Single-phase NPC type full-bridge three-level square wave frequency converter circuit

Abstract

The utility model relates to a single-phase NPC type full-bridge three-level square-wave frequency converter circuit, comprising a rectification circuit for rectifying a three-phase alternating current into a direct current; the bridge arm circuit is connected with the rectifying circuit and inverts direct current into variable alternating current, the bridge arm circuit is formed by connecting a plurality of groups of switching devices in series, a diode is connected between two groups of switching devices, and a capacitor bank is connected between the bridge arm circuit and the rectifying circuit in series; any level state of a positive bus level, a capacitor series connection contact level or a negative bus level is output through capacitor group voltage division, four groups of semiconductor switch devices are arranged on a frequency converter circuit, and the maximum voltage borne by the switch devices is half of the direct current total input voltage. According to the three-level frequency converter, small semiconductor switch tubes are selected to reduce the switching loss of the three-level frequency converter, and the voltage stress of part of the switch tubes is reduced while the number of devices of the three-level frequency converter is kept minimum, so that small-power semiconductor switch tubes can be selected, the loss is reduced, and the conversion efficiency is improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to frequency converter circuit field especially relates to a single -phase NPC type full -bridge three electric square wave frequency converter circuit. BACKGROUND

[0002] Frequency converter refers to the opening and closing action through semiconductor power switch device, converts fixed frequency electric energy into frequency variable AC electric energy. UTILITY MODEL CONTENTS

[0003] The utility model solves the technical problem in at the restriction of power device capacity, single -phase two electric square wave frequency converter voltage grade is generally lower, and the frequency converter of high -voltage large capacity adopts three -level form mostly, but mostly is the frequency converter of high -voltage large capacity adopts the semiconductor switch tube of larger power, leads to larger loss, and conversion efficiency is lower.

[0004] In order to solve the above technical problem, the technical scheme adopted by the utility model is:

[0005] A single -phase NPC type full -bridge three electric square wave frequency converter circuit is constructed, including rectifier circuit, the rectifier circuit connects three -phase AC power supply, and three -phase AC is rectified into DC;

[0006] Still including at least one group of bridge arm circuit, the bridge arm circuit is connected with rectifier circuit and inverts DC into variable AC, the bridge arm circuit is connected with multiple groups of switch devices in series, and two groups of switch devices are connected with diode, and the bridge arm circuit and rectifier circuit are connected with capacitor group in series, and the capacitor group divides voltage and realizes any one level state of output positive bus level, capacitor series connection point level or negative bus level.

[0007] Preferably, the switch device includes switch tube and diode in antiparallel with the switch tube, the switch device is equipped with four groups, and the fifth diode and the sixth diode are connected between four groups of switch devices, the fifth diode is arranged at the connection of two groups of switch devices, the sixth diode is arranged at the connection of the other two groups of switch devices, and the fifth diode and the sixth diode are connected in series.

[0008] Preferably, the switch tube is a transistor or thyristor, and the diode connected in anti-parallel with the switch tube is an independent diode or a diode connected in anti-parallel with the switch tube internally.

[0009] Preferably, the drain or collector of the switch tube is connected with the cathode of the diode connected in anti-parallel with the switch tube to form a first end of the switch device, and the source or emitter of the switch tube is connected with the anode of the diode connected in anti-parallel with the switch tube to form a second end of the switch device.

[0010] Preferably, the bridge arm circuit is provided in two groups, and the midpoint of the switch devices of the two groups of bridge arm circuits serves as two groups of output ends of the bridge arm circuit, and a filter circuit is arranged in the middle of the output ends to filter out high-frequency components in the output signal.

[0011] Preferably, the eight groups of switch devices are not simultaneously turned on and the driving signals are complementary, and the filter circuit is an inductor connected across the output load.

[0012] Preferably, the bridge arm circuit is provided in one group, and the midpoint of the switch devices and the connection point of the diodes serve as two groups of output ends of the bridge arm circuit, and a filter circuit is arranged in the middle of the output ends to filter out high-frequency components in the output signal.

[0013] Preferably, the filter circuit is an L-type, LC-type or LCL-type filter circuit.

[0014] Preferably, the rectifier circuit is composed of multiple groups of diodes, and two groups of diodes are connected across each line of the three-phase alternating current power supply and are arranged between the diodes, and a direct current bus is output by the rectifier circuit.

[0015] Preferably, the capacitor groups are connected in series across the direct current buses, and the capacitor groups are composed of multiple capacitors with equal capacitive reactance and perform voltage division on the direct current buses, the connection points of the multiple capacitor groups serve as voltage division midpoints of the direct current buses and are connected with the bridge arm circuits, and the bridge arm circuits are connected across the direct current buses, and when multiple bridge arm circuits are provided, the multiple bridge arm circuits are connected in series.

[0016] The utility model discloses a three-level frequency converter, which comprises a frequency converter circuit, a three-phase alternating current power supply, a rectifier circuit, a capacitor group, a bridge arm circuit and a driving circuit. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the present application will be further described below with reference to the drawings and embodiments, and the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the premise of not paying creative labor.

[0018] Figure 1 The frequency converter circuit structure schematic diagram of the preferred embodiment of the present application;

[0019] Figure 2 The circuit structure schematic diagram of one bridge arm with load of the preferred embodiment of the present application;

[0020] Figure 3 The single bridge arm topological structure schematic diagram of the preferred embodiment of the present application;

[0021] Figure 4 The PWM modulation principle one of the three-electric square wave frequency converter of the preferred embodiment of the present application;

[0022] Figure 5 The PWM modulation principle two of the three-electric square wave frequency converter of the preferred embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described below clearly and completely, obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0024] The single-phase NPC type full-bridge three-electric square wave frequency converter circuit of the preferred embodiment one of the present application; as shown in the figure, Figure 1 The three-phase alternating current input power supply and the rectifier bridge connected with the three-phase alternating current input power supply are included, and the three-phase alternating current is rectified into direct current through the rectifier bridge. The rectifier bridge is connected with a capacitor group and two NPC bridge arms, and the frequency variable alternating current is inverted. Two capacitors C1 and C2 with equal capacitive reactance are connected in series between the direct current positive and negative bus voltage to obtain three-level, which includes positive bus level, two capacitor series connection point level and negative bus level, and the two bridge arms are connected between the direct current bus respectively, and each bridge arm includes a topological unit, so as to form the NPC type topological structure. The energy output by the fixed frequency three-phase alternating current power supply is converted into the frequency variable alternating current from 50Hz to 500Hz through the NPC type topological structure.

[0025] Specifically, as shown in the figure, Figure 1As shown, the first topology unit includes four switching devices and two diodes, wherein the first switching device, the second switching device, the third switching device and the fourth switching device are connected in series between the DC bus, the first end of the first switching device is connected to the positive end of the DC bus, the second end of the fourth switching device is connected to the negative end of the DC bus, the first end of the second switching device is connected to the second end of the first switching device, the second end of the second switching device is connected to the first end of the third switching device, the second end of the third switching device is connected to the first end of the fourth switching device, the second end of the first switching device and the second end of the third switching device are connected through two groups of diodes D5 and D6, and the positive poles of the diodes D5 and D6 are connected to the second end of the third switching device. The structure of the second topology unit is the same as that of the first topology unit, which will not be repeated here, wherein the second end of the second switching device of the first topology unit and the second end of the second switching device of the second topology unit are both connected through an inductor as the output end of the frequency converter, and the positive poles of the diodes D5 of the two groups of topology units are connected to each other.

[0026] Further, two voltage division capacitors are connected in series between the DC bus for voltage division of the DC bus, and the connection points of the two voltage division capacitors are the voltage division midpoints of the DC bus. The single-phase three-level frequency converter circuit further includes a filter circuit connected between the output ends of the two bridge arms for filtering out high-frequency components in the frequency converter output signal. The filter circuit can be L-type, LC-type, LCL-type, etc. In this embodiment, the filter circuit includes an inductor L1 connected to the output end of one of the bridge arms and the AC load respectively, and an inductor L2 connected to the output end of the other bridge arm and the AC load respectively.

[0027] In the above embodiment, the working process of each topology unit is as follows: when the semiconductor switch tubes T1 and T2 are turned on, and the semiconductor switch tubes T3 and T4, the diodes D3, D4, D5 and D6 are turned off, the level of the output node a is equal to the positive bus level. When the output side current flows from the point a to the inductor L1, the diodes D1 and D2 are turned off, and the current loop is T1-T2-L1-Rload-L2-Cl-T1; when the output side current flows from the inductor L1 to the point a, the diodes D1 and D2 are turned on, and the current loop is D2-D1-Cl-L2-Rload-L1-D2. When the semiconductor switch tubes T2 and T3 are turned on, and the semiconductor switch tubes T1 and T4, the diodes D1, D2, D3 and D4 are turned off, the level of the output node a is equal to the level of the point of series connection of the two capacitors. When the output side current flows from the point a to the inductor L1, the diode D5 is turned on, and the diode D6 is turned off, and the current loop is D5-T2-L1-Rload-L2-D5; when the output side current flows from the inductor L1 to the point a, the diode D6 is turned on, and the diode D5 is turned off, and the current loop is T3-D6-L2-Rload-L1-T3. When the semiconductor switch tubes T3 and T4 are turned on, and the semiconductor switch tubes T1 and T2, the diodes D1, D2, D5 and D6 are turned off, the level of the output node a is equal to the negative bus level. When the output side current flows from the point a to the inductor L1, the diodes D3 and D4 are turned on, and the current loop is D4-D3-L1-Rload-L2-C2-D4; when the output side current flows from the inductor L1 to the point a, the diodes D3 and D4 are turned off, and the current loop is T3-T4-C2-L2-Rload-L1-T3. It can be known from the above working process that the maximum voltage borne by the four groups of semiconductor switch tubes (T1 and D1, T2 and D2, T3 and D3, and T4 and D4) of the NPC three-level frequency converter is half of the total input voltage of the direct current, and therefore, semiconductor switch tubes with smaller rated voltage can be selected to reduce the switching loss. However, in the topology, two diodes D5 and D6 are needed, which increases the number of electronic components and the loss thereof, and also increases the on-state loss of the semiconductor switch tubes T2 and T3.

[0028] The utility model discloses a single -phase NPC type full -bridge three electric square wave frequency converter circuit of preferable embodiment two, as shown in Figures 2-3 The second end of the second switch device of the first topology unit is connected with the first end of the third switch device and serves as an output end of the frequency converter.

[0029] Further, each switching device comprises a switching tube and a diode connected in anti-parallel with the switching tube. The driving signals of the eight switching devices in the topology unit are generated by the intersection of the square wave modulation wave Vref and two triangular carrier waves Vr1 and Vr2. In the present application, there are two in-phase equilateral triangular carrier waves Vr1 and Vr2 in the PWM modulation, and the amplitudes of the two triangular carrier waves are the same, Vr1 is upwardly shifted from Vr2 by an amplitude of Vr2, and then the intersection of Vr1 and Vr2 with the two square wave modulation waves Vref and -Vref respectively can generate four different pulse width signals A, B, C and D. Figure 4 , Figure 5 The PWM modulation principle of the three-level square wave frequency converter is shown in Fig. 3. Figure 4 When the amplitude of the square wave modulation wave Vref is less than or equal to the maximum amplitude of the triangular carrier wave Vr2, the PWM modulation principle is shown in Fig. 4, in which signals A and C are always low. In the positive half cycle of the square wave modulation wave, Vref is greater than or equal to Vr2, signal B is high, otherwise it is low. In the negative half cycle of the square wave modulation wave, -Vref is greater than or equal to Vr2, signal D is high, otherwise it is low. Figure 5 When the amplitude of the square wave modulation wave Vref is greater than the maximum amplitude of the triangular carrier wave Vr2, the PWM modulation principle is shown in Fig. 5, in which signals B and D are always high. In the positive half cycle of the square wave modulation wave, Vref is greater than or equal to Vr1, signal A is high, otherwise it is low. In the negative half cycle of the square wave modulation wave, -Vref is greater than or equal to Vr1, signal C is high, otherwise it is low. VAB is the output voltage across the frequency converter AB when each switching tube is turned on. Vbus is the bus voltage.

[0030] Further, the single-phase full-bridge three-level square wave frequency converter has eight switching devices T1, T2, T3, T4, _T1, _T2, _T3 and _T4, wherein T1 and T3, T4 and T2, _T1 and _T3, and _T4 and _T2 cannot be turned on at the same time and the driving signals are complementary. The logic relationship between the eight switching devices T1, T2, T3, T4, _T1, _T2, _T3 and _T4 and the four driving signals A, B, C and D is shown in Fig. 6. .

[0031] In the above manner, the voltage stress of part of the switching tubes can be reduced while keeping the number of devices of the three-level frequency converter to be the least, so that small power semiconductor switching tubes can be selected, the loss can be reduced, and the conversion efficiency can be improved.

[0032] Further, the above Figure 3Each switch device comprises a switch tube and a diode in anti-parallel connection with the switch tube. The switch tube can be a semiconductor switch tube such as MOSFET (Metal Oxide Silicon Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), IGCT (Integrated Gate Commutated Thyristor), IEGT (Injection Enhanced Gate Transistor) and the like. The diode can be an independent diode or an anti-parallel diode internally provided in the switch tube. Accordingly, the drain or collector of the switch tube is connected with the cathode of the diode to form a first end of the switch device, and the source or emitter of the switch tube is connected with the anode of the diode to form a second end of the switch device. Of course, the type of the switch tube is not limited in the embodiment, and other types of switch tubes can also be used.

[0033] It should be understood that the present application is described by some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to the features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, the features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application belong to the scope of protection of the present application.

Claims

1. A single-phase NPC full-bridge three-electrode square wave frequency converter circuit, comprising a rectifier circuit connected to a three-phase alternating current power supply and rectifying the three-phase alternating current into direct current, characterized in that: further comprising at least one set of bridge arm circuit connected to the rectifier circuit and inverting the direct current into variable alternating current, the bridge arm circuit is connected in series by multiple sets of switching devices, and a diode is connected between two sets of switching devices, a capacitor set is connected in series between the bridge arm circuit and the rectifier circuit, and any one of the output positive bus level, capacitor series connection point level or negative bus level is realized by voltage division of the capacitor set. The switching device comprises a switching tube and a diode connected in antiparallel with the switching tube, the switching device is provided as four sets, and the fifth diode and the sixth diode are connected between the four sets of switching devices, the fifth diode is arranged at the connection between two sets of switching devices, the sixth diode is arranged at the connection between the other two sets of switching devices, and the fifth diode and the sixth diode are connected in series.

2. The frequency converter circuit of claim 1, wherein: The switching tube is a transistor or a thyristor, and the diode connected in antiparallel with the switching tube is an independent diode or an internal antiparallel diode of the switching tube.

3. The frequency converter circuit of claim 2, wherein: The drain or collector of the switching tube is connected to the cathode of the diode connected in antiparallel with the switching tube to form the first end of the switching device, and the source or emitter of the switching tube is connected to the anode of the diode connected in antiparallel with the switching tube to form the second end of the switching device.

4. The frequency converter circuit of claim 3, wherein: The bridge arm circuit is provided as two sets, and the midpoint of the switching devices of the two sets of bridge arm circuit is used as the output end of the two sets of bridge arm circuit, and a filter circuit is arranged between the output ends, and the filter circuit is used to filter out high-frequency components in the output signal.

5. The frequency converter circuit of claim 1, wherein: Eight sets of switching devices are not turned on at the same time and the driving signals are complementary, and the filter circuit is an inductor connected to the output load.

6. The frequency converter circuit of claim 5, wherein: The bridge arm circuit is provided as one set, and the midpoint of the switching device and the diode connection point are used as the output end of the two sets of bridge arm circuit, and a filter circuit is arranged between the output ends, and the filter circuit is used to filter out high-frequency components in the output signal.

7. The frequency converter circuit of claim 1, wherein: The filter circuit is an L-type, LC-type or LCL-type filter circuit.

8. A frequency converter circuit according to any of claims 5-7, characterized in that: The rectifier circuit is composed of multiple sets of diodes, and each line of the three-phase alternating current power supply is connected to two sets of diodes arranged between the diodes, and a direct current bus is output by the rectifier circuit.

9. The frequency converter circuit of claim 1, wherein: The capacitor set is connected in series between the direct current buses, and the capacitor set is composed of multiple capacitors with equal capacitive reactance and divides the voltage of the direct current buses, and the connection points of the multiple capacitors are used as the voltage division points of the direct current buses and are connected to the bridge arm circuit, the bridge arm circuit is connected between the direct current buses, and when multiple bridge arm circuits are provided, the multiple bridge arm circuits are connected in series.

10. The frequency converter circuit of claim 9, wherein: ​

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