Standby power supply switching control device capable of reducing load impact

Abstract

The utility model provides a standby power supply switching control device capable of reducing load impact. Comprising a device main machine body, a main control circuit board arranged in the device main machine body, and a power supply module, an isolation conversion module, an optical isolation driving module, a test module, a GPS time synchronization interface, a photoelectric isolation module, a keyboard, a liquid crystal display screen, a printing interface, a 485 communication interface and a 232 communication interface which are electrically connected with the main control circuit board, the 232 communication interface is connected with the portable computer assembly; the 485 communication assembly is connected with a power plant DCS system. The photoelectric isolation module is connected with a signal relay and an outlet relay; the optical isolation driving module is connected with the switching value input interface; according to the technical scheme, the problem that the load impact is too large in the switching process of the standby power supply is reduced, the load can be stably switched to the standby power supply from the main power supply, and the problem that no load is lost in the switching process of the standby power supply is solved.

Description

[Technical field]

[0001] The utility model relates to the technical field of power switching control devices, and in particular to a standby power switching control device capable of reducing load impact. [Background Technology]

[0002] In the power system, the backup power switching device is an important technical measure to ensure uninterrupted power supply, which is related to the safe operation of the generator set, electrical equipment and even the entire power system.

[0003] In the past, there were generally three starting criteria for the backup power switching device: one was no current, that is, ensuring that the working power supply was disconnected; two was voltage, that is, the backup power supply voltage was normal; three was no voltage, that is, the bus residual voltage was very low or even no voltage.

[0004] It has been found in many practical cases that the criterion of busbar no voltage is outdated and can no longer meet the power supply reliability requirements of current power plants and industrial enterprises. When the load busbar voltage is very low or even zero, the speed of the load on the busbar, such as the motor, has dropped too much or even stopped running, and the production process has been interrupted. At this time, even if the backup power supply is put into use, it is impossible to avoid serious damage to the production process. In addition, the starting current of a large number of motors is very large, and the busbar voltage may be difficult to restore. If the busbar voltage is not judged and the backup power supply is directly put into use, the phase angle between the busbar residual voltage and the backup power supply may be close to 180°, which will cause a great impact on the load. [Contents of the utility model]

[0005] The problems existing in the prior art solved by this application are:

[0006] The criterion of busbar no pressure is outdated and can no longer meet the power supply reliability requirements of current power plants and industrial enterprises. When the load busbar voltage is very low or even zero, the speed of the load on the busbar, such as the motor, has dropped too much or even stopped running, and the production process has been interrupted. At this time, even if the backup power supply is put into use, it is impossible to avoid serious damage to the production process.

[0007] The solution to the technical problem of the utility model is:

[0008] Provided is a standby power switching control device capable of reducing load impact, comprising a device main body and a main control circuit board arranged inside the device main body, a power module electrically connected to the main control circuit board, an isolation conversion module, an optical isolation drive module, a test module, a GPS timing interface, a photoelectric isolation module, a keyboard, a liquid crystal display, a printing interface, a 485 communication interface and a 232 communication interface; the 232 communication interface is connected to a portable computer component; the 485 communication component is connected to a power plant DCS system; the optical isolation module is connected to a signal relay and an output relay; the optical isolation drive module is connected to a switch quantity input interface; and the isolation conversion module is connected to an AC quantity input interface.

[0009] The technical effects of solving the technical problem in this application are as follows:

[0010] Compared with the prior art, the utility model provides a backup power supply switching control device which can reduce load impact. Its technical solution reduces the problem of excessive load impact during the backup power supply switching process, enables the load to be smoothly switched from the main power supply to the backup power supply, and solves the problem of no load loss during the backup power supply input process. [Drawings]

[0011] Figure 1 The utility model is a schematic diagram of a module structure of a standby power supply switching control device capable of reducing load impact.

[0012] Figure 2 The utility model is a schematic diagram of the implementation flow corresponding to a standby power supply switching control device capable of reducing load impact.

[0013] Figure 3 The utility model discloses a phasor diagram of in-phase switching of a standby power supply switching control device capable of reducing load impact.

[0014] Figure 4 The utility model discloses a main wiring diagram of a control system corresponding to a standby power supply switching control device capable of reducing load impact.

[0015] Figure 5 The utility model is a schematic diagram of the relationship between the bus residual voltage, the backup power supply voltage and the differential voltage corresponding to a backup power supply switching control device capable of reducing load impact.

[0016] Figure 6 The utility model discloses a polar coordinate diagram of the working bus residual voltage relative to the standby voltage corresponding to a standby power supply switching control device capable of reducing load impact.

[0017] Figure 7The utility model discloses a phase diagram after the working power supply is cut off, which corresponds to a standby power supply switching control device capable of reducing load impact.

[0018] Figure 8 The utility model discloses a main wiring and equivalent circuit connection diagram corresponding to a standby power supply switching control device capable of reducing load impact.

[0019] Fig. 9 The utility model discloses a static voltage characteristic diagram of an induction motor corresponding to a standby power supply switching control device capable of reducing load impact.

[0020] Fig.10 The utility model discloses a same-phase switching phasor diagram corresponding to a standby power supply switching control device capable of reducing load impact.

[0021] Fig.11 The utility model is a software framework diagram corresponding to a standby power supply switching control device capable of reducing load impact.

[0022] Fig.12 The utility model discloses an LCD menu structure diagram corresponding to a standby power supply switching control device capable of reducing load impact. [Specific implementation method]

[0023] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit this utility model.

[0024] See also Figures 1 to 12 The utility model is a backup power supply switching control device 1 that can reduce load impact, which includes a device main body and a main control circuit board arranged inside the device main body, a power module electrically connected to the main control circuit board, an isolation conversion module, an optical isolation drive module, a test module, a GPS timing interface, a photoelectric isolation module, a keyboard, a liquid crystal display, a printing interface, a 485 communication interface and a 232 communication interface; the 232 communication interface is connected to a portable computer component; the 485 communication component is connected to a power plant DCS system; the photoelectric isolation module is connected to a signal relay and an output relay; the optical isolation drive module is connected to a switch input interface; the isolation conversion module is connected to an AC input interface;

[0025] 1. Quick switch:

[0026] At the moment of switching start, if the angle difference and frequency difference between the bus and the backup power supply line are within the set value range, and the bus voltage is not lower than the fast-cut low-voltage closing value, "fast switching" can be performed at the moment of starting, and the outlet can be closed immediately. Field test data show that the time and speed of bus voltage and frequency decay are mainly related to the load carried by the bus section. The more load, the slower the voltage amplitude and frequency decrease, and the rate of decrease continues to accelerate with the passage of time. Within the first 0.3S, the voltage amplitude and frequency decrease in magnitude is small, and the phase angle difference within 60° is safe for electrical equipment. Therefore, if the fast closing is performed in this range, it is undoubtedly the best choice. When the average frequency difference is 1Hz, the angle between the bus and the backup incoming line phase increases by 36°, calculated based on the inherent closing time of the switch as 100ms. Therefore, in order to ensure the success of fast switching, it is advisable to use a fast switch for switching, and when the device sends a closing outlet command, the angle difference measured immediately should be less than 20°, that is, the fast switching angle difference constant is set to 20°.

[0027] 2. Asynchronous in-phase switching;

[0028] After the working power supply is cut off due to a fault or other reasons, if the rapid switching conditions cannot be met due to various reasons, all motors on the bus will rely on the original inertia and rotor residual magnetism to enter the asynchronous power generation state, that is, a residual voltage with a gradually decreasing voltage and frequency will appear on the working bus. In the absence of a synchronous motor, since the asynchronous motor does not have the problem of out-of-step of the synchronous motor, the conditions for synchronous capture are relaxed under the conditions of high residual voltage amplitude and frequency, so as to quickly put the backup power supply into use. According to previous on-site experience, when the angle between the bus and the backup incoming line phase is within 65°, the backup power supply is turned on, which will pull the motor group into synchronization without much impact.

[0029] 3. Capture the switching of the same phase point;

[0030] Capturing the same-phase point switching means that after the working power supply is cut off due to an accident, the residual voltage phase on the bus will rotate around the backup voltage phase in the lagging direction, and the backup power supply switching will be completed when the phase angle difference is zero for the first time. The condition factor depends on the closing time of the backup power switch and the change speed of the phase angle difference Ψ; as shown in the attached Figure 3 As shown:

[0031] Uby: standby voltage

[0032] U: bus voltage

[0033] Ψ: bus voltage and standby voltage angle difference

[0034] dΨ / dt: angular velocity of bus voltage relative to standby voltage

[0035] First, after the faulty working power supply is cut off by the protection, the voltage and frequency on the bus decay according to a certain rule. During the decay process, the residual voltage moves 360° relative to the backup power supply voltage, and a closing time point that may meet the same-phase switching criterion appears. The ideal situation is to achieve the first zero-degree closing. At this moment, the bus voltage generally decays by about 30-40% of the rated voltage, the output of the motor equipment does not drop very much, and the impact when the backup power supply is closed is not too large, and the self-starting condition of the equipment is better. However, during the decay process, as the bus residual voltage decreases with the decrease of frequency, its voltage amplitude and phase angle will change faster and faster. As shown in the figure above, the original linear model and simple acceleration model can no longer accurately express the changes in voltage amplitude and phase angle. The backup power supply fast switching device of the present invention adopts the method of automatic frequency tracking technology and fuzzy theory to establish a segmented model of frequency, which accurately expresses the changes in frequency, phase angle and amplitude. According to the real-time frequency, phase angle and amplitude change rules, the arrival time of the first phase coincidence between the bus residual voltage and the backup power supply voltage vector is calculated. When the time is equal to the total action time of the closing circuit before the arrival of this time, a closing command is issued to achieve accurate zero-crossing point, that is, the first same-phase closing. This closing method is not affected by load changes and is beneficial to the self-starting of the equipment.

[0036] Attached photos Figure 4 It is a typical power supply system with dual incoming lines and a bus tie configuration.

[0037] Dark standby: dual incoming lines supply power to the bus at the same time, ML is disconnected, and busbars I and II serve as backup for each other.

[0038] Open standby: ML is closed or there is no ML, forming a busbar, one incoming line supplies power to the busbar, and the other incoming line serves as a backup power supply.

[0039] When the working incoming line fails, in order to minimize the power outage time, fast switching of the backup power supply is the best switching method.

[0040] As shown in the wiring diagram of Scheme 1, during normal operation:

[0041] 1DL is in the closed position, and incoming line 1 supplies power to bus I through 1DL;

[0042] 2DL is closed, and incoming line 2 supplies power to bus I through 2DL;

[0043] ML quantile, I mother and II mother are backup for each other through ML.

[0044] The device only needs to access bus voltage (three-phase), incoming line voltage (single-phase), bus current (three-phase), incoming line current (single-phase), and voltage and current as important logic switching criteria;

[0045] Figure 5VD is the bus residual voltage, VS is the backup power supply voltage, and △U is the difference voltage between the backup power supply voltage and the bus residual voltage. After the backup power supply is turned on, the voltage UM that the load bears is:

[0046] UM=XM / (XS+XM)△U(1)

[0047] In the formula, XM is the equivalent reactance of the motor units and low-voltage loads on the bus after conversion to the high-voltage plant voltage.

[0048] XS--Equivalent reactance of power supply.

[0049] Let K = XM / (XS+XM), then

[0050] UM=K△U(2)

[0051] To ensure the safe self-starting of the load, UM should be less than the allowable starting voltage of the motor, set to 1.1 times the rated voltage UDe, then:

[0052] K△U<1.1UDe(3)

[0053] △U(%)<1.1 / K(4)

[0054] Assume K = 0.67, then △U (%) < 1.64. In the figure, take A as the center and 1.64 as the radius to draw the arc A'-A", then the right side of A'-A" is the safe area where the backup power supply is allowed to close, and the left side is the unsafe area. If K = 0.95, then △U (%) < 1.15, Figure 2 The left side of B'-B" is an unsafe area.

[0055] Assuming that the working power supply and the backup power supply are in phase during normal operation, and their voltage phasor endpoint is A, the residual voltage phasor endpoint will move from A to B along the residual voltage curve after the bus loses power. If the backup power supply can be closed within the A-B section, the motor safety can be guaranteed without causing the motor speed to drop too much. This is "fast switching".

[0056] Figure 2 In the fast switching time, the fast switching time should be less than 0.2S. In practical applications, point B is usually defined by the phase angle, such as 60°. Considering the inherent time of the closing circuit, the angle when the closing command is issued should be less than 60°, that is, there should be a certain advance amount. The size of the advance amount depends on the frequency difference and closing time. For example, if the average frequency difference within the inherent time of closing is 1Hz and the closing time is 100ms, the advance amount is about 36°.

[0057] After the working power supply and other power supply branches and capacitor branches are cut off, all loaded motors rely on the original inertia and rotor residual magnetism to enter the asynchronous power generation state, that is, a residual voltage with a gradually decreasing voltage and frequency will appear on the working bus, such as Figure 3 As shown in the figure, the angle θ of the residual voltage V moving in the lagging direction relative to the backup power supply VB is increasing, and the residual voltage value is also decreasing, and it takes a period of time to decay to zero. In the past, people were worried that turning on the backup power supply when there was voltage on the working bus would result in damage to the electrical equipment, but in fact this is incorrect. Figure 4 It is the phase diagram of the change of the phase difference voltage ΔU between the backup power supply voltage UB and the residual voltage UG after the working power supply is cut off. δ0 is the initial power angle of the backup power supply UB and the working bus voltage UG0 during normal operation. When the working power supply is cut off, the working bus voltage changes from UG0 to the residual voltage UG1, UG2, UG3, UG4, UG5, UG6..., and at the same time, the corresponding differential voltage is generated. ΔU1, ΔU2…ΔU6, with the phase difference between UB and the residual pressure UG;

[0058] As Φ increases, ΔU increases from small to large, and then from large to small. If the backup power supply is turned on at a certain ΔU value, we can get Figure 5 It can be seen that part of ΔU falls on the reactance XB of the standby transformer (or line), and the other part falls on the equivalent impedance XM of the load (motor). Generally, the motor can withstand 1.1 to 1.2 times the rated voltage for a long time. Therefore, the voltage applied to the motor when the standby power supply is turned on should not exceed this value. In addition, when the motor group (which can be replaced by an equivalent motor) is disconnected from the power supply, a counter-electromotive force will be generated. When the standby power supply is turned on, it may be superimposed with the sub-transient and transient potential of the equivalent motor to generate a large-amplitude impact current, which may cause the standby power supply relay protection to trip and make the replacement control fail. Theory and practice have proved that the impact current value generated at the moment of standby power supply is not only related to the closing phase angle, but also to the opening angle when the working power is cut off. For this reason, we adopted the principle of monitoring the opening and closing angles to capture asynchronous same-phase switching to achieve fast and safe switching of the standby power supply. In this way, the motor is safe. We call this control criterion the asynchronous same-phase switching criterion. The method to implement this criterion is to monitor the working power supply removal angle in real time, and then continuously measure the current ΔU value, and predict the change of ΔU based on the sampled data. Before the ΔU value increases to exceed the allowable value, the closing angle is calculated based on the captured opening angle to complete the input of the backup power supply. This ensures that all motors are not damaged, not cut off, and not stopped, which is greatly conducive to the rapid resumption of work. Although there may be a certain phase difference between the bus residual voltage UG and the backup power supply voltage UB when the backup power supply is put into use, because this group of motors in the asynchronous power generation state have no prime mover to supplement their kinetic energy, and no exciter to support their excitation. Therefore, they are just generators that emit voltage, and can be easily pulled into synchronization without loss by the powerful backup power supply.

[0059] ΔU is allocated according to the ratio of the standby transformer (or line) impedance XB to the load impedance XM. Since the working transformer (or line) impedance XG and the standby transformer (or line) impedance XB can be known in advance, we can continuously measure UG and UM during normal operation and calculate the real-time equivalent impedance XM of the load by the following formula:

[0060]

[0061] Once the working power supply is cut off due to a fault, the last XM calculated value is recorded immediately, and the maximum ΔU value allowed for closing can be calculated through the known XB, so as to ensure that the backup power supply is put into use quickly and safely. In fact, the equivalent reactance XM continues to decrease during the deceleration process of the motor losing power. That is to say, the maximum allowable ΔU value for ensuring safety when the backup power supply is put into use, which is calculated based on the XM calculated when the power is just cut off and the known XG, is higher than when the backup power supply is put into use;

[0062] The ΔU value is small, that is, the voltage distributed to both ends of the motor load is smaller than the calculated value, so this algorithm adds a safer guarantee to the motor.

[0063] In addition, it should be pointed out that the induction motors widely used in industrial enterprises have the following characteristics: Figure 1-4 The static voltage characteristic curve describes the relationship between the active power P and reactive power Q absorbed by the motor from the power supply and the terminal voltage V. It is not difficult to see that when the motor terminal voltage drops to 60% of the rated voltage, the motor will absorb a large amount of reactive power and the torque will drop sharply. This means that if the backup power supply is connected when the residual voltage of the working bus drops below the critical voltage Uk, the self-starting condition of the motor will be greatly deteriorated, and even the self-starting failure will cause the backup power supply to trip due to overcurrent and low voltage. Therefore, in order to ensure the continuity of the production process, the backup power supply should be put into operation before the critical voltage. In this way, the motor power supply contactor of many industrial enterprises will no longer have the so-called "shaking power" problem caused by the slow input of the backup power supply, and the motor will not trip automatically.

[0064] Capturing the same-phase point switching means that after the working power supply is cut off due to an accident, the residual voltage phase on the bus will rotate around the backup voltage phase in the lagging direction, and the backup power supply switching will be completed when the phase angle difference is zero for the first time. The condition factor depends on the closing time of the backup power switch and the change speed of the phase angle difference Ψ. The switching process phase diagram is shown in the attached figure. Fig.10 As shown;

[0065] Uby: standby voltage

[0066] U: bus voltage

[0067] Ψ: bus voltage and standby voltage angle difference

[0068] dΨ / dt: angular velocity of bus voltage relative to standby voltage

[0069] First, after the faulty working power supply is cut off by the protection, the voltage and frequency on the bus decay according to a certain rule. During the decay process, the residual voltage moves 360° relative to the backup power supply voltage, and a closing time point that may meet the same-phase switching criterion appears. The ideal situation is to achieve the first zero-degree closing. At this moment, the bus voltage generally decays by about 30-40% of the rated voltage, the output of the motor equipment does not drop very much, and the impact when the backup power supply is closed is not too large, and the self-starting conditions of the equipment are better. However, during the decay process, as the bus residual voltage decreases with the decrease of frequency, its voltage amplitude and phase angle will change faster and faster. As shown in the figure above, the original linear model and simple acceleration model have been difficult to accurately express the changes in voltage amplitude and phase angle. The present invention adopts the method of segmenting the frequency model using frequency automatic tracking technology and fuzzy theory to accurately express the changes in frequency, phase angle, and amplitude. According to the real-time frequency, phase angle, and amplitude change rules, the arrival time of the first phase overlap between the bus residual voltage and the backup power supply voltage vector is calculated. When the total action time of the closing circuit is equal to the arrival of this time, a closing command is issued to achieve accurate zero-crossing point, that is, same-phase closing. This closing method is not affected by load changes and is beneficial to the self-starting of the equipment. However, the disadvantage is that part of the load will be cut off by the low-voltage protection during the decline of the bus residual voltage. All loads using contactors will lose the opportunity to receive power again due to the release of the contactor due to low voltage. It is impossible to restore the original production process after the backup power supply is put into use;

[0070] Compared with the prior art, the utility model provides a backup power supply switching control device 1 capable of reducing load impact, which can solve the following problems:

[0071] 1. Reduce the problem of excessive load impact during the backup power supply switching process, so that the load can be smoothly switched from the main power supply to the backup power supply;

[0072] 2. The problem of no load loss during the backup power supply operation has been solved.

[0073] The above-described implementation methods of the utility model do not constitute a limitation on the protection scope of the utility model. Any modification, equivalent replacement and improvement made within the spirit and principle of the utility model shall be included in the protection scope of the claims of the utility model.

Claims

1. A backup power supply switching control device capable of reducing load impact, characterized in that: The device comprises a main body and a main control circuit board arranged inside the main body of the device, a power module electrically connected to the main control circuit board, an isolation conversion module, an optical isolation drive module, a test module, a GPS timing interface, a photoelectric isolation module, a keyboard, a liquid crystal display, a printing interface, a 485 communication interface and a 232 communication interface; the 232 communication interface is connected to a portable computer component; the 485 communication interface is connected to a power plant DCS system; the photoelectric isolation module is connected to a signal relay and an output relay; the optical isolation drive module is connected to a switch quantity input interface; and the isolation conversion module is connected to an AC quantity input interface.

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