Combined active phase commutation high voltage direct current transmission converter

Abstract

This invention belongs to the field of converter and its control technology, specifically relating to a combined active-commutation HVDC converter and its control method, aiming to solve the problems of large size and heavy weight of filter elements in existing active-commutation HVDC converters. The invention includes: N active-commutation converters, N corresponding transformers, three-phase filter capacitors and three-phase filter inductors on the AC side, and filter inductors on the DC side. By controlling the switching time and conduction time of the turn-off devices inside each active-commutation converter, three-phase grid current control can be achieved. This invention effectively avoids the risk of commutation failure in traditional technologies, and the three-level square wave currents of different phases output from the grid-side transformer windings can be superimposed to form a multi-level stepped wave current, which outputs high-power-quality AC current to the grid side after passing through the AC-side filter network. Furthermore, by controlling each active-commutation converter, the active and reactive power on the grid side can be decoupled.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of converter and its control, and particularly relates to a combined active commutation high-voltage direct current transmission converter and a control method thereof. BACKGROUND

[0002] At present, compared with the traditional high-voltage alternating current transmission technology, the high-voltage direct current transmission technology has the advantages of larger power supply capacity, longer power supply radius, no outstanding power quality problems, and no reactive power compensation problems. The high-voltage direct current transmission converter is an important part of this technology, which can realize the conversion of electric energy between alternating current and direct current. In the field of high-voltage direct current transmission, the existing converters are mainly divided into two categories, including grid commutation converters based on thyristors and flexible direct current converters based on voltage sources. The grid commutation converter based on thyristors needs to be passively commutated according to the grid voltage, and the number of output levels is small. When used, there is a large amount of reactive power on the alternating current side, and a large number of filtering devices and reactive power compensation devices need to be configured to realize high power factor and high power quality output. The flexible direct current converter based on voltage source, taking the modular multilevel converter as an example, can output multiple levels, has good harmonic characteristics, and can independently control active power and reactive power, without the need to set filters and reactive power compensation devices. However, the power module of this type of converter integrates a large number of energy storage capacitors, resulting in large equipment size and high cost.

[0003] To solve the above problems, some existing patents propose an active commutation type high-voltage direct current transmission converter [1][2], which can realize a maximum of six-level current output through the cooperation of two active commutation converters, and the waveform presents a stepped shape. Although the high-frequency harmonics in the current can be removed through filtering devices to improve the output power quality, the filtering elements are large in size and heavy in weight.

[0004] The following documents are related technical background information of the present application:

[0005] [1] Li Zixin, Xu Fei, Zhao Cong, et al. Active commutation type high-voltage direct current transmission converter, 2019-10-23, CN201911008816.

[0006] [2] Zhao Cong, Luan Kedong, Li Zixin, et al. An active commutation type high-voltage direct current transmission converter, 2019-11-04, CN201911066054. SUMMARY

[0007] In order to solve the above problems in the prior art, that is, the problem of large size and heavy weight of the filtering elements of the existing active commutation type high-voltage direct current transmission converter, the present application provides a combined active commutation high-voltage direct current transmission converter, which comprises:

[0008] DC side filtering inductor L dc, for filtering the input DC current on the DC side;

[0009] N active commutation converters, for converting the input DC current to the output AC current;

[0010] N transformers corresponding to the active commutation converters, for changing the AC voltage output by the active commutation converters through electromagnetic induction;

[0011] an AC measurement three-phase filter capacitor C a , an AC measurement three-phase filter capacitor C b , an AC measurement three-phase filter capacitor C c , and an AC side three-phase filter inductor L a , an AC side three-phase filter inductor L b , an AC side three-phase filter inductor L c , for filtering the output AC current.

[0012] In some preferred embodiments, the combined active commutation HVDC converter has the following connection relationship:

[0013] one end of the DC side filter inductor L dc is connected to the DC side input Pin, and the other end is connected to the DC input end of the first active commutation converter in the N active commutation converters, and the DC output end of the Nth active commutation converter in the active commutation converters is connected to the DC side input Nin;

[0014] The AC output ends of the N active commutation converters are respectively connected to the input ends of the N corresponding transformers;

[0015] The DC output end of the i-th active commutation converter in the N active commutation converters is connected to the DC input end of the i+1-th active commutation converter, where 1≤i

[0016] The A phase, B phase and C phase of the output ends of the N transformers are connected together and connected to one end of the AC side three-phase filter inductor L a , the AC side three-phase filter inductor L b , the AC side three-phase filter inductor L c and the AC measurement three-phase filter capacitor C a , the AC measurement three-phase filter capacitor C b , the AC measurement three-phase filter capacitor C c ;

[0017] The AC measurement three-phase filter capacitor C a , the AC measurement three-phase filter capacitor C b , the AC measurement three-phase filter capacitor Cc The AC side three-phase filter inductance L a , the AC side three-phase filter inductance L b and the AC side three-phase filter inductance L c The other ends of the AC side three-phase filter inductance L

[0018] In some preferred embodiments, the i-th active commutation converter comprises a reverse blocking controllable device Si1, a reverse blocking controllable device Si2, a reverse blocking controllable device Si3, a reverse blocking controllable device Si4, a reverse blocking controllable device Si5, and a reverse blocking controllable device Si6, wherein 1≤i≤N.

[0019] The anodes of the reverse blocking controllable device Si1, the reverse blocking controllable device Si3, and the reverse blocking controllable device Si5 are connected together as a DC input end of the i-th active commutation converter.

[0020] The cathodes of the reverse blocking controllable device Si2, the reverse blocking controllable device Si4, and the reverse blocking controllable device Si6 are connected together as a DC output end of the i-th active commutation converter.

[0021] The cathode of the reverse blocking controllable device Si1 and the anode of the reverse blocking controllable device Si4 are connected together as an AC output end a-phase of the i-th active commutation converter.

[0022] The cathode of the reverse blocking controllable device Si3 and the anode of the reverse blocking controllable device Si6 are connected together as an AC output end b-phase of the i-th active commutation converter.

[0023] The cathode of the reverse blocking controllable device Si5 and the anode of the reverse blocking controllable device Si2 are connected together as an AC output end c-phase of the i-th active commutation converter.

[0024] In some preferred embodiments, the AC side of the active commutation converter has three-phase AC power supply voltages uga, ugb, and ugc, and uga, ugb, and ugc are sine waves with equal voltage amplitudes and a frequency f.

[0025] In some preferred embodiments, the primary winding and the secondary winding of each of the N transformers are connected in Y / Y mode, and the transformation ratio of the primary winding to the secondary winding is n:1, wherein n is a positive integer.

[0026] In another aspect of the present application, a control method for the combined active commutation HVDC converter is provided, based on the combined active commutation HVDC converter described above, and the control method comprises:

[0027] By adjusting the initial phase angle and the on-time of the switch of the reverse blocking controllable device of the N active phase commutated converters, the control of the current I dc and the reactive power of the grid side is realized; the current I dc flows from the DC side input Pin, through the DC side filter inductor L dc to the first active phase commutated converter of the N active phase commutated converters.

[0028] By adjusting the main power regulation phase angle a of the combined active phase commutated HVDC converter, the control of the current I dc is realized.

[0029] In some preferred embodiments, the initial phase angle and the on-time of the switch of the reverse blocking controllable device are determined by:

[0030] In each cycle 1 / f, the phase of uga when uga and ugc of the three-phase AC power supply voltage uga, ugb and ugc of the AC side are both positive and uga=ugc is defined as γ; the main power regulation phase angle of the combined active phase commutated HVDC converter is defined as a, a∈[0π], and the reactive power regulation phase angle is defined as β, β∈[-ππ].

[0031] The switching frequency of the reverse blocking controllable device Si1, Si2, Si3, Si4, Si5 and Si6 in the i-th active phase commutated converter is f, and the on-time in each cycle 1 / f is 1 / 3f, and the remaining 2 / 3f is in the off state.

[0032] In some preferred embodiments, after phase locking, the on and off phases of the reverse blocking controllable device of the i-th active phase commutated converter are referenced to the phase of the three-phase AC power supply voltage uga of the AC side:

[0033] The on phase of the reverse blocking controllable device Si1 is γ-a-β*(i-1) / N-1, and the off phase is γ-a-β*(i-1) / N-1+2*π / 3;

[0034] The on phase of the reverse blocking controllable device Si2 is γ-a-β*(i-1) / N-1+π / 3, and the off phase is γ-a-β*(i-1) / N-1+π;

[0035] The on phase of the reverse blocking controllable device Si3 is γ-a-β*(i-1) / N-1+2*π / 3, and the off phase is γ-a-β*(i-1) / N-1+4*π / 3;

[0036] The phase of the reverse blocking turn-off device Si4 when turned on is gamma-alpha-beta*(i-1) / N-1+pi, and the phase when turned off is gamma-alpha-beta*(i-1) / N-1+5*Pi / 3.

[0037] The phase of the reverse blocking turn-off device Si5 when turned on is gamma-alpha-beta*(i-1) / N-1+4*Pi / 3, and the phase when turned off is gamma-alpha-beta*(i-1) / N-1+2*Pi.

[0038] The phase of the reverse blocking turn-off device Si6 when turned on is gamma-alpha-beta*(i-1) / N-1+5*Pi / 3, and the phase when turned off is gamma-alpha-beta*(i-1) / N-1+7*Pi / 3.

[0039] In the calculation of the turn-on or turn-off phase of the reverse blocking turn-off device, if a phase greater than 2Pi appears, the phase after subtracting 2Pi is taken as the actual turn-on or turn-off phase; if a phase less than 0 appears, the phase after adding 2Pi is taken as the actual turn-on or turn-off phase.

[0040] In some preferred embodiments, the current I dc is controlled by adjusting the main power regulation phase angle alpha of the combined active commutation high-voltage direct-current transmission converter.

[0041] When the average value of the direct-current voltage between the direct-current side input Pin and the direct-current side input Nin is positive, if the current I dc is less than the reference value, the regulation phase angle alpha is increased, otherwise the regulation phase angle alpha is decreased.

[0042] When the average value of the direct-current voltage between the direct-current side input Pin and the direct-current side input Nin is negative, if the current I dc is less than the reference value, the regulation phase angle alpha is decreased, otherwise the regulation phase angle alpha is increased.

[0043] In some preferred embodiments, the reactive power regulation phase angle beta of the combined active commutation high-voltage direct-current transmission converter is obtained by the following method:

[0044] The current i ga , i gb , i gc of the three-phase alternating current power grid is taken as positive, and the reactive power Q of the three-phase alternating current power grid is obtained.

[0045] The reactive power Q is compared with a preset value, and the reactive power regulation phase angle beta of the combined active commutation high-voltage direct-current transmission converter is obtained by a PI controller.

[0046] The beneficial effects of the present application are as follows:

[0047] (1) The combined active commutation high-voltage direct current transmission converter of the application can realize multi-level approximate sine wave current output through coordinated control of multiple active commutation converters, thereby reducing the size and quantity of network side filter network elements and improving the quality of network side electric energy output.

[0048] (2) The combined active commutation high-voltage direct current transmission converter of the application introduces reactive power regulation phase angle in the control link, thereby realizing independent control of active power and reactive power. BRIEF DESCRIPTION OF DRAWINGS

[0049] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments made with reference to the accompanying drawings:

[0050] Figure 1 is a structural schematic diagram of the combined active commutation high-voltage direct current transmission converter of the application;

[0051] Figure 2 is a control process and inverse resistance type controllable turn-off device conduction phase schematic diagram of the combined active commutation high-voltage direct current transmission converter of the application. DETAILED DESCRIPTION

[0052] The application will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0053] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0054] The combined active commutation high-voltage direct current transmission converter of the application comprises:

[0055] DC side filter inductance L dc for filtering high-voltage DC side input DC current;

[0056] N active commutation converters for converting input side DC current to output side AC current;

[0057] N transformers corresponding to the active commutation converters for changing the AC voltage output by the active commutation converters through electromagnetic induction;

[0058] AC measurement three-phase filter capacitor C a AC measurement three-phase filter capacitor C b AC measurement three-phase filter capacitor Cc and the AC side three-phase filter inductance L a and the AC side three-phase filter inductance L b and the AC side three-phase filter inductance L c for filtering the output side AC current.

[0059] In order to more clearly illustrate the combined active commutation high voltage direct current transmission converter of the present application, the following will combine Figure 1 The modules in the embodiment of the present application will be described in detail.

[0060] The combined active commutation high voltage direct current transmission converter of the first embodiment of the present application comprises a DC side filter inductance L dc N active commutation converters, N transformers corresponding to the active commutation converters, an AC measurement three-phase filter capacitor and an AC side three-phase filter inductance, and each module is described in detail as follows:

[0061] The DC side filter inductance L dc for filtering the high voltage DC side input DC current.

[0062] The N active commutation converters are used for converting the input side DC current to the output side AC current.

[0063] The i-th active commutation converter comprises an inverse blocking type turn-off device Si1, an inverse blocking type turn-off device Si2, an inverse blocking type turn-off device Si3, an inverse blocking type turn-off device Si4, an inverse blocking type turn-off device Si5, and an inverse blocking type turn-off device Si6, wherein 1≤i≤N:

[0064] The anodes of the inverse blocking type turn-off devices Si1, Si3 and Si5 are connected together as the DC input end of the i-th active commutation converter;

[0065] The cathodes of the inverse blocking type turn-off devices Si2, Si4 and Si6 are connected together as the DC output end of the i-th active commutation converter;

[0066] The cathode of the inverse blocking type turn-off device Si1 and the anode of the inverse blocking type turn-off device Si4 are connected together as the AC output end a phase of the i-th active commutation converter;

[0067] The cathode of the inverse blocking type turn-off device Si3 and the anode of the inverse blocking type turn-off device Si6 are connected together as the AC output end b phase of the i-th active commutation converter;

[0068] The cathode of the inverse blocking type turn-off device Si5 and the anode of the inverse blocking type turn-off device Si2 are connected together as the AC output end c phase of the i-th active commutation converter.

[0069] The active phase commutated converter has three-phase alternating current power voltages uga, ugb and ugc on the alternating current side, and the voltages uga, ugb and ugc are sine waves with equal voltage amplitudes and a frequency f.

[0070] N transformers corresponding to the active phase commutated converter are used to change the alternating current voltage output by the active phase commutated converter through electromagnetic induction.

[0071] The primary winding and the secondary winding of the N transformers are connected in Y / Y mode, and the transformation ratio of the primary winding to the secondary winding is n:1, wherein n is a positive integer.

[0072] The alternating current measurement three-phase filter capacitor C a The alternating current measurement three-phase filter capacitor C b The alternating current measurement three-phase filter capacitor C c The alternating current side three-phase filter inductor L a The alternating current side three-phase filter inductor L b The alternating current side three-phase filter inductor L c for filtering the output side alternating current.

[0073] As Figure 1 shown in the structure schematic diagram of the combined active phase commutated high-voltage direct current transmission converter, the connection relationship of the combined active phase commutated high-voltage direct current transmission converter is:

[0074] One end of the direct current side filter inductor L dc is connected to the direct current side input Pin, and the other end is connected to the direct current input end Py1 of the first active phase commutated converter in the N active phase commutated converters, and the direct current output end Ny N of the Nth active phase commutated converter in the active phase commutated converters is connected to the direct current side input Nin.

[0075] The alternating current output ends of the N active phase commutated converters are respectively connected to the input ends of the one-to-one corresponding N transformers.

[0076] The direct current output end Ny i of the i-th active phase commutated converter in the N active phase commutated converters is connected to the direct current input end Py i+1 of the i+1-th active phase commutated converter, wherein 1≤i

[0077] The A phase (A1 end, A2 end, …, AN-1 end, AN end connected together), B phase (B1 end, B2 end, …, BN-1 end, BN end connected together), and C phase (C1 end, C2 end, …, CN-1 end, CN end connected together) of the output ends of the N transformers are respectively connected together and connected to the alternating current side three-phase filter inductor L a(d terminal), AC side three-phase filter inductance L b (e terminal), AC side three-phase filter inductance L c (f terminal) and AC measurement three-phase filter capacitance C a (d terminal), AC measurement three-phase filter capacitance C b (e terminal), AC measurement three-phase filter capacitance C c (f terminal) one end;

[0078] AC measurement three-phase filter capacitance C a , AC measurement three-phase filter capacitance C b , AC measurement three-phase filter capacitance C c are connected together (Mc terminal), AC side three-phase filter inductance L a , AC side three-phase filter inductance L b and AC side three-phase filter inductance L c The other end of the AC side three-phase filter inductance L is connected to the three-phase input end of the three-phase AC power grid.

[0079] The control method of the combined active commutation high-voltage direct-current transmission converter of the second embodiment of the application is based on the combined active commutation high-voltage direct-current transmission converter described above, and the control method comprises the following steps:

[0080] By adjusting the switch initial phase angle and conduction time of the reverse blocking controllable device of the N active commutation converters, the control of the current I dc input from the DC side and the grid-side reactive power is realized; the current I dc flows from the DC side input Pin, passes through the DC side filter inductance L dc , and flows to the first active commutation converter of the N active commutation converters.

[0081] The switch initial phase angle and conduction time of the reverse blocking controllable device are determined by the following method:

[0082] In each cycle 1 / f, define the phase of uga as γ when uga and ugc in the three-phase AC power supply voltage uga, ugb and ugc on the AC side are both positive and uga=ugc; define the main power regulation phase angle of the combined active commutation high-voltage direct-current transmission converter as α, and α∈[0π]; define the reactive power regulation phase angle as β, and β∈[-ππ];

[0083] The switch frequency of the reverse blocking controllable device Si1, Si2, Si3, Si4, Si5 and Si6 in the i-th active commutation converter is f, and the conduction time in each cycle 1 / f is 1 / 3f, and the remaining 2 / 3f time is in the off state.

[0084] As Figure 2As shown, it is the control process and conducting phase diagram of the combination type active commutation high voltage direct current transmission converter of the application, after phase locking, taking the phase of three-phase alternating current power voltage uga on the alternating current side as the reference, the conducting and shutting off phases of the reverse resistance type controllable semiconductor device of the i-th active commutation converter are respectively:

[0085] The conducting phase of the reverse resistance type controllable semiconductor device Si1 is γ-α-β*(i-1) / N-1, and the shutting off phase is γ-α-β*(i-1) / N-1+2*π / 3;

[0086] The conducting phase of the reverse resistance type controllable semiconductor device Si2 is γ-α-β*(i-1) / N-1+π / 3, and the shutting off phase is γ-α-β*(i-1) / N-1+π;

[0087] The conducting phase of the reverse resistance type controllable semiconductor device Si3 is γ-α-β*(i-1) / N-1+2*π / 3, and the shutting off phase is γ-α-β*(i-1) / N-1+4*π / 3;

[0088] The conducting phase of the reverse resistance type controllable semiconductor device Si4 is γ-α-β*(i-1) / N-1+π, and the shutting off phase is γ-α-β*(i-1) / N-1+5*π / 3;

[0089] The conducting phase of the reverse resistance type controllable semiconductor device Si5 is γ-α-β*(i-1) / N-1+4*π / 3, and the shutting off phase is γ-α-β*(i-1) / N-1+2*π;

[0090] The conducting phase of the reverse resistance type controllable semiconductor device Si6 is γ-α-β*(i-1) / N-1+5*π / 3, and the shutting off phase is γ-α-β*(i-1) / N-1+7*π / 3.

[0091] In the conducting or shutting off phase calculation of the reverse resistance type controllable semiconductor device, if the phase is greater than 2π, then the phase after subtracting 2π is taken as the actual conducting or shutting off phase; if the phase is less than 0, then the phase after adding 2π is taken as the actual conducting or shutting off phase.

[0092] By adjusting the main power regulation phase angle α of the combination type active commutation high voltage direct current transmission converter, the control of the current I dc is realized.

[0093] When the average value of the direct current voltage between the direct current side input Pin and the direct current side input Nin is positive, if the current I dc is less than its reference value, then the regulation phase angle α is increased, otherwise the regulation phase angle α is decreased;

[0094] When the average value of the direct current voltage between the direct current side input Pin and the direct current side input Nin is negative, if the current I dc is less than its reference value, the adjustment phase angle a is decreased, otherwise the adjustment phase angle a is increased.

[0095] The method for obtaining the reactive power adjustment phase angle b of the combined active commutation high voltage direct current transmission converter is as follows:

[0096] The current i ga , i gb , i gc of the three-phase alternating current power grid is taken as positive, and the reactive power Q of the three-phase alternating current power grid is obtained.

[0097] The reactive power Q is compared with a preset value, and is adjusted by a PI controller, so as to obtain the reactive power adjustment phase angle b of the combined active commutation high voltage direct current transmission converter.

[0098] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process and related description of the above-described method can refer to the corresponding process in the foregoing system embodiments, which will not be described here.

[0099] It should be noted that the combined active commutation high voltage direct current transmission converter and the control method thereof provided in the foregoing embodiments are only exemplified by the division of the above-described functional modules, and in actual application, the above-described functions can be completed by different functional modules according to needs, that is, the modules or steps in the embodiments of the present application are further divided or combined, for example, the modules in the foregoing embodiments can be combined into one module, or can be further split into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present application are only for distinguishing the modules and steps, and should not be considered as an improper limitation on the present application.

[0100] The terms "first", "second", and the like are used to distinguish similar objects, and are not used to describe or indicate a particular order or sequence.

[0101] The term "comprising" or any other similar term is intended to encompass non-exclusive inclusion, so that the process, method, article or equipment / device including a series of elements includes not only those elements, but also other elements not explicitly listed, or further includes the elements inherent to the process, method, article or equipment / device.

[0102] The technical scheme of the present application has been described in combination with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical schemes after the changes or replacements will all fall within the protection scope of the present application.

Claims

1. A combined active commutation high voltage direct current converter, characterized in that The combined active commutation high-voltage direct current transmission converter comprises: Direct current side filter inductance L dc for filtering the direct current input from the high voltage direct current side; N active commutation converters for converting input side direct current into output side alternating current; N transformers corresponding to the active commutation converters for changing alternating voltage output by the active commutation converters through electromagnetic induction; AC measurement three-phase filter capacitor C a AC measurement three-phase filter capacitor C b AC measurement three-phase filter capacitor C c and AC side three-phase filter inductor L a AC side three-phase filter inductor L b AC side three-phase filter inductor L c for performing filtering of the output side AC current; The control method of the combined active commutation high-voltage direct current transmission converter comprises: By adjusting the switch initial phase angle and conduction time of the reverse blocking turn-off device of N said active phase commutated converters, the current I dc input from the DC side and the control of the reactive power on the grid side are realized; the current I dc flows from the DC side input Pin, through the DC side filter inductance L dc to the first active phase commutated converter among N said active phase commutated converters; The control of the current I is achieved by adjusting the main power regulating phase angle a of the combined active commutation high voltage direct current converter dc .

2. The combined line-commutated high voltage direct current converter according to claim 1, characterized in that The combined active commutation high-voltage direct current transmission converter has the following connection relationship: The direct current side filtering inductance L dc One end of the direct current side filtering inductance L is connected to the direct current side input Pin, and the other end is connected to a direct current input end of a first active phase commutation converter in the N active phase commutation converters, and a direct current output end of an Nth active phase commutation converter in the N active phase commutation converters is connected to a direct current side input Nin. The alternating current output ends of the N active commutation converters are respectively connected to the input ends of the N transformers; The direct current output end of the i-th active commutation converter is connected to the direct current input end of the i+1-th active commutation converter, wherein 1≤i A phase, B phase and C phase of the output end of N transformers are connected together and connected to the three-phase filter inductance L on the AC side a , the three-phase filter inductance L on the AC side b , the three-phase filter inductance L on the AC side c and the three-phase filter capacitor C on the AC side a , the three-phase filter capacitor C on the AC side b , the three-phase filter capacitor C on the AC side c one end of the three-phase filter capacitor C on the AC side The AC measurement three-phase filter capacitor C a The AC measurement three-phase filter capacitor C b The AC measurement three-phase filter capacitor C c The AC side three-phase filter inductor L a The AC side three-phase filter inductor L b The AC side three-phase filter inductor L c The other ends of the AC side three-phase filter inductor L 3. The combined line-commutated high voltage direct current converter according to claim 2, characterized in that The anodes of the reverse blocking controllable devices Si1, Si3 and Si5 are connected together as the direct current input end of the i-th active commutation converter; The cathodes of the reverse blocking controllable devices Si2, Si4 and Si6 are connected together as the direct current output end of the i-th active commutation converter; The cathode of the reverse blocking controllable device Si1 and the anode of the reverse blocking controllable device Si4 are connected together as the alternating current output end a-phase of the i-th active commutation converter; The cathode of the reverse blocking controllable device Si3 and the anode of the reverse blocking controllable device Si6 are connected together as the alternating current output end b-phase of the i-th active commutation converter; The cathode of the reverse blocking controllable device Si5 and the anode of the reverse blocking controllable device Si2 are connected together as the alternating current output end c-phase of the i-th active commutation converter. The three-phase alternating current supply voltages on the alternating current side of the active commutation converter are uga, ugb and ugc, and uga, ugb and ugc are sine waves with equal voltage amplitudes and frequency f.

4. The combined line-commutated high voltage direct current converter according to claim 3, characterized in that The primary winding and the secondary winding of the N transformers are connected in Y / Y mode, and the transformation ratio of the primary winding to the secondary winding is n:1, wherein n is a positive integer.

5. The combined line-commutated high voltage direct current converter according to claim 4, characterized in that The switch initial phase angle and the conduction time of the reverse blocking controllable device are determined by the following method:

6. The combined line-commutated high voltage direct current converter of claim 1, wherein, In each cycle 1 / f, the phase of uga is defined as γ when uga and ugc are both positive and uga=ugc in the three-phase alternating current supply voltages uga, ugb and ugc on the alternating current side; the main power regulation phase angle of the combined active commutation high-voltage direct current transmission converter is defined as α, and α∈[0π]; the reactive power regulation phase angle is defined as β, and β∈[-ππ]. ​ The switching frequency of the reverse blocking turn-off device Si1, Si2, Si3, Si4, Si5 and Si6 in the i-th active commutation converter is f, and the conduction time in each cycle 1 / f is 1 / 3f, and the remaining 2 / 3f is in the off state.

7. The combined line-commutated high voltage direct current converter of claim 6, wherein, After phase locking, the conduction and off phases of the reverse blocking turn-off device of the i-th active commutation converter are referenced to the phase of the three-phase alternating current power supply voltage uga on the alternating current side, and are respectively: The phase of the reverse blocking turn-off device Si1 when conducting is γ-α-β*(i-1) / N-1, and the phase when turning off is γ-α-β*(i-1) / N-1+2*π / 3; The phase of the reverse blocking turn-off device Si2 when conducting is γ-α-β*(i-1) / N-1+π / 3, and the phase when turning off is γ-α-β*(i-1) / N-1+π; The phase of the reverse blocking turn-off device Si3 when conducting is γ-α-β*(i-1) / N-1+2*π / 3, and the phase when turning off is γ-α-β*(i-1) / N-1+4*π / 3; The phase of the reverse blocking turn-off device Si4 when conducting is γ-α-β*(i-1) / N-1+π, and the phase when turning off is γ-α-β*(i-1) / N-1+5*π / 3; The phase of the reverse blocking turn-off device Si5 when conducting is γ-α-β*(i-1) / N-1+4*π / 3, and the phase when turning off is γ-α-β*(i-1) / N-1+2*π; The phase of the reverse blocking turn-off device Si6 when conducting is γ-α-β*(i-1) / N-1+5*π / 3, and the phase when turning off is γ-α-β*(i-1) / N-1+7*π / 3; In the conduction or off phase calculation of the reverse blocking turn-off device, if a phase greater than 2π appears, the phase after subtracting 2π is taken as the actual on or off phase; if a phase less than 0 appears, the phase after adding 2π is taken as the actual on or off phase.

8. The combined line-commutated high voltage direct current converter of claim 7, wherein, The control of the current I is achieved by adjusting the main power regulating phase angle a of the combined active commutation high voltage direct current converter dc The method is characterized by comprising the following steps. When the average value of the direct current voltage between the direct current side input Pin and the direct current side input Nin is positive, if the current I dc is less than its reference value, the adjustment phase angle a is increased, otherwise the adjustment phase angle a is decreased; When the average of the direct current voltage between the direct current side input Pin and the direct current side input Nin is negative, if the current I dc is less than its reference value, the adjustment phase angle a is decreased, otherwise the adjustment phase angle a is increased.

9. The combined line-commutated high voltage direct current converter of claim 8, wherein, The method for obtaining the reactive power regulation phase angle β of the combined active commutation high-voltage direct current transmission converter is: with the current i of the three-phase alternating current network ga , i gb , i gc in the direction of the current flow into the network is positive, the reactive power Q of the three-phase alternating current network is determined The reactive power Q is compared with a pre-set value, and the reactive power regulation phase angle β of the combined active commutation high-voltage direct current transmission converter is obtained through a PI controller.

Images