AC arc furnace flexible power supply equipment and control method thereof

Abstract

The embodiments of the present disclosure provide an AC electric arc furnace flexible power supply device and a control method thereof, which are applied in the field of power supply technology. The AC electric arc furnace flexible power supply device includes 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, and the inverter bridge is connected to the AC arc furnace transformer; the rectifier bridge controller is responsible for controlling the rectifier bridge and stabilizing the DC voltage of the rectifier bridge, and the inverter bridge controller is responsible for controlling the inverter bridge and stabilizing the primary current of the AC arc furnace. The AC arc furnace flexible power supply device realizes dual isolation of AC arc furnace fluctuations and power supply systems through the inverter bridge and the rectifier bridge, significantly reducing the grid flicker caused by AC arc furnace fluctuations and reducing the impact of the arc furnace smelting process on the grid.

Description

Technical Field

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

[0002] AC arc furnace uses scrap steel as the main raw material, and uses the high temperature of the arc generated between the electrode and the charge to heat and melt the charge. After the traditional AC arc furnace reduces the voltage of the AC power through a transformer, it limits the arc furnace current under normal operation and short-circuit conditions through a series reactor, and stabilizes the arc by controlling the rise and fall of the electrode. It has the advantages of flexible temperature control, high thermal efficiency, simple and reliable equipment, and short process flow.

[0003] However, as the capacity of AC arc furnace monomers continues to increase, the interference problem of AC arc furnaces on the power supply system has become increasingly prominent: when the arc is extinguished, the active and reactive power taken from the power grid is zero; and when the electrode and the charge are short-circuited, the reactive power consumed by the AC arc furnace reaches the maximum value. During the melting period of the charge, due to the random changes and rapid fluctuations in the arc length, the AC arc furnace will cause strong flicker, asymmetry and high-order harmonic currents in the power supply system.

[0004] In order to solve the problem of AC arc furnace interference to the power supply system, the industry generally uses STATCOM dynamic reactive compensation to reduce flicker, but this method requires a large-capacity STATCOM device and has limited flicker suppression effect. The industry also uses a method of connecting multiple power electronic converters in parallel with a multi-winding phase-shifting transformer on the grid side to isolate the fluctuation of the AC arc furnace from the power supply system while supplying power to the arc furnace, but this method requires the connection of a multi-winding phase-shifting transformer on the grid side, and the system is complex and the cost is very high; in addition, a large number of existing AC arc furnaces are powered by transformers after stepping down the voltage. The above method directly outputs a low-voltage and high-current power supply and cannot be used for the transformation of existing AC arc furnace systems.

[0005] The industry also uses modular multi-level converters, which can directly realize the conversion of high-voltage AC / high-voltage DC, and are suitable for providing flexible power supply for AC arc furnaces. In order to reduce the cost of the converter, considering that the AC arc furnace load is a pure active consumption load and there is no possibility of any energy feedback, the diode bridge arm can be mixed with the modular multi-level bridge arm to reduce the topology of the rectifier bridge cost. However, the control of this topology is complex, the bridge arm current is non-sinusoidal and intermittent, which has high requirements for system control and may cause excessive harmonics flowing into the power grid. Summary of the invention

[0006] 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.

[0007] 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 through positive and negative DC busbars; the rectifier bridges of each phase 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.

[0008] According to the aspects described above and any possible implementation method, 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.

[0009] According to the aspects described above and any possible implementation method, an implementation method is further provided, 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 composed of a reactor 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.

[0010] 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.

[0011] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the electrode position controller is connected to an AC electric arc furnace electrode manipulation mechanism.

[0012] 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.

[0013] 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:

[0014] Detect the grid-side voltage of the rectifier bridge and lock the grid phase through a phase-locked loop;

[0015] 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 * ;

[0016] 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;

[0017] 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 * ;

[0018] Calculate the rectifier bridge DC modulation command value u com * : where u N is the power module capacitor voltage;

[0019] 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.

[0020] 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 current of the AC arc furnace, including:

[0021] 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;

[0022] Calculate the inverter bridge DC modulation command value u com * : where u N is the power module capacitor voltage;

[0023] 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.

[0024] According to the aspects described above and any possible implementation methods, an implementation method is further provided, wherein the electrode position controller is responsible for the electrode manipulation mechanism of the AC arc furnace to control and stabilize 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 command value.

[0025] According to a third aspect of the present disclosure, a working method of an AC arc furnace flexible power supply device is provided, the method comprising:

[0026] 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;

[0027] 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;

[0028] The electrode position controller is used to control the electrode operating mechanism of the AC arc furnace and stabilize the three-phase arc impedance.

[0029] It should be understood that the contents described in the summary of the invention 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 easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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 used to better understand the present solution 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:

[0031] Figure 1 A block diagram of an AC arc furnace flexible power supply device according to an embodiment of the present disclosure is shown;

[0032] Figure 2 A schematic diagram of the structure 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 is shown;

[0033] Figure 3 A schematic diagram of the structure of a bridge arm in a rectifier according to an embodiment of the present disclosure is shown;

[0034] Figure 4 A schematic diagram of a half-bridge structure of a power module according to an embodiment of the present disclosure is shown;

[0035] Figure 5 A schematic diagram of a full-bridge structure of a power module according to an embodiment of the present disclosure is shown;

[0036] Figure 6 A schematic diagram of a current path in a rectifier bridge arm of one phase of the rectifier bridge when grid current flows into the rectifier bridge according to an embodiment of the present disclosure is shown;

[0037] Figure 7 A schematic diagram of a current path in a rectifier bridge arm of one phase of the rectifier bridge when the grid current flows out of the rectifier bridge according to an embodiment of the present disclosure is shown;

[0038] Figure 8 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 is shown;

[0039] Fig. 9 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 is shown;

[0040] Fig.10A schematic diagram of 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 is shown. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0042] In addition, the term "and / or" in this article is only a description of the association relationship between the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0043] Figure 1 A block diagram of an AC arc furnace flexible power supply device 100 according to an embodiment of the present disclosure is shown.

[0044] like Figure 1 As shown, the AC arc furnace flexible power supply device 100 includes:

[0045] 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,

[0046] The rectifier bridge 1 includes three-phase rectifier bridge arms 11, 12, 13; the inverter bridge 2 includes three-phase inverter bridge arms 21, 22, 23; the rectifier bridge arms 11, 12, 13 and the inverter bridge arms 21, 22, 23 are arranged in sequence and connected in parallel through the positive and negative DC busbars. In some embodiments, the inverter bridge 2 includes at least one phase inverter bridge arm, such as any one of the inverter bridge arms 21, 22, 23.

[0047] Each rectifier bridge arm 11, 12, 13 has the same structure, and includes a rectifier upper bridge arm 111, a rectifier middle bridge arm 112, a rectifier lower bridge arm 113, and a diode bridge arm 114 and a diode bridge arm 115. The rectifier upper bridge arm 111, the rectifier middle bridge arm 112, and the rectifier lower bridge arm 113 are sequentially connected in series. After the diode bridge arm 114 and the diode bridge arm 115 are connected in series, they are connected in parallel at both ends of the rectifier middle 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 network. Among them, the connection points of the diode bridge arm 114 and the diode bridge arm 115 in each rectifier bridge arm 11, 12, 13 are respectively connected to each phase of the AC power supply network.

[0048] The inverter bridge arms 21, 22, and 23 respectively 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 of the inverter upper bridge arm 211 and the inverter lower bridge arm 212 is connected to the arc furnace transformer 3. Among them, the connection points of the inverter upper bridge arm 211 and the inverter lower bridge arm 212 in each inverter bridge arm 21, 22, and 23 are respectively connected to each phase of the arc furnace transformer 3.

[0049] In some embodiments, the rectifier bridge controller 4 is responsible for controlling the rectifier bridge 1 and stabilizing the rectifier bridge DC voltage.

[0050] In some embodiments, the inverter bridge controller 5 is responsible for controlling the inverter bridge 2 and stabilizing the arc furnace current.

[0051] like Figure 2 As shown, 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 a reactor and at least two power modules connected in series; the power module can be as follows Figure 4 The half-bridge module shown can also be Figure 5 The full-bridge module shown.

[0052] like Figure 3 As shown, the bridge arm 112 in the rectifier is composed of at least two power modules connected in series; the power module can be as follows Figure 4 The half-bridge module shown can also be Figure 5 The full-bridge module shown.

[0053] In some embodiments, during normal operation, such as Figure 4 There is a stable DC voltage on the capacitor of the half-bridge module shown. For example, when a 4.5kV IGBT is used, the capacitor voltage is about 2.5kV. Through the on-off action of IGBT1 and IGBT2, the half-bridge module can output 0 voltage or capacitor voltage. In normal operation, such as Figure 5There is a stable DC voltage on the capacitor of the full-bridge module shown. For example, when a 4.5kV IGBT is used, the capacitor voltage is about 2.5kV. Through the on-off actions of IGBT1, IGBT2, IGBT3, and IGBT4, the full-bridge module can output 0 voltage, capacitor voltage, or negative capacitor voltage.

[0054] In some embodiments, the bridge arms composed of half-bridge modules and / or full-bridge modules connected in series, 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, require the number of series power modules, which depends on the maximum voltage at both ends of the bridge arms and the capacitor voltage of the power modules.

[0055] Taking the 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 the rectifier bridge 1. Assuming that the DC voltage of the 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, 23 of the inverter bridge 2 is: The number of modules required for the single-phase inverter bridge arms 21 , 22 , and 23 of the inverter bridge 2 is 32 respectively.

[0056] 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 rectifier state: Figure 6 As shown, when the AC grid voltage of the phase rectifier bridge arm is in the positive half-wave, when the AC grid current enters the phase rectifier bridge arm, 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 the highest of the rectifier bridge DC voltage; as shown in FIG. Figure 7 As shown, 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 middle bridge arm 112 of the rectifier bridge 1 can be designed to bear up to 50% of the rectifier bridge DC voltage, 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, 13 requires 24 power modules, which is significantly lower than the number of modules 32 required by each single-phase inverter bridge arm 21, 22, 23 in the inverter bridge 2.

[0057] According to the embodiments of the present disclosure, the following technical effects are achieved:

[0058] 1. The inverter bridge and rectifier bridge realize the dual isolation of AC arc furnace fluctuation and power supply system: AC arc furnace fluctuation first affects the AC current of the inverter bridge, and then affects the capacitor voltage of the power module of the inverter bridge, and then affects the voltage and current of the DC bus. The accumulation of DC bus voltage and current fluctuations will then affect the voltage of the rectifier bridge power module, and finally affect the current flowing into the AC power grid. The dual isolation of the inverter bridge and rectifier bridge significantly reduces the electric flash caused by AC arc furnace fluctuations and reduces the impact of the arc furnace smelting process on the power grid.

[0059] 2. The currents in the upper arm and the lower arm 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.

[0060] 3. The AC arc furnace flexible power supply device is directly connected between the AC power grid and the AC arc furnace to supply power to the AC arc furnace without adding a multi-winding transformer or a phase-shifting transformer. At the same time, the arc furnace flexible power supply device can directly output medium voltage and can be applied to the transformation of existing AC arc furnaces.

[0061] 4. The maximum voltage that the upper bridge arm and the lower bridge arm of the rectifier bridge bear is only equivalent to the DC voltage of the rectifier bridge minus the voltage of the middle bridge arm of the rectifier bridge, which can significantly reduce the cost of the rectifier bridge. By using the diode bridge arm in the rectifier bridge arm, the combined operation of the upper, middle and lower bridge arms of the rectifier bridge is automatically realized, and the system control is simple without increasing the control complexity.

[0062] The above is an introduction to the device embodiment. The control method of the AC arc furnace flexible power supply equipment disclosed in the present invention is further explained below through a method embodiment.

[0063] The working method of the AC arc furnace flexible power supply device disclosed in the present invention is as follows:

[0064] The rectifier bridge is controlled by a rectifier bridge controller to achieve the purpose of stabilizing the DC voltage and reducing the flicker of the AC power grid, so that energy flows from the AC power grid to the DC bus through the rectifier bridge; wherein the input end of the rectifier bridge is connected to the AC power grid, and the DC bus at the output end of the rectifier bridge is connected to the input end of the inverter bridge;

[0065] The purpose of stabilizing the primary side current of the arc furnace transformer is achieved by using an inverter bridge controller, so that energy flows from the DC bus to the arc furnace through the inverter bridge; wherein the output end of the inverter bridge is connected to the primary side of the AC arc furnace transformer;

[0066] The electrode position controller is used to control the electrode operating mechanism of the AC electric arc furnace and stabilize the three-phase arc impedance; wherein the secondary side of the AC electric arc furnace transformer is connected to the electrode of the electric arc furnace.

[0067] like Figure 1 As shown, 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.

[0068] like Figure 8 As shown, the rectifier bridge controller 4 is responsible for controlling the rectifier bridge 1 and stabilizing the rectifier bridge DC voltage, and its control method includes:

[0069] 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);

[0070] 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 active current command value i of the rectifier bridge is generated by the DC voltage controller. d * ;in,

[0071] If the rectifier bridge DC voltage u dc If it is too high, reduce the active current command value i of the rectifier bridge d * , if the rectifier bridge DC voltage u dc If it is too low, increase the active current command value i of the rectifier bridge. d * ;

[0072] In some embodiments, the DC voltage controller uses 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.

[0073] 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 reactive current command value i of the rectifier bridge q * To compensate for the reactive power consumed by the grid-side impedance;

[0074] In some embodiments, the generating of the rectifier bridge reactive current command value i q * include:

[0075] 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:

[0076]

[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 * 、u q * , 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 the nearest level approximation method is used according to the direction of the AC current.

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

[0082] Through the above operation, no matter whether the direction of the AC current is entering the rectifier bridge arms 11, 12, 13 of each phase or leaving the rectifier bridge arms 11, 12, 13 of each phase, the AC current is evenly distributed in the rectifier upper bridge arm 111 and the rectifier lower bridge arm 113, which solves the topology solution of mixing the diode bridge arm with the modular multi-level bridge arm to reduce the cost of the rectifier bridge. The control of this topology is complex, the bridge arm current is non-sinusoidal and intermittent, the system control requirements are very high, and the harmonics flowing into the power grid may exceed the standard. Technical problems.

[0083] Take the rectifier bridge A phase 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 nearest level approximation method according to the rectifier bridge modulation command value. 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 modulated by the nearest level approach method according to the rectifier bridge command value. Generate; the trigger pulse of the lower bridge arm is modulated by the nearest level approximation method according to the rectifier bridge command value generate.

[0085] like Fig. 9 As shown, the inverter bridge controller 5 is responsible for controlling the inverter bridge 2 and stabilizing the arc furnace current, and its 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 the preset value, which is calculated according to 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 bridge 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 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.

[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 command 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 according to 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 embodiment of the present disclosure, the control method of the electric arc furnace flexible power supply equipment realizes the independent decoupling control of the rectifier bridge, the inverter bridge and the electric arc furnace electrode position, with less mutual influence, and the system control is simple and reliable. At the same time, the control of the electric arc furnace flexible power supply equipment realizes the 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 implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present 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; The rectifier bridge controller is specifically used for: 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; Add and subtract the AC modulation command value of the rectifier bridge and the DC modulation command value of the rectifier bridge, and use the nearest level approximation method according to the direction of the AC current to obtain the trigger pulse of the rectifier bridge arm of each phase; The inverter bridge controller is specifically used for: 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.

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 the power modules is determined according to the maximum voltage across the bridge arm and the capacitor voltage of the power module.

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. The control method of the AC arc furnace flexible power supply device 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; 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; Add and subtract the AC modulation command value of the rectifier bridge and the DC modulation command value of the rectifier bridge, and use the nearest level approximation method according to the direction of the AC current to obtain the trigger pulse of the rectifier bridge arm of each phase; 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, obtain the trigger pulse of each phase bridge arm of the inverter bridge by the nearest level approximation method; 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.

7. The working method of the AC arc furnace flexible power supply device 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; The controlling of the rectifier bridge to stabilize the DC voltage by the rectifier bridge controller comprises: 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; Add and subtract the AC modulation command value of the rectifier bridge and the DC modulation command value of the rectifier bridge, and use the nearest level approximation method according to the direction of the AC current to obtain the trigger pulse of the rectifier bridge arm of each phase; The method of stabilizing the primary current of the arc furnace transformer by using the inverter bridge controller includes: 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, obtain the trigger pulse of each phase bridge arm of the inverter bridge by the nearest level approximation method; The method of controlling the electrode operating mechanism of the AC arc furnace and stabilizing the three-phase arc impedance by using the electrode position controller includes: 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.

Images