CN109787532B - A three-phase variable structure inverter and its control method - Google Patents

Abstract

The invention discloses a three-phase variable structure inverter and a control method thereof, comprising four bridge arms and four bidirectional thyristors, the output node of the first bridge arm is connected to the positive end of the A-phase winding; the second The output node of the bridge arm is connected to the negative end of the A-phase winding; the output node of the third bridge arm is connected to the positive end of the C-phase winding; the output node of the fourth bridge arm is connected to the negative end of the C-phase winding; the B The positive end of the phase winding is connected to the third bridge arm through the first triac, and the negative end is connected to the second bridge arm through the second triac; or the positive end of the B-phase winding is also connected to the second bridge through the third triac The bridge arm, the negative terminal is connected to the third bridge arm through the fourth bidirectional thyristor. The invention enables the three-phase AC motor to reduce the power loss of the motor driver under the working condition of high torque; under the working condition of high speed, the utilization rate of the DC voltage of the motor driver is improved, and the high-speed operation range of the motor is expanded.

Description

A three-phase variable structure inverter and its control method

technical field

The invention belongs to the field of AC motor and drive control, and more particularly, relates to a three-phase variable structure inverter and a control method thereof.

Background technique

In the field of AC drive, the three-phase half-bridge inverter topology is currently the most widely used drive topology. This topology consists of three bridge legs, resulting in low driver cost and high power density. However, this topology can provide low utilization of DC voltage, and the back EMF of the motor is proportional to the speed. In high-speed conditions, the back EMF of the motor is high and high DC voltage utilization is required, so this topology limits the performance of the motor in high-speed conditions.

The three-phase full-bridge inverter topology has twice the DC voltage utilization of the three-phase half-bridge inverter topology. It can be seen that the topology consists of six bridge arms, and each bridge arm has a phase current flowing. Therefore, the use of this topology will greatly increase the cost and volume of the driver, and the power loss of the motor driver during operation will also greatly increase. These shortcomings are the most important reasons that limit the difficulty of popularizing and applying the three-phase full-bridge inverter topology in the industrial field.

Patent CN201810051626.3 discloses an open-winding motor driver topology and its modulation method. This topology has the same DC voltage utilization as the three-phase full-bridge inverter topology, and reduces two bridge arms. Therefore, compared with the three-phase full-bridge inverter topology, the cost and volume of this topology and the power loss during operation are greatly increased. reduce. But when applied to a traditional three-phase AC motor, the bridge arm 2 and the bridge arm 3 in this topology need to flow 1.717 times the phase current. Compared with the three-phase half-bridge topology, the power loss during operation of this topology is still greatly increased. In the case of high torque, the motor needs the driver topology to provide a large current output capability. Therefore, this defect limits the performance of the motor under high torque conditions.

SUMMARY OF THE INVENTION

In view of the defects of the prior art, the purpose of the present invention is to provide a three-phase variable structure inverter and a control method thereof, aiming at solving the problems of large power loss and low utilization rate of DC voltage of the motor driver in the prior art.

In order to achieve the above purpose, the present invention provides a three-phase variable structure inverter, comprising a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a first bidirectional thyristor T1, and a second bidirectional thyristor T2, the third bidirectional thyristor T3 and the fourth bidirectional thyristor T4;

The upper node of each bridge arm is connected to the DC bus voltage, and the lower node is connected to the power ground;

The output node of the first bridge arm is connected to the positive end of the A-phase winding; the output node of the second bridge arm is connected to the negative end of the A-phase winding;

The output node of the third bridge arm is connected to the positive end of the C-phase winding; the output node of the fourth bridge arm is connected to the negative end of the C-phase winding;

the first bidirectional thyristor is connected between the output node of the third bridge arm and the positive end of the B-phase winding;

the second bidirectional thyristor is connected between the output node of the second bridge arm and the negative end of the B-phase winding;

the third bidirectional thyristor is connected between the output node of the second bridge arm and the positive end of the B-phase winding;

the fourth bidirectional thyristor is connected between the output node of the third bridge arm and the negative end of the B-phase winding;

The first bidirectional thyristor and the second bidirectional thyristor are used for reversely connecting the B-phase winding to the inverter, and by changing the inverter phase voltage, the rotational speed of the rotor of the motor is reduced, and the operation of the motor in the first mode is realized;

The third bidirectional thyristor and the fourth bidirectional thyristor are used to connect the B-phase windings to the inverter in the forward direction, and by changing the inverter phase voltage, the rotational speed of the rotor of the motor is increased, and the operation of the motor in the second mode is realized;

The first bidirectional thyristor and the second bidirectional thyristor are turned on in the first mode of the motor and turned off in the second mode;

The third bidirectional thyristor and the fourth bidirectional thyristor are turned on in the second mode of the motor and turned off in the first mode;

The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm are used to control the phase voltage and phase current of the motor.

Preferably, each of the bridge arms includes an upper bridge arm power switch device and a lower bridge arm power switch device, and the lower node of the upper bridge arm power switch device is connected to the upper node of the lower bridge arm power switch device as a bridge arm The output node is used to control the phase voltage and phase current of the motor; the power switching devices are current fully controlled switches, including MOSFETs and IGBTs with anti-parallel diodes.

On the other hand, based on the above-mentioned three-phase variable structure inverter, the present invention provides a control method for a three-phase variable structure inverter, including:

(1) When the target working mode of the inverter is inconsistent with the actual working mode, the driving signals on the two bidirectional thyristors that are turned on in the actual working mode will be removed at the same time, so that the corresponding two bidirectional thyristors are turned off at zero-crossing;

(2) In the target operating mode, the corresponding two triacs are simultaneously applied with driving signals to conduct, and the voltage modulation mode is switched, so that the inverter operates in the target operating mode.

The switching between the actual working mode and the target working mode includes switching from the first mode to the second mode, and switching from the second mode to the first mode.

Through the above technical solutions conceived by the present invention, compared with the prior art, the following beneficial effects can be achieved:

(1) Compared with the three-phase half-bridge topology in the present invention, the proposed three-phase variable structure inverter can double the speed range without weakening the field, and the inverter has all the freedom of current control. degree, and has better fault tolerance performance.

(2) The mode switching of the three-phase variable structure inverter proposed by the present invention only changes the connection mode of the B-phase windings, and the corresponding control method uses the B-phase zero-crossing point to perform mode switching, so that the switching process is short and fast, and the switching process is not correct. The speed and torque of the motor are affected, thereby avoiding the impact on the user.

(3) When the present invention adopts the three-phase variable structure inverter to drive the traditional AC motor, the cost, volume and power loss of the motor driver are similar to those of the three-phase half-bridge topology, but the performance of the driver is much better than that of the three-phase half-bridge topology. Prospects for industrial applications.

Description of drawings

Figure 1 is the three-phase symmetrical AC current of the three-phase AC motor;

Fig. 2 is the structure of the three-phase variable structure inverter in the low-speed mode provided by the present invention;

3 is a structure of a three-phase variable structure inverter in a high-speed mode provided by the present invention;

Fig. 4 is the motor speed torque relation diagram when the three-phase half-bridge topology is adopted;

FIG. 5 is a diagram showing the relationship between the rotational speed and torque of the motor when the three-phase variable structure inverter provided by the present invention is adopted.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The present invention provides a three-phase variable structure inverter, comprising a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a first bidirectional thyristor T1, a second bidirectional thyristor T2, and a third bidirectional thyristor thyristor T3 and the fourth bidirectional thyristor T4;

The upper node of each bridge arm is connected to the DC bus voltage, and the lower node is connected to the power ground;

The output node of the first bridge arm is connected to the positive end of the A-phase winding; the output node of the second bridge arm is connected to the negative end of the A-phase winding;

The output node of the third bridge arm is connected to the positive end of the C-phase winding; the output node of the fourth bridge arm is connected to the negative end of the C-phase winding;

the first bidirectional thyristor is connected between the output node of the third bridge arm and the positive end of the B-phase winding;

the second bidirectional thyristor is connected between the output node of the second bridge arm and the negative end of the B-phase winding;

the third bidirectional thyristor is connected between the output node of the second bridge arm and the positive end of the B-phase winding;

the fourth bidirectional thyristor is connected between the output node of the third bridge arm and the negative end of the B-phase winding;

The first bidirectional thyristor and the second bidirectional thyristor are used to reversely connect the B-phase winding to the inverter, and reduce the rotational speed of the motor rotor by changing the inverter phase voltage, so as to realize the operation of the motor in the first mode;

The third bidirectional thyristor and the fourth bidirectional thyristor are used to connect the B-phase windings to the inverter in the forward direction, and increase the rotational speed of the motor rotor by changing the inverter phase voltage, so as to realize the operation of the motor in the second mode;

The first bidirectional thyristor and the second bidirectional thyristor are turned on in the first mode of the motor and turned off in the second mode;

The third bidirectional thyristor and the fourth bidirectional thyristor are turned on in the second mode of the motor and turned off in the first mode;

The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm are used to control the phase voltage and phase current of the motor.

Preferably, each of the bridge arms includes an upper arm power switch device and a lower arm power switch device, and a lower node of the upper arm power switch device is connected to an upper node of the lower arm power switch device for controlling The phase voltage and phase current of the motor; the power switching devices are current fully controlled switches, including MOSFETs and IGBTs with anti-parallel diodes.

Preferably, since the maximum phase voltage output in the second mode is greater than the maximum phase voltage that can be output in the first mode, the rotation speed of the motor in the second mode is higher than the rotation speed in the first mode. Therefore, in the present invention, the first mode is referred to as the motor low-speed mode, and the second mode is referred to as the motor high-speed mode; in other words, the three-phase variable structure inverter includes two modes, namely the motor low-speed mode and the motor high-speed mode .

Preferably, when the first bidirectional thyristor and the second bidirectional thyristor are turned on, and the third bidirectional thyristor and the fourth triac When the first bidirectional thyristor and the second bidirectional thyristor are turned off, it is the inverter structure in the high speed mode of the motor.

Preferably, the inverter structure in the low-speed mode can provide high current but cannot provide high DC voltage utilization, so it is suitable for the motor to operate under low-speed and high-torque conditions;

The inverter structure in high-speed mode can provide high DC voltage utilization but cannot provide large current, so when using the motor to run at high speed, the torque needs to be derated.

On the other hand, based on the above-mentioned three-phase variable structure inverter, the present invention provides a control method for a three-phase variable structure inverter, including:

(1) When the target working mode of the inverter is inconsistent with the actual working mode, the driving signals on the two bidirectional thyristors that are turned on in the actual working mode will be removed at the same time, so that the corresponding two bidirectional thyristors are turned off at zero-crossing;

(2) In the target operating mode, the corresponding two triacs are simultaneously applied with driving signals to conduct, and the voltage modulation mode is switched, so that the inverter operates in the target operating mode.

Specifically, when the inverter works in the low-speed mode, the first triac T1 and the second triac T2 are always turned on by the driving signal, and the third triac T3 and the fourth triac T4 are always turned off without the driving signal. off, at this time the control scheme adopts the motor control method corresponding to the low-speed mode;

When the inverter works in the high-speed mode, the third triac T3 and the fourth triac T4 are always turned on for the driving signal, and the first bidirectional thyristor T1 and the second bidirectional thyristor T2 are always turned off without the driving signal. The time control scheme adopts the motor control method corresponding to the high-speed mode.

When switching from low-speed mode to high-speed mode from a three-phase variable structure inverter,

d1: Remove the driving signals of the triacs T1 and T2, wait for the current of the triacs to naturally cross zero and turn off. At this time, the controller still adopts the motor control method corresponding to the low-speed mode;

d2: Detect the B-phase current. When the B-phase current is equal to zero, the first triac T1 and the second triac T2 have naturally zero-crossed and turned off;

d3: The third triac T3 and the fourth triac T4 are turned on by applying the driving signal, and the control scheme is switched to the motor control method corresponding to the high-speed mode.

At this time, the three-phase variable structure inverter is switched to the high-speed mode.

When switching from high-speed mode to low-speed mode from a three-phase variable structure inverter,

d1: Remove the driving signals of the triac T3 and T4, wait for the current of the triac to cross zero naturally and turn off, at this time, the controller still adopts the motor control method corresponding to the high-speed mode;

d2: Detect the B-phase current. When the B-phase current is equal to zero, the third triac T3 and the fourth triac T4 have naturally zero-crossed and turned off;

d3: The first triac T1 and the second triac T2 are turned on by applying the driving signal, and the control scheme is switched to the motor control method corresponding to the low-speed mode.

At this time, the three-phase variable structure inverter is switched to the low-speed mode.

Figure 1 shows the three-phase symmetrical AC current waveform of a typical three-phase AC motor. The three-phase current expression corresponding to the current waveform is as follows:

Among them, i _a , i _b , and ic are the phase currents of phase A, phase B and phase _C respectively; I _ac is the effective value of the phase current, and θ _e is the electrical angle, which is related to the rotor angle.

The three-phase symmetrical AC current will cause different current stress to the bridge arm power devices in the inverter in different inverter topologies. As shown in Figure 2, according to the connection method of the phase winding and the bridge arm in the low-speed mode, the current flowing into the bridge arm can be obtained as follows:

It can be seen from the above formula that the first bridge arm and the fourth bridge arm flow the A-phase and C-phase currents respectively, while the second bridge arm flows the sum of the A-phase and B-phase currents, and the third bridge arm flows the B-phase and C-phase currents. and. However, due to the phase difference between the phase currents, according to the above formula, the effective value of the current flowing in the second bridge arm and the third bridge arm is the same as the effective value of the phase current, so the current stress of each bridge arm is the same, and the magnitude is RMS value of phase current. Therefore, the current loss of the motor operation is small, and it can operate under the condition of low speed and high torque. However, after analysis, the topology in the low-speed mode only has the same DC voltage utilization as the three-phase half-bridge topology, so it cannot be applied in high-speed conditions that require high DC voltage utilization.

As shown in Figure 3, according to the connection method of the phase winding and the bridge arm in the high-speed mode, the current flowing into the bridge arm can be obtained as follows:

It can be seen from the above formula that the first bridge arm and the fourth bridge arm flow the A-phase and C-phase currents respectively, while the bridge arm 2 flows the difference between the A-phase and B-phase currents, and the bridge arm 3 flows the B-phase and C-phase currents. Difference. It can be seen from the above formula that the effective value of the current flowing in the second bridge arm and the third bridge arm is 1.717 times the effective value of the phase current. Therefore, the current loss of the motor operation is relatively large. Torque requires derated output. However, compared with the three-phase half-bridge structure or the topology in the low-speed mode, the topology in the high-speed mode can output twice the DC voltage utilization rate, thereby expanding the high-speed operation range of the motor and reducing the field weakening control.

Figures 4 and 5 are the speed and torque relationship diagrams of the three-phase motor driven by the three-phase half-bridge topology and the three-phase variable structure topology, respectively. It can be seen that the operating range of the three-phase motor in the low-speed mode is different from that in the three-phase half-bridge. The operating range in the topology is the same, but in the three-phase variable structure topology, a high-speed mode is added, which doubles the speed range of the motor and greatly improves the operating capability of the motor.

Another important advantage of the three-phase variable structure topology is that the switching process is smooth and fast. During the switching process, neither the current nor the torque is subject to fluctuations or transient processes, so that it does not affect the user. On the one hand, the smooth switching process benefits from the fact that when the topology is switched, only the connection mode of one-phase windings is switched, and in this topology, the controls of the three-phase windings do not affect each other, so that the phase currents in the windings can be waited for. Smooth switching at zero-crossing; on the other hand, it also benefits from the use of the control characteristics of the triac. Since the turn-on of the triac is controllable and the turn-off is uncontrollable, the current needs to be turned off by natural zero-crossing when it is turned off. Therefore, the driving signal of the triac can be removed at any time without changing the control method, and then the phase current can be turned off after the natural zero-crossing. break.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (6)

1. A three-phase variable structure inverter, characterized in that it comprises a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a first bidirectional thyristor, a second bidirectional thyristor, and a third bidirectional thyristor. thyristor and a fourth bidirectional thyristor; The upper node of each bridge arm is connected to the DC bus voltage, and the lower node is connected to the power ground; The output node of the first bridge arm is connected to the positive end of the A-phase winding; the output node of the second bridge arm is connected to the negative end of the A-phase winding; The output node of the third bridge arm is connected to the positive end of the C-phase winding; the output node of the fourth bridge arm is connected to the negative end of the C-phase winding; the first bidirectional thyristor is connected between the output node of the third bridge arm and the positive end of the B-phase winding; the second bidirectional thyristor is connected between the output node of the second bridge arm and the negative end of the B-phase winding; the third bidirectional thyristor is connected between the output node of the second bridge arm and the positive end of the B-phase winding; the fourth bidirectional thyristor is connected between the output node of the third bridge arm and the negative end of the B-phase winding; The first bidirectional thyristor and the second bidirectional thyristor are used to reversely connect the B-phase winding to the inverter, and reduce the rotation speed of the motor rotor by changing the inverter phase voltage, so as to realize the operation of the motor in the first mode; The third bidirectional thyristor and the fourth bidirectional thyristor are used to connect the B-phase windings to the inverter in the forward direction, and increase the rotation speed of the motor rotor by changing the inverter phase voltage, so as to realize the operation of the motor in the second mode; the first bidirectional thyristor and the second bidirectional thyristor are kept on in the first mode of the motor, and are kept off in the second mode; the third bidirectional thyristor and the fourth bidirectional thyristor are kept on in the second mode of the motor, and are kept off in the first mode; The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm are used to control the phase voltage and phase current of the motor. 2 . The three-phase variable structure inverter according to claim 1 , wherein each bridge arm comprises an upper bridge arm power switch device and a lower bridge arm power switch device, and the upper bridge arm power switch The lower node of the device is connected with the upper node of the power switching device of the lower bridge arm, and is used for controlling the phase voltage and phase current of the motor. 3 . The three-phase variable structure inverter according to claim 2 , wherein the power switching device is a current fully controlled switch. 4 . 4 . The three-phase variable structure inverter according to claim 3 , wherein the fully current-controlled switch comprises a MOSFET and an IGBT with an anti-parallel diode. 5 . 5. The control method for a three-phase variable structure inverter according to claim 1, characterized in that, comprising: (1) When the target working mode of the inverter is inconsistent with the actual working mode, the driving signals on the two bidirectional thyristors that are turned on in the actual working mode will be removed at the same time, so that the corresponding two bidirectional thyristors are turned off at zero-crossing; (2) In the target operating mode, the corresponding two triacs are simultaneously applied with driving signals to conduct, and the voltage modulation mode is switched, so that the inverter operates in the target operating mode. 6 . The control method according to claim 5 , wherein the switching between the actual working mode and the target working mode comprises switching from the first mode to the second mode, and switching from the second mode to the first mode. 7 .

Images