KR102594764B1 - Expansion method of current reconstruction areas for detecting phase currents by three-shunt resistors of three-leg two-phase inverters - Google Patents

Abstract

The method of expanding the current recovery area when detecting phase current using the 3-shunt resistance of a 3-leg type 2-phase inverter according to an embodiment of the present invention is to increase the phase current by using a 3-shunt resistor inserted in series with the lower switch of each leg. detecting; A control unit operation step of a two-phase AC motor driving circuit using the detected phase current information; Including the step of switching the upper and lower inverter switches by receiving a gating signal given by the operation of the control unit,
The control unit operation step includes restoring phase current that cannot be measured in a specific operating region when the voltage modulation index of the inverter is high; performing current control using the restored phase current, and then performing a DPWM (Discontinuous PWM) operation to expand the current recovery area using a given command voltage; Characterized by including the step of generating a gating signal through the PWM operation.
According to the present invention, when DPWM (Discontinuous PWM) technique is applied for PWM operation of the inverter when detecting phase current of a 2-phase AC motor using the shunt resistance of a 3-leg inverter, the current is higher than when SVPWM (Space Vector PWM) is applied. The recovery area can be expanded, which can improve the voltage utilization of the inverter and improve the reliability of the motor drive system.

Description

Method for expanding current restoration area when detecting phase current by 3-shunt resistance of 3-leg type 2-phase inverter

The present invention relates to a method of expanding the current recovery area when detecting phase current by the 3-shunt resistance of a 3-leg type 2-phase inverter. More specifically, it relates to a method of expanding the current recovery area using a shunt resistor inserted into each leg of a 3-leg inverter. This relates to a method of expanding the current restoration area using DPWM (Discontinuous Pulse Width Modulation) technique to improve the problem of not being able to restore the phase current in a specific operation area where the voltage modulation index is high when detecting the phase current of an electric motor.

An H-bridge circuit is generally used to drive two-phase AC motors such as stepping motors used in fields such as robots and printers, but a three-leg type two-phase inverter is used to reduce costs in small-capacity, low-cost motor drive systems. can be used When driving a two-phase AC motor using such an inverter, a method of detecting phase current by inserting a shunt resistor under the bottom switch of each leg of the inverter can be used instead of an expensive current sensor, and a three-shunt resistor can be used. By doing so, the current measurement area can be expanded compared to when using only a 2-shunt resistor.

However, in this case, there are areas where restoration of phase current becomes impossible in high-speed operation areas where the output voltage modulation index of the inverter increases. In these areas, current control performance deteriorates and torque ripple and noise occur due to incorrectly restored current. I do it. Additionally, the output voltage of the inverter is limited, reducing voltage utilization.

Therefore, when detecting phase current using the shunt resistance of a 3-leg type 2-phase inverter, a new method is required to expand the restoreable area of phase current in order to improve the voltage utilization of the inverter and improve the reliability of the driving system, and the present invention is for this purpose. It is proposed.

The technical problem that the present invention aims to solve is the problem that the current recovery area is limited in the high-speed operation area where the voltage modulation index of the inverter increases when detecting the phase current of a 2-phase AC motor using the 3-shunt resistance of a 3-leg type inverter. To improve this, we provide a method to improve the voltage utilization of the inverter by expanding the current recovery area using DPWM (Discontinuous PWM) technique.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

In order to solve the above-described technical problem, the method of expanding the current recovery area when detecting phase current using a 3-shunt resistance of a 3-leg type 2-phase inverter according to an embodiment of the present invention includes a method of expanding the current recovery area when detecting phase current, 3-Detecting phase current using a shunt resistor; A control unit operation step of a two-phase AC motor driving circuit using the detected phase current information; Including the step of switching the inverter upper and lower switches by receiving a gating signal given by the operation of the control unit,

The control unit operation step includes restoring phase current that cannot be measured in a specific operating region when the voltage modulation index of the inverter is high; performing current control using the restored phase current, and then performing a DPWM (Discontinuous PWM) operation to expand the current recovery area using a given command voltage; Characterized by including the step of generating a gating signal through the PWM operation.

The two-phase AC motor driving circuit for detecting phase current using a three-shunt resistor includes an input power unit to which direct current power is applied; an upper switch connected to each leg; Lower switches connected to each leg; Shunt resistors connected to each of the lower switches; It is characterized by being composed of a control unit.

In some embodiments of the present invention, switching the upper and lower switches by the DPWM method may include using the DPWMMIN method of discontinuous modulation in a section where the magnitude of the phase-to-phase voltage is the smallest.

In some embodiments of the present invention, using the DPWMMIN method, the polar voltage command is is fixed and the two zero voltage vectors are , 0 voltage vector This may include authorizing only

Specific details of other embodiments are included in the detailed description and drawings.

According to the present invention, when DPWM (Discontinuous PWM) technique is applied for PWM operation of the inverter when detecting phase current of a 2-phase AC motor using the shunt resistance of a 3-leg inverter, the current is higher than when SVPWM (Space Vector PWM) is applied. The recovery area can be expanded, which can improve the voltage utilization of the inverter and improve the reliability of the motor drive system.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

Figure 1 is a two-phase AC motor driving circuit including a three-leg type inverter in which a shunt resistor is inserted into each leg to detect phase current according to an embodiment of the present invention.
Figure 2 is a diagram to explain the minimum turn-on time of the bottom switch of the inverter required for accurate current measurement using a shunt resistor.
Figures 3 and 4 are diagrams showing the switching state and limited current recovery area of the inverter when the SVPWM technique is applied to the PWM operation of the 3-leg inverter, respectively.
Figures 5 and 6 are diagrams showing the switching state and expanded current recovery area of a 3-leg inverter when the DPWM technique is applied to expand the current recovery area, respectively, according to an embodiment of the present invention.
Figures 7 and 8 are diagrams showing a comparison of phase current restoration experiment results when SVPWM and DPWM are applied, respectively, according to an embodiment of the present invention.

The advantages and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. The present embodiments only serve to ensure that the disclosure of the present invention is complete and that common knowledge in the technical field to which the present invention pertains is not limited. It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

One component is said to be “connected to” or “coupled to” another component when it is directly connected or coupled to another component or with an intervening other component. Includes all cases. On the other hand, when one component is referred to as “directly connected to” or “directly coupled to” another component, it indicates that there is no intervening other component. “And/or” includes each and every combination of one or more of the mentioned items.

The terminology used herein is for describing embodiments and is not intended to limit the invention. As used herein, singular forms also include plural forms, unless specifically stated otherwise in the context. As used herein, “comprises” and/or “comprising” refers to the presence of one or more other components, steps, operations and/or elements. or does not rule out addition.

Although first, second, etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are merely used to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may also be a second component within the technical spirit of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with meanings that can be commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless clearly specifically defined.

1 is a two-phase AC motor driving circuit including a three-leg type inverter in which a shunt resistor is inserted into each leg for phase current detection according to some embodiments of the present invention.

Referring to FIG. 1, a two-phase AC motor driving circuit 10 using a 3-leg inverter according to some embodiments of the present invention includes an input power supply unit ( ), first to third upper switches (US1, US2, US3) connected to each leg of the inverter, first to third respectively connected in series to the first to third upper switches (US1 to US3) Current detected through the lower switches (LS1, LS2, LS3), first to third shunt resistors (SR1, SR2, SR3) and shunt resistors respectively connected in series with the first to third lower switches (LS1 to LS3) After performing current control using a given command voltage, a control unit 110 performs a DPWM (Discontinuous PWM) operation to expand the current recovery area using a given command voltage and applies a gating signal to the upper and lower switches of the inverter. may include.

When detecting phase current using only the 2-shunt resistors (SR1, SR2) located on the a and b phase legs of the inverter, there is an area where two phase currents cannot be measured simultaneously. This phenomenon occurs when the phase current is detected using all three shunt resistors. can be improved by measuring. When it is impossible to simultaneously measure two phase currents using only a 2-shunt resistor, the current of one phase and the neutral point current flowing through the third shunt resistor (SR3) can be measured by using a 3-shunt resistor. It is possible to restore unmeasurable phase currents using , and for this, at least two of the three currents must be measurable.

When the neutral point of a 3-leg type inverter is not connected to another circuit, the sum of the currents flowing through the three legs is 0, so the phase current restoration can use this feature to restore the unmeasurable current of one phase.

However, in the high-speed operation range of AC motors where the output voltage modulation index of the inverter increases, the turn-on time of the inverter lower switches (LS1 to LS3) is sufficiently secured despite using 3-shunt resistors (SR1 to SR3). Failure to do so may cause an unrecoverable phenomenon in the phase current in a specific operating area.

Figure 2 is a diagram for explaining the minimum turn-on time of the inverter lower switches (LS1 to LS3) required for accurate current measurement according to an embodiment of the present invention.

Referring to Figure 2, the minimum turn-on time of the inverter lower switches (LS1 to LS3) required for accurate phase current measurement. is the dead time of the lower switch , which is the sum of the turn-on delay time, rise time, settling time of the lower switch, and the slew rate of the OP-AMP. And, analog-to-digital conversion time It can appear as the sum of .

For accurate restoration of phase current using a 3-shunt resistor, the minimum required turn-on time is when two or more lower switches are turned on. It must be maintained for a longer period of time.

Figures 3 and 4 respectively show the switching state and limited current recovery area of the inverter when the space vector voltage modulation (Space Vector PWM, SVPWM) technique is applied to modulate the voltage of the 3-leg inverter.

Referring to Figures 3 and 4, when the command voltage is located in sector 3 (the area marked with a red square in Figure 4) within the output voltage range of the inverter, two or more lower switches are turned on to accurately restore the two phase currents. The zero vector application time is the time and 3rd effective vector application time sum of This minimum turn-on time It must be maintained for a longer time, and this can be expressed as Equation 1 below. This is the 1st effective vector because the command voltage is located in a different sector. or 5 effective vectors The same can be applied even when is approved.

[Equation 1]

If the output voltage modulation index of the inverter is high as described above, the time during which two or more lower switches are on. This minimum turn-on time A shorter region exists, and in this region, only one of the currents of the three legs of the inverter can be measured, making restoration of the phase current impossible. When using the SVPWM technique, areas where restoration of phase current is impossible are shown in blue areas in Figure 4, and these areas are the specifications of the motor drive system, that is, the switching cycle. , minimum turn-on time It may vary depending on.

For example, switching cycles =100㎲, minimum turn-on time When =15㎲, the maximum voltage modulation index that can restore phase current is limited to 0.44, the red circle in Figure 3. In these areas, current control performance deteriorates, which may cause motor output torque ripple and noise, and the output voltage of the inverter is limited, reducing direct current voltage utilization. Here, the voltage modulation index is the same as Equation 2, and is the fundamental wave size for the maximum output voltage during 4-step operation of the inverter. It can be defined as the ratio of . in this case ≤ 0.785 ( = / ) corresponds to the linear modulation area of the inverter.

[Equation 2]

The motor driving circuit 10 according to an embodiment of the present invention uses the DPWM technique for the PWM operation of the inverter, so that the minimum turn-on time of the inverter lower switch is shorter than when the SVPWM technique is applied. Since more can be secured, the restoreable area of the phase current can be expanded.

Figures 5 and 6 are diagrams showing the switching state and expanded current restoration area of a 3-leg inverter when the DPWM technique is applied to expand the current recovery area, respectively.

Referring to FIG. 5, in the motor driving circuit 10 according to an embodiment of the present invention, the control unit 110 uses the DPWMMIN method of discontinuous modulation in the section where the size of the phase voltage is smallest among the DPWM techniques for PWM operation of the inverter. It can be applied. This method uses a polar voltage command for discontinuous modulation. The two zero voltage vectors are fixed only to , Always 0 voltage vector Unlike other DPWM techniques, the restoreable area of phase current can be expanded.

Referring to Figure 6, which shows the expanded recovery area of phase current when applying the DPWM technique, the maximum voltage modulation index at which phase current can be restored under the same system specifications as when applying the SVPWM technique previously described using Figures 3 and 4. can be expanded to 0.78, shown in the red circle, and in this case, the inverter's voltage utilization can be improved compared to the SVPWM technique.

The SVPWM technique has better harmonic characteristics than the DPWM technique under low voltage modulation conditions, and the DPWM technique can reduce switching loss and has better harmonic characteristics than the SVPWM technique under high voltage modulation conditions. Therefore, the specification of the electric motor drive system is the switching cycle =100㎲, minimum turn-on time = 15㎲, the maximum voltage modulation index that can restore the phase current is M = 0.44, so by applying the SVPWM technique in the area of M ≤ 0.44 and the DPWM technique in the area of M > 0.44, the current restoration area is expanded and the harmonic characteristics of the phase current are improved at the same time. It can be improved.

Figures 7 and 8 show the specifications of the electric motor drive system switching cycle, respectively. =100㎲, minimum turn-on time This is a diagram comparing the results of the phase current restoration experiment when applying the SVPWM technique and the DPWM technique when =15㎲.

Referring to FIG. 7, the drawing located at the top shows the six sectors where the command voltage vector is located during one cycle of the fundamental wave, and the drawing located in the middle shows the current measured through the shunt resistors (SR1 to SR3) at each sampling period. Sampled Current , , , and the drawing located at the bottom shows the phase current restored using the sampled currents. , represents. In a situation where the maximum voltage modulation index that can restore phase current is M = 0.44, when a command voltage with voltage modulation index M = 0.72 is given, in the case of SVPWM technique, sufficient turn-on time of the lower switch of the inverter is not secured, so phase current restoration cannot be properly achieved. can confirm.

On the other hand, referring to FIG. 8, it can be seen that when using the DPWM method, the phase current can be restored even in areas where current restoration is impossible using the SVPWM technique due to the expansion of the current restoration area.

So far, we have explained the current recovery area expansion method and experimental results when detecting phase current by the 3-shunt resistance of a 3-leg type 2-phase inverter. According to the present invention, when detecting the phase current of a two-phase AC motor using a 3-shunt resistor, there is a region where restoration of the phase current is impossible because a sufficient turn-on time of the lower switch is not secured in a high-speed operation region where the voltage modulation index of the inverter increases. It comes into existence. To improve this, when using the DPWM technique, the current recovery area can be expanded compared to when applying the SVPWM technique, thus improving the voltage utilization rate of the inverter and improving the reliability of the motor drive system.

Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical idea or essential features. You will be able to understand it. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive.

10: 2-phase AC motor driving circuit US1~3: upper switch
LS1~3: Lower switch SR1~3: Shunt resistance

Claims (4)

In a method of expanding the current recovery area when detecting phase current using a 3-shunt resistance of a 3-leg type 2-phase inverter,
Detecting phase current using a 3-shunt resistor inserted in series with the lower switch of each leg of the inverter;
A control unit operation step of a two-phase AC motor driving circuit using the detected phase current information;
Including the step of switching the upper and lower inverter switches by receiving a gating signal given by the operation of the control unit,
The control unit operation step includes restoring phase current that cannot be measured in a specific operating region when the voltage modulation index of the inverter is high;
performing current control using the restored phase current, and then performing a DPWM (Discontinuous PWM) operation to expand the current recovery area using a given command voltage;
Characterized in that it includes the step of generating a gating signal through the DPWM operation,
Method for expanding the current recovery area when detecting phase current using a 3-shunt resistor. According to claim 1,
The two-phase AC motor driving circuit for detecting phase current using a three-shunt resistance,
An input power unit to which direct current power is applied;
an upper switch connected to each leg;
Lower switches connected to each leg;
Shunt resistors connected in series to each of the lower switches; and
Characterized in that it consists of a control unit,
Method for expanding the current recovery area when detecting phase current using a 3-shunt resistor. According to clause 1,
The upper and lower switches are switched using the DPWM (Discontinuous PWM) method.
Including using the DPWMMIN method of discontinuous modulation in the section where the size of the phase voltage is smallest,
Method for expanding the current recovery area when detecting phase current using a 3-shunt resistor. According to clause 3,
Using the DPWMMIN method,
extreme voltage command is fixed and the two zero voltage vectors are , 0 voltage vector Including authorizing only,
Method for expanding the current recovery area when detecting phase current using a 3-shunt resistor.