CN1896288A - Electric-heating control system of large vertical quench furnace - Google Patents

Abstract

A electric heating control system of large-size vertical quench stove. It controls the electric current in the electric heating elements with the solid state relay and regulates the output power via pulse width modulation. The temperature-rising and temperature-keeping heating of the quench stove is completed through three stages: the solid state relay is always under the all-pass state; the duty ratio of the solid state relay is regulated when the temperature is close to the set point; when the average temperature in the stove reaches the critical region of the given temperature, via decoupling self-learning incremental PID intelligent control, the coupling between adjacent sections is considered, the product of temperature difference between adjacent sections and the coefficient obtained by self-learning is taken as the correction value of the control variable, and the coupling effect between sections is countervailed via adjusting the coefficient value, as a result the temperature in the stove achieves the control accuracy and meets the need of homogeneity.

Description

The electric-heating control system of large vertical quench furnace

[technical field] the present invention relates to a kind of electric-heating control system, especially for the electric-heating control system of large vertical quench furnace.

[background technology] quenching furnance is to be used for main equipment that metal is heat-treated, is widely used in iron and steel, machinery and controls golden industry.With suitable temperature forging is heat-treated, can reduce its resistance to deformation, but the too high meeting of temperature causes grain growth, oxidation or burning, has a strong impact on quality product.At present, in the thermal treatment of quenching furnance, heat-processed is divided into intensification, two stages of insulation, but the electric heating master loop adopts thyristor circuit, and phase shift triggers control voltage change electric power and comes controlled temperature, the major loop structure complexity, the failure rate height produces harmonic pollution to electrical network; Guarantee that temperature rise rate causes the temperature rise period overshoot excessive, cause the product burning, satisfy overshoot and require that then temperature-rise period is oversize; The temperature fluctuation of holding stage is excessive, influences quality product, adopts multi-region section type of heating, and body of heater is huge, and each section intercouples.

[summary of the invention] for satisfy being rapidly heated of large-scale quenching furnance, the temperature rise period overshoot is little and the high precision of holding stage control requirement, the present invention carries out syllogic modulation (PWM) intelligent control to quenching furnance, comprises following content:

Replace thyristor directly to control the connecting and disconnecting of electrical heating element with solid state relay, the output rating of control electrical heating element.The characteristics that solid state relay has is simple in structure, control convenient, failure rate is low, cut-off by PLC control heating unit with pulse-width modulation (PWM) method, can reduce the velocity of variation of voltage and current, prolong the work-ing life of controlling elements, replace phase shift in zero cross fired Power Regulation mode simultaneously and trigger, eliminate electric network pollution.Modulate intelligent control technology with segmentation, with self study increment type PID intelligent control algorithm, the whole heat tracing process of heat treatment furnace is divided into three phases, the fs solid state relay is in the all-pass state; Subordinate phase reduces the break-make dutycycle of solid state relay according to furnace temperature and measurement temperature conditions; When medial temperature in the stove arrived critical zone to fixed temperature, system entered holding-zone, i.e. Kong Zhi phase III.

After adopting above-mentioned control strategy, guaranteed to be rapidly heated, low overshoot has improved the intensification of quenching furnance and the temperature control precision and the homogeneity of holding stage, has eliminated the harmonic pollution to electrical network.Simplify system architecture simultaneously, reduced failure rate.

[description of drawings]

Fig. 1 is the structural representation of batch kiln of the present invention;

Fig. 2 is the schematic diagram of phase III decoupling zero control of the present invention;

Fig. 3 is a syllogic modulation (PWM) intelligent control process synoptic diagram of the present invention.

The present invention is described in further detail below in conjunction with accompanying drawing.

Quenching furnance heating furnace body structure iron as shown in Figure 1.Stove adopts bottom-dump forced air circulation heating work mode, strengthens temperature uniformity by two typhoon machines, 1 forced air circulation, improves heating-cooling speed, and 2 is workpiece surface, and the furnace wall lagging material is selected slag wool for use, and chamber wall 3 is a stainless material.Furnace temperature is regulated by changing electrical heating element 4 power, and electrical heating element 4 is divided into the tight obedient furnace wall of multistage vertically, places in the heating chamber 5, be called furnace wall electric heating face 6, form a plurality of heating zone, by a three-phase solid state relay control, 7 is thermopair to electrical heating element 4 heating currents of each heating zone respectively.

The heat-processed of quenching furnance is divided into three phases, and the break-make dutycycle of fs solid state relay is 1, is in the all-pass state all the time, realizes being rapidly heated; Subordinate phase is after temperature reaches certain value, reduces the break-make dutycycle of solid state relay, controlled temperature overshoot; The increment type PID intelligence control method is adopted in the control output of fs and subordinate phase, does not consider the coupling between each section.When medial temperature in the stove arrives critical zone to fixed temperature, system enters the phase III of control, the phase III quenching furnance adopts decoupling zero self study increment type PID intelligent control method, according to actual engineering characteristic, ignore the coupling between the non-contiguous sectors, only consider the coupling between the adjacent sections, the coefficient product that the temperature head between the adjacent sections and self study are obtained is as the modified value of manipulated variable, offset coupling between each section by adjusting coefficient magnitude, detailed process is as follows:

The weighted mean Δ T＜Δ of fs difference between the measured temperature of each section and set(ting)value ₁The time, the break make ratio of solid state relay is 100%, wherein:

Δ ₁＝T _g×(70％-80％)

T _gFor being set at the set(ting)value of workpiece temperature.

$\mathrm{\ΔT}=\frac{\underset{i=1}{\overset{I}{\mathrm{\Σ}}}(T_g-{\mathrm{Tc}}_i)P_i}{I}$

Tc _iBe the measured temperature of each section, I is the section sum.

$\underset{i=1}{\overset{I}{\mathrm{\Σ}}}{P}_i=1$ Be weighting coefficient, the heat affecting that adds of workpiece determined according to each section, little as the weighting coefficient of the coefficient ratio centre portion of furnace roof and fire door.

The subordinate phase Δ ₁＜Δ T＜Δ ₂, furnace temperature is near desired temperature, for reducing overshoot, Δ K _{P, i}Get negative value, carry out self aligning, thereby reduce the furnace temperature lift velocity by the deviation size.And Δ T _{I, i}With Δ T _{D, i}Constantly increase to the expertise value, and make suitably to adjust benchmark based on this, guarantee that temperature steadily rises to set(ting)value as next stage.

Δ ₂＝T _g×(90％-95％)

Δ ₂According to the difference of member thermal inertia to be heated, get the 90%-95% of desired temperature

$\mathrm{\Δ}{u}_i\left(k\right)=K_{p,i}\{e_i\left(k\right)-e_i(k-1)\}+\frac{T_0}{T_{I,i}}{e}_i\left(k\right)+\frac{T_{D,i}}{T_0}\{e_i\left(k\right)-2e_i(k-1)+e_i(k-2)\}$

Phase III, Δ T＞Δ ₂, for further suppressing overshoot, Δ K _{P, i}＜0, Δ T _{I, i}＜0, T _{D, i}=0, finally eliminate static difference.Control principle figure as shown in Figure 2.

$\mathrm{\Δ}{u}_i\left(k\right)=K_{P,i}\{e_i\left(k\right)-e_i(k-1)\}+\frac{T_0}{T_{I,i}}{e}_i\left(k\right)$

$+{\mathrm{\α}}_{i,i-1}\left(k\right)\{e_{i,i-1}\left(k\right)-e_{i,i-1}(k-1)\}+{\mathrm{\α}}_{i,i+1}\left(k\right)\{e_{i,i+1}\left(k\right)-e_{i,i+1}(k-1)\}$

α _{I, i-1}(k) { e _{I, i-1}(k)-e _{I, i-1}And α (k-1) } _{I, i+1}(k) { e _{I, i+1}(k)-e _{I, i+1}(k-1) } be the decoupling zero item, be respectively applied for the coupling of payment i-1 and i+1 bar branch road i bar branch road.

α _1，0(k)＝a _I，l-1(k)＝0

e _i，i-1(k)＝[Y _i(k)-Y _i-1(k)] e _i，i+1(k)＝[Y _i(k)-Y _i+1(k)]

If r ₁＞ε ₁, | α _{I, i-1}(k) |=r ₁| α _{I, i-1}(k-1) |

If r ₂＞ε ₂, | α _{I, i+1}(k) |=r ₂| α _{I, i+1}(k-1) |

Work as e _{I, i-1}(k-1)＞ε ₃e _{I, i+1}(k-1)＞ε ₄,

r ₁, r ₂Meet the following conditions: ${\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20051003186800061.png"\; state="\{\{state\}\}">r</figure-callout>}}_1=\left|\frac{e_{i,i-1}\left(k\right)}{e_{i,i-1}(k-1)}\right|$ ${\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="A20051003186800061.png"\; state="\{\{state\}\}">r</figure-callout>}}_2=\left|\frac{e_{i,i+1}\left(k\right)}{e_{i,i+1}(k-1)}\right|$

ε ₁, ε ₂, ε ₃, ε ₄It is very little constant.

If e _{I, i-1}(k-1)＜ε ₃, e _{I, i+1}(k-1)＜ε ₄, | α _{I, i-1}|, | α _{I, i+1}|=0

α _{I, i-1}(k) and α _{I, i+1}(k) symbol is by e _{I, i-1}(k-1) and { e _{I, i-1}(k)-e _{I, i-1}(k-1) } symbol decision.

Last each branch-Parameter Calculation that is obtained by self study goes out the current switching dutycycle, by the PLC control electrical heating element galvanization time, thereby the temperature of each section of holding stage is remained in the scope of design temperature permission fluctuation, and whole process syllogic modulation (PWM) intelligent control process synoptic diagram as shown in Figure 3.

Claims (1)

1. the electric-heating control system of a large vertical quench furnace, comprise PLC controller, power regulating cabinet, Heating element and temperature gauge, it is characterized in that: the conduction time of in power regulating cabinet, controlling electrical heating element with solid state relay, by the output rating that PLC regulates electrical heating element, control the intensification and the insulation heating of quenching furnance with pulse-width modulation method in three stages:

When (1) weighted mean of the observed value of Dang Ge district temperature and set(ting)value difference was less than the 70-80% of workpiece temperature set(ting)value, solid state relay was in the all-pass state all the time;

(2) temperature reaches (1) described condition to the weighted mean of observed value and set(ting)value difference during less than the 90-95% of workpiece temperature set(ting)value, reduces the break-make dutycycle of solid state relay with the increment type PID intelligent control method;

When (3) medial temperature arrives the critical zone of 90-95% of desired temperature in the stove, adopt decoupling zero self study increment type PID intelligent control method, consider the coupling between the adjacent sections, the coefficient product that temperature head between the adjacent sections and self study are obtained is as the modified value of manipulated variable, offsets coupling between each section by adjusting coefficient magnitude.

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