A converter power module multiplexing system and control method

Abstract

The application discloses a converter power module multiplexing system, which comprises a converter and a machine-grid side multiplexing module, wherein a direct current end of the machine-grid side multiplexing module is connected with a direct current bus; an alternating current end of the machine-grid side multiplexing module is connected with a power grid through a first switch K1 and is connected in parallel with a machine side converter through a second switch K2; when the machine-grid side multiplexing module is connected in parallel with the grid side converter, the output capacity of the grid side converter is increased; when the machine-grid side multiplexing module is connected in parallel with the machine side converter, the output capacity of the machine side converter is increased; the converter power module multiplexing system can reduce the configuration capacity of the converter, reduce the cost, realize the online configuration of the machine-grid side multiplexing module capacity in the case that the capacity demands of the machine side and the grid side are not equal, increase the output capacity of the converter module, and make the machine-grid side multiplexing module be able to flexibly select an output point according to the needs of different working conditions, and the realization method is simple.

Description

Technical Field

[0001] This invention relates to the field of power electronics control technology, and particularly to a converter power module multiplexing system and control method. Background Technology

[0002] With the depletion of fossil fuel resources, new energy power generation is rapidly emerging. Wind power has already secured a place in the power generation sector due to its inexhaustible supply, low pollution, short infrastructure construction period, wide distribution, flexible installed capacity, and low operation and maintenance costs. Meanwhile, the double-feed induction generator (DFIG), with its rotor winding connected to an AC converter and grid-connected, has also experienced rapid development due to its small capacity, low cost, and variable speed constant frequency power generation advantages.

[0003] The circuit structure of DFIG: the stator winding is connected to the power frequency grid, and the rotor winding is connected to the machine-side converter of the AC (grid-side converter) - DC (bus) - AC (machine-side converter) bidirectional converter; the working principle of DFIG converter: under the condition of speed change, the converter can reasonably control the frequency, amplitude, phase or phase sequence of the rotor winding according to the motor slip s, so that the stator output frequency can remain constant, so that the stator frequency and the grid frequency are consistent.

[0004] With the advent of the era of grid parity for wind power, the increase in short-term power generation of DFIG at various speeds will be an inevitable trend. However, under synchronous speed conditions, excessive power generation by the generator will pose a great risk to the stable operation of the doubly-fed converter. The main reason is that the generator-side converter module is very prone to hardware failure under such conditions.

[0005] The risk of excessive power generation in a doubly-fed induction generator (DFIG) at synchronous speed lies mainly in the fact that, at synchronous speed, the stator voltage frequency is the same as the grid frequency to meet grid connection requirements. The generator-side converter needs to provide DC current to the rotor side of the DFIG. The generator-side converter operates in buck converter circuit mode. At this time, the upper or lower bridge arm of the generator-side converter is always in the on or off state throughout the synchronous speed state, which causes the IGBT devices to bear greater stress.

[0006] To address the aforementioned issues, common methods currently include: reducing power output during synchronous speed operation to minimize the impact on the generator-side converter. However, this method reduces power generation. Alternatively, the generator-side converter capacity can be increased based on the calculated current at synchronous speed, but this increases costs.

[0007] In addition to the problems mentioned above, the existing doubly fed grid-side capacity is only 1 / 3 of the rated capacity of the generating units. Therefore, when grid-side static reactive power support is required, there will be a demand for grid-side capacity expansion.

[0008] The aforementioned problem is not limited to doubly-fed converters; full-power or other converters also encounter this issue at low frequencies.

[0009] Therefore, there is an urgent need for a new type of circuit that can reduce the configuration capacity of the grid-connected converter, reduce costs, reduce losses, improve efficiency, and make the output more flexible. It can also increase the output capability of the converter module at low frequencies, enabling low-frequency operation without derating or even over-derating. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention proposes a converter power module multiplexing system. This system and control method can reduce the grid-side current configuration capacity and lower costs; it can also increase the current output capability of the converter module at low frequencies; and it can increase the output capability of the grid-side converter during grid-side static reactive power support. The grid-side multiplexing module can flexibly select its output point according to different operating conditions, and the implementation method is simple, reducing losses, improving efficiency, and providing flexible output.

[0011] This invention provides a converter power module multiplexing system, including a converter comprising a grid-side converter and a generator-side converter, and a DC bus connecting the grid-side converter and the generator-side converter; it also includes a grid-side multiplexing module, the DC terminal of which is connected to the DC bus; the AC terminal of which is connected to the power grid via a first switch K1, and connected in parallel with the generator-side converter via a second switch K2 to the generator rotor side, the stator side of which is connected to the power grid; under different operating conditions, the grid-side multiplexing module controls the on / off state of the first switch K1 and the second switch K2; when the grid-side multiplexing module is connected in parallel with the grid-side converter, it increases the output capacity of the grid-side converter; when the grid-side multiplexing module is connected in parallel with the generator-side converter, it increases the output capacity of the generator-side converter.

[0012] Preferably, there are at least two machine-grid side multiplexing modules, namely: a first machine-grid side multiplexing module, ..., an Nth machine-grid side multiplexing module; the AC terminal of the first machine-grid side multiplexing module is connected to the power grid through a first switch K1, and the first machine-grid side multiplexing module is connected to the generator rotor side through a second switch K2 in parallel with the machine-side converter, ..., the AC terminal of the Nth machine-grid side multiplexing module is connected to the power grid through an (N+1)th switch Kn+1, and the Nth machine-grid side multiplexing module is connected to the generator rotor side through an (N+2)th switch Kn+2 in parallel with the machine-side converter, and the stator side of the generator is connected to the power grid, where N≥2.

[0013] Preferably, the converter further includes a grid-side filter, which is an RC filter or an LCL filter.

[0014] Preferably, the converter further includes a pre-charging circuit, which is connected to the power grid and the DC bus respectively.

[0015] Preferably, the converter further includes a pre-charging circuit, which is connected to the power grid and the DC bus respectively.

[0016] To address the aforementioned problems, this invention also discloses a control method applied to the aforementioned converter power module multiplexing system, comprising the following steps:

[0017] Determine whether the machine-side converter and the grid-side converter need to be configured with a larger current capacity. If expansion is required, determine whether only the machine-side converter needs expansion, only the grid-side converter needs expansion, or both the machine-side converter and the grid-side converter need expansion.

[0018] If only the machine-side converter needs to be expanded, disconnect switch K1 and close switch K2 to connect the machine-network side multiplexing module in parallel with the machine-side converter, thereby increasing the output capacity of the machine-side converter.

[0019] If only the grid-side converter needs to be expanded, disconnect switch K2 and close switch K1 to connect the machine-grid side multiplexing module in parallel with the grid-side converter, thereby increasing the output capacity of the grid-side converter.

[0020] If both the machine-side converter and the grid-side converter need to be expanded, then determine whether the machine-side converter needs to be configured with a larger current capacity than the grid-side converter. If the machine-side converter needs to be configured with a larger current capacity, then open the first switch K1 and close the second switch K2; then determine whether the grid-side converter needs to be configured with a larger current capacity than the machine-side converter. If the grid-side converter needs to be configured with a larger current capacity, then open the second switch K2 and close the first switch K1.

[0021] If neither the generator-side converter nor the grid-side converter requires a larger current capacity, then disconnect the first switch K1 and the second switch K2, and the converter will operate as a standalone unit.

[0022] Preferably, it is detected whether the machine-side converter is at a low frequency;

[0023] When the generator-side converter is detected to be operating at a low frequency, it is determined whether the grid-side converter is in a static reactive power support state. If the grid side is not in a static reactive power support state and only the generator-side converter needs capacity expansion, then the first switch K1 is opened and the second switch K2 is closed to increase the output capacity of the generator-side converter and achieve non-derating operation of the generator-side converter. If the grid side is in a static reactive power support state, it is determined whether the grid-side converter needs a larger current capacity than currently configured. If the grid-side converter needs a larger current capacity than currently configured, then the second switch K2 is opened and the first switch K1 is closed; otherwise, the first switch K1 is opened and the second switch K2 is closed.

[0024] When it is detected that the generator-side converter is not at a lower frequency, it is determined whether the grid-side converter is in a static reactive power support state. If the grid-side converter is not in a static reactive power support state and the converter is operating in single-unit mode, then the first switch K1 is disconnected and the second switch K2 is disconnected. If the grid-side converter is in a static reactive power support state and only the grid-side converter needs to be expanded, then the second switch K2 is disconnected and the first switch K1 is closed to increase the output capacity of the grid-side converter.

[0025] To address the aforementioned issues, this invention also discloses a control method for the aforementioned converter power module multiplexing system, comprising the following steps: determining whether the machine-side converter and the grid-side converter need to be configured with a larger current capacity; if expansion is required, determining whether only the machine-side converter needs expansion, or only the grid-side converter needs expansion, or both the machine-side converter and the grid-side converter need expansion.

[0026] If only the machine-side converter needs expansion, determine whether the first machine-to-network multiplexing module can meet the expansion requirements. If the first machine-to-network multiplexing module can meet the machine-side expansion requirements, then open switch K1 and close switch K2, so that the first machine-to-network multiplexing module and the machine-side converter are connected in parallel, increasing the output capacity of the machine-side converter. If the first machine-to-network multiplexing module cannot meet the machine-side expansion requirements, then simultaneously activate the second machine-to-network multiplexing module. In this case, simultaneously open switch K3 and close switch K4, so that the second machine-to-network multiplexing module, the first machine-to-network module, and the machine-side converter are connected in parallel, increasing the output capacity of the machine-side converter.

[0027] If only the grid-side converter needs expansion, determine whether the first-machine grid-side multiplexing module can meet the expansion requirements. If the first-machine grid-side multiplexing module can meet the grid-side expansion requirements, then open switch K2 and close switch K1, so that the grid-side multiplexing module and the grid-side converter are connected in parallel, increasing the output capacity of the grid-side converter. If the first-machine grid-side multiplexing module cannot meet the grid-side expansion requirements, then the second-machine grid-side multiplexing module needs to be put into operation at the same time. In this case, switch K4 needs to be opened and switch K3 needs to be closed at the same time, so that the second-machine grid-side multiplexing module, the first-machine grid-side module, and the grid-side converter are connected in parallel, increasing the output capacity of the grid-side converter.

[0028] If both the machine-side converter and the grid-side converter need to be expanded, first determine whether the machine-side converter needs to be configured with a larger current capacity than the grid-side converter:

[0029] If the machine-side converter requires a larger current capacity, then open the first switch K1 and close the second switch K2. The first machine-grid side multiplexing module is connected in parallel with the machine-side converter. After configuring the first machine-grid side multiplexing module, it is determined whether the machine-side converter still needs a larger current capacity than the grid-side converter. If the machine-side converter needs a larger current capacity, then open the switch K3 and close the switch K4. The second machine-grid side multiplexing module is still connected in parallel with the machine-side converter to increase the capacity of the machine-side converter. If, after configuring the first machine-grid side multiplexing module, the grid-side converter needs a larger current capacity than the machine-side converter, then open the switch K4 and close the switch K3. The second machine-grid side multiplexing module is connected in parallel with the grid-side converter to increase the output capacity of the grid-side converter.

[0030] If the grid-side converter needs to be configured with a larger current capacity, then the first switch K2 is opened and the second switch K3 is closed. The first grid-side multiplexing module is connected in parallel with the grid-side converter. After configuring the first grid-side multiplexing module, it is determined whether the machine-side converter still needs to be configured with a larger current capacity than the grid-side converter. If the machine-side converter still needs to be configured with a larger current capacity, then switch K3 is opened and switch K4 is closed. The second grid-side multiplexing module is connected in parallel with the machine-side converter to increase the capacity of the machine-side converter. If, after configuring the first grid-side multiplexing module, the grid-side converter still needs to be configured with a larger current capacity than the machine-side converter, then switch K4 is opened and switch K3 is closed. The second grid-side multiplexing module is still connected in parallel with the grid-side converter to increase the output capacity of the grid-side converter.

[0031] If neither the generator-side converter nor the grid-side converter requires a larger current capacity, then disconnect the first generator-grid-side multiplexing module and the second generator-grid-side multiplexing module, and the converter will operate as a standalone unit.

[0032] To address the aforementioned issues, this invention also discloses a control method for the aforementioned converter power module multiplexing system. The grid-side multiplexing module can also serve as a pre-charging circuit to establish the DC bus voltage, thus completely replacing the original pre-charging circuit.

[0033] Preferably, a pre-charging resistor R1 is added between the machine-network side multiplexing module and the first switch K1, and a switch K5 is added across R1.

[0034] During pre-charging, the first switch K1 is closed, and the power grid charges the DC bus through the pre-charging resistor and the grid-machine side multiplexing module. Once the bus voltage is established, the switch K5, which is connected in parallel with the charging resistor, is closed to cut off the charging resistor and reduce the energy loss of the circuit.

[0035] During pre-charging, the first switch K1 is closed, and the power grid charges the DC bus through the pre-charging resistor and the grid-machine side multiplexing module. Once the bus voltage is established, the switch K5, which is connected in parallel with the charging resistor, is closed to cut off the charging resistor and reduce the energy loss of the circuit.

[0036] The beneficial effects of this converter power module multiplexing system and control method are: it can reduce the current capacity configuration of the converter, reduce costs, increase the output capacity of the module at low frequencies or when the grid side provides static reactive power support, and enable the grid-machine side multiplexing module to flexibly select the output point according to the needs of different operating conditions. The method is simple, reduces losses, improves efficiency, and provides flexible output. Attached Figure Description

[0037] Figure 1 This is a circuit diagram of a first embodiment of the converter power module multiplexing system of the present invention;

[0038] Figure 2 This is a circuit diagram of Embodiment 2 of the converter power module multiplexing system of the present invention;

[0039] Figure 3 This is a circuit diagram of Embodiment 3 of the converter power module multiplexing system of the present invention;

[0040] Figure 4 This is a circuit diagram of Embodiment 4 of the converter power module multiplexing system of the present invention;

[0041] Figure 5 This is a flowchart of the control method of the converter power module multiplexing system according to claim 1 of the present invention;

[0042] Figure 6 The flowchart of the control method for the five-converter power module multiplexing system of the present invention. Figure 1 ;

[0043] Figure 7The machine-side converter operating frequency diagram for implementing the control method of the five-converter power module multiplexing system of the present invention;

[0044] Figure 8 This is a flowchart illustrating the control method for the six-converter power module multiplexing system of the present invention;

[0045] Figure 9 The flowchart of the control method for the seven-converter power module multiplexing system of the present invention. Figure 1 ;

[0046] Figure 10 The flowchart of the control method for the seven-converter power module multiplexing system of the present invention. Figure 2 ;

[0047] Figure 11 The flowchart of the control method for the seven-converter power module multiplexing system of the present invention. Figure 3 ;

[0048] Figure 12 The circuit diagram of the eight-converter power module multiplexing system implemented in this invention;

[0049] Figure 13 This is a flowchart of the control method of claim 2 of the converter power module multiplexing system of the present invention. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0051] Example 1

[0052] Please see Figure 1 , Figure 1 This is a circuit diagram of a converter power module multiplexing system according to Embodiment 1 of the present invention. This embodiment discloses a converter power module multiplexing system, including a converter and a grid-side multiplexing module. The converter includes a grid-side converter and a generator-side converter, and a DC bus connecting the grid-side converter and the generator-side converter. The DC terminal of the grid-side multiplexing module is connected to the DC bus. The AC terminal of the grid-side multiplexing module is connected to the power grid via a first switch K1, and connected to the generator rotor side via a second switch K2 in parallel with the generator-side converter. The stator side of the generator is connected to the power grid. Under different operating conditions, the grid-side multiplexing module controls the on / off state of the first switch K1 and the second switch K2. When the grid-side multiplexing module is connected in parallel with the grid-side converter, it increases the output capacity of the grid-side converter; when the grid-side multiplexing module is connected in parallel with the generator-side converter, it increases the output capacity of the generator-side converter.

[0053] In this embodiment, the converter further includes a grid-side filter, a grid-connected grid-side filter, and the grid-side filter is then connected to the grid-side converter.

[0054] The machine-side and network-side filters are RC filters or LCL filters.

[0055] Example 2

[0056] Please see Figure 2 , Figure 2 This is a circuit diagram of a converter power module multiplexing system according to Embodiment 2 of the present invention. This embodiment discloses a converter power module multiplexing system, including a converter and a machine-grid side multiplexing module. The converter includes a grid-side converter and a machine-side converter, and a DC bus connecting the grid-side converter and the machine-side converter. The DC terminal of the machine-grid side multiplexing module is connected in parallel with the DC bus. There are at least two machine-grid side multiplexing modules, namely: a first machine-grid side multiplexing module, ..., an Nth machine-grid side multiplexing module. The AC terminal of the first machine-grid side multiplexing module is connected to the power grid through a first switch K1. The first machine-grid side multiplexing module is connected to the generator rotor side after being connected in parallel with the machine-side converter through a second switch K2, ... The AC terminal of the Nth machine-grid side multiplexing module is connected to the power grid through an (N+1)th switch Kn+1. The Nth machine-grid side multiplexing module is connected to the generator rotor side after being connected in parallel with the machine-side converter through an (N+2)th switch Kn+2. The stator side of the generator is connected to the power grid, where N≥2.

[0057] In this embodiment, the converter further includes a grid-side filter and a generator-side filter. The grid is connected to the grid-side filter, which is then connected to the grid-side converter. The AC terminal of the first generator-grid-side multiplexing module is connected to the back end of the grid-side filter via a first switch K1. Simultaneously, the AC terminal of the second generator-grid-side multiplexing module is connected in parallel with the back end of the grid-side filter via a switch K3. The first generator-grid-side multiplexing module is connected in parallel with the generator-side converter via a second switch K2. Simultaneously, the AC terminal of the second generator-grid-side multiplexing module is connected in parallel with the first generator-grid-side multiplexing module via a switch K4, which is then connected to the generator-side filter and subsequently to the generator rotor.

[0058] The network-side filter is an RC filter or an LCL filter.

[0059] Example 3

[0060] Please see Figure 3 In this embodiment, based on the first embodiment, the converter further includes a pre-charging circuit, which is connected to the power grid and the DC bus respectively.

[0061] Example 4

[0062] Please see Figure 4In this embodiment, based on embodiment two, the converter further includes a pre-charging circuit, which is connected to the power grid and the DC bus respectively.

[0063] Example 5

[0064] Please see Figure 5 , Figure 6 , Figures 8 to 11 This embodiment discloses a control method for a converter power module multiplexing system, including the following steps: determining whether the machine-side converter and the grid-side converter need to be configured with a larger current capacity; if expansion is required, determining whether only the machine-side converter needs expansion, or only the grid-side converter needs expansion, or both the machine-side converter and the grid-side converter need expansion.

[0065] If only the machine-side converter needs to be expanded, disconnect switch K1 and close switch K2 to connect the machine-network side multiplexing module in parallel with the machine-side converter, thereby increasing the output capacity of the machine-side converter.

[0066] If only the grid-side converter needs to be expanded, disconnect switch K2 and close switch K1 to connect the machine-grid side multiplexing module in parallel with the grid-side converter, thereby increasing the output capacity of the grid-side converter.

[0067] If both the machine-side converter and the grid-side converter need to be expanded, then determine whether the machine-side converter needs to be configured with a larger current capacity than the grid-side converter. If the machine-side converter needs to be configured with a larger current capacity, then open the first switch K1 and close the second switch K2; then determine whether the grid-side converter needs to be configured with a larger current capacity than the machine-side converter. If the grid-side converter needs to be configured with a larger current capacity, then open the second switch K2 and close the first switch K1.

[0068] If neither the generator-side converter nor the grid-side converter requires a larger current capacity, then disconnect the first switch K1 and the second switch K2, and the converter will operate as a standalone unit.

[0069] Example 6

[0070] Please see Figure 5 and Figure 7This embodiment discloses a control method for a converter power module multiplexing system, including the following steps: detecting whether the generator-side converter is at a low frequency; when the generator-side converter is detected to be at a low frequency, determining whether the grid-side converter is in a static reactive power support state; if the grid side is not in a static reactive power support state and only the generator-side converter needs capacity expansion, then disconnecting the first switch K1 and closing the second switch K2 to increase the output capacity of the generator-side converter and achieve non-derating operation of the generator-side converter; if the grid side is in a static reactive power support state, determining whether the grid-side converter needs a larger current capacity than currently configured; if the grid-side converter needs a larger current capacity than currently configured, then disconnecting the second switch K2 and closing the first switch K1; otherwise, disconnecting the first switch K1 and closing the second switch K2.

[0071] When it is detected that the generator-side converter is not at a lower frequency, it is determined whether the grid-side converter is in a static reactive power support state. If the grid-side converter is not in a static reactive power support state and the converter is operating in single-unit mode, then the first switch K1 is disconnected and the second switch K2 is disconnected. If the grid-side converter is in a static reactive power support state and only the grid-side converter needs to be expanded, then the second switch K2 is disconnected and the first switch K1 is closed to increase the output capacity of the grid-side converter.

[0072] Example 7

[0073] This embodiment discloses a control method for a converter power module multiplexing system. If both the generator and grid sides need to be expanded, for example, when a doubly fed converter is running at overspeed, it will raise the stator side voltage. The generator side needs to generate inductive reactive power to pull down the grid voltage on the generator side, and the grid side also needs to generate capacitive reactive power to cancel the extra inductive reactive power generated by the generator side.

[0074] For situations where both the generator and grid sides require capacity expansion—that is, whether the generator-side modules alone can meet the required inductive reactive power generation, and whether the grid-side converter alone can meet the required capacitive reactive power generation—if neither the generator nor the grid side can complete the task independently, it is necessary to determine whether the generator-side converter needs to be configured with a larger current capacity than the grid-side converter. If the generator-side converter needs to be configured with a larger current capacity, please refer to [reference needed]. Figure 9 If the first switch K1 is open and the second switch K2 is closed, the machine-grid side multiplexing module and the machine-side converter will be connected in parallel, increasing the power output capacity of the machine-side converter; otherwise, please refer to [the relevant documentation]. Figure 10 Disconnect the second switch K2 and close the first switch K1, so that the machine-network side multiplexing module is connected in parallel with the network side converter, thereby increasing the output capacity of the network side converter.

[0075] If neither the generator nor the grid-side converter requires a larger current capacity, please refer to [link / reference]. Figure 11 If the first switch K1 is disconnected and the second switch K2 is disconnected, the converter will operate as a standalone unit.

[0076] Example 8

[0077] Please see Figure 13 This embodiment discloses a control method for a converter power module multiplexing system as described in Embodiment 2, including the following steps:

[0078] Determine whether the machine-side converter and the grid-side converter need to be configured with a larger current capacity. If expansion is required, determine whether only the machine-side converter needs expansion, only the grid-side converter needs expansion, or both the machine-side converter and the grid-side converter need expansion.

[0079] If only the machine-side converter needs expansion, determine whether the first machine-to-network multiplexing module can meet the expansion requirements. If the first machine-to-network multiplexing module can meet the machine-side expansion requirements, then open switch K1 and close switch K2, so that the first machine-to-network multiplexing module and the machine-side converter are connected in parallel, increasing the output capacity of the machine-side converter. If the first machine-to-network multiplexing module cannot meet the machine-side expansion requirements, then simultaneously activate the second machine-to-network multiplexing module. In this case, simultaneously open switch K3 and close switch K4, so that the second machine-to-network multiplexing module, the first machine-to-network module, and the machine-side converter are connected in parallel, increasing the output capacity of the machine-side converter.

[0080] If only the grid-side converter needs expansion, determine whether the first-machine grid-side multiplexing module can meet the expansion requirements. If the first-machine grid-side multiplexing module can meet the grid-side expansion requirements, then open switch K2 and close switch K1, so that the grid-side multiplexing module and the grid-side converter are connected in parallel, increasing the output capacity of the grid-side converter. If the first-machine grid-side multiplexing module cannot meet the grid-side expansion requirements, then the second-machine grid-side multiplexing module needs to be put into operation at the same time. In this case, switch K4 needs to be opened and switch K3 needs to be closed at the same time, so that the second-machine grid-side multiplexing module, the first-machine grid-side module, and the grid-side converter are connected in parallel, increasing the output capacity of the grid-side converter.

[0081] If both the machine-side converter and the grid-side converter need to be expanded, first determine whether the machine-side converter needs to be configured with a larger current capacity than the grid-side converter:

[0082] If the machine-side converter requires a larger current capacity, then open the first switch K1 and close the second switch K2. The first machine-grid side multiplexing module is connected in parallel with the machine-side converter. After configuring the first machine-grid side multiplexing module, it is determined whether the machine-side converter still needs a larger current capacity than the grid-side converter. If the machine-side converter needs a larger current capacity, then open the switch K3 and close the switch K4. The second machine-grid side multiplexing module is still connected in parallel with the machine-side converter to increase the capacity of the machine-side converter. If, after configuring the first machine-grid side multiplexing module, the grid-side converter needs a larger current capacity than the machine-side converter, then open the switch K4 and close the switch K3. The second machine-grid side multiplexing module is connected in parallel with the grid-side converter to increase the output capacity of the grid-side converter.

[0083] If the grid-side converter needs to be configured with a larger current capacity, then the first switch K2 is opened and the second switch K3 is closed. The first grid-side multiplexing module is connected in parallel with the grid-side converter. After configuring the first grid-side multiplexing module, it is determined whether the machine-side converter still needs to be configured with a larger current capacity than the grid-side converter. If the machine-side converter still needs to be configured with a larger current capacity, then switch K3 is opened and switch K4 is closed. The second grid-side multiplexing module is connected in parallel with the machine-side converter to increase the capacity of the machine-side converter. If, after configuring the first grid-side multiplexing module, the grid-side converter still needs to be configured with a larger current capacity than the machine-side converter, then switch K4 is opened and switch K3 is closed. The second grid-side multiplexing module is still connected in parallel with the grid-side converter to increase the output capacity of the grid-side converter.

[0084] If neither the generator-side converter nor the grid-side converter requires a larger current capacity, then disconnect the first generator-grid-side multiplexing module and the second generator-grid-side multiplexing module, and the converter will operate as a standalone unit.

[0085] Example 9

[0086] Please see Figure 12 For doubly fed, full-power converters, a pre-charge circuit is needed to establish the bus voltage in the initial state of the model in order to achieve soft start of the grid-side converter.

[0087] Regarding the circuits of Embodiments 1 and 2 of the present invention, the grid-machine side multiplexing module or any grid-machine side multiplexing module can be used as a pre-charging circuit at the initial moment of the converter's startup and operation.

[0088] In addition, to make the machine-network side multiplexing module more reliable than the pre-charging circuit and reduce the current surge in the circuit, a pre-charging resistor R1 can be added between the machine-network side multiplexing module and the first switch K1, and a switch K5 can be added across R1.

[0089] During pre-charging, the first switch K1 is closed, and the power grid charges the DC bus through the pre-charging resistor and the grid-machine side multiplexing module. Once the bus voltage is established, the switch K5, which is connected in parallel with the charging resistor, is closed to cut off the charging resistor and reduce the energy loss of the circuit.

[0090] Example 10

[0091] This embodiment discloses a control method for a converter power module multiplexing system as described in Embodiment 2, including the following steps:

[0092] The converter's machine side and grid side are tested to determine whether more current capacity is required under specific operating conditions.

[0093] When it is detected that only the output capacity of the generator-side converter needs to be increased, such as whether the speed of the generator in a doubly-fed or full-power converter is near the generator synchronous speed, it is necessary to determine whether the first generator-grid side multiplexing module can meet the current operating condition expansion requirements. If the first generator-grid side multiplexing module can meet the current capacity configuration for this operating condition, then control the disconnect switches K1, K3, and K4 and close switch K2, connecting only the first generator-grid side multiplexing module in parallel with the generator side. If the first generator-grid side multiplexing module cannot meet the current capacity configuration for this operating condition, then control the disconnect switches K1 and K3 and close switches K2 and K4, connecting both the first and second generator-grid side multiplexing modules in parallel with the generator side, thus achieving non-derating or even over-rated operation of the generator near synchronous speed.

[0094] When it is detected that only the output capacity of the grid-side converter needs to be increased, such as when the grid side of the doubly-fed converter is in a static reactive power support state, and the current grid-side capacity of the doubly-fed converter is only one-third of the unit capacity, it is necessary to increase the grid-side configuration capacity. It is determined whether the grid-side multiplexing module of the first unit can meet the current capacity expansion requirements under the current operating condition. If the grid-side multiplexing module of the first unit can meet the current capacity configuration under this operating condition, then switches K2, K3, and K4 are opened, and switch K3 is closed, connecting only the grid-side multiplexing module of the first unit in parallel with the unit side. If the grid-side multiplexing module of the first unit cannot meet the current capacity configuration under this operating condition, then switches K2 and K4 are opened, and switches K1 and K3 are closed, connecting both the grid-side multiplexing modules of the first and second units in parallel with the grid side, increasing the output capacity of the grid-side converter.

[0095] When it is detected that both the generator and grid sides require capacity expansion, such as when a doubly-fed converter is operating at overspeed, it will raise the stator voltage. This necessitates the generator side generating inductive reactive power to pull down the grid voltage, while the grid side needs to generate capacitive reactive power to offset the excess inductive reactive power generated by the generator side. In this condition, it is first necessary to determine which side (generator or grid) is limiting the converter's output capacity. If the generator side's current output limits the entire unit's output capacity, then switch K1 is opened and switch K2 is closed, connecting the first generator-grid side multiplexing module in parallel to the generator side to increase the generator side's output capacity, thereby improving the unit's output capacity. Conversely, if switch K2 is opened and switch K1 is closed, connecting the first generator-grid side multiplexing module in parallel to the grid side increases the grid side's output capacity. After connecting the first machine-grid side multiplexing module, it is determined again which side of the machine-grid side is limiting the output capacity of the converter. If the current output of the machine side limits the output capacity of the entire unit, switch K3 is opened and switch K4 is closed, and the second machine-grid side multiplexing module is connected in parallel to the machine side to increase the output capacity of the machine side, thereby improving the output capacity of the unit. Conversely, switch K4 is opened and switch K3 is closed, and the second machine-grid side multiplexing module is connected in parallel to the grid side to increase the output capacity of the grid side.

[0096] With the increase in the number of machine-network side multiplexing modules, the control of machine-network side multiplexing modules can be more flexible according to the needs of different working conditions, and is not limited to the above-mentioned control method.

[0097] It should be understood that the above are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A converter power module multiplexing system comprising a converter, the converter comprising a grid side converter and a machine side converter and a DC bus connecting the grid side converter and the machine side converter; characterized in that, It also includes a grid-side multiplexing module, the DC terminal of which is connected to the DC bus; the AC terminal of which is connected to the power grid via a first switch K1, and connected to the generator rotor side via a second switch K2 in parallel with the generator-side converter, while the stator side of the generator is connected to the power grid; under different operating conditions, the grid-side multiplexing module controls the on / off state of the first switch K1 and the second switch K2. When the grid-side multiplexing module is connected in parallel with the grid-side converter, it increases the output capacity of the grid-side converter; when the grid-side multiplexing module is connected in parallel with the generator-side converter, it increases the output capacity of the generator-side converter.

2. The multiplexing system of power converter power modules according to claim 1, characterized in that, The machine-grid side multiplexing module comprises at least two modules: a first machine-grid side multiplexing module, ..., an Nth machine-grid side multiplexing module; the AC terminal of the first machine-grid side multiplexing module is connected to the power grid via a first switch K1, and the first machine-grid side multiplexing module is connected to the generator rotor side via a second switch K2 in parallel with the machine-side converter, ..., the AC terminal of the Nth machine-grid side multiplexing module is connected to the power grid via an (N+1)th switch Kn+1, and the Nth machine-grid side multiplexing module is connected to the generator rotor side via an (N+2)th switch Kn+2 in parallel with the machine-side converter, and the stator side of the generator is connected to the power grid, where N≥2.

3. The multiplexing system of power converter power modules of claim 1, wherein, The network-side filter is an RC filter or an LCL filter.

4. The multiplexing system of variable frequency power modules of claim 1, wherein, The converter also includes a pre-charging circuit, which is connected to the power grid and the DC bus.

5. The multiplexing system of variable frequency power modules of claim 2, wherein, The converter also includes a pre-charging circuit, which is connected to the power grid and the DC bus.

6. A control method applied to the multiplexing system of power modules of the converter according to any one of claims 1 to 5, characterized in that, Includes the following steps: Determine whether the machine-side converter and the grid-side converter need to be configured with a larger current capacity. If expansion is required, determine whether only the machine-side converter needs expansion, only the grid-side converter needs expansion, or both the machine-side converter and the grid-side converter need expansion. If only the machine-side converter needs to be expanded, disconnect switch K1 and close switch K2 to connect the machine-network side multiplexing module in parallel with the machine-side converter, thereby increasing the output capacity of the machine-side converter. If only the grid-side converter needs to be expanded, disconnect switch K2 and close switch K1 to connect the machine-grid side multiplexing module in parallel with the grid-side converter, thereby increasing the output capacity of the grid-side converter. If both the machine-side converter and the grid-side converter need to be expanded, then determine whether the machine-side converter needs to be configured with a larger current capacity than the grid-side converter. If the machine-side converter needs to be configured with a larger current capacity, then open the first switch K1 and close the second switch K2; determine whether the grid-side converter needs to be configured with a larger current capacity than the machine-side converter. If the grid-side converter needs to be configured with a larger current capacity, then open the second switch K2 and close the first switch K1. If neither the generator-side converter nor the grid-side converter requires a larger current capacity, then disconnect the first switch K1 and the second switch K2, and the converter will operate as a standalone unit.

7. The control method for the converter power module multiplexing system according to claim 6, characterized in that, Detect whether the machine-side converter is at a low frequency; When the generator-side converter is detected to be at a low frequency, it is determined whether the grid-side converter is in a static reactive power support state. If the grid-side converter is not in a static reactive power support state and only the generator-side converter needs to be expanded, the first switch K1 is opened and the second switch K2 is closed to increase the output capacity of the generator-side converter and realize the generator-side converter to operate without de-rating. If the grid side is in a static reactive power support state, determine whether the grid-side converter needs a larger current capacity than the current configuration. If the grid-side converter needs a larger current capacity than the current configuration, then disconnect the second switch K2 and close the first switch K1. Conversely, the first switch K1 is disconnected and the second switch K2 is closed. When it is detected that the machine-side converter is not at a low frequency, it is determined whether the grid-side converter is in a static reactive power support state. If the grid-side converter is not in a static reactive power support state and the converter is operating in single-machine mode, the first switch K1 is disconnected and the second switch K2 is disconnected. If the grid-side converter is in a static reactive power support state and only the grid-side converter needs to be expanded, then the second switch K2 is disconnected and the first switch K1 is closed to increase the output capacity of the grid-side converter.

8. A control method applied to the multiplexing system of the power module of the converter of claim 2, characterized in that, Includes the following steps: Determine whether the machine-side converter and the grid-side converter need to be configured with a larger current capacity. If expansion is required, determine whether only the machine-side converter needs expansion, only the grid-side converter needs expansion, or both the machine-side converter and the grid-side converter need expansion. If only the machine-side converter needs expansion, determine whether the first machine-to-network multiplexing module can meet the expansion requirements. If the first machine-to-network multiplexing module can meet the machine-side expansion requirements, then open switch K1 and close switch K2, so that the first machine-to-network multiplexing module and the machine-side converter are connected in parallel, increasing the output capacity of the machine-side converter. If the first machine-to-network multiplexing module cannot meet the machine-side expansion requirements, then simultaneously activate the second machine-to-network multiplexing module. In this case, simultaneously open switch K3 and close switch K4, so that the second machine-to-network multiplexing module, the first machine-to-network module, and the machine-side converter are connected in parallel, increasing the output capacity of the machine-side converter. If only the grid-side converter needs expansion, determine whether the first-machine grid-side multiplexing module can meet the expansion requirements. If the first-machine grid-side multiplexing module can meet the grid-side expansion requirements, then open switch K2 and close switch K1, so that the grid-side multiplexing module and the grid-side converter are connected in parallel, increasing the output capacity of the grid-side converter. If the first-machine grid-side multiplexing module cannot meet the grid-side expansion requirements, then the second-machine grid-side multiplexing module needs to be put into operation at the same time. In this case, switch K4 needs to be opened and switch K3 needs to be closed at the same time, so that the second-machine grid-side multiplexing module, the first-machine grid-side module, and the grid-side converter are connected in parallel, increasing the output capacity of the grid-side converter. If both the machine-side converter and the grid-side converter need to be expanded, first determine whether the machine-side converter needs to be configured with a larger current capacity than the grid-side converter: If the machine-side converter requires a larger current capacity, then open the first switch K1 and close the second switch K2. The first machine-grid side multiplexing module is connected in parallel with the machine-side converter. After configuring the first machine-grid side multiplexing module, it is determined whether the machine-side converter still needs a larger current capacity than the grid-side converter. If the machine-side converter needs a larger current capacity, then open the switch K3 and close the switch K4. The second machine-grid side multiplexing module is still connected in parallel with the machine-side converter to increase the capacity of the machine-side converter. If, after configuring the first machine-grid side multiplexing module, the grid-side converter needs a larger current capacity than the machine-side converter, then open the switch K4 and close the switch K3. The second machine-grid side multiplexing module is connected in parallel with the grid-side converter to increase the output capacity of the grid-side converter. If the grid-side converter requires a larger current capacity, then open the first switch K2 and close the second switch K3. The first grid-side multiplexing module is connected in parallel with the grid-side converter. After configuring the first grid-side multiplexing module, it is determined whether the machine-side converter still needs a larger current capacity than the grid-side converter. If the machine-side converter still needs a larger current capacity, then open switch K3 and close switch K4, connecting the second grid-side multiplexing module in parallel with the machine-side converter to increase the capacity of the machine-side converter. If, after configuring the first grid-side multiplexing module, the grid-side converter still needs a larger current capacity than the machine-side converter, then open switch K4 and close switch K3, still connecting the second grid-side multiplexing module in parallel with the grid-side converter to increase the output capacity of the grid-side converter. If neither the generator-side converter nor the grid-side converter requires a larger current capacity, then disconnect the first generator-grid-side multiplexing module and the second generator-grid-side multiplexing module, and the converter will operate as a standalone unit.

9. A control method applied to the multiplexing system of power modules of the converter according to claim 1 or claim 2, characterized in that, The machine-grid side multiplexing module acts as a pre-charging circuit to establish the DC bus voltage.

10. The control method of claim 9, wherein, Includes the following steps: A pre-charging resistor R1 is added between the machine-network side multiplexing module and the first switch K1, and a switch K5 is added across R1. During pre-charging, the first switch K1 is closed, and the power grid charges the DC bus through the pre-charging resistor and the grid-machine side multiplexing module. Once the bus voltage is established, the switch K5, which is connected in parallel with the charging resistor, is closed to cut off the charging resistor and reduce the energy loss of the circuit.

Images