A starting method and system for a power electronic converter

Abstract

This invention provides a startup method and system for a power electronic converter. The method includes: starting the converter from the DC side when the DC side of the converter is connected to an active system; starting the converter from the AC side when the AC side of the converter is connected to an active system; and starting the converter from either the DC side or the AC side when both the AC and DC sides of the converter are connected to an active system. This invention enables stable pre-charging during startup of the power electronic converter.

Description

Technical Field

[0001] This invention belongs to the technical field of DC power transmission systems, and specifically relates to a starting method and system for a power electronic converter. Background Technology

[0002] Power electronics is a key characteristic of new power systems, and power electronic converters are the core equipment of these systems. High voltage and high capacity are the development direction of power electronic converters. Existing high-voltage, high-capacity power electronic converters are mainly based on modular multilevel converters (MMCs). MMCs were proposed in 2001 and have since seen considerable practical application. Numerous domestic and international projects have been conducted and put into operation based on MMC topologies, proving their feasibility. However, to date, MMCs have not achieved widespread market adoption, primarily due to their high cost. MMCs consist of numerous modules containing expensive components such as power semiconductor switches and capacitors, resulting in a cost far exceeding that of various devices in traditional power systems. This directly impacts the promotion and application of new power systems.

[0003] Existing pre-charging technologies can only be used for MMC converter topologies. However, for new power electronic converter topologies, whose topologies differ from MMC, existing pre-charging technologies cannot be applied.

[0004] Therefore, it is necessary to design a startup method and system for power electronic converters to solve the above-mentioned technical problems. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention provides a startup method for a power electronic converter, wherein the method includes:

[0006] When the DC side of the converter is connected to an active system, the converter is started from the DC side;

[0007] When the AC side of the converter is connected to an active system, the converter is started from the AC side;

[0008] When both the AC and DC sides of the converter are connected to an active system, the converter is started from the DC side or the AC side.

[0009] Furthermore, the DC side of the converter is provided with a pre-charging circuit, and the AC side of the converter is provided with a switch S3; or,

[0010] The AC side of the converter is equipped with a pre-charging circuit, and the DC side of the converter is equipped with a switch S3; or...

[0011] The converter is provided with a pre-charging circuit on both the DC and AC sides, and a switch S3 is provided on both the DC and AC sides of the converter.

[0012] in,

[0013] The pre-charging circuit includes a switch S1, a switch S2, and a pre-charging resistor R. One end of the switch S1 is connected to one end of the pre-charging resistor R, one end of the switch S2 is connected to the other end of the switch S1, and the other end of the switch S2 is connected to the other end of the pre-charging resistor R.

[0014] Furthermore, the converter includes parallel-connected switched capacitor valves and a novel switching valve, the novel switching valve being used to achieve AC / DC conversion; the switched capacitor valve is used to achieve soft switching of the converter, wherein...

[0015] The switched capacitor valve includes multiple switched capacitor modules connected in series;

[0016] The novel switching valve includes two parallel bridge arms, each of which includes multiple power switching device modules connected in series.

[0017] Furthermore, the power switching device module includes a power switching device T1, a diode D1, a voltage equalization capacitor C1, and a power dissipation element H1. The anode of the diode D1 is connected to the anode of the power switching device T1. One end of the voltage equalization capacitor C1 is connected to the cathode of the diode D1, and the other end of the voltage equalization capacitor C1 is connected to the cathode of the power switching device T1. One end of the power dissipation element H1 is connected to one end of the voltage equalization capacitor C1, and the other end of the power dissipation element H1 is connected to the other end of the voltage equalization capacitor C1. A diode D2 is connected in anti-parallel to the power switching device T1.

[0018] Furthermore, starting the converter from the DC side includes:

[0019] The converter is locked out; switch S2 and switch S3 are disconnected, and switch S1 is closed.

[0020] Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2;

[0021] Control the voltage of all power switching device modules to reach the pre-charge target value Usmr4;

[0022] Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup process.

[0023] Furthermore, controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2 includes:

[0024] Start the sorting and equalizing control until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr1. Bypass N0 switched capacitor modules. After the voltage of the switched capacitor modules reaches k*Udc / (N1-NA), bypass N0 switched capacitor modules again.

[0025] Repeat the above process until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2, where,

[0026] Usmr l=k*Udc / N1;

[0027] Where Udc is the DC bus voltage, N1 is the number of switched capacitor modules, and 0 < k ≤ 100%.

[0028] NA represents the number of bypassed switched capacitor modules.

[0029] Furthermore, controlling the voltage of all power switching device modules to reach the pre-charge target value Usmr4 includes:

[0030] Start the sorting and equalizing control until the voltage of all power switching device modules reaches the pre-charge target value Usmr3, bypass dN2 power switching device modules, and after the voltage of the power switching device modules reaches k*Udc / (N2-NB), bypass dN2 power switching device modules again.

[0031] Repeat the above process until the voltage of all power switching device modules reaches the pre-charge target value Usmr4;

[0032] Wherein, Usmr3 = k * Udc / N2;

[0033] Where Udc is the DC bus voltage, N2 is the number of power switching device modules in one phase bridge arm, 0 < k ≤ 100%, and NB represents the number of bypassed switched capacitor modules.

[0034] Furthermore, starting the converter from the AC side includes:

[0035] Converter lockout: Open switch S2, close switch S1;

[0036] Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2;

[0037] Control the voltage of all power switching device modules to reach the pre-charge target value Usmr4;

[0038] Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup process.

[0039] Furthermore, controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2 includes:

[0040] Start the sorting and equalizing control until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr1, bypass N0 switched capacitor modules, and after the voltage of the switched capacitor modules reaches k*Uac / N1, bypass N0 switched capacitor modules again.

[0041] Repeat the above process until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2.

[0042] Where, Usmr1=k*Uac / N1;

[0043] Where Uac is the peak value of the AC phase voltage, N1 is the number of switched capacitor modules, and 0 < k ≤ 100%.

[0044] Furthermore, controlling the voltage of all power switching device modules to reach the pre-charge target value Usmr4 includes:

[0045] Start the sorting and equalizing control until the voltage of all power switching device modules reaches the pre-charge target value Usmr3, bypass dN2 power switching device modules, and after the voltage of the power switching device modules reaches 2*k*Uac / N2, bypass dN2 power switching device modules again.

[0046] Repeat the above process until the voltage of all power switching device modules reaches the pre-charge target value Usmr4;

[0047] Wherein, Usmr3=2*k*Uac / N2;

[0048] Where Uac is the peak value of the AC phase voltage, N2 is the number of power switching device modules in one phase arm, and 0 < k ≤ 100%.

[0049] Furthermore, the energy-consuming element H1 is any one or a combination of an energy-consuming power source, a first energy-consuming resistor, and a switchable energy-consuming resistor, wherein the switchable energy-consuming resistor includes a second energy-consuming resistor and a switch connected in series with the second energy-consuming resistor.

[0050] On the other hand, the present invention also provides a startup system for a power electronic converter, wherein the system includes:

[0051] The first startup module is used to start the converter from the DC side when an active system is connected to the DC side of the converter;

[0052] The first startup module is used to start the converter from the AC side when an active system is connected to the AC side of the converter;

[0053] The first startup module is used to start the converter from the DC side or the AC side when both the AC side and the DC side of the converter are connected to an active system.

[0054] Furthermore,

[0055] The converter has a pre-charging circuit on its DC side and a switch S3 on its AC side; or...

[0056] The AC side of the converter is equipped with a pre-charging circuit, and the DC side of the converter is equipped with a switch S3; wherein...

[0057] The pre-charging circuit includes a switch S1, a switch S2, and a pre-charging resistor R. One end of the switch S1 is connected to one end of the pre-charging resistor R, one end of the switch S2 is connected to the other end of the switch S1, and the other end of the switch S2 is connected to the other end of the pre-charging resistor R.

[0058] This invention provides a startup method and system for a power electronic converter, which can achieve stable pre-charging during startup, avoid damage to components caused by inrush current, and prevent overvoltage damage to some power switching device modules due to imbalance of module voltage (voltage of the voltage equalizing capacitor in the power switching device module) of the bridge arm.

[0059] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0060] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 A flowchart illustrating a startup method for a power electronic converter according to an embodiment of the present invention is shown.

[0062] Figure 2 A topology diagram of a power electronic converter according to an embodiment of the present invention is shown.

[0063] Figure 3 A topology diagram of a power switching device module according to an embodiment of the present invention is shown.

[0064] Figure 4A topology diagram of a switched capacitor valve is shown when the switched capacitor module is a half-bridge module according to an embodiment of the present invention.

[0065] Figure 5 The topology of the energy-consuming element H1 is shown in the embodiment of the present invention when the energy-consuming element H1 is a power source.

[0066] Figure 6 The topology of the energy-consuming element H1 is shown in an embodiment of the present invention when the energy-consuming element H1 is a first energy-consuming resistor.

[0067] Figure 7 The topology of the energy-consuming element H1 is shown in an embodiment of the present invention, where the energy-consuming element H1 is a switchable energy-consuming resistor.

[0068] Figure 8 A topology diagram of a combination form one according to an embodiment of the present invention is shown.

[0069] Figure 9 A topology diagram of a combination form two according to an embodiment of the present invention is shown.

[0070] Figure 10 A topological diagram of combination form three according to an embodiment of the present invention is shown.

[0071] Figure 11 A converter topology diagram is shown when the pre-charge circuit according to an embodiment of the present invention is provided on the AC side.

[0072] Figure 12 An embodiment of the present invention based on three Figure 2 The diagram shows the topology of a combined converter, which is transformed from a converter, with the pre-charge circuit located on the DC positive bus.

[0073] Figure 13 An embodiment of the present invention based on three Figure 2 The topology diagram of the combined converter, which is transformed from the converter shown, with switch S3 set on the DC positive bus.

[0074] Figure 14 A topology diagram of the converter corresponding to an embodiment of the present invention is shown. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0076] like Figure 1 As shown, the present invention provides a startup method for a power electronic converter, wherein the method includes:

[0077] When the DC side of the converter is connected to an active system, the converter is started from the DC side;

[0078] When the AC side of the converter is connected to an active system, the converter is started from the AC side;

[0079] When both the AC and DC sides of the converter are connected to an active system, the converter is started from the DC side or the AC side.

[0080] The following is a detailed description.

[0081] In one embodiment of the present invention, such as Figure 2 As shown, the converter includes parallel switched capacitor valves and a novel switching valve. The novel switching valve is used to achieve AC / DC conversion, or AC to pulsating DC conversion. The switched capacitor valve is used to achieve the conversion between the converter's stable DC voltage and pulsating DC voltage.

[0082] The switched capacitor valve includes multiple switched capacitor modules connected in series;

[0083] The novel switching valve includes two parallel bridge arms, each of which includes multiple power switching device modules connected in series.

[0084] In one embodiment of the present invention, such as Figure 3 As shown, the power switching device module includes a power switching device T1, a diode D1, a voltage equalizing capacitor C1, and a power dissipating element H1. The anode of the diode D1 is connected to the anode of the power switching device T1. One end of the voltage equalizing capacitor C1 is connected to the cathode of the diode D1, and the other end of the voltage equalizing capacitor C1 is connected to the cathode of the power switching device T1. One end of the power dissipating element H1 is connected to one end of the voltage equalizing capacitor C1, and the other end of the power dissipating element H1 is connected to the other end of the voltage equalizing capacitor C1. A diode is connected in anti-parallel on the power switching device T1.

[0085] In one embodiment of the present invention, the power switching device T1 can be an insulated gate bipolar transistor (IGBT), an integrated gate-commutated thyristor (IGCT), a field-effect transistor (FET), or the like.

[0086] In one embodiment of the present invention, for each phase arm, the anode of the subsequent power switching device T1 is connected to the cathode of the preceding power switching device T1. The power switching device module further includes a bypass element K1, one end of which is connected to the anode of the power switching device T1, and the other end of which is connected to the cathode of the power switching device T1.

[0087] The bypass element K1 has two functions: first, to bypass faulty power switching device modules and ensure the normal operation of other power switching device modules in the bridge arm; second, to bypass corresponding black modules (i.e., some power switching device modules fail to power on the control system for some reason, such as a damaged power supply). Since the power supply of the black module is not working properly, the traditional controllable bypass switch does not have the power to control it to bypass the module. The overvoltage breakdown characteristics of thyristors or diodes are required to achieve automatic bypass of the module.

[0088] The bypass element K1 can be any one or more combinations of mechanical switches, semiconductor switches, and thyristors (e.g., their parallel combination), or K1 can be omitted. In particular, when T1 is an I GCT, K1 does not need to be a thyristor, because the I GCT has the overvoltage breakdown and long-term current-carrying characteristics of a thyristor, which can achieve bypassing of the black module.

[0089] In one embodiment of the present invention, the converter further includes a transformer, wherein one end of a winding on one side of the transformer is connected to the midpoint of one phase bridge arm of the novel switching valve via a connecting inductor L1, and the other end of a winding on one side of the transformer is connected to the midpoint of another phase bridge arm of the novel switching valve.

[0090] In one embodiment of the present invention, the switched capacitor module may be any one or more combinations of a half-bridge module, a full-bridge module, and a hybrid module (e.g., a series combination of a half-bridge module and a full-bridge module), wherein, regardless of whether it is a half-bridge module or a full-bridge module, a power-dissipating element H2 is connected in parallel on the corresponding capacitor portion.

[0091] In this embodiment, T2 can be an IGBT, IGCT, FET, etc. Additionally, in this embodiment, a bypass switch K2 is connected to the switched capacitor module. The bypass element K2 has two functions: firstly, it bypasses the faulty switched capacitor module to ensure the normal operation of other switched capacitor modules; secondly, it bypasses the corresponding black module.

[0092] In addition, in this embodiment, the bypass switch K2 is any one or more combinations of mechanical switches, semiconductor switches and thyristors (e.g., their parallel combination), or in this embodiment, the bypass switch K2 may not be configured.

[0093] In one embodiment of the present invention, such as Figure 4 The illustration uses a switched capacitor module as an example of a half-bridge module. When the switched capacitor module is a half-bridge module, the half-bridge module has a capacitor C2 and two power switching devices T2. The cathode of one power switching device T2 is connected to the anode of the other power switching device T2. One end of the capacitor C2 is connected to the anode of one power switching device T2, and the other end of the capacitor C2 is connected to the cathode of the other power switching device T2. The energy-consuming element H2 mentioned above is connected in parallel on the corresponding capacitor part. Here, the energy-consuming element H2 is connected in parallel on the capacitor C2.

[0094] In this configuration, the anode of one power switch device T2 in the first half-bridge module is connected to the anode of the first power switch device T1 in one phase arm (one phase arm of the novel switching valve). Similarly, the cathode of the other power switch device T2 in the last half-bridge module is connected to the cathode of the first power switch device T1 in one phase arm (one phase arm of the novel switching valve). In the remaining half-bridge modules, the anode of one power switch device T2 in the latter half-bridge module is connected to the cathode of the other power switch device T2 in the former half-bridge module.

[0095] In one embodiment of the present invention, the energy-consuming element H is any one or combination of the energy-harvesting power supply V, the first energy-consuming pre-charging resistor R1, and the switchable energy-consuming resistor, wherein the energy-harvesting power supply V is used to obtain energy from the voltage equalization capacitor C1.

[0096] like Figure 5 As shown, when the energy-consuming element H is the energy-harvesting power supply V, the positive terminal + of the energy-harvesting power supply V is connected to the positive terminal of the voltage equalization capacitor C1, and the negative terminal - is connected to the negative terminal of the voltage equalization capacitor C1.

[0097] like Figure 6 As shown, when the energy-consuming element H is the first energy-consuming pre-charging resistor R1, one end of the first energy-consuming pre-charging resistor R1 is connected to the positive terminal of the voltage equalization capacitor C1, and the other end is connected to the negative terminal of the voltage equalization capacitor C1.

[0098] like Figure 7 As shown, when the energy-consuming element H is a switchable energy-consuming resistor, the switchable energy-consuming resistor includes a second energy-consuming pre-charging resistor R2 and a switch S (exemplarily, the switch S can be a relay, contactor, circuit breaker, semiconductor switch, or other switch with interruptible current). One end of the switch S is connected to one end of the second energy-consuming pre-charging resistor R2, and the other end of the switch S is connected to the positive terminal of the voltage equalizing capacitor C1. The other end of the second energy-consuming pre-charging resistor R2 is connected to the negative terminal of the voltage equalizing capacitor C1. By setting the switch S, the switching control of the second energy-consuming pre-charging resistor R2 can be realized.

[0099] When the energy-consuming element H is a combination of the energy-harvesting power supply V, the first energy-consuming pre-charging resistor R1, and the switchable energy-consuming resistor, the structure of this combination includes, but is not limited to, the following combinations:

[0100] First combination form: such as Figure 8 As shown, the system includes a switchable energy-consuming resistor and an energy-harvesting power supply V. One end of the switch S in the switchable energy-consuming resistor is connected to one end of the second energy-consuming pre-charging resistor R2, and the other end is connected to the positive terminal (+) of the energy-harvesting power supply V. The other end of the second energy-consuming pre-charging resistor R2 is connected to the negative terminal (-) of the energy-harvesting power supply V. The positive terminal (+) of the energy-harvesting power supply V is connected to the positive terminal of the voltage-equalizing capacitor C1, and the negative terminal (-) is connected to the negative terminal of the voltage-equalizing capacitor C1. Furthermore, in this configuration, the switch S can also be modified as follows:

[0101] One end of the switch S in the switchable energy-consuming resistor is connected to the other end of the second energy-consuming pre-charging resistor R2, and the other end of the switch S in the switchable energy-consuming resistor is connected to the negative terminal - of the energy-consuming power supply V; one end of the second energy-consuming pre-charging resistor R2 is connected to the positive terminal + of the energy-consuming power supply V.

[0102] Second combination form: such as Figure 9 As shown, it includes a first energy-consuming pre-charging resistor R1 and an energy-harvesting power supply V. One end of the first energy-consuming pre-charging resistor R1 is connected to the positive terminal + of the energy-harvesting power supply V, and the other end is connected to the negative terminal - of the energy-harvesting power supply V. The positive terminal + of the energy-harvesting power supply V is connected to the positive terminal of the voltage equalization capacitor C1, and the negative terminal - is connected to the negative terminal of the voltage equalization capacitor C1.

[0103] Third combination form: such as Figure 10 The configuration includes a first pre-charging resistor R1, a power supply V, and a switchable pre-charging resistor. One end of the first pre-charging resistor R1 is connected to the positive terminal (+) of the power supply V, and the other end is connected to the negative terminal (-) of the power supply V. The positive terminal (+) of the power supply V is connected to the positive terminal of the voltage equalization capacitor C1, and the negative terminal (-) is connected to the negative terminal of the voltage equalization capacitor C1. One end of the switch S is connected to one end of the second pre-charging resistor R2, and the other end is connected to one end of the first pre-charging resistor R1. The other end of the second pre-charging resistor R2 is connected to the other end of the first pre-charging resistor R1. Furthermore, this configuration can also have the following variations:

[0104] One end of switch S is connected to the other end of the second energy-consuming pre-charging resistor R2, and the other end of switch S is connected to the other end of the first energy-consuming pre-charging resistor R1. One end of the second energy-consuming pre-charging resistor R2 is connected to one end of the first energy-consuming pre-charging resistor R1.

[0105] In one embodiment of the present invention, such as Figure 2As shown, the DC side of the converter is provided with a pre-charging circuit. The pre-charging circuit includes a switch S1, a switch S2 and a pre-charging resistor R. One end of the switch S1 is connected to one end of the pre-charging resistor R, one end of the switch S2 is connected to the other end of the switch S1, and the other end of the switch S2 is connected to the other end of the pre-charging resistor R.

[0106] In this embodiment, the function of the pre-charge resistor R is to limit the charging current and prevent excessive current from damaging the components during charging; the function of switch S1 is to switch the pre-charge resistor R on and off; the function of switch S2 is to bypass the pre-charge resistor R and switch S1 after charging is completed.

[0107] In one embodiment of the present invention, the pre-charging circuit is disposed on the DC positive bus (the embodiment of the present invention is illustrated by taking the pre-charging circuit disposed on the DC positive bus as an example) or the DC negative bus. The DC negative bus is connected to the anode of the first power switching device T1 of a phase bridge arm (a phase bridge arm of the novel switching valve), and the cathode of the last power switching device T1 of the phase bridge arm (a phase bridge arm of the novel switching valve) is connected. In this embodiment, both the DC positive bus and the DC negative bus are also provided with a smoothing reactor L2.

[0108] In this embodiment, the AC side of the converter is provided with a switch S3, that is, the switch S3 is connected to one end of the winding on the other side of the transformer; wherein, in this case, one end of the switch S2 is also connected to the corresponding smoothing reactance L2, and the other end of the switch S2 is also connected to the anode of the first power switching device T1 of a phase bridge arm (a phase bridge arm of the new type of switching valve).

[0109] In this embodiment, the function of switch S3 is to disconnect the converter output terminal before pre-charging is completed, so as to prevent the power supply on the output side from charging the converter and causing undesigned situations, such as overcurrent damage to circuit components.

[0110] In one embodiment of the present invention, such as Figure 11 As shown, the AC side of the converter is provided with a pre-charging circuit, and the DC side of the converter is provided with a switch S3; that is, at this time, one end of the switch S2 is also connected to one end of the winding on the other side of the transformer, and the switch S3 is set on the DC positive bus (the embodiment of the present invention takes the switch S3 being set on the DC positive bus as an example for illustrative explanation) or the DC negative bus. One end of the switch S3 is also connected to the corresponding smoothing reactance L2, and the other end of the switch S3 is also connected to the anode of the first power switching device T1 of a phase bridge arm (a phase bridge arm of the novel switching valve).

[0111] In one embodiment of the present invention, the converter is provided with a pre-charging circuit on both the DC side and the AC side. In this case, the switch S3 is configured on both the DC side and the AC side of the converter, and the configuration is such that the switch S3 is between the corresponding pre-charging circuit and the corresponding power grid (such as the DC power grid or the AC power grid).

[0112] In one embodiment of the present invention, in a single-phase structure, a transformer may not be required.

[0113] In one embodiment of the present invention, in the above-described method for starting a power electronic converter, starting the converter from the DC side includes:

[0114] Step 1: Converter lockout, disconnect switches S2 and S3, and close switch S1.

[0115] Step 2: Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2; control the voltage of all power switching device modules to reach the pre-charge target value Usmr4.

[0116] Step 3: Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup.

[0117] In step 2, controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2 includes:

[0118] Once the voltage of the switched capacitor module rises above the operating voltage of the corresponding power-consuming component of the power supply, the power supply is powered on. (It should be noted that if no power supply is configured within the switched capacitor module, i.e., external power is used, this step is ignored, and the sorting and voltage equalization control is initiated directly.) The sorting and voltage equalization control is then initiated to ensure the consistency of the voltage of all switched capacitor modules until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr1 (assuming the DC bus voltage is Udc and the number of switched capacitor modules is N1, then Usmr...). l = k * Udc / N1, where 0 < k ≤ 100%, usually 95%), bypass N0 switching capacitor modules (the larger N0 is, the faster the charging speed, but the more difficult it is to equalize the voltage of the switched capacitor modules. Therefore, N0 is selected according to the actual circuit parameters to ensure the consistency of module voltage during the charging process). After the voltage of the switched capacitor module reaches k * Udc / (N1 - the number of switched capacitor modules that have been bypassed NA), bypass N0 more switched capacitor modules and repeat the above process until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2, which is usually 95% of the rated value of the switched capacitor module voltage.

[0119] In step 2 of this embodiment, controlling the voltage of all power switching device modules to reach the pre-charge target value Usmr4 includes:

[0120] After the voltage of the power switching device module of the new type of switching valve rises to the rated value of the corresponding power supply, the energy-consuming components of the power supply are powered on (it should be noted that if the power switching device module does not have a power supply configured inside, i.e., external power is used, this step is ignored, and the sorting and equalizing control is started directly). The sorting and equalizing control is started to ensure the consistency of the voltage of all power switching device modules until the voltage of all power switching device modules reaches the pre-charge target value Usmr3 (assuming the DC bus voltage is Udc and the number of power switching device modules in one phase arm is N2, then Usmr3=k*Udc / N). 2, where k is usually 95%), bypass dN2 power switching modules (the larger dN2 is, the faster the charging speed, but the more difficult it is to equalize the voltage of the switched capacitor modules. Therefore, select dN2 according to the actual circuit parameters to ensure the consistency of module voltage during the charging process). After the voltage of the power switching module reaches k*Udc / (N2-number of bypassed power switching modules NB), bypass dN2 more power switching modules and repeat the above process until the voltage of all power switching modules reaches the pre-charge target value Usmr4, which is usually 95% of the rated value of the power switching module voltage.

[0121] In one embodiment of the present invention, in the above-described method for starting a power electronic converter, starting the converter from the AC side includes:

[0122] Step 1: Converter lockout, open switch S2, close switch S1.

[0123] Step 2: Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2; control the voltage of all power switching device modules to reach the pre-charge target value Usmr4.

[0124] Step 3: Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup.

[0125] In step 2 of this embodiment, controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2 includes:

[0126] Once the voltage of the switched capacitor module rises above the corresponding operating voltage of the power supply, the power supply is powered on and the sorting and equalization control is initiated to ensure the consistency of the voltage of all switched capacitor modules. This continues until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr1 (assuming the peak AC phase voltage is Uac and the number of switched capacitor modules is N1, then Usmr1 is k*Uac / N1, where k is usually 95%). N0 switched capacitor modules are bypassed (the larger N0 is, the faster the charging speed, but the more difficult it is to equalize the voltage of the modules. Therefore, N0 is selected based on actual testing to ensure the consistency of the module voltage during the charging process). After the voltage of the switched capacitor module reaches k*Uac / (N1 - the number of bypassed switched capacitor modules NA), another N0 switched capacitor modules are bypassed, and the above process is repeated until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2, which is usually 95% of the rated voltage of the switched capacitor module (95% is just an example and can be 0-100%).

[0127] In step 2 of this embodiment, controlling the voltage of all power switching device modules to reach the pre-charge target value Usmr4 includes:

[0128] After the voltage of the power switching device module of the new switching valve rises to the rated value, the power supply is powered on, and the sorting and equalization control is started to ensure the consistency of the voltage of all power switching device modules until the voltage of all power switching device modules reaches the pre-charge target value Usmr3 (assuming the peak value of the AC phase voltage is Uac, and the number of power switching device modules in one phase arm is N2, then Usmr3=2*k*Uac / N2, where k is usually 95%). dN2 power switching device modules are bypassed (the larger dN2 is, the faster the charging speed, but the more difficult it is to equalize the voltage of the modules. Therefore, dN2 is selected according to the actual circuit parameters to ensure the consistency of the module voltage during the charging process). After the voltage of the power switching device module reaches 2*k*Uac / (N2-number of bypassed power switching device modules NB), another dN2 power switching device modules are bypassed, and the above process is repeated until the voltage of all power switching device modules reaches the pre-charge target value Usmr4, which is usually 95% of the rated value of the power switching device module voltage.

[0129] The method for the sequencing and pressure equalization control of the above-mentioned novel on / off valves is as follows:

[0130] Step 1: Sort the voltage of the equalizing capacitors of all power switching devices inside the new switching valve;

[0131] Step 2: According to the startup strategy (i.e. bypassing dN2 power switching device modules), some power switching devices in the new switching valve bridge arm are bypassed, and others are engaged. Then: after voltage sorting, the power switching device with the higher voltage is selected to bypass (i.e., the power switching device is turned on), and the remaining power switching devices are selected to engage (i.e., the power switching devices are turned off).

[0132] Step 3: Repeat steps 1 to 2 to ensure the long-term consistency of the voltage of the equalizing capacitors of the power switching devices.

[0133] In one embodiment of the present invention, the converter may also be a multiphase combined converter, for example, Figure 12 The combined converter shown and Figure 13 The converter shown is based on 3 Figure 2 The converter shown is transformed, that is, the three Figure 2 The converters shown are connected in series, for example, to... Figure 12 The following is an explanation of the series connection method using an example:

[0134] In the three converters, the cathode of the last power switch T1 in one phase arm of the first converter is connected to the anode of the first power switch T1 in one phase arm of the middle converter; the cathode of the last power switch T1 in one phase arm of the middle converter is connected to the anode of the first power switch T1 in one phase arm of the third converter. The DC positive bus is connected to the anode of the first power switch T1 in the first converter, and the DC negative bus is connected to the cathode of the last power switch T1 in one phase arm of the third converter.

[0135] The three converters can be configured as follows:

[0136] like Figure 12 As shown, a pre-charging circuit is provided on the DC positive bus or DC negative bus, and a switch S3 is provided at one end of the other winding of each of the three transformers. The other ends of the other windings of the three transformers are connected to each other.

[0137] Or, such as Figure 13 As shown, in the three converters, a switch S3 is provided on either the DC positive bus or the DC negative bus. A pre-charging circuit is provided at one end of the other winding of each of the three transformers, and the other ends of the other windings of the three transformers are interconnected.

[0138] The following example illustrates an exemplary method for starting up a power electronic converter according to the present invention.

[0139] by Figure 2 Taking the application of a corresponding single-phase converter as an example for analysis, such as Figure 14As shown, the DC side is connected to the DC power grid, while the AC side can be connected to the AC power grid or directly to an AC load. The pre-charge circuit is located on the DC positive bus.

[0140] The switched capacitor module of this invention only needs to withstand the peak value of the DC bus voltage. The upper and lower bridge arms of the novel switching valve (each phase bridge arm includes an upper bridge arm and a lower bridge arm) together withstand 1 times the peak value of the DC bus voltage, and the power switching device module contains only one fully controlled power switching device. Therefore, Figure 14 The number of power switching devices shown is reduced by more than 25% compared to MMC.

[0141] The bridge arm of the novel switching valve of this invention has no bridge arm reactance, and there is no follow current after the bridge arm is turned off. Therefore, the power switching device module does not have a large charging and discharging power, and the capacitance of the power switching device is small. In contrast, the switched capacitor valve, because its current is twice the frequency of the rectified current obtained by the novel switching valve, has a capacitor voltage fluctuation frequency twice that of the MMC. Furthermore, due to the cancellation of the current at the DC port (forming a DC port between one end of the two L2s), the fluctuation power of the switched capacitor module is 1 / 8 of that of the MMC, and the module capacitance (the capacitance in the switched capacitor module) is also 1 / 8 of that of the MMC.

[0142] The main reason why Multi-Module Converters (MMCs) have not been widely adopted in the market is their high cost. MMCs consist of numerous modules containing expensive components such as power semiconductor switches and capacitors, resulting in a cost far exceeding that of various devices in traditional power systems. This directly hinders the promotion and application of new power systems. The power electronic converter of this invention can significantly reduce the number of power switches and module capacitors, thereby greatly optimizing cost and size, making it suitable for widespread market application.

[0143] Regarding pre-charging, the reason why we can ensure safe completion of pre-charging is as follows:

[0144] A pre-charge resistor R is used to limit the charging current and prevent damage to components caused by inrush current.

[0145] Limiting the number of switched capacitor modules and power switching device modules that are bypassed each time reduces the charging speed when the bypass / exit states of modules in the bridge arm are inconsistent, providing time for module voltage equalization control and ensuring the consistency of module voltage.

[0146] In this invention, a starting system for a power electronic converter is also provided, wherein the system includes:

[0147] The first startup module is used to start the converter from the DC side when an active system is connected to the DC side of the converter;

[0148] The first startup module is used to start the converter from the AC side when an active system is connected to the AC side of the converter;

[0149] The first startup module is used to start the converter from the DC side or the AC side when both the AC side and the DC side of the converter are connected to an active system.

[0150] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A starting method for a power electronic converter, wherein, The method includes: When the DC side of the converter is connected to an active system, the converter is started from the DC side; When the AC side of the converter is connected to an active system, the converter is started from the AC side; When both the AC and DC sides of the converter are connected to an active system, the converter is started from the DC side or the AC side. The converter has a pre-charging circuit on its DC side and a switch S3 on its AC side; or... The AC side of the converter is equipped with a pre-charging circuit, and the DC side of the converter is equipped with a switch S3; or... The converter is provided with a pre-charging circuit on both the DC and AC sides, and a switch S3 is provided on both the DC and AC sides of the converter. in, The pre-charging circuit includes a switch S1, a switch S2, and a pre-charging resistor R, wherein one end of the switch S1 is connected to one end of the pre-charging resistor R, one end of the switch S2 is connected to the other end of the switch S1, and the other end of the switch S2 is connected to the other end of the pre-charging resistor R. The converter includes parallel-connected switched capacitor valves and switching valves. The switching valves are used to achieve AC / DC conversion; the switched capacitor valves are used to achieve soft switching of the converter. The switched capacitor valve includes multiple switched capacitor modules connected in series; The switching valve includes two parallel bridge arms, each of which includes multiple power switching device modules connected in series. The power switching device module includes a power switching device T1, a diode D1, a voltage equalizing capacitor C1, and an energy-consuming element H1. The anode of the diode D1 is connected to the anode of the power switching device T1. One end of the voltage equalizing capacitor C1 is connected to the cathode of the diode D1, and the other end of the voltage equalizing capacitor C1 is connected to the cathode of the power switching device T1. One end of the energy-consuming element H1 is connected to one end of the voltage equalizing capacitor C1, and the other end of the energy-consuming element H1 is connected to the other end of the voltage equalizing capacitor C1. A diode D2 is connected in anti-parallel to the power switching device T1. Starting the converter from the DC side includes: The converter is locked out; switch S2 and switch S3 are disconnected, and switch S1 is closed. Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2; Control the voltage of all power switching device modules to reach the pre-charge target value Usmr4; Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup process; This includes controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2, including: Initiate the sorting and voltage equalization control until all switched capacitor module voltages reach the pre-charge target value Usmr1, then bypass N0 switched capacitor modules until the switched capacitor module voltages reach k. After Udc / (N1-NA), bypass N0 switched capacitor modules; Repeat the above process until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2, where, Usmr1=k Udc / N1; Where Udc is the DC bus voltage, N1 is the number of switched capacitor modules, 0 < k ≤ 100%, and NA represents the number of switched capacitor modules that have been bypassed.

2. The starting method for a power electronic converter according to claim 1, wherein, Controlling the voltage of all power switching device modules to reach the pre-charge target value Usmr4 includes: Initiate the sequential voltage equalization control until all power switch module voltages reach the pre-charge target value Usmr3. Then bypass dN2 power switch modules until the power switch module voltage reaches k. After Udc / (N2-NB), bypass dN2 power switching device modules; Repeat the above process until the voltage of all power switching device modules reaches the pre-charge target value Usmr4; Where Usmr3=k Udc / N2; Where Udc is the DC bus voltage, N2 is the number of power switching device modules in one phase bridge arm, 0 < k ≤ 100%, and NB represents the number of power switching device modules that have been bypassed.

3. The starting method for a power electronic converter according to claim 1, wherein, Starting the converter from the AC side includes: Converter lockout: Open switch S2, close switch S1; Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2; Control the voltage of all power switching device modules to reach the pre-charge target value Usmr4; Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup process.

4. The starting method for a power electronic converter according to claim 3, wherein, Controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2 includes: Initiate the sorting and voltage equalization control until all switched capacitor module voltages reach the pre-charge target value Usmr1, then bypass N0 switched capacitor modules until the switched capacitor module voltages reach k. After Uac / (N1-NA), bypass N0 switched capacitor modules; Repeat the above process until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2; Where Usmr1=k Uac / N1; Where Uac is the peak value of the AC phase voltage, N1 is the number of switched capacitor modules, and 0 < k ≤ 100%.

5. The starting method for a power electronic converter according to claim 3, wherein, Controlling the voltage of all power switching device modules to reach the pre-charge target value Usmr4 includes: Initiate the sequential voltage equalization control until all power switch module voltages reach the pre-charge target value Usmr3. Then bypass dN2 power switch modules until the power switch module voltage reaches 2... k After Uac / (N2-NB), bypass dN2 power switching device modules; Repeat the above process until the voltage of all power switching device modules reaches the pre-charge target value Usmr4; Where Usmr3=2 k Uac / N2; Where Uac is the peak value of the AC phase voltage, N2 is the number of power switching device modules in one phase arm, 0 < k ≤ 100%, and NB represents the number of power switching device modules that have been bypassed.

6. A starting method for a power electronic converter according to any one of claims 1-5, wherein, The energy-consuming element H1 is any one or a combination of an energy-consuming power source, a first energy-consuming resistor, and a switchable energy-consuming resistor, wherein the switchable energy-consuming resistor includes a second energy-consuming resistor and a switch connected in series with the second energy-consuming resistor.

7. A starting system for a power electronic converter, wherein, The system includes: The first startup module is used to start the converter from the DC side when an active system is connected to the DC side of the converter; The second startup module is used to start the converter from the AC side when an active system is connected to the AC side of the converter; The third startup module is used to start the converter from the DC side or the AC side when both the AC side and the DC side of the converter are connected to an active system. The converter has a pre-charging circuit on its DC side and a switch S3 on its AC side; or... The AC side of the converter is equipped with a pre-charging circuit, and the DC side of the converter is equipped with a switch S3; or... The converter is provided with a pre-charging circuit on both the DC and AC sides, and a switch S3 is provided on both the DC and AC sides of the converter. in, The pre-charging circuit includes a switch S1, a switch S2, and a pre-charging resistor R, wherein one end of the switch S1 is connected to one end of the pre-charging resistor R, one end of the switch S2 is connected to the other end of the switch S1, and the other end of the switch S2 is connected to the other end of the pre-charging resistor R. The converter includes parallel-connected switched capacitor valves and switching valves. The switching valves are used to achieve AC / DC conversion; the switched capacitor valves are used to achieve soft switching of the converter. The switched capacitor valve includes multiple switched capacitor modules connected in series; The switching valve includes two parallel bridge arms, each of which includes multiple power switching device modules connected in series. The power switching device module includes a power switching device T1, a diode D1, a voltage equalizing capacitor C1, and an energy-consuming element H1. The anode of the diode D1 is connected to the anode of the power switching device T1. One end of the voltage equalizing capacitor C1 is connected to the cathode of the diode D1, and the other end of the voltage equalizing capacitor C1 is connected to the cathode of the power switching device T1. One end of the energy-consuming element H1 is connected to one end of the voltage equalizing capacitor C1, and the other end of the energy-consuming element H1 is connected to the other end of the voltage equalizing capacitor C1. A diode D2 is connected in anti-parallel to the power switching device T1. Starting the converter from the DC side includes: The converter is locked out; switch S2 and switch S3 are disconnected, and switch S1 is closed. Control the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2; Control the voltage of all power switching device modules to reach the pre-charge target value Usmr4; Lock the entire converter, disconnect switch S1, and close switches S2 and S3 to complete the startup process; This includes controlling the voltage of all switched capacitor modules to reach the pre-charge target value Usmr2, including: Initiate the sorting and voltage equalization control until all switched capacitor module voltages reach the pre-charge target value Usmr1, then bypass N0 switched capacitor modules until the switched capacitor module voltages reach k. After Udc / (N1-NA), bypass N0 switched capacitor modules; Repeat the above process until the voltage of all switched capacitor modules reaches the pre-charge target value Usmr2, where, Usmr1=k Udc / N1; Where Udc is the DC bus voltage, N1 is the number of switched capacitor modules, 0 < k ≤ 100%, and NA represents the number of switched capacitor modules that have been bypassed.

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