KR20200086154A - System and method for six-step voltage synthesize of inverter - Google Patents

Abstract

The present invention relates to a method for synthesizing a six-step voltage of an inverter. According to the present invention, a system for synthesizing a six-step voltage of an inverter comprises: a memory in which a six-step voltage synthesizing program is stored; and a processor executing the program. The processor receives a voltage command and boundary angle information of the voltage command from a weak magnetic flux controller and current controller based on fixed sampling, and moves a voltage vector to a vector existing on a side of a voltage hexagon for specific sampling.

Description

System and method for synthesizing a six-step voltage of an inverter{SYSTEM AND METHOD FOR SIX-STEP VOLTAGE SYNTHESIZE OF INVERTER}

The present invention relates to a method for synthesizing a six-step voltage of an inverter.

According to the prior art, a drive system for driving a motor includes a power supply for an inverter, a main relay, an inverter, and a three-phase AC motor.

The inverter generates an AC voltage by controlling on/off of a switching element through pulse width modulation of a DC voltage input from a power supply or a battery, and serves to supply the generated AC voltage to the motor.

At this time, when the AC voltage is supplied from the inverter to the motor, when the AC voltage is supplied to the motor in a 6-step by the inverter operation, the current consumed by the motor under the same output condition can be reduced.

However, according to the prior art, when the ratio of the sampling frequency and the rotational frequency is not an integer multiple, the synthesized phase voltage does not maintain each voltage vector constant, and there is a problem with the current or torque pulsating at a frequency lower than the rotational frequency. .

In addition, according to the prior art in which the time when the voltage vector used for maintaining the six steps is directly transmitted is transmitted, variable sampling synchronized with the speed must be applied, and there is a problem that the configuration of the system is complicated.

The present invention has been proposed to solve the above-mentioned problems, and provides a synthesis method capable of accurately synthesizing six-step voltages in a fixed sampling system, and being easily used in a general fixed sampling-based controller due to low system configuration complexity. It has a purpose.

The six-step voltage synthesis system of the inverter according to the present invention includes a processor for executing a memory and a program in which the six-step voltage synthesis program is stored, and the processor is a boundary angle between the voltage command and the voltage command from a fixed sampling-based weak magnetic flux controller and a current controller. It is characterized by receiving information and moving the voltage vector to a vector existing on the side of the hexagon with respect to the maximum voltage vector that can be synthesized for a specific sampling.

According to an embodiment of the present invention, since accurate six-step voltage synthesis is possible and the system configuration complexity is low compared to the prior art, it is possible to use it in a general fixed sampling-based controller.

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

1 shows the structure of an inverter according to the prior art.
2 shows a voltage vector synthesized through switching according to the prior art.
FIG. 3 shows each phase switch signal and the synthesized U-phase voltage waveform during V _ref synthesis in FIG. 2.
4 shows a switching signal and a U-phase voltage waveform when synthesizing a six-step voltage according to the prior art.
5 is a block diagram showing a six-step voltage synthesis system according to the prior art.
Figure 6 shows the voltage command and counterclockwise rotation outside the voltage hexagon.
7 shows the number of allocated samplings according to the prior art.
8 shows a synthesized phase voltage according to the prior art.
9 is a block diagram showing a six-step voltage synthesis system according to the prior art.
FIG. 10 shows the corresponding time/corresponding vector maintenance according to the prior art shown in FIG. 9.
FIG. 11 shows a synthesized phase voltage according to the prior art shown in FIG. 9.
12 shows a six-step voltage synthesis system of an inverter according to an embodiment of the present invention.
13 shows the movement of the voltage command during six-step operation according to an embodiment of the present invention.
14 shows the movement of a voltage vector according to an embodiment of the present invention.
15 illustrates an ideal six-step voltage form in which each voltage vector is kept constant according to an embodiment of the present invention.
16 illustrates boundary angle information according to an embodiment of the present invention.
17 is a flowchart illustrating a method for synthesizing a six-step voltage of an inverter according to an embodiment of the present invention.

The above-mentioned objects and other objects, advantages and features of the present invention, and methods for achieving them will be apparent with reference to embodiments described below in detail together with the accompanying drawings.

However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the following embodiments are intended for those skilled in the art to which the present invention pertains, It is merely provided to easily inform the configuration and effect, the scope of the present invention is defined by the description of the claims.

On the other hand, the terms used in this specification are for describing the embodiments and are not intended to limit the present invention. In the present specification, the singular form also includes the plural form unless otherwise specified in the phrase. As used herein, "comprises" and/or "comprising" refers to the components, steps, operations and/or elements in which one or more other components, steps, operations and/or elements are present. Or added.

Hereinafter, in order to help those skilled in the art to understand, the background proposed by the present invention will be described first, and embodiments of the present invention will be described.

1 shows the structure of an inverter according to the prior art.

As shown in Fig. 1, the inverter according to the prior art is composed of six switches and one DC terminal in series and parallel connection.

Each phase (U, V, W) consists of two switches in series, and the middle of the two switches is the output of each phase, which is mainly connected to each phase of the motor.

At this time, the two switches apply the appropriate switching signal from the controller so that they are not turned ON simultaneously.

2 shows a voltage vector synthesized through switching according to the prior art.

Referring to FIG. 2, a three-phase voltage synthesized through an inverter can be expressed as a voltage vector in space.

When the upper phase switch of U phase is ON and the lower phase switch of V and W phase is ON, it is expressed as "100", and the synthesized voltage vector is V ₁ .

As shown in Fig. 2, all combinations that can be synthesized using a three-phase switch are eight, V ₁ to V ₆ are effective vectors, and V ₀ and V ₇ are zero vectors.

During a given sampling period t _samp , some vectors of V ₀ to V ₇ are selected and applied, and on average, the applied vector is synthesized to become V _ref .

FIG. 3 shows each phase switch signal and the synthesized U-phase voltage waveform during V _ref synthesis in FIG. 2.

V ₁ and V ₂ are applied for t ₁ and t ₂ hours, respectively, and V ₀ and V ₇ vectors are synthesized for t _samp -t ₁ -t ₂ hours, and the maximum voltage vector that can be synthesized is limited to within a hexagon.

The area that can synthesize the average voltage vector of a constant size during one rotation of the voltage command vector is the area within the inscribed circle of the hexagon.

Therefore, the area within the hexagonal inscribed circle is called a linear modulation area, and when the DC terminal voltage is V _dc , the size of the inscribed circle is V _dc /sqrt(3).

The area beyond the hexagonal inscribed circle, and the area within the hexagon is called the overmodulation area, and if the voltage command vector of a certain size rotates once in this section, the voltage of the command size cannot be synthesized in some sections.

The magnitude of the phase voltage fundamental wave synthesized during one rotation of the voltage command vector is larger than that of the linear modulation region, but has a harmonic voltage component.

The method of moving the voltage command outside the hexagon into a vector within the hexagon is called an overmodulation method.

Six-step voltage synthesis is a method that can have a maximum phase voltage fundamental wave size that can be synthesized by an inverter.

When synthesizing the voltage in the overmodulation region, a zero vector is used depending on the section, and when using the six-step voltage synthesis, there is no use of the zero vector for one period of the fundamental wave.

4 shows a switching signal and a U-phase voltage waveform when synthesizing an ideal six-step voltage according to the prior art, which is a very long time compared to the x-axis time of FIG. 3.

Referring to FIG. 4, a total of six effective vectors are used for one phase of the fundamental wave for the output phase voltage, and on/off switching is performed only once for each phase switch.

Assuming that the rotation speed of the voltage command vector is constant, t _V1 to t _{V6, which} are the times each effective vector is applied, are the same.

Motors used in EV or HEV require low-speed, high-torque operation and torque output in a wide speed range. Efficient operation is possible as the magnitude of the phase voltage fundamental wave that can be output in the high-speed range and low-speed operation of the motor increases. Do.

Because the output voltage of the battery or the limit of the device used in the inverter has a limited DC link voltage, a six-step voltage synthesis technology capable of outputting the maximum voltage of the inverter under the limited DC link voltage condition is essential.

Hereinafter, a conventional technique for synthesizing a six-step voltage (Y. -C. Kwon, S. Kim, and S. -K, Sul "Six-step operation of PMSM with instantaneous current control," IEEE Trans. on Ind. Appl. , Vol. 50, No. 4, Jul./Aug. 2014.).

5 shows a six-step voltage synthesis system according to the prior art.

The above-described internal structure of the controller of FIG. 1 is as shown in FIG. 5, and the weak magnetic flux controller and the current controller 10 are driven with a PWM switching frequency or a fixed sampling frequency corresponding to twice the same.

The sampling frequency is independent of the rotor frequency, which is the type commonly used in inverter systems.

The outputs of the weak magnetic flux controller and the current controller 10 are used as voltage commands and as inputs of the overmodulation voltage synthesizer 20.

The overmodulation voltage synthesizer 20 limits its magnitude from the voltage command to the voltage within the voltage hexagon, transmits the limited voltage magnitude information to the weak magnetic flux controller and the current controller 10, calculates the uvw switching signal, and sends a signal to each switch. To deliver.

FIG. 6 shows a counterclockwise rotation outside the voltage command and the voltage hexagon in the prior art described above with reference to FIG. 5, and rotates counterclockwise outside the voltage hexagon in a situation where the voltage command is maintained at a constant size V _mag Case.

Red v _[n-2] , v _[n-1] , v _[n] , v _[n+1] , and v _[n+2] are voltage references for a specific sampling cycle.

When the six-step voltage is synthesized, the red dots are all shifted to the voltage vectors V ₁ and V ₂ of the hexagonal vertices of the blue dots, and the dotted line represents the movement of these vectors.

At this time, based on the one-dot chain line, which is the vertical bisector of the triangle consisting of (V ₁ , V ₂ , and zero vector), the voltage vector with a smaller cabinet moves to V ₁ , and the voltage vector with a larger cabinet becomes V ₂ Move.

When the voltage command outside the hexagonal limit line moves to one side of the hexagon according to the overmodulation method, the overmodulation voltage smaller than the six-step voltage is synthesized.

Depending on the overmodulation method such as Bolognani overmodulation or switching state maintenance overmodulation, from which V _mag size, the six step operation is different.

In the Bolognani method, the V _mag is 2V _dc /3 or higher, and the switching state maintenance overmodulation method can operate six steps from 2V _dc /sqrt(3).

According to the above-mentioned prior art, ideal six-step voltage synthesis is not possible under all operating conditions, causing low-frequency pulsation when driving the motor.

For example, when the ratio of the sampling frequency and the rotation frequency is 48, which is an integer multiple of 6, according to the implementation of the six-step operation, the number of sampling allocated to each voltage vector V ₁ to V ₆ is 8 and the same number is applied, and application of each vector is applied. The times t _V1 to t _V6 are the same, which is the same as the ideal six-step form.

However, as another example, when the ratio of the sampling frequency and the rotation frequency is 44 rather than an integer multiple of 6, as shown in FIG. 7, the number of sampling allocated from V ₁ to V ₆ is 7 or 8 .

As shown in FIG. 8, the synthesized phase voltages are not maintained at a constant voltage vector t _V1 to t _V6 , and when driving the motor, there is a problem in that a current or torque pulsating at a frequency lower than the rotation frequency is output. .

Hereinafter, another conventional technique for synthesizing a six-step voltage (J. Park, S. Jung, and J. -I. Ha, "Variable time step control for six-step operation in surface-mounted permanent magnet machine drives," IEEE Trans. Power Elec. Vol. 33, No. 2, Feb. 2018.)

The internal structure of the controller in FIG. 1 described above is as shown in FIG. 9.

The six-step voltage synthesizer 40 directly receives the time ts _amp1 to t _samp6 at which the voltage vectors V ₁ to V ₆ used for maintaining the six steps are applied.

As shown in FIG. 10, a method of maintaining a corresponding vector for a corresponding time is used.

According to the prior art, a variable sampling-based weak magnetic flux controller and a current controller 30 are used. Since the controllers operate based on the holding time calculated in the previous sampling, if the speed is transient or the speed of the rotor changes, the time accordingly It also changes synchronously.

That is, according to the prior art, variable sampling synchronized with speed must be applied, and there is a problem in that the configuration of the system is complicated.

As illustrated in FIG. 10, it is possible to set the application times of the vectors V ₁ to V ₆ during the six step operation as many times as desired regardless of the speed of the rotor.

At this time, the synthesized phase voltage can maintain the application time t _V1 to t _V6 of each vector constant regardless of the rotor speed, as shown in FIG. 11.

However, according to the prior art, since the output voltage is fixed only at the six-step voltage, there is a problem that voltage synthesis smaller than the six-step transient is impossible.

According to the prior art, since it is necessary to switch to a fixed sampling system for driving under the rated speed of the electric motor, there is a problem that the system configuration is complicated.

In addition, it is possible to apply the prior art to the embedded permanent magnet motor, but it is inefficient operation, and there is a problem that additional verification is required.

The present invention has been proposed to solve the above-mentioned problems, and proposes a method for synthesizing an accurate six-step voltage in a fixed sampling system.

12 shows a six-step voltage synthesis system of an inverter according to an embodiment of the present invention.

Referring to FIG. 12, in order to apply the method according to an embodiment of the present invention, a fixed sampling-based weak magnetic flux controller and a current controller 110 are used, and the controller output includes voltage command boundary angle information in addition to the voltage command information. do.

The six-step voltage synthesis system of the inverter according to an embodiment of the present invention includes a memory 130 in which the six-step voltage synthesis program is stored and a processor 120 executing the program, and the processor 120 is a fixed sampling-based weak magnetic flux controller And receiving the voltage command and the boundary angle information of the voltage command from the current controller 110, and moving the voltage vector to a vector existing on the side of the voltage hexagon for a specific sampling.

The processor 120 according to an embodiment of the present invention receives boundary angle information according to bisecting an angle between voltage commands according to adjacent sampling cycles.

The processor 120 according to an embodiment of the present invention compares the size of the voltage command and the voltage command that can be synthesized by six steps, and when the size of the voltage command is greater than the voltage command that can be synthesized by six steps, the sector in the voltage hexagon of the voltage command is displayed. Determine and calculate the reference angle.

The processor 120 according to an embodiment of the present invention moves the voltage vector in an overmodulation method when the magnitude of the voltage command is equal to or less than the voltage command capable of six-step synthesis.

The processor 120 according to an embodiment of the present invention checks whether the reference angle is between the boundary angles and moves the voltage vector to a vector existing on the side of the voltage hexagon when the reference angles are present between the boundary angles. .

When the reference angle does not exist between the boundary angles, the processor 120 according to an embodiment of the present invention moves to a voltage vector of a vertex of a voltage hexagon.

The processor 120 according to an embodiment of the present invention transmits the switching signal and limited voltage magnitude information on the UVW that synthesizes the shifted voltage vector.

13 shows the movement of the voltage command during six-step operation according to an embodiment of the present invention.

In the conventional overmodulation method, if the voltage command is greater than a specific size, six-step voltage synthesis is performed, and the moving voltage vector is a voltage vector of V ₁ to V ₆ .

According to an embodiment of the present invention, at a specific sampling cycle voltage command, rather than synthesizing the vectors present at the vertex of the voltage hexagon, the movement to the vectors present at the sides of the voltage hexagon is performed as shown in FIG. 13.

As an application example according to an embodiment of the present invention, it is assumed that the ratio of the sampling frequency and the rotation frequency is 44, not an integer multiple of 6.

14 illustrates the movement of a voltage vector according to an embodiment of the present invention.

For each sampling in sectors 1, 2, and 3, it moves to the vector existing on the hexagonal side, and adjusts the time when moving between the vertex voltage vectors.

15 illustrates an ideal six-step voltage form in which each voltage vector is kept constant according to an embodiment of the present invention.

As shown in FIG. 15, each voltage vector t _V1 to t _V6 has the form of an ideal six-step voltage maintained constant.

16 illustrates boundary angle information according to an embodiment of the present invention.

Referring to FIG. 16, v _[n] is the voltage command in the current sampling, v _[n-1] is the voltage command in the previous sampling, and v _[n+1] is the voltage sampling size of the current sampling in the next sampling This is the voltage command vector at the next sampling when it is maintained at.

Referring to FIG. 16, a reference line dividing the angle between v _[n] and v _[n-1] is represented by a dotted line, and this angle is defined as a boundary angle θ _[n-1] .

Accordingly, the voltage angle of the stop coordinate system can be easily calculated from the voltage command information from the previous sampling and the voltage command information from the next sampling, and the median value of the two angles is θ _[n-1] .

Also, v is defined as _[n] and v _{[n + 1]} to the boundary reference line bisecting the angle between each of the respective θ _{[n + 1].}

Accordingly, θ _[n+1] can be calculated by adding the value of the current coordinate of the stop coordinate system of the current sampling voltage command to the rotor speed multiplied by 0.5 t _samp .

The boundary angle information θ _[n-1] and θ _[n+1] of the voltage command calculated through the above-described process are transferred to the voltage synthesis block.

According to an embodiment of the present invention, whether the voltage command calculated by the weak magnetic flux controller and the current controller in the current sampling should be located on one side of the hexagon, or whether the voltage command calculated in the next sampling should be on one side of the hexagon. To determine, it operates according to the flowchart shown in FIG. 17.

17 is a flowchart illustrating a method for synthesizing a six-step voltage of an inverter according to an embodiment of the present invention.

According to an embodiment of the present invention, in step S1710, the voltage command v _[n] and the voltage command boundary angle θ _[n-1] and θ _[n+1] are received from the weak magnetic flux controller and the current controller.

In step S1720, it is determined whether the absolute magnitude of the voltage command v _[n] is greater than or equal to the magnitude of the synthesis of the six-step voltage.

As described above, six-step operation is possible from 2V _dc /3 in the case of the Bolognani overmodulation method and 2V _dc /sqrt(3) in the case of the switching state maintenance overmodulation method.

In step S1720, when the magnitude of the voltage command is less than the magnitude of synthesizing the six-step voltage, the voltage vector is moved in an overmodulation method (S1730).

In step S1720, when the magnitude of the voltage command is equal to or larger than the size of combining the six-step voltage, the sector existing in the hexagon of the voltage command is determined, and the reference angle δ according to the sector is calculated (S1740).

At this time, the reference angle for each sector is shown in [Table 1] below.

Sector Reference angle δ One 30 degrees 2 90 degrees 3 150 degrees 4 -150 degrees 5 -90 degree 6 -30 degrees

In step S1750, it is checked whether the reference angle δ exists between the boundary angles θ _[n-1] and θ _[n+1] .

When the reference angle δ is present between the boundary angles θ _[n-1] and θ _[n+1] , the step S1760 moves to a voltage vector existing on the side of the hexagon.

When the reference angle δ does not exist between the boundary angles θ _[n-1] and θ _[n+1] , the step S1770 moves to the voltage vector present at the vertex of the hexagon.

Subsequent to the above-described process, in step S1780, a uvw phase switch operation command signal for synthesizing the voltage vector is generated, transmitted to the switch, and information of the voltage magnitude generated when synthesizing the voltage with the moved voltage vector is generated to generate voltage magnitude information. Feedback.

On the other hand, the six-step voltage synthesis method of the inverter according to an embodiment of the present invention may be implemented in a computer system, or recorded on a recording medium. The computer system may include at least one processor, memory, a user input device, a data communication bus, a user output device, and storage. Each of the above-described components communicates through a data communication bus.

The computer system can further include a network interface coupled to the network. The processor may be a central processing unit (CPU) or a semiconductor device that processes instructions stored in memory and/or storage.

The memory and storage may include various types of volatile or non-volatile storage media. For example, the memory may include ROM and RAM.

Therefore, the six-step voltage synthesis method of the inverter according to the embodiment of the present invention can be implemented by a method executable in a computer. When the method for synthesizing the six-step voltage of the inverter according to the embodiment of the present invention is performed in a computer device, computer-readable instructions may perform the synthesis method according to the present invention.

Meanwhile, the above-described method for synthesizing the six-step voltage of the inverter according to the present invention may be implemented as a computer-readable code on a computer-readable recording medium. Computer-readable recording media includes all kinds of recording media storing data that can be read by a computer system. For example, there may be a read only memory (ROM), a random access memory (RAM), a magnetic tape, a magnetic disk, a flash memory, and an optical data storage device. In addition, the computer-readable recording medium may be distributed over computer systems connected through a computer communication network, and stored and executed as code readable in a distributed manner.

So far, we have focused on the embodiments of the present invention. Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in terms of explanation, not limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the equivalent range should be interpreted as being included in the present invention.

110: weak sampling controller/current controller based on fixed sampling
120: processor
130: memory

Claims (7)

A memory in which a six-step voltage synthesis program is stored; And
It includes a processor for executing the program,
The processor receives the voltage command and the voltage command boundary angle information from a fixed sampling-based weak magnetic flux controller and a current controller, and moves the voltage vector to a vector existing on the side of the voltage hexagon for a specific sampling.
Six-step voltage synthesis system of the inverter, characterized in that.
According to claim 1,
The processor receives the boundary angle by dividing the angle between voltage commands according to adjacent sampling cycles into the boundary angle information.
Six-step voltage synthesis system of the Inverter.
According to claim 1,
The processor compares the size of the voltage command with a voltage command capable of six-step synthesis, and when the size of the voltage command is greater than a voltage command capable of six-step synthesis, determines a sector in the hexagon of the voltage command and calculates a reference angle that
Six-step voltage synthesis system of the Inverter.
According to claim 3,
When the magnitude of the voltage command is equal to or less than the voltage command that can be synthesized in six steps, the processor moves the voltage vector in an overmodulation method.
Six-step voltage synthesis system of the Inverter.
According to claim 3,
The processor checks whether the reference angle is between the boundary angles, and if the reference angle is between the boundary angles, moves the voltage vector to a vector existing on the side of the hexagon.
Six-step voltage synthesis system of the Inverter.
According to claim 3,
The processor checks whether the reference angle exists between the boundary angles, and if the reference angle does not exist between the boundary angles, moves to the voltage vector of the vertex of the hexagon.
Six-step voltage synthesis system of the Inverter.
According to claim 1,
The processor transmits the switching signal and limited voltage magnitude information on the UVW that synthesizes the shifted voltage vector.
Six-step voltage synthesis system of the Inverter.

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