Three-phase MISN converter, control method and system

Abstract

The invention discloses a three-phase MISN converter and a control method and system, and relates to the field of electric energy conversion, a three-phase MISN module, a three-phase inductor and a three-level rectifying bridge are arranged in the three-phase MISN converter, according to the scheme, the three-level rectifying bridge is additionally arranged on the basis of an existing three-phase MISN module and an existing three-phase inductor, and therefore the three-phase MISN converter can be used for controlling the three-phase MISN module and the three-phase inductor. Compared with a two-level rectifying bridge, the three-level rectifying bridge has the advantages that the difference value between the neutral-point voltage of the three-level rectifying bridge and any phase voltage of the power grid is smaller, so that the instantaneous power of the three-phase MISN module can be reduced, and the size of a clamping capacitor in the MISN module does not need to be greatly increased on the basis of ensuring the wide voltage output range of the three-level rectifying bridge.

Description

Technical Field

[0001] The present invention relates to the field of electric energy conversion, and in particular to a three-phase MISN converter, a control method and a system. Background Art

[0002] With the continuous development of electric vehicles, their battery capacity has also increased, necessitating higher-power on-board chargers (OBCs). However, due to limited onboard space, the increased charging power demands higher efficiency and power density from high-power three-phase OBCs. Compared to the traditional two-level six-switch circuit (2L6B), the MISN (Modular Inductive Switching Network) converter offers advantages in efficiency and power density. This is due to the fact that MISN converters can use lower-loss low-voltage components and their smaller inductors and filters. However, existing MISN converters consist of a three-phase inductor, a three-phase MISN module, and a two-level rectifier bridge. The input of the three-phase MISN module is connected to the three-phase inductor, and the output is connected to the two-level rectifier bridge. However, this solution results in excessive instantaneous power consumption, making it unsuitable for applications with a wide output voltage range. Specifically, increasing the output voltage of the two-level rectifier bridge requires a significant increase in the size of the clamping capacitors in the three-phase MISN module. Summary of the Invention

[0003] The object of the present invention is to provide a three-phase MISN converter, a control method and a system. In this solution, a three-level rectifier bridge is added on the basis of a three-phase MISN module and a three-phase inductor. Compared with a two-level rectifier bridge, the three-level rectifier bridge can reduce the instantaneous power of the MISN module, thereby ensuring a wide voltage output range of the three-level rectifier bridge without significantly increasing the volume of the clamping capacitor in the MISN module.

[0004] To solve the above technical problems, the present invention provides a three-phase MISN converter, comprising: a three-phase MISN module, a three-phase inductor, and a three-level rectifier bridge;

[0005] The three-phase input terminals of the three-phase inductor are respectively connected to the output terminals of the three-phase power grid in a one-to-one correspondence, and the three-phase output terminals are respectively connected to the three-phase input terminals of the three-phase MISN module in a one-to-one correspondence;

[0006] The three-phase output terminals of the three-phase MISN module are correspondingly connected to the input terminals of the three-level rectifier bridge, and the product of the port voltage of any phase MISN module in the three-phase MISN module and the current value of the corresponding phase inductance in the three-phase inductor is less than a preset power threshold;

[0007] The midpoint of the three-level rectifier bridge is respectively connected to the neutral point of the three-phase power grid and the input end of the three-level rectifier bridge, and the midpoint of the three-level rectifier bridge is respectively connected to the positive output end of the three-level rectifier bridge and the negative output end of the three-level rectifier bridge through two corresponding electrolytic capacitors, and the positive output end of the three-level rectifier bridge and the negative output end of the three-level rectifier bridge are both connected to the load.

[0008] Optionally, any phase MISN module includes: a plurality of H-bridge units; any H-bridge unit includes: a first switch, a second switch, a third switch, a fourth switch, and a clamping capacitor;

[0009] The first end of the first switch is respectively connected to the anode of the clamping capacitor and the first end of the third switch, and the second end is respectively connected to the first end of the second switch, the second end of the third switch of the next H-bridge unit, or the input end of the three-level rectifier bridge, or the midpoint of the three-level rectifier bridge;

[0010] The second end of the second switch is connected to the cathode of the clamping capacitor and the second end of the fourth switch;

[0011] The second end of the third switch is connected to the output end of the three-phase inductor or the second end of the first switch of the previous H-bridge unit.

[0012] Optionally, the three-level rectifier bridge includes: a first rectifier tube, a second rectifier tube, a third rectifier tube, a fourth rectifier tube, a fifth rectifier tube, a sixth rectifier tube, a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, a first capacitor, and a second capacitor;

[0013] The first end of the first rectifier tube is connected to the first phase output end of the three-phase MISN module, and the second end is connected to the second end of the third rectifier tube and the second end of the fifth rectifier tube respectively, and the second end of the first rectifier tube serves as the positive output end of the three-level rectifier bridge;

[0014] The first end of the second rectifier tube is connected to the first phase output end of the three-phase MISN module, and the second end is connected to the second end of the fourth rectifier tube and the second end of the sixth rectifier tube respectively, and the second end of the second rectifier tube serves as the negative output end of the three-level rectifier bridge;

[0015] The first end of the third rectifier tube is connected to the second phase output end of the three-phase MISN module;

[0016] The first end of the fourth rectifier tube is connected to the second phase output end of the three-phase MISN module;

[0017] The first end of the fifth rectifier tube is connected to the third phase output end of the three-phase MISN module;

[0018] The first end of the sixth rectifier tube is connected to the third phase output end of the three-phase MISN module;

[0019] The first end of the first bidirectional switch is connected to the first phase output end of the three-phase MISN module, and the second end is connected to the second end of the second bidirectional switch and the second end of the third bidirectional switch respectively, and the second end of the first bidirectional switch is the midpoint of the three-level rectifier bridge;

[0020] A first end of the second bidirectional switch is connected to a second phase output end of the three-phase MISN module;

[0021] A first end of the third bidirectional switch is connected to the third phase output end of the three-phase MISN module;

[0022] The negative electrode of the first capacitor is respectively connected to the positive electrode of the second capacitor, the second end of the first bidirectional switch, the second end of the second bidirectional switch, and the second end of the third bidirectional switch, and the positive electrode is the positive output end of the three-level rectifier bridge;

[0023] The cathode of the second capacitor serves as the negative output terminal of the three-level rectifier bridge.

[0024] To solve the above technical problems, the present invention further provides a three-phase MISN converter control method, which is applied to the three-phase MISN converter as described above, comprising:

[0025] Obtaining three-phase current values ​​of a three-phase power grid, three-phase voltage values ​​of the three-phase power grid, and output voltage of a three-level rectifier bridge;

[0026] performing a corresponding first proportional integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value;

[0027] A first PWM signal is determined according to the D-axis current reference value, a preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values.

[0028] Optionally, also include:

[0029] Determine the clamping voltage value of the clamping capacitor in the three-phase MISN module;

[0030] performing a corresponding third proportional-integral operation on the clamping voltage value and the second preset voltage to generate a corresponding target chopping angle;

[0031] A corresponding second PWM signal is generated according to the target chopping angle, and the duty cycle of the switching device in the three-level rectifier bridge is adjusted based on the second PWM signal.

[0032] Optionally, performing a corresponding third proportional-integral operation on the clamping voltage value and the second preset voltage to generate a corresponding target chopping angle includes:

[0033] adjusting the position of the preset chopping angle within the half period according to the proportional integral calculation result obtained by the third proportional integral operation;

[0034] The preset chopping angle after position adjustment is used as the target chopping angle.

[0035] Optionally, determining the first PWM signal according to the D-axis current reference value, the preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values ​​includes:

[0036] Performing a transformation from an ABC coordinate system to a DQ coordinate system according to the three-phase current values ​​of the three-phase inductor and the three-phase voltage values ​​of the three-phase inductor to generate a D-axis current component and a Q-axis current component;

[0037] performing a second proportional integral operation on the D-axis current component and the D-axis current reference value to generate a first operation result;

[0038] performing the second proportional integral operation on the Q-axis current component and the Q-axis current reference value to generate a second operation result;

[0039] Determining a D-axis operation result according to the first operation result, the Q-axis current component, the output voltage, the inductance values ​​of the three-phase inductors, and the angular frequency of the three-phase power grid;

[0040] determining a Q-axis operation result according to the second operation result, the D-axis current component, the output voltage, the inductance value, and the angular frequency;

[0041] Performing a DQ coordinate system to an ABC coordinate system transformation on the D-axis calculation result and the Q-axis calculation result to generate a three-phase voltage signal;

[0042] The first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the three-phase voltage signal and the first PWM signal.

[0043] Optionally, before determining the first PWM signal corresponding to the three-phase voltage signal according to the correspondence between the three-phase voltage signal and the first PWM signal, the method further includes:

[0044] Performing transient compensation control according to the three-phase voltage values ​​of the three-phase inductor and the output voltage to generate a three-phase voltage symmetrical modulation signal;

[0045] Accordingly, determining the first PWM signal corresponding to the three-phase voltage signal according to the corresponding relationship between the three-phase voltage signal and the first PWM signal includes:

[0046] Determining a voltage difference signal between the three-phase voltage signal and the three-phase voltage symmetrical modulation signal;

[0047] The first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the voltage difference signal and the first PWM signal.

[0048] Optionally, after controlling the duty cycle of the H-bridge unit in the three-phase MISN module based on the first PWM signal, the method further includes:

[0049] Determining the frequency of the port voltage of the three-phase MISN module and the number of H-bridge units in the three-phase MISN module;

[0050] determining a product of the number and a preset switching frequency;

[0051] Determining whether a difference between the frequency and the product is within a preset range;

[0052] If the difference between the frequency and the product is within a preset range, triggering the step of obtaining the three-phase current value of the three-phase power grid, the three-phase voltage value of the three-phase power grid, and the output voltage of the three-level rectifier bridge;

[0053] If the difference between the frequency and the product is not within a preset range, it is determined that a fault has occurred.

[0054] To solve the above technical problems, the present invention further provides a three-phase MISN converter control system, which is applied to the three-phase MISN converter as described above, comprising:

[0055] An acquisition unit, configured to acquire a three-phase current value of a three-phase power grid, a three-phase voltage value of the three-phase power grid, and an output voltage of a three-level rectifier bridge;

[0056] a proportional-integral operation unit, configured to perform a corresponding first proportional-integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value;

[0057] A determining unit is configured to determine a first PWM signal according to the D-axis current reference value, a preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values.

[0058] The object of the present invention is to provide a three-phase MISN converter, a control method and a system. The three-phase MISN converter is provided with a three-phase MISN module, a three-phase inductor and a three-level rectifier bridge. On the basis of the existing three-phase MISN module and three-phase inductor, this solution adds a three-level rectifier bridge. Because the difference between the midpoint voltage and the voltage of any phase of the power grid is smaller than that of the two-level rectifier bridge, the instantaneous power of the three-phase MISN module can be reduced, and thus, on the basis of ensuring the wide voltage output range of the three-level rectifier bridge, the volume of the clamping capacitor in the MISN module does not need to be significantly increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0060] Figure 1 A schematic structural diagram of a three-phase MISN converter provided by the present invention;

[0061] Figure 2 A schematic structural diagram of another three-phase MISN converter provided by the present invention;

[0062] Figure 3 A schematic structural diagram of a MISN module provided by the present invention;

[0063] Figure 4 A schematic structural diagram of an A-phase equivalent MISN converter provided by the present invention;

[0064] Figure 5 A schematic diagram of the operating waveform of an A-phase equivalent MISN converter provided by the present invention;

[0065] Figure 6 A schematic diagram of the capacitor voltage waveform of the MISN module under different chopping angles provided by the present invention;

[0066] Figure 7 A schematic diagram showing the effect of output voltage on the capacitance volume of a MISN module provided by the present invention;

[0067] Figure 8 Schematic diagram of the effect of a three-level low-frequency bridge provided by the present invention on the capacitance volume of the MISN module;

[0068] Figure 9 Schematic diagram of the effect of a two-level low-frequency bridge provided by the present invention on the capacitance volume of the MISN module;

[0069] Figure 10 A process flow chart of a three-phase MISN converter control method provided by the present invention;

[0070] Figure 11 A schematic diagram of a low-frequency bridge driving method provided by the present invention;

[0071] Figure 12 A schematic diagram of another low-frequency bridge driving method provided by the present invention;

[0072] Figure 13 A schematic diagram of another low-frequency bridge driving method provided by the present invention;

[0073] Figure 14 A schematic diagram of another low-frequency bridge driving method provided by the present invention;

[0074] Figure 15 A schematic diagram of another low-frequency bridge driving method provided by the present invention;

[0075] Figure 16 A control schematic diagram of a three-phase MISN converter provided by the present invention;

[0076] Figure 17 A schematic diagram of a current loop structure based on DQ control provided by the present invention;

[0077] Figure 18 A schematic diagram of a transient compensation control method provided by the present invention to generate an ideal modulation signal;

[0078] Figure 19 This is a structural diagram of a three-phase MISN converter control system provided by the present invention. DETAILED DESCRIPTION

[0079] The core of the present invention is to provide a three-phase MISN converter, control method and system. Based on the three-phase MISN module and three-phase inductor, this solution adds a three-level rectifier bridge. Compared with the two-level rectifier bridge, the three-level rectifier bridge can reduce the instantaneous power of the MISN module, thereby ensuring the wide voltage output range of the three-level rectifier bridge without significantly increasing the volume of the clamping capacitor in the MISN module.

[0080] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0081] Please refer to Figure 1 , Figure 1 This is a structural diagram of a three-phase MISN converter provided by the present invention. The three-phase MISN converter includes: a three-phase MISN module 1, a three-phase inductor 2, and a three-level rectifier bridge 3;

[0082] The three-phase input terminals of the three-phase inductor 2 are connected one-to-one with the output terminals of the three-phase power grid, and the three-phase output terminals are connected one-to-one with the three-phase input terminals of the three-phase MISN module 1;

[0083] The three-phase output terminals of the three-phase MISN module 1 are connected to the input terminals of the three-level rectifier bridge 3, and the product of the port voltage of any phase MISN module in the three-phase MISN module 1 and the current value of the corresponding phase inductor in the three-phase inductor 2 is less than the preset power threshold;

[0084] The midpoint of the three-level rectifier bridge 3 is respectively connected to the neutral point of the three-phase power grid and the input end of the three-level rectifier bridge 3. The midpoint of the three-level rectifier bridge 3 is respectively connected to the positive output end of the three-level rectifier bridge 3 and the negative output end of the three-level rectifier bridge 3 through two corresponding electrolytic capacitors. The positive output end of the three-level rectifier bridge 3 and the negative output end of the three-level rectifier bridge 3 are both connected to the load.

[0085] In the present invention, considering that if a two-level rectifier bridge is used to have a wide voltage output range, it is necessary to significantly increase the volume of the clamping capacitor in the MISN module, so this solution changes the two-level rectifier bridge to a three-level rectifier bridge 3. Because the midpoint of the three-level rectifier bridge 3 is connected to the three-phase output end of the three-phase MISN module 1 through the corresponding switch tube, when there is no neutral line in the three-phase power grid, if the corresponding switch tube is closed, the voltage difference between the midpoint voltage of the three-level rectifier bridge 3 and the corresponding phase power grid voltage will be very small, thereby reducing the instantaneous power of the MISN module, and thus, on the basis of ensuring the wide voltage output range of the three-level rectifier bridge 3, there is no need to significantly increase the volume of the clamping capacitor in the MISN module.

[0086] This embodiment provides a three-phase MISN converter, which is provided with a three-phase MISN module 1, a three-phase inductor 2, and a three-level rectifier bridge 3. Based on the existing three-phase MISN module 1 and the three-phase inductor 2, this solution further provides a three-level rectifier bridge 3. Because the difference between the midpoint voltage of the three-level rectifier bridge 3 and the voltage of any phase of the power grid is smaller than that of the two-level rectifier bridge, the instantaneous power of the three-phase MISN module 1 can be reduced, and thus, on the basis of ensuring a wide voltage output range of the three-level rectifier bridge 3, there is no need to significantly increase the volume of the clamping capacitor in the MISN module.

[0087] Based on the above embodiment:

[0088] As an optional embodiment, any phase MISN module includes: a plurality of H-bridge units; any H-bridge unit includes: a first switch, a second switch, a third switch, a fourth switch, and a clamping capacitor;

[0089] The first end of the first switch is respectively connected to the anode of the clamping capacitor and the first end of the third switch, and the second end is respectively connected to the first end of the second switch, the second end of the third switch of the next H-bridge unit, or the input end of the three-level rectifier bridge 3 or the midpoint of the three-level rectifier bridge 3;

[0090] The second end of the second switch is connected to the cathode of the clamping capacitor and the second end of the fourth switch;

[0091] The second end of the third switch is connected to the output end of the three-phase inductor 2 or the second end of the first switch of the previous H-bridge unit.

[0092] In the present invention, a plurality of H-bridge units are provided within any phase MISN module, and each H-bridge unit is provided with a first switch, a second switch, a third switch, a fourth switch, and a clamping capacitor. The H-bridge units are connected in series. According to the principles of the MISN converter, the output voltage of the MISN module can be adjusted by controlling the chopping angle, that is, the duty cycle of the switches within the MISN module. Furthermore, the larger the chopping angle, the greater the output voltage in steady state. Therefore, the MISN converter can achieve voltage boosting, ensuring that the three-phase MISN converter has a wide voltage output range.

[0093] It should be noted that the structure of the three-phase MISN converter with a wide output voltage range proposed in this application is as follows: Figure 2 As shown, it mainly includes MISN (module, three-level T-type low-frequency rectifier bridge, grid-side inductor L and AC source (three-phase grid). The low-frequency bridge is a T-type structure, in which , , , , , For synchronous rectifiers, diodes or unidirectional blocking devices can be used. , , It is a bidirectional blocking device. The MISN module is composed of multiple H-bridge units cascaded, such as Figure 3 As shown in Figure 1, each H-bridge unit contains four switching transistors and a clamping capacitor. One end of the MISN module is connected to the inductor, and the other end is connected to the midpoint of the bridge arm of the three-level low-frequency bridge. The number of H-bridge units in the MISN module can be any number N, and the rated working voltage of the clamping capacitor of each H-bridge unit is , the voltage of all clamping capacitors of MISN module is , With DC output voltage There is no need to satisfy the integer multiple relationship. Figure 2 shown , , Switching devices with bidirectional blocking capability or devices with unidirectional blocking capability connected head-to-head can be used. The remaining switches can use unidirectional blocking devices, such as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), etc.

[0094] It should also be noted that when the MISN converter is connected to a grid with a neutral line, the converter operates in a three-phase four-wire mode. At this time, the grid neutral point N and the output bus midpoint O are forced to be at the same potential, the three phases are decoupled, and can be controlled by three independent control loops. If the converter is connected to a grid without a neutral line, the converter operates in a three-phase three-wire mode. Figure 2 Without a neutral line, there will be a potential difference between the grid neutral point N and the output bus midpoint O, and the potential balance between the two points needs to be maintained through control. In order to make the MISN converter compatible with both working modes, the present invention proposes a corresponding control method.

[0095] It should also be noted that in steady-state operation, the equivalent circuit of phase A of the three-phase MISN converter is as follows: Figure 4 As shown, including A-phase AC power supply , A-phase inductor, A-phase MISN module, and A-phase T-type low-frequency bridge. Figure 5 The first figure is the key waveform of the circuit in steady state, and the first figure corresponds to the midpoint voltage of the low-frequency bridge arm and A-phase grid voltage ; The second picture corresponds to the port voltage of the MISN module , which is numerically approximately equal to ; The third picture corresponds to the inductor voltage ; The fourth figure corresponds to the inductor current and the filtered power frequency component i grid (To simplify the analysis, the input filter is omitted in the circuit schematic.) The midpoint voltage of the low-frequency bridge arm There is a big difference between them, and the MISN module will generate corresponding multi-level step waves. This reduces the volt-seconds on the inductor, significantly reducing the inductor size of the MISN converter. Because the inductor volt-seconds are controlled by the voltage at the MISN module port, the MISN module serves to reduce the inductor volt-seconds, thereby reducing the required inductor size; on the other hand, the MISN module controls the inductor current to achieve power factor correction.

[0096] It should also be noted that within the chopping angle range, the MISN module is in a charging state, while in other phases, the MISN module is mainly in a discharging state. Figure 6 As shown in Figure 2, the waveform of the capacitor voltage of the MISN module at different output voltages is given, where is the voltage sum of the MISN module capacitors. According to the above analysis, the larger the output voltage of the MISN converter, the larger the required chopping angle, which in turn leads to an increase in the energy absorbed by the MISN module and an increase in the voltage ripple of the MISN module capacitor.

[0097] As an optional embodiment, a three-level rectifier bridge 3 includes: a first rectifier tube S1, a second rectifier tube S2, a third rectifier tube S3, a fourth rectifier tube S4, a fifth rectifier tube S5, a sixth rectifier tube S6, a first bidirectional switch SA, a second bidirectional switch SB, a third bidirectional switch SC, a first capacitor, and a second capacitor;

[0098] The first end of the first rectifier tube S1 is connected to the first phase output end of the three-phase MISN module 1, and the second end is connected to the second end of the third rectifier tube S3 and the second end of the fifth rectifier tube S5 respectively. The second end of the first rectifier tube S1 serves as the positive output end of the three-level rectifier bridge 3;

[0099] The first end of the second rectifier tube S2 is connected to the first phase output end of the three-phase MISN module 1, and the second end is connected to the second end of the fourth rectifier tube S4 and the second end of the sixth rectifier tube S6 respectively. The second end of the second rectifier tube S2 serves as the negative output end of the three-level rectifier bridge 3;

[0100] A first end of the third rectifier tube S3 is connected to the second phase output end of the three-phase MISN module 1;

[0101] A first end of the fourth rectifier tube S4 is connected to the second phase output end of the three-phase MISN module 1;

[0102] A first end of the fifth rectifier tube S5 is connected to the third phase output end of the three-phase MISN module 1;

[0103] A first end of the sixth rectifier tube S6 is connected to the third phase output end of the three-phase MISN module 1;

[0104] The first end of the first bidirectional switch SA is connected to the first phase output end of the three-phase MISN module 1, and the second end is connected to the second end of the second bidirectional switch SB and the second end of the third bidirectional switch SC respectively. The second end of the first bidirectional switch SA is the midpoint of the three-level rectifier bridge 3;

[0105] A first end of the second bidirectional switch SB is connected to the second phase output end of the three-phase MISN module 1;

[0106] A first end of the third bidirectional switch SC is connected to the third phase output end of the three-phase MISN module 1;

[0107] The negative electrode of the first capacitor is connected to the positive electrode of the second capacitor, the second end of the first bidirectional switch SA, the second end of the second bidirectional switch SB, and the second end of the third bidirectional switch SC, respectively. The positive electrode is the positive output end of the three-level rectifier bridge 3.

[0108] The cathode of the second capacitor is the negative output terminal of the three-level rectifier bridge 3 .

[0109] In the present invention, compared with the two-level rectifier bridge, the three-level rectifier bridge 3 adds a first bidirectional switch SA, a second bidirectional switch SB and a third bidirectional switch SC, and the first end of each bidirectional switch is connected to the corresponding phase power grid through the corresponding phase MISN module and the corresponding phase inductor. When the bidirectional switch is closed based on control, the voltage difference between the corresponding phase power grid and the midpoint of the three-level rectifier bridge 3 can be significantly reduced, thereby reducing the instantaneous power of the MISN module. Therefore, on the basis of ensuring the wide voltage output range of the three-level rectifier bridge 3, there is no need to significantly increase the volume of the clamping capacitor in the MISN module.

[0110] It should be noted that when the output voltage range of the converter is increased, the volume of the MISN module capacitor will increase dramatically, which will seriously damage the power density of the circuit. Figure 7 The present invention uses a three-phase MISN converter constructed with a T-type three-level low-frequency bridge. In this case, the capacitance and volume of the MISN module increase only slightly with the increase of the output voltage.

[0111] It should also be noted that in Figure 8 and Figure 9 The influence of T-type three-level low-frequency bridge and two-level low-frequency bridge on the capacitance volume of MISN module is compared. With input voltage The difference is smaller than that of the two-level low-frequency bridge, so the T-type three-level low-frequency bridge will reduce the voltage of the MISN module port Since the energy absorbed by the MISN module is the MISN port voltage within the chopping angle time range, Multiply the inductor current by The smaller the value, the less energy the MISN module capacitor absorbs. In contrast, the difference between the midpoint voltage of the two-level low-frequency bridge arm and the input voltage is larger, so the capacitor volume of the MISN module needs to buffer a larger amount of energy.

[0112] Please refer to Figure 10 , Figure 10 A process flow chart of a three-phase MISN converter control method provided by the present invention. The three-phase MISN converter control method is applied to the three-phase MISN converter as described above, comprising:

[0113] S11: Obtain three-phase current values ​​of the three-phase grid, three-phase voltage values ​​of the three-phase grid, and output voltage of the three-level rectifier bridge 3;

[0114] S12: performing a corresponding first proportional integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value;

[0115] S13: Determine a first PWM signal according to the D-axis current reference value, the preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values.

[0116] In the present invention, considering that if the load connected to the three-level rectifier bridge 3 changes, the output voltage of the three-level rectifier bridge 3 will also change, thereby causing the instantaneous power of the MISN module to change, so in order to ensure that the instantaneous power of the MISN module is less than the preset power threshold, this solution requires the three-phase current value of the three-phase power grid, the three-phase voltage value of the three-phase power grid, and the output voltage of the three-level rectifier bridge 3 in real time, and performs a corresponding first proportional integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value. Because the D-axis current reference value represents the adjustment amount of the active power, it is also necessary to determine the preset Q-axis current. A current reference value, that is, a reactive power adjustment amount, is obtained by calculating the D-axis current reference value, the preset Q-axis current reference value, the three-phase current value of the three-phase power grid, and the three-phase voltage value of the three-phase power grid. A first PWM signal is determined based on the first PWM signal, and the duty cycle of the H-bridge unit in the three-phase MISN module 1 is controlled based on the first PWM signal until the product of the port voltage of any phase MISN module in the three-phase MISN module 1 and the current value of the corresponding phase inductor in the three-phase inductor 2 is less than the preset power threshold, thereby ensuring that the instantaneous power of the MISN module is never too large, so that the three-phase MISN converter can output a stable voltage, and improving the stability of the solution.

[0117] As an optional embodiment, the method further includes:

[0118] Determine the clamping voltage value of the clamping capacitor in the three-phase MISN module 1;

[0119] performing a corresponding third proportional-integral operation on the clamp voltage value and the second preset voltage to generate a corresponding target chopping angle;

[0120] A corresponding second PWM signal is generated according to the target chopping angle, and the duty cycle of the switching device in the three-level rectifier bridge is adjusted based on the second PWM signal.

[0121] In the present invention, it is necessary to control the capacitor voltage of the three-phase MISN module 1. On the one hand, it can avoid the voltage of the clamping capacitor of the MISN module being too low, resulting in the inductor volt-second being out of control. On the other hand, it can avoid the voltage overvoltage of the clamping capacitor of the MISN module causing device damage. The way of controlling the capacitor voltage in this scheme is to control the duty cycle of the switching device in the three-level rectifier bridge 3. The specific process is: first determine the clamping voltage value of the clamping capacitor in the three-phase MISN module 1, and then perform a corresponding third proportional integral operation on the clamping voltage value and the second preset voltage to generate a corresponding target chopping angle. Finally, generate a corresponding second PWM signal according to the target chopping angle, and adjust the duty cycle of the switching device in the three-level rectifier bridge 3 based on the second PWM signal to ensure the voltage stability of the clamping capacitor of the MISN module, so that the MISN module can significantly reduce the volt-second of the inductor, and also ensure the safety of the devices in the three-phase MISN converter.

[0122] It should be noted that the capacitor voltage of the MISN module also needs to be controlled to prevent the capacitor voltage of the MISN module from being too low, which may lead to loss of control of the inductor volt-second, and to prevent overvoltage in the MISN module from causing damage to the device. In the present invention, each of the three MISN modules of the three-phase MISN converter is equipped with a voltage control loop. The output of the control loop is the chopping angle, which is modulated to drive the corresponding low-frequency bridge.

[0123] As an optional embodiment, performing a corresponding third proportional-integral operation on the clamping voltage value and the second preset voltage to generate a corresponding target chopping angle includes:

[0124] adjusting the position of the preset chopping angle within the half period according to the proportional integral calculation result obtained by the third proportional integral operation;

[0125] The preset chopping angle after position adjustment is used as the target chopping angle.

[0126] In the present invention, after performing the corresponding third proportional integral operation on the clamping voltage value and the second preset voltage, the position of the preset chopping angle within the half cycle is adjusted, and the preset chopping angle after the position adjustment is used as the target chopping angle. Figure 11-15As shown in the figure, it corresponds to the changes in the positions of various preset chopping angles. Because the different positions of the preset chopping angles within the half cycle will lead to different capacitor voltage ripples of the MISN module, which in turn affects the inductor volt-seconds, this scheme can control the inductor volt-seconds in real time by changing the position of the preset chopping angle within the half cycle, thereby improving the reliability of the scheme.

[0127] It should be noted that in the above analysis, the driving method of the low-frequency bridge is as follows Figure 11-15 As shown, the chopping angles are symmetrically distributed on both sides. In principle, there are many ways to control the chopping angle of the low-frequency bridge. Figure 11 The example shown is that the chopping angle is set on both sides of the positive and negative half-cycle. Figure 12-15 In the example shown, the chopping angle is concentrated on the left or right side of the positive and negative half cycles; in addition, the chopping angle can also be arbitrarily distributed at any position. Different driving methods will result in different capacitor voltage ripples of the MISN module.

[0128] As an optional embodiment, determining the first PWM signal according to the D-axis current reference value, the preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values ​​includes:

[0129] Performing a transformation from the ABC coordinate system to the DQ coordinate system according to the three-phase current values ​​of the three-phase inductor 2 and the three-phase voltage values ​​of the three-phase inductor 2 to generate a D-axis current component and a Q-axis current component;

[0130] performing a second proportional integral operation on the D-axis current component and the D-axis current reference value to generate a first operation result;

[0131] performing a second proportional integral operation on the Q-axis current component and the Q-axis current reference value to generate a second operation result;

[0132] Determine the D-axis operation result according to the first operation result, the Q-axis current component, the output voltage, the inductance value of the three-phase inductor 2, and the angular frequency of the three-phase power grid;

[0133] Determine a Q-axis operation result based on the second operation result, the D-axis current component, the output voltage, the inductance value, and the angular frequency;

[0134] Performing a DQ coordinate system to an ABC coordinate system transformation on the D-axis calculation results and the Q-axis calculation results to generate a three-phase voltage signal;

[0135] The first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the three-phase voltage signal and the first PWM signal.

[0136] In the present invention, the process of determining the first PWM signal is actually the process of performing DQ transformation and inverse transformation. The specific process is: performing a transformation from the ABC coordinate system to the DQ coordinate system according to the three-phase current value and the three-phase voltage value of the three-phase inductor 2 to generate a D-axis current component and a Q-axis current component, and performing a second proportional integral operation on the D-axis current component and the D-axis current reference value to generate a first operation result; performing a second proportional integral operation on the Q-axis current component and the Q-axis current reference value to generate a second operation result, and determining the D-axis operation result according to the first operation result, the Q-axis current component, the output voltage, the inductance value of the three-phase inductor 2 and the angular frequency of the three-phase power grid; determining the Q-axis operation result according to the second operation result, the D-axis current component, the output voltage, the inductance value and the angular frequency, and performing a transformation from the DQ coordinate system to the ABC coordinate system on the D-axis operation result and the Q-axis operation result to generate a three-phase voltage signal, and finally determining the first PWM signal corresponding to the three-phase voltage signal according to the corresponding relationship between the three-phase voltage signal and the first PWM signal, thereby ensuring the integrity of the first PWM signal determination process.

[0137] It should be noted that the MISN converter control method used in the present invention can not only work in the three-phase four-wire mode, but also in the three-phase three-wire mode. The control block diagram of the converter is shown in FIG. Figure 11 As shown in the figure, the three oblique lines indicate that the path is a three-phase symmetrical signal. The control system mainly consists of four parts: the current control link based on DQ control, output voltage control, MISN module capacitor voltage control, and transient compensation control.

[0138] It should also be noted that, according to the above analysis, the MISN module port voltage can control the volt-second of the inductor, so the inductor current control can be achieved by controlling the duty cycle of the MISN module through the current loop. Considering that the power grid may lack a neutral line, DQ transformation is used to control the three-phase inductor current, such as Figure 17 First, the three-phase phase-locked loop is used to calculate the current of the three-phase inductor 2. Transform the ABC coordinate system to the DQ (Park's Transformation) coordinate system to obtain the D-axis component and Q-axis component When the MISN converter is used for PFC (Power Factor Correction) function, the D-axis reference signal The output voltage loop determines the Q-axis reference signal, and the Q-axis reference signal is zero. When the MISN converter is used for grid-connected operation, the D-axis component is determined by the active power closed-loop control, and the Q-axis component is determined by the reactive power closed-loop control. To prevent mutual influence between the D-axis and Q-axis controls, a decoupling control is implemented between the two. Finally, the calculated results are inversely transformed from the DQ coordinate system to the ABC coordinate system. The result is then used for PWM (Pulse Width Modulation) modulation to generate the duty cycle drive signal for the MISN module.

[0139] As an optional embodiment, before determining the first PWM signal corresponding to the three-phase voltage signal according to the correspondence between the three-phase voltage signal and the first PWM signal, the method further includes:

[0140] Performing transient compensation control according to the three-phase voltage values ​​of the three-phase inductor 2 and the output voltage to generate a three-phase voltage symmetrical modulation signal;

[0141] Accordingly, determining the first PWM signal corresponding to the three-phase voltage signal according to the corresponding relationship between the three-phase voltage signal and the first PWM signal includes:

[0142] Determine a voltage difference signal between a three-phase voltage signal and a three-phase voltage symmetrical modulation signal;

[0143] The first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the voltage difference signal and the first PWM signal.

[0144] In the present invention, considering that the MISN module also needs to reduce the volt-second of the inductance, the MISN module also needs to be transiently compensated and controlled while considering the influence of the load on the port voltage of the MISN module. That is, the three-phase voltage value of the three-phase power grid is first determined, and then transient compensation control is performed according to the three-phase voltage value and the output voltage to generate a three-phase voltage symmetrical modulation signal, and then the voltage difference signal between the three-phase voltage signal and the three-phase voltage symmetrical modulation signal is determined. Finally, the first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the voltage difference signal and the first PWM signal, thereby improving the accuracy of the duty cycle modulation of the MISN module.

[0145] It should be noted that in order to reduce the volt-second of the inductor, the duty cycle of the MISN module will switch when the low-frequency bridge switch is in operation. Figure 16 In the control block diagram shown in FIG, the present invention adds transient compensation control to the output side of the current loop to obtain an ideal three-phase symmetrical modulation signal. .like Figure 18 As shown, in the shaded area, the duty cycle of the MISN module needs to be switched quickly.

[0146] As an optional embodiment, after controlling the duty cycle of the H-bridge unit in the three-phase MISN module 1 based on the first PWM signal, the method further includes:

[0147] Determine the frequency of the port voltage of the three-phase MISN module 1 and the number of H-bridge units in the three-phase MISN module 1;

[0148] Determine the product of the number and the preset switching frequency;

[0149] Determine whether the difference between the frequency and the product is within a preset range;

[0150] If the difference between the frequency and the product is within a preset range, the step of obtaining the three-phase current value of the three-phase grid, the three-phase voltage value of the three-phase grid, and the output voltage of the three-level rectifier bridge 3 is triggered;

[0151] If the difference between the frequency and the product is not within the preset range, it is determined that a fault has occurred.

[0152] In the present invention, considering that the frequency of the port voltage of the MISN module needs to maintain a preset size relationship with the product of the preset switching frequency and the number of H-bridge units in order to significantly reduce the inductance volt-seconds, after modulating the duty cycle of the H-bridge unit in the three-phase MISN module 1, it is also necessary to determine the frequency of the port voltage of the three-phase MISN module 1 and the number of H-bridge units in the three-phase MISN module 1, and judge whether the difference between the frequency of the port voltage of the three-phase MISN module 1 and the product of the number of H-bridge units in the three-phase MISN module 1 and the preset switching frequency is within a preset range. If the difference between the frequency and the product is within the preset range, the duty cycle of the H-bridge unit in the MISN module continues to be modulated in real time. Conversely, if the difference between the frequency and the product is not within the preset range, it is determined that a fault has occurred, which facilitates users or maintenance personnel to promptly check the components in the three-phase MISN converter to ensure that the MISN module can significantly reduce the inductance volt-seconds, thereby improving the accuracy and reliability of the solution.

[0153] It should also be noted that the MISN module uses carrier phase shift pulse width modulation (PS-PWM), which makes the port voltage of the MISN module Frequency doubling significantly reduces inductance volt-seconds.

[0154] Please refer to Figure 19 , Figure 19 This is a schematic diagram of the structure of a three-phase MISN converter control system provided by the present invention. The three-phase MISN converter control system is applied to the three-phase MISN converter as described above, and includes:

[0155] An acquisition unit 11 is used to acquire the current value of the three-phase inductor, the voltage value of the three-phase grid, and the output voltage of the three-level rectifier bridge;

[0156] a proportional-integral operation unit 12 for performing a corresponding first proportional-integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value;

[0157] The determining unit 13 is configured to determine a first PWM signal according to a D-axis current reference value, a preset Q-axis current reference value, three-phase current values, and three-phase voltage values ​​of three-phase inductors.

[0158] The three-phase MISN converter control system provided in this embodiment corresponds to the above method and has the same beneficial effects as the above method. Therefore, for the embodiments of the three-phase MISN converter control system, please refer to the description of the embodiments of the method part, which will not be repeated here.

[0159] It should be noted that, in this specification, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0160] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-phase MISN converter, characterized in that: include: Three-phase MISN module, three-phase inductor, three-level rectifier bridge; The three-phase input ends of the three-phase inductor are respectively connected to the output ends of the three-phase power grid in a one-to-one correspondence, and the three-phase output ends are respectively connected to the three-phase input ends of the three-phase MISN module in a one-to-one correspondence; The three-phase output end of the three-phase MISN module is correspondingly connected to the input end of the three-level rectifier bridge; The midpoint of the three-level rectifier bridge is respectively connected to the neutral point of the three-phase power grid and the input end of the three-level rectifier bridge, the midpoint of the three-level rectifier bridge is respectively connected to the positive output end of the three-level rectifier bridge and the negative output end of the three-level rectifier bridge through two corresponding electrolytic capacitors, and the positive output end of the three-level rectifier bridge and the negative output end of the three-level rectifier bridge are both connected to the load.

2. The three-phase MISN converter according to claim 1, characterized in that: Any phase MISN module includes: a plurality of H-bridge units; any H-bridge unit includes: a first switch, a second switch, a third switch, a fourth switch, and a clamping capacitor; The first end of the first switch is respectively connected to the anode of the clamping capacitor and the first end of the third switch, and the second end is respectively connected to the first end of the second switch, the second end of the third switch of the next H-bridge unit, or the input end of the three-level rectifier bridge or the midpoint of the three-level rectifier bridge; The second end of the second switch is connected to the cathode of the clamping capacitor and the second end of the fourth switch; The second end of the third switch is connected to the output end of the three-phase inductor or the second end of the first switch of the previous H-bridge unit.

3. The three-phase MISN converter according to claim 1 or 2, characterized in that: The three-level rectifier bridge comprises: a first rectifier tube, a second rectifier tube, a third rectifier tube, a fourth rectifier tube, a fifth rectifier tube, a sixth rectifier tube, a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, a first capacitor, and a second capacitor; The first end of the first rectifier is connected to the first phase output end of the three-phase MISN module, and the second end is respectively connected to the second end of the third rectifier and the second end of the fifth rectifier, and the second end of the first rectifier serves as the positive output end of the three-level rectifier bridge; The first end of the second rectifier is connected to the first phase output end of the three-phase MISN module, and the second end is respectively connected to the second end of the fourth rectifier and the second end of the sixth rectifier, and the second end of the second rectifier serves as the negative output end of the three-level rectifier bridge; The first end of the third rectifier is connected to the second phase output end of the three-phase MISN module; The first end of the fourth rectifier is connected to the second phase output end of the three-phase MISN module; The first end of the fifth rectifier tube is connected to the third phase output end of the three-phase MISN module; The first end of the sixth rectifier tube is connected to the third phase output end of the three-phase MISN module; The first end of the first bidirectional switch is connected to the first phase output end of the three-phase MISN module, and the second end is respectively connected to the second end of the second bidirectional switch and the second end of the third bidirectional switch, and the second end of the first bidirectional switch is the midpoint of the three-level rectifier bridge; A first end of the second bidirectional switch is connected to a second phase output end of the three-phase MISN module; A first end of the third bidirectional switch is connected to a third phase output end of the three-phase MISN module; The negative electrode of the first capacitor is respectively connected to the positive electrode of the second capacitor, the second end of the first bidirectional switch, the second end of the second bidirectional switch and the second end of the third bidirectional switch, and the positive electrode is the positive output end of the three-level rectifier bridge; The cathode of the second capacitor is the negative output terminal of the three-level rectifier bridge.

4. A three-phase MISN converter control method, characterized in that: The three-phase MISN converter according to any one of claims 1 to 3 comprises: Obtaining the three-phase current value of the three-phase power grid, the three-phase voltage value of the three-phase power grid, and the output voltage of the three-level rectifier bridge; Performing a corresponding first proportional integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value; A first PWM signal is determined according to the D-axis current reference value, the preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values.

5. The three-phase MISN converter control method according to claim 4, characterized in that: Also includes: Determine the clamping voltage value of the clamping capacitor in the three-phase MISN module; performing a corresponding third proportional integral operation on the clamping voltage value and the second preset voltage to generate a corresponding target chopping angle; A corresponding second PWM signal is generated according to the target chopping angle, and the duty cycle of the switching device in the three-level rectifier bridge is adjusted based on the second PWM signal.

6. The three-phase MISN converter control method according to claim 5, characterized in that: The performing a corresponding third proportional integral operation on the clamping voltage value and the second preset voltage to generate a corresponding target chopping angle includes: adjusting the position of the preset chopping angle within the half period according to the proportional integral calculation result obtained by the third proportional integral operation; The preset chopping angle after position adjustment is used as the target chopping angle.

7. The three-phase MISN converter control method according to claim 4, characterized in that: The determining of the first PWM signal according to the D-axis current reference value, the preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values ​​comprises: Performing a transformation from an ABC coordinate system to a DQ coordinate system according to the three-phase current values ​​of the three-phase inductance and the three-phase voltage values ​​of the three-phase inductance to generate a D-axis current component and a Q-axis current component; performing a second proportional integral operation on the D-axis current component and the D-axis current reference value to generate a first operation result; performing the second proportional integral operation on the Q-axis current component and the Q-axis current reference value to generate a second operation result; Determine a D-axis operation result according to the first operation result, the Q-axis current component, the output voltage, the inductance value of the three-phase inductor and the angular frequency of the three-phase power grid; determining a Q-axis operation result according to the second operation result, the D-axis current component, the output voltage, the inductance value, and the angular frequency; Transforming the D-axis calculation result and the Q-axis calculation result from a DQ coordinate system to an ABC coordinate system to generate a three-phase voltage signal; The first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the three-phase voltage signal and the first PWM signal.

8. The three-phase MISN converter control method according to claim 7, characterized in that: Before determining the first PWM signal corresponding to the three-phase voltage signal according to the corresponding relationship between the three-phase voltage signal and the first PWM signal, the method further includes: Performing transient compensation control according to the three-phase voltage values ​​of the three-phase inductor and the output voltage to generate a three-phase voltage symmetrical modulation signal; Correspondingly, determining the first PWM signal corresponding to the three-phase voltage signal according to the corresponding relationship between the three-phase voltage signal and the first PWM signal includes: Determine a voltage difference signal between the three-phase voltage signal and the three-phase voltage symmetrical modulation signal; The first PWM signal corresponding to the three-phase voltage signal is determined according to the corresponding relationship between the voltage difference signal and the first PWM signal.

9. The three-phase MISN converter control method according to claim 4, characterized in that: After controlling the duty cycle of the H-bridge unit in the three-phase MISN module based on the first PWM signal, the method further includes: Determining the frequency of the port voltage of the three-phase MISN module and the number of H-bridge units in the three-phase MISN module; Determining the product of the number and a preset switching frequency; Determining whether the difference between the frequency and the product is within a preset range; If the difference between the frequency and the product is within a preset range, triggering the step of obtaining the three-phase current value of the three-phase power grid, the three-phase voltage value of the three-phase power grid, and the output voltage of the three-level rectifier bridge; If the difference between the frequency and the product is not within a preset range, it is determined that a fault occurs.

10. A three-phase MISN converter control system, characterized in that: The three-phase MISN converter according to any one of claims 1 to 3 comprises: An acquisition unit, used to acquire a three-phase current value of a three-phase power grid, a voltage value of the three-phase power grid, and an output voltage of a three-level rectifier bridge; a proportional-integral operation unit, configured to perform a corresponding first proportional-integral operation on the output voltage and the first preset voltage to generate a D-axis current reference value; A determination unit is used to determine a first PWM signal according to the D-axis current reference value, a preset Q-axis current reference value, the three-phase current values, and the three-phase voltage values ​​of the three-phase inductance.

Images