CN105680711A - SHEPWM adopted T type three-level inverter neutral-point voltage balance control method - Google Patents

Abstract

The invention discloses an SHEPWM (selective harmonic elimination pulse width modulation) adopted T type three-level inverter neutral-point voltage balance control method. The number of switching angles in each period is determined according to the number of harmonic orders needing to be eliminated; a selective harmonic elimination pulse width modulation switching angle is solved based on a multi-objective particle swarm optimization method to generate a corresponding selective harmonic elimination pulse width modulation signal; the T type three-level inverter neutral-point voltage is collected; the signal is optimized; if the T type three-level inverter neutral-point voltage is within a threshold value range, the T type three-level inverter is not changed and the signal directly enters the three-level inverter; and or otherwise, the switching state is replaced by a corresponding low-vector signal to modify the selective harmonic elimination pulse width modulation signal. The control method provided by the invention has the same function of eliminating low-order harmonics as the conventional SHEPWM; and in addition, the control method can maintain the neutral-point voltage balance and can enable the T type three-level inverter to operate stably and efficiently.

Description

A kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM

Technical field

The present invention relates to a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM.

Background technology

Accessing low pressure distribution network with photovoltaic generating system on a large scale at interior distributed energy, combining inverter output current wave quality is proposed higher requirement by electrical network, and traditional two level combining inverters are difficult to meet bulk power grid high quality of power supply requirement. The appearance of T-shaped three level combining inverter solves the problems referred to above, as shown in Figure 1, compares with traditional two level, and this invertor has the advantages such as harmonic wave is little, switch loss is low, electromagnetic interference is little; Comparing with conventional diode clamper type three-level inverter, this invertor has the advantages such as have less number of switches, conduction loss is little and power loss is even; And T-shaped three-level inverter switching frequency is most effective between 4kHz to 30kHz. Therefore T-shaped three-level inverter has been widely applied to photovoltaic generation and micro-capacitance sensor distributed generating occasion, and neutral point voltage balance problem is the key of T-shaped three-level inverter steady running.

Modulate compared to sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM), particular harmonic null method (SHEPWM) has that switching frequency is low, switch loss is little, output voltage quality is good and the series of advantages such as loss is little, it is applicable to large-power occasions, it is the modulator approach being often used in a kind of field of power electronics and eliminating low-order harmonic.

Summary of the invention

The present invention is in order to solve the problem, propose a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM, the present invention is based on T-shaped three-level topology and SHEPWM modulation strategy, the gordian technique of three-level inverter has been studied, neutral point voltage balance problem for inverter direct-flow side carries out detailed analysis, for the advantage of SHEPWM and T-shaped three-level inverter, it is proposed to a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM. System calculates switch angle by tradition SHEPWM correlation formula, then after the modulation of conventional three-phase SHEPWM, add a small vector replacement system, determine whether that the switch state replacing the small vector of invertor regulates mid point to balance by measuring invertor mid-point voltage.The method proposed does not affect the line voltage waveform that invertor exports, so having 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.

In order to realize above-mentioned purpose, the present invention adopts following technical scheme:

Adopt a T-shaped three-level inverter neutral-point voltage balance method of SHEPWM, comprise the following steps:

(1) number of the harmonic order eliminated as required determines the switching angle number in each cycle;

(2) solve the switch angle of selective harmonic elimination pulsewidth modulation based on multi-objective particle swarm optimization method, generate 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 is in threshold range, does not then change switch state so that it is directly act on three-level inverter; Otherwise replace small vector switch state, selective harmonic elimination pulsewidth modulation signal is rewritten.

In described step (1), the switching angle number in every four/one-period is need the harmonic order of cancellation to add 1.

If eliminating N-1 specific harmonic component, then N number of switching angle is set, just can form N number of independent equation, thus while selecting fundamental voltage amplitude, it is also possible to eliminate N-1 the harmonic component wishing to eliminate.

In described step (2), multi-objective particle swarm optimization (MOPSO) algorithm is adopted to solve three level selective harmonic elimination pulsewidth modulation switching angle.

In described step (4), gather mid-point voltage, if small vector switch state occurs, determine whether to replace small vector by detection mid-point voltage; When small voltage vector switch state does not occur, do not change switch state.

Further, in described step (4), when the absolute value of the appearance of small vector switch state and mid-point voltage is greater than mid-point voltage threshold value, if mid-point voltage is greater than zero, switch state is changed to N-type small vector; If mid-point voltage is less than zero, switch state is changed to P type small vector, and when the absolute value of mid-point voltage is less than mid-point voltage threshold value, switch state does not change.

The particular harmonic being applied to T-shaped three-level inverter eliminates system, comprise selective harmonic elimination pulsewidth modulation signal generator, small vector controller, switches set, PWM signal generator and T-shaped three-level inverter, wherein, described selective harmonic elimination pulsewidth modulation signal generator exports selective harmonic elimination pulsewidth modulation signal to switches set, described small vector controller gathers the mid-point voltage of T-shaped three-level inverter, is judged by mid-point voltage;

If mid-point voltage is in setting threshold range, does not then change the state of switches set, make selective harmonic elimination pulsewidth modulation signal generate control signal by PWM signal generator, control the switch device of T-shaped three-level inverter;

If mid-point voltage is not in setting threshold range, small vector controller changes switches set state, replaces small vector, generates control signal by PWM signal generator, control the switch device of T-shaped three-level inverter.

Described mid-point voltage is the half of the voltage difference between DC side two shunt capacitances of T-shaped three-level inverter.

When the absolute value of described mid-point voltage is greater than mid-point voltage threshold value, if mid-point voltage is greater than zero, switch state is replaced by N-type small vector; If mid-point voltage is less than zero, switch state is replaced by P type small vector.

The useful effect of the present invention is:

(1) mid-point voltage can be limited to a less fluctuation region by the present invention;

(2) the present invention can make rapidly it recover balance when mid-point voltage deviates trim point;

(3) the present invention maintains the ability that particular harmonic is eliminated.

Accompanying drawing explanation

Fig. 1 is three-level inverter topology figure;

Fig. 2 is the typical waveform of three-level inverter SHEPWM;

Fig. 3 is for as N=7, modulation factor is by switch angle changing conditions during 0 to 1 change;

Fig. 4 is that mid-point voltage is affected schematic diagram by small vector;

Three-level inverter mid-point voltage is affected schematic diagram for big voltage vector [PPN] by Fig. 5 (a);

Three-level inverter mid-point voltage is affected schematic diagram for middle voltage vector [PON] by Fig. 5 (b);

Three-level inverter mid-point voltage is affected schematic diagram for Zero voltage vector [PPP] by Fig. 5 (c);

Three-level inverter mid-point voltage is affected schematic diagram for P type small voltage vector [POO] by Fig. 5 (d);

Fig. 5 (e)) three-level inverter mid-point voltage is affected schematic diagram for N-type small voltage vector [ONN];

Fig. 6 by the operation logic of proposition SHEPWM algorithm;

Fig. 7 by the schema of proposition SHEPWM algorithm;

Fig. 8 is tradition SHEPWM modulation factor is switch state when 0.99;

Fig. 9 (a) is the emulation result of tradition SHEPWM;

The SHEPWM that Fig. 9 (b) is the present invention emulates result;

Figure 10 (a) is the emulation result of tradition SHEPWM;

The SHEPWM that Figure 10 (b) is the present invention emulates result;

Figure 11 (a) is the emulation result of tradition SHEPWM;

The SHEPWM that Figure 11 (b) is the present invention emulates result.

Embodiment:

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

Inverter control strategy is set forth with T-shaped three-level inverter structure as shown in Figure 1.

Comprising three-phase bridge arm in parallel, every phase bridge arm comprises the IGBT pipe of two series connection, and connecting the different IGBT pipe in two directions in the mid point side of each phase bridge arm, another side is connected with resistance through wave filter; At each bridge arm input terminus access input voltage source of parallel connection; Input voltage source two ends are parallel with two electric capacity, and two electric capacity junctions connect one end of two direction different I GBT pipes of every bridge arm, and each IGBT pipe drives by control signal.

DC side is connected two electric capacity C₁And C₂, mid point is Z, thus gentle for generation positive electricity negative electricity is put down by the upper device of invertor and the switch of lower device. A, b, c three-phase respectively connects four with the switch device of anti-paralleled diode, passes through L_A、L_B、L_CThree-phase load is connected after filtering. Each half-bridge inverter has three kinds of states: positive level, negative electricity are flat, zero level. In the present invention, three level T-shaped SHEPWM control method mainly comprises following content:

(1) number according to cancellation harmonic order determines the switching angle number in every four/one-period;

(2) switch angle is calculated according to tradition SHEPWM principle;

(3) after the modulation of conventional three-phase SHEPWM, increase a small vector replacement system and control mid-point voltage;

(4) the switch state of small vector is determined whether to replace by measuring mid-point voltage.

In step (1), if to be eliminated N-1 specific harmonic component, then N number of switching angle is set, just can form N number of independent equation, thus while selecting fundamental voltage amplitude, it is also possible to eliminate N-1 the harmonic component wishing to eliminate.

In step (2), multi-objective particle swarm optimization (MOPSO) algorithm is adopted to solve three level SHEPWM switching angle.

In step (3), SHEPWM switch signal is produced by tradition SHEPWM signal generator, increases thereafter small vector and replaces device. When small voltage vector switch state occurs, small voltage vector replacement system replaces small vector by detection mid-point voltage; When small voltage vector switch state does not occur, small vector replacement system does not change switch state.

In step (4), V_ZRepresent mid-point voltage, when | V_Z| it is greater than mid-point voltage threshold value V_rangeTime, if V_Z> 0, switch state is changed to N-type small vector; If V_Z< 0, switch state is changed to P type small vector. When | V_Z|<V_range, switch state does not change.

The conventional procedure of SHEPWM has: design the pulse signal switching angle in every 1/4th cycles, eliminates predetermined number of times harmonic wave; Control the amplitude of each basic module. As shown in Figure 2, wherein Vxz is single-phase output voltage to a kind of typical T-shaped SHEPWM invertor waveform of three level, and its Fourier series is:

$V_{xZ}=\underset{n=1,\mathrm{3...}}{\overset{\mathrm{\&infin;}}{\&Sigma;}}{b}_n\sin nq,n=1,2,3,\mathrm{...}---\left(1\right)$

Wherein x=a, b, c; Bn is fourier coefficient; Bn is provided by following formula

$b_n=\frac{4}{n\mathrm{\&pi;}}\left(\underset{i=1}{\overset{N}{\&Sigma;}}{\left(-1\right)}^{i+1}\cos {\mathrm{n\&alpha;}}_i\right),0<{\mathrm{\&alpha;}}_1<{\mathrm{\&alpha;}}_2<...<{\mathrm{\&alpha;}}_N<\mathrm{\&pi;}/2---\left(2\right)$

Wherein n=1,5,7,3N-2.

By following value function, choose equation optimum solution

$F({\mathrm{\&alpha;}}_1,{\mathrm{\&alpha;}}_2,...,{\mathrm{\&alpha;}}_N)={(b_1-M)}^2+b_5^2+...+b_n^2---\left(3\right)$

Wherein M is modulation index. Fig. 3 gives modulation index by switch angle during 0 to 1 change. Pulse signal switching angle number in every 1/4th cycles is 7 (N=7) herein, and modulation factor is 0.99 (M=0.99). The calculation formula producing these angles is:

$b_1=\frac{4}{\mathrm{\&pi;}}\left(\begin{array}{c}{\mathrm{cos\&alpha;}}_1-{\mathrm{cos\&alpha;}}_2+{\mathrm{cos\&alpha;}}_3-{\mathrm{cos\&alpha;}}_4+{\mathrm{cos\&alpha;}}_5\\ -{\mathrm{cos\&alpha;}}_6+{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$b_5=\frac{4}{5\mathrm{\&pi;}}\left(\begin{array}{c}5{\mathrm{cos\&alpha;}}_1-5{\mathrm{cos\&alpha;}}_2+5{\mathrm{cos\&alpha;}}_3-5{\mathrm{cos\&alpha;}}_4\\ +5{\mathrm{cos\&alpha;}}_5-5{\mathrm{cos\&alpha;}}_6+5{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$b_7=\frac{4}{7\mathrm{\&pi;}}\left(\begin{array}{c}7{\mathrm{cos\&alpha;}}_1-7{\mathrm{cos\&alpha;}}_2+7{\mathrm{cos\&alpha;}}_3-7{\mathrm{cos\&alpha;}}_4\\ +7{\mathrm{cos\&alpha;}}_5-7{\mathrm{cos\&alpha;}}_6+7{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$b_{11}=\frac{4}{11\mathrm{\&pi;}}\left(\begin{array}{c}11{\mathrm{cos\&alpha;}}_1-11{\mathrm{cos\&alpha;}}_2+11{\mathrm{cos\&alpha;}}_3-11{\mathrm{cos\&alpha;}}_4\\ +11{\mathrm{cos\&alpha;}}_5-11{\mathrm{cos\&alpha;}}_6+11{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$b_{13}=\frac{4}{13\mathrm{\&pi;}}\left(\begin{array}{c}13{\mathrm{cos\&alpha;}}_1-13{\mathrm{cos\&alpha;}}_2+13{\mathrm{cos\&alpha;}}_3-13{\mathrm{cos\&alpha;}}_4\\ +13{\mathrm{cos\&alpha;}}_5-13{\mathrm{cos\&alpha;}}_6+13{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$b_{17}=\frac{4}{17\mathrm{\&pi;}}\left(\begin{array}{c}17{\mathrm{cos\&alpha;}}_1-17{\mathrm{cos\&alpha;}}_2+17{\mathrm{cos\&alpha;}}_3-17{\mathrm{cos\&alpha;}}_4\\ +17{\mathrm{cos\&alpha;}}_5-17{\mathrm{cos\&alpha;}}_6+17{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$b_{19}=\frac{4}{19\mathrm{\&pi;}}\left(\begin{array}{c}19{\mathrm{cos\&alpha;}}_1-19{\mathrm{cos\&alpha;}}_2+19{\mathrm{cos\&alpha;}}_3-19{\mathrm{cos\&alpha;}}_4\\ +19{\mathrm{cos\&alpha;}}_5-19{\mathrm{cos\&alpha;}}_6+19{\mathrm{cos\&alpha;}}_7\end{array}\right)$

$F({\mathrm{\&alpha;}}_1,{\mathrm{\&alpha;}}_2,......,{\mathrm{\&alpha;}}_7)={(b_1-0.99)}^2+b_5^2+b_7^2+b_{11}^2+b_{13}^2+b_{17}^2+b_{19}^2---\left(4\right)$

According to above formula, when formula (3) provides in Table 1 close to the switch angle calculated when 0. The first time harmonic wave now occurred in phase voltage 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

Switch state can represent for space voltage vector, is divided into zero vector, small vector, big vector, middle vector according to the big I of space voltage vector, and small voltage vector can be divided into again P type vector N-type vector, as shown in Fig. 4 and table 2.

Table 2

Adopt the invertor mid-point voltage V of SHEPWM_ZExpression is

$V_Z=\frac{V_{C2}-V_{C1}}{2}---\left(5\right)$

Wherein V_C1And V_C2It is DC bus capacitor C₁And C₂Magnitude of voltage. Switch state is on the impact of mid-point voltage as shown in Figure 5: mid-point voltage is not affected by big vector zero vector, because mid point Z does not have the positive and negative electrode with DC side to be connected in this case, because two electric capacity do not have discharge and recharge, so two capacitance voltages do not change, mid-point voltage does not also change, as shown in Fig. 5 (a), (c); Fig. 5 (b) shows the design sketch of middle vector, and now mid point is connected with the positive and negative side of DC side, the changing conditions of mid-point voltage thus time mid point electric current determine; When P type small vector switch state selected by invertor, load is connected on the positive pole of mid point and DC side, electric capacity C₁Electric discharge, electric current flows to mid point, and mid-point voltage rises, as shown in Fig. 5 (d); In contrast, N-type small vector can make mid-point voltage decline, as shown in Fig. 5 (e).

The invertor applying SHEPWM in the present invention keeps neutral point voltage balance by replacement small voltage vector, and control principle is as shown in Figure 6. SHEPWM switch signal is produced by tradition SHEPWM system, the small voltage vector controller effect when small voltage vector switch state occurs; When small voltage vector switch state does not occur, small vector controller is blocked, and switch state is constant.

In the present invention, the schema of neutral-point voltage balance is provided by Fig. 7, wherein V_rangeIt is the restriction fluctuating range of mid-point voltage, V_ZBeing mid-point voltage, the working order of small vector controller is as follows:

State one: | V_Z|>V_range, under this state, small vector is replaced.

a)V_Z> 0: according to table 2, switch state is changed to N-type small vector.

b)V_Z< 0: according to table 2, switch state is changed to P type small vector.

State two: | V_Z|<V_range, switch state does not change.

The SHEPWM control mode proposed in the present invention can reduce the concussion scope of mid-point voltage significantly, what is more important, when mid-point voltage substantial deviation trim point, uses this control mode that it can be made to recover rapidly balance. The SHEPWM control mode proposed emulates with the sampling period of 5 μ s in MATLAB.

In MATLAB/simulink2012B, in order to verify the effect of neutral-point voltage balance device, switch state signal was shielded before 0.1s. The tradition SHEPWM mid-point voltage SHEPWM control mode that time of recovery, utilization the present invention mentioned in 0.7s, Fig. 9 (b) in Fig. 9 (a), the voltage resume time is 0.032s. Figure 10 (a), Figure 10 (b) show V_C1And V_C2Concussion waveform, the peak value that wherein fluctuates in the SHEPWM of tradition shown in Figure 10 (a) is 1.4V, and in Figure 10 (b) the present invention put forward SHEPWM control mode under its peak value that fluctuates less than 0.4. The line voltage V produced by SHEPWM in tradition SHEPWM and the present invention_abHarmonic spectrum as shown in Figure 11 (a), (b), wherein, 25 subharmonic are first harmonic waves occurred, the ability that in the present invention, particular harmonic is eliminated by SHEPWM and traditional SHEPWM is substantially identical.

By emulating result above, the ability that in the present invention, particular harmonic is eliminated by SHEPWM with tradition SHEPWM is substantially identical, and mid-point voltage can be limited to a less fluctuation region, balance can be recovered rapidly when mid-point voltage deviates trim point simultaneously.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of the technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (8)

1. adopt a T-shaped three-level inverter neutral-point voltage balance method of SHEPWM, it is characterized in that: comprise the following steps:

(1) number of the harmonic order eliminated as required determines the switching angle number in each cycle;

(2) solve the switch angle of selective harmonic elimination pulsewidth modulation based on multi-objective particle swarm optimization method, generate 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 is in threshold range, then do not change T-shaped three-level inverter, it is made directly to enter three-level inverter, otherwise it is small vector signal by switch status modifier, selective harmonic elimination pulsewidth modulation signal is rewritten.

2. a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM as claimed in claim 1, is characterized in that: in described step (1), and the switching angle number in every four/one-period is need the harmonic order of cancellation to add 1.

3. a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM as claimed in claim 1, it is characterized in that: in described step (2), adopt multi-objective particle swarm optimization algorithm to solve three level selective harmonic elimination pulsewidth modulation switching angle.

4. a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM as claimed in claim 1, it is characterized in that: in described step (4), gather mid-point voltage, if the small voltage vector switch state of setting occurs, replace small vector by detection mid-point voltage;When small voltage vector switch state does not occur, do not change switch state.

5. a kind of T-shaped three-level inverter neutral-point voltage balance method adopting SHEPWM as claimed in claim 4, it is characterized in that: in described step (4), when the absolute value of mid-point voltage is greater than mid-point voltage threshold value, if mid-point voltage is greater than zero, switch state is replaced by N-type small vector; If mid-point voltage is less than zero, switch state is replaced by P type small vector, and when the absolute value of mid-point voltage is less than mid-point voltage threshold value, switch state does not change.

6. the particular harmonic being applied to T-shaped three-level inverter eliminates system, it is characterized in that: comprise selective harmonic elimination pulsewidth modulation signal generator, small vector controller, switches set, PWM signal generator and T-shaped three-level inverter, wherein, described selective harmonic elimination pulsewidth modulation signal generator exports selective harmonic elimination pulsewidth modulation signal to switches set, described small vector controller gathers the mid-point voltage of T-shaped three-level inverter, is judged by mid-point voltage;

If mid-point voltage is in setting threshold range, does not then change the state of switches set, make selective harmonic elimination pulsewidth modulation signal generate control signal by PWM signal generator, control the switch device of T-shaped three-level inverter;

If mid-point voltage is not in setting threshold range, small vector controller changes switches set state, selective harmonic elimination pulsewidth modulation signal is changed and becomes small voltage vector, generate control signal by PWM signal generator, control the switch device of T-shaped three-level inverter.

7. a kind of particular harmonic being applied to T-shaped three-level inverter eliminates system as claimed in claim 6, it is characterized in that: described mid-point voltage is the half of the voltage difference between DC side two shunt capacitances of T-shaped three-level inverter.

8. a kind of particular harmonic being applied to T-shaped three-level inverter eliminates system as claimed in claim 6, it is characterized in that: when the absolute value of described mid-point voltage is greater than mid-point voltage threshold value, if mid-point voltage is greater than zero, switch state is replaced by N-type small vector; If mid-point voltage is less than zero, switch state is replaced by P type small vector.