A method of converter control and a converter

Abstract

The application provides a converter control method and a converter, the converter connects a slow-start contactor and a grid-connected switch in parallel; after a controller of the converter receives a converter starting instruction, the controller calculates a DC voltage calculation value of a grid-side power unit after rectification according to a grid voltage, determines a time point when the DC voltage calculation value and a current collected DC bus voltage actual value satisfy a preset charging condition as an action time point of the slow-start contactor; then when the action time point comes, the slow-start contactor is controlled to be closed to charge a DC bus capacitor between positive and negative poles of the DC bus, so that the slow-start starting of the converter can be realized by using only one slow-start contactor, the slow-start resistor in the prior art is cancelled, and the cost of the converter is reduced.

Description

Technical Field

[0001] This invention relates to the field of control technology, and in particular to a converter control method and a converter. Background Technology

[0002] Existing wind power converters employ soft-start contactors and soft-start resistors to achieve slow start-up. Upon receiving a start command, the wind power converter charges the DC bus by closing the soft-start contactor. Once the DC bus rises to a certain value, the soft-start contactor opens, and the circuit breaker closes to initiate normal power generation. However, this method increases the manufacturing cost of the wind power converter due to the addition of the soft-start contactor and resistor.

[0003] Therefore, how to reduce the cost of wind power converters while achieving slow start-up of converters has become an urgent problem to be solved in this field. Summary of the Invention

[0004] In view of this, the present invention provides a converter control method and a converter to reduce the cost of wind power converters while achieving converter slow start-up.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The first aspect of this invention provides a converter control method applied to a converter controller, the converter control method comprising:

[0007] Receive converter start command;

[0008] The DC voltage after rectification by the grid-side power unit in the converter is calculated based on the grid voltage and used as the calculated DC voltage value.

[0009] The moment when the calculated DC voltage value and the currently collected actual DC bus voltage value meet the preset charging conditions is taken as the action moment of the slow-start contactor;

[0010] When the specified action time arrives, the slow-start contactor connected in parallel with the grid-connected switch in the converter is closed to charge the DC bus capacitor between the positive and negative terminals of the DC bus.

[0011] Optionally, the preset charging conditions are:

[0012] The difference between the calculated DC voltage value and the actual DC bus voltage value is less than a first preset value.

[0013] Optionally, if the soft-start contactor is a thyristor, then the preset charging condition is:

[0014] During the negative half-cycle of the grid voltage, the difference between the calculated DC voltage value and the actual DC bus voltage value is less than a first preset value.

[0015] Optionally, after controlling the soft-start contactor to close and charge the DC bus capacitor between the positive and negative terminals of the DC bus when the actuation moment arrives, the method further includes:

[0016] Determine whether the DC bus capacitor has finished charging;

[0017] If the DC bus capacitor is fully charged, the grid-connected switch is closed to start the converter.

[0018] Optionally, if the soft-start contactor is not a thyristor, then after the DC bus capacitor has finished charging, the following steps are also included:

[0019] Control the soft-start contactor to turn off.

[0020] Optionally, controlling the grid-connected switch to close to start the converter includes:

[0021] Control the grid connection switch to close;

[0022] Control the operation of the grid-side power unit to stabilize the actual value of the DC bus voltage at a second preset value.

[0023] Optionally, if the converter is a wind power converter, then after controlling the operation of the grid-side power unit to stabilize the actual value of the DC bus voltage at a second preset value, the method further includes:

[0024] Control the operation of the generator-side power unit in the wind power converter to provide excitation current to the motor rotor;

[0025] Determine whether the stator voltage of the wind power converter is synchronized with the grid voltage;

[0026] If the stator voltage is synchronized with the grid voltage, the stator contactor in the wind power converter is closed to start the converter.

[0027] Optionally, if the converter is a wind power converter, after controlling the grid connection switch to close to start the converter, the method further includes:

[0028] Receive converter shutdown command;

[0029] The slow-start contactor, the grid-connected switch, and the stator contactor in the wind power converter are disconnected to control the converter to shut down.

[0030] A second aspect of the present invention also provides a converter, comprising: a controller, a grid-side power unit, a grid-connected switch, and a soft-start contactor; wherein,

[0031] The DC side of the grid-side power unit is connected to the DC bus;

[0032] The grid-connected switch is located between the AC side of the grid-side power unit and the grid connection point;

[0033] The slow-start contactor is connected in parallel with the grid-connected switch;

[0034] The grid-side power unit, the grid-connected switch, and the soft-start contactor are all controlled by the controller;

[0035] The controller is used to execute the converter control method as described in any of the first aspects above.

[0036] Optionally, the grid-side power unit is an inverter, and the DC side of the grid-side power unit is connected to the photovoltaic string.

[0037] Optionally, the converter is a wind power converter, and the converter further includes: a stator contactor, an input filter inductor, a machine-side power unit, and an output filter inductor;

[0038] The grid-connected switch is connected to the rotor winding of the motor in sequence through the input filter inductor, the grid-side power unit, the DC bus, the machine-side power unit, and the output filter inductor;

[0039] The grid-connected switch is also connected to the stator winding of the motor via the stator contactor;

[0040] Both the machine-side power unit and the stator contactor are controlled by the controller.

[0041] Optionally, the converter is a wind power converter, and the converter further includes: a stator contactor, an input filter inductor, a machine-side power unit, and an output filter inductor;

[0042] The grid connection point is connected to the rotor winding of the motor in sequence through the grid connection switch, the input filter inductor, the grid-side power unit, the DC bus, the machine-side power unit, and the output filter inductor;

[0043] The grid connection point is also connected to the stator winding of the motor via the stator contactor;

[0044] Both the machine-side power unit and the stator contactor are controlled by the controller.

[0045] The converter control method provided by this invention, after the converter controller receives the converter start command, calculates the DC voltage after rectification by the grid-side power unit based on the grid voltage, and determines the moment when the calculated DC voltage and the currently collected actual DC bus voltage meet the preset charging conditions, which is taken as the action moment of the slow-start contactor; then, when the action moment arrives, the slow-start contactor is controlled to close to charge the DC bus capacitor between the positive and negative poles of the DC bus, so that the slow-start of the converter can be realized by using only one slow-start contactor, eliminating the slow-start resistor in the prior art, thereby reducing the cost of the converter. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the converter structure provided in an embodiment of the present invention;

[0048] Figure 2 A flowchart of a converter control method provided in an embodiment of the present invention;

[0049] Figure 3 Another flowchart of the converter control method provided in the embodiment of the present invention;

[0050] Figure 4 Another specific flowchart of the converter control method provided in the embodiment of the present invention;

[0051] Figure 5 and Figure 6 Two other specific flowcharts of the converter control method provided in the embodiments of the present invention;

[0052] Figure 7 and Figure 8 These are schematic diagrams of two other converter structures provided in embodiments of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] This invention provides a converter control method to reduce the cost of wind power converters while achieving converter slow start-up.

[0056] The converter control method provided by this invention is applied to the controller of a converter, such as... Figure 1 As shown, the converter includes: a grid-side power unit 101, a grid-connected switch Q1, and a slow-start contactor Q2; wherein, the DC side of the grid-side power unit 101 is connected to the DC bus, the grid-connected switch Q1 is disposed between the AC side of the grid-side power unit 101 and the grid connection point, and the slow-start contactor Q2 is connected in parallel with the grid-connected switch Q1.

[0057] It is worth noting that the soft-start contactor Q2 includes, but is not limited to, any one of power electronic devices and non-power electronic devices. In practical applications, the soft-start contactor Q2 can also be any one of thyristors, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and IGBTs (Insulated Gate Bipolar Transistors). No specific limitation is made here; it depends on the actual application environment, and all are within the protection scope of this application.

[0058] like Figure 2 As shown, the converter control method specifically includes:

[0059] S101, Receive converter start command.

[0060] S102. Calculate the DC voltage after rectification of the grid-side power unit based on the grid voltage, and use it as the calculated DC voltage value.

[0061] After receiving the converter start-up command, the converter controller obtains the grid voltage and calculates the voltage at that grid voltage. Figure 1 The DC voltage output after rectification by the power unit 101 on the grid side is used as the calculated DC voltage value. Since the specific value of the grid voltage changes in real time, the calculated DC voltage value will be different at different times.

[0062] S103. Determine the moment when the calculated DC voltage value and the currently collected actual DC bus voltage value meet the preset charging conditions, and use this moment as the action moment of the slow-start contactor.

[0063] It is worth noting that the preset charging condition can be: the difference between the calculated DC voltage value and the currently acquired actual DC bus voltage value is less than a first preset value. If the difference between the calculated DC voltage value and the currently acquired actual DC bus voltage value is not less than the first preset value, it means that the calculated DC voltage value and the currently acquired actual DC bus voltage value do not meet the preset charging condition. In this case, the controller continues to calculate until the difference is less than the first preset value.

[0064] In practical applications, if the slow-start contactor Q2 is a thyristor, it can automatically turn off at the zero-crossing point during the negative half-cycle of the grid voltage due to its zero-crossing turn-off characteristic. Therefore, the preset charging condition can be set as follows: during the negative half-cycle of the grid voltage, the difference between the calculated DC voltage value and the currently collected actual DC bus voltage value is less than the first preset value.

[0065] S104. When the action time arrives, control the slow-start contactor to close, charging the DC bus capacitor between the positive and negative terminals of the DC bus.

[0066] Figure 1 In the process, when the calculated DC voltage value and the currently acquired actual DC bus voltage value meet the preset charging conditions, the slow-start contactor Q2 is controlled to close, so as to conduct the branch where the slow-start contactor Q2 is located. The voltage difference between the calculated DC voltage value and the currently acquired actual DC bus voltage value is used to charge the DC bus capacitor between the positive and negative poles of the DC bus, so as to realize the slow start of the converter.

[0067] In practical applications, the AC side of the grid-side power unit 101 is usually equipped with an input filter inductor. Since the input filter inductor has an impedance effect on the AC current, and the voltage difference between the calculated DC voltage value and the actual value of the DC bus voltage currently collected is controllable, the impact of the actual value of the DC bus voltage on the DC bus is avoided, and the slow start-up of the converter is realized.

[0068] The converter control method provided in this embodiment, based on the above principle, can achieve the slow start of the converter using only one slow start contactor Q2, eliminating the slow start resistor in the prior art and thus reducing the cost of the converter.

[0069] Based on the previous embodiment, optionally, the converter control method is as follows: Figure 3 As shown, after step S104, the method further includes:

[0070] S201. Determine whether the DC bus capacitor has finished charging.

[0071] In practical applications, the voltage value of the DC bus capacitor can be detected to determine whether it has reached a preset voltage value, thus confirming whether the DC bus capacitor has completed charging. If the DC bus capacitor voltage value reaches the preset voltage value, it indicates that the DC bus capacitor is fully charged and the converter's soft start-up is complete; if the DC bus capacitor voltage value has not reached the preset voltage value, it indicates that the DC bus capacitor still needs charging, and the converter has not completed the soft start-up.

[0072] In practical applications, the preset voltage value can be obtained through theoretical calculation or experimental testing. No specific limitation is made here, but it depends on the actual application environment. All of these are within the scope of protection of this application.

[0073] If the voltage value of the DC bus capacitor reaches the preset voltage value, it indicates that the DC bus capacitor is fully charged, and step S202 is executed. Simultaneously, if the soft-start contactor Q2 is not a thyristor, the controller should also control the soft-start contactor Q2 to turn off during step S202 to terminate its soft-start function. If the voltage value of the DC bus capacitor does not reach the preset voltage value, it indicates that the DC bus capacitor is not fully charged, and step S102 is executed.

[0074] S202. Control the grid connection switch to close to start the converter.

[0075] In practical applications, the grid-connected switch Q1 is closed to start the converter and bring it into generator mode. This process can specifically include... Figure 4 As shown:

[0076] S301, Control the closing of the grid connection switch.

[0077] S302, control the operation of the grid-side power unit to stabilize the actual value of the DC bus voltage at the second preset value.

[0078] After the converter controller closes the grid-connected switch Q1, it controls the grid-side power unit 101 to operate. The grid-side power unit 101 rectifies the AC power at the grid connection point and charges the DC bus to stabilize the DC bus voltage at the second preset value, thus enabling the converter to enter the power generation state.

[0079] In addition, in practical applications, if the converter is a wind power converter, it also includes a generator-side power unit connected to the DC bus on the DC side. In this case, the converter control method is as follows: Figure 5 As shown, after step S302, the following is also included:

[0080] S303 controls the operation of the generator-side power unit in the wind power converter to provide excitation current to the motor rotor.

[0081] If the converter is a wind power converter, the controller of the wind power converter controls the operation of the power unit on the machine side, and the current flowing through the rotor of the synchronous motor provides the excitation current for the rotor of the motor.

[0082] S304. Determine whether the stator voltage of the wind power converter is synchronized with the grid voltage.

[0083] In practical applications, by controlling the operation of the power unit on the wind turbine side, the stator voltage of the wind turbine converter can be synchronized with the grid voltage. If the stator voltage of the wind turbine converter is synchronized with the grid voltage, then step S305 is executed; if the stator voltage of the wind turbine converter is not synchronized with the grid voltage, then step S304 is executed.

[0084] S305. Control the closing of the stator contactor in the wind power converter to complete the start-up of the converter.

[0085] If the stator voltage of the wind power converter is synchronized with the grid voltage, the controller of the wind power converter will control the stator contactor to close, so that the wind power converter can enter the power generation state.

[0086] It is worth noting that, Figure 4 and Figure 5 This is merely an exemplary demonstration of step S202 of the converter control method. In actual applications, it is not limited to this and can be determined according to the actual application environment. All of these are within the scope of protection of this application.

[0087] Based on the above embodiments, if the converter is a wind power converter, then the converter control method is as follows: Figure 6 (in order to be in) Figure 3 As shown in the example (based on which step S202 is taken), the following is also included after step S202:

[0088] S401, Receive converter shutdown command.

[0089] S402, control the slow-start contactor, grid connection switch and stator contactor in wind power converter to disconnect to control converter shutdown.

[0090] In other words, after the wind power converter has started up, if the controller receives a shutdown command, it will control the slow-start contactor Q2, the grid connection switch Q1, and the stator contactor in the wind power converter to disconnect, thereby shutting down the converter. The initial state upon the next startup is that the slow-start contactor Q2, the grid connection switch Q1, and the stator contactor in the wind power converter are all in the open state.

[0091] Another embodiment of the present invention also provides a converter, such as Figure 1 As shown, it includes: a controller ( Figure 1(Not shown in the text), grid-side power unit 101, grid-connected switch Q1, and soft-start contactor Q2; wherein:

[0092] The DC side of the grid-side power unit 101 is connected to the DC bus. The grid-connected switch Q1 is located between the AC side of the grid-side power unit 101 and the grid connection point. The slow-start contactor Q2 is connected in parallel with the grid-connected switch Q1. The grid-side power unit 101, the grid-connected switch Q1, and the slow-start contactor Q2 are all controlled by a controller, which is used to implement the converter control method described in any of the above embodiments.

[0093] In practical applications, the soft-start contactor Q2 includes, but is not limited to, any one of power electronic devices and non-power electronic devices; the soft-start contactor Q2 can also be any one of thyristors, MOSFETs, and IGBTs, without specific limitations, depending on the actual application environment, and all are within the protection scope of this application.

[0094] It is worth noting that if the converter is applied to a photovoltaic power generation system, then the grid-side power unit 101 is an inverter, and its DC side is connected to the photovoltaic string. If the converter is applied to a wind power generation system, then the converter is a wind power converter, and the converter also includes: a stator contactor, an input filter inductor, a machine-side power unit, and an output filter inductor; specifically:

[0095] like Figure 7 As shown, the grid-connected switch Q1 is connected to the rotor winding of the motor in sequence through the input filter inductor L1, the grid-side power unit 101, the DC bus, the machine-side power unit 102, and the output filter inductor L2; the grid-connected switch Q1 is also connected to the stator winding of the motor through the stator contactor KM1; the machine-side power unit 102 and the stator contactor KM1 are both controlled by the controller.

[0096] Or, it can be like Figure 8 As shown, the grid connection point is connected to the rotor winding of the motor via the grid connection switch Q1, input filter inductor L1, grid-side power unit 101, DC bus, machine-side power unit 102 and output filter inductor L2 in sequence; the grid connection point is also connected to the stator winding of the motor via stator contactor KM1; both machine-side power unit 102 and stator contactor KM1 are controlled by the controller.

[0097] It is worth noting that, Figure 7 and Figure 8 This is merely an exemplary demonstration of the converter, and its actual application is not limited to this, depending on the actual application environment, and all are within the scope of protection of this application.

[0098] The converter provided in this embodiment achieves slow start-up of the converter by using only one slow start contactor Q2. Compared with existing converters, the slow start resistor is eliminated. At the same time, by using power electronic switch technology for slow start-up, the risk of failure of the slow start contactor Q2 and arcing and burnout of the slow start resistor is reduced, thereby reducing the slow start-up cost of the converter and improving the reliability of the converter.

[0099] Similar or identical parts between the various embodiments in this specification can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment solution according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0100] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0101] The features described above regarding the disclosed embodiments can be substituted for or combined with each other to enable those skilled in the art to implement or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of controlling a current transformer, characterized by, A controller applied to a converter, wherein the grid-connected switch and a soft-start contactor in the converter are connected in parallel; the converter control method includes: Receive converter start command; The DC voltage after rectification by the grid-side power unit in the converter is calculated based on the grid voltage and used as the calculated DC voltage value. The moment when the calculated DC voltage value and the currently collected actual DC bus voltage value meet the preset charging conditions is taken as the action moment of the slow-start contactor; When the specified action time arrives, the slow-start contactor is controlled to close, charging the DC bus capacitor between the positive and negative terminals of the DC bus. The preset charging conditions are as follows: The difference between the calculated DC voltage value and the actual DC bus voltage value is less than a first preset value.

2. The converter control method according to claim 1, characterized in that, If the soft-start contactor is a thyristor, then the operating time of the soft-start contactor is: The moment when the difference between the calculated DC voltage value and the actual DC bus voltage value is less than a first preset value during the negative half-cycle of the grid voltage.

3. The converter control method according to any one of claims 1 to 2, characterized in that, When the specified action time arrives, the slow-start contactor is controlled to close, charging the DC bus capacitor between the positive and negative terminals of the DC bus. The process further includes: Determine whether the DC bus capacitor has finished charging; If the DC bus capacitor is fully charged, the grid-connected switch is closed to start the converter.

4. The converter control method according to claim 3, characterized in that, If the soft-start contactor is not a thyristor, then after the DC bus capacitor has finished charging, the following steps are also included: Control the soft-start contactor to turn off.

5. The converter control method according to claim 3, characterized in that, Controlling the grid connection switch to close in order to start the converter includes: Control the grid connection switch to close; Control the operation of the grid-side power unit to stabilize the actual value of the DC bus voltage at a second preset value.

6. The converter control method according to claim 5, characterized in that, If the converter is a wind power converter, then after controlling the operation of the grid-side power unit to stabilize the actual value of the DC bus voltage at a second preset value, the method further includes: Control the operation of the generator-side power unit in the wind power converter to provide excitation current to the motor rotor; Determine whether the stator voltage of the wind power converter is synchronized with the grid voltage; If the stator voltage is synchronized with the grid voltage, the stator contactor in the wind power converter is closed to start the converter.

7. The converter control method according to claim 3, characterized in that, If the converter is a wind power converter, then after controlling the grid connection switch to close to start the converter, the method further includes: Receive converter shutdown command; The slow-start contactor, the grid-connected switch, and the stator contactor in the wind power converter are disconnected to control the converter to shut down.

8. A converter, characterized in that, include: Controller, grid-side power unit, grid-connected switch and soft-start contactor; among which, The DC side of the grid-side power unit is connected to the DC bus; The grid-connected switch is located between the AC side of the grid-side power unit and the grid connection point; The slow-start contactor is connected in parallel with the grid-connected switch; The grid-side power unit, the grid-connected switch, and the soft-start contactor are all controlled by the controller; The controller is used to perform the converter control method as described in any one of claims 1 to 7.

9. The converter according to claim 8, characterized in that, The grid-side power unit is an inverter, and its DC side is connected to the photovoltaic string.

10. The converter according to claim 8, characterized in that, The converter is a wind power converter, and the converter also includes: a stator contactor, an input filter inductor, a machine-side power unit, and an output filter inductor; The grid-connected switch is connected to the rotor winding of the motor in sequence through the input filter inductor, the grid-side power unit, the DC bus, the machine-side power unit, and the output filter inductor; The grid-connected switch is also connected to the stator winding of the motor via the stator contactor; Both the machine-side power unit and the stator contactor are controlled by the controller.

11. The converter according to claim 8, characterized in that, The converter is a wind power converter, and the converter also includes: a stator contactor, an input filter inductor, a machine-side power unit, and an output filter inductor; The grid connection point is connected to the rotor winding of the motor in sequence through the grid connection switch, the input filter inductor, the grid-side power unit, the DC bus, the machine-side power unit, and the output filter inductor; The grid connection point is also connected to the stator winding of the motor via the stator contactor; Both the machine-side power unit and the stator contactor are controlled by the controller.

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