A five-level power topology for a four-phase switched reluctance motor

Abstract

The present invention discloses a five-level power topology for a four-phase switched reluctance motor, which is applied to a switched reluctance motor drive system. This structure adopts a double-bridge topology. Phases A and C share the same arm, including switching transistors S3, S4 and diode D4. Phases B and D share the same arm, including switching transistor S9, S 10 and diode D 10 . Two independent bridge topologies can achieve more voltage levels with fewer switching transistors, and there is no phase overlap in each phase. In the electric mode, by controlling the conduction and cutoff of the switching transistors, the switched reluctance motor can operate in five modes: fast excitation (+2), normal pressure excitation (+1), freewheeling (0), normal pressure demagnetization (-1), and fast demagnetization (-2), to realize the drive of the switched reluctance motor. Similarly, in the inductance decline region, different operating modes can be adopted to realize the braking of the switched reluctance motor. The present invention reduces the device cost, improves the control flexibility, realizes the fast excitation and demagnetization of the winding, and solves the problem of weakened current tracking ability caused by the large back electromotive force of the switched reluctance motor at high speed.

Description

Technical Field

[0001] The present invention relates to a power converter for an electric motor, and in particular to a five-level power converter applied to a four-phase switched reluctance motor. Background Art

[0002] As a new type of AC speed regulation motor, the switched reluctance motor (SRM) has a simple structure, low cost, high efficiency, large starting torque, and wide speed regulation range, and has been applied to many fields such as electric vehicles, mechanical transmissions, aerospace, etc. The switched reluctance motor drive system (SRD) consists of an SRM, a controller, a power converter, a position sensor, and a voltage and current sensor. Among them, the topology of the power converter has a great influence on the performance of the SRD. Studying the power converter with a multi-level topology is of great significance for improving the dynamic performance of the SRM and enhancing the system efficiency.

[0003] The traditional asymmetric half-bridge power converter has a simple structure and easy control, and is widely used in SRD. However, when the motor operates at high speed, the weakening of the current tracking ability of the traditional asymmetric half-bridge power converter will cause excessive torque ripple and reduce the system efficiency; and due to the limitation of the rated volt-ampere value of the switching device, the traditional asymmetric half-bridge power converter can only be adapted to medium and small power occasions.

[0004] The five-level switched reluctance motor power converter disclosed in the patent application number: 200810023692.6, compared with the traditional asymmetric half-bridge power converter, has a reduced switching frequency, a low withstand voltage value, and multiple selectable voltage levels, with flexible control; but the total rated volt-ampere value of this five-level power converter is basically the same as that of the traditional power converter, and the number of required power devices doubles, resulting in a relatively high total conduction loss. Summary of the Invention

[0005] The purpose of the present invention is to improve the deficiencies of the existing power converter, and provide a five-level power topology for a four-phase switched reluctance motor, adopting a double-bridge topology to achieve more voltage levels with fewer switching devices and reduce the system cost.

[0006] The technical solution of the present invention is: a five-level power topology for a four-phase switched reluctance motor, including a DC power supply, filter voltage-dividing capacitors C U , C L , and a double-topology bridge. It is characterized in that: the two filter voltage-dividing capacitors C U , C L on the right side of the DC power supply are connected in series and respectively connected to the upper series-connected double-switch tubes S 3 , S 1 with a lower freewheeling diode D 2 , and the upper freewheeling diode D 4The lower series-connected dual-switch tube S 3 and S 4 , with a lower freewheeling diode D 6 The upper series-connected dual-switch tube S 5 and S 6 are connected in parallel; the drain of the switch tube S 3 in the middle branch and the source of the switch tube S 2 in the left branch are connected to the winding L A , and the source of the switch tube S 6 in the right branch is connected to the winding L C ; the midpoints of the filter voltage-dividing capacitors C U and C L are connected to the midpoints of the upper series-connected dual-switch tubes S 1 and S 1 through the upper clamping diode D 2 , are connected to the midpoints of the upper series-connected dual-switch tubes S 5 and S 5 through the upper clamping diode D 6 , and are connected to the midpoints of the lower series-connected dual-switch tubes S 2 and S 3 through the lower clamping diode D 4 ; the structure on the left side of the DC power supply is symmetrical to the structure on the right side of the DC power supply.

[0007] The described five-level power topology structure for a four-phase switched reluctance motor adopts a double-bridge topology. Phases A and C share the same bridge arm and include the switch tubes S 3 and S 4 and the diode D 4 , and phases B and D share the same bridge arm and include the switch tubes S 9 and S 10 and the diode D 10 .

[0008] The described five-level power topology structure for a four-phase switched reluctance motor enables the switched reluctance motor to operate in multiple voltage states by turning on and off the switch tubes.

[0009] The beneficial effects of the present invention compared with the prior art are as follows:

[0010] 1. Adopting a double-bridge topology, more voltage levels are achieved with fewer switching devices.

[0011] 2. Under the same DC power supply, the voltage withstand of the power device is only half of that of the power device in the traditional converter; and since phases A and C (phases B and D) share the same bridge arm, the use of power devices is reduced. Compared with the traditional converter and the five-level switched reluctance motor power converter disclosed in the patent application No. 200810023692.6, the total rated volt-ampere value of the present invention is lower than that of the above two power converters, and the system cost is further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is the structure diagram of the asymmetric half-bridge power converter in the prior art.

[0013] Figure 2 is the structure diagram of the five-level switched reluctance motor power converter in the prior art.

[0014] Figure 3 is the five-level power topology structure diagram for a four-phase switched reluctance motor proposed in the present invention.

[0015] Figure 4 is the excitation voltage state diagram of the present invention.

[0016] Figure 5 is the freewheeling voltage state diagram of the present invention.

[0017] Figure 6 is the demagnetizing voltage state diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be further described below with reference to the accompanying drawings.

[0019] As Figure 3 shown, the present invention provides a five-level power converter for a four-phase switched reluctance motor, including a DC power supply, filter voltage-dividing capacitors C U , C L , and a double-topology bridge. The two filter voltage-dividing capacitors C U , C L on the right side of the DC power supply are connected in series and respectively connected in parallel with the upper series-connected double-switch tubes S 3 with a lower freewheeling diode D 1 , S 2 , the lower series-connected double-switch tubes S 4 with an upper freewheeling diode D 3 , S 4 , and the upper series-connected double-switch tubes S 6 with a lower freewheeling diode D 5 , S 6 ; the drain of the switch tube S 3 in the middle branch is connected to the source of the switch tube S 2 in the left branch to connect the winding LA and is connected to the source of the switching transistor S in the right branch 6 of the winding L C ; The midpoint of the filter voltage-dividing capacitors C U and C L is connected to the midpoint of the upper series-connected dual switching transistors S 1 and S 1 through the upper clamping diode D 2 , is connected to the midpoint of the upper series-connected dual switching transistors S 5 and S 5 through the upper clamping diode D 6 , and is connected to the midpoint of the lower series-connected dual switching transistors S 2 and S 3 through the lower clamping diode D 4 ; The structure on the left side of the DC power supply is symmetrical to the structure on the right side of the DC power supply.

[0020] By calculating the rated volt-ampere value, the cost of the five-level power converter for a four-phase switched reluctance motor proposed in the present invention, Figure 1 the asymmetrical half-bridge power converter shown in Figure 2 and the five-level switched reluctance motor power converter shown in

[0021] Table 1

[0022]

[0023] As shown in Table 1, for the five-level power converter for a four-phase switched reluctance motor proposed in the present invention, the total rated volt-ampere value is lower than Figure 1 and Figure 2 the power converters shown in, and the system cost is further reduced.

[0024] The five-level power converter for a four-phase switched reluctance motor described above has five operating states. Taking phase A as an example:

[0025] As Figure 4 shown is the exciting voltage state. Figure 4 (a) is the fast excitation mode, and the switching transistors S 1 , S 2 , S 3 , S 4 are all turned on, and the winding voltage is U; Figure 4 (b) or (c) is the normal pressure excitation mode, and the switching transistors S 1 , S 2 , S 3 are turned on, S 4 is turned off, or the switching transistors S 2 , S 3 , S 4 are turned on, S1 Turn off, the winding voltage is U / 2 under the normal pressure excitation mode.

[0026] As Figure 5 shown is the freewheeling voltage state. Figure 5 (a) The switch tubes S 3 and S 4 are turned on, S 1 and S 2 are turned off. Figure 5 (b) The switch tubes S 1 and S 2 are turned on, S 3 and S 4 are turned off. Figure 5 (c) The switch tubes S 2 and S 3 are turned on, S 1 and S 4 are turned off. The winding voltage is 0 under the freewheeling state.

[0027] As Figure 6 shown is the demagnetization voltage state. Figure 6 (a) or (b) is the normal pressure demagnetization mode. The switch tube S 2 is turned on, S 1 , S 3 , S 4 are turned off, or the switch tube S 3 is turned on, S 1 , S 2 , S 4 are turned off. The winding voltage is -U / 2. Figure 6 (c) is the fast demagnetization mode. The switch tubes S 1 , S 2 , S 3 , S 4 are all turned off. The winding voltage is -U.

[0028] The power conversion circuit of the present invention with the fast excitation and fast demagnetization modes can improve the current tracking performance of the motor and enhance the dynamic performance of the SRD; and under the condition of the same voltage-resistant components, the power conversion circuit of the present invention can be applied to high-power occasions.

Claims

1. A five-level power topology for a four-phase switched reluctance motor, including a DC power supply, filter and voltage-dividing capacitors C U , C L , and a dual-topology bridge; A five-level power topology for a four-phase switched reluctance motor as described above, Characterized in that: Adopt a double-bridge topology, where phases A and C share the same bridge arm, including switch tubes S 3 、S 4 and diode D 4 , phases B and D share the same bridge arm, including switch tubes S 9 、S 10 and diode D 10 ; The two filtering and voltage-dividing capacitors C on the right side of the DC power supply U and C L are connected in series and then respectively connected in parallel with the upper series-connected dual-switch tubes S 3 with a lower freewheeling diode D 1 and S 2 , the lower series-connected dual-switch tubes S 4 with an upper freewheeling diode D 3 and S 4 , and the upper series-connected dual-switch tubes S 6 with a lower freewheeling diode D 5 and S 6 ; the drain of the switch tube S in the middle branch 3 is connected to the source of the switch tube S in the left branch 2 to the winding L A , and is also connected to the source of the switch tube S in the right branch 6 to the winding L C ; the midpoints of the filtering and voltage-dividing capacitors C U and C L are connected to the midpoints of the upper series-connected dual-switch tubes S 1 and S 1 through the upper clamping diode D 2 , are connected to the midpoints of the upper series-connected dual-switch tubes S 5 and S 5 through the upper clamping diode D 6 , and are connected to the midpoints of the lower series-connected dual-switch tubes S 2 and S 3 through the lower clamping diode D 4 ; the structure on the left side of the DC power supply is symmetrical to the structure on the right side of the DC power supply.

2. The five-level power topology according to claim 1, Characterized in that: Under the control mode of current chopping or direct instantaneous torque control, at most two phases of the motor windings are conducting, so each phase can be independently controlled when the motor windings conduct in sequence.

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