CN115720048A - Hybrid rectification circuit based on multi-winding transformer and control method - Google Patents
Hybrid rectification circuit based on multi-winding transformer and control method Download PDFInfo
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- CN115720048A CN115720048A CN202211495790.6A CN202211495790A CN115720048A CN 115720048 A CN115720048 A CN 115720048A CN 202211495790 A CN202211495790 A CN 202211495790A CN 115720048 A CN115720048 A CN 115720048A
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Abstract
The invention discloses a hybrid rectification circuit based on a multi-winding transformer and a control method, wherein the control method comprises the following steps: the power generation device comprises a generator, a multi-winding transformer, a voltage source converter, a chopping module and at least two groups of rectifier bridges; the multi-winding transformer is used for converting alternating current generated by the generator into a plurality of alternating currents and distributing the plurality of alternating currents to the voltage source converter and the rectifier bridge; the rectifier bridge is used for converting alternating current distributed by the multi-winding transformer into direct current, the voltage source converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, and the output end of the chopping module is sequentially connected with the output ends of at least two groups of rectifier bridges in series. The power of the generator is shared by the rectifier bridge and the voltage source converter and rectified into direct current power, so that the high-power high-voltage AC/DC conversion function can be realized, the waveform quality of the stator current is purified, and the power generation efficiency of the system is improved.
Description
Technical Field
The invention relates to the technical field of power generation, in particular to a hybrid rectification circuit based on a multi-winding transformer and a control method.
Background
Wind energy is clean, pollution-free, widely distributed and large-storage-capacity renewable energy, is the most mature new energy variety developed on a large scale at present, and becomes the main force for realizing the aim of carbon neutralization at present. Wind power generation is a main form of wind energy development and utilization, and can be divided into onshore wind power and offshore wind power according to development environments. Compared with the continuously reduced onshore wind energy development resources, offshore wind power has the remarkable advantages of abundant resources, high electricity generation utilization hours, no land occupation, suitability for large-scale development and the like, and becomes an important direction for current wind power development.
Aiming at the technical problems that an alternating current sending-out scheme is limited by sea cable capacitive charging power and the like in a large-scale long-distance wind power collecting-transmitting system, particularly in an offshore wind power scene, the flexible direct current transmission scheme is difficult to be applied to a deep and distant wind power sending-out scene, and has obvious technical advantages. However, as the capacity and the area of a wind power plant are continuously increased, the technical and economic problems of applying flexible direct current to remote wind power integration are increasingly prominent, the wind power integration link still adopts alternating current, direct current and alternating current to cause low overall efficiency of the system, and the development of a direct current output type fan unit has positive significance on integration cost and power generation efficiency.
At present, high direct current voltage in a large-scale wind power direct current collection-transmission scheme is realized by direct series-parallel connection of a DC/DC converter or a fan, a multi-stage conversion structure is adopted, a high-capacity high-transformation-ratio DC/DC converter basically needs multi-stage conversion, and the system efficiency is low.
Disclosure of Invention
In view of this, embodiments of the present invention provide a hybrid rectifier circuit based on a multi-winding transformer and a control method thereof, so as to solve the technical problem of low efficiency in the prior art.
The technical scheme provided by the invention is as follows:
the first aspect of the embodiments of the present invention provides a hybrid rectifier circuit based on a multi-winding transformer, including: the power generation device comprises a generator, a multi-winding transformer, a voltage source converter, a chopping module and at least two groups of rectifier bridges; the generator is used for generating alternating current; the multi-winding transformer comprises a primary side three-phase winding and at least three secondary side three-phase windings, the primary side three-phase winding of the multi-winding transformer is connected with the generator, at least one secondary side three-phase winding of the multi-winding transformer is connected with the alternating current side of the voltage source converter, the other secondary side three-phase windings of the multi-winding transformer are respectively connected with the input ends of at least two groups of rectifier bridges, and the multi-winding transformer is used for converting the alternating current generated by the generator into a plurality of alternating currents and distributing the plurality of alternating currents to the voltage source converter and the rectifier bridges; the rectifier bridge is used for converting alternating current distributed by the multi-winding transformer into direct current, the direct current side of the voltage source converter is connected with the input end of the chopping module, the voltage source converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, the output end of the chopping module and the output ends of at least two groups of rectifier bridges are sequentially connected in series to form a total direct current output port, and the chopping module is used for controlling direct current voltage of the output end of the chopping module to further adjust the total direct current output voltage.
Optionally, the voltage source converter comprises a controller and an AC/DC converter; the AC side of the AC/DC converter is connected with at least one set of secondary three-phase windings of the multi-winding transformer, and the DC side of the AC/DC converter is connected with the input end of the chopping module; the AC/DC converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, and the AC/DC converter and the chopping module are both connected with the controller; the controller is used for controlling the AC/DC converter and the chopping module to be turned on and off, and adjusting the direct-current voltage of the output end of the chopping module and the total direct-current output end.
Optionally, the AC/DC converter includes at least one group of three-phase two-level converters or three-phase three-level converters, each cross current side of each group of three-phase two-level converters or three-phase three-level converters is connected with one of the secondary three-phase windings of the multi-winding transformer, and the DC side of each group of three-phase two-level converters or the DC side of each group of three-phase three-level converters and the DC side of the adjacent group of three-phase two-level converters or three-phase three-level converters are sequentially connected in series or in parallel with each other.
Optionally, the rectifier bridge is a three-phase diode rectifier bridge, a bridge arm of the three-phase diode rectifier bridge includes a plurality of diode valves connected in series in sequence, and each of the diode valves is connected in parallel with a resistance-capacitance buffer circuit.
Optionally, the rectifier bridge is a three-phase thyristor semi-controlled rectifier bridge, a bridge arm of the three-phase thyristor semi-controlled rectifier bridge includes a plurality of thyristors connected in series in sequence, and each thyristor is connected in parallel with a resistance-capacitance buffer circuit.
Optionally, the hybrid rectifier circuit based on the multi-winding transformer further comprises at least two sets of switching modules which are correspondingly arranged with the rectifier bridge, each switching module comprises a switching switch and a bypass switch, one end of each switching switch is connected with the input end of the rectifier bridge, the other end of each switching switch is connected with the secondary three-phase winding of the multi-winding transformer, the bypass switches are connected with the corresponding output ends of the rectifier bridge in parallel, and the switching switches and the bypass switches are used for adjusting the number of the rectifier bridges which are connected with the output ends of the chopper modules in series.
Optionally, the multi-winding transformer based hybrid rectifier circuit further comprises a three-phase ac filter, one end of the three-phase ac filter is connected to the ac side of the voltage source converter, and the other end is grounded.
Optionally, the multi-winding transformer-based hybrid rectification circuit further comprises a dc reactor, and the dc reactor is connected in series between the output end of the chopper module and the output ends of at least two sets of the rectifier bridges.
Optionally, the hybrid rectification circuit based on the multi-winding transformer is applied to a wind power direct current fan.
A second aspect of the embodiments of the present invention provides a control method for a hybrid rectifier circuit, which is applied to the hybrid rectifier circuit based on the multi-winding transformer according to any one of the first aspect and the first aspect of the embodiments of the present invention, and includes: acquiring a real-time rotating speed of a generator, and acquiring a power control instruction based on the real-time rotating speed, wherein the power control instruction is a maximum power value corresponding to the real-time rotating speed; calculating a difference value between the power control instruction and the real-time output power of the generator, and acquiring a direct-current voltage instruction based on the difference value; acquiring the sum of the direct current voltages of all rectifier bridges, and obtaining a voltage output instruction of the chopper module by subtracting the direct current voltage instruction from the sum of the direct current voltages; acquiring direct-current voltage of the voltage source converter, and comparing the voltage output instruction with the direct-current voltage of the voltage source converter to obtain a duty ratio; and controlling the chopping module to work based on the duty ratio.
Optionally, after obtaining the voltage output command of the chopper module, the method further includes: and judging whether the voltage output instruction reaches a set upper limit value, and if so, controlling the number of the accessed rectifier bridges through a switching switch.
Optionally, after obtaining the dc voltage command, the method further includes: and judging whether the real-time rotating speed and the direct-current voltage instruction reach a set maximum value or not, if so, fixing the duty ratio to a maximum threshold value, obtaining a pitch angle adjusting instruction through a motor rotating speed control ring, adjusting the real-time rotating speed and the real-time output power based on the pitch angle adjusting instruction, and if the pitch angle adjusting instruction is increased back to 0 degree, re-executing the step of obtaining the duty ratio and the step of controlling the chopping module to work based on the duty ratio.
According to the technical scheme, the embodiment of the invention has the following advantages:
the embodiment of the invention provides a hybrid rectification circuit based on a multi-winding transformer, which comprises: the power generation device comprises a generator, a multi-winding transformer, a voltage source converter, a chopping module and at least two groups of rectifier bridges; the generator is used for generating alternating current; the multi-winding transformer comprises a primary side three-phase winding and at least three secondary side three-phase windings, the primary side three-phase winding of the multi-winding transformer is connected with the generator, at least one secondary side three-phase winding of the multi-winding transformer is connected with the alternating current side of the voltage source converter, the other secondary side three-phase windings of the multi-winding transformer are respectively connected with the input ends of at least two groups of rectifier bridges, and the multi-winding transformer is used for converting the alternating current generated by the generator into a plurality of alternating currents and distributing the plurality of alternating currents to the voltage source converter and the rectifier bridges; the rectifier bridge is used for converting alternating current distributed by the multi-winding transformer into direct current, the direct current side of the voltage source converter is connected with the input end of the chopping module, the voltage source converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, the output end of the chopping module and the output ends of at least two groups of rectifier bridges are sequentially connected in series to form a total direct current output port, and the chopping module is used for controlling direct current voltage of the output end of the chopping module to further adjust the total direct current output voltage. The power of the generator is shared by the rectifier bridge and the voltage source converter and rectified into direct current power, so that the high-power high-voltage AC/DC conversion function can be realized, the waveform quality of the stator current is purified, and the power generation efficiency of the system is improved.
According to the control method of the hybrid rectification circuit, the real-time rotating speed of the generator is obtained, and the power control instruction is obtained based on the real-time rotating speed, wherein the power control instruction is the maximum power value corresponding to the real-time rotating speed; calculating a difference value between the power control instruction and the real-time output power of the generator, and acquiring a direct-current voltage instruction based on the difference value; acquiring the sum of direct current voltages of all rectifier bridges, and subtracting the sum of the direct current voltage instruction and the direct current voltage instruction to obtain a voltage output instruction of the chopper module; the method comprises the steps of obtaining the direct-current voltage of a voltage source converter, comparing the voltage output instruction with the direct-current voltage of the voltage source converter to obtain a duty ratio, controlling the chopping module to work based on the duty ratio, and adjusting the total output voltage of the fan by adjusting the duty ratio of the chopping module, so that the fan can stably work at the maximum power point.
Drawings
In order to express the technical scheme of the embodiment of the invention more clearly, the drawings used for describing the embodiment will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic diagram of a multi-winding transformer based hybrid rectifier circuit in an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a chopper module formed by half-bridge modules according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a chopper module formed by a full-bridge module according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of the connection of a voltage source converter and a chopper module in an embodiment of the invention;
fig. 5 is a schematic structural diagram of a modular multilevel converter according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of an AC/DC converter according to an embodiment of the present invention;
fig. 7 is a schematic diagram of another AC/DC converter according to an embodiment of the present invention;
FIG. 8 is a schematic structural diagram of a rectifier bridge according to an embodiment of the present invention;
FIG. 9 is a diagram illustrating a method for controlling a hybrid rectifier circuit according to an embodiment of the present invention;
fig. 10 is a diagram illustrating another control method of a hybrid rectifier circuit according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a hybrid rectification circuit based on a multi-winding transformer, which comprises: the device comprises a generator, a multi-winding transformer, a voltage source converter, a chopping module and at least two groups of rectifier bridges.
The generator is used for generating alternating current; the multi-winding transformer comprises a primary side three-phase winding and at least three secondary side three-phase windings, the primary side three-phase winding of the multi-winding transformer is connected with the generator, at least one secondary side three-phase winding of the multi-winding transformer is connected with the alternating current side of the voltage source converter, the other secondary side three-phase windings of the multi-winding transformer are respectively connected with the input ends of at least two groups of rectifier bridges, and the multi-winding transformer is used for converting alternating current generated by the generator into a plurality of alternating currents and distributing the plurality of alternating currents to the voltage source converter and the rectifier bridges; the rectifier bridge is used for converting the alternating current of multi-winding transformer distribution into direct current, and the direct current side of voltage source converter is connected with the input of chopper module, and voltage source converter is used for converting the alternating current of multi-winding transformer distribution into direct current and exports direct current to chopper module, and chopper module's output and at least two sets of rectifier bridge's output are established ties in proper order and are formed total direct current output port, and chopper module is used for controlling its output direct current voltage and then adjusts total direct current output voltage.
As shown in fig. 1, the generator is a high-voltage high-power Synchronous generator, and can convert mechanical energy into electrical energy, and includes a Permanent magnet Synchronous generator or an asynchronous generator, the Permanent magnet Synchronous generator (PMSM) is a three-phase or six-phase medium-speed generator, and includes a rotor excited by a Permanent magnet and a three-phase or six-phase armature winding embedded in a stator slot, each three-phase stator winding is in a Y or D connection mode, and the asynchronous generator includes a double-fed type and a squirrel-cage type asynchronous generator. In the embodiment, the generator is a three-phase permanent magnet synchronous generator. Stator ports (01, 02, 03) of a three-phase permanent magnet synchronous generator are connected to primary side three-phase windings of a multi-winding transformer, two sets of secondary side three-phase windings (04, 05, 06, 07, 08, 09) are respectively connected with two rectifier bridge alternating current ports, wherein the two sets of secondary side three-phase windings of the multi-winding transformer are respectively Y and D connection wires, the output line voltages mutually differ by 30 degrees in electrical angle, the two rectifier bridge direct current sides are connected in series to form uncontrollable rectifier direct current output ends (10, 11), and alternating current ports (12, 13, 14) of a voltage source converter are connected with one secondary side three-phase winding of the multi-winding transformer. The input side of the chopping module is connected with direct current buses (15, 16) of the voltage source converter, and chopping output ports (17, 18) of the chopping module and an uncontrolled rectification direct current output end are connected in series through a direct current reactor to form total direct current output ports (19, 20). The positive and negative ends of the total direct current output end are connected with direct current cut-off equipment (SQ 1) in series, a quick switch (SQ 2) is connected between the positive and negative electrodes in parallel, and the opening and closing of the total direct current output are controlled through the direct current cut-off equipment (SQ 1) and the quick switch (SQ 2).
Specifically, the multi-winding transformer is a power frequency transformer, and compared with a conventional power frequency transformer, the development of a large-capacity high-frequency transformer is difficult, and the electric heating stress and the insulation technology are complex. With the development of the capacity of the existing offshore wind power single machine to 15 MW-20 MW level, the technology of the high-frequency transformer matched with the capacity of the offshore wind power single machine is not mature enough, and the defect of poor system reliability is brought, so that the multi-winding transformer in the embodiment of the invention selects the power-frequency transformer instead of the high-frequency transformer. The primary side and the secondary side of the multi-winding transformer can adopt a high-insulation structure design, and high direct-current potential between the generator side and the direct-current side can be isolated.
Specifically, the multi-winding transformer sequentially differs by 30 electrical degrees among three-phase windings connected with a rectifier bridge through the configuration of a connection group, and the direct-current side phases of the rectifier bridges are connected in series to form at least 12 ripple-free rectifiers.
The chopping module can be a half-bridge module or a full-bridge module, a direct current input port of the module is connected to a direct current side of the voltage source converter, and a chopping output port is connected with the direct current side of the three-phase diode rectifier bridge in series and serves as a direct current output port of the direct current fan unit.
Fig. 2 is a schematic diagram of a chopping module formed by a half-bridge module in the embodiment of the present invention, a dc terminal of the half-bridge module is connected to a dc side of a voltage source converter, a dc terminal of the half-bridge module and a midpoint of the half-bridge form a chopping output port, the chopping output is a PWM voltage waveform, a dc component of the output voltage can be continuously adjusted from 0 to a dc voltage of the voltage source converter, and a power device T1 and a power device T2 of the half-bridge module are locked, so that fault isolation can be achieved.
Fig. 3 is a schematic diagram of a chopper module formed by a full-bridge module according to an embodiment of the present invention, where a dc end of the full-bridge module is connected to a dc side of a voltage source converter, and midpoints of two bridge arms of the full-bridge module form a chopper output end, where one of the upper and lower bridge arms is a chopper bridge arm, and the other of the upper and lower bridge arms is a chopper voltage polarity selection bridge arm, a dc component of an output voltage can be continuously adjusted from 0 to a dc voltage of the voltage source converter, and a negative polarity or a positive polarity output voltage is realized by controlling a power device T5 or a power device T6 to be turned on. When an interelectrode short-circuit fault occurs at the total direct current port, the control power device T4 and the control power device T5 are conducted, so that the rising speed of direct current fault current can be effectively reduced, and fault isolation and clearing are facilitated.
The voltage source converter has reactive compensation and active filtering functions, adjusts the stator voltage of the permanent magnet synchronous generator and filters low-order harmonic waves generated by the rectifier bridge on the alternating current side. The chopper module has the function of adjusting the total direct-current voltage, and the direct-current output voltage of the chopper module is adjusted by controlling the duty ratio of the chopper module, so that the total direct-current voltage is adjusted.
The hybrid rectification circuit based on the multi-winding transformer comprises a generator, the multi-winding transformer, a voltage source converter, a chopping module and at least two groups of rectifier bridges, wherein the rectifier bridges and the voltage source converter share the power of the generator and rectify the power into direct current power, so that the high-power high-voltage-level AC/DC conversion function can be realized, the waveform quality of stator current is purified, and the power generation efficiency of a system is improved.
In addition, the hybrid rectification circuit based on the multi-winding transformer has high power density, reduces the total control power module required by the rectifier, effectively improves the reliability and economy of the system, and reduces the volume and weight of the device.
In one embodiment, as shown in fig. 4, the voltage source converter comprises a controller and an AC/DC converter; the AC side of the AC/DC converter is connected with at least one set of secondary three-phase windings of the multi-winding transformer, and the DC side of the AC/DC converter is connected with the input end of the chopping module; the AC/DC converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, and the AC/DC converter and the chopping module are both connected with the controller; the controller is used for controlling the AC/DC converter and the chopping module to be turned on and off, and regulating the direct-current voltage of the output end of the chopping module and the total direct-current output end. The AC/DC converter has reactive compensation and active filtering functions, adjusts the stator voltage of the permanent magnet synchronous generator and filters low-order harmonic waves generated by the three-phase diode rectifier bridge on the alternating current side. As shown in fig. 5, the AC/DC Converter has a Modular Multilevel Converter (MMC) structure, the sub-module is a full-bridge or half-bridge sub-module, and the AC-side three-phase port is connected to a set of three-phase windings of the multi-winding transformer. The MMC structure is suitable for a voltage source converter which needs to bear higher voltage and larger capacity, and only one group of secondary windings of the transformer are used for supplying power to the voltage source converter.
The controller has the functions of acquiring signals such as voltage, current, rotating speed and the like and controlling strategy execution, and respectively sends device trigger signals to the voltage source converter and the chopping module. The input end of the chopping module is connected with a direct-current bus of the voltage source converter, the chopping output end of the chopping module is connected with the reactor in series to form direct-current positive and negative electrode output ends of the chopping module, and a bypass thyristor and a bypass switch are connected in parallel between the output ends and used for fault bypass locking and converter cutting. The controller can acquire the rotating speed of the generator and direct current voltage and current signals, or receive adjusting instructions of other generator machines or systems, control the direct current voltage of the AC/DC converter to be stable, adjust the direct current output voltage of the chopping module and stabilize the output of the power of the fan.
In one embodiment, the AC/DC converter includes at least one set of three-phase two-level converters or three-phase three-level converters, each of the three-phase two-level converters or three-phase three-level converters has one of the secondary three-phase windings of the multi-winding transformer connected to each of the current-intersecting sides, and the DC side of each set of three-phase two-level converters or the DC side of each three-phase three-level converter is connected in series or in parallel with the DC side of the adjacent set of three-phase two-level converters or three-phase three-level converters. The structure of the AC/DC converter when the AC/DC converter comprises three groups of single-phase two-level converters is shown in figure 6, the AC/DC converter is formed by integrating an H-bridge module and a multi-winding transformer, each phase winding of the multi-winding transformer is connected with the H-bridge module, the direct current sides of the three-phase H-bridge modules are connected in parallel to form a group of three-phase AC/DC sub-converters, and the direct current sides of each group of three-phase AC/DC sub-converters are connected in series to form the AC/DC converter. Fig. 7 shows that the direct current sides of a plurality of groups of sub-converters are connected in parallel to form an AC/DC converter, and the rest of the structure is the same as that in fig. 6.
In one embodiment, the rectifier bridge is a three-phase diode rectifier bridge, a bridge arm of the three-phase diode rectifier bridge comprises a plurality of diode valves connected in series in sequence, and each diode valve is connected with a resistance-capacitance buffer circuit in parallel. Specifically, as shown in fig. 8, the ac side of the three-phase diode rectifier bridge is connected to a set of secondary three-phase windings of the multi-winding transformer, and the dc side series reactor forms the dc output end of the three-phase diode rectifier bridge; each phase bridge arm of the three-phase diode rectifier bridge is formed by connecting a series of diode valves in series, and each diode valve is provided with a valve resistance-capacitance buffer branch circuit to ensure that each diode valve at the end of phase change can be reliably and reversely cut without overvoltage breakdown to cause cascading failure.
In one embodiment, the multi-winding transformer-based hybrid rectification circuit further comprises at least two groups of switching modules which are arranged corresponding to the rectification bridges, each switching module comprises a switching switch and a bypass switch, one end of each switching switch is connected with the input end of the corresponding rectification bridge, the other end of each switching switch is connected with the secondary three-phase winding of the multi-winding transformer, the bypass switches are connected with the output ends of the corresponding rectification bridges in parallel, and the switching switches and the bypass switches are used for adjusting the number of the rectification bridges which are connected with the output ends of the chopping modules in series. As shown in fig. 1, the switching switch includes ac circuit breakers (SQ 3, SQ 4) on the ac side of the rectifier bridge, bypass switches (S1, S2) are configured on the dc side of the rectifier bridge, the bypass switches (S1, S2) and the ac circuit breakers (SQ 3, SQ 4) form an uncontrolled rectifier module switching switch, packet switching can be realized by using the ac circuit breakers (SQ 3, SQ 4) and the bypass switches (S1, S2), the dc side series voltage is equivalently adjusted, and the adjustment of the total dc port voltage is participated in.
In one embodiment, the rectifier bridge is a three-phase thyristor half-controlled rectifier bridge, a bridge arm of the three-phase thyristor half-controlled rectifier bridge comprises a plurality of thyristors which are sequentially connected in series, and each thyristor is connected with a resistance-capacitance buffer circuit in parallel. In the embodiment, the thyristor replaces a semiconductor, is a semi-controlled rectifier, can realize the soft regulation of the direct-current voltage, and does not need to be additionally provided with a switching module.
In one embodiment, the multi-winding transformer based hybrid rectifier circuit further comprises a three-phase ac filter, one end of the three-phase ac filter being connected to the ac side of the voltage source converter and the other end being grounded. The three-phase ac filter is composed of a capacitor, a damping resistor, and a small reactor, and as shown in fig. 1, three-phase terminals of the three-phase ac filter are connected in parallel to ac ports (12, 13, 14) of the voltage source converter. The three-phase alternating current filter can improve the quality of the voltage waveform of the winding of the multi-winding transformer, improve the efficiency of the transformer and have certain reactive compensation function.
In one embodiment, the multi-winding transformer-based hybrid rectification circuit further comprises a direct current reactor, and the direct current reactor is connected between the output end of the chopping module and the output ends of the at least two groups of rectifier bridges in series. The dc reactor can reduce the ripple of the total dc output voltage.
In one embodiment, the hybrid rectification circuit based on the multi-winding transformer is applied to a wind power direct current fan. At present, the high direct current voltage in a large-scale wind power direct current collection-transmission scheme is realized by direct series-parallel connection of a DC/DC converter or a fan, and the following technical difficulties exist: 1. the multi-stage conversion is inefficient. The high-capacity high-transformation-ratio DC/DC converter basically needs multi-stage transformation, so that the system efficiency is reduced; 2. high potential insulation problem. The direct current fans are connected in series, so that the insulation problems of a high-potential converter and a generator can be caused; 3. the IGBT has a large number of applications and high cost. The high-voltage high-capacity full-power converter adopts an MMC structure, and the number of required sub-modules and power devices is large, so that the device is high in cost and large in size. With the continuous increase of the single-machine power of the wind turbine generator, the conventional converter device limits the development of the large capacity and the high power density of the wind turbine generator. The hybrid rectification circuit based on the multi-winding transformer is applied to the wind power direct current fan, and has the advantages of low cost, high reliability, high efficiency and the like, so that the circuit is a powerful support for realizing the convergence and transmission of wind power generation direct current to the development of large capacity and high power density, the problem of high potential insulation on the motor side of the direct current fan is solved, the using amount of a voltage source converter is greatly reduced, the level number of power conversion is reduced, the power generation efficiency of a direct current fan unit is improved, and the volume, the weight and the cost of a rectification unit are reduced.
The working principle of the hybrid rectification circuit based on the multi-winding transformer in the embodiment of the invention is as follows:
a three-phase diode rectifier bridge and a voltage source converter are fused to form a hybrid rectifier, the hybrid rectifier is distributed and connected with an alternating current port of a permanent magnet synchronous generator through a multi-winding transformer, meanwhile, the multi-winding transformer enables output ends of rectifier bridge modules to be connected in series to form direct current high voltage, and electrical isolation of a valve side and a fan side is effectively achieved. The quality of the voltage waveform of the transformer winding can be improved by connecting the three-phase alternating current filter in parallel at the alternating current side of the voltage source converter.
When the fan operates in a maximum power tracking mode, the wind power captured by the fan is different corresponding to different motor rotating speeds, at the moment, the induced voltage of a fan stator winding is in direct proportion to the rotating speed, corresponding 6n (n represents the number of three-phase diode rectifier bridges) pulse wave rectified voltage is output through the three-phase diode rectifier bridges, at the moment, the direct current voltage of the voltage source converter is stabilized at a rated value through the controller, when the total direct current voltage of the fan is stabilized at the rated value by an external direct current system, the direct current output voltage of the chopper module is controlled by adjusting the duty ratio of the chopper module at the direct current side of the voltage source converter, the chopper module can indirectly control the direct current voltage divided at the output end of the three-phase diode rectifier bridges according to the voltage law of a series loop, when the direct current voltage is lower than the actual uncontrolled rectified voltage, current is generated in an Alternating Current (AC) and Direct Current (DC) loop due to the load effect caused by phase commutation in the three-phase diode rectifier bridges, and the power at the AC side is transmitted to the DC side. When the rectification power is the same as the motor power, the controller stabilizes the duty ratio of the chopping module, and the fan power is stably output. When the capture power of the fan is increased, the control system increases the output voltage of the chopper module, so that the voltage of the direct current side of the three-phase diode rectifier bridge is reduced, the alternating current and direct current of the three-phase diode rectifier bridge are increased, and the rectification power is improved; conversely, increasing the dc voltage on the rectifying side of the diode will decrease the dc current and reduce the rectified power. The number of three-phase diode rectifier bridges connected in series to the direct current side is controlled through the switching of the alternating current circuit breaker, the three-phase diode rectifier bridges and the chopper module participate in direct current voltage regulation of the main port, and the output voltage range of the fan unit is expanded.
When the wind speed exceeds the rated wind speed, the motor operates in the rated rotating speed state, the rectifier bridge is in the maximum power output state, and the voltage output of the chopper module is approximate to the limit value. In order to stabilize the normal operation of the system, the control system is required to be switched to a pitch angle control mode, the wind turbine is controlled to exit from a zero pitch angle state through a motor rotating speed ring, the wind power captured by the fan is limited, and the system is maintained to operate stably.
An embodiment of the present invention further provides a control method of a hybrid rectifier circuit, which is applied to any one of the above hybrid rectifier circuits based on a multi-winding transformer, as shown in fig. 9, and includes:
and S100, acquiring the real-time rotating speed of the generator, and acquiring a power control instruction based on the real-time rotating speed, wherein the power control instruction is a maximum power value corresponding to the real-time rotating speed.
And S200, calculating a difference value between the power control command and the real-time output power of the generator, and acquiring a direct-current voltage command based on the difference value.
And step S300, acquiring the sum of the direct current voltages of all the rectifier bridges, and subtracting the sum of the direct current voltage instruction and the direct current voltage instruction to obtain a voltage output instruction of the chopper module.
And S400, acquiring the direct current voltage of the voltage source converter, and comparing the voltage output instruction with the direct current voltage of the voltage source converter to obtain a duty ratio.
And S500, controlling the chopping module to work based on the duty ratio.
Specifically, the generator is a wind driven generator, also called a fan, and detects the real-time rotating speed omega of the motor r Obtaining a maximum power value corresponding to the real-time rotating speed according to the MPPT power curve, and obtaining a power control instruction P of the current working condition direct current port wdref . Collecting real-time output power P of generator wd Calculating a power control command P wdref And real-time output power P wd Obtaining a direct current voltage instruction U of the fan unit through the PI regulator dc1ref . When the rectifier bridge does not participate in the direct-current voltage regulation function, the direct-current port voltage regulation of the fan unit is undertaken by the chopper module, and the direct-current voltage instruction U dc1ref The sum of the direct current voltages of the rectifier bridge part is subtracted to obtain a voltage output instruction U of the chopper module dc2ref . Voltage output command U dc2ref DC voltage U to voltage source converter dvsc Obtaining the duty ratio D of the chopping module by doing a ratio ref And controlling the chopping module to work based on the duty ratio. The control method of the hybrid rectification circuit of the embodiment of the invention adjusts the duty ratio D of the chopper module ref The total output voltage of the fan is adjusted, so that the fan can stably work at the maximum power point.
In one embodiment, the voltage source converter further implements a dual-loop control strategy of a DC voltage, an AC voltage outer loop and a current decoupling inner loop to stabilize the voltage of the DC bus of the voltage source converter and generate powerThe motor stator voltage specifically comprises: converting a direct voltage U of a converter of a voltage source converter dc1 And a DC voltage command U dc1ref Obtaining an active current instruction I at the AC side of the voltage source converter through the PI regulator by taking difference dref . Calculating reactive current I required to be compensated according to current of generator stator qref . According to the active current instruction I dref Reactive current I qref AC side inductor L of voltage source converter vsc And a voltage feedforward current decoupling control strategy is adopted to obtain a voltage instruction on the alternating current side of the voltage source converter, so that the direct current bus voltage of the voltage source converter and the stator voltage of the generator are stabilized.
In an embodiment, after obtaining the voltage output command of the chopper module, the method further includes: and judging whether the voltage output instruction reaches a set upper limit value or not, and if so, controlling the number of the accessed rectifier bridges through the fling-cut switch. In the embodiment, the rectifier bridge participates in direct-current voltage regulation, the chopper module is adopted for voltage regulation firstly, and when the voltage outputs a command U dc2ref When the amplitude limit is reached, the number of the connected rectifier bridges is adjusted through switching of the switching switch. If the bridge is half-controlled, e.g. thyristor, the command U is still output as a voltage dc2ref And regulating the thyristor rectifier bridge after the amplitude limit is reached. U shape dc2ref DC voltage U to voltage source converter dvsc Ratio is made to obtain chopping module duty ratio D ref . The total direct-current voltage output range is expanded by adjusting the number of the connected rectifier bridges.
In one embodiment, after acquiring the dc voltage command, the method further includes: and judging whether the real-time rotating speed and the direct-current voltage command reach a set maximum value or not, if so, fixing the duty ratio to a maximum threshold value, obtaining a pitch angle adjusting command through a motor rotating speed control ring, adjusting the real-time rotating speed and the real-time output power based on the pitch angle adjusting command, and if the pitch angle adjusting command is increased back to 0 degree, re-executing the step of obtaining the duty ratio and the step of controlling the operation of the chopping module based on the duty ratio. Specifically, if the motor rotates at the real-time speed omega r And DC voltage command U dc1ref All exceed the set maximum value, namely the maximum limit value, and are startedA hysteresis loop mode, wherein the control system is switched from a power control mode to a voltage amplitude limiting mode, the original power control strategy is locked in the voltage amplitude limiting mode, and the duty ratio D of a chopper module ref Fixing the motor speed command to the maximum value, starting the pitch angle adjusting ring, obtaining a pitch angle adjusting command through the motor speed control ring, and fixing the motor speed command to be the rated motor speed which is equal to the real-time motor speed omega r And outputting a pitch angle instruction through a PI (proportional integral) regulator, and regulating the real-time rotating speed and the real-time output power based on the pitch angle regulation instruction. And if the pitch angle is increased to 0 degrees again, switching the control mode to the maximum power tracking control mode again, and operating according to the flow from the step S100 to the step S500.
In an embodiment, as shown in fig. 10, the operation of the fan is divided into two control modes, when the wind speed is lower than the rated wind speed, the control mode is a maximum power tracking control mode, the real-time rotation speed of the generator is detected, the maximum power value corresponding to the real-time rotation speed is calculated according to the MPPT power curve, the correct output of the chopping voltage is realized according to the closed-loop control strategy of steps S100 to S500, and the motor operates at the rotation speed corresponding to the maximum power value through dynamic adjustment. And executing a double-loop control strategy of a direct current voltage, an alternating current voltage outer loop and a current decoupling inner loop, and stabilizing the direct current bus voltage of the voltage source converter and the stator voltage of the generator.
When the real-time rotating speed of the generator and the duty ratio of the chopping module exceed the set maximum value, the total output power of the hybrid rectification circuit reaches the maximum value, when the wind speed is continuously increased, the control mode needs to be switched into the voltage amplitude limiting mode, the real-time rotating speed of the generator is limited to the rated rotating speed, the chopping output duty ratio is fixed at the maximum value, the pitch angle of the wind turbine is adjusted through the rotating speed ring, the motor stably operates in the rated rotating speed state, and in order to avoid frequent switching of the control mode, a hysteresis loop is introduced for mode judgment.
The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (12)
1. A hybrid rectifier circuit based on a multi-winding transformer, comprising: the device comprises a generator, a multi-winding transformer, a voltage source converter, a chopping module and at least two groups of rectifier bridges;
the generator is used for generating alternating current;
the multi-winding transformer comprises a primary side three-phase winding and at least three secondary side three-phase windings, the primary side three-phase winding of the multi-winding transformer is connected with the generator, at least one secondary side three-phase winding of the multi-winding transformer is connected with the alternating current side of the voltage source converter, the other secondary side three-phase windings of the multi-winding transformer are respectively connected with the input ends of at least two groups of rectifier bridges, and the multi-winding transformer is used for converting the alternating current generated by the generator into a plurality of alternating currents and distributing the plurality of alternating currents to the voltage source converter and the rectifier bridges;
the rectifier bridge is used for converting alternating current distributed by the multi-winding transformer into direct current, the direct current side of the voltage source converter is connected with the input end of the chopping module, the voltage source converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, the output end of the chopping module and the output ends of at least two groups of rectifier bridges are sequentially connected in series to form a total direct current output port, and the chopping module is used for controlling direct current voltage of the output end of the chopping module to further adjust the total direct current output voltage.
2. The multi-winding transformer based hybrid rectifier circuit of claim 1, wherein the voltage source converter comprises a controller and an AC/DC converter ；
The alternating current side of the AC/DC converter is connected with at least one set of secondary three-phase windings of the multi-winding transformer, and the direct current side of the AC/DC converter is connected with the input end of the chopping module;
the AC/DC converter is used for converting the alternating current distributed by the multi-winding transformer into direct current and outputting the direct current to the chopping module, and the AC/DC converter and the chopping module are both connected with the controller;
the controller is used for controlling the AC/DC converter and the chopping module to be turned on and off, and adjusting the direct-current voltage of the output end of the chopping module and the total direct-current output end.
3. The multi-winding transformer-based hybrid rectification circuit according to claim 2, wherein the AC/DC converter comprises at least one set of three-phase two-level converter or three-phase three-level converter, each current-intersecting side of each set of three-phase two-level converter or three-phase three-level converter is respectively connected with one of the secondary three-phase windings of the multi-winding transformer, and the DC side of each set of three-phase two-level converter or the DC side of the three-phase three-level converter is sequentially connected in series or in parallel with the DC sides of the adjacent set of three-phase two-level converter or three-phase three-level converter.
4. The multi-winding transformer-based hybrid rectification circuit of claim 1, wherein the rectification bridge is a three-phase diode rectification bridge, a bridge arm of the three-phase diode rectification bridge comprises a plurality of diode valves which are sequentially connected in series, and each of the diode valves is connected with a resistance-capacitance buffer circuit in parallel.
5. The multi-winding transformer based hybrid rectifier circuit according to claim 1, wherein the rectifier bridge is a three-phase thyristor half-controlled rectifier bridge, a bridge arm of the three-phase thyristor half-controlled rectifier bridge comprises a plurality of thyristors connected in series in sequence, and each thyristor is connected with a resistor-capacitor buffer circuit in parallel.
6. The multi-winding transformer-based hybrid rectification circuit according to claim 1, further comprising at least two sets of switching modules corresponding to the rectifier bridges, wherein each switching module comprises a switching switch and a bypass switch, one end of each switching switch is connected with an input end of each rectifier bridge, the other end of each switching switch is connected with a secondary three-phase winding of each multi-winding transformer, each bypass switch is connected with a corresponding output end of each rectifier bridge in parallel, and the switching switches and the bypass switches are used for adjusting the number of the rectifier bridges connected in series with the output ends of the chopper modules.
7. The multi-winding transformer based hybrid rectifier circuit of claim 1 further comprising a three-phase ac filter having one end connected to the ac side of the voltage source converter and the other end connected to ground.
8. The multi-winding transformer based hybrid rectification circuit according to claim 1, further comprising a dc reactor connected in series between the output terminals of the chopping module and the output terminals of at least two sets of the rectifier bridges.
9. The multi-winding transformer based hybrid rectification circuit of claim 1, wherein the multi-winding transformer based hybrid rectification circuit is applied to a wind power direct current fan.
10. A control method of a hybrid rectifier circuit applied to the multi-winding transformer-based hybrid rectifier circuit according to any one of claims 1 to 9, comprising:
acquiring a real-time rotating speed of a generator, and acquiring a power control instruction based on the real-time rotating speed, wherein the power control instruction is a maximum power value corresponding to the real-time rotating speed;
calculating a difference value between the power control instruction and the real-time output power of the generator, and acquiring a direct-current voltage instruction based on the difference value;
acquiring the sum of the direct current voltages of all rectifier bridges, and obtaining a voltage output instruction of the chopper module by subtracting the direct current voltage instruction from the sum of the direct current voltages;
acquiring direct-current voltage of the voltage source converter, and comparing the voltage output instruction with the direct-current voltage of the voltage source converter to obtain a duty ratio;
and controlling the chopping module to work based on the duty ratio.
11. The method for controlling a hybrid rectifier circuit according to claim 10, further comprising, after obtaining the voltage output command of the chopper module: and judging whether the voltage output instruction reaches a set upper limit value, and if so, controlling the number of the accessed rectifier bridges through a switching switch.
12. The method for controlling a hybrid rectifier circuit according to claim 10, further comprising, after acquiring the dc voltage command: and judging whether the real-time rotating speed and the direct-current voltage instruction reach a set maximum value or not, if so, fixing the duty ratio to a maximum threshold value, obtaining a pitch angle adjusting instruction through a motor rotating speed control ring, adjusting the real-time rotating speed and the real-time output power based on the pitch angle adjusting instruction, and if the pitch angle adjusting instruction is increased back to 0 degree, re-executing the step of obtaining the duty ratio and the step of controlling the chopping module to work based on the duty ratio.
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