CN109742775B - Three-phase load balancing device and method - Google Patents
Three-phase load balancing device and method Download PDFInfo
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Abstract
The invention discloses a three-phase load balancing device and a method, wherein the three-phase load balancing device comprises a phase detection module, a switching module and a switching module, wherein the phase detection module is used for detecting the switching state of a load switch with the phase of a load to be switched; the zero detection module is used for detecting the current zero state and the voltage zero state of the same switching load; the controller is connected with the phase detection module, the zero point detection module and the load switches of each phase, and when the load switch of the phase where the load to be switched is detected by the phase detection module is closed, the controller controls the load switch of the phase where the load to be switched is opened in a current zero point state, and cuts the load to be switched into a phase switching line in a voltage zero point state; the load switch state can be accurately detected, and the problems of interphase short circuit and load switch damage caused by unresponsiveness of the load switch in the phase change process of the power grid are avoided.
Description
Technical Field
The invention relates to the technical field of power grid circuits, in particular to a three-phase load balancing device and method.
Background
In low-voltage power networks, most of the power networks are three-phase four-wire system power networks, and as most of electric equipment is single-phase power, the phenomenon of unbalanced three-phase load often occurs. Unbalance of the three-phase load can cause damage to the transformer and the power grid, and the output efficiency of the power supply transformer, damage and damage of the transformer, accelerated aging of the power transmission line and the like are caused. Therefore, in a power grid, dynamic balance distribution is often required to be carried out on the three-phase load of the transformer, so that the relative balance of the three-phase load of the transformer is maintained, the loss of line equipment is reduced, and the safety of power equipment is ensured. The most effective mode of load balancing is a load switch switching mode, at present, a software method is mainly adopted to perform zero point acquisition on three-phase voltage respectively, a current closed-phase switch is opened after a commutation command is received, and then the closed-phase switch is closed. In this process, since it cannot be determined whether the switch to be opened is opened, when the switch to be closed is closed, a serious grid accident such as a phase-to-phase short circuit and an open circuit may occur.
Disclosure of Invention
According to the three-phase load balancing device and method, the problems of phase-to-phase short circuit and damage of the load switch caused by unresponsiveness of the load switch in the phase-change balancing process of the power grid in the prior art are solved, the condition of the load switch can be accurately detected, and the phase-to-phase short circuit of the load of the power grid in the phase-change process is avoided; the load switching phase is carried out in the state of the current zero point and the voltage zero point, so that the damage or the damage to the load switch caused by the overlarge current or voltage at the moment of cutting-in under the condition of high voltage and high current is avoided, and the safety and the accuracy of load transfer are further ensured.
The embodiment of the application provides a three-phase load balancing device, which comprises:
the phase detection module is used for detecting the opening and closing states of the load switches of the phase where the load to be switched is located;
the zero detection module is used for detecting the current zero state and the voltage zero state of the same switching load;
the controller is connected with the phase detection module, the zero point detection module and the load switches of each phase, when the load switch of the phase where the load to be switched is detected by the phase detection module is closed, the controller controls the load switch of the phase where the load to be switched is disconnected in a current zero point state, and when the load switch is in a voltage zero point state, the load to be switched is switched into a phase switching circuit.
Optionally, the time interval between the current zero state and the voltage zero state is smaller than or equal to the alternating current single cycle time of the power grid where the three-phase balancing device is located.
Optionally, the phase detection module comprises a collection unit and a signal conversion unit, the detection end of the collection unit is connected with the load to be switched, the output end of the collection unit is connected with the input end of the signal conversion unit, and the output end of the signal conversion unit is connected with the controller; the acquisition unit is used for detecting the open-close state of the same load switch where the load to be switched is located, and the signal conversion unit converts the open-close state into a corresponding level signal and transmits the corresponding level signal to the controller.
Optionally, the collecting unit includes a rectifier bridge, an optocoupler, a first resistor and a second resistor, where a first input end of the rectifier bridge is used as a collecting end of the collecting unit and is connected with an output end of a load switch where the load to be switched is located, a second input end of the rectifier bridge is connected with an output end of the load switch where the load to be switched is located, a first output end of the rectifier bridge is connected with an anode of a light emitting diode of the optocoupler through the first resistor, and a second output end of the rectifier is connected with a cathode of the light emitting diode of the optocoupler through the second resistor; and the collector electrode of the phototriode of the optical coupler is used as the output end of the acquisition unit to be connected with the input end of the signal conversion unit, and the emitter electrode of the phototriode of the optical coupler is grounded.
Optionally, the collecting unit further includes a first diode, an anode of the first diode is connected with a common end between the second output end of the rectifier and the second resistor, and a cathode of the first diode is connected with the common end between the first resistor and the anode of the light emitting diode of the optocoupler.
Optionally, the signal conversion unit includes a not gate logic part, a third resistor, a fourth resistor, a fifth resistor and a first capacitor, one end of the third resistor is connected with a power supply, the other end of the third resistor is used as an input end of the signal conversion unit and is connected with an output end of the acquisition unit and one end of the fourth resistor, the other end of the fourth resistor is connected with an input end of the not gate logic part, an output end of the not gate logic part is connected with one end of the fifth resistor, and the other end of the fifth resistor is used as an output end of the signal conversion unit and is connected with the controller; one end of the first capacitor is connected with the power supply, and the other end of the first capacitor is connected with the input end of the NOT logic piece.
Optionally, the signal conversion unit further includes a second diode, an anode of the second diode is connected to an input end of the not gate logic element, and a cathode of the second diode is connected to a common end between the third resistor and the fourth resistor.
The embodiment of the application also provides a three-phase load balancing method, which comprises the following steps:
receiving a commutation instruction;
detecting the opening and closing states of the load switches with the same load to be switched;
and when the load switch of the same load to be switched is in a closed state, controlling the load to be switched to cut into a switching phase line.
Optionally, the step of controlling the load to be switched to switch into the switching phase line specifically includes:
detecting the current zero state and the voltage zero state of the same load to be switched;
when the load to be switched is in a current zero state, controlling a load switch of the same load to be switched to be disconnected;
and controlling the load to be switched into the switching phase line in the next adjacent voltage zero state.
Optionally, the time interval between the current zero state and the next adjacent voltage zero state is smaller than or equal to the alternating current single cycle time of the power grid where the three-phase balancing device is located.
One or more technical solutions provided in the embodiments of the present application at least have the following technical effects or advantages:
1. the switching state of the load switch is detected by adopting the phase detection module, the phase zero state and the voltage zero state of the phase switch are detected on the basis of closing the load switch, the phase switch of the load to be switched is disconnected in the current zero state, and the load to be switched is switched into a phase switching circuit in the next adjacent voltage zero state, so that the problem of phase-to-phase short circuit caused by uncertain load switch states in the phase switching balance process of the power grid load is solved; and the load switching phase is carried out in the current zero point and the voltage zero point state, so that the damage or the damage to the load switch caused by the overlarge current or voltage at the switching-in moment under the conditions of high voltage and high current is avoided.
2. Because the scheme of completing load switching in 20ms is adopted, the problem of accurately switching the load switch is solved, and the effect of safety and accuracy of load transfer in the phase change process is improved.
3. The switching state of the load switch acquired by the corresponding detection module is converted into a corresponding level signal and the corresponding level signal is transmitted to the controller, so that the problem that the load switch does not respond to the action in the phase change process controlled by the controller is solved, and the effect of controlling the switching accuracy of the load switch is improved.
4. The specific hardware circuit is adopted to realize detection of the open-close state of the load switch and the scheme of converting the open-close state into corresponding electric signal transmission, so that the problem of load balance failure caused by inaccurate acquisition of the state data of the load switch in the traditional software control phase change process is solved, and the effect of load balance accuracy is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a three-phase load balancing apparatus according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of current and voltage waveforms of each phase of a three-phase load balancing device according to the present invention;
FIG. 3 is a schematic circuit diagram of a three-phase load balancing apparatus according to an embodiment of the present invention;
FIG. 4 is a flow chart of an embodiment of a three-phase load balancing method according to the present invention;
fig. 5 is a specific flowchart of step S300 in fig. 4.
Reference numerals illustrate:
| reference numerals | Name of the name | Reference numerals | Name of the name |
| 100 | Phase detection module | R1 | First resistor |
| 110 | Acquisition module | R2 | Second resistor |
| 120 | Signal conversion unit | R3 | Third resistor |
| 200 | Zero point detection module | R4 | Fourth resistor |
| 300 | Controller for controlling a power supply | R5 | Fifth resistor |
| 400 | Load switch for each phase | C1 | First capacitor |
| U1 | Rectifier bridge | D1 | First diode |
| U2 | Optical coupler | D2 | Second diode |
| U3 | NOT logic |
The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that all directional indicators (such as up, down, left, right, front, and rear … …) in the embodiments of the present invention are merely used to explain the relative positional relationship, movement, etc. between the components in a particular posture (as shown in the drawings), and if the particular posture is changed, the directional indicator is changed accordingly.
Furthermore, the description of "first," "second," etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention.
In order to better understand the above technical solutions, the following detailed description will refer to the accompanying drawings and specific embodiments.
Example 1
Referring to fig. 1, an embodiment of the present application provides a three-phase load balancing apparatus, including:
the phase detection module 100 is used for detecting the opening and closing states of the load switches of the phase of the load to be switched;
the zero detection module 200 is used for detecting the current zero state and the voltage zero state of the same switching load;
the controller 300 is connected to the phase detection module 100, the zero detection module 200, and the load switches of each phase, when the load switch of the phase where the load to be switched is detected by the phase detection module 100 is turned on, the controller 300 controls the load switch of the phase where the load to be switched is turned off in a current zero state, and cuts the load to be switched into a phase switching line in a voltage zero state.
In this embodiment, for a three-phase power grid, three groups of phase detection modules 100 may be provided and connected to each phase of the power grid respectively, and are configured to detect an open/close state of a load switch of each phase of load to be switched, and when detecting that the load switch of the phase where the load to be switched is located is in an open state, it indicates that the load of the phase has been subjected to the balance adjustment of the present wheel, and the present wheel does not perform adjustment on the load of the phase any more; when the same load switch where the load to be switched is detected to be in a closed state, the fact that the same load is not subjected to balance adjustment of the wheel is indicated, and balance adjustment can be performed, namely load commutation balance adjustment can be performed.
In addition, in this embodiment, the load switches on which phase line are turned off.
In the process of carrying out load commutation balance adjustment, the current load to be switched is required to be switched into a switching phase line, in the process, a load switch of the phase where the current load to be switched is required to be disconnected, and then the load to be switched is required to be switched into the switching phase line, so that the balance adjustment of the current phase is completed.
In the load commutation process, from the aspect of alternating current power consumption load, when the load is commutated, we should commutate under the condition that the line load of the phase where the load to be switched is located is at the lowest. Because when the line load is large, the load switch is damaged or even destroyed by disconnecting the same load switch where the load to be switched is located; when the switching phase voltage is high, the load to be switched is suddenly switched on, so that the excessive current at the switching moment is easy to cause damage or destroy to the load switch. Therefore, the disconnection operation of the load switch should be performed at the zero point of the line current, and the damage or even the damage to the load switch caused by the fact that the load switch where the load to be switched is disconnected is located can be avoided because the line load is smaller at the moment; when switching the phase voltage zero point, the load to be switched is switched, and the damage or damage to the load switch caused by the overlarge current at the switching moment is avoided.
By the scheme, the load switch state can be accurately detected in the phase change balance process of the power grid load, and the phase-to-phase short circuit of the power grid load in the phase change process is avoided; and the load switching phase is carried out in the current zero state and the voltage zero state, so that the damage or the damage to a load switch caused by the overlarge current or voltage at the switching-in moment under the conditions of high voltage and high current is avoided, and the safety and the accuracy of load transfer are further ensured.
Specifically, referring to fig. 2, in this embodiment, the time interval between the current zero state and the voltage zero state is less than or equal to the ac single cycle time of the power grid where the three-phase balancing device is located.
The zero point detection of each current and voltage is divided into two aspects, namely rising edge zero point detection and falling edge zero point detection. The current and voltage signals can be sampled in real time through a hardware circuit, the sampled voltage and current are processed by combining auxiliary software (the software can be integrated in the controller 300), a waveform diagram of the current and the voltage is obtained, zero fitting is carried out through the waveform diagram, and the arrival time of the current and voltage zero signals can be accurately predicted in advance. Typically, the load commutation process is completed at two time nodes at which the current zero signal arrives and the next adjacent voltage zero signal arrives. When the load switch is opened and closed, the load switch can be accurately opened when the current is zero, and the load switch is accurately switched into the phase-change load switch when the next adjacent voltage is zero. In China, the frequency of the alternating current of the power grid is generally 50Hz, the single cycle time of the alternating current of the power grid is 20ms, and the total phase change switch action time (comprising the opening time of a load switch of the phase where the load to be switched is and the closing time of the load switch of the phase switching circuit) of one-time load phase change process is required to be completed within 20ms (the single cycle of the alternating current of the power grid).
According to theoretical analysis results, the shortest time of the total commutation switch action time in the one-time load commutation process is 20/6ms, and the longest time is 100/6ms. Two zero points are arranged in the same cross phase in a single period, so that in the switching process of each phase of load switch 400, voltage zero points are required to be obtained rapidly after current zero points, switching and closing work of the load switches can be captured accurately, and phase change balance work of line loads is completed.
Further, referring to fig. 3, in this embodiment, the phase detection module 100 includes a collection unit 110 and a signal conversion unit 120, a detection end of the collection unit 110 is connected to the load to be switched, an output end of the collection unit 110 is connected to an input end of the signal conversion unit 120, and an output end of the signal conversion unit 120 is connected to the controller 300; the collection unit 110 is configured to detect an open/close state of a load switch of the load to be switched, and the signal conversion unit 120 converts the open/close state into a corresponding level signal and transmits the level signal to the controller 300.
In this embodiment, the collection unit 110 of each of the same detection modules 100 is connected with the load switch corresponding to the load to be switched, and the detection end of the collection unit 110 is used to collect the open/close states of the load switches corresponding to the load to be switched. When the collection unit 110 collects that the load switch is in the closed state, the closed state is transmitted to the signal conversion unit 120, and the signal conversion unit 120 converts the closed state into a corresponding level signal and transmits the corresponding level signal to the controller 300, in this embodiment, the signal conversion unit 120 converts the closed state of the load switch into a low level signal and converts the open state of the load switch into a high level signal. When the controller 300 receives the signal transmitted by the signal conversion unit 120 as a low level signal, it determines that the load switch of the phase where the load to be switched is connected to the phase detection module 100 is in a closed state, and then performs a phase-change balanced load operation; when the controller 300 receives the signal transmitted by the signal conversion unit 120 as a high level signal, it determines that the load switch of the phase where the load to be switched is connected to the phase detection module 100 is in an off state, and does not perform the phase change balancing load operation. Of course, the signal conversion unit 120 may also convert the closed state of the load switch detected by the acquisition unit 110 into a high-level signal and convert the open state of the load switch into a low-level signal.
Through the above scheme, the switching state of the load switch acquired by the corresponding detection module 100 is converted into the corresponding level signal and transmitted to the controller 300, so that the problem that the load switch does not respond to the action in the process of controlling the commutation by the controller 300 is solved, and the effect of controlling the switching accuracy of the load switch is improved.
Specifically, the collecting unit 110 includes a rectifier bridge U1, an optocoupler U2, a first resistor R1 and a second resistor R2, where a first input end of the rectifier bridge U1 is used as a collecting end of the collecting unit 110 and is connected with a different Ux where the load to be switched is located, a second input end of the rectifier bridge U1 is connected with an output end Uout of a load switch where the load to be switched is located, a first output end of the rectifier bridge U1 is connected with an anode of a light emitting diode of the optocoupler U2 through the first resistor R1, and a second output end of the rectifier is connected with a cathode of the light emitting diode of the optocoupler U2 through the second resistor R2; the collector of the phototriode of the optocoupler U2 is connected with the input end of the signal conversion unit 120 as the output end of the acquisition unit 110, and the emitter of the phototriode of the optocoupler U2 is grounded.
In this embodiment, the balanced load vector sum of the three-phase alternating currents is 0, and the included angle between any two phases of the three-phase alternating currents is 120 °, i.e. the inter-phase voltage is 380V. When the load switch of the same load to be switched is disconnected, the two input ends of the rectifier bridge U1 are out of phase, and the voltage is 380V alternating current; when the load switch of the same load to be switched is closed, the two input ends of the rectifier bridge U1 are in phase, and the voltage is 0V.
In this embodiment, when the load switch corresponding to the load to be switched is turned on, the voltages of the first input end and the second input end of the rectifier bridge U1 are the same, the phases are the same, the rectified voltage passing through the rectifier bridge U1 is 0, no voltage is output between the first output end and the second output end, the optocoupler U2 is not turned on, and no voltage is output between the collector of the optocoupler U2.
When the load switch of the same load to be switched is turned off, the voltage phases of the first input end and the second input end of the rectifier bridge U1 are different, and any two phases equivalent to three-phase alternating current are respectively connected to the two input ends of the rectifier bridge U1. At this time, the rectified voltage passing through the rectifier bridge U1 is 380V ac, and after rectification, the voltage output exists between the first output end and the second output end, so that the optocoupler U2 is turned on, and the voltage output exists at the collector of the optocoupler U2.
In this embodiment, the first resistor R1 and the second resistor R2 both have current limiting effects, and the resistance value can be selected according to actual requirements.
Further, the collecting unit 110 further includes a first diode D1, an anode of the first diode D1 is connected to a common terminal between the second output terminal of the rectifier and the second resistor R2, and a cathode of the first diode D1 is connected to a common terminal between the first resistor R1 and an anode of the light emitting diode of the optocoupler U2.
The first diode D1 is used for stabilizing voltage and filtering clutter signals, and when the rectifier bridge U1 has voltage output, the first diode D1 can provide stable voltage signals to be loaded at two ends of the light emitting diode of the optocoupler U2.
Further, the signal conversion unit 120 includes a not gate logic unit U3, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a first capacitor C1, where one end of the third resistor R3 is connected to the power supply VCC, the other end of the third resistor R3 is connected to the output end of the acquisition unit 110 and one end of the fourth resistor R4 as the input end of the signal conversion unit 120, the other end of the fourth resistor R4 is connected to the input end of the not gate logic unit U3, the output end of the not gate logic unit U3 is connected to one end of the fifth resistor R5, and the other end of the fifth resistor R5 is connected to the controller 300 as the output end of the signal conversion unit 120; one end of the first capacitor C1 is connected to the power supply VCC, and the other end is connected to the input end of the not gate logic unit U3.
When no voltage signal is output by the acquisition unit 110, that is, when the load switch of the same load to be switched is in the closed state, the power supply VCC loads the input end of the not gate logic unit U3 through the third resistor R3 and the fourth resistor R4, which is equivalent to inputting a high level signal into the input end of the not gate logic unit U3, outputs a low level signal after passing through the not gate logic unit U3, and outputs the low level signal to the controller 300 through the fifth resistor R5. Then, as described above, when the phase detection unit outputs the low level signal to the controller 300, it can be determined that the phase load switch where the load to be detected is located is in the closed state. In this embodiment, the third resistor R3 and the fourth resistor R4 perform a current limiting function to prevent the input of excessive current to the input terminal of the not gate logic unit U3 from damaging the not gate logic unit U3.
When the voltage signal is output by the acquisition unit 110, that is, when the load switch of the same load to be switched is in the off state, the phototransistor of the optocoupler U2 is in the on state, the collector of the phototransistor is pulled down to a relatively low level signal through the emitter, the signal is shaped and filtered by the RC circuit formed by the first capacitor C1 and the fourth resistor R4 and then becomes a low level to be loaded to the input end of the not gate logic unit U3, and after passing through the not gate logic unit U3, a high level signal is output and is output to the controller 300 through the fifth resistor R5. Then, as described above, when the phase detection unit outputs the high level signal to the controller 300, it can be determined that the phase load switch where the load to be detected is located is in the off state.
In the present embodiment, the fifth resistor R5 acts as a current limiting function.
Further, the signal conversion unit 120 further includes a second diode D2, where an anode of the second diode D2 is connected to the input terminal of the not gate logic unit U3, and a cathode of the second diode D2 is connected to a common terminal between the third resistor R3 and the fourth resistor R4.
The second diode D2 also has the functions of stabilizing voltage and filtering clutter signals, and a stable voltage signal can be provided to be loaded on the input end of the not gate logic element U3 through the second diode D2.
Based on the same inventive concept, the embodiment of the invention also provides a balancing method corresponding to the balancing device in the first embodiment, which is shown in the second embodiment.
Example two
Referring to fig. 4, the present embodiment provides a three-phase load balancing method, including the steps of:
step S100: receiving a commutation instruction;
step S200: detecting the opening and closing states of the load switches with the same load to be switched;
step S300: and when the load switch of the same load to be switched is in a closed state, controlling the load to be switched to cut into a switching phase line.
The method of this embodiment is based on the balancing device of the first embodiment, and the principle of the device of the first embodiment is described, for a three-phase power grid, when load balancing is required, the three-phase load balancing device will receive a phase change instruction, first, a phase detection module 100 will be started to detect the open/close state of a load switch, three groups of phase detection modules 100 may be set, and are respectively connected to each phase of the power grid, to detect the open/close state of the load switch of each phase to be switched, when detecting that the load switch of the phase to be switched is in the open state, it is described that the load switch of the phase has been subjected to the balance adjustment of the current wheel, and the current wheel will not adjust the load of the phase; when the same load switch where the load to be switched is detected to be in a closed state, the fact that the same load is not subjected to balance adjustment of the wheel is indicated, and balance adjustment can be performed, namely load commutation balance adjustment can be performed.
In addition, in this embodiment, the load switches on which phase line are turned off.
In the process of carrying out load commutation balance adjustment, the current load to be switched is required to be switched into a switching phase line, in the process, a load switch of the phase where the current load to be switched is required to be disconnected, and then the load to be switched is required to be switched into the switching phase line, so that the balance adjustment of the current phase is completed.
Through the scheme, the load switch state of the power grid can be accurately detected in the phase change balance process, the inter-phase short circuit of the load of the power grid in the phase change process is avoided, and the safety and the accuracy of load transfer are ensured.
Further, referring to fig. 5, in step S300, the step of controlling the load to be switched to switch into the switching phase line specifically includes:
step S310: detecting the current zero state and the voltage zero state of the same load to be switched;
step S320: when the load to be switched is in a current zero state, controlling a load switch of the same load to be switched to be disconnected;
step S330: and controlling the load to be switched into the switching phase line in the next adjacent voltage zero state.
In the load commutation process, from the aspect of alternating current power consumption load, when the load is commutated, we should commutate under the condition that the line load of the phase where the load to be switched is located is at the lowest. Because when the line load is large, the load switch is damaged or even destroyed by disconnecting the same load switch where the load to be switched is located; when the switching phase voltage is high, the load to be switched is suddenly switched on, so that the excessive current at the switching moment is easy to cause damage or destroy to the load switch. Therefore, the disconnection operation of the load switch should be performed at the zero point of the line current, and the damage or even the damage to the load switch caused by the fact that the load switch where the load to be switched is disconnected is located can be avoided because the line load is smaller at the moment; when switching the phase voltage zero point, the load to be switched is switched, and the damage or damage to the load switch caused by the overlarge current at the switching moment is avoided.
The load switching phases are carried out in the current zero state and the voltage zero state, so that the damage or the damage to the load switch caused by the overlarge current or voltage at the moment of cutting-in under the conditions of high voltage and high current is avoided, and the safety and the accuracy of load transfer are further ensured.
Further, the time interval between the current zero state and the next adjacent voltage zero state is smaller than or equal to the alternating current single cycle time of the power grid where the three-phase balancing device is located.
The zero point detection of each current and voltage is divided into two aspects, namely rising edge zero point detection and falling edge zero point detection. The current and voltage signals can be sampled in real time through a hardware circuit, the sampled voltage and current are processed by combining auxiliary software (the software can be integrated in the controller 300), a waveform diagram of the current and the voltage is obtained, zero fitting is carried out through the waveform diagram, and the arrival time of the current and voltage zero signals can be accurately predicted in advance. Typically, the load commutation process is completed at two time nodes at which the current zero signal arrives and the next adjacent voltage zero signal arrives. When the load switch is opened and closed, the load switch can be accurately opened when the current is zero, and the load switch is accurately switched into the phase-change load switch when the next adjacent voltage is zero. In China, the frequency of the alternating current of the power grid is generally 50Hz, the single cycle time of the alternating current of the power grid is 20ms, and the total phase change switch action time (comprising the opening time of a load switch of the phase where the load to be switched is and the closing time of the load switch of the phase switching circuit) of one-time load phase change process is required to be completed within 20ms (the single cycle of the alternating current of the power grid).
According to theoretical analysis results, the shortest time of the total commutation switch action time in the one-time load commutation process is 20/6ms, and the longest time is 100/6ms. Two zero points are arranged in the same cross phase in a single period, so that in the switching process of each phase of load switch 400, voltage zero points are required to be obtained rapidly after current zero points, switching and closing work of the load switches can be captured accurately, and phase change balance work of line loads is completed.
The foregoing description is only of the preferred embodiments of the present invention and is not intended to limit the scope of the invention, and all equivalent structural changes made by the description of the present invention and the accompanying drawings or direct/indirect application in other related technical fields are included in the scope of the invention.
Claims (7)
1. A three-phase load balancing apparatus, comprising:
the phase detection module is used for detecting the opening and closing states of the phase load switches where the load to be switched is located, three groups of phase detection modules are arranged and are respectively connected to each phase of the power grid, when the phase load switches where the load to be switched is detected to be in the opening state, the phase load is subjected to the balance adjustment of the wheel, and the wheel does not adjust the phase load any more; when the same load switch where the load to be switched is detected to be in a closed state, the balance adjustment of the load is not performed, and the balance adjustment can be performed, namely the load commutation balance adjustment can be performed;
the zero detection module is used for detecting the current zero state and the voltage zero state of the same switching load;
the controller is connected with the phase detection module, the zero point detection module and the load switches of each phase, and when the load switch of the phase where the load to be switched is detected by the phase detection module is closed, the controller controls the load switch of the phase where the load to be switched is disconnected in a current zero point state and cuts the load to be switched into a phase switching line in a voltage zero point state;
the controller is further configured to control the load switch to be turned off in the current zero state when the phase detection module detects that the load switch is turned on, and switch the load to be switched into the switching phase line in a next adjacent voltage zero state of the current zero state;
the phase detection module comprises a collection unit and a signal conversion unit, wherein the detection end of the collection unit is connected with the load to be switched, the output end of the collection unit is connected with the input end of the signal conversion unit, and the output end of the signal conversion unit is connected with the controller; the acquisition unit is used for detecting the opening and closing states of the load switches with the same load to be switched, and the signal conversion unit converts the opening and closing states into corresponding level signals and transmits the corresponding level signals to the controller;
the signal conversion unit comprises a NOT logic piece, a third resistor, a fourth resistor, a fifth resistor and a first capacitor, one end of the third resistor is connected with a power supply, the other end of the third resistor is used as an input end of the signal conversion unit to be connected with an output end of the acquisition unit and one end of the fourth resistor, the other end of the fourth resistor is connected with an input end of the NOT logic piece, an output end of the NOT logic piece is connected with one end of the fifth resistor, and the other end of the fifth resistor is used as an output end of the signal conversion unit to be connected with the controller; one end of the first capacitor is connected with the power supply, and the other end of the first capacitor is connected with the input end of the NOT logic piece.
2. The three-phase load balancing device of claim 1, wherein a time interval between the current zero state and the voltage zero state is less than or equal to a single cycle time of an alternating current of a power grid in which the three-phase balancing device is located.
3. The three-phase load balancing device according to claim 1, wherein the acquisition unit comprises a rectifier bridge, an optocoupler, a first resistor and a second resistor, the first input end of the rectifier bridge is used as the acquisition end of the acquisition unit and is respectively connected with the load to be switched, the second input end of the rectifier bridge is connected with the output end of a load switch which is respectively connected with the load to be switched, the first output end of the rectifier bridge is connected with the anode of the light emitting diode of the optocoupler through the first resistor, and the second output end of the rectifier is connected with the cathode of the light emitting diode of the optocoupler through the second resistor; and the collector electrode of the phototriode of the optical coupler is used as the output end of the acquisition unit to be connected with the input end of the signal conversion unit, and the emitter electrode of the phototriode of the optical coupler is grounded.
4. The three-phase load balancing device according to claim 3, wherein the collecting unit further comprises a first diode, an anode of the first diode is connected to a common terminal between the second output terminal of the rectifier and the second resistor, and a cathode of the first diode is connected to a common terminal between the first resistor and an anode of the light emitting diode of the optocoupler.
5. The three-phase load balancing apparatus according to claim 1, wherein the signal converting unit further comprises a second diode, an anode of the second diode is connected to an input terminal of the not gate logic, and a cathode of the second diode is connected to a common terminal between the third resistor and the fourth resistor.
6. A method of three-phase load balancing comprising the steps of:
receiving a commutation instruction;
detecting the opening and closing states of the same load switch of the load to be switched, and when the same load switch of the load to be switched is in an opening state, performing balance adjustment on the same load, and not adjusting the same load on the same wheel; when the same load switch where the load to be switched is detected to be in a closed state, the balance adjustment of the load is not performed, and the balance adjustment can be performed, namely the load commutation balance adjustment can be performed;
when the load switch of the same load to be switched is in a closed state, controlling the load to be switched to cut into a switching phase line;
the step of controlling the load to be switched into the switching phase line specifically comprises the following steps:
detecting the current zero state and the voltage zero state of the same load to be switched;
when the load to be switched is in a current zero state, controlling a load switch of the same load to be switched to be disconnected;
and controlling the load to be switched into the switching phase line in the next adjacent voltage zero state.
7. The method of three-phase load balancing according to claim 6, wherein a time interval between the current zero state and a next adjacent voltage zero state is less than or equal to a single cycle time of alternating current of a power grid in which the three-phase balancing apparatus is located.
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