Converter system of wind generating set, wind generating set and offshore wind power plant

Abstract

The invention provides a current converter system of a wind generating set, the wind generating set and an offshore wind farm, the current converter system comprises a voltage source type current converter and a current source type current converter, the voltage source type current converter and the current source type current converter are connected in parallel between the output side of a generator of the wind generating set and a grid connection point, and the current source type current converter is connected in parallel between the output side of the generator of the wind generating set and the grid connection point. The voltage source type current converter comprises a first machine side current converter and a first network side current converter which are connected in sequence, and the current source type current converter comprises a second machine side current converter and a second network side current converter which are connected in sequence; the current converter control device is configured to control the operation of the voltage source type current converter and the current source type current converter by considering the internal circulation of the wind generating set in the voltage outer loop control of the voltage source type current converter and considering the internal circulation in the active power and reactive power control links of the current source type current converter, the internal loop current is determined based on an output current of the first grid-side converter and an output current of the second grid-side converter.

Description

Technical Field

[0001] The present disclosure relates to the field of wind power generation, and more specifically, to a converter system of a wind generator set, a wind generator set and an offshore wind farm. Background Art

[0002] A wind turbine is a device that converts wind energy into electrical energy, and outputs the electrical energy to a wind farm through a converter system installed therein. At present, converter systems can generally be divided into voltage source converters (i.e., grid-forming converters) and current source converters (grid-following converters). Voltage source converters have similar inertia characteristics to synchronous generators, which enables them to provide stable frequency support for offshore power grids. They have attracted much attention from the industry in recent years, but they are still in the theoretical stage and have hardly been put into practical use. Current source converters have fast power response capabilities and have been widely used, but they need to be synchronized with the power grid and generally do not have frequency support capabilities. Summary of the invention

[0003] Therefore, the present disclosure provides a converter system for a wind turbine generator set, a wind turbine generator set and an offshore wind farm, wherein the converter system for the wind turbine generator set combines a voltage source converter and a current source converter, thereby having the capabilities of both frequency support and rapid power response.

[0004] In a general aspect, a converter system for a wind generator set is provided, the converter system comprising: a voltage source converter and a current source converter, wherein the voltage source converter and the current source converter are connected in parallel between the output side of the generator of the wind generator set and the grid connection point of the wind generator set, the voltage source converter comprises a first machine-side converter and a first grid-side converter connected in sequence, and the current source converter comprises a second machine-side converter and a second grid-side converter connected in sequence; a converter control device is configured to control the operation of the voltage source converter and the current source converter by considering the internal circulating current of the wind generator set in the voltage outer loop control of the voltage source converter and by considering the internal circulating current of the wind generator set in the active power control link and the reactive power control link of the current source converter, wherein the internal circulating current of the wind generator set is determined based on the output current of the first grid-side converter and the output current of the second grid-side converter.

[0005] Optionally, the converter control device is configured to: determine the d-axis component of the converter output voltage reference value based on the active power reference value and actual value of the first grid-side converter; determine the q-axis component of the converter output voltage reference value based on the output current value and virtual angular frequency of the wind turbine generator set; determine the d-axis component and q-axis component of the first current reference value by performing voltage outer loop control on the d-axis component and q-axis component of the converter output voltage reference value, and based on the internal circulating current value of the wind turbine generator set; obtain the d-axis component and q-axis component of the modulation voltage reference value of the first grid-side converter by performing current inner loop control on the d-axis component and q-axis component of the first current reference value; control the operation of the first grid-side converter according to the virtual internal potential phase and the d-axis component and q-axis component of the modulation voltage reference value of the first grid-side converter; wherein the output current of the wind turbine generator set is determined based on the output current of the first grid-side converter and the output current of the second grid-side converter.

[0006] Optionally, based on the active power reference value and actual value of the second grid-side converter and the output current value and internal circulating current value of the wind turbine generator set, the d-axis component and q-axis component of the second current reference value are determined; by performing current inner-loop control on the d-axis component and q-axis component of the second current reference value, the d-axis component and q-axis component of the modulation voltage reference value of the second grid-side converter are obtained; according to the virtual internal potential phase and the d-axis component and q-axis component of the modulation voltage reference value of the second grid-side converter, the operation of the second grid-side converter is controlled, wherein the output current of the wind turbine generator set is determined based on the output current of the first grid-side converter and the output current of the second grid-side converter.

[0007] Optionally, the converter control device is further configured to determine the virtual angular frequency and the virtual internal potential phase based on the voltage value of the filter capacitor of the first grid-side converter.

[0008] Optionally, the converter control device is also configured to: obtain a second proportional integral operation result by performing a proportional integral operation on the difference between the active power reference value and the actual value of the first grid-side converter; and determine the d-axis component of the converter output voltage reference value based on the second proportional integral operation result and a preset voltage feedforward compensation value of the wind turbine generator set.

[0009] Optionally, the converter control device is further configured to: obtain a first proportional operation result by performing a proportional operation on the output current value of the wind turbine generator set; and obtain a q-axis component of the converter output voltage reference value by performing a proportional operation on the difference between the first proportional operation result and the virtual angular frequency.

[0010] Optionally, the converter control device includes a first grid-side controller and a second grid-side controller communicating with each other, wherein the first grid-side controller is configured to control the operation of the first grid-side converter, and the second grid-side controller is configured to control the operation of the second grid-side converter.

[0011] Optionally, the wind turbine generator set is an offshore wind turbine generator set, and the generator is a six-phase permanent magnet synchronous wind turbine generator.

[0012] Optionally, the capacity of the current source converter is the same as that of the voltage source converter.

[0013] Optionally, the output current value of the wind turbine generator set is the sum of the output current value of the first grid-side converter and the output current value of the second grid-side converter, and the internal circulating current value of the wind turbine generator set is the difference between the output current value of the first grid-side converter and the output current value of the second grid-side converter.

[0014] In another general aspect, a wind turbine generator set is provided, the wind turbine generator set comprising the inverter system of the wind turbine generator set as described above.

[0015] In another general aspect, an offshore wind farm is provided, comprising a plurality of wind turbine generator sets as described above.

[0016] According to the converter system of the wind turbine generator set, the wind turbine generator set and the offshore wind farm of the embodiment of the present disclosure, by combining the voltage source converter and the current source converter in the wind turbine generator set, the voltage source converter is used to provide frequency support and the current source converter is used to achieve rapid power response, so that the offshore low-frequency AC transmission system has the ability of both frequency support and rapid power response. In addition, in the control strategy of the converter system, the circulating current suppression strategy is applied to reduce the problem of power imbalance caused by the circulating current between the voltage source converter and the current source converter, thereby eliminating the adverse effect of power imbalance on the power of the offshore low-frequency AC transmission system. In addition, in the wind turbine generator set, a six-phase permanent magnet synchronous wind turbine is used, which has the advantages of high rated power, small size, low harmonic content and good economy on the one hand, and supports the simultaneous access of the voltage source converter and the current source converter on the other hand, so as to achieve frequency support and rapid power response. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects and features of the present disclosure will become more apparent from the following description in conjunction with the accompanying drawings.

[0018] Figure 1 is a block diagram illustrating a converter system of a wind turbine generator system according to an exemplary embodiment of the present disclosure.

[0019] Figure 2Ais a schematic diagram showing a control strategy of a voltage source converter according to an exemplary embodiment of the present disclosure, Figure 2B is a schematic diagram illustrating a control strategy of a current source converter according to an exemplary embodiment of the present disclosure.

[0020] Figure 3 : is a diagram showing an equivalent model at the outlet of a voltage source converter and a current source converter.

[0021] Figure 4 is a topology diagram showing a DRU-based offshore low-frequency AC transmission system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0022] The following specific embodiments are provided to help the reader obtain a comprehensive understanding of the methods, devices and / or systems described herein. However, after understanding the disclosure of the present application, various changes, modifications and equivalents of the methods, devices and / or systems described herein will be clear. For example, the order of operations described herein is only an example and is not limited to those orders set forth herein, but can be changed as will be clear after understanding the disclosure of the present application, except for operations that must occur in a specific order. In addition, for greater clarity and simplicity, the description of features known in the art may be omitted.

[0023] The features described herein can be implemented in different forms and should not be construed as being limited to the examples described herein. Rather, the examples described herein have been provided to illustrate only some of the many possible ways to implement the methods, devices, and / or systems described herein, which will be clear after understanding the disclosure of the present application.

[0024] As used herein, the term "and / or" includes any one of the associated listed items and any combination of any two or more.

[0025] Although terms such as "first", "second", and "third" may be used herein to describe various members, components, regions, layers, or portions, these members, components, regions, layers, or portions should not be limited by these terms. Instead, these terms are only used to distinguish one member, component, region, layer, or portion from another member, component, region, layer, or portion. Therefore, without departing from the teachings of the examples described herein, the first member, first component, first region, first layer, or first portion referred to in the examples may also be referred to as the second member, second component, second region, second layer, or second portion.

[0026] In the specification, when an element (such as a layer, a region or a substrate) is described as being “on”, “connected to” or “coupled to” another element, the element may be directly “on”, “connected to” or “coupled to” another element, or one or more other elements may be present therebetween. Conversely, when an element is described as being “directly on”, “directly connected to” or “directly coupled to” another element, there may be no other elements present therebetween.

[0027] The terms used herein are only used to describe various examples and are not intended to limit the disclosure. Unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. The terms "comprise", "include" and "have" indicate the presence of the described features, quantities, operations, components, elements and / or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, operations, components, elements and / or combinations thereof.

[0028] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by a person of ordinary skill in the art to which the present disclosure belongs after understanding the present disclosure. Unless explicitly defined as such herein, terms (such as those defined in a general dictionary) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present disclosure, and should not be interpreted in an idealized or overly formal manner.

[0029] Furthermore, in the description of examples, when it is considered that a detailed description of a well-known related structure or function would cause vague interpretation of the present disclosure, such a detailed description will be omitted.

[0030] Figure 1 is a block diagram illustrating a converter system of a wind turbine generator system according to an exemplary embodiment of the present disclosure. Figure 2A is a schematic diagram showing a control strategy of a voltage source converter according to an exemplary embodiment of the present disclosure, Figure 2B is a schematic diagram showing a control strategy of a current source converter according to an exemplary embodiment of the present disclosure. Figures 1 to 2B A converter system of a wind turbine generator system and a control method thereof according to an exemplary embodiment of the present disclosure are described in detail.

[0031] Reference Figure 1The converter system 100 of the wind turbine generator set includes a voltage source converter 110, a current source converter 120 and a converter control device 130. The voltage source converter 110 and the current source converter 120 are connected in parallel between the output side of the generator of the wind turbine generator set and the grid connection point (i.e., the first common connection point) PCC1 of the wind turbine generator set. The voltage source converter 110 includes a first machine-side converter (MSC1) 111 and a first grid-side converter (GSC1) 112 connected in sequence, and the current source converter 120 includes a second machine-side converter (MSC2) 121 and a second grid-side converter (GSC2) 122 connected in sequence. The converter control device 130 controls the operation of the voltage source converter 110 and the current source converter 120 by considering the internal circulating current of the wind turbine generator set in the voltage outer loop control of the voltage source converter 110, and by considering the internal circulating current of the wind turbine generator set in the active power control link and the reactive power control link of the current source converter 120. Here, the internal circulating current of the wind turbine generator set can be determined based on the output current of the first grid-side converter GSC1 112 and the output current of the second grid-side converter GSC2 122. According to an embodiment of the present disclosure, the converter control device 130 can control the first machine-side converter MSC1 111 and the second machine-side converter MSC2 121 according to an existing control strategy. Therefore, the converter control device 130 described herein controls the operation of the voltage source converter 110 and the current source converter 120, which means that the converter control device 130 controls the operation of the first grid-side converter GSC1 112 and the second grid-side converter GSC2 122. The first grid-side converter GSC1 112 is a voltage source GSC, and the second grid-side converter GSC2 122 is a current source GSC.

[0032] According to an embodiment of the present disclosure, the wind turbine generator set is an offshore wind turbine generator set, and the generator of the wind turbine generator set is a six-phase permanent magnet synchronous wind generator (PMSG). The six-phase PMSG has the advantages of high rated power, small size, low harmonic content and good economy. At the same time, the three-phase output of the six-phase PMSG can be connected to the voltage source converter 110, and the other three phases can be connected to the current source converter 120, so as to achieve frequency support and rapid power response. On the other hand, in order to suppress the internal circulation of the wind turbine generator set, the capacity of the voltage source converter 110 and the current source converter 120 can be the same, that is, the power ratio of the voltage source converter 110 and the current source converter 120 is 1:1.

[0033] According to an embodiment of the present disclosure, the converter control device 130 may be based on the active power reference value of the first grid-side converter GSC1112. and the actual value P GFM , determine the d-axis component of the converter output voltage reference value Based on the output current value i of the wind turbine flow and virtual angular frequency ω wt , determine the q-axis component of the converter output voltage reference value By comparing the d-axis component of the inverter output voltage reference value and the q-axis component The voltage outer loop is controlled, and based on the internal circulating current value i of the wind turbine generator set cir , determine the d-axis component of the first current reference value and the q-axis component By performing current inner loop control on the d-axis component and the q-axis component of the first current reference value, the d-axis component of the modulation voltage reference value of the first grid-side converter GSC1 112 is obtained. and the q-axis component According to the virtual internal potential phase theta and the d-axis component of the modulation voltage reference value of the first grid-side converter GSC1 112 and the q-axis component Control the operation of the first grid-side converter GSC1 112. Here, the output current i flow The output current of the first grid-side converter GSC1 112 and the output current of the second grid-side converter GSC2 122 are determined.

[0034] The following briefly describes the operation mode of controlling the first grid-side converter GSC1 112. The d-axis component of the modulation voltage reference value can be modulated according to the virtual internal potential phase theta. and the q-axis component The voltage is converted into a three-phase voltage in the abc coordinate system or a two-phase voltage in the αβ coordinate system, and then input into a PWM (pulse width modulation) modulation module for modulation. The modulated signal after pulse width modulation can be input into GSC1 112 to control the switch of the IGBT device in GSC1 112, thereby adjusting the output (e.g., output power, output current, output voltage, etc.) of GSC1 112. Since the above method of controlling the operation of the first grid-side converter GSC1 112 is well known to those skilled in the art, its detailed description is omitted here.

[0035] Reference Figure 2A , an LC filter circuit is provided at the output end of the first grid-side converter GSC1 112. The current outputted to PCC1 by the first grid-side converter GSC1 112 via the LC filter circuit (i.e., the output current of the first grid-side converter GSC1 112) can be transformed from the abc coordinate system to the dq coordinate system by coordinate transformation (e.g., Park transformation). s_GFM Transform to i sd_GFM and i sq_GFMThe filter capacitor voltage can be transformed from the abc coordinate system to the dq coordinate system by coordinate transformation, that is, u f Transform to u fd and u fq The filter inductor current can be transformed from the abc coordinate system to the dq coordinate system by coordinate transformation, that is, i w Transform to i wd and i wq .

[0036] According to an embodiment of the present disclosure, the converter control device 130 may also be based on the filter capacitor voltage value u of the first grid-side converter GSC1 112. f , determine the virtual angular frequency ω wt and the virtual internal potential phase theta.

[0037] Specifically, the virtual angular frequency ω can be determined by a phase-locked loop (PLL) wt That is, the voltage value u of the filter capacitor f The q-axis component u fq Perform an integral operation and add the result of the integral operation to the rated angular frequency ω0 of the power grid to obtain the virtual angular frequency ω wt ω wt The specific calculation method of is shown in the following equation (1).

[0038] ω t =k lp u fq +k li ∫u fq dt+ω0 (1)

[0039] Among them, k lp represents the proportionality coefficient, k li Represents the integral coefficient.

[0040] Then, the virtual angular frequency ω can be wt Perform an integral operation to obtain the virtual internal potential phase theta.

[0041] According to an embodiment of the present disclosure, the converter control device 130 can adjust the active power reference value of the first grid-side converter GSC1 112 by and the actual value P GFM The difference between the proportional integral operation and the voltage feedforward compensation value u of the wind turbine generator set is calculated based on the second proportional integral operation result and the preset voltage feedforward compensation value u of the wind turbine generator set. f0 , determine the d-axis component of the converter output voltage reference value like Figure 2A As shown, the converter control device 130 determines the d-axis component of the converter output voltage reference value through active power control. The specific calculation method of is shown in the following equation (2).

[0042]

[0043] Among them, k pp_GFM represents the proportionality coefficient, k pi_GFM Represents the integral coefficient.

[0044] According to an embodiment of the present disclosure, the converter control device 130 can control the output current value i of the wind turbine generator set by flow Perform proportional calculation (in Figure 2A The proportionality factor is shown as -k q ), and obtain the first proportional operation result Then, by calculating the result of the first ratio With virtual angular frequency ω wt The difference is proportional to the difference (in Figure 2A The proportionality factor is shown as k fq ), and obtain the q-axis component of the converter output voltage reference value like Figure 2A As shown, the converter control device 130 determines the virtual angular frequency ω through reactive power control and frequency closed-loop control. wt and the virtual internal potential phase theta and the q-axis component of the converter output voltage reference value

[0045] Here, it is worth noting that in the current traditional control strategy for wind turbines connected to the grid, the voltage amplitude of the grid is determined by the d-axis reference voltage (i.e., the d-axis component of the above-mentioned converter output voltage reference value) Adjustment, and the q-axis reference voltage (i.e., the q-axis component of the above converter output voltage reference value) Typically set to zero. The significance of setting it to zero is that it is assumed that the phase-locked loop rotates completely according to the reference angular frequency and reference phase, requiring the grid-connected voltage to be strongly synchronized with the grid voltage. However, in the control strategy of the voltage source converter (or voltage source wind turbine), there is no angular frequency supported by the strong grid, and the angular frequency of the offshore wind farm is completely generated by the wind farm itself, so Setting it to zero is no longer appropriate. Since the ω measured by the phase-locked loop wt and theta reflects the output u of the offshore low-frequency AC transmission system fq , which indicates that the q-axis reference voltage can be used to control the AC frequency. Therefore, the inverter control device 130 can determine the q-axis reference voltage by the above-mentioned processing. At the same time, by controlling the output current value i of the wind turbine generator set flow The proportional coefficient used in proportional calculation is used to control Thereby keeping the frequency of the wind turbine generator set stable at 20Hz, so as to realize the grid-building function of the wind turbine generator set.

[0046] According to an embodiment of the present disclosure, the converter control device 130 can output the d-axis component of the converter voltage reference value by and the q-axis component The voltage outer loop control is performed to obtain the d-axis component and q-axis component of the voltage outer loop output current reference value. The voltage outer loop is a control method well known to those skilled in the art, and its detailed description is omitted here. On the other hand, the converter control device 130 can determine the internal circulating current value i of the wind turbine generator set. cir After obtaining the d-axis component and q-axis component of the voltage outer loop output current reference value and determining the internal circulating current value i of the wind turbine generator set cir After the d-axis component and the q-axis component of the voltage outer loop output current reference value are determined, the converter control device 130 can determine the d-axis component of the first current reference value based on the d-axis component of the voltage outer loop output current reference value and the d-axis component of the internal circulating current value. And based on the q-axis component of the voltage outer loop output current reference value and the q-axis component of the internal circulating current value, the q-axis component of the first current reference value is determined like Figure 2A As shown, the converter control device 130 can determine the sum of the d-axis component of the voltage outer loop output current reference value and the d-axis component of the internal loop current value as The sum of the q-axis component of the voltage outer loop output current reference value and the q-axis component of the internal circulating current value can be determined as In this way, Figure 2A The voltage outer loop control shown may be a voltage outer loop control with loop current control added.

[0047] Optionally, the converter control device 130 can transform the internal circulating current value i of the wind turbine generator set by coordinate transformation. cir Transformed into the first d-axis component i in the dq coordinate system cird and the first q-axis component i cirq ; By integrating the first d-axis component (in Figure 2A The integral coefficient is shown as -k cird ), obtain the d-axis component of the internal circulation value; by integrating the first q-axis component (in Figure 2A The integral coefficient is shown as -k cirq ), and obtain the q-axis component of the internal circulation value.

[0048] Since the control strategies of the voltage source converter 110 and the current source converter 120 are asynchronous or the hardware parameters of the voltage source converter 110 and the current source converter 120 are inconsistent, it is inevitable that there is an internal circulation in the wind turbine generator set, and the internal circulation of the wind turbine generator set will cause the wind turbine generator set to have a power imbalance problem. Therefore, the internal circulation is used as a feedforward control quantity. Figure 2A The circulating current control is added to the voltage outer loop control to eliminate the phase fluctuation caused by the asynchronism between the voltage source converter 110 and the current source converter 120 .

[0049] Figure 3 : is a diagram showing an equivalent model at the outlet of a voltage source converter and a current source converter. Figure 3 ,u w_GFM represents the voltage source converter, u w_GFL represents a current source type converter, and the output current value and the internal circulating current value of the wind turbine generator set can be determined by the following equation (3).

[0050]

[0051] That is to say, the output current value i of the wind turbine generator set flow is the output current value i of the first grid-side converter 110 s_GFM The output current value i of the second grid-side converter 120 s_GFL The sum of the internal circulation value i of the wind turbine generator set cir is the output current value i of the first grid-side converter 110 s_GFM The output current value i of the second grid-side converter 120 s_GFL difference.

[0052] In this way, the voltage outer loop control with circulating current control added can be expressed by the following equation (4).

[0053]

[0054] Among them, k vp is the proportionality coefficient, k vi is the integral coefficient, and C is the capacitance of the filter capacitor.

[0055] According to an embodiment of the present disclosure, the converter control device 130 may be based on the active power reference value of the second grid-side converter GSC2 122. and the actual value P GFL And the output current value i of the wind turbine flow and the internal circulation value i cir , determine the d-axis component of the second current reference value and the q-axis component By calculating the d-axis component of the second current reference value and the q-axis component Perform current inner loop control to obtain the d-axis component of the modulation voltage reference value of the second grid-side converter GSC2 122 and the q-axis component According to the virtual internal potential phase theta and the d-axis component of the modulation voltage reference value of the second grid-side converter and the q-axis component Control the operation of the second grid-side converter GSC2 122. As mentioned above, the output current i flow The virtual internal potential phase theta is determined based on the output current of the first grid-side converter GSC1 112 and the output current of the second grid-side converter GSC2 122. Here, the virtual internal potential phase theta is as described above. That is, the converter control device 130 can be based on the filter capacitor voltage value u of the first grid-side converter GSC1 112. f , determine the virtual internal potential phase theta. The manner of controlling the operation of the second grid-side converter GSC2 122 may be similar to the manner of controlling the operation of the first grid-side converter GSC1 112 described above, and a detailed description thereof is omitted here.

[0056] Reference Figure 2B ,and Figure 2A Similarly, an LC filter circuit is provided at the output end of the second grid-side converter GSC2 122. The current outputted to PCC1 by the second grid-side converter GSC2 122 via the LC filter circuit (i.e., the output current of the second grid-side converter GSC2 122) can be transformed from the abc coordinate system to the dq coordinate system by coordinate transformation (e.g., Park transformation). s_GFL Transform to i sd_GFL and i sq_GFL The filter capacitor voltage can be transformed from the abc coordinate system to the dq coordinate system by coordinate transformation, that is, u f Transform to u fd and u fq The filter inductor current can be transformed from the abc coordinate system to the dq coordinate system by coordinate transformation, that is, i w Transform to i wd and i wq .

[0057] According to an embodiment of the present disclosure, the converter control device 130 can adjust the active power reference value of the second grid-side converter GSC2 122 by and the actual value P GFL The difference between the proportional integral operation and the voltage feedforward compensation value u of the wind turbine generator set is calculated based on the third proportional integral operation result and the preset voltage feedforward compensation value u of the wind turbine generator set. f0, determine the d-axis current reference value The output current value i of the wind turbine generator set is transformed by coordinate transformation flow Transformed into the d-axis component and q-axis component in the dq coordinate system By adjusting the output current value i of the wind turbine flow The q-axis component is proportional (in Figure 2B The proportionality factor is shown as -k q ), obtain the q-axis current reference value; determine the internal circulation value i of the wind turbine generator set cir The d-axis component and q-axis component of the current are based on the d-axis current reference value. The d-axis component of the second current reference value is determined by combining the d-axis component of the internal circulating current value And based on the q-axis current reference value The q-axis component of the second current reference value is determined by combining the q-axis component of the internal circulating current value like Figure 2B As shown, the d-axis component of the second current reference value is determined by adding active power control of circulating current control. And the q-axis component of the second current reference value is determined by adding the reactive power control of the circulating current control In addition, the converter control device 130 can set the d-axis current reference value The sum of the d-axis component of the internal circulating current value is determined as the d-axis component of the second current reference value. And the q-axis current reference value can be The sum of the q-axis component of the internal circulating current value is determined as the q-axis component of the second current reference value.

[0058] Here, the d-axis current reference value can be calculated by the following equation (5): The d-axis component of the second current reference value can be determined by the following equation (6):

[0059]

[0060]

[0061] Among them, k pp_GFL , k cird and k cirq represents the proportionality coefficient, k pi_GFL Represents the integral coefficient.

[0062] As described above, the converter control device 130 can transform the internal circulating current value i of the wind turbine generator set by coordinate transformation. cir Transformed into the first d-axis component i in the dq coordinate system cird and the first q-axis component i cirq; By integrating the first d-axis component (in Figure 2B The integral coefficient is shown as -k cird ), obtain the d-axis component of the internal circulation value; by integrating the first q-axis component (in Figure 2B The integral coefficient is shown as -k cirq ), and obtain the q-axis component of the internal circulation value.

[0063] According to an embodiment of the present disclosure, the converter control device 130 may include a first grid-side controller (not shown) and a second grid-side controller (not shown) that communicate with each other. The first grid-side controller may control the operation of the first grid-side converter, and the second grid-side controller may control the operation of the second grid-side converter. In other words, the above reference Figure 2A The operations described above can all be performed by the first network side controller, and the above reference Figure 2B The described operations can all be executed by the second network-side controller.

[0064] According to the converter system of the wind turbine generator set of the embodiment of the present disclosure, by combining the voltage source converter and the current source converter in the wind turbine generator set, the voltage source converter is used to provide frequency support and the current source converter is used to achieve rapid power response, so that the offshore low-frequency AC transmission system has the ability of both frequency support and rapid power response. On the other hand, by applying the circulating current suppression strategy in the control strategy of the converter system, the problem of power imbalance caused by the circulating current between the voltage source converter and the current source converter is reduced, thereby eliminating the adverse effect of power imbalance on the power of the offshore low-frequency AC transmission system.

[0065] Refer to the following Figure 4 A wind turbine generator set and an offshore low-frequency AC transmission system based on a diode rectifier unit (DRU) according to embodiments of the present disclosure are described.

[0066] Figure 4 is a topology diagram showing a DRU-based offshore low-frequency AC transmission system according to an embodiment of the present disclosure.

[0067] Reference Figure 4 The offshore low-frequency AC transmission system 400 may include n wind turbine generator sets 100' connected in parallel, a step-up transformer 410 and a DRU 420, wherein n is an integer greater than 2. The n wind turbine generator sets 100' connected in parallel may constitute an offshore wind farm.

[0068] Each wind turbine generator set 100' may include the converter system as described above, and may also include a generator (i.e., a six-phase PMSG) 140 and a wind turbine transformer 150. The converter system includes a voltage source converter 110' and a current source converter 120'. The output ends of the voltage source converter 110' and the current source converter 120' may be provided with an LC filter circuit, and may be connected to the primary side of the wind turbine transformer 150 (e.g., but not limited to, a 690V / 35KV transformer) via a first common connection point (i.e., PCC1), the secondary side of the wind turbine transformer 150 is connected to the primary side of a boost transformer 410 (e.g., but not limited to, a 35KV / 220KV transformer) via a second common connection point (i.e., PCC2), and the secondary side of the boost transformer 410 is connected to the DRU 420 via a low-frequency AC submarine cable 430. The low-frequency AC submarine cable 430 may transmit the low-frequency AC power output from the wind farm to the DRU 420. The DC power output by the DRU 420 can be transmitted to the onshore converter station via a submarine cable and converted into AC power, and connected to the grid via the onshore substation. The structure and connection method of the DRU unit are well known to those skilled in the art, and a detailed description thereof is omitted here.

[0069] Optionally, the offshore low-frequency AC transmission system 400 may further include a filter and reactive power compensation system 440 and a converter transformer 450. The primary side of the converter transformer 450 (for example, but not limited to, a 220KV / 194KV / 194KV converter transformer) is connected to the secondary side of the step-up transformer 410 via a low-frequency AC submarine cable 430, and the secondary side of the converter transformer 450 is connected to the DRU 420. In addition, the primary side of the converter transformer 450 is also connected to the filter and reactive power compensation system 440.

[0070] Here, it should be explained that since the onshore MMC (modular multilevel converter) controls the DC voltage output by the DRU 420 to a rated value, it can be equivalent to a DC voltage source, so the transmitted active power is largely determined by the DC voltage generated by the DRU 420. The DC voltage U generated by the DRU 420 dc_DRU As shown in the following equation (7).

[0071]

[0072] Where, X is the reactance of DRU 420, I dc_DRU is the DC current output by DRU 420, U r is the offshore AC grid voltage (i.e., the AC voltage of the low-frequency AC submarine cable 430). Therefore, the active power transmitted by the wind farm can be calculated by the offshore AC grid voltage U r and the filter capacitor voltage value u of the voltage source converter f Based on this, we can construct Figure 2A The active power control link of the voltage source grid-side converter shown is configured so that its output is the d-axis component of the converter output voltage reference value, that is, the amplitude of the offshore AC voltage.

[0073] As described above, since the wind turbines in the offshore wind farm are equipped with both voltage source converters and current source converters, the voltage source converter can be used to provide frequency support and the current source converter can be used to achieve rapid power response, so that the offshore low-frequency AC transmission system 400 has the capabilities of both frequency support and rapid power response.

[0074] The control strategy of the voltage source converter and the control strategy of the current source converter as described above can be written as a computer program and stored on a computer-readable storage medium. When the computer program is executed by a processor, the control strategy of the voltage source converter and the control strategy of the current source converter as described above can be implemented. Examples of computer-readable storage media include: read-only memory (ROM), random access programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, non-volatile memory, CD-ROM, CD-R, CD+R, CD-RW, CD+RW, DVD-ROM, DVD-R, DVD+R, DVD-RW, DVD+RW, DVD-RAM, BD-ROM, BD-R, BD-R LTH, BD-RE, Blu-ray or optical disk storage, hard disk drive (HDD), solid state drive (SSD), card storage (such as, multimedia card, secure digital (SD) card or extreme digital (XD) card), magnetic tape, floppy disk, magneto-optical data storage device, optical data storage device, hard disk, solid state disk and any other device, any other device is configured to store computer program and any associated data, data files and data structures in a non-transitory manner and provide the computer program and any associated data, data files and data structures to a processor or computer so that the processor or computer can execute the computer program. In one example, the computer program and any associated data, data files and data structures are distributed on a networked computer system so that the computer program and any associated data, data files and data structures are stored, accessed and executed in a distributed manner by one or more processors or computers.

[0075] Although some embodiments of the present disclosure have been shown and described, it will be appreciated by those skilled in the art that modifications may be made to the embodiments without departing from the principles and spirit of the present disclosure, the scope of which is defined by the claims and their equivalents.

Claims

1. A converter system for a wind turbine generator set, characterized in that: The inverter system comprises: A voltage source converter and a current source converter, wherein the voltage source converter and the current source converter are connected in parallel between the output side of the generator of the wind generator set and the grid connection point of the wind generator set, the voltage source converter comprises a first machine-side converter and a first grid-side converter connected in sequence, and the current source converter comprises a second machine-side converter and a second grid-side converter connected in sequence; A converter control device is configured to control the operation of a voltage source converter and a current source converter by considering the internal circulating current of the wind generator set in the voltage outer loop control of the voltage source converter, and by considering the internal circulating current of the wind generator set in the active power control link and the reactive power control link of the current source converter, wherein the internal circulating current of the wind generator set is determined based on the output current of the first grid-side converter and the output current of the second grid-side converter.

2. The inverter system according to claim 1, characterized in that The inverter control device is configured to: Determine a d-axis component of a converter output voltage reference value based on an active power reference value and an actual value of the first grid-side converter; Determine the q-axis component of the converter output voltage reference value based on the output current value and the virtual angular frequency of the wind turbine generator set; By performing voltage outer loop control on the d-axis component and the q-axis component of the converter output voltage reference value, and based on the internal circulating current value of the wind turbine generator set, the d-axis component and the q-axis component of the first current reference value are determined; By performing current inner loop control on the d-axis component and the q-axis component of the first current reference value, the d-axis component and the q-axis component of the modulation voltage reference value of the first grid-side converter are obtained; Controlling the operation of the first grid-side converter according to the virtual internal potential phase and the d-axis component and the q-axis component of the modulation voltage reference value of the first grid-side converter; The output current of the wind turbine generator set is determined based on the output current of the first grid-side converter and the output current of the second grid-side converter.

3. The inverter system according to claim 1, characterized in that: The inverter control device is configured to: Determine a d-axis component and a q-axis component of a second current reference value based on an active power reference value and an actual value of the second grid-side converter and an output current value and an internal circulating current value of the wind turbine generator set; By performing current inner loop control on the d-axis component and the q-axis component of the second current reference value, the d-axis component and the q-axis component of the modulation voltage reference value of the second grid-side converter are obtained; controlling the operation of the second grid-side converter according to the virtual internal potential phase and the d-axis component and the q-axis component of the modulation voltage reference value of the second grid-side converter, The output current of the wind turbine generator set is determined based on the output current of the first grid-side converter and the output current of the second grid-side converter.

4. The inverter system according to claim 2 or 3, characterized in that: The converter control device is further configured to determine a virtual angular frequency and a virtual internal potential phase based on a filter capacitor voltage value of the first grid-side converter.

5. The inverter system according to claim 2, characterized in that: The inverter control device is further configured to: Obtaining a second proportional integral operation result by performing a proportional integral operation on a difference between a reference value and an actual value of the active power of the first grid-side converter; Based on the second proportional-integral operation result and a preset voltage feed-forward compensation value of the wind turbine generator set, a d-axis component of the converter output voltage reference value is determined.

6. The inverter system according to claim 2, characterized in that: The inverter control device is further configured to: By performing a proportional operation on the output current value of the wind turbine generator set, a first proportional operation result is obtained; By performing a proportional operation on the difference between the first proportional operation result and the virtual angular frequency, a q-axis component of the converter output voltage reference value is obtained.

7. The inverter system according to claim 2 or 3, characterized in that: The converter control device includes a first grid-side controller and a second grid-side controller communicating with each other, wherein the first grid-side controller is configured to control the operation of the first grid-side converter, and the second grid-side controller is configured to control the operation of the second grid-side converter.

8. The inverter system according to claim 1, characterized in that: The wind turbine generator set is an offshore wind turbine generator set, and the generator is a six-phase permanent magnet synchronous wind turbine generator.

9. The inverter system according to claim 1, characterized in that: The current source converter has the same capacity as the voltage source converter.

10. The inverter system according to claim 2 or 3, characterized in that: The output current value of the wind generator set is the sum of the output current value of the first grid-side converter and the output current value of the second grid-side converter, and the internal circulation value of the wind generator set is the difference between the output current value of the first grid-side converter and the output current value of the second grid-side converter.

11. A wind turbine generator set, characterized in that: The wind turbine generator set comprises the inverter system of the wind turbine generator set according to any one of claims 1-10.

12. An offshore wind farm, characterized in that: The offshore wind farm comprises a plurality of wind turbine generator sets as claimed in claim 11.

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