CN105680711B - A kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM - Google Patents
A kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM Download PDFInfo
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- CN105680711B CN105680711B CN201610165414.9A CN201610165414A CN105680711B CN 105680711 B CN105680711 B CN 105680711B CN 201610165414 A CN201610165414 A CN 201610165414A CN 105680711 B CN105680711 B CN 105680711B
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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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- 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
- H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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Abstract
The invention discloses a kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM, the number of the overtone order eliminated as needed determines the switching angle number in each cycle；The switch angle of selective harmonic elimination pulsewidth modulation is solved based on multi-objective particle swarm optimization method, generates corresponding selective harmonic elimination pulsewidth modulation signal；Gather the mid-point voltage of T-shaped three-level inverter；Signal is optimized, if the mid-point voltage of T-shaped three-level inverter in threshold range, does not change T-shaped three-level inverter, it is directly entered three-level inverter, otherwise on off state is replaced with into corresponding small vector signal, selective harmonic elimination pulsewidth modulation signal is rewritten.The present invention has the function of the elimination low-order harmonic identical with tradition SHEPWM, and can maintain neutral point voltage balance, can make T-shaped three-level inverter stable and high effective operation.
Description
Technical field
The present invention relates to a kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM.
Background technology
Low-voltage network is accessed on a large scale with the distributed energy including photovoltaic generating system, and power grid is to parallel network reverse
Device output current wave quality is put forward higher requirements, and traditional two level grid-connected inverters are difficult to meet the high power quality of bulk power grid
It is required that.The appearance of T-shaped three level grid-connected inverter solves the above problem, as shown in Figure 1, being compared with traditional two level, this is inverse
Becoming utensil has the advantages that harmonic wave is small, switching loss is low, electromagnetic interference is small；With conventional diode clamper type three-level inverter phase
Have the advantages that to have less number of switches than, the inverter, conduction loss is small and power attenuation is uniform；And T-shaped three-level inverter is opened
Close frequency efficiency highest between 4kHz to 30kHz.Therefore T-shaped three-level inverter has been widely applied to photovoltaic generation and micro-
Power grid distributed power generation occasion, and neutral point voltage balance problem is the key of T-shaped three-level inverter stable operation.
Modulated compared to sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM), particular harmonic null method
(SHEPWM) have switching frequency is low, switching loss is small, output voltage quality is good and the series of advantages such as small is lost, suitable for big
Power occasion, is the modulator approach for being often used in eliminating low-order harmonic in a kind of field of power electronics.
The content of the invention
The present invention is to solve the above-mentioned problems, it is proposed that a kind of T-shaped three-level inverter mid-point voltage using SHEPWM
Balance control method, the present invention is based on T-shaped three-level topology and SHEPWM modulation strategies, to the key technology of three-level inverter
Studied, detailed analysis is carried out for the neutral point voltage balance problem of inverter direct-flow side, for SHEPWM and T-shaped three
The advantages of electrical level inverter, propose a kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM.System
Switch angle is calculated by traditional SHEPWM correlation formulas, a small arrow is then added after the modulation of conventional three-phase SHEPWM
Replacement system is measured, is adjusted by measuring inverter mid-point voltage to determine whether to replace the on off state of the small vector of inverter
Neutral balance.The method proposed does not influence the line voltage waveform of inverter output, so with identical with traditional SHEPWM
The function of low-order harmonic is eliminated, and neutral point voltage balance can be maintained, T-shaped three-level inverter stable and high effective operation can be made.
To achieve these goals, the present invention adopts the following technical scheme that：
A kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM, comprises the following steps：
(1) number of the overtone order eliminated as needed determines the switching angle number in each cycle；
(2) the switch angle of selective harmonic elimination pulsewidth modulation is solved based on multi-objective particle swarm optimization method, generates phase
The selective harmonic elimination pulsewidth modulation signal answered；
(3) mid-point voltage of T-shaped three-level inverter is gathered；
(4) signal is optimized, if the mid-point voltage of T-shaped three-level inverter does not change out in threshold range
Off status, makes it directly act on three-level inverter；Otherwise small vector on off state is replaced, pulsewidth tune is eliminated to particular harmonic
Signal processed is rewritten.
In the step (1), the switching angle number in the per quart cycle adds 1 for the overtone order that needs eliminate.
If eliminating N-1 specific harmonic components, N number of switching angle is set, just can form N number of independent side
Journey, so that while fundamental voltage amplitude is selected, can also eliminate the N-1 harmonic component for wishing to eliminate.
In the step (2), arteries and veins is eliminated using three level particular harmonic of multi-objective particle swarm optimization (MOPSO) Algorithm for Solving
Wide modulation switch angle.
In the step (4), gather mid-point voltage, if small vector on off state occur, by detect mid-point voltage come
Determine whether to replace small vector；When small voltage vector switch state does not occur, do not change on off state.
Further, in the step (4), small vector on off state occurs and the absolute value of mid-point voltage is more than midpoint electricity
When pressing threshold value, if mid-point voltage is more than zero, on off state is changed to N-type small vector；If mid-point voltage is less than zero, on off state
P-type small vector is changed to, when the absolute value of mid-point voltage is less than mid-point voltage threshold value, on off state does not change.
Particular harmonic applied to T-shaped three-level inverter eliminates system, including selective harmonic elimination pulsewidth modulation signal
Generator, small vector controller, switching group, PWM signal generator and T-shaped three-level inverter, wherein, the particular harmonic disappears
Except pulse-duration modulation signal generator exports selective harmonic elimination pulsewidth modulation signal to switching group, the small vector controller collection
The mid-point voltage of T-shaped three-level inverter, alignment voltage are judged；
If mid-point voltage in the range of given threshold, does not change the state of switching group, particular harmonic is set to eliminate pulsewidth tune
Signal processed generates control signal by PWM signal generator, controls the switching device of T-shaped three-level inverter；
If mid-point voltage, not in the range of given threshold, small vector controller changes switching group state, small vector is replaced, is led to
PWM signal generator generation control signal is crossed, controls the switching device of T-shaped three-level inverter.
The one of voltage difference of the mid-point voltage between two shunt capacitances of DC side of T-shaped three-level inverter
Half.
When the absolute value of the mid-point voltage is more than mid-point voltage threshold value, if mid-point voltage be more than zero, on off state by for
It is changed to N-type small vector；If mid-point voltage is less than zero, on off state is replaced by p-type small vector.
Beneficial effects of the present invention are：
(1) mid-point voltage can be limited to the surge area of a smaller by the present invention；
(2) present invention can make it restore balance rapidly when mid-point voltage deviates equalization point；
(3) present invention maintains the ability eliminated to particular harmonic.
Brief description of the drawings
Fig. 1 is three-level inverter topology figure；
Fig. 2 is the typical waveform of three-level inverter SHEPWM；
Fig. 3 is the switch angle situation of change when index of modulation is changed by 0 to 1 as N=7；
Fig. 4 is the influence schematic diagram of small vector alignment voltage；
Fig. 5 (a) influences schematic diagram for big voltage vector [PPN] on three-level inverter mid-point voltage；
Fig. 5 (b) influences schematic diagram for middle voltage vector [PON] on three-level inverter mid-point voltage；
Fig. 5 (c) influences schematic diagram for Zero voltage vector [PPP] on three-level inverter mid-point voltage；
Fig. 5 (d) influences schematic diagram for p-type small voltage vector [POO] on three-level inverter mid-point voltage；
Fig. 5 (e)) it is that N-type small voltage vector [ONN] influences schematic diagram to three-level inverter mid-point voltage；
Fig. 6 by proposition SHEPWM algorithms operation logic；
Fig. 7 by proposition SHEPWM algorithms flow chart；
Fig. 8 is on off state when traditional SHEPWM indexes of modulation are 0.99；
Fig. 9 (a) is the simulation result of traditional SHEPWM；
Fig. 9 (b) is the SHEPWM simulation results of the present invention；
Figure 10 (a) is the simulation result of traditional SHEPWM；
Figure 10 (b) is the SHEPWM simulation results of the present invention；
Figure 11 (a) is the simulation result of traditional SHEPWM；
Figure 11 (b) is the SHEPWM simulation results of the present invention.
Embodiment：
The invention will be further described with embodiment below in conjunction with the accompanying drawings.
Control strategy for inverter is illustrated with T-shaped three-level inverter structure as shown in Figure 1.
Including three-phase bridge arm in parallel, the IGBT that two series connection are included per phase bridge arm is managed, the midpoint side string of each phase bridge arm
Join the different IGBT pipes of both direction, the filtered device of opposite side is connected with resistance；Input is accessed in each bridge arm input terminal in parallel
Voltage source；Input voltage source both ends are parallel with two capacitances, and the both direction that every bridge arm is connected at two capacitance connections is different
One end of IGBT pipes, each IGBT pipes drive by control signal.
Two capacitance C of DC side series connection1And C2, midpoint Z, so that the upper device of inverter and lower device are opened
Positive level and negative level will be produced by closing.A, b, c three-phase respectively connect four switching devices for carrying anti-paralleled diode, pass through LA、
LB、LCThreephase load is connected after filtering.Each half-bridge inverter has three kinds of states：Positive level, negative level, zero level.The present invention
In the T-shaped SHEPWM control methods of three level mainly include herein below：
(1) the switching angle number in the per quart cycle is determined according to the number for eliminating overtone order；
(2) switch angle is calculated according to traditional SHEPWM principles；
(3) a small vector replacement system is increased after the modulation of conventional three-phase SHEPWM to control mid-point voltage；
(4) on off state of replacement small vector is determined whether by measuring mid-point voltage.
In step (1), if to eliminate N-1 specific harmonic components, N number of switching angle is set, can just be formed N number of
Independent equation, so that while fundamental voltage amplitude is selected, can also eliminate the N-1 harmonic component for wishing to eliminate.
In step (2), using three level SHEPWM switching angles of multi-objective particle swarm optimization (MOPSO) Algorithm for Solving.
In step (3), SHEPWM switching signals are produced by traditional SHEPWM signal generators, are increased small vector thereafter and are replaced
Device.When small voltage vector switch state occurs, small voltage vector replacement system replaces small vector by detecting mid-point voltage；
When small voltage vector switch state does not occur, small vector replacement system does not change on off state.
In step (4), VZRepresent mid-point voltage, when | VZ| more than mid-point voltage threshold value VrangeWhen, if VZ>0, on off state
It is changed to N-type small vector；If VZ<0, on off state is changed to p-type small vector.When | VZ|<Vrange, on off state do not change
Become.
The conventional procedure of SHEPWM has：The pulse signal switching angle in the per quart cycle is designed, eliminates predetermined number of times
Harmonic wave；Control the amplitude of each basic module.A kind of typical T-shaped SHEPWM inverters waveform of three level is as shown in Fig. 2, wherein
Vxz is single-phase output voltage, its Fourier space is：
Wherein x=a, b, c；Bn is fourier coefficient；Bn is given by
Wherein n=1,5,7,3N-2.
By following cost function, to choose equation optimal solution
Wherein M is modulation index.Fig. 3 gives switch angle when modulation index is changed by 0 to 1.Herein every four/
Pulse signal switching angle number in one cycle is 7 (N=7), and the index of modulation is 0.99 (M=0.99).Produce these angles
Calculation formula be：
According to above formula, the switch angle being calculated when formula (3) is close to 0 is given in Table 1.Phase voltage at this time
The first subharmonic occurred in frequency spectrum is 23 subharmonic.
Table 1
| αi(i=1,2,3 ..., 7) | Switching angle angle |
| α1 | 16.8219372902964 |
| α2 | 20.5429675506475 |
| α3 | 28.5400781589016 |
| α4 | 35.4455857159152 |
| α5 | 41.1064415478475 |
| α6 | 50.450052639555 |
| α7 | 54.816452557851 |
On off state can be expressed as space voltage vector, and null vector is classified as according to the big I of space voltage vector
Amount, small vector, big vector, middle vector, small voltage vector can be divided into p-type vector sum N-type vector again, as shown in Fig. 4 and table 2.
Table 2
Using the inverter mid-point voltage V of SHEPWMZIt is expressed as
Wherein VC1And VC2It is DC bus capacitor C1And C2Magnitude of voltage.Influence such as Fig. 5 institutes of on off state alignment voltage
Show：Big vector sum zero vector alignment voltage does not influence because in this case midpoint Z without and DC side it is positive and negative
Extremely it is connected, because two capacitances do not have discharge and recharge, two capacitance voltages do not change, and mid-point voltage does not also change, such as Fig. 5
(a), shown in (c)；Fig. 5 (b) shows the design sketch of middle vector, and midpoint is connected with the positive negative side of DC side at this time, midpoint electricity
The situation of change of pressure thus when midpoint electric current determine；When inverter selects p-type small vector on off state, load is connected on midpoint
With the cathode of DC side, capacitance C1Electric discharge, electric current flow into midpoint, and mid-point voltage rises, as shown in Fig. 5 (d)；In contrast, N-type
Small vector can decline mid-point voltage, as shown in Fig. 5 (e).
Neutral point voltage balance is kept by replacing small voltage vector using the inverter of SHEPWM in the present invention, control is former
Reason is as shown in Figure 6.SHEPWM switching signals are produced by traditional SHEPWM systems, the small electricity when small voltage vector switch state occurs
Press vector controller effect；When small voltage vector switch state does not occur, small vector controller is blocked, and on off state is not
Become.
The flow chart of neutral-point voltage balance is provided by Fig. 7 in the present invention, wherein VrangeIt is the restriction ripple of mid-point voltage
Dynamic amplitude, VZIt is mid-point voltage, the working status of small vector controller is as follows：
State one：|VZ|>Vrange, under this state small vector be replaced.
a)VZ>0：According to table 2, on off state is changed to N-type small vector.
b)VZ<0：According to table 2, on off state is changed to p-type small vector.
State two：|VZ|<Vrange, on off state do not change.
SHEPWM control modes proposed in the present invention can significantly reduce the concussion scope of mid-point voltage, more attach most importance to
Want, when mid-point voltage substantial deviation equalization point, with this control mode it can be made to restore balance rapidly.It is proposed
SHEPWM control modes are emulated in MATLAB with the sampling period of 5 μ s.
In MATLAB/simulink 2012B, in order to verify the effect of neutral-point voltage balance device, on off state letter
Number shielded before 0.1s.Tradition SHEPWM mid-point voltage recovery times are middle with this close to 0.7s, Fig. 9 (b) in Fig. 9 (a)
Invent the SHEPWM control modes being previously mentioned, voltage recovery time 0.032s.Figure 10 (a), Figure 10 (b) show VC1And VC2
Concussion waveform, it be 1.4V to fluctuate peak value in tradition SHEPWM wherein shown in Figure 10 (a), and of the invention in Figure 10 (b) is carried
It fluctuates peak value less than 0.4 under SHEPWM control modes.The line voltage as caused by SHEPWM in traditional SHEPWM and the present invention
VabHarmonic spectrum such as Figure 11 (a), (b) shown in, wherein, 25 subharmonic be first appearance harmonic wave, the present invention in SHEPWM
The ability eliminated with traditional SHEPWM to particular harmonic is essentially identical.
By above simulation result, SHEPWM and tradition SHEPWM eliminate particular harmonic in the present invention ability base
This is identical, and mid-point voltage can be limited to the surge area of a smaller, while can deviate equalization point in mid-point voltage
When restore balance rapidly.
Although above-mentioned be described the embodiment of the present invention with reference to attached drawing, model not is protected to the present invention
The limitation enclosed, those skilled in the art should understand that, on the basis of technical scheme, those skilled in the art are not
Need to make the creative labor the various modifications that can be made or deformation still within protection scope of the present invention.
Claims (6)
1. a kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM, it is characterized in that：Including following step
Suddenly：
(1) number of the overtone order eliminated as needed determines the switching angle number in each cycle；
(2) the switch angle of selective harmonic elimination pulsewidth modulation is solved based on multi-objective particle swarm optimization method, generation is corresponding
Selective harmonic elimination pulsewidth modulation signal；
(3) mid-point voltage of T-shaped three-level inverter is gathered；
(4) signal is optimized, if the mid-point voltage of T-shaped three-level inverter in threshold range, does not change T-shaped three electricity
Flat inverter, makes it be directly entered three-level inverter, and on off state otherwise is revised as small vector signal, is disappeared to particular harmonic
Except pulse-width signal is rewritten；
Wherein, in the step (1), the switching angle number in the per quart cycle adds 1 for the overtone order that needs eliminate；
In the step (4), mid-point voltage is gathered, if the small voltage vector switch state of setting occurs, by detecting midpoint
Voltage replaces small vector；When small voltage vector switch state does not occur, do not change on off state.
2. a kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM as claimed in claim 1, its
It is characterized in：In the step (2), three level selective harmonic elimination pulsewidth modulations are solved using multi-objective particle and are opened
Close angle.
3. a kind of T-shaped three-level inverter neutral-point voltage balance method using SHEPWM as claimed in claim 1, its
It is characterized in：In the step (4), when the absolute value of mid-point voltage is more than mid-point voltage threshold value, if mid-point voltage is more than zero, switch
State is replaced by N-type small vector；If mid-point voltage is less than zero, on off state is replaced by p-type small vector, when mid-point voltage
When absolute value is less than mid-point voltage threshold value, on off state does not change.
4. a kind of particular harmonic applied to T-shaped three-level inverter eliminates system, it is characterized in that：Arteries and veins is eliminated including particular harmonic
Wide modulation signal generator, small vector controller, switching group, PWM signal generator and T-shaped three-level inverter, wherein, it is described
Selective harmonic elimination pulsewidth modulation signal generator exports selective harmonic elimination pulsewidth modulation signal to switching group, the small vector
Controller gathers the mid-point voltage of T-shaped three-level inverter, and alignment voltage is judged；
If mid-point voltage in the range of given threshold, does not change the state of switching group, believes selective harmonic elimination pulsewidth modulation
Number control signal is generated by PWM signal generator, control the switching device of T-shaped three-level inverter；
If mid-point voltage, not in the range of given threshold, small vector controller changes switching group state, particular harmonic is set to eliminate arteries and veins
Wide modulated signal is changed as small voltage vector, and control signal is generated by PWM signal generator, controls T-shaped three level against device
Switching device.
5. a kind of particular harmonic applied to T-shaped three-level inverter as claimed in claim 4 eliminates system, it is characterized in that：
The mid-point voltage is the half for the voltage difference being connected in parallel between two series capacitances of T-shaped three-level inverter DC side.
6. a kind of particular harmonic applied to T-shaped three-level inverter as claimed in claim 4 eliminates system, it is characterized in that：
When the absolute value of the mid-point voltage is more than mid-point voltage threshold value, if mid-point voltage is more than zero, it is small that on off state is replaced by N-type
Vector；If mid-point voltage is less than zero, on off state is replaced by p-type small vector.
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