Unloading circuit for wind power converter and control method thereof
阅读说明：本技术 一种风电变流器用卸荷电路及其控制方法 (Unloading circuit for wind power converter and control method thereof ) 是由 郭明珠 屈鲁 尹立坤 余占清 孙长平 陈煜坤 郝峰杰 曾嵘 赵彪 于 2021-08-26 设计创作，主要内容包括：本发明提供本发明提供一种风电变流器用卸荷电路及其控制方法,所述风电变流器用卸荷电路包括：串联的第一电容(C-(bus1))和第二电容(C-(bus2)),所述第一电容(C-(bus1))的第二端连接第二电容(C-(bus2))的第一端,所述第一电容(C-(bus1))并联有第一并联电路,所述第二电容(C-(bus2))并联有第二并联电路。本发明的风电变流器用卸荷电路中,开关管配有吸收电路,可防止开关管在开断过程中产生过电压、过电流,抑制du/dt、di/dt,能减小开关损耗并起到保护器件的作用。本发明的控制方法采用了直流功率偏差、直流电压的双判据,控制难度适中,控制效果好。(The invention provides an unloading circuit for a wind power converter and a control method thereof, wherein the unloading circuit for the wind power converter comprises: a first capacitor (C) connected in series bus1 ) And a second capacitance (C) bus2 ) Said first capacitance (C) bus1 ) Is connected to a second capacitor (C) bus2 ) Said first capacitor (C) bus1 ) A first parallel circuit, the second capacitor (C) bus2 ) A second parallel circuit is connected in parallel. In the unloading circuit for the wind power converter, the switching tube is provided with the absorption circuit, so that overvoltage and overcurrent can be prevented from being generated in the switching-on and switching-off process of the switching tube, du/dt and di/dt are inhibited, the switching loss can be reduced, and the effect of protecting devices can be achieved. The control method of the invention adopts double criteria of direct current power deviation and direct current voltage, the control difficulty is moderate, and the control effect is good.)
1. The unloading circuit for the wind power converter is characterized by comprising:
a first capacitor (C) connected in seriesbus1) And a second capacitance (C)bus2) Said first capacitance (C)bus1) Is connected to a second capacitor (C)bus2) The first end of the first tube is provided with a first end,
the first capacitor (C)bus1) A first parallel circuit is connected in parallel with the first parallel circuit,
the second capacitance (C)bus2) Is connected in parallel with a secondA parallel circuit.
2. The unloading circuit for the wind power converter according to claim 1,
the first parallel circuit comprises first switching tubes (T) connected in series in sequence1) And a first resistance (R)1)，
The first switch tube (T)1) As a first terminal of the first parallel circuit is connected to the first capacitor (C)bus1) The first switch tube (T)1) Is connected to the first resistor (R)1) The first terminal of (A), the first resistor (R)1) As a second terminal of the first parallel circuit is connected to the first capacitor (C)bus1) A second end of (a);
the second parallel circuit comprises second resistors (R) connected in series in sequence2) And a second switching tube (T)2)，
The second resistor (R)2) As a first terminal of the second parallel circuit is connected to the second capacitor (C)bus2) The second resistor (R), the second resistor (R)2) Is connected to the second switching tube (T)2) The second switching tube (T)2) As a second terminal of the second parallel circuit is connected to the second capacitor (C)bus2) The second end of (a).
3. The unloading circuit for the wind power converter according to claim 2,
further comprising a first diode (D)1) And a second diode (D)2)，
The first switch tube (T)1) And the first diode (D)1) Form an anti-parallel structure, i.e. the first switch tube (T)1) Is connected to the first diode (D)1) The first switching tube (T)1) Is connected to the first diode (D)1) The anode of (a) is provided,
the second switch tube (T)2) And the second diode (D)2) Form an anti-parallel structure, i.e. the second switch tube (T)2) Is connected to the second diode (D)2) The second switching tube (T)2) Is connected to the second diode (D)2) Of (2) an anode.
4. The unloading circuit for the wind power converter according to claim 3,
further comprising a first resistor-capacitor circuit and a second resistor-capacitor circuit,
the first switch tube (T)1) In parallel with said first resistor-capacitor circuit, i.e. said first switching tube (T)1) Is connected to a first terminal of said first resistor-capacitor circuit, said first switching tube (T)1) Is connected to a second terminal of the first resistor-capacitor circuit;
the second switch tube (T)2) In parallel with said second resistor-capacitor circuit, i.e. said second switching tube (T)2) Is connected to a first terminal of said second resistor-capacitor circuit, said second switching tube (T)2) Is connected to a second terminal of the second resistor-capacitor circuit.
5. The unloading circuit for the wind power converter according to claim 4,
the first resistor-capacitor circuit comprises a first series resistor (R) connected in seriesS1) And a first series capacitance (C)S1) The first series resistance (R)S1) As a first terminal of said first resistor-capacitor circuit, said first series resistor (R)S1) Is connected to said first series capacitance (C)S1) The first series capacitance (C)S1) As a second terminal of the first resistor-capacitor circuit;
the second resistor-capacitor circuit comprises a second series resistor (R) connected in seriesS2) And a second series capacitance (C)S2) Said second series resistance (R)S2) As a first terminal of said second resistor-capacitor circuitSaid second series resistance (R)S2) Is connected to the second series capacitance (C)S2) Said second series capacitance (C)S2) As a second terminal of the second resistor-capacitor circuit.
6. The unloading circuit for the wind power converter according to any one of claims 2 to 5,
the first switch tube (T)1) And a second switching tube (T)2) For integrated gate commutated thyristors or insulated gate bipolar transistors,
the first switch tube (T)1) And a second switching tube (T)2) For an integrated gate commutated thyristor, the first switching transistor (T)1) And a second switching tube (T)2) The first end of the anode is an anode, and the second end of the anode is a cathode;
the first switch tube (T)1) And a second switching tube (T)2) In the case of an insulated gate bipolar transistor, the first switching tube (T)1) And a second switching tube (T)2) The first terminal of (a) is a collector and the second terminal is an emitter.
7. An unloading circuit control method for a wind power converter, which is used for controlling the unloading circuit for the wind power converter as claimed in any one of claims 1 to 6, and is characterized by comprising the following steps:
to the first capacitor (C) collectedbus1) Or a second capacitance (C)bus2) Comparing the input active power and the output active power at the direct current side to obtain an active difference value delta P;
A. determining the switching of an unloading circuit by taking the active difference value delta P as a first judgment condition, and determining the duty ratio of a power device according to the active difference value delta P when the unloading circuit is put into use, wherein the active difference value delta P is equal to Pmdc-Pgdc，PmdcActive power, P, flowing to the DC bus for the machine side convertergdcThe active power flowing to the grid-side converter for the direct current bus;
B. with said first capacitance (C)bus1) Or a second capacitance (C)bus2) Direct current side currentAnd the voltage is used as a second judgment condition to determine the switching of the unloading circuit.
8. The unloading circuit control method for the wind power converter according to claim 7,
in the step a, when the active power difference Δ P reaches or exceeds a certain set value, an unloading circuit is put into operation.
9. The unloading circuit control method for the wind power converter according to claim 8,
when the load is loaded into the unloading circuit, the active difference value delta P is used as a modulation wave signal after passing through a PI regulator, and the first switch tube (T) is controlled1) Or a second switching tube (T)2) Duty cycle D of (D).
10. An unloading circuit control method for a wind power converter according to claim 9,
the duty ratio D satisfies:
wherein the content of the first and second substances,
Rdis a first resistance (R)1) Or a first resistance (R)2) Resistance value of Udc_refIs a DC bus voltage target value;
when the DC bus voltage UdcGreater than Udc_maxThen, let the duty ratio D be 1, Udc_maxThe set maximum value of the direct current bus voltage is obtained.
11. The unloading circuit control method for the wind power converter according to any one of claims 7 to 10,
in the step (B),
when the control delay of the unloading circuit reaches or exceeds a preset value according to the active difference value delta P or the voltage rising speed of the direct current side reaches or exceeds a preset value, the load circuit is controlled to be in a direct current stateThe current side voltage is controlled as a judgment condition: when the DC bus voltage UdcGreater than Udc_maxWhile, making the duty ratio 1, Udc_maxThe set maximum value of the direct current bus voltage is obtained.
Technical Field
The invention belongs to the field of offshore wind power, and particularly relates to an unloading circuit for a wind power converter and a control method thereof.
Background
When an offshore wind farm is connected to a power grid in a flexible direct-current transmission mode, if a receiving end power grid fails, the voltage of a grid connection point drops, the power transmitted to the power grid by an offshore wind power grid side converter drops, the power is accumulated at a direct-current bus, the voltage of the direct-current bus rises, the wind farm can be shut down for protection and grid disconnection in severe cases, and the instability of the voltage of the grid connection point is further aggravated. Therefore, certain measures must be taken to enable the flexible direct current grid-connected system to "ride through" the low-voltage time, which is the fault ride-through problem of offshore wind power.
To realize the low voltage ride through of the offshore wind power converter, the key point is the processing method of the unbalanced power P, and the method can be started from the following three aspects: the input power of the machine side converter is reduced, the output power of the grid side converter is increased, and unbalanced energy at a direct current bus is directly consumed. The unbalanced energy consumption method based on the unloading circuit has the advantages of simple scheme, high action speed, high reliability and the like. However, the existing unloading circuit is mostly suitable for a two-level converter and does not meet the requirement of a three-level neutral point clamping type converter. In addition, the influence of stray inductance in the converter on the switching tube is not considered in the existing unloading circuit, overvoltage and overcurrent may occur in the circuit in the switching process, and the switching loss is large.
Disclosure of Invention
Aiming at the problems, the invention provides an unloading circuit for a wind power converter and a control method thereof.
The invention relates to an unloading circuit for a wind power converter, which comprises:
a first capacitor (C) connected in seriesbus1) And a second capacitance (C)bus2) Said first capacitance (C)bus1) Is connected to a second capacitor (C)bus2) The first end of the first tube is provided with a first end,
the first capacitor (C)bus1) A first parallel circuit is connected in parallel with the first parallel circuit,
the second capacitance (C)bus2) A second parallel circuit is connected in parallel.
Further, in the present invention,
the first parallel circuit comprises first switching tubes (T) connected in series in sequence1) And a first resistance (R)1)，
The first switch tube (T)1) As a first terminal of the first parallel circuit is connected to the first capacitor (C)bus1) The first switch tube (T)1) Is connected to the first resistor (R)1) The first terminal of (A), the first resistor (R)1) As a second terminal of the first parallel circuit is connected to the first capacitor (C)bus1) A second end of (a);
the second parallel circuit comprises second resistors (R) connected in series in sequence2) And a second switching tube (T)2)，
The second resistor (R)2) As a first terminal of the second parallel circuit is connected to the second capacitor (C)bus2) The second resistor (R), the second resistor (R)2) Is connected to the second switching tube (T)2) The second switching tube (T)2) As a second terminal of the second parallel circuit is connected to the second capacitor(Cbus2) The second end of (a).
Further, in the present invention,
further comprising a first diode (D)1) And a second diode (D)2)，
The first switch tube (T)1) And the first diode (D)1) Form an anti-parallel structure, i.e. the first switch tube (T)1) Is connected to the first diode (D)1) The first switching tube (T)1) Is connected to the first diode (D)1) The anode of (a) is provided,
the second switch tube (T)2) And the second diode (D)2) Form an anti-parallel structure, i.e. the second switch tube (T)2) Is connected to the second diode (D)2) The second switching tube (T)2) Is connected to the second diode (D)2) Of (2) an anode.
Further, in the present invention,
further comprising a first resistor-capacitor circuit and a second resistor-capacitor circuit,
the first switch tube (T)1) In parallel with said first resistor-capacitor circuit, i.e. said first switching tube (T)1) Is connected to a first terminal of said first resistor-capacitor circuit, said first switching tube (T)1) Is connected to a second terminal of the first resistor-capacitor circuit;
the second switch tube (T)2) In parallel with said second resistor-capacitor circuit, i.e. said second switching tube (T)2) Is connected to a first terminal of said second resistor-capacitor circuit, said second switching tube (T)2) Is connected to a second terminal of the second resistor-capacitor circuit.
Further, in the present invention,
the first resistor-capacitor circuit comprises a first series resistor (R) connected in seriesS1) And a first series capacitance (C)S1) The first series resistance (R)S1) As a first terminal of said first resistor-capacitor circuit, said first series resistor (R)S1) Second terminal of the first series circuit is connected with the first series circuitCapacitor (C)S1) The first series capacitance (C)S1) As a second terminal of the first resistor-capacitor circuit;
the second resistor-capacitor circuit comprises a second series resistor (R) connected in seriesS2) And a second series capacitance (C)S2) Said second series resistance (R)S2) As a first terminal of said second resistor-capacitor circuit, said second series resistor (R)S2) Is connected to the second series capacitance (C)S2) Said second series capacitance (C)S2) As a second terminal of the second resistor-capacitor circuit.
Further, in the present invention,
the first switch tube (T)1) And a second switching tube (T)2) For integrated gate commutated thyristors or insulated gate bipolar transistors,
the first switch tube (T)1) And a second switching tube (T)2) For an integrated gate commutated thyristor, the first switching transistor (T)1) And a second switching tube (T)2) The first end of the anode is an anode, and the second end of the anode is a cathode;
the first switch tube (T)1) And a second switching tube (T)2) In the case of an insulated gate bipolar transistor, the first switching tube (T)1) And a second switching tube (T)2) The first terminal of (a) is a collector and the second terminal is an emitter.
The invention also provides a control method of the unloading circuit for the wind power converter, which is used for controlling the unloading circuit for the wind power converter, and the control method comprises the following steps:
to the first capacitor (C) collectedbus1) Or a second capacitance (C)bus2) Comparing the input active power and the output active power at the direct current side to obtain an active difference value delta P;
A. determining the switching of an unloading circuit by taking the active difference value delta P as a first judgment condition, and determining the duty ratio of a power device according to the active difference value delta P when the unloading circuit is put into use, wherein the active difference value delta P is equal to Pmdc-Pgdc，PmdcActive work of machine side converter flowing to direct current busRate, PgdcThe active power flowing to the grid-side converter for the direct current bus;
B. with said first capacitance (C)bus1) Or a second capacitance (C)bus2) And the direct-current side voltage is used as a second judgment condition to determine the switching of the unloading circuit.
Further, in the present invention,
in the step a, when the active power difference Δ P reaches or exceeds a certain set value, an unloading circuit is put into operation.
Further, in the present invention,
when the load is loaded into the unloading circuit, the active difference value delta P is used as a modulation wave signal after passing through a PI regulator, and the first switch tube (T) is controlled1) Or a second switching tube (T)2) Duty cycle D of (D).
Further, in the present invention,
the duty ratio D satisfies:
wherein the content of the first and second substances,
Rdis a first resistance (R)1) Or a first resistance (R)2) Resistance value of Udc_refIs a DC bus voltage target value;
when the DC bus voltage UdcGreater than Udc_maxThen, let the duty ratio D be 1, Udc_maxThe set maximum value of the direct current bus voltage is obtained.
Further, in the present invention,
in the step (B),
when the control delay of the unloading circuit reaches or exceeds a preset value according to the active difference value delta P, or the rising speed of the voltage on the direct current side reaches or exceeds a preset value, the voltage on the direct current side is used as a judgment condition to control: when the DC bus voltage UdcGreater than Udc_maxThen, let the duty ratio D be 1, Udc_maxThe set maximum value of the direct current bus voltage is obtained.
The unloading circuit for the wind power converter and the control method thereof are suitable for the three-level neutral point clamping type converter. In the unloading circuit for the wind power converter, the switching tube is provided with the absorption circuit, so that overvoltage and overcurrent can be prevented from being generated in the switching-on and switching-off process of the switching tube, du/dt and di/dt are inhibited, the switching loss can be reduced, and the effect of protecting devices can be achieved. The control method of the invention adopts double criteria of direct current power deviation and direct current voltage, the control difficulty is moderate, and the control effect is good.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an unloading circuit for a wind power converter according to an embodiment of the invention;
FIG. 2 shows a functional block diagram of an unloading circuit control method for a wind power converter according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 some, but not all, embodiments of the present invention. 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.
Fig. 1 shows an unloading circuit structure for a wind power converter according to the present invention. As shown in FIG. 1, the wind of the present inventionThe unloading circuit for the current transformer is based on three-level active clamping wind power converter topology, and comprises: first capacitors C connected in seriesbus1And a second capacitor Cbus2First capacitor Cbus1Second terminal of the first capacitor is connected with a second capacitor Cbus2The first end of (a).
A first capacitor Cbus1A first parallel circuit connected in parallel and including a first switch tube T connected in series in sequence1And a first resistor R1A first switch tube T1As a first terminal of a first parallel circuit is connected to a first capacitor Cbus1A first switch tube T1Is connected with the first resistor R1A first terminal of (1), a first resistor R1As a second terminal of the first parallel circuit, is connected to a first capacitor Cbus1The second end of (a). The first switch tube T1And a first diode D1Forming an anti-parallel structure, i.e. the first switching tube T1Is connected with a first diode D1A first switching tube T1Second terminal of the first diode D1Of (2) an anode. The first switch tube T1And is also connected in parallel with a first resistor-capacitor (RC) circuit, i.e. a first switch tube T1Is connected to the first end of the first RC circuit, a first switch tube T1Is connected to the second terminal of the first RC circuit. The first RC circuit comprises a first series resistor R connected in seriesS1And a first series capacitance CS1First series resistance RS1As a first terminal of a first RC-circuit, a first series resistance RS1Is connected with the first series capacitor CS1A first terminal of (C), a first series capacitor CS1As a second terminal of the first RC circuit.
Second capacitor Cbus2A second parallel circuit connected in parallel and comprising a second resistor R connected in series in sequence2And a second switching tube T2A second resistance R2As a first terminal of a second parallel circuit is connected to a second capacitor Cbus2A first terminal of (1), a second resistor R2The second end of the first switch tube T is connected with the second switch tube T2A first end of the second switching tube T2As a second terminal of the second parallel circuit is connected to a second capacitor Cbus2The second end of (a). The second switch tube T2And a second diode D2Forming an anti-parallel structure, i.e. the second switching tube T2Is connected to a second diode D2A second switching tube T2Is connected to a second diode D2Of (2) an anode. The second switch tube T2Also connected in parallel with a second RC-circuit, i.e. a second switching tube T2Is connected to the first end of the second RC circuit, and a second switch tube T2Is connected to the second terminal of the second RC circuit. The second RC circuit comprises a second series resistor R connected in seriesS2And a second series capacitor CS2Second series resistance RS2As a first terminal of a second RC-circuit, a second series resistance RS2Second terminal of the first series capacitor is connected with a second series capacitor CS2A first terminal of (C), a second series capacitor CS2As a second terminal of the second RC circuit.
The first switch tube T1And a second switching tube T2Which may be an Integrated Gate Commutated Thyristor (IGCT) or an Insulated Gate Bipolar Transistor (IGBT). The first switch tube T1And a second switching tube T2In the case of IGCT, the first switch tube T1And a second switching tube T2The first end of the first switch tube T is an anode1And a second switching tube T2The second end of (a) is a cathode. The first switch tube T1And a second switching tube T2When being IGBT, the first switch tube T1And a second switching tube T2First end collector of, a first switching tube T1And a second switching tube T2The second end of (a) is an emitter.
Based on the unloading circuit for the wind power converter, the invention also provides a control method of the unloading circuit for the wind power converter, which is used for adjusting the power deviation of the unloading circuit. FIG. 2 is a functional block diagram of an unloading circuit control method for a wind power converter, wherein P is PmdcActive power, P, flowing to the DC bus for the machine side convertergdcThe active power flowing to the grid-side converter for the direct current bus. As shown in fig. 2, aWhen the current transformer works normally, the DC bus voltage VdcA support capacitor (i.e. the first capacitor C)bus1Or a second capacitance Cbus2) Power difference between two ends, i.e. active difference (P)mdc-Pgdc) There is a certain ripple, at which time the unloading resistor should not act. When the active difference (P) between the two ends of the supporting capacitormdc-Pgdc) When the active power difference value reaches or exceeds a certain set value, the active power difference value is used as a modulation wave signal after passing through a PI regulator to control a power device (namely the first switch tube T)1Or a second switch tube T2) Duty cycle D of (D). Recording the active difference value delta P ═ P between two ends of the supporting capacitormdc-PgdcIn the switching period T of a power device (the T1 or T2), the energy dissipation resistor (namely the first resistor R)1Or a second resistance R2The resistance value of the energy consumption resistor is Rd) The consumed energy should satisfy:
wherein, UdcIs a DC bus voltage (i.e. the V)dc) T represents time, assuming that the DC bus voltage remains at the target value Udc_refThen the duty ratio D should satisfy
In addition, when the collected DC bus voltage UdcGreater than a set maximum value Udc_maxWhen the load is loaded, the duty ratio D is 1, and the load is completely loaded into the unloading circuit.
The unloading circuit control method for the wind power converter is characterized in that the direct current side voltage and power deviation of the wind power converter are used as double criteria, and active power (namely the first capacitor C) is input and output to the direct current side of the collected wind power converterbus1Or a second capacitance Cbus2The power difference at the two ends) is compared to obtain the power deviation of the input active power and the output active power at the direct current side, namely the power difference or the active difference value. The power deviation of input and output active power at the DC side is used asThe switching of the unloading circuit is determined according to the primary judgment condition, and when the unloading circuit is put into use, the duty ratio of the power device is determined by the regulator according to the power deviation. The DC side voltage is used as an auxiliary judgment condition, when the control delay of the unloading circuit is large (namely the control delay of the unloading circuit by the active difference value delta P reaches or exceeds a preset value) or the DC side voltage is increased too fast (namely the rising speed of the DC side voltage reaches or exceeds a preset value), the DC side voltage is used as the judgment condition for control, namely when the collected DC bus voltage U is used as an auxiliary judgment conditiondcGreater than a set maximum value Udc_maxWhen the load is loaded, the duty ratio D is 1, and the load is completely loaded into the unloading circuit.
The unloading circuit for the wind power converter and the control method thereof are suitable for the three-level neutral point clamping type converter. In the unloading circuit for the wind power converter, the switching tube is provided with the absorption circuit, so that overvoltage and overcurrent can be prevented from being generated in the switching-on and switching-off process of the switching tube, du/dt and di/dt are inhibited, the switching loss can be reduced, and the effect of protecting devices can be achieved. The control method of the invention adopts double criteria of direct current power deviation and direct current voltage, the control difficulty is moderate, and the control effect is good.
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.