CN102545665B - Three-level PWM (Pulse-Width Modulation) rectifier direct power control method - Google Patents

Abstract

The invention discloses a three-level PWM (Pulse-Width Modulation) rectifier direct power control method, which comprises the following steps of: deducing an instantaneous power control model of a rectifier by utilizing a high frequency mathematical model and an instantaneous power theory of the three-level rectifier; substituting basic vectors corresponding to 27 groups of switch statuses of a three-level converter into the instantaneous power control model, and carrying out normalization to obtain formulas of active power variation rate and reactive power variation rate under the action of the basic vectors; calculating the active power variation rate and the reactive power variation rate corresponding to each basic vector in a whole vector space, and classifying basic vectors according to the types of the vectors, the active and the reactive power variation trends and the variation rates; and quantizing the reactive power variation rate needed to be tracked into two levels, quantizing the active power variation rate into four levels, and building a switch list controlled by rectifier direct power. The method can realize network side unit power factors, quickly stabilize direct current bus voltage and balanced midpoint potential, and is more effective for fast tracking the instantaneous active power and reactive power.

Description

A kind of three-level PWM rectifier direct Power Control method

Technical field

The present invention relates to the convertor controls field of a kind of power electronics and electric drive, particularly a kind of three level pulse widths modulation (Pulse Width Modulation, PWM) rectifier direct Power Control methods.

Background technology

In the high-power application scenario, be subject to the restriction of switching device power grade, two traditional level rectifiers can not meet the demands, and diode clamp formula (Neutral Point Clamped, NPC) three-level PWM rectifier not only can realize that energy in bidirectional flow, power factor are controlled, but also there is the advantages such as the switching device pressure-bearing is low, switching frequency is low, Harmonics of Input content is few, make it at engineering field, obtain application more and more widely.

Traditional NPC three-level PWM rectifier is the synthetic control method of space voltage vector adopted based on the line voltage orientation, need Rotating Transition of Coordinate, a plurality of pi regulator and complicated modulation strategy, and direct Power Control (Direct Power Control, DPC) do not need Rotating Transition of Coordinate and modulation strategy, through the stagnant chain rate of overpower, directly from switch list, select suitable space voltage vector to realize the control to active power and reactive power.Therefore, DPC has control structure and control algolithm is simple, and the system dynamic response is faster, the advantages such as efficiency is high, strong robustness.

In DPC, the quality of switch list directly affects the control performance of whole system, and the building way of multiple switch list is arranged at present: by analyzing the relation of electric current and space voltage vector and power; From the angle of power conservation, three-level PWM rectifier is carried out to modeling analysis; The relation of meritorious with input in conjunction with instantaneous power theory qualitative analysis voltage vector on the basis of rectifier Mathematical Modeling, reactive power; By a kind of optimal vector Universal Criterion based on DPC, select suitable voltage vector to realize control of active power and reactive power etc.Simultaneously, in NPC three-level converter topological structure, the imbalance of DC bus capacitor midpoint potential is its intrinsic problem, and the midpoint potential imbalance can cause single tube to bear too high voltage, in serious situation, can cause system unstable, controls unsuccessfully.Therefore, must take into account the balance of DC side midpoint potential in the foundation of switch list.But, numerous three level rectifier DPC all adopt qualitative analysis in the switch list design process, be not given in the concrete influence degree of each space voltage vector to active power and reactive power in each sector, make switch list poor effect in the control to power of traditional design.How to build and to optimize the key that suitable switch list is three level rectifier direct Power Control systems.

Summary of the invention

Technical problem underlying to be solved by this invention is, overcome the above-mentioned defect that prior art exists, and provide a kind of control system structure and control algolithm simple, the three-level PWM rectifier direct Power Control method that dynamic response is fast, further to strengthen the control to NPC three-level PWM rectifier instantaneous active power and reactive power, the present invention's power new at rectifier is controlled on the model basis method for designing that has proposed a kind of new direct Power Control switch list, newly-designed switch list not only can be realized net side unity power factor, fast and stable DC bus-bar voltage and balance midpoint potential, and more effective to the quick tracking of instantaneous active power and reactive power.

The technical solution adopted for the present invention to solve the technical problems is:

The instantaneous power of utilizing the instantaneous power theory of the high frequency Mathematical Modeling of NPC three-level PWM rectifier and three-phase circuit to derive rectifier is controlled model, according to inputting the quantitative relationship of active power, reactive power and 27 basic vectors in each sector of this model analysis, and then set up the switch list of rectifier direct Power Control, the method comprises the following steps:

The first step: utilize switch function and Kirchhoff's second law, set up the Mathematical Modeling under diode clamp formula three level voltage type PWM rectifier net side α β rest frames, ignore net side line road resistance, within the sampling period, to above-mentioned Mathematical Modeling discretization, the expression formula that obtains curent change is as follows:

$\left\{\begin{array}{c}{\mathrm{\Δi}}_{\mathrm{\α}}=i_{\mathrm{\α}}\left(k\right)-i_{\mathrm{\α}}(k-1)=\frac{T_s}{L}[e_{\mathrm{\α}}\left(k\right)-u_{\mathrm{\α}}\left(k\right)]\\ {\mathrm{\Δi}}_{\mathrm{\β}}=i_{\mathrm{\β}}\left(k\right)-i_{\mathrm{\β}}(k-1)=\frac{T_s}{L}[e_{\mathrm{\β}}\left(k\right)-u_{\mathrm{\β}}\left(k\right)]\end{array}\right.$

Wherein, u _α, u _β, i _α, i _β, e _α, e _βbe respectively α, the beta-axis component of rectifier input terminal voltage, rectifier input electric current and line voltage; Δ i _α, Δ i _βfor the input current variable quantity; T _sfor the sampling period; The inductance value that L is reactor; K means sampling instant;

Second step: under α β rest frame, by instantaneous power discretization within the sampling period of electrical network transmission, and, the current expression substitution of discretization, the instantaneous power that obtains rectifier is controlled model;

$\left\{\begin{array}{c}\mathrm{\Δp}=\frac{T_S}{L}[{e_{\mathrm{\α}}}^2\left(k\right)+{e_{\mathrm{\β}}}^2\left(k\right)-e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\α}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\β}}\left(k\right)]\\ \mathrm{\Δq}=\frac{T_S}{L}[e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\β}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\α}}\left(k\right)]\end{array}\right.$

The 3rd step: 27 groups of on off states for three-level converter obtain 27 basic vector v _i, its substitution instantaneous power is controlled to model, and carry out normalization, obtain

$\left\{\begin{array}{c}\stackrel{\‾}{{\mathrm{\Δp}}_i}=\sqrt{\frac{3}{2}}\frac{\left|\right|e_{\mathrm{\α\β}}\left|\right|}{U_{\mathrm{dc}}}-(\stackrel{\‾}{u_{\mathrm{\αi}}}\·\cos \mathrm{\θ}+\stackrel{\‾}{u_{\mathrm{\βi}}}\·\sin \mathrm{\θ})\\ \stackrel{\‾}{{\mathrm{\Δq}}_i}=\stackrel{\‾}{u_{\mathrm{\βi}}}\·\cos \mathrm{\θ}-\stackrel{\‾}{u_{\mathrm{\αi}}}\·\sin \mathrm{\θ}\end{array}\right.,$ i＝1，2，......，27

Wherein,

u _{α i}and u _{β i}for v _icomponent under α β coordinate system; || v _i|| _maxfor v _imaximum norm long; || e _{α β}|| be the effective value of grid line voltage; U _dcfor the DC bus total voltage; The position angle that θ is the line voltage space vector;

with

for basic vector v _ithe lower meritorious and idle rate of change of effect;

The 4th step: when calculating θ and changing in 0～360 degree scope, each v _icorresponding

with

value; By v _ibe divided into long vector, middle vector, small vector and zero vector four classes by length, according to the position of long vector and middle vector, whole polar plot be divided into to 12 sectors; The present invention according to

with

the variation tendency of value in each sector, sorted out long vector, middle vector, small vector and zero vector, of the same type in each vector meritorious and idle impact are arranged from big to small by rate of change, obtain in 12 sectors v _iright with affect big or small classification chart;

The 5th step: the present invention will need the reactive power variation of following the tracks of to be quantized into two grade S through stagnant chain rate _q=1,0, mean respectively to need to increase or reduce reactive power; The active power variable quantity changes into four grade S _p=2,1,0 ,-1, mean that respectively the load needs of uprushing increase fast active power, needs and increase increase and decrease, the needs minimizing active power that active power, active power change major control reactive power in little situation; For S _pand S _q8 kinds of combinations, select suitable v the classification chart obtained from the 4th step _i, obtain the switch list of three-level PWM rectifier direct Power Control;

The 6th step: the actual measured value of active power, reactive power and the error of reference value are quantized into S through stagnant chain rate after _pand S _qsignal, they and sector signals Ф _ilook into together switch list; When realizing that power is controlled more than one of the basic vector of target, utilize the small vector that midpoint potential information S and line current Information Selection wherein can the balance midpoint potential; Thereby obtain rectifier perfect switch S _a1～S _a4, S _b1～S _b4, S _c1～S _c4pwm control signal, finally realize the direct Power Control of three-level PWM rectifier.

The invention has the beneficial effects as follows, the present invention controls the suitable basic vector of Model Selection according to the discretization instantaneous power of three level rectifiers and reaches the effective control to instantaneous active power and reactive power, by the multi-stage quantization to power ring, sets up corresponding direct power control switching table.Than existing switch list method for building up, method of the present invention can embody the concrete influence degree of different basic vectors to instantaneous power in each sector, can follow the tracks of fast uprushing of load, eliminates the idle uncontrollable zone in conventional method.The method for building up of this switch list, the switch list that also can be applicable to other multi-level rectifier direct Power Control is set up, and is beneficial to and analyzes and expand application.

The accompanying drawing explanation

Below in conjunction with drawings and Examples, the present invention is further described.

Fig. 1 is NPC three-level PWM rectifier main circuit topology figure of the present invention

Fig. 2 is three-level converter basic vector figure of the present invention

Fig. 3 a is basic vector of the present invention and instantaneous active power variation relation figure

Fig. 3 b is basic vector of the present invention and instantaneous reactive power variation relation figure

Fig. 4 is the present invention's three level rectifier direct Power Control system block diagrams

Embodiment

Although the switch list direct Power Control method of three-level PWM rectifier based on the line voltage orientation needs higher sample frequency, but it does not need Rotating Transition of Coordinate and modulation strategy, according to stagnant chain rate result directly from switch list, select suitable basic vector effectively to control the variation of instantaneous active power and reactive power, control algolithm and control structure are simple, dynamic response is fast, strong robustness.Its switch list is to control on the basis of model in the discretization instantaneous power of rectifier, by analyzing, in each sector, each vows the concrete influence degree to instantaneous power substantially, the stagnant ring of power is carried out to multi-stage quantization, take into account that DC side midpoint potential balance is controlled simultaneously and set up.

Implementation procedure of the present invention is as follows:

Fig. 1 is NPC three-level PWM rectifier main circuit diagram of the present invention.

In figure, three brachium pontis are by the perfect switch S of anti-paralleled diode _a1～S _a4, S _b1～S _b4, S _c1～S _c4form; e _a, e _b, e _cfor the electrical network three-phase voltage; L and R are respectively AC reactance and equivalent resistance; i _a, i _b, i _cfor the rectifier input current; u _a, u _b, u _cthe rectifier input voltage, U _dc1, U _dc2be respectively the upper and lower capacitance voltage of DC bus.Can obtain the Mathematical Modeling of rectifier net side part under α β coordinate system by deriving be:

$\left\{\begin{array}{c}\frac{{\mathrm{di}}_{\mathrm{\α}}}{\mathrm{dt}}=\frac{1}{L}(e_{\mathrm{\α}}-{\mathrm{Ri}}_{\mathrm{\α}}-u_{\mathrm{\α}})\\ \frac{{\mathrm{di}}_{\mathrm{\β}}}{\mathrm{dt}}=\frac{1}{L}(e_{\mathrm{\β}}-{\mathrm{Ri}}_{\mathrm{\β}}-u_{\mathrm{\β}})\end{array}\right.---\left(1\right)$

In formula, u _α, u _β, i _α, i _β, e _α, e _βbe respectively α, the beta-axis component of rectifier input terminal voltage, rectifier input electric current and line voltage; The inductance value that L is reactor.

Ignore net side line road resistance, within the sampling period, to above-mentioned Mathematical Modeling discretization, the expression formula that obtains curent change is as follows:

$\left\{\begin{array}{c}{\mathrm{\Δi}}_{\mathrm{\α}}=i_{\mathrm{\α}}\left(k\right)-i_{\mathrm{\α}}(k-1)=\frac{T_s}{L}[e_{\mathrm{\α}}\left(k\right)-u_{\mathrm{\α}}\left(k\right)]\\ {\mathrm{\Δi}}_{\mathrm{\β}}=i_{\mathrm{\β}}\left(k\right)-i_{\mathrm{\β}}(k-1)=\frac{T_s}{L}[e_{\mathrm{\β}}\left(k\right)-u_{\mathrm{\β}}\left(k\right)]\end{array}\right.---\left(2\right)$

Wherein, T _sfor the sampling period; K means sampling instant.

Above formula substitution instantaneous active power and reactive power, in the estimation formula in sampling period, can be obtained

$\left\{\begin{array}{c}\mathrm{\Δp}=\frac{T_S}{L}[{e_{\mathrm{\α}}}^2\left(k\right)+{e_{\mathrm{\β}}}^2\left(k\right)-e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\α}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\β}}\left(k\right)]\\ \mathrm{\Δq}=\frac{T_S}{L}[e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\β}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\α}}\left(k\right)]\end{array}\right.---\left(3\right)$

Fig. 2 is three-level converter basic vector figure of the present invention.

On the α β plane, have corresponding 27 the basic vector v of 27 groups of on off states ₁～v ₂₇.P means positive level, means that output is connected to the high level end of DC bus; O means zero level, means that output is connected to the mid point of DC bus; N means negative level, means that output is connected to the low level end of DC bus.The mould length of four class vector long vectors, middle vector, small vector and zero vector is respectively

with 0.Hence one can see that, within each sampling period, the instantaneous meritorious control with reactive power had to 27 kinds of selections:

$\left\{\begin{array}{c}\mathrm{\Δ}{p}_i=\frac{T_S}{L}[{e_{\mathrm{\α}}}^2\left(k\right)+{e_{\mathrm{\β}}}^2\left(k\right)-e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\αi}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\βi}}\left(k\right)]\\ \mathrm{\Δ}{q}_i=\frac{T_S}{L}[e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\βi}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\αi}}\left(k\right)]\end{array}\right.---\left(4\right)$

i＝1，…26，27.

Both sides are simultaneously divided by constant

obtain

$\left\{\begin{array}{c}\stackrel{\‾}{{\mathrm{\Δp}}_i}=\sqrt{\frac{3}{2}}\frac{\left|\right|e_{\mathrm{\α\β}}\left|\right|}{U_{\mathrm{dc}}}-(\stackrel{\‾}{u_{\mathrm{\αi}}}\·\cos \mathrm{\θ}+\stackrel{\‾}{u_{\mathrm{\βi}}}\·\sin \mathrm{\θ})\\ \stackrel{\‾}{{\mathrm{\Δq}}_i}=\stackrel{\‾}{u_{\mathrm{\βi}}}\·\cos \mathrm{\θ}-\stackrel{\‾}{u_{\mathrm{\αi}}}\·\sin \mathrm{\θ}\end{array}\right.,$ i＝1，2，......，27 (5)

Wherein,

u _{α i}and u _{β i}for v _icomponent under α β coordinate system; || v _i|| _maxfor v _ithe large mould of amount long; || e _{α β}|| be the effective value of grid line voltage; U _dcfor the DC bus total voltage; The position angle that θ is the line voltage space vector;

with

for by v _imeritorious and the idle rate of change produced.

Can find out different space vector v _iimpact in all sectors on the active power rate of change becomes sinusoidal distribution of offsets, and the impact of reactive power rate of change is become to Sine distribution, and the rate of change of its instantaneous active power, reactive power as shown in Figure 3 a, 3 b.

By Fig. 3 a, Fig. 3 b are known, in each sector, can on variation tendency and the size of meritorious and idle impact, select according to each vector.With sector Ф ₁for example, each vector is as shown in table 1 on the impact of meritorious and reactive power.Because vector is more, according to long vector, middle vector, small vector and zero vector, classified, of the same type in the rate of change of the meritorious and reactive power of each vector effect by arranging from big to small.

At sector Ф ₁in,

be quantized into four grade S through stagnant chain rate _p=2,1,0 ,-1;

be quantized into two grade S through stagnant chain rate _q=1,0.Wherein, S _p=-1 means to need to reduce active power; S _p=0 is illustrated in active power changes major control reactive power in little situation; S _p=1 means to need to increase active power; S _p=2 are illustrated in load increases the weight of to need to increase fast active power; S _q=0 means to need to reduce reactive power; S _q=1 means to need to increase reactive power.

Table 1 is sector Φ of the present invention ₁in each basic vector active power and reactive power affected to the magnitude classification table:

Table 1

With sector Φ ₁for example: work as S _p=-1, S _q, can only select vector v as known from Table 1 at=0 o'clock ₁; Work as S _p=-1, S _q, also can only select vector v at=1 o'clock ₂; Work as S _p, from Fig. 3 a and table 1, analyze known vector v at=0 o'clock ₃and v ₁₂in the situation that can effectively control idle increase and minimizing to meritorious impact is little; Work as S _p=1 or 2 while need increasing active power, and selective vector is numerous, for can better the balance midpoint potential, selects small vector as far as possible.

Table 2 is sector Ф of the present invention ₁the option table of vector:

Table 2

According to mentioned above principle, same analysis is done in all sectors, the switch list that can obtain the three level voltage type PWM rectifier direct Power Control based on the line voltage orientation is as shown in table 3.Wherein, the integer that k is 2～4.

Table 3 is the present invention's three level rectifier direct Power Control switch lists:

Table 3

Equally, according to table 3, come the control change device obviously can't avoid the too high saltus step of voltage magnitude.For example, in the first sector, if current vector is v ₁₂, and wait that sending out vector is v ₃, directly select v ₃can cause the direct saltus step of b phase phase voltage from n to p.Therefore, waiting to send out vector v ₃insert a vector v before ₂₆, at next cycle, nature can be switched to v ₃, similar for other situation.

Analysis to vector is known, only has middle vector small vector can affect the balance of midpoint potential.There is redundant state in identical small vector, although they are identical on meritorious and idle impact, the impact of alignment current potential is just contrary.Therefore, in the design of switch list, the choose reasonable small vector can not only effectively be controlled active power and reactive power, can also effectively suppress mid-point potential offset.

Table 4 is first sector Φ of balance midpoint potential of the present invention ₁option table:

Table 4

Wherein S reflects midpoint potential information, and the voltage difference that its value is upper and lower electric capacity is quantized into 1 and 0 by hysteresis comparator, means that respectively midpoint potential is too high and too low.

Fig. 4 is three-level PWM rectifier DPC control system block diagram of the present invention.

By the upper and lower electric capacity voltage sample of DC bus is obtained to midpoint potential information S and bus total voltage U _dc, U _dcwith its set-point U _{dc_ref}error obtain meritorious reference current through pi regulator, it and DC bus-bar voltage U _dcproduct as the reference value p of active power _ref, for making power factor, be unit 1, idle reference value q _refbe zero.Meritorious, the actual measured value of reactive power and the error of reference value are quantized into switching signal S after stagnant ring _pand S _q, they and midpoint potential information S, sector number Φ _i, line current information forms five signals and tabled look-up, thereby obtain the perfect switch S on three brachium pontis of rectifier _a1～S _a4, S _b1～S _b4, S _c1～S _c4switching signal.

The above, it is only preferred embodiment of the present invention, not the present invention is done to any pro forma restriction, any simple modification, equivalent variations and modification that every foundation technical spirit of the present invention is done above embodiment, all still belong in the scope of technical solution of the present invention.

In sum, the present invention is on structural design, use practicality and cost benefit, meet industry development fully required, and the structure disclosed is also to have unprecedented innovative structure, there is novelty, creativeness, practicality, the regulation that meets relevant patent of invention important document, therefore mention application in accordance with the law.

Claims (1)

1. a three-level PWM rectifier direct Power Control method, comprise voltage on line side current sample, the upper and lower electric capacity voltage sample of DC bus, the stagnant chain rate of capacitance voltage, the stagnant chain rate of power, power and sector number calculates and switching algorithm is realized, it is characterized in that the Design and implementation of switching algorithm, comprise the following steps;

The first step: utilize switch function and Kirchhoff's second law, set up the Mathematical Modeling under diode clamp formula three level voltage type PWM rectifier net side α β rest frames, ignore net side line road resistance, within the sampling period, to above-mentioned Mathematical Modeling discretization, the expression formula that obtains curent change is as follows:

$\left\{\begin{array}{c}{\mathrm{\Δi}}_{\mathrm{\α}}=i_{\mathrm{\α}}\left(k\right)-i_{\mathrm{\α}}(k-1)=\frac{T_s}{L}[e_{\mathrm{\α}}\left(k\right)-u_{\mathrm{\α}}\left(k\right)]\\ {\mathrm{\Δi}}_{\mathrm{\β}}=i_{\mathrm{\β}}\left(k\right)-i_{\mathrm{\β}}(k-1)=\frac{T_s}{L}[e_{\mathrm{\β}}\left(k\right)-u_{\mathrm{\β}}\left(k\right)]\end{array}\right.$

Wherein, u _α, u _β, i _α, i _β, e _α, e _βbe respectively α, the beta-axis component of rectifier input terminal voltage, rectifier input electric current and line voltage; Δ i _α, Δ i _βfor the input current variable quantity; T _sfor the sampling period; The inductance value that L is reactor; K means sampling instant;

Second step: under α β rest frame, by instantaneous power discretization within the sampling period of electrical network transmission, and, the current expression substitution of discretization, the instantaneous power that obtains rectifier is controlled model:

$\left\{\begin{array}{c}\mathrm{\Δp}=\frac{T_S}{L}[{e_{\mathrm{\α}}}^2\left(k\right)+{e_{\mathrm{\β}}}^2\left(k\right)-e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\α}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\β}}\left(k\right)]\\ \mathrm{\Δq}=\frac{T_S}{L}[e_{\mathrm{\α}}\left(k\right)\·u_{\mathrm{\β}}\left(k\right)-e_{\mathrm{\β}}\left(k\right)\·u_{\mathrm{\α}}\left(k\right)]\end{array}\right.$

The 3rd step: 27 groups of on off states for three-level converter obtain 27 basic vector v _i, its substitution instantaneous power is controlled to model, and carry out normalization, obtain

$\left\{\begin{array}{c}\stackrel{\‾}{{\mathrm{\Δp}}_i}=\sqrt{\frac{3}{2}}\frac{\left|\right|e_{\mathrm{\α\β}}\left|\right|}{U_{\mathrm{dc}}}-(\stackrel{\‾}{u_{\mathrm{\αi}}}\·\cos \mathrm{\θ}+\stackrel{\‾}{u_{\mathrm{\βi}}}\·\sin \mathrm{\θ})\\ \stackrel{\‾}{{\mathrm{\Δq}}_i}=\stackrel{\‾}{u_{\mathrm{\βi}}}\·\cos \mathrm{\θ}-\stackrel{\‾}{u_{\mathrm{\αi}}}\·\sin \mathrm{\θ}\end{array}\right.,$ i＝1，2，......，27

Wherein,

u _{α i}and u _{β i}for v _icomponent under α β coordinate system; || v _i|| _maxfor v _ithe large mould of amount long; || e _{α β}|| be the effective value of grid line voltage; U _dcfor the DC bus total voltage; The position angle that θ is the line voltage space vector; with

for basic vector v _ithe lower meritorious and idle rate of change of effect;

The 4th step: when calculating θ and changing in 0～360 degree scope, each v _icorresponding

with

value; By v _ibe divided into long vector, middle vector, small vector and zero vector four classes by length, according to the position of long vector and middle vector, whole polar plot be divided into to 12 sectors; The present invention according to with the variation tendency of value in each sector, sorted out long vector, middle vector, small vector and zero vector, of the same type in each vector meritorious and idle impact are arranged from big to small by rate of change, obtain in 12 sectors v _iright

with

affect big or small classification chart;

The 5th step: the present invention will need the reactive power variation of following the tracks of to be quantized into two grade S through stagnant chain rate _q=1,0, mean respectively to need to increase or reduce reactive power; The active power variable quantity changes into four grade S _p=2,1,0 ,-1, mean that respectively the load needs of uprushing increase fast active power, needs and increase increase and decrease, the needs minimizing active power that active power, active power change major control reactive power in little situation; For S _pand S _q8 kinds of combinations, select suitable v the classification chart obtained from the 4th step _i, obtain the switch list of three-level PWM rectifier direct Power Control;

The 6th step: the actual measured value of active power, reactive power and the error of reference value are quantized into S through stagnant chain rate after _pand S _qsignal, they and sector signals Ф _ilook into together switch list; When realizing that power is controlled more than one of the basic vector of target, utilize the wherein small vector of balance midpoint potential of midpoint potential information S and line current Information Selection; Thereby obtain rectifier perfect switch S _a1～S _a4, S _b1～S _b4, S _c1～S _c4pwm control signal, finally realize the direct Power Control of three-level PWM rectifier.

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