A Method for Eliminating Third Harmonics of a Traction Four-Quadrant Rectifier

Abstract

The present invention discloses a method for eliminating the third harmonic of a traction four-quadrant rectifier, which includes a sampling unit for obtaining the sampling value of the four-quadrant rectifier and the grid angle at the sampling moment, a third harmonic extraction unit for extracting the third harmonic of the sampling value and the grid angle at the sampling moment, a third harmonic modulation wave calculation unit for obtaining the harmonic modulation voltage based on the third harmonic, a third harmonic compensation unit for obtaining the third harmonic modulation voltage by using the harmonic modulation voltage, and using the third harmonic modulation voltage as the four-quadrant modulation voltage to eliminate the third harmonic in the four-quadrant input current. The method for eliminating the third harmonic of the input current of the four-quadrant rectifier in the present invention can quickly detect the third harmonic in the four-quadrant input current and perform compensation and elimination. This method has a high response bandwidth, strong robustness, small calculation amount, and less storage space occupancy.

Description

Technical Field

[0001] The present invention relates to the field of harmonic elimination, and particularly to a method for eliminating the third harmonic of a traction four-quadrant rectifier. Background Art

[0002] With the development of China's economy, the railway passenger and freight volumes have reached new highs continuously, and the electrification rate of the national railway has also been increasing continuously. AC-DC-AC electric locomotives and multiple units have become the main types of locomotives for electrified railway transportation. The traction four-quadrant rectifier on railway locomotives and multiple units is a pulse-width modulation four-quadrant rectifier, and its working principle is to adjust the phase and amplitude of the input current of the traction four-quadrant rectifier by pulse-modulating the voltage. The waveform of the input current of the traction four-quadrant rectifier should be as close to a sine wave as possible. However, since the input-side voltage of the traction four-quadrant rectifier is a pulse-modulated voltage, there are ripples in the input current of the four-quadrant rectifier, and this kind of ripple is synchronously reflected to the grid side, causing grid-side harmonic current. This kind of pulse-width modulation technology is a kind of harmonic pollution to the power grid. In severe cases, it may cause harmonic current amplification and resonant overvoltage, resulting in damage to on-vehicle electrical equipment, affecting the normal operation of locomotives or multiple units, and causing certain economic losses. The inherent second-order (100Hz) pulsation characteristic of the DC voltage in the intermediate circuit of the single-phase four-quadrant rectifier on railway locomotives and multiple units determines that the proportion of the third harmonic content in the input side of the four-quadrant rectifier is the largest. Therefore, the elimination of the third harmonic has always been an important research topic in the field of traction control.

[0003] The existing common methods for eliminating the third harmonic of the traction four-quadrant rectifier are usually divided into the specific harmonic elimination method and the proportional-resonant control elimination method.

[0004] The specific harmonic elimination method requires more computing resources and storage space, and can only eliminate the harmonics generated by the modulation wave itself, and cannot eliminate the harmonics contained in the power grid.

[0005] The proportional-resonant control elimination method can only produce an inhibitory effect near the resonant frequency, has a relatively narrow response bandwidth, and is easily affected by the changes of the power grid and traction system parameters, is more sensitive to the system, and has poor robustness. Summary of the Invention

[0006] The present invention provides a method for eliminating the third harmonic of a traction four-quadrant rectifier to overcome the disadvantages of occupying more storage space and having poor robustness.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] A method for eliminating the third harmonic of a traction four-quadrant rectifier, characterized by comprising:

[0009] Step 1: The sampling unit acquires the sampling value I of the four-quadrant rectifier and the grid angle θ at the sampling moment, and transmits the sampling value I and the grid angle θ at the sampling moment to the third-harmonic extraction unit;

[0010] Step 2: The third-harmonic extraction unit extracts the third harmonics of the sampling value I and the grid angle θ at the sampling moment, and transmits the third harmonics to the third-harmonic modulation wave calculation unit;

[0011] Step 3: The third-harmonic modulation wave calculation unit obtains the harmonic modulation voltage U 3 , and transmits the harmonic modulation voltage U 3 to the third-harmonic compensation unit;

[0012] Step 4: The third-harmonic compensation unit uses the harmonic modulation voltage U 3 to obtain the elimination of the third-harmonic modulation voltage U all ;

[0013] Step 5: The elimination of the third-harmonic modulation voltage U all is used as the four-quadrant modulation voltage Ur to eliminate the third harmonics in the four-quadrant input current.

[0014] Furthermore, in Step 2, the third-harmonic extraction unit extracts the d-axis component I 3d of the sampling value I and the grid angle θ at the sampling moment and the q-axis component I 3q , and the component I 3d and the component I 3q constitute the third harmonics.

[0015] Furthermore, the formulas for extracting the component I 3d and the component I 3q in Step 2 are:

[0016] I 3d = [I * cos(3 * θ) + I * sin(θ - 0.167 * π) / sinθ * sin(3 * θ)];

[0017] I 3q = [I * sin(3 * θ) + I * sin(θ - 0.167 * π) / sinθ * cos(3 * θ)].

[0018] Furthermore, the formula for obtaining the harmonic modulation voltage U 3 in Step 3 is:

[0019] U 3 = [I 3d * cos(3 * θ) - I 3q * sin(3 * θ)] * R - [I 3d * sin(3 * θ) + I 3q*cos(3*θ)]*300*π*L

[0020] Where R is the value of the equivalent resistance of the secondary side of the transformer, and L is the value of the equivalent leakage inductance of the secondary side of the transformer.

[0021] Furthermore, the modulation voltage U for eliminating the third harmonic obtained in step 4 all has the following formula:

[0022] U all = U basic - U 3

[0023] Where U basic is the modulation voltage without harmonics of the four-quadrant rectifier.

[0024] Advantageous effects:

[0025] 1. The method for eliminating the third harmonic of a traction four-quadrant rectifier according to the present invention can quickly detect the third harmonic in the four-quadrant input current and compensate and eliminate it. This method can not only eliminate the third harmonic, but also eliminate the harmonics near the third harmonic frequency, and has a high response bandwidth; at the same time, this method has a small calculation amount and a fast response speed, so it has strong robustness; it does not require pre-solving equations, so it occupies less storage space;

[0026] 2. The method of the present invention only needs to sample the four-quadrant input current, does not strictly depend on the electrical parameters of the traction system, has a simple principle, and can still eliminate harmonics even when there are deviations in the designed electrical parameters, so it has high reliability. Description of the drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0028] Figure 1 is the flow chart of the method of the present invention;

[0029] Figure 2 is the schematic diagram of eliminating the third harmonic of the input current of the traction four-quadrant rectifier of the present invention;

[0030] Figure 3 is the input current diagram when the power grid is interrupted in the present invention;

[0031] Figure 4 is the grid voltage diagram when the power grid is interrupted in the present invention;

[0032] Figure 5It is the verification effect diagram of the elimination of the third harmonic of the four - quadrant input current before using the method of the present invention;

[0033] Figure 6 It is the verification effect diagram of the elimination of the third harmonic of the four - quadrant input current after using the method of the present invention. Specific implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] This embodiment provides a method for eliminating the third harmonic of a traction four - quadrant rectifier, as Figure 1 , which is characterized by including:

[0036] Step 1: The sampling unit acquires the sampling value I of the four - quadrant rectifier and the grid angle θ at the sampling moment, and transmits the sampling value I and the grid angle θ at the sampling moment to the third - harmonic extraction unit;

[0037] Step 2: The third - harmonic extraction unit extracts the component I 3d of the sampling value I and the grid angle θ at the sampling moment on the d - axis and the component I 3q on the q - axis. The component I 3d and the component I 3q constitute the third harmonic.

[0038] Among them, the formulas for extracting the component I 3d and the component I 3q are:

[0039] I 3d = [I * cos(3 * θ)+I * sin(θ - 0.167 * π) / sinθ * sin(3 * θ)];

[0040] I 3q = [I * sin(3 * θ)+I * sin(θ - 0.167 * π) / sinθ * cos(3 * θ)].

[0041] Step 3: The third - harmonic modulation - wave calculation unit obtains the harmonic modulation voltage U 3 from the third harmonic, and transmits the harmonic modulation voltage U 3 to the third - harmonic compensation unit;

[0042] Among them, the formula for obtaining the harmonic modulation voltage U 3 is:

[0043] U 3 = [I 3d * cos(3 * θ) - I 3q * sin(3 * θ)] * R - [I 3d * sin(3 * θ) + I 3q * cos(3 * θ)] * 300 * π * L

[0044] Among them, R is the value of the equivalent resistance of the secondary side of the transformer, and L is the value of the equivalent leakage inductance of the secondary side of the transformer.

[0045] Step 4: The third - harmonic compensation unit uses the harmonic modulation voltage U 3 to obtain the third - harmonic elimination modulation voltage U all ; among them, the third - harmonic elimination modulation voltage U all contains the total voltage for third - harmonic elimination;

[0046] The formula for obtaining the third - harmonic elimination debugging voltage is U all = U basic - U 3 where U basic is the modulation voltage without harmonics in the traction four - quadrant.

[0047] Step 5: The third - harmonic elimination modulation voltage U all is used as the four - quadrant modulation voltage Ur to eliminate the third - harmonic in the four - quadrant input current.

[0048] In a specific embodiment, as Figure 2 , Figure 2 on the left is the schematic diagram of the traction four - quadrant rectifier, u s is the secondary - side voltage of the transformer, u r is the modulation voltage on the four - quadrant input side, the equivalent leakage inductance of the transformer secondary side is L, the equivalent resistance is R, i s is the four - quadrant input current, i c is the capacitor current, C is the intermediate - circuit support capacitor, S b , S a ′, S a , and S b are the switching devices of the four - quadrant rectifier, u dc is the intermediate voltage, and the current in the equivalent leakage inductance of the transformer, which is the four - quadrant input current, is generated by the subtraction control of the two.

[0049] In a specific embodiment, as Figure 3 and Figure 4 , the principle of the present invention is to extract the third - harmonic I S3 in the current, u r3is the third harmonic compensation voltage. The voltage generated by the third harmonic current in the resistor R has the same direction as the current, and the voltage generated in the inductor L leads the current by 90 degrees. The vector addition of the two gives the third harmonic modulation voltage. By injecting the third harmonic modulation voltage in the reverse direction into the four-quadrant modulation wave, the third harmonic in the current can be cancelled out.

[0050] In a specific embodiment, Figure 5 is the verification effect diagram of the elimination of the third harmonic of the four-quadrant input current before the method of the present invention is used. Figure 6 is the verification effect diagram of the elimination of the third harmonic of the four-quadrant input current after the method of the present invention is used. From Figure 5 and Figure 6 it can be seen that when the four-quadrant input current contains the third harmonic, after adopting the present invention, the sinusoidality of the four-quadrant input current becomes better, and the content of the third harmonic is significantly reduced, which proves the effectiveness of the present invention.

[0051] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for eliminating the third harmonic of a traction four - quadrant rectifier, characterized in that, it includes: Step 1: The sampling unit obtains the sampling value I of the four - quadrant rectifier and the grid angle θ at the sampling moment, and transmits the sampling value I and the grid angle θ at the sampling moment to the third - harmonic extraction unit; Step 2: The third - harmonic extraction unit extracts the third harmonic of the sampling value I and the grid angle θ at the sampling moment, and transmits the third harmonic to the third - harmonic modulation wave calculation unit; In step 2, the third-harmonic extraction unit extracts the component I of the sampled value I on the d-axis at the grid angle θ at the sampling moment 3d and the component I on the q-axis 3q , the component I 3d and the component I 3q constitute the third harmonic; where the extraction component I 3d and component I 3q The formula is: I 3d = [I * cos(3 * θ) + I * sin(θ - 0.167 * π) / sinθ * sin(3 * θ)]; I 3q = [I * sin(3 * θ) + I * sin(θ - 0.167 * π) / sinθ * cos(3 * θ)]; Step 3: The third-harmonic modulation wave calculation unit obtains the harmonic modulation voltage U 3 , and transmits the harmonic modulation voltage U 3 to the third-harmonic compensation unit; Step 4. The third harmonic compensation unit uses the harmonic modulation voltage U 3 to obtain the third harmonic modulation voltage U all eliminated; Step 5, eliminate the third harmonic modulation voltage U all As the quadrant modulation voltage Ur to eliminate the third harmonic in the quadrant input current.

2. The method for eliminating the third harmonic of a traction four - quadrant rectifier according to claim 1, characterized in that, The formula for the harmonic modulation voltage U 3 obtained in Step 3 is as follows: U 3 = [I 3d * cos(3 * θ) - I 3q * sin(3 * θ)] * R - [I 3d * sin(3 * θ) + I 3q * cos(3 * θ)] * 300 * π * L where R is the value of the equivalent resistance of the secondary side of the transformer, and L is the value of the equivalent leakage inductance of the secondary side of the transformer.

3. The method for eliminating the third harmonic of a traction four - quadrant rectifier according to claim 2, characterized in that, The modulation voltage U for eliminating the third harmonic obtained in step 4 all has the following formula: U all = U basic - U 3 Where U basic is the modulation voltage without harmonics of the four - quadrant rectifier.

Images