Three-phase half-wave rectification burn-through device and control method

Abstract

This invention belongs to the field of electrical control technology for submerged arc furnaces, specifically a three-phase half-wave rectifier burn-through device and control method. The three-phase AC input circuit includes phases A, B, and C, and a common return terminal. Three controlled rectifier switches are connected to the three phases respectively, and their outputs converge to form a positive bus. The positive bus is connected to the burn-through electrode, which passes through the furnace charge, furnace shell, or return electrode and returns to the common return terminal via the return bus, forming a closed burn-through circuit where the burn-through power is provided by all three phases. The control unit estimates the overall electrode loss based on the burn-through current, burn-through voltage, electrode displacement, temperature, and accumulated energy. It prioritizes rapid electrical compensation using trigger angle or pulse parameters, and outputs electrode replenishment when the electrical compensation margin is insufficient to control the burn-through current stability. This invention overcomes the technical bias of isolating the burn-through and smelting circuits, allowing the three phases to share the burn-through power, thus eliminating the three-phase load imbalance caused by single-phase connection at its source.

Description

Technical Field

[0001] This invention belongs to the field of electrical control technology for submerged arc furnaces, specifically a three-phase half-wave rectifier burn-through device and control method. Background Technology

[0002] The statements in this section merely refer to the background art related to this invention and do not necessarily constitute prior art.

[0003] During operation, electric arc furnaces often experience blockages in conductive paths due to charge crusting, bridging, or the formation of localized high-resistivity layers. A burn-through device is needed to apply a large local current to restore the conductive path. Existing burn-through devices mostly employ a single-phase connection method, where one phase from the three-phase power supply system is randomly selected as the burn-through power source, which is then connected to the burn-through electrode via a separate burn-through transformer or rectifier.

[0004] This wiring method has a simple structure, but the connected phase must bear the entire burn-through current during the burn-through operation, while the other two phases hardly participate in the power output, resulting in a serious imbalance in the three-phase load. This imbalance not only causes instantaneous overload in the power supply circuit of the connected phase, but also causes asymmetry in the three-phase magnetic flux of the furnace transformer through transformer coupling, thereby inducing current distortion, additional losses, and disordered power distribution in the furnace.

[0005] For large and medium-sized submerged arc furnaces using multi-electrode power supply, the three-phase imbalance caused by single-phase connection directly affects the stability of the furnace, causing frequent operation of the electrode adjustment system, and even secondary problems such as electrode breakage or localized overheating of the furnace lining. In addition, to meet the large current required for burn-through, single-phase circuits need to be equipped with large-section copper busbars and independent overcurrent protection devices, which increases equipment costs and wiring complexity. Summary of the Invention

[0006] This invention provides a three-phase half-wave rectifier burn-through device and control method, aiming to solve the problem of three-phase load imbalance and reduced furnace stability caused by the use of single-phase connection in existing electric arc furnace burn-through devices. The invention designs a burn-through device and control method that can share the burn-through power among the three phases, maintain three-phase load balance, and retain the pulsating DC characteristics that are beneficial to burn-through operation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention discloses a three-phase half-wave rectifier burn-through device, comprising: The three-phase AC input circuit includes phase A, phase B, phase C, and a common return terminal; The three-phase half-wave controlled rectifier unit includes three controlled rectifier switching devices connected to phases A, B, and C respectively. The output terminals of the three controlled rectifier switching devices are combined to form a positive bus. The DC bus unit includes a positive bus and a return bus. The positive bus is connected to the burn-through electrode. The burn-through electrode passes through the furnace charge, furnace shell or return electrode and returns to the common return terminal through the return bus, forming a closed burn-through circuit in which the burn-through power is provided by the three phases. The control unit is electrically connected to the control terminals of three controlled rectifier switching devices and is used to control the burn-through current stability.

[0008] Furthermore, the common return terminal is the transformer secondary neutral point, a dedicated return bus, or a return terminal electrically connected to the furnace shell.

[0009] Furthermore, the control unit includes: The sampling module is used to collect burn-through current, burn-through voltage, electrode displacement and temperature, and update the cumulative energy according to the burn-through current, burn-through voltage and sampling period; The loss estimation module is used to calculate the total electrode loss based on burn-through current, burn-through voltage, electrode displacement, temperature, and cumulative energy. The compensation module is configured to: first convert the total electrode loss into a trigger angle compensation or a pulse parameter compensation, and determine the electrical compensation margin based on the remaining adjustable range between the trigger angle or pulse parameter and its preset adjustment boundary; when the trigger angle compensation or pulse parameter compensation exceeds the corresponding remaining adjustable range, and the burn-through current or burn-through voltage deviation has not converged for several consecutive power frequency cycles, output the electrode compensation amount.

[0010] Furthermore, the loss estimation module is configured as follows: When the filtered burn-through current is not less than the effective current threshold, the equivalent burn-through circuit resistance is calculated by dividing the difference between the burn-through voltage and the fixed voltage drop by the burn-through current; when the filtered burn-through current is less than the effective current threshold, the previous effective equivalent burn-through circuit resistance or the freezing resistance loss component is maintained. The resistance loss length is calculated by temperature correction based on the change in the equivalent burn-through circuit resistance relative to the initial value. The displacement loss length is calculated based on the change in the displacement sensor reading relative to the initial value. The cumulative energy is converted into the energy equivalent loss length using an energy-length calibration coefficient. The total electrode loss is obtained by combining the resistance loss length, displacement loss length, and energy equivalent loss length according to their weights.

[0011] Furthermore, the loss estimation module is also configured to freeze the electrode to compensate for the output when the direction of change of the resistance loss length and the displacement loss length is inconsistent or the difference exceeds the preset verification threshold, and only allow electrical compensation of the trigger angle or pulse parameters within the safety limit.

[0012] Furthermore, the control unit has constant current burn-through mode, constant voltage burn-through mode and pulse burn-through mode; In constant current burn-through mode, the control unit corrects the firing angle based on the target current and the total electrode loss. In constant voltage burn-through mode, the control unit corrects the firing angle according to the target voltage and corrects the lower limit of the allowable current according to the total electrode loss. In pulsed burn-through mode, the control unit corrects the pulse peak value, pulse width, pulse interval, or duty cycle based on the total electrode loss.

[0013] Furthermore, the positive bus is connected to the burn-through electrode via a small current-limiting reactor. The small current-limiting reactor is used to limit the rate of rise of the conduction current of the controlled rectifier switching device and suppress commutation impact. The inductance of the small current-limiting reactor is configured to be no greater than the set multiple of the inductance of the smoothing reactor configured for smoothing three-pulse output under the same rated current, and / or to make the DC circuit time constant no greater than the set proportion of the power frequency half cycle.

[0014] Furthermore, it also includes protection branches, which include RC snubber circuits connected in parallel across each controlled rectifier switching device, a freewheeling branch connected in parallel between the DC-side rear end and the return path, and a damping branch connected in parallel between the DC output terminals.

[0015] Furthermore, the control unit is electrically connected to the sampling unit, which includes a current detection element for detecting burn-through current, a voltage detection element for detecting burn-through voltage, a displacement sensor for detecting electrode displacement, and a temperature detection element for detecting temperature.

[0016] A second aspect of the present invention discloses a control method for a three-phase half-wave rectifier burn-through device, comprising the following steps: The system collects burn-through current, burn-through voltage, electrode displacement, and temperature, updates the cumulative energy based on the burn-through current, burn-through voltage, and sampling period, and preprocesses the sampled data. When the burn-through current is not less than the effective current threshold, the current equivalent burn-through circuit resistance is calculated based on the burn-through voltage, burn-through current and fixed voltage drop; when the burn-through current is less than the effective current threshold, the previous effective equivalent burn-through circuit resistance or the freezing resistance loss component is maintained; the changes in equivalent burn-through circuit resistance, displacement changes, temperature correction and accumulated energy are converted into the comprehensive electrode loss. Determine whether the total electrode loss, burn-through current deviation, or burn-through voltage deviation exceeds a preset threshold; prioritize converting the loss exceeding the threshold into a firing angle compensation or pulse parameter compensation. The electrical compensation margin is determined based on the remaining adjustable range between the trigger angle or pulse parameter and its preset adjustment boundary. When the trigger angle compensation or pulse parameter compensation exceeds the corresponding remaining adjustable range, and the burn-through current deviation or burn-through voltage deviation persists, the electrical compensation margin is determined to be insufficient, and the electrode supplement amount is output to the electrode execution unit. The next cycle is corrected based on the feedback results of the compensated current and voltage.

[0017] Compared with existing technologies, one or more of the above technical solutions have the following beneficial effects: By employing a three-phase half-wave controlled rectification topology, phases A, B, and C are respectively connected to the positive bus via their respective controlled rectifier switching devices. A closed burn-through circuit is formed by the burn-through electrode, the furnace charge, and the common return terminal, allowing all three phases to jointly provide burn-through power. Under this topology, each phase only carries current within its corresponding 120° conduction interval. From the perspective of the average power frequency cycle, the power output of the three phases is equal, and the sum equals the power required for burn-through. This completely eliminates the three-phase load asymmetry caused by single-phase connection at the circuit structure level. It maintains the three-phase magnetic flux symmetry of the furnace transformer without the need for any additional balancing compensation equipment, avoiding problems such as overload of the connected phase, idle power of the unconnected phases, and uneven heating of the three-phase windings of the transformer. This breaks through the long-standing prejudice in the field of submerged arc furnace burn-through that "burn-through is isolated from the smelting circuit," treating burn-through as a load shared by all three phases rather than an interference with the main circuit. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 A schematic diagram illustrating the structural principle of the three-phase half-wave rectifier burn-through device for an electric arc furnace provided by the present invention. Figure 2 A circuit connection diagram for the DC-side high-power smoothing reactor provided by the present invention; Figure 3 A schematic diagram of the control process for online compensation of electrode loss provided by the present invention.

[0020] In the diagram: 10 Three-phase AC input circuit, 11 Three-phase power supply, 12 Common return terminal, 20 Three-phase half-wave controlled rectifier unit, 30 Positive bus, 31 Return bus, 40 Burn-through electrode, 41 Furnace charge, 42 Furnace shell or return electrode, 50 Sampling unit, 60 Small current-limiting reactor Lx, 70 Protection branch, 71 Freewheeling branch Df, 72 Damping branch Rf / Cf, 80 Electrode execution unit, 90 Control unit. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] A submerged arc furnace is an electric heating device that smelts metal by applying electric arc heat energy through three-phase electrodes inserted into the furnace charge. During the smelting process, a crust layer is easily formed on the surface of the furnace charge, or local bridging or high-resistivity material layers may occur, blocking the conductive channels. In this case, a "burn-through" operation is required, which involves applying a local large current to the target area to break down the high-resistivity layer and restore the conductive path.

[0024] As described in the background section, existing burn-through devices typically employ a single-phase connection method, which involves selecting one phase from a three-phase power supply circuit as the burn-through power source, connecting it to the burn-through electrode via an independent transformer or rectifier, and then forming a circuit through the furnace shell or return electrode.

[0025] This wiring method is prone to causing three-phase load imbalance because the burn-through current only flows through the connected phase, while the other two phases hardly participate in power output, resulting in a severe asymmetry in the three-phase current. This asymmetry causes magnetic flux distortion through transformer magnetic circuit coupling, which in turn causes overload of the connected phase, idle power of the unconnected phase, and uneven heating and voltage drop in the three-phase windings of the furnace transformer.

[0026] In addition to three-phase imbalance, a single-phase circuit needs to independently bear the entire burn-through current, which places high demands on the local capacity of the power supply circuit and transformer, and is prone to triggering overcurrent protection or causing local overheating. Secondly, the return path depends on the furnace shell or a single circuit, resulting in a large grounding current and potential safety hazards. At the same time, the burn-through power is provided by only one phase, which limits the adjustable range and adjustment flexibility.

[0027] In the power supply system of an electric arc furnace, the three electrodes are arranged in an equilateral triangle inside the furnace. The impedance between each phase electrode and the furnace charge naturally differs and changes dynamically with the smelting process. Secondly, the furnace transformer usually adopts Δ / Y or Y / Δ connection, and the neutral point is not brought out or is unusable, making it difficult to directly obtain the neutral point as the return terminal. In addition, the burn-through operation is intermittent and has a large current impact. If the three phases participate in the power supply at the same time, the industry is generally concerned that it will cause circulating current and mutual interference between the three phases through transformer coupling, which will aggravate the fluctuation of furnace conditions.

[0028] Based on the above understanding, a fixed mindset has long existed in this field: the burn-through power supply should be independent of the main circuit power supply system, drawing power from one phase in a single-phase connection manner to avoid affecting the operation of the other two phases. This design concept of "burn-through isolation from the smelting circuit" treats burn-through as an interference to the main circuit and isolates it, rather than treating burn-through as a load shared by all three phases and balancing it.

[0029] Therefore, this solution provides a three-phase half-wave rectifier burn-through device and control method, which distributes the burn-through current across the three phases, allowing each of the three phase electrodes to supply power to the burn-through electrode through a controlled rectifier device. By combining the three-phase AC inputs through controlled rectifier switching devices to the positive bus, a closed loop is formed via the burn-through electrode, furnace charge, and common return terminal. Each phase shares the burn-through power, fundamentally eliminating the three-phase imbalance caused by single-phase connection. Simultaneously, this topology naturally outputs three-pulse DC, eliminating the need for a high-power smoothing reactor to generate concentrated thermal shock during peak periods and provide intermittent recovery during valley periods, thus enabling the device to achieve both three-phase balance and excellent burn-through performance.

[0030] like Figure 1 and Figure 2 As shown, the three-phase half-wave rectifier burn-through device for an electric arc furnace includes: The three-phase AC input circuit 10 includes phase A, phase B, phase C, and a common return terminal; The three-phase half-wave controlled rectifier unit 20 includes three controlled rectifier switching devices connected to phase A, phase B, and phase C respectively, and the output terminals of the three controlled rectifier switching devices are combined to form a positive bus. The DC bus unit includes a positive bus 30 and a return bus 31. The positive bus 30 is connected to the burn-through electrode 40. The burn-through electrode 40 returns to the common return terminal via the furnace charge 41, the furnace shell or the return electrode 42 and the return bus 31, forming a closed burn-through circuit in which the three phases jointly provide the burn-through power. The burn-through circuit, consisting of the burn-through electrode 40, the furnace charge 41, the furnace shell or return electrode 42 and the return bus 31, forms a closed path to carry the pulsating DC output of the three-phase half-wave rectifier, so that the current flows through the target high-resistance area to achieve local breakdown and restoration of the conductive path. Protection branch 70 is used to suppress commutation spikes, limit voltage and current surges during device turn-on, and provide a current attenuation path during load changes, ensuring safe and reliable operation of the device without a high-power smoothing reactor.

[0031] The outputs of three controlled rectifier switches are directly connected in parallel to the positive bus. The effect is that phases A, B, and C conduct alternately in time, with each phase only bearing the burn-through current during its corresponding 120° conduction interval, while remaining off for the remaining 240°. Therefore, at any given moment, the burn-through current flowing through the positive bus is provided by only one phase. However, from the perspective of the power frequency cycle, the power provided by the three phases is equal, and the sum equals the power required for burn-through. This "instantaneous single-phase, average three-phase" power supply method avoids continuous single-phase overload and reduces the three-phase imbalance to its theoretical minimum.

[0032] In this embodiment, the three-phase AC input circuit 10 can be the secondary three-phase power supply 11 from the furnace transformer of the electric arc furnace, and the common return terminal 12 can be the secondary neutral point of the transformer, a dedicated return bus, or the furnace shell return terminal connected by safety grounding.

[0033] In this embodiment, as Figure 2 As shown, the three-phase half-wave controlled rectifier unit 20 includes SCR1, SCR2 and SCR3. SCR1 is connected to phase A, SCR2 is connected to phase B and SCR3 is connected to phase C. The output terminals of the three are combined to form the positive bus 30.

[0034] The sampling unit 50 includes a current detection element, a burn-through voltage detection element, a displacement sensor, and a temperature detection element, which are used to monitor the current I1, burn-through voltage U1, displacement S1, and temperature T1, respectively.

[0035] In this embodiment, the positive bus 30 is connected to the burn-through electrode 40 via a small current-limiting reactor Lx60. A current detection element acquires the current I1 flowing through the small current-limiting reactor 60, and a burn-through voltage detection element is connected in parallel between the burn-through electrode 40 and the return path to detect the actual burn-through voltage U1. A displacement sensor is installed in the electrode pressure release cylinder, lead screw mechanism, electrode clamping mechanism, or near the burn-through electrode to detect the cumulative release amount and the displacement change S1 per unit time. A temperature detection element is set at the electrode clamping end, near the furnace opening, or at a location that can characterize the thermal state of the electrode.

[0036] The protection branch 70 includes the resistor-capacitor absorption circuits R1 / C1-R3 / C3 connected in parallel to the two ends of SCR1-SCR3, the freewheeling branch (Df) 71, and the damping branch (Rf / Cf) 72.

[0037] The freewheeling branch 71 can be a diode, thyristor, or a unidirectional release branch with a current limiting element, and is connected between the rear end of the small current limiting reactor 60 and the return path to provide a current attenuation path during load changes or commutation gaps.

[0038] The damping branch 72 can be a series resistor-capacitor branch, connected between the two ends of the burn-through electrode 40 or the DC output terminal, to suppress overvoltage and high-frequency oscillation.

[0039] In this embodiment, no high-power smoothing reactor is provided on the DC side for smoothing the three-pulse output. A high-power smoothing reactor refers to a reactor connected in series in the DC output circuit, whose main purpose is to reduce the ripple of the three-pulse output current and improve the continuity of the DC current, and whose inductance and energy storage capacity are sufficient to significantly weaken the three-pulse ripple characteristics.

[0040] Although the small current-limiting reactor 60 in this embodiment is also an inductive element, its functional positioning is different from that of the high-power smoothing reactor mentioned above. The small current-limiting reactor 60 is not intended to smooth the three-pulse output, nor is it a replacement for the high-power smoothing reactor. Instead, it is used to limit the current rise rate di / dt at the moment the controlled rectifier switching device is turned on, suppress commutation spikes, and release transient energy in conjunction with the freewheeling branch 71 and the damping branch 72.

[0041] When selecting a reactor for a project, the minimum inductance of the miniature current-limiting reactor 60 can be determined first based on the allowable di / dt of the controlled rectifier switching device. Then, its upper limit inductance can be determined based on Lx ≤ 0.1Ls or tau = Lx / Rload ≤ γ·T / 2, where Lx is the inductance of the miniature current-limiting reactor 60, Ls is the equivalent inductance of the high-power smoothing reactor required to achieve smooth three-pulse output under the same load conditions, Rload is the equivalent load resistance of the burn-through circuit, T is the power frequency period, and γ is 0.05-0.30. Through these upper limit constraints, the miniature current-limiting reactor 60 only serves to limit current and suppress transients, preventing the formation of a large energy storage smoothing circuit on the DC side. This allows it to protect the device while preserving the three-pulse pulsating DC characteristics of the three-phase half-wave rectifier output.

[0042] The electrode execution unit 80 is connected to the electrode pressing and releasing mechanism and is used to receive the mechanical compensation command output by the control unit 90, drive the burn-through electrode 40 to feed downward, so as to compensate for the length consumed by the electrode due to continuous burn-through and maintain the stability of the electrode insertion depth and burn-through current.

[0043] The control unit 90 can be a PLC, an industrial controller, a DSP control board, or an embedded controller with an isolated trigger unit.

[0044] In this embodiment, the control unit 90 collects If(k), Uf(k), sf(k), and T(k) according to the power frequency synchronous beat. It updates E(k) based on If(k), Uf(k), and the sampling period Ts, and performs moving average, amplitude limiting, and outlier removal. For single-cycle anomalies caused by sparking, slag turning, instantaneous short circuits, or sudden changes in the contact channel, the control unit 90 maintains the firing angle and compensation amount of the previous cycle; only when the same-direction deviation condition is met for M consecutive power frequency cycles is the overall electrode loss amount updated.

[0045] The electrode loss estimation process is as follows: First, the control unit 90 determines the validity of the burn-through current If(k). The If(k) is the burn-through current value after power-frequency synchronous sampling, filtering, and averaging processing in the effective conduction interval. An effective current threshold Imin is set. Only when If(k) ≥ Imin, it is determined that the current burn-through current is in the effective calculation interval, and the equivalent burn-through loop resistance is calculated: Re(k) = [Uf(k) - Uc] / If(k); When If(k) < Imin, or when it is detected that the current is in the zero-crossing, discontinuous conduction, instantaneous open circuit, arc starting and unstable, or sampling abnormal state, the control unit 90 does not perform the above division operation, and marks the current equivalent burn-through loop resistance as an invalid value, maintaining the previous effective equivalent resistance Re(k - 1) or freezing the resistance loss component. When If(k) satisfies If(k) ≥ Imin and the change is within the allowable range for M consecutive power-frequency cycles, the calculation of the equivalent burn-through loop resistance is resumed.

[0046] Secondly, calculate ΔR(k) = Re(k) - Re(0); Among them, Re(k) is the equivalent resistance of the burn-through loop at the kth sampling moment, Uf(k) is the filtered burn-through voltage at the kth sampling moment, Uc is the fixed voltage drop calibration value caused by the fuse, busbar, contact end, and connecting parts, and If(k) is the filtered burn-through current at the kth sampling moment.

[0047] Uc can be calibrated through a standard low-resistance load or a short-circuit verification loop during the commissioning and debugging stage of the device, that is, the DC output voltage is collected under a preset verification current, and the fixed voltage drop caused by the fuse, busbar, contact end, and connecting parts is obtained after deducting the standard load voltage drop; the calibrated Uc is stored in the control unit 90 and can be recalibrated after equipment maintenance or replacement of connecting parts.

[0048] Considering the influence of temperature on the resistivity of the electrode material, temperature correction is carried out, and ΔR(k) is converted into an equivalent length loss ΔLR(k) = AeΔR(k) / rho_T(k), where Ae is the effective cross-sectional area of the electrode.

[0049] Temperature correction is carried out as shown in the following formula: rho_T(k) = rho_20[1 + a(T(k) - T0)]; Among them, rho_T(k) is the resistivity of the electrode material after temperature correction, rho_20 is the resistivity of the electrode material at the reference temperature T0 (usually 20°C), a is the resistance temperature coefficient, and T(k) is the measured temperature at the kth sampling moment (from T1).

[0050] Meanwhile, the displacement loss length ΔLs(k)=sf(k)-s0 is obtained from the displacement sensor, the cumulative burn-through energy is obtained from E(k)=ΣUf(i)If(i)Ts, and the energy equivalent loss length ΔLE(k)=β·E(k) is converted into energy equivalent loss length ΔLE(k)=β·E(k) through the energy-length calibration coefficient β. Wherein, β is in units of length / energy, such as mm / J or mm / kWh, and is used to convert the cumulative burn-through energy into a length quantity with the same dimensions as the resistance loss length ΔLR(k) and the displacement loss length ΔLs(k).

[0051] Finally, the total loss ΔL(k) is obtained as ΔL(k) = w1ΔLR(k) + w2ΔLs(k) + w3ΔLE(k); Where sf(k) is the filtered displacement value at the kth sampling time (derived from S1), and s0 is the initial value (zero position) of the displacement sensor.

[0052] Where E(k) is the cumulative burn-through energy up to the kth sampling time, Uf(i) is the filtered burn-through voltage at the ith sampling time (detected by U1 and filtered), If(i) is the filtered burn-through current at the ith sampling time (detected by I1 and filtered), and Ts is the sampling period.

[0053] β can be determined during the commissioning and debugging phase of the device or during the calibration phase of historical operating data. During calibration, under the same electrode material, similar burn-through current level and typical furnace conditions, the actual electrode consumption length ΔLtest and the corresponding cumulative burn-through energy ΔEtest during a burn-through process are recorded, and β is determined according to β=ΔLtest / ΔEtest; alternatively, β can be obtained by fitting multiple sets of calibration data and stored in the control unit 90.

[0054] w1, w2, and w3 are the dimensionless fusion weights corresponding to the resistance loss length ΔLR(k), displacement loss length ΔLs(k), and energy equivalent loss length ΔLE(k), respectively, and w1, w2, and w3 are all not less than 0 and satisfy w1+w2+w3=1.

[0055] w1, w2, and w3 can be determined during the commissioning and historical data calibration phase of the device. During calibration, under the same electrode material, furnace type, and burn-through current level, multiple sets of burn-through process data are collected to obtain ΔLR(k), ΔLs(k), ΔLE(k), and the actual measured electrode consumption length ΔLtest. The goal is to minimize the error between the comprehensive loss ΔL(k) = w1ΔLR(k) + w2ΔLs(k) + w3ΔLE(k) and the actual electrode consumption length ΔLtest, thereby determining w1, w2, and w3.

[0056] In situations where data volume is insufficient or during the initial commissioning phase, weights can be determined based on the reliability coefficients of each detection quantity. The reliability coefficients can be determined by sensor accuracy, sampling noise, data loss rate, drift, and historical verification errors; the higher the reliability of the loss component, the greater its corresponding weight. If the displacement signal is stable and closely matches the actual electrode consumption, then w2 should be increased; if the displacement signal is significantly affected by mechanical clearance or jamming, and the resistance change or accumulated energy is more correlated with the actual loss, then w1 or w3 should be increased.

[0057] To improve estimation accuracy, the control unit 90 is equipped with delayed confirmation and cross-checking logic. When a sudden change in current, voltage, or displacement occurs in a single sampling cycle, only the abnormal flag is recorded and the output of the previous cycle is maintained; the effective loss change is only confirmed when the detected value meets the same-direction deviation condition for M consecutive power frequency cycles. If ΔLR(k) and ΔLs(k) are in opposite directions, or the difference between them exceeds the preset check threshold, the control unit 90 enters the verification state, freezes the mechanical compensation output, and only allows electrical compensation of the trigger angle or pulse parameters within the safety limits.

[0058] The control unit supports three modes: constant current burn-through, constant voltage burn-through, and pulse burn-through.

[0059] In constant current burn-through mode, the control unit 90 calculates the corrected target current as the main setpoint and calculates the firing angle correction Δα(k) based on Iref'(k)-If(k).

[0060] The corrected target current is calculated as shown in the following formula: Iref'(k)=Iset+KLΔL(k)+KD[ΔL(k)-ΔL(k-1)] / Ts; Where Iset is the target current setting value under constant current burn-through mode, KL is the loss ratio compensation coefficient, KD is the loss differential compensation coefficient, ΔL(k) is the comprehensive loss at the kth sampling time, and Ts is the sampling period.

[0061] In constant voltage burn-through mode, the control unit 90 uses the target voltage Uset as the main setpoint and corrects the lower limit of the allowable current according to ΔL(k) to avoid instability of the burn-through channel due to electrode wear.

[0062] In the pulsed burn-through mode, the control unit 90 corrects the pulse peak value, pulse width, pulse interval or duty cycle according to ΔL(k) so that the thermal shock intensity of the three pulse peak segments matches the electrode state.

[0063] When switching modes, the control unit freezes the compensation amount of the previous cycle and updates the new setpoint in a ramp transition manner.

[0064] The compensation process employs a two-tiered strategy: fast electrical compensation and slow mechanical compensation. Fast electrical compensation prioritizes converting the overall electrode loss or current deviation into a trigger angle correction Δα(k), thereby obtaining the control angle αcmd of each phase's controlled rectifier switching device. In pulsating burn-through mode, the compensation amount is converted into a pulse parameter correction. Only when the trigger angle correction or pulse parameter correction exceeds the corresponding remaining adjustable range, and the burn-through current or burn-through voltage deviation fails to converge for N consecutive power frequency cycles, does the control unit output a slow mechanical compensation command, driving the electrode pressing and releasing mechanism to perform electrode replenishment according to Δscmd=KsΔL(k) or the limited replenishment amount.

[0065] In this embodiment, the control unit 90 determines whether there is still a margin for rapid electrical compensation based on the remaining adjustable range between the compensation command and the preset adjustment boundary. Taking the constant current burn-through mode as an example, when the actual burn-through current If(k) is lower than the target current, the control unit 90 needs to increase the output current by reducing the firing angle. At this time, the electrical compensation margin is the difference between the current firing angle and the preset lower limit of the firing angle. When the actual burn-through current If(k) is higher than the target current, the control unit 90 needs to decrease the output current by increasing the firing angle. At this time, the electrical compensation margin is the difference between the preset upper limit of the firing angle and the current firing angle. If the firing angle correction amount calculated based on the current deviation or the comprehensive electrode loss does not exceed the remaining adjustable range in the corresponding direction, it is determined that there is still a margin for rapid electrical compensation, and the control unit 90 only changes the firing angle or pulse parameters of SCR1-SCR3.

[0066] When the trigger angle correction exceeds the remaining adjustable range in the corresponding direction, or when the trigger angle has reached the preset lower or upper limit, and the actual burn-through current is below the lower threshold for N consecutive power frequency cycles or the current deviation has not yet converged, it is determined that the rapid electrical compensation margin is insufficient. At this time, the control unit 90 outputs a slow mechanical compensation command to the electrode execution unit 80, causing the electrode pressing and releasing mechanism to perform compensation according to Δscmd=KsΔL(k) or the compensation amount after limiting processing. Wherein, Δscmd is the electrode compensation command value, Ks is the compensation ratio coefficient, and ΔL(k) is the comprehensive loss amount at the k-th sampling time.

[0067] In the pulsed burn-through mode, the electrical compensation margin is determined based on the remaining adjustable range between the pulse peak value, pulse width, pulse interval or duty cycle and their respective preset upper and lower limits. When the required pulse parameter correction exceeds the corresponding remaining adjustable range, and the burn-through current or burn-through voltage deviation does not converge for N consecutive power frequency cycles, the electrical compensation margin is determined to be insufficient.

[0068] After the compensation is replenished, the control unit 90 re-acquires current, voltage and displacement feedback, and corrects the compensation amount in the next cycle.

[0069] like Figure 3As shown, a control method for a three-phase half-wave rectifier burn-through device includes the following steps: S101 collects burn-through current, burn-through voltage, electrode displacement and temperature, and updates the accumulated energy; S102 performs filtering, amplitude limiting, outlier removal, and power frequency synchronization alignment on the sampled data; S103, identify the equivalent resistance of the burn-through circuit; S104 integrates resistance increment, displacement change, temperature correction and accumulated energy to estimate the overall electrode loss. S105 determines whether the loss or current / voltage deviation exceeds the threshold. S106 prioritizes outputting firing angle or pulse parameter compensation within the electrical regulation margin; S107: When the electrical regulation margin is insufficient and the deviation persists, output a mechanical compensation command and return to S101 for closed-loop correction.

[0070] In the above embodiments, the controlled rectifier switching device is preferably a thyristor, so as to achieve three-phase half-wave controlled rectification through the power frequency synchronous firing angle. For embodiments using IGBTs, MOSFETs, GTOs, or other fully controlled power devices, the firing angle control can be replaced with equivalent pulse width modulation, phase modulation, or conduction window control while maintaining the three-phase common power supply, positive bus junction, closed return path, small current-limiting reactor, and protection branch configuration unchanged. This alternative embodiment still needs to meet the technical boundary of not setting a high-power smoothing reactor on the DC side and retaining three-pulse or controlled pulsating DC output.

[0071] Because three-phase half-wave pulsating DC has a high instantaneous power density during the peak segment, it can promote local heating and the establishment of burn-through channels at the crust, bridging, high-resistivity material layer, or cold conductive channel; the valley segment provides short-time intervals for local gasification, slag removal, and conductive channel recovery. The control unit 90 maintains the stability of the average burn-through current through power frequency synchronous sampling and closed-loop trigger control, enabling the device to have both thermal shock resistance and control stability.

[0072] The core of this solution lies in employing a three-phase half-wave controlled rectifier topology. Phases A, B, and C are each connected to the positive bus via their respective controlled rectifier switching devices, with all three phases sharing the burn-through power. Under this topology, each phase only carries current within its corresponding 120° conduction interval, remaining off during the rest of the interval. From the perspective of the average power frequency cycle, the output power of the three phases is equal, and their sum equals the power required for burn-through. This "instantaneous single-phase conduction, average three-phase balance" power supply method completely eliminates the three-phase load asymmetry caused by single-phase connection at the circuit structure level, maintaining the three-phase magnetic flux symmetry of the furnace transformer without the need for any additional balancing compensation equipment.

[0073] The DC side does not include a smoothing reactor to smooth the three-pulse output into near-continuous DC; instead, it only includes a current-limiting reactor Lx to suppress conduction and commutation transients. This design ensures that the burn-through power supply output retains the inherent three-pulse pulsating DC characteristics of a three-phase half-wave rectifier. Pulsating DC exhibits high instantaneous power density during its peak phase, enabling concentrated thermal shock to the junction shell, bridging region, or high-resistivity material layer, promoting rapid local heating and melting. During its trough phase, it creates current intermittent current, providing a buffer time window for gasification slag removal and conductive channel recovery. Compared to DC smoothed by a large reactor, pulsating DC offers superior thermal shock efficiency and channel recovery speed.

[0074] During the burn-through process, the electrodes are continuously consumed, accompanied by interference phenomena such as sparking, slag rolling, and momentary short circuits. Judging electrode loss solely based on instantaneous changes in current or voltage can easily lead to misinterpreting interference as actual loss, causing frequent fluctuations in the firing angle or malfunctions in the electrode pressing and releasing mechanism. This device integrates information from three dimensions: equivalent resistance change, displacement change, and cumulative energy. After temperature correction and weighted fusion, it obtains the comprehensive electrode loss and incorporates delayed confirmation and cross-checking logic: a single sampling anomaly does not trigger adjustment; only consecutive deviations in the same direction across multiple power frequency cycles are confirmed as effective loss. This estimation method effectively distinguishes between actual loss and instantaneous interference, improving the control system's anti-disturbance capability.

[0075] After electrode loss occurs, the control system prioritizes rapid electrical compensation by adjusting the firing angle or pulse parameters of the controlled rectifier switching device to maintain the stability of the burn-through current or voltage. Only when the firing angle has been adjusted to its limit and the actual current is continuously below the lower threshold is a slow mechanical compensation command output to drive the electrode execution unit to compensate. This two-stage strategy prioritizes fast-response, wear-free electrical regulation and uses slow-response, wear-prone compensation as a backup, avoiding frequent start-stop of the mechanical mechanism and extending the service life of the execution unit while improving control continuity.

[0076] This device is based on a three-phase half-wave rectifier topology. By eliminating the high-power smoothing reactor, the DC-side structure is simplified. Through multi-sensor fusion and a two-stage control strategy, accurate estimation and intelligent compensation of electrode losses are achieved. The entire system can output pulsating DC with thermal shock advantages while maintaining three-phase load balance, without the need for large-capacity energy storage components, active compensation devices, or complex mechanical voltage regulation mechanisms, and adaptively compensate for parameter changes caused by electrode consumption. For burn-through operations in submerged arc furnaces, this device represents an improvement in structural simplicity, power supply balance, thermal shock efficiency, and adaptive control capabilities.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-phase half-wave rectifier burn-through device, characterized in that, include: The three-phase AC input circuit includes phase A, phase B, phase C, and a common return terminal; The three-phase half-wave controlled rectifier unit includes three controlled rectifier switching devices connected to phases A, B, and C respectively. The output terminals of the three controlled rectifier switching devices are combined to form a positive bus. The DC bus unit includes a positive bus and a return bus. The positive bus is connected to the burn-through electrode. The burn-through electrode passes through the furnace charge, furnace shell or return electrode and returns to the common return terminal through the return bus, forming a closed burn-through circuit in which the burn-through power is provided by the three phases. The control unit is electrically connected to the control terminals of three controlled rectifier switching devices and is used to control the burn-through current stability.

2. The three-phase half-wave rectifier burn-through device as described in claim 1, characterized in that, The common return terminal is the transformer secondary neutral point, a dedicated return bus, or a return terminal electrically connected to the furnace shell.

3. The three-phase half-wave rectifier burn-through device as described in claim 1, characterized in that, The control unit includes: The sampling module is used to collect burn-through current, burn-through voltage, electrode displacement and temperature, and update the cumulative energy according to the burn-through current, burn-through voltage and sampling period; The loss estimation module is used to calculate the total electrode loss based on burn-through current, burn-through voltage, electrode displacement, temperature, and cumulative energy. The compensation module is configured to: first convert the total electrode loss into a trigger angle compensation or a pulse parameter compensation, and determine the electrical compensation margin based on the remaining adjustable range between the trigger angle or pulse parameter and its preset adjustment boundary; when the trigger angle compensation or pulse parameter compensation exceeds the corresponding remaining adjustable range, and the burn-through current or burn-through voltage deviation has not converged for several consecutive power frequency cycles, output the electrode compensation amount.

4. The three-phase half-wave rectifier burn-through device as described in claim 3, characterized in that, The loss estimation module is configured as follows: When the filtered burn-through current is not less than the effective current threshold, the equivalent burn-through circuit resistance is calculated by dividing the difference between the burn-through voltage and the fixed voltage drop by the burn-through current; when the filtered burn-through current is less than the effective current threshold, the previous effective equivalent burn-through circuit resistance or the freezing resistance loss component is maintained. The resistance loss length is calculated by temperature correction based on the change in the equivalent burn-through circuit resistance relative to the initial value. The displacement loss length is calculated based on the change in the displacement sensor reading relative to the initial value. The cumulative energy is converted into the energy equivalent loss length using the energy-length calibration coefficient; the resistance loss length, displacement loss length, and energy equivalent loss length are then weighted and fused to obtain the comprehensive electrode loss.

5. The three-phase half-wave rectifier burn-through device as described in claim 3, characterized in that, The loss estimation module is also configured to freeze the electrode to compensate for the output when the direction of change of the resistance loss length and the displacement loss length is inconsistent or the difference exceeds the preset verification threshold, and only allow electrical compensation of the trigger angle or pulse parameters within the safety limit.

6. The three-phase half-wave rectifier burn-through device as described in claim 1, characterized in that, The control unit has a constant current burn-through mode, a constant voltage burn-through mode, and a pulse burn-through mode; In constant current burn-through mode, the control unit corrects the firing angle based on the target current and the total electrode loss. In constant voltage burn-through mode, the control unit corrects the firing angle according to the target voltage and corrects the lower limit of the allowable current according to the total electrode loss. In pulsed burn-through mode, the control unit corrects the pulse peak value, pulse width, pulse interval, or duty cycle based on the total electrode loss.

7. The three-phase half-wave rectifier burn-through device as described in claim 1, characterized in that, The positive bus is connected to the burn-through electrode via a small current-limiting reactor. The small current-limiting reactor is used to limit the rate of rise of the conduction current of the controlled rectifier switching device and suppress commutation impact. The inductance of the small current-limiting reactor is configured to be no greater than the set multiple of the inductance of the smoothing reactor configured for smoothing three-pulse output under the same rated current, and / or to make the DC circuit time constant no greater than the set proportion of the power frequency half cycle.

8. The three-phase half-wave rectifier burn-through device as described in claim 1, characterized in that, It also includes protection branches, which include RC snubber circuits connected in parallel across each controlled rectifier switching device, freewheeling branch connected in parallel between the DC side rear end and the return path, and damping branch connected in parallel between the DC output terminals.

9. A three-phase half-wave rectifier burn-through device as described in claim 1, characterized in that, The control unit is electrically connected to the sampling unit, which includes a current detection element for detecting burn-through current, a voltage detection element for detecting burn-through voltage, a displacement sensor for detecting electrode displacement, and a temperature detection element for detecting temperature.

10. A control method based on the three-phase half-wave rectifier burn-through device as described in any one of claims 1-9, characterized in that, Includes the following steps: The system collects burn-through current, burn-through voltage, electrode displacement, and temperature, updates the cumulative energy based on the burn-through current, burn-through voltage, and sampling period, and preprocesses the sampled data. When the burn-through current is not less than the effective current threshold, the current equivalent burn-through circuit resistance is calculated based on the burn-through voltage, burn-through current and fixed voltage drop; when the burn-through current is less than the effective current threshold, the previous effective equivalent burn-through circuit resistance or the freezing resistance loss component is maintained; the changes in equivalent burn-through circuit resistance, displacement changes, temperature correction and accumulated energy are converted into the comprehensive electrode loss. Determine whether the total electrode loss, burn-through current deviation, or burn-through voltage deviation exceeds a preset threshold. Prioritize converting losses exceeding the threshold into firing angle compensation or pulse parameter compensation. The electrical compensation margin is determined based on the remaining adjustable range between the trigger angle or pulse parameter and its preset adjustment boundary. When the trigger angle compensation or pulse parameter compensation exceeds the corresponding remaining adjustable range, and the burn-through current deviation or burn-through voltage deviation persists, the electrical compensation margin is determined to be insufficient, and the electrode supplement amount is output to the electrode execution unit. The next cycle is corrected based on the feedback results of the compensated current and voltage.

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