CN104201922A - Clamping-type three-phase voltage-source type inverter and control method thereof - Google Patents

Abstract

The invention relates to a clamping-type three-phase voltage-source type inverter and a control method thereof and belongs to the technical field of three-phase voltage-source type inverters. The clamping-type three-phase voltage-source type inverter comprises a direct-current power source, a three-phase three-level inverter bridge, a three-phase LC filter and a three-phase load. In order to control output voltage waveforms, a mathematical model of the three-level inverter is established, an instantaneous value control system of the output voltage is put forward, a scheme combining a fundamental-wave disturbance instantaneous value controlled internal model with a harmonic disturbance repetitive controlled internal model under rotating coordinates is adopted, disturbance of the internal models is realized to acquire voltage output waveforms high in quality by adopting structural controllers in parallel, and a control method for fixing resultant vectors is adopted with an aim to solve problems about voltage jump of the three-level inverter and neutral voltage potential balance. The clamping-type three-phase voltage-source type inverter is ideal in comprehensive output voltage performance and good in output waveform quality, and meanwhile, the problems about voltage jump and neutral voltage potential balance are solved.

Description

Extremely control method of a kind of clamping type three-phase voltage source type inverter

Technical field

The present invention relates to extremely control method of a kind of clamping type three-phase voltage source type inverter, belong to three-phase voltage source type inverter technology field.

Background technology

In recent years, along with industrial circle increases day by day to the requirement of high-capacity power converting means, multi-electrical level inverter receives increasing concern, and starts to be studied widely and apply, multi-electrical level inverter was developed so far from the eighties in 20th century, on topological structure, had occurred multiple branches.The Basic Topological of multi-electrical level inverter can be divided three classes: diode-clamped multi-electrical level inverter; Leap capacitor type multi-electrical level inverter and cascaded multilevel inverter.Three level topologys are widely used in multiple fields such as the transmission of mesohigh alternating current machine, electric network reactive compensation and absorptions.Compared with two level structures, many level tool has the following advantages: the voltage stress that 1) each power tube bears significantly reduces; 2), under identical switching frequency, output harmonic wave content significantly reduces; 3) power tube switching loss reduces.With other more than two kinds compared with level topological structure, diode-clamped multi-electrical level inverter is due to simple in structure, control easily and realize, become gradually the main flow of multi-electrical level inverter, three-level inverter is in the time of operation, must ensure capacitance voltage balance, the least favorable factor that restricts its application is exactly capacitance voltage skew.The quality of output voltage waveforms is the important indicator of examination inverter performance, is also the focus that inverter is studied in recent ten years, and the index of general standard is: the single harmonic component aberration rate of output voltage is no more than 3%, and total percent harmonic distortion is no more than 5%.From the beginning of the nineties at the end of the eighties in last century till now, the waveform feedback control technology proposing based on reducing inverter harmonic wave of output voltage distortion has obtained very large development, has proposed various control programs.

In multiple fields such as the transmission of mesohigh alternating current machine, electric network reactive compensation and absorption, the instantaneous transition rate du/dt of voltage has very important impact to system, in the moment of power device conducting, will make pulse voltage produce very high transient voltage rate of change du/dt.Suppose that this very high voltage change ratio du/dt acts on capacity load, will certainly produce the electric current that a size is du/dt, be referred to as impulse current, this electric current not only makes power electronic device moment bear very large electric current and power consumption, even can cause the damage of capacity load.

Different from two-level inverter, in diode clamp type three-level inverter, intrinsic shortcoming surely belongs to the unbalanced problem of mid-point voltage, and the electric capacity on its DC bus has the effect of filtering and support.Suppose that significantly variation occurs midpoint potential, will be to make power electronic device bear excessive voltage, to such an extent as to exceed its tolerance range, power electronic device is caused to damage.Therefore, keep three-level inverter midpoint potential stable be one of important symbol of ensureing system safety reliability service.So must control by alignment current potential in Three-Level Inverter System, it is very important keeping its stability.

Summary of the invention

Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides extremely control method of a kind of clamping type three-phase voltage source type inverter, its comprehensive output voltage performance, output waveform quality of not only realizing ideal is good, to voltage jump, midpoint potential equilibrium problem is improved simultaneously.

For achieving the above object, the technical solution used in the present invention is: a kind of based on three-level NPC inverter, comprise DC power supply, three-phase tri-level inverter bridge, three-phase LC filter and threephase load, described three-phase tri-level inverter bridge comprises three single phase circuits that are connected in parallel and first, second electric capacity; Described the first electric capacity, DC power supply, the second electric capacity are cascaded successively; Each single phase circuit comprises first, second, third, fourth power device, first, second, third, fourth fly-wheel diode and first, second clamp diode; Described first, second, third, fourth fly-wheel diode is connected in parallel on respectively on first, second, third, fourth power device successively, describedly connect successively at first, second, third, fourth power device and second, the first electric capacity, the wire that is connected between described first clamp diode one end and first, second four power device connects, and the other end connects in 0 of the zero potential of the connection wire between first, second electric capacity; The wire that is connected between described second clamp diode one end and the 3rd, the four or four power device connects, 0 of the zero potential that the other end connects the connection wire between first, second electric capacity goes up, and described first, second clamp diode is positioned on the neutral point in intermediate dc loop; Also comprise first, second, third filter inductance and first, second, third filter capacitor, described first, second filter capacitor is connected in parallel on the two ends of threephase load with the 3rd filter capacitor after mutually connecting, described three single phase circuits are respectively first, second, third single phase circuit, described first filter inductance one end is connected on the connection wire between second, third power device on the first single phase circuit, and the other end is connected on the first filter capacitor; Described second filter inductance one end is connected on the connection wire between second, third power device on the second single phase circuit, and the other end is connected in threephase load; The 3rd filter inductance one end is connected on the connection wire between second, third power device on the first single phase circuit, and the other end is connected on the second filter capacitor; Described three level refer to that the every phase output terminal of inverter AC obtains the output voltage of three kinds of states from middle DC loop, be respectively positive terminal voltage P, negative terminal voltage N and zero potential 0; The output voltage of described inverter has three kinds of state :+U _dC/ 2 ,-U _dC/ 2,0.

A control method for clamping type three-phase voltage source type inverter, first obtains two DC quantity u by three-phase symmetrical sinusoidal quantity by the instantaneous value control method based on synchronous rotating frame _dfand u _qf, secondly adopt double-layer structure controller, realize disturbance internal mold, finally the space voltage vector of inverter output is carried out to vector by fixing resultant vector method compound, and compound vector after compound is evenly distributed on α β coordinate plane.

Described employing double-layer structure controller, realize the method for disturbance internal mold: adopt pi regulator and repetitive controller parallel operation, the adjusting of the tracking of described traditional PI adjuster to Constant Direct Current instruction can reach floating, and pi regulator can be realized the first-harmonic disturbance internal mold of DC input voitage, linear load disturbance; Repetitive controller is the controller based on the cycle, for the non differential regulation of the periodicity amount of repetition, is used for suppressing harmonic wave and asymmetrical component, realizes harmonic disturbance and the asymmetric load disturbance internal molds such as dead band, nonlinear load, asymmetric load.

Described pi regulator continuous domain model is:

G(s)＝K _p+K _i/s

The output that G in formula (s) is controller and the biography letter of error; K _pfor proportionality coefficient; K _ifor integral coefficient, s is s territory;

The form of described repetitive controller is as follows:

G(s)＝C(s)e ^-τs/(1-Q(s)e ^-τs)

(12)

In formula, the output that G (s) is controller and the biography letter of error; τ is the interference signal cycle, and C (s) is the transfer function of PI controller, and Q (s) is the transfer function of secondary low pass filter.

The described work that also will complete at repetitive controller passage is exactly the different phase shifts that compensate each secondary frequencies that output filtering and possible C (s) cause.

It is compound that the space voltage vector of described inverter output carries out vector by fixing resultant vector method, comprises middle vector resultant vector and large vector resultant vector.

The method of described middle vector resultant vector: utilize i ₀=i _a+ i _b+ i _c=0 this principle, 2 small vectors that the electric current corresponding from middle vector is different of selection, and make their action time identical, and be zero thereby make mid point electric current, midpoint potential is not offset.

The method of described large vector resultant vector: two small vectors of selection and the large same direction of vector, because their size of current equate, opposite direction, thus be zero at mid point electric current, midpoint potential does not occur, in the situation of skew, to have reduced voltage jump.

Extremely control method of a kind of clamping type three-phase voltage source type inverter provided by the invention, compared to existing technology, has following beneficial effect:

1. owing to having adopted the control program that adopts first-harmonic disturbance PI controller internal mold to be combined with harmonic wave and asymmetrical disturbance repetitive controller internal mold under synchronous rotating frame, the comprehensive output voltage performance that therefore can realize ideal.

2. use the Instantaneous value control system based on synchronous rotating frame to suppress the impact of fundamental voltage output of voltage disturbance on output waveform quality, therefore its output waveform quality is good.

3. owing to having adopted the method for fixing resultant vector, the defect that therefore can exist for three-level inverter, is voltage jump according to the cis-position of priority, and midpoint potential equilibrium problem is improved.

Brief description of the drawings

Fig. 1 three-level inverter schematic diagram

Fig. 2 single-phase diode clamper type three-level inverter topology structure

When Fig. 3 electric current flows into load, three-level inverter is by the conversion of P → O

When the load of Fig. 4 outflow of bus current, three-level inverter is by the conversion of P → O

Fig. 5 three-phase output end voltage waveform

Fig. 6 exports phase voltage and line voltage waveform

The voltage vector that Fig. 7 three-phase inverter produces

Fig. 8 three-level inverter Instantaneous value control system block diagram

The synthetic large vector of vector (b) during Fig. 9 resultant vector (a) is synthetic

Figure 10 fixes resultant vector figure

Embodiment

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

A kind of based on three-level NPC inverter, as shown in Figure 1, comprise DC power supply, three-phase tri-level inverter bridge, three-phase LC filter and threephase load, described three-phase tri-level inverter bridge comprises three single phase circuits that are connected in parallel and first, second electric capacity; First, second electric capacity is respectively C ₁, C ₂described the first capacitor C ₁, DC power supply, the second capacitor C ₂be cascaded successively; In figure, filter inductance is L, and filter capacitor is C, R _orepresent that inductor loss, line impedance and switching tube open and the gross effect of turn-off power loss etc.So-called three level refer to that the every phase output terminal of inverter AC obtains the output voltage of three kinds of states from middle DC loop, be respectively positive terminal voltage P, negative terminal voltage N and zero potential 0.Each single phase circuit, as shown in Figure 2, comprises first, second, third, fourth power device, and described first, second, third, fourth power device is respectively VT ₁, VT ₂, VT ₃, VT ₄, first, second, third, fourth fly-wheel diode and first, second clamp diode; Described first, second, third, fourth fly-wheel diode is respectively VD ₁, VD ₂, VD ₃, VD ₄; Described first, second, third, fourth fly-wheel diode is connected in parallel on respectively on first, second, third, fourth power device successively, describedly connect successively at first, second, third, fourth power device and second, the first electric capacity, the wire that is connected between described first clamp diode one end and first, second four power device connects, and the other end connects in 0 of the zero potential of the connection wire between first, second electric capacity; The wire that is connected between described second clamp diode one end and the 3rd, the four or four power device connects, 0 of the zero potential that the other end connects the connection wire between first, second electric capacity goes up, and described first, second clamp diode is positioned on the neutral point in intermediate dc loop; Also comprise first, second, third filter inductance and first, second, third filter capacitor, described first, second filter capacitor is connected in parallel on the two ends of threephase load with the 3rd filter capacitor after mutually connecting, described three single phase circuits are respectively first, second, third single phase circuit, described first filter inductance one end is connected on the connection wire between second, third power device on the first single phase circuit, and the other end is connected on the first filter capacitor; Described second filter inductance one end is connected on the connection wire between second, third power device on the second single phase circuit, and the other end is connected in threephase load; The 3rd filter inductance one end is connected on the connection wire between second, third power device on the first single phase circuit, and the other end is connected on the second filter capacitor; Described three level refer to that the every phase output terminal of inverter AC obtains the output voltage of three kinds of states from middle DC loop, be respectively positive terminal voltage P, negative terminal voltage N and zero potential 0; On the neutral point in intermediate dc loop, settling a pair of IGBT is VT ₂and VT ₃, no matter the flow direction of load current how, the output voltage of inverter has three kinds of state :+U _dC/ 2 ,-U _dC/ 2,0.

As seen from Figure 2, in three-level inverter, each all needs 4 main power electronic device, 4 fly-wheel diodes and two clamp diodes mutually.The steady operation situation of this inverter can be divided into three kinds of mode of operations, as follows.

(1) mode of operation 1-----power device VT ₁, VT ₂conducting, VT ₃, VT ₄turn-off.

If electric current flows through VT from P point ₁, VT ₂arrive output terminals A, electric current flows to load from output.If ignore the conduction voltage drop in power electronic device, output terminals A point current potential equals P point current potential.If electric current flows through fly-wheel diode VD from output terminals A ₂, VD ₁arrive P point, electric current is from load flow to output, and output terminals A point current potential still equates with P point current potential.Therefore, under being operated in this pattern time, output end voltage still equals P point current potential.Now, taking direct voltage central point O as zero potential, output voltage is U _dC/ 2, we represent this mode of operation with state code " P ", are called again " 2 " state.

(2) mode of operation 2-----VT ₂, VT ₃conducting, VT ₁, VT ₄turn-off.

If electric current is from neutral point O process clamp diode VD ₅, main power device VT ₂arrive output terminals A, electric current flows to load from output, and output current potential A equals O point current potential.If electric current is from output process main power device VT ₃, clamp diode flow into VD ₆neutral point, electric current is from load flow to output, and output current potential still equals O point electricity.VD in this case ₅, VD ₆with VT ₂, VT ₃together output current potential is clamped down in neutral point O current potential.Now, taking direct voltage central point 0 as 0 current potential, output voltage is 0, and we represent this mode of operation with state code " O ", are called again one state.

(3) mode of operation 3-----VT ₃, VT ₄conducting, VT ₁, VT ₂turn-off.

Similar with operating state 1, in like manner analysis, is not difficult to obtain the result that output terminals A point current potential is identical with N point current potential, now can obtain output end voltage to be-U _dC/ 2, we represent this mode of operation with state code " O ", are called again one state.

The steady operation of three level NPC type inverters has P, O, tri-kinds of patterns of N, need commutation from a kind of working mode change to another kind of mode of operation, can change to arbitrary another kind of mode of operation from a kind of mode of operation so? obviously, from three-level inverter in nature, do not allow two kinds of mode of operations of P and N directly to change, only allow the switching of P → O → N or N → O → P, this point must ensure in control procedure.

Taking a phase bridge arm circuit as example, introduce the process of NPC type inverter from the commutation of P state to O state below.

(1) if electric current flows to load from inverter

Suppose VT ₁, VT ₂for conducting state, current flowing path is P end → VT ₁→ VT ₂→ A end, inverter, in P state, as shown in Fig. 3 (a), in order to make inverter from P state to O state-transition, is first given VT ₁cut-off signals.Work as VT ₁after reliable turn-off, current flowing path becomes O end → VD ₅→ VT ₂→ A end, inverter is in O state, like this by VT ₁to VD ₅commutation process finish after, current flowing path becomes as shown in Fig. 3 (b).Now load end A point is current potential at zero point, and inverter enters O state mode of operation.

(2) if electric current flows to inverter from load end

Suppose the initial condition that Fig. 4 (a) is inverter conducting, current flowing path is A end → VD ₂→ VD ₁→ P end, the operating state of inverter is P this moment.In order to make inverter be transformed into O state from P state, should give VT ₂, VT ₃apply Continuity signal, give VT ₁, VT ₄apply cut-off signals, wherein to VT ₁shutoff can not impact whole circuit, but because the O point voltage of order than P is low, thereby the electric current major part that load comes is passed through from A end → VT ₃→ VD ₆the current flowing path of → O end, and the VD that flows through before making ₂→ VD ₁electric current reducing always, until be zero, as shown in Fig. 4 (b).This has just completed the commutation process that is switched to O state from P state.

In like manner obtain the handoff procedure between other mode of operations.

A control method for clamping type three-phase voltage source type inverter, first obtains two DC quantity u by three-phase symmetrical sinusoidal quantity by the instantaneous value control method based on synchronous rotating frame _dfand u _qf, secondly adopt double-layer structure controller, realize disturbance internal mold, finally the space voltage vector of inverter output is carried out to vector by fixing resultant vector method compound, and compound vector after compound is evenly distributed on α β coordinate plane.

In engineering reality, what people were concerned about is the voltage waveform in load.If the output of three brachium pontis of inverter joint three phase symmetry load, and connect neutral point n with Y.Output phase voltage is u _an(t), line voltage is u _aB(t).

Because load neutral point n and DC power supply neutral point O might not be equipotentials, establishing its potential difference is u _on, now load phase voltage u _anuseful following formula represents:

$u_{\mathrm{An}}=\frac{2}{3}{u}_{\mathrm{AO}}-\frac{1}{3}{u}_{\mathrm{BO}}-\frac{1}{3}{u}_{\mathrm{CO}}---\left(1\right)$

U _aO, u _aOand u _aObe respectively A, B, the C voltage with respect to neutral point O, under mono pulse control mode, in the time of α=30, trigger delay angle °, the voltage waveform between three phase terminals output centering point O as shown in Figure 5.Each phase power device has all experienced P, O, tri-states of N.Taking A mutually as example, interval works in O state, u _a0=0; ? interval operating state is P state, u _a0=+U _dC/ 2; Work in O state, u in (π/6, π～7) interval _a0=0; Work in N state, u in (7 π/6～2 π) interval _a0=-U _dC/ 2.According to the waveform of Fig. 5, can be listed in the interior residing operating state of every π/6 interval inverter three-phase brachium pontis of one-period in table 1.

Table 1

Can obtain A phase load at Bu Tong interval voltage u according to table 1 and formula 1 _an:

Interval $(0~\frac{\mathrm{\π}}{6})$ ? $u_{\mathrm{An}}=\frac{2}{3}\×0-\frac{1}{3}\×(-\frac{1}{2}{U}_{\mathrm{DC}})-\frac{1}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}=0$

Interval $(\frac{\mathrm{\π}}{6}~\frac{2\mathrm{\π}}{6})$ ? $u_{\mathrm{An}}=\frac{2}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}-\frac{1}{3}\×(-\frac{1}{2}{U}_{\mathrm{DC}})-\frac{1}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}=\frac{1}{3}{U}_{\mathrm{DC}}$

Interval $(\frac{2\mathrm{\π}}{6}~\frac{3\mathrm{\π}}{6})$ ? $u_{\mathrm{An}}=\frac{2}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}-\frac{1}{3}\×(-\frac{1}{2}{U}_{\mathrm{DC}})-\frac{1}{3}\×0=\frac{1}{2}{U}_{\mathrm{DC}}$

Interval $(\frac{3\mathrm{\π}}{6}~\frac{4\mathrm{\π}}{6})$ ? $u_{\mathrm{An}}=\frac{2}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}-\frac{1}{3}\×(-\frac{1}{2}{U}_{\mathrm{DC}})-\frac{1}{3}\×(-\frac{1}{2}{U}_{\mathrm{DC}})=\frac{2}{3}{U}_{\mathrm{DC}}$

Interval $(\frac{4\mathrm{\π}}{6}~\frac{5\mathrm{\π}}{6})$ ? $u_{\mathrm{An}}=\frac{2}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}-\frac{1}{3}\×0-(-\frac{1}{2}{U}_{\mathrm{DC}})=\frac{1}{2}{U}_{\mathrm{DC}}$

Interval $(\frac{5\mathrm{\π}}{6}~\mathrm{\π})$ ? $u_{\mathrm{An}}=\frac{2}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}-\frac{1}{3}\×\frac{1}{2}{U}_{\mathrm{DC}}-\frac{1}{3}\×(-\frac{1}{2}{U}_{\mathrm{DC}})=\frac{1}{3}{U}_{\mathrm{DC}}$

In like manner can try to achieve the u of 6 minizones in second half cycle _an, be followed successively by 0 ,-U _dC/ 3 ,-U _dC/ 2 ,-2U _dC/ 3 ,-U _dC/ 2 ,-U _dC/ 3.With u _anthe same, obtain after the same method u _bnand u _cnnumerical value, but other point of the time occurring lag behind 2 π/3 and 4 π/3 moment, therefore we just can obtain phase voltage waveform and the line voltage waveform of every phase load.Fig. 6 (a) is A phase phase voltage waveform, and Fig. 6 (b) is B phase phase voltage waveform, and Fig. 6 (c) is the line voltage waveform u between A, B _aB.

From the waveform of Fig. 6 phase voltage, can see, the trapezoidal wave that it is made up of 7 kinds of different voltages, these 7 kinds of magnitudes of voltage are respectively ± 2U _dC/ 3, ± U _dC/ 2, ± U _dC/ 3,0.

We use threephase switch S _a, S _b, S _cwith input voltage U _dCrepresent the three-phase phase voltage u of three-level inverter output _ao, u _bo, u _co

u _Ao＝(S _a-1)U _DC/2(S _a＝0,1,2) (2)

u _Bo＝(S _b-1)U _DC/2(S _b＝0,1,2) (3)

u _Co＝(S _c-1)U _DC/2(S _c＝0,1,2) (4)

The three-phase line voltage of inverter output is:

u _AB＝u _Ao-u _Bo＝(S _a-S _b)U _DC/2 (5)

u _AB＝u _Ao-u _Bo＝(S _a-S _b)U _DC/2 (6)

u _AB＝u _Ao-u _Bo＝(S _a-S _b)U _DC/2 (7)

After arrangement, obtain:

$\left[\begin{array}{c}{u}_{\mathrm{AB}}\\ u_{\mathrm{BC}}\\ u_{\mathrm{CA}}\end{array}\right]=\frac{U_{\mathrm{DC}}}{2}\left[\begin{array}{ccc}1& -1& 0\\ 0& 1& -1\\ -1& 0& 1\end{array}\right]\left[\begin{array}{c}{S}_a\\ S_b\\ S_c\end{array}\right]---\left(8\right)$

Three-phase tri-level inverter, by Park vector, obtains the expression formula of space voltage vector:

$\begin{array}{c}{u}_s=\frac{2}{3}(u_{\mathrm{An}}+{\mathrm{\αu}}_{\mathrm{Bn}}+{\mathrm{\α}}^2{u}_{\mathrm{Cn}})=\frac{2}{3}[(u_{\mathrm{Ao}}-u_{\mathrm{no}})+\mathrm{\α}(u_{\mathrm{Bo}}-u_{\mathrm{no}})+{\mathrm{\α}}^2(u_{\mathrm{Co}}-u_{\mathrm{no}})]\\ =\frac{2}{3}(u_{\mathrm{An}}+{\mathrm{\αu}}_{\mathrm{Bn}}+{\mathrm{\α}}^2{u}_{\mathrm{Cn}})\end{array}---\left(9\right)$

In formula, bring formula (9) into, obtain:

$u_s=\frac{1}{3}{U}_{\mathrm{DC}}(S_a+\mathrm{\α}{S}_b+{\mathrm{\α}}^2{S}_c)=\frac{1}{6}{U}_{\mathrm{DC}}[({2S}_a-S_b-S_c)+j\sqrt{3}(S_b-S_c)]---\left(10\right)$

Three-phase tri-level inverter has 27 kinds of different switch combinations, and each switch combination is a voltage vector of corresponding output all.Because the existence of redundancy, only 19 voltage vectors on corresponding α β plane, are referred to as basic voltage vectors.Fig. 7 corresponding space voltage vector figure while having provided corresponding all switch combinations.

Large hexagonal summit state (200,220,020,022,002,202).There are three kinds of possible nought states (222,111,000), correspond respectively to the full conducting of upper arm device, the full conducting of additional device, the full conducting of underarm device.As shown in Figure 7, interior hexagonal each space vector correspondence two kinds of possible on off states, in addition, also has the neutral point of six space vectors corresponding to the outer six each limits of distortion.

As shown in Figure 1, three-level inverter is made up of DC power supply, three-phase tri-level inverter bridge, three-phase LC filter and threephase load.Filter inductance is L, and filter capacitor is C, R _orepresent that inductor loss, line impedance and switching tube open and the gross effect of turn-off power loss etc.The reference direction of each voltage, electric current defines as shown in Figure 1.Adopt the instantaneous value control method based on synchronous rotating frame herein.Control system block diagram is as shown in Fig. 3,8.Three-phase symmetrical sinusoidal quantity, after coordinate transform, obtains two DC quantity u _dfand u _qf, as shown in Fig. 7 dotted line, adopt 2 layers of structure controller, realize disturbance internal mold: the adjusting of the tracking of traditional PI adjuster to Constant Direct Current instruction can reach floating, pi regulator can be realized the first-harmonic disturbance internal mold of DC input voitage, linear load disturbance; Repetitive controller is the controller based on the cycle, is applicable to the periodically non differential regulation of the amount of repetition, is used for suppressing harmonic wave and asymmetrical component, realizes harmonic disturbance and the asymmetric load disturbance internal molds such as dead band, nonlinear load, asymmetric load.Pi regulator and repetitive controller parallel operation, because pi regulator is the adjusting based on switch periods, and repetitive controller is the adjusting based on the primitive period, response speed difference, therefore two-layer controller is decoupling zero in time.

Pi regulator continuous domain model is

G(s)＝K _p+K _i/s (11)

The output that G in formula (s) is controller and the biography letter of error; K _pfor proportionality coefficient; K _ifor integral coefficient, s is s territory;

K _p, K _ivalue can adopt traditional PI method for designing, dynamic property and the steady-state error of main taking into account system.

Repetitive controller (RC) adopts following form

G(s)＝C(s)e ^-τs/(1-Q(s)e ^-τs) (12)

In formula, the output that G (s) is controller and the biography letter of error; τ is the interference signal cycle, and C (s) is the transfer function of PI controller, and Q (s) is the transfer function of secondary low pass filter.

The work that also will complete at repetitive controller passage is exactly the different phase shifts that compensate each secondary frequencies that output filtering and possible C (s) cause.Because the phase place of control object lags behind along with frequency increases, and differentiation element e ^{-τ s}amplitude is 1, and its phase angle is linear increasing along with frequency, if choose suitable parameter, likely in certain scope, fits, and therefore, ph_c differentiation element is taken as e ^{-τ s}, τ is the interference signal cycle.

After we replace two-level inverter with three-level inverter, although there had been the more selection of multivoltage vector, but increase undoubtedly the complexity of space voltage vector and optimization vector switch table, the problem of considering voltage jump and midpoint potential balance, this this patent has proposed the method for fixing resultant vector.

Fixing resultant vector refers to the compound vector that some specific resolutes are combined, the space voltage vector that they are exported by inverter combines according to certain synthesis mode, and be evenly distributed on α β coordinate plane, such as two fixing small vectors and fixing large vector are according to certain synthetic compound vector that becomes.Fixing resultant vector is divided into two kinds, and the first is middle vector correlation resultant vector, and the second is large vector correlation resultant vector.If three-level inverter is the excessive and midpoint potential imbalance of voltage jump in order to solve two problems, therefore we can select suitable resolute and combine according to reasonable manner two the above problems that solve.

With S _abc=210 is example, carrys out centering vector correlation resultant vector and describes, and the on off state of supposing a sampling period is 210, and can check the mid point electric current of answering according to table 2 is i _b, can not be generally zero, therefore midpoint potential can be offset.According to mid point current i ₀=i _a+ i _b+ i _c=0 this character, we can look for i _aand i _bcorresponding on off state, can find as small vector 100 and 221 according to table 2, so we add small vector 221 and 100 within this cycle, and make the action time of their three vectors identical, so that the mean value vanishing of mid point electric current has solved the problem of mid-point potential offset.And because action time of three vectors is identical, so the vector after synthetic by them and the direction of original middle vector are identical as Fig. 9 (a), only variable size.We can find out in fixed vector and solve thus.

The mid point electric current that in table 2, small vector is corresponding

There is not the problem of mid-point potential offset in large vector, but in the time that converting other vectors to, large vector is easy to develop the phenomenon of voltage jump, use zero vector or small vector to synthesize and contribute to reduce voltage jump, be therefore also very important for the synthetic of large vector.Taking 200 as example, large vector correlation resultant vector is described.The on off state of supposing one-period is large vector 200, as finding out the direction of large vector, Fig. 7 equates with small vector 100 and 211 directions, table 2 is found 100 and 211 corresponding mid point current opposite in direction, in this one-period, add small vector 100 and 211 simultaneously, and equated to their action time, therefore the median average current potential that can release in this cycle is zero, and the direction of resultant vector is constant as Fig. 9 (b), and ensures that shift phenomenon does not occur mid-point voltage.

Can be found out by analysis above, for vector in synthetic, length is the longest can be 2/3 times of raw footage, if add zero vector, synthetic in the length of vector can between 0～2/3 of raw footage times, change; For synthetic large vector, can there is the small vector action time of adjustment and add two kinds of methods of zero vector: the former can make large vector change between 1/2～1 times of raw footage; The latter can make it between 0～1 times of raw footage, adjust arbitrarily.

In the control method of fixed vector, in centering vector synthetic, we utilize i ₀=i _a+ i _b+ i _c=0 this principle, in centering vector synthetic, 2 small vectors that the electric current corresponding from middle vector is different selecting, and make their action time identical, and be zero thereby make mid point electric current, midpoint potential is not offset.To in large vector synthetic, we select and two small vectors of the large same direction of vector, because their size of current equate, opposite direction, thus be zero at mid point electric current, and midpoint potential does not occur in the situation of skew, reduced voltage jump, table 3 is synthetic sequence list.

The composition sequence of the fixing resultant vector of table 3

As can be seen from the above table, in fixing resultant vector process, vector between two vectors switches can not produce too high voltage jump, in order better to reduce voltage jump, in fixed vector synthetic, we always think that zero vector is as synthetic starting point, thereby realize taking over seamlessly between vector, reduced voltage jump.

According to the composition principle of above-mentioned space vector, we can be synthetic vector in large vector 12 space vectors, and the direction of these 12 space vectors and the direction of former vector constant, only variable size, and all fixing resultant vectors are numbered in order; By fixing resultant vector, can divide 3 level space vector according to the division methods of two level direct torque control space vectors.As Figure 10 shows, taking resultant vector as dotted line, be the regulation of 30 ° according to each equal portions, α β plane is divided into 12 equal-sized equal portions, number identical with the fixing resultant vector taking it as center line.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (8)

1. one kind based on three-level NPC inverter, it is characterized in that: comprise DC power supply, three-phase tri-level inverter bridge, three-phase LC filter and threephase load, described three-phase tri-level inverter bridge comprises three single phase circuits that are connected in parallel and first, second electric capacity; Described the first electric capacity, DC power supply, the second electric capacity are cascaded successively; Each single phase circuit comprises first, second, third, fourth power device, first, second, third, fourth fly-wheel diode and first, second clamp diode; Described first, second, third, fourth fly-wheel diode is connected in parallel on respectively on first, second, third, fourth power device successively, describedly connect successively at first, second, third, fourth power device and second, the first electric capacity, the wire that is connected between described first clamp diode one end and first, second four power device connects, and the other end connects in 0 of the zero potential of the connection wire between first, second electric capacity; The wire that is connected between described second clamp diode one end and the 3rd, the four or four power device connects, 0 of the zero potential that the other end connects the connection wire between first, second electric capacity goes up, and described first, second clamp diode is positioned on the neutral point in intermediate dc loop; Also comprise first, second, third filter inductance and first, second, third filter capacitor, described first, second filter capacitor is connected in parallel on the two ends of threephase load with the 3rd filter capacitor after mutually connecting, described three single phase circuits are respectively first, second, third single phase circuit, described first filter inductance one end is connected on the connection wire between second, third power device on the first single phase circuit, and the other end is connected on the first filter capacitor; Described second filter inductance one end is connected on the connection wire between second, third power device on the second single phase circuit, and the other end is connected in threephase load; The 3rd filter inductance one end is connected on the connection wire between second, third power device on the first single phase circuit, and the other end is connected on the second filter capacitor; Described three level refer to that the every phase output terminal of inverter AC obtains the output voltage of three kinds of states from middle DC loop, be respectively positive terminal voltage P, negative terminal voltage N and zero potential 0; The output voltage of described inverter has three kinds of state :+U _dC/ 2 ,-U _dC/ 2,0.

2. the control method based on clamping type three-phase voltage source type inverter claimed in claim 1, is characterized in that: first three-phase symmetrical sinusoidal quantity is obtained to two DC quantity u by the instantaneous value control method based on synchronous rotating frame _dfand u _qf, secondly adopt double-layer structure controller, realize disturbance internal mold, finally the space voltage vector of inverter output is carried out to vector by fixing resultant vector method compound, and compound vector after compound is evenly distributed on α β coordinate plane.

3. the control method of clamping type three-phase voltage source type inverter according to claim 2, it is characterized in that: described employing double-layer structure controller, realize the method for disturbance internal mold: adopt pi regulator and repetitive controller parallel operation, the adjusting of the tracking of described traditional PI adjuster to Constant Direct Current instruction can reach floating, and pi regulator can be realized the first-harmonic disturbance internal mold of DC input voitage, linear load disturbance; Repetitive controller is the controller based on the cycle, for the non differential regulation of the periodicity amount of repetition, is used for suppressing harmonic wave and asymmetrical component, realizes harmonic disturbance and the asymmetric load disturbance internal molds such as dead band, nonlinear load, asymmetric load.

4. the control method of clamping type three-phase voltage source type inverter according to claim 2, is characterized in that: described pi regulator continuous domain model is:

G(s)＝K _p+K _i/s

The output that G in formula (s) is controller and the biography letter of error; K _pfor proportionality coefficient; K _ifor integral coefficient, s is s territory; The form of described repetitive controller is as follows:

G(s)＝C(s)e ^-τs/(1-Q(s)e ^-τs)

(12)

In formula, the output that G (s) is controller and the biography letter of error; τ is the interference signal cycle, and C (s) is the transfer function of PI controller, and Q (s) is the transfer function of secondary low pass filter.

5. the control method of clamping type three-phase voltage source type inverter according to claim 2, is characterized in that: the described work that also will complete at repetitive controller passage is exactly the different phase shifts that compensate each secondary frequencies that output filtering and possible C (s) cause.

6. the control method of clamping type three-phase voltage source type inverter according to claim 2, it is characterized in that: it is compound that the space voltage vector of described inverter output carries out vector by fixing resultant vector method, comprises middle vector resultant vector and large vector resultant vector.

7. the control method of clamping type three-phase voltage source type inverter according to claim 2, is characterized in that: the method for described middle vector resultant vector: utilize i ₀=i _a+ i _b+ i _c=0 this principle, 2 small vectors that the electric current corresponding from middle vector is different of selection, and make their action time identical, and be zero thereby make mid point electric current, midpoint potential is not offset.

8. the control method of clamping type three-phase voltage source type inverter according to claim 2, it is characterized in that: the method for described large vector resultant vector: select two small vectors with the large same direction of vector, because their size of current equate, opposite direction, thereby be zero at mid point electric current, midpoint potential does not occur, in the situation of skew, to have reduced voltage jump.