A hybrid converter control method for offshore wind power

Abstract

The present invention discloses a hybrid converter control method, device, equipment and storable medium for offshore wind power, and the steps are as follows: given a reference initial value of the effective value of the AC bus voltage of the hybrid converter, the operating angular frequency of the hybrid converter and the reference value of the MMC DC voltage, the AC bus voltage of the hybrid converter, the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage are obtained; the d-axis and q-axis components of the AC bus voltage of the hybrid converter in a dq rotating coordinate system are calculated; the reference value of the effective value of the AC bus voltage of the hybrid converter is calculated; the reference value of the MMC modulation voltage in the dq rotating coordinate system is calculated; the MMC modulation voltage in a three-phase stationary coordinate system is calculated; according to the reference value of the MMC modulation voltage in the three-phase stationary coordinate system, the trigger pulses of each IGBT of the MMC are obtained through pulse width modulation to realize steady-state control of the hybrid converter.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power direct current transmission, and in particular to a control method, device, computer equipment and storable medium for a large-scale offshore wind power cascade hybrid direct current transmission system using diode rectifier units and modular multilevel converters (DRU-MMC). Background Art

[0002] With the continuous expansion of offshore wind farms, the problem of large size and heavy weight of offshore wind power transmission solutions through flexible direct current has become more prominent. Among the many lightweight offshore wind power transmission technologies, the hybrid converter transmission solution based on diode rectifier units and modular multilevel converters has attracted widespread attention due to its independent active and reactive power regulation capabilities, autonomous voltage building capabilities and high technical maturity. In the following, the diode rectifier unit is referred to as DRU, and the modular multilevel converter is referred to as MMC. Among them, compared with the parallel transmission solution of DRU and MMC, the cascade transmission solution of DRU and MMC has a lower voltage level, lower insulation requirements, and fewer sub-modules, which has the advantage of lighter weight and is very suitable for the construction of large-scale offshore wind power point-to-point direct current transmission projects in the future.

[0003] In order to reduce transmission loss and investment cost, in the DRU and MMC cascade transmission scheme, DRU usually transmits most of the active power, and MMC is responsible for reactive power compensation and a small part of active power transmission. It can be seen from the DRU transmission characteristics that when the transformer ratio is the same, the active power it transmits is proportional to the AC bus voltage. Therefore, in order to control the distribution of active power between MMC and DRU, the MMC control outer loop usually adopts an active-voltage loop. However, under this control, the PCC bus voltage cannot be accurately controlled at the rated value, and in order to make the DRU power always follow its reference value, the bus voltage fluctuates greatly. In order to improve the system operation reliability and reduce the AC bus voltage fluctuation rate, fixed bus voltage control is proposed to be applied to the MMC control structure of the hybrid converter. However, under this scheme, the DRU transmission power cannot be stably controlled at 1p.u., resulting in the need to retain a larger margin for power devices, and because the bus voltage is fixed, the fluctuation of wind power is entirely borne by MMC, and the MMC DC voltage fluctuates greatly. Summary of the invention

[0004] In view of the shortcomings of large MMC DC voltage fluctuation and large power device capacity in the existing DRU and MMC cascade transmission scheme, the present invention proposes a hybrid converter control method, device, computer equipment and storable medium for offshore wind power, while ensuring that MMC has the functions of establishing offshore AC voltage and frequency and compensating system reactive power. The present invention can achieve stable control of the offshore wind power double-end DRU and MMC cascade DC system, reduce the difficulty of voltage insulation design of the offshore wind power double-end DRU and MMC cascade DC system, reduce the power device margin requirement, and is conducive to the lightweight and low-cost development of offshore wind power DC transmission system.

[0005] The first object of the present invention is to provide a hybrid converter control method for offshore wind power, wherein the hybrid converter includes a diode rectifier unit and a modular multilevel converter; the diode rectifier unit, Diode Rectifier Units, hereinafter referred to as DRU, modular multilevel converter, Modular Multilevel Converter, hereinafter referred to as MMC; the DRU AC side and the MMC AC side are connected in parallel at the AC bus, and the DRU DC side and the MMC DC side are connected in series; the hybrid converter control method comprises the following steps:

[0006] S1. Given a reference initial value of the effective value of the AC bus voltage of the hybrid converter, an operating angular frequency ω of the hybrid converter, and a reference value of the DC voltage of the MMC, the AC bus voltage of the hybrid converter, the effective value of the AC bus voltage of the hybrid converter, and the DC voltage of the MMC are obtained;

[0007] S2, transforming the AC bus voltage of the hybrid converter from the abc stationary three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter;

[0008] S3, calculating the reference value of the effective value of the AC bus voltage of the hybrid converter according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the effective value of the AC bus voltage of the hybrid converter;

[0009] S4. Calculate the reference value of the MMC modulation voltage in the dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage;

[0010] S5. Calculate the MMC modulation voltage in the three-phase stationary coordinate system according to the reference value of the MMC modulation voltage in the dq rotating coordinate system;

[0011] S6. According to the MMC modulation voltage in the three-phase stationary coordinate system, the MMC modulation voltage is used to perform pulse width modulation to obtain the trigger signal of each switch device in the MMC, and the steady-state control of the hybrid converter is realized through the trigger signal of the MMC switch device. The modulation wave is the MMC modulation voltage in the three-phase stationary coordinate system, the carrier is a triangular carrier, and the trigger signal of each switch device in the MMC is obtained through pulse width modulation.

[0012] Furthermore, in step S2, for the convenience of control, the AC bus voltage of the hybrid converter is transformed from the abc stationary three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis DC component and q-axis DC component of the AC bus voltage of the hybrid converter. The transformation matrix T 3s / 2r The expression of (ωt) is

[0013] (1)

[0014] Where: ω is the operating angular frequency of the hybrid converter, and t is the operating time of the hybrid converter.

[0015] Furthermore, in step S3, the MMC DC voltage reference value U * dcm With the actual value U dcm The error is passed through the first PI controller, and then added to the reference initial value U of the effective value of the AC bus voltage of the hybrid converter. * v , and obtain the reference value U of the effective value of the AC bus voltage of the hybrid converter * vrms The calculation formula is

[0016] (2)

[0017] Where: s is the Laplace operator, U * v is the reference initial value of the effective value of the AC bus voltage of the hybrid converter, K P1 and K I1 are the proportional parameter and integral parameter of the first PI controller, U dcm and U * dcm They are MMC DC voltage and MMC DC voltage reference value respectively.

[0018] Furthermore, the process of step S4 is as follows:

[0019] S41, the hybrid converter AC bus voltage effective value reference value U * vrms The AC bus voltage effective value U of the hybrid converter vThe error is passed through the second PI controller and then added to half of the MMC DC voltage E. dc / 2, and obtain the d-axis component reference value U of the MMC modulation voltage * diff The calculation formula is as follows

[0020] (3)

[0021] Where: K P2 and K I2 are the proportional parameter and integral parameter of the second PI controller respectively;

[0022] S42, setting the q-axis reference value of the MMC modulation voltage to zero, because when the phase-locked loop locks the AC grid voltage phase, the d-axis component of the MMC modulation voltage is equal to the AC voltage bus voltage amplitude, and the q-axis component of the MMC modulation voltage is equal to zero.

[0023] Furthermore, in step S5, the d-axis reference value and the q-axis reference value of the MMC modulation voltage are transformed from the dq rotating coordinate system to the abc stationary three-phase coordinate system to obtain the MMC modulation voltage in the three-phase stationary coordinate system. The transformation matrix T 2r / 3s The expression of (ωt) is

[0024] (4)

[0025] Where: ω is the operating angular frequency of the hybrid converter, and t is the operating time of the hybrid converter.

[0026] A second object of the present invention is to provide a hybrid converter control device for offshore wind power, the control device comprising:

[0027] A voltage acquisition module, which acquires the hybrid converter AC bus voltage, the hybrid converter AC bus voltage effective value and the MMC DC voltage by giving a reference initial value of the hybrid converter AC bus voltage effective value, the hybrid converter operating angular frequency ω and the MMC DC voltage reference value;

[0028] A voltage coordinate conversion module, which converts the AC bus voltage of the hybrid converter from the abc static three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter;

[0029] A first voltage reference value calculation module, which calculates a reference value of the effective value of the AC bus voltage of the hybrid converter according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the effective value of the AC bus voltage of the hybrid converter;

[0030] A second voltage reference value calculation module, which calculates a reference value of the MMC modulation voltage in a dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage;

[0031] An MMC modulation voltage calculation module, which calculates the MMC modulation voltage in a three-phase stationary coordinate system according to a reference value of the MMC modulation voltage in a dq rotating coordinate system;

[0032] The steady-state control module uses the MMC modulation voltage in the three-phase stationary coordinate system to perform pulse width modulation to obtain the trigger signal of each switch device in the MMC, and realizes the steady-state control of the hybrid converter through the trigger signal of the MMC switch device.

[0033] The third object of the present invention is to provide a computer device, comprising a processor and a memory for storing a program executable by the processor, wherein when the processor executes the program stored in the memory, the above-mentioned hybrid converter control method for offshore wind power is implemented.

[0034] A fourth object of the present invention is to provide a storage medium storing a program, characterized in that when the program is executed by a processor, the above-mentioned hybrid converter control method for offshore wind power is implemented.

[0035] Compared with the prior art, the present invention has the following advantages and effects:

[0036] (1) The present invention proposes a hybrid converter control method for a hybrid converter, which makes the MMC DC voltage fluctuate less when the wind power fluctuates, under the premise that the DRU transmits most of the wind farm active power. The control proposed by the present invention reduces the difficulty of DC voltage insulation design and the MMC power device margin requirements in offshore wind power transmission projects on the basis of stable control of the hybrid converter, thereby reducing the investment cost of the system.

[0037] (2) The capacity selection of the present invention is applicable to the field of large-scale offshore wind power DC transmission through hybrid converters. The effectiveness and applicability of the control method proposed in the present invention are verified through theoretical analysis and simulation examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0039] Figure 1 This is the topological structure diagram of the hybrid converter for offshore wind power disclosed in the present invention

[0040] Figure 2 It is a flow chart of a hybrid converter control method for offshore wind power disclosed in the present invention;

[0041] Figure 3 It is a control block diagram of a hybrid converter for offshore wind power disclosed in the present invention;

[0042] Figure 4 It is a topological structure diagram of a large-scale offshore wind power double-end DRU and MMC cascaded DC transmission system disclosed in the present invention;

[0043] Figure 5 It is the steady-state simulation result of a large-scale offshore wind power double-end DRU and MMC cascade transmission system using the control method disclosed in the present invention;

[0044] Figure 6 It is a hybrid converter AC bus voltage effective value, AC current waveform diagram and active power diagram of wind farm, DRU and MMC under wind speed change by using the control method disclosed in the present invention;

[0045] Figure 7 It is the waveform diagram of the corresponding electrical quantity of the system when the wind speed changes in the same way by using the constant AC voltage control method;

[0046] Figure 8 It is a waveform diagram of system DC voltage, DRU DC voltage and MMC DC voltage under wind speed change using the control method disclosed in the present invention;

[0047] Fig. 9 It is the DC voltage waveform diagram corresponding to the system when the wind speed changes in the same way using the constant AC voltage control method;

[0048] Fig.10 is a structural block diagram of a hybrid converter control device for offshore wind power in Embodiment 3 of the present invention;

[0049] Fig.11 It is a structural block diagram of the computer device in Example 4 of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment discloses a control method for a hybrid converter for offshore wind power, which is applicable to Figure 1 In the hybrid converter shown, the diode rectifier unit is referred to as DRU, and the modular multilevel converter is referred to as MMC. The AC side of the DRU is connected in parallel with the AC side of the MMC at the AC bus, and the DC side of the DRU is connected in series with the DC side of the MMC.

[0053] Based on the hybrid converter disclosed above, the process of a control method for a hybrid converter for offshore wind power disclosed in this embodiment is as follows: Figure 2 As shown, the control block diagram is as follows Figure 3 As shown, the MMC DC voltage reference value U * dcm With the actual value U dcm The error is passed through the first PI controller, and then added to the reference initial value U of the effective value of the AC bus voltage of the hybrid converter. * v , then we can get the reference value U of the effective value of the AC bus voltage * rms ; AC bus voltage effective value reference value U * rms With the actual value U v The error is passed through the second PI controller and then added to the MMC DC voltage E dc The final result is the d-axis component reference value U of the MMC modulation voltage. * diff , and the q-axis reference value of the MMC modulation voltage is set to zero. The hybrid converter control method comprises the following steps:

[0054] S1. Given a reference initial value of the effective value of the AC bus voltage of the hybrid converter, an operating angular frequency of the hybrid converter and a reference value of the DC voltage of the MMC, the AC bus voltage of the hybrid converter, the effective value of the AC bus voltage of the hybrid converter and the DC voltage of the MMC are obtained;

[0055] S2, transform the AC bus voltage of the hybrid converter from the abc stationary three-phase coordinate system to the dq rotating coordinate system, and transform the matrix T 3s / 2r The expression of (ωt) is

[0056] (1)

[0057] Where: ω is the operating angular frequency of the hybrid converter, and t is the operating time of the hybrid converter.

[0058] S3, reference value U of the effective value of the AC bus voltage of the hybrid converter * vrms The calculation formula is

[0059] (2)

[0060] Where: s is the Laplace operator; U * v K is the reference initial value of the effective value of the AC bus voltage of the hybrid converter; P1 and K I1 are the proportional parameter and integral parameter of the first PI controller respectively; U dcm and U * dcm are the MMC DC voltage and its reference value respectively.

[0061] S4. Calculate the reference value of the MMC modulation voltage in the dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage. The process includes:

[0062] S41, according to the effective value of the AC bus voltage U of the hybrid converter v , Reference value U of the effective value of the AC bus voltage of the hybrid converter * vrms and MMC DC voltage E dc , the d-axis component reference value U of the MMC modulation voltage * diff The calculation formula is as follows

[0063] (3)

[0064] Where: K P2 and K I2 are the proportional parameter and integral parameter of the second PI controller respectively.

[0065] S42, setting the q-axis reference value of the MMC modulation voltage to zero, because when the phase-locked loop locks the AC grid voltage phase, the d-axis component of the MMC modulation voltage is equal to the AC voltage bus voltage amplitude, and the q-axis component of the MMC modulation voltage is equal to zero.

[0066] S5, transform the MMC modulation voltage from the dq rotating coordinate system to the abc stationary three-phase coordinate system, and its transformation matrix T 2r / 3s The expression of (ωt) is

[0067] (4)

[0068] Where: ω is the operating angular frequency of the hybrid converter, and t is the operating time of the hybrid converter.

[0069] S6. According to the reference value of the MMC modulation voltage in the abc static three-phase coordinate system, the trigger signal of each switching device in the MMC is controlled by pulse width modulation to achieve steady-state control of the hybrid converter.

[0070] Pulse width modulation refers to the book "Principles and Applications of High Voltage Direct Current Transmission (2nd Edition)" compiled by Zhang Yongjun, Liu Ziwen and Xiao Huangqing in 2021. MMC includes 6 bridge arms, namely the 1st bridge arm, the 2nd bridge arm, the 3rd bridge arm, the 4th bridge arm, the 5th bridge arm and the 6th bridge arm, each of which includes N submodules. The high-voltage end of the N submodules in each bridge arm is the D port. The D ends of the 1st bridge arm, the 2nd bridge arm and the 3rd bridge arm are connected to the DC positive pole, and the D ends of the 4th bridge arm, the 5th bridge arm and the 6th bridge arm are connected to the DC negative pole. The low-voltage end of the N submodules in series corresponds to the bridge arm S port. The S port of the 1st bridge arm and the S port of the 4th bridge arm are connected to the a-phase AC line; the S port of the 2nd bridge arm and the S port of the 5th bridge arm are connected to the b-phase AC line; the S port of the 3rd bridge arm and the S port of the 6th bridge arm are connected to the c-phase AC line. The pulse width modulation steps for the above MMC are as follows: introduce N triangular carriers of equal amplitude and unequal width, and the phase θ of each carrier is i Expressed as

[0071] (5)

[0072] The modulation voltage of the MMC bridge arm is compared with the N carriers to obtain the number of submodules N required for the bridge arm. on According to the voltage sorting results of each submodule in the bridge arm and the current polarity of the bridge arm, select N in the bridge arm. on The sub-modules are put into operation and generate corresponding trigger pulses.

[0073] like Figure 4 As shown in the figure, the large-scale offshore wind power double-end DRU and MMC cascaded DC transmission system includes: offshore wind farm, onshore converter, hybrid converter, DC submarine cable and AC power grid; in the figure, U v is the AC bus voltage of the hybrid converter, I v is the AC current of the hybrid converter, P is the active power of the hybrid converter, Q is the reactive power of the hybrid converter, and U dc is the DC voltage of the hybrid converter, I dc is the DC current of the hybrid converter. The hybrid converter includes DRU and MMC, such as Figure 1 shown.

[0074] Each wind farm uses a direct-drive wind turbine with a single unit capacity of 2MW. The wind farm is connected to the offshore converter station by two 66kV submarine cables. The rated active power of the wind farm is 1000 MW, and the system DC voltage level is ±320 kV. The DRU uses a 12-pulse rectifier bridge with a rated DC voltage of 480kV. The offshore MMC uses a half-bridge submodule with a rated DC voltage of 160kV. The onshore MMC uses a full-bridge submodule with a rated DC voltage of 640kV. The number of MMC submodules is 320 per bridge arm. The system capacity benchmark value is 750MVA, the AC voltage benchmark value is 66kV, and the DC voltage benchmark value is 640kV. The active power transmitted by the DRU is set to 3 / 4 of the active power generated by the wind farm. Based on PSCAD / EMTDC, a simulation model of a large-scale offshore wind power double-end DRU and MMC cascade DC transmission system containing hybrid converters is established.

[0075] Referring to step S1 in embodiment 1, a reference initial value U of the effective value of the AC bus voltage of the hybrid converter is given. * v is 1p.u., given the hybrid converter operating angular frequency ω is 100π, given the MMC DC voltage reference value U * dcm 1 pu. Referring to step S2 in Example 1, the AC bus voltage of the hybrid converter is transformed from the abc stationary three-phase coordinate system to the dq rotating coordinate system. Referring to step S3 in Example 1, the proportional parameter K of the first PI controller is P1 and the integration parameter K I1 are set to 0.4 and 0.08 respectively, and the reference value U of the effective value of the AC bus voltage of the hybrid converter is calculated. * rms is 0.983. Referring to step S4 in Example 1, the proportional parameter K of the second PI controller is P2 and the integration parameter K I2 Set them to 2.5 and 0.01 respectively, and calculate the d-axis component reference value U of the MMC modulation voltage * diff is 0.955, and the q-axis component reference value of the MMC modulation voltage is set to 0. Referring to step S5 in Example 1, the MMC modulation voltage is transformed from the dq rotating coordinate system to the abc stationary three-phase coordinate system. Based on the MMC modulation voltage waveform, the trigger signal of each switch device in the MMC is controlled by pulse width modulation, and finally the steady-state control of the hybrid converter is realized. When the hybrid converter is in steady-state operation, its AC bus voltage, AC current, DC voltage, DC voltage and transmission power are as follows: Figure 5 As shown. Figure 5 It can be seen that the present invention can achieve stable control of the offshore wind power double-end DRU and MMC cascade DC system.

[0076] Example 2

[0077] Based on a hybrid converter control method and simulation model for offshore wind power disclosed in Example 1, this embodiment will compare the effects of the control method disclosed in the present invention and the traditional control method. Strategy 1 is the control method disclosed in the present invention, and Strategy 2 is the traditional control method of constant AC voltage amplitude.

[0078] The simulation control sequence is as follows: Assume that the system has reached a steady state at t=3.5s. The initial wind speed is 12m / s, the wind speed slowly decreases to 8m / s at t=4s, and the wind speed slowly recovers to 12m / s at t=6s.

[0079] Figure 6 The effective value of the system AC bus voltage, AC current waveform, and active power diagrams of the wind farm, DRU, and MMC using strategy 1 are shown when the wind speed changes. Figure 7 The graph shows the change in electrical quantity of the system using strategy 2 when the wind speed changes. Figure 8 The waveforms of system DC voltage, DRU DC voltage and MMC DC voltage using strategy 1 when wind speed changes are given. Fig. 9 The three corresponding DC voltage waveforms of strategy 2 when the wind speed changes are given.

[0080] Depend on Figure 6 and Figure 8 It can be seen that, with Strategy 1, when the wind power changes, the MMC DC voltage can be accurately controlled at 1p.u., i.e. 160kV. Therefore, the active power transmitted by the DRU is always controlled to 0.75 times the power generated by the wind farm, and the fluctuating wind power changes are all borne by the DRU. Although the PCC bus voltage cannot be accurately controlled at the rated value, the bus voltage fluctuation is small and acceptable. During the wind speed change, the bus voltage fluctuates from 62.3kV to 65.1kV, with a fluctuation rate of 4.2%; the system DC voltage fluctuates from 621.6kV to 672.0kV, with a ripple of 7.9%; the MMC DC voltage fluctuates from 155.3kV to 163.0kV, with a ripple of only 4.8%.

[0081] Depend on Figure 7 and Fig. 9It can be seen that when strategy 2 is adopted, when the wind power changes, the AC bus voltage fluctuates very little and can be accurately controlled at 66kV. However, the DRU transmission power cannot be stably controlled at its set value. It can be seen from the simulation that the DRU transmission power is too large throughout the process. Since the bus voltage is fixed, the fluctuation of wind power is entirely borne by the MMC, and the MMC DC voltage fluctuates greatly. During the wind speed change, the bus voltage fluctuates from 65.9kV to 66.3kV, with a fluctuation rate of 0.56%; the system DC voltage fluctuates from 620.2kV to 671.4kV, with a ripple of 8.0%; the MMC DC voltage fluctuates from 129.8kV to 153.4kV, with a ripple of 14.7%. Table 1 shows the comparison results of the above electrical quantities of the DRU-MMC cascade DC system using strategy 1 and strategy 2.

[0082] Table 1. Comparison results of electrical quantities of DRU-MMC cascade DC systems using the present invention and other control methods

[0083]

[0084] In summary, the control proposed in this embodiment can reduce the MMC DC voltage fluctuation and avoid the MMC overmodulation problem, and has the advantages of small device margin requirement, low equipment insulation design difficulty and low control difficulty.

[0085] Example 3

[0086] like Fig.10 As shown, based on the control method of a hybrid converter for offshore wind power disclosed in the above embodiment 1, this embodiment further provides a control device for a hybrid converter for offshore wind power.

[0087] The device includes a voltage acquisition module 101, a voltage coordinate conversion module 102, a first voltage reference value calculation module 103, a second voltage reference value calculation module 104, an MMC modulation voltage calculation module 105 and a steady-state control module 106. The specific functions of each module are as follows:

[0088] A voltage acquisition module 101, which acquires the hybrid converter AC bus voltage, the hybrid converter AC bus voltage effective value and the MMC DC voltage by giving a reference initial value of the hybrid converter AC bus voltage effective value, the hybrid converter operating angular frequency ω and the MMC DC voltage reference value;

[0089] A voltage coordinate conversion module 102, which converts the AC bus voltage of the hybrid converter from the abc static three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter;

[0090] A first voltage reference value calculation module 103, which calculates a reference value of the effective value of the AC bus voltage of the hybrid converter according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the effective value of the AC bus voltage of the hybrid converter;

[0091] A second voltage reference value calculation module 104, which calculates a reference value of the MMC modulation voltage in a dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage;

[0092] An MMC modulation voltage calculation module 105, which calculates the MMC modulation voltage in the three-phase stationary coordinate system according to the reference value of the MMC modulation voltage in the dq rotating coordinate system;

[0093] The steady-state control module 106 obtains trigger signals of various switch devices in the MMC by pulse width modulation based on the MMC modulation voltage in the three-phase stationary coordinate system, and realizes steady-state control of the hybrid converter through the trigger signals of the MMC switch devices.

[0094] The specific implementation of each module in this embodiment can refer to the above-mentioned embodiment 1, which will not be described one by one here; it should be noted that the device provided in this embodiment is only illustrated by the division of the above-mentioned functional modules. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure can be divided into different functional modules to complete all or part of the functions described above.

[0095] Example 4

[0096] This embodiment provides a computer device, which may be a computer, such as Fig.11 As shown, a processor 1102, a memory, an input device 1103, a display 1104 and a network interface 1105 connected through a system bus 1101 are provided. The processor is used to provide computing and control capabilities. The memory includes a non-volatile storage medium 1106 and an internal memory 1107. The non-volatile storage medium 1106 stores an operating system, a computer program and a database. The internal memory 1107 provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. When the processor 1102 executes the computer program stored in the memory, a control method for a hybrid converter for offshore wind power proposed in the above-mentioned embodiment 1 is implemented as follows:

[0097] S1. Given a reference initial value of the effective value of the AC bus voltage of the hybrid converter, an operating angular frequency ω of the hybrid converter, and a reference value of the DC voltage of the MMC, the AC bus voltage of the hybrid converter, the effective value of the AC bus voltage of the hybrid converter, and the DC voltage of the MMC are obtained;

[0098] S2, transforming the AC bus voltage of the hybrid converter from the abc stationary three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter;

[0099] S3, calculating the reference value of the effective value of the AC bus voltage of the hybrid converter according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the effective value of the AC bus voltage of the hybrid converter;

[0100] S4. Calculate the reference value of the MMC modulation voltage in the dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage;

[0101] S5. Calculate the MMC modulation voltage in the three-phase stationary coordinate system according to the reference value of the MMC modulation voltage in the dq rotating coordinate system;

[0102] S6. According to the MMC modulation voltage in the three-phase stationary coordinate system, pulse width modulation is performed using the MMC modulation voltage to obtain trigger signals of various switching devices in the MMC, and steady-state control of the hybrid converter is achieved through the trigger signals of the MMC switching devices.

[0103] Example 5

[0104] This embodiment provides a storage medium, which is a computer-readable storage medium, storing a computer program. When the computer program is executed by a processor, a control method for a hybrid converter for offshore wind power in the above embodiment 1 is implemented as follows:

[0105] S1. Given a reference initial value of the effective value of the AC bus voltage of the hybrid converter, an operating angular frequency ω of the hybrid converter, and a reference value of the DC voltage of the MMC, the AC bus voltage of the hybrid converter, the effective value of the AC bus voltage of the hybrid converter, and the DC voltage of the MMC are obtained;

[0106] S2, transforming the AC bus voltage of the hybrid converter from the abc stationary three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter;

[0107] S3, calculating the reference value of the effective value of the AC bus voltage of the hybrid converter according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the effective value of the AC bus voltage of the hybrid converter;

[0108] S4. Calculate the reference value of the MMC modulation voltage in the dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage;

[0109] S5. Calculate the MMC modulation voltage in the three-phase stationary coordinate system according to the reference value of the MMC modulation voltage in the dq rotating coordinate system;

[0110] S6. According to the MMC modulation voltage in the three-phase stationary coordinate system, pulse width modulation is performed using the MMC modulation voltage to obtain trigger signals of various switching devices in the MMC, and steady-state control of the hybrid converter is achieved through the trigger signals of the MMC switching devices.

[0111] The storage medium described in this embodiment can be a magnetic disk, an optical disk, a computer memory, a random access memory (RAM), a U disk, a mobile hard disk, and the like.

[0112] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A hybrid converter control method for offshore wind power, wherein the hybrid converter comprises a diode rectifier unit and a modular multilevel converter, hereinafter referred to as a diode rectifier unit DRU, and a modular multilevel converter MMC, wherein the AC side of the DRU is connected in parallel with the AC side of the MMC at the AC bus, and the DC side of the DRU is connected in series with the DC side of the MMC, characterized in that: The hybrid converter control method comprises the following steps: S1. Given a reference initial value of the effective value of the AC bus voltage of the hybrid converter, an operating angular frequency ω of the hybrid converter, and a reference value of the DC voltage of the MMC, the AC bus voltage of the hybrid converter, the effective value of the AC bus voltage of the hybrid converter, and the DC voltage of the MMC are obtained; S2, transforming the AC bus voltage of the hybrid converter from the abc stationary three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter; S3, according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the AC bus voltage effective value of the hybrid converter, calculate the reference value of the AC bus voltage effective value of the hybrid converter; wherein the reference value U of the AC bus voltage effective value of the hybrid converter is * vrms The calculation formula is （2） Where: s is the Laplace operator, U * v is the reference initial value of the effective value of the AC bus voltage of the hybrid converter, K P1 and K I1 are the proportional parameter and integral parameter of the first PI controller, U dcm and U * dcm They are MMC DC voltage and MMC DC voltage reference value respectively; S4, according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage, calculate the reference value of the MMC modulation voltage in the dq rotating coordinate system; the process of step S4 is as follows: S41, according to the effective value of the AC bus voltage U of the hybrid converter v , Reference value U of the effective value of the AC bus voltage of the hybrid converter * vrms and MMC DC voltage E dc , the d-axis component reference value U of the MMC modulation voltage * diff The calculation formula is as follows （3） Where: K P2 and K I2 are the proportional parameter and integral parameter of the second PI controller respectively; S42, setting the q-axis reference value of the MMC modulation voltage to zero; S5. Calculate the MMC modulation voltage in the three-phase stationary coordinate system according to the reference value of the MMC modulation voltage in the dq rotating coordinate system; S6. According to the MMC modulation voltage in the three-phase stationary coordinate system, pulse width modulation is performed using the MMC modulation voltage to obtain trigger signals of various switching devices in the MMC, and steady-state control of the hybrid converter is achieved through the trigger signals of the MMC switching devices.

2. A hybrid converter control method for offshore wind power according to claim 1, characterized in that: In step S2, the AC bus voltage of the hybrid converter is transformed from the abc stationary three-phase coordinate system to the dq rotating coordinate system, and the transformation matrix T 3s / 2r The expression of (ωt) is （1） Where: ω is the operating angular frequency of the hybrid converter, and t is the operating time of the hybrid converter.

3. A hybrid converter control method for offshore wind power according to claim 1, characterized in that: In step S5, the AC bus voltage of the hybrid converter is transformed from the dq rotating coordinate system to the abc stationary three-phase coordinate system, and the transformation matrix T 2r / 3s The expression of (ωt) is （4） Where: ω is the operating angular frequency of the hybrid converter, and t is the operating time of the hybrid converter.

4. A control device for a hybrid converter control method for offshore wind power according to any one of claims 1 to 3, characterized in that: The control device comprises: A voltage acquisition module, which acquires the hybrid converter AC bus voltage, the hybrid converter AC bus voltage effective value and the MMC DC voltage by giving a reference initial value of the hybrid converter AC bus voltage effective value, the hybrid converter operating angular frequency ω and the MMC DC voltage reference value; A voltage coordinate conversion module, which converts the AC bus voltage of the hybrid converter from the abc static three-phase coordinate system to the dq rotating coordinate system to obtain the d-axis component and the q-axis component of the AC bus voltage of the hybrid converter; A first voltage reference value calculation module, which calculates a reference value of the effective value of the AC bus voltage of the hybrid converter according to the MMC DC voltage, the MMC DC voltage reference value and the reference initial value of the effective value of the AC bus voltage of the hybrid converter; A second voltage reference value calculation module, which calculates a reference value of the MMC modulation voltage in a dq rotating coordinate system according to the effective value of the AC bus voltage of the hybrid converter, the reference value of the effective value of the AC bus voltage of the hybrid converter and the MMC DC voltage; An MMC modulation voltage calculation module, which calculates the MMC modulation voltage in a three-phase stationary coordinate system according to a reference value of the MMC modulation voltage in a dq rotating coordinate system; The steady-state control module uses the MMC modulation voltage in the three-phase stationary coordinate system to perform pulse width modulation to obtain the trigger signal of each switch device in the MMC, and realizes the steady-state control of the hybrid converter through the trigger signal of the MMC switch device.

5. A computer device comprising a processor and a memory for storing a program executable by the processor, characterized in that: When the processor executes the program stored in the memory, the hybrid converter control method for offshore wind power described in any one of claims 1 to 3 is implemented.

6. A storage medium storing a program, characterized in that: When the program is executed by a processor, the hybrid converter control method for offshore wind power as described in any one of claims 1 to 3 is implemented.

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