CN102545665A - 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, the particularly a kind of modulation of three level pulse widths (Pulse Width Modulation, PWM) rectifier direct Power Control method.

Background technology

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

Traditional NPC three-level PWM rectifier is to adopt based on the directed synthetic control method of space voltage vector of line voltage; 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, stagnating through overpower, chain rate is direct selects suitable space voltage vector to realize the control to active power and reactive power from switch list.Therefore, DPC has control structure and control algolithm is simple, and the system dynamics response is faster, advantages such as efficient is high, strong robustness.

In DPC, the quality of switch list directly influences the control performance of whole system, and the approach of setting up of multiple switch list is arranged at present: through 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 modeling analysis; On the basis of rectifier Mathematical Modeling, combine instantaneous power theory qualitative analysis voltage vector and import relation meritorious, reactive power; Select the suitable voltage vector realization active power and the control of reactive power etc. through the general criterion of a kind of optimal vector based on DPC.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, can cause system unstable under the serious situation, the control failure.Therefore, in the foundation of switch list, must take into account the balance of DC side midpoint potential.But; Numerous three level rectifier DPC all adopt qualitative analysis in the switch list design process; Be not given in each sector each space voltage vector to the concrete influence degree of active power and reactive power, make switch list poor effect on of traditional design the control of power.How to make up and optimize the key that suitable switch list is three level rectifier direct Power Control system designs.

Summary of the invention

Technical problem underlying to be solved by this invention is; Overcome the above-mentioned defective that prior art exists; And a kind of control system structure and control algolithm is simple, dynamic response is fast three-level PWM rectifier direct Power Control method are provided; With the control of further enhancing to NPC three-level PWM rectifier instantaneous active power and reactive power; The present invention has proposed a kind of method for designing of new direct Power Control switch list on the new power controlling models basis of rectifier; Newly-designed switch list not only can realize netting the side unity power factor, fast and stable DC bus-bar voltage and balance midpoint potential, and also 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:

Utilize the instantaneous power theory of high frequency Mathematical Modeling and the three-phase circuit of NPC three-level PWM rectifier to derive the instantaneous power controlling models of rectifier; According to the quantitative relationship of importing 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, this method comprises the following steps:

The first step: utilize switch function and Kirchhoff's second law; Set up the Mathematical Modeling under the diode clamp formula three level voltage type PWM rectifier net side α β rest frames; Ignore net side line road resistance; To above-mentioned Mathematical Modeling discretization, the expression formula that obtains the electric current variation is following in the sampling period:

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

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 _βBe the input current variable quantity; T _sBe the sampling period; L is the inductance value of reactor; K representes sampling instant;

Second step: under α β rest frame,, and, obtain the instantaneous power controlling models of rectifier the current expression substitution of discretization with instantaneous power discretization in the sampling period of electrical network transmission;

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

The 3rd step: 27 groups of on off states to three-level converter obtain 27 basic vector v _i, with its substitution instantaneous power controlling models, 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}Be v _iComponent under α β coordinate system; || v _i|| _MaxBe v _iMaximum norm long; || e _{α β}|| be the effective value of grid line voltage; U _DcBe the dc bus total voltage; θ is the position angle of line voltage space vector;

With

Be basic vector v _iThe meritorious down and idle rate of change of effect;

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

Value; With v _iBe divided into four types of long vector, middle vector, small vector and zero vectors by length, whole polar plot be divided into 12 sectors according to the position of long vector and middle vector; 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 arrange from big to small by rate of change with idle influence meritorious, obtain in 12 sectors v _iRight

With

The classification chart of influence size;

The 5th step: the reactive power that the present invention will follow the tracks of changes through the chain rate that stagnates and is quantized into two grade S _q=1,0, expression needs to increase or reduce reactive power respectively; The active power variable quantity changes into four grade S _p=2,1,0 ,-1, represent 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 under the little situation; To S _pAnd S _q8 kinds of combinations, from the 4th classification chart that obtain of step, select suitable v _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 switch list together; When more than one of the basic vector of realizing the power controlled 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 selects suitable basic vector to reach the effective control to instantaneous active power and reactive power according to the discretization instantaneous power controlling models of three level rectifiers, through the multi-stage quantization of power ring being set up corresponding direct power control switching table.Than existing switch list method for building up, method of the present invention can embody in each sector different basic vectors can follow the tracks of uprushing of load fast to the concrete influence degree of instantaneous power, eliminates the idle uncontrollable zone in the 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 analyze and expand and use.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention is further specified.

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

Though three-level PWM rectifier needs higher sample frequency based on the directed switch list direct Power Control method of line voltage; But it does not need Rotating Transition of Coordinate and modulation strategy; Chain rate directly selects suitable basic vector effectively to control the variation of instantaneous active power and reactive power from switch list than the result according to stagnating; Control algolithm and control structure are simple, and dynamic response is fast, strong robustness.Its switch list is on the basis of the discretization instantaneous power controlling models of rectifier; Through analyze in each sector each basically arrow to the concrete influence degree of instantaneous power; The stagnant ring of power is carried out multi-stage quantization, take into account DC side midpoint potential Balance Control simultaneously and set up.

Implementation procedure of the present invention is following:

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

Three brachium pontis are by the perfect switch S of inverse parallel diode among the figure _A1～S _A4, S _B1～S _B4, S _C1～S _C4Constitute; e _a, e _b, e _cBe the electrical network three-phase voltage; L and R are respectively AC side reactance and equivalent resistance; i _a, i _b, i _cBe the rectifier input current; u _a, u _b, u _cBe the rectifier input voltage, U _Dc1, U _Dc2Be respectively dc bus capacitance voltage up and down.Can get the Mathematical Modeling of rectifier net side sections under α β coordinate system through deriving is:

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

In the 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; L is the inductance value of reactor.

Ignore net side line road resistance, to above-mentioned Mathematical Modeling discretization, the expression formula that obtains the electric current variation is following in the sampling period:

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

Wherein, T _sBe the sampling period; K representes sampling instant.

Following 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 βPing Mian, have corresponding 27 the basic vector v of 27 groups of on off states ₁～v ₂₇P representes positive level, and the expression output is connected to the high level end of dc bus; O representes zero level, and the expression output is connected to the mid point of dc bus; N representes negative level, and the expression output is connected to the low level end of dc bus.The mould length of four types of vector long vectors, middle vector, small vector and zero vectors is respectively

and 0.Hence one can see that, in each sampling period, instantaneous meritorious control with reactive power had 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 obtain divided by constant

simultaneously

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

Wherein,

u _{α i}And u _{β i}Be v _iComponent under α β coordinate system; || v _i|| _MaxBe v _iThe big mould of amount long; || e _{α β}|| be the effective value of grid line voltage; U _DcBe the dc bus total voltage; θ is the position angle of line voltage space vector; With

For by v _iMeritorious and the idle rate of change that are produced.

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

Can know in each sector and can select the variation tendency and the size of meritorious and idle influence by Fig. 3 a, Fig. 3 b based on each vector.With sector Ф ₁Be example, each vector is as shown in table 1 to meritorious influence with reactive power.Because vector is more, classify according to long vector, middle vector, small vector and zero vector, of the same type in the meritorious rate of change with reactive power of each vector effect by arranging from big to small.

The Ф in the sector ₁In, Chain rate is quantized into four grade S through stagnating _p=2,1,0 ,-1; Chain rate is quantized into two grade S through stagnating _q=1,0.Wherein, S _p=-1 expression needs to reduce active power; S _p=0 is illustrated in active power changes major control reactive power under the little situation; S _p=1 expression needs to increase active power; S _p=2 are illustrated in load needs to increase the weight of to increase fast active power; S _q=0 expression needs to reduce reactive power; S _q=1 expression needs to increase reactive power.

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

Table 1

With sector Φ ₁Be example: work as S _p=-1, S _q=0 o'clock, can know from table 1 and can only select vector v ₁Work as S _p=-1, S _q, also can only select vector v at=1 o'clock ₂Work as S _p, can know vector v at=0 o'clock from Fig. 3 a and table 1 analysis ₃And v ₁₂Under to the little situation of meritorious influence, can control idle increase and minimizing effectively; Work as S _p=1 or 2 when 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, can obtain based on the switch list of three directed level voltage type PWM rectifier direct Power Control of line voltage as shown in table 3.Wherein, k is 2～4 integer.

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

Table 3

Equally, come the control change device obviously can't avoid the too high saltus step of voltage magnitude according to table 3.For example in 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 switch to v ₃, similar for other situation.

Analysis to vector can know to have only middle vector and small vector can influence the balance of midpoint potential.There is redundant state in identical small vector, though they are identical to meritorious and idle influence, the influence of alignment current potential is just opposite.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 suppress mid-point potential offset effectively.

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 its value is that the voltage difference of electric capacity up and down is quantized into 1 and 0 by hysteresis comparator, representes that respectively midpoint potential is too high and low excessively.

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

Through electric capacity voltage sample about the dc bus is obtained 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, be unit 1 for making power factor, idle reference value q _RefBe zero.After encircling through stagnating, the actual measured value of meritorious, reactive power and the error of reference value be quantized into switching signal S _pAnd S _q, they and midpoint potential information S, sector number Φ _i, line current information forms five signals and tables 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 only is preferred embodiment of the present invention; Be not that the present invention is done any pro forma restriction, every foundation technical spirit of the present invention all still belongs in the scope of technical scheme of the present invention any simple modification, equivalent variations and modification that above embodiment did.

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

Claims (1)

1. three-level PWM rectifier direct Power Control method; Comprise voltage on line side current sample, dc bus up and down electric capacity voltage sample, capacitance voltage stagnate chain rate, power stagnate chain rate, power and sector number calculates and switching algorithm is realized; It is characterized in that the design and the realization of switching algorithm, may further comprise the steps;

The first step: utilize switch function and Kirchhoff's second law; Set up the Mathematical Modeling under the diode clamp formula three level voltage type PWM rectifier net side α β rest frames; Ignore net side line road resistance; To above-mentioned Mathematical Modeling discretization, the expression formula that obtains the electric current variation is following in the sampling period:

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

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 _βBe the input current variable quantity; T _sBe the sampling period; L is the inductance value of reactor; K representes sampling instant;

Second step: under α β rest frame,, and, obtain the instantaneous power controlling models of rectifier the current expression substitution of discretization with instantaneous power discretization in the sampling period of electrical network transmission:

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

The 3rd step: 27 groups of on off states to three-level converter obtain 27 basic vector v _i, with its substitution instantaneous power controlling models, 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}Be v _iComponent under α β coordinate system; || v _i|| _MaxBe v _iThe big mould of amount long; || e _{α β}|| be the effective value of grid line voltage; U _DcBe the dc bus total voltage; θ is the position angle of line voltage space vector;

With

Be basic vector v _iThe meritorious down and idle rate of change of effect;

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

With

Value; With v _iBe divided into four types of long vector, middle vector, small vector and zero vectors by length, whole polar plot be divided into 12 sectors according to the position of long vector and middle vector; 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 arrange from big to small by rate of change with idle influence meritorious, obtain in 12 sectors v _iRight

With The classification chart of influence size;

The 5th step: the reactive power that the present invention will follow the tracks of changes through the chain rate that stagnates and is quantized into two grade S _q=1,0, expression needs to increase or reduce reactive power respectively; The active power variable quantity changes into four grade S _p=2,1,0 ,-1, represent 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 under the little situation; To S _pAnd S _q8 kinds of combinations, from the 4th classification chart that obtain of step, select suitable v _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 switch list together; When more than one of the basic vector of realizing the power controlled 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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