阅读说明：本技术 一种变频器及其升压控制方法、电机 (Frequency converter, boost control method thereof and motor ) 是由 张良浩 周维邦 赵文超 于 2021-07-05 设计创作，主要内容包括：本发明公开了一种变频器及其升压控制方法、电机,该装置包括：整流端,将三相交流电源分为两组相同的三相供电电源,并分别对两组相同的三相供电电源进行整流,输出两组相互独立、且电压相等的直流电源,记为第一直流电源和第二直流电源；第一直流电源和第二直流电源,通过变频器的三电平中点串联；在支撑电容单元中,第一支撑电容模块,对第一直流电源进行储能；第二支撑电容模块,对第二直流电源进行储能；三电平逆变单元,对第一支撑电容模块和第二支撑电容模块所储存的直流电进行逆变,得到设备所需的交流电。该方案,通过抑制三电平拓扑的中点电位偏移,以避免三电平拓扑变频器的性能下降。(The invention discloses a frequency converter, a boost control method thereof and a motor, wherein the device comprises the following components: the rectifying end divides the three-phase alternating current power supply into two groups of same three-phase power supply, respectively rectifies the two groups of same three-phase power supply, outputs two groups of mutually independent direct current power supplies with equal voltage, and records the two groups of mutually independent direct current power supplies as a first direct current power supply and a second direct current power supply; the first direct current power supply and the second direct current power supply are connected in series through the middle point of the three levels of the frequency converter; in the supporting capacitor unit, a first supporting capacitor module stores energy for a first direct current power supply; the second support capacitor module is used for storing energy for the second direct-current power supply; and the three-level inversion unit inverts the direct current stored in the first support capacitor module and the second support capacitor module to obtain the alternating current required by the equipment. According to the scheme, the performance reduction of the three-level topology frequency converter is avoided by restraining the midpoint potential offset of the three-level topology.)

1. A frequency converter, comprising: the rectification end, the support capacitor unit and the inversion end; the support capacitor unit includes: the first support capacitor module and the second support capacitor module; the inverting terminal comprises: a three-level inversion unit; wherein the content of the first and second substances,

the rectifying end is configured to divide a three-phase alternating-current power supply into two groups of same three-phase power supplies, rectify the two groups of same three-phase power supplies respectively, and output two groups of independent direct-current power supplies with equal voltage, which are marked as a first direct-current power supply and a second direct-current power supply; the first direct-current power supply and the second direct-current power supply are connected in series through the middle point of the three levels of the frequency converter; the first support capacitor module and the second support module are connected in series, and the common end of the first support capacitor module and the second support capacitor module is the middle point of the three levels of the frequency converter;

in the supporting capacitor unit, the first supporting capacitor module, as a bus capacitor of the first dc power supply, is configured to store energy for the first dc power supply; the second support capacitor module is used as a bus capacitor of the second direct current power supply and is configured to store energy for the second direct current power supply;

the three-level inversion unit is configured to invert the direct current stored in the first support capacitor module and the second support capacitor module to obtain the alternating current required by the equipment.

2. The frequency converter of claim 1, wherein the rectifying end comprises: the first isolation unit, the second isolation unit, the first rectifying unit and the second rectifying unit; wherein the content of the first and second substances,

rectifier end divides into two sets of the same three-phase power supply with three-phase AC power supply to carry out the rectification to two sets of the same three-phase power supply respectively, output two sets of mutually independent and the DC power supply that voltage equals, record as first DC power supply and second DC power supply, include:

the first isolation unit is configured to isolate the three-phase alternating-current power supply to obtain a first power supply;

the first rectifying unit is configured to rectify the first power supply to obtain the first direct-current power supply; the positive end of the output end of the first rectifying unit is connected to the first connecting end of the first support capacitor module; the negative end of the output end of the first rectifying unit is connected to the second connecting end of the first support capacitor module;

and the number of the first and second groups,

the second isolation unit is configured to isolate the three-phase alternating-current power supply to obtain a second power supply;

the second rectifying unit is configured to rectify the second power supply to obtain the second direct-current power supply; the positive end of the output end of the second rectifying unit is connected to the first connecting end of the second support capacitor module; and the negative end of the output end of the second rectifying unit is connected to the second connecting end of the second support capacitor module.

3. The frequency converter of claim 2, wherein the first isolation unit comprises: a first transformer; the three-phase alternating current power supply is connected to the primary winding of the first transformer; a secondary winding of the first transformer connected to the first rectifying unit;

the second isolation unit includes: a second transformer; the three-phase alternating current power supply is connected to the primary winding of the second transformer; and the secondary winding of the second transformer is connected to the second rectifying unit.

4. The frequency converter according to claim 2 or 3, wherein the first rectifying unit comprises: the first uncontrolled rectifier module and the first voltage stabilizing and filtering module; the first isolation unit is connected to the first support capacitor module after passing through the first uncontrolled rectifier module and the first voltage stabilizing and filtering module;

the second rectifying unit includes: the second uncontrolled rectifier module and the second voltage stabilizing and filtering module; and the second isolation unit is connected to the second support capacitor module after passing through the second uncontrolled rectifier module and the second voltage stabilizing and filtering module.

5. The frequency converter according to claim 2 or 3, wherein the first rectifying unit comprises: a first fully controlled rectifier module; the first isolation unit is connected to the first support capacitor module after passing through the first full-control rectification module;

the second rectifying unit includes: a second fully-controlled rectifier module; and the second isolation unit is connected to the second support capacitor module after passing through the second full-control rectification module.

6. The frequency converter of claim 5, further comprising: a sampling unit and a control unit;

the sampling unit is configured to sample the bus voltage of the first bus-supported capacitor module and the bus voltage of the second bus-supported capacitor module after the frequency converter is started, and the sampled bus voltages are recorded as a first bus voltage and a second bus voltage;

the control unit is configured to control the first fully-controlled rectifying module and the second fully-controlled rectifying module to boost voltage according to the first bus voltage, the second bus voltage and a blocking voltage value of a switching tube in the three-level inversion unit.

7. The frequency converter according to claim 2 or 3, wherein the three-level inverting unit comprises: any one of a NPC type three-level inverter, a TNPC type three-level inverter, and an ANPC type three-level inverter.

8. An electric machine, comprising: a frequency converter according to any one of claims 1 to 7.

9. A boost control method of a frequency converter according to claim 6, characterized by comprising:

after the frequency converter is started, sampling the bus voltage of the first bus supporting capacitor module and the bus voltage of the second bus supporting capacitor module, and recording the bus voltages as a first bus voltage and a second bus voltage;

and controlling the first fully-controlled rectifying module and the second fully-controlled rectifying module to boost according to the first bus voltage, the second bus voltage and the blocking voltage value of a switching tube in the three-level inversion unit.

Technical Field

The invention belongs to the technical field of frequency converters, and particularly relates to a frequency converter, a boost control method thereof and a motor, in particular to a frequency converter for inhibiting three-level midpoint offset, a boost control method thereof and a motor with the frequency converter.

Background

With the increasing requirements on harmonic content and efficiency of frequency converters, three-level topology frequency converters (i.e., frequency converters using three-level topology) are increasingly used. However, the midpoint potential of the three-level topology frequency converter is shifted, which causes the performance of the three-level topology frequency converter to be degraded.

The above is only for the purpose of assisting understanding of the technical aspects of the present invention, and does not represent an admission that the above is prior art.

Disclosure of Invention

The invention aims to provide a frequency converter, a boost control method thereof and a motor, which are used for solving the problem that the performance of a three-level topology frequency converter is reduced due to the midpoint potential offset of the three-level topology frequency converter and achieving the effect of preventing the performance of the three-level topology frequency converter from being reduced by restraining the midpoint potential offset of the three-level topology frequency converter.

The present invention provides a frequency converter, comprising: the rectification end, the support capacitor unit and the inversion end; the support capacitor unit includes: the first support capacitor module and the second support capacitor module; the inverting terminal comprises: a three-level inversion unit; the rectifying end is configured to divide a three-phase alternating-current power supply into two groups of same three-phase power supplies, rectify the two groups of same three-phase power supplies respectively, and output two groups of independent direct-current power supplies with equal voltage, which are marked as a first direct-current power supply and a second direct-current power supply; the first direct-current power supply and the second direct-current power supply are connected in series through the middle point of the three levels of the frequency converter; the first support capacitor module and the second support module are connected in series, and the common end of the first support capacitor module and the second support capacitor module is the middle point of the three levels of the frequency converter; in the supporting capacitor unit, the first supporting capacitor module, as a bus capacitor of the first dc power supply, is configured to store energy for the first dc power supply; the second support capacitor module is used as a bus capacitor of the second direct current power supply and is configured to store energy for the second direct current power supply; the three-level inversion unit is configured to invert the direct current stored in the first support capacitor module and the second support capacitor module to obtain the alternating current required by the equipment.

In some embodiments, the rectifying end comprises: the first isolation unit, the second isolation unit, the first rectifying unit and the second rectifying unit; wherein, the rectifier end divides into two sets of the same three-phase power supply with three-phase AC power supply to carry out the rectification to two sets of the same three-phase power supply respectively, export two sets of mutually independent and the DC power supply that voltage equals, mark as first DC power supply and second DC power supply, include: the first isolation unit is configured to isolate the three-phase alternating-current power supply to obtain a first power supply; the first rectifying unit is configured to rectify the first power supply to obtain the first direct-current power supply; the positive end of the output end of the first rectifying unit is connected to the first connecting end of the first support capacitor module; the negative end of the output end of the first rectifying unit is connected to the second connecting end of the first support capacitor module; the second isolation unit is configured to isolate the three-phase alternating-current power supply to obtain a second power supply; the second rectifying unit is configured to rectify the second power supply to obtain the second direct-current power supply; the positive end of the output end of the second rectifying unit is connected to the first connecting end of the second support capacitor module; and the negative end of the output end of the second rectifying unit is connected to the second connecting end of the second support capacitor module.

In some embodiments, the first isolation unit comprises: a first transformer; the three-phase alternating current power supply is connected to the primary winding of the first transformer; a secondary winding of the first transformer connected to the first rectifying unit; the second isolation unit includes: a second transformer; the three-phase alternating current power supply is connected to the primary winding of the second transformer; and the secondary winding of the second transformer is connected to the second rectifying unit.

In some embodiments, the first rectifying unit includes: the first uncontrolled rectifier module and the first voltage stabilizing and filtering module; the first isolation unit is connected to the first support capacitor module after passing through the first uncontrolled rectifier module and the first voltage stabilizing and filtering module; the second rectifying unit includes: the second uncontrolled rectifier module and the second voltage stabilizing and filtering module; and the second isolation unit is connected to the second support capacitor module after passing through the second uncontrolled rectifier module and the second voltage stabilizing and filtering module.

In some embodiments, the first rectifying unit includes: a first fully controlled rectifier module; the first isolation unit is connected to the first support capacitor module after passing through the first full-control rectification module; the second rectifying unit includes: a second fully-controlled rectifier module; and the second isolation unit is connected to the second support capacitor module after passing through the second full-control rectification module.

In some embodiments, further comprising: a sampling unit and a control unit; the sampling unit is configured to sample the bus voltage of the first bus-supported capacitor module and the bus voltage of the second bus-supported capacitor module after the frequency converter is started, and the sampled bus voltages are recorded as a first bus voltage and a second bus voltage; the control unit is configured to control the first fully-controlled rectifying module and the second fully-controlled rectifying module to boost voltage according to the first bus voltage, the second bus voltage and a blocking voltage value of a switching tube in the three-level inversion unit.

In some embodiments, the three-level inversion unit includes: any one of a NPC type three-level inverter, a TNPC type three-level inverter, and an ANPC type three-level inverter.

In accordance with another aspect of the present invention, there is provided a motor including: the frequency converter described above.

In another aspect, the present invention provides a method for controlling boost of a frequency converter, including: after the frequency converter is started, sampling the bus voltage of the first bus supporting capacitor module and the bus voltage of the second bus supporting capacitor module, and recording the bus voltages as a first bus voltage and a second bus voltage; and controlling the first fully-controlled rectifying module and the second fully-controlled rectifying module to boost according to the first bus voltage, the second bus voltage and the blocking voltage value of a switching tube in the three-level inversion unit.

Therefore, according to the scheme of the invention, three-phase power (namely three-phase alternating current power) is divided into two groups of same three-phase power supplies, the two groups of same three-phase power supplies are respectively rectified, and two groups of independent direct current power supplies with equal voltage are output; two groups of independent direct current power supplies with equal voltage are connected in series through the middle point of the three-level frequency converter; therefore, the performance degradation of the three-level frequency converter topology is avoided by restraining the midpoint potential offset of the three-level topology frequency converter.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is a schematic diagram of an embodiment of a three-level converter topology;

FIG. 2 is a schematic structural diagram of an embodiment of a frequency converter according to the present invention;

FIG. 3 is a schematic diagram of an embodiment of a frequency converter topology that suppresses three-level midpoint offsets;

FIG. 4 is a schematic diagram of an embodiment of a frequency converter topology for suppressing three-level midpoint offsets in FIG. 3;

FIG. 5 is a schematic diagram of another embodiment of the frequency converter topology of FIG. 3 for suppressing three-level midpoint offset;

FIG. 6 is a schematic diagram illustrating a rectification boosting flow of an embodiment of the frequency converter topology for suppressing three-level midpoint offset in FIG. 5;

fig. 7 is a flowchart illustrating a boost control method according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of an embodiment of a three-level converter topology (i.e., a three-level topology converter). As shown in fig. 1, the three-level topology frequency converter includes: three-phase alternating current power supply, an inductor L, a rectifier, a capacitor C1, a capacitor C2, an inverter and a motor M. The inverter has a three-level inversion topology. And the inductor L can play the roles of filtering, energy storage and boosting.

The output end U, V, W of the three-phase alternating current power supply outputs a bus voltage value capacitor C1 and a capacitor C2 after passing through the inductor L and the rectifier. The output ends of the capacitor C1 and the capacitor C2 are output to the motor M after passing through the inverter. The rectifier is composed of a switch tube T1, a switch tube T2, a switch tube T3, a switch tube T4, a switch tube T5 and a switch tube T6. Switch T1 has diode D1, switch T2 has diode D2, switch T3 has diode D3, switch T4 has diode D4, switch T5 has diode D5, and switch T6 has diode D6. The common end of the capacitor C1 and the capacitor C2 is point O, the end of the capacitor C1 far away from the point O is point P, and the end of the capacitor C2 far away from the point O is point N. The inverter is composed of 12 switching tubes with diodes. In the inverter, each arm is composed of 4-diode switching tubes, the upper arm of each arm is composed of 2-diode switching tubes, and the lower arm of each arm is composed of 2-diode switching tubes. In each bridge arm of the inverter, two diodes are connected in series between the middle points of 2 switching tubes of the upper bridge arm and the middle points of two switching tubes of the lower bridge arm. In the first bridge arm, the midpoint of the upper bridge arm and the lower bridge arm is an A point. In the second bridge arm, the midpoint of the upper bridge arm and the lower bridge arm is a point B. And in the third bridge arm, the midpoint of the upper bridge arm and the lower bridge arm is a point C.

In the example shown in FIG. 1The topology of the three-level frequency converter can output V_dc/2、0、-V_dcAnd 2, the output voltage can be more approximate to a sine wave shape by three level signals. Wherein, V_dcIs the value of the bus voltage output by the rectifier. Because the midpoint level, namely the O point level is introduced, the capacitor C1 and the capacitor C2 supply power to the motor in a time sharing mode in the working process. In the topology of the three-level frequency converter shown in fig. 1, the potential at the point O is a floating potential, and if the charging and discharging of the capacitor C1 and the capacitor C2 cannot reach dynamic balance in the control process, the problem of midpoint potential (i.e., midpoint level) shift is caused, that is, the situation that the voltage of the capacitor C1 is too high and the voltage of the capacitor C2 is too low may occur. The neutral point potential offset can cause the performance reduction of the topology of the three-level frequency converter; if offset too much, it can even cause overvoltage of the back-end devices of the three-level converter topology, which can lead to failure of the converter.

In order to solve the problem of midpoint potential offset of the topology of the three-level frequency converter, some algorithms are proposed in related schemes. For example: virtual vector control (VSVPWM) aims at uniformly taking electricity on a capacitor C1 and a capacitor C2 at any time so as to realize dynamic balance; however, the method for solving the midpoint offset by using the algorithm needs to be continuously corrected in different applications, and the universality is poor.

According to an embodiment of the present invention, there is provided a frequency converter. Referring to fig. 2, a schematic diagram of an embodiment of the apparatus of the present invention is shown. The frequency converter may include: rectifying end, support capacitor unit and contravariant end. The alternating current input power supply is output to the motor after passing through the rectifying end, the supporting capacitor unit and the inverting end. The support capacitor unit includes: the first support capacitor module and the second support capacitor module. A first supporting capacitive module, such as capacitor C1. A second supporting capacitive module, such as capacitor C2. The inverting terminal comprises: and a three-level inversion unit.

The rectifying end is configured to divide a three-phase alternating-current power supply into two groups of same three-phase power supplies, rectify the two groups of same three-phase power supplies respectively, and output two groups of independent direct-current power supplies with equal voltage, which are marked as a first direct-current power supply and a second direct-current power supply. The first direct current power supply and the second direct current power supply are connected in series through the middle point of the three levels of the frequency converter. The first supporting capacitor module and the second supporting capacitor module are connected in series, and the common end of the first supporting capacitor module and the common end of the second supporting capacitor module are the three-level midpoint of the frequency converter, namely the O point. And the common end (namely, O point) of the first support capacitor module and the second support capacitor module is connected to the three-level inverter unit. And the three-level output end of the three-level inversion unit is connected to the motor.

In the supporting capacitor unit, the first supporting capacitor module, as a bus capacitor of the first dc power supply, is configured to store energy for the first dc power supply. The second support capacitor module is used as a bus capacitor of the second direct current power supply and is configured to store energy for the second direct current power supply.

The three-level inversion unit is configured to invert the direct current stored in the first support capacitor module and the second support capacitor module to obtain an alternating current required by the equipment, so as to supply power to the equipment. The device, may be an electric motor.

The scheme of the invention provides a frequency converter design method for inhibiting three-level midpoint offset, namely the frequency converter design method for inhibiting the three-level midpoint potential offset problem, which can effectively and reliably solve the problem of the three-level topology midpoint potential offset and avoid the performance reduction of the three-level frequency converter topology, thereby improving the reliability and stability of the frequency converter. In addition, the frequency converter design method for inhibiting the three-level midpoint offset has strong universality, reliability and practicability.

The three-level topology used by the frequency converter is shown in fig. 1, the rectifying end (i.e. the rectifier end) supplies power to a point P and a point N, and the point O is in a floating state. Therefore, the voltage distribution between PO (i.e., between the P point and the O point) and ON (i.e., between the O point and the N point) depends ON the power supply strategy of the inverter side (i.e., the inverter side) to the motor. In the scheme of the invention, the core idea of the algorithm for inhibiting the midpoint potential offset is how to balance the power taking of the three-level inverter ON PO and ON.

The core idea of inhibiting the neutral point potential offset in the three levels provided by the scheme of the invention is how to stably supply power to two sections of PO and ON. The power supply voltages of the PO and ON sections are equal, the power is large enough and stable enough, so that the voltages of the PO and ON can be in a stable state no matter how the load end gets power, and the phenomenon of midpoint potential deviation can not occur.

In some embodiments, the rectifying end comprises: the first isolation unit, the second isolation unit, the first rectifying unit and the second rectifying unit. The three-phase alternating current power supply is output to the first support capacitor module after passing through the first isolation unit and the first rectification unit. And the three-phase alternating current power supply passes through the second isolation unit and the second rectification unit and then is output to the second support capacitor module. Wherein the content of the first and second substances,

rectifier end divides into two sets of the same three-phase power supply with three-phase AC power supply to carry out the rectification to two sets of the same three-phase power supply respectively, output two sets of mutually independent and the DC power supply that voltage equals, record as first DC power supply and second DC power supply, include:

the first isolation unit is configured to isolate the three-phase alternating-current power supply to obtain a first power supply. The first power supply is a three-phase power supply.

The first rectifying unit is configured to rectify the first power supply to obtain the first direct-current power supply. The positive end of the output end of the first rectifying unit is connected to the first connection end of the first support capacitor module. And the negative end of the output end of the first rectifying unit is connected to the second connecting end of the first supporting capacitor module.

And the number of the first and second groups,

the second isolation unit is configured to isolate the three-phase alternating-current power supply to obtain a second power supply. The second power supply is a three-phase power supply. The first power supply and the second power supply form two groups of same three-phase power supplies.

The second rectifying unit is configured to rectify the second power supply to obtain the second direct-current power supply. The positive end of the output end of the second rectifying unit is connected to the first connecting end of the second support capacitor module. And the negative end of the output end of the second rectifying unit is connected to the second connecting end of the second support capacitor module. And the second connecting end of the first supporting capacitor module is connected with the first connecting end of the second supporting capacitor module and is used as a three-level midpoint of the frequency converter.

Fig. 3 is a schematic diagram of an embodiment of a frequency converter topology for suppressing three-level midpoint offset. As shown in fig. 3, a frequency converter topology for suppressing three-level midpoint offset includes: the three-phase power supply comprises three-phase power electricity, a first isolation unit, a second isolation unit, a first rectification unit, a second rectification unit, a support capacitor unit and a three-level inversion unit. And the three-phase power electricity is output to a point P and a point O after passing through the first isolation unit and the first rectification unit. And the three-phase power electricity is output to the N point and the O point after passing through the second isolation unit and the second rectification unit. And the point P, the point O and the point N are output to the point A, the point B and the point C after passing through the supporting capacitor unit and the three-level inverter unit.

In the example shown in fig. 3, three-phase power (i.e., three-phase ac power) is divided into two identical three-phase power supplies by the first and second isolation units, and is input to the first and second rectification units, respectively. Two groups of independent direct current power supplies V with equal voltage are output through the first rectifying unit and the second rectifying unit_POAnd V_ON. The first isolation unit and the second isolation unit can be isolated transformers. Therefore, the voltage at the point O is changed from the floating voltage in the original topology to a stable voltage point which is connected by the output ends of the first rectifying unit and the second rectifying unit together, and V is always kept_POAnd V_ONAre equal. That is, the positive terminal of the output terminal of the first rectification unit is connected to the point P, and the negative terminal of the output terminal of the first rectification unit is connected to the point O. The positive end of the output end of the second rectifying unit is connected to the point O, and the negative end of the output end of the second rectifying unit is connected to the point N.

Through supporting the capacitor unit, realize the effect that the energy storage supported to the voltage on the generating line, realize carrying out stable power supply to the three-level contravariant unit of rear end.

According to the design method for suppressing the three-level midpoint offset frequency converter provided by the scheme of the invention, two embodiments with strong universality (namely, the first embodiment and the second embodiment) are provided below, and the implementation process of the scheme of the invention is exemplarily explained.

Example one

In some embodiments, the first isolation unit comprises: a first transformer, such as transformer T1. And the three-phase alternating current power supply is connected to the primary winding of the first transformer. And the secondary winding of the first transformer is connected to the first rectifying unit.

The second isolation unit includes: a second transformer, such as transformer T2. And the three-phase alternating current power supply is connected to the primary winding of the second transformer. And the secondary winding of the second transformer is connected to the second rectifying unit.

In some embodiments, the first rectifying unit includes: the first uncontrolled rectifier module and the first voltage stabilizing and filtering module. The first isolation unit is connected to the first support capacitor module after passing through the first uncontrolled rectifier module and the first voltage stabilizing and filtering module. The first uncontrolled rectifying module is a three-phase uncontrolled rectifying module.

The second rectifying unit includes: the second uncontrolled rectifier module and the second voltage stabilizing and filtering module. And the second isolation unit is connected to the second support capacitor module after passing through the second uncontrolled rectifier module and the second voltage stabilizing and filtering module.

Fig. 4 is a schematic structural diagram of an embodiment of the frequency converter topology for suppressing three-level midpoint offset in fig. 3. As shown in fig. 4, the first isolation unit includes a transformer T1, the second isolation unit includes a transformer T2, the first rectification unit includes a first uncontrolled rectification module and a first voltage stabilization and filtering module, and the second rectification unit includes a second uncontrolled rectification module and a second voltage stabilization and filtering module. A supporting capacitor unit comprising: a capacitor C1 and a capacitor C2. The second uncontrolled rectifying module is a three-phase uncontrolled rectifying module.

Wherein, first uncontrolled rectifier module includes: and the three-phase uncontrolled rectifier bridge consists of a diode D11, a diode D12, a diode D13, a diode D14, a diode D15 and a diode D16. A first voltage stabilization and filtering module comprising: the inductor L1 and the inductor L1 can play a role in filtering. And the inductor L1 is connected between the positive end of the output end of the three-phase uncontrolled rectifier bridge and the point P. And the negative end of the output end of the three-phase uncontrolled rectifier bridge is connected to the point O.

A second uncontrolled rectifier module, comprising: and the three-phase uncontrolled rectifier bridge consists of a diode D21, a diode D22, a diode D23, a diode D24, a diode D25 and a diode D26. A second voltage stabilization and filtering module comprising: the inductor L2 and the inductor L2 can play a role in filtering and voltage stabilization. And the inductor L2 is connected between the positive end of the output end of the three-phase uncontrolled rectifier bridge and the point O. And the negative end of the output end of the three-phase uncontrolled rectifier bridge is connected to the point N.

In the example shown in fig. 4, two groups of three-phase uncontrolled rectifying topologies are used for the rectifying ends, the power supply at the front end is isolated by a transformer T1 and a transformer T2, respectively, and the rectified positive output end at the rear end is connected to a direct current reactor (such as an inductor L1 and an inductor L2) for voltage stabilization. And the positive and negative output ends of one group are connected with P, O power supply input ends of the three-level inverter. And the positive and negative output ends of the other group are connected with O, N power supply input ends of the three-level inverter. At this time, equal and stable power supply voltage is provided between the PO and ON sections. Taking an input three-phase 380V alternating current power AC as an example, the three-phase input power respectively passes through a transformer T1, a transformer T2 and a three-phase uncontrolled rectifier, at this time, the voltages between the PO and ON sections are both stable and equal 540V, the voltage between the PN two points is about 1080V, and the power supply requirement of the rear-end three-level inverter is met.

In some embodiments, the first rectifying unit includes: the first full-control rectifying module. The first isolation unit is connected to the first support capacitor module after passing through the first full-control rectification module.

The first full-control rectifier module is a three-phase full-control rectifier module, such as a three-phase full-control rectifier bridge.

The second rectifying unit includes: and the second fully-controlled rectifying module. And the second isolation unit is connected to the second support capacitor module after passing through the second full-control rectification module. The second full-control rectifier module is a three-phase full-control rectifier module, such as a three-phase full-control rectifier bridge.

Example two

Fig. 5 is a schematic structural diagram of another embodiment of the frequency converter topology for suppressing three-level midpoint offset in fig. 3. As shown in fig. 5, the first isolation unit includes a transformer T3, the second isolation unit includes a transformer T4, the first rectification unit includes a first fully controlled rectification module, and the second rectification unit includes a second fully controlled rectification module. A supporting capacitor unit comprising: a capacitor C1 and a capacitor C2.

Wherein, first full accuse rectifier module includes: the three-phase fully-controlled rectifier bridge is formed by six switching tubes with diodes. The positive end of the output end of the three-phase fully-controlled rectifier bridge is connected to the point P. And the negative end of the output end of the three-phase fully-controlled rectifier bridge is connected to the point O.

A second fully controlled rectifier module comprising: the three-phase fully-controlled rectifier bridge is formed by six switching tubes with diodes. The positive end of the output end of the three-phase fully-controlled rectifier bridge is connected to the point O. And the negative end of the output end of the three-phase fully-controlled rectifier bridge is connected to the point N.

In some embodiments, further comprising: a sampling unit and a control unit. A voltage is sampled, such as a voltage sampling resistor. A control unit, such as a controller of the frequency converter. Through the sampling unit and the control unit, the first full-control rectifying module and the second full-control rectifying module can be controlled to boost.

The sampling unit is configured to sample the bus voltage of the first bus-supported capacitor module and the bus voltage of the second bus-supported capacitor module after the frequency converter is started, and the sampled bus voltages are recorded as a first bus voltage and a second bus voltage.

The control unit is configured to control the first fully-controlled rectifying module and the second fully-controlled rectifying module to boost voltage according to the first bus voltage, the second bus voltage and a blocking voltage value of a switching tube in the three-level inversion unit.

In the example shown in fig. 5, two sets of three-phase fully-controlled rectifying topologies are used for the rectifying ends, the power supply at the front end is isolated by a transformer T1 and a transformer T2, and the positive and negative outputs at the rear end are respectively connected to PO and ON. At this time, the bus voltage V_PNNot only can a stable midpoint level be obtained, but also bus boosting can be performed through a full-section three-phase fully-controlled rectifier due to the presence of the transformer, as shown in fig. 6.

Fig. 6 is a schematic diagram of a rectification boosting flow of an embodiment of the frequency converter topology for suppressing the three-level midpoint offset in fig. 5. As shown in fig. 6, the rectification and boosting process of the frequency converter topology for suppressing the three-level midpoint offset includes:

step 1, electrifying the frequency converter, and rectifying the first rectifying unit and the second rectifying unit to enable the bus voltage to rise to a set voltage such as 1000V.

And 2, electrifying a controller of the frequency converter, and judging whether the frequency converter is started.

And 3, after the frequency converter is started, the controller respectively carries out PFC algorithm modulation on the first rectifying unit and the second rectifying unit. The purpose of the modulation is to boost the bus and reduce input current harmonics.

Step 4, judging whether the boosting target values of the first rectifying unit and the second rectifying unit are smaller than or equal to the IGBT blocking voltage value, if so, executing step 5; the boost target value is a bus voltage value preset artificially and can be adjusted according to the terminal voltage requirement of the motor. Otherwise, starting fault protection; that is, the bus voltage is greater than the blocking voltage of the IGBT, which can cause the IGBT to fail.

And 6, judging whether the bus voltage reaches a boosting target value, and if so, determining that the rectification boosting is finished. Otherwise, returning to the step 3, and performing PFC algorithm modulation on the first rectifying unit and the second rectifying unit again.

In the example shown in fig. 6, after the frequency converter is powered on, full-control rectification needs to be performed through the diode, and bus boosting needs to be performed after the controller is powered on. The diode refers to a diode which is connected in an anti-parallel mode in the IGBT module; in the topology, the frequency converter firstly utilizes the diode to carry out uncontrolled rectification, and then utilizes the IGBT to carry out full-controlled rectification after the controller is powered on.

The two groups of three-phase fully-controlled rectifiers respectively acquire voltage values of PO and ON sections, PFC algorithm modulation is carried out through the controller, and finally boost of the bus is achieved through driving of the rectification end IGBT. However, the target values of the two stages of boosting for PO and ON are set to be the same. And according to the characteristics of the three-level topology, the highest voltage at two ends of the bus PN can not exceed the blocking voltage value of the IGBT in the three-level inverter, otherwise, the failure of the three-level inverter can be caused by overvoltage. When the voltage values of the PO and the ON sections are collected, the voltage collecting unit can be utilized, and particularly, a differential sampling circuit can be constructed by adopting a resistor and an operational amplifier.

In some embodiments, the three-level inversion unit includes: any one of a NPC type three-level inverter, a TNPC type three-level inverter, and an ANPC type three-level inverter.

The three-level inversion topology (i.e., the three-level inversion unit) includes, but is not limited to, NPC (midpoint clamping) three-level topology, TNPC (T-type midpoint clamping) three-level topology, and ANPC (active midpoint clamping) three-level topology.

The scheme of the invention mainly solves the problem of midpoint voltage offset in the loading process of the three-level frequency converter, and effectively realizes the purpose of inhibiting the midpoint offset by adopting a two-way isolation and rectification design method (such as transformer isolation and two-way diode or IGBT rectification topology).

By adopting the technical scheme of the invention, three-phase power is divided into two groups of same three-phase power supplies, and the two groups of same three-phase power supplies are respectively rectified to output two groups of independent direct current power supplies with equal voltage. Two groups of independent DC power supplies with equal voltage are connected in series through the middle point of the three-level frequency converter. Therefore, the performance degradation of the three-level frequency converter topology is avoided by restraining the midpoint potential offset of the three-level topology frequency converter.

According to the embodiment of the invention, a motor corresponding to the frequency converter is also provided. The motor may include: the frequency converter described above.

Since the processes and functions implemented by the motor of this embodiment substantially correspond to the embodiments, principles and examples of the foregoing devices, reference may be made to the related descriptions in the foregoing embodiments without being detailed in the description of this embodiment.

By adopting the technical scheme of the invention, three-phase power is divided into two groups of same three-phase power supplies, the two groups of same three-phase power supplies are respectively rectified, and two groups of independent direct current power supplies with equal voltage are output; two groups of direct current power supplies which are independent from each other and have equal voltage can effectively and reliably solve the problem of point potential deviation in the three-level topology by connecting the midpoints of the three-level frequency converters in series, and the performance reduction of the three-level frequency converter topology is avoided.

According to an embodiment of the present invention, there is also provided a boost control method for an inverter corresponding to a motor, as shown in fig. 7, which is a schematic flow chart of an embodiment of the method of the present invention. The boost control method of the frequency converter can comprise the following steps: step S110 and step S120.

In step S110, after the frequency converter is started, the bus voltage of the first bus-supported capacitor module and the bus voltage of the second bus-supported capacitor module are sampled and recorded as the first bus voltage and the second bus voltage.

At step S120, the first fully-controlled rectifier module and the second fully-controlled rectifier module are controlled to boost voltage according to the first bus voltage, the second bus voltage and a blocking voltage value of a switching tube in the three-level inverter unit.

In the example shown in fig. 5, two sets of three-phase fully-controlled rectifying topologies are used for the rectifying ends, the power supply at the front end is isolated by a transformer T1 and a transformer T2, and the positive and negative outputs at the rear end are respectively connected to PO and ON. At this time, the bus voltage V_PNNot only can a stable midpoint level be obtained, but also bus boosting can be performed through a full-section three-phase fully-controlled rectifier due to the presence of the transformer, as shown in fig. 6.

Fig. 6 is a schematic diagram of a rectification boosting flow of an embodiment of the frequency converter topology for suppressing the three-level midpoint offset in fig. 5. As shown in fig. 6, the rectification and boosting process of the frequency converter topology for suppressing the three-level midpoint offset includes:

step 1, electrifying the frequency converter, and rectifying the first rectifying unit and the second rectifying unit to enable the bus voltage to rise to a set voltage such as 1000V.

And 2, electrifying a controller of the frequency converter, and judging whether the frequency converter is started.

And 3, after the frequency converter is started, the controller respectively carries out PFC algorithm modulation on the first rectifying unit and the second rectifying unit.

Step 4, judging whether the boosting target values of the first rectifying unit and the second rectifying unit are smaller than or equal to the IGBT blocking voltage value, if so, executing step 5; otherwise, fault protection is started.

Step 6, judging whether the bus voltage reaches a boosting target value, if so, determining that the rectification boosting is finished; otherwise, returning to the step 3, and performing PFC algorithm modulation on the first rectifying unit and the second rectifying unit again.

In the example shown in fig. 6, after the frequency converter is powered on, full-control rectification is performed through the triode, and bus boosting is performed after the controller is powered on. The two groups of three-phase fully-controlled rectifiers respectively acquire voltage values of PO and ON sections, PFC algorithm modulation is carried out through the controller, and finally boost of the bus is achieved through driving of the rectification end IGBT. However, the target values of the two stages of boosting for PO and ON are set to be the same. And according to the characteristics of the three-level topology, the highest voltage at two ends of the bus PN can not exceed the blocking voltage value of the IGBT in the three-level inverter, otherwise, the failure of the three-level inverter can be caused by overvoltage.

The scheme of the invention mainly solves the problem of midpoint voltage offset in the loading process of the three-level frequency converter, and effectively realizes the purpose of inhibiting the midpoint offset by adopting a two-way isolation and rectification design method (such as transformer isolation and two-way diode or IGBT rectification topology).

Since the processing and functions implemented by the method of this embodiment substantially correspond to the embodiments, principles and examples of the motor, reference may be made to the related descriptions in the foregoing embodiments without being detailed in the description of this embodiment, which is not described herein.

By adopting the technical scheme of the embodiment, three-phase power is divided into two groups of same three-phase power supplies, the two groups of same three-phase power supplies are respectively rectified, and two groups of independent direct-current power supplies with equal voltage are output; two groups of direct current power supplies which are independent from each other and have equal voltage can effectively and reliably solve the problem of neutral point potential deviation in three-level topology by connecting neutral points of three-level frequency converters in series, and the reliability and the stability of the frequency converters are improved.

In summary, it is readily understood by those skilled in the art that the advantageous modes described above can be freely combined and superimposed without conflict.

The above description is only an example of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.