Multi-level conversion circuit and wave-by-wave protection method thereof

Abstract

The invention provides a multi-level conversion circuit and a wave-by-wave protection method thereof, the multi-level conversion circuit is provided with a flying capacitor, and the wave-by-wave protection method comprises the following steps: (a) determining a main switch and a synchronous rectification switch; (b) controlling the main switch to operate in a normal mode; (c) detecting the current flowing through the inductor, and judging whether the current exceeds a threshold value or not; (d) when the current exceeds a threshold value, regarding the main switch which is in a conduction state and has the shortest conduction duration as a target main switch, switching the target main switch to a current limiting mode so as to turn off the target main switch, and controlling the other main switches to be maintained in a normal mode; and (e) after the target main switch is switched to the current limiting mode, if the current is smaller than the threshold value, switching the target main switch to a state corresponding to the reference mode at the moment when the control signals of all the main switches in the reference mode have falling edges for the first time.

Description

Technical Field

[0001] This case involves a multi-level conversion circuit and a wave-by-wave protection method thereof, and in particular, a flying capacitor multi-level conversion circuit and a wave-by-wave protection method thereof. Background Art

[0002] In a multi-level conversion circuit with a flying capacitor, if the inductor current has a peak or a maximum value, it will damage the circuit, so it is necessary to use wave-by-wave current limiting to ensure that the inductor current does not exceed the set value at any time.

[0003] The existing wave-by-wave current limiting method is to block the control signal of the main switch (ie, turn off the main switch) when the inductor current is greater than a preset value, so as to reduce the inductor current. Figure 1 The control signal of the main switch and the waveform of the inductor current of the existing flying capacitor two-level conversion circuit are shown as an example. Figure 1 In the figure, the dotted line depicts the waveform when the normal mode is continuously operated, and the solid line depicts the waveform when the wave-by-wave current limiting is adopted. Figure 1 As shown in FIG. 1 , when the wave-by-wave current limiting is adopted, if the inductor current is detected to be greater than the set value, the control signal of the main switch is blocked until the end of the current switching cycle, and then the main switch is controlled to operate in the normal mode again. It should be noted that during the period from blocking the control signal to the end of the current switching cycle, no additional adjustment or restart of the control signal is performed.

[0004] However, when the number of levels is large, the existing wave-by-wave current limiting method will cause large current fluctuations in the inductor current. For example, Figure 2 The waveforms of the control signal of the main switch and the inductor current of the existing flying capacitor three-level conversion circuit are shown as an example. Figure 2 As shown, since the inductor current fall time is too long, not only the characteristic of having two inductor current cycles in a single switching cycle is destroyed, but also a larger current fluctuation is generated. This larger current fluctuation will lead to increased loss and even cause the voltage on the flying capacitor to deviate.

[0005] Therefore, it is an urgent need to provide a multi-level conversion circuit and a wave-by-wave protection method thereof that can improve the above-mentioned prior art. Summary of the invention

[0006] The purpose of this case is to provide a multi-level conversion circuit and a wave-by-wave protection method thereof, which can prevent the inductor current from causing excessive fluctuations while maintaining the inductor current within a threshold value.

[0007] To achieve the above-mentioned purpose, the present case provides a wave-by-wave protection method for a multi-level conversion circuit, wherein the number of levels of the multi-level conversion circuit is N, and N is an integer greater than or equal to 3. The multi-level conversion circuit comprises a first input terminal, a second input terminal, a first output terminal, a second output terminal, an inductor, N-1 first switches, N-1 second switches, and N-2 flying capacitors. The first input terminal and the second input terminal are configured to receive an input voltage, and the first output terminal and the second output terminal are configured to provide an output voltage. When the potential of the first input terminal is lower than the potential of the second input terminal, the first input terminal is electrically connected to the second output terminal, and when the potential of the first input terminal is higher than the potential of the second input terminal, the first input terminal is electrically connected to the first output terminal. The first end of the inductor is electrically connected to the second input terminal. N-1 first switches are connected in series between the second end of the inductor and the second output terminal, and the first first switch and the N-1 first switch are coupled to the second end of the inductor and the second output terminal, respectively. The N-1 second switches are connected in series between the second end of the inductor and the first output end, the 1st second switch and the N-1th second switch are coupled to the second end of the inductor and the first output end respectively. The kth flying capacitor is connected across a common connection point between the kth first switch and the k+1th first switch and a common connection point between the kth second switch and the k+1th second switch, where k is a positive integer less than or equal to N-2. The wave-by-wave protection method comprises the following steps: (a) when the potential of the first input terminal is lower than the potential of the second input terminal, N-1 first switches and N-1 second switches are used as main switches and synchronous rectification switches respectively, and when the potential of the first input terminal is higher than the potential of the second input terminal, N-1 first switches and N-1 second switches are used as synchronous rectification switches and main switches respectively; (b) controlling the N-1 main switches to operate in a normal mode, wherein in the normal mode, the i-th first switch and the i-th second switch are complementary turned on, and i is a positive integer less than or equal to N-1; (c) detecting the current flowing through the inductor and determining whether the current exceeds a threshold; (d) if the occupation voltage of the main switch exceeds the threshold, the inductor is turned off; and (e) if the occupation voltage of the main switch exceeds the threshold, the inductor is turned off. The duty cycle is greater than 1 / (N-1), when the current exceeds the threshold, the main switch in the N-1 main switches that is in the on state and has the shortest on time is regarded as the target main switch, and the target main switch is switched to the current limiting mode to turn off the target main switch, and the remaining main switches in the N-1 main switches are controlled to maintain in the normal mode; and (e) after the target main switch is switched to the current limiting mode, if the current is less than the threshold, at the moment when the control signal of the N-1 main switch in the reference mode has a falling edge for the first time, the target main switch is switched to the state corresponding to the reference mode at this moment, wherein the reference mode is a mode assuming that the N-1 main switches do not enter the current limiting mode and continue to operate in the normal mode.

[0008] To achieve the above-mentioned purpose, the present case further provides a multi-level conversion circuit, wherein the number of levels of the multi-level conversion circuit is N, and N is an integer greater than or equal to 3. The multi-level conversion circuit comprises a first input terminal, a second input terminal, a first output terminal, a second output terminal, an inductor, N-1 first switches, N-1 second switches, N-2 flying capacitors and a controller. The first input terminal and the second input terminal are configured to receive an input voltage, and the first output terminal and the second output terminal are configured to provide an output voltage. When the potential of the first input terminal is lower than the potential of the second input terminal, the first input terminal is electrically connected to the second output terminal, and when the potential of the first input terminal is higher than the potential of the second input terminal, the first input terminal is electrically connected to the first output terminal. The first end of the inductor is electrically connected to the second input terminal. N-1 first switches are connected in series between the second end of the inductor and the second output terminal, and the first first switch and the N-1 first switch are coupled to the second end of the inductor and the second output terminal, respectively. The N-1 second switches are connected in series between the second end of the inductor and the first output end, the 1st second switch and the N-1th second switch are coupled to the second end of the inductor and the first output end respectively. The kth flying capacitor is connected across a common connection point between the kth first switch and the k+1th first switch and a common connection point between the kth second switch and the k+1th second switch, where k is a positive integer less than or equal to N-2. The controller architecture is as follows: when the potential of the first input terminal is lower than the potential of the second input terminal, N-1 first switches and N-1 second switches are used as main switches and synchronous rectification switches respectively, and when the potential of the first input terminal is higher than the potential of the second input terminal, N-1 first switches and N-1 second switches are used as synchronous rectification switches and main switches respectively; the N-1 main switches are controlled to operate in a normal mode, wherein in the normal mode, the i-th first switch and the i-th second switch are complementary turned on, i being a positive integer less than or equal to N-1; the current flowing through the inductor is detected, and whether the current exceeds a threshold value; if the duty cycle of the main switch is greater than 1 / (N-1), when the current exceeds the threshold, the main switch in the N-1 main switches that is in the on state and has the shortest on time is regarded as the target main switch, and the target main switch is switched to the current limiting mode to turn off the target main switch, and the remaining main switches in the N-1 main switches are controlled to maintain in the normal mode; and after the target main switch is switched to the current limiting mode, if the current is less than the threshold, at the moment when the control signal of the N-1 main switch in the reference mode has a falling edge for the first time, the target main switch is switched to the state corresponding to the reference mode at this moment, wherein the reference mode is a mode assuming that the N-1 main switches do not enter the current limiting mode and continue to operate in the normal mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The waveforms of the control signal of the main switch and the inductor current of the conventional flying capacitor two-level conversion circuit are illustrated.

[0010] Figure 2 The waveforms of the control signal of the main switch and the inductor current of the conventional flying capacitor three-level conversion circuit are illustrated.

[0011] Figure 3 FIG. 4 is a schematic diagram of a circuit structure of a multi-level conversion circuit according to an embodiment of the present invention.

[0012] Figure 4 FIG. 4 is a flow chart of a first wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention.

[0013] Figure 5 FIG. 4 is a flow chart of a second wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention.

[0014] Figure 6 FIG. 4 is a flow chart of a third wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention.

[0015] Fig. 7A and Figure 7B The waveforms of the main switch and the inductor current of the three-level conversion circuit when executing the first wave-by-wave protection method are illustrated.

[0016] Fig. 8A and Figure 8B The waveforms of the main switch and the inductor current of the three-level conversion circuit when executing the second wave-by-wave protection method are illustrated.

[0017] Fig.9A and Fig. 9B The waveforms of the main switch and the inductor current of the three-level conversion circuit when executing the third wave-by-wave protection method are illustrated.

[0018] Fig. 10A , Fig. 10B and Fig. 10C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the first wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 1 / 3 and less than 2 / 3.

[0019] Fig.11A , Fig. 11B and Fig. 11C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the second wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 1 / 3 and less than 2 / 3.

[0020] Fig. 12A , Fig. 12B and Fig. 12C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the third wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 1 / 3 and less than 2 / 3.

[0021] Fig.13A , Fig. 13B and Fig. 13C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the first wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 2 / 3.

[0022] Fig.14A , Fig. 14B and Fig. 14C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the second wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 2 / 3.

[0023] Fig.15A , Fig. 15B and Fig. 15C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the third wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 2 / 3.

[0024] The reference numerals are described as follows:

[0025] 1: Multi-level conversion circuit

[0026] 11: First input terminal

[0027] 12: Second input terminal

[0028] 13: First output terminal

[0029] 14: Second output terminal

[0030] L: Inductance

[0031] Sa1, Sa2, Sa(N-1): first switch

[0032] Sb1, Sb2, Sb(N-1): Second switch

[0033] Cf1, Cf2, Cf(N-2): Flying capacitors

[0034] 15: Controller

[0035] Vin: input voltage

[0036] S1: First input switch

[0037] S2: Second input switch

[0038] Cp: ​​output voltage stabilizing capacitor

[0039] iL: current flowing through inductor L

[0040] iTH: Threshold

[0041] ST1, ST2, ST3, ST4, ST5a, ST6a: Steps

[0042] ST5b, ST6b, ST5c, ST6c: Steps

[0043] Sm1, Sm2, Sm3: Main switches

[0044] G1, G2, G3: control signal DETAILED DESCRIPTION

[0045] Some typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different implementations without departing from the scope of the present invention, and the descriptions and illustrations therein are essentially only for illustration, not for limiting the present invention.

[0046] Figure 3 FIG. 1 is a schematic diagram of the circuit structure of a multi-level conversion circuit according to an embodiment of the present invention. Figure 3As shown, the number of levels of the multi-level conversion circuit 1 is N, where N is an integer greater than or equal to 3. The multi-level conversion circuit 1 includes a first input terminal 11, a second input terminal 12, a first output terminal 13, a second output terminal 14, an inductor L, N-1 first switches Sa1, Sa2, ..., Sa(N-1), N-1 second switches Sb1, Sb2, ..., Sb(N-1), N-2 flying capacitors Cf1, Cf2, ..., Cf(N-2) and a controller 15. The first input terminal 11 and the second input terminal 12 are configured to connect to a power supply (DC or AC) to receive an input voltage Vin. The first output terminal 13 and the second output terminal 14 are configured to provide an output voltage. When the potential of the first input terminal 11 is lower than the potential of the second input terminal 12, the first input terminal 11 is electrically connected to the second output terminal 14; when the potential of the first input terminal 11 is higher than the potential of the second input terminal 12, the first input terminal 11 is electrically connected to the first output terminal 13. The first end of the inductor L is electrically connected to the second input end 12. All first switches Sa1, Sa2, ..., Sa(N-1) are connected in series between the second end of the inductor L and the second output end 14, wherein the first first switch Sa1 and the N-1th first switch Sa(N-1) are coupled to the second end of the inductor L and the second output end 14, respectively. All second switches Sb1, Sb2, ..., Sb(N-1) are connected in series between the second end of the inductor L and the first output end 13, wherein the first second switch Sb1 and the N-1th second switch Sb(N-1) are coupled to the second end of the inductor L and the first output end 13, respectively. Among all N-2 flying capacitors Cf1, Cf2, ..., Cf(N-2), the kth flying capacitor Cfk is connected between the common connection point of the kth first switch Sak and the k+1th first switch Sa(k+1) and the common connection point of the kth second switch Sbk and the k+1th second switch Sb(k+1), where k is a positive integer less than or equal to N-2, that is, k=1, 2, ..., (N-2). The control unit 15 is configured to control the operation of all switches in the multi-level conversion circuit 1.

[0047] The input voltage Vin received by the first input terminal 11 and the second input terminal 12 may be a DC voltage or an AC voltage. When the input voltage Vin is a DC voltage, and the potential of the first input terminal 11 is fixedly lower than the potential of the second input terminal 12, the first input terminal 11 is connected to the second output terminal 14. When the input voltage Vin is a DC voltage, and the potential of the first input terminal 11 is fixedly higher than the potential of the second input terminal 12, the first input terminal 11 is connected to the first output terminal 13. When the input voltage Vin is an AC voltage, if the input voltage Vin is in the positive half cycle, the potential of the first input terminal 11 is lower than the potential of the second input terminal 12, and the first input terminal 11 is connected to the second output terminal 14; and if the input voltage Vin is in the negative half cycle, the potential of the first input terminal 11 is higher than the potential of the second input terminal 12, and the first input terminal 11 is connected to the first output terminal 13.

[0048] In addition, in some embodiments, in order to control the first input terminal 11 to be connected to the first output terminal 13 or the second output terminal 14, the multi-level conversion circuit 1 further includes a first input switch S1 and a second input switch S2. Specifically, the first input switch S1 is coupled between the first input terminal 11 and the first output terminal 13, and the second input switch S2 is coupled between the first input terminal 11 and the second output terminal 14. When the potential of the first input terminal 11 is lower than the potential of the second input terminal 12, the controller 15 turns off the first input switch S1 and turns on the second input switch S2, so that the first input terminal 11 is connected to the second output terminal 14. When the potential of the first input terminal 11 is higher than the potential of the second input terminal 12, the controller 15 turns on the first input switch S1 and turns off the second input switch S2, so that the first input terminal 11 is connected to the first output terminal 13.

[0049] In some embodiments, the multi-level conversion circuit 1 further includes an output stabilizing capacitor Cp connected between the first output terminal 13 and the second output terminal 14 .

[0050] The following Figure 4 , Figure 5 and Figure 6 Three wave-by-wave protection methods for the multi-level conversion circuit 1 are illustrated, namely a first wave-by-wave protection method, a second wave-by-wave protection method and a third wave-by-wave protection method.

[0051] Figure 4 The first wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention is a flow chart showing a first wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention. The first wave-by-wave protection method comprises the following steps.

[0052] First, in step ST1, the main switch and the synchronous rectification switch of the multi-level conversion circuit 1 are determined. Specifically, when the potential of the first input terminal 11 is lower than the potential of the second input terminal 12, all N-1 first switches Sa1~Sa(N-1) are used as main switches, and all N-1 second switches Sb1~Sb(N-1) are used as synchronous rectification switches; and when the potential of the first input terminal 11 is higher than the potential of the second input terminal 12, all N-1 first switches Sa1~Sa(N-1) are used as synchronous rectification switches, and all N-1 second switches Sb1~Sb(N-1) are used as main switches. The control signals of the corresponding main switches and synchronous rectification switches are complementary.

[0053] Then, in step ST2, all N-1 main switches are controlled to operate in normal mode. In normal mode, the i-th main switch and the i-th synchronous rectification switch are complementary turned on, and i is a positive integer less than or equal to N-1. It should be noted that the wave-by-wave protection method of this case focuses on the situation where the duty cycle of the main switch is greater than 1 / (N-1). Since when the duty cycle of the main switch is less than or equal to 1 / (N-1), the rise and fall of the current iL flowing through the inductor L at any time is only affected by one main switch. Therefore, in this case, the existing wave-by-wave current limiting method can be adopted, and the wave-by-wave protection method of this case will not be described in detail.

[0054] Then, in step ST3 , the current iL flowing through the inductor L is detected.

[0055] Next, in step ST4, it is determined whether the current iL exceeds a threshold value iTH. The threshold value iTH can be determined according to actual application requirements.

[0056] When the duty cycle of the main switch is greater than 1 / (N-1), when the judgment result of step ST4 is yes, that is, when the current iL exceeds the threshold value iTH, step ST5a is executed. In step ST5a, the main switch in the on state is regarded as the target main switch, and the target main switch is switched to the current limiting mode to turn off the target main switch, and the remaining main switches are controlled to maintain the normal mode. In this way, when the current iL exceeds the threshold value iTH, the main switch in the on state is immediately turned off to reduce the current iL, thereby playing a role of current limiting protection.

[0057] As shown in step ST6a, after the target main switch is switched to the current limiting mode, if the current iL is less than the threshold value iTH, at the moment when the control signals of all N-1 main switches in the reference mode first have a falling edge, the target main switch is switched to the state corresponding to the reference mode at this moment, wherein the reference mode is a mode assuming that all N-1 main switches do not enter the current limiting mode and continue to operate in the normal mode. It should be noted that the reference mode is an assumed rather than an actual operating mode, and is used to determine the time point for the target main switch to exit the current limiting mode.

[0058] In some embodiments, when the determination result of step ST4 is negative and after step ST6a is executed, step ST3 may be executed again to continuously monitor whether the current iL exceeds the threshold value iTH.

[0059] Figure 5 FIG. 1 is a flow chart of a second wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention. The same steps as those in the first wave-by-wave protection method are represented by the same reference numerals and are not described in detail herein. However, in the second wave-by-wave protection method, steps ST5a and ST6a in the first wave-by-wave protection method are replaced by steps ST5b and ST6b, respectively.

[0060] In the second wave-by-wave protection method, if Figure 5 As shown, when the judgment result of step ST4 is yes, that is, when the current iL exceeds the threshold value iTH, step ST5b is executed. In step ST5b, the main switch in the on state and the shortest on time among all N-1 main switches is regarded as the target main switch, and the target main switch is switched to the current limiting mode to turn off the target main switch, and the remaining main switches are controlled to maintain in the normal mode. In this way, when the current iL exceeds the threshold value iTH, the main switch in the on state and the shortest on time is immediately turned off to reduce the current iL, thereby playing a role of current limiting protection. In some embodiments, when the current iL exceeds the threshold value iTH, the on time of the target main switch is less than Ts / (N-1), where Ts is the switching period of the main switch.

[0061] As shown in step ST6b, after the target main switch is switched to the current limiting mode, if the current iL is less than the threshold value iTH, then at the moment when the control signals of all N-1 main switches in the reference mode first have a falling edge, the target main switch is switched to the state corresponding to the reference mode at this moment. In some embodiments, when the judgment result of step ST4 is no, and after executing step ST6b, step ST3 may be executed again to continuously monitor whether the current iL exceeds the threshold value iTH.

[0062] Figure 6 FIG. 1 is a flow chart of a third wave-by-wave protection method for a multi-level conversion circuit according to an embodiment of the present invention. The same steps as those in the first wave-by-wave protection method are represented by the same reference numerals and are not described in detail herein. However, in the third wave-by-wave protection method, steps ST5c and ST6c replace steps ST5a and ST6a in the first wave-by-wave protection method, respectively.

[0063] In the third wave-by-wave protection method, if Figure 6As shown, when the judgment result of step ST4 is yes, that is, when the current iL exceeds the threshold value iTH, step ST5c is executed. In step ST5c, the main switch in the on state and the longest on time among all N-1 main switches is regarded as the target main switch, and the target main switch is switched to the current limiting mode to turn off the target main switch, and the remaining main switches are controlled to maintain in the normal mode. In this way, when the current iL exceeds the threshold value iTH, the main switch in the on state and the longest on time is immediately turned off to reduce the current iL, thereby playing a role of current limiting protection. In some embodiments, when the current iL exceeds the threshold value iTH, the on time of the target main switch is greater than Ts×(N-2) / (N-1), where Ts is the switching period of the main switch.

[0064] As shown in step ST6c, after the target main switch is switched to the current limiting mode, if the current iL is less than the threshold value iTH, at the moment when the control signal of the target main switch in the reference mode first appears a rising edge, the target main switch is switched to the state corresponding to the reference mode at this moment. In some embodiments, when the judgment result of step ST4 is no, and after executing step ST6c, step ST3 may be executed again to continuously monitor whether the current iL exceeds the threshold value iTH.

[0065] As can be seen from the above, in this case, after the current limiting protection is triggered, when a period of time has passed and the current iL is less than the threshold value iTH, the target main switch is switched to the state corresponding to the reference mode at this moment, without waiting for the end of the current switching cycle to switch the target main switch to the state corresponding to the reference mode at this moment. In this way, the inductor current (i.e., the current iL) can be maintained within the threshold while avoiding excessive fluctuations in the inductor current.

[0066] In addition, it should be noted that the aforementioned wave-by-wave protection method mainly determines the time point of switching the target main switch based on the control signal of the main switch in the reference mode. Since the control signals of the main switch and the synchronous rectification switch are complementary, the time point of switching the target main switch can actually also be determined based on the control signal of the synchronous rectification switch in the reference mode. The principle is the same and will not be repeated here.

[0067] In order to facilitate the understanding of the actual application of the wave-by-wave protection method, the waveforms of the main switch and the inductor current of the multi-level conversion circuit 1 when the first wave-by-wave protection method, the second wave-by-wave protection method and the third wave-by-wave protection method are illustrated below, but the actual application of the present case is not limited to this. In addition, it should be noted that in the waveform diagrams corresponding to the following description, G1, G2 and G3 respectively represent the control signals of the main switches Sm1, Sm2 and Sm3 (corresponding to the first switches Sa1, Sa2 and Sa3 or corresponding to the second switches Sb1, Sb2 and Sb3 respectively according to actual conditions), the dotted line represents the waveform in the reference mode, the solid line represents the waveform when the wave-by-wave protection method is adopted, and the shaded area highlights the actual conduction interval of the main switch near the moment of triggering the current limiting protection.

[0068] In the first implementation, the number of levels of the multi-level conversion circuit 1 is three (ie, N=3), the multi-level conversion circuit is a three-level conversion circuit, and the duty cycle of the main switch is greater than 0.5.

[0069] Fig. 7A and Figure 7B The waveforms of the main switch and the inductor current of the three-level conversion circuit when executing the first wave-by-wave protection method are shown as an example. Fig. 7A and Figure 7B The corresponding waveforms of the current limiting protection that triggers the wave-by-wave protection method at different time points (or different switching cycles) are shown. However, in fact, the three-level conversion circuit can continuously execute the wave-by-wave protection method rather than only executing the wave-by-wave protection method in a single switching cycle. Similar situations also exist in the subsequent waveform diagrams.

[0070] At Fig. 7A In the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1 and Sm2 in the on state are switched to the current limiting mode to turn off the main switches Sm1 and Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1 and G2 of all the main switches Sm1 and Sm2 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G1 of the main switch Sm1 in the reference mode), the main switches Sm1 and Sm2 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is maintained in the off state, and the main switch Sm2 is turned on.

[0071] At Figure 7BIn the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1 and Sm2 in the on state are switched to the current limiting mode to turn off the main switches Sm1 and Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1 and G2 of all the main switches Sm1 and Sm2 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G2 of the main switch Sm2 in the reference mode), the main switches Sm1 and Sm2 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on, and the main switch Sm2 is maintained in the off state.

[0072] Fig. 8A and Figure 8B The waveforms of the main switch and the inductor current of the three-level conversion circuit when executing the second wave-by-wave protection method are illustrated.

[0073] At Fig. 8A In the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm2 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1 and G2 of all the main switches Sm1 and Sm2 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G1 of the main switch Sm1 in the reference mode), the main switch Sm2 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is turned on.

[0074] At Figure 8B In the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm1 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm1 and reduce the current iL. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1 and G2 of all the main switches Sm1 and Sm2 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G2 of the main switch Sm2 in the reference mode), the main switch Sm1 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on.

[0075] Fig.9A and Fig. 9B The waveforms of the main switch and the inductor current of the three-level conversion circuit when executing the third wave-by-wave protection method are illustrated.

[0076] At Fig.9A In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm1 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm1, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G1 of the main switch Sm1 in the reference mode first appears a rising edge, the main switch Sm1 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on.

[0077] At Fig. 9B In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm2 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm1, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G2 of the main switch Sm2 in the reference mode first appears a rising edge, the main switch Sm2 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is turned on.

[0078] In the second implementation, the number of levels of the multi-level conversion circuit 1 is four (ie, N=4), the multi-level conversion circuit is a four-level conversion circuit, and the duty cycle of the main switch is greater than 1 / 3.

[0079] Fig. 10A , Fig. 10B and Fig. 10C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the first wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 1 / 3 and less than 2 / 3.

[0080] At Fig. 10A In the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1 and Sm3 in the on state are switched to the current limiting mode to turn off the main switches Sm1 and Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., the falling edge of the control signal G3 of the main switch Sm3 in the reference mode), the main switches Sm1 and Sm3 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on, and the main switch Sm3 is maintained in the off state.

[0081] At Fig. 10B In the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1 and Sm2 in the on state are switched to the current limiting mode to turn off the main switches Sm1 and Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., the falling edge of the control signal G1 of the main switch Sm1 in the reference mode), the main switches Sm1 and Sm2 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is maintained in the off state, and the main switch Sm2 is turned on.

[0082] At Fig. 10CIn the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm2 and Sm3 in the on state are switched to the current limiting mode to turn off the main switches Sm2 and Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., the falling edge of the control signal G2 of the main switch Sm2 in the reference mode), the main switches Sm2 and Sm3 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is maintained in the off state, and the main switch Sm3 is turned on.

[0083] Fig.11A , Fig. 11B and Fig. 11C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the second wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 1 / 3 and less than 2 / 3.

[0084] At Fig.11A In the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm1 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm1, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G3 of the main switch Sm3 in the reference mode), the main switch Sm1 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on.

[0085] At Fig. 11B In the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm2 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G1 of the main switch Sm1 in the reference mode), the main switch Sm2 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is turned on.

[0086] At Fig. 11CIn the embodiment, when the current iL exceeds the threshold value iTH, the main switch Sm3 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G2 of the main switch Sm2 in the reference mode), the main switch Sm3 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm3 is turned on.

[0087] Fig. 12A , Fig. 12B and Fig. 12C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the third wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 1 / 3 and less than 2 / 3.

[0088] At Fig. 12A In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm3 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G3 of the main switch Sm3 in the reference mode first appears a rising edge, the main switch Sm3 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm3 is turned on.

[0089] At Fig. 12B In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm1 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm1, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G1 of the main switch Sm1 in the reference mode first appears a rising edge, the main switch Sm1 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on.

[0090] At Fig. 12C In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm2 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G2 of the main switch Sm2 in the reference mode first appears a rising edge, the main switch Sm2 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is turned on.

[0091] Fig.13A , Fig. 13B and Fig. 13C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the first wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 2 / 3.

[0092] At Fig.13A In the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1, Sm2 and Sm3 in the on state are switched to the current limiting mode to turn off the main switches Sm1, Sm2 and Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., the falling edge of the control signal G2 of the main switch Sm2 in the reference mode), the main switches Sm1, Sm2 and Sm3 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on, the main switch Sm2 is maintained in the off state, and the main switch Sm3 is turned on.

[0093] At Fig. 13B In the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1, Sm2 and Sm3 in the on state are switched to the current limiting mode to turn off the main switches Sm1, Sm2 and Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., the falling edge of the control signal G3 of the main switch Sm3 in the reference mode), the main switches Sm1, Sm2 and Sm3 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on, the main switch Sm2 is turned on, and the main switch Sm3 is maintained in the off state.

[0094] At Fig. 13C In the embodiment, when the current iL exceeds the threshold value iTH, the main switches Sm1, Sm2 and Sm3 in the on state are switched to the current limiting mode to turn off the main switches Sm1, Sm2 and Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., the falling edge of the control signal G1 of the main switch Sm1 in the reference mode), the main switches Sm1, Sm2 and Sm3 are switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is maintained in the off state, the main switch Sm2 is turned on, and the main switch Sm3 is turned on.

[0095] Fig.14A , Fig. 14B and Fig. 14C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the second wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 2 / 3.

[0096] At Fig.14AIn the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm1 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm1 and reduce the current iL. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G2 of the main switch Sm2 in the reference mode), the main switch Sm1 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on.

[0097] At Fig. 14B In the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm2 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G3 of the main switch Sm3 in the reference mode), the main switch Sm2 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is turned on.

[0098] At Fig. 14C In the present invention, when the current iL exceeds the threshold value iTH, the main switch Sm3 which is in the on state and has the shortest on time is switched to the current limiting mode to turn off the main switch Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signals G1, G2 and G3 of all the main switches Sm1, Sm2 and Sm3 in the reference mode first have a falling edge (i.e., at the falling edge of the control signal G1 of the main switch Sm1 in the reference mode), the main switch Sm3 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm3 is turned on.

[0099] Fig.15A , Fig. 15B and Fig. 15C The waveforms of the main switch and the inductor current of the four-level conversion circuit when executing the third wave-by-wave protection method are illustrated, wherein the duty cycle of the main switch is greater than 2 / 3.

[0100] At Fig.15A In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm2 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm2, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G2 of the main switch Sm2 in the reference mode first appears a rising edge, the main switch Sm2 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm2 is turned on.

[0101] At Fig. 15BIn the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm3 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm3, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G3 of the main switch Sm3 in the reference mode first appears a rising edge, the main switch Sm3 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm3 is turned on.

[0102] At Fig. 15C In the reference mode, when the current iL exceeds the threshold value iTH, the main switch Sm1 which is in the on state and has the longest on time is switched to the current limiting mode to turn off the main switch Sm1, so that the current iL decreases. After the current iL is lower than the threshold value iTH, at the moment when the control signal G1 of the main switch Sm1 in the reference mode first appears a rising edge, the main switch Sm1 is switched to the state corresponding to the reference mode at this moment. At this time, the main switch Sm1 is turned on.

[0103] In summary, the present invention provides a multi-level conversion circuit and a wave-by-wave protection method thereof, which can prevent the inductor current from causing excessive fluctuations while maintaining the inductor current within a threshold value.

[0104] It should be noted that the above is only a preferred embodiment for illustrating the present invention, and the present invention is not limited to the embodiment described. The scope of the present invention is determined by the attached claims. Moreover, the present invention may be modified in various ways by those skilled in the art, but all of them are within the scope of the protection intended by the attached claims.

Claims

1. A wave-by-wave protection method for a multi-level conversion circuit, wherein the number of levels of the multi-level conversion circuit is N, N is an integer greater than or equal to 3, the multi-level conversion circuit comprises a first input terminal, a second input terminal, a first output terminal, a second output terminal, an inductor, N-1 first switches, N-1 second switches and N-2 flying capacitors, the first input terminal and the second input terminal are configured to receive an input voltage, the first output terminal and the second output terminal are configured to provide an output voltage, when the potential of the first input terminal is lower than the potential of the second input terminal, the first input terminal is electrically connected to the second output terminal, and when the potential of the first input terminal is higher than the potential of the second input terminal, the first input terminal is electrically connected to the first output terminal; the electrical The first end of the inductor is electrically connected to the second input end, the N-1 first switches are connected in series between the second end of the inductor and the second output end, the first first switch and the N-1th first switch are coupled to the second end of the inductor and the second output end respectively, the N-1 second switches are connected in series between the second end of the inductor and the first output end, the first second switch and the N-1th second switch are coupled to the second end of the inductor and the first output end respectively, the kth flying capacitor is connected across a common connection point between the kth first switch and the k+1th first switch and a common connection point between the kth second switch and the k+1th second switch, k is a positive integer less than or equal to N-2, and the wave-by-wave protection method comprises the steps of: (a) when the potential at the first input terminal is lower than the potential at the second input terminal, the N-1 first switches and the N-1 second switches are used as a main switch and a synchronous rectification switch, respectively; and when the potential at the first input terminal is higher than the potential at the second input terminal, the N-1 first switches and the N-1 second switches are used as a synchronous rectification switch and a main switch, respectively; (b) controlling N-1 of the main switches to operate in a normal mode, wherein in the normal mode, the i-th first switch and the i-th second switch are complementarily turned on, and i is a positive integer less than or equal to N-1; (c) detecting a current flowing through the inductor and determining whether the current exceeds a threshold; (d) if the duty cycle of the main switch is greater than 1 / (N-1), when the current exceeds the threshold, the main switch in the N-1 main switches that is in the on state and has the shortest on time is regarded as the target main switch, and the target main switch is switched to a current limiting mode to turn off the target main switch, and the remaining main switches in the N-1 main switches are controlled to maintain in the normal mode; and (e) After the target main switch is switched to the current limiting mode, if the current is less than the threshold, at the moment when the control signals of the N-1 main switches in the reference mode first have a falling edge, the target main switch is switched to a state corresponding to the reference mode at that moment, wherein the reference mode is a mode assuming that the N-1 main switches do not enter the current limiting mode and continue to operate in the normal mode.

2. The wave-by-wave protection method as claimed in claim 1, wherein in step (d), when the current exceeds the threshold, the on-time of the target main switch is less than Ts / (N-1), where Ts is the switching period of the main switch.

3. The wave-by-wave protection method as claimed in claim 1, wherein the multi-level conversion circuit further comprises a first input switch and a second input switch, the first input switch is coupled between the first input terminal and the first output terminal, and the second input switch is coupled between the first input terminal and the second output terminal, and the wave-by-wave protection method further comprises: When the potential of the first input terminal is lower than the potential of the second input terminal, turning off the first input switch and turning on the second input switch; and When the potential of the first input terminal is higher than the potential of the second input terminal, the first input switch is turned on and the second input switch is turned off. 4 . The wave-by-wave protection method as claimed in claim 1 , wherein the input voltage is a DC voltage, the potential of the first input terminal is fixedly lower than the potential of the second input terminal, and the first input terminal is connected to the second output terminal. 5 . The wave-by-wave protection method as claimed in claim 1 , wherein the input voltage is a direct current voltage, the potential of the first input terminal is fixedly higher than the potential of the second input terminal, and the first input terminal is connected to the first output terminal.

6. The wave-by-wave protection method as described in claim 1, wherein the input voltage is an AC voltage, and when the input voltage is in a positive half cycle, the potential of the first input terminal is lower than the potential of the second input terminal, and when the input voltage is in a negative half cycle, the potential of the first input terminal is higher than the potential of the second input terminal.

7. A multi-level conversion circuit, wherein the number of levels of the multi-level conversion circuit is N, N is an integer greater than or equal to 3, and the multi-level conversion circuit comprises: A first input terminal and a second input terminal are configured to receive an input voltage; A first output terminal and a second output terminal, configured to provide an output voltage, wherein when the potential of the first input terminal is lower than the potential of the second input terminal, the first input terminal is electrically connected to the second output terminal, and when the potential of the first input terminal is higher than the potential of the second input terminal, the first input terminal is electrically connected to the first output terminal; an inductor, a first end of which is electrically connected to the second input end; N-1 first switches are connected in series between the second end of the inductor and the second output end, wherein the first first switch and the N-1th first switch are coupled to the second end of the inductor and the second output end respectively; N-1 second switches are connected in series between the second end of the inductor and the first output end, wherein the first second switch and the N-1 second switch are coupled to the second end of the inductor and the first output end respectively; N-2 flying capacitors, wherein the kth flying capacitor is connected between a common connection point between the kth first switch and the k+1th first switch and a common connection point between the kth second switch and the k+1th second switch, and k is a positive integer less than or equal to N-2; as well as A controller, based on: When the potential of the first input terminal is lower than the potential of the second input terminal, the N-1 first switches and the N-1 second switches are used as a main switch and a synchronous rectification switch, respectively; and when the potential of the first input terminal is higher than the potential of the second input terminal, the N-1 first switches and the N-1 second switches are used as a synchronous rectification switch and a main switch, respectively. Controlling N-1 of the main switches to operate in a normal mode, wherein in the normal mode, the i-th first switch and the i-th second switch are complementarily turned on, and i is a positive integer less than or equal to N-1; Detecting a current flowing through the inductor and determining whether the current exceeds a threshold; If the duty cycle of the main switch is greater than 1 / (N-1), when the current exceeds the threshold, the main switch in the N-1 main switches that is in the on state and has the shortest on time is regarded as the target main switch, and the target main switch is switched to a current limiting mode to turn off the target main switch, and the remaining main switches in the N-1 main switches are controlled to maintain in the normal mode; and After the target main switch is switched to the current limiting mode, if the current is less than the threshold, at the moment when the control signals of the N-1 main switches in the reference mode have a falling edge for the first time, the target main switch is switched to a state corresponding to the reference mode at that moment, wherein the reference mode is a mode assuming that the N-1 main switches do not enter the current limiting mode and continue to operate in the normal mode. 8 . The multi-level conversion circuit as claimed in claim 7 , wherein when the current exceeds the threshold, the on-time of the target main switch is less than Ts / (N−1), where Ts is a switching period of the main switch.

9. The multi-level conversion circuit as described in claim 7 further comprises a first input switch and a second input switch, wherein the first input switch is coupled between the first input terminal and the first output terminal, and the second input switch is coupled between the first input terminal and the second output terminal, the controller turns off the first input switch and turns on the second input switch when the potential of the first input terminal is lower than the potential of the second input terminal, and the controller turns on the first input switch and turns off the second input switch when the potential of the first input terminal is higher than the potential of the second input terminal. 10 . The multi-level conversion circuit as claimed in claim 7 , wherein the input voltage is a DC voltage, the potential of the first input terminal is fixedly lower than the potential of the second input terminal, and the first input terminal is connected to the second output terminal. 11 . The multi-level conversion circuit as claimed in claim 7 , wherein the input voltage is a DC voltage, the potential of the first input terminal is fixedly higher than the potential of the second input terminal, and the first input terminal is connected to the first output terminal.

12. A multi-level conversion circuit as described in claim 7, wherein the input voltage is an AC voltage, when the input voltage is in a positive half cycle, the potential of the first input terminal is lower than the potential of the second input terminal, and when the input voltage is in a negative half cycle, the potential of the first input terminal is higher than the potential of the second input terminal.

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