Pulse Width Modulation Method for Synthesizing DC Voltage by Three-Phase AC Chopping

Abstract

The present invention discloses a pulse width modulation method for synthesizing a direct current voltage by three-phase alternating current chopping. By performing pulse width modulation chopping and voltage synthesis on the input three-phase alternating current voltage through a direct alternating chopper, a direct current voltage with controllable amplitude and polarity can be obtained. The present invention does not contain a rectification link and will not inject a large amount of harmonics into the input current. Multiple direct current voltages can also be output through multiple modulations and voltage synthesis. In addition, the current harmonics generated by the present invention can offset each other to avoid current harmonic pollution to the input node. The present invention also has the ability to adjust the input power factor.

Description

Technical Field

[0001] The invention belongs to the technical field of electric energy conversion, and in particular relates to a pulse width modulation method for synthesizing a direct current voltage by three-phase alternating current chopping. Background Art

[0002] With the continuous development of semiconductor technology and control technology, power electronic converters have been widely used. The application of power electronic converters will bring about large reactive power and current harmonics, thus affecting the quality of power. In order to solve the impact of reactive power and current harmonics on the system, domestic and foreign scholars have paid more and more attention to PWM rectifiers, and PWM rectifiers have become an indispensable part of the power electronics field.

[0003] The development of rectifiers has gone through three stages: uncontrolled rectification, phase-controlled rectification and PWM rectification. Among the rectification equipment, the most commonly used ones are diode rectification or thyristor phase-controlled rectification. The diode rectification circuit has the advantages of economy, simple implementation and high system reliability, but it also has disadvantages such as low power factor, severe current waveform distortion and uncontrollable output voltage. Compared with diode uncontrolled rectification, traditional thyristor phase-controlled rectification technology has a higher power factor, but it has disadvantages such as large output voltage ripple and severe input current waveform distortion. PWM rectification technology has higher controllability, but it still has the shortcoming of large input current harmonic content. Finding a superior AC-DC conversion technology has become an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present invention is to provide a pulse width modulation method for synthesizing a direct current voltage by three-phase alternating current chopping, which utilizes three-phase alternating current input voltage and pulse width modulation for chopping synthesis to obtain a direct current voltage with controllable amplitude and polarity.

[0005] The technical solution adopted by the present invention is a pulse width modulation method for synthesizing a DC voltage by three-phase AC chopping, which performs pulse width modulation chopping on the three-phase AC input voltage through a direct AC chopper, and performs series synthesis and low-pass filtering on the chopped voltage to obtain a DC output voltage.

[0006] The present invention is also characterized in that:

[0007] The pulse width modulation method of synthesizing a DC voltage by three-phase AC chopping is specifically implemented according to the following steps:

[0008] Step 1: The three-phase AC input voltage is represented as phase A voltage, phase B voltage, and phase C voltage respectively;

[0009] Step 2: Design the modulation wave, use the direct cross-chopper and the modulation wave to perform pulse width modulation chopping on the A phase voltage, B phase voltage, and C phase voltage respectively, and obtain the three-phase modulation voltage, which is expressed as: The modulation voltage V of phase A DA, the modulation voltage V of phase B DB , W phase modulation voltage V DC ;

[0010] Step 3: The three-phase modulated voltage is synthesized by series addition and low-pass filtering to obtain a DC output voltage V O .

[0011] The specific process of step 2 is:

[0012] Phase A AC input voltage adopts modulation wave D A , and get the voltage V DA ; B phase AC input voltage adopts modulation wave D B , and get the voltage V DB ; The C phase AC input voltage adopts the modulation wave D C , and get the voltage V DC ;

[0013] A phase AC input voltage U IA , B phase AC transmission voltage U IB , C phase AC input voltage U IC The expression is:

[0014]

[0015] Where V in Indicates the input voltage amplitude, ω 1 Indicates the angular frequency of the input three-phase voltage;

[0016] Modulation voltage V DA 、V DB 、V DC The expression is:

[0017]

[0018] Among them, D A Indicates the A phase modulation wave, D B represents the B phase modulation wave, D C Represents the C-phase modulation wave.

[0019] Step 2: Design the modulation wave process:

[0020] Determine the calculation formula D according to the desired output voltage amplitude and polarity. 1 , D 2 :

[0021]

[0022] Among them, V D The calculation formula D 1 and D 2 The amplitude, ω 1is the angular frequency of the input three-phase voltage, The calculation formula is the initial phase difference of input voltage phase A;

[0023] The calculation formula D 1 and D 2 The process of performing the Clarke inverse transform is shown in formula (4):

[0024]

[0025] When the direct-type AC / AC chopper is a bipolar direct-type AC / AC chopper, the modulation wave expression obtained according to formulas (3)-(4) is:

[0026]

[0027] Step 3 DC output voltage V O Expressed as:

[0028] The three V DA 、V DB 、V DC Add them in series to get the DC output voltage V O ,but

[0029] V O =V DA +V DB +V DC (6)

[0030] Substituting formula (1)-(5) into formula (6), we can get the DC output voltage V O Expressed as:

[0031]

[0032] Step 2: When the direct AC / AC chopper is a unipolar direct AC / AC chopper, set D A , D B , D C After unipolarization, the instantaneous values ​​of the three modulation waves will be greater than zero, and the output voltage coefficient will be half of the original value. According to formula (4), the modulation wave expression is:

[0033]

[0034] In step 3, the DC output voltage V O Expressed as:

[0035] The three V DA 、V DB 、V DC By adding in series and low-pass filtering, the DC output voltage V O ,but

[0036] V O =V DA +V DB +V DC (6)

[0037] Combining formulas (1)-(4) and formula (8), we can get the DC output voltage V O ,

[0038]

[0039] The beneficial effects of the present invention are:

[0040] (1) The output voltage of the present invention is direct current, but does not contain a rectification link, and will not inject a large amount of harmonics into the input side current.

[0041] (2) The output DC voltage of the present invention is fully controllable, and both the amplitude and polarity can be independently controlled.

[0042] (3) The current harmonics generated by the present invention can offset each other, thus avoiding current harmonic pollution to the input node.

[0043] (4) By synthesizing and modulating the three-phase input voltage multiple times, multiple arbitrary DC voltages can be output, and the generated current harmonics can still cancel each other out.

[0044] (5) After adopting the present invention, the phase of the input current is adjustable, so the input power factor can be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a flow chart of the pulse width modulation method of synthesizing DC voltage by three-phase AC chopping;

[0046] Figure 2 It is a topological structure diagram used when implementing the pulse width modulation method of synthesizing direct current voltage by three-phase alternating current chopping of the present invention;

[0047] Figure 3 When the input voltage is 50Hz, V D Take 0.7, When 0 is taken, the calculation formula D 1 and D 2 The waveform of

[0048] Figure 4 When the input voltage is 50Hz, V D Take 0.7, The modulation wave D after the single polarity is taken as 0 A , D B and D C The waveform of

[0049] Figure 5It is based on the proposed pulse width modulation method and Figure 2 The topology shown in the figure shows the waveforms of the output positive polarity DC voltage and reverse polarity DC voltage. DETAILED DESCRIPTION

[0050] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] The pulse width modulation method for synthesizing a DC voltage by three-phase AC chopping of the present invention performs pulse width modulation chopping on a three-phase AC input voltage by a direct AC chopper, and performs series synthesis and low-pass filtering on the chopped voltage to obtain a DC output voltage, which is specifically implemented according to the following steps:

[0052] The three-phase AC input voltage is represented as phase A voltage, phase B voltage, and phase C voltage respectively; the modulation wave is designed, and the pulse width modulation chopping of phase A voltage, phase B voltage, and phase C voltage is performed using a direct AC chopper and the modulation wave to obtain a three-phase modulation voltage, which is represented as: the modulation voltage V of phase A DA , the modulation voltage V of phase B DB , W phase modulation voltage V DC ; The three-phase modulated voltage is added in series to obtain the DC output voltage V O .

[0053] Among them, the A phase AC input voltage U IA , B phase AC transmission voltage U IB , C phase AC input voltage U IC The expression is:

[0054]

[0055] Where V in Indicates the input voltage amplitude, ω 1 Indicates the angular frequency of the input three-phase voltage;

[0056] Modulation voltage V DA 、V DB 、V DC The expression is:

[0057]

[0058] Among them, D A Indicates the A phase modulation wave, D B represents the B phase modulation wave, D C Represents the C-phase modulation wave.

[0059] The process of designing the modulation wave is:

[0060] Determine the calculation formula D according to the desired output voltage amplitude and polarity. 1 , D 2 :

[0061]

[0062] Among them, V D The calculation formula D 1 and D 2 The amplitude ranges from 0 to 1, ω 1 is the angular frequency of the input three-phase voltage, The calculation formula is the initial phase difference of input voltage phase A;

[0063] The calculation formula D 1 and D 2 The process of performing the Clarke inverse transform is shown in formula (4):

[0064]

[0065] In the present invention, the direct-type cross-chopped chopper chops the input voltage according to the modulation wave. The direct-type cross-chopped chopper can be a bipolar direct-type AC / AC chopper or a unipolar direct-type AC / AC chopper. When the direct-type cross-chopped chopper is a bipolar direct-type AC / AC chopper:

[0066] According to formulas (1)-(4), the modulation wave expression is:

[0067]

[0068] The three V DA 、V DB 、V DC By adding in series and low-pass filtering, the DC output voltage V O ,but

[0069] V O =V DA +V DB +V DC (6)

[0070] Substituting formula (1)-(5) into formula (6), we can get the DC output voltage V O Expressed as:

[0071]

[0072] It can be seen from formula (7) that the present invention can output a DC voltage with controllable amplitude and polarity. D or angle The amplitude and polarity of the DC voltage can be controlled. When the angle is greater than 90° and less than 270°, the output voltage is negative. When it is greater than -90° and less than 90°, the output is positive voltage.

[0073] When the direct-type AC / AC chopper is a bipolar direct-type AC / AC chopper: D A , D B , D C After unipolarization, the instantaneous values ​​of the three modulation waves will be greater than zero, and the output voltage coefficient will be half of the original value. Formula (7) shows a unipolarization method, and formula (8) is the output voltage expression after adopting the unipolarized modulation wave.

[0074]

[0075] The three V DA 、V DB 、V DC By adding in series and low-pass filtering, the DC output voltage V O ,but

[0076] V O =V DA +V DB +V DC (6)

[0077]

[0078] Example

[0079] Take the output of two DC as an example to explain. Figure 2 The topological structure used in the pulse width modulation method of the present invention is not limited to Figure 2 Run on the topology shown.

[0080] like Figure 2 As shown in the figure, the three-phase core-type multi-winding transformer is connected by an iron yoke to form three core columns. Each core column has three windings, namely, T a1 、T a2 、T a3 , T b1 、T b2 、T b3 , T c1 、T c2 、T c3 All windings have the same winding ratio; each secondary winding has two wires leading out, the one with a black solid dot is the positive polarity wire and the other is the negative polarity wire. Winding T a1 , T b1 , T c1 is the primary winding, connected to a three-phase voltage. The remaining windings are secondary windings, connected to each unipolar direct AC / AC chopper. Winding T a2 Power supply for unipolar direct AC / AC chopper ZA; winding T a3Power supply for unipolar direct AC / AC chopper FA; winding T b2 Power supply for unipolar direct AC / AC chopper ZB; winding T b3 Power supply to unipolar direct AC / AC chopper FB; winding T c2 Power supply for unipolar direct AC / AC chopper ZC; winding T c3 Power is supplied to the unipolar direct AC / AC chopper FC; the positive input port of each unipolar direct AC / AC chopper is connected to the positive polarity line of its corresponding winding, and the negative input port is connected to the negative polarity line of its corresponding winding. The negative pole of the output port of chopper ZA is connected to the positive pole of the output port of chopper ZB, the negative pole of the output port of chopper ZB is connected to the positive pole of the output port of chopper ZC, the positive pole of the output port of chopper ZA and the negative pole of the output port of chopper ZC are connected to the two input ports of the positive polarity DC LC filter, and the two output ports of the LC filter constitute a positive polarity DC output voltage. The negative pole of the port of chopper FA is connected to the positive pole of the output port of chopper FB, the negative pole of the output port of chopper FB is connected to the positive pole of the output port of chopper FC, the positive pole of the output port of chopper FA and the negative pole of the output port of chopper FC are connected to the two input ports of the negative polarity DC LC filter, and the two output ports of the LC filter constitute a negative polarity DC output voltage. The negative poles of the two LC filter output ports are connected to a point N, and the positive poles of the two LC filter output ports form two DC voltages U OZ and U OF .

[0081] Assume that the input voltage expression of the primary winding of the transformer is (10):

[0082]

[0083] Since the winding ratios of each winding are the same, the input voltage of each unipolar AC / AC chopper is the same as the input voltage of the primary winding. Taking the output positive polarity voltage as an example for deduction, the output negative polarity voltage is symmetrical and the same.

[0084] Calculation formula D 1 and D 2 As shown in formula (10)

[0085]

[0086] In formula (11), V D The calculation formula D 1 and D 2 The amplitude of , ranging from 0 to 1. 1 is the angular frequency of the input three-phase voltage. is the initial phase difference of input voltage phase A. 1and D 2 The modulated wave D can be obtained by performing inverse Clarke transform A , D B , D C , and the modulated wave is converted to a single polarity. The final modulated wave is shown in formula (12):

[0087]

[0088] Chopper ZA uses modulation wave D A , chopper ZB uses modulation wave D B , chopper ZC uses modulation wave D C Since the output ports of choppers ZA, ZB, and ZC are connected in series, the output voltage U OZ The expression of is (13):

[0089]

[0090] U OF The synthesis and modulation methods are similar to those of U OZ Symmetrically the same, the difference is The angular difference is 180°. The result of the two-phase DC voltage is shown in (13)

[0091]

[0092] Taking the transformer A phase iron core column as an example, the harmonic current is analyzed and the output current is set as formula (15). The unipolar direct AC / AC chopper Za, Fa and the transformer input side are coupled through the A phase iron core column magnetic circuit, and the coupling current can be expressed by formula (16).

[0093]

[0094]

[0095] I IA is the input current expression of phase A. It can be seen that the current frequency after coupling is ω 1 , which has the same frequency as the input voltage and current, so the current harmonics generated by the present invention can cancel each other out, avoiding current harmonic pollution to the input node. In addition, it can be seen that I IA The phase is adjustable, so the present invention can also adjust the input power factor.

[0096] Figure 3 When the input voltage is 50Hz, V D Take 0.7, When 0 is taken, the calculation formula D 1 and D 2 waveform.

[0097] Figure 4When the input voltage is 50Hz, V D Take 0.7, The modulation wave D after the single polarity is taken as 0 A , D B and D C waveform.

[0098] Figure 5 It is based on the proposed pulse width modulation method and Figure 2 The topology shown in the figure shows the waveform of the output positive polarity DC voltage and reverse polarity DC voltage. At this time, the input voltage is 50Hz, V D Take 0.7, Take 0° and 180° respectively. It can be seen from the figure that the two DC voltages are positive and negative 150V respectively, which meets the set values.

[0099] Depend on Figure 5 It can be seen that by using the modulation method of the present invention to perform chopping synthesis on the three-phase AC input voltage and pulse width modulation, a DC voltage with controllable amplitude and polarity can be obtained.

[0100] Through the above-mentioned method, the present invention discloses a pulse width modulation method for synthesizing a direct current voltage by three-phase AC chopping. By performing pulse width modulation chopping and voltage synthesis on the input three-phase AC voltage through a direct AC chopper, a direct current voltage with controllable amplitude and polarity can be obtained. The present invention does not contain a rectification link and will not inject a large amount of harmonics into the input current. Multiple DC voltages can also be output through multiple modulations and voltage synthesis. In addition, the current harmonics generated by the present invention can offset each other to avoid current harmonic pollution to the input node. The present invention also has the ability to adjust the input power factor.

Claims

1. Pulse width modulation method for synthesizing DC voltage by three-phase AC chopping, It is characterized in that The three-phase AC input voltage is pulse-width modulated and chopped by a direct AC chopper, and the chopped voltage is synthesized in series and low-pass filtered to obtain a DC output voltage; the specific implementation is as follows: Step 1: The three-phase AC input voltage is expressed as A Phase voltage, B Phase voltage, C Phase voltage; Step 2: Design the modulation wave, and use the direct cross-chopper and the modulation wave to A Phase voltage, B Phase voltage, C The phase voltage is pulse-width modulated and chopped to obtain a three-phase modulated voltage, which is expressed as: A Phase modulation voltage V DA , modulation voltage of phase B V DB , W Phase modulation voltage V DC ; Step 3: Add the three-phase modulated voltages in series and perform low-pass filtering to obtain a DC output voltage. V O ; The specific process of step 2 is: A Phase AC input voltage adopts modulation wave D A , and the voltage V DA ; B Phase AC input voltage adopts modulation wave D B , and the voltage V DB ; C Phase AC input voltage adopts modulation wave D C , and the voltage V DC ; A Phase AC input voltage U IA , B Phase AC transmission voltage U IB , C Phase AC input voltage U IC The expression is: (1) in V in Indicates the input voltage amplitude, Indicates the angular frequency of the input three-phase voltage; Modulation voltage V DA , V DB , V DC The expression is: (2)； in, D A express A Phase modulated wave, D B express B Phase modulated wave, D C express C Phase modulated wave; The process of designing the modulation wave in step 2 is as follows: Determine the calculation formula based on the desired output voltage amplitude and polarity D 1 , D 2 : (3) in, V D For calculation D 1 and D 2 The amplitude of ω 1 is the angular frequency of the input three-phase voltage, For the calculation formula, the input voltage A The initial phase difference; The calculation formula D 1 and D 2 The process of performing the Clarke inverse transform is shown in formula (4): （4）； When the direct-type AC / AC chopper is a bipolar direct-type AC / AC chopper, the modulation wave expression obtained according to formulas (3)-(4) is: （5）。 2. According to the pulse width modulation method of synthesizing a DC voltage by three-phase AC chopping according to claim 1, It is characterized in that The DC output voltage in step 3 V O Expressed as: Put three V DA , V DB , V DC By series addition and low-pass filtering, a DC output voltage can be obtained. V O ,but (6) Substituting formula (1)-(5) into formula (6) yields the DC output voltage V O Expressed as: （7）。 3. According to the pulse width modulation method of synthesizing a DC voltage by three-phase AC chopping as claimed in claim 1, It is characterized in that When the direct-type AC / AC chopper described in step 2 is a unipolar direct-type AC / AC chopper, D A , D B , D C After unipolarization, the instantaneous values ​​of the three modulation waves will be greater than zero, and the output voltage coefficient will be half of the original value. According to formula (5), the modulation wave expression is: (8)。 4. According to the pulse width modulation method of synthesizing a DC voltage by three-phase AC chopping as claimed in claim 3, It is characterized in that The DC output voltage in step 3 V O Expressed as: Put three V DA , V DB , V DC By series addition and low-pass filtering, a DC output voltage can be obtained. V O ,but (6) Combining formulas (1)-(4) and formula (8), the DC output voltage can be obtained V O It is expressed as: （9）。

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