the SVPWM implementation method of control with changed scale factor neutral balance control strategy, comprises the following steps:

Step 1, according to the positive and negative attribute of sense of current judgement small vector;

Step 2, calculates scale factor ρ;

Step 3, the scale factor ρ that in foundation, step obtains, calculates positive small vector t action time _justwith negative small vector t action time _negative;

Step 4, calculates the 1st comparison point time T cmp1 of triangular carrier comparison;

Step 5, according to symmetrical seven segmentation Vector Modulation algorithms, calculates the 2nd and the 3rd comparison point time T cmp2 of triangular carrier, Tcmp3;

Step 6, is Ts by comparison point time T cmp1, Tcmp2, Tcmp3 with the cycle, and the triangular wave that peak-to-peak value is Ts/2 compares, and finally obtains the driving pulse of three-level PWM rectifier switching tube.

The SVPWM implementation method of described control with changed scale factor neutral balance control strategy, the positive and negative determined property method of described small vector is, establishes 6 small vectors in the space vector of voltage of three-level PWM rectifier and is respectively V ₀₁, V ₀₂, V ₀₃, V ₀₄, V ₀₅, V ₀₆, each small vector has 2 kinds of switching configurations, is distinguished respectively with subscript p and n, and the three-phase current of net side is i _a, i _b, i _c, as follows to the result judgement of the positive and negative attribute of small vector according to current on line side direction.

The SVPWM implementation method of described control with changed scale factor neutral balance control strategy, described scale factor ρ computational methods are to establish u _dc1for the both end voltage of electric capacity above in the DC side dividing potential drop electric capacity of three-level PWM rectifier, establish u _dc2for the both end voltage of electric capacity below in the dividing potential drop electric capacity of three-level PWM rectifier, V is the maximum difference of DC side two electric capacity that obtain of expectation, and the computing formula of scale factor ρ is

$\mathrm{\ρ}=\frac{u_{\mathrm{dc}1}-u_{\mathrm{dc}2}}{V}=\frac{\mathrm{\ΔV}}{V}$

When ρ is greater than 1, ρ is composed into 1, when ρ is less than-1, ρ is composed into-1, the span of described ρ is [1,1].

The SVPWM implementation method of described control with changed scale factor neutral balance control strategy, the method of the 1st comparison point time T cmp1 of described calculating triangular carrier comparison is, in voltage vector space, if 6 large sector labels are I-VI, little sector label in each large sector is 1-6, the positive and negative attribute of having judged small vector according to the sense of current, the distribution method of Tcmp1 is as follows.

The SVPWM implementation method of described control with changed scale factor neutral balance control strategy, is characterized in that, after obtaining Tcmp1, according to symmetrical seven segmentation Vector Modulation algorithms, can obtain Tcmp2 and Tcmp3

The present invention can effectively control the mid-point voltage of three-level PWM rectifier, and can keep neutral point voltage balance in the dynamic processes such as load switching, mains fluctuations, thereby makes three-level PWM rectifier stable and high effective operation more.

Accompanying drawing explanation

Fig. 1 is the topological diagram of three-level PWM rectifier.

Fig. 2 is the space voltage vector distribution map of three-level PWM rectifier.

Fig. 3 is little sector division figure.

Fig. 4 is that triangular carrier relatively produces driving pulse schematic diagram.

Fig. 5 is the mid-point voltage deviation schematic diagram under stable state while loading as 3.5kW.

Fig. 6 drops into the mid-point voltage deviation schematic diagram of load during moment.

Fig. 7 is the mid-point voltage deviation schematic diagram under stable state while loading as 10.5kW.

Embodiment

Below in conjunction with accompanying drawing, the present invention is elaborated.

With a simulation example, verify the validity of designed control algolithm, emulation topological diagram still as shown in Figure 1, comes from business simulation software PSCAD for the result of check algorithm correctness.In PSCAD, the unit of electric current and voltage is kV and kA, and the unit of power is MW.

In the circuit topology of emulation, three-phase power line voltage effective value is 381V, and DC side setting voltage is 700V, and the maximum difference V of DC side two electric capacity that expectation obtains is 2V, and mid-point voltage deviation is u _dc1-u _dc2.

When load is 3.5kW, under stable state, mid-point voltage deviation size as shown in Figure 5, can find out that mid-point voltage is balance under stable state, in be controlled at ± 1V of error.

Rectifier initial load is 3.5kW, when 0.4s, drop into the load of 7kW, drop into the mid-point voltage deviation size of moment as shown in Figure 6, finishing load and entering mid-point voltage deviation size after stable state as shown in Figure 7, can find out to throw load moment and finish the rear mid-point voltage of load and still keep balance, because load becomes large, mid-point voltage deviation is slightly become greatly, but in still remain on ± 2V.

By above simulation result, can find out, when control with changed scale factor neutral balance control strategy is applied to after SVPWM algorithm, can effectively control the mid-point voltage of three-level PWM rectifier, and in the dynamic processes such as load switching, can keep neutral point voltage balance, thereby verify the validity of designed control algolithm.

More than show and described basic principle of the present invention and principal character and advantage of the present invention.The technical staff of the industry should understand; the present invention is not restricted to the described embodiments; that in above-described embodiment and specification, describes just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.The claimed scope of the present invention is defined by appending claims and equivalent thereof.

Claims (5)

1. the SVPWM implementation method of control with changed scale factor neutral balance control strategy, is characterized in that, comprises the following steps:

Step 1, according to the positive and negative attribute of sense of current judgement small vector;

Step 2, calculates scale factor ρ;

Step 3, the scale factor ρ that in foundation, step obtains, calculates positive small vector t action time _justwith negative small vector t action time _negative;

Step 4, calculates the 1st comparison point time T cmp1 of triangular carrier comparison;

Step 5, according to symmetrical seven segmentation Vector Modulation algorithms, calculates the 2nd and the 3rd comparison point time T cmp2 of triangular carrier, Tcmp3;

Step 6, is Ts by comparison point time T cmp1, Tcmp2, Tcmp3 with the cycle, and the triangular wave that peak-to-peak value is Ts/2 compares, and finally obtains the driving pulse of three-level PWM rectifier switching tube.

2. the SVPWM implementation method of control with changed scale factor neutral balance control strategy according to claim 1, is characterized in that, the positive and negative determined property method of described small vector is, establishes 6 small vectors in the space vector of voltage of three-level PWM rectifier and is respectively V ₀₁, V ₀₂, V ₀₃, V ₀₄, V ₀₅, V ₀₆, each small vector has 2 kinds of switching configurations, is distinguished respectively with subscript p and n, and the three-phase current of net side is i _a, i _b, i _c, as follows to the result judgement of the positive and negative attribute of small vector according to current on line side direction.

3. the SVPWM implementation method of control with changed scale factor neutral balance control strategy according to claim 1, is characterized in that, described scale factor ρ computational methods are to establish u _dc1for the both end voltage of electric capacity above in the DC side dividing potential drop electric capacity of three-level PWM rectifier, establish u _dc2for the both end voltage of electric capacity below in the dividing potential drop electric capacity of three-level PWM rectifier, V is the maximum difference of DC side two electric capacity that obtain of expectation, and the computing formula of scale factor ρ is

$\mathrm{\ρ}=\frac{u_{\mathrm{dc}1}-u_{\mathrm{dc}2}}{V}=\frac{\mathrm{\ΔV}}{V}$

When ρ is greater than 1, ρ is composed into 1, when ρ is less than-1, ρ is composed into-1, the span of described ρ is [1,1].

4. the SVPWM implementation method of control with changed scale factor neutral balance control strategy according to claim 1, it is characterized in that, the method of the 1st comparison point time T cmp1 of described calculating triangular carrier comparison is, in voltage vector space, if 6 large sector labels are I-VI, little sector label in each large sector is 1-6, has judged the positive and negative attribute of small vector according to the sense of current, and the distribution method of Tcmp1 is as follows.

5. the SVPWM implementation method of control with changed scale factor neutral balance control strategy according to claim 1, is characterized in that, after obtaining Tcmp1, according to symmetrical seven segmentation Vector Modulation algorithms, can obtain Tcmp2 and Tcmp3