CN104065292B - Three-level converter neutral-point potential balance control method and device - Google Patents

Abstract

The present invention relates to neutral-point potential balance control method and the device of a kind of three-level converter, it is possible to the zero potential realizing midpoint potential controls, and has important Practical significance.The present invention, uses multicarrier CBPWM method based on injected zero-sequence voltage, it is achieved neutral-point-potential balance control.By gathering the voltage of dc bus midpoint upper and lower sides, both deviations are inputted Sliding Mode Controller, obtains residual voltage, then be superimposed to original three-phase modulations ripple, the effect controlling neutral point voltage balance can be played.This programme has the feature such as fast response time, strong robustness, it is possible to adapt to different capacity factor, the operating mode of load.

Description

Three-level converter neutral-point potential balance control method and device

Technical field

The present invention relates to neutral-point potential balance control method and the device of a kind of NPC three-level converter.

Background technology

In recent years, along with the development of high-power electric and electronic technology, multi-level converter is widely applied, and it has The features such as harmonic content is low, efficiency is high, capacity is big.The common topological structure of three-level converter is diode neutral point clamp type (NPC) structure, as shown in Figure 1.1 is had the advantage that compared with two level topologys) under same switch frequency, output voltage, electricity The harmonic content of stream is greatly reduced；2) voltage that power tube bears is the half of busbar voltage；3) power tube switching loss is low.

Neutral-point potential balance problem is focus and the difficult point of three level researchs.In three-level modulation algorithm, frequently with overloading Ripple pulsewidth modulation (CBPWM), space vector pulse width modulation (SVPWM).In order to make the reliability service of three-level converter, it is necessary to really Protecting midpoint potential is the half of DC voltage.The method of neutral-point-potential balance control mainly has a following two: 1) increase hardware Circuit；2) control algolithm is improved.Increase hardware circuit and can cause the increase of cost；Change control algolithm and will not increase cost, tool Have superiority.

Improving in control algolithm, more common method mainly has two kinds: 1) multicarrier CBPWM based on injected zero-sequence voltage Method；2) the SVPWM method calculated based on redundancy small vector.

The multicarrier CBPWM method of injected zero-sequence voltage is, gathers busbar voltage Udc1 of both sides, midpoint, Udc2, will The voltage deviation of Udc1, Udc2 is compensated residual voltage U0, the more original three-phase modulations that is added to by U0 through closed loop controller On ripple, the mid-point voltage being carried out control system by the closed loop of voltage x current is fluctuated.The method realizes simple, wherein closed loop controller Design particularly significant, improperly control parameter can not stablize mid-point voltage.

The multicarrier PWM method of existing injected zero-sequence voltage, to different capacity factor, the adaptation ability of load Poor.

Summary of the invention

It is an object of the invention to provide neutral-point potential balance control method and the device of a kind of NPC three-level converter, use In solve the multicarrier PWM method of existing injected zero-sequence voltage to different capacity factor, that load adapts to ability is poor Problem.

For achieving the above object, the solution of the present invention includes: three-level converter neutral-point potential balance control method, step As follows:

1) the voltage U of dc bus midpoint upper and lower sides electric capacity is gathered_dc1、U_dc2；

2) U is calculated_dc1、U_dc2The deviation of two voltages, inputs Sliding Mode Controller by deviation, calculates

To zero sequence voltage component U₀, described Sliding Mode Controller is

Δ、k₁、ε₁For setup parameter；

3) by U₀It is superimposed to modulating wave U_a,U_b,U_cOn, obtain total modulating wave U_{a_total,}U_{b_total,}U_{c_total}；

4) by U_{a_total,}U_{b_total,}U_{c_total}Carry out CBPWM modulation to obtain controlling the pulse needed for power switch.

And to U₀、U_{a_total,}U_{b_total,}U_{c_total}Carry out amplitude limiting processing.

k₁、ε₁Choose and meet condition 0 ＜ ε₁-k₁/ R ＜ 1,0 ＜ ε₁＜ 1/x₁, R is the equiva lent impedance controlling loop.

The three-level converter neutral-point-potential balance control device of the present invention, including such as lower module:

For gathering the voltage U of dc bus midpoint upper and lower sides electric capacity_dc1、U_dc2Module；

For calculating U_dc1、U_dc2The deviation of two voltages, inputs Sliding Mode Controller by deviation, calculates To zero sequence voltage component U₀Module, described Sliding Mode Controller isΔ、k₁、 ε₁For setup parameter；

For by U₀It is superimposed to modulating wave U_a,U_b,U_cOn, obtain total modulating wave U_{a_total,}U_{b_total,}U_{c_total}Module；

For by U_{a_total,}U_{b_total,}U_{c_total}Carry out CBPWM modulation and obtain controlling the mould of the pulse needed for power switch Block.

And to U₀、U_{a_total,}U_{b_total,}U_{c_total}Carry out amplitude limiting processing.

k₁、ε₁Choose and meet condition 0 ＜ ε₁-k₁/ R ＜ 1,0 ＜ ε₁＜ 1/x₁, R is the equiva lent impedance controlling loop.

Three-level converter neutral-point-potential balance control device is realized by interrupt service routine.

The DC voltage deviation closed loop controller of the present invention uses Sliding Mode Controller, and this is a kind of non-linear control Device processed, has the features such as preferable robustness and quick response.Through overtesting, it is found to adapt to different capacity factor, load Operating mode, preferably realize neutral-point-potential balance control.

Accompanying drawing explanation

Fig. 1 is the topology diagram of NPC three-level converter of the present invention；

Fig. 2 is the multi-carrier PWM algorithm arrangement figure of injected zero-sequence voltage of the present invention；

Fig. 3 is saturation function sat (s) schematic diagram of the present invention.

Detailed description of the invention

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

The three-level converter topological structure of diode neutral point clamp as it is shown in figure 1, wherein name variable and symbol as follows:

The midpoint of N--changer dc bus；U_dc1--the DC bus-bar voltage on the upside of changer midpoint；U_dc2--changer DC bus-bar voltage on the downside of midpoint.

Midpoint potential imbalance Producing reason:

A) difference of dc-link capacitance hardware parameter, the error i.e. existed due to hardware manufacturing causes DC side two electric capacity On capacitance, voltage distribution inequality.

B) manufacturing variation of the hardware differences of device for power switching, i.e. device for power switching can cause switch time delay, pulse Distribution inequality, can produce impact to DC side mid-point voltage.

C) unsymmetry that loads, non-linear, this can cause the three-phase current unbalance of system so that mid-point voltage produces Skew.

D) error that control algolithm itself exists, idealizes control algolithm often in emulation, Theoretical Calculation, and actual fortune During row control algolithm can by sampling, circuit disturbance is affected causes pulse distribution uneven, can cause DC component meansigma methods Change.Even if using some neutral-point potential balance control method, without reasonably selecting to control parameter, during actual application still There is drift in the midpoint potential that can make system.

The multi-carrier PWM algorithm arrangement of injected zero-sequence voltage is as shown in Figure 2.

Wherein, U_dc1--the DC bus-bar voltage on the upside of changer midpoint；U_dc2--the dc bus on the downside of changer midpoint Voltage；U₀--the calculated residual voltage of via controller Controller；U_a,U_b,U_c--changer original three-phase modulations ripple； U_{a_total,}U_{b_total,}U_{c_total}--the superposition final modulating wave of three-phase of residual voltage.

Hereinafter use variable-structure control technology, design closed loop controller Controller.

Variable-structure control, is substantially a kind of special nonlinear Control, and its non-linear behavior is to control not connecting of input Continuous property.Owing to the design of sliding mode is unrelated with control object parameter and disturbance, this allows for variable-structure control and has response The advantages such as speed is fast, insensitive to Parameters variation and disturbance, physics realization is simple.In variable structure control theory, exponential approach The method for designing of rule, the most whether inspection sliding-mode surface meets existence condition, overall situation reaching condition and steady-state conditions, can make again be System has convergence rate faster.Reaching law method is below used to design controller.

In actual engineering design, due to temporal delay and spatially delayed, the switch in variable-structure control rule Switching characteristic can make sliding mode buffet.For reducing the buffeting of sliding mode, saturation function sat (s) is selected to replace reason Think sign function sgn (s) in sliding mode.Saturation function curve is as shown in Figure 3.Being in the nature of saturation function, in boundary region Outward, switching control is used；In boundary region, Linearization Feedback is used to control.

The function expression of sat (s) is as follows:

$sat\left(s\right)=\left\{\begin{array}{ccc}1& s>\mathrm{\&Delta;}& \\ ks& \left|s\right|\&le;\mathrm{\&Delta;}& k=\frac{1}{\mathrm{\&Delta;}}\\ -1& s<-\mathrm{\&Delta;}& \end{array}\right.$

For Fig. 2, introduce state variable x₁=U_dc1-U_dc2,

The design object of controller is:Application variable-structure control principle, takes diverter surfaceEmploying becomes Closely restrain method for designing, orderThe variable-structure control rule that then can obtain system is as follows:

$U_0=k_1(x_1^{*}-x_1)+{\mathrm{\&epsiv;}}_1\mathrm{sgn}(x_1^{*}-x_1)$

Wherein sgn (s₁) it is sign function, herein with saturation function sat (s₁) replace.

The basic scheme of the present invention is the voltage U by gathering dc bus midpoint upper and lower sides_dc1、U_dc2, inclined by both Difference input Sliding Mode Controller, obtains residual voltage U₀, then by U₀It is superimposed to original three-phase modulations ripple.

Concrete, the step of the embodiment of the present invention is as follows:

1) the voltage U of dc bus midpoint upper and lower sides electric capacity is gathered_dc1、U_dc2。

2) design Sliding Mode Controller.

3) U is calculated_dc1、U_dc2The deviation of two voltages, inputs Sliding Mode Controller by deviation, can be calculated zero sequence electricity Pressure component U₀, and to U₀Carry out amplitude limit.

4) by U₀It is superimposed to original modulating wave U_a,U_b,U_cOn, obtain total modulating wave U_{a_total,}U_{b_total,}U_{c_total}, and right U_{a_total,}U_{b_total,}U_{c_total}Carry out amplitude limit.5) by U_{a_total,}U_{b_total,}U_{c_total}Carry out CBPWM modulation obtain control power open Pulse needed for pass.

The points for attention that above step relates to also include:

Gather the voltage U of dc bus midpoint upper and lower sides electric capacity_dc1、U_dc2, have employed DSP and carry out A/D sample conversion, sampling Frequency is 10kHz.

Design Sliding Mode Controller, k₁、ε₁Selection, condition should be met

R is the equiva lent impedance controlling loop, by capacitance C of upper and lower electric capacity₁,C₂Conversion obtains, i.e. R=1/ (ω C₁+ω C₂), ω=50.

Choose x herein₁Fluctuate for maximum voltage deviation, take x₁=0.1 (p.u.), then ε₁=1/0.1=10.

Calculate ε₁, further according to C₁,C₂Occurrence can calculate k₁=(ε₁-1)/(ωC₁+ωC₂)。

C herein₁=C₂=0.012F, then calculate k₁=7.5.

For preventing the saturated of controller, it is right to needCarry out anti-saturation process, whenWhen exceeding limit value, RightItem is zeroed out.Controller uses dsp software to interrupt realizing, and interruption frequency is 3kHz.

Calculate U_dc1、U_dc2The deviation of two voltages, inputs Sliding Mode Controller by deviation, can be calculated residual voltage Component U₀, and to U₀Carry out amplitude limit.Employing standardization calculates, U₀Limit value is within 0.2.

By U₀It is superimposed to original modulating wave U_a,U_b,U_cOn, obtain total modulating wave U_{a_total,}U_{b_total,}U_{c_total}, and right U_{a_total,}U_{b_total,}U_{c_total}Carry out amplitude limit.Employing standardization calculates, U₀Limit value is within 0.98.

k₁Can not select too small, if too small, then can response speed the slowest.

ε₁Selection to calculate according to system transter.

It is presented above specific embodiment, but the present invention is not limited to described embodiment.The base of the present invention This thinking is above-mentioned basic scheme, for those of ordinary skill in the art, according to the teachings of the present invention, designs various change The model of shape, formula, parameter are not required to spend creative work.The most right Change that embodiment is carried out, revise, replace and modification still falls within protection scope of the present invention.

Claims (5)

1. three-level converter neutral-point potential balance control method, it is characterised in that step is as follows:

1) the voltage U of dc bus midpoint upper and lower sides electric capacity is gathered_dc1、U_dc2；

2) U is calculated_dc1、U_dc2The deviation of two voltages, inputs Sliding Mode Controller by deviation, is calculated zero sequence voltage component U₀, described Sliding Mode Controller isx₁=U_dc1-U_dc2, Δ、k₁、ε₁For setup parameter；

3) by U₀It is superimposed to modulating wave U_a,U_b,U_cOn, obtain total modulating wave U_{a_total},U_{b_total},U_{c_total}；

4) by U_{a_total},U_{b_total},U_{c_total}Carry out CBPWM modulation to obtain controlling the pulse needed for power switch；k₁、ε₁Choose Meet condition 0 ＜ ε₁-k₁/ R ＜ 1,0 ＜ ε₁＜ 1/x₁, R is the equiva lent impedance controlling loop.

Three-level converter neutral-point potential balance control method the most according to claim 1, it is characterised in that and to U₀、 U_{a_total},U_{b_total},U_{c_total}Carry out amplitude limiting processing.

3. three-level converter neutral-point-potential balance control device, it is characterised in that include such as lower module:

For gathering the voltage U of dc bus midpoint upper and lower sides electric capacity_dc1、U_dc2Module；

For calculating U_dc1、U_dc2The deviation of two voltages, inputs Sliding Mode Controller by deviation, is calculated residual voltage and divides Amount U₀Module, described Sliding Mode Controller isx₁=U_dc1-U_dc2, Δ、k₁、ε₁For setup parameter；

For by U₀It is superimposed to modulating wave U_a,U_b,U_cOn, obtain total modulating wave U_{a_total},U_{b_total},U_{c_total}Module；

For by U_{a_total},U_{b_total},U_{c_total}Carry out CBPWM modulation and obtain controlling the module of the pulse needed for power switch；

k₁、ε₁Choose and meet condition 0 ＜ ε₁-k₁/ R ＜ 1,0 ＜ ε₁＜ 1/x₁, R is the equiva lent impedance controlling loop.

Three-level converter neutral-point-potential balance control device the most according to claim 3, it is characterised in that and to U₀、 U_{a_total},U_{b_total},U_{c_total}Carry out amplitude limiting processing.

Three-level converter neutral-point-potential balance control device the most according to claim 4, it is characterised in that three level become Parallel operation neutral-point-potential balance control device is realized by interrupt service routine.