CN106160541A - The mid-point voltage Ripple Suppression system and method optimized based on off state - Google Patents

Abstract

The invention discloses a kind of mid-point voltage Ripple Suppression system and method optimized based on off state.This system includes three-level inverter and digital processing control module, and wherein digital processing control module includes sampling unit, Closed Loop Control Unit and the space vector pulse width modulation unit being sequentially connected with；The outfan of described space vector pulse width modulation unit accesses three-level inverter every phase each switching tube of brachium pontis by drive circuit.The method is: in each switch periods, and sampling unit gathers the DC bus-bar voltage signal of three-level inverter, the three-phase voltage signal of three-level inverter output and three-phase current signal respectively；The signal collected processes through Closed Loop Control Unit and obtains three-phase fundamental modulation signal；Three-phase fundamental modulation signal obtains pulse-width modulation control signal through space vector pulse width modulation cell processing, and this signal controls the duty of three-level inverter every phase switching tube through drive circuit.The present invention can suppress three-level inverter dc bus mid-point voltage ripple, optimize the output waveform quality of three-level inverter.

Description

The mid-point voltage Ripple Suppression system and method optimized based on off state

Technical field

The invention belongs to the control technical field in Technics of Power Electronic Conversion technology, particularly a kind of based on off state optimization Mid-point voltage Ripple Suppression system and method.

Background technology

In recent years, high-power conversion occasion during three-level inverter has been widely used in high pressure；Its circuit topology is tied Structure and control method become current study hotspot.Comparing two-level inverter, three-level inverter has switch tube voltage The plurality of advantages such as stress is low, electromagnetic noise is little, harmonic wave of output voltage aberration rate is low.

The topology of three-level inverter substantially can be divided three classes: diode-clamped, cascade connection type, striding capacitance type, its In most widely used for Diode-clamped inverter.Three level Diode-clamped inverters can be divided into neutral point clamp type (NPC) inverter and T-shaped inverter.The control method of three-level inverter mainly has: sinusoidal pulse width modulation (SPWM), space are vowed Amount pulsewidth modulation (SVPWM), third-harmonic zero-sequence voltage pulsewidth modulation (THIPWM), discontinuous PWM (DPWM) etc..With SPWM Method is compared, and SVPWM method improves DC bus-bar voltage utilization rate, it is easier to the optimization of whole switch mode peace treaty bundle condition Process, and be more suitable for being realized by Digital Signal Processing (digital signal processor, DSP).Therefore, ordinary circumstance Under, SVPWM method is more favourable.

In recent years, in order to optimize traditional three level SVPWM methods, experts and scholars propose various new modulator approach. For the three-level inverter of high switching frequency, professor J.Holtz proposes a kind of based on field programmable gate array (Field Programmable Gate Array, FPGA) novel SVPWM manipulator, which overcome the basic shortcoming of existing scheme.One A little scholars, such as at document Comparisons of space-vector modulation and carrier-based modulation of multilevel inverter[J].IEEE Transactions on Power Electronics, 2008,23 (1): 45-51, associate professor Yao Wenxi et al. proposes based on 60^oThe novel SVPWM method of coordinate system.Also have Scholar, such as at document Comprehensive Study on Equivalent Modulation Waveforms of the SVM Sequence for Three-Level Inverters[J].IEEE Transactions on Power Electronics, 2015,30 (12): 7149-7158, Chen Juan et al. are by injecting zero in the sinusoidal modulation wave to SPWM method The mode of order components or common-mode voltage realizes SVPWM method, although carried modulator approach reduces the complexity of Vector operation, But the on off state of SVPWM modulating wave is not optimized.

When using traditional three level SVPWM method, it is relatively big to there is mid-point voltage ripple in three-level inverter, output waveform Of low quality, modulating wave expression formula is more complicated, it is difficult to set up unified mid-point voltage model, is not easy to mid-point voltage controller and sets The shortcoming of meter.

Summary of the invention

It is an object of the invention to provide that a kind of control method is simple, be prone to optimizing based on off state of Digital Implementation Mid-point voltage Ripple Suppression system and method.

The technical solution realizing the object of the invention is: a kind of mid-point voltage Ripple Suppression optimized based on off state System, it is characterised in that include three-level inverter and digital processing control module, wherein digital processing control module includes suitable The sampling unit of secondary connection, Closed Loop Control Unit and space vector pulse width modulation unit；Described sampling unit gathers three electricity respectively The three-phase voltage signal of the DC bus-bar voltage signal of flat inverter, three-level inverter output, three-level inverter export Three-phase current signal, the outfan of space vector pulse width modulation unit accesses three-level inverter every phase brachium pontis by drive circuit Each switching tube；

In each switch periods, the sampling unit of digital processing control module gathers the direct current of three-level inverter respectively The three-phase voltage signal of bus voltage signal, three-level inverter output, the three-phase current signal of three-level inverter output；Adopt Collect to signal through Closed Loop Control Unit process obtain three-phase fundamental modulation signal；Three-phase fundamental modulation signal is through space vector arteries and veins Wide modulating unit processes and obtains pulse-width modulation control signal, and this pulse-width modulation control signal can suppress three-level inverter direct current Bus mid-point voltage ripple, the output waveform quality of optimization three-level inverter；Described pulse-width modulation control signal is through driving electricity Road controls the duty of three-level inverter every phase switching tube.

Preferably, described digital processing control module is TMS320F28335 chip.

A kind of mid-point voltage Ripple Suppression method optimized based on off state, the method is used for using space vector modulation The three-level inverter of method, comprises the following steps:

Step 1, in each switch periods, the sampling unit of digital processing control module gathers three-level inverter respectively DC bus-bar voltage signal, three-level inverter output three-phase voltage signal, three-level inverter output three-phase current Signal；

Step 2, Closed Loop Control Unit through Clarke conversion, Park conversion, obtain two according to the signal collected in step 1 D axle under cordic phase rotator system and q axle component, d axle and q axle component carry out PID tune with base reference signal respectively Joint obtains error signal, and error signal, again through Park inverse transformation, Clarke inverse transformation, exports three-phase fundamental modulation signal；

Step 3, space vector pulse width modulation unit, according to the three-phase fundamental modulation signal obtained in step 2, optimize three-phase The on off state of brachium pontis, obtains the switching instant t of three-phase brachium pontis output level_a、t_b、t_c, by t_a、t_b、t_cCompare with triangular carrier, Obtain pulse-width modulation control signal；

Gained pulse-width modulation control signal in step 3 is distributed to three-level inverter every phase brachium pontis by step 4, drive circuit Each switching tube, controls the duty of three-level inverter, suppresses three-level inverter dc bus mid-point voltage simultaneously Ripple, the output waveform quality of optimization three-level inverter.

Further, space vector pulse width modulation unit described in step 3 is according to the three-phase fundamental modulation obtained in step 2 Signal, optimizes the on off state of three-phase brachium pontis, obtains the switching instant t of three-phase brachium pontis output level_a、t_b、t_c, by t_a、t_b、t_cWith Triangular carrier compares, it is thus achieved that pulse-width modulation control signal, concretely comprises the following steps:

(1) interval division and judgement:

Under biphase rest frame i.e. alpha-beta coordinate system, α axle is transverse axis, and β axle is the longitudinal axis, divides space vector interval, α Positive and negative 30 degree of scopes of axle, as big sector I, successively counterclockwise, every 60 degree divide a big sector, complete 6 big fans Division；

To synthesis reference vector V_refDeduct a small vector V_m, V_refChange into the synthesized reference vector V of equivalence_r′_ef, i.e. Three dimensional vector diagram is equivalent to two level space vector interval graphs；After determining big sector, according to V_r′_efPhase angle judge institute Minizone, place；And it is similar to two level SVPWM Vector modulation Computing Principles, obtain synthesizing V_refThree vector these three vectors Action time；

(2) optimization of on off state in switch periods:

Switch periods T_sIn, by controlling the persistent period of three-level inverter a certain phase brachium pontis P-state with another The persistent period of one phase brachium pontis N-state is equal, or the holding of the persistent period of a certain phase brachium pontis N-state and another phase brachium pontis P-state The continuous time is equal, thus optimizes on off state, reduces dc bus mid-point voltage undulate quantity；

(3) vector participating in synthesis calculates action time:

According to the optimization method of on off state in switch periods, respectively obtain synthesis V_refAction time of three vectors, And then obtain the switching instant t of three-level inverter three-phase brachium pontis output level_a、t_b、t_c；

(4) pulse-width modulation control signal generates

Switching instant value t by the three-phase brachium pontis output level of step (3) gained_a、t_b、t_cCompare with triangular carrier, Obtain three-phase brachium pontis pulse-width modulation control signal.

Compared with prior art, its remarkable advantage is the present invention: (1) is interval by repartitioning space vector, will pass Three level SVPWMs of uniting are reduced to two level SVPWMs so that interval judgement and Vector modulation calculate and be more easy to realize；(2) in switch week In phase, according to the phase angle range condition of synthesized reference vector, select phase brachium pontis " P " (or " N ") state and another phase brachium pontis " N " The persistent period of (or " P ") state is equal, simplifies the expression formula of modulating wave；(3) at fundamental modulation than the model for [0,1.15] In enclosing, modulating wave is saddle type ripple, effectively reduces mid-point voltage ripple, improves output waveform quality.

Accompanying drawing explanation

Fig. 1 is the structure chart of the mid-point voltage Ripple Suppression system that the present invention optimizes based on off state.

Fig. 2 is traditional three level SVPWM space vector interval division figures.

Fig. 3 is the space vector interval division figure of the present invention.

Fig. 4 is the equivalence two level space vector interval graph of the present invention, and wherein (a) is synthesized reference vector V_refIn I-3 district Between vector interval graph, (b) be equivalence synthesized reference vector V_ref' at I-3 interval vector interval graph.

Fig. 5 is to work as V_refThe on off sequence figure of tradition three level SVPWM methods when the I-1 interval shown in Fig. 2.

Fig. 6 is to work as V_refThe on off sequence figure of the present invention when the I-3 interval shown in Fig. 3.

Fig. 7 is a phase brachium pontis modulating wave oscillogram of traditional three level SVPWMs.

Fig. 8 is a phase brachium pontis modulating wave oscillogram of the inventive method.

Fig. 9 is the main circuit structure figure of NPC three-level inverter.

Figure 10 is the mid-point voltage ripple curve chart of two kinds of modulator approaches.

Figure 11 is the experimental result comparison diagram of two kinds of modulator approaches, and wherein (a) is the experiment of traditional three level SVPWM methods Oscillogram, (b) is the experimental waveform figure of the inventive method, and (c) is the THD analysis result figure of traditional three level SVPWM methods, D () is the THD analysis result figure of the inventive method.

Figure 12 is THD and mid-point voltage ripple measurement result figure, and wherein (a) is THD measurement result figure, and (b) is midpoint electricity Embossing wave measurements figure.

Detailed description of the invention

Below in conjunction with the accompanying drawings and the present invention is described in further detail by specific embodiment.

The mid-point voltage Ripple Suppression system that the present invention optimizes based on off state, by repartitioning space vector district Between, traditional three level SVPWMs are reduced to two level SVPWMs so that interval judgement and Vector modulation calculate and be more easy to realize.Opening In the cycle of pass, according to the phase angle range condition of synthesized reference vector, select phase brachium pontis " P " (or " N ") state and another phase bridge The persistent period of arm " N " (or " P ") state is equal, simplifies the expression formula of modulating wave.At fundamental modulation than the model for 0-1.15 In enclosing, modulating wave is saddle type ripple, reduces the ripple of mid-point voltage, solve mid-point voltage model be difficult to set up, mid-point voltage The problem that controller is difficult to design.Compared with traditional three level SVPWMs, the present invention can effectively reduce mid-point voltage ripple, improves Output waveform quality.

In conjunction with Fig. 1, the mid-point voltage Ripple Suppression system that the present invention optimizes based on off state, including three-level inverter With digital processing control module, sampling unit that wherein digital processing control module includes being sequentially connected with, Closed Loop Control Unit and Space vector pulse width modulation unit；Described sampling unit gathers the DC bus-bar voltage signal of three-level inverter, three electricity respectively The three-phase voltage signal of flat inverter output, the three-phase current signal of three-level inverter output, space vector pulse width modulation list The outfan of unit accesses three-level inverter every phase each switching tube of brachium pontis by drive circuit；Described digital processing control module For TMS320F28335 chip.

In each switch periods, the sampling unit of digital processing control module gathers the direct current of three-level inverter respectively The three-phase voltage signal of bus voltage signal, three-level inverter output, the three-phase current signal of three-level inverter output；Adopt Collect to signal through Closed Loop Control Unit process obtain three-phase fundamental modulation signal；Three-phase fundamental modulation signal is through space vector arteries and veins Wide modulating unit processes and obtains pulse-width modulation control signal, and this pulse-width modulation control signal can suppress three-level inverter direct current Bus mid-point voltage ripple, the output waveform quality of optimization three-level inverter；Described pulse-width modulation control signal is through driving electricity Road controls the duty of three-level inverter every phase switching tube.

A kind of mid-point voltage Ripple Suppression method optimized based on off state, the method is used for using space vector modulation Three-level inverter in the case of method, comprises the following steps:

Step 1, in each switch periods, the sampling unit of digital processing control module gathers three-level inverter respectively DC bus-bar voltage signal, three-level inverter output three-phase voltage signal, three-level inverter output three-phase current Signal；

Step 2, Closed Loop Control Unit through Clarke conversion, Park conversion, obtain two according to the signal collected in step 1 D axle under cordic phase rotator system and q axle component, d axle and q axle component carry out PID tune with base reference signal respectively Joint obtains error signal, and error signal, again through Park inverse transformation, Clarke inverse transformation, exports three-phase fundamental modulation signal；

Step 3, space vector pulse width modulation unit, according to the three-phase fundamental modulation signal obtained in step 2, optimize three-phase The on off state of brachium pontis, obtains the switching instant t of three-phase brachium pontis output level_a, t_b, t_c, by t_a、t_b、t_cCompare with triangular carrier, Acquisition can suppress the ripple of three-level inverter dc bus mid-point voltage, optimize the output waveform quality of three-level inverter Pulse-width modulation control signal, concretely comprise the following steps:

(1) interval division and judgement:

Under three-phase static coordinate system, the three-phase fundamental modulation signal v obtained in step 2_ao、v_bo、v_coChange through Clarke Change to the biphase rest frame of alpha-beta, synthesized reference vector V can be obtained_ref:

$\left\{\begin{array}{c}{V}_{ref}=\frac{2}{3}(v_{ao}+v_{bo}{e}^{j2\mathrm{\π}/3}+v_{co}{e}^{-j2\mathrm{\π}/3})=V_{\mathrm{\α}}+{\mathrm{jV}}_{\mathrm{\β}}\\ \left|V_{ref}\right|=\sqrt{{V_{\mathrm{\α}}}^2+{V_{\mathrm{\β}}}^2}\\ \mathrm{\θ}=arctg\left(\frac{V_{\mathrm{\β}}}{V_{\mathrm{\α}}}\right)\end{array}\right.---\left(1\right)$

Wherein V_αAnd V_βIt is respectively V_refReal part and imaginary part.|V_ref| and θ is V respectively_refMould length and phase angle.

(every phase bridge arm voltage divides to assume to represent three kinds of duties of NPC three-level inverter phase brachium pontis in " P ", " 0 ", " N " It is not V_dc/2、0、-V_dc/2).Therefore a total of 27 kinds of duties of NPC three-level inverter, every kind of state is corresponding to alpha-beta two A vector in dimension coordinate system vectogram.Tradition three level SVPWM space vector interval division figures, as in figure 2 it is shown, this vector Scattergram is divided into 6 big sectors, and every 60 ° of intervals are a big sector, and each big sector includes between 4 little deltas.Figure In " I, II, III, IV, V, VI " represent the numbering of big sector, " 1,2,3,4 " numbering between little delta in representing each sector. In fig. 2,27 vectors are specifically divided into: 6 a length of 2V of mould_dcThe big vector of/3；6 moulds are a length of isMiddle vector；12 The a length of V of individual mould_dcThe small vector of/3；3 zero vectors.

When using the inventive method, the sector of space vector and minizone need to redefine division, as shown in Figure 3.6 Tetragon represents 6 big sectors, and every 60 ° of intervals are a sector, and each big sector includes 6 minizones.In figure " I, II, III, IV, V, VI " represent that the numbering of big sector, " 1,2,3,4,5,6 " represent the numbering of 6 minizones in each sector.

Fig. 4 gives as synthesized reference vector V_refWhen minizone, I big sector the 3rd (I-3 is interval) shown in Fig. 3, this The equivalence two level space vector interval graph of invention.Comparison diagram 4 (a) and (b) understand, by deducting a small vector V_m(V here_m =V_o), V_refChange into the synthesized reference vector V of equivalence_r′_ef。

As shown in Fig. 4 (b), after being converted into the Vector operation of two level SVPWMs, V_r′_efBy V₀', V₁', V₂' synthesis, and full Foot equation below:

V_r′_efT_s=V₀′T₀+V₁′T₁+V₂′T₂ (2)

T₀+T₁+T₂=T_s (3)

V in formula₀', V₁', V₂' it is the V after converting_r′_efSynthesis three vector, T₀、T₁、T₂Represent V respectively₀', V₁', V₂' Action time.

Analysis chart 4 understands: formula (2) is also denoted as:

(V_ref-V_m)T_s=(V₀-V_m)T₀+(V₁-V_m)T₁+(V₂-V_m)T₂ (4)

Formula (2) is updated in formula (4), can be by formula (4) abbreviation:

V_refT_s=V₀T₀+V₁T₁+V₂T₂ (5)

Therefore, inverted rear calculated T₀、T₁、T₂The V of the most traditional three level SVPWMs_refSynthesis three vector V₀, V₁, V₂Time.

Therefore, when using the inventive method, the Vector operation of traditional three level SVPWMs is reduced to the arrow of two level SVPWMs Amount calculates, after determining big sector, and only need to be according to V '_refPhase angle judge residing minizone.And it is similar to two level SVPWMs Vector modulation Computing Principle, obtains synthesizing V_refTheir action time of synthesis three vector.

(2) optimization of on off state in switch periods

With V_refWhen the I-1 interval shown in Fig. 2 as a example by the on off sequence of tradition three level SVPWMs, as shown in Figure 5.From figure Time in 5 it can be seen that use tradition SVPWM method, switch periods T_sIn, V₀The action time of [P00] and V₀[0NN] Effect equal, equal to T₀/2.Again due to V₀[P00] and V₀[0NN] is a pair positive and negative small vector, the shadow of they alignment voltages Sound is contrary, and can cancel out each other.But V₁[00N] is another negative small vector so that mid-point voltage reduces, therefore, in Point voltage fluctuation problem occurs as soon as.

Switch periods T_sIn, in order to reduce negative small vector V₁The impact of [00N] alignment voltage, it should just increasing Small vector V₀The action time of [P00], corresponding minimizing bears small vector V₀The action time of [0NN], i.e. redistribute V₀[P00] And V₀The action time of [0NN] so that mid-point voltage rises, be conducive to reducing the undulate quantity of mid-point voltage.

What Fig. 6 represented is to work as V_refWhen the I-3 interval shown in Fig. 3, the on off sequence of the inventive method.This sequence and Fig. 5 Middle V_refWhen the I-1 interval shown in Fig. 2, the on off sequence of tradition three level SVPWMs is identical.In figure 6, a switch periods T_sIn, it is assumed that the persistent period of a phase brachium pontis " P " state is equal with the persistent period of c phase brachium pontis " N " state, i.e. meets following Inequality:

T₀ ⁺=T₀ ^-+T₁ (6)

T₀ ⁺+T₀ ^-+T₁+T₂=T_s (7)

T₀ ⁺+T₀ ^-=T₀ (8)

T in formula₀ ^-, T₀ ⁺Represent negative small vector V respectively₀[0NN] and positive small vector V₀The action time of [P00].

Contrasted from Fig. 5 and Fig. 6, switch periods T_sIn, traditional three level SVPWM method and the inventive method During effect, synthesize and action time of three vectors contrast situation and be given in Table 1.

Table 1 synthesizes contrast action time of three vectors

Wherein T₀Represent negative small vector V₀[0NN] and positive small vector V₀The total contribution time of [P00], T₁, T₂Represent V respectively₁, V₂Action time.

Be can be seen that by formula (5)-(7) and table 1, although negative small vector V₁The action time of [00N] does not adjust, but negative Small vector V₀[0NN] and positive small vector V₀The action time of [P00] is the most equal.Positive small vector V₀The action time of [P00] increases , meanwhile, negative small vector V₀The action time of [0NN] reduces.Therefore, when using the inventive method, V is worked as_refIn Fig. 3 institute During the I-3 interval shown so that the persistent period of a phase brachium pontis " P " state is equal with the persistent period of c phase brachium pontis " N " state, midpoint Voltage will rise, and have the trend reducing mid-point voltage undulate quantity.

According to above-mentioned analysis, switch periods T_sIn, the inventive method is by controlling NPC three-level inverter The persistent period of a certain phase brachium pontis " P " (or N ") state is equal with the persistent period of another phase brachium pontis " N " (or " P ") state, from And optimize on off state and reduce mid-point voltage undulate quantity.The rule of concrete optimization on off state is as follows:

The on off state principle of optimality of table 2 the inventive method

T in table_aon, T_bon, T_conRepresent respectively switch periods T_sIn, NPC three-level inverter each phase brachium pontis " P " The persistent period of (or " N ") state.θ is V_refPhase angle.

(3) vector participating in synthesis calculates action time

Still with V_refAs a example by the I-3 interval shown in Fig. 3, when using the inventive method, can be in the hope of T by formula (4)-(7)₀ ^-, T₀ ⁺, T₁, T₂:

$\left\{\begin{array}{c}{T_0}^{+}=\frac{T_s}{2}\left(\frac{3M}{2}cos\right(\mathrm{\θ})+\frac{\sqrt{3}M}{2}sin(\mathrm{\θ}\left)\right)\\ {T_0}^{-}=\frac{T_s}{2}\left(\frac{3M}{2}cos\right(\mathrm{\θ})-\frac{3\sqrt{3}M}{2}sin(\mathrm{\θ}\left)\right)\\ T_1=\sqrt{3}Msin\left(\mathrm{\θ}\right)T_s\\ T_2=T_s-(\frac{\sqrt{3}\sin \left(\mathrm{\θ}\right)}{2}+\frac{3}{2}\cos (\mathrm{\θ}\left)\right){\mathrm{MT}}_s\end{array}\right.---\left(9\right)$

Here, M represents fundamental modulation ratio, M=| V_ref|/(V_dc/ 2), the scope of M is [0,1.15].

As shown in Figure 6, V is worked as_refWhen the I-3 interval shown in Fig. 3, the inventive method switch in a switch periods Sequence.In figure, t_a, t_b, t_cIt is respectively the switching instant of NPC three-level inverter three-phase brachium pontis output level, t_a, t_b, t_cFor:

$\left\{\begin{array}{c}{t}_a={T_0}^{-}/2+T_1/2+T_2/2\\ t_b={T_0}^{-}/2\\ t_c={T_0}^{-}/2+T_1/2\end{array}\right.---\left(10\right)$

(4) pulse-width modulation control signal generates

Again formula (9) is substituted into formula (10), t can be obtained_a, t_b, t_c.In sum, V is worked as_refWhen being in other regions, in like manner may be used Obtain the switching instant value of three-level inverter three-phase brachium pontis output level.The t that will try to achieve_a、t_b、t_cCompare permissible with triangular carrier Obtain three-phase brachium pontis pulse-width modulation control signal.

Gained pulse-width modulation control signal in step 3 is distributed to three-level inverter every phase brachium pontis by step 4, drive circuit Each switching tube, controls the duty of three-level inverter, suppresses three-level inverter dc bus mid-point voltage simultaneously Ripple, the output waveform quality of optimization three-level inverter.

Below as a example by NPC three-level inverter, elaborate implementation process of the present invention.

(1) traditional three level SVPWM control method modulated wave analysiss:

As in figure 2 it is shown, with V_refAs a example by the I-I district shown in Fig. 2, when using traditional three level SVPWM method, V₀、V₁、 V₂T action time₀、T₁、T₂For:

$\left\{\begin{array}{c}{T}_0=\left(\frac{3}{2}cos\right(\mathrm{\θ})-\frac{\sqrt{3}sin\left(\mathrm{\θ}\right)}{2}){\mathrm{MT}}_s\\ T_1=\sqrt{3}M\sin \left(\mathrm{\θ}\right)T_s\\ T_2=T_s-(\frac{\sqrt{3}\sin \left(\mathrm{\θ}\right)}{2}+\frac{3}{2}\cos (\mathrm{\θ}\left)\right){\mathrm{MT}}_s\end{array}\right.---\left(11\right)$

V_refWhen I-I district, the on off sequence in a switch periods is as shown in Figure 5.In figure, t_asv, t_bsv, t_csvIt is respectively The switching instant of NPC three-level inverter three-phase brachium pontis output level, t_asv, t_bsv, t_csvFor:

$\left\{\begin{array}{c}{t}_{asv}=T_0/4+T_1/2+T_2/2\\ t_{bsv}=T_0/4\\ t_{csv}=T_0/4+T_1/2\end{array}\right.---\left(12\right)$

Again formula (11) is substituted into formula (12), t can be obtained_asv, t_bsv, t_csv.In sum, V is worked as_refWhen being in other regions, In like manner can obtain the switching instant value of NPC three-level inverter output three-phase level.With V_refAs a example by the I-1 interval shown in Fig. 2, Three-phase brachium pontis modulating wave u_asv, u_bsv, u_csvCan be expressed as:

$\left\{\begin{array}{c}{u}_{asv}=V_{dc}(T_s-2t_{asv})/\left(2T_s\right)\\ u_{bsv}=-V_{dc}{t}_{bsv}/T_s\\ u_{csv}=-V_{dc}{t}_{csv}/T_s\end{array}\right.---\left(13\right)$

In formula, V_dcInput direct voltage for NPC three-level inverter.

To V_dcAfter/2 carry out standardization process, formula (11)-formula (13) can be by formula (13) abbreviation:

$\left\{\begin{array}{c}{u}_{asv}=\frac{\sqrt{3}}{2}M\sin (\mathrm{\ω}t+\frac{\mathrm{\π}}{6}))\\ u_{bsv}=-\frac{\sqrt{3}}{2}M\sin (\mathrm{\ω}t+\frac{\mathrm{\π}}{6})\\ u_{csv}=-\frac{3}{2}M\sin (\mathrm{\ω}t-\frac{\mathrm{\π}}{3})\end{array}\right.---\left(14\right)$

In formula, ω is the three-phase modulations angular frequency of NPC three-level inverter, and ω t=θ+pi/2.

According to above-mentioned analysis, work as V_refWhen being positioned at the arbitrarily interval of space vector interval division figure, traditional three level The three-phase modulations ripple expression formula of SVPWM method all can obtain, as shown in table 3.

Make the trendgram that each phase modulating wave changes with M further.As a example by a phase modulating wave, in a power frequency period, Its with M change trendgram as shown in Figure 7.

From table 3 and Fig. 7 it can be seen that in a power frequency period, when M changes in the range of [0,1.15], tradition three The modulating wave expression formula of level SVPWM is extremely complex, and its waveform shape is different with M change.Only when M=1.15, it is adjusted Ripple processed is saddle type ripple.It addition, from the principle analysis of traditional three level SVPWM methods it can be seen that in order to realize V_refInterval Judge, V_refPhase angle theta and Qi Mo length | V_ref| it is essential to calculate, and its interval judgement and resultant vector calculate more complicated.

The modulating wave expression formula that the traditional three level SVPWM space vectors of table 3 are interval

Wherein, u_{ZX_Y}Represent in X sector, the Z phase modulating wave of Y community.Wherein, that Z represents is a, b, c three-phase.X represents Sector number " I, II, III, IV, V, VI ".What Y represented is minizone number " 1,23,4 ", and what " 23 " represented is the 2nd and 3 communities.

(2) the inventive method modulated wave analysis

When the inventive method effect, work as V_refBeing in space vector interval division figure regional, NPC tri-level is inverse Become the output level switching instant t of each phase brachium pontis of device_a、t_b、t_cAfter calculating, it becomes possible to obtain the modulation of every brachium pontis Ripple u_a, u_b, u_cExpression formula.With V_refAs a example by the I-3 interval shown in Fig. 3, u_a, u_b, u_cFor:

$\left\{\begin{array}{c}{u}_a=V_{dc}(T_s-2t_a)/\left(2T_s\right)\\ u_b=-V_{dc}{t}_b/T_s\\ u_c=-V_{dc}{t}_c/T_s\end{array}\right.---\left(15\right)$

To V_dcAfter/2 carry out standardization process, formula (9)-(10) can be by formula (15) abbreviation:

$\left\{\begin{array}{c}{u}_a=\frac{\sqrt{3}}{2}Msin(\mathrm{\ω}t-\frac{\mathrm{\π}}{6})\\ u_b=\frac{3}{2}Msin(\mathrm{\ω}t-\frac{2\mathrm{\π}}{3})\\ u_c=-\frac{\sqrt{3}}{2}Msin(\mathrm{\ω}t-\frac{\mathrm{\π}}{6})\end{array}\right.---\left(16\right)$

In formula, ω is the three-phase modulations angular frequency of NPC three-level inverter, and ω t=θ+pi/2.

According to above-mentioned analysis, work as V_refWhen being positioned at the arbitrarily interval of space vector interval division figure, NPC tri-level is inverse The three-phase modulations ripple expression formula becoming device all can obtain.

In a power frequency period, a phase modulating wave u_aWaveform under the conditions of different M is as shown in Figure 8.

Compared with the modulating wave expression formula interval with traditional three level SVPWM space vectors, the modulation wave table of the inventive method Reach formula to be easier to obtain.Comparison diagram 8 understands with Fig. 7, when M changes in the range of [0,1.15], in a power frequency period, this The modulating wave of inventive method always saddle type ripple, its waveform does not changes with M.And the modulating wave expression formula of traditional three level SVPWMs is non- The most complicated, its waveform is different with M change, and only when M=1.15 when, its waveform is saddle type.

It addition, by the modulating wave expression formula of relative analysis above two modulator approach, traditional three level SVPWMs Modulating wave expression formula is more complicated, it is difficult to set up unified mid-point voltage model.And in the range of fundamental modulation is than for [0,1.15], The modulating wave expression formula of the inventive method is relatively simple, under the same conditions, does not changes with minizone.And during the method effect, The averaging model of mid-point voltage is relatively easily set up, it is easy to the design of mid-point voltage controller.

(3) mid-point voltage ripple contrast

Under traditional three level SVPWM method effects, when the three-phase brachium pontis of NPC three-level inverter is operated in " 0 " respectively During state, switch periods T_sIn, dutycycle D that every phase brachium pontis " 0 " state is corresponding_aosv, D_bosv, D_cosvCan be expressed as:

$\left\{\begin{array}{c}{D}_{aosv}=1-\left|u_{asv}\right|\\ D_{bosv}=1-\left|u_{bsv}\right|\\ D_{cosv}=1-\left|u_{csv}\right|\end{array}\right.---\left(17\right)$

U in formula_asv, u_bsv, u_csvRepresent when using traditional three level SVPWM method, the modulating wave of each phase brachium pontis.

Same, when using the inventive method, switch periods T_sIn, every phase brachium pontis " 0 " corresponding accounting for of state Sky compares D_ao, D_bo, D_coCan be expressed as:

$\left\{\begin{array}{c}{D}_{ao}=1-\left|u_a\right|\\ D_{bo}=1-\left|u_b\right|\\ D_{co}=1-\left|u_c\right|\end{array}\right.---\left(18\right)$

U in formula_a, u_b, u_cRepresent when using traditional three level SVPWM method, the modulating wave of each phase brachium pontis.

The expression formula of threephase load electric current is:

I in formula_mRepresent the amplitude of threephase load phase current,Power-factor angle for threephase load.

NPC three-level inverter is as it is shown in figure 9, i_oSwitch periods T can be defined as_sThe meansigma methods of interior midpoint electric current, Its positive direction is to flow out the direction of midpoint o.Make i_osv and i_oRepresent and be respectively adopted traditional three level SVPWM method and present invention Midpoint electric current during method, meets below equation:

i_osv=D_aosvi_a+D_bosvi_b+D_cosvi_c (20)

i_o=D_aoi_a+D_boi_b+D_coi_c (21)

In fig .9, i₁And i₂Respectively flow through electric capacity C₁And C₂Electric current, v_c1And v_c2It is respectively electric capacity C₁And C₂Voltage, v_cFor v_c1And v_c2Voltage difference.

v_c=v_c1-v_c2 (22)

Assume electric capacity C₁And C₂Capacitance equal, equal to C.Therefore, i_o, i₁And i₂Relation can be expressed as:

$\left\{\begin{array}{c}{i}_1=C{\mathrm{dv}}_{c1}/dt\\ i_2=C{\mathrm{dv}}_{c2}/dt\\ i_o=i_1-i_2\end{array}\right.---\left(23\right)$

V can be derived by by formula (22)-(23)_c:

$v_c=\frac{i_o}{C}{T}_s---\left(24\right)$

According to formula (20), (21) and (24), the v of above two modulator approach_cCan be expressed as:

$v_{csv}=\frac{T_s}{C}(D_{asv}{i}_a+D_{bsv}{i}_b+D_{csv}{i}_c)---\left(25\right)$

$v_{csA}=\frac{T_s}{C}(D_{ao}{i}_a+D_{bo}{i}_b+D_{co}{i}_c)---\left(26\right)$

In formula: v_csvAnd v_cSARepresent v when traditional three level SVPWM methods and the inventive method respectively_c。

Assume that threephase load is resistive loadWhen to I_m, T_s, after C carries out standardization process, v_{csv_pp}And v_{cSA_PP}With M The curve of change is as shown in Figure 10.Here, v_{csv_pp}, v_{cSA_PP}Represent v respectively_csvAnd v_cSARipple quantity.Can from Figure 10 Going out, compared with traditional three level SVPWM methods, during the inventive method effect, the ripple quantity of mid-point voltage is obviously reduced.Therefore, root According to above-mentioned analysis, the inventive method effect in terms of reducing mid-point voltage ripple has obtained theoretical validation.

Embodiment 1

In order to verify the effectiveness of the inventive method, based on digital signal processor-CPLD (Digital Signal Processor and Complex Programmable Logic Device, DSP-CPLD's) Experimental verification has been carried out on NPC three-level inverter experiment porch.

The major parameter arranged in experiment is:

Input direct voltage: 200V

Input direct-current bus capacitor capacitance: C₁=C₂=150uF

Fundamental modulation compares: M=0.8

Switching frequency: f_s=20kHz

Output: P_out=0-215W

Digital processing element: TMS320F28335 DSP

Logical drive processing unit: EPM1270T (CPLD)

Power model unit: IGBT FZ06NPA070FP

Each phase output filter: L=1.5mH, C=10uF

Loading condition: resistive load.

When being respectively adopted traditional three level SVPWMs and put forward inventive method, v_c1, v_c2, v_A, v_{a_ref}, i_a, v_aWaveform with And the frequency analysis result of output waveform is as shown in figure 11.In Figure 11, v_c1, v_c2Represent electric capacity C respectively₁, C₂On voltage, v_ATable Show is a phase bridge arm voltage, v_{a_ref}Represent is a phase modulating wave waveform, i_aRepresent is a phase load electric current, and v_aRepresent Be a phase load voltage.

From Figure 11 (a) (b) it can be seen that use traditional three level SVPWM method time, v_c1Or v_c2Ripple be 12.4V (oscillograph is arranged on AC coupled modes), when the inventive method, v_c1Or v_c2Ripple effectively reduced.Therefore, experiment knot Fruit shows: compared with traditional three level SVPWM methods, and the inventive method has preferably performance in terms of mid-point voltage ripple.

That Figure 11 (c) (d) is given is v_a, i_aTHD analysis result.Tradition three level SVPWM methods are compared, when using this During inventive method, i_aTHD value drop to 1.96% from 5.17%, v_aTHD value drop to 1.94% from 5.13%.Therefore, with tradition Three level SVPWM methods are compared, and the inventive method has a clear superiority in terms of output waveform quality.

Under the conditions of different M, the v of above two modulator approach_c1Ripple value and THD result such as Figure 12 institute of output electric current Show.When M changes in the range of 1.15 from 0, compared with traditional three level SVPWM methods, the inventive method can reduce midpoint electricity The ripple of pressure, improves the output waveform quality of NPC three-level inverter.

In sum, the mid-point voltage Ripple Suppression system and method that the present invention optimizes based on off state, it is applied to sky Between three-level inverter in the case of Vector Modulation, this control method is interval by repartitioning space vector, and tradition three is electric Flat SVPWM is reduced to two level SVPWMs so that interval judgement and Vector modulation calculate and be more easy to realize.In switch periods, according to The phase angle range condition of synthesized reference vector, selects phase brachium pontis " P " (or " N ") state and another phase brachium pontis " N " (or " P ") shape The persistent period of state is equal, simplifies the expression formula of modulating wave.It is that in the range of [0,1.15], modulating wave is at fundamental modulation ratio Saddle type ripple, reduces the ripple of mid-point voltage, solve mid-point voltage model be difficult to set up, mid-point voltage controller be difficult to design Problem.Compared with traditional three level SVPWMs, the present invention can effectively reduce mid-point voltage ripple, improves output waveform quality.Should Control method, without increasing extra hardware circuit, has output waveform harmonic content low, and real-time is good, and control method is simple, It is easy to the advantages such as Digital Realization.

Claims (4)

1. the mid-point voltage Ripple Suppression system optimized based on off state, it is characterised in that include three-level inverter With digital processing control module, sampling unit that wherein digital processing control module includes being sequentially connected with, Closed Loop Control Unit and Space vector pulse width modulation unit；Described sampling unit gathers the DC bus-bar voltage signal of three-level inverter, three electricity respectively The three-phase voltage signal of flat inverter output, the three-phase current signal of three-level inverter output, space vector pulse width modulation list The outfan of unit accesses three-level inverter every phase each switching tube of brachium pontis by drive circuit；

In each switch periods, the sampling unit of digital processing control module gathers the dc bus of three-level inverter respectively The three-phase voltage signal of voltage signal, three-level inverter output, the three-phase current signal of three-level inverter output；Collect Signal through Closed Loop Control Unit process obtain three-phase fundamental modulation signal；Three-phase fundamental modulation signal is adjusted through space vector pulse width Cell processing processed obtains pulse-width modulation control signal, and this pulse-width modulation control signal can suppress three-level inverter dc bus Mid-point voltage ripple, the output waveform quality of optimization three-level inverter；Described pulse-width modulation control signal is through drive circuit control The duty of three-level inverter processed every phase switching tube.

The mid-point voltage Ripple Suppression system optimized based on off state the most according to claim 1, it is characterised in that institute Stating digital processing control module is TMS320F28335 chip.

3. the mid-point voltage Ripple Suppression method optimized based on off state, it is characterised in that the method is used for using sky Between the three-level inverter of vector modulation method, comprise the following steps:

Step 1, in each switch periods, the sampling unit of digital processing control module gathers the straight of three-level inverter respectively Stream bus voltage signal, the three-phase voltage signal of three-level inverter output, the three-phase current signal of three-level inverter output；

Step 2, Closed Loop Control Unit through Clarke conversion, Park conversion, obtain biphase rotation according to the signal collected in step 1 Turn the d axle under coordinate system and q axle component, d axle and q axle component to carry out PID with base reference signal respectively and regulate To error signal, error signal, again through Park inverse transformation, Clarke inverse transformation, exports three-phase fundamental modulation signal；

Step 3, space vector pulse width modulation unit, according to the three-phase fundamental modulation signal obtained in step 2, optimize three-phase brachium pontis On off state, obtain the switching instant t of three-phase brachium pontis output level_a、t_b、t_c, by t_a、t_b、t_cCompare with triangular carrier, it is thus achieved that Pulse-width modulation control signal；

Step 4, drive circuit gained pulse-width modulation control signal in step 3 is distributed to three-level inverter every phase brachium pontis each Switching tube, control three-level inverter duty, simultaneously suppression three-level inverter dc bus mid-point voltage ripple, Optimize the output waveform quality of three-level inverter.

The mid-point voltage Ripple Suppression method optimized based on off state the most according to claim 3, it is characterised in that step Space vector pulse width modulation unit described in rapid 3, according to the three-phase fundamental modulation signal obtained in step 2, optimizes three-phase brachium pontis On off state, obtains the switching instant t of three-phase brachium pontis output level_a、t_b、t_c, by t_a、t_b、t_cCompare with triangular carrier, it is thus achieved that arteries and veins Wide modulator control signal, concretely comprises the following steps:

(1) interval division and judgement:

Under biphase rest frame i.e. alpha-beta coordinate system, α axle is transverse axis, and β axle is the longitudinal axis, divides space vector interval, α axle Positive and negative 30 degree of scopes, as big sector I, successively counterclockwise, every 60 degree divide a big sector, complete 6 big sectors and draw Point；

To synthesis reference vector V_refDeduct a small vector V_m, V_refChange into the synthesized reference vector V ' of equivalence_ref, will space Vectogram is equivalent to two level space vector interval graphs；After determining big sector, according to V '_refPhase angle judge residing community Between；And it is similar to two level SVPWM Vector modulation Computing Principles, obtain synthesizing V_refThe effect of three vector these three vectors Time；

(2) optimization of on off state in switch periods:

Switch periods T_sIn, by controlling persistent period and another phase bridge of three-level inverter a certain phase brachium pontis P-state The persistent period of arm N-state is equal, or the persistent period of the persistent period of a certain phase brachium pontis N-state and another phase brachium pontis P-state Equal, thus optimize on off state, reduce dc bus mid-point voltage undulate quantity；

(3) vector participating in synthesis calculates action time:

According to the optimization method of on off state in switch periods, respectively obtain synthesis V_refAction time of three vectors, and then Obtain the switching instant t of three-level inverter three-phase brachium pontis output level_a、t_b、t_c；

(4) pulse-width modulation control signal generates

Switching instant value t by the three-phase brachium pontis output level of step (3) gained_a、t_b、t_cCompare with triangular carrier, it is thus achieved that Three-phase brachium pontis pulse-width modulation control signal.