RESONANCE CONTROL METHOD FOR DIFFERENTIATED PHASE CORRECTION

Abstract

A resonance control method for differentiated phase correction under asymmetric positive and negative bilateral frequency domains includes a differentiated phase correction resonance control link with an independent phase correction angle at each resonance point, a decoupling link and a delay compensation link. As a high power converter has the characteristic of asymmetric positive and negative bilateral frequency domains under resonance control with decoupling, stability margin of a control link is enhanced while a negative-sequence current suppression capability is realized by means of differentiated phase correction at positive and negative resonance poles.

Claims

1. A resonance control method for differentiated phase correction, comprising the following steps: sampling a current of each phase in a controlled converter, performing abc/αβ coordinate transformation to obtain currents i.sub.α and i.sub.β under a static coordinate system and defining a current sampling value i.sub.αβ=i.sub.α+ji.sub.β, wherein i.sub.α and i.sub.β are respectively current values of an axis α and an axis β under the static coordinate system, i.sub.αβ is a complex vector and j is an imaginary unit; subtracting the current sampling value i.sub.αβ from a current reference value i.sub.αβ_R to obtain a current error i.sub.αβ_E; taking the current error as an input of a resonance control link, and calculating a resonance output m.sub.αβ_R, wherein a calculating formula of the resonance control link is as follows:
m.sub.αβ_R=i.sub.αβ_E.Math.[K.sub.p+K.sub.i1.Math.e.sup.−jθ1/(s+jω.sub.0)+K.sub.i2.Math.e.sup.jθ2/(s−jω.sub.0)], wherein K.sub.p is a proportionality coefficient, K.sub.i1 and K.sub.i2 are respectively resonance coefficients of a negative resonance link and a positive resonance link, θ1 and θ2 are respectively phase correction angles of the negative resonance link and the positive resonance link, ω.sub.0 is a fundamental wave angular frequency and s is a Laplace operator; taking the current sampling value i.sub.αβ as an input of a decoupling link, and calculating a decoupling output m.sub.αβ_D; adding the resonance output m.sub.αβ_R and the decoupling output m.sub.αβ_D together to obtain m.sub.αβ_RD as an input of a delay compensation link, and calculating a total output m.sub.αβ of the control link; and performing αβ/abc coordinate transformation on the total output map of the control link to obtain three phase modulating waves m.sub.a, m.sub.b and m.sub.c, and comparing the three phase modulating waves with carrier waves in a modulating and driving module to generate a driving signal to drive converting topology, thereby realizing electric energy conversion.

2. The resonance control method for differentiated phase correction according to claim 1, wherein the calculating formula of the decoupling link is as follows:
m.sub.αβ_D=i.sub.αβ.Math.jω.sub.0L, wherein L is an inductance value on an alternating current side.

3. The resonance control method for differentiated phase correction according to claim 1, wherein the calculating formula of the delay compensation link is as follows:
m.sub.αβ=m.sub.αβ_RD, wherein n is a compensation coefficient and T.sub.s is a control period.

4. The resonance control method for differentiated phase correction according to claim 1, wherein the calculating formula of the delay compensation link is as follows:
m.sub.αβ=m.sub.αβ_RD.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic diagram of a power conversion circuit;

[0019] FIG. 2 is a total control block diagram;

[0020] FIG. 3 is a block diagram of a control link with differentiated phase correction resonance control;

[0021] FIG. 4 is a block diagram of realizing a complex vector in the control link in a real number field;

[0022] FIG. 5 is a bilateral frequency domain bode diagram of a system with differentiated phase correction resonance control; and

[0023] FIG. 6 is a transient current oscillograph under the synchronous coordinate system of the conventional scheme and the scheme of the present invention.

DETAILED DESCRIPTION

[0024] Detailed description on the objective, scheme and advantage of the present invention is made in combination with drawings and embodiments by taking current loop control of universal three-phase bridge type inverting topology as an example.

[0025] FIG. 1 is a schematic diagram of a power conversion circuit, and FIG. 2 is a total control block diagram, wherein a three-phase current is sampled to obtain alternating current side currents i.sub.a, i.sub.b and i.sub.c, and abc/αβ coordinate transformation is performed to obtain currents i.sub.α and i.sub.β under a static coordinate system as an input of a control link. Then, the control link outputs modulating waves m.sub.α and m.sub.β under the static coordinate system, αβ/abc coordinate transformation is performed on the control link to obtain three phase modulating waves m.sub.a, m.sub.b and m.sub.c, and the three phase modulating waves are compared with carrier waves in a modulating and driving module to generate a driving signal to drive converting topology, thereby realizing electric energy conversion.

[0026] FIG. 3 is a specific realization block diagram of the control link, including a resonance control link, a feedback decoupling link and a delay compensation link. An expression mode of the complex vector and the complex transfer function is adopted herein and an implementation mode thereof in the real number field will be further described in the FIG. 4 subsequently. By taking a current sampling value i.sub.αβ under the static coordinate system as an example, the complex vector represents i.sub.α+ji.sub.β, wherein j is an imaginary unit, i.sub.α and i.sub.β respectively represent current values of an axis α and an axis β, and definitions of the rest complex vectors containing αβ in subscript are same.

[0027] The control link samples and obtains corresponding i.sub.αβ from a controlled object and outputs the modulating wave map to control the controlled object. The resonance control method for differentiated phase correction under asymmetric positive and negative bilateral frequency domains corresponding to the control link includes the following steps:

[0028] 1) in the static coordinate system, the current sampling value i.sub.αβ is subtracted from a current reference value i.sub.αβ_R to obtain a current error i.sub.αβ_E;

[0029] 2) the current error i.sub.αβ_E is calculated by the formula I corresponding to the differentiated phase correction resonance controller to obtain a resonance control link output m.sub.αβ_R:

m.sub.αβ_R=i.sub.αβ_E[K.sub.p+K.sub.i1.Math.e.sup.−jθ1/(s+jω.sub.0)+K.sub.i2.Math.e.sup.jθ2/(s−jω.sub.0)]  formula I

wherein K.sub.p is a proportionality coefficient, K.sub.i1 and K.sub.i2 are respectively resonance coefficients of a negative resonance link and a positive resonance link, θ.sub.1 and θ.sub.2 are respectively phase correction angles of the negative resonance link and the positive resonance link, and ω.sub.0 is a fundamental wave angular frequency;

[0030] 3) the current sampling value i.sub.αβ is calculated by the formula II corresponding to decoupling to obtain a decoupling output m.sub.αβ_D:

m.sub.αβ_D=i.sub.αβ.Math.jω.sub.0L  formula II

the formula corresponds to the feedback decoupling scheme, wherein L is an inductance value on the alternating current side. In addition, the decoupling output m.sub.αβ_D may further be obtained by obtained by the current reference value i.sub.αβ_R via m.sub.αβ_D=i.sub.αβ_R.Math.ω.sub.C/s+ω.sub.C.Math.e.sup.−sTd) or the current error value i.sub.αβ_E via m.sub.αβ_D=i.sub.αβ_E.Math.K.sub.pjω.sub.0/s and other decoupling schemes, wherein ω.sub.C is an electric current loop bandwidth and T.sub.d is control and modulation delay;

[0031] 4) the resonance output m.sub.αβ_R and the decoupling output m.sub.αβ_D are added together to obtain m.sub.αβ_RD;

[0032] 5) m.sub.αβ_RD may be directly taken as a total output m.sub.αβ of the control link or m.sub.αβ_RD obtains the total output map of the control link via the formula III corresponding to the delay compensation link;

m.sub.αβ=m.sub.αβ_RD.Math.e.sup.inT.sup.s.sup.ω.sup.0, or m.sub.αβ=m.sub.αβ_RD.Math.e.sup.inT.sup.s.sup.ω.sup.0  formula III

wherein the compensation coefficient n may be a typical value 1.5 or 0 or other any value, and T.sub.s is a control period.

[0033] The implementation mode of the complex vector in the real number field is described briefly below. The expression formula of the control link includes the imaginary unit j which represents cross coupling between the axis α and the axis β. The feedback decoupling link includes an item jω.sub.0L, wherein j is located in a numerator, i.e., m.sub.αβ_D=i.sub.αβ.Math.jω.sub.0L, and its implementation mode in the real number field is as shown in (a) in FIG. 4:

m.sub.α_D=i.sub.β.Math.ω.sub.0L, m.sub.β-D=i.sub.α.Math.ω.sub.0L  formula IV

The resonance control link includes an item 1/(s±jw.sub.0), wherein j is located in a denominator. By taking y.sub.αβ=u.sub.αβ/(s−jω.sub.0) as an example, its implementation mode in the real number field is as shown in (b) in FIG. 4:

y.sub.α=(u.sub.α−y.sub.β/ω.sub.0)/s, y.sub.β=(u.sub.β+y.sub.α/ω.sub.0)/s  formula V

In addition, the resonance controller link and the delay compensation link include an exponential function e.sup.jθ, and by taking y.sub.αβ=u.sub.αβ.Math.e.sup.jθ as an example, its implementation mode in the real number field is as shown in (c) in the FIG. 4:

y.sub.α=u.sub.α.Math.cosθ−u.sub.β.Math.sinθ, y.sub.β=u.sub.α.Math.sinθ+u.sub.βcosθ  formula VI

An application example of the present invention is given below.

[0034] For the three-phase power conversion circuit shown in FIG. 1, a universal control scheme is as follows: a three-phase current is sampled to obtain alternating current side currents i.sub.a, i.sub.b and i.sub.c, and abc/αβ coordinate transformation is performed to obtain currents i.sub.α and i.sub.β under a static coordinate system as an input of a control link. The specific implementation process of the control link is the same as the above, including the resonance link corresponding to the formula I put by the present invention and the decoupling link shown in the formula III. The resonance link in the conventional scheme corresponds to the formula VII:

m.sub.αβ_R=i.sub.αβ_E.Math.[K.sub.p+K.sub.i.Math.(s.Math.cosθ+ω.sub.0.Math.sinθ)/(s.sup.2+ω.sub.0.sup.2)]  formula VII

Then, the control link outputs modulating waves m.sub.α and m.sub.β under the static coordinate system, αβ/abc coordinate transformation is performed on the control link to obtain three phase modulating waves m.sub.a, m.sub.b and m.sub.c, and the three phase modulating waves are compared with carrier waves in a modulating and driving module to generate a driving signal to drive converting topology to realize electric energy conversion. When the three-phase converter adopts the decoupling and resonance control scheme, the frequency domains have positive and negative bilateral asymmetrical characteristic, shown in FIG. 5, i.e., the amplitude-frequency characteristic and the phase-frequency characteristic are not positively and negatively symmetrical about 0 Hz. In order to solve the problem of insufficient stability margin caused by the asymmetrical positive and negative bilateral frequency domains, compared with the conventional control scheme, the present invention is primarily improved that the scheme is the resonance link for differentiated phase correction corresponding to formula I, the conventional scheme is the resonance link for equivalent phase correction corresponding to the formula VII and only has one phase correction positive angle degree of freedom θ, and corresponding to the formula I for differentiated phase correction, θ.sub.1 is only equal to θ.sub.2. By introducing the resonance controller for differentiated phase correction with a multi-phase correction degree of freedom, differentiated phase correction angles θ.sub.1 and θ.sub.2 may be adopted.

[0035] The resonance control system for differentiated phase correction with asymmetrical positive and negative bilateral frequency domains is analyzed by means of a complex transfer function to obtain the bilateral frequency domain bode diagram shown in FIG. 5, and a comparison result between corresponding stability margin indexes such as cross-over frequency and phase margin and those in the conventional scheme is as shown in a table 1. It may be seen that the whole system has a harmonic peak of −50 Hz, which may suppress the negative sequence component of the current better. Compared with the conventional scheme, the cross-over frequency fcpi and the phase margin φ.sub.P2 at the positive resonance pole and the phase margin φ.sub.N1 at the negative resonance pole are improved obviously, for example, fcpi is improved by about one time, φ.sub.P2 and φ.sub.N1 are improved by about 50%, and the rest stability margin indexes are maintained in an optimized range.

TABLE-US-00001 TABLE 1 Comparison table between phase correction positive angle parameter and stability margin of the control link θ.sub.1/° θ.sub.2/° f.sub.CN1 f.sub.CN2 f.sub.CP1 f.sub.CP2 φ.sub.N1/° φ.sub.N2/° φ.sub.P1/° φ.sub.P2/° Conventional −57.5 57.5 0.23 0.10 0.38 0.92 32 165 68.3 30.7 scheme f.sub.0 f.sub.0 f.sub.0 f.sub.0 The present −120 14 0.23 0.10 0.80 0.82 45.1 87.4 48.1 47.2 invention f.sub.0 f.sub.0 f.sub.0 f.sub.0

[0036] After a current index of the axis d is stepped from 0pu to 1pu at 0.02 s, a current waveform is as shown in FIG. 6. When the conventional scheme is used, under a dp coordinate system, the current represents a low oscillating component at 11 Hz and is slow to attenuate, and the restoration time reaches 0.144 s. After adopting the scheme of the patent, I.sub.q is attenuated to below 2% in 0.034 s.

[0037] Therefore, through the differentiated phase correction at different resonance poles, the stability margin and the dynamic performance of the converter with asymmetrical positive and negative frequency domains are improved, thereby obtaining a beneficial technical effect.

[0038] The present invention is not limited to the specific implementation mode. Those skilled in the art may adopt other various implementation modes according to the content of the present invention, for example, the feedback decoupling link is replaced by a feedforward decoupling link, two-level converting topology is replaced by three-level converting topology and the like. Therefore, claims aim to cover all variations in true concept and scope of the present invention.