CN100382426C - Vector optimizing control for medium-voltage high-power three-level DC-to-AC inverter - Google Patents

Abstract

The present invention relates to a vector optimizing and controlling method for a medium-voltage, high-power and three-level inverting device, which is characterized in that voltage space vectors of alternating-current output voltage of an inverter, which are corresponding to 27 kinds of combined states of three phases of switches, are arranged into an orthohexagonal vector distributing map composed of 24 regular triangles in an alpha coordinate system and a beta coordinate system according to the sizes of the voltage space vectors, and then the modulation of a selecting optimizing sequence is carried out according to voltage vectors represented by three nodes of the regular triangles that reference voltage vectors with different modulating depths are positioned and the states of the three phases of switches corresponding to the voltage vectors. The state of a switch is only permitted by the selecting optimizing sequence to be changed when the states of the adjacent switches are exchanged. The technical problems that the smooth transition of output voltage of the inverter is realized in the process of PWM modulation exchange, harmonic contents are reduced, a switching device is prevented from being damaged by bearing oversize stress, and operating reliability is enhanced are solved by the present invention.

Description

Middle vector optimization control method of pressing high-power three level inverter

Technical field:

The invention relates to power transformation, particularly about the control method of three level inverter.

Background technology:

Advance over year, along with the expansion utilization of electric energy in each field, the scope of application of high-power three-level inverter also enlarges gradually.How the control inverter reliability service also seems becomes more and more important.At present the known control method of multi-electrical level inverter by the PWM modulation mostly is the control that the inverter neutral point voltage is fluctuateed, for example the ZL96199540.8 Chinese invention patent disclose a kind of by control rectifying device control neutral point voltage, except wanting voltage-operated device, still needing is provided with correcting device, with the deviation signal that neutral point voltage point detects the voltage of neutral point is controlled.This method of coming the fluctuation of control inverter neutral point voltage by the control rectifying device with voltage-operated device and correcting device is the device therefor complex structure not only, and seems loaded down with trivial details.Solve the vector optimization of inverter in the PWM modulated process and the technical problem of minimum pulse width processing owing to be provided with, cause inverter in the modulation handoff procedure, it is excessive unexpected fluctuation and the harmonic content of output voltage from+E to-E to occur, and it is not steady to work, and switching device stress is excessive fragile.

Summary of the invention:

The present invention aims to provide a kind of middle vector optimization control method of pressing high-power three level inverter, solve inverter output voltage in PWM modulation handoff procedure and realize seamlessly transitting, reducing harmonic content, avoid switching device to bear excessive stresses and damage, improve the technical problem of its reliability of operation.

The technical scheme that the present invention solves the problems of the technologies described above is as follows:

Press the vector optimization control method of high-power three level inverter in a kind of, it is characterized in that: with the space voltage vector of the inverter ac output voltage of 27 kinds of assembled state of corresponding threephase switch by its size at α, be arranged in an orthohexagonal vector distribution map of forming by 24 equilateral triangles in the β coordinate system, the modulation of selecting to optimize order according to voltage vector and its corresponding on off state of three node representatives of the reference voltage vector of different modulating degree of depth equilateral triangle of living in then, this optimization order is only permitted when the adjacent switch state switches, is had only the state of a switch to change.

Press the vector optimization control method of high-power three level inverter in described, it is characterized in that: when modulation depth during in the low modulation district, this vector optimization order adopts the Vector Modulation scheme of two level P type vector order of actions of two level N type vectors of no-voltage O level, negative voltage N level or no-voltage O level, positive voltage P level.

Press the vector optimization control method of high-power three level inverter in described, it is characterized in that: when modulation depth during in the high modulation district, this vector optimization order adopts three level Vector Modulation schemes of positive voltage P level, no-voltage O level, negative voltage N level.

Press the vector optimization control method of high-power three level inverter in described, it is characterized in that: with the burst pulse that program software is differentiated and processing exists in PWM period T s, its program is as follows:

1) determines the modulator zone at place according to modulation depth;

2) if be in the low modulation district, adopt two level vector optimization schemes that burst pulse does not take place;

3), judge whether the three level vector optimization schemes that adopted can exist burst pulse if not in the low modulation district;

4) if do not have burst pulse, then do not adjust;

5) if having burst pulse, then this burst pulse duration of forcibly changing t _dTo eliminate burst pulse.

Press the vector optimization control method of high-power three level inverter in described, it is characterized in that: judge if there is burst pulse to exist, then by following processing:

(1) t _dThe minimum pulse width time t that＜switching device allowed _Min, force t at/2 o'clock _d=0;

(2) t _Min/ 2＜t _d＜t _MinThe time, force t _d=t _Min

(3) Ts-t _Min＜t _d＜Ts-t _Min/ 2, force t _d=Ts-t _Min

(4) Ts-t _Min/ 2＜t _d＜Ts forces T _d=Ts.

Press the vector optimization control method of high-power three level inverter in described, it is characterized in that: when modulation depth is in the low modulation district, if inverter neutral point voltage fluctuation, adopt the mutual Vector Modulation scheme of using of P type vector and N type vector order of action, make neutral point voltage in a basic balance.

Press the vector optimization control method of high-power three level inverter in described, it is characterized in that: when modulation depth is in the high modulation district, if inverter neutral point voltage fluctuation, adopt the balance that keeps neutral point voltage in a PWM changes small vector in the P type vector or the small vector in the N type vector in the cycle duration.

The invention has the advantages that:

Through behind the vector optimization, can make between the adjacent switch device when state switches, have only the switching device of a brachium pontis to move, reduced the harmonic content in the output voltage, runnability is provided.

The variation of every phase on off state all E, O or O ,-change between the E, do not exist E to arrive-the direct variation of E, reduced the suffered stress of switching device greatly, avoid the damage of switching device effectively, improved reliability of operation.

Can handle minimum pulse width easily, guarantee at any PWM in the cycle, pulse duration is all greater than the necessary minimum pulse width of switching device, makes the switching device can reliably working.

Make inverter itself directly control the voltage fluctuation that suppresses neutral point, saved a set of equipment rectifying device control.

Description of drawings:

Fig. 1 is three level space voltage vector distribution maps of the present invention.

Fig. 2 is the vector and the time layout of O sector among Fig. 1.

Fig. 3 is a low modulation district vector time layout.

Fig. 4 is a high modulation district vector time layout.

Fig. 5 is the schematic diagram of three-level inverter.

Fig. 6 is burst pulse handling procedure figure.

Embodiment:

The switch of the every phase of three-level inverter has-1,0,1 three kind of state, the AC side output voltage of corresponding these three kinds of states for-E, O, E (being negative voltage N, no-voltage O, positive voltage P), concerning a three-phase symmetrical system, 27 kinds of on off state combinations of one-tenth capable of being combined altogether, the then corresponding space voltage vector of each on off state combination, therefore a symmetrical three-level inverter is had 27 different space voltage vectors, wherein, amplitude is that the big vector of 2/3E has

Six, amplitude is that the middle vector of 1/3E has

Six, amplitude is that the P type small vector of 1/3E has

Six, amplitude is that the N type small vector of 1/3E has

Six, amplitude is that 0 zero vector has

Three.With

Vector is an example, expression three-level inverter AC side A, B, C three with respect to the output voltage of neutral point just be divided into, zero, negative, and the state of corresponding three brachium pontis switching devices of inverter (referring to Fig. 5) is respectively: A phase Sa1, Sa2 are open-minded, and Sa3, Sa4 turn-off; B phase Sb2, Sb3 are open-minded, and Sb1, Sb4 turn-off; C phase Sc1, Sc2 turn-off, and Sc3, Sc4 are open-minded.

Keep constant and two capacitor C 1 equate that with C2 voltage the distribution of then above-mentioned 27 different space voltage vectors in α, β coordinate system is illustrated in figure 1 as a regular hexagon of being made up of 24 equilateral triangles at its DC side bus P, N voltage.Three zero vectors Be positioned at the hexagon mid point, six big vectors

Divide to occupy six summits of hexagon, six P types and N type small vector are corresponding respectively be in medium and small hexagonal six summits, and six middle vectors are positioned at the mid point on the every limit of hexagon.With the α axle is that benchmark is rotated counterclockwise, and can be that an interval division becomes 0～5 six sector with 60 ° with above-mentioned hexagon, and existing to be example with 0 sector elaborate to the modulation scheme of vector optimization order of the present invention.

Be divided in 0 sector among Fig. 2 is 7 zones, wherein be equal to or less than the area 0 of set point (this set point is 0.15 in actual applications) for modulation depth k by the little sector that camber line surrounded, also be the low modulation district, 1～6 zone is the high modulation district of modulation depth greater than set point.Because any one space voltage vector is all formed with its nearest vector by three, so any order of action of vector all is combined into by three vectors, and vector optimization is exactly in the time of will making the order of action of vector should guarantee that the adjacent switch state switches, to have only a state to change.With the difference of modulation depth, the scheme of vector order of action is also different.When modulation depth is low, reference voltage vector V _Ref(being the corresponding effective voltage of exporting of the actual institute of inverter) in low modulation area 0, the order of action of its vector optimization is as follows:

${\stackrel{\‾}{V}}_{\mathrm{OOO}}-{\stackrel{\‾}{V}}_{\mathrm{POO}}-{\stackrel{\‾}{V}}_{\mathrm{PPO}}-{\stackrel{\‾}{V}}_{\mathrm{PPP}}-{\stackrel{\‾}{V}}_{\mathrm{PPO}}-{\stackrel{\‾}{V}}_{\mathrm{POO}}-{\stackrel{\‾}{V}}_{\mathrm{OOO}}$ (P type)

Or

${\stackrel{\‾}{V}}_{\mathrm{OOO}}-{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{ONN}}-{\stackrel{\‾}{V}}_{\mathrm{NNN}}-{\stackrel{\‾}{V}}_{\mathrm{ONN}}-{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{OOO}}$ (N type)

From the vector optimization order of action of above-mentioned P type or N type as can be known the level state of inverter threephase switch only at O to P again to O (being O-E-O), or O to N again to changing between the O (being O-E-O), also promptly adopt two level scoping schemes.Can see simultaneously that the space voltage vector that initial sum stops in the low modulation district is

So in switching device attonity from PWM cycle inverter to another PWM cycle handoff procedure.When modulation depth is high, press reference voltage vector

The N type of residing regional 1～6 triangular apex or P type small vector are start vector, serve as to stop vector with the homotype small vector of triangular apex, adopt three level scoping schemes to carry out vector optimization.Reference voltage vector for example

At regional 3 o'clock, be that the optimization order that initial sum stops vector is with N type small vector ${\stackrel{\‾}{V}}_{\mathrm{ONN}}-{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{PON}}-{\stackrel{\‾}{V}}_{\mathrm{POO}}-{\stackrel{\‾}{V}}_{\mathrm{PON}}-{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{ONN}},$ In this order of action, the inverter threephase switch have P, O, N (be E, O ,-E) three kinds of level states, but the on off state of A phase only be by O to P again to O, B, C two-phase on off state all are to be changed to N to O by N again, do not exist P to the direct variation between the N; In this order of action, when switching between the adjacent switch state, have only the switching device of a brachium pontis to move.Work as reference voltage vector

When low modulation district (area 0) switches between high modulation district (zone 1～6), vector be

With Or

With

Between switch, the switching device that promptly has only a brachium pontis is in action.Work as reference voltage vector

When switching between the high modulation district, be example with N type small vector, its vector changes to be had: ${\stackrel{\‾}{V}}_{\mathrm{ONN}}-{\stackrel{\‾}{V}}_{\mathrm{ONN}},{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{OON}},{\stackrel{\‾}{V}}_{\mathrm{ONN}}-{\stackrel{\‾}{V}}_{\mathrm{OON}},{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{ONN}}$ Four kinds of forms, preceding two kinds of situations inverter switch device state in handoff procedure does not change, and back two kinds of situations have only the switching device action of a brachium pontis of inverter equally in handoff procedure.

The vector duration on each summit is respectively in each equilateral triangle shown in Fig. 2: t _a=Ts * ksin (θ-π/3); t _b=Ts * Ksin (θ), t _c=1/2Ts[1-2Ksin (θ+2/3)], Ts is PWM cycle time in the formula, k is a modulation depth.Reference voltage vector for example

In the low modulation district of area 0, select the optimization function order of P type small vector: ${\stackrel{-}{V}}_{\mathrm{OOO}}-{\stackrel{-}{V}}_{\mathrm{POO}}-{\stackrel{-}{V}}_{\mathrm{PPO}}-{\stackrel{-}{V}}_{\mathrm{PPP}}-{\stackrel{-}{V}}_{\mathrm{PPO}}-{\stackrel{-}{V}}_{\mathrm{POO}}-{\stackrel{-}{V}}_{\mathrm{OOO}},$ Then a PWM in the cycle vector time distribute and pairing PWM ripple as shown in Figure 3, wherein minimum is t the pulsewidth time of A phase _c/ 2, B mutually with the C pulsewidth time mutually all greater than t _c/ 2, because modulation depth k is less, t _cMuch larger than the minimum pulse width that switching device allowed, so the two level vector optimization order of actions that the present invention adopts when modulation depth is hanged down k less than set point have been avoided the appearance of minimum pulse.And when modulation depth is high, as work as reference voltage vector

At regional 3 o'clock, be the three level vector optimization order of actions that initial sum stops vector with N type small vector ${\stackrel{\‾}{V}}_{\mathrm{ONN}}-{\stackrel{\‾}{V}}_{\mathrm{OON}}-$ ${\stackrel{\‾}{V}}_{\mathrm{PON}}-{\stackrel{\‾}{V}}_{\mathrm{POO}}-{\stackrel{\‾}{V}}_{\mathrm{PON}}-{\stackrel{\‾}{V}}_{\mathrm{OON}}-{\stackrel{\‾}{V}}_{\mathrm{ONN}}$ Be example, its PWM in the cycle vector time distribute and pairing PWM ripple as shown in Figure 4, wherein minimum is t the B phase pulsewidth time _a/ 2, A mutually with the C pulsewidth time mutually all greater than t _a/ 2, because the modulation depth height, the k value changes t in a big way _aNumerical value is interior in a big way to change t _a/ 2 minimum pulse width is little to the influence of systematic function.Now establish t _a/ 2=t _d, have only the t of working as _dLess than the minimum pulse width time t that switching device allowed _Min(be t _d＜t _MinThe service time of switching device is too short), or t _d＞Ts-t _MinWhen (turn-off time of switching device is too short), just burst pulse can occur, remove in addition, not have burst pulse.When burst pulse occurring, need to be optimized at the different situations paired pulses, change pulse duration t _d:

If t _d＜t _Min/ 2, force t _d=0;

If t _Min/ 2＜t _d＜t _Min, force t _d=t _Min

If Ts-t _Min＜t _d＜Ts-t _Min/ 2, force t _d=Ts-t _Min

If Ts-t _Min/ 2＜t _d＜Ts forces t _d=Ts-t _Min

Above-mentioned burst pulse is handled and is undertaken by following program (referring to Fig. 6) by software:

1. program begins;

2. differentiate modulation depth and whether be in the low modulation district, differentiating really, low modulation district, place then adopts two flat arrow electro ultrafiltration scheme, termination routines then;

3. if differentiate modulation depth not in the low modulation district, then further whether differentiation has the burst pulse existence, if judge that not having burst pulse exists, with regard to termination routine;

4. if differentiation has burst pulse to be existed, prolong the burst pulse duration by four kinds of different situations;

5. termination routine.

Table 1

The electric current of various P types and N type small vector inflow neutral point is as shown in table 1, and the electric current that corresponding P type and N type small vector flow into neutral point is just in time opposite.When modulation depth is in the low modulation district, if voltage fluctuation appears in the inverter neutral point, because employing is two level vector optimization order of action schemes, at a PWM P type small vector or N type small vector only appearred in the cycle.Therefore adopt P type vector optimization order of action when the last PWM cycle, then next PWM cycle is adopted corresponding N type small vector optimization function order, can keep the voltage of neutral point in a basic balance, and not need to control by transformer.When modulation depth during in the high modulation district, because what adopt is three level vector optimization order of action schemes, there are P type and N type small vector in cycle simultaneously at a PWM, these two kinds of small vectors are identical to the voltage effect of output, but the effect of voltage to neutral is opposite, therefore can keep changing the duration of P, N type small vector as required under the constant condition of vector duration summation, keep the voltage weighing apparatus of neutral point fixed.See also Fig. 5, if flow into neutral point current i _Np＞0, capacitor C then ₂Be recharged capacitor C ₁Discharge also is a capacitor C ₂Voltage Vc ₂Greater than capacitor C ₁Voltage Vc ₁What adopt is three level vector optimization order of action, wherein P type small vectors shown in Figure 4

N type small vector with correspondence The electric current that flows into neutral point separately is respectively-Ia and Ia, then can increase P type small vector Duration, flow into the current i of neutral point _Np=-Ia＜0, capacitor C ₁Charging, and capacitor C ₂Discharge makes voltage Vc ₂Reduce voltage Vc ₁Increase, both are tending towards equal, thereby keep neutral voltage balancing; In this simultaneously, corresponding minimizing N type small vector Duration, but total vector duration is constant.On the contrary, if voltage Vc ₁Greater than voltage Vc ₂, then increase N type small vector

Duration, the current i of inflow neutral point _Np=Ia＞0, capacitor C ₁Discharge, capacitor C ₂Charging makes voltage Vc ₁Descend and voltage Vc ₂Increase, both are tending towards equal.As seen the present invention can make the balance of voltage of inverter self control neutral point, and needn't be by external devices or equipment such as transformers.

Claims (7)

1. press the vector optimization control method of high-power three level inverter in one kind, it is characterized in that; The space voltage vector of the inverter ac output voltage of 27 kinds of assembled state of corresponding threephase switch is arranged in an orthohexagonal vector distribution map of being made up of 24 equilateral triangles by its size in α, β coordinate system, the modulation of selecting to optimize order according to voltage vector and its corresponding on off state of three node representatives of the reference voltage vector of different modulating degree of depth equilateral triangle of living in then, this optimization order is only permitted when the adjacent switch state switches, is had only the state of a switch to change.

2. press the vector optimization control method of high-power three level inverter in according to claim 1, it is characterized in that: when modulation depth during in the low modulation district, this vector optimization order adopts the Vector Modulation scheme of two level P type vector order of actions of two level N type vectors of no-voltage O level, negative voltage N level or no-voltage O level, positive voltage P level.

3. press the vector optimization control method of high-power three level inverter in according to claim 1, it is characterized in that: when modulation depth during in the high modulation district, this vector optimization order adopts three level Vector Modulation schemes of positive voltage P level, no-voltage O level, negative voltage N level.

4. according to claim 1,2 or 3 described middle vector optimization control methods of pressing high-power three level inverter, it is characterized in that: with the burst pulse that program software is differentiated and processing exists in PWM period T s, its program is as follows:

1) determines the modulator zone at place according to modulation depth;

2) if be in the low modulation district, adopt two level vector optimization schemes, burst pulse does not take place;

3), judge whether the three level vector optimization schemes that adopted can exist burst pulse if not in the low modulation district;

4) if do not have burst pulse, then do not adjust;

5) if having burst pulse, then this burst pulse duration of forcibly changing t _dTo eliminate burst pulse.

5. press the vector optimization control method of high-power three level inverter in according to claim 4, it is characterized in that: judge if there is burst pulse to exist, then by following processing:

(1) t _dThe minimum pulse width time t that＜switching device allowed _Min, force t at/2 o'clock _d=0;

(2) t _Min/ 2＜t _d＜t _MinThe time, force t _d=t _Min

(3) Ts-t _Min＜t _d＜Ts-t _Min/ 2, force t _d=Ts-t _Min

(4) Ts-t _Min/ 2＜t _d＜Ts forces T _d=Ts.

6. press the vector optimization control method of high-power three level inverter in according to claim 2, it is characterized in that: when modulation depth is in the low modulation district, if inverter neutral point voltage fluctuation, adopt the mutual Vector Modulation scheme of using of P type vector and N type vector order of action, make neutral point voltage in a basic balance.

7. press the vector optimization control method of high-power three level inverter in according to claim 3, it is characterized in that: when modulation depth is in the high modulation district, if inverter neutral point voltage fluctuation, adopt the balance that keeps neutral point voltage in a PWM changes small vector in the P type vector or the small vector in the N type vector in the cycle duration.

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