A power converter and a control method of a midpoint potential fluctuation suppression circuit thereof

Abstract

The application provides a power converter and a control method of a midpoint potential fluctuation suppression circuit. When the midpoint potential fluctuation suppression circuit is an RSCC, the control method first initializes the switching frequency, then periodically detects the temperatures of two series-connected switch tubes connected in parallel with any half bus capacitor on the DC bus side of the power converter. Since the two temperatures can respectively represent the losses of the corresponding switch tubes, when the switch tubes can all achieve soft switching, the losses of the switch tubes are low and the temperature difference is small, and a preset isothermal condition can be met. If the preset isothermal condition is not met, it means that the loss of one switch tube is too large. At this time, the switching frequency is adjusted and updated to make the two temperatures meet the preset isothermal condition. Furthermore, the relationship between the temperatures of two adjacent switch tubes can be used to adjust the switching frequency, so that the switching frequency approaches the resonance frequency of the RSCC, and ensures that the switch tubes can all achieve soft switching.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power conversion, in particular to a power converter and a control method of a neutral point potential fluctuation suppression circuit. BACKGROUND

[0002] The neutral point embedded three-level converter uses a split capacitor to lead out the neutral point on the DC bus side; in some output states, the currents on the two half bus capacitors are not equal, causing the potential fluctuation at the neutral point; and the large neutral point potential fluctuation will cause excessive stress on the switching device, overheating of the bus capacitor, and also cause the output waveform quality of the converter to decrease.

[0003] At present, in order to realize neutral point potential fluctuation suppression, compared with the software method which needs to cooperate with a specific modulation method, the equivalent switching frequency of the converter is increased, the loss is increased and the efficiency is reduced, and the hardware method can decouple the neutral point potential suppression and the body of the converter, and can obtain a better overall suppression effect. The existing hardware method usually adds a Figure 1 The RSCC (Resonant Switched Capacitor Converter) shown in the figure, and by controlling the switching tubes S1 and S3 to act simultaneously, the switching tubes S2 and S4 to act simultaneously, and the switching tubes S1 and S2 to be complementary to each other, the voltages on the two half bus capacitors C1 and C2 are balanced, and the function of neutral point potential fluctuation suppression is realized.

[0004] However, in the control process of each switching tube of the RSCC, it is not easy to realize soft switching of each switching tube under the condition of meeting ZVS (Zero Voltage Switch), so as to reduce the loss and ensure the safety of the device. SUMMARY

[0005] Therefore, the present application provides a power converter and a control method of a neutral point potential fluctuation suppression circuit, so that each switching tube in the RSCC can realize soft switching.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] The first aspect of the present application provides a control method of a neutral point potential fluctuation suppression circuit of a power converter, the neutral point potential fluctuation suppression circuit being a resonant switched capacitor converter RSCC, and the control method comprising:

[0008] initializing the switching frequency of the neutral point potential fluctuation suppression circuit;

[0009] periodically detecting the temperature of the two series switching tubes connected in parallel with any half bus capacitor on the DC bus side of the power converter.

[0010] determining whether the two temperatures satisfy a preset isothermal condition;

[0011] If not, adjusting and updating the switching frequency with the target of making the two temperatures satisfy the preset isothermal condition.

[0012] Optionally, the preset isothermal condition is that the difference between the two temperatures is less than a preset temperature difference.

[0013] Optionally, the preset isothermal condition is that the difference between the superposition of one temperature and a preset bias and the other temperature is less than a preset temperature difference.

[0014] Optionally, the preset temperature difference is 5℃.

[0015] Optionally, there is a hysteresis between the preset temperature differences in the corresponding two preset isothermal conditions before and after the switching frequency is adjusted and updated.

[0016] Optionally, adjusting and updating the switching frequency with the target of making the two temperatures satisfy the preset isothermal condition comprises:

[0017] If the temperature of the switch tube connected to the positive or negative pole of the DC bus is higher, the switching frequency is decreased;

[0018] If the temperature of the switch tube connected to the midpoint of the DC bus is higher, the switching frequency is increased.

[0019] Optionally, initializing the switching frequency of the midpoint potential fluctuation suppression circuit comprises:

[0020] The switching frequency is set to the sum of the resonant frequency of the RSCC and a preset value.

[0021] Optionally, the detection period of the two temperatures is 10 seconds.

[0022] The second aspect of the present application provides a power converter, comprising: a main circuit, a DC bus capacitor, a midpoint potential fluctuation suppression circuit, a temperature detection module, a switching frequency adjustment module and a controller; wherein,

[0023] The DC bus capacitor is arranged on the DC bus side of the main circuit; the DC bus capacitor comprises two series-connected half bus capacitors;

[0024] The midpoint potential fluctuation suppression circuit is an RSCC, and the RSCC is connected to the positive and negative poles and the midpoint of the DC bus capacitor respectively;

[0025] The main circuit is controlled by the controller;

[0026] The temperature detection module is configured to detect the temperature of two series switch tubes connected in parallel with any of the half bus capacitances in the RSCC, and transmit the detection result to the switching frequency adjustment module.

[0027] The switching frequency of the RSCC is controlled by the switching frequency adjustment module.

[0028] The switching frequency adjustment module is configured to perform the control method of the midpoint potential fluctuation suppression circuit of the power converter according to any of the first aspect.

[0029] Optionally, the temperature detection module comprises two temperature measuring elements and their detection circuits.

[0030] The temperature measuring elements are arranged in a preset range of the corresponding switch tubes.

[0031] The temperature measuring elements generate the detection result through the corresponding detection circuits.

[0032] Optionally, the switching frequency adjustment module comprises a temperature difference comparison circuit and a frequency adjustment circuit.

[0033] The temperature difference comparison circuit is configured to determine whether the temperature of the corresponding two switch tubes meets a preset isothermal condition.

[0034] The frequency adjustment circuit is configured to adjust and update the switching frequency so that the temperature of the two switch tubes meets the preset isothermal condition when the temperature of the two switch tubes does not meet the preset isothermal condition.

[0035] Optionally, the switching frequency adjustment module is an independent microprocessor or is integrated into the controller.

[0036] Optionally, the main circuit is a midpoint embedded three-level conversion circuit.

[0037] Optionally, the RSCC comprises four switch tubes connected in series, a resonant capacitor and a resonant inductor.

[0038] The first switch tube and the second switch tube are connected in series and connected in parallel with the upper half bus capacitor.

[0039] The third switch tube and the fourth switch tube are connected in series and connected in parallel with the lower half bus capacitor.

[0040] The connection point between the first switch tube and the second switch tube is connected to the connection point between the third switch tube and the fourth switch tube through the series-connected resonant capacitor and resonant inductor.

[0041] The application provides a control method of a midpoint potential fluctuation suppression circuit of a power converter, and when the midpoint potential fluctuation suppression circuit is an RSCC, the control method first initializes the switching frequency of the midpoint potential fluctuation suppression circuit; then, the temperatures of two series-connected switch tubes in parallel with any half bus capacitor on the DC bus side of the power converter are periodically detected; since the two temperatures can respectively represent the losses of the corresponding switch tubes, when the soft switching of each switch tube can be realized, the losses of the switch tubes are low and the temperature difference is small, and a preset isothermal condition can be met; therefore, when the two temperatures do not meet the preset isothermal condition, it is indicated that the loss of one switch tube is too large; at this time, the switching frequency is adjusted and updated so that the two temperatures meet the preset isothermal condition; then, the switching frequency can be adjusted by using the relationship between the temperatures of two adjacent switch tubes, so that the switching frequency approaches the resonance frequency of the RSCC, and the soft switching of each switch tube can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on the provided drawings.

[0043] Figure 1 A topology diagram of an RSCC type midpoint embedded three-level converter provided by the prior art;

[0044] Figure 2 A current flow direction schematic diagram of an output state of a midpoint embedded three-level converter provided by the embodiments of the present application;

[0045] Figure 3 An equivalent circuit diagram of an RSCC in a midpoint embedded three-level converter provided by the embodiments of the present application;

[0046] Figure 4 A control signal and current waveform schematic diagram of an RSCC provided by the embodiments of the present application;

[0047] Figure 5 and Figure 6 Current flow direction schematic diagrams of an RSCC provided by the embodiments of the present application in two stages;

[0048] Figure 7 A flowchart of a control method of a midpoint potential fluctuation suppression circuit of a power converter provided by the embodiments of the present application;

[0049] Figure 8a , Figure 8b , Figure 8c and8d Schematic diagrams of current flow in four stages of the RSCC provided in the embodiments of the present application when VC1 > VC2;

[0050] Figure 9a and Figure 9b and Figure 9c and 9d Schematic diagrams of current flow in four stages of the RSCC provided in the embodiments of the present application when VC1 < VC2;

[0051] Figure 10a and Figure 10b Two simulation waveform diagrams provided in the embodiments of the present application;

[0052] Figure 11 Schematic diagram of the structure of the power converter provided in the embodiments of the present application;

[0053] Figure 12 Schematic diagram of the structure of a temperature measurement element and its detection circuit provided in the embodiments of the present application;

[0054] Figure 13 Schematic diagram of the structure of the switching frequency adjustment module provided in the embodiments of the present application. Detailed implementation manners

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0056] In the present application, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "including a..." does not exclude the presence of additional identical elements in the process, method, article or device including the element.

[0057] Taking the neutral-point clamped three-level converter as an example in the output state shown in Figure 2 , its inverter circuit discharges the upper half-bus capacitor C1 (the discharge current is i shown in the figure inv ), but its pre-stage such as the BOOST circuit or the photovoltaic array will simultaneously charge the two half-bus capacitors C1 and C2 (the charging current is i shown in the figure boost), according to KCL (Kirchhoff's Current Law), the current I flowing through the upper half bus capacitor C1 and the current I flowing through the lower half bus capacitor C2 are respectively: C1 C2

[0058] I C1 =i boost -i inv ;

[0059] I C2 =i boost .

[0060] From the above formula, it can be seen that the currents flowing through the two half bus capacitors C1 and C2 are obviously not equal, which will cause the potential fluctuation at the midpoint O.

[0061] When the RSCC shown in Figure 1 is used to realize the midpoint potential fluctuation suppression, the RSCC mainly includes four active switching devices (i.e. switching tubes S1 to S4), a resonant inductor Lr and a resonant capacitor Cr, and its equivalent circuit is shown in Figure 3 , the DC power supply voltage connected thereto is 2Vdc, the control signals of the switching tubes S1 to S4, the resonant current i r and the current i PB flowing to the midpoint are shown in Figure 4 .

[0062] Suppose the voltage V C1 on the upper half bus capacitor C1 is greater than the voltage V C2 on the lower half bus capacitor C2, i.e. V C1 >V C2 :

[0063] As shown in Figure 5 , at 0-t1 time: the switching tubes S1 and S3 are turned on, the switching tubes S2 and S4 are turned off, the resonant network bears the voltage V C1 on the upper half bus capacitor C1, and V C1 >Vdc, the average value of the resonant capacitor Cr voltage in a period is Vdc, the voltage V C1 on the upper half bus capacitor C1 is greater than the voltage Vcr on the resonant capacitor Cr, and the resonant current i r is in the positive direction, as shown in Figure 4 , the upper half bus capacitor C1 transfers energy to the resonant network.

[0064] As shown in Figure 6 , at t1-t2 time: the switching tubes S2 and S4 are turned on, the switching tubes S1 and S3 are turned off, the resonant network bears the voltage V C2 ​​, and V C2 C2 r Figure 4 The resonant network transfers energy to the lower half bus capacitor C2.

[0065] Therefore, through a switching cycle, energy is transferred from the upper half bus capacitor C1 with high voltage to the lower half bus capacitor C2 with low voltage, thereby gradually achieving midpoint voltage balancing. C1 C2 The case will not be repeated.

[0066] The above scheme can realize the function of suppressing midpoint potential fluctuation, but it is not easy to realize soft switching for each switch tube in the RSCC. Therefore, the application provides a control method of a midpoint potential fluctuation suppression circuit of a power converter, so that each switch tube in the RSCC can realize soft switching.

[0067] The midpoint potential fluctuation suppression circuit is the RSCC shown in Figure 1 The control method is as shown in Figure 7 The control method specifically comprises:

[0068] S101, initializing the switching frequency of the midpoint potential fluctuation suppression circuit.

[0069] Specifically, the switching frequency can be initialized at the best resonant frequency according to the hardware design parameters of the RSCC, i.e. the values of the resonant inductance Lr and the resonant capacitance Cr. In actual circuit operation, the best resonant frequency is preferably slightly higher than the resonant frequency, i.e. the step S101 specifically can be: setting the switching frequency to the sum of the resonant frequency of the RSCC and a preset value. The preset value can be a small value close to 0, as long as the switching frequency is initialized to a frequency slightly higher than the resonant frequency, which is not limited here.

[0070] S102, periodically detecting the temperatures of the two series switch tubes connected in parallel with any half bus capacitor on the DC bus side of the power converter.

[0071] In actual application, the temperatures of the switch tubes S1 and S2, or the temperatures of the switch tubes S3 and S4 can be detected, which is determined by the specific application environment and is within the protection scope of the application.

[0072] Moreover, the detection period of the two temperatures can be 10 seconds, but is not limited to this.

[0073] S103, judging whether the two temperatures meet the preset isothermal condition. ​​​​

[0074] Since the two temperatures can represent the respective losses of the switch tubes, when the switch tubes can all achieve soft switching, the losses of the switch tubes are all low and the temperature difference is small, a preset isothermal condition can be met; as long as the difference between the two temperatures is within a certain range, the preset isothermal condition can be determined, and the specific value of the range can be determined according to the application environment, which is not limited here.

[0075] If the two temperatures do not meet the preset isothermal condition, step S104 is performed. If the two temperatures meet the preset isothermal condition, the temperature detection of the next cycle is performed in step S102.

[0076] S104, taking the two temperatures meeting the preset isothermal condition as the adjustment target, the switching frequency is adjusted and updated.

[0077] Since the resonant inductor Lr and the resonant capacitor Cr in the RSCC are connected in series between the connection points of the switch tubes S1 and S2 and the connection points of the switch tubes S3 and S4, when the switching frequency is greater than the resonant frequency and when the switching frequency is less than the resonant frequency, the loss size relationship of the switch tubes S1 / S4 and S2 / S3 will be different. When the above two temperatures do not meet the preset isothermal condition, it must be one of the two cases that the temperature of the switch tube S1 / S4 is higher than that of S2 / S3 or the temperature of the switch tube S2 / S3 is higher than that of S1 / S4, that is, there is a switch tube with excessive loss in S1 and S2 (or S3 and S4). At this time, as long as the switching frequency of each switch tube is adjusted in the direction of making the losses of the switch tubes S1 / S4 and S2 / S3 similar, the two temperatures can meet the adjustment target of the preset isothermal condition.

[0078] The control method of the midpoint potential fluctuation suppression circuit of the power converter provided by the embodiment can suppress the fluctuation of the midpoint potential when the RSCC works in an open-loop state. When the switching frequency is not equal to the resonant frequency, the power consumption of the two adjacent switch tubes in the upper half (or the lower half) has a large difference, which causes different temperature rises. The switching frequency is adjusted by using the relationship between the temperatures of the two adjacent switch tubes, so that the switching frequency approaches the resonant frequency of the circuit, so that all the four switch tubes in the RSCC can achieve soft switching.

[0079] In addition, the embodiment can eliminate the influence of the resonant frequency drift of the circuit caused by the long-term running parameter drift of the RSCC on the soft switching state of the switch tubes such as MOSFET by closed-loop control of the switching frequency through the temperature signal.

[0080] On the basis of the above embodiment, optionally, the preset isothermal condition can be that the difference between the two temperatures is less than a preset temperature difference. The preset temperature difference can be 5°C, or other values, depending on the application environment, which is within the protection scope of the present application.

[0081] In practical applications, if the MOSFET switch tube has inconsistent temperature due to layout and other hardware design, a bias can also be added in the initialization calibration. At this time, the preset isothermal condition is that the difference between the superimposed value of one temperature and the preset bias and the other temperature is less than the preset temperature difference. The preset bias is determined by the specific hardware design, which is not limited here.

[0082] In addition, during the actual circuit operation, a hysteresis can also be added to the adjustment value between the switching frequency and the resonant frequency to prevent frequency jitter. That is, between the preset temperature differences in the corresponding two preset isothermal conditions before and after the switching frequency is adjusted and updated, there is a hysteresis.

[0083] Next, assume that the voltage V C1 on the upper half bus capacitor C1 is greater than the voltage V C2 on the lower half bus capacitor C2, that is, V C1 >V C2 , at this time, Figure 8a to Figure 8d the corresponding equivalent circuits of RSCC in different stages are as follows:

[0084] Referring to Figure 8a , stage 1: the switch tubes S1 and S3 are turned on, and the resonant current flows through the MOSFET channels of S1 and S3.

[0085] Referring to Figure 8b , stage 2: entering the dead zone state, the switch tube S1 parallel capacitor is charged, and the switch tube S2 parallel capacitor is discharged. The resonant current ir flows through the body diode of the switch tube S3.

[0086] Referring to Figure 8c , stage 3: the charging and discharging of the switch tube S1 parallel capacitor and the switch tube S2 parallel capacitor are completed, the resonant current ir flows through the body diode of the switch tubes S2 and S3, and the ZVS condition is achieved.

[0087] Referring to Figure 8d , stage 4: the switch tubes S2 and S4 are turned on, the switch tube S2 parallel capacitor is discharged, the voltage Vds between the source and the drain of the switch tube S2 is 0, and the switch tube is turned on in the ZVS state.

[0088] Assume that the voltage V C2 on the lower half bus capacitor C2 is greater than the voltage V C1 on the upper half bus capacitor C1, that is, V C2 >V C1 , at this time, Figure 9a to Figure 9dThe corresponding equivalent circuit of the RSCC in different stages is as follows:

[0089] Referring to Figure 9a , stage 1: the switch tubes S1 and S3 are turned on, and the resonant current flows through the MOSFET channels of S1 and S3.

[0090] Referring to Figure 9b , stage 2: the dead zone state is entered, the switch tube S3 is charged in parallel with the capacitor, and the switch tube S4 is discharged in parallel with the capacitor. The resonant current ir flows through the body diode of the switch tube S1.

[0091] Referring to Figure 9c , stage 3: the charging and discharging of the switch tube S3 in parallel with the capacitor and the switch tube S4 in parallel with the capacitor are completed, the resonant current ir flows through the body diode of the switch tube S1 and S4, and the ZVS condition is achieved.

[0092] Referring to Figure 9d , stage 4: the switch tubes S2 and S4 are turned on, the switch tube S4 is discharged in parallel with the capacitor, the voltage Vds between the source and the drain of the switch tube S4 is 0, and the switch tube is turned on in the ZVS state.

[0093] Figure 10a When the switching frequency fs is greater than the resonant frequency fr, the voltage Vds between the source and the drain of the switch tubes S1 to S4 and the drain current Id are shown in the waveform diagram, Figure 10b When the switching frequency fs is less than the resonant frequency fr, the voltage Vds between the source and the drain of the switch tubes S1 to S4 and the drain current Id are shown in the waveform diagram; wherein Vm12 refers to the waveform of the voltage Vds between the source and the drain of the switch tube S1, Am11 refers to the waveform of the drain current Id of the switch tube S1, Vm11 refers to the waveform of the voltage Vds between the source and the drain of the switch tube S2, Am10 refers to the waveform of the drain current Id of the switch tube S2, Vm10 refers to the waveform of the voltage Vds between the source and the drain of the switch tube S3, Am9 refers to the waveform of the drain current Id of the switch tube S3, Vm9 refers to the waveform of the voltage Vds between the source and the drain of the switch tube S4, Am8 refers to the waveform of the drain current Id of the switch tube S4, Vm6 refers to the waveform of the voltage V C1 on the upper half bus capacitor C1, Vm7 refers to the waveform of the voltage V C2 on the lower half bus capacitor C2, and Am3 refers to the waveform of the current i PB flowing to the midpoint; it can be seen from the simulation waveform that:

[0094] When fs>fr, the switch tubes S2 and S3 can achieve ZVS turn-on, but the switch tubes S1 and S4 cannot achieve ZVS turn-on, when the difference between fs and fr is large, the loss of the switch tubes S1 and S4 is certainly greater than that of the switch tubes S2 and S3, and the temperature of the switch tubes S1 and S4 is certainly greater than that of the switch tubes S2 and S3.

[0095] When fs<fr, the switch tubes S1 and S4 can realize ZVS turn-on, but the switch tubes S2 and S3 cannot realize ZVS turn-on, when fs and fr have a large difference, the loss of the switch tubes S2 and S3 is certainly greater than that of S1 and S4, and the temperature of the switch tubes S2 and S3 is certainly greater than that of S1 and S4.

[0096] According to the size relationship between the corresponding two temperatures, the relationship between the switching frequency fs and the resonance frequency fr can be determined.

[0097] Then, in step S104, the switching frequency is adjusted and updated with the preset isothermal condition as the adjustment target, which can specifically include: if the temperature of the switch tube connected to the positive or negative pole of the DC bus is high, that is, the temperature of S1 in the switch tubes S1 and S2 or S4 in the switch tubes S3 and S4 is high, the switching frequency is reduced; and if the temperature of the switch tube connected to the midpoint of the DC bus is high, that is, the temperature of S2 in the switch tubes S1 and S2 or S3 in the switch tubes S3 and S4 is high, the switching frequency is increased.

[0098] In actual application, the adjustment can be made in a certain step size, or a corresponding adjustment amount can be calculated according to the difference between the two temperatures, which is determined according to the application environment and is within the protection scope of the present application.

[0099] Another embodiment of the present application further provides a power converter, which, as shown in Figure 11 , comprises a main circuit 10, a DC bus capacitor (including C1 and C2), a midpoint potential fluctuation suppression circuit 20, a temperature detection module 30, a switching frequency adjustment module 40 and a controller 50; wherein:

[0100] The main circuit 10 can be specifically a midpoint embedding type three-level conversion circuit as shown in Figure 1 . The main circuit 10 is controlled by the controller 50.

[0101] The DC bus capacitor is arranged on the DC bus side of the main circuit 10; and the DC bus capacitor comprises two series-connected half bus capacitors C1 and C2.

[0102] The midpoint potential fluctuation suppression circuit 20 is an RSCC, and the RSCC is connected to the positive pole, the negative pole and the midpoint of the DC bus capacitor. As shown in Figure 1As shown in the figure, the RSCC includes four switch tubes S1-S4 connected in series, a resonance capacitor Cr and a resonance inductor Lr; the first switch tube S1 and the second switch tube S2 are connected in series and then connected in parallel with the upper half bus capacitor C1; the third switch tube S3 and the fourth switch tube S4 are connected in series and then connected in parallel with the lower half bus capacitor C2; the connection point between the first switch tube S1 and the second switch tube S2 is connected to the connection point between the third switch tube S3 and the fourth switch tube S4 through the series connection of the resonance capacitor Cr and the resonance inductor Lr. The RSCC is realized by the above-mentioned four switch tubes S1-S4 connected in series, and is very suitable for high-voltage systems of 1500V and above.

[0103] The temperature detection module 30 is used to detect the temperature of the two switch tubes connected in series in parallel with any half bus capacitor, i.e., the temperature of the switch tubes S1 and S2 or the temperature of the switch tubes S3 and S4, and transmit the detection result to the switching frequency adjustment module 40.

[0104] The switching frequency of the RSCC is controlled by the switching frequency adjustment module 40. The switching frequency adjustment module 40 is used to perform the control method of the midpoint potential fluctuation suppression circuit of the power converter as described in any of the above-mentioned embodiments. Specifically, according to the values of the hardware design parameters Lr and Cr, the switching frequency is initialized to the optimal resonance frequency; then the temperature of the switch tubes S1 and S2 or the temperature of the switch tubes S3 and S4 is detected, the relationship between the switching frequency fs and the resonance frequency fr is determined according to the temperature relationship, and finally the switching frequency is dynamically adjusted, for example, the switching frequency is adjusted every 10 seconds. For other processes and principles of the control method, please refer to the above-mentioned embodiments, which will not be described here.

[0105] The embodiment essentially controls the switching frequency through the temperature signal in a closed loop, which can eliminate the resonance frequency drift of the RSCC circuit caused by long-term operation parameter drift and the influence on the soft switching state of the MOSFET.

[0106] In practical applications, the temperature detection module 30 can include two temperature measuring elements and their detection circuits; each temperature measuring element is arranged in a predetermined range of the corresponding switch tube, and each temperature measuring element generates a detection result through the corresponding detection circuit.

[0107] To realize dynamic compensation of the temperature difference of the four switching tubes within a preset temperature difference, such as 5℃, two NTC (Negative Temperature Coefficient) thermistors can be symmetrically placed at the ends of the switching tubes S1 and S2 (or S3 and S4) as temperature measuring elements, to realize the condition that the heat dissipation of the four switching tubes on the PCB (Printed Circuit Board) is as consistent as possible, and to dynamically adjust the difference between the switching frequency fs and the resonant frequency fr through periodic temperature detection.

[0108] The specific structure and connection relationship of a temperature measuring element R and its detection circuit can be as shown in Figure 12 The detection circuit specifically adopts an LTC2063 zero drift operational amplifier U1 to receive a reference signal REF and a voltage signal of the temperature measuring element R, combines low temperature coefficient feedback and series resistance, generates a corresponding detection result OUT, and realizes high-resolution temperature detection with extremely low power consumption.

[0109] It is worth noting that some existing solutions detect the frequency by detecting voltage or current, but the corresponding solutions have the problems of large size and high cost. The present embodiment only needs to add a simple temperature detection device, such as an NTC (Negative Temperature Coefficient) thermistor, to make the circuit operating frequency close to or equal to the circuit resonant frequency, and to realize soft switching. Compared with voltage or current detection, the frequency detection has the advantages of small size and low cost.

[0110] In actual application, the functions of temperature comparison and judgment, frequency adjustment, etc. can be realized by using corresponding hardware circuits or in a digital controller such as a DSP (Digital Signal Processing) or a single-chip microcomputer.

[0111] When realized by a hardware circuit, the switching frequency adjustment module 40 can include a temperature difference comparison circuit 401 and a frequency adjustment circuit 402, as shown in Figure 13 The temperature difference comparison circuit 401 is used to determine whether the temperatures of the corresponding two switching tubes meet the preset isothermal condition, and the frequency adjustment circuit 402 is used to adjust and update the switching frequency so that the two temperatures meet the preset isothermal condition.

[0112] When realized by software, the switching frequency adjustment module 40 can be a separate microprocessor, or can be integrated into the controller 50. The specific application environment determines the implementation, which is within the protection scope of the present application.

[0113] The same parts and features of each of the embodiments described in the specification can be referred to, and each of the embodiments focuses on the differences from other embodiments. In particular, for the system or system embodiments, since they are basically similar to the method embodiments, they are described more simply, and the relevant parts can be referred to the part of the method embodiments. The above-described system and system embodiments are only illustrative, wherein the units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, i.e. they can be located in one place or distributed on multiple network units. Part or all of the modules can be selected according to actual needs to achieve the purpose of the present embodiment. Those skilled in the art can understand and implement without creative labor.

[0114] The skilled person can further realize that the units and algorithm steps of the examples described in conjunction with the embodiments disclosed herein can be realized in electronic hardware, computer software or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been described in the above description in general terms. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0115] The above description of the disclosed embodiments, the features recorded in each embodiment of the specification can be replaced or combined with each other, so that the skilled person in the art can implement or use the present application. Various modifications of the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method of a midpoint potential fluctuation suppression circuit of a power converter, characterized by, The midpoint potential fluctuation suppression circuit is a resonant switched capacitor converter (RSCC), and the control method comprises: initializing a switching frequency of the midpoint potential fluctuation suppression circuit; periodically detecting temperatures of two series switch tubes connected in parallel with any half bus capacitor on a DC bus side of a power converter; judging whether the two temperatures satisfy a preset isothermal condition; if not, adjusting and updating the switching frequency with a target of making the two temperatures satisfy the preset isothermal condition.

2. The control method of the midpoint potential fluctuation suppression circuit of the power converter according to claim 1, characterized by, The preset isothermal condition is that a difference between the two temperatures is less than a preset temperature difference.

3. The control method of the midpoint potential fluctuation suppression circuit of the power converter according to claim 1, characterized by, The preset isothermal condition is that a difference between a superposition of one temperature and a preset bias and another temperature is less than a preset temperature difference.

4. The control method of the neutral point potential fluctuation suppressing circuit of the power converter according to claim 2 or 3, characterized by, The preset temperature difference is 5℃.

5. The control method of the neutral point potential fluctuation suppressing circuit of the power converter according to claim 2 or 3, characterized by, There is a hysteresis between the preset temperature differences in the corresponding two preset isothermal conditions before and after the switching frequency is adjusted and updated.

6. The control method of the neutral-point-potential fluctuation suppressing circuit of a power converter according to any one of claims 1 to 3, characterized by, The adjusting and updating of the switching frequency with the target of making the two temperatures satisfy the preset isothermal condition comprises: if a temperature of a switch tube connected to a positive or negative pole of the DC bus is higher, decreasing the switching frequency; if a temperature of a switch tube connected to a midpoint of the DC bus is higher, increasing the switching frequency.

7. The control method of the circuit for suppressing the neutral point potential fluctuation of the power converter according to any one of claims 1 to 3, characterized by, The initializing of the switching frequency of the midpoint potential fluctuation suppression circuit comprises: setting the switching frequency as a sum of a resonant frequency of the RSCC and a preset value.

8. The control method of the neutral-point-potential fluctuation suppressing circuit of a power converter according to any one of claims 1 to 3, characterized by, A detection period of the two temperatures is 10 seconds.

9. A power converter, characterized by It comprises: a main circuit, a DC bus capacitor, a midpoint potential fluctuation suppression circuit, a temperature detection module, a switching frequency adjusting module and a controller; wherein, the DC bus capacitor is arranged on a DC bus side of the main circuit; the DC bus capacitor comprises two series connected half bus capacitors; the midpoint potential fluctuation suppression circuit is the RSCC, and the RSCC is connected to positive and negative poles and a midpoint of the DC bus capacitor respectively; the main circuit is controlled by the controller; the temperature detection module is used for detecting temperatures of two series switch tubes connected in parallel with any half bus capacitor in the RSCC, and transmitting detection results to the switching frequency adjusting module; the switching frequency of the RSCC is controlled by the switching frequency adjusting module; the switching frequency adjusting module is used for executing the control method of the midpoint potential fluctuation suppression circuit of the power converter as claimed in any one of claims 1 to 8.

10. The power converter of claim 9, wherein, The temperature detection module comprises two temperature measuring elements and detection circuits thereof; the temperature measuring elements are arranged in a preset range of corresponding switch tubes; the temperature measuring elements generate the detection results through corresponding detection circuits.

11. The power converter of claim 9, wherein, The switching frequency adjusting module comprises a temperature difference comparison circuit and a frequency adjusting circuit; the temperature difference comparison circuit is used for judging whether temperatures of corresponding two switch tubes satisfy a preset isothermal condition; the frequency adjusting circuit is used for adjusting and updating the switching frequency with a target of making the two temperatures satisfy the preset isothermal condition when the two temperatures do not satisfy the preset isothermal condition.

12. The power converter of claim 9, wherein, The switching frequency adjusting module is an independent microprocessor or is integrated in the controller.

13. The power converter of any one of claims 9 to 12, wherein, The main circuit is a midpoint clamping three-level conversion circuit.

14. The power converter of any one of claims 9 to 12, wherein, The RSCC comprises four switch tubes connected in series, a resonance capacitor and a resonance inductor; The first switch tube and the second switch tube are connected in series and then connected in parallel with the upper half bus capacitor; The third switch tube and the fourth switch tube are connected in series and then connected in parallel with the lower half bus capacitor; The connection point between the first switch tube and the second switch tube is connected to the connection point between the third switch tube and the fourth switch tube through the series connection of the resonance capacitor and the resonance inductor.

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