Power switching system

Abstract

A power switching system, comprising a first power source and a second power source each having three-phase AC power. The power switching system comprises a first power switch group, a second power switch group, and a three-phase transformer. The three-phase transformer comprises a first winding, a second winding, and a third winding, the first winding, the second winding, and the third winding being connected in a delta configuration to form three common connection points. The first common connection point is connected to a first switch and a fourth switch, the second common connection point is connected to a second switch and a fifth switch, and the third common connection point is connected to a third switch and a sixth switch.

Description

Power switching system TECHNICAL FIELD

[0001] The present invention relates to a power switching system, and more particularly to a power switching system capable of providing a forced commutation procedure. BACKGROUND

[0002] Static transfer switch (STS) is an essential component in the configuration of data center power system, which provides uninterrupted power supply for loads such as critical equipment, and usually includes multiple silicon controlled rectifiers (SCRs) inside. STS is usually powered by two or more independent power sources, and one set of STS corresponds to one independent power source. Once the preferred primary power source exceeds the acceptable range, the power switching from the preferred primary power source to the backup power source is automatically performed to provide uninterrupted power supply for the critical equipment, so as to avoid the forced shutdown of the critical equipment due to the interruption of power supply.

[0003] Generally, the outputs of multiple sets of STSs are connected in common and then connected to the critical equipment through a transformer. Since the transformer is an inductive device, when the magnetic flux accumulated therein is too high, the problem of magnetic saturation occurs. Therefore, if the preferred primary power source exceeds the acceptable range and improper switching between the two power sources occurs, for example, the voltage discontinuity of the transformer is caused, the magnetic flux offset is generated, and high inrush current is caused in the downstream transformer. When the inrush current is too high, the upstream circuit is overloaded or the circuit breaker is tripped, resulting in power failure of the entire system or damage to the STS. Therefore, the current power switching method is as follows: after the current flowing through the SCRs of the primary power source is reduced to zero, the SCRs of the backup power source are turned on after a suitable time is waited, so as to avoid the high inrush current. However, this switching method needs to wait for the current to be reduced to zero and additionally wait for a suitable time for switching, resulting in too long waiting time and too low output voltage, which still has the risk of causing the forced shutdown of the critical equipment.

[0004] Therefore, how to design a power switching system and the forced commutation procedure provided thereby to solve the problems and technical bottlenecks in the prior art is an important subject of the present invention.

[0005] SUMMARY

[0006] The present application provides a power switching system with a first power source and a second power source. The power switching system includes a first power switching group, a second power switching group and a three-phase transformer. The first power switching group includes a first switch, a second switch and a third switch, which are connected to a first phase, a second phase and a third phase of the first power source in sequence. The second power switching group includes a fourth switch, a fifth switch and a sixth switch, which are connected to a first phase, a second phase and a third phase of the second power source in sequence. The three-phase transformer includes a first winding, a second winding and a third winding, which form three common nodes in a delta connection. The first common node is connected to the first switch and the fourth switch, the second common node is connected to the second switch and the fifth switch, and the third common node is connected to the third switch and the sixth switch. The power switching system provides a forced commutation procedure, which includes detecting the magnetic flux of the first winding, the second winding and the third winding, and selecting the winding with the fastest magnetic flux switching as the fastest magnetic flux switching winding; turning on two switches connected to the fastest magnetic flux switching winding, and then turning on two switches connected to the fastest magnetic flux switching winding; and turning on the remaining two switches of the first switch, the second switch and the third switch, and then turning on the remaining two switches of the fourth switch, the fifth switch and the sixth switch.

[0007] The present application provides a power switching system with a first power source and a second power source. The power switching system includes a first power switching group, a second power switching group and a three-phase transformer. The first power switching group includes a first switch, a second switch and a third switch, which are connected to a first phase, a second phase and a third phase of the first power source in sequence. The second power switching group includes a fourth switch, a fifth switch and a sixth switch, which are connected to a first phase, a second phase and a third phase of the second power source in sequence. The three-phase transformer includes a first winding, a second winding and a third winding, which form one common node and three nodes in a star connection, and the common node is grounded. The first node is connected to the first switch and the fourth switch, the second node is connected to the second switch and the fifth switch, and the third node is connected to the third switch and the sixth switch. The power switching system provides a forced commutation procedure, which includes detecting the magnetic flux of the first winding, the second winding and the third winding, and selecting the winding with the fastest magnetic flux switching as the fastest magnetic flux switching winding; turning on one switch connected to the fastest magnetic flux switching winding, and then turning on one switch connected to the fastest magnetic flux switching winding; and turning on the remaining two switches of the first switch, the second switch and the third switch, and then turning on the remaining two switches of the fourth switch, the fifth switch and the sixth switch.

[0008] For further understanding of the technical means, methods and effects taken by the present application to achieve the predetermined purposes, please refer to the following detailed description of the present application and the attached drawings. It is believed that the purposes, features and characteristics of the present application can be deeply and specifically understood from the above description, however, the attached drawings are provided for reference and illustration only, and are not used to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 is a circuit block diagram of the power switching system of the present application;

[0010] Fig. 2 is a waveform diagram of the main power supply, the backup power supply and the output power supply of the present application;

[0011] Fig. 3 is a schematic diagram of the forced commutation of the power switching system of the present application;

[0012] Fig. 4 is a flow chart of the forced commutation method of the power switching system of the present application;

[0013] Fig. 5 is a waveform diagram of the voltage and the magnetic flux of the forced commutation of the power switching system of the present application;

[0014] Fig. 6 is a circuit block diagram of the three-phase three-wire power switching system of the present application;

[0015] Fig. 7 is a circuit block diagram of the three-phase four-wire power switching system of the present application;

[0016] Fig. 8 is a flow chart of the forced commutation method of the three-phase three-wire power switching system of the present application;

[0017] Fig. 9 is a flow chart of the forced commutation method of the three-phase four-wire power switching system of the present application.

[0018] 100: power switching system 110: first power supply 111: second power supply 130: first static transfer switch 131: second static transfer switch 130a: first thyristor 130b: second thyristor 131a: third thyristor 131b: fourth thyristor 122: first voltage sensor 123: second voltage sensor 124: third voltage sensor 132: first current sensor 133: second current sensor 134: controller 120: inductive device 120A: primary side winding 120B: secondary side winding 121: load V1: first voltage signal V2: second voltage signal Vo: third voltage signal I1: first current signal I2: second current signal Sc1: first control signal Sc2: second control signal Sc3: third control signal Sc4: fourth control signal f1: first magnetic flux f2: second magnetic flux fo: third magnetic flux S-pri: main power supply, first power supply S-alt: backup power supply, second power supply ipri, ialt: current Vpri, Valt: voltage Vload: load voltage T1P, T1N, T2P, T2N: thyristor ΔVpri: voltage difference Vthz: voltage threshold 31: first power supply switch group 32: second power supply switch group 311: first switch 312: second switch 313: third switch 321: fourth switch 322: fifth switch 323: sixth switch 33: three-phase transformer W12: first winding W23: second winding W31: third winding N1: first common connection point N2: second common connection point N3: third common connection point 41: first power supply switch group 42: second power supply switch group 411: first switch 412: second switch 413: third switch 421: fourth switch 422: fifth switch 423: sixth switch 43: three-phase transformer W11: first winding W22: second winding W33: third winding GND: ground S101-S108: steps S201-S203: steps S301-S303: steps DETAILED DESCRIPTION

[0019] The technical content and detailed description of the present application are described below with reference to the accompanying drawings.

[0020] Referring to FIG. 1, a circuit block diagram of a power switching system according to the present application is shown. The power switching system 100 is used to supply power to a load 121, such as a critical device, and includes static transfer switch devices 130, 131, an inductive device 120, and a controller 134. The static transfer switch devices 130, 131 include a first static transfer switch 130 and a second static transfer switch 131. The load 121 can be, for example, but is not limited to, a critical load such as a server, a communication system, or the like that requires uninterrupted and continuous operation, without limitation.

[0021] The first static transfer switch 130 has an input side coupled to a first power source 110, and the second static transfer switch 131 has an input side coupled to a second power source 111. The output side of the first static transfer switch 130 and the output side of the second static transfer switch 131 are coupled to a common node. The inductive device 120 can be, for example, but is not limited to, a transformer that includes a primary winding 120A and a secondary winding 120B. The primary winding 120A is coupled to the first static transfer switch 130 and the second static transfer switch 131 at the common node, and the secondary winding 120B is coupled to the load 121.

[0022] The controller 134 is used to detect the power from the first power source 110 and the second power source 111 to collect power information from the first power source 110 and the second power source 111 in real time. The controller 134 also detects the output power received by the inductive device 120 from the first static transfer switch 130 or the second static transfer switch 131 to adjust and control the first static transfer switch 130 and the second static transfer switch 131. The controller 134 selects the first power source 110 or the second power source 111 to supply power to the load 121 coupled to the inductive device 120 by controlling the first static transfer switch 130 and the second static transfer switch 131. In one embodiment, the controller 134 can be a digital signal processor (DSP), but is not limited thereto. Any entity that can use a signal to control a circuit, a control device including control software, or the like should be included in the scope of the present embodiment.

[0023] Specifically, the power switching system 100 further comprises voltage sensors 122, 123, 124 and current sensors 132, 133. The voltage sensors 122, 123, 124 include a first voltage sensor 122, a second voltage sensor 123 and a third voltage sensor 124. The first voltage sensor 122 and the second voltage sensor 123 are coupled to the first power source 110 and the second power source 111, respectively, to detect a first voltage signal VI and a second voltage signal V2 corresponding to the first power source 110 and the second power source 111, respectively. The current sensors 132, 133 include a first current sensor 132 and a second current sensor 133, which are coupled to the first power source 110 and the second power source 111, respectively, to detect a first current signal II and a second current signal I2 corresponding to the first power source 110 and the second power source 111, respectively, to obtain power from the first power source 110 and the second power source 111. In addition, the third voltage sensor 124 is coupled to the primary winding 120A (as shown in Fig. 1) or the secondary winding 120B (not shown, but should be included in the scope of the present embodiment) of the inductive device 120 to detect a third voltage signal Vo corresponding to the primary winding 120A or the secondary winding 120B. Thus, the voltage signals and the current signals detected by the voltage sensors 122, 123, 124 and the current sensors 132, 133 are transmitted to the controller 134 as the basis for the control of the controller 134.

[0024] Referring to Fig. 2, which is a waveform diagram of the main power source, the backup power source and the output power source of the present application. The voltage waveforms of the first power source 110 and the second power source 111 have a phase difference, but this is only for illustration, and the two are not related to each other, that is, the switching control method of the present application is mainly aimed at controlling the magnetic flux, regardless of the size of the phase difference. The controller 134 obtains the first voltage signal VI, the second voltage signal V2 and the third voltage signal Vo, and integrates the first voltage signal VI, the second voltage signal V2 and the third voltage signal Vo to obtain the magnetic fluxes fl, f2 corresponding to the first power source 110, the second power source 111 and the magnetic flux fo on the inductive device 120, which is the expected magnetic flux. Among them, the first magnetic flux fl is the integral of the first voltage signal VI, and the second magnetic flux f2 is the integral of the second voltage signal V2. The third magnetic flux fo is the integral of the third voltage signal Vo. It is worth mentioning that because the first static transfer switch 130 is turned on, the first power source 110 is connected to the inductive device 120 and the first power source 110, so the first magnetic flux fl is consistent with the third magnetic flux fo. Among them, since the integral of the voltage is the magnetic flux, and the integral of the sine wave is still a sine wave, the first, second and third magnetic fluxes fl, f2 and fo are still sine waveforms.

[0025] Referring to FIG. 1, the first static transfer switch 130 and the second static transfer switch 131 each include a plurality of silicon controlled rectifiers (SCRs), wherein the first static transfer switch 130 includes a first SCR 130a and a second SCR 130b, which are respectively the active SCRs for positive and negative half cycles, and are connected in anti-parallel to each other, for example, the anode of the first SCR 130a is connected to the cathode of the second SCR 130b, and the cathode of the first SCR 130a is connected to the anode of the second SCR 130b. The second static transfer switch 131 includes a third SCR 131a and a fourth SCR 131b, which are respectively the active SCRs for positive and negative half cycles, and are connected in anti-parallel to each other, for example, the anode of the third SCR 131a is connected to the cathode of the fourth SCR 131b, and the cathode of the third SCR 131a is connected to the anode of the fourth SCR 131b. Preferably, the SCRs 130a-131b are silicon controlled rectifiers, but are not limited thereto.

[0026] Further, the controller 134 generates a plurality of independent control signals Sc1-Sc4 to control the first SCR 130a to the fourth SCR 131b, respectively. Specifically, the first control signal Sc1 controls the gate of the first SCR 130a, the second control signal Sc2 controls the gate of the second SCR 130b, the third control signal Sc3 controls the gate of the third SCR 131a, and the fourth control signal Sc4 controls the gate of the fourth SCR 131b. In addition, the anode / cathode of the first SCR 130a and the third SCR 131a are arranged in the same direction, and the anode / cathode of the second SCR 130b and the fourth SCR 131b are arranged in the same direction. Therefore, the first SCR 130a and the fourth SCR 131b have the same conduction direction, and the second SCR 130b and the third SCR 131a have the same conduction direction.

[0027] Since the SCRs 130a-131b cannot be turned off by the controller 134 when current flows through the SCRs 130a-131b, the SCRs 130a-131b can only be turned off when the current naturally commutates to zero or when the anode current is removed by a forced commutation technique.

[0028] Specifically, the controller 134 of the present application selectively controls the first thyristor 130a, the second thyristor 130b, the third thyristor 131a and the fourth thyristor 131b according to the power supply source being the first power supply 110 or the second power supply 111. In this regard, the controller 134 is configured to continuously and instantaneously calculate the first magnetic flux f1, the second magnetic flux f2 and the third magnetic flux fo in the first power supply 110, the second power supply 111 and the inductive device 120 (e.g. a transformer or other inductive element) respectively. If a power supply failure event occurs (e.g. an abnormality occurs in the first power supply 110), the controller 134 provides the first control signal Sc1 and the second control signal Sc2 to turn off the first thyristor 130a and the second thyristor 130b in the working path of the first power supply 110 respectively.

[0029] The controller 134 then provides the third control signal Sc3 and the fourth control signal Sc4 to turn on the third thyristor 131a and the fourth thyristor 131b in the standby path (i.e. the second power supply 111) according to the magnetic flux calculated from the first voltage signal V1, the second voltage signal V2 and the third voltage signal Vo detected at the moment and in accordance with the specific operation mode designed in the present application, so as to avoid the improper switching between the two power supplies to cause high inrush current in the downstream inductive device 120 and at the same time avoid the output power dropping to a too low level due to the waiting of the silicon controlled rectifier freewheeling to zero, which is insufficient to maintain the stable operation of the load 121. In this regard, in accordance with the specific operation mode designed in the present application, the third control signal Sc3 and the fourth control signal Sc4 can be provided in segments to turn on the third thyristor 131a and the fourth thyristor 131b respectively, i.e. only one of the third thyristor 131a and the fourth thyristor 131b is turned on at a certain period of commutation.

[0030] In another aspect, the controller 134 can detect the first current (i.e., the corresponding first current signal I1) flowing through the first static transfer switch 130 via the first current sensor 132 to determine whether the first static transfer switch 130 is turned on or turned off. That is, the controller 134 can confirm whether the first static transfer switch 130 is properly turned on or turned off via the first current (i.e., the corresponding first current signal I1) to confirm whether the entire power switching system 100 is operating normally. In another aspect, the controller 134 can easily determine whether the first thyristor 130a and the second thyristor 130b are properly turned on or turned off by detecting the cross voltage (via the first voltage signal V1 and the third voltage signal Vo) across the two terminals of the first thyristor 130a and the second thyristor 130b. Similarly, the controller 134 can detect the second current (i.e., the corresponding second current signal I2) flowing through the second static transfer switch 131 via the second current sensor 133 to determine whether the second static transfer switch 131 is turned on or turned off. That is, the controller 134 can confirm whether the second static transfer switch 131 is properly turned on or turned off via the second current (i.e., the corresponding second current signal I2) to confirm whether the entire power switching system 100 is operating normally. In another aspect, the controller 134 can easily determine whether the third thyristor 131a and the fourth thyristor 131b are properly turned on or turned off by detecting the cross voltage (via the second voltage signal V2 and the third voltage signal Vo) across the two terminals of the third thyristor 131a and the fourth thyristor 131b.

[0031] Referring to FIG. 3, a schematic diagram of the forced commutation of the power switching system of the present application is shown. To avoid the simultaneous power supply of the two power sources S-pri, S-alt or the short circuit between the two power sources, the controller 134 provides a forced commutation mechanism. Unlike the prior art natural commutation method, the present application provides a control method with forced commutation. Referring to FIG. 4, a flowchart of the method of the forced commutation of the power switching system of the present application is shown. The permission of the forced commutation mechanism, i.e., the opportunity of forced commutation, can be compared to a ticket. When the abnormal event occurs in the primary power source S-pri, the controller 134 first turns off all the thyristors connected to the primary power source S-pri, i.e., turns off the thyristors T1P, T1N by controlling the gate (step S101). As described above, due to the characteristics of the thyristors, the turned-off thyristors T1P, T1N can not be completely turned off by the gate control.

[0032] Then, the controller 134 judges whether the current ipri of the detected main power source S-pri is greater than zero (step S102). If the current ipri is greater than zero, it indicates that there is a thyristor T1P that has not been completely turned off. At this time, the thyristor T1P is in a conducting state. Next, the controller 134 judges whether the voltage Valt of the alternate power source S-alt is greater than the load voltage Vload (step S103). If the voltage Valt is greater than the load voltage Vload, the controller 134 turns on the thyristor T2P so that the voltage Valt reverse excites the thyristor T1P, turns off the still-conducting thyristor T1P (positive switch) with a reverse voltage, which is a permission for forced commutation of the conducting positive switch, i.e., a FC ticket-Pos is obtained (step S104).

[0033] On the contrary, in the judgment of step S102, if the current ipri of the main power source S-pri is less than zero, it indicates that there is a thyristor T1N that has not been completely turned off. At this time, the thyristor T1N is in a conducting state. Next, the controller 134 judges whether the voltage Valt of the alternate power source S-alt is less than the load voltage Vload (step S105). If the voltage Valt is less than the load voltage Vload, the still-conducting thyristor T1N (negative switch) can be forced to turn off by turning on the thyristor T2N, which is a permission for forced commutation of the conducting negative switch, i.e., a FC ticket-Neg is obtained (step S106).

[0034] Incidentally, when the FC ticket-Pos for forced commutation of the conducting positive switch is obtained (may be obtained once or multiple times), or when the FC ticket-Neg for forced commutation of the conducting negative switch is obtained (may be obtained once or multiple times), it is not necessarily required to immediately perform the forced commutation, because the effect of the present forced commutation is not necessarily ideal, because the magnetic flux shift can be too large due to the introduction of the forced commutation. Preferably, the time point of the introduction of the forced commutation can be determined according to the magnetic flux switching speed, the magnetic flux size, etc., which will be described later.

[0035] Further, if forced commutation is not introduced because of consideration of the magnetic flux switching speed, the magnetic flux size, etc. (even if the condition for forced commutation of the conducting positive switch and / or the condition for forced commutation of the conducting negative switch is satisfied), at this time, since the thyristor that was originally conducting is naturally commutated to zero, it is turned off for natural commutation. Therefore, there is a voltage difference ΔVpri between the voltage Valt and the load voltage Vload. Therefore, the controller 134 determines whether the voltage difference ΔVpri is greater than a voltage threshold value Vthz (step S107). If the voltage difference ΔVpri is greater than the voltage threshold value Vthz, it indicates that the thyristors connected to the primary power supply S-pri, i.e., both the thyristors T1P and T1N have been turned off. Therefore, a ticket (FC ticket-NoCare) for turning on the off positive switch or the off negative switch is obtained (step S108). In this case, regardless of which thyristor is conducting, an abnormality in which a short circuit occurs between the primary power supply S-pri and the alternate power supply S-alt does not occur.

[0036] Hereinafter, the determination of the timing of introduction of forced commutation, i.e., the determination of the timing of using the forced commutation ticket will be described. Referring to FIG. 5, which is a schematic view of the waveforms of the voltage and the magnetic flux of the forced commutation of the power supply switching system of the present application, since the load voltage Load voltage is in the form of a sine wave (as shown in the upper waveform of FIG. 5), the magnetic flux is also in the form of a sine wave:

[0037] Since the magnetic flux is a fixed sine wave, the excitation amount generated by the magnetic flux within the period of the sine wave is predictable, i.e., the integral of the voltage can be obtained (as shown in the middle waveform of FIG. 5).

[0038] Since the excitation amount generated by the magnetic flux is predictable, as long as the excitation size of the voltage during the period when the thyristor is not conducting is calculated, it can be deduced how much excitation amount of the magnetic flux can be obtained when the thyristor is conducting. Therefore, by using this method, the timing of introduction of forced commutation can be determined according to the size of the load voltage at the present time and according to the size of the excitation amount of the magnetic flux that can be deduced.

[0039] On the contrary, when the size of the accumulated excitation amount obtained after the switch is conducting can exceed the saturation magnetic flux, the forced commutation of the thyristor can be waited for introduction temporarily until the size of the accumulated excitation amount obtained does not exceed the saturation magnetic flux, and then the forced commutation of the thyristor is introduced.

[0040] In particular, the polarity of the flux offset is further considered in relation to the polarity of the voltage. In one case, when the polarity of the flux offset is the same as the polarity of the voltage, for example, when the voltage is in the positive half cycle and the flux is positive, the forced commutation of the thyristor can be selected at the right time. In other words, when the accumulated excitation is too large, then it can wait; otherwise, when the accumulated excitation is not too large, the forced commutation of the thyristor can be introduced so that the condition of flux saturation does not occur.

[0041] In another case, when the polarity of the flux offset is not the same as the polarity of the voltage, for example, when the power supply fails in the negative half cycle, thus generating the excitation in the negative half cycle, and the demagnetization can be provided in the positive half cycle, the condition of flux saturation is less likely to occur. In the case of demagnetization, the forced commutation of the thyristor can be introduced as early as possible, which is the preferred way. Therefore, as long as the controller 134 determines that the polarity of the flux offset is not the same as the polarity of the voltage and does not lead to flux saturation, the forced commutation of the thyristor can be introduced immediately. The above-mentioned content can be achieved by the following relationship. Load_past + = v Load • T calc … (Equation 2) φ future = φ max - φ altLoad _ past or - φ max - φ altLoad + past … (Equation 3) k flux = sgn (φ LoadReal • φ future ) … (Equation 4)

[0042] Wherein, the accumulated flux offset of the load can be calculated according to Equation 2; the future flux can be calculated according to Equation 3, and the maximum flux and the minimum flux in the future are obtained (as shown in the lower waveform of Figure 5) to determine whether the saturation flux is exceeded; the polarity of the future flux and the present flux can be determined according to Equation 4. As mentioned above, if the polarities are the same, the forced commutation of the thyristor needs to be introduced at the right time; otherwise, if the polarities are different, the forced commutation of the thyristor can be introduced under more relaxed conditions.

[0043] As for how the flux, the voltage and the forced commutation of the thyristor are applied in the three-phase power supply system, more specific thyristor control will be described later. Please refer to Figure 6, which is a circuit block diagram of the three-phase three-wire power supply switching system of the present application. In Figure 6, two power supplies, including the main power supply S-pri and the standby power supply S-alt, are connected to the downstream three-phase transformer 33 through the respective three-phase static transfer switch devices 31, 32.

[0044] As shown in FIG. 6, the three-phase power switching system includes a first power source S-pri and a second power source S-alt with three-phase alternating current power. The power switching system includes a first power source switch group 31 and a second power source switch group 32. The first power source switch group 31 includes a first switch 311, a second switch 312, and a third switch 313, which are electrically connected to a first phase sequence (R phase), a second phase sequence (S phase), and a third phase sequence (T phase) of the first power source S-pri in sequence. The second power source switch group 32 includes a fourth switch 321, a fifth switch 322, and a sixth switch 323, which are electrically connected to a first phase sequence (R phase), a second phase sequence (S phase), and a third phase sequence (T phase) of the second power source S-alt in sequence.

[0045] The three-phase transformer 33 includes a first winding W12, a second winding W23, and a third winding W31. The first winding W12, the second winding W23, and the third winding W31 of the three-phase transformer 33 form three common nodes N1, N2, N3 in a delta connection (Δ connection), in which the first common node N1 connects the first switch 311 and the fourth switch 321, the second common node N2 connects the second switch 312 and the fifth switch 322, and the third common node N3 connects the third switch 313 and the sixth switch 323.

[0046] By the way, for a three-phase three-wire system, there are two common problems: one is overexcitation, and the other is ineffective excitation.

[0047] As for the overexcitation problem, since part of the windings of the three-phase transformer 33 are powered by the main power source S-pri, and the other part of the windings are powered by the backup power source S-alt, for a certain winding, it may be powered by the main power source S-pri and the backup power source S-alt at the same time. At this time, if the phase difference between the main power source S-pri and the backup power source S-alt is floating, the worst case is that the winding may bear twice the rated voltage, thus causing the insulation of the three-phase transformer 33 to be damaged or the three-phase transformer 33 to be saturated and generate inrush current.

[0048] As for the ineffective excitation problem, when the forced commutation time is determined by the magnetic flux calculation disclosed above, and the forced commutation is introduced, if only one thyristor is turned on, there will be no current path to flow back, so the thyristor conduction is ineffective, and has no effect on the excitation and demagnetization of the three-phase transformer 33.

[0049] Therefore, to avoid the overexcitation and invalid excitation problems, the application designs a technical solution that can effectively achieve the successful switching of two power sources. When the main power source S-pri has an abnormal event, first, all the thyristor signals connected to the main power source S-pri are turned off through the control gate. Then, the permission (ticket) for forced commutation is selected to turn on two-phase thyristors at the same time to avoid invalid excitation. Then, wait for half a cycle, for example, when it is a positive half cycle, then turn on the remaining two-phase thyristors in the negative half cycle of the next half cycle to complete the turn-on of the four thyristors of the two phases.

[0050] The turn-on time of the last-phase thyristor is determined according to whether the future magnetic flux obtained after calculation will cause magnetic flux saturation. If magnetic flux saturation occurs, wait for the turn-on time. If magnetic flux saturation does not occur, sequentially complete the turn-on of the remaining two thyristors of the phase.

[0051] For a three-phase three-wire power switching system, a better forced commutation procedure is provided, as shown in FIG. 8, and as shown in FIG. 6. The procedure includes: first, detecting the magnetic flux speed of the first winding W12, the second winding W23, and the third winding W31 of the three-phase transformer 33, and selecting the winding with the fastest magnetic flux switching as a fastest magnetic flux switching winding (step S201). For example, but not limited to the application, the first winding W12 is the fastest magnetic flux switching winding.

[0052] Then, after turning on two of the first switch, the second switch, and the third switch connected to the fastest magnetic flux switching winding, turn on two of the fourth switch, the fifth switch, and the sixth switch connected to the fastest magnetic flux switching winding (step S202). If the first winding W12 is the fastest magnetic flux switching winding, turn on the first switch 311 and the second switch 312 of the first power switch group 31 and the fourth switch 321 and the fifth switch 322 of the second power switch group 32. Incidentally, if the second winding W23 is the fastest magnetic flux switching winding, turn on the second switch 312 and the third switch 313 of the first power switch group 31 and the fifth switch 322 and the sixth switch 323 of the second power switch group 32.

[0053] Finally, after turning on the remaining non-conducting switches of the first switch 311, the second switch 312, and the third switch 313, turn on the remaining non-conducting switches of the fourth switch 321, the fifth switch 322, and the sixth switch 323 (step S203). If the first winding W12 is the fastest magnetic flux switching winding, after turning on the remaining non-conducting third switch 313, turn on the remaining non-conducting sixth switch 313. Incidentally, if the second winding W23 is the fastest magnetic flux switching winding, after turning on the remaining non-conducting first switch 311, turn on the remaining non-conducting fourth switch 321.

[0054] According to the above, the optimal timing of the forced commutation of the introduced thyristor can be achieved by evaluating and considering the permission of the forced commutation, the polarity of the magnetic flux shift, and the polarity of the voltage, thereby effectively achieving the purpose of successful switching of the two power sources.

[0055] It is noted that the above is implemented by taking the "fastest magnetic flux switching" as an example. However, another embodiment of the present application can also be implemented by taking the "maximum magnetic flux" as an example, which should be included in the scope of the present application, and any changes or modifications that can be easily thought of by those skilled in the art within the scope of the present application can be covered by the claims of the present application.

[0056] Referring to FIG. 7, which is a circuit block diagram of a three-phase four-wire power switching system according to the present application. In FIG. 7, two power sources, including a primary power source S-pri and a backup power source S-alt, are connected to a downstream three-phase transformer 43 through respective three-phase static transfer switch devices 41, 42.

[0057] As shown in FIG. 7, the three-phase power switching system includes a first power source S-pri and a second power source S-alt having three-phase alternating current power. The power switching system includes a first power source switch group 41 and a second power source switch group 42. The first power source switch group 41 includes a first switch 411, a second switch 412, and a third switch 413, which are sequentially electrically connected to a first phase sequence (R phase), a second phase sequence (S phase), and a third phase sequence (T phase) of the first power source S-pri. The second power source switch group 42 includes a fourth switch 421, a fifth switch 422, and a sixth switch 423, which are sequentially electrically connected to a first phase sequence (R phase), a second phase sequence (S phase), and a third phase sequence (T phase) of the second power source S-alt.

[0058] The three-phase transformer 43 includes a first winding W11, a second winding W22, and a third winding W33. The first winding W11, the second winding W22, and the third winding W33 of the three-phase transformer 43 form a common connection point Nc and three connection points N1, N2, N3 in a star connection (Y connection), and the common connection point Nc is grounded GND. The first connection point N1 is connected to the first switch 411 and the fourth switch 421, the second connection point N2 is connected to the second switch 412 and the fifth switch 422, and the third connection point N3 is connected to the third switch 413 and the sixth switch 423.

[0059] It is noted that for a three-phase four-wire system, there are common problems: 1. overexcitation problem, 2. passive excitation problem.

[0060] As to the over-excitation problem, please refer to the corresponding description above. As to the passive excitation problem, for the three-phase four-wire system, when the forced commutation is introduced, two thyristors cannot be turned on because the third thyristor will be affected by the magnetic flux even if it is not turned on.

[0061] Therefore, to avoid the over-excitation and passive excitation problems, the present application designs a technical solution that can effectively achieve successful switching of two power sources. When the main power source S-pri has an abnormal event, all the thyristors connected to the main power source S-pri are first turned off by controlling the gate. Then, the permission (ticket) for forced commutation is selected to turn on a phase thyristor to avoid passive excitation. Then, the thyristor is turned on in the negative half cycle of the next half cycle to complete the turn-on of two phase thyristors.

[0062] The turn-on time of the last two phase thyristors is determined according to whether the future magnetic flux obtained after calculation will cause magnetic flux saturation. If magnetic flux saturation occurs, the turn-on time is waited for. If magnetic flux saturation does not occur, the remaining two phase thyristors are sequentially turned on.

[0063] For the three-phase four-wire power switching system, a better forced commutation procedure is provided, as shown in FIG. 9, and please refer to FIG. 7. The procedure includes: first, detecting the magnetic flux speed of the first winding W11, the second winding W22, and the third winding W33 of the three-phase transformer 43, and selecting the winding with the fastest magnetic flux switching as a fastest magnetic flux switching winding (step S301). For example, the first winding W11 is the fastest magnetic flux switching winding, but this is not a limitation of the present application.

[0064] Then, after turning on one of the first switch, the second switch, and the third switch connected to the fastest magnetic flux switching winding, one of the fourth switch, the fifth switch, and the sixth switch connected to the fastest magnetic flux switching winding is turned on (step S302). If the first winding W11 is the fastest magnetic flux switching winding, the first switch 411 of the first power switch group 41 and the fourth switch 421 of the second power switch group 42 are turned on. Incidentally, if the second winding W22 is the fastest magnetic flux switching winding, the second switch 412 of the first power switch group 41 and the fifth switch 422 of the second power switch group 42 are turned on.

[0065] Finally, after turning on the first switch 411, the second switch 412 and the third switch 413 of the remaining two switches, the fourth switch 421, the fifth switch 422 and the sixth switch 423 of the remaining two switches are turned on (step S303). If the first winding W11 is the fastest magnetic flux switching winding, after turning on the second switch 412 and the third switch 413 of the remaining two switches, the fifth switch 422 and the sixth switch 423 of the remaining two switches are turned on. It is incidentally mentioned that if the second winding W22 is the fastest magnetic flux switching winding, after turning on the first switch 411 and the third switch 413 of the remaining two switches, the fourth switch 421 and the sixth switch 423 of the remaining two switches are turned on.

[0066] Accordingly, the timing of the forced commutation of the thyristor can be optimized by evaluating the above-mentioned conditions, thereby achieving the goal of successfully switching the two power sources.

[0067] The above description is only a detailed description of the preferred embodiments of the present application with reference to the accompanying drawings, and the features of the present application are not limited to this, and are not intended to limit the present application. The scope of the present application should be based on the following claims, and any embodiments similar to the claims of the present application and similar changes should be included in the scope of the present application. Any changes or modifications easily thought of by those skilled in the art in the field of the present application can be covered by the claims of the present application.

Claims

1. A power switching system, comprising a first power source and a second power source having three-phase AC power, the power switching system comprising: The first power switch group includes a first switch, a second switch and a third switch, which are electrically connected in sequence to the first phase sequence, the second phase sequence and the third phase sequence of the first power supply. The second power switch group includes a fourth switch, a fifth switch and a sixth switch, which are electrically connected in sequence to the first phase sequence, the second phase sequence and the third phase sequence of the second power supply. as well as A three-phase transformer includes a first winding, a second winding, and a third winding. The first winding, the second winding, and the third winding of the three-phase transformer form three common connection points in a delta connection. The first common connection point connects the first switch and the fourth switch, the second common connection point connects the second switch and the fifth switch, and the third common connection point connects the third switch and the sixth switch. The power switching system described herein provides a forced commutation procedure, including: The magnetic flux of the first winding, the second winding, and the third winding is detected, and the winding with the fastest magnetic flux switching is selected as the fastest magnetic flux switching winding. After energizing two of the first, second, and third switches of the fastest flux switching winding, energizing two of the fourth, fifth, and sixth switches of the fastest flux switching winding; and After turning on the first switch, the second switch, and the remaining unconnected switches of the third switch, turn on the fourth switch, the fifth switch, and the remaining unconnected switches of the sixth switch.

2. The power switching system according to claim 1, wherein any of the first switch, the second switch and the third switch comprises two thyristors connected in reverse parallel; wherein any of the fourth switch, the fifth switch and the sixth switch comprises two thyristors connected in reverse parallel.

3. The power switching system according to claim 2, wherein, based on the intention to switch the first power supply to the second power supply, in the forced commutation procedure, when it is determined that the current flowing out of the first power supply is greater than zero, it is further determined whether the voltage of the second power supply is greater than the load voltage.

4. The power switching system according to claim 3, wherein if the voltage is greater than the load voltage, the voltage turns on the thyristor connected to the second power source and in the forward direction, so as to turn off the thyristor connected to the first power source and still in operation.

5. The power switching system according to claim 2, wherein, based on the intention to switch the first power supply to the second power supply, in the forced commutation procedure, when it is determined that the current flowing out of the first power supply is less than zero, it is further determined whether the voltage of the second power supply is less than the load voltage.

6. The power switching system according to claim 5, wherein if the voltage is less than the load voltage, the load voltage turns on the thyristor connected to the second power source in the reverse direction, so as to turn off the thyristor connected to the first power source and still in operation.

7. The power switching system according to claim 2, wherein, based on the intention to switch from the first power supply to the second power supply, in the forced switching procedure, when it is determined that the voltage difference between the voltage of the second power supply and the load voltage is greater than a voltage threshold, the thyristor connected to the first power supply has been turned off.

8. The power switching system according to claim 2, wherein when the polarity of the magnetic flux offset is the same as the polarity of the voltage, forced commutation of the thyristor can be introduced without magnetic flux saturation.

9. The power switching system according to claim 2, wherein when the polarity of the magnetic flux deflection is not the same as the polarity of the voltage, forced commutation of the thyristor can be immediately introduced.

10. A power switching system, comprising a first power source and a second power source having three-phase AC power, the power switching system comprising: The first power switch group includes a first switch, a second switch and a third switch, which are electrically connected in sequence to the first phase sequence, the second phase sequence and the third phase sequence of the first power supply. The second power switch group includes a fourth switch, a fifth switch and a sixth switch, which are electrically connected in sequence to the first phase sequence, the second phase sequence and the third phase sequence of the second power supply. as well as A three-phase transformer includes a first winding, a second winding, and a third winding. The first winding, the second winding, and the third winding of the three-phase transformer are connected in a star configuration to form a common connection point and three connection points. The common connection point is grounded. The first connection point is connected to the first switch and the fourth switch, the second connection point is connected to the second switch and the fifth switch, and the third connection point is connected to the third switch and the sixth switch. The power switching system described herein provides a forced commutation procedure, including: The magnetic flux of the first winding, the second winding, and the third winding is detected, and the winding with the fastest magnetic flux switching is selected as the fastest magnetic flux switching winding. The first switch, the second switch, and the circuit that connect the fastest flux switching winding are electrically connected. After one of the third switches, one of the fourth, fifth, and sixth switches connected to the fastest flux switching winding is electrically connected; and After turning on the first switch, the second switch, and the two remaining unconnected switches of the third switch, turn on the fourth switch, the fifth switch, and the two remaining unconnected switches of the sixth switch.

11. The power switching system of claim 10, wherein any of the first switch, the second switch, and the third switch comprises two thyristors connected in anti-parallel; wherein any of the fourth switch, the fifth switch, and the sixth switch comprises two thyristors connected in anti-parallel.

12. The power switching system according to claim 11, wherein, based on the intention to switch the first power supply to the second power supply, in the forced commutation procedure, when it is determined that the current flowing out of the first power supply is greater than zero, it is further determined whether the voltage of the second power supply is greater than the load voltage.

13. The power switching system of claim 12, wherein if the voltage is greater than the load voltage, the voltage turns on the thyristor connected to the second power source and in the forward direction, so as to turn off the thyristor connected to the first power source and still in operation.

14. The power switching system according to claim 11, wherein, based on the intention to switch the first power supply to the second power supply, in the forced switching procedure, when it is determined that the current flowing out of the first power supply is less than zero, it is further determined whether the voltage of the second power supply is less than the load voltage.

15. The power switching system of claim 14, wherein if the voltage is less than the load voltage, the load voltage turns on the thyristor connected to the second power source in the reverse direction to turn off the thyristor connected to the first power source and still in operation.

16. The power switching system according to claim 11, wherein, based on the intention to switch from the first power supply to the second power supply, in the forced switching procedure, when it is determined that the voltage difference between the voltage of the second power supply and the load voltage is greater than a voltage threshold, the thyristor connected to the first power supply has been turned off.

17. The power switching system according to claim 11, wherein when the polarity of the magnetic flux deflection is the same as the polarity of the voltage, forced commutation of the thyristor can be introduced without magnetic flux saturation.

18. The power switching system according to claim 11, wherein when the polarity of the magnetic flux deflection is not the same as the polarity of the voltage, forced commutation of the thyristor can be immediately introduced.

Images