CN102377360A - Trisync removing system and method for narrow pulse of SVPWM (space vector pulse width modulation) system - Google Patents

Abstract

The invention relates to a removing system for a narrow pulse, in particular to a trisync removing system and method for the narrow pulse of an SVPWM (space vector pulse width modulation) system, which is used for judging a voltage space vector for the next period, amplitude limiting can be carried out if the voltage space vector enters into a narrow pulse area so that the voltage space vector can not be influenced by the narrow pulse, and the influence for the output voltage due to the amplitude limiting can be compensated through the current space vector and the amplitude correction of the space vector jumping out of the narrow pulse area. The system comprises an attribute calculating unit for the voltage space vector, a current position judging unit for the voltage space vector, a position judging unit for the voltage space vector in two forward and back working periods, an amplitude correction unit of the current voltage space vector, a linear amplitude limiting unit for the voltage space vector, a correction unit for the voltage space vector after jumping out of the narrow pulse area and a modulation unit for the voltage space vector. By adopting the system and the method, the dead zone of the narrow pulse can be removed.

Description

Three-level SVPWM High Modulation Narrow Pulse Elimination System and Method

technical field

The invention relates to narrow pulse elimination, in particular to a three-level SVPWM high modulation narrow pulse elimination system and method.

Background technique

Due to the symmetry of the structure, the clamped three-level converter can realize the bidirectional flow of energy. Moreover, the withstand voltage requirement of the switch tube is only 1/2 of that of the DC bus, and the output power quality is greatly improved compared with the two-level converter. So it is getting more and more applications in solar energy, wind energy, transportation and other fields.

Voltage space vector modulation (SVPWM) is a common control method for three-level converters. Because of different vector arrangement sequences and different vector selection methods, the modulation methods are also different. For the traditional way of synthesizing the nearest three vectors as the reference vector, the problem of narrow pulses will appear when the modulation is too low or too high. The appearance of the narrow pulse increases the harmonic content of the output voltage and current, increases the power consumption of the switching tube, and may cause the problem of instantaneous failure of the switching tube. With the in-depth study of the narrow pulse problem, many methods have been proposed. For low modulation, there are methods such as reducing the switching frequency, exchanging the order of vector arrangement, or limiting the output pulse width.

For narrow pulse control with high modulation degree, there are two traditional methods for dealing with narrow pulses. One is to directly filter out pulses smaller than the minimum pulse width. Although this method can avoid narrow pulses, it only changes the The pulse width will inevitably affect the output line voltage waveform, resulting in voltage distortion.

There is also a commonly used zero-sequence voltage injection method. Although this method eliminates narrow pulses by simultaneously adjusting the width of the three-phase pulses, the pulse width is not adjusted arbitrarily. It is limited by the action time, so there is a dead zone.

When the degree of modulation is high, there is always a control blind zone, that is, no matter which method is used, the narrow pulse cannot be eliminated in a certain spatial position.

Contents of the invention

The technical problem to be solved in the present invention is to realize the pre-judgment of voltage space vector falling into the blind area of eliminating narrow pulses and the elimination of narrow pulses in view of voltage space vector modulation having a blind area for eliminating narrow pulses in a high modulation degree.

For solving above-mentioned technical problem, the present invention provides a kind of three-level SVPWM high modulation degree narrow pulse elimination method, it is characterized in that comprising the following steps:

Calculate the attribute variables of the reference voltage space vector, including the voltage space vector magnitude kp, phase angle θ and single-cycle step angle Δθ;

Determine the spatial position of the current voltage space vector in the coordinate system;

According to the attribute variable of the current space vector, it is judged whether the voltage space vector of the next working cycle falls into the narrow pulse region;

If it falls into a narrow pulse region, limit and modulate the voltage space vector of the next duty cycle;

Perform amplitude correction and modulation on the current voltage space vector and the voltage space vector after jumping out of the narrow pulse region;

According to the principle of vector synthesis, the influence of limiting on the output voltage is compensated by the amplitude correction of the current voltage vector and the voltage space vector after jumping out of the narrow pulse area.

The present invention also provides a three-level SVPWM high-modulation narrow pulse elimination system, including:

A voltage space vector attribute calculation unit for calculating reference voltage attribute variables;

The current position judgment unit of the voltage space vector is used to determine its spatial position in the coordinate system according to the attribute variable of the voltage space vector;

The voltage space vector position judging unit of the two working cycles before and after is used to judge whether the voltage space vector of the two working cycles before and after falling into the narrow pulse region;

The current voltage space vector amplitude correction unit is used for performing amplitude correction on the current voltage space vector;

The voltage space vector linear limiting unit is used for linearly limiting the voltage space vector falling into the narrow pulse region;

After jumping out of the narrow pulse region, the voltage space vector correction unit is used to correct the amplitude of the voltage space vector jumping out of the narrow pulse region;

The voltage space vector modulation unit is used for modulating the voltage space vector after linear clipping or amplitude correction.

By adopting the system and method of the present invention, the narrow pulse blind area can be effectively eliminated without affecting the output voltage amplitude.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

FIG. 1 is a flow chart of the three-level SVPWM narrow pulse elimination method of the present invention.

Fig. 2 is a system structure block diagram of the present invention.

FIG. 3 is a diode-clamped three-level converter in an embodiment of the present invention.

Fig. 4 is a space vector distribution diagram of the first sector of the three-level converter of the present invention.

Fig. 5 is a vector relationship diagram of linear clipping in the present invention.

Fig. 6 is a graph showing the relationship between the linear clipping region and the vector amplitude correction before and after the working cycle in the narrow pulse region of the present invention.

Detailed ways

The three-level SVPWM high modulation degree narrow pulse elimination method of the present invention takes the diode-clamped converter as shown in FIG. 3 as an example. As shown in FIG. 1 , the flow chart of the three-level SVPWM high modulation degree narrow pulse elimination method of the present invention is shown. The process starts at step S101. Then, in step S102 to step S112, according to the cycle of the program, determine the spatial position of the current voltage space vector, pre-judge whether the voltage space vector of the next working cycle falls into the narrow pulse region, and the voltage space falling into the narrow pulse region The vector is clipped and modulated, and then the influence on the output voltage due to clipping is compensated by the vector synthesis of the current voltage space vector and the voltage space vector jumping out of the narrow pulse area after the amplitude correction.

For example, in steps S102 and S103, the spatial position of the current voltage space vector in the coordinate system is determined by calculating the voltage space vector magnitude kp, the phase angle θ and the single-cycle step angle Δθ. The basic voltage vector adopts the Nearest Three Space-Vector (NTV), that is, the three basic vectors closest to the reference vector are used to synthesize V _ref . The modulation cycle T _S is allocated by adopting seven-segment symmetry. The specific operation takes the first small sector as an example, as shown in FIG. 4 .

The phase angle and modulation degree of the reference voltage vector can be calculated in the α-β coordinate system:

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; ac</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; kp</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; *</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; DC</span>}}}$

式中V_α，V_β为参考电压矢量在α-β坐标系上的投影，如图4所示。f为参考矢量运行频率，f_carry为载波频率。If the voltage space vector falls into the second small area, then the order of action of the basic vectors is: ONN-OON-PON-POO-PON-OON-ONN; if the space voltage vector falls into the fourth small area, then the action order of the basic vectors For: ONN-PNN-PON-POO-PON-PNN-ONN. And so on for other small sectors and other areas. Judging the step angle Δθ of the reference voltage space vector V _ref and the operating frequency are related to the switching frequency, that is, the angle at which the reference voltage advances in one switching cycle:

In the formula, V _{α and} V _β are the projections of the reference voltage vector on the α-β coordinate system, as shown in Figure 4. f is the operating frequency of the reference vector, and f _carry is the carrier frequency.

After determining the position of the voltage space vector on the α-β coordinate system by calculating the attribute variable of the voltage space vector, step S106 and step S107 are to pre-judge whether the voltage space vector of the next working cycle falls into the narrow pulse region. If the voltage space vector of the next working cycle falls into the narrow pulse region, step S104 and step S105 can limit the voltage space vector of the next working cycle after one cycle. Here, the limiter adopts the method of linear limiter, as shown in Figure 5 and Figure 6, from the formula t _narrow = 2T _s -2kT _s sin (π/3+θ), when kp is 1, the angle range of the narrow pulse appears is the largest, calculate the angle δ at this time. It is known from the formula t _narrow =2kT _s sinθ that when the vector is close to the medium vector PON, kp is the smallest when a narrow pulse appears. Calculate the kp' value at this time. K ₁ θ(t)+b ₁ can be obtained by drawing a straight line through the point (π/6, kp′) and the point (π/6-δ, 1) respectively. Symmetrically, k ₂ θ(t)+b ₂ can be obtained by drawing a straight line through the point (π/6, kp′) and the point (π/6+δ, 1). Linearly clipping the voltage space vector of the next working cycle within the above two straight lines can prevent the voltage space vector of the next working cycle from falling into the narrow pulse region.

In step S108 , after it is determined that the voltage space vector of the next working cycle falls into the narrow pulse region, an amplitude correction Δx ₁ is performed on the current voltage space vector. Then step S109 and step S110 are used to judge the first voltage space vector that jumps out of the narrow pulse region, because the first one is easy to realize from the program point of view. After determining the first voltage space vector out of the narrow pulse region, step S111 performs amplitude correction Δx ₂ on it.

By correcting the current voltage space vector and the amplitude of the first voltage space vector that jumps out of the narrow pulse area, the voltage space vector of the next working cycle is vector synthesized and compensated. The compensation relationship follows the volt-second balance relationship: Δx ₁ e ^jθ T _S +kp′*e ^j(θ+Δθ) T _S +Δx ₂ e ^j(θ+2Δθ) T _S ＝kp*e ^j(θ+Δθ) T _S. After simplification, the relation is only related to the step angle.

The simplified relationship is:

Δx ₁ +kp′*e ^jΔθ +Δx ₂ e ^j2Δθ ＝kp*e ^jΔθ

Expand the above formula to get:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; kp</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; kp</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span>\end{array}\right.$

Δx ₁ , Δx ₂ can be obtained from the equations.

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; kp</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; kp</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; )</span>}\end{array}\right.$

Through the principle of vector synthesis, the amplitude-corrected current voltage space vector and the first voltage space vector jumping out of the narrow pulse area are synthesized to realize the compensation for the voltage space vector limit of the next working cycle.

Fig. 2 is the structural block diagram according to the narrow pulse elimination system of three-level SVPWM high modulation degree of the present invention, and described system comprises voltage space vector attribute calculation unit 201, voltage space vector current position judging unit 202, before and after two working cycles voltage space vector position judgment Unit 203, the current voltage space vector amplitude correction unit 205, the voltage space vector linear clipping unit 204, the voltage space vector correction unit 206 and the voltage space vector modulation unit 207 after jumping out of the narrow pulse region.

The voltage space vector attribute calculation unit 201 is used to calculate reference voltage attribute variables.

The voltage space vector current position judgment unit 202 is configured to determine its spatial position in the coordinate system according to the attribute variable of the voltage space vector obtained by the point space vector attribute calculation unit 201 .

The voltage space vector position judging unit 203 of the two working cycles before and after is used to judge whether the voltage space vectors of the two working cycles before and after fall into the narrow pulse region. Branches are formed by the judgment of the voltage space vector position judging unit 203 in two working cycles before and after, the current voltage space vector amplitude correction unit 205 and the voltage space vector correction unit 206 after jumping out of the narrow pulse region can compare the current voltage space vector and the jumping out of the narrow pulse region The voltage space vector is corrected for amplitude.

The voltage space vector linear limiting unit 204 is configured to linearly limit the voltage space vector falling into the narrow pulse region.

The voltage space vector modulation unit 207 is configured to modulate the voltage space vector after linear clipping or amplitude correction.

Of course, other coordinate systems can also be used in the specific implementation manner of the present invention, so that only the calculation process is different, and the method used is the same. At the same time, the present invention can also adopt applicable clipping methods other than linear clipping. The scope of the present invention is only limited by the appended claims, as long as it does not deviate from the principle and essence of the present invention, it is within the protection scope of the present invention.

Claims (3)

1. a kind of three-level SVPWM high modulation degree narrow pulse elimination method is characterized in that, comprises the following steps: Calculate the attribute variables of the reference voltage space vector, including the voltage space vector magnitude kp, phase angle θ and single-cycle step angle Δθ; Determine the spatial position of the current voltage space vector in the coordinate system; According to the attribute variable of the current space vector, it is judged whether the voltage space vector of the next working cycle falls into the narrow pulse region; If it falls into a narrow pulse region, limit and modulate the voltage space vector of the next duty cycle; Perform amplitude correction and modulation on the current voltage space vector and the voltage space vector after jumping out of the narrow pulse region; According to the principle of vector synthesis, the influence of limiting on the output voltage is compensated by the amplitude correction of the current voltage vector and the voltage space vector after jumping out of the narrow pulse area. 2. According to the three-level SVPWM high modulation degree narrow pulse elimination method according to claim 1, it is characterized in that, in the above-mentioned step of clipping the voltage space vector of the next duty cycle, the clipping adopts linear clipping, Include the following steps: Calculate the angle δ when the narrow pulse appears in the maximum angle range; Calculate the minimum amplitude kp' of a narrow pulse when the vector is close to the mid-vector; Make a straight line through the vertex of the kp' vector and the vertex of the kp vector with a magnitude of 1 and a phase angle of π/6-δ vector; Construct another straight line that is symmetrical about the mid-vector of the straight line mentioned in the previous step. 3. A three-level SVPWM high modulation narrow pulse elimination system, characterized in that: A voltage space vector attribute calculation unit for calculating reference voltage attribute variables; The current position judgment unit of the voltage space vector is used to determine its spatial position in the coordinate system according to the attribute variable of the voltage space vector; The voltage space vector position judging unit of the two working cycles before and after is used to judge whether the voltage space vector of the two working cycles before and after falling into the narrow pulse region; The current voltage space vector amplitude correction unit is used for performing amplitude correction on the current voltage space vector; The voltage space vector linear limiting unit is used to linearly limit the voltage space vector of the next working cycle falling into the narrow pulse region; After jumping out of the narrow pulse region, the voltage space vector correction unit is used to correct the amplitude of the voltage space vector jumping out of the narrow pulse region; The voltage space vector modulation unit is used for modulating the voltage space vector after linear clipping or amplitude correction.

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