CN103986361A - Method for space vector pulse width modulation of two-level converter - Google Patents

Abstract

The invention relates to a method for space vector pulse width modulation of a two-level converter and belongs to the technical field of power electronics and conversion. The method includes the steps that according to sampling values of a three-phase reference voltage, the maximum value and the minimum value of the three-phase reference voltage are calculated, connection time of a three-phase switching device in a sampling period is obtained through direct calculation, and therefore a control signal of each switching device is obtained. According to the method, coordinate transformation and sector judgment are not needed, operations of irrational numbers and trigonometric functions are avoided, the switching control signals of the devices can be obtained only by a small number of comparison operations and simple four arithmetic operations, an algorithm flow is simple and easy to achieve, the calculated amount is small, optimal control over midpoint electric potential low-frequency components on the direct current side can be achieved, cost of a processor in the space vector pulse width modulation technology is reduced, and generality of the space vector pulse width modulation technology is improved.

Description

A kind of space vector width pulse modulation method of two level current transformers

Technical field

The present invention relates to a kind of space vector width pulse modulation method of two level current transformers, belong to power electronics and Semiconductor Converting Technology field.

Background technology

Pulse modulation technology is the key technology that the current transformer based on power electronic device is realized electric energy conversion, and the conventional pulse modulation technology of current two level current transformers (its circuit diagram as shown in Figure 1) comprises two kinds of SPWM Technique and space vector pulse width modulations.Compare with SPWM Technique, space vector pulse width modulation have fast response time, direct voltage utilance high, be easy to the advantages such as Digital Implementation, thereby obtained studying widely and applying.

Traditional space vector pulse width modulation need to carry out abc-α β coordinate transform to three-phase reference voltage, according to the phase angle of voltage vector under α β coordinate system, judgement sector, voltage vector place (as shown in Figure 2), and pass through trigonometric function operation, obtain the action time of two basic vectors that voltage vector is adjacent, and then obtain the ON time of each switching device of three-phase within a sampling period, and finally obtain the switch controlling signal of each switching device.Because needs carry out the judgement of coordinate transform, sector, compute vectors action time, and need to carry out a large amount of irrational numbers and trigonometric function operation, therefore traditional space vector pulse width modulation algorithm is complicated, operand is large, this operational performance to digital processing unit has proposed higher requirement, has also promoted the cost of processor.Quick computing for implementation space vector pulse modulation technology, Chinese scholars has proposed some method for simplifying, but be mainly reflected in aspects such as simplifying sector judgment principle, minimizing trigonometric function operation, and algorithm itself still needs to carry out coordinate transform and sector judgement, contain a large amount of judgement branch and trigonometric function operation, arithmetic speed promotes and is not obvious.Document [1] (Zhou Weiping, Wu Zhengguo, Tang Jingsong, Deng the equivalent algorithm of .SVPWM and the essential connection [J] of SVPWM and SPWM. Proceedings of the CSEE, 2006,1 (2): 133-137.) propose the shortcut calculation of a kind of SVPWM, this shortcut calculation does not need in fact to carry out coordinate transform, but need to carry out sector judgement, algorithm is realized still more complicated.Document [2] (Fang Sichen, Li Dan, cycle, etc. novel without sector spatial vector pulse width modulation algorithm [J]. Proceedings of the CSEE, 2008,28 (30): 35-40.) by setting up 120 ° of coordinate systems of two phase spaces, proposed a kind ofly without sector SVPWM algorithm, this algorithm does not need to carry out sector judgement, and algorithm is realized comparatively simple, but need to carry out twice coordinate transform computing, the operand of irrational number and trigonometric function is still larger.

Summary of the invention

The object of the invention is to propose a kind of space vector width pulse modulation method of two level current transformers, existing space vector width pulse modulation method is improved, save coordinate transform and sector judgement in existing method, to simplify space vector pulse width modulation, shorten operation time, reduce storage, improve versatility.

The space vector width pulse modulation method of two level current transformers that the present invention proposes, comprises the following steps:

(1) at a sampling period T _sthe t zero hour ₀, the three-phase reference voltage of two level current transformers is sampled, obtain t ₀three-phase reference voltage constantly, is designated as respectively u _a(t ₀), u _b(t ₀) and u _c(t ₀), by three-phase reference voltage u _a(t ₀), u _b(t ₀) and u _c(t ₀) in maximum be designated as u _max(t ₀), minimum value is designated as u _min(t ₀), measure t simultaneously ₀the DC voltage U of the moment two level current transformers _dc;

(2) by following formula, calculate above-mentioned sampling period T _sthe ON time length T of brachium pontis switch on the three-phase of interior two level current transformers _a, T _band T _c:

$T_a=\frac{T_s}{U_{\mathrm{dc}}}[u_a\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

$T_b=\frac{T_s}{U_{\mathrm{dc}}}[u_b\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

$T_c=\frac{T_s}{U_{\mathrm{dc}}}[u_c\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

Wherein, l=k[U _dc-u _max(t ₀)+u _min(t ₀)], k is that zero vector (111) accounts for the whole zero vector ratio of action time action time, the span of k is k ∈ [0,1];

(3) utilize following formula, calculate on the three-phase of two level current transformers brachium pontis switch at sampling period T _sinterior conducting is t constantly _aon, t _bonand t _con:

$t_{\mathrm{aon}}=t_0+\frac{1}{2}(T_s-T_a),$

$t_{\mathrm{bon}}=t_0+\frac{1}{2}(T_s-T_b),$

$t_{\mathrm{con}}=t_0+\frac{1}{2}(T_s-T_c),$

And shutoff moment t _aoff, t _boffand t _coff:

$t_{\mathrm{aoff}}=t_0+\frac{1}{2}(T_s+T_a),$

$t_{\mathrm{boff}}=t_0+\frac{1}{2}(T_s+T_b),$

$t_{\mathrm{coff}}=t_0+\frac{1}{2}(T_s+T_c);$

(4) utilize following formula, obtain the control signal S of brachium pontis switch on the three-phase of two level current transformers _ap(t), S _bpand S (t) _cp(t):

$S_{\mathrm{ap}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{aon}},t_{\mathrm{aoff}}]\\ 0,t\∉[t_{\mathrm{aon}},t_{\mathrm{aoff}}]\end{array}\right.,$

$S_{\mathrm{bp}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{bon}},t_{\mathrm{boff}}]\\ 0,t\∉[t_{\mathrm{bon}},t_{\mathrm{boff}}]\end{array}\right.$

$S_{\mathrm{cp}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{con}},t_{\mathrm{coff}}]\\ 0,t\∉[t_{\mathrm{con}},t_{\mathrm{coff}}]\end{array}\right.$

(5) utilize following formula, obtain the control signal S of brachium pontis switch under the three-phase of two level current transformers _an(t), S _bnand S (t) _cn(t):

$S_{\mathrm{an}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{aon}}-\mathrm{\Δt},t_{\mathrm{aoff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{aon}}-\mathrm{\Δt},t_{\mathrm{aoff}}+\mathrm{\Δt}]\end{array}\right.,$

$S_{\mathrm{bn}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{bon}}-\mathrm{\Δt},t_{\mathrm{boff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{bon}}-\mathrm{\Δt},t_{\mathrm{boff}}+\mathrm{\Δt}]\end{array}\right.$

$S_{\mathrm{cn}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{con}}-\mathrm{\Δt},t_{\mathrm{coff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{con}}-\mathrm{\Δt},t_{\mathrm{coff}}+\mathrm{\Δt}]\end{array}\right.$

Wherein, Δ t is Dead Time, and span is 1-10 microsecond.

The space vector width pulse modulation method of two level current transformers that the present invention proposes, its advantage is:

The space vector width pulse modulation method of two level current transformers of the present invention, directly according to the sampled value of three-phase reference voltage, calculate threephase switch device ON time within the sampling period, do not need to carry out coordinate transform and sector judgement, in implementation procedure, do not need to carry out trigonometric function operation, thereby also needn't store trigonometric table, only need carry out a small amount of comparison operation and simple arithmetic and can obtain the switch controlling signal of device, method flow is simple, be easy to realize, amount of calculation is little, required computing time and memory space reduce greatly, reduced the processor cost of space vector pulse width modulation, and improved the versatility of space vector pulse width modulation.In addition, this the inventive method is identical with traditional spatial vector pulse width modulation algorithm effect, can be by suitably distributing the action time of zero vector, to reduce the switching frequency of two level current transformers, reduce the harmonic content of voltage and current in two level current transformers, reduce the electromagnetic noise of two level current transformers, thereby improve the service behaviour of two level current transformers.

Accompanying drawing explanation

Fig. 1 is the circuit theory diagrams of two level current transformers that relate in the inventive method.

Fig. 2 is space vector pulse width modulation space vector of voltage and sector distribution map.

Fig. 3 is the control signal schematic diagram of brachium pontis switch on three-phase in the inventive method.

Fig. 4 is the modulation effect comparison diagram of one embodiment of the present of invention and conventional method.

Embodiment

The space vector width pulse modulation method of two level current transformers that the present invention proposes, comprises the following steps:

(1) at a sampling period T _sthe t zero hour ₀, the three-phase reference voltage of two level current transformers is sampled, obtain t ₀three-phase reference voltage constantly, is designated as respectively u _a(t ₀), u _b(t ₀) and u _c(t ₀), by three-phase reference voltage u _a(t ₀), u _b(t ₀) and u _c(t ₀) in maximum be designated as u _max(t ₀), minimum value is designated as u _min(t ₀), measure t simultaneously ₀the DC voltage U of the moment two level current transformers _dc;

(2) by following formula, calculate above-mentioned sampling period T _sthe ON time length T of brachium pontis switch on the three-phase of interior two level current transformers _a, T _band T _c:

$T_a=\frac{T_s}{U_{\mathrm{dc}}}[u_a\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

$T_b=\frac{T_s}{U_{\mathrm{dc}}}[u_b\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

$T_c=\frac{T_s}{U_{\mathrm{dc}}}[u_c\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

Wherein, l=k[U _dc-u _max(t ₀)+u _min(t ₀)], k is that zero vector (111) accounts for the whole zero vector ratio of action time action time, the span of k is k ∈ [0,1].As shown in Figure 3, wherein k value and zero vector T action time ₇and T ₀pass be by the value of suitable selection k, can realize the different optimization aim of two level space vector pulse-width modulations.For example, if take, reduce switching frequency as optimization aim, k=0; If take harmonic reduction content as optimization aim, if take, reduce electromagnetic noise as optimization aim, k gets the random number between [0,1], and the k value in n+1 sampling period can produce by following ordered series of numbers recursion: k (n+1)=4k (n) [1-k (n)], wherein k (0)=0.1

(3) utilize following formula, calculate on the three-phase of two level current transformers brachium pontis switch at sampling period T _sinterior conducting is t constantly _aon, t _bonand t _con:

$t_{\mathrm{aon}}=t_0+\frac{1}{2}(T_s-T_a),$

$t_{\mathrm{bon}}=t_0+\frac{1}{2}(T_s-T_b),$

$t_{\mathrm{con}}=t_0+\frac{1}{2}(T_s-T_c),$

And shutoff moment t _aoff, t _boffand t _coff:

$t_{\mathrm{aoff}}=t_0+\frac{1}{2}(T_s+T_a),$

$t_{\mathrm{boff}}=t_0+\frac{1}{2}(T_s+T_b),$

$t_{\mathrm{coff}}=t_0+\frac{1}{2}(T_s+T_c);$

(4) utilize following formula, obtain the control signal S of brachium pontis switch on the three-phase of two level current transformers _ap(t), S _bpand S (t) _cp(t):

$S_{\mathrm{ap}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{aon}},t_{\mathrm{aoff}}]\\ 0,t\∉[t_{\mathrm{aon}},t_{\mathrm{aoff}}]\end{array}\right.,$

$S_{\mathrm{bp}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{bon}},t_{\mathrm{boff}}]\\ 0,t\∉[t_{\mathrm{bon}},t_{\mathrm{boff}}]\end{array}\right.$

$S_{\mathrm{cp}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{con}},t_{\mathrm{coff}}]\\ 0,t\∉[t_{\mathrm{con}},t_{\mathrm{coff}}]\end{array}\right.$

(5) utilize following formula, obtain the control signal S of brachium pontis switch under the three-phase of two level current transformers _an(t), S _bnand S (t) _cn(t):

$S_{\mathrm{an}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{aon}}-\mathrm{\Δt},t_{\mathrm{aoff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{aon}}-\mathrm{\Δt},t_{\mathrm{aoff}}+\mathrm{\Δt}]\end{array}\right.,$

$S_{\mathrm{bn}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{bon}}-\mathrm{\Δt},t_{\mathrm{boff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{bon}}-\mathrm{\Δt},t_{\mathrm{boff}}+\mathrm{\Δt}]\end{array}\right.$

$S_{\mathrm{cn}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{con}}-\mathrm{\Δt},t_{\mathrm{coff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{con}}-\mathrm{\Δt},t_{\mathrm{coff}}+\mathrm{\Δt}]\end{array}\right.$

Wherein, Δ t is Dead Time, and span is 1-10 microsecond.

Below introduce an embodiment of the inventive method:

In the present embodiment, with the circuit diagram of two level current transformers of resistance sense load as shown in Figure 1, its structural parameters and service conditions are as follows:

(1) at a sampling period T _sthe t zero hour of=0.2ms ₀, the three-phase reference voltage of two level current transformers is sampled, obtain t ₀three-phase reference voltage is constantly u _a(t ₀), u _b(t ₀) and u _c(t ₀), by three-phase reference voltage u _a(t ₀), u _b(t ₀) and u _c(t ₀) in the maximum be designated as u _max(t ₀), reckling is designated as u _min(t ₀), measure t simultaneously ₀the DC voltage U of the moment two level current transformers _dc=0.73kV;

(2) by following formula, calculate above-mentioned sampling period T _sthe ON time T of brachium pontis switch on the three-phase of interior two level current transformers _a, T _b, T _cfor:

$\left[\begin{array}{c}{T}_A\\ T_B\\ T_C\end{array}\right]=\frac{T_s}{U_{\mathrm{dc}}}\left[\begin{array}{c}{u}_a\left(t_0\right)-u_{\min }\left(t_0\right)+l\\ u_b\left(t_0\right)-u_{\min }\left(t_0\right)+l\\ u_c\left(t_0\right)-u_{\min }\left(t_0\right)+l\end{array}\right]$

Wherein, l=k[U _dc-u _max(t ₀)+u _min(t ₀)], k is that zero vector (111) accounts for the whole zero vector ratio of action time action time, the span of k is k ∈ [0,1], in an embodiment, gets respectively the modulation effect that k=0 and k=0.5 checking propose algorithm herein.

(3) utilize following formula, calculate on the three-phase of two level current transformers brachium pontis switch at sampling period T _sin open constantly t _aon, t _bon, t _con:

$\left[\begin{array}{c}{t}_{\mathrm{Aon}}\\ t_{\mathrm{Bon}}\\ t_{\mathrm{Con}}\end{array}\right]=\left[\begin{array}{c}{t}_0\\ t_0\\ t_0\end{array}\right]+\frac{1}{2}\left[\begin{array}{c}{T}_s-T_A\\ T_s-T_B\\ T_s-T_C\end{array}\right],$

With shutoff moment t _aoff, t _boff, t _coff:

$\left[\begin{array}{c}{t}_{\mathrm{Aoff}}\\ t_{\mathrm{Boff}}\\ t_{\mathrm{Coff}}\end{array}\right]=\left[\begin{array}{c}{t}_0\\ t_0\\ t_0\end{array}\right]+\frac{1}{2}\left[\begin{array}{c}{T}_s+T_A\\ T_s+T_B\\ T_s+T_C\end{array}\right]$

(4) by above-mentioned calculate open constantly t _aon, t _bon, t _conwith shutoff moment t _aoff, t _boff, t _coffas the control signal of brachium pontis switch on the three-phase of two level current transformers, the control signal negate to upper brachium pontis switch, obtains the control signal of lower brachium pontis switch.Wherein, negate refers to that the switching signal of lower brachium pontis can obtain by 1 switching signal that deducts upper brachium pontis; When negate, should when upper and lower brachium pontis on off state switches, suitably add certain Dead Time, dead band time setting is 3 μ s, and in Dead Time, the switching signal of upper and lower brachium pontis is 0.

Fig. 4 is the modulation effect figure of above-described embodiment, U in figure _aObe two level current transformer AC phase voltages, U _aBbe that two level current transformers exchange side line voltage, I _abe two level current transformer AC phase current and T _abe the ON time of brachium pontis switching device within a sampling period on two level current transformers.Wherein, Fig. 4 (a) is for adopting Traditional Space vector pulse width modulation algorithm and the above-mentioned oscillogram of respectively measuring when k=0.5, Fig. 4 (b) is the above-mentioned oscillogram of respectively measuring when adopting algorithm of the present invention and when k=0.5, Fig. 4 (c) for adopt Traditional Space vector pulse width modulation algorithm and when k=0 the above-mentioned oscillogram of respectively measuring, Fig. 4 (d) is the above-mentioned oscillogram of respectively measuring when adopting algorithm of the present invention and when k=0.As seen from Figure 4, the two level current transformer AC phase voltages, line voltage, the phase current waveform that adopt the inventive method to obtain, identical with traditional spatial vector pulse width modulation algorithm, on two level current transformers, the ON time of brachium pontis switching device within a sampling period is also identical, illustrates that the inventive method is identical with the modulation effect of traditional spatial vector pulse width modulation algorithm.

Claims (1)

1. a space vector width pulse modulation method for two level current transformers, comprises the following steps:

(1) at a sampling period T _sthe t zero hour ₀, the three-phase reference voltage of two level current transformers is sampled, obtain t ₀three-phase reference voltage constantly, is designated as respectively u _a(t ₀), u _b(t ₀) and u _c(t ₀), by three-phase reference voltage u _a(t ₀), u _b(t ₀) and u _c(t ₀) in maximum be designated as u _max(t ₀), minimum value is designated as u _min(t ₀), measure t simultaneously ₀the DC voltage U of the moment two level current transformers _dc;

(2) by following formula, calculate above-mentioned sampling period T _sthe ON time length T of brachium pontis switch on the three-phase of interior two level current transformers _a, T _band T _c:

$T_a=\frac{T_s}{U_{\mathrm{dc}}}[u_a\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

$T_b=\frac{T_s}{U_{\mathrm{dc}}}[u_b\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

$T_c=\frac{T_s}{U_{\mathrm{dc}}}[u_c\left(t_0\right)-u_{\min }\left(t_0\right)+l],$

Wherein, l=k[U _dc-u _max(t ₀)+u _min(t ₀)], k is that zero vector (111) accounts for the whole zero vector ratio of action time action time, the span of k is k ∈ [0,1];

(3) utilize following formula, calculate on the three-phase of two level current transformers brachium pontis switch at sampling period T _sinterior conducting is t constantly _aon, t _bonand t _con:

$t_{\mathrm{aon}}=t_0+\frac{1}{2}(T_s-T_a),$

$t_{\mathrm{bon}}=t_0+\frac{1}{2}(T_s-T_b),$

$t_{\mathrm{con}}=t_0+\frac{1}{2}(T_s-T_c),$

And shutoff moment t _aoff, t _boffand t _coff:

$t_{\mathrm{aoff}}=t_0+\frac{1}{2}(T_s+T_a),$

$t_{\mathrm{boff}}=t_0+\frac{1}{2}(T_s+T_b),$

$t_{\mathrm{coff}}=t_0+\frac{1}{2}(T_s+T_c);$

(4) utilize following formula, obtain the control signal S of brachium pontis switch on the three-phase of two level current transformers _ap(t), S _bpand S (t) _cp(t):

$S_{\mathrm{ap}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{aon}},t_{\mathrm{aoff}}]\\ 0,t\∉[t_{\mathrm{aon}},t_{\mathrm{aoff}}]\end{array}\right.,$

$S_{\mathrm{bp}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{bon}},t_{\mathrm{boff}}]\\ 0,t\∉[t_{\mathrm{bon}},t_{\mathrm{boff}}]\end{array}\right.$

$S_{\mathrm{cp}}\left(t\right)=\left\{\begin{array}{c}1,t\∈[t_{\mathrm{con}},t_{\mathrm{coff}}]\\ 0,t\∉[t_{\mathrm{con}},t_{\mathrm{coff}}]\end{array}\right.$

(5) utilize following formula, obtain the control signal S of brachium pontis switch under the three-phase of two level current transformers _an(t), S _bnand S (t) _cn(t):

$S_{\mathrm{an}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{aon}}-\mathrm{\Δt},t_{\mathrm{aoff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{aon}}-\mathrm{\Δt},t_{\mathrm{aoff}}+\mathrm{\Δt}]\end{array}\right.,$

$S_{\mathrm{bn}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{bon}}-\mathrm{\Δt},t_{\mathrm{boff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{bon}}-\mathrm{\Δt},t_{\mathrm{boff}}+\mathrm{\Δt}]\end{array}\right.$

$S_{\mathrm{cn}}\left(t\right)=\left\{\begin{array}{c}0,t\∈[t_{\mathrm{con}}-\mathrm{\Δt},t_{\mathrm{coff}}+\mathrm{\Δt}]\\ 1,t\∉[t_{\mathrm{con}}-\mathrm{\Δt},t_{\mathrm{coff}}+\mathrm{\Δt}]\end{array}\right.$

Wherein, Δ t is Dead Time, and span is 1-10 microsecond.