Series type 36-pulse rectifier with passive current injection circuit on dc side

Abstract

The application discloses a series type 36-pulse rectifier with passive current injection circuit on the DC side, and belongs to the technical field of power electronics. The auxiliary transformer secondary side and primary side in the parallel pulse multiplication link introduced on the DC side of the existing 36-pulse rectifier have a large turn ratio, which leads to increased leakage inductance, reduced harmonic suppression effect of the parallel link and increased manufacturing difficulty of the transformer. The passive current injection circuit is arranged on the DC side of the series type 12-pulse rectifier, and the 12-pulse of the series type 12-pulse rectifier is multiplied to 36-pulse. The connection relationship of the passive current injection circuit is improved, and on the basis of the structural improvement, the conduction time of the diode is in a proportional relationship with the voltage period received by the diode, and the turn ratio of the primary side and secondary side windings of each auxiliary transformer is greatly reduced. The number of diodes is also reduced in structure, the harmonic suppression effect is improved, and the circuit structure is simpler. The application is mainly used for pulse number multiplication.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a novel 36-pulse rectifier with a passive current injection circuit on the DC side. Background Technology

[0002] Series-type 12-pulse rectifiers are widely used in medium- and high-voltage high-power applications such as ship electric propulsion, high-voltage direct current transmission, and metal smelting due to their advantages of simple structure, high reliability, and low cost. However, when a series-type 12-pulse rectifier is used alone, the rectifier will generate serious harmonic pollution, which will not only reduce the power quality of the power grid, but also affect the normal operation of nearby sensitive electrical equipment.

[0003] To effectively suppress the input current harmonic content and reduce the output voltage ripple coefficient of a series-type 12-pulse rectifier, increasing the rectifier's pulse count is a common method. Existing technologies use a series-parallel hybrid pulse multiplier circuit on the DC side to obtain a 36-pulse rectifier. However, because the auxiliary transformer in the parallel pulse multiplier circuit introduced on the DC side has a large turns ratio between the secondary and primary sides, this results in significant leakage inductance in the transformer, reducing the harmonic suppression effect of the parallel circuit and increasing the manufacturing difficulty of the transformer. Therefore, these problems urgently need to be addressed. Summary of the Invention

[0004] The purpose of this invention is to address the problem in existing 36-pulse rectifiers where the large turns ratio between the secondary and primary sides of the auxiliary transformer in the parallel pulse multiplier circuit introduced on the DC side leads to increased leakage inductance, reduced harmonic suppression effect of the parallel pulse multiplier circuit, and increased transformer manufacturing difficulty. Therefore, this invention provides three different series-type 36-pulse rectifiers with passive current injection circuits on the DC side to solve the aforementioned technical problems.

[0005] First structure:

[0006] A series-type 36-pulse rectifier with a passive current injection circuit on the DC side includes a series-type 12-pulse rectifier and a passive current injection circuit. The passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses. The series-type 12-pulse rectifier includes a phase-shifting transformer, a first diode rectifier bridge, and a second diode rectifier bridge.

[0007] The passive current injection circuit includes a first auxiliary single-phase transformer, a second auxiliary single-phase transformer, a third auxiliary single-phase transformer, a first auxiliary single-phase rectifier bridge, a voltage multiplier rectifier, capacitor C1, and capacitor C2.

[0008] A phase-shifting transformer is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by the phase-shifting transformer are then output to the first diode rectifier bridge and the second diode rectifier bridge, respectively.

[0009] After the positive output terminal of the first diode rectifier bridge is connected to one end of capacitor C1 and the positive output terminal of the voltage multiplier rectifier, it is connected as the positive output terminal of the 36-pulse rectifier and the positive input terminal of the load.

[0010] The negative output terminal of the first diode rectifier bridge is connected to the positive output terminal of the second diode rectifier bridge and the same-name terminal of the primary winding of the first auxiliary single-phase transformer.

[0011] The negative output terminal of the second diode rectifier bridge is connected to one end of capacitor C2 and the positive output terminal of the first auxiliary single-phase rectifier bridge at the same time.

[0012] After the negative output terminal of the first auxiliary single-phase rectifier bridge is connected to the negative output terminal of the voltage multiplier rectifier, it is connected to the negative output terminal of the 36-pulse rectifier and the negative input terminal of the load.

[0013] The opposite-named terminal of the primary winding of the first auxiliary single-phase transformer is simultaneously connected to the opposite-named terminal of the primary winding of the second auxiliary single-phase transformer and the same-named terminal of the primary winding of the third auxiliary single-phase transformer; the same-named and opposite-named terminals of the secondary winding of the first auxiliary single-phase transformer are respectively connected to the two AC input terminals of the first auxiliary single-phase rectifier bridge.

[0014] The primary winding of the second auxiliary single-phase transformer is connected to the other end of capacitor C1, and the secondary winding of the second auxiliary single-phase transformer is connected to the secondary winding of the third auxiliary single-phase transformer.

[0015] The opposite end of the primary winding of the third auxiliary single-phase transformer is connected to the other end of capacitor C2.

[0016] The corresponding terminals of the secondary windings of the second auxiliary single-phase transformer and the third auxiliary single-phase transformer are respectively connected to the two AC input terminals of the voltage multiplier rectifier.

[0017] By setting the turns ratio of the primary and secondary windings of the first, second, and third auxiliary single-phase transformers, the conduction time of the diodes in the voltage multiplier rectifier is made 1 / 3 of the voltage cycle received between the two AC input terminals of the voltage multiplier rectifier, and the conduction time of the diodes in the first auxiliary single-phase rectifier bridge is 2 / 3 of the voltage cycle received between the two AC input terminals of the first auxiliary single-phase rectifier bridge. This allows the first diode rectifier bridge and the second diode rectifier bridge to work simultaneously, and the output currents of the first diode rectifier bridge and the second diode rectifier bridge are both equal-width 3-level stepped DC currents.

[0018] The second structure:

[0019] A series-type 36-pulse rectifier with a passive current injection circuit on the DC side includes a series-type 12-pulse rectifier and a passive current injection circuit. The passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses. The series-type 12-pulse rectifier includes a phase-shifting transformer, a first diode rectifier bridge, and a second diode rectifier bridge.

[0020] The passive current injection circuit includes a first multi-winding auxiliary single-phase transformer, a second multi-winding auxiliary single-phase transformer, a first auxiliary single-phase rectifier bridge, a voltage multiplier rectifier, capacitor C1, and capacitor C2.

[0021] A phase-shifting transformer is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by the phase-shifting transformer are then output to the first diode rectifier bridge and the second diode rectifier bridge, respectively.

[0022] The positive output terminal of the first diode rectifier bridge is connected to one end of capacitor C1 and the negative output terminal of the first auxiliary single-phase rectifier bridge at the same time.

[0023] The negative output terminal of the first diode rectifier bridge is connected to the positive output terminal of the second diode rectifier bridge, the opposite terminal of the primary winding of the first multi-winding auxiliary single-phase transformer, and the same terminal of the primary winding of the second multi-winding auxiliary single-phase transformer.

[0024] After the negative output terminal of the second diode rectifier bridge is connected to one end of capacitor C2 and the negative output terminal of the voltage multiplier rectifier, it is connected to the negative output terminal of the 36-pulse rectifier and the negative terminal of the load.

[0025] The primary winding of the first multi-winding auxiliary single-phase transformer is connected to the other end of capacitor C1.

[0026] The same-name terminal of the secondary winding of the first multi-winding auxiliary single-phase transformer is connected to the first AC input terminal of the first auxiliary single-phase rectifier bridge; the opposite-name terminal of the secondary winding of the first multi-winding auxiliary single-phase transformer is connected to the opposite-name terminal of the secondary winding of the second multi-winding auxiliary single-phase transformer.

[0027] The same-name terminal of the secondary second winding of the first multi-winding auxiliary single-phase transformer is connected to the first AC input terminal of the voltage multiplier rectifier; the opposite-name terminal of the secondary second winding of the first multi-winding auxiliary single-phase transformer is connected to the opposite-name terminal of the secondary second winding of the second multi-winding auxiliary single-phase transformer.

[0028] The opposite end of the primary winding of the second multi-winding auxiliary single-phase transformer is connected to the other end of capacitor C2.

[0029] The same-name terminal of the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer is connected to the second AC input terminal of the first auxiliary single-phase rectifier bridge; the same-name terminal of the second winding of the secondary side of the second multi-winding auxiliary single-phase transformer is connected to the second AC input terminal of the voltage multiplier rectifier.

[0030] After the positive output terminal of the voltage multiplier rectifier of the first auxiliary single-phase rectifier bridge is connected, it is used as the positive output terminal of the 36-pulse rectifier and connected to the positive terminal of the load.

[0031] By setting the turns ratio of the primary and secondary windings of the first multi-winding auxiliary single-phase transformer and the second multi-winding auxiliary single-phase transformer, the conduction time of the diode in the first auxiliary single-phase rectifier bridge is made to be 1 / 2 of the voltage period received between the two AC input terminals of the first auxiliary single-phase rectifier bridge; the conduction time of the diode in the voltage multiplier rectifier is 1 / 6 of the voltage period received between the two AC input terminals of the voltage multiplier rectifier; thus, the first diode rectifier bridge and the second diode rectifier bridge work simultaneously or alternately, and when the first diode rectifier bridge and / or the second diode rectifier bridge are working, the current output by the rectifier bridge is a 4-level stepped DC current with equal width.

[0032] The third structure:

[0033] A series-type 36-pulse rectifier with a passive current injection circuit on the DC side includes a series-type 12-pulse rectifier and a passive current injection circuit. The passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses. The series-type 12-pulse rectifier includes a phase-shifting transformer, a first diode rectifier bridge, and a second diode rectifier bridge.

[0034] The passive current injection circuit includes a phase-shifting transformer, a first diode rectifier bridge, a first auxiliary single-phase transformer, a second auxiliary single-phase transformer, a third auxiliary single-phase transformer, a first auxiliary single-phase rectifier bridge, a voltage multiplier rectifier, capacitor C1, and capacitor C2.

[0035] A phase-shifting transformer is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by the phase-shifting transformer are then output to the first diode rectifier bridge and the second diode rectifier bridge, respectively.

[0036] After the positive output terminal of the first diode rectifier bridge is connected to one end of capacitor C1 and the positive output terminal of the voltage multiplier rectifier, it is connected as the positive output terminal of the 36-pulse rectifier and the positive input terminal of the load.

[0037] The negative output terminal of the first diode rectifier bridge is connected to the positive output terminal of the first auxiliary single-phase rectifier bridge, and the negative output terminal of the first auxiliary single-phase rectifier bridge is connected to the positive output terminal of the first diode rectifier bridge.

[0038] After the negative output terminal of the first diode rectifier bridge is connected to one end of capacitor C2 and the negative output terminal of the voltage multiplier rectifier, it is connected as the negative output terminal of the 36-pulse rectifier and the negative input terminal of the load.

[0039] The opposite-named terminal of the primary winding of the first auxiliary single-phase transformer is connected to the first AC input terminal of the first auxiliary single-phase rectifier bridge, and the same-named terminal of the primary winding, the opposite-named terminal of the secondary winding, and the second AC input terminal of the first auxiliary single-phase rectifier bridge are connected simultaneously.

[0040] The same-name terminal of the secondary winding of the second auxiliary single-phase transformer is connected to the opposite-name terminal of the primary winding of the second auxiliary single-phase transformer and the same-name terminal of the primary winding of the third auxiliary single-phase transformer at the same time.

[0041] The opposite end of the primary winding of the second auxiliary single-phase transformer is connected to the other end of capacitor C1.

[0042] The same-name terminal of the secondary winding of the second auxiliary single-phase transformer is connected to the first AC input terminal of the voltage multiplier rectifier, and the opposite-name terminal of the secondary winding of the second auxiliary single-phase transformer is connected to the opposite-name terminal of the secondary winding of the third auxiliary single-phase transformer; the same-name terminal of the secondary winding of the third auxiliary single-phase transformer is connected to the second AC input terminal of the voltage multiplier rectifier.

[0043] The opposite end of the primary winding of the third auxiliary single-phase transformer is connected to the other end of capacitor C2.

[0044] By setting the turns ratio of the primary and secondary windings of the first, second, and third auxiliary single-phase transformers, the conduction time of the diodes in the first auxiliary single-phase rectifier bridge is made 2 / 3 of the voltage cycle received by the two AC input terminals of the first auxiliary single-phase rectifier bridge, and the conduction time of the diodes in the second auxiliary single-phase rectifier bridge is 1 / 3 of the voltage cycle received by the two AC input terminals of the second auxiliary single-phase rectifier bridge. This allows the first and second diode rectifier bridges to operate simultaneously, and the output current of the first and second diode rectifier bridges is a three-level stepped DC current with equal width.

[0045] The beneficial effects of this invention are:

[0046] Compared to the prior art where the pulse number of a rectifier is increased from 12 to 36 by introducing a series-parallel hybrid pulse multiplier circuit on the DC side of a series-type 12-pulse rectifier, the series-type 36-pulse rectifier with a passive current injection circuit on the DC side of the present invention improves the connection relationship and structure, making the conduction time of the diodes proportional to the period of the voltage they receive, thus greatly reducing the turns ratio of the primary and secondary windings of each auxiliary transformer. Furthermore, the number of diodes in the overall structure of the 36-pulse rectifier is reduced by at least two, further significantly lowering the turns ratio of the primary and secondary windings of the auxiliary transformers, improving harmonic suppression, and simplifying the circuit structure for easier manufacturing. Simultaneously, it solves the problems of high input current harmonic content and large output voltage ripple in existing series-type 12-pulse rectifiers without significantly increasing the complexity of the rectifier or reducing output voltage stability.

[0047] The three types of series-type 36-pulse rectifiers with DC-side passive current injection circuits described in this invention have advantages such as simple circuit structure, high reliability, and low cost. The 36-pulse rectifier with DC-side passive current injection circuit described in this invention only requires adding a passive current injection circuit to the DC side of an existing series-type 12-pulse rectifier to double the pulse number from 12 pulses to 36 pulses, effectively suppressing the input current harmonic content of the series-type 12-pulse rectifier, so that the input current THD of the rectifier can meet the requirements of harmonic standards such as IEEE-519 and most industrial applications.

[0048] The 36-pulse rectifier with a passive current injection circuit on the DC side described in this invention can achieve a 3-fold increase in the number of pulses of the rectifier output voltage without using a multi-phase phase-shifting transformer structure with a more complex manufacturing process and any active switching technology on the grid side.

[0049] The 36-pulse rectifier with a passive current injection circuit on the DC side described in this invention eliminates the need for active or passive filters on the grid side of the rectifier. This avoids the problems of limited harmonic suppression performance of the rectifier when using passive filters and the complexity of control strategies when using active filters. As a result, the rectifier can achieve input-output characteristics with low input current distortion rate and low output voltage pulse coefficient, making it suitable for various medium- and high-voltage high-power applications. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the first structure of the series-type 36-pulse rectifier with a passive current injection circuit on the DC side as described in Specific Implementation 1.

[0051] Figure 2 This is a schematic diagram of the current loop in the passive current injection circuit of the first type of 36-pulse rectifier when it is operating in mode I.

[0052] Figure 3 This is a schematic diagram of the current loop in the passive current injection circuit of the first type of 36-pulse rectifier when it is operating in Mode II.

[0053] Figure 4 This is a schematic diagram of the current loop in the passive current injection circuit of the first type of 36-pulse rectifier when it is operating in Mode III.

[0054] Figure 5 This is a schematic diagram of the second structure of the series-type 36-pulse rectifier with a passive current injection circuit on the DC side, as described in Specific Implementation Method 4.

[0055] Figure 6 This is a schematic diagram of the current loop in the passive current injection circuit of the second type of 36-pulse rectifier when it is operating in mode I.

[0056] Figure 7 This is a schematic diagram of the current loop in the passive current injection circuit of the second type of 36-pulse rectifier when it is operating in Mode II.

[0057] Figure 8 This is a schematic diagram of the current loop in the passive current injection circuit of the second type of 36-pulse rectifier when it is operating in mode III.

[0058] Figure 9 This is a schematic diagram of the current loop in the passive current injection circuit of the second type of 36-pulse rectifier, when it is operating in mode IV.

[0059] Figure 10 This is a schematic diagram of the third structure of the series-type 36-pulse rectifier with a passive current injection circuit on the DC side as described in Specific Implementation Method 7.

[0060] Figure 11 This is a schematic diagram of the current loop in the passive current injection circuit of the third type of 36-pulse rectifier, when it is operating in mode I.

[0061] Figure 12 This is a schematic diagram of the current loop in the passive current injection circuit of the third type of 36-pulse rectifier when it is operating in Mode II.

[0062] Figure 13 This is a schematic diagram of the current loop in the passive current injection circuit of the third type of 36-pulse rectifier when it is operating in Mode III.

[0063] Figures 1 to 13 middle,

[0064] i A i B i C These are the three-phase input currents a, b, and c of phase-shifting transformer 1, respectively.

[0065] u A u B u C The three-phase AC voltage sources a, b, and c, respectively, are input from the power grid to the phase-shifting transformer 1;

[0066] i a1 i b1 i c1 These are the three-phase currents a, b, and c input to the first diode rectifier bridge 2, respectively.

[0067] i a2 i b2 i c2 These are the three-phase currents a, b, and c input to the second diode rectifier bridge 3, respectively.

[0068] i c1 i c2 These are the currents flowing through capacitor C1 and capacitor C2, respectively;

[0069] i c3 i c4 These are the currents flowing through capacitor C3 and capacitor C4, respectively;

[0070] i d1 This is the current output from the positive terminal of the first diode rectifier bridge 2;

[0071] i d2 This is the current input to the negative terminal of the second diode rectifier bridge 3;

[0072] i d The current input to the positive terminal of the load;

[0073] Figures 1 to 4 middle,

[0074] u p This refers to the voltage across the primary winding of the first auxiliary single-phase transformer 4.

[0075] u s This refers to the voltage across the secondary winding of the first auxiliary single-phase transformer 4.

[0076] u p1 This refers to the voltage across the primary winding of the second auxiliary single-phase transformer 5.

[0077] u s1 This refers to the voltage across the secondary winding of the second auxiliary single-phase transformer 5.

[0078] u p2 This refers to the voltage across the primary winding of the third auxiliary single-phase transformer 6.

[0079] u s2 This refers to the voltage across the secondary winding of the third auxiliary single-phase transformer 6.

[0080] i s1 The current flowing through the first auxiliary single-phase rectifier bridge 7;

[0081] i s2 This is the current flowing into the voltage multiplier rectifier 8;

[0082] i s The current flowing out of the voltage multiplier rectifier 8;

[0083] in, Figures 5 to 9 middle,

[0084] u p1 The voltage across the primary winding of the first multi-winding auxiliary single-phase transformer 4;

[0085] u s1 The voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4; u s2 The voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4; u p2 The voltage across the primary winding of the second multi-winding auxiliary single-phase transformer 5;

[0086] u s3 The voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5; u s4 i is the voltage across the secondary winding of the second multi-winding auxiliary single-phase transformer 5; s1 The current flowing through the first auxiliary single-phase rectifier bridge 6;

[0087] i s2 The current flowing into the voltage multiplier rectifier 7;

[0088] i s The current flowing out of the voltage multiplier rectifier 7;

[0089] in, Figures 10 to 13 middle,

[0090] u p1 This refers to the voltage across the primary winding of the first auxiliary single-phase transformer 4.

[0091] u s1 This refers to the voltage across the secondary winding of the first auxiliary single-phase transformer 4.

[0092] u p2 This refers to the voltage across the primary winding of the second auxiliary single-phase transformer 5.

[0093] u s2 This refers to the voltage across the secondary winding of the second auxiliary single-phase transformer 5.

[0094] u p3 This refers to the voltage across the primary winding of the third auxiliary single-phase transformer 6.

[0095] u s3 This refers to the voltage across the secondary winding of the third auxiliary single-phase transformer 6.

[0096] i s1 The current flowing out of the first auxiliary single-phase rectifier bridge 7;

[0097] i s2 This is the current flowing into the voltage multiplier rectifier 8;

[0098] i s The current flowing out of the voltage multiplier rectifier 8. Detailed Implementation

[0099] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0100] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0101] This invention provides three structures of a series-type 36-pulse rectifier with a passive current injection circuit on the DC side, and the three structures are respectively described in [reference 1]. Figure 1 , Figure 5 and Figure 10The first type of 36-pulse rectifier is described in specific embodiments one to three; the second type of 36-pulse rectifier is described in specific embodiments four to six; and the third type of 36-pulse rectifier is described in specific embodiments seven to nine, as detailed below:

[0102] Specific Implementation Method 1: The following is combined with... Figure 1 This embodiment describes a series-type 36-pulse rectifier with a passive current injection circuit on the DC side, comprising a series-type 12-pulse rectifier and a passive current injection circuit. The passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses. The series-type 12-pulse rectifier includes a phase-shifting transformer 1, a first diode rectifier bridge 2, and a second diode rectifier bridge 3.

[0103] The passive current injection circuit includes a first auxiliary single-phase transformer 4, a second auxiliary single-phase transformer 5, a third auxiliary single-phase transformer 6, a first auxiliary single-phase rectifier bridge 7, a voltage multiplier rectifier 8, capacitor C1, and capacitor C2.

[0104] Phase-shifting transformer 1 is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by phase-shifting transformer 1 are output to the first diode rectifier bridge 2 and the second diode rectifier bridge 3, respectively.

[0105] After the positive output terminal of the first diode rectifier bridge 2 is connected to one end of the capacitor C1 and the positive output terminal of the voltage multiplier rectifier 8, it is connected to the positive output terminal of the 36-pulse rectifier and the positive input terminal of the load 9.

[0106] The negative output terminal of the first diode rectifier bridge 2 is simultaneously connected to the positive output terminal of the second diode rectifier bridge 3 and the same-name terminal of the primary winding of the first auxiliary single-phase transformer 4.

[0107] The negative output terminal of the second diode rectifier bridge 3 is connected to one end of capacitor C2 and the positive output terminal of the first auxiliary single-phase rectifier bridge 7 at the same time.

[0108] After the negative output terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the negative output terminal of the voltage multiplier rectifier 8, it is connected to the negative output terminal of the 36-pulse rectifier and the negative input terminal of the load 9.

[0109] The opposite-named terminal of the primary winding of the first auxiliary single-phase transformer 4 is simultaneously connected to the opposite-named terminal of the primary winding of the second auxiliary single-phase transformer 5 and the same-named terminal of the primary winding of the third auxiliary single-phase transformer 6; the same-named and opposite-named terminals of the secondary winding of the first auxiliary single-phase transformer 4 are respectively connected to the two AC input terminals of the first auxiliary single-phase rectifier bridge 7.

[0110] The primary winding of the second auxiliary single-phase transformer 5 is connected to the other end of capacitor C1, and the secondary winding of the second auxiliary single-phase transformer 5 is connected to the secondary winding of the third auxiliary single-phase transformer 6.

[0111] The opposite end of the primary winding of the third auxiliary single-phase transformer 6 is connected to the other end of capacitor C2.

[0112] The corresponding terminals of the secondary windings of the second auxiliary single-phase transformer 5 and the third auxiliary single-phase transformer 6 are respectively connected to the two AC input terminals of the voltage multiplier rectifier 8.

[0113] By setting the turns ratio of the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6, the conduction time of the diodes in the voltage multiplier rectifier 8 is made 1 / 3 of the voltage cycle received between the two AC input terminals of the voltage multiplier rectifier 8, and the conduction time of the diodes in the first auxiliary single-phase rectifier bridge 7 is 2 / 3 of the voltage cycle received between the two AC input terminals of the first auxiliary single-phase rectifier bridge 7. This allows the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to work simultaneously, and the output currents of the first diode rectifier bridge 2 and the second diode rectifier bridge 3 are both equal-width 3-level stepped DC currents.

[0114] In this embodiment, based on the specific structure of the 36-pulse rectifier of the first structure, by setting the turns ratio of the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6, the conduction time of the diode in the voltage multiplier rectifier 8 is 1 / 3 of the voltage period received between the two AC input terminals of the voltage multiplier rectifier 8, and the conduction time of the diode in the first auxiliary single-phase rectifier bridge 7 is 2 / 3 of the voltage period received between the two AC input terminals of the first auxiliary single-phase rectifier bridge 7. When diode rectifier bridge 2 and diode rectifier bridge 3 operate simultaneously, and their output currents are both 3-level DC currents of equal width, the passive current injection circuit precisely multiplies the pulse number of the series-type 12-pulse rectifier to 36 pulses, effectively reducing the harmonic content of the rectifier's input current and the pulsation of the output voltage. Based on this improvement in circuit structure, the conduction time of the diode is proportional to the period of the voltage it receives, which greatly reduces the turns ratio of the primary and secondary windings of each auxiliary transformer; the circuit structure is simpler and more conducive to manufacturing.

[0115] In practical applications, the phase-shifting transformer 1 can be any type of isolated phase-shifting transformer or power electronic phase-shifting transformer that can output phase-shifting angles with a difference of 30°.

[0116] The series-type 36-pulse rectifier with a passive current injection circuit on the DC side described in this embodiment does not require changing the structure of the phase-shifting transformer, adding a series inductor on the input side, or using any active switching devices. It can achieve a 3-fold increase in the rectifier pulse number through modulation by the passive current injection circuit. This invention has the advantages of simple circuit structure, small current injection circuit capacity, low cost, ease of implementation, and high reliability, and has great application value in high-power applications.

[0117] Specific Implementation Method Two: The following is combined with... Figure 1 This embodiment further explains embodiment one. The first auxiliary single-phase rectifier bridge 7 includes diode D. p1 Diode D p2 Diode D p3 and diode D p4 ,

[0118] The first auxiliary single-phase rectifier bridge 7 includes diode D. p1 Diode D p2 Diode D p3 and diode D p4 ,

[0119] Diode D p1 anode and diode D p3 After the cathode is connected, the first AC input terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the opposite terminal of the secondary winding of the first auxiliary single-phase transformer 4.

[0120] Diode D p2 anode and diode D p4 After the cathode is connected, the second AC input terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the same-name terminal of the secondary winding of the first auxiliary single-phase transformer 4.

[0121] Diode D p1 Cathode and diode D p2 After the cathode is connected, it serves as the positive output terminal of the first auxiliary single-phase rectifier bridge 7;

[0122] Diode D p3 anode and diode D p4 After the anode is connected, it serves as the negative output terminal of the first auxiliary single-phase rectifier bridge 7;

[0123] The voltage multiplier rectifier 8 includes diode D m1 diode D m2 Capacitors C3 and C4;

[0124] Diode D m1 anode and diode D m2After the cathode is connected, it is connected to the same-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 as the first AC input terminal of the voltage multiplier rectifier 8.

[0125] After one end of capacitor C3 and one end of capacitor C4 are connected, they serve as the second AC input terminal of voltage multiplier rectifier 8 and are connected to the same-name terminal of the secondary winding of the third auxiliary single-phase transformer 6.

[0126] Diode D m1 After the cathode is connected to the other end of capacitor C3, it serves as the positive output terminal of voltage multiplier rectifier 8.

[0127] Diode D m2 After the anode of the capacitor is connected to the other end of the capacitor C4, it serves as the negative output terminal of the voltage multiplier rectifier 8.

[0128] In this embodiment, a resistor with an appropriate resistance value can be connected in parallel across capacitors C3 and C4 to achieve voltage equalization.

[0129] Specific Implementation Method Three: The following is combined with... Figures 2 to 4 This embodiment further explains embodiment two. The passive current injection circuit includes three operating modes, specifically:

[0130] Working Mode I: See Figure 2 , when |u s |<(u d1 +u d2 -u d ), u s1 -u s2 <(u d1 +u d2 -u s -u c4 ) and u s2 -u s1 <(u d1 +u d2 +u s +u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 diode D p2 diode D p3 and diode D p4 Forward conduction, diode D in voltage multiplier rectifier 8 m1 and diode D m2 When reverse biased and cut off, the voltages across capacitors C3 and C4 remain constant.

[0131] Both the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are in a non-operating state. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the two ends of the load 9.

[0132] u p This is the voltage across the primary winding of the first auxiliary single-phase transformer 4;

[0133] u s This is the voltage across the secondary winding of the first auxiliary single-phase transformer 4;

[0134] u d The voltage across load 9;

[0135] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0136] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0137] u s1 This is the voltage output from the secondary winding of the second auxiliary single-phase transformer 5;

[0138] u s2 This is the voltage output from the secondary winding of the third auxiliary single-phase transformer 6;

[0139] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8;

[0140] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8;

[0141] Working Mode II: See Figure 3 , when -u s >(u d1 +u d2 -u d ), u s1 -u s2 >(u d1 +u d2 -u s -u c4 ) and u s2 -u s1 <(u d1 +u d2 +u s +u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p2 and diode D p3 Reverse bias cutoff, diode Dp1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 8 m1 Forward conduction, diode D m2 Reverse bias cutoff; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 9; among which,

[0142] u p This is the voltage across the primary winding of the first auxiliary single-phase transformer 4;

[0143] u s This is the voltage across the secondary winding of the first auxiliary single-phase transformer 4;

[0144] u p1 This is the voltage output from the primary winding of the second auxiliary single-phase transformer 5;

[0145] u p2 This is the voltage output from the primary winding of the second auxiliary single-phase transformer 5;

[0146] u s1 This is the voltage output from the secondary winding of the second auxiliary single-phase transformer 5;

[0147] u s2 This is the voltage output from the secondary winding of the third auxiliary single-phase transformer 6;

[0148] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0149] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0150] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8;

[0151] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8;

[0152] Working Mode III: See Figure 4 , when u s >(u d1 +u d2 -u d ), u s1 -u s2 <(u d1 +u d2 -u s -u c4 ) and u s2 -us1 >(u d1 +u d2 +u s +u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; diode D in voltage multiplier rectifier 8 m1 Reverse bias cutoff, diode D m2 Forward conduction; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the two ends of the load 9; among which,

[0153] u s This is the voltage across the secondary winding of the first auxiliary single-phase transformer 4;

[0154] u d The voltage across load 9;

[0155] u s1 This is the voltage output from the secondary winding of the second auxiliary single-phase transformer 5;

[0156] u s2 This is the voltage output from the secondary winding of the third auxiliary single-phase transformer 6;

[0157] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0158] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0159] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8;

[0160] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8.

[0161] In this preferred embodiment, in operating mode II, the current i s2 The current flows sequentially from capacitor C4 through the secondary winding of the third auxiliary single-phase transformer 6 and the secondary winding of the second auxiliary single-phase transformer 5, and then into diode D. m1 diode D m1 The output current is split into two paths. One path flows out from the positive output terminal of the voltage multiplier rectifier 8 and is injected into the load 9. The other path is output through capacitor C3 and injected into the secondary winding of the third auxiliary single-phase transformer 6. The output current i of the voltage multiplier rectifier 8 is...s AC power at 12 times the grid input frequency; i s2 This is the current flowing into the voltage multiplier rectifier 8;

[0162] In operating mode III, the current i s2 Starting with diode D m2 The current flows through the secondary windings of the second auxiliary single-phase transformer 5 and the third auxiliary single-phase transformer 6. The output current of the secondary winding of the third auxiliary single-phase transformer 6 is split into two paths: one path flows out through capacitor C3 and is injected into the load 9; the other path flows out through capacitor C4 and is injected into the secondary winding of the second auxiliary single-phase transformer 5. The output current i of the voltage multiplier rectifier 8... s It provides AC power at 12 times the grid input frequency.

[0163] Specific Implementation Method Four: The following is combined with... Figure 5 This embodiment describes a second type of series-type 36-pulse rectifier with a passive current injection circuit on the DC side. It includes a series-type 12-pulse rectifier and a passive current injection circuit. The passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses. The series-type 12-pulse rectifier includes a phase-shifting transformer 1, a first diode rectifier bridge 2, and a second diode rectifier bridge 3.

[0164] The passive current injection circuit includes a first multi-winding auxiliary single-phase transformer 4, a second multi-winding auxiliary single-phase transformer 5, a first auxiliary single-phase rectifier bridge 6, a voltage multiplier rectifier 7, capacitor C1, and capacitor C2.

[0165] Phase-shifting transformer 1 is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by phase-shifting transformer 1 are sent to the first diode rectifier bridge 2 and the second diode rectifier bridge 3 respectively.

[0166] The positive output terminal of the first diode rectifier bridge 2 is connected to one end of capacitor C1 and the negative output terminal of the first auxiliary single-phase rectifier bridge 6 at the same time.

[0167] The negative output terminal of the first diode rectifier bridge 2 is simultaneously connected to the positive output terminal of the second diode rectifier bridge 3, the opposite terminal of the primary winding of the first multi-winding auxiliary single-phase transformer 4, and the same terminal of the primary winding of the second multi-winding auxiliary single-phase transformer 5.

[0168] After the negative output terminal of the second diode rectifier bridge 3 is connected to one end of capacitor C2 and the negative output terminal of voltage multiplier rectifier 7, it is connected to the negative output terminal of the 36-pulse rectifier and the negative terminal of load 8.

[0169] The primary winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the other end of capacitor C1.

[0170] The same-name terminal of the secondary first winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the first AC input terminal of the first auxiliary single-phase rectifier bridge 6; the opposite-name terminal of the secondary first winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the opposite-name terminal of the secondary first winding of the second multi-winding auxiliary single-phase transformer 5.

[0171] The same-name terminal of the secondary second winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the first AC input terminal of the voltage multiplier rectifier 7; the opposite-name terminal of the secondary second winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the opposite-name terminal of the secondary second winding of the second multi-winding auxiliary single-phase transformer 5.

[0172] The opposite end of the primary winding of the second multi-winding auxiliary single-phase transformer 5 is connected to the other end of capacitor C2.

[0173] The same-name terminal of the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5 is connected to the second AC input terminal of the first auxiliary single-phase rectifier bridge 6; the same-name terminal of the second winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5 is connected to the second AC input terminal of the voltage multiplier rectifier 7.

[0174] After the positive output terminal of the voltage multiplier rectifier 7 of the first auxiliary single-phase rectifier bridge 6 is connected, it is connected to the positive output terminal of the 36-pulse rectifier and the positive terminal of the load 8.

[0175] By setting the turns ratio of the primary and secondary windings of the first multi-winding auxiliary single-phase transformer 4 and the second multi-winding auxiliary single-phase transformer 5, the conduction time of the diodes in the first auxiliary single-phase rectifier bridge 6 is made to be 1 / 2 of the voltage period received between the two AC input terminals of the first auxiliary single-phase rectifier bridge 6; the conduction time of the diodes in the voltage multiplier rectifier 7 is made to be 1 / 6 of the voltage period received between the two AC input terminals of the voltage multiplier rectifier 7; thereby enabling the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to work simultaneously or alternately, and when the first diode rectifier bridge 2 and / or the second diode rectifier bridge 3 are working, the current output by the rectifier bridge is a 4-level stepped DC current with equal width.

[0176] In this embodiment, based on the specific structure of the 36-pulse rectifier of the second type, by setting the turns ratio of the primary and secondary windings of the first multi-winding auxiliary single-phase transformer 4 and the second multi-winding auxiliary single-phase transformer 5, the conduction time of the diode in the first auxiliary single-phase rectifier bridge 6 is 1 / 2 of the voltage period received between the two AC input terminals of the first auxiliary single-phase rectifier bridge 6; the conduction time of the diode in the voltage multiplier rectifier 7 is 1 / 6 of the voltage period received between the two AC input terminals of the voltage multiplier rectifier 7; the first diode... When rectifier bridge 2 and second diode rectifier bridge 3 operate simultaneously or alternately, and their output current is a 4-level DC current of equal width, the passive current injection circuit precisely multiplies the pulse number of the series-type 12-pulse rectifier to 36 pulses, effectively reducing the harmonic content of the rectifier's input current and the pulsation of the output voltage. Based on this improvement in circuit structure, the conduction time of the diode is proportional to the period of the voltage it receives, which greatly reduces the turns ratio of the primary and secondary windings of each auxiliary transformer; the circuit structure is simpler and more conducive to manufacturing.

[0177] In practical applications, the phase-shifting transformer 1 can be any type of isolated phase-shifting transformer or power electronic phase-shifting transformer that can output phase-shifting angles with a difference of 30°.

[0178] The series-type 36-pulse rectifier with a passive current injection circuit on the DC side described in this embodiment does not require changing the structure of the phase-shifting transformer, adding a series inductor on the input side, or using any active switching devices. It can achieve a 3-fold increase in the rectifier pulse number through modulation by the passive current injection circuit. This invention has the advantages of simple circuit structure, small current injection circuit capacity, low cost, ease of implementation, and high reliability, and has great application value in high-power applications.

[0179] Specific Implementation Method Five: The following is combined with... Figure 5 This embodiment further explains embodiment four, and the first auxiliary single-phase rectifier bridge 6 includes diode D. p1 diode D p2 diode D p3 and diode D p4 ;

[0180] Diode D p1 anode and diode D p2 After the anode is connected, it serves as the negative output terminal of the first auxiliary single-phase rectifier bridge 6;

[0181] Diode D p2 cathode and diode D p4 After the anode is connected, it serves as the first AC input terminal of the first auxiliary single-phase rectifier bridge 6; diode D p1 Cathode and diode Dp3 After the anode is connected, it serves as the second AC input terminal of the first auxiliary single-phase rectifier bridge 6;

[0182] Diode D p3 Cathode and diode D p4 After the cathode is connected, it serves as the positive output terminal of the first auxiliary single-phase rectifier bridge 6;

[0183] The voltage multiplier rectifier 7 includes diode D. m1 diode D m2 Capacitors C3 and C4;

[0184] Diode D m1 anode and diode D m2 After the cathode is connected, it is connected as the first AC input terminal of the voltage multiplier rectifier 7;

[0185] One end of capacitor C3 is connected to one end of capacitor C4, which serves as the second AC input terminal of voltage multiplier rectifier 7;

[0186] Diode D m1 After the cathode is connected to the other end of capacitor C3, it serves as the positive output terminal of voltage multiplier rectifier 7.

[0187] Diode D m2 After the anode of the capacitor is connected to the other end of the capacitor C4, it serves as the negative output terminal of the voltage multiplier rectifier 7.

[0188] In this embodiment, a resistor with an appropriate resistance value can be connected in parallel across capacitors C3 and C4 to achieve voltage equalization.

[0189] Specific Implementation Method Six: The following is combined with... Figures 6 to 9 This embodiment further explains embodiment four. The passive current injection circuit includes four operating modes, specifically:

[0190] Working Mode I: See Figure 6 , when u s3 -u s1 <(u d1 +u d2 -u d ) and u s2 -u s4 <(u d1 +u d2 +u s1 -u s3 -u c4 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p2 and diode D p3 Reverse bias cutoff, diode D p1 and diode Dp4 Forward conduction; diode D in voltage multiplier rectifier 7 m1 diode D m2 With reverse bias cutoff, the voltages across capacitors C3 and C4 remain constant. The primary winding and the first secondary winding of the first multi-winding auxiliary single-phase transformer 4 are both operational, while the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 is inactive. Similarly, the primary winding and the first secondary winding of the second multi-winding auxiliary single-phase transformer 5 are both operational, while the second secondary winding of the second multi-winding auxiliary single-phase transformer 5 is inactive. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 8.

[0191] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0192] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0193] u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0194] u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0195] u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0196] u s4 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0197] u d This is the voltage across load 8;

[0198] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 7;

[0199] Working Mode II: See Figure 7 , when u s3 -u s1 <(u d1 +u d2 -u d ) and u s2 -u s4 >(u d1 +u d2 +u s1 -u s3 -u c4 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p2 and diode Dp3 Reverse bias cutoff, diode D p1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 7 m1 Forward conduction, diode D m2 Reverse bias cutoff; the primary winding, secondary first winding, and secondary second winding of the first multi-winding auxiliary single-phase transformer 4 are all in working condition, as are the primary winding, secondary first winding, and secondary second winding of the second multi-winding auxiliary single-phase transformer 5. At this time, the first diode rectifier bridge 2 supplies power to both ends of the load 8; among which,

[0200] u d This is the voltage across load 8;

[0201] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0202] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0203] u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0204] u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0205] u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0206] u s4 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0207] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 7;

[0208] Working Mode III: See Figure 8 , when u s1 -u s3 <(u d1 +u d2 -u d ) and u s4 -u s2 <(u d1 +u d2 -u s1 +u s3 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p1 and diode D p4 Reverse bias cutoff, diode Dp2 and diode D p3 Forward conduction; diode D in voltage multiplier rectifier 7 m1 diode D m2 With reverse bias cutoff, the voltages across capacitors C3 and C4 remain constant. The primary winding and the first secondary winding of the first multi-winding auxiliary single-phase transformer 4 are both operational, while the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 is inactive. Similarly, the primary winding and the first secondary winding of the second multi-winding auxiliary single-phase transformer 5 are both operational, while the second secondary winding of the second multi-winding auxiliary single-phase transformer 5 is inactive. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 8.

[0209] u d This is the voltage across load 8;

[0210] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0211] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0212] u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0213] u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0214] u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0215] u s4 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0216] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 7;

[0217] Working Mode IV: See Figure 9 , when u s1 -u s3 <(u d1 +u d2 -u d ) and u s4 -u s2 >(u d1 +u d2 -u s1 +u s3 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 6p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; diode D in voltage multiplier rectifier 7 m1 Reverse bias cutoff, diode D m2 In forward conduction, the primary winding, the first secondary winding, and the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 are all in operation, as are the primary winding, the first secondary winding, and the second secondary winding of the second multi-winding auxiliary single-phase transformer 5. At this time, the second diode rectifier bridge 3 supplies power to both ends of the load 8; whereby...

[0218] u d This is the voltage across load 8;

[0219] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0220] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0221] u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0222] u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4.

[0223] u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0224] u s4 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5.

[0225] u c3 This is the voltage across capacitor C3 in voltage multiplier rectifier 7.

[0226] In this embodiment, in operating mode II, the current i s2 The current flows sequentially from capacitor C4 through the secondary second winding of the second multi-winding auxiliary single-phase transformer 5 and the secondary second winding of the first multi-winding auxiliary single-phase transformer 4. The output current from the secondary second winding of the first multi-winding auxiliary single-phase transformer 4 is split into two paths, one of which passes through diode D. m1 The current then flows out from the positive output terminal of the voltage multiplier rectifier 7 and is injected into the load 8. Another path flows out through capacitor C3 and is injected into the secondary winding of the second multi-winding auxiliary single-phase transformer 5. The output current i of the voltage multiplier rectifier 7... s AC power at 12 times the grid input frequency; i s2The current flowing into the overvoltage multiplier rectifier 7;

[0227] In operating mode IV, the current i s2 Starting with diode D m2 The current flows through the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 and the second secondary winding of the second multi-winding auxiliary single-phase transformer 5. The output current of the second secondary winding of the second multi-winding auxiliary single-phase transformer 5 is split into two paths: one path flows out through capacitor C3 and is injected into the load 8, and the other path flows out through capacitor C4 and is injected into the second secondary winding of the first multi-winding auxiliary single-phase transformer 4. The output current i of the voltage multiplier rectifier 7... s It provides AC power at 12 times the grid input frequency.

[0228] Specific Implementation Method Seven: The following is combined with... Figure 10 This embodiment describes a third type of series-type 36-pulse rectifier with a passive current injection circuit on the DC side. It includes a series-type 12-pulse rectifier and a passive current injection circuit. The passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses. The series-type 12-pulse rectifier includes a phase-shifting transformer 1, a first diode rectifier bridge 2, and a second diode rectifier bridge 3.

[0229] The passive current injection circuit includes a phase-shifting transformer 1, a first diode rectifier bridge 2, a first diode rectifier bridge 3, a first auxiliary single-phase transformer 4, a second auxiliary single-phase transformer 5, a third auxiliary single-phase transformer 6, a first auxiliary single-phase rectifier bridge 7, a voltage multiplier rectifier 8, capacitor C1, and capacitor C2.

[0230] Phase-shifting transformer 1 is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by phase-shifting transformer 1 are sent to the first diode rectifier bridge 2 and the second diode rectifier bridge 3 respectively.

[0231] After the positive output terminal of the first diode rectifier bridge 2 is connected to one end of the capacitor C1 and the positive output terminal of the voltage multiplier rectifier 8, it is connected to the positive output terminal of the 36-pulse rectifier and the positive input terminal of the load 9.

[0232] The negative output terminal of the first diode rectifier bridge 2 is connected to the positive output terminal of the first auxiliary single-phase rectifier bridge 7, and the negative output terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the positive output terminal of the first diode rectifier bridge 3.

[0233] After the negative output terminal of the first diode rectifier bridge 3 is connected to one end of capacitor C2 and the negative output terminal of voltage multiplier rectifier 8, it is connected to the negative output terminal of the 36-pulse rectifier and the negative input terminal of load 9.

[0234] The opposite-named end of the primary winding of the first auxiliary single-phase transformer 4 is connected to the first AC input terminal of the first auxiliary single-phase rectifier bridge 7, and the same-named end of the primary winding of the first auxiliary single-phase transformer 4, the opposite-named end of the secondary winding, and the second AC input terminal of the first auxiliary single-phase rectifier bridge 7 are connected simultaneously.

[0235] The same-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 is connected to the opposite-name terminal of the primary winding of the second auxiliary single-phase transformer 5 and the same-name terminal of the primary winding of the third auxiliary single-phase transformer 6 at the same time.

[0236] The opposite end of the primary winding of the second auxiliary single-phase transformer 5 is connected to the other end of capacitor C1.

[0237] The same-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 is connected to the first AC input terminal of the voltage multiplier rectifier 8, and the opposite-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 is connected to the opposite-name terminal of the secondary winding of the third auxiliary single-phase transformer 6; the same-name terminal of the secondary winding of the third auxiliary single-phase transformer 6 is connected to the second AC input terminal of the voltage multiplier rectifier 8.

[0238] The opposite end of the primary winding of the third auxiliary single-phase transformer 6 is connected to the other end of capacitor C2.

[0239] By setting the turns ratio of the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6, the conduction time of the diode in the first auxiliary single-phase rectifier bridge 7 is 2 / 3 of the voltage cycle received by the two AC input terminals of the first auxiliary single-phase rectifier bridge 7, and the conduction time of the diode in the second auxiliary single-phase rectifier bridge 8 is 1 / 3 of the voltage cycle received by the two AC input terminals of the second auxiliary single-phase rectifier bridge 8. This allows the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to work simultaneously, and the output current of the first diode rectifier bridge 2 and the second diode rectifier bridge 3 is a three-level stepped DC current with equal width.

[0240] In this embodiment, based on the specific structure of the third type of 36-pulse rectifier, by setting the turns ratio of the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6, the conduction time of the diode in the first auxiliary single-phase rectifier bridge 7 is 2 / 3 of the voltage period received by the two AC input terminals of the first auxiliary single-phase rectifier bridge 7, and the conduction time of the diode in the second auxiliary single-phase rectifier bridge 8 is 1 / 3 of the voltage period received by the two AC input terminals of the second auxiliary single-phase rectifier bridge 8. This allows the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to operate simultaneously, and when their output current is a 3-level DC current of equal width, the passive current injection circuit precisely multiplies the pulse number of the series-type 12-pulse rectifier to 36 pulses, effectively reducing the harmonic content of the rectifier's input current and the pulsation of the output voltage. Based on this improvement in circuit structure, the conduction time of the diode is proportional to the period of the voltage it receives, which greatly reduces the turns ratio of the primary and secondary windings of each auxiliary transformer; the circuit structure is simpler and more conducive to manufacturing.

[0241] In practical applications, the phase-shifting transformer 1 can be any type of isolated phase-shifting transformer or power electronic phase-shifting transformer that can output phase-shifting angles with a difference of 30°.

[0242] The series-type 36-pulse rectifier with a passive current injection circuit on the DC side described in this embodiment does not require changing the structure of the phase-shifting transformer, adding a series inductor on the input side, or using any active switching devices. It can achieve a 3-fold increase in the rectifier pulse number through modulation by the passive current injection circuit. This invention has the advantages of simple circuit structure, small current injection circuit capacity, low cost, ease of implementation, and high reliability, and has great application value in high-power applications.

[0243] Detailed Implementation Method Eight: The following is combined with... Figure 10 This embodiment describes the implementation method, and further explains the implementation method seven.

[0244] The first auxiliary single-phase rectifier bridge 7 includes diode D. p1 diode D p2 diode D p3 and diode D p4 ;

[0245] Diode D p1 anode and diode D p2 After the cathode is connected, it serves as the first AC input terminal of the first auxiliary single-phase rectifier bridge 7;

[0246] Diode D p3 anode and diode D p4After the cathode is connected, it serves as the second AC input terminal of the first auxiliary single-phase rectifier bridge 7;

[0247] Diode D p1 Cathode and diode D p3 After the cathode is connected, it serves as the positive output terminal of the first auxiliary single-phase rectifier bridge 7;

[0248] Diode D p2 Cathode and diode D p4 After the cathode is connected, it serves as the negative output terminal of the first auxiliary single-phase rectifier bridge 7;

[0249] The voltage multiplier rectifier 8 includes a diode D. m1 diode D m2 Capacitors C3 and C4;

[0250] Diode D m1 anode and diode D m2 After the cathode is connected, it serves as the first AC input terminal of the voltage multiplier rectifier 8;

[0251] One end of capacitor C3 is connected to one end of capacitor C4, which serves as the second AC input terminal of voltage multiplier rectifier 8;

[0252] Diode D m1 After the cathode is connected to the other end of capacitor C3, it serves as the positive output terminal of voltage multiplier rectifier 8.

[0253] Diode D m2 After the anode of the capacitor is connected to the other end of the capacitor C4, it serves as the negative output terminal of the voltage multiplier rectifier 8.

[0254] In this embodiment, a resistor with an appropriate resistance value can be connected in parallel across capacitors C3 and C4 to achieve voltage equalization.

[0255] Specific Implementation Method Nine: The following is combined with... Figures 11 to 13 This embodiment further explains embodiment eight. The passive current injection circuit includes three operating modes, specifically:

[0256] Working Mode I: See Figure 11 , when |u p1 |<(u d1 +u d2 -u d ), u s2 -u s3 <(u d1 +u d2 +u p1 -u c4 ) and u s3 -u s2 <(ud1 +u d2 -u p1 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 diode D p2 diode D p3 and diode D p4 Forward conduction, diode D in voltage multiplier rectifier 8 m1 diode D m2 With reverse bias cutoff, the voltages across capacitors C3 and C4 remain constant; the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in a non-operating state. At this time, the first diode rectifier bridge 2 and the first diode rectifier bridge 3 jointly supply power to the load 9; among which,

[0257] u d The voltage across load 9;

[0258] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0259] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0260] u s2 This is the voltage output across the secondary winding of the second auxiliary single-phase transformer 5;

[0261] u s3 This is the voltage output across the secondary winding of the third auxiliary single-phase transformer 6;

[0262] u p1 This is the voltage output across the primary winding of the first auxiliary single-phase transformer 4;

[0263] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8;

[0264] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8;

[0265] Working Mode II: See Figure 12 , when u p1 >(u d1 +u d2 -u d ), u s2 -u s3 >(u d1 +u d2 +u p1 -u c4 ) and u s3 -u s2 <(ud1 +u d2 -u p1 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; Voltage multiplier rectifier 8D m1 Forward conduction, diode D m2 Reverse bias cutoff; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the first diode rectifier bridge 3 jointly supply power to the two ends of the load 9; among which,

[0266] u d The voltage across load 9;

[0267] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0268] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0269] u s2 This is the voltage output across the secondary winding of the second auxiliary single-phase transformer 5;

[0270] u s3 This is the voltage output across the secondary winding of the third auxiliary single-phase transformer 6;

[0271] u p1 This is the voltage output across the primary winding of the first auxiliary single-phase transformer 4;

[0272] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8;

[0273] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8;

[0274] Working Mode III: See Figure 13 , when -u p1 >(u d1 +u d2 -u d ), u s2 -u s3 <(u d1 +u d2 +u p1 -u c4 ) and u s3 -u s2 >(ud1 +u d2 -u p1 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p2 and diode D p3 Reverse bias cutoff, diode D p1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 8 m1 Reverse bias cutoff, diode D m2 Forward conduction; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the first diode rectifier bridge 3 jointly supply power to the two ends of the load 9; among which,

[0275] u d The voltage across load 9;

[0276] u d1 This is the voltage output of the first diode rectifier bridge 2;

[0277] u d2 This is the voltage output of the second diode rectifier bridge 3;

[0278] u s2 This is the voltage output across the secondary winding of the second auxiliary single-phase transformer 5;

[0279] u s3 This is the voltage output across the secondary winding of the third auxiliary single-phase transformer 6;

[0280] u p1 This is the voltage output across the primary winding of the first auxiliary single-phase transformer 4;

[0281] u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8;

[0282] u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8.

[0283] In this embodiment, in operating mode II, the current i s2 The current flows sequentially through capacitor C4, the secondary winding of the third auxiliary single-phase transformer 6, and the secondary winding of the second auxiliary single-phase transformer 5. The output current of the secondary winding of the second auxiliary single-phase transformer 5 is split into two paths, one of which passes through diode D. m1 The current flows out from the positive output terminal of the voltage multiplier rectifier 8 and is injected into the load 9. Another path flows through capacitor C3 and into the secondary winding of the third auxiliary single-phase transformer 6. The output current i of the voltage multiplier rectifier 8... sIt provides AC power at 12 times the grid input frequency;

[0284] In operating mode III, the current i s2 Starting with diode D m2 The current flows through the secondary windings of the second auxiliary single-phase transformer 5 and the third auxiliary single-phase transformer 6. The output current of the secondary winding of the third auxiliary single-phase transformer 6 is divided into two paths. One path flows through capacitor C3 and exits from the positive output terminal of the voltage multiplier rectifier 8 before being injected into the load 9. The other path flows through capacitor C4 and is injected into the secondary winding of the second auxiliary single-phase transformer 5. The output current i of the voltage multiplier rectifier 8... s It provides AC power at 12 times the grid input frequency.

[0285] Principle Analysis:

[0286] The present invention discloses three types of series-type 36-pulse rectifiers with passive current injection circuits on the DC side. All of these are achieved by adding a passive current injection circuit to the DC side of a conventional series-type 12-pulse rectifier. Through reasonable design of the primary and secondary turns ratio of the auxiliary single-phase transformer, the conduction time of the diodes in the auxiliary single-phase rectifier bridge is proportional to the period of its input voltage, and the conduction time of the diodes in the voltage multiplier rectifier is proportional to the period of the voltage received between the two AC input terminals of the voltage multiplier rectifier. This allows the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to operate simultaneously or alternately. When the first diode rectifier bridge 2 and / or the second diode rectifier bridge 3 are operating, the current output by the rectifier bridge is a "multi-level stepped DC current with equal width." Then, based on the AC / DC side current relationship and the DC side voltage relationship, the pulse number of the rectifier is increased from 12 to 36, effectively suppressing the harmonic content of the input current and the pulsation of the output voltage.

[0287] Furthermore, compared with the existing 36-pulse rectifier, the series-type 36-pulse rectifier with passive current injection circuit on the DC side described in this invention, through improvements in connection relationship and structure, makes the conduction time of the diodes proportional to the period of the voltage they receive, thus greatly reducing the turns ratio of the primary and secondary windings of each auxiliary transformer; the number of diodes in the overall structure of the 36-pulse rectifier is also reduced by at least two, further significantly reducing the turns ratio of the primary and secondary windings of the auxiliary transformers, improving the harmonic suppression effect, and making the circuit structure simpler and more conducive to manufacturing. At the same time, it solves the problems of high input current harmonic content and large output voltage ripple of the existing series-type 12-pulse rectifier without increasing the complexity of the rectifier or reducing the stability of the output voltage.

[0288] The rectifier bridge output current of this invention is an N-level stepped DC current with equal width, where N is an integer greater than 2. "N-level stepped DC current" means that there are N different current states in one cycle, and the current value output by the rectifier bridge is constant under the same current state. "Equal width" means that the duration of each current state is the same.

[0289] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A series-type 36-pulse rectifier with a passive current injection circuit on the DC side, comprising a series-type 12-pulse rectifier and a passive current injection circuit, wherein the passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses; the series-type 12-pulse rectifier comprises a phase-shifting transformer 1, a first diode rectifier bridge 2, and a second diode rectifier bridge 3; characterized in that, The passive current injection circuit includes a first auxiliary single-phase transformer 4, a second auxiliary single-phase transformer 5, a third auxiliary single-phase transformer 6, a first auxiliary single-phase rectifier bridge 7, a voltage multiplier rectifier 8, capacitor C1, and capacitor C2. Phase-shifting transformer 1 is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by phase-shifting transformer 1 are output to the first diode rectifier bridge 2 and the second diode rectifier bridge 3, respectively. After the positive output terminal of the first diode rectifier bridge 2 is connected to one end of the capacitor C1 and the positive output terminal of the voltage multiplier rectifier 8, it is connected to the positive output terminal of the 36-pulse rectifier and the positive input terminal of the load 9. The negative output terminal of the first diode rectifier bridge 2 is simultaneously connected to the positive output terminal of the second diode rectifier bridge 3 and the same-name terminal of the primary winding of the first auxiliary single-phase transformer 4. The negative output terminal of the second diode rectifier bridge 3 is connected to one end of capacitor C2 and the positive output terminal of the first auxiliary single-phase rectifier bridge 7 at the same time. After the negative output terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the negative output terminal of the voltage multiplier rectifier 8, it is connected to the negative output terminal of the 36-pulse rectifier and the negative input terminal of the load 9. The opposite-named terminal of the primary winding of the first auxiliary single-phase transformer 4 is simultaneously connected to the opposite-named terminal of the primary winding of the second auxiliary single-phase transformer 5 and the same-named terminal of the primary winding of the third auxiliary single-phase transformer 6; the same-named and opposite-named terminals of the secondary winding of the first auxiliary single-phase transformer 4 are respectively connected to the two AC input terminals of the first auxiliary single-phase rectifier bridge 7. The primary winding of the second auxiliary single-phase transformer 5 is connected to the other end of capacitor C1, and the secondary winding of the second auxiliary single-phase transformer 5 is connected to the secondary winding of the third auxiliary single-phase transformer 6. The opposite end of the primary winding of the third auxiliary single-phase transformer 6 is connected to the other end of capacitor C2. The corresponding terminals of the secondary windings of the second auxiliary single-phase transformer 5 and the third auxiliary single-phase transformer 6 are respectively connected to the two AC input terminals of the voltage multiplier rectifier 8. By setting the turns ratio of the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6, the conduction time of the diodes in the voltage multiplier rectifier 8 is made 1 / 3 of the voltage cycle received between the two AC input terminals of the voltage multiplier rectifier 8, and the conduction time of the diodes in the first auxiliary single-phase rectifier bridge 7 is 2 / 3 of the voltage cycle received between the two AC input terminals of the first auxiliary single-phase rectifier bridge 7. This allows the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to work simultaneously, and the output currents of the first diode rectifier bridge 2 and the second diode rectifier bridge 3 are both equal-width 3-level stepped DC currents.

2. The series-type 36-pulse rectifier with a passive current injection circuit on the DC side according to claim 1, characterized in that, The first auxiliary single-phase rectifier bridge 7 includes diode D. p1 diode D p2 diode D p3 and diode D p4 , Diode D p1 anode and diode D p3 After the cathode is connected, the first AC input terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the opposite terminal of the secondary winding of the first auxiliary single-phase transformer 4. Diode D p2 anode and diode D p4 After the cathode is connected, the second AC input terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the same-name terminal of the secondary winding of the first auxiliary single-phase transformer 4. Diode D p1 Cathode and diode D p2 After the cathode is connected, it serves as the positive output terminal of the first auxiliary single-phase rectifier bridge 7; Diode D p3 anode and diode D p4 After the anode is connected, it serves as the negative output terminal of the first auxiliary single-phase rectifier bridge 7; The voltage multiplier rectifier 8 includes diode D m1 diode D m2 Capacitors C3 and C4; Diode D m1 anode and diode D m2 After the cathode is connected, it is connected to the same-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 as the first AC input terminal of the voltage multiplier rectifier 8. After one end of capacitor C3 and one end of capacitor C4 are connected, they serve as the second AC input terminal of voltage multiplier rectifier 8 and are connected to the same-name terminal of the secondary winding of the third auxiliary single-phase transformer 6. Diode D m1 After the cathode is connected to the other end of capacitor C3, it serves as the positive output terminal of voltage multiplier rectifier 8. Diode D m2 After the anode of the capacitor is connected to the other end of the capacitor C4, it serves as the negative output terminal of the voltage multiplier rectifier 8.

3. The series-type 36-pulse rectifier with a passive current injection circuit on the DC side according to claim 2, characterized in that, The passive current injection circuit includes three operating modes, specifically: Working Mode I: When | u s |<( u d1 + u d2 - u d ), u s1 - u s2 <( u d1 + u d2 - u s - u c4 )and u s2 - u s1 <( u d1 + u d2 + u s +u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 diode D p2 diode D p3 and diode D p4 Forward conduction, diode D in voltage multiplier rectifier 8 m1 and diode D m2 When reverse biased, the voltage across capacitors C3 and C4 remains constant. Both the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are in a non-operating state. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the two ends of the load 9. u p This is the voltage across the primary winding of the first auxiliary single-phase transformer 4; u s This is the voltage across the secondary winding of the first auxiliary single-phase transformer 4; u d The voltage across load 9; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s1 This is the voltage output from the secondary winding of the second auxiliary single-phase transformer 5; u s2 This is the voltage output from the secondary winding of the third auxiliary single-phase transformer 6; u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8; Working Mode II: When - u s >( u d1 + u d2 - u d ), u s1 - u s2 >( u d1 + u d2 - u s - u c4 )and u s2 - u s1 <( u d1 + u d2 + u s +u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p2 and diode D p3 Reverse bias cutoff, diode D p1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 8 m1 Forward conduction, diode D m2 Reverse bias cutoff; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 9; among which, u p This is the voltage across the primary winding of the first auxiliary single-phase transformer 4; u s This is the voltage across the secondary winding of the first auxiliary single-phase transformer 4; u p1 This is the voltage output from the primary winding of the second auxiliary single-phase transformer 5; u p2 This is the voltage output from the primary winding of the third auxiliary single-phase transformer 6; u s1 This is the voltage output from the secondary winding of the second auxiliary single-phase transformer 5; u s2 This is the voltage output from the secondary winding of the third auxiliary single-phase transformer 6; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8; Work Mode III: When u s >( u d1 + u d2 - u d ), u s1 - u s2 <( u d1 + u d2 - u s - u c4 )and u s2 - u s1 >( u d1 + u d2 + u s +u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; diode D in voltage multiplier rectifier 8 m1 Reverse bias cutoff, diode D m2 Forward conduction; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the two ends of the load 9; among which, u s This is the voltage across the secondary winding of the first auxiliary single-phase transformer 4; u d The voltage across load 9; u s1 This is the voltage output from the secondary winding of the second auxiliary single-phase transformer 5; u s2 This is the voltage output from the secondary winding of the third auxiliary single-phase transformer 6; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8.

4. A series-type 36-pulse rectifier with a passive current injection circuit on the DC side, comprising a series-type 12-pulse rectifier and a passive current injection circuit, wherein the passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses; the series-type 12-pulse rectifier comprises a phase-shifting transformer 1, a first diode rectifier bridge 2, and a second diode rectifier bridge 3; Its features are, The passive current injection circuit includes a first multi-winding auxiliary single-phase transformer 4, a second multi-winding auxiliary single-phase transformer 5, a first auxiliary single-phase rectifier bridge 6, a voltage multiplier rectifier 7, capacitor C1, and capacitor C2. Phase-shifting transformer 1 is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by phase-shifting transformer 1 are output to the first diode rectifier bridge 2 and the second diode rectifier bridge 3, respectively. The positive output terminal of the first diode rectifier bridge 2 is connected to one end of capacitor C1 and the negative output terminal of the first auxiliary single-phase rectifier bridge 6 at the same time. The negative output terminal of the first diode rectifier bridge 2 is simultaneously connected to the positive output terminal of the second diode rectifier bridge 3, the opposite terminal of the primary winding of the first multi-winding auxiliary single-phase transformer 4, and the same terminal of the primary winding of the second multi-winding auxiliary single-phase transformer 5. After the negative output terminal of the second diode rectifier bridge 3 is connected to one end of capacitor C2 and the negative output terminal of voltage multiplier rectifier 7, it is connected to the negative output terminal of the 36-pulse rectifier and the negative terminal of load 8. The primary winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the other end of capacitor C1. The same-name terminal of the secondary first winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the first AC input terminal of the first auxiliary single-phase rectifier bridge 6; the opposite-name terminal of the secondary first winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the opposite-name terminal of the secondary first winding of the second multi-winding auxiliary single-phase transformer 5. The same-name terminal of the secondary winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the first AC input terminal of the voltage multiplier rectifier 7. The opposite-named terminal of the secondary second winding of the first multi-winding auxiliary single-phase transformer 4 is connected to the opposite-named terminal of the secondary second winding of the second multi-winding auxiliary single-phase transformer 5. The opposite end of the primary winding of the second multi-winding auxiliary single-phase transformer 5 is connected to the other end of capacitor C2. The same-name terminal of the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5 is connected to the second AC input terminal of the first auxiliary single-phase rectifier bridge 6. The same-name terminal of the secondary winding of the second multi-winding auxiliary single-phase transformer 5 is connected to the second AC input terminal of the voltage multiplier rectifier 7. After the positive output terminal of the first auxiliary single-phase rectifier bridge 6 is connected to the positive output terminal of the voltage multiplier rectifier 7, it is connected to the positive output terminal of the 36-pulse rectifier and the positive terminal of the load 8. By setting the turns ratio of the primary and secondary windings of the first multi-winding auxiliary single-phase transformer 4 and the second multi-winding auxiliary single-phase transformer 5, the conduction time of the diodes in the first auxiliary single-phase rectifier bridge 6 is made to be 1 / 2 of the voltage period received between the two AC input terminals of the first auxiliary single-phase rectifier bridge 6; the conduction time of the diodes in the voltage multiplier rectifier 7 is made to be 1 / 6 of the voltage period received between the two AC input terminals of the voltage multiplier rectifier 7; thereby enabling the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to work simultaneously or alternately, and when the first diode rectifier bridge 2 and / or the second diode rectifier bridge 3 are working, the current output by the rectifier bridge is a 4-level stepped DC current with equal width.

5. The series-type 36-pulse rectifier with a passive current injection circuit on the DC side according to claim 4, characterized in that, The first auxiliary single-phase rectifier bridge 6 includes diode D. p1 diode D p2 diode D p3 and diode D p4 ; Diode D p1 anode and diode D p2 After the anode is connected, it serves as the negative output terminal of the first auxiliary single-phase rectifier bridge 6; Diode D p2 cathode and diode D p4 After the anode is connected, it serves as the first AC input terminal of the first auxiliary single-phase rectifier bridge 6; diode D p1 Cathode and diode D p3 After the anode is connected, it serves as the second AC input terminal of the first auxiliary single-phase rectifier bridge 6; Diode D p3 Cathode and diode D p4 After the cathode is connected, it serves as the positive output terminal of the first auxiliary single-phase rectifier bridge 6; The voltage multiplier rectifier 7 includes diode D. m1 diode D m2 Capacitors C3 and C4; Diode D m1 anode and diode D m2 After the cathode is connected, it serves as the first AC input terminal of the voltage multiplier rectifier 7; One end of capacitor C3 is connected to one end of capacitor C4, which serves as the second AC input terminal of voltage multiplier rectifier 7; Diode D m1 After the cathode is connected to the other end of capacitor C3, it serves as the positive output terminal of voltage multiplier rectifier 7. Diode D m2 After the anode of the capacitor is connected to the other end of the capacitor C4, it serves as the negative output terminal of the voltage multiplier rectifier 7.

6. The series-type 36-pulse rectifier with a passive current injection circuit on the DC side according to claim 5, characterized in that, The passive current injection circuit includes four operating modes, specifically: Working Mode I: When u s3 - u s1 <( u d1 + u d2 - u d )and u s2 - u s4 <( u d1 + u d2 + u s1 -u s3 -u c4 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p2 and diode D p3 Reverse bias cutoff, diode D p1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 7 m1 diode D m2 With reverse bias cutoff, the voltages across capacitors C3 and C4 remain constant. The primary winding and the first secondary winding of the first multi-winding auxiliary single-phase transformer 4 are both operational, while the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 is inactive. Similarly, the primary winding and the first secondary winding of the second multi-winding auxiliary single-phase transformer 5 are both operational, while the second secondary winding of the second multi-winding auxiliary single-phase transformer 5 is inactive. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 8. u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u s4 This refers to the voltage across the second winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u d This is the voltage across load 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 7; Working Mode II: When u s3 - u s1 <( u d1 + u d2 - u d )and u s2 - u s4 >( u d1 + u d2 + u s1 -u s3 -u c4 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p2 and diode D p3 Reverse bias cutoff, diode D p1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 7 m1 Forward conduction, diode D m2 Reverse bias cutoff; the primary winding, secondary winding 1, and secondary winding 2 of the first multi-winding auxiliary single-phase transformer 4 are all in operation, as are the primary winding, secondary winding 1, and secondary winding 2 of the second multi-winding auxiliary single-phase transformer 5. At this time, the first diode rectifier bridge 2 supplies power to both ends of the load 8; among which, u d This is the voltage across load 8; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u s4 This refers to the voltage across the second winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 7; Work Mode III: When u s1 - u s3 <( u d1 + u d2 - u d )and u s4 - u s2 <( u d1 + u d2 - u s1 +u s3 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; diode D in voltage multiplier rectifier 7 m1 diode D m2 With reverse bias cutoff, the voltages across capacitors C3 and C4 remain constant. The primary winding and the first secondary winding of the first multi-winding auxiliary single-phase transformer 4 are both operational, while the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 is inactive. Similarly, the primary winding and the first secondary winding of the second multi-winding auxiliary single-phase transformer 5 are both operational, while the second secondary winding of the second multi-winding auxiliary single-phase transformer 5 is inactive. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 8. u d This is the voltage across load 8; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u s4 This refers to the voltage across the second winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 7; Working Mode IV: When u s1 - u s3 <( u d1 + u d2 - u d )and u s4 - u s2 >( u d1 + u d2 - u s1 +u s3 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 6 p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; diode D in voltage multiplier rectifier 7 m1 Reverse bias cutoff, diode D m2 In forward conduction, the primary winding, the first secondary winding, and the second secondary winding of the first multi-winding auxiliary single-phase transformer 4 are all in operation, as are the primary winding, the first secondary winding, and the second secondary winding of the second multi-winding auxiliary single-phase transformer 5. At this time, the second diode rectifier bridge 3 supplies power to both ends of the load 8; whereby... u d This is the voltage across load 8; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s1 This refers to the voltage across the first winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s2 This refers to the voltage across the second winding of the secondary side of the first multi-winding auxiliary single-phase transformer 4. u s3 This refers to the voltage across the first winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u s4 This refers to the voltage across the second winding of the secondary side of the second multi-winding auxiliary single-phase transformer 5. u c3 This is the voltage across capacitor C3 in voltage multiplier rectifier 7.

7. A series-type 36-pulse rectifier with a passive current injection circuit on the DC side, comprising a series-type 12-pulse rectifier and a passive current injection circuit, wherein the passive current injection circuit is located on the DC side of the series-type 12-pulse rectifier and is used to multiply the 12 pulses of the series-type 12-pulse rectifier to 36 pulses; the series-type 12-pulse rectifier comprises a phase-shifting transformer 1, a first diode rectifier bridge 2, and a second diode rectifier bridge 3; Its features are, The passive current injection circuit includes a phase-shifting transformer 1, a first diode rectifier bridge 2, a second diode rectifier bridge 3, a first auxiliary single-phase transformer 4, a second auxiliary single-phase transformer 5, a third auxiliary single-phase transformer 6, a first auxiliary single-phase rectifier bridge 7, a voltage multiplier rectifier 8, capacitor C1, and capacitor C2. Phase-shifting transformer 1 is used to shift the three-phase voltage input from the power grid to generate two three-phase voltages with a phase difference of 30° and the same amplitude. The two three-phase voltages generated by phase-shifting transformer 1 are output to the first diode rectifier bridge 2 and the second diode rectifier bridge 3, respectively. After the positive output terminal of the first diode rectifier bridge 2 is connected to one end of the capacitor C1 and the positive output terminal of the voltage multiplier rectifier 8, it is connected to the positive output terminal of the 36-pulse rectifier and the positive input terminal of the load 9. The negative output terminal of the first diode rectifier bridge 2 is connected to the positive output terminal of the first auxiliary single-phase rectifier bridge 7, and the negative output terminal of the first auxiliary single-phase rectifier bridge 7 is connected to the positive output terminal of the second diode rectifier bridge 3. After the negative output terminal of the second diode rectifier bridge 3 is connected to one end of capacitor C2 and the negative output terminal of voltage multiplier rectifier 8, it is connected to the negative output terminal of 36-pulse rectifier and the negative input terminal of load 9. The opposite-named end of the primary winding of the first auxiliary single-phase transformer 4 is connected to the first AC input terminal of the first auxiliary single-phase rectifier bridge 7, and the same-named end of the primary winding of the first auxiliary single-phase transformer 4, the opposite-named end of the secondary winding, and the second AC input terminal of the first auxiliary single-phase rectifier bridge 7 are connected simultaneously. The same-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 is connected to the opposite-name terminal of the primary winding of the second auxiliary single-phase transformer 5 and the same-name terminal of the primary winding of the third auxiliary single-phase transformer 6 at the same time. The opposite end of the primary winding of the second auxiliary single-phase transformer 5 is connected to the other end of capacitor C1. The same-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 is connected to the first AC input terminal of the voltage multiplier rectifier 8, and the opposite-name terminal of the secondary winding of the second auxiliary single-phase transformer 5 is connected to the opposite-name terminal of the secondary winding of the third auxiliary single-phase transformer 6; the same-name terminal of the secondary winding of the third auxiliary single-phase transformer 6 is connected to the second AC input terminal of the voltage multiplier rectifier 8. The opposite end of the primary winding of the third auxiliary single-phase transformer 6 is connected to the other end of capacitor C2. By setting the turns ratio of the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6, the conduction time of the diodes in the first auxiliary single-phase rectifier bridge 7 is 2 / 3 of the voltage cycle received by the two AC input terminals of the first auxiliary single-phase rectifier bridge 7, and the conduction time of the diodes in the voltage multiplier rectifier 8 is 1 / 3 of the voltage cycle received by the two AC input terminals of the voltage multiplier rectifier 8. This allows the first diode rectifier bridge 2 and the second diode rectifier bridge 3 to work simultaneously, and the output current of the first diode rectifier bridge 2 and the second diode rectifier bridge 3 is a three-level stepped DC current with equal width.

8. The series-type 36-pulse rectifier with a passive current injection circuit on the DC side according to claim 7, characterized in that, The first auxiliary single-phase rectifier bridge 7 includes diode D. p1 diode D p2 diode D p3 and diode D p4 ; Diode D p1 anode and diode D p2 After the cathode is connected, it serves as the first AC input terminal of the first auxiliary single-phase rectifier bridge 7; Diode D p3 anode and diode D p4 After the cathode is connected, it serves as the second AC input terminal of the first auxiliary single-phase rectifier bridge 7; Diode D p1 Cathode and diode D p3 After the cathode is connected, it serves as the positive output terminal of the first auxiliary single-phase rectifier bridge 7; Diode D p2 Cathode and diode D p4 After the cathode is connected, it serves as the negative output terminal of the first auxiliary single-phase rectifier bridge 7; The voltage multiplier rectifier 8 includes a diode D. m1 diode D m2 Capacitors C3 and C4; Diode D m1 anode and diode D m2 After the cathode is connected, it serves as the first AC input terminal of the voltage multiplier rectifier 8; One end of capacitor C3 is connected to one end of capacitor C4, which serves as the second AC input terminal of voltage multiplier rectifier 8; Diode D m1 After the cathode is connected to the other end of capacitor C3, it serves as the positive output terminal of voltage multiplier rectifier 8. Diode D m2 After the anode of the capacitor is connected to the other end of the capacitor C4, it serves as the negative output terminal of the voltage multiplier rectifier 8.

9. The series-type 36-pulse rectifier with a passive current injection circuit on the DC side according to claim 8, characterized in that, The passive current injection circuit includes three operating modes, specifically: Working Mode I: When | u p1 |<( u d1 + u d2 - u d ), u s2 - u s3 <( u d1 + u d2 + u p1 - u c4 )and u s3 - u s2 <( u d1 + u d2 - u p1 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 diode D p2 diode D p3 and diode D p4 Forward conduction, diode D in voltage multiplier rectifier 8 m1 diode D m2 With reverse bias cutoff, the voltages across capacitors C3 and C4 remain constant; the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in a non-operating state. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the load 9; among which, u d The voltage across load 9; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s2 This is the voltage output across the secondary winding of the second auxiliary single-phase transformer 5; u s3 This is the voltage output across the secondary winding of the third auxiliary single-phase transformer 6; u p1 This is the voltage output across the primary winding of the first auxiliary single-phase transformer 4; u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8; Working Mode II: When u p1 >( u d1 + u d2 - u d ), u s2 - u s3 >( u d1 + u d2 + u p1 - u c4 )and u s3 - u s2 <( u d1 + u d2 - u p1 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p1 and diode D p4 Reverse bias cutoff, diode D p2 and diode D p3 Forward conduction; Voltage multiplier rectifier 8D m1 Forward conduction, diode D m2 Reverse bias cutoff; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the two ends of the load 9; among which, u d The voltage across load 9; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s2 This is the voltage output across the secondary winding of the second auxiliary single-phase transformer 5; u s3 This is the voltage output across the secondary winding of the third auxiliary single-phase transformer 6; u p1 This is the voltage output across the primary winding of the first auxiliary single-phase transformer 4; u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8; Working Mode III: When - u p1 >( u d1 + u d2 - u d ), u s2 - u s3 <( u d1 + u d2 + u p1 - u c4 )and u s3 - u s2 >( u d1 + u d2 - u p1 -u c3 When ), diode D in the first auxiliary single-phase rectifier bridge 7 p2 and diode D p3 Reverse bias cutoff, diode D p1 and diode D p4 Forward conduction; diode D in voltage multiplier rectifier 8 m1 Reverse bias cutoff, diode D m2 Forward conduction; the primary and secondary windings of the first auxiliary single-phase transformer 4, the second auxiliary single-phase transformer 5, and the third auxiliary single-phase transformer 6 are all in operation. At this time, the first diode rectifier bridge 2 and the second diode rectifier bridge 3 jointly supply power to the two ends of the load 9; among which, u d The voltage across load 9; u d1 This is the voltage output of the first diode rectifier bridge 2; u d2 This is the voltage output of the second diode rectifier bridge 3; u s2 This is the voltage output across the secondary winding of the second auxiliary single-phase transformer 5; u s3 This is the voltage output across the secondary winding of the third auxiliary single-phase transformer 6; u p1 This is the voltage output across the primary winding of the first auxiliary single-phase transformer 4; u c3 This is the voltage across capacitor C3 of voltage multiplier rectifier 8; u c4 This is the voltage across capacitor C4 of voltage multiplier rectifier 8.

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