TWI815357B - System for improving total harmonic distortion - Google Patents

Abstract

A system for improving total harmonic distortion (THD) is disclosed in the present invention. The system for improving THD includes a Clarke transform module, a first computing module, a notch filter, a second computing module, an output control module, and a space vector modulation module. The system for improving THD is utilized to receive three-phase input voltage, generate two transformation voltages, compute two transformation currents, filter third-times harmonic of the transformation currents, compute a modulation index and a phase angle of output voltage, and generate a pulse-width modulation command to a matrix converter. Thus, the system for improving THD is able to improve total harmonic distortion.

Description

Total harmonic distortion improvement system

The present invention relates to a system, in particular to a total harmonic distortion improvement system.

Generally speaking, AC/AC converters can be mainly divided into categories such as frequency converters, cycloconverters, composite matrix converters, and matrix converters; among them, because matrix converters can provide sinusoidal output voltages and generate sinusoidal input currents , and has a compact structure without intermediate DC links, and even has the advantages of fast dynamic response, so it has always been the focus of research in the field of power transmission.

Please refer to Figures 1 to 4 together. The first Figure is a schematic diagram showing the prior art; the second Figure is a schematic diagram showing the phase input voltage waveform of the first Figure; and the third figure is a schematic diagram showing the phase of the first Figure. A schematic diagram of the input current waveform; and, the fourth figure is a schematic diagram showing the fast Fourier transform of the third figure. As shown in the figure, a matrix converter PA1 is electrically connected to a three-phase AC power supply PA2 and a load, and includes an input filter PA11, a matrix switch module PA12 and a clamp circuit PA13. Input filter PA11 is used to improve the power quality of three-phase AC power supply PA2 (mains). The matrix switch module PA12 is used to generate a preset output voltage or frequency. The clamp circuit PA13 is used to absorb discontinuous energy to protect the matrix switch module PA12. The load here is a load motor PA3.

However, since there is no DC bus (DC link) energy storage element in the matrix converter PA1, any abnormal over-interference on the input side of the matrix converter PA1 will be directly reflected on the output side. As shown in the second figure, the amplitudes of the three-phase input voltage waveforms V1, V2, and V3 input by the three-phase AC power supply PA2 to the matrix converter PA1 are different from each other. This is a situation where the three-phase voltages are unbalanced. The reasons for the unbalanced three-phase voltage may be different capacitance parameters in the three-phase AC power supply PA2, loads that focus on a single phase, high-order harmonic currents, poor contacts, external environment, etc., and may cause current imbalance in the load motor PA3 , temperature rise, efficiency reduction, loss increase, vibration, overload, short circuit and other problems.

As shown in the third figure, when the phase input voltage waveforms V1, V2, and V3 are unbalanced, the corresponding three phase input current waveforms PAI1, PAI2, and PAI3 will not approach sinusoidal waves. As shown in the figure, the phase input current waveform PAI1 can be regarded as shifted to the left and deformed compared to the theoretical sine wave.

As shown in the fourth figure, when the phase input voltage waveforms V1, V2, and V3 are unbalanced (the three-phase voltages are unbalanced), the harmonic components in the phase input current waveforms PAI1, PAI2, and PAI3 will increase significantly. After performing Fast Fourier Transform (FFT) on the phase input current waveforms PAI1, PAI2, and PAI3, it can be clearly seen that the phase input voltage waveforms V1, V2, and V3 are unbalanced (three-phase voltage unbalanced). The third harmonic PAF3 and the fifth harmonic PAF5. Therefore, when the phase input voltage waveforms V1, V2, and V3 are unbalanced, the problem of total harmonic distortion (Total Harmonic Distortion; THD) will also occur. Among them, the third harmonic PAF3 is three times the fundamental frequency harmonic PAF1, and the fifth harmonic PAF5 is five times the fundamental frequency harmonic PAF1. Therefore, there is room for improvement in prior art.

In view of the fact that in the previous technology, when the phase input voltage waveform is unbalanced (three-phase voltage unbalanced), it will cause total harmonic distortion and load current imbalance, temperature rise, efficiency reduction, loss increase, vibration, Problems such as overloading and short circuit. One of the main objectives of the present invention is to provide a total harmonic distortion improvement system to solve at least one problem in the prior art.

In order to solve the problems of the prior art, the necessary technical means adopted by the present invention are to provide a total harmonic distortion improvement system, which is applied to a matrix converter. The matrix converter is electrically connected to a three-phase AC power supply and a load, and includes a Input filter, a matrix switch module and a clamp circuit, the total harmonic distortion improvement system includes a Clark conversion module, a first calculation module, a notch filter, a second calculation module, a The output control module and a space vector modulation module. The Clark conversion module is electrically connected between the three-phase AC power supply and the input filter, receives the three-phase input voltage waveforms from the three-phase AC power supply to the matrix converter, and uses Clark conversion to convert them into two conversion voltage waveforms. . The first calculation module is electrically connected to the Clark conversion module, receives the conversion voltage waveform and an input power command, and calculates two conversion current waveform commands accordingly. The notch filter is electrically connected to the first computing module for receiving the conversion current waveform command and filtering the third harmonic in the conversion current waveform command to form two filtered current waveforms. The second calculation module is electrically connected to the notch filter, and is used to receive the filtered current waveform, and calculate an angle between a modulation index and an input current vector accordingly. The output control module is electrically connected between the matrix switch module and the load, and is used to receive the three-phase output current waveforms output by the matrix switch module to the load, and calculate the DC bus current waveform and an output voltage based on it. phase angle. The space vector modulation module is electrically connected to the second calculation module, the output control module and the matrix switch module, and is used to receive the input current vector angle, the modulation index and the output voltage phase angle, thereby generating a pulse width modulation. command, and transmits the pulse width modulation command to the matrix switch module to reduce the total harmonic distortion of the three phase input current waveforms corresponding to the phase input voltage waveform when the phase input voltage waveform is unbalanced.

On the basis of the above necessary technical means, an additional technical means derived from the present invention is a Clark conversion module, which is a converter, in the total harmonic distortion improvement system.

On the basis of the above necessary technical means, an additional technical means derived from the present invention is a space vector modulation module in the total harmonic distortion improvement system, which is a modulator.

On the basis of the above necessary technical means, an ancillary technical means derived from the present invention is an output control module in the total harmonic distortion improvement system, which further includes a motor control unit, a third calculation unit and a fourth calculation unit. unit. The motor control unit is used to receive the phase output current waveform and calculate the output voltage phase angle accordingly. The third calculation unit is electrically connected to the motor control unit for receiving the phase output current waveform and calculating the DC bus current waveform accordingly. The fourth calculation unit is electrically connected to the motor control unit for receiving the phase output current waveform and calculating the input power command accordingly.

As mentioned above, the total harmonic distortion improvement system provided by the present invention is applied to the matrix converter. Compared with the prior art, the present invention uses the Clark conversion module, the first calculation module, the notch filter, and the third The second calculation module, output control module and space vector modulation module filter out the third harmonic, thereby achieving the effect of reducing the total harmonic distortion when the three-phase input voltage waveforms are unbalanced, thereby solving the overall problem. Harmonic distortion causes problems such as load current imbalance, temperature rise, efficiency reduction, loss increase, vibration, overload, short circuit and other problems.

Specific embodiments of the present invention will be described in more detail below with reference to the schematic diagrams. The advantages and features of the present invention will become clearer from the following description and patent claims. It should be noted that the drawings are in a very simplified form and use imprecise proportions, and are only used to conveniently and clearly assist in explaining the embodiments of the present invention.

Please refer to the second figure and the fifth to eighth figures. The fifth figure is a schematic diagram showing the total harmonic distortion improvement system provided by the preferred embodiment of the present invention applied to the matrix converter; the sixth figure is a schematic diagram showing the total harmonic distortion improvement system provided by the preferred embodiment of the present invention. A schematic diagram of the notch filter of the total harmonic distortion improvement system provided by the preferred embodiment of the invention; the seventh figure is a schematic diagram showing the phase input current waveform of the fifth figure; and the eighth figure is a schematic diagram showing the fast phase input current waveform of the seventh figure. Schematic diagram of Fourier transform. As shown in the figure, a total harmonic distortion improvement system 1 is applied to a matrix converter 2 and includes a Clark conversion module 11, a first calculation module 12, a notch filter 13, and a second calculation module 14. An output control module 15 and a space vector modulation module 16.

The matrix converter 2 is electrically connected to a three-phase AC power supply 3 and a load, and includes an input filter 21 , a matrix switch module 22 and a clamping circuit (Clamping Circuit) 23 . Among them, the matrix converter 2, the three-phase AC power supply 3 and the load are exactly the same as the matrix converter PA1, the three-phase AC power supply PA2 and the load in the previous technology. Therefore, the total harmonic distortion improvement system 1 of the present invention can be regarded as It is externally connected to the matrix converter PA1 of the prior art, the three-phase AC power supply PA2 and the load, where the load here is a load motor 4 .

The three-phase AC power supply 3 (mains) will still input the three-phase input voltage waveforms V1, V2, and V3 as shown in the second figure to the matrix converter 2, and the amplitudes of the three-phase input voltage waveforms V1, V2, and V3 are different from each other. Not the same, this is a situation where the three-phase voltage is unbalanced. The reasons for the unbalanced three-phase voltage may be different capacitance parameters in the three-phase AC power supply 3, loads that focus on a single phase, high-order harmonic currents, poor contacts, external environment, etc., and may cause current imbalance in the load motor 4 , temperature rise, efficiency reduction, loss increase, vibration, overload, short circuit and other problems.

The Clark conversion module 11 is electrically connected between the three-phase AC power supply 3 and the input filter 21, and receives the three-phase input voltage waveforms V _IA , V _IB , and V _IC input from the three-phase AC power supply 3 to the matrix converter. And use Clarke Transformation (Clarke Transformation, Alpha-beta Transformation) to convert into two conversion voltage waveforms V _Iα and V _Iβ . Among them, Clark transformation is a mathematical transformation used to simplify three-phase circuit analysis. Simply put, Clark transformation converts the time-domain components of a three-phase circuit in an abc reference frame into components in a stationary αβ0 reference frame. Because Clark's translation is common knowledge in the technical field, it is only briefly described. Therefore, the Clark conversion module 11 receives three phase input voltage waveforms and converts and outputs two converted voltage waveforms. The Clark conversion module 11 may be a converter or other chips, circuits, modules, etc. with Clark conversion functions.

It should be noted that in the technical field, different codes will be marked with subscripts in circuit diagrams or related schematic diagrams to distinguish different phases, different reference frames, inputs and outputs, etc. Therefore, in the fifth figure, the three phase input voltage waveforms are marked as phase input voltage waveforms V _IA , V _IB , and V _IC , and their respective waveforms are the phase input voltage waveforms V1 and V2 in the second figure. , V3. Similarly, the two conversion waveforms converted and output by the Clark conversion module 11 are marked as conversion voltage waveforms V _Iα and V _Iβ .

The first calculation module 12 is electrically connected to the Clark conversion module 11, receives the conversion voltage waveforms V _Iα and V _Iβ , and calculates two conversion current waveform commands i ^* _Iα and i ^* _Iβ accordingly. The calculation formula is as follows:

In this embodiment, the first calculation module 12 also receives an input power command P ^* _i to assist in calculating the conversion current waveform commands i ^* _Iα and i ^* _Iβ , where the calculation process of the input power command P ^* _i It will be described in the following content.

The notch filter (Notch Filter) 13 is electrically connected to the first computing module 12 for receiving the conversion current waveform commands i ^* _Iα and i ^* _Iβ , and converting the conversion current waveform commands i ^* _Iα and i ^* _Iβ into The third harmonic is filtered to form two filtered current waveforms. The notch filter 13 can quickly attenuate the input signal at a certain frequency point to achieve a filtering effect of preventing the signal at this frequency point from passing through. The notch filter 13 is a type of band stop filter, but the stop band of the notch filter 13 is very narrow. φ _i is the input power factor angle (Input Power Factor Angle), and φ _i can be set to 0 in some cases.

Because the prior art will obviously produce the third harmonic PAF3 (marked in the fourth figure) and the fifth harmonic PAF5 (marked in the fourth figure), the notch filter 13 in the present invention is used to convert The third harmonic in the current waveform commands i ^* _Iα and i ^* _Iβ is filtered, thereby suppressing the third harmonic PAF3 generated by the previous technology.

In addition, as shown in the equivalent block diagram of the notch filter 13 in Figure 6, the notch filter 13 receives an input parameter IN and outputs an output parameter OUT, which is an open loop. In this embodiment, the converted current waveform commands i ^* _Iα and i ^* _Iβ are the input parameters IN, and the filtered current waveform is the output parameter OUT. The calculation formula of notch filter 13 is as follows:

Among them, the code name of the notch filter 13 in the calculation formula is the abbreviation NF(s) of the English name (Notch Filter). Therefore, the notch filter 13 can change the frequency range to be filtered by changing the K value. That is to say, the K value can be regarded as the width to be filtered. In this embodiment, the range of the K value is 0.01. to 1, but not limited to this; ω _i in the formula is the fundamental frequency of the system, which in this embodiment is the frequency of the mains. Therefore, ω _i =120π can also be set; s is the Laplace transformer ( Laplace Operator), which is a Complex Number. The above formula is common knowledge in the technical field, so it will not be described again.

The second calculation module 14 is electrically connected to the notch filter 13 for receiving the filtered current waveforms and calculating the angle between a modulation index m and an input current vector Ɵ _ii . The first computing module 12 and the second computing module 14 may be a calculator, a computing chip, or other circuits or modules with computing functions. The calculation formula of the second calculation module 14 is as follows:

The output control module 15 is electrically connected between the matrix switch module 22 and the load motor 4, and is used to receive the three-phase output current waveforms I _oA , I _oB , and I _oC output by the matrix switch module 22 to the load motor 4. And calculate the DC bus current waveform (DC Bus Current) i _dc and an output voltage phase angle Ɵ _OV accordingly, and includes a motor control unit 151, a third calculation unit 152 and a fourth calculation unit 153. The calculation formula of the output control module 15 is as follows:

To explain in more detail, the motor control unit 151 will receive three phase output current waveforms I _OA , I _OB , I _OC and a motor signal feedback Ɵ _m , and calculate the output voltage vector phase angle Ɵ _OV accordingly, where, the output The voltage vector phase angle Ɵ _OV is the angle of the output voltage vector, which can be calculated using the output voltage command under the αβ coordinate axis and belongs to common knowledge in the technical field. The motor control unit 151 mainly controls the current, speed and position of the motor. The third calculation unit 152 is electrically connected to the motor control unit 151, receives the output conversion currents I _Oα , I _Oβ and the output conversion voltage commands V ^* _Oα , V ^* _Oβ , and calculates the DC bus current waveform i _dc accordingly. The fourth calculation unit 153 is electrically connected to the motor control unit 151, receives the output conversion currents I _Oα , I _Oβ and the output conversion voltage commands V ^* _Oα , V ^* _Oβ , and calculates the input power command P ^* _i accordingly. Among them, i _dc is calculated using the instantaneous power, and V ^* _om is the output voltage vector.

The Space Vector Modulation (SVM) module 16 is electrically connected to the second calculation module 14, the output control module 15 and the matrix switch module 22, and is used to receive the input current vector angle Ɵ _ii and the modulation index m with the output voltage phase angle Ɵ _OV , thereby generating a pulse width modulation command, and transmitting the pulse width modulation command to the matrix switch module 22, so as to adjust the phase input voltage waveforms V1, V2, and V3 when the phase is unbalanced. Under this condition, the total harmonic distortion of the three phase input current waveforms I1, I2, and I3 corresponding to the phase input voltage waveforms V1, V2, and V3 is reduced. The third figure and the seventh figure can be compared together. After the total harmonic distortion improvement system 1 of the present invention is applied to the matrix converter 2, the phase input current waveforms I1, I2, and I3 of the seventh figure are compared with those of the third figure. The phase input current waveforms PAI1, PAI2, and PAI3 are closer to sine waves. Because the phase input current waveforms I1, I2, and I3 are closer to sine waves, the total harmonic distortion (Total Harmonic Distortion; THD) can be reduced. To explain in more detail, the phase input current waveforms I1, I2, I3 and the phase input current waveforms PAI1, PAI2, PAI3 shown in the figure are current waveforms before being input to the input filter 21 and the input filter PA11.

Comparing the fourth and eighth figures together, after the phase input current waveforms I1, I2, and I3 are subjected to Fast Fourier Transform (FFT), it can be clearly seen that the phase input voltage waveforms V1, V2, and V3 are unbalanced ( In the case of unbalanced three-phase voltage), compared with the third harmonic PAF3 of the prior art, the amplitude of the third harmonic F3 generated by the present invention is smaller and less obvious. In addition, at the same position in the eighth figure where the fifth harmonic PAF5 of the prior art corresponds, almost no particularly prominent harmonics are generated, which is equivalent to eliminating the fifth harmonic component altogether. Therefore, the figure proves that the present invention effectively reduces harmonic components, and further proves that the present invention can achieve the effect of reducing total harmonic distortion compared with the prior art. By the way, the third harmonic F3 is three times the fundamental frequency harmonic F1. It should be noted that the top of the figure is the input current waveform of one of the current phases, for example: A-phase current.

In summary, the total harmonic distortion improvement system provided by the present invention is applied to the matrix converter. Compared with the prior art, the present invention uses the Clark conversion module, the first calculation module, the notch filter, and the third The second calculation module, output control module and space vector modulation module only receive phase input voltage waveforms and filter out the third harmonics, thereby reducing the total harmonics when the three phase input voltage waveforms are unbalanced. The effect of wave distortion can solve the problems of load current imbalance, temperature rise, efficiency reduction, loss increase, vibration, overload, short circuit and other problems derived from total harmonic distortion.

Through the above detailed description of the preferred embodiments, it is hoped that the characteristics and spirit of the present invention can be more clearly described, but the scope of the present invention is not limited by the above disclosed preferred embodiments. On the contrary, the intention is to cover various modifications and equivalent arrangements within the scope of the patent for which the present invention is intended.

PA1:Matrix converter

PA11: input filter

PA12:Matrix switch module

PA13: clamp circuit

PA2: Three-phase AC power supply

PA3: Load motor

PAF1: Fundamental frequency harmonics

PAF3: third harmonic

PAF5: fifth harmonic

PAI1, PAI2, PAI3, I1, I2, I3: phase input current waveforms

1: Total harmonic distortion improvement system

11: Clark conversion module

12:The first computing module

13: Notch filter

14:Second computing module

15:Output control module

151: Motor control unit

152: The third computing unit

153: The fourth computing unit

16: Space vector modulation module

2:Matrix converter

21:Input filter

22:Matrix switch module

23: Clamp circuit

3: Three-phase AC power supply

4:Load motor

F1: Fundamental frequency harmonics

F3: Third harmonic

IN: input parameters

I _OA ,I _OB ,I _OC : Phase output current waveform

i _dc : DC bus current waveform

i ^* _Iα , i ^* _Iβ : Convert current waveform command

I _Oα , I _Oβ : output conversion current

m: modulation index

OUT: output parameters

P ^* _i : input power command

V1, V2, V3, V _IA , V _IB , V _IC : phase input voltage waveform

V _Iα , V _Iβ : conversion voltage waveform

V ^* _Oα , V ^* _Oβ : Output conversion voltage command

Ɵ _ii :Input current vector angle

Ɵ _m : Motor signal feedback

Ɵ _OV :Output voltage phase angle

The first figure is a schematic diagram showing the prior art; The second figure is a schematic diagram showing the phase input voltage waveform of the first figure; The third figure is a schematic diagram showing the phase input current waveform of the first figure; The fourth figure is a schematic diagram showing the fast Fourier transform of the third figure; The fifth figure is a schematic diagram showing the total harmonic distortion improvement system provided by the preferred embodiment of the present invention applied to a matrix converter; The sixth figure is a schematic diagram showing the notch filter of the total harmonic distortion improvement system provided by the preferred embodiment of the present invention; The seventh figure is a schematic diagram showing the phase input current waveform of the fifth figure; and The eighth figure is a schematic diagram showing the fast Fourier transform of the seventh figure.

1: Total harmonic distortion improvement system

11: Clark conversion module

12:The first computing module

13: Notch filter

14:Second computing module

15:Output control module

151: Motor control unit

152: The third computing unit

153: The fourth computing unit

16: Space vector modulation module

2:Matrix converter

21:Input filter

22:Matrix switch module

23: Clamp circuit

3: Three-phase AC power supply

4:Load motor

I _OA ,I _OB ,I _OC : Phase output current waveform

i _dc : DC bus current waveform

i ^* _Iα , i ^* _Iβ : Convert current waveform command

I _Oα , I _Oβ : output conversion current

m: modulation index

P ^* _i : input power command

V _IA , V _IB , V _IC : Phase input voltage waveform

V _Iα , V _Iβ : conversion voltage waveform

V ^* _Oα , V ^* _Oβ : Output conversion voltage command

θ _ii : angle between input current vectors

θ _m : Motor signal feedback

θ _OV : Output voltage phase angle

Claims (3)

A total harmonic distortion improvement system is applied to a matrix converter. The matrix converter is electrically connected to a three-phase AC power supply and a load, and includes an input filter, a matrix switch module and a clamping circuit. The total harmonic distortion improvement system includes: a Clark conversion module, which is electrically connected between the three-phase AC power supply and the input filter, and receives three inputs of the three-phase AC power supply to the matrix converter. The phase input voltage waveform is converted into two converted voltage waveforms using Clark conversion; a first calculation module is electrically connected to the Clark conversion module, receives the converted voltage waveforms and an input power command, and based on Two conversion current waveform commands are calculated; a notch filter is electrically connected to the first calculation module to receive the conversion current waveform commands and filter the third harmonic in the conversion current waveform commands. divided to form two filtered current waveforms; a second calculation module is electrically connected to the notch filter for receiving the filtered current waveforms and calculating a modulation index and an input current accordingly. Vector angle; an output control module is electrically connected between the matrix switch module and the load, and is used to receive the three-phase output current waveforms output by the matrix switch module to the load, and calculate the A DC bus current waveform and an output voltage phase angle, and includes: a motor control unit for receiving the three-phase output current waveforms and calculating the output voltage phase angle accordingly; a third calculation unit, The motor control unit is electrically connected to Receive the three-phase output current waveforms and calculate the DC bus current waveform accordingly; and a fourth calculation unit is electrically connected to the motor control unit for receiving the three-phase output current waveforms and calculating the DC bus current waveforms accordingly. to calculate the input power command; and a space vector modulation module electrically connected to the second calculation module, the output control module and the matrix switch module to receive the input current vector angle, the The modulation index and the output voltage phase angle are used to generate a pulse width modulation command, and the pulse width modulation command is transmitted to the matrix switch module, so that when the input voltage waveforms of the phases are unbalanced, Reduce the total harmonic distortion of the three phase input current waveforms corresponding to these phase input voltage waveforms. The total harmonic distortion improvement system of claim 1, wherein the Clark conversion module is a converter. The total harmonic distortion improvement system of claim 1, wherein the space vector modulation module is a modulator.

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