CN109347358A - A kind of three level NPC current transformer neutral-point potential balance control methods - Google Patents
A kind of three level NPC current transformer neutral-point potential balance control methods Download PDFInfo
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- CN109347358A CN109347358A CN201811265428.3A CN201811265428A CN109347358A CN 109347358 A CN109347358 A CN 109347358A CN 201811265428 A CN201811265428 A CN 201811265428A CN 109347358 A CN109347358 A CN 109347358A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
- H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
- H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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Abstract
A kind of three level NPC current transformer neutral-point potential balance control methods.The control method is to calculate target to keep in each sampling period midpoint potential oscillation to be zero, obtains corresponding neutral-point potential balance formula in different sectors and region when midpoint potential oscillation is more than limit value；It is adjusted in real time for alignment potential balance, sector and regional location where the control method first determines whether present instruction voltage, then three-phase electricity flow valuve and space vector angle are detected, current sector and region is substituted into correspond to neutral-point potential balance formula and calculated, obtain the action time factor of redundancy small vector, the action time of two redundancy small vectors is controlled, it can be achieved that the dynamic equilibrium of alignment current potential is adjusted using the action time factor.Control method of the present invention can control three level NPC current transformer midpoint potential deviations in smaller range, improve the reliability of three level NPC current transformers.
Description
Technical field
The present invention relates to a kind of neutral-point potential balance control methods, more particularly to a kind of three level NPC current transformer midpoints electricity
Position balance control method.
Background technique
The topology of three level NPC (Neutral Point Clamped) current transformer as shown in Figure 1, by control three-phase by
The conducting and shutdown of top to bottm each four switching devices P1, P2, P3, P4, the exportable three kinds of different electricity of three level NPC current transformers
Level state.The advantages of three level NPC current transformers have small volume, structure simple, easily realize energy in bidirectional flow, it is general at present
All over the speed regulation occasion for being applied to mesohigh heavy-duty motor.
SVPWM (Space Vector Pulse Width Modulation) is that three level NPC current transformers are commonly used
A kind of modulation strategy.Classical SVPWM method is based on nearest three vectors principle, i.e., converts to obtain instruction electricity by three-phase voltage dq
Press Vref, then by command voltage VrefThree space vector of voltage and respective action time are decomposed into the product in sampling period
Product exports target voltage by the sequence of operation of three space vector of voltage of reasonable arrangement, to realize modulation.
Space vector of voltage distribution of the three level NPC current transformers in each space angle section is as shown in Figure 2.V in Fig. 2A、
VB、VCRespectively correspond the phase voltage of A phase, B phase, C phase, such as 0 °, the 90 ° space vector angle for angularly representing corresponding degree, i.e., three
Acquired command voltage V after phase voltage dq variationrefWith the angle between A phase phase voltage.Define command voltage VrefIt coincides with A
When space vector angle be 0 °, 360 degree space vector angles, one voltage fundamental period of correspondence.Fig. 2 PPP, PPO etc. represent phase
The space vector of voltage answered, the corresponding switch state of each space vector of voltage is summarized in table 1 in Fig. 2.
Each space vector of voltage of 1 SVPWM of table and corresponding switch state
As shown in table 1, each space vector of voltage of SVPWM can be divided into zero vector, small vector, middle vector sum according to amplitude size
Big vector, wherein there are redundant states for zero vector and small vector.For small vector, identical two p-types of space vector angular phasing
Small vector and N-type small vector are mutually redundant small vector.Each redundancy small vector and its corresponding electric current for flowing through midpoint are summarized in table 2.
2 redundancy small vector of table and its corresponding midpoint electric current
In table 2, ioThe corresponding midpoint electric current for flowing through midpoint, ia、ib、icRespectively correspond the phase current of A phase, B phase, C phase.By
Table 2 knows that the corresponding current direction for flowing through midpoint of two redundancy small vectors is on the contrary, therefore the shadow of two redundancy small vector alignment current potentials
It rings opposite.
For tri- level NPC current transformer of Fig. 1, if flowing into the electric current at midpoint and the product of time in a sampling period
Not equal to the electric current and the product of time at outflow midpoint, charging voltage and the discharge voltage that will lead to capacitor C1, C2 are unequal, into
And cause midpoint potential uneven.Unbalanced midpoint potential can generate low-order harmonic in output voltage and make three level NPC
The switching device of current transformer one side of something bridge arm bears excessively high voltage, jeopardizes operational safety, it is therefore necessary to take measures to guarantee
Three level NPC current transformer neutral-point potential balances.
Existing neutral-point potential balance control method can be classified as hardware approach and software approach.Document is " based on mixing SVPWM
The NPC three-level inverter neutral-point voltage balance of method " (Tianjin Shao Hongjun, [D]: University Of Tianjin, 2012:4-7) detailed
It compared common hardware approach and software approach.Compared to hardware approach, software approach, which does not need to increase additional hardware, to be set
Standby and control system just can control neutral point voltage balance, can reduce volume, save cost, be a kind of preferable selection.Three
The usually used software approach of level NPC current transformer can be divided into two classes:
1) Hysteresis control: basic principle is when there is midpoint potential energy imbalance, according to the direction of three-phase current, choosing
The redundancy small vector switch state for being conducive to neutral-point potential balance is taken to be regulated and controled.The advantages of Hysteresis control is not will increase out
Frequency is closed, the disadvantage is that there are power uncontrolled range domains when the bigger or power-factor angle of modulation is lower.
2) active control: the method for representative has Virtual Space vector method.Active control advantage be complete modulation ratio and power because
Neutral-point potential balance can be regulated and controled in number angular region, the disadvantage is that will increase the switching frequency of one third.
For high-power three-level NPC current transformer, the switching loss that switching device acts every time is very important, therefore to use up
Amount reduces the switching frequency of switching device.Only when the bigger or power-factor angle of modulation is lower, there are uncontrollable areas for Hysteresis control
Domain can effectively control neutral-point potential balance in most cases.Therefore stagnant for high-power three-level NPC current transformer
Ring control is most common neutral-point potential balance control method.
Hysteresis control needs to design Hysteresis control parameter, and whether proper will have a direct impact on is the design of Hysteresis control parameter value
The control effect of system alignment potential balance.When the design of Hysteresis control parameter value is not accurate enough, the robustness of system is poor, right
The control effect of neutral-point potential balance is poor.And under different operating conditions, Hysteresis control parameter value may be different, need to set again
Meter.
Summary of the invention
The purpose of the present invention is overcoming the disadvantages mentioned above of the prior art, a kind of three level NPC current transformer midpoint potentials are proposed
Balance control method.Three level NPC current transformer neutral-point potential balance control method principles of the invention are identical with Hysteresis control, are
Neutral-point potential balance is maintained using the action time for redistributing two redundancy small vectors, but is different from the stagnant ring method of tradition,
Control method of the present invention is without designing Hysteresis control parameter, it is only necessary to know that three-phase electricity flow valuve and space vector angle value, it can be online
Calculate the two redundancy small vector action time factors.Control method of the present invention can be inclined by three level NPC current transformer midpoint potentials
Difference control in smaller range, improves the reliability of three level NPC current transformers.
Three level NPC current transformer neutral-point potential balance control methods of the invention when midpoint potential oscillation is more than limit value,
It is to calculate target to keep in each sampling period midpoint potential oscillation to be zero, obtains corresponding midpoint in different sectors and region
Potential balance formula；It is adjusted in real time for alignment potential balance, control method of the present invention first determines whether present instruction voltage
Then place sector and regional location detect three-phase electricity flow valuve and space vector angle, it is corresponding to be substituted into current sector and region
Neutral-point potential balance formula is calculated, and obtains the redundancy small vector action time factor, using redundancy small vector action time because
The action time of son two redundancy small vectors of control is, it can be achieved that the dynamic equilibrium of alignment current potential is adjusted.
When midpoint potential oscillation is more than limit value, three level NPC current transformer neutral-point potential balance control methods of the invention
It is specific as follows:
1, sector position number where judging present instruction voltage；
Control method of the present invention judges that each sector position is numbered using space vector angle θ value, and specific judgment method is as follows:
1) when π/3 0≤θ <, current sector number is sector 0；
2) when π/3≤2 π/3 θ <, current sector number is sector 1；
3) as 2 π/3≤θ < π, current sector number is sector 2；
4) when 4 π/3 π≤θ <, current sector number is sector 3；
5) when 4 π/3≤5 π/3 θ <, current sector number is sector 4；
6) as 5 π/3≤2 π of θ <, current sector number is sector 5.
2, judge present instruction voltage region Position Number；
Control method of the present invention utilizes t1, t2, t3 and θ1Size judge each sector inner region Position Number, it is specific to judge
Method is as follows:
In formula (1), TsFor the sampling period, m is modulation ratio, t1, t2, t3 be judge time of each sector inner region position because
Son, θ1The corresponding angle in sector 0 is rotated to for current spatial azimuth θ, there is θ1=θ-int (θ/(π/3)), int are indicated one
Numerical value is rounded downwards as immediate integer.
1) when t1 >=0, t2 < 0, t3 >=0,0≤θ1π/6 <, current region number is region 1；
2) as t1 >=0, t2 < 0, t3 >=0, the < of π/6 θ1≤ π/3, current region number is region 2；
3) when t1 >=0, t2 >=0, t3 >=0,0≤θ1π/6 <, current region number is region 3；
4) as t1 >=0, t2 >=0, t3 >=0, the < of π/6 θ1≤ π/3, current region number is region 4；
5) as t1 >=0, t2 >=0,0,0≤θ of t3 <1π/6 <, current region number is region 5；
6) as t1 < 0, t2 >=0, t3 >=0, the < of π/6 θ1≤ π/3, current region number is region 6.
Each sector and regional location are expressed as sector number zone number, such as 1 position of region of sector 0, are expressed as 0.1,
1 position of region of sector 1, is expressed as 1.1.
3, three-phase electricity flow valuve and space vector angle are detected, current sector and region is substituted into and corresponds to neutral-point potential balance public affairs
Formula is calculated, and obtains the action time factor k of redundancy small vector；
Control method of the present invention is to calculate target so as to keep in each sampling period mid-point voltage oscillation be zero, is calculated not
With neutral-point potential balance formula corresponding in sector and region.When midpoint electrical oscillation is more than limit value, controlling party of the present invention
Method by detection three-phase electricity flow valuve and space vector angle, substituted into current sector and region correspond to neutral-point potential balance formula into
Row calculates, and obtains redundancy small vector action time factor k.Corresponding neutral-point potential balance formula is specifically such as in each sector and region
Table 3.
Corresponding neutral-point potential balance formula in each sector of table 3 and region
In table 3, m is modulation ratio, θ1It is corresponding to rotate to sector 0 for current spatial azimuth θ by=θ-int (θ/(π/3))
Angle, ia, ib, ic are respectively the electric current of A phase, B phase, C phase, and k represents the redundancy small vector action time factor in each sector zone.
The k value range being calculated by neutral-point potential balance formula should be limited to 0 to 1, it may be assumed that
4, the action time of two redundancy small vectors is controlled using redundancy small vector action time factor k, thus realization pair
The dynamic equilibrium of midpoint potential is adjusted；
The corresponding current direction for flowing through midpoint of two redundancy small vectors of same space azimuth is on the contrary, its alignment current potential
Function and effect it is opposite.Control method of the present invention maintains three level by redistributing the action time of two redundancy small vectors
The balance of NPC current transformer midpoint potential.If Tx is two redundancy small vector resultant action times, the time is utilized in different sectors region
Factor k controls redundancy small vector action time, and the specific method is as follows:
It 1) be (1-k) * Tx, ONN action time for redundancy small vector POO/ONN, POO action time is k*Tx；
It 2) be (1-k) * Tx, PPO action time for redundancy small vector PPO/OON, OON action time is k*Tx；
It 3) be (1-k) * Tx, NON action time for redundancy small vector OPO/NON, OPO action time is k*Tx；
It 4) be (1-k) * Tx, OPP action time for redundancy small vector OPP/NOO, NOO action time is k*Tx；
It 5) be (1-k) * Tx, NNO action time for redundancy small vector OOP/NNO, OOP action time is k*Tx；
It 6) be (1-k) * Tx, POP action time for redundancy small vector POP/ONO, ONO action time is k*Tx；
Above in concrete mode, Tx represents two redundancy small vector resultant action times, the corresponding three level NPC current transformers of P
The level state of two switching device P1, P2 conducting output of bridge arm, O are corresponded in three level NPC current transformer phases under bridge arm in phase
The level state of switching device P3 conducting output above the switching device P2 and lower bridge arm in face, the corresponding three level NPC current transformers of N
The level state of two switching device P3, P4 conducting output of certain phase lower bridge arm.
5, after electrical oscillation is decreased in limit value when midpoint, redundancy small vector action time factor k=0.5 is enabled；
Control method of the present invention is only calculated when midpoint potential oscillation is more than limit value, according to present instruction voltage institute
Corresponding neutral-point potential balance formula computing redundancy small vector action time factor k is selected in sector and regional location, when utilization
Between factor k controlled for two redundancy small vector action times to maintain the balances of three level NPC current transformer midpoint potentials.Work as midpoint potential
After oscillation is decreased in limit value, in order to obtain better harmonic performance, control method of the present invention does not recycle midpoint potential flat
The formula that weighs calculates k, but enables k=0.5.
Detailed description of the invention
Tri- level NPC converter topology figure of Fig. 1；
Fig. 2 is directed to the SVPWM space voltage vector figure of three level NPC current transformers；
The specific implementation flow chart of Fig. 3 three level NPC current transformer neutral-point potential balance control methods of the present invention；
Each regional location in 0 position of the sector Fig. 4 SVPWM divides and corresponding space vector of voltage；
Fig. 5 is embodiment fundamental frequency 24Hz, and modulation ratio fixes 0.38, on DC bus at the beginning of bridge arm capacitor C1 voltage Udc1
Initial value 3500V, DC bus lower bridge arm capacitor C2 voltage Udc2 initial value 1500V, does not add neutral-point potential balance safeguard measure
Under Udc1 and Udc2 situation of change；
Fig. 6 is embodiment fundamental frequency 24Hz, and modulation ratio fixes 0.38, on DC bus at the beginning of bridge arm capacitor C1 voltage Udc1
Initial value 3500V, DC bus lower bridge arm capacitor C2 voltage Udc2 initial value 1500V, the reality under control method of the present invention effect
Apply a result；
Fig. 7 is embodiment fundamental frequency 24Hz, and modulation ratio fixes 0.38, on DC bus bridge arm capacitor C1 voltage Udc1 and
Lower bridge arm capacitance voltage Udc2 initial value 2500V does not add Udc1 and Udc2 variation feelings under neutral-point potential balance safeguard measure
Condition；
Fig. 8 is embodiment fundamental frequency 24Hz, and modulation ratio fixes 0.38, on DC bus bridge arm capacitor C1 voltage Udc1 and
Lower bridge arm capacitor C2 voltage Udc2 initial value 2500V, the embodiment result under control method of the present invention effect；
Fig. 9 is embodiment fundamental frequency 24Hz, modulation ratio 0.1-0.9 circulation change, bridge arm capacitor C1 electricity on DC bus
Udc1 and lower bridge arm capacitance voltage Udc2 initial value 2500V is pressed, does not add Udc1, Udc2 under neutral-point potential balance safeguard measure
With modulation ratio m situation of change；
Figure 10 is embodiment fundamental frequency 24Hz, modulation ratio 0.1-0.9 circulation change, bridge arm capacitor C1 electricity on DC bus
Udc1 and lower bridge arm capacitance voltage Udc2 initial value 2500V is pressed, the embodiment result under control method of the present invention effect.
Specific embodiment
Present invention will be further explained below with reference to the attached drawings and specific embodiments.
Three level NPC current transformer neutral-point potential balance control methods of the invention when midpoint potential oscillation is more than limit value,
It is to calculate target to keep in each sampling period midpoint potential oscillation to be zero, obtains corresponding midpoint in different sectors and region
Potential balance formula；It is adjusted in real time for alignment potential balance, control method of the present invention first determines whether present instruction voltage
Then place sector and regional location detect three-phase electricity flow valuve and space vector angle, it is corresponding to be substituted into current sector and region
Neutral-point potential balance formula is calculated, and obtains the redundancy small vector action time factor, using redundancy small vector action time because
The action time of son two redundancy small vectors of control realizes that the dynamic equilibrium of alignment current potential is adjusted.
The process of the three level NPC current transformer neutral-point potential balance control methods based on calculating is as shown in Figure 3:
First determine whether midpoint potential shake number is more than limit value, if so, following steps are executed, if not, setting is superfluous
Remaining small vector action time factor k=0.5.
When midpoint electrical oscillation is more than limit value, steps are as follows for control method execution of the present invention:
1, it is to calculate target so as to keep in each sampling period midpoint potential oscillation be zero, obtains in different sectors and region
Corresponding neutral-point potential balance formula:
(1) corresponding neutral-point potential balance formula when command voltage region number is 1
Presumptive instruction voltage falls in sector 0.1 as shown in Figure 4, by nearest three vectors principle, the electricity of synthetic instruction voltage
Pressure space vector acting sequences are POO-OOO-OON-ONN.If the sampling period is Ts, redundancy small vector POO, ONN adopt at one
The sum of action time is T in the sample periodS1, OOO action time is T0, OON action time is TS2, then have:
In formula (2), m represents modulation ratio, and θ represents space vector angle, TsFor sampling period, TS1For redundancy small vector POO,
ONN the sum of action time, T within a sampling period0For OOO action time, TS2When being acted within a sampling period for OON
Between.If ONN action time is k*TS1, then POO action time is (1-k) * TS1, then have:
In formula (3), TONNFor ONN action time, TPOOFor POO within a sampling period action time, TOONExist for OON
Action time in one sampling period, k are the redundancy small vector action time factor.
It is ia that ONN, which corresponds to midpoint electric current, and it is-ia that POO, which corresponds to midpoint electric current, and it is-ic that OON, which corresponds to midpoint electric current, then can obtain
Out within a sampling period midpoint potential shake number, it is as follows:
VO=TS*((2k-1)*2m*sin(π/3-θ)*ia-2m*sin(θ)*ic)/C (4)
In formula (4), VOFor the shake number of midpoint potential, ia, ib, ic are respectively the phase voltage of A phase, B phase, C phase, C tri-
Level NPC current transformer direct current bus bar holds the sum of C1 and lower capacitor C2 capacitance.When midpoint potential shakes in each sampling period
It swings when being zero, there is VO=0, it substitutes into formula (4), can obtain:
Formula (5) is command voltage position 0.1, the corresponding midpoint when midpoint potential oscillation is zero in each sampling period
Potential balance formula.The corresponding neutral-point potential balance in command voltage position 1.1,2.1,3.1,4.1,5.1 can be obtained in same principle
Formula has then obtained corresponding neutral-point potential balance formula when command voltage region number is 1.
(2) corresponding neutral-point potential balance formula when command voltage region number is 2
Presumptive instruction voltage falls in sector 0.2 as shown in Figure 4, by nearest three vectors principle, the electricity of synthetic instruction voltage
Pressure space vector acting sequences are PPO-POO-OOO-OON.If the sampling period is Ts, redundancy small vector PPO, OON adopt at one
The sum of action time is T in the sample periodS2, OOO action time is T0, POO action time is TS1, then have:
In formula (6), m represents modulation ratio, and θ represents space vector angle, TsFor sampling period, TS1For POO action time, T0For
OOO action time, TS2For redundancy small vector PPO, OON within a sampling period the sum of action time.If PPO action time is
k*TS2, then OON action time is (1-k) * TS2, then have:
In formula (7), TPPOFor PPO action time, TOONFor OON within a sampling period action time, TPOOExist for POO
Action time in one sampling period, k are the redundancy small vector action time factor.
It is ic that PPO, which corresponds to midpoint electric current, and it is-ic that OON, which corresponds to midpoint electric current, and it is-ia that POO, which corresponds to midpoint electric current, then can obtain
Out within a sampling period midpoint potential shake number, it is as follows:
VO=TS*((2k-1)*2m*sin(θ)*ic-2m*sin(π/3-θ)*ia)/C (8)
In formula (8), VOFor the shake number of midpoint potential, ia, ib, ic are respectively the phase voltage of A phase, B phase, C phase, C tri-
Level NPC current transformer direct current bus bar holds the sum of C1 and lower capacitor C2 capacitance.When midpoint potential shakes in each sampling period
It swings when being zero, there is VO=0, it substitutes into formula (8), can obtain:
Formula (9) is command voltage position 0.2, the corresponding midpoint when midpoint potential oscillation is zero in each sampling period
Potential balance formula.The corresponding neutral-point potential balance in command voltage position 1.2,2.2,3.2,4.2,5.2 can be obtained in same principle
Formula has then obtained corresponding neutral-point potential balance formula when command voltage region number is 2.
(3) corresponding neutral-point potential balance formula when command voltage region number is 3
Presumptive instruction voltage falls in sector 0.3 as shown in Figure 4, by nearest three vectors principle, the electricity of synthetic instruction voltage
Pressure space vector acting sequences are POO-PON-OON-ONN.If the sampling period is Ts, redundancy small vector POO, ONN adopt at one
The sum of action time is T in the sample periodS1, PON action time is TM, OON action time is TS2, then have:
In formula (10), m represents modulation ratio, and θ represents space vector angle, TsFor sampling period, TS1For redundancy small vector POO,
ONN the sum of action time, T within a sampling periodMFor PON action time, TS2When being acted within a sampling period for OON
Between.If ONN action time is k*TS1, then POO action time is (1-k) * TS1, then have:
In formula (11), TONNFor ONN action time, TPOOFor POO within a sampling period action time, TOONExist for OON
Action time in one sampling period, TPONFor PON, action time, k are redundancy small vector action time within a sampling period
The factor.
It is ia that ONN, which corresponds to midpoint electric current, and it is-ia that POO, which corresponds to midpoint electric current, and it is-ic that OON, which corresponds to midpoint electric current, and PON is corresponding
Midpoint electric current is ib, then can obtain the shake number of the midpoint potential within a sampling period, as follows:
In formula (12), VOFor the shake number of midpoint potential, ia, ib, ic are respectively the phase voltage of A phase, B phase, C phase, C tri-
Level NPC current transformer direct current bus bar holds the sum of C1 and lower capacitor C2 capacitance.When midpoint potential shakes in each sampling period
It swings when being zero, there is VO=0, it substitutes into formula (12), can obtain:
Formula (13) is command voltage position 0.3, when in each sampling period midpoint potential oscillation be zero when it is corresponding in
Point potential balance formula.It is flat that the corresponding midpoint potential in command voltage position 1.3,2.3,3.3,4.3,5.3 can be obtained in same principle
Weigh formula, then has obtained corresponding neutral-point potential balance formula when command voltage region number is 3.
(4) corresponding neutral-point potential balance formula when command voltage region number is 4
Presumptive instruction voltage falls in sector 0.4 as shown in Figure 4, by nearest three vectors principle, the electricity of synthetic instruction voltage
Pressure space vector acting sequences are PPO-POO-PON-OON.If the sampling period is Ts, redundancy small vector PPO, OON adopt at one
The sum of action time is T in the sample periodS2, PON action time is TM, POO action time is TS1, then have:
In formula (14), m represents modulation ratio, and θ represents space vector angle, TsFor sampling period, TS2For redundancy small vector PPO,
OON the sum of action time, T within a sampling periodMFor PON action time, TS1When being acted within a sampling period for POO
Between.If PPO action time is k*TS2, then OON action time is (1-k) * TS2, then have:
In formula (15), TPPOFor PPO action time, TOONFor OON within a sampling period action time, TPOOExist for POO
Action time in one sampling period, TPONFor PON, action time, k are redundancy small vector action time within a sampling period
The factor.
It is ic that PPO, which corresponds to midpoint electric current, and it is-ic that OON, which corresponds to midpoint electric current, and it is-ia that POO, which corresponds to midpoint electric current, and PON is corresponding
Midpoint electric current is ib, then can obtain the shake number of the midpoint potential within a sampling period, as follows:
In formula (16), VOFor the shake number of midpoint potential, ia, ib, ic are respectively A phase, B phase, C phase phase voltage, and C is three electricity
Flat NPC current transformer direct current bus bar holds the sum of C1 and lower capacitor C2 capacitance.When midpoint potential vibrates in each sampling period
When being zero, there is VO=0, it substitutes into formula (16), can obtain:
Formula (17) is command voltage position 0.4, when in each sampling period midpoint potential oscillation be zero when it is corresponding in
Point potential balance formula.It is flat that the corresponding midpoint potential in command voltage position 1.4,2.4,3.4,4.4,5.4 can be obtained in same principle
Weigh formula, then has obtained corresponding neutral-point potential balance formula when command voltage region number is 4.
(5) corresponding neutral-point potential balance formula when command voltage region number is 5
Presumptive instruction voltage falls in sector 0.5 as shown in Figure 4, by nearest three vectors principle, the electricity of synthetic instruction voltage
Pressure space vector acting sequences are POO-PON-PNN-ONN.If the sampling period is Ts, redundancy small vector POO, ONN adopt at one
The sum of action time is T in the sample periodS1, PON action time is TM, PNN action time is TL1, then have:
In formula (18), m represents modulation ratio, and θ represents space vector angle, TsFor sampling period, TS1For redundancy small vector POO,
ONN the sum of action time, T within a sampling periodMFor PON action time, TL1When being acted within a sampling period for PNN
Between.If ONN action time is k*TS1, then POO action time is (1-k) * TS1, then have:
In formula (19), TONNFor ONN action time, TPOOFor POO within a sampling period action time, TPONExist for PON
Action time in one sampling period, k are the redundancy small vector action time factor.
It is ia that ONN, which corresponds to midpoint electric current, and it is-ia that POO, which corresponds to midpoint electric current, and it is ib that PON, which corresponds to midpoint electric current, then can obtain
The shake number of midpoint potential within a sampling period, as follows:
VO=TS*((2k-1)*(2-2m*sin(π/3+θ))*ia+(2m*sin(θ))*ib)/C (20)
In formula (20), VOFor the shake number of midpoint potential, ia, ib, ic are respectively A phase, B phase, C phase phase voltage, and C is three electricity
Flat NPC current transformer direct current bus bar holds the sum of C1 and lower capacitor C2 capacitance.When midpoint potential vibrates in each sampling period
When being zero, there is VO=0, it substitutes into formula (20), can obtain:
Formula (21) is command voltage position 0.5, when in each sampling period midpoint potential oscillation be zero when it is corresponding in
Point potential balance formula.It is flat that the corresponding midpoint potential in command voltage position 1.5,2.5,3.5,4.5,5.5 can be obtained in same principle
Weigh formula, then has obtained corresponding neutral-point potential balance formula when command voltage region number is 5.
(6) corresponding neutral-point potential balance formula when command voltage region number is 6
Presumptive instruction voltage falls in sector 0.6 as shown in Figure 4, by nearest three vectors principle, the electricity of synthetic instruction voltage
Pressure space vector acting sequences are PPO-PPN-PON-OON.If the sampling period is Ts, redundancy small vector PPO, OON adopt at one
The sum of action time is T in the sample periodS2, PON action time is TM, PPN action time is TL2, then have:
In formula (22), m represents modulation ratio, and θ represents space vector angle, TsFor sampling period, TS2For redundancy small vector PPO,
OON the sum of action time, T within a sampling periodMFor PON action time, TL2When being acted within a sampling period for PPN
Between.If PPO action time is k*TS2, then OON action time is (1-k) * TS2, then have:
In formula (23), TPPOFor PPO action time, TOONFor OON within a sampling period action time, TPONExist for PON
Action time in one sampling period, k are the redundancy small vector action time factor.
It is ic that PPO, which corresponds to midpoint electric current, and it is-ic that OON, which corresponds to midpoint electric current, and it is ib that PON, which corresponds to midpoint electric current, then can obtain
The shake number of midpoint potential within a sampling period, as follows:
VO=TS*((2k-1)*(2-2m*sin(π/3+θ))*ic+(2m*sin(π/3-θ))*ib)/C (24)
In formula (24), VOFor the shake number of midpoint potential, ia, ib, ic are respectively A phase, B phase, C phase phase voltage, and C is three electricity
Flat NPC current transformer direct current bus bar holds the sum of C1 and lower capacitor C2 capacitance.When midpoint potential vibrates in each sampling period
When being zero, there is VO=0, it substitutes into formula (24), can obtain:
Formula (25) is command voltage position 0.6, when in each sampling period midpoint potential oscillation be zero when it is corresponding in
Point potential balance formula.It is flat that the corresponding midpoint potential in command voltage position 1.6,2.6,3.6,4.6,5.6 can be obtained in same principle
Weigh formula, then has obtained corresponding neutral-point potential balance formula when command voltage region number is 6.
By calculating above, neutral-point potential balance formula in each sector and regional location has been obtained.
2, the present invention controls the action time of two redundancy small vectors using redundancy small vector action time factor k, thus
Realize that the dynamic equilibrium of alignment current potential is adjusted.
If Tx is two redundancy small vector resultant action times, in different sectors region utilization redundancy small vector action time because
The concrete mode of sub- k control redundancy small vector action time is as follows:
It 1) be (1-k) * Tx, ONN action time for redundancy small vector POO/ONN, POO action time is k*Tx；
It 2) be (1-k) * Tx, PPO action time for redundancy small vector PPO/OON, OON action time is k*Tx；
It 3) be (1-k) * Tx, NON action time for redundancy small vector OPO/NON, OPO action time is k*Tx；
It 4) be (1-k) * Tx, OPP action time for redundancy small vector OPP/NOO, NOO action time is k*Tx；
It 5) be (1-k) * Tx, NNO action time for redundancy small vector OOP/NNO, OOP action time is k*Tx；
It 6) be (1-k) * Tx, POP action time for redundancy small vector POP/ONO, ONO action time is k*Tx；
I.e. ONN, PPO, NON, OPP, NNO, POP correspond to action time k*Tx, and POO, OON, OPO, NOO, OOP, ONO are corresponding
Action time (1-k) * Tx.The reason for this is that ONN, PPO, NON, OPP, NNO, POP correspond to midpoint electric current be certain phase current values, POO,
OON, OPO, NOO, OOP, ONO correspond to the opposite number that midpoint current value is certain phase current values.Alignment potential balance equation pushes away
In leading, the corresponding redundancy small vector of redundancy small vector action time factor k value, midpoint electric current is certain phase current values, and 1-k value
Corresponding redundancy small vector, midpoint electric current are certain phase current values opposite number, therefore when the effect of the available above redundancy small vector
Between the method for salary distribution.
Above in concrete mode, Tx represents two redundancy small vector resultant action times, the corresponding three level NPC current transformers of P
The level state of two switching device P1, P2 conducting output of bridge arm, O are corresponded in three level NPC current transformer phases under bridge arm in phase
The level state of switching device P3 conducting output above the switching device P2 and lower bridge arm in face, the corresponding three level NPC current transformers of N
The level state of two switching device P3, P4 conducting output of certain phase lower bridge arm.
Three level NPC current transformer neutral-point potential balance control methods of the invention utilize two redundancy small vector alignment current potentials
The opposite principle of function and effect is to calculate target so as to control in each period midpoint potential oscillation be zero, it is only necessary to know that three-phase electricity
The two redundancy small vector action time factors can be calculated online in flow valuve and space vector angle value.Control method of the present invention can be with
In smaller range by the control of three level NPC current transformer midpoint potential deviations, the reliability of three level NPC current transformers is improved.
Illustrate implementation result of the invention below with reference to embodiment.
The embodiment of the present invention builds three level NPC inverter models by PSIM software, verifies this hair using emulation experiment
The validity of three level NPC current transformer neutral-point potential balance control methods of bright proposition.
Emulation experiment condition is as follows: DC side busbar voltage 5000V, bridge arm capacitor and lower bridge arm capacitor on DC bus
Capacitance is 10mF, and it is 5 Ω resistance series connection 10mH inductance that inversion, which exports lateral load,.System emulation step-length 10us, with 1200Hz
Frequency is sampled.
Fig. 5 is fundamental frequency 24Hz, and modulation ratio fixes 0.38, bridge arm capacitor C1 voltage Udc1 initial value on DC bus
3500V, DC bus lower bridge arm capacitor C2 voltage Udc2 initial value 1500V, is not added under neutral-point potential balance safeguard measure
Udc1 and Udc2 situation of change.Fig. 5 the result shows that, it is larger in Udc1 and Udc2 difference, when there is midpoint potential imbalance problem,
If not adding neutral-point potential balance safeguard measure, Udc1 and Udc2 energy imbalance can be always existed, therefore need to add midpoint
Potential balance safeguard measure allows midpoint potential to restore balance.
Fig. 6 is fundamental frequency 24Hz, and modulation ratio fixes 0.38, bridge arm capacitor C1 voltage Udc1 initial value on DC bus
3500V, DC bus lower bridge arm capacitor C2 voltage Udc2 initial value 1500V, the embodiment under control method of the present invention effect
As a result.Wherein, Fig. 6 a is Udc1 and Udc2 situation of change, and Fig. 6 b is that midpoint potential shake number Vo and midpoint potential vibrate limit value,
Fig. 6 c is the redundancy small vector action time factor k that the present invention is calculated.Emulation sets midpoint potential oscillation limit value as (Udc1
+ Udc2) * 0.05, i.e., when midpoint electrical oscillation value is more than DC bus-bar voltage 5%, start neutral-point potential balance control of the present invention
Method processed.Fig. 6 embodiment the result shows that, it is larger in Udc1 and Udc2 difference, i.e., in the unbalanced situation of midpoint potential, use this
Midpoint potential shake number can be gradually decrease in DC bus-bar voltage 5% by invention neutral-point potential balance control method, effectively
The balance that ensure that midpoint potential.The redundancy small vector action time factor k that the method for the present invention is calculated is in midpoint potential
Shake number is assigned a value of 0.5 when being less than in DC bus-bar voltage 5%, is only counted online in the unbalanced situation of midpoint potential
It calculates, and value is limited to 0 to 1.
Fig. 7 is fundamental frequency 24Hz, and modulation ratio fixes 0.38, bridge arm capacitor C1 voltage Udc1 and lower bridge arm on DC bus
Capacitance voltage Udc2 initial value 2500V, does not add Udc1 the and Udc2 situation of change under neutral-point potential balance safeguard measure.Fig. 7
The result shows that even if Udc1 with Udc2 initial value is identical, if not adding neutral-point potential balance safeguard measure, in three level NPC
Midpoint potential imbalance problem may also be will appear in current transformer operation, be presented as that the difference of Udc1 and Udc2 are increasing, therefore
Need to add neutral-point potential balance safeguard measure to prevent three level NPC current transformers from occurring midpoint potential injustice in the process of running
Weighing apparatus problem.
Fig. 8 is fundamental frequency 24Hz, and modulation ratio fixes 0.38, bridge arm capacitor C1 voltage Udc1 and lower bridge arm on DC bus
Capacitor C2 voltage Udc2 initial value 2500V, the embodiment result under control method of the present invention effect.Wherein, Fig. 8 a is Udc1
With Udc2 situation of change, Fig. 8 b is midpoint potential shake number Vo and midpoint potential oscillation limit value.Emulation setting midpoint potential oscillation
Limit value is (Udc1+Udc2) * 0.05, i.e., when midpoint electrical oscillation value is more than DC bus-bar voltage 5%, starts midpoint of the present invention
Potential balance control method.Fig. 8 embodiment the result shows that, in the identical situation of Udc1 and Udc2 initial value, use the present invention
Midpoint potential shake number can be limited to always in DC bus-bar voltage 5% by neutral-point potential balance control method, three level NPC
Current transformer is not in midpoint potential imbalance problem in the process of running.
Fig. 9 is fundamental frequency 24Hz, modulation ratio 0.1-0.9 circulation change, bridge arm capacitor C1 voltage Udc1 on DC bus
With lower bridge arm capacitance voltage Udc2 initial value 2500V, the Udc1 under neutral-point potential balance safeguard measure and Udc2 variation are not added
Situation.Fig. 9 the result shows that, when modulation ratio constantly changes, if not adding neutral-point potential balance safeguard measure, in three level
It is possible that midpoint potential imbalance problem in the operation of NPC current transformer, therefore need to add neutral-point potential balance safeguard measure
Prevent three level NPC current transformers from occurring midpoint potential imbalance problem in modulation ratio change procedure.
Figure 10 is fundamental frequency 24Hz, modulation ratio 0.1-0.9 circulation change, bridge arm capacitor C1 voltage Udc1 on DC bus
With lower bridge arm capacitor C2 voltage Udc2 initial value 2500V, control method of the present invention effect under embodiment result.Wherein, scheme
10a is Udc1 and Udc2 situation of change, and Figure 10 b is that midpoint potential shake number Vo and midpoint potential oscillation limit value and modulation ratio m become
Change situation, Figure 10 c is the redundancy small vector action time factor k that the present invention is calculated.Modulation ratio m is in 0.1- for emulation setting
Circulation change between 0.9 sets midpoint potential oscillation limit value as (Udc1+Udc2) * 0.05, i.e., when midpoint, electrical oscillation value is more than
When DC bus-bar voltage 5%, start neutral-point potential balance control method of the present invention.Figure 10 embodiment the result shows that, in modulation ratio
When constantly changing, midpoint potential shake number can be limited to always to direct current mother using neutral-point potential balance control method of the present invention
In line voltage 5%, three level NPC current transformers are not in midpoint potential imbalance problem in modulation ratio change procedure.This hair
The redundancy small vector action time factor k that bright method is calculated is less than in DC bus-bar voltage 5% in midpoint potential shake number
When be assigned a value of 0.5, only carry out in the unbalanced situation of midpoint potential in line computation, and value is limited to 0 to 1.
As shown in Fig. 5~Figure 10, the three level NPC current transformer neutral-point potential balance controls of the invention of the result verification of embodiment
The validity of method processed, in bridge arm capacitor C1 voltage Udc1 on DC bus and lower bridge arm capacitor C2 voltage Udc2 close,
It can guarantee that three level NPC current transformers do not occur midpoint potential imbalance problem in the process of running；It is initial in Udc1 and Udc2
Difference is larger, that is,, can by the online computing redundancy small vector action time factor k when there is midpoint potential imbalance problem
Midpoint potential shake number to be effectively restricted in DC bus-bar voltage 5%；When modulation ratio constantly changes, by counting online
Calculate redundancy small vector action time factor k, it is ensured that three level NPC current transformers midpoint do not occur in modulation ratio change procedure
Current potential imbalance problem.The present invention is without designing Hysteresis control parameter, it is only necessary to know that three-phase electricity flow valuve and space vector angle value, just
The two redundancy small vector action time factors can be calculated online.The present invention can be by three level NPC current transformer midpoint potential deviations
Control in smaller range, improves the reliability of three level NPC current transformers.
Claims (7)
1. a kind of three level NPC current transformer neutral-point potential balance control methods, which is characterized in that the control method is in three level
It is calculating to keep in each sampling period midpoint potential oscillation to be zero when the oscillation of NPC current transformer midpoint potential is more than limit value
Target obtains corresponding neutral-point potential balance formula in different sectors and region；Sector and area where judging present instruction voltage
Then three-phase electricity flow valuve and space vector angle are detected in domain position, the three-phase electricity flow valuve and space vector angle are substituted into current
Sector and region correspond to neutral-point potential balance formula, and the redundancy small vector action time factor is calculated, utilizes redundancy small vector
The action time factor controls the action time of two redundancy small vectors, realizes that the dynamic equilibrium of alignment current potential is adjusted.
2. three level NPC current transformer neutral-point potential balance control method according to claim 1, which is characterized in that described
Control method judges that the method for each sector position number is as follows:
1) when π/3 0≤θ <, current sector number is sector 0；
2) when π/3≤2 π/3 θ <, current sector number is sector 1；
3) as 2 π/3≤θ < π, current sector number is sector 2；
4) when 4 π/3 π≤θ <, current sector number is sector 3；
5) when 4 π/3≤5 π/3 θ <, current sector number is sector 4；
6) as 5 π/3≤2 π of θ <, current sector number is sector 5；
In above-mentioned judgment mode, θ corresponds to space vector angle.
3. three level NPC current transformer neutral-point potential balance control method according to claim 1, which is characterized in that described
Control method judges that the method for each regional location number is as follows:
In above formula, TsFor the sampling period, m is modulation ratio, and t1, t2, t3 are the time factor for judging each sector inner region position, θ1
The corresponding angle in sector 0 is rotated to for current spatial azimuth θ, there is θ1=θ-int (θ/(π/3)), int are indicated a numerical value
Be rounded downwards is immediate integer；
0 corresponding angle θ of sector is rotated to using time factor t1, t2, t3 and current spatial azimuth θ1Size judge each sector
Inner region Position Number, the method is as follows:
1) when t1 >=0, t2 < 0, t3 >=0,0≤θ1π/6 <, current region number is region 1；
2) as t1 >=0, t2 < 0, t3 >=0, the < of π/6 θ1≤ π/3, current region number is region 2；
3) when t1 >=0, t2 >=0, t3 >=0,0≤θ1π/6 <, current region number is region 3；
4) as t1 >=0, t2 >=0, t3 >=0, the < of π/6 θ1≤ π/3, current region number is region 4；
5) as t1 >=0, t2 >=0,0,0≤θ of t3 <1π/6 <, current region number is region 5；
6) as t1 < 0, t2 >=0, t3 >=0, the < of π/6 θ1≤ π/3, current region number is region 6；
Each sector and regional location are expressed as sector number zone number, and 1 position of region of sector 0 is expressed as 0.1, sector 1
1 position of region, be expressed as 1.1.
4. three level NPC current transformer neutral-point potential balance control method according to claim 1, which is characterized in that three
It is zero to be to keep in each sampling period mid-point voltage oscillation when the oscillation of level NPC current transformer midpoint potential is more than limit value
Target is calculated, show that corresponding neutral-point potential balance formula is as follows in each sector and region:
Position 0.1,
Position 0.2,
Position 0.3,
Position 0.4,
Position 0.5,
Position 0.6,
Position 1.1,
Position 1.2,
Position 1.3,
Position 1.4,
Position 1.5,
Position 1.6,
Position 2.1,
Position 2.2,
Position 2.3,
Position 2.4,
Position 2.5,
Position 2.6,
Position 3.1,
Position 3.2,
Position 3.3,
Position 3.4,
Position 3.5,
Position 3.6,
Position 4.1,
Position 4.2,
Position 4.3,
Position 4.4,
Position 4.5,
Position 4.6,
Position 5.1,
Position 5.2,
Position 5.3,
Position 5.4,
Position 5.5,
Position 5.6,
In above-mentioned formula, m is modulation ratio, θ1=θ-int (θ/(π/3)) is that rotate to sector 0 corresponding by current spatial azimuth θ
Angle, ia, ib, ic are respectively the electric current of A phase, B phase, C phase, and k represents the redundancy small vector action time factor in each sector zone.
5. three level NPC current transformer neutral-point potential balance control method according to claim 4, which is characterized in that described
Control method is when midpoint potential oscillation is more than limit value, by the way that current three-phase electricity flow valuve and space vector angle are substituted into current fan
Area and region correspond to neutral-point potential balance formula and are calculated, and obtain redundancy small vector action time factor k in each sector zone；
The k value range being calculated by neutral-point potential balance formula should be limited to 0 to 1, it may be assumed that
6. three level NPC current transformer neutral-point potential balance control method according to claim 1, which is characterized in that when three
For level NPC current transformer midpoint potential shake number when limiting in range, two redundancy small vector action times are identical, there is k=
0.5, k is the redundancy small vector action time factor.
7. three level NPC current transformer neutral-point potential balance control method according to claim 1, which is characterized in that described
Control method controls the action time of two redundancy small vectors using redundancy small vector action time factor k, realizes alignment electricity
The dynamic equilibrium of position is adjusted；If Tx is two redundancy small vector resultant action times, utilize k control redundancy small in different sectors region
The method of vector action time is as follows:
It 1) be (1-k) * Tx, ONN action time for redundancy small vector POO/ONN, POO action time is k*Tx；
It 2) be (1-k) * Tx, PPO action time for redundancy small vector PPO/OON, OON action time is k*Tx；
It 3) be (1-k) * Tx, NON action time for redundancy small vector OPO/NON, OPO action time is k*Tx；
It 4) be (1-k) * Tx, OPP action time for redundancy small vector OPP/NOO, NOO action time is k*Tx；
It 5) be (1-k) * Tx, NNO action time for redundancy small vector OOP/NNO, OOP action time is k*Tx；
It 6) be (1-k) * Tx, POP action time for redundancy small vector POP/ONO, ONO action time is k*Tx；
In aforesaid way, Tx represents two redundancy small vector resultant action times, bridge arm in the corresponding three level NPC current transformer phases of P
The level state of two switching device P1, P2 conducting output, O correspond to the switching device of bridge arm in three level NPC current transformer phases
The level state of the P2 and switching device P3 of lower bridge arm conducting output, corresponding three level NPC current transformer phases lower bridge arm two of N are opened
Close the level state of device P3, P4 conducting output.
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