A charging control method for a three-phase bridge two-level voltage source converter

Abstract

This invention discloses a charging control method for a three-phase bridge two-level voltage source converter, comprising: step S10, closing the pre-charging switch on each connection line and performing pre-charging through a charging resistor; step S11, after pre-charging is completed, closing the main switch on each connection line; step S12, periodically charging and discharging the connected reactor by triggering pulses to the switching transistors, thereby boosting the voltage of the charged reactors to the DC-side charging capacitor of the three-phase bridge two-level voltage source converter. Implementing this invention allows for the periodic charging and discharging of the connected reactors through the timing control of the switching transistors, achieving voltage boosting of the DC-side charging capacitor. It offers high reliability, good economy, and a simple implementation method.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converters, specifically relating to a charging control method for a three-phase bridge two-level voltage source converter. Background Technology

[0002] Three-phase bridge two-level voltage source converters have advantages such as simple circuit structure, low manufacturing cost, and easy implementation of control systems, and are therefore widely used.

[0003] When the three-phase bridge uncontrolled rectifier circuit is unloaded, its DC-side charging capacitor can be charged up to 2.45 times the effective value of the AC-side phase voltage. Therefore, the DC-side charging capacitor voltage cannot reach the rated value by the uncontrolled rectification charging of the converter alone. In order to ensure the rated output of the DC side of the three-phase bridge two-level voltage source converter, the DC-side charging capacitor must be boosted after the uncontrolled rectification charging.

[0004] To boost the DC-side charging capacitor of the converter, it is usually possible to add additional circuits or change the circuit topology, but this is not economical and reliable. Therefore, it is necessary to propose a charging control method for a three-phase bridge two-level voltage source converter circuit. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a charging control method for a three-phase bridge two-level voltage source converter, which can realize the voltage boost of the DC side charging capacitor by only controlling the timing of the switching transistors to periodically charge and discharge the connected reactor. It has high reliability, good economy and simple implementation method.

[0006] To address the aforementioned technical problems, as one aspect of this invention, a charging control method for a three-phase bridge two-level voltage source converter is introduced. This method utilizes a three-phase bridge two-level voltage source converter circuit, which includes: a bridge circuit unit; a DC-side charging capacitor (C) connected in parallel with the bridge circuit unit; and three connecting lines extending from the three-phase arms of the bridge circuit, each connecting line connected in series with a reactor (L) and a main switch (K2), connecting to the three-phase AC power supply. Each main switch (K2) has a branch connected in parallel with a pre-charging switch (K1) and a charging resistor (R) connected in series.

[0007] The method is characterized by comprising at least the following steps:

[0008] Step S10: Close the pre-charge switch on each connection line of the three-phase bridge arm of the voltage source converter, and pre-charge the DC side charging capacitor of the converter through the charging resistor.

[0009] Step S11: After pre-charging is complete, close the main switch on each connection line;

[0010] Step S12: By triggering the switch transistor with a pulse, the connected reactor is periodically charged and discharged. The voltage of the connected reactor after charging is boosted to increase the voltage of the DC side charging capacitor of the three-phase bridge two-level voltage source converter.

[0011] This further includes:

[0012] In boost mode, the three-phase bridge two-level voltage source converter circuit is controlled to operate in the following two modes:

[0013] Energy storage mode: The fourth, sixth and second switches (T4, T6 and T2) of the lower bridge arm of the control voltage source converter are kept off, while the first, third and fifth switches (T1, T3 and T5) of the upper bridge arm are turned on, and the AC power supply of the converter charges the connected reactor to store energy.

[0014] Boost mode: All switches (T1 to T6) of the control voltage source converter are kept off. The reactor on each connection line charges the DC side charging capacitor through the anti-parallel diode of the corresponding switch, thereby boosting the DC side voltage.

[0015] The bridge circuit unit includes a first power diode (D1), a second power diode (D2), a third power diode (D3), a fourth power diode (D4), a fifth power diode (D5), a sixth power diode (D6), and a first switch (T1), a second switch (T2), a third switch (T3), a fourth switch (T4), a fifth switch (T5), and a sixth switch (T6); wherein:

[0016] The positive terminal of the first power diode is connected to the negative terminal of the fourth power diode, the positive terminal of the third power diode is connected to the negative terminal of the sixth power diode, and the positive terminal of the fifth power diode is connected to the negative terminal of the second power diode.

[0017] The negative terminals of the first power diode, the third power diode, and the fifth power diode are connected together and then connected to the positive terminal of the DC-side charging capacitor.

[0018] The positive terminals of the fourth power diode, the sixth power diode, and the second power diode are connected together and connected to the negative terminal of the DC-side charging capacitor.

[0019] A connecting line is drawn from the positive terminal of each of the first power diode, the third power diode, and the fifth power diode;

[0020] The collector of the first switching transistor is connected to the negative terminal of the first power diode, and its emitter is connected to the positive terminal of the first power diode; the collector of the third switching transistor is connected to the negative terminal of the third power diode, and its emitter is connected to the positive terminal of the third power diode; the collector of the fifth switching transistor is connected to the negative terminal of the fifth power diode, and its emitter is connected to the positive terminal of the fifth power diode.

[0021] The collector of the fourth switching transistor is connected to the negative terminal of the fourth power diode, and its emitter is connected to the positive terminal of the fourth power diode; the collector of the sixth switching transistor is connected to the negative terminal of the sixth power diode, and its emitter is connected to the positive terminal of the sixth power diode; the collector of the second switching transistor is connected to the negative terminal of the second power diode, and its emitter is connected to the positive terminal of the second power diode.

[0022] Step S12 further includes:

[0023] Trigger signals for the first, third, and fifth switches (T1, T3, and T5) of the upper arm of the bridge circuit unit are generated by comparing a triangular carrier wave with a constant value of m. No trigger signals are given to the fourth, sixth, and second switches (T4, T6, and T2) of the lower arm of the bridge circuit unit, keeping these three switches always off. The amplitude of the triangular carrier wave varies from -n to n, and the constant m ranges from -n. <m<0;

[0024] Specifically, when the amplitude of the triangular carrier wave is less than a constant m, the trigger signals of the first, third, and fifth switches (T1, T3, and T5) of the upper bridge arm are at a high level, and the three switches are turned on; when the amplitude of the triangular carrier wave is greater than a constant m, the trigger signals of the first, third, and fifth switches (T1, T3, and T5) of the upper bridge arm are at a low level, and the three switches are turned off.

[0025] The voltage boosting speed of the DC-side charging capacitor can be adjusted by changing the value of the constant m. The larger the value of m in the range of -n to 0, the faster the DC-side charging capacitor charges and boosts.

[0026] Implementing the embodiments of the present invention has the following beneficial effects:

[0027] This invention provides a charging control method for a three-phase bridge two-level voltage source converter, which can effectively boost the DC-side charging capacitor of the three-phase bridge two-level voltage source converter. The method continues to boost the voltage after charging the DC-side charging capacitor by three-phase bridge uncontrolled rectification. The boosting process is achieved only by the timing combination of the switching transistors and does not require additional circuitry. It has high reliability, good economy, and simple implementation.

[0028] Furthermore, this invention can also adjust the DC-side voltage boosting speed by changing the duty cycle of the trigger pulse, offering good flexibility and high engineering application value. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0030] Figure 1 This is a schematic diagram of an embodiment of a three-phase bridge two-level voltage source converter circuit according to the present invention.

[0031] Figure 2 A schematic diagram of the main flow of an embodiment of a charging control method for a three-phase bridge two-level voltage source converter circuit provided by the present invention;

[0032] Figure 3 for Figure 2 The main circuit structure diagram after the pre-charge switch is closed in the middle;

[0033] Figure 4 for Figure 3 The main circuit structure diagram after the main switch is closed in the middle;

[0034] Figure 5 This is a diagram illustrating the generation of the boost trigger pulse involved in this invention;

[0035] Figure 6 This is a schematic diagram illustrating the principle of energy storage mode during the boost process involved in this invention.

[0036] Figure 7 This is a schematic diagram illustrating the principle of the boost mode during the boost process involved in this invention.

[0037] Figure 8 This is a simulation diagram of the DC-side voltage waveform during the boost process using the method of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] like Figure 1 The diagram shown illustrates a structural schematic of an embodiment of a three-phase bridge two-level voltage source converter circuit according to the present invention. Figure 1 in, u a u b and u cFor the AC three-phase power supply, R is the charging resistor, L is the three-phase connecting reactor, C is the DC charging capacitor, T1, T3, and T5 are the upper bridge arm switches, T4, T6, and T2 are the lower bridge arm switches, D1 to D6 are the anti-parallel diodes of their respective switches, K1 is the pre-charge switch, and K2 is the three-phase main switch. Specifically, the three-phase bridge two-level voltage source converter circuit includes at least:

[0040] Bridge circuit unit;

[0041] A DC-side charging capacitor (C) connected in parallel with the bridge circuit unit;

[0042] The three connecting lines drawn from the three-phase bridge arms of the bridge circuit are each connected in series with a reactor (L) and a main switch (K2), and are respectively connected to one phase of the three-phase power supply on the AC side;

[0043] Each of the main switches (K2) has a branch connected in parallel with a pre-charge switch (K1) and a charging resistor (R) connected in series.

[0044] More specifically, the bridge circuit unit includes a first power diode D1, a second power diode D2, a third power diode D3, a fourth power diode D4, a fifth power diode D5, a sixth power diode D6, and a first switch T1, a second switch T2, a third switch T3, a fourth switch T4, a fifth switch T5, and a sixth switch T6; wherein:

[0045] The positive terminal of the first power diode is connected to the negative terminal of the fourth power diode, the positive terminal of the third power diode is connected to the negative terminal of the sixth power diode, and the positive terminal of the fifth power diode is connected to the negative terminal of the second power diode.

[0046] The negative terminals of the first power diode, the third power diode, and the fifth power diode are connected together and then connected to the positive terminal of the DC-side charging capacitor.

[0047] The positive terminals of the fourth power diode, the sixth power diode, and the second power diode are connected together and connected to the negative terminal of the DC-side charging capacitor.

[0048] A connecting line is drawn from the positive terminal of each of the first power diode, the third power diode, and the fifth power diode;

[0049] The collector of the first switching transistor is connected to the negative terminal of the first power diode, and its emitter is connected to the positive terminal of the first power diode; the collector of the third switching transistor is connected to the negative terminal of the third power diode, and its emitter is connected to the positive terminal of the third power diode; the collector of the fifth switching transistor is connected to the negative terminal of the fifth power diode, and its emitter is connected to the positive terminal of the fifth power diode.

[0050] The collector of the fourth switching transistor is connected to the negative terminal of the fourth power diode, and its emitter is connected to the positive terminal of the fourth power diode; the collector of the sixth switching transistor is connected to the negative terminal of the sixth power diode, and its emitter is connected to the positive terminal of the sixth power diode; the collector of the second switching transistor is connected to the negative terminal of the second power diode, and its emitter is connected to the positive terminal of the second power diode.

[0051] Figure 2 The diagram shown illustrates the main flow of an embodiment of a charging control method for a three-phase bridge two-level voltage source converter circuit provided by the present invention; in conjunction with... Figures 3 to 7 As shown, in this embodiment, the method utilizes Figure 1 The circuit shown is used to implement this, which includes at least the following steps:

[0052] Step S10: Close the pre-charge switch K1 on each connection line of the three-phase unit of the voltage source converter. The three-phase bridge uncontrolled rectifier circuit is composed of anti-parallel diodes D1 to D6. The three-phase power supply (u a u b and u c The DC-side charging capacitor of the converter is pre-charged through the charging resistor R; its circuit structure is as follows: Figure 3 As shown;

[0053] Step S11: After pre-charging is completed, close the main switch K2 on each connection line (after the pre-charging switch is closed and pre-charging is completed, the state of the pre-charging switch can be closed or open). Figure 4 The main circuit structure after the main switch is closed is shown.

[0054] Step S12: By triggering the switch transistor with a pulse, the connected reactor is periodically charged and discharged. The voltage of the connected reactor after charging is boosted to increase the voltage of the DC side charging capacitor of the three-phase bridge two-level voltage source converter.

[0055] More specifically, step S12 further includes:

[0056] Trigger signals for the first, third, and fifth switches (T1, T3, and T5) of the upper arm of the bridge circuit unit are generated by comparing a triangular carrier wave with a constant value of m. No trigger signals are given to the fourth, sixth, and second switches (T4, T6, and T2) of the lower arm of the bridge circuit unit, which remain in an off state. The amplitude of the triangular carrier wave varies from -n to n, and the constant m ranges from -n. <m<0;

[0057] When the amplitude of the triangular carrier wave is less than a constant m, the trigger signals of the first, third, and fifth switches (T1, T3, and T5) of the upper bridge arm are high, and the three switches are turned on; when the amplitude of the triangular carrier wave is greater than a constant m, the trigger signals of the first, third, and fifth switches (T1, T3, and T5) of the upper bridge arm are low, and the three switches are turned off.

[0058] The voltage boosting speed of the DC-side charging capacitor can be adjusted by changing the value of the constant m. The larger the value of m in the range of -n to 0, the faster the DC-side charging capacitor charges and boosts.

[0059] More specifically, it further includes:

[0060] In boost mode, the three-phase bridge two-level voltage source converter circuit is controlled to operate in the following two modes:

[0061] Energy storage mode: The fourth, sixth, and second switches (T4, T6, and T2) of the lower bridge arm of the control voltage source converter are kept off, while the first, third, and fifth switches (T1, T3, and T5) of the upper bridge arm are turned on. The AC power supply of the converter charges and stores energy in the connected reactor L; specifically, as follows... Figure 6 As shown, phase A has the highest voltage among the three phases. By triggering the pulse to turn on the switching transistors T3 and T5, the system voltage charges and stores energy in the connected reactor L through the anti-parallel diode D1.

[0062] Boost mode: All switches in the control voltage source converter remain off. The reactors on each connection line charge the DC-side charging capacitors through the anti-parallel diodes of the switches, thus boosting the DC-side voltage. Taking phase A as an example, if... Figure 7 As shown, all switches (T1, T4) in phase A are kept off, and the inductor L charges and boosts the DC-side charging capacitor through the anti-parallel diodes (D1 and D4) of the aforementioned switches.

[0063] To verify the effectiveness of the method provided by this invention, a simulation can be built using MATLAB / Simulink to verify the effect of the charging control method. In one example, the pre-charge switch is closed at 0s to pre-charge the DC side charging capacitor, the main switch is closed at 0.5s to maintain the three-phase bridge uncontrolled rectification state, a trigger pulse is activated at 1s to boost the voltage, and the boosting ends at 7s to complete the entire charging process. Figure 8 The figure shows the DC side voltage waveform when m = -1800 and n = 2500. It reaches the rated value of 850V in 7s and remains stable. It can be seen that the maximum charging voltage exceeds 2.45 times the effective value of the AC side phase voltage, and the boost effect is very good.

[0064] Implementing the embodiments of the present invention has the following beneficial effects:

[0065] This invention provides a charging control method for a three-phase bridge two-level voltage source converter, which can effectively boost the DC-side charging capacitor of the three-phase bridge two-level voltage source converter. The method continues to boost the voltage after charging the DC-side charging capacitor by three-phase bridge uncontrolled rectification. The boosting process is achieved only by the timing combination of the switching transistors and does not require additional circuitry. It has high reliability, good economy, and simple implementation.

[0066] Furthermore, this invention can also adjust the boost rate of the DC-side charging capacitor by changing the duty cycle of the trigger pulse, offering good flexibility and high engineering application value.

[0067] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, apparatus, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0068] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0069] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A charging control method of a three-phase bridge two-level voltage source converter, characterized by, The method includes at least the following steps: Step S10: Close the pre-charge switch on each connection line of the three-phase bridge arm of the voltage source converter, and pre-charge the DC side charging capacitor of the converter through the charging resistor. Step S11: After pre-charging is complete, close the main switch on each connection line; Step S12: By triggering the switching transistor with a pulse, the connected reactor is periodically charged and discharged. The voltage of the connected reactor after charging is boosted to boost the DC side charging capacitor of the three-phase bridge two-level voltage source converter. The method is implemented using a three-phase bridge two-level voltage source converter circuit, which includes: Bridge circuit unit; A DC-side charging capacitor (C) connected in parallel with the bridge circuit unit. The three connecting lines drawn from the three-phase bridge arms of the bridge circuit unit are connected in series with a connecting reactor (L) and a main switch (K2) to the three-phase power supply on the AC side. Each of the main switches (K2) is connected in parallel with a branch consisting of a pre-charge switch (K1) and a charging resistor (R) connected in series. The bridge circuit unit includes a first power diode (D1), a second power diode (D2), a third power diode (D3), a fourth power diode (D4), a fifth power diode (D5), and a sixth power diode (D6), as well as a first switch (T1), a second switch (T2), a third switch (T3), a fourth switch (T4), a fifth switch (T5), and a sixth switch (T6); wherein: The positive terminal of the first power diode is connected to the negative terminal of the fourth power diode, the positive terminal of the third power diode is connected to the negative terminal of the sixth power diode, and the positive terminal of the fifth power diode is connected to the negative terminal of the second power diode. The negative terminals of the first power diode, the third power diode, and the fifth power diode are connected together and then connected to the positive terminal of the DC-side charging capacitor. The positive terminals of the fourth power diode, the sixth power diode, and the second power diode are connected together and connected to the negative terminal of the DC-side charging capacitor. A connecting line is drawn from the positive terminal of each of the first power diode, the third power diode, and the fifth power diode; The collector of the first switching transistor is connected to the negative terminal of the first power diode, and its emitter is connected to the positive terminal of the first power diode; the collector of the third switching transistor is connected to the negative terminal of the third power diode, and its emitter is connected to the positive terminal of the third power diode; the collector of the fifth switching transistor is connected to the negative terminal of the fifth power diode, and its emitter is connected to the positive terminal of the fifth power diode. The collector of the fourth switch is connected to the negative terminal of the fourth power diode, and its emitter is connected to the positive terminal of the fourth power diode; the collector of the sixth switch is connected to the negative terminal of the sixth power diode, and its emitter is connected to the positive terminal of the sixth power diode; the collector of the second switch is connected to the negative terminal of the second power diode, and its emitter is connected to the positive terminal of the second power diode. The method further includes: In boost mode, the three-phase bridge two-level voltage source converter circuit is controlled to operate in the following two modes: Energy storage mode: The fourth, sixth, and second switches (T4, T6, T2) of the lower bridge arm of the control voltage source converter are kept off, while the first, third, and fifth switches (T1, T3, T5) of the upper bridge arm are turned on, and the AC power supply of the converter charges the connected reactor to store energy. Boost mode: All switches (T1~T6) of the control voltage source converter are kept off. The connecting reactor on each connection line charges the DC side charging capacitor through the anti-parallel diode of the corresponding switch, thereby boosting the DC side voltage.

2. The charging control method of a three-phase bridge two-level voltage source converter as claimed in claim 1, characterized by, Step S12 further includes: Trigger signals for the first, third, and fifth switches (T1, T3, T5) of the upper arm of the bridge circuit unit are generated by comparing a triangular carrier wave with a constant value of m. No trigger signals are given to the fourth, sixth, and second switches (T4, T6, T2) of the lower arm of the bridge circuit unit, ensuring that these switches remain off at all times. The amplitude of the triangular carrier wave varies from -n to n, and the constant m ranges from -n. <m<0; Specifically, when the amplitude of the triangular carrier wave is less than a constant m, the trigger signals of the first, third, and fifth switches (T1, T3, T5) of the upper bridge arm are at a high level, and all three switches are turned on; when the amplitude of the triangular carrier wave is greater than a constant m, the trigger signals of the first, third, and fifth switches (T1, T3, T5) of the upper bridge arm are at a low level, and all three switches are turned off. The voltage boosting speed of the DC-side charging capacitor can be adjusted by changing the value of the constant m. The larger the value of m in the range of -n to 0, the faster the DC-side charging capacitor charges and boosts.

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