Three-phase three-level converter topological structure and rectifier

Abstract

The invention belongs to the technical field of high-frequency rectifiers, and particularly relates to a three-phase three-level converter topological structure and a rectifier, and the three-phase three-level converter topological structure is composed of a load, a rectifier, a high-frequency transformer, a clamping circuit, a three-phase three-level converter, a three-phase power supply and a filter circuit. The system has the advantages that voltage spikes generated by leakage inductance of a transformer and parasitic capacitance resonance of a switching tube in the converter can be effectively absorbed by adding the clamping circuit, so that safe and stable operation of the switching tube is ensured, neutral-point potential balance is maintained, and secondary efficient utilization of energy is also realized; the T-type neutral point clamping converter is adopted, so that the number of switching tubes is reduced, the structural complexity is reduced, and the cost is saved; and meanwhile, several groups of switch tubes are added, so that decoupling modulation of the rectifier can be realized, and the difficulty of designing system modulation is simplified.

Description

Technical Field

[0001] The present application belongs to the technical field of high-frequency rectifiers, and specifically relates to a three-phase three-level converter topology structure and a rectifier. Background Art

[0002] At present, three-phase rectifier circuits are mainly divided into non-isolated rectifier circuits and isolated rectifier circuits. For isolated rectifier circuits, according to the type of transformer used in the isolation link, if the transformer is an industrial frequency transformer, then this type of rectifier circuit is called a low-frequency isolated rectifier circuit; if a high-frequency transformer is used, it is correspondingly called a high-frequency isolated rectifier circuit.

[0003] Compared with the industrial frequency rectifier, the three-phase high-frequency rectifier has the advantages of good energy saving effect, high output stability and high power factor, so it is widely used. At the same time, the three-phase high-frequency rectifier can be divided into two categories according to the voltage level of the output voltage. One is a three-phase two-level high-frequency rectifier, which has a simple structure, low cost, easy to implement and control, but the disadvantage is that the output voltage has only two levels, resulting in an increase in harmonic content, which will have a certain impact on the power grid. The other is a three-phase three-level high-frequency rectifier, which has the advantages of stable output voltage, a large adjustable range, and is suitable for various application scenarios; it can achieve bidirectional power flow capability, which can significantly reduce energy waste and energy loss; at the same time, in this rectifier, the voltage borne by a single switch tube on the bridge arm is only half of the DC bus voltage, thereby reducing the requirements for the device's withstand voltage level.

[0004] However, there is a problem with the three-phase three-level high-frequency rectifier. Because it requires multiple switching tubes and diodes, the rectifier has a complex structure and high manufacturing cost, and also makes the modulation strategy more difficult to design and implement. The voltage spike caused by the resonance between the transformer leakage inductance and the parasitic capacitance will reduce the service life of the rectifier. The existence of these problems has greatly affected the promotion and application of this type of rectifier. Summary of the invention

[0005] Based on the above problems, the present invention aims to provide a three-phase three-level high-frequency rectifier topology with a clamping circuit and a modulation method thereof, and its technical solution is:

[0006] A three-phase three-level converter topology structure includes a controllable switch tube S q1 -S q8 , S n1 -S n8 , S W1 -S W6 The controllable switch tube S q1 , S n1 Series branch, controllable switch tube S q2 , S n2 Series branch, controllable switch tube Sq3 , S n3 Series branches in parallel, S n1 , S n2 , S n3 The collectors are connected to three-phase alternating current e a , three-phase alternating current b and three-phase alternating current c ;

[0007] The controllable switch tube S q4 , S n4 Series branch, controllable switch tube S q5 , S n5 Series branch, controllable switch tube S q6 , S n6 Series branches in parallel, S q4 , S q5 , S q6 The collectors are connected to three-phase alternating current e a , three-phase alternating current b and three-phase alternating current c ;

[0008] Controllable switch tube S W1 With S W2 The series branches are connected to the controllable switch tube S W3 With S W4 Series branch, controllable switch tube S W5 With S W6 The series branches are connected in parallel and are connected to the three-phase AC a , three-phase alternating current b and three-phase alternating current c Connect to the controllable switch tube S n7 , S q8 The collector connection of

[0009] Controllable switch tube S q1 , S q2 , S q3 The collector of the q7 , controllable switch tube S q7 The emitter is connected to S n7 Emitter; controllable switch tube S n4 , S n5 , S n6 The collector of the n8 , controllable switch tube S n8 The emitter is connected to S q8 Emitter.

[0010] Preferably, three-phase alternating current a , e b , e cRespectively with the corresponding line impedance R a , R b , R c Connection; line impedance R a , R b , R c Respectively with the filter inductor L a , L b , L c connect.

[0011] Preferably, the controllable switch tube S n1 The collector of the controllable switch tube S q4 The collector and controllable switch tube S W1 The collector and filter inductor L a The negative electrode is connected to the controllable switch tube S n2 The collector of the controllable switch tube S q5 The collector and controllable switch tube S W3 The collector and filter inductor L b The negative electrode is connected to the controllable switch tube S n3 The collector of the controllable switch tube S q6 The collector and controllable switch tube S W5 The collector and filter inductor L c The negative electrode is connected to the controllable switch tube S q1 The emitter and the controllable switch tube S n1 The emitter of the controllable switch tube S q2 The emitter and the controllable switch tube S n2 The emitter of the controllable switch tube S q3 The emitter and the controllable switch tube S n3 The emitter of the controllable switch tube S q4 The emitter and the controllable switch tube S n4 The emitter of the controllable switch tube S q5 The emitter and the controllable switch tube S n5 The emitter of the controllable switch tube S q6 The emitter and the controllable switch tube S n6 The emitter of the controllable switch tube S W1 The emitter and the controllable switch tube S W2 The emitter of the controllable switch tube S W3 The emitter and the controllable switch tube S W4 The emitter of the controllable switch tube S W5 The emitter and the controllable switch tube S W6 The emitter of the controllable switch tube S q7 The emitter and the controllable switch tube S n7 The emitter of the controllable switch tube S q8The emitter and the controllable switch tube S n8 The emitter of the controllable switch tube S q7 The collector and the controllable switch tube S q3 The collector of the controllable switch tube S n7 The collector and the controllable switch tube S W4 The collector of the controllable switch tube S q8 The collector and the controllable switch tube S W4 The collector of the controllable switch tube S n8 The collector and the controllable switch tube S n6 The collector is connected.

[0012] A high-frequency rectifier with a clamping circuit, comprising a rectifier, a high-frequency transformer, a clamping circuit and a filter circuit; the clamping circuit comprises R 1 , C 1 , D 1 , R 2 , C 2 and D 2 ; The rectifier includes a controllable switch tube S 1 -S 4 ; The filter circuit includes resistor R and capacitor C f ; The clamping circuit is connected in parallel with the output of the three-phase three-level converter to absorb the voltage spike generated by the resonance of the transformer leakage inductance and the parasitic capacitance of the switch tube in the converter, and maintain the midpoint potential balance; the input end of the rectifier is connected to the three-phase three-level converter through a high-frequency transformer, and its output end is connected to the filter capacitor C f In parallel with resistor R.

[0013] Preferably, the capacitor C 1 With diode D 1 The series branch composed of the controllable switch tube S q7 , S n7 The series branches are connected in parallel, and the two series branches are connected to the controllable switch tube S W1 -S W6 In a parallel circuit; capacitor C 2 With diode D 2 The series branch composed of the controllable switch tube S q8 , S n8 The series branches are connected in parallel, and the two series branches are connected to the controllable switch tube S W1 -S W6 In a parallel circuit; capacitor C 1 The parallel resistor R 1 ; Capacitor C 2 The parallel resistor R 2 .

[0014] Preferably, the modulation method is as follows:

[0015] Controllable switch tube S q1 -S q8 , S W1 -S W6 The positive group converter N1 is composed of controllable switch tube S n1 -S n8 , S W1 -S W6 The negative group converter N2 is formed. When the converter input voltage is greater than zero, the positive group converter is PWM-controlled; when the converter input voltage is less than zero, the negative group converter is modulated by PWM; by adopting symmetrical wave generation, in each modulation cycle, only one phase of the switch state of two adjacent switch states changes. 7. The high-frequency rectifier with clamping circuit according to claim 4 is characterized in that when the positive half cycle of the input signal arrives, the diode D of the clamping circuit 1 or D 2 conduction, capacitor C 1 or C 2 is charged to a certain voltage value; when the negative half cycle of the input signal arrives, the diode D 1 or D 2 Cut-off, capacitor C 1 or C 2 The voltage on the input signal is superimposed on the input signal, thereby outputting a voltage clamped at a predetermined level;

[0016] When the midpoint potential is unbalanced and there is a potential difference, the clamp circuit works with diode D 1 or D 2 conduction, capacitor C 1 or C 2 Start charging; the clamping circuit clamps the peak value of the input voltage to a predetermined level through the coordinated action of the capacitor and the diode without changing the waveform of the signal.

[0017] Preferably, the SVPWM space voltage vector distribution of the positive group converter is set as follows:

[0018] Determine U according to θ ref The major sector:

[0019] When θ=0~60°, U ref Located in the first largest sector;

[0020] When θ=60~120°, U ref Located in the second largest sector;

[0021] When θ=120~180°, U ref Located in the third largest sector;

[0022] When θ=180~240°, U ref Located in the fourth largest sector;

[0023] When θ=240~300°, U ref Located in the fifth largest sector;

[0024] When θ=300~360°, U ref Located in the sixth largest sector.

[0025] Then, according to |U ref | and θ determine U ref The small area where it is located;

[0026] Assume that the projections of the reference voltage vector of the first sector on the x and y coordinate axes are:

[0027] x=|U ref |cosθ and y=|U ref |sinθ;

[0028] The boundary line equations of regions 1, 2 and 3, 4 are:

[0029]

[0030] The boundary line equations of regions 3 and 5 are:

[0031]

[0032] The boundary line equations of regions 4 and 6 are:

[0033]

[0034] (1) The boundary between the three small areas 1, 3, 5 and the three small areas 2, 4, 6 is θ = 30°; thus, it can be determined that U ref Is it located in the three sub-areas 1, 3, 5 or the three sub-areas 2, 4, 6?

[0035] (2)When U ref When it is located in the three small areas 1, 3, and 5, the above formula is used to determine the small area it is in;

[0036] (3)When U ref When it is in the three small areas 2, 4, and 6, the above formula is used to determine the small area it is in;

[0037] From the volt-second balance principle, the following equation can be derived:

[0038]

[0039] Among them, V1, V2, V3 are the selected state vectors, the action time is T1, T2, T3 respectively, and Ts is the reference voltage vector modulation period;

[0040] Solved:

[0041]

[0042] Among them, the space voltage vector modulation ratio m is:

[0043]

[0044] Where U ref For the voltage vector, U dc is the DC side voltage.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] By adding a clamping circuit, the voltage spike generated by the resonance of the transformer leakage inductance and the parasitic capacitance of the switch tube in the converter can be effectively absorbed, which not only ensures the safe and stable operation of the switch tube and maintains the midpoint potential balance, but also realizes the secondary efficient utilization of energy; by using a T-type neutral point clamping converter, this topology reduces the number of switches, reduces structural complexity and saves costs; by adding several groups of switches at the same time, the decoupling modulation of the rectifier can be realized, which simplifies the difficulty of designing system modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is the main circuit topology of a three-phase three-level high-frequency rectifier.

[0048] Figure 2 This is the decoupling diagram of the three-phase three-level high-frequency rectifier circuit.

[0049] Figure 3 It is the SVPWM space voltage vector distribution diagram. DETAILED DESCRIPTION

[0050] The technical solution of the present application is described in detail below through specific embodiments and drawings. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations on the technical solution of the present application, and the specific technical features may be combined with each other.

[0051] A three-phase three-level converter topology structure includes a controllable switch tube S q1 -S q8 , S n1 -S n8 , S W1 -S W6 The controllable switch tube S q1 , S n1 Series branch, controllable switch tube S q2 , S n2 Series branch, controllable switch tube S q3 , S n3 Series branches in parallel, Sn1 , S n2 , S n3 The collectors are connected to three-phase alternating current e a , three-phase alternating current b and three-phase alternating current c ;

[0052] The controllable switch tube S q4 , S n4 Series branch, controllable switch tube S q5 , S n5 Series branch, controllable switch tube S q6 , S n6 Series branches in parallel, S q4 , S q5 , S q6 The collectors are connected to three-phase alternating current e a , three-phase alternating current b and three-phase alternating current c ;

[0053] Controllable switch tube S W1 With S W2 The series branches are connected to the controllable switch tube S W3 With S W4 Series branch, controllable switch tube S W5 With S W6 The series branches are connected in parallel and are connected to the three-phase AC a , three-phase alternating current b and three-phase alternating current c Connect to the controllable switch tube S n7 , S q8 The collector connection of

[0054] Controllable switch tube S q1 , S q2 , S q3 The collector of the q7 , controllable switch tube S q7 The emitter is connected to S n7 Emitter; controllable switch tube S n4 , S n5 , S n6 The collector of the n8 , controllable switch tube S n8 The emitter is connected to S q8 Emitter.

[0055] Three-phase alternating current a , e b , e c Respectively with the corresponding line impedance R a , R b , Rc Connection; line impedance R a , R b , R c Respectively with the filter inductor L a , L b , L c connect.

[0056] Controllable switch tube S n1 The collector of the controllable switch tube S q4 The collector and controllable switch tube S W1 The collector and filter inductor L a The negative electrode is connected to the controllable switch tube S n2 The collector of the controllable switch tube S q5 The collector and controllable switch tube S W3 The collector and filter inductor L b The negative electrode is connected to the controllable switch tube S n3 The collector of the controllable switch tube S q6 The collector and controllable switch tube S W5 The collector and filter inductor L c The negative electrode is connected to the controllable switch tube S q1 The emitter and the controllable switch tube S n1 The emitter of the controllable switch tube S q2 The emitter and the controllable switch tube S n2 The emitter of the controllable switch tube S q3 The emitter and the controllable switch tube S n3 The emitter of the controllable switch tube S q4 The emitter and the controllable switch tube S n4 The emitter of the controllable switch tube S q5 The emitter and the controllable switch tube S n5 The emitter of the controllable switch tube S q6 The emitter and the controllable switch tube S n6 The emitter of the controllable switch tube S W1 The emitter and the controllable switch tube S W2 The emitter of the controllable switch tube S W3 The emitter and the controllable switch tube S W4 The emitter of the controllable switch tube S W5 The emitter and the controllable switch tube S W6 The emitter of the controllable switch tube S q7 The emitter and the controllable switch tube S n7 The emitter of the controllable switch tube S q8 The emitter and the controllable switch tube S n8 The emitter of the controllable switch tube S q7The collector and the controllable switch tube S q3 The collector of the controllable switch tube S n7 The collector and the controllable switch tube S W4 The collector of the controllable switch tube S q8 The collector and the controllable switch tube S W4 The collector of the controllable switch tube S n8 The collector and the controllable switch tube S n6 The collector is connected.

[0057] The main circuit of three-phase three-level rectifier is as follows Figure 1 As shown. It is mainly composed of load, rectifier, high-frequency transformer, clamping circuit, three-phase three-level converter, three-phase power supply and filter circuit. a , e b , e c is the input three-phase AC power; R a , R b , R c is the line impedance; L a , L b , L c is the filter inductor; the controllable switch tube S q1 -S q8 , S n1 -S n8 , S W1 -S W6 Together they form a three-phase three-level converter. In order to achieve decoupling modulation, the original S q1 -S q8 The eight controllable switch tubes are symmetrically connected to the S n1 -S n8 Eight controllable switch tubes. The rectifier clamp circuit consists of R 1 , C 1 and D 1 Composition, and R 2 , C 2 and D 2 Composition; the rectifier consists of a controllable switch tube S 1 -S 4 Composition: resistor R and capacitor C f Consists of filtering links and loads.

[0058] In the present invention, the AC power supply network is composed of e a , e b , e c Three-phase alternating current, R a , R b , R c Line impedance and filter inductance L a , L b , L cThe output end of each phase power supply is connected to the line impedance and the filter inductor in sequence, and then connected in parallel with the three-phase three-level converter.

[0059] The clamping circuit of the present invention is respectively composed of R 1 , C 1 and D 1 Composition, and R 2 , C 2 and D 2 The passive clamping circuit is composed of two parts and connected in parallel with the output of the three-phase three-level converter to absorb the voltage spike generated by the resonance of the transformer leakage inductance and the parasitic capacitance of the switch tube in the converter and maintain the balance of the midpoint potential.

[0060] In the present invention, the rectifier link is composed of a controllable switch tube S 1 , controllable switch tube S 2 , controllable switch tube S 3 , controllable switch tube S 4 The full-bridge rectifier composed of the original uncontrollable diode is transformed into a controllable switch tube, which facilitates the subsequent bidirectional power conversion. Its input end is connected to the three-phase three-level converter through a high-frequency transformer, and its output end is connected to the filter capacitor C f It is connected in parallel with the resistor R to form the whole system.

[0061] The modulation method of the three-phase three-level rectifier topology proposed in the present invention is characterized by combining decoupling with SVPWM modulation. The idea of ​​decoupling is to divide the converter into two reverse-connected converters according to the polarity of the three-phase power output. Figure 2 As shown: positive group converter N1 (controllable switch tube S q1 -S q8 , S W1 -S W6 ) and negative group converter N2 (controllable switch tube S n1 -S n8 , S W1 -S W6 ); According to the idea of ​​this topological decoupling, when the voltage input to the converter is greater than zero, we can use the PWM modulation method to control the upper switch tube, i.e., the positive group converter; when the voltage input to the converter is less than zero, we can use the PWM modulation method to control the lower switch tube, i.e., the negative group converter. In this way, the control method used for traditional converters can be applied to this converter, reducing the difficulty of analyzing the converter.

[0062] The application of SVPWM in the rectifier achieves high-precision regulation of output voltage and current by precisely controlling the switching state and time distribution. This technology not only improves the conversion efficiency of the rectifier and the stability of the output voltage, but also reduces the harmonic content, optimizes the utilization of the DC voltage, and improves the performance and efficiency of the system.

[0063] Taking the positive group converter as an example, Figure 3 is a schematic diagram of SVPWM space voltage vector distribution. First, determine U according to θ ref Located in a large sector.

[0064] When θ=0~60°, U ref Located in the first largest sector;

[0065] When θ=60~120°, U ref Located in the second largest sector;

[0066] When θ=120~180°, U ref Located in the third largest sector;

[0067] When θ=180~240°, U ref Located in the fourth largest sector;

[0068] When θ=240~300°, U ref Located in the fifth largest sector;

[0069] When θ=300~360°, U ref Located in the sixth largest sector.

[0070] Then, according to |U ref | and θ determine U ref The small area where it is located.

[0071] Taking the first sector as an example, the projections of the reference voltage vector on the x and y coordinate axes are

[0072] x=|U ref |cosθ and y=|U ref |sinθ.

[0073] The boundary line equations of regions 1, 2 and 3, 4 are:

[0074]

[0075] The boundary line equations of regions 3 and 5 are:

[0076]

[0077] The boundary line equations of regions 4 and 6 are:

[0078]

[0079] (1) The boundary between the three small areas 1, 3, 5 and the three small areas 2, 4, 6 is θ = 30°. ref Are they located in the three small areas 1, 3, 5 or the three small areas 2, 4, 6?

[0080] (2)When U ref When it is located in the three small areas 1, 3, and 5, the above formula is used to determine which small area it is in.

[0081] (3)When U ref When it is located in small areas 2, 4, and 6, the above formula is used to determine which small area it is in.

[0082] The judgment method for other large sectors is similar.

[0083] From the volt-second balance principle, the following equation can be derived:

[0084]

[0085] Among them, V1, V2, V3 are selected state vectors, the action times are T1, T2, T3 respectively, and Ts is the reference voltage vector modulation period.

[0086] Solved:

[0087]

[0088] Among them, the space voltage vector modulation ratio is

[0089]

[0090] The vector action time in other areas can be obtained in the same way.

[0091] By adopting symmetrical wave generation, even harmonics can be effectively eliminated. On this basis, in each modulation cycle, only one of the two adjacent switching states changes. This design aims to reduce switching losses and reduce switching frequency. Based on these principles, after adjustment, the switching state of each sector is finally determined, as shown in the following table. Taking phase a as an example, p represents the controllable switch tube S q1 And controllable switch tube S q7 Open, o represents the controllable switch tube S W1 And controllable switch tube S W2 Open, n represents the controllable switch tube S q4 And controllable switch tube S q8 Open.

[0092]

[0093]

[0094] The working principle of the clamp circuit is mainly based on the characteristics of capacitors and diodes. When the input signal changes, the capacitor is charged or discharged through the unidirectional conduction characteristics of the diode, so that the output voltage is maintained at a predetermined level. Specifically, when the positive half cycle of the input signal arrives, the diode is turned on and the capacitor is charged to a certain voltage value; when the negative half cycle of the input signal arrives, the diode is cut off, and the voltage on the capacitor is superimposed on the input signal, thereby outputting a voltage clamped at a predetermined level.

[0095] When the midpoint potential is unbalanced and there is a potential difference, the clamping circuit working diode is turned on and the capacitor begins to charge. The clamping circuit clamps the peak value of the input voltage to a predetermined level through the synergistic effect of the capacitor and the diode without changing the waveform of the signal.

[0096] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A three-phase three-level converter topology, characterized in that: Including controllable switch tube S q1 -S q8 , S n1 -S n8 , S W1 -S W6 The controllable switch tube S q1 , S n1 Series branch, controllable switch tube S q2 , S n2 Series branch, controllable switch tube S q3 , S n3 Series branches in parallel, S n1 , S n2 , S n3 The collectors are connected to three-phase alternating current e a , three-phase alternating current b and three-phase alternating current c ; The controllable switch tube S q4 , S n4 Series branch, controllable switch tube S q5 , S n5 Series branch, controllable switch tube S q6 , S n6 Series branches in parallel, S q4 , S q5 , S q6 The collectors are connected to three-phase alternating current e a , three-phase alternating current b and three-phase alternating current c ; Controllable switch tube S W1 With S W2 The series branches are connected to the controllable switch tube S W3 With S W4 Series branch, controllable switch tube S W5 With S W6 The series branches are connected in parallel and are connected to the three-phase AC a , three-phase alternating current b and three-phase alternating current c Connect to the controllable switch tube S n7 , S q8 The collector connection of Controllable switch tube S q1 , S q2 , S q3 The collector of the q7 , controllable switch tube S q7 The emitter is connected to S n7 Emitter; controllable switch tube S n4 , S n5 , S n6 The collector of the n8 , controllable switch tube S n8 The emitter is connected to S q8 Emitter.

2. The three-phase three-level converter topology structure according to claim 1, characterized in that: Three-phase alternating current a , e b , e c Respectively with the corresponding line impedance R a , R b , R c Connection; line impedance R a , R b , R c Respectively with the filter inductor L a , L b , L c connect.

3. The three-phase three-level converter topology structure according to claim 1, characterized in that: Controllable switch tube S n1 The collector of the controllable switch tube S q4 The collector and controllable switch tube S W1 The collector and filter inductor L a The negative electrode is connected to the controllable switch tube S n2 The collector of the controllable switch tube S q5 The collector and controllable switch tube S W3 The collector and filter inductor L b The negative electrode is connected to the controllable switch tube S n3 The collector of the controllable switch tube S q6 The collector and controllable switch tube S W5 The collector and filter inductor L c The negative electrode is connected to the controllable switch tube S q1 The emitter and the controllable switch tube S n1 The emitter of the controllable switch tube S q2 The emitter and the controllable switch tube S n2 The emitter of the controllable switch tube S q3 The emitter and the controllable switch tube S n3 The emitter of the controllable switch tube S q4 The emitter and the controllable switch tube S n4 The emitter of the controllable switch tube S q5 The emitter and the controllable switch tube S n5 The emitter of the controllable switch tube S q6 The emitter and the controllable switch tube S n6 The emitter of the controllable switch tube S W1 The emitter and the controllable switch tube S W2 The emitter of the controllable switch tube S W3 The emitter and the controllable switch tube S W4 The emitter of the controllable switch tube S W5 The emitter and the controllable switch tube S W6 The emitter of the controllable switch tube S q7 The emitter and the controllable switch tube S n7 The emitter of the controllable switch tube S q8 The emitter and the controllable switch tube S n8 The emitter of the controllable switch tube S q7 The collector and the controllable switch tube S q3 The collector of the controllable switch tube S n7 The collector and the controllable switch tube S W4 The collector of the controllable switch tube S q8 The collector and the controllable switch tube S W4 The collector of the controllable switch tube S n8 The collector and the controllable switch tube S n6 The collector is connected.

4. A high-frequency rectifier with a clamping circuit, adopting the three-phase three-level converter topology structure as described in any one of claims 1 to 3, characterized in that: The invention comprises a rectifier, a high-frequency transformer, a clamping circuit and a filtering circuit; the clamping circuit comprises R1, C1, D1, R2, C2 and D2; the rectifier comprises controllable switch tubes S1-S4; the filtering circuit comprises a resistor R and a capacitor C f ; The clamping circuit is connected in parallel with the output of the three-phase three-level converter to absorb the voltage spike generated by the resonance of the transformer leakage inductance and the parasitic capacitance of the switch tube in the converter, and maintain the midpoint potential balance; the input end of the rectifier is connected to the three-phase three-level converter through a high-frequency transformer, and its output end is connected to the filter capacitor C f In parallel with resistor R.

5. The high frequency rectifier with a clamping circuit according to claim 4, characterized in that: The series branch composed of capacitor C1 and diode D1 and controllable switch tube S q7 , S n7 The series branches are connected in parallel, and the two series branches are connected to the controllable switch tube S W1 -S W6 In the parallel circuit, the series branch composed of capacitor C2 and diode D2 and the controllable switch tube S q8 , S n8 The series branches are connected in parallel, and the two series branches are connected to the controllable switch tube S W1 -S W6 In the parallel circuit, resistor R1 is connected in parallel across capacitor C1, and resistor R2 is connected in parallel across capacitor C2.

6. The high frequency rectifier with a clamping circuit according to claim 4, characterized in that: The modulation method is as follows: Controllable switch tube S q1 -S q8 , S W1 -S W6 The positive group converter N1 is composed of controllable switch tube S n1 -S n8 , S W1 -S W6 The negative group converter N2 is composed. When the converter inputs a voltage greater than zero, PWM is used to modulate the positive group converter. When the converter inputs a voltage less than zero, PWM is used to modulate the negative group converter. By adopting symmetrical wave generation, only one phase of the two adjacent switch states changes in each modulation cycle.

7. The high frequency rectifier with a clamping circuit according to claim 4, characterized in that: When the positive half cycle of the input signal arrives, the diode D1 or D2 of the clamping circuit is turned on, and the capacitor C1 or C2 is charged to a certain voltage value; when the negative half cycle of the input signal arrives, the diode D1 or D2 is turned off, and the voltage on the capacitor C1 or C2 is superimposed on the input signal, thereby outputting a voltage clamped at a predetermined level; When the midpoint potential is unbalanced and there is a potential difference, the working diode D1 or D2 of the clamping circuit is turned on, and the capacitor C1 or C2 begins to charge; the clamping circuit clamps the peak value of the input voltage to a predetermined level through the synergistic effect of the capacitor and the diode without changing the waveform of the signal.

8. The high frequency rectifier with a clamping circuit according to claim 6, characterized in that: The SVPWM space voltage vector distribution of the positive group converter is set as follows: Determine U according to θ ref The major sector: When ε=0~60°, U ref Located in the first largest sector; When ε=60~120°, U ref Located in the second largest sector; When ε=120~180°, U ref Located in the third largest sector; When ε=180~240°, U ref Located in the fourth largest sector; When θ=240~300°, U ref Located in the fifth largest sector; When θ=300~360°, U ref Located in the sixth largest sector. Then, according to |U ref | and θ determine U ref The small area where it is located; Assume that the projections of the reference voltage vector of the first sector on the x and y coordinate axes are: x = |U ref | cosθ and y = |U ref | sinθ; The boundary line equations of regions 1, 2 and 3, 4 are: The boundary line equations of area 3 and area 5 are: The boundary line equations of regions 4 and 6 are: (1) The boundary between the three small areas 1, 3, 5 and the three small areas 2, 4, 6 is θ = 30°; thus, it can be determined that U ref Is it located in the three sub-areas 1, 3, 5 or the three sub-areas 2, 4, 6? (2)When U ref When it is located in the three small areas 1, 3, and 5, the above formula is used to determine the small area it is in; (3)When U ref When it is in the three small areas 2, 4, and 6, the above formula is used to determine the small area it is in; From the volt-second balance principle, the following equation can be derived: Among them, V1, V2, V3 are the selected state vectors, the action time is T1, T2, T3 respectively, and Ts is the reference voltage vector modulation period; Solved: Among them, the space voltage vector modulation ratio m is: Where U ref For the voltage vector, U dc is the DC side voltage.

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