CN104319800B - A kind of flexible direct current power transmission system inverter switching frequency optimizes modulator approach - Google Patents

Abstract

The invention discloses a kind of flexible direct current power transmission system inverter switching frequency and optimize modulator approach, the present invention makes the switching frequency in modulated process along with reference voltage vector angle is changed by specific rule in each sector, to reach to reduce magnetic linkage error, and then reduce each alternating voltage, current harmonics containing ratio and the purpose of resultant distortion rate (THD) of output.Owing to SVPWM modulation system and multi-carrier modulation scheme exist specific equivalence, therefore present invention is equally applicable to multi-carrier modulation scheme.

Description

A kind of flexible direct current power transmission system inverter switching frequency optimizes modulator approach

Technical field

The invention belongs to current conversion station especially flexible direct-current transmission system converter station control system is adjusted The design field of mode processed, relates to a kind of switching frequency and optimizes modulator approach, is specifically related to a kind of soft Property law enforcement.

Background technology

Flexible direct current power transmission system based on voltage converter, its core is to utilize full-control type to close Disconnected power electronic devices and pulsewidth modulation (PWM) technology.It both may be used for connecting conventional exchange Electrical network, can power and improve again its quality of power supply, and can realize wattful power to passive network The independence of rate and reactive power controls and four quadrant running, connects multi-terminal direct current transmission system easily, Realize the effect of STATCOM (STATCOM), reactive power in electrical network is compensated. Based on above-mentioned advantage, Technology of HVDC based Voltage Source Converter be widely used in wind energy, solar energy etc. renewable, Distributed power source is grid-connected, and isolated island, urban power distribution network such as are powered at the field.

One of key technology as VSC-HVDC system, its modulation system is the most widely used SVPWM modulation and carrier wave (phase shift) modulator approach.Analyzing the conjunction that its switching voltage vector is formed After becoming the error between the Reference Stator Flux Linkage of magnetic linkage and reference voltage vector formation, can obtain: due to Sampling (carrier wave) frequency-invariant, this magnetic linkage curve of error in each sector with reference voltage vector angle Degree change is near sinusoidal rule, when high-power applications occasion inverter switching frequency is relatively low, becomes Change amplitude is relatively big, thus its output AC voltage, electric current exist single harmonic component containing ratio, THD relatively The problem such as big.

Summary of the invention

It is an object of the invention to the shortcoming overcoming above-mentioned prior art, it is provided that a kind of flexible direct current Transmission system inverter switching frequency optimizes modulator approach, and the method can effectively be improved The output AC that VSC-HVDC system is brought owing to switching frequency is constant under conventional modulated method There is particular harmonic containing ratio, problem bigger for total THD in voltage, electric current.

For reaching above-mentioned purpose, flexible direct current power transmission system inverter switching frequency of the present invention Optimize modulator approach to comprise the following steps:

1) use the switching vector selector of flexible direct current power transmission system inverter by vector by SVPWM modulation Space is divided into 6 sectors, calculates the switching voltage that the reference voltage vector of each sector is corresponding respectively Vector action time；

2) dividing for three-phase voltage modulating wave sector, in obtaining each sector, to send out ripple suitable for symmetrical 7 segmentations Sequence, and calculate synthesis magnetic linkage and the reference magnetic of reference voltage vector formation that switching voltage vector is formed Error between chain；

3) from step 2), zero in first sector, the 3rd sector and the 5th sector Maximum magnetic linkage error during vector effect is with maximum magnetic linkage error during two vector effects | Δ ψ₀|, The maximum magnetic linkage error of the vector effect in first sector, the 3rd sector and the 5th sector It is | Δ ψ₁|, in second sector, the 4th sector and the 6th sector during zero vector effect Big magnetic linkage error is with the maximum magnetic linkage error of a vector effect | Δ ψ₀|, second sector, the 4th In individual sector and the 6th sector, the maximum magnetic linkage error of two vector effects is | Δ ψ₁|, and work as During m >=2/3, have | Δ ψ₁| it is consistently greater than | Δ ψ₀|, use SIN function to represent maximum magnetic linkage error |Δψ₁|,

$\begin{array}{c}{\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}^2=\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}\sin \mathrm{\σ}\cos \mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}-\\ \frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}m\sin \mathrm{\σ}+\frac{3\sqrt{3}}{4}m\sin \mathrm{\σ}{\cos }^2\mathrm{\σ}\}\end{array};$

If benchmark uses cycle T_s0=1/f₀, the sampling period of space vector modulation T_s=(1+T_dcos6σ)T_s0, then maximum magnetic linkage error during zero vector effect in each sector after optimizing, VectorMaximum magnetic linkage error during effect and two vectorsMaximum magnetic linkage error during effect is equal For maximum magnetic linkage error | Δ ψ |, wherein, maximum magnetic linkage error | Δ ψ | for:

$\mathrm{\ψ}\frac{\mathrm{mE}{T}_{s0}}{16}(1+T_d\cos 6\mathrm{\σ})\{(1+\frac{1}{\sqrt{3}}-\frac{3}{4}m)-(\frac{1}{\sqrt{3}}-1+\frac{3}{4}m)\cos 6\mathrm{\σ}\}$

The maximum of the maximum magnetic linkage error by obtaining is that | Δ ψ | is to flexible DC power transmission system the most again System inverter switching frequency is optimized, and wherein, m is reference voltage vector modulation degree, and E is straight Stream voltage, σ is reference voltage vector angle, T_dFor the sampling period change amplitude allowed.

Step 1) in

The Vector modulation expression formula of SVPWM modulation is

$\left\{\begin{array}{c}{\stackrel{\·}{U}}_1{T}_1+{\stackrel{\·}{U}}_2{T}_2+{\stackrel{\·}{U}}_0{T}_0={\stackrel{\·}{U}}_r{T}_s\\ T_0+T_1+T_2=T_s\end{array}\right.$

Wherein, T₀For the time of zero vector effect, T₁It it is a vectorThe time of effect, T₂It is two VectorThe time of effect；

If reference voltage vector falls in the n-th sector, n ∈ 1 ... 6}, i.e.

$\frac{(n-1)\mathrm{\π}}{3}\≤\mathrm{\θ}\≤\frac{\mathrm{n\π}}{3}$

$\mathrm{\θ}=\arccos \left(\frac{U_{\mathrm{\α}}}{\sqrt{{U_{\mathrm{\α}}}^2+{U_{\mathrm{\β}}}^2}}\right)$

Then have

$\frac{2}{3}E\left[\begin{array}{c}\cos \left((n-1)\frac{\mathrm{\π}}{3}\right)\\ \sin \left((n-1)\frac{\mathrm{\π}}{3}\right)\end{array}\right]T_1+\frac{2}{3}E\left[\begin{array}{c}\cos \left(n\frac{\mathrm{\π}}{3}\right)\\ \sin \left(n\frac{\mathrm{\π}}{3}\right)\end{array}\right]T_2=m\frac{E}{2}\left[\begin{array}{c}\cos \left(\mathrm{\θ}\right)\\ \sin \left(\mathrm{\θ}\right)\end{array}\right]T_s$

Solve to obtain the time T of zero vector effect₀, a vectorThe time T of effect₁And two vectorsEffect Time T₂It is respectively as follows:

$\left\{\begin{array}{c}{T}_1=\frac{\sqrt{3}{T}_s}{2}m\sin (\frac{\mathrm{\π}}{3}-\mathrm{\σ})\\ T_2=\frac{\sqrt{3}{T}_s}{2}m\sin \left(\mathrm{\σ}\right)\\ T_0=T_s-\frac{\sqrt{3}{T}_s}{2}m\sin (\frac{\mathrm{\π}}{3}+\mathrm{\σ})\end{array}\right.$

Wherein, θ is the reference voltage vector angle relative to α axle, and σ is reference voltage vector phase For sector, placeThe angle of vector.

Step 2) in, owing to reference voltage vector is positioned at the first sector, the 3rd sector and the 5th fan The sequence of operation of the switching voltage vector in district is Then there are first sector, the 3rd sector and the 5th fan Maximum magnetic linkage error during zero vector effect in district and two vectorsMaximum magnetic linkage during effect is by mistake Difference | Δ ψ₀| it isFirst sector, the 3rd sector and A vector in five sectorsThe maximum magnetic linkage error of effect | Δ ψ₁| it is

$\begin{array}{c}{\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}^2={\left(\frac{2}{3}E\frac{T_1}{2}\right)}^2+{\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)}^2-2\left(\frac{2}{3}E\frac{T_1}{2}\right)\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)\cos \left(\mathrm{\σ}\right)\\ =\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}\sin \mathrm{\σ}\cos \mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}\\ -\frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}m\sin \mathrm{\σ}+\frac{3\sqrt{3}}{4}m\sin \mathrm{\σ}{\cos }^2\mathrm{\σ}\}\end{array}.$

Step 2) in, owing to reference voltage vector is positioned at the second sector, the 4th sector and the 6th fan The sequence of operation of the switching voltage vector in district is ${\stackrel{\·}{U}}_0(T_0/4)\→{\stackrel{\·}{U}}_2(T_2/2)\→{\stackrel{\·}{U}}_1(T_1/2)\→{\stackrel{\·}{U}}_0(T_0/4),$ Then there is maximum magnetic linkage during zero vector effect in second sector, the 4th sector and the 6th sector Error and a vectorThe maximum magnetic linkage error of effect | Δ ψ₀| it isIn second sector, the 4th sector and the 6th sector Two vectorsThe maximum magnetic linkage error of effect | Δ ψ₁| it is

$\begin{array}{c}{\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}^2={\left(\frac{2}{3}E\frac{T_1}{2}\right)}^2+{\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)}^2-2\left(\frac{2}{3}E\frac{T_1}{2}\right)\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)\cos \left(\mathrm{\σ}\right)\\ =\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}\sin \mathrm{\σ}\cos \mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}\\ -\frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}m\sin \mathrm{\σ}+\frac{3\sqrt{3}}{4}m\sin \mathrm{\σ}{\cos }^2\mathrm{\σ}\}\end{array}.$

The method have the advantages that

Flexible direct current power transmission system inverter switching frequency of the present invention optimizes modulator approach and first leads to Crossing SVPWM modulation uses the switching vector selector of flexible direct current power transmission system inverter to be divided by vector space It is 6 sectors, divides for three-phase voltage modulating wave sector, symmetrical 7 segmentations in obtaining each sector Send out ripple order, calculate the ginseng that the synthesis magnetic linkage of switching voltage vector formation is formed with reference voltage vector Examine the error between magnetic linkage, then represented the maximum magnetic linkage error in each sector by SIN function, So that the switching frequency in modulated process presses spy along with reference voltage vector angle in each sector Rule of establishing rules change, to reach to reduce magnetic linkage error, and then each alternating voltage of realization reduction output, Current harmonics containing ratio and the purpose of resultant distortion rate (THD), due to SVPWM modulation system with There is specific equivalence in multi-carrier modulation scheme, therefore present disclosure applies equally to multi-carrier modulation scheme.

Accompanying drawing explanation

Fig. 1 is first sector reference vector and composite diagram thereof；

Fig. 2 is first sector maximum magnetic linkage error map；

Fig. 3 is second sector reference vector and composite diagram thereof；

Fig. 4 is second sector maximum magnetic linkage error map；

Fig. 5 is maximum magnetic linkage back propagation net and fitting result figure in any sector；

Fig. 6 is that the sampling period is constant and T_dMaximum magnetic linkage Error Graph during increase；

Fig. 7 be switching frequency (f=2kHz) fixing SVPWM modulation produce power network current frequency spectrum Figure；

Fig. 8 is the power network current frequency spectrum that the SVPWM modulation that switching frequency (f=2kHz) optimizes produces Figure；

Fig. 9 be switching frequency (f=1kHz) fixing SVPWM modulation produce power network current frequency spectrum Figure；

Figure 10 is the power network current frequency spectrum that the SVPWM modulation that switching frequency (f=1kHz) optimizes produces Figure.

Detailed description of the invention

Below in conjunction with the accompanying drawings the present invention is described in further detail:

With reference to Fig. 1, and Fig. 2, flexible direct current power transmission system inverter switching frequency of the present invention Optimize modulator approach to comprise the following steps:

1) use the switching vector selector of flexible direct current power transmission system inverter by vector by SVPWM modulation Space is divided into 6 sectors, calculates the switching voltage that the reference voltage vector of each sector is corresponding respectively Vector action time；

2) dividing for three-phase voltage modulating wave sector, in obtaining each sector, to send out ripple suitable for symmetrical 7 segmentations Sequence, and calculate synthesis magnetic linkage and the reference magnetic of reference voltage vector formation that switching voltage vector is formed Error between chain；

3) with reference to Fig. 4, from step 2), first sector, the 3rd sector and the 5th Maximum magnetic linkage error when maximum magnetic linkage error during zero vector effect in sector and two vector effects It is | Δ ψ₀|, the vector effect in first sector, the 3rd sector and the 5th sector is Big magnetic linkage error is | Δ ψ₁|, zero vector in second sector, the 4th sector and the 6th sector Maximum magnetic linkage error during effect is with the maximum magnetic linkage error of a vector effect | Δ ψ₀|, second In sector, the 4th sector and the 6th sector, the maximum magnetic linkage error of two vector effects is | Δ ψ₁|, And | Δ ψ₁| it is consistently greater than | Δ ψ₀|, use SIN function to represent maximum magnetic linkage error | Δ ψ₁|,

$\begin{array}{c}{\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}^2=\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}\sin \mathrm{\σ}\cos \mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}-\\ \frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}m\sin \mathrm{\σ}+\frac{3\sqrt{3}}{4}m\sin \mathrm{\σ}{\cos }^2\mathrm{\σ}\}\end{array};$

It can thus be appreciated that when σ=30 °, | Δ ψ₁| obtaining maximum is:

${\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}_{\max }=\frac{1}{8\sqrt{3}}\mathrm{mE}{T}_s$

When σ=0 °, | Δ ψ₁| obtaining minima is:

${\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}_{\min }=\frac{1}{32}\mathrm{mE}{T}_s\×(4-3m)$

Then SIN function formula can be constructed as follows to approximate sign | Δ ψ₁|, it is fitted.

$F_n=\frac{\mathrm{mE}{T}_s}{16}\{(1+\frac{1}{\sqrt{3}}-\frac{3}{4}m)-(\frac{1}{\sqrt{3}}-1+\frac{3}{4}m)\cos 6\mathrm{\σ}\}$

Matlab emulates, the maximum magnetic linkage back propagation net in available any sector And fitting result is as shown in Figure 5, it will thus be seen that maximum magnetic flux chain back propagation net and matching thereof Error between result is less, and simple SIN function therefore can be used to be fitted it, from And simplify the sign of maximum magnetic linkage back propagation net.

If benchmark sampling period T_s0=1/f₀, the sampling period of space vector modulation T_s=(1+T_dcos6σ)T_s0, then maximum magnetic linkage error during zero vector effect in each sector after optimizing, VectorMaximum magnetic linkage error during effect and two vectorsMaximum magnetic linkage error during effect is equal For maximum magnetic linkage error | Δ ψ |, wherein, maximum magnetic linkage error | Δ ψ | for:

$\mathrm{\ψ}\frac{\mathrm{mE}{T}_{s0}}{16}(1+T_d\cos 6\mathrm{\σ})\{(1+\frac{1}{\sqrt{3}}-\frac{3}{4}m)-(\frac{1}{\sqrt{3}}-1+\frac{3}{4}m)\cos 6\mathrm{\σ}\}$

The maximum of the maximum magnetic linkage error by obtaining is that | Δ ψ | is to flexible DC power transmission system the most again System inverter switching frequency is optimized, and wherein, m is reference voltage vector modulation degree, and E is straight Stream voltage, σ is reference voltage vector angle, T_dFor the sampling period change amplitude allowed.

Thus can obtain the maximum magnetic linkage error Changing Pattern with reference voltage vector angle, and work as T_dIncrease Added-time, the Changing Pattern of maximum magnetic linkage error can be obtained further,

It will be appreciated from fig. 6 that when using the optimization sampling period shown in the present invention, maximum magnetic linkage error Can effectively be reduced.

It should be noted that due to SVPWM modulation and the employing regular sampling injecting zero sequence Carrier modulation equivalent, therefore, more than use obtained by SVPWM modulation meter calculation and Analysis is excellent Melt the rule in sampling period to can be completely applied in carrier modulation in order to optimize maximum magnetic linkage by mistake Difference, reduces current harmonics, now optimizes sampling period rule and is the rule optimizing carrier frequency, Thus can effectively reduce voltage, current harmonics containing ratio and the THD that PWM produces.

Step 1) in

The Vector modulation expression formula of SVPWM modulation is

$\left\{\begin{array}{c}{\stackrel{\·}{U}}_1{T}_1+{\stackrel{\·}{U}}_2{T}_2+{\stackrel{\·}{U}}_0{T}_0={\stackrel{\·}{U}}_r{T}_s\\ T_0+T_1+T_2=T_s\end{array}\right.$

Wherein, T₀For the time of zero vector effect, T₁It it is a vectorThe time of effect, T₂It is two VectorThe time of effect；

If reference voltage vector falls in the n-th sector, n ∈ 1 ... 6}, i.e.

$\frac{(n-1)\mathrm{\π}}{3}\≤\mathrm{\θ}\≤\frac{\mathrm{n\π}}{3}$

$\mathrm{\θ}=\arccos \left(\frac{U_{\mathrm{\α}}}{\sqrt{{U_{\mathrm{\α}}}^2+{U_{\mathrm{\β}}}^2}}\right)$

Then have

$\frac{2}{3}E\left[\begin{array}{c}\cos \left((n-1)\frac{\mathrm{\π}}{3}\right)\\ \sin \left((n-1)\frac{\mathrm{\π}}{3}\right)\end{array}\right]T_1+\frac{2}{3}E\left[\begin{array}{c}\cos \left(n\frac{\mathrm{\π}}{3}\right)\\ \sin \left(n\frac{\mathrm{\π}}{3}\right)\end{array}\right]T_2=m\frac{E}{2}\left[\begin{array}{c}\cos \left(\mathrm{\θ}\right)\\ \sin \left(\mathrm{\θ}\right)\end{array}\right]T_s$

Solve to obtain the time T of zero vector effect₀, a vectorThe time T of effect₁And two vectorsMake Time T₂It is respectively as follows:

$\left\{\begin{array}{c}{T}_1=\frac{\sqrt{3}{T}_s}{2}m\sin (\frac{\mathrm{\π}}{3}-\mathrm{\σ})\\ T_2=\frac{\sqrt{3}{T}_s}{2}m\sin \left(\mathrm{\σ}\right)\\ T_0=T_s-\frac{\sqrt{3}{T}_s}{2}m\sin (\frac{\mathrm{\π}}{3}+\mathrm{\σ})\end{array}\right.$

Wherein, θ is the reference voltage vector angle relative to α axle, and σ is reference voltage vector phase For sector, placeThe angle of vector.

Step 2) in, owing to switch flux-linkage vector is linear to the synthesis of Reference Stator Flux Linkage vector, Sending out ripple order due to symmetrical 7 segmentations again makes the switch flux-linkage vector half period symmetrical, therefore calculates one In maximum magnetic linkage error in the individual sampling period only need to calculate half sampling period, each switching voltage is vowed The synthesis magnetic linkage of amount effect finish time compares with the maximum difference of Reference Stator Flux Linkage, due to Reference voltage vector is positioned at the work of the switching voltage vector of the first sector, the 3rd sector and the 5th sector By order it is ${\stackrel{\·}{U}}_0(T_0/4)\→{\stackrel{\·}{U}}_1(T_1/2)\→{\stackrel{\·}{U}}_2(T_2/2)\→{\stackrel{\·}{U}}_0(T_0/4),$ Then have first sector, Maximum magnetic linkage error during zero vector effect in three sectors and the 5th sector and two vectors Maximum magnetic linkage error during effect | Δ ψ₀| it isFirst fan A vector in district, the 3rd sector and the 5th sectorThe maximum magnetic linkage error of effect | Δ ψ₁| all For

$\begin{array}{c}{\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}^2={\left(\frac{2}{3}E\frac{T_1}{2}\right)}^2+{\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)}^2-2\left(\frac{2}{3}E\frac{T_1}{2}\right)\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)\cos \left(\mathrm{\σ}\right)\\ =\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}\sin \mathrm{\σ}\cos \mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}\\ -\frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}m\sin \mathrm{\σ}+\frac{3\sqrt{3}}{4}m\sin \mathrm{\σ}{\cos }^2\mathrm{\σ}\}\end{array}.$

It should be noted that when reference voltage vector is positioned at σ=30 °, centre position, sector, maximum Magnetic linkage error | Δ ψ₁| obtain maximum.

With reference to Fig. 3 and Fig. 4, in like manner, due to the synthesis to Reference Stator Flux Linkage vector of the switch flux-linkage vector It is linear, sends out ripple order due to symmetrical 7 segmentations again and make the switch flux-linkage vector half period symmetrical, Therefore calculate the maximum magnetic linkage error in a sampling period and only need to calculate in half sampling period each The synthesis magnetic linkage of switching voltage vector effect finish time compares with the maximum difference of Reference Stator Flux Linkage , owing to reference voltage vector is positioned at the switch electricity of the second sector, the 4th sector and the 6th sector The sequence of operation of pressure vector is ${\stackrel{\·}{U}}_0(T_0/4)\→{\stackrel{\·}{U}}_2(T_2/2)\→{\stackrel{\·}{U}}_1(T_1/2)\→{\stackrel{\·}{U}}_0(T_0/4),$ Then there is second In sector, the 4th sector and the 6th sector, maximum magnetic linkage error during zero vector effect is vowed with one AmountThe maximum magnetic linkage error of effect | Δ ψ₀| it isSecond Two vectors in sector, the 4th sector and the 6th sectorThe maximum magnetic linkage error of effect | Δ ψ₁| all For

$\begin{array}{c}{\left|\mathrm{\Δ}{\mathrm{\ψ}}_1\right|}^2={\left(\frac{2}{3}E\frac{T_1}{2}\right)}^2+{\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)}^2-2\left(\frac{2}{3}E\frac{T_1}{2}\right)\left(m\frac{E}{2}(\frac{T_0}{4}+\frac{T_1}{2})\right)\cos \left(\mathrm{\σ}\right)\\ =\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}\sin \mathrm{\σ}\cos \mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}\\ -\frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}m\sin \mathrm{\σ}+\frac{3\sqrt{3}}{4}m\sin \mathrm{\σ}{\cos }^2\mathrm{\σ}\}\end{array}.$

The simulation study that the switching frequency of SVPWM modulation optimizes

For verifying the effectiveness of said method of the present invention, build in Matlab/Simulink The sample frequency optimization Simulation model of SVPWM modulation.In emulation, the optimal way of sample frequency is adopted With the sampling period by fixing rule variation pattern.Simulation parameter is as follows: line voltage is 10kV, directly Stream busbar voltage is 20kV, and through-put power is 10MW, and power factor is 1.0, system AC Filter inductance value is 5mH, and equivalent a.c resistor is 0.2 Ω.

When system switching frequency is 2kHz, traditional SVPWM of fixed switching frequency is used to adjust The power network current frequency spectrum that system produces optimizes switching frequency as it is shown in fig. 7, use the present invention to be carried The power network current frequency spectrum that SVPWM modulation produces is as shown in Figure 8.Comparison diagram 7 and Fig. 8 understands, When switching frequency is 2kHz, use power network current THD the subtracting compared with conventional modulated optimizing modulation Little by about 0.4%, and the amplitude of single harmonic current is obviously reduced, the frequency spectrum of harmonic current is abundanter. Owing to switching frequency is higher, that electric current THD reduces and few, and switching frequency (and frequency multiplication) The electricity reduced significantly improving system under limited filtering condition of vicinity harmonic current Energy quality, it is easier to meet corresponding mains by harmonics standard, such as the Utility grid harmonic standard of China Deng.

When system switching frequency is 1kHz, use traditional SVPWM modulation of fixed switching frequency The power network current frequency spectrum produced is as it is shown in figure 9, use and carried optimization switching frequency herein The power network current frequency spectrum that SVPWM modulation produces is as shown in Figure 10.

Comparison diagram 9 and Figure 10 understands, and when switching frequency is 1kHz, uses the electricity optimizing modulation Net electric current THD relatively conventional modulated reduces about 0.9%, and the amplitude of single harmonic current is obviously reduced, The frequency spectrum of harmonic current is abundanter.Owing to switching frequency is relatively low, the reduction of electric current THD is The most notable.In like manner, the reduction of switching frequency (and frequency multiplication) vicinity harmonic current will be The quality of power supply of system is significantly improved under limited filtering condition.

Claims (3)

1. flexible direct current power transmission system inverter switching frequency optimizes a modulator approach, and its feature exists In, comprise the following steps:

1) use the switching vector selector of flexible direct current power transmission system inverter by vector by SVPWM modulation Space is divided into 6 sectors, calculates the switching voltage arrow that the reference voltage vector of each sector is corresponding respectively Measure action time；

2) dividing for three-phase voltage modulating wave sector, in obtaining each sector, to send out ripple suitable for symmetrical 7 segmentations Sequence, and calculate synthesis magnetic linkage and the Reference Stator Flux Linkage of reference voltage vector formation that switching voltage vector is formed Between error；

3) from step 2), the null vector in first sector, the 3rd sector and the 5th sector Maximum magnetic linkage error during amount effect is with maximum magnetic linkage error during two vector effects | Δ ψ₀|, first The maximum magnetic linkage error of the vector effect in individual sector, the 3rd sector and the 5th sector is |Δψ₁|, maximum magnetic linkage during zero vector effect in second sector, the 4th sector and the 6th sector Error is with the maximum magnetic linkage error of a vector effect | Δ ψ₀|, second sector, the 4th sector and In 6th sector, the maximum magnetic linkage error of two vector effects is | Δ ψ₁|, and when m >=2/3, have |Δψ₁| it is consistently greater than | Δ ψ₀|, use SIN function to represent maximum magnetic linkage error | Δ ψ₁|,

$\begin{array}{c}|{\mathrm{\Δ\ψ}}_1{|}^2=\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}sin\mathrm{\σ}cos\mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}-\\ \frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}msin\mathrm{\σ}+\frac{3\sqrt{3}}{4}{\mathrm{msin\σcos}}^2\mathrm{\σ}\}\end{array};$

If benchmark sampling period T_s0=1/f₀, the sampling period of space vector modulation T_s=(1+T_dcos 6σ)T_s0, then maximum magnetic linkage error during zero vector effect in each sector after optimizing, VectorMaximum magnetic linkage error during effect and two vectorsMaximum magnetic linkage error during effect is Big value is | Δ ψ |:

$\left|\mathrm{\Δ}\mathrm{\ψ}\right|=\frac{{\mathrm{mET}}_{s0}}{16}(1+T_{d}cos6\mathrm{\σ})\{(1+\frac{1}{\sqrt{3}}-\frac{3}{4}m)-(\frac{1}{\sqrt{3}}-1+\frac{3}{4}m)cos6\mathrm{\σ}\}$

Flexible direct current power transmission system is changed by maximum | the Δ ψ | of the maximum magnetic linkage error by obtaining the most again Stream device switching frequency is optimized, and wherein, m is reference voltage vector modulation degree, and E is DC voltage, σ is that reference voltage vector is relative to sector, placeThe angle of vector, T_dSampling period for allowing becomes Change amplitude.

Flexible direct current power transmission system inverter switching frequency optimization the most according to claim 1 is adjusted Method processed, it is characterised in that step 2) in, due to reference voltage vector be positioned at the first sector, The sequence of operation of the switching voltage vector of three sectors and the 5th sector is Then there are first sector, the 3rd sector and the 5th sector In zero vector effect time maximum magnetic linkage error and two vectorsMaximum magnetic linkage error during effect |Δψ₀| it isFirst sector, the 3rd sector and the 5th A vector in individual sectorThe maximum magnetic linkage error of effect | Δ ψ₁| it is

$\begin{array}{c}|{\mathrm{\Δ\ψ}}_1{|}^2={\left(\frac{2}{3}E\frac{T_1}{2}\right)}^2+{\left(m\frac{E}{2}\right(\frac{T_0}{4}+\frac{T_1}{2}\left)\right)}^2-2\left(\frac{2}{3}E\frac{T_1}{2}\right)\left(m\frac{E}{2}\right(\frac{T_0}{4}+\frac{T_1}{2}))\cos \left(\mathrm{\σ}\right)\\ =\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}sin\mathrm{\σ}cos\mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}\\ -\frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}msin\mathrm{\σ}+\frac{3\sqrt{3}}{4}{\mathrm{msin\σcos}}^2\mathrm{\σ}\}\end{array}.$

Flexible direct current power transmission system inverter switching frequency optimization the most according to claim 1 is adjusted Method processed, it is characterised in that step 2) in, due to reference voltage vector be positioned at the second sector, The sequence of operation of the switching voltage vector of four sectors and the 6th sector isThen there are second sector, the 4th sector and Maximum magnetic linkage error during zero vector effect and a vector in six sectorsThe maximum magnetic linkage of effect is by mistake Difference | Δ ψ₀| it isSecond sector, the 4th sector and Two vectors in six sectorsThe maximum magnetic linkage error of effect | Δ ψ₁| it is

$\begin{array}{c}|{\mathrm{\Δ\ψ}}_1{|}^2={\left(\frac{2}{3}E\frac{T_1}{2}\right)}^2+{\left(m\frac{E}{2}\right(\frac{T_0}{4}+\frac{T_1}{2}\left)\right)}^2-2\left(\frac{2}{3}E\frac{T_1}{2}\right)\left(m\frac{E}{2}\right(\frac{T_0}{4}+\frac{T_1}{2}))\cos \left(\mathrm{\σ}\right)\\ =\frac{1}{12}{m}^2{E}^2{T_s}^2\×\{\frac{1}{4}{\sin }^2\mathrm{\σ}-\frac{\sqrt{3}}{4}sin\mathrm{\σ}cos\mathrm{\σ}+\frac{3}{16}+\frac{27}{256}{m}^2+\frac{54}{256}{m}^2{\sin }^2\mathrm{\σ}\\ -\frac{27\sqrt{3}}{128}{m}^2\sin \mathrm{\σ}\cos \mathrm{\σ}-\frac{9}{32}m\cos \mathrm{\σ}-\frac{9\sqrt{3}}{32}msin\mathrm{\σ}+\frac{3\sqrt{3}}{4}{\mathrm{msin\σcos}}^2\mathrm{\σ}\}\end{array}.$