Wind power converter soft start circuit and wind power converter
By adding filter branch input contactor and current transformer to the wind power converter soft start circuit, the soft start contactor and the filter branch are cut off in advance, the damage caused by shock current in low temperature environment and the energy consumption during network operation is solved, and higher reliability and efficiency are achieved.
Patent Information
- Application Number
- CN202421819506.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-30
- Publication Date
- 2025-05-09
- Estimated Expiration
- 2034-07-30
AI Technical Summary
In the soft-start circuit of the wind power converter, the impact current when charging the DC bus capacitor in a low temperature environment will cause damage to the current limiting resistor and the main contactor, and during long-term standby network operation, the filter branch consumes the power grid energy and causes energy loss.
A wind power converter soft start circuit is designed, and the filter branch input contactor and current transformer are added. By changing the breaking conditions of the soft start contactor in series with the current limiting resistor, the soft start contactor is disconnected in advance, reducing the time when large current in the current limiting resistor passes, and the filter branch is cut from the power grid through the contactor, reducing energy consumption.
It effectively avoids damage to the current limiting resistor and main contactor, reduces the consumption of the grid energy by the filter branch during the on-network operation, and improves the reliability and efficiency of the system.
Smart Images
Figure CN222852175U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of wind power converters, in particular to a wind power converter soft start circuit and a wind power converter. Background Art
[0002] In the soft-start circuit of a wind power converter, when the DC bus capacitor is charged, a sudden change in the DC bus capacitor voltage at the moment of closing the switch will cause a large impact current. This impact current is much higher than the rated current of the circuit, causing significant damage to the contactor, power module and DC bus capacitor. Therefore, the current must be limited during charging. The usual practice is to limit the current by connecting a series resistor when the DC bus capacitor is charged.
[0003] like Figure 1 The figure shows a common wind power converter soft start circuit topology diagram, which includes a grid-connected switch MCB, a three-phase isolating switch Q21, a soft start contactor KM2, a current limiting resistor R1, a main contactor KM1, a main contactor fuse FU1, a power module, a DC bus capacitor Cdc and a filter branch. Figure 1 The soft start control method corresponding to the circuit topology is usually: close the grid-connected switch MCB, the three-phase isolating switch Q21, and the soft start contactor KM2, pre-charge the DC bus capacitor Cdc and the filter, and after the pre-charging is completed, close the main contactor KM1, and then disconnect the soft start contactor KM2. In a low temperature environment, the action time of the contactor feedback contact will be longer, even reaching 1.5 times the action time at normal temperature. Therefore, the arrival time of the closing feedback signal of the auxiliary contact of the main contactor KM1 at low temperature is much later than that at normal temperature, resulting in the inability of the soft start contactor KM2 to disconnect in time. In the soft start circuit of the wind power converter, the capacitance value of the filter is usually large, so the charging current is large. In a low temperature environment, the time for a large current to flow through the current limiting resistor R1 is too long, which will cause the current limiting resistor R1 to be easily damaged by heat. Similarly, the voltage difference across the current limiting resistor R1 is large, which will cause the main contactor KM1 connected in parallel with the current limiting resistor R1 to be easily damaged.
[0004] In addition, when the converter is in long-term standby operation, the filter branch must also be connected to the grid. If the wind farm has no reactive power demand at this time, the filter branch will consume grid energy, causing energy loss. Utility Model Content
[0005] The technical problem to be solved by the utility model is: in view of the above-mentioned defects of the prior art, a soft start circuit of a wind power converter and a wind power converter are provided.
[0006] To achieve the above-mentioned object, in a first aspect, the utility model provides a soft-start circuit for a wind power converter, the circuit comprising a three-phase isolating switch, a first contactor, a first resistor, a grid-connected switch, a first inductor, a power module, a DC bus capacitor, a second contactor, a current transformer, and a filter branch;
[0007] One end of the three-phase isolating switch is connected to the power grid, and the other end is connected to the first end of the first resistor through the first contactor; the second end of the first resistor is connected to the DC bus capacitor through the current transformer, the second contactor, the first inductor, and the power module in sequence; the second end of the first resistor is also connected to the filter branch;
[0008] One end of the grid-connected switch is connected to the grid, and the other end is connected to the common end of the second contactor and the first inductor;
[0009] The filter branch includes a capacitor.
[0010] Preferably, the wind power converter soft start circuit further includes a controller, and the controller is connected to the three-phase isolating switch, the first contactor, the grid-connected switch, the control end of the second contactor, and the auxiliary contacts of the first contactor and the second contactor.
[0011] Preferably, the filter branch comprises an RC filter branch and an LC filter branch connected in parallel with each other.
[0012] Preferably, the RC filter branch includes a second resistor and a first capacitor, one end of the second resistor is connected to the second end of the first resistor, and the other end is grounded via the first capacitor.
[0013] Preferably, the LC filter branch includes a second inductor and a second capacitor, one end of the second inductor is connected to the second end of the first resistor, and the other end is grounded via the second capacitor.
[0014] In a second aspect, the utility model further provides a wind power converter, wherein the wind power converter comprises the wind power converter soft start circuit as described above.
[0015] The utility model has the following beneficial effects: the wind power converter soft start circuit of the utility model adds a filter branch switching contactor and a current transformer, reduces the main contactor and the main contactor fuse connected in parallel with the current limiting resistor, and avoids the problem of easy damage to the main contactor; when the converter is in standby and grid-connected operation for a long time, the filter branch is cut off from the grid by the filter branch switching contactor, reducing the energy consumption of the grid by the filter branch during the grid-connected period. The current transformer can be used to detect the current in the circuit, so as to assist in judging the state of the second contactor KM3 according to the current value, and reduce the control delay caused by the longer feedback time of the contactor contact at low temperature. In terms of control method, by changing the disconnection condition of the soft start contactor KM2 connected in series with the current limiting resistor, the soft start contactor KM2 can be disconnected in advance at low temperature, reducing the time for large current to pass through the current limiting resistor, avoiding overheating and damage of the current limiting resistor, and accelerating the soft start speed. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:
[0017] Figure 1 The topology diagram of the soft-start circuit of the wind power converter in the prior art is shown in FIG.
[0018] Figure 2 A topological diagram of a soft-start circuit for a wind power converter provided in an embodiment of the utility model.
[0019] Figure 3 for Figure 2 Schematic diagram of current flow during the pre-charging phase of the circuit shown.
[0020] Figure 4 for Figure 2 The circuit shown is a schematic diagram of current flow during the formal charging phase.
[0021] Figure 5 A schematic diagram of the steps of a soft start control method for a wind power converter provided in an embodiment of the utility model. DETAILED DESCRIPTION
[0022] In order to make the purpose, technical solution and advantages of the embodiment of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0023] The following is a further detailed description of the embodiments of the utility model in conjunction with the accompanying drawings of the specification. It should be understood that the embodiments described herein are only used to illustrate and explain the utility model, and are not used to limit the utility model.
[0024] like Figure 2-4 As shown, an embodiment of the utility model provides a soft start circuit for a wind power converter, the circuit comprising a three-phase isolating switch Q21, a first contactor KM2, a first resistor R1, a grid-connected switch MCB, a first inductor L1, a power module, a DC bus capacitor Cdc, a second contactor KM3, a current transformer H11, and a filter branch.
[0025] One end of the three-phase isolating switch Q21 is connected to the power grid, and the other end is connected to the first end of the first resistor R1 through the first contactor KM2; the second end of the first resistor R1 is connected to the DC bus capacitor Cdc through the current transformer H11, the second contactor KM3, the first inductor L1, and the power module in sequence; the second end of the first resistor R1 is also connected to the filter branch;
[0026] One end of the grid-connected switch MCB is connected to the grid, and the other end is connected to the common end of the second contactor KM3 and the first inductor L1;
[0027] The filter branch includes a capacitor.
[0028] In some embodiments of the utility model, the filter branch includes an RC filter branch and an LC filter branch connected in parallel. The RC filter branch includes a second resistor R2 and a first capacitor C2, one end of the second resistor R2 is connected to the second end of the first resistor R1, and the other end is grounded via the first capacitor C2. The LC filter branch includes a second inductor L2 and a second capacitor C3, one end of the second inductor L2 is connected to the second end of the first resistor R1, and the other end is grounded via the second capacitor C3.
[0029] In an embodiment of the utility model, the wind power converter soft start circuit also includes a controller, and the controller is connected to the three-phase isolating switch Q21, the first contactor KM2, the grid-connected switch MCB, the control end of the second contactor KM3, and the auxiliary contacts of the first contactor KM2 and the second contactor KM3. The controller is used to control the on and off of each of the above-mentioned switch devices, and to understand the status of the first contactor KM2 and the second contactor KM3 through the feedback signals of the auxiliary contacts of the first contactor KM2 and the second contactor KM3. In some embodiments of the utility model, the controller is a DSP chip and its peripherals, and in other embodiments of the utility model, the controller is a single-chip microcomputer and its peripherals.
[0030] In the embodiment of the utility model, a voltage sampling circuit is connected to both ends of the DC bus capacitor Cdc, and the output end of the voltage sampling circuit is connected to the controller. The voltage sampling circuit is used to detect the voltage across the DC bus capacitor Cdc, and the controller determines the charging state of the DC bus capacitor Cdc through the output of the voltage sampling circuit.
[0031] In the embodiment of the utility model, the output end of the current transformer H11 is connected to the current sampling circuit, and the output end of the current sampling circuit is connected to the controller.
[0032] Figure 2-Figure 4 The wind power converter soft start circuit is the grid side part of the wind power converter, wherein AC is the grid side three-phase AC terminal voltage, and its voltage value can be modified according to actual needs. The parameters of the second resistor R2 and the first capacitor C2 in the RC filter branch can be adapted according to actual needs. The parameters of the second inductor L2 and the second capacitor C3 in the LC filter branch can be adapted according to actual needs.
[0033] and Figure 1 In comparison, the circuit topology provided by the embodiment of the utility model adds a second contactor KM3 as a filter branch switching contactor, reduces the main contactor and the main contactor fuse connected in parallel with the current limiting resistor R1, and solves the problem of easy damage to the main contactor. When the converter is in standby and grid-connected operation for a long time, the filter branch can be cut off from the grid through the second contactor KM3, reducing the consumption of grid energy by the filter branch during the grid connection period. The circuit topology provided by the embodiment of the utility model also adds a current transformer H11, which can be used to detect the current in the circuit, thereby assisting in judging the state of the second contactor KM3 according to the current value, and reducing the control delay caused by the longer feedback time of the contactor contacts at low temperatures.
[0034] like Figure 5 As shown, the embodiment of the utility model further provides a wind power converter soft start control method, which is applied to the wind power converter soft start circuit as described above, and the method comprises the following steps:
[0035] Step S1, close the three-phase isolating switch Q21, the first contactor KM2, and the second contactor KM3 to pre-charge the DC bus capacitor Cdc. When the DC bus capacitor Cdc is charged to a preset pre-charging voltage threshold, disconnect the first contactor KM2.
[0036] In actual applications, the preset pre-charge voltage threshold is set according to specific circumstances. In some implementations of the utility model embodiments, the pre-charge voltage threshold is set to the effective value of the grid voltage ×√2×80%. In other implementations of the utility model embodiments, the pre-charge voltage threshold is set to the effective value of the grid voltage ×√2×75%.
[0037] Step S2, after the first contactor KM2 is disconnected successfully, the DC bus capacitor Cdc acts as a DC source to perform self-test on the filter of the filter branch; if the self-test passes, jump to step S3; if the self-test fails, skip all subsequent steps and stop for inspection.
[0038] In the soft start phase, self-checking the filter can timely discover the fault of the filter, and avoid damage to the whole system due to the filter fault after the whole machine is working. In the embodiment of the utility model, in the step S2, the method of self-checking the filter of the filter branch is: the DC bus capacitor Cdc acts as a DC source, and the filter branch is self-checked by the diode in the power module. In practical applications, the driver of the power module automatically realizes the self-check of the filter.
[0039] Step S3, closing the first contactor KM2, and pre-charging the DC bus capacitor Cdc again; when the DC bus capacitor Cdc is charged to a preset pre-charging voltage threshold, closing the grid-connected switch MCB and disconnecting the first contactor KM2.
[0040] Because the power of the DC bus capacitor Cdc is consumed during the filter self-test in step S2, the DC bus capacitor Cdc needs to be pre-charged again.
[0041] Step S4, after the first contactor KM2 is disconnected successfully, the second contactor KM3 is disconnected and the start command is waited.
[0042] After the first contactor KM2 is disconnected successfully, the filter branch is still connected to the grid. In order to reduce the consumption of the filter branch on the grid during the long-term connection to the grid, the second contactor KM3 is disconnected to cut off the filter branch from the grid. Then, the start command is waited for. During the process of waiting for the start command, the DC bus capacitor Cdc is always connected to the grid and remains charged.
[0043] The steps S1-S4 are the pre-charging stage. After the first contactor KM2 and the second contactor KM3 are disconnected, the first resistor R1 is bypassed, the filter branch is cut off, and the power module and the DC bus capacitor Cdc are connected to the grid through the grid-connected switch MCB. At this time, although the power module is connected to the grid, it is not working and is in standby mode. After receiving the start-up command from the whole machine manufacturer, the formal charging stage of steps S5-S6 will be entered.
[0044] In some embodiments of the present invention, the method further comprises:
[0045] A pre-charge maximum time threshold is set. If the time before "waiting for the startup command" in step S4 exceeds the pre-charge maximum time threshold, a prompt of soft start failure is given.
[0046] At low temperatures, affected by temperature, the feedback time of the auxiliary contacts of the first contactor KM2 and the second contactor KM3 will be longer, and the duration of the entire pre-charging stage will be longer. The maximum duration threshold needs to be set according to the soft start duration of the system at low temperatures. When the pre-charging duration exceeds the pre-charging maximum duration threshold, the soft start fails.
[0047] Step S5, after receiving the start command, close the first contactor KM2 to pre-charge the capacitor of the filter branch; and jump to step S6 after a preset delay.
[0048] Because the filter branch is cut off during the grid connection, the capacitor in the filter has lost power, and the filter self-test has been done in the pre-charging stage, so after receiving the start-up command, the filter branch is pre-charged again, and then the filter branch can be connected to the grid. In some embodiments of the utility model, a preset delay is set according to the charging time of the filter branch. After the preset delay time, it is considered that the charging of the filter branch has been completed, and the filter branch can be connected to the grid.
[0049] Step S6, closing the second contactor KM3; after the second contactor KM3 is successfully closed, disconnecting the first contactor KM2.
[0050] In the embodiment of the utility model, the judgment condition for the successful closing of the second contactor KM3 is: receiving the closing feedback signal of the auxiliary contact of the second contactor KM3 or the current value detected by the current transformer H11 reaches the preset current threshold, which indicates successful closing; otherwise, it indicates that it has not been successfully closed.
[0051] At low temperatures, the feedback signal delay of the second contactor KM3 causes the time for the current to flow through the first resistor R1 to be too long. Therefore, in the embodiment of the utility model, the closing feedback signal of the auxiliary contact of the second contactor KM3 and the current value detected by the current transformer H11 are used to determine whether the second contactor KM3 is successfully closed. When the closing feedback signal of the auxiliary contact of the second contactor KM3 is received or the current value detected by the current transformer H11 reaches the preset current threshold, it indicates a successful closure. The preset current threshold is set according to the capacitance value of the filter branch. After the second contactor KM3 is successfully closed, the first contactor KM2 is immediately disconnected, so as to achieve the purpose of disconnecting the first contactor KM2 in advance and reducing the time of the large current flowing through the first resistor R1.
[0052] After the first contactor KM2 is disconnected, it means that the soft start of the wind power converter is completed.
[0053] The above control method is executed in the controller, which is connected to the control end of each switch device, and controls the on and off of each switch device according to the voltage across the DC bus capacitor Cdc acquired by the voltage acquisition circuit and the current flowing through the current transformer H11 acquired by the current acquisition circuit.
[0054] The embodiment of the utility model further provides a wind power converter, which includes the wind power converter soft start circuit as described above. In addition, the wind power converter also includes a machine-side power module, a machine-side motor, and a machine-side filter.
[0055] The utility model has the following beneficial effects: the wind power converter soft start circuit of the utility model adds a filter branch switching contactor and a current transformer, reduces the main contactor and the main contactor fuse connected in parallel with the current limiting resistor, and avoids the problem of easy damage to the main contactor; when the converter is in standby and grid-connected operation for a long time, the filter branch is cut off from the grid by the filter branch switching contactor, reducing the energy consumption of the grid by the filter branch during the grid-connected period. The current transformer can be used to detect the current in the circuit, so as to assist in judging the state of the second contactor KM3 according to the current value, and reduce the control delay caused by the longer feedback time of the contactor contact at low temperature. In terms of control method, by changing the disconnection condition of the soft start contactor KM2 connected in series with the current limiting resistor, the soft start contactor KM2 can be disconnected in advance at low temperature, reducing the time for large current to pass through the current limiting resistor, avoiding overheating and damage of the current limiting resistor, and accelerating the soft start speed.
[0056] In addition, through the control method of the utility model, the use time of the current limiting resistor in a single soft start process is shortened, which is beneficial to improving the service life of the current limiting resistor, reducing the requirements for the process of the current limiting resistor, and reducing the cost of the converter in the long run. Bypassing the current limiting resistor and the filter branch in time is beneficial to the heat dissipation of the converter, reducing the specifications and process requirements of the cable, and improving the efficiency and reliability of the converter.
[0057] The above are only specific implementation methods of the present invention, which cannot be used to limit the scope of the present invention. Equal changes made by ordinary technicians in this technical field based on this creation, as well as changes well known to technicians in this field, should still fall within the scope of the present invention.
Claims
1. A soft start circuit for a wind power converter, characterized in that: The circuit comprises a three-phase isolating switch (Q21), a first contactor (KM2), a first resistor (R1), a grid-connected switch (MCB), a first inductor (L1), a power module, a DC bus capacitor (Cdc), a second contactor (KM3), a current transformer (H11), and a filter branch; One end of the three-phase isolating switch (Q21) is connected to the power grid, and the other end is connected to the first end of the first resistor (R1) through the first contactor (KM2); the second end of the first resistor (R1) is connected to the DC bus capacitor (Cdc) in sequence through the current transformer (H11), the second contactor (KM3), the first inductor (L1), and the power module; the second end of the first resistor (R1) is also connected to the filter branch; One end of the grid-connected switch (MCB) is connected to the power grid, and the other end is connected to the common end of the second contactor (KM3) and the first inductor (L1); The filter branch includes a capacitor.
2. The soft start circuit of the wind power converter according to claim 1, characterized in that: The invention comprises a controller, wherein the controller is connected to the three-phase isolating switch (Q21), the first contactor (KM2), the grid-connected switch (MCB), the control end of the second contactor (KM3), the first contactor (KM2) and the auxiliary contacts of the second contactor (KM3).
3. The soft start circuit of the wind power converter according to claim 1, characterized in that: The filter branch includes an RC filter branch and an LC filter branch connected in parallel with each other.
4. The soft start circuit of the wind power converter according to claim 3, characterized in that: The RC filter branch comprises a second resistor (R2) and a first capacitor (C2), one end of the second resistor (R2) is connected to the second end of the first resistor (R1), and the other end is grounded via the first capacitor (C2).
5. The soft start circuit of the wind power converter according to claim 3, characterized in that: The LC filter branch comprises a second inductor (L2) and a second capacitor (C3); one end of the second inductor (L2) is connected to the second end of the first resistor (R1), and the other end is grounded via the second capacitor (C3).
6. A wind power converter, characterized in that: The wind power converter comprises the wind power converter soft start circuit according to any one of claims 1 to 5.