Flexible power supply device for alternating-current electric arc furnace, and control method therefor

Abstract

Embodiments of the present disclosure provide a flexible power supply device for an alternating-current electric arc furnace and a control method therefor, applied to the technical field of power supply. The flexible power supply device for the alternating-current electric arc furnace comprises a rectifier bridge, an inverter bridge, an electric arc furnace transformer, a rectifier bridge controller, an inverter bridge controller, and an electrode position controller; the rectifier bridge is connected to an alternating-current power grid, and the inverter bridge is connected to an alternating-current electric arc furnace transformer; the rectifier bridge controller is used for controlling the rectifier bridge and stabilizing the direct-current voltage of the rectifier bridge; the inverter bridge controller is used for controlling the inverter bridge and stabilizing the primary-side current of the alternating-current electric arc furnace. The flexible power supply device for the alternating-current electric arc furnace achieves double isolation of the fluctuation of the alternating-current electric arc furnace and a power supply system by means of the inverter bridge and the rectifier bridge, significantly reduces power grid flicker caused by the fluctuation of the alternating-current electric arc furnace, and reduces the influence of an electric arc furnace smelting process on the power grid.

Description

AC arc furnace flexible power supply equipment and control method thereof Technical Field

[0001] The present disclosure relates to the field of power supply technology, and in particular to flexible power supply equipment for an AC arc furnace and a control method thereof. Background Art

[0002] AC arc furnaces use scrap steel as their primary raw material, utilizing the high temperature of the arc generated between electrodes and the charge to heat and melt the material. Traditional AC arc furnaces use a transformer to step down the AC voltage, then use series reactors to limit the arc current during normal operation and short-circuit conditions. The arc is stabilized by controlling the raising and lowering of the electrodes. These furnaces offer advantages such as flexible temperature control, high thermal efficiency, simple and reliable equipment, and a short process flow.

[0003] However, as the capacity of AC arc furnaces continues to increase, interference with power supply systems is becoming increasingly prominent. When the arc is extinguished, the active and reactive power drawn from the grid is zero; however, when the electrodes and charge are short-circuited, the AC arc furnace consumes maximum reactive power. During the charge melting period, random variations and rapid fluctuations in arc length can cause strong flicker, asymmetry, and high-order harmonic currents in the power supply system.

[0004] To address the interference of AC arc furnaces on power supply systems, the industry typically uses STATCOM dynamic reactive power compensation to reduce flicker. However, this method requires large-capacity STATCOM equipment and has limited flicker suppression effectiveness. Another approach uses multiple power electronic converters connected in parallel via a multi-winding phase-shifting transformer on the grid side to power the arc furnace while isolating the AC arc furnace's fluctuations from the power supply system. However, this method requires a multi-winding phase-shifting transformer on the grid side, making the system complex and costly. Furthermore, many existing AC arc furnaces use transformers to step down the voltage before powering the furnace. This method directly outputs low-voltage, high-current power, making it unsuitable for retrofitting existing AC arc furnace systems.

[0005] The industry also uses modular multilevel converters, which can directly convert high-voltage AC to high-voltage DC and are suitable for providing flexible power supply for AC arc furnaces. To reduce converter costs, and given that AC arc furnace loads are purely active loads with no potential for energy regeneration, a topology combining diode bridge arms with modular multilevel bridge arms can reduce the cost of the rectifier bridge. However, this topology is complex to control, with non-sinusoidal and intermittent bridge arm currents. This places high demands on system control and can potentially cause excessive harmonics to enter the grid.

[0006] Summary of the Invention

[0007] The present disclosure provides an AC arc furnace flexible power supply device and a control method thereof, which solves the problem of interference of the AC arc furnace on the power supply system.

[0008] According to the first aspect of the present disclosure, there is provided an AC arc furnace flexible power supply device, comprising: a rectifier bridge, an inverter bridge, an arc furnace transformer, a rectifier bridge controller, an inverter bridge controller, and an electrode position controller; the rectifier bridge is connected to the AC power grid; the inverter bridge is connected to the AC arc furnace transformer; wherein the rectifier bridge comprises a three-phase rectifier bridge arm; the inverter bridge comprises at least one phase inverter bridge arm; the three-phase rectifier bridge arm and the at least one phase inverter bridge arm are arranged in sequence and connected in parallel via a positive and negative DC bus; the rectifier bridges of each phase are connected in parallel via a positive and negative DC bus; The bridge arms have the same structure, and respectively include a rectifier upper bridge arm, a rectifier middle bridge arm, a rectifier lower bridge arm and two diode bridge arms. The rectifier upper bridge arm, the rectifier middle bridge arm and the rectifier lower bridge arm are connected in series in sequence. After the two diode bridge arms are connected in series in the same direction, they are connected in parallel at both ends of the rectifier middle bridge arm. The connection point of the two diode bridge arms is connected to each phase of the AC power supply grid; the at least one phase inverter bridge arm has the same structure, and respectively includes an inverter upper bridge arm and an inverter lower bridge arm. The inverter upper bridge arm and the inverter lower bridge arm are connected in series, and the connection point is connected to the corresponding phase of the arc furnace transformer.

[0009] According to the aspects and any possible implementation methods described above, an implementation method is further provided, wherein the inverter bridge includes a three-phase inverter bridge arm; the connection points of the inverter upper bridge arm and the inverter lower bridge arm in the three-phase inverter bridge arm are respectively connected to each phase of the arc furnace transformer.

[0010] According to the aspects described above and any possible implementation method, an implementation method is further provided, in which the structures of the rectifier upper bridge arm, the rectifier lower bridge arm, the inverter upper bridge arm and the inverter lower bridge arm are the same, and are composed of an inductor and at least two power modules connected in series; the rectifier middle bridge arm is composed of at least two power modules connected in series; the power module is a half-bridge module and / or a full-bridge module.

[0011] According to the above aspects and any possible implementation manner, an implementation manner is further provided, wherein the number of the power modules is determined according to the maximum voltage across the bridge arm and the capacitor voltage of the power module.

[0012] According to the above aspects and any possible implementation manner, an implementation manner is further provided, wherein the electrode position controller is connected to an AC electric arc furnace electrode manipulation mechanism.

[0013] According to the second aspect of the present disclosure, a control method for flexible power supply equipment of an AC arc furnace is provided, the method comprising: the rectifier bridge controller is responsible for controlling the rectifier bridge and stabilizing the DC voltage of the rectifier bridge; the inverter bridge controller is responsible for controlling the inverter bridge and stabilizing the primary side current of the AC arc furnace; the electrode position controller is responsible for controlling the electrode manipulation mechanism of the AC arc furnace and stabilizing the three-phase arc impedance.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein the rectifier bridge controller is responsible for controlling the rectifier bridge and stabilizing the rectifier bridge DC voltage, including:

[0015] Detect the grid-side voltage of the rectifier bridge and lock the grid phase through the phase-locked loop;

[0016] Based on the rectifier bridge DC voltage u dc and the rectifier bridge DC voltage command value u dc * The relationship between the rectifier bridge active current command value i is generated by the DC voltage controller d * ;

[0017] Based on the rectifier bridge active current command value i d * , calculate the reactive power consumed on the grid side impedance, and generate the rectifier bridge reactive current command value i q * To compensate for the reactive power consumed by the grid-side impedance;

[0018] The rectifier bridge active current command value i d * , rectifier bridge reactive current command value i q * The rectifier bridge dq voltage command value u is generated through the current regulator d * 、u q * , after 2 / 3 transformation, the rectifier bridge AC modulation command value u is generated a * 、u b * 、u c * ;

[0019] Calculate the rectifier bridge DC modulation command value u com * : where u N is the power module capacitor voltage;

[0020] The AC modulation command value of the rectifier bridge and the DC modulation command value of the rectifier bridge are added and subtracted, and the trigger pulse of each phase rectifier bridge arm is obtained by using the nearest level approximation method according to the direction of the AC current.

[0021] According to the above aspects and any possible implementation, an implementation is further provided, wherein the inverter bridge controller is responsible for controlling the inverter bridge and stabilizing the primary side current of the AC arc furnace, including:

[0022] According to the inverter bridge active current command value i d * , inverter bridge reactive current command value i q * The current regulator realizes i d Current, i q Current control and generate inverter bridge dq voltage command value u d * 、u q * , after 2 / 3 transformation, the inverter bridge AC modulation command value u is generated a * 、u b * 、u c * ; Among them, the inverter bridge active current command value i d * is the preset value, the inverter bridge reactive current command value i q * The default value is 0;

[0023] Calculate the inverter bridge DC modulation command value u com * : where u N is the power module capacitor voltage;

[0024] The DC modulation command value of the inverter bridge is subtracted from the AC modulation command value of the inverter bridge to obtain the modulation signal of the upper arm of the inverter bridge; the DC modulation command value of the inverter bridge is added to the AC modulation command value of the inverter bridge to obtain the modulation signal of the lower arm of the inverter bridge; finally, the trigger pulse of each phase arm of the inverter bridge is obtained by the nearest level approximation method.

[0025] According to the aspects described above and any possible implementation method, an implementation method is further provided, in which the electrode position controller is responsible for controlling the electrode manipulation mechanism of the AC arc furnace and stabilizing the three-phase arc impedance, including: detecting the voltage and current on the secondary side of the AC arc furnace transformer; calculating the current three-phase arc impedance of the AC arc furnace based on the voltage and current; and generating and sending control instructions to manipulate the arc furnace electrode manipulation mechanism to adjust the electrode position based on the relationship between the three-phase arc impedance and the arc impedance instruction value.

[0026] According to a third aspect of the present disclosure, a method for operating an AC arc furnace flexible power supply device is provided, the method comprising:

[0027] The rectifier bridge controller controls the rectifier bridge to stabilize the DC voltage and reduce AC grid flicker, allowing energy to flow from the AC grid through the rectifier bridge to the DC bus;

[0028] The inverter bridge controller is used to stabilize the primary current of the arc furnace transformer, so that energy flows from the DC bus to the arc furnace through the inverter bridge;

[0029] The electrode position controller is used to control the electrode operating mechanism of the AC arc furnace and stabilize the three-phase arc impedance.

[0030] It should be understood that the contents described in the Summary of the Invention section are not intended to limit the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. The accompanying drawings are provided for a better understanding of the present disclosure and do not constitute a limitation of the present disclosure. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, among which:

[0032] FIG1 shows a block diagram of a flexible power supply device for an AC arc furnace according to an embodiment of the present disclosure;

[0033] FIG2 shows a schematic structural diagram of a rectifier upper bridge arm, a rectifier lower bridge arm, an inverter upper bridge arm, and an inverter lower bridge arm according to an embodiment of the present disclosure;

[0034] FIG3 shows a schematic structural diagram of a bridge arm in a rectifier according to an embodiment of the present disclosure;

[0035] FIG4 shows a schematic diagram of a half-bridge structure of a power module according to an embodiment of the present disclosure;

[0036] FIG5 shows a schematic diagram of a full-bridge structure of a power module according to an embodiment of the present disclosure;

[0037] FIG6 shows a schematic diagram of a current path in a single-phase rectifier bridge arm of a rectifier bridge when grid current flows into the rectifier bridge according to an embodiment of the present disclosure;

[0038] FIG7 shows a schematic diagram of a current path in a single-phase rectifier bridge arm of a rectifier bridge when grid current flows out of the rectifier bridge according to an embodiment of the present disclosure;

[0039] FIG8 is a schematic diagram showing a working method of a rectifier bridge controller of an AC arc furnace flexible power supply device according to an embodiment of the present disclosure;

[0040] FIG9 is a schematic diagram showing a working method of an inverter bridge controller of an AC arc furnace flexible power supply device according to an embodiment of the present disclosure;

[0041] FIG10 is a schematic diagram showing a working method of an electrode position controller of an AC arc furnace flexible power supply device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present disclosure.

[0043] In this document, the term "and / or" simply describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0044] FIG1 shows a block diagram of an AC arc furnace flexible power supply device 100 according to an embodiment of the present disclosure.

[0045] As shown in FIG1 , the AC arc furnace flexible power supply device 100 includes:

[0046] Rectifier bridge 1, inverter bridge 2, arc furnace transformer 3, rectifier bridge controller 4, inverter bridge controller 5, and arc furnace electrode position controller 6; the rectifier bridge 1 is connected to the AC power grid; the arc furnace transformer 3 is connected to the electrodes of the AC arc furnace; wherein,

[0047] Rectifier bridge 1 includes three-phase rectifier bridge arms 11, 12, and 13; inverter bridge 2 includes three-phase inverter bridge arms 21, 22, and 23. Rectifier bridge arms 11, 12, and 13 and inverter bridge arms 21, 22, and 23 are arranged sequentially and connected in parallel via positive and negative DC busbars. In some embodiments, inverter bridge 2 includes at least one phase inverter bridge arm, such as any one of inverter bridge arms 21, 22, and 23.

[0048] Each rectifier bridge arm 11, 12, and 13 has the same structure, and includes an upper rectifier bridge arm 111, a middle rectifier bridge arm 112, a lower rectifier bridge arm 113, and a diode bridge arm 114 and a diode bridge arm 115. The upper rectifier bridge arm 111, the middle rectifier bridge arm 112, and the lower rectifier bridge arm 113 are connected in series. The diode bridge arm 114 and the diode bridge arm 115 are connected in series and then in parallel at both ends of the middle rectifier bridge arm 112. The connection point of the diode bridge arm 114 and the diode bridge arm 115 is connected to the AC power supply grid. The connection point of the diode bridge arm 114 and the diode bridge arm 115 in each rectifier bridge arm 11, 12, and 13 is respectively connected to each phase of the AC power supply grid.

[0049] The inverter bridge arms 21, 22, and 23 each include an inverter upper bridge arm 211 and an inverter lower bridge arm 212. The inverter upper bridge arm 211 and the inverter lower bridge arm 212 are connected in series, and the connection point between the inverter upper bridge arm 211 and the inverter lower bridge arm 212 is connected to the arc furnace transformer 3. The connection point between the inverter upper bridge arm 211 and the inverter lower arm 212 in each of the inverter bridge arms 21, 22, and 23 is respectively connected to each phase of the arc furnace transformer 3.

[0050] In some embodiments, the rectifier bridge controller 4 is responsible for controlling the rectifier bridge 1 and stabilizing the rectifier bridge DC voltage.

[0051] In some embodiments, the inverter bridge controller 5 is responsible for controlling the inverter bridge 2 and stabilizing the arc furnace current.

[0052] As shown in Figure 2, the rectifier upper bridge arm 111, the rectifier lower bridge arm 113, the inverter upper bridge arm 211 and the inverter lower bridge arm 212 have the same structure, which is composed of an inductor and at least two power modules connected in series; the power module can be a half-bridge module as shown in Figure 4, or a full-bridge module as shown in Figure 5.

[0053] As shown in FIG3 , the rectifier bridge arm 112 is formed by at least two power modules connected in series; the power module may be a half-bridge module as shown in FIG4 , or a full-bridge module as shown in FIG5 .

[0054] In some embodiments, during normal operation, as shown in FIG4 , a stable DC voltage is present on the capacitor of the half-bridge module. For example, when a 4.5 kV IGBT is used, the capacitor voltage is approximately 2.5 kV. Through the on / off actions of IGBT1 and IGBT2, the half-bridge module can output 0 voltage or a capacitor voltage. During normal operation, as shown in FIG5 , a stable DC voltage is present on the capacitor of the full-bridge module. For example, when a 4.5 kV IGBT is used, the capacitor voltage is approximately 2.5 kV. Through the on / off actions of IGBT1, IGBT2, IGBT3, and IGBT4, the full-bridge module can output 0 voltage, a capacitor voltage, or a negative capacitor voltage.

[0055] In some embodiments, the number of series-connected power modules required for the bridge arms composed of half-bridge modules and / or full-bridge modules, such as the rectifier upper bridge arm 111, the rectifier middle bridge arm 112, the rectifier lower bridge arm 113, the inverter upper bridge arm 211 and the inverter lower bridge arm 212, depends on the maximum voltage at both ends of the bridge arm and the capacitor voltage of the power module.

[0056] Taking inverter bridge 2 as an example, the maximum voltage between the terminals of each bridge arm (inverter upper bridge arm 211 or inverter lower bridge arm 212) is equivalent to the DC voltage of rectifier bridge 1. Assuming that the DC voltage of rectifier bridge 1 is 40kV and the module capacitor voltage is 2.5kV, the number of modules connected in series in the inverter upper bridge arm 211 or inverter lower bridge arm 212 of each single-phase inverter bridge arm 21, 22, and 23 of inverter bridge 2 is: The single-phase inverter bridge arms 21 , 22 , and 23 of the inverter bridge 2 each require 32 modules.

[0057] Taking the rectifier bridge 1 as an example, consider the situation of its single-phase rectifier bridge arms 11, 12, and 13, because they are in the rectification state: as shown in Figure 6, when the AC grid voltage of the rectifier bridge arm of this phase is in the positive half-wave, when the AC grid current enters the rectifier bridge arm of this phase, the rectifier upper bridge arm 111 bears the voltage between the positive DC bus and the AC bus, which will not exceed 50% of the rectifier bridge DC voltage; the rectifier lower bridge arm 113 and the rectifier middle bridge arm 112 jointly bear the voltage between the negative DC bus and the AC bus, which is up to the rectifier bridge DC voltage; as shown in Figure 7, when the AC grid voltage of the phase bridge arm is in the negative half-wave, when the AC grid current leaves the bridge arm, the rectifier upper bridge arm 111 and the rectifier middle bridge arm 112 jointly bear the voltage between the positive DC bus and the AC bus, which will not exceed the rectifier bridge DC voltage; the rectifier lower bridge arm 113 bears the voltage between the negative DC bus and the AC bus, which is up to 50% of the rectifier bridge DC voltage. Assuming that the DC voltage of the rectifier bridge 1 is 40kV and the power module capacitor voltage is 2.5kV, then the rectifier arm 112 of the rectifier bridge 1 can be designed to bear at most 50% of the DC voltage of the rectifier bridge, connected in series: power modules, so that the rectifier upper bridge arm 111 and the rectifier lower bridge arm 113 of the rectifier bridge 1 need to bear at most 50% of the rectifier bridge DC voltage and need to be connected in series: Each single-phase rectifier bridge arm 11, 12, and 13 requires 24 power modules, which is significantly lower than the number of modules (32) required for each single-phase inverter bridge arm 21, 22, and 23 in the inverter bridge 2.

[0058] According to the embodiments of the present disclosure, the following technical effects are achieved:

[0059] 1. The inverter bridge and rectifier bridge achieve dual isolation between AC arc furnace fluctuations and the power supply system: AC arc furnace fluctuations first affect the AC current of the inverter bridge, which in turn affects the capacitor voltage of the inverter bridge's power module. Only then do they affect the voltage and current of the DC bus. The accumulation of DC bus voltage and current fluctuations subsequently affects the voltage of the rectifier bridge's power module, and finally the current flowing into the AC grid. The dual isolation of the inverter bridge and rectifier bridge significantly reduces the electrical flicker caused by AC arc furnace fluctuations and mitigates the impact of the arc furnace smelting process on the grid.

[0060] 2. The currents in the upper and lower arms of the rectifier bridge are sinusoidal currents. The rectifier bridge is controlled continuously and stably. The harmonics on the AC side are very small. Due to the effect of the cascaded power modules, the harmonics flowing into the power grid are very small, and no additional AC filtering equipment is required.

[0061] 3. The AC arc furnace flexible power supply device is directly connected between the AC grid and the AC arc furnace, providing power to the AC arc furnace without the need for a multi-winding transformer or phase-shifting transformer. Furthermore, the arc furnace flexible power supply device can directly output medium voltage, making it suitable for retrofitting existing AC arc furnaces.

[0062] 4. The maximum voltage supported by the upper and lower arms of the rectifier bridge is equivalent to the DC voltage of the rectifier bridge minus the voltage of the middle arm, which can significantly reduce the cost of the rectifier bridge. By using diode bridge arms in the rectifier bridge arms, the combined operation of the upper, middle and lower arms of the rectifier bridge is automatically achieved, simplifying system control without increasing control complexity.

[0063] The above is an introduction to the device embodiment. The following method embodiment is used to further illustrate the control method of the AC arc furnace flexible power supply equipment disclosed in the present invention.

[0064] The working method of the AC arc furnace flexible power supply device disclosed in the present invention is as follows:

[0065] The rectifier bridge controller controls the rectifier bridge to achieve the purpose of stabilizing the DC voltage and reducing the flicker of the AC grid, so that energy flows from the AC grid through the rectifier bridge to the DC bus. The input end of the rectifier bridge is connected to the AC grid, and the DC bus at the output end of the rectifier bridge is connected to the input end of the inverter bridge.

[0066] The inverter bridge controller is used to stabilize the current on the primary side of the arc furnace transformer, so that energy flows from the DC bus to the arc furnace through the inverter bridge. The output end of the inverter bridge is connected to the primary side of the AC arc furnace transformer.

[0067] The electrode position controller is used to control the electrode operating mechanism of the AC arc furnace and stabilize the three-phase arc impedance; wherein the secondary side of the AC arc furnace transformer is connected to the electrodes of the arc furnace.

[0068] As shown in Figure 1, the rectifier bridge controller 4 is responsible for controlling the rectifier bridge 1 and stabilizing the rectifier bridge DC voltage. The inverter bridge controller 5 is responsible for controlling the inverter bridge 2 and stabilizing the arc furnace current.

[0069] As shown in FIG8 , the rectifier bridge controller 4 is responsible for controlling the rectifier bridge 1 and stabilizing the rectifier bridge DC voltage. The control method includes:

[0070] In step S1, the rectifier bridge controller 4 detects the grid-side voltage of the rectifier bridge and locks the grid phase through a phase-locked loop (PLL);

[0071] In step S2, based on the rectifier bridge DC voltage u dc and the rectifier bridge DC voltage command value u dc * The relationship between the rectifier bridge active current command value i is generated by the DC voltage controller d * ;in,

[0072] If the rectifier bridge DC voltage u dc If it is too high, reduce the rectifier bridge active current command value i d * , if the rectifier bridge DC voltage u dc If it is too low, increase the rectifier bridge active current command value i d * ;

[0073] In some embodiments, the DC voltage controller adopts a PI regulator, and the transfer function formula of the PI regulator is as follows: Among them, k p is the proportional gain coefficient, k i is the integral gain coefficient, and s is the frequency variable in the complex function.

[0074] In step S3, based on the rectifier bridge active current command value i d * , calculate the reactive power consumed on the grid side impedance, and generate the rectifier bridge reactive current command value i q * To compensate for the reactive power consumed by the grid-side impedance;

[0075] In some embodiments, the generating of the rectifier bridge reactive current command value i q * include:

[0076] Assume that the grid-side equivalent reactance is L g , the grid voltage is u g , rectifier bridge reactive current command value i q * for:

[0077] In step S4, the rectifier bridge active current command value i d * , rectifier bridge reactive current command value i q * The rectifier bridge dq voltage command value u is generated through the current regulator d * 、uq * , after 2 / 3 transformation, the AC modulation command value u is generated a * 、u b * 、u c * ;

[0078] In step S5, the DC modulation command value u is calculated. com * :

[0079] In some embodiments, the rectifier bridge DC modulation command value where u N is the power module capacitor voltage.

[0080] In step S6, the rectifier bridge AC modulation command value u a * 、u b * 、u c * and the rectifier bridge DC modulation command value u com * The trigger pulses of the rectifier bridge arms of each phase are obtained by adding and subtracting the phases and adopting the nearest level approximation method according to the direction of the AC current.

[0081] In some embodiments, if the bridge arm current enters the rectifier bridge arms 11, 12, and 13 of each phase, as shown in Figure 6, the (rectifier bridge DC modulation command value - rectifier bridge AC modulation command value) is modulated by the nearest level approximation to obtain a trigger pulse for the rectifier upper bridge arm 111, and the (rectifier bridge DC modulation command value + rectifier bridge AC modulation command value) is modulated by the nearest level approximation to obtain trigger pulses for the rectifier middle bridge arm 112 and the rectifier lower bridge arm 113; if the bridge arm current leaves the rectifier bridge arms 11, 12, and 13 of each phase, as shown in Figure 7, the (rectifier bridge DC modulation command value - rectifier bridge AC modulation command value) is modulated by the nearest level approximation to obtain trigger pulses for the rectifier upper bridge arm 111 and the rectifier middle bridge arm 112, and the (rectifier bridge DC modulation command value + rectifier bridge AC modulation command value) is modulated by the nearest level approximation to obtain a trigger pulse for the rectifier lower bridge arm 113.

[0082] Through the above operation, regardless of whether the AC current enters or leaves the rectifier bridge arms 11, 12, and 13 of each phase, the AC current is evenly distributed between the upper rectifier bridge arm 111 and the lower rectifier bridge arm 113. This solves the technical problem of a topology that mixes diode bridge arms with modular multi-level bridge arms to reduce the cost of the rectifier bridge. The control of this topology is complex, the bridge arm current is non-sinusoidal and discontinuous, it places high demands on system control, and it may cause harmonics flowing into the power grid to exceed the standard.

[0083] Take phase A of the rectifier bridge as an example:

[0084] When the AC current enters the A-phase bridge arm, the trigger pulse of the upper bridge arm is modulated by the rectifier bridge command value according to the nearest level approximation method. The trigger pulses of the middle bridge arm and the lower bridge arm are generated by the nearest level approximation method according to the rectifier bridge modulation command value When the AC current leaves the A-phase bridge arm, the trigger pulses of the upper and middle bridge arms are approximated by the nearest level according to the rectifier bridge modulation command value. Generate; the trigger pulse of the lower bridge arm is modulated by the nearest level approximation method according to the rectifier bridge modulation command value generate.

[0085] As shown in FIG9 , the inverter bridge controller 5 is responsible for controlling the inverter bridge 2 and stabilizing the arc furnace current. The control method includes:

[0086] In step S1, according to the inverter bridge active current command value i d * , inverter bridge reactive current command value i q * The inverter bridge i is realized through the current regulator d Current, i q Current control; and generate the inverter bridge dq voltage command value u d * 、u q * , after 2 / 3 transformation, the inverter bridge AC modulation command value u is generated a * 、u b * 、u c * ; Among them, the inverter bridge active current command value i d * is a preset value, which is calculated based on the target current of the arc furnace; the inverter bridge reactive current command value i q * The default value is 0;

[0087] In step S2, the inverter bridge DC modulation command value u is calculated. com * :

[0088] In some embodiments, the inverter bridge DC modulation command value where u N is the power module capacitor voltage.

[0089] In step S3, the DC modulation command value of the inverter bridge is subtracted from the AC modulation command value of the inverter bridge to obtain the modulation signal of the upper arm of the inverter bridge; the AC modulation command value of the inverter bridge is added to the DC modulation command value of the inverter bridge to obtain the modulation signal of the lower arm of the inverter bridge; finally, the trigger pulse of each phase arm of the inverter bridge is obtained by the nearest level approximation method.

[0090] In some embodiments, the inverter bridge controller 5 controls the inverter bridge 2 as follows: Taking the inverter bridge A phase as an example: (the inverter bridge DC modulation instruction value u com * -Inverter bridge AC modulation command value u a * ) After the nearest level approximation modulation, the trigger pulse of each power module in the inverter upper bridge arm 211 is obtained; (the inverter bridge DC modulation command value u com * +Inverter bridge AC modulation command value u a * ) After the nearest level approximation modulation, the modulation pulse of the inverter lower bridge arm 212 is obtained.

[0091] In some embodiments, the control method of the AC arc furnace flexible power supply device further includes:

[0092] The electrode position controller 6 is responsible for controlling the electrodes of the AC arc furnace by detecting the voltage and current on the secondary side of the AC arc furnace transformer; then calculating the current three-phase arc impedance of the AC arc furnace based on the voltage and current on the secondary side of the AC arc furnace transformer; based on the relationship between the current three-phase arc impedance of the AC arc furnace and the arc impedance command value; generating and sending control instructions to operate the arc furnace electrode control mechanism: wherein, if the impedance of the three-phase arc is lower than the arc impedance command value, the electrode position is raised to increase the arc impedance; if the impedance of the three-phase arc is higher than the arc impedance command value, the electrode position is lowered to reduce the arc impedance; if a current interruption occurs, the electrode position is lowered to trigger the arc reignition.

[0093] According to the embodiments of the present disclosure, the control method for the electric arc furnace flexible power supply device realizes independent decoupling control of the rectifier bridge, inverter bridge, and arc furnace electrode position, with minimal mutual influence, and simple and reliable system control. At the same time, controlling the electric arc furnace flexible power supply device realizes reliable power supply to the AC electric arc furnace, stabilizes the AC arc to improve the production efficiency of the AC electric arc furnace, and reduces the interference problem of the electric arc furnace on the power supply system.

[0094] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the described module can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0095] The above specific embodiments do not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure shall be included within the scope of protection of this disclosure.

Claims

1. An AC arc furnace flexible power supply device, comprising: Rectifier bridge, inverter bridge, arc furnace transformer, rectifier bridge controller, inverter bridge controller, electrode position controller; The rectifier bridge is connected to an AC power grid; The inverter bridge is connected to the AC arc furnace transformer; wherein, The rectifier bridge includes a three-phase rectifier bridge arm; the inverter bridge includes at least one-phase inverter bridge arm; the three-phase rectifier bridge arm and the at least one-phase inverter bridge arm are arranged in sequence and connected in parallel through positive and negative DC busbars; The rectifier bridge arms of each phase have the same structure, and respectively include an upper rectifier bridge arm, a middle rectifier bridge arm, a lower rectifier bridge arm and two diode bridge arms. The upper rectifier bridge arm, the middle rectifier bridge arm and the lower rectifier bridge arm are sequentially connected in series. After the two diode bridge arms are connected in series in the same direction, they are connected in parallel at both ends of the middle rectifier bridge arm. The connection point of the two diode bridge arms is connected to each phase of the AC power supply grid. The at least one phase inverter bridge arm has the same structure, and comprises an inverter upper bridge arm and an inverter lower bridge arm respectively. The inverter upper bridge arm and the inverter lower bridge arm are connected in series, and the connection point is connected to the corresponding phase of the arc furnace transformer.

2. The AC arc furnace flexible power supply device according to claim 1, wherein: The inverter bridge comprises a three-phase inverter bridge arm; The connection points of the inverter upper bridge arm and the inverter lower bridge arm in the three-phase inverter bridge arm are respectively connected to each phase of the arc furnace transformer.

3. The AC arc furnace flexible power supply device according to claim 1, wherein: The rectifier upper bridge arm, rectifier lower bridge arm, inverter upper bridge arm and inverter lower bridge arm have the same structure, and are formed by a reactor and at least two power modules connected in series; the rectifier middle bridge arm is formed by at least two power modules connected in series; The power module is a half-bridge module and / or a full-bridge module.

4. The AC arc furnace flexible power supply device according to claim 3, wherein: The number of power modules is determined based on the maximum voltage across the bridge arm and the capacitor voltage of the power module. Sure.

5. The AC arc furnace flexible power supply device according to claim 1, wherein: The electrode position controller is connected to the electrode operating mechanism of the AC electric arc furnace.

6. A control method for a flexible power supply device for an AC arc furnace according to any one of claims 1 to 5, the method comprising: The bridge rectifier controller is responsible for controlling the bridge rectifier and stabilizing the bridge rectifier DC voltage; The inverter bridge controller is responsible for controlling the inverter bridge and stabilizing the primary current of the AC arc furnace; The electrode position controller is responsible for controlling the electrode operating mechanism of the AC arc furnace and stabilizing the three-phase arc impedance.

7. The method according to claim 6, wherein: The rectifier bridge controller is responsible for controlling the rectifier bridge and stabilizing the rectifier bridge DC voltage, including: Detect the grid-side voltage of the rectifier bridge and lock the grid phase through a phase-locked loop; Based on the rectifier bridge DC voltage u dc and the rectifier bridge DC voltage command value u dc * The relationship between the active current command value i of the rectifier bridge is generated by the DC voltage controller. d * ; Based on the rectifier bridge active current command value i d * , calculate the reactive power consumed on the grid-side impedance, and generate the reactive current command value i of the rectifier bridge q * To compensate for the reactive power consumed by the grid-side impedance; The rectifier bridge active current command value i d * , rectifier bridge reactive current command value i q * The rectifier bridge dq voltage command value u is generated through the current regulator d * 、u q * , after 2 / 3 transformation, the rectifier bridge AC modulation command value u is generated a * 、u b * 、u c * ; Calculate the rectifier bridge DC modulation command value u com * : where u N is the power module capacitor voltage; The AC modulation command value of the rectifier bridge and the DC modulation command value of the rectifier bridge are added and subtracted, and the trigger pulse of each phase rectifier bridge arm is obtained by using the nearest level approximation method according to the direction of the AC current.

8. The method according to claim 6, wherein: The inverter bridge controller is responsible for controlling the inverter bridge and stabilizing the primary current of the AC arc furnace, including: According to the inverter bridge active current command value i d * , inverter bridge reactive current command value i q * The current regulator realizes i d Current, i q The current is controlled and the inverter bridge dq voltage command value u is generated. d * 、u q * , after 2 / 3 transformation, the inverter bridge AC modulation command value u is generated a * 、u b * 、u c * ; Among them, the inverter bridge active current command value i d * is the preset value, the inverter bridge reactive current command value i q * The default value is 0; Calculate the inverter bridge DC modulation command value u com * : where u N is the power module capacitor voltage; Subtract the DC modulation command value of the inverter bridge from the AC modulation command value of the inverter bridge to obtain the modulation signal of the upper bridge arm of the inverter bridge; add the DC modulation command value of the inverter bridge to the AC modulation command value of the inverter bridge to obtain the modulation signal of the lower bridge arm of the inverter bridge; finally, the trigger pulse of each phase bridge arm of the inverter bridge is obtained by the nearest level approximation method.

9. The method according to claim 6, wherein: The electrode position controller is responsible for controlling the electrode operating mechanism of the AC arc furnace and stabilizing the three-phase arc impedance, including: Detect the secondary voltage and current of AC arc furnace transformer; Calculating the current three-phase arc impedance of the AC arc furnace according to the voltage and current; According to the relationship between the three-phase arc impedance and the arc impedance command value, a control command is generated and sent to manipulate the arc furnace electrode manipulation mechanism to adjust the electrode position.

10. A working method for a flexible power supply device for an AC arc furnace according to any one of claims 1 to 5, the method comprising: The rectifier bridge controller is used to control the rectifier bridge to stabilize the DC voltage and reduce the flicker of the AC grid, so that energy flows from the AC grid to the DC bus through the rectifier bridge; The primary current of the arc furnace transformer is stabilized by the inverter bridge controller, so that energy flows from the DC bus to the arc furnace through the inverter bridge; The electrode position controller is used to control the electrode operating mechanism of the AC arc furnace and stabilize the three-phase arc impedance.

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