Series 48-pulse rectifier using DC-side hybrid harmonic suppression method

Abstract

An embodiment of the present invention discloses a series-type 48-pulse rectifier using a DC-side hybrid harmonic suppression method, which includes an input inductor, an isolation transformer, a first three-phase full-bridge rectifier circuit, a second three-phase full-bridge rectifier circuit, a control circuit, a first DC-side capacitor, a second DC-side capacitor, a load, a harmonic injection circuit, and a clamping diode. Among them, the first and second three-phase full-bridge rectifier circuits are connected in series and in parallel with the load; the harmonic injection circuit consists of an injection transformer, a single-phase full-wave rectifier circuit, and a switching tube. The sampling end of the control circuit is connected to the same-name end of the injection transformer, and the output end is connected to the gate of the switching tube. The present invention combines the DC-side passive harmonic suppression method and the active harmonic suppression method. Compared with the rectifier without using the harmonic injection circuit, the THD value of the input voltage is reduced from 12% to less than 2%, greatly improving the power quality of the rectifier.

Description

Technical Field

[0001] The present invention relates to the field of electric power electronics, and in particular, to a series-type 48-pulse rectifier using a DC-side hybrid harmonic suppression method. Background Art

[0002] A multi-pulse rectifier is a high-power power conversion device with a simple structure and strong robustness. However, since the rectifier uses diode rectification, a large amount of harmonic pollution is generated due to the strong nonlinearity of the diodes, reducing the input and output power quality of the rectifier. Therefore, finding an effective method to suppress the input current and voltage harmonics of the multi-pulse rectifier has become the key to the current research on multi-pulse rectification technology.

[0003] There are three methods to improve the input and output power quality of the multi-pulse rectifier. The first method is to increase the number of output phases of the phase-shifting transformer to increase the number of rectifier bridges, thereby increasing the input voltage or current steps of the rectifier and the load voltage and current pulse numbers, and improving the input and output power quality of the rectifier. However, when the number of output phases of the phase-shifting transformer exceeds 3, the structure of the transformer is complex, the design is difficult, and the asymmetry problem is serious. The second method is to use an AC-side filter, which cancels the harmonics generated by the rectifier by injecting harmonic signals with equal effective values and opposite phases on the AC side of the rectifier. However, it is difficult to take into account the power quality on the DC side by this method. The third method is to use a DC-side harmonic suppression method, including a DC-side passive harmonic suppression method, an active harmonic suppression method, and a hybrid harmonic suppression method, which inject voltage or current harmonics into the DC side of the rectifier to cancel specific-order harmonics generated by the rectifier. Among them, the DC-side passive harmonic suppression method does not require switching tubes and control circuits, and the circuit reliability is high, but the harmonic suppression ability is limited. The DC-side active harmonic suppression method has a significant harmonic suppression effect, but its reliability is low, and the harmonic injection circuit loss is large. The DC-side hybrid harmonic suppression method combines the above two methods, taking into account the advantages of the above two methods, with high reliability and low loss, and is the most commonly used method in the current multi-pulse rectification technology.

[0004] In the invention patent with the application number 2018104096783 and the invention name "Series-type 36-pulse rectifier using DC-side hybrid voltage harmonic injection method", although the DC-side hybrid voltage harmonic injection method is used, its harmonic suppression effect is poor and cannot meet the requirements. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a series-type 48-pulse rectifier using a DC-side hybrid harmonic suppression method to improve the harmonic suppression effect and improve the power quality of the rectifier.

[0006] To solve the above technical problems, an embodiment of the present invention provides a series 48-pulse rectifier using a DC-side hybrid harmonic suppression method, which includes an input inductor, an isolation transformer, a first three-phase full-bridge rectifier circuit, a second three-phase full-bridge rectifier circuit, a control circuit, a first DC-side capacitor, a second DC-side capacitor, and a load. The input inductor consists of three inductors of the same size. One end of each of the three inductors is connected to a three-phase voltage source, and the other end is connected to the primary winding of the isolation transformer. The primary winding of the isolation transformer is connected in a delta configuration, and the secondary winding forms a star-delta connection. The secondary winding generates two sets of three-phase voltages that are equal in magnitude and 30° out of phase. The two sets of secondary windings are respectively connected to the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit. The series 48-pulse rectifier further includes a harmonic injection circuit and a clamping diode. Among them, the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit are connected in series and then connected in parallel with the load. The first DC-side capacitor and the second DC-side capacitor are connected in series and then connected in parallel with the load. The harmonic injection circuit consists of an injection transformer, a single-phase full-wave rectifier circuit, and a switching tube. Among them, the two ends of the primary winding of the injection transformer are respectively connected to the midpoints of the two sets of three-phase full-bridge rectifier circuits and the midpoints of the two DC-side capacitors. The secondary winding is connected to the single-phase full-wave rectifier circuit. The collector of the switching tube is connected to the primary winding of the injection transformer, and the emitter is connected to the anode of the diode of the single-phase full-wave rectifier circuit and the cathode of the clamping diode. The anode of the clamping diode is connected between the first three-phase full-bridge rectifier circuit and the first DC-side capacitor. The sampling terminal of the control circuit is connected to the same-name terminal of the injection transformer, and the output terminal is connected to the gate of the switching tube.

[0007] Further, the isolation transformer is a phase-shifting transformer, and the primary and secondary sides of the isolation transformer are electrically isolated. The isolation transformer consists of three core columns, and each core column has 3 windings, including 1 primary winding and 2 secondary windings. Each winding is independent. The primary winding forms a delta connection, and the secondary winding forms a star-delta connection, generating two sets of three-phase voltages that are equal in magnitude and 30° out of phase.

[0008] Further, the first DC-side capacitor and the second DC-side capacitor have the same capacitance value.

[0009] Further, both the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit adopt uncontrolled rectifier devices.

[0010] Further, the injection transformer consists of one core column, and each core column has one primary winding and two secondary windings.

[0011] Further, the injection transformer is a single-phase transformer, and its turns ratio is 0.02456.

[0012] The beneficial effects of the present invention are as follows: The secondary winding of the isolation transformer in the present invention is star-delta connected, effectively suppressing the third harmonic generated by the rectifier; the harmonic injection circuit adopted by the present invention is composed of a passive harmonic injection circuit and an active harmonic injection circuit. The harmonic injection circuit has good adaptability. Even if a switching tube fails, the passive harmonic injection circuit can still work and still has a certain inhibitory effect on harmonics; the rectifier bridge adopted by the present invention is a diode rectifier bridge, which does not require complex control, has high reliability, and is suitable for high-power occasions. Brief Description of the Drawings

[0013] Figure 1 is the circuit diagram of a series-type 48-pulse rectifier using the DC-side hybrid harmonic suppression method in an embodiment of the present invention.

[0014] Figure 2 is the winding structure diagram of the isolation transformer in an embodiment of the present invention.

[0015] Figure 3 is the winding structure diagram of the injection transformer in an embodiment of the present invention.

[0016] Figure 4 is the circuit diagram of the working mode I of the harmonic injection circuit in an embodiment of the present invention.

[0017] Figure 5 is the circuit diagram of the working mode II of the harmonic injection circuit in an embodiment of the present invention.

[0018] Figure 6 is the circuit diagram of the working mode III of the harmonic injection circuit in an embodiment of the present invention.

[0019] Figure 7 is the circuit diagram of the working mode IV of the harmonic injection circuit in an embodiment of the present invention.

[0020] Figure 8 is the working waveform of a series-type 48-pulse rectifier using the DC-side hybrid harmonic suppression method in an embodiment of the present invention. Detailed Embodiment

[0021] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0022] In the embodiments of the present invention, if there are directional indications (such as up, down, left, right, front, back...), they are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0023] In addition, in the present invention, descriptions such as "first" and "second" are for descriptive purposes only, and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature.

[0024] Please refer to Figure 1 , the series 48-pulse rectifier using the DC-side hybrid harmonic suppression method in the embodiment of the present invention includes an input inductor 1, an isolation transformer 2, a first three-phase full-bridge rectifier circuit 3, a second three-phase full-bridge rectifier circuit 4, a harmonic injection circuit 5, a clamping diode 6, a control circuit 7, a first DC-side capacitor 8, a second DC-side capacitor 9, and a load 10.

[0025] The input inductor 1 consists of three inductors of the same size, with the left ends respectively connected to the three-phase voltage source and the right end connected to the primary winding of the isolation transformer. The input power supply is equivalent to a three-phase balanced current source.

[0026] The isolation transformer 2 serves as a phase-shifting transformer. The primary winding is connected in a delta configuration, and the secondary winding forms a star-delta connection. The secondary winding generates two sets of three-phase voltages that are equal in magnitude and have a phase difference of 30°. The primary winding is connected to the input inductor, and the two sets of secondary windings are respectively connected to the first three-phase full-bridge rectifier circuit 3 and the second three-phase full-bridge rectifier circuit 4.

[0027] The first three-phase full-bridge rectifier circuit 3 and the second three-phase full-bridge rectifier circuit 4 are connected in series. The first DC-side capacitor 8 and the second DC-side capacitor 9 are connected in series. The first three-phase full-bridge rectifier circuit 3, the second three-phase full-bridge rectifier circuit 4, the first DC-side capacitor 8, the second DC-side capacitor 9, and the load 10 are connected in parallel, and the output voltage becomes twice. Both the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit use uncontrolled rectifier devices, which have high reliability.

[0028] The first DC-side capacitor 8 and the second DC-side capacitor 9 are equal in size. The output voltage of the rectifier is filtered by the capacitors to be DC. The upper end of the first DC-side capacitor 8 is connected to the positive pole of the output of the first three-phase full-bridge rectifier circuit 3 and the positive pole of the load 10, and the lower end is connected to the upper end of the second DC-side capacitor 9. The lower end of the second DC-side capacitor 9 is connected to the negative pole of the output of the second three-phase full-bridge rectifier circuit 4 and the negative pole of the load 10.

[0029] The harmonic injection circuit 5 consists of an injection transformer, a single-phase full-wave rectifier circuit, and a switching transistor. Among them, the primary winding of the single-phase transformer is connected to the midpoint of the single-phase full-bridge rectifier circuit and the midpoint of the two DC-side capacitors respectively, the secondary winding is connected to the single-phase full-wave rectifier circuit, the collector of the switching transistor is connected to the primary winding of the injection transformer, and the emitter is connected to the anode of the diode of the single-phase full-wave rectifier circuit. The harmonic injection circuit 5 of the present invention consists of a passive harmonic suppression circuit and an active harmonic suppression circuit. When the switching transistor fails, the rectifier still has a good harmonic suppression effect and high reliability. The single-phase full-wave rectifier circuit consists of only two diodes and has low losses.

[0030] The anode of the clamping diode 6 is connected between the first three-phase full-bridge rectifier circuit 3 and the first DC-side capacitor 8, and the cathode is connected to the anode of the diode of the single-phase full-wave rectifier circuit. In the embodiment of the present invention, the harmonic suppression effect is improved by changing the position of the switching transistor. When the switching transistor is turned on, the voltage of the primary winding of the injection transformer is ±N4 / (2N5)u o , increasing the injection voltage u FP of the step number, and the harmonic suppression effect is more obvious.

[0031] The sampling terminal of the control circuit 7 is connected to the same-named terminal of the injection transformer, and the output terminal is connected to the gate of the switching transistor.

[0032] As an implementation manner, please refer to Figure 1 , Figure 8 , the series-type 48-pulse rectifier using the DC-side hybrid harmonic suppression method in the embodiment of the present invention, and the specific method for suppressing harmonics is as follows:

[0033] The control circuit 7 samples the current i x , the sampling signal is in the same phase as the sampling current, and the sampling signal generates a square-wave signal u t through zero-crossing comparison, and u t generates a ramp signal u i through the integration circuit, and u i is compared with each reference voltage signal to obtain Figure 8 the control signal u c , and the control signal u c generates the injection voltage u Figure 8 in FP by controlling the on and off of the switching transistor, modulates the output voltage of the rectifier bridge, eliminates the harmonic components of the rectifier bridge input voltage, and further suppresses the rectifier input voltage harmonics, making the rectifier input voltage waveform tend to be sinusoidal. The capacity of the harmonic injection circuit 5 of the rectifier in the embodiment of the present invention is only 2% of the input power, and the embodiment of the present invention achieves a better harmonic suppression effect at a lower cost.

[0034] As an implementation manner, please refer toFigure 1 and Figure 2 The isolation transformer 2 of the embodiment of the present invention is composed of 3 identical core columns. Each core column has 3 windings, including 1 primary winding and 2 secondary windings. The turn ratio of the 3 windings is N1:N2:N3 = 1.73:1.73:1. Windings a1, a2, and a3 are located on the same core column, windings b1, b2, and b3 are located on the same core column, and windings c1, c2, and c3 are located on the same core column. The primary windings a1, b1, and c1 form a delta connection, and their positive ends are respectively connected to points A, B, and C. The secondary windings a2, b2, and c2 form a delta connection and are connected to the first single-phase full-bridge rectifier circuit 3. The secondary windings a3, b3, and c3 form a star connection and are connected to the second single-phase full-bridge rectifier circuit 4.

[0035] The embodiment of the present invention adopts an isolation transformer. There is electrical isolation between the primary and secondary sides of the transformer, making the transformer have high safety.

[0036] As an implementation manner, please refer to Figure 1 、 Figure 3 The injection transformer of the embodiment of the present invention is a single-phase transformer. The transformer is composed of 1 core column. There are 3 windings on the core column, one primary winding and two secondary windings. The left side of the input end of the injection transformer is connected to the connection point F of the rectifier bridge, and the right side of the input end of the injection transformer is connected to the connection point P of the two DC-side capacitors. The secondary winding of the injection transformer has a center tap and is connected to the input end of the single-phase full-wave rectifier circuit. The injection transformer and the single-phase full-wave rectifier circuit together form a harmonic injection circuit.

[0037] The injection transformer adopted in this implementation manner has a simple structure, strong symmetry, small capacity, and low cost for harmonic suppression.

[0038] As an implementation manner, please refer to Figure 1 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 The working mode of the harmonic injection circuit 5 of the embodiment of the present invention is as follows:

[0039] The harmonic injection circuit 5 is composed of an injection transformer and a single-phase full-wave rectifier circuit. According to the structure of the transformer and the conduction mode of the rectifier bridge, it can be known that i x is a triangular wave with a frequency 6 times that of the power supply; when i x >0 and Q is turned on, u FP = N4 / (2N5)u o , the working mode I of the harmonic injection circuit 5 is as shown in Figure 4 ; when i x >0 and Q is turned off, u FP = N4 / N5u o, the operating mode II of the harmonic injection circuit 5 is as Figure 5 shown; when i x < 0 and Q is turned off, u FP = -N4 / N5u o , the operating mode III of the harmonic injection circuit 5 is as Figure 6 shown; when i x < 0 and Q is turned on, u FP = -N4 / (2N5)u o , the operating mode IV of the harmonic injection circuit 5 is as Figure 7 shown.

[0040] As an implementation, please refer to Figure 1 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , the injection transformer of the embodiment of the present invention is a single-phase transformer. According to Kirchhoff's voltage law, the expressions for the effective value and fundamental wave amplitude of its input voltage can be obtained:

[0041]

[0042]

[0043] According to the above formula and the definition of the THD value, when its turn ratio (the ratio of the number of turns of the primary coil to the number of turns of the secondary coil) is N4 / N5 = 0.02456, the THD value of the rectifier input current is the smallest. When the turn ratio of the injection transformer is N4 / N5 = 0.02456, the THD of the rectifier input voltage reaches the minimum value of 3.83%. The embodiment of the present invention significantly improves the harmonic suppression effect of the rectifier.

[0044] By changing the turn ratio of the injection transformer, the position and control method of the switching tube, the voltage waveform of the primary winding of the injection transformer is changed from a 6-step wave to an 8-step wave, the step value of the rectifier input voltage is increased from 36 to 48, and its theoretical THD value is reduced from 5.093% to 3.83%, significantly improving the harmonic suppression effect; and the effective value of the current flowing through the switching tube is halved, reducing the loss of the harmonic suppression circuit.

[0045] The present invention combines the DC-side passive harmonic suppression method and the active harmonic suppression method, uses the DC-side passive harmonic suppression method to suppress the low-order harmonics generated by the rectifier, and uses the active harmonic suppression method to suppress the high-order harmonics generated by the rectifier; compared with the rectifier without using the harmonic injection circuit, the THD value of the input voltage is reduced from 12% to below 2%, greatly improving the power quality of the rectifier.

[0046] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A series 48-pulse rectifier using a DC-side hybrid harmonic suppression method, comprising an input inductor, an isolation transformer, a first three-phase full-bridge rectifier circuit, a second three-phase full-bridge rectifier circuit, a control circuit, a first DC-side capacitor, a second DC-side capacitor, and a load. The input inductor consists of three inductors of the same size. One end of each of the three inductors is connected to a three-phase voltage source, and the other end is connected to the primary winding of the isolation transformer. The primary winding of the isolation transformer is connected in a delta configuration, and the secondary winding is connected in a star-delta configuration. The secondary winding generates two sets of three-phase voltages that are equal in magnitude and 30° out of phase with each other. The two sets of secondary windings are respectively connected to the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit. It is characterized in that, The series-connected 48-pulse rectifier further includes a harmonic injection circuit and a clamping diode. Among them, the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit are connected in series and are connected in parallel with the load after series connection; the first DC-side capacitor and the second DC-side capacitor are connected in series and are connected in parallel with the load after series connection; the harmonic injection circuit consists of an injection transformer, a single-phase full-wave rectifier circuit and a switching tube. Among them, both ends of the primary winding of the injection transformer are respectively connected to the midpoints of the two groups of three-phase full-bridge rectifier circuits and the midpoints of the two DC-side capacitors, and the secondary winding is connected to the single-phase full-wave rectifier circuit; the collector of the switching tube is connected to the primary winding of the injection transformer, and the emitter is connected to the anode of the diode of the single-phase full-wave rectifier circuit and the cathode of the clamping diode; the anode of the clamping diode is connected between the first three-phase full-bridge rectifier circuit and the first DC-side capacitor; the sampling terminal of the control circuit is connected to the same-name terminal of the injection transformer, and the output terminal is connected to the gate of the switching tube; It is characterized in that the injection transformer is a single-phase transformer, and its turns ratio is 0.02456.

2. The series 48-pulse rectifier using the DC-side hybrid harmonic suppression method according to claim 1, wherein The isolation transformer is a phase-shifting transformer, and the primary and secondary sides of the isolation transformer are electrically isolated; the isolation transformer consists of three core columns, and each core column has 3 windings, including 1 primary winding and 2 secondary windings. Each winding is independent of each other. The primary windings form a delta connection, and the secondary windings form a star-delta connection, generating two sets of three-phase voltages that are equal in magnitude and 30° out of phase with each other.

3. The series 48-pulse rectifier using the DC-side hybrid harmonic suppression method according to claim 1, wherein The first DC-side capacitor and the second DC-side capacitor have the same capacitance value.

4. The series 48-pulse rectifier using the DC-side hybrid harmonic suppression method as claimed in claim 1, wherein, Both the first three-phase full-bridge rectifier circuit and the second three-phase full-bridge rectifier circuit adopt uncontrolled rectifier devices.

5. The series 48-pulse rectifier using the DC-side hybrid harmonic suppression method according to claim 1, characterized in that, The injection transformer consists of one core column, and each core column has one primary winding and two secondary windings.

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