WO2023178887A1 - Large-capacity off-grid wind-photovoltaic hybrid hydrogen-production direct-current micro-grid and control method therefor - Google Patents

Abstract

A large-capacity off-grid wind-photovoltaic hybrid hydrogen-production direct-current (DC) micro-grid and a control method therefor. The large-capacity off-grid wind-photovoltaic hybrid hydrogen-production DC micro-grid comprises m medium-voltage alternating-current (AC) sub-networks, a medium-voltage DC distribution board, k DC/DC hydrogen production power sources, and r DC/AC inverter power sources and a low-voltage AC network. Each medium-voltage AC sub-network comprises a renewable energy station, an energy storage apparatus and a medium-voltage AC distribution board. By means of an operation mode in which the energy storage apparatuses use a voltage-rise constant-frequency control mode, photovoltaic power stations and wind turbines use a constant-power control mode, and the DC/DC hydrogen production power sources use a constant-input DC voltage plus constant-output current control mode, the control goal of "a load being adjusted according to the output of a power source" can be achieved, and the system load can be automatically adjusted according to the change in output of the renewable energy stations, such that the maximum utilization of the power generation capacity of renewable energy is realized. Meanwhile, all devices are based on local control, thereby reducing the dependence of system cooperative control on a communication system and an energy management system.

Description

A large-capacity off-grid wind-solar hybrid hydrogen production DC microgrid and its control method Technical field

The invention relates to the technical field of off-grid wind and solar complementary hydrogen production power systems, and specifically relates to a large-capacity off-grid wind and solar complementary hydrogen production DC microgrid and a control method.

technical background

Hydrogen energy is a clean, carbon-free, flexible and efficient secondary energy source with rich application scenarios. It has the characteristics of high energy density, large capacity, long life, easy storage and transmission, etc. It can be used as a large-scale comprehensive green development and storage of wind power and photovoltaic power. The best option to use. The use of wind and solar complementary hydrogen production can solve the problems of wind and photovoltaic energy storage and maximum utilization, and is an important way for my country to achieve the goal of "carbon peak carbon neutrality". Electrolyzers in traditional grid-connected hydrogen production systems generally operate under stable power conditions and constant hydrogen production rates. Since wind power and photovoltaic power generation are easily affected by the external environment, when wind power and photovoltaic power generation are insufficient to meet the power demand of the hydrogen production load , a large power grid is required to participate in power supply to ensure production, and the hydrogen production efficiency of the electrolyzer is low and the demand for electricity is large, which increases the production cost of the grid-connected hydrogen production system, and the electricity from the large power grid is secondary energy. Traditional Grid-connected hydrogen production systems cannot fully guarantee green hydrogen production requirements. As the penetration rate of wind power and photovoltaic systems gradually increases, due to the intermittency and randomness of wind power and photovoltaic power generation, the output fluctuates greatly and the frequency of fluctuations is irregular. Therefore, the grid-connected operation of large-capacity wind and photovoltaic power generation systems is not conducive to The security and stability of large power grids. The off-grid wind and solar hybrid hydrogen production power system can achieve the perfect combination of green power generation and electricity consumption without affecting the security of the large power grid system. It can achieve zero carbon emissions while improving the utilization rate of wind and solar power generation. In order to improve efficiency, microgrid systems with large-capacity wind and solar power generation generally adopt higher transmission voltage levels to reduce losses. When the current large-capacity off-grid wind-solar hybrid hydrogen production power system adopts the traditional AC scheme for networking, the following problems mainly need to be solved:

1) Design of off-grid wind and solar hybrid power generation hydrogen production system under extremely high penetration rate. Under off-grid operation, the safe and stable operation of extremely high-penetration new energy power systems poses great risks and challenges. The system has high harmonic content and large reactive power demand, which places higher requirements on the voltage and power support capabilities of the energy storage system. , the demand for energy storage capacity is large. The design requirements of the hydrogen production system can improve the power factor of the power grid, reduce the network loss of the system, minimize the energy storage configuration, realize the system synergy and intensiveness of heterogeneous power sources, and seek the best configuration between power generation and energy storage system capacity. Proportion.

2) Control of the load following the source. Under off-grid conditions, due to the intermittent and random nature of wind power and photovoltaic power generation, the hydrogen production load needs to be automatically controlled to follow changes in system power. When multiple photovoltaic power stations and wind power stations are connected to a single AC main network, Issues such as frequency, phase angle, and reactive power between different power stations need to be considered, and communication needs to be relied upon to achieve "load-following source movement." The control is very complex, and the scalability is poor, making it inconvenient for modular expansion.

3) Power supply reliability. Due to the randomness of power generation capacity of different new energy stations, it is easy to cause voltage fluctuations and oscillations in different frequency bands on the same AC power grid, bringing greater safety risks to the entire system; when a source-end short circuit occurs in the system, the voltage at each node and All power is affected, and the fault affects a wide range.

In order to solve the above practical problems faced by large-capacity wind and solar complementary off-grid hydrogen production systems, it is necessary to propose a DC microgrid structure for wind and solar complementary off-grid hydrogen production. Under the basic premise of maximizing the utilization of the power generation capacity of new energy stations, Optimize the system configuration as much as possible, reduce energy storage requirements, reduce control difficulty, and improve the operational safety, reliability, and scalability of the system.

Contents of the invention

The purpose of the present invention is to provide a large-capacity off-grid wind-solar complementary hydrogen production DC microgrid and a control method in view of the shortcomings of the existing technology, and propose a "load follows the source" system networking control method, which is suitable for New energy installed capacity can achieve maximum complementary hydrogen production from new energy sources in off-grid wind and solar complementary hydrogen production scenarios ranging from several MW to hundreds of MW.

The present invention is a large-capacity off-grid wind-solar complementary hydrogen production DC microgrid, which includes m medium voltage AC subnets, medium voltage DC distribution boards, k DC/DC hydrogen production power supplies, and r DC/AC inverter power supplies. and low-voltage AC network power supply; each medium-voltage AC subnetwork is connected to the medium-voltage DC distribution board through the corresponding transformer rectifier device, and the input terminals of the k DC/DC hydrogen production power supplies pass through the corresponding medium-voltage DC circuit breaker. B _k is connected to the medium voltage DC distribution board, the output end of each DC/DC hydrogen production power supply is connected to an electrolyzer, and the input ends of r DC/AC inverter power supplies pass through the corresponding medium voltage DC circuit breaker B _k Connected to the medium-voltage DC distribution board, the output end of each DC/AC inverter power supply supplies power to the low-voltage AC network;

Each medium-voltage AC subnetwork includes new energy stations, energy storage devices and medium-voltage AC distribution boards. New energy stations and energy storage devices are connected to the medium-voltage AC distribution board through AC circuit breakers _Sk ; medium-voltage AC An AC circuit breaker _Sk is connected between the distribution board and the transformer rectifier device, and a medium-voltage DC circuit breaker B _k is connected between the transformer rectifier device and the medium-voltage DC distribution board; the low-voltage AC network includes a low-voltage AC distribution board and several electrical loads. The output end of each DC/AC inverter power supply is connected to the low-voltage AC distribution board through the AC circuit breaker _Sk , and the low-voltage AC distribution board is connected to the backup power supply through the AC circuit breaker _Sk .

Further, the new energy station is a photovoltaic power station or a wind power station composed of several wind turbines. The solar photovoltaic array in the photovoltaic power station is connected to the medium voltage AC distribution board after being boosted by a DC/AC inverter and transformer. The wind power The direct output voltage of the stator of the doubly-fed wind turbine in the unit is boosted by a transformer and then connected to the medium voltage AC distribution board or the permanent magnet direct-drive wind turbine in the wind turbine unit is connected via a back-to-back full power converter. to the medium voltage AC distribution board.

Further, the transformer and rectifier device includes a rectifier transformer and a rectifier. The rectifier transformer uses two 12-pulse rectifier transformers with primary sides shifted by +7.5° and -7.5° respectively. The rectifier uses four groups of full-wave uncontrolled Rectifier for bridge rectifier.

Further, the energy storage device is composed of a bidirectional energy storage converter, a battery system and a transformer. The bidirectional energy storage converter adopts a three-phase two-level voltage source type SVPWM converter structure with AC side inductance and capacitance. The DC side of the energy storage converter is connected to the battery system. Through the on-off control of IGBT devices S _D1 -S _D6 , the electric energy conversion between DC and AC is realized. After being boosted by the transformer, it is connected to the central power supply through the AC circuit breaker. Pressure AC distribution board.

Further, the DC/DC hydrogen production power supply includes a single-phase diode clamped three-level inverter, a transformer and a single-phase bridge rectifier; the DC/AC inverter power supply includes a DC/AC inverter and a transformer. , the DC/AC inverter consists of three single-phase diode clamped three-level inverters and three single-phase transformers.

A control method for the above-mentioned large-capacity off-grid wind-solar complementary hydrogen production DC microgrid is also provided, and the control method is:

The hydrogen production system adjusts the output of the photovoltaic power station or wind turbine to the system according to the dispatching instructions;

The bidirectional energy storage converter in the energy storage device adopts voltage rising constant frequency control to keep the system frequency of the medium voltage AC subnet unchanged and the active power output of the energy storage device to be 0;

Transformer rectifier device converts AC into DC;

Under constant input DC voltage control, the DC/DC hydrogen production power supply compares the DC input terminal capacitor voltage with a constant voltage reference value. After PI control, the DC input terminal capacitor voltage is maintained stable. Under constant output current control, the DC/DC hydrogen production power supply The hydrogen power supply adjusts the output current according to the change in capacitance voltage at the DC input end. By adjusting the output DC current, the system load is automatically adjusted as the output of the new energy source changes.

Further, the DC/AC inverter in the photovoltaic power station, the rotor-side converter of the doubly-fed wind turbine of the wind turbine generator, or the machine-side converter of the permanent magnet direct-drive wind turbine adopts the constant power control mode. PI control of active and reactive power; in the constant power control of DC/AC inverter in photovoltaic power station, P _s and Q _s are the active output and reactive power of the photovoltaic power station respectively, and P _sref and Q _sref are given Scheduling instructions for the active power and reactive power of the photovoltaic power station; calculate the maximum power output capability P _smax of the current photovoltaic power station through maximum power point tracking control. As the maximum limit of P _sref , set P _sref to be less than P _smax . The reactive power command Q _sref is set to 0 to keep the reactive power output of the photovoltaic power station at 0; the differences between P _s and P _sref and Q _s and Q _sref are respectively passed through the PI controller as the DC/AC inverter in the photovoltaic power station. The d-axis current reference command i _sdref and q-axis current reference command i _sqref of the inverter, i _sd and i _sq are respectively the component of the active output current of the DC/AC inverter on the dq axis and the component of the reactive output current on the dq axis. , i _sd and i _sq are the components of the output current of the DC/AC inverter on the d-axis and q-axis respectively. The differences between i _sd and i _sdref , i _sq and i _sqref are added separately after passing through the PI controller. On the d-axis output voltage feedforward term u _sd and q-axis output voltage feedforward term u _sq of the DC/AC inverter, the output voltages u _sdref and u _sqref are the dq-axis modulated voltage signals of the DC/AC inverter;

In the constant power control of the doubly-fed wind turbine rotor side converter in the wind turbine, P _w and Q _w are the active power output and reactive power output of the wind turbine respectively, and P _wref and Q _wref are given Active power dispatching instructions and reactive power dispatching instructions; the maximum power output capability P _wmax of the current wind turbine is calculated by maximum power point tracking control. As the maximum limit of P _wref , set P _wref less than P _wmax , and the reactive power instruction Q _wref is set to 0, so that the reactive power output of the wind turbine remains at 0; the output results i _wdref and i _wqref of the differences between P _w and P _wref , Q _w and Q _wref respectively after passing through the PI controller are respectively the rotor side converter current The d-axis current reference command and q-axis current reference command of the rotor side converter. The components of the output current of the rotor side converter in the dq axis are i _wd and _{i wq} respectively. The differences between i wd and i _wdref , i _wq and i _wqref are calculated by After the PI controller, the output results are subtracted and added to ω _s [-L _m U _s /(ω _e L _s ) + σL _r i _wd ] and ω _s σL _r i _wd respectively, and the rotor side converter is obtained in dq The active modulated voltage signal u _wdref and the reactive modulated voltage signal u _wqref on the shaft, where ω _s and ω _e are the slip angular velocity and synchronous angular velocity respectively, L _s is the dq-axis stator self-inductance, and L _r is the dq-axis rotor self-inductance , L _m is the mutual inductance of the equivalent winding of the dq-axis stator and rotor, σ is the magnetic leakage coefficient of the generator, and U _s is the stator voltage;

In the constant power control of the machine-side converter of the permanent magnet direct-drive wind turbine in the wind turbine, P _g and Q _g are the active power output and inactive power of the wind turbine respectively. Active power output, P _gref and Q _gref are the given active power scheduling instructions and reactive power scheduling instructions respectively; the maximum power output capability P _gmax of the current wind turbine is calculated by maximum power point tracking control as the maximum limit of P _gref , set P _gref less than P _gmax , set the reactive power command Q _gref to 0, so that the reactive power output of the wind turbine remains at 0; the differences between Q _g and Q _gref , P _g and P _gref are passed through the PI controller respectively. The output results i _gdref and i _gqref are the d-axis current reference command and q-axis current reference command of the machine-side converter respectively. The components of the output current of the machine-side converter in the d-axis and q-axis are i _gd and i respectively. _gq , the difference between i _gd and i _gdref , i _gq and i _gqref is passed through the PI controller, the output results are subtracted and added respectively (ω _g L _fq i _gq -R _f i _gd ) and (R _f i _gq + ω _g L _fd i _gd +ω _g ψ _f ), the d-axis and q-axis modulated voltage signals u _gdref and u _gqref of the machine-side converter are obtained, where ω _g is the synchronous angular velocity, R _f is the stator resistance, L _fd and L _fq is the stator dq axis inductance, and ψ _f is the rotor flux linkage.

Further, in the voltage rise constant frequency control mode of the energy storage device, the converter in the energy storage device adopts dq-axis double closed-loop control, and the outer loop of the double-closed loop control adopts voltage PI control. The voltage rise refers to the voltage outside the d-axis. The PI control of active power is introduced into the loop. The PI control of active power compares the active power output P of the energy storage system with P _ref . The difference result u _pf after passing through the PI controller is used as the feedback of the voltage outer loop. The voltage outer loop The ring compares u _pd with u _pdref and u _pq with u _pqref respectively on the dq axis. The difference between u _pdref and u _pd on the d-axis voltage outer ring minus u _pf and passes through the PI controller is combined with the cross coupling term. ωC ₁ u _pq is subtracted to obtain the d-axis current command value i _pdref . After passing through the PI controller, the difference between u _pqref and u _pq on the q-axis voltage outer ring is added to the cross-coupling term ωC ₁ u _pd to obtain the q-axis. Current command value i _pqref , the addition of active power adjustment link makes the adjustment of the converter output voltage by voltage PI control affected by the droop characteristics of power transmission. Under voltage PI control, the medium voltage AC subgrid voltage changes with the system power flow, and P _ref Set to 0 to keep the active power output of the energy storage system at 0; in the inner loop current PI control, the difference between i _pdref and i _pd on the d-axis current inner loop is connected with the cross coupling term ωL ₁ after passing through the PI controller i _pq is added to obtain the d-axis modulation voltage command value u _d . After passing through the PI controller, the difference between i _pqref and i _pq on the q-axis current inner loop is subtracted from the cross-coupling term ωL ₁ i _pd to obtain the q-axis modulation voltage. The command value u _q ; u _q and u _d are then transformed by dq to obtain the modulated wave signals u _a , u _b and u _c controlled by SVPWM; constant frequency means that the output voltage frequency f of the converter in the energy storage device is directly set to a constant value , the synchronous rotation angle only changes with time t;

Among them, P _ref and P are the active power reference command and actual active power output of the energy storage device respectively; L ₁ and C ₁ are the AC side inductance and capacitance; u _pd and u _pq are the output side of the converter in the energy storage device respectively. The dq-axis components of the three-phase voltage u _pa , u _pb , u _pc obtained by dq transformation, u _pdref and u _pqref are the d-axis and q-axis voltage reference commands respectively, which are set to constant values; i _pd and i _pq are storage respectively. The dq axis component obtained by dq transformation of the three-phase current i _pa , i _pb , and i _pc on the output side of the converter in the energy device; ω is the angular velocity.

Further, in the constant input DC voltage + constant output current control mode of the DC/DC hydrogen production power supply, the inverter in the DC/DC hydrogen production power supply adopts double closed-loop control, and the outer loop of the double closed-loop control adopts voltage PI control. Stabilize the capacitor voltage at the DC input terminal. The voltage outer loop compares the capacitor voltage value U ₁ at the DC input terminal with the constant voltage reference value U _ref . The difference is outputted through the PI controller to the DC current command value I _1ref . Double closed-loop control The inner loop uses current PI control to stabilize the output current of the DC/DC hydrogen production power supply. The current inner loop collects the output DC current I ₁ of the DC/DC hydrogen production power supply and compares it with I _1ref . The difference is used as the SVPWM after passing through the PI controller. control signal.

The beneficial effects of the present invention are: the present invention adopts "different types of new energy stations to independently form medium-voltage AC subnets under the support of their respective energy storage devices, and multiple medium-voltage AC subnets are connected to a unified medium-voltage AC subnet through a transformer rectifier device. "DC main grid" topology and "load follows source" system network control method: energy storage devices adopt voltage rise constant frequency control, photovoltaic power stations and wind power stations adopt constant power control, and DC/DC hydrogen production power sources adopt Constant input DC voltage + constant output current control. This topology and its control method are suitable for off-grid wind and solar complementary hydrogen production scenarios with new energy installed capacity ranging from several MW to hundreds of MW. It can not only achieve maximum complementary hydrogen production from new energy sources, but also have high power supply reliability and scalability. With the advantages of strong power and simple control, it can maximize the utilization of new energy power generation. The specific beneficial effects are as follows:

1. Photovoltaic power stations and wind power stations form a number of independent medium-voltage AC subnets with the support of their respective energy storage devices. The medium-voltage AC subnets are connected to the unified medium-voltage DC main grid through multi-phase transformer rectifier devices. , this network structure can enhance the future scalability of the system. At the same time, the DC networking method of the multi-phase transformer rectifier device improves the power factor and harmonic quality of the AC side system, reduces the reactive power demand of the system, and can greatly Greatly reduce the capacity of the converter connected to the energy storage system.

2. Photovoltaic power stations or wind power stations are independently networked, which avoids voltage fluctuations and oscillations in different frequency bands caused by different forms of heterogeneous power sources on the same power grid due to the randomness of power generation capabilities, and improves the controllability, inertia and oscillation of the system. The stability margin can also ensure the normal operation of other system parts when a single medium-voltage AC subnet fails, reducing safety risks and improving system operation reliability.

3. By adopting the operating mode of voltage rise constant frequency control for energy storage devices, constant power control for photovoltaic power stations and wind turbines, and constant input DC voltage + constant output current control for DC/DC hydrogen production power supply, "load follows the source" can be realized. "The control goal is that the system load can be automatically adjusted according to the changes in the output of the new energy station, so that the new energy power generation capacity can be maximized. At the same time, all equipment is based on local control, which reduces the impact of system collaborative control on the communication system and energy management. System dependencies.

Description of the drawings

Figure 1 is a schematic diagram of a large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to the present invention;

Figure 2 is a schematic structural diagram of a preferred embodiment of the large-capacity off-grid wind-solar complementary hydrogen production DC microgrid of the present invention;

Figure 3 is a circuit diagram of the multi-phase transformer rectifier device of the present invention;

Figure 4 is a circuit diagram of the energy storage device of the present invention;

Figure 5 is a circuit diagram of the DC/DC hydrogen production power supply of the present invention;

Figure 6 is a circuit diagram of the DC/AC inverter power supply of the present invention;

Figure 7 is a strategy diagram for the new energy station adopting constant power control according to the present invention;

Figure 8 is a strategy diagram for the energy storage system of the present invention to adopt voltage rise and constant frequency control;

Figure 9 is a strategy diagram for the DC/DC hydrogen production power supply of the present invention to adopt constant input DC voltage + constant output current control.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clear, this application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

It should be understood that the terms "length", "width", "top", "bottom", "front", "back", "left", "right", "vertical", "horizontal", "top" The orientations or positional relationships indicated by "bottom", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply the device referred to. Or elements must have a specific orientation, be constructed and operate in a specific orientation and therefore are not to be construed as limitations on the application.

In addition, the terms “first” and “second” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Therefore, features defined as "first" and "second" may explicitly or implicitly include one or more of these features. In the description of this application, "plurality" means two or more than two, unless otherwise explicitly and specifically limited.

As shown in Figure 1, this solution includes m medium-voltage AC subnets, medium-voltage DC distribution boards, k DC/DC hydrogen production power supplies, r DC/AC inverter power supplies and low-voltage AC network power supply. Each medium-voltage AC subgrid is connected to the medium-voltage DC distribution board through the corresponding transformer rectifier device, and the input ends of the k DC/DC hydrogen production power supplies are connected to the medium-voltage through the corresponding medium-voltage DC circuit breaker B _k DC distribution board, the output end of each DC/DC hydrogen production power supply is connected to an electrolyzer and supplies power to the electrolyzer, and the input ends of the r DC/AC inverter power supplies are connected through the corresponding medium voltage DC circuit breaker B _k Into the medium voltage DC distribution board, the output of each DC/AC inverter power supply supplies power to the low voltage AC network. In this embodiment, the new energy station can be a photovoltaic power station or a wind power station composed of several wind turbines. The solar photovoltaic array in the photovoltaic power station is connected to the medium voltage AC distribution board after being boosted by a DC/AC inverter and transformer. In wind turbines, the stator of the doubly-fed wind turbine directly outputs voltage or the permanent magnet direct-drive wind turbine outputs the voltage through the back-to-back full-power converter and is boosted by the transformer before being connected to the medium-voltage AC distribution board.

Each medium-voltage AC subnetwork includes new energy stations, energy storage devices and medium-voltage AC distribution boards. New energy stations and energy storage devices are connected to the medium-voltage AC distribution board through AC circuit breakers _Sk ; medium-voltage AC An AC circuit breaker _Sk is connected between the distribution board and the transformer rectifier device, and a medium voltage DC circuit breaker B _k is connected between the transformer rectifier device and the medium voltage DC distribution board. The low-voltage AC network includes a low-voltage AC distribution board and several electrical loads. The output end of each DC/AC inverter power supply is connected to the low-voltage AC distribution board through an AC circuit breaker _Sk . The low-voltage AC distribution board passes through an AC circuit breaker S _k is connected to the backup power supply to ensure the power demand of the auxiliary production power load. Medium-voltage DC distribution boards and low-voltage AC distribution boards can be divided into several sections of DC busbars or AC busbars to meet different power supply and distribution needs. Several sections of busbars are connected through circuit breakers.

Figure 2 shows a schematic diagram of a large-capacity off-grid wind-solar complementary hydrogen production DC microgrid provided by the preferred embodiment of the present application. For ease of explanation, only the parts related to this embodiment are shown, and the details are as follows:

In the figure: G ₁ , G ₂ ,...G _m are m new energy stations; C ₁ , C ₂ ,...C _m are m sets of energy storage devices; K _{1_1} , K _{1_2} ,...K _{1_2m} are m sets of energy storage devices. The new energy station and m sets of energy storage devices are connected to the AC circuit breaker _Sk of the 35kV medium-voltage AC distribution board; K _{2_1} , K _{2_2} ,...K _{2_m} are m units used for the medium-voltage AC distribution board and transformer rectification The AC circuit breaker S _k ; S _{1_1} , S _{1_2} ,...S _{1_m} connected to the device is the medium voltage DC circuit breaker B _k used to connect m transformer rectifier devices to the 4000V medium voltage DC distribution board; S _{2_1} , S _{2_2} ,…S _{2_k} is the medium voltage DC circuit breaker B _k used for connecting k DC/DC hydrogen production power supplies to the medium voltage DC distribution board; S _{3_1} ,S _{3_2} ,…S _{3_r} is used for r sets of DC/AC inverters The transformer power supply is connected to the medium voltage DC circuit breaker B _k of the medium voltage DC distribution board; D ₁ , D ₂ ,…D _k are k DC/DC hydrogen production power supplies, and Z ₁ , Z ₂ ,…Z _k are k Electrolyzer; T ₁ , T ₂ ,...T _m are m transformer rectifier devices; I ₁ , I ₂ ,...I _r are r DC/AC inverter power supplies; K _{3_1} , K _{3_2} ,...K _{3_r} are r An AC circuit breaker _Sk is used to connect the DC/AC inverter power supply to the low-voltage AC distribution board. K _D is the AC circuit breaker _Sk used to connect the 390V low-voltage AC distribution board to the backup power supply.

This embodiment is a large-capacity off-grid wind-solar hybrid hydrogen production DC microgrid, including m new energy stations, m energy storage devices, medium-voltage AC distribution boards, m transformer rectifier devices, medium-voltage DC Distribution board, k DC/DC hydrogen production power supplies, k electrolyzers, r DC/AC inverter power supplies, low-voltage AC distribution board, auxiliary production power load, m new energy stations (G ₁ , G ₂ ,...G _m ) can be a photovoltaic power station or a wind power station composed of several wind turbines. The photovoltaic power station and the wind power station are supported by their respective energy storage devices (C ₁ , C ₂ ,...C _m ) through 35kV medium voltage. The AC distribution board forms m independent medium-voltage AC subnets. Each new energy station and the corresponding energy storage device are connected to the medium-voltage AC distribution through AC circuit breakers (K _{1_1} , K _{1_2} ,...K _{1_2m} ). The m medium-voltage AC subnets are connected to the unified medium-voltage DC distribution board through their respective transformer rectifier devices (T ₁ , T ₂ ,...T _m ). Each medium-voltage AC distribution board is connected to the transformer. There are AC circuit breakers (K _{2_1} , K _{2_2} ,...K _{2_m} ) connected between each transformer rectifier device and the 4000V medium voltage DC distribution board. A medium voltage DC circuit breaker (S _{1_1} , S _{1_2} ,…S _{1_m} ), the medium-voltage DC distribution board passes k medium-voltage DC circuit breakers (S _{2_1} ,S _{2_2} ,…S _{2_k} ) and k DC/DC hydrogen production power supplies (D ₁ ,D ₂ ,…D _k ) is connected to supply power to the electrolytic tank (Z ₁ , Z ₂ ,...Z _k ) through r medium-voltage DC circuit breakers (S _{3_1} , S _{3_2} ,...S _{3_r} ) and r DC/AC inverter power supplies connected in sequence (I ₁ ,I ₂ ,…I _r ), r AC circuit breakers (K _{3_1} ,K _{3_2} ,…K _{3_r} ) are connected to the 390V low-voltage AC distribution board to supply power to the low-voltage AC network, and the low-voltage AC distribution board is disconnected through AC Device K _D is connected to the backup power supply to ensure the power demand of the auxiliary production electrical load.

Preferably, the solar photovoltaic array in the photovoltaic power station is boosted by a DC/AC inverter and transformer and then connected to the medium voltage AC distribution board. The wind turbine set uses a doubly-fed induction generator set or a permanent magnet direct drive synchronous generator set. The generator set The output voltage is boosted through a transformer and connected to the medium voltage AC distribution board.

As shown in Figure 3, the transformer rectifier device includes a rectifier transformer and a rectifier. The rectifier transformer uses two 12-pulse rectifier transformers, and the rectifier uses four sets of full-wave uncontrolled rectifier bridge rectifiers. The three-phase AC power supplies u _a0 , u _b0 , and _uc0 obtain two sets of six-phase power supplies (u _a1 , u _b1 , u _c1 ), (u _a2 ) with equal phase voltage amplitudes and a phase difference of 15° through two phase-shifting transformers. , u _b2 , u _c2 ) and (u _a3 , u _b3 , u _c3 ), (u _a4 , u _b4 , u _c4 ), the two groups of three-phase power supplies in each six-phase power supply have a phase difference of 30°, and each group of three phases The power supply obtains a six-pulse DC voltage through a three-phase uncontrolled rectifier, in which D ₁₁ ~ D ₁₆ , D ₂₁ ~ D ₂₆ , D ₃₁ ~ D ₃₆ and D ₄₁ ~ D ₄₆ are diodes in the three-phase uncontrolled rectifier, connected in parallel After output, a twelve-pulse DC voltage is obtained. The upper and lower twelve-pulse uncontrolled rectifiers are connected in series to finally form a twenty-four-pulse DC voltage. The system grounding method adopts the midpoint to be grounded through high resistance R _0. In the figure, R and L is the equivalent impedance of the rectifier transformer.

As shown in Figure 4, the energy storage device consists of a bidirectional energy storage converter, a battery system and a transformer, which can realize bidirectional flow of energy between the medium voltage AC distribution board and the energy storage device. The bidirectional energy storage converter adopts a three-phase two-level voltage source type SVPWM converter structure with AC side inductance and capacitance. The DC side of the bidirectional energy storage converter is connected to the battery system. Through the IGBT devices S _D1 -S _D6 On-off control realizes the electric energy conversion between DC and AC (bidirectional type). After being boosted by the transformer, it is connected to the medium-voltage AC distribution board through the AC circuit breaker. In the figure, U _D and I _D are the DC side batteries. The output voltage and current of the system, C is the DC side support capacitor, L ₁ and C ₁ are the AC side inductance and capacitance, u _pa , u _pb , u _pc and i _pa , i _pb , i _pc are the three-phase voltages on the AC side respectively. and current.

As shown in Figure 5, the DC/DC hydrogen production power supply includes a single-phase diode clamped three-level inverter, a transformer and a single-phase bridge rectifier. _CD1 and _CD2 are the clamping capacitors on the DC input side of the single-phase diode clamped three-level inverter. By controlling the on and off of the IGBT devices S _T1 -S _T8 , the power conversion between DC and AC is realized. Among them, D _T1 ~ D _T4 and D _B1 ~ D _B4 are the diodes in the single-phase diode clamped three-level inverter and the single-phase bridge rectifier respectively. U ₁ and U ₂ are the capacitor voltage value and output of the input end respectively. The DC voltage on the side, I ₁ is the DC current on the output side of the DC/DC hydrogen production power supply, and diodes D ₁ and D ₂ are connected in series at both ends of the DC loop to limit the one-way flow of current and prevent the load from providing short-circuit feed current.

As shown in Figure 6, the DC/AC inverter power supply includes a DC/AC inverter and a transformer. The DC side of the DC/AC inverter power supply is connected to the medium-voltage DC distribution board. There are diodes D ₃ and D in series at both ends of the DC loop. ₄ to limit the one-way flow of current and prevent the load from providing short-circuit feed current. _CD3 and _CD4 are the clamping capacitors on the DC input side of the DC/AC inverter, and _U3 is the capacitor voltage value at the DC input end. The DC/AC inverter consists of three single-phase diode clamped three-level inverters. By controlling the IGBT devices S ₁₁ -S ₁₈ , S ₂₁ -S ₂₈ and S ₃₁ of the three single-phase inverters respectively, -S ₃₈ 's on-off control inverts DC power into three-phase AC power. After passing through the LC filter, the three single-phase AC voltages are three-phase integrated through three transformers, and then supplied to low-voltage AC distribution through the AC circuit breaker. The electric panel supplies power, of which _DS11 to _DS14 , _DS21 to _DS24 and _DS31 to _DS34 are the diodes in three single-phase inverters respectively, and L _s1 , L _s2 and L _s3 are respectively the diodes in three single-phase inverters. The AC side filter inductor in the inverter, C _s1 , C _s2 , and C _s3 are the AC side filter capacitors in the three single-phase inverters respectively.

Production electricity mainly supplies power for the hydrogen production system and daily use in the factory, including compressors, air compressors, circulating water pumps, control systems, factory lighting, etc.

The invention provides a control method for a large-capacity off-grid wind-solar complementary hydrogen production DC microgrid:

In the hydrogen production system, the photovoltaic power stations and wind turbines adopt constant power control, the energy storage system adopts voltage rise constant frequency control, and the DC/DC hydrogen production power supply adopts the operation mode of constant input DC voltage + constant output current control to achieve "load follows the source". "Control objectives.

The hydrogen production system adjusts the output of the photovoltaic power station or wind turbine to the system according to the dispatching instructions;

The bidirectional energy storage converter in the energy storage device adopts voltage rise constant frequency control to keep the system frequency of the medium voltage AC subnet unchanged and the active power output of the energy storage device to 0, and only provides voltage reference and reactive power support for the system. ; Since the system power flow changes when the photovoltaic power station or wind turbine generator adjusts the output according to the dispatching instructions, the voltage adjustment of the energy storage device under the voltage rise constant frequency control is affected by the power transmission droop characteristics, so that the medium voltage AC subgrid voltage is affected by the system power flow. And change;

Transformer rectifier device converts AC into DC;

Under constant input DC voltage control, the DC/DC hydrogen production power supply compares the DC input capacitor voltage with a constant voltage reference value. After PI control, the voltage of the DC input capacitor is maintained stable. Under constant output current control, the DC/DC The hydrogen production power supply adjusts the output current according to changes in the capacitor voltage at the DC input end. By adjusting the output DC current, the system load is automatically adjusted as the output of the new energy source changes. Since voltage changes in the medium-voltage AC subgrid cause voltage fluctuations in the medium-voltage DC main grid, the DC/DC hydrogen production power supply adopts constant input DC voltage control + constant output current control to achieve the "load follows the source" control goal.

In this embodiment, each photovoltaic power station or wind power station adopts a constant power control mode. In this mode, the output voltage of the energy storage system is tracked through a phase-locked loop and only the output current is controlled. As shown in Figure 7, the DC in the photovoltaic power station /The AC inverter, the rotor-side converter of the doubly-fed induction generator of the wind turbine (or the machine-side converter of the permanent magnet direct-drive wind turbine) adopts the PI of active and reactive power in the constant power control mode. control. In the constant power control of the DC/AC inverter in the photovoltaic power station, P _s and Q _s are the active power output and reactive power output of the photovoltaic power station respectively. P _sref and Q _sref are the scheduling instructions and the active power of the given photovoltaic power station. Scheduling instructions for reactive power; the maximum power output capability P _smax of the current photovoltaic power station is calculated by the maximum power point tracking control (MPPT) as the maximum limit of P _sref , that is, P _sref is set to be less than P _smax to avoid the photovoltaic power station's impact on Frequent fluctuations in system output, the reactive power command Q _sref is set to 0, so that the reactive power output of the photovoltaic power station remains at 0; the differences between P _s and P _sref , Q _s and Q _sref are passed through the PI controller as the photovoltaic power station. The d-axis current reference command i _sdref and q-axis current reference command i _sqref of the DC/AC inverter, i _sd and i _sq are the components of the output current of the DC/AC inverter in the d-axis and q-axis respectively, The differences between i _sd and i _sdref , i _sq and i _sqref are respectively passed through the PI controller, and then the d-axis output voltage feedforward term u _sd and q-axis output voltage feedforward term u of the DC/AC inverter are added respectively. _sq , the output voltage u _sdref and u _sqref are the d-axis and q-axis modulated voltage signals of the DC/AC inverter.

When the generator in the wind turbine is a doubly-fed induction generator, in the control of the rotor side converter, P _w and Q _w are the active power output and reactive power output of the wind turbine respectively, and P _wref and Q _wref are respectively Given the active power dispatching instruction and reactive power dispatching instruction; the maximum power output capability P _wmax of the current wind turbine is calculated by the maximum power point tracking control (MPPT) as the maximum limit of P _wref , that is, setting P _wref less than P _wmax , to avoid frequent fluctuations in the system output from wind power stations, the reactive power command Q _wref is set to 0, so that the reactive power output of the wind turbine remains at 0; the differences between P _w and P _wref , Q _w and Q _wref are respectively The output results i _wdref and i _wqref after passing through the PI controller are the d-axis current reference command and q-axis current reference command of the rotor-side converter respectively. The components of the output current of the rotor-side converter in the dq axis are i _wd respectively. and i _wq , the differences between i _wd and i _wdref , i _wq and i _wqref are passed through the PI controller, the output results are subtracted and added to ω _s [-L _m U _s /(ω _e L _s )+σL _r respectively i _wd ] and ω _s σL _r i _wd , the modulated voltage signals u _wdref and u _wqref on the dq axis of the rotor side converter are obtained, where ω _s and ω _e are the slip angular velocity and synchronous angular velocity respectively, and L _s is the dq axis. Stator self-inductance, L _r is the dq-axis rotor self-inductance, L _m is the mutual inductance of the dq-axis stator and rotor equivalent windings, σ is the generator leakage coefficient, and U _s is the stator voltage.

When the generator in the wind turbine is a permanent magnet direct-drive wind turbine, in the constant power control of the machine-side converter, P _g and Q _g are the active power output and reactive power output of the wind turbine respectively, P _gref and Q _grref are the given active power scheduling instructions and reactive power scheduling instructions respectively; the maximum power output capability P _gmax of the current wind turbine is calculated by maximum power point tracking control. As the maximum limit of P _gref , set P _gref less than P _gmax , the reactive power command Q _gref is set to 0, so that the reactive power output of the wind turbine remains at 0; the differences between Q _g and Q _gref , P _g and P _gref are respectively the output results i _gdref and i after passing through the PI controller _gqref are the d-axis current reference command and q-axis current reference command of the machine-side converter respectively. The components of the output current of the machine-side converter in the d-axis and q-axis are i _gd and i _gq respectively, i _gd and i _gdref , the difference between i _gq and i _gqref is passed through the PI controller, the output results are subtracted and added respectively (ω _g L _fq i _gq -R _f i _gd ) and (R _f i _gq +ω _g L _fd i _gd + ω _g ψ _f ), the d-axis and q-axis modulated voltage signals u _gdref and u _gqref of the machine-side converter are obtained, where ω _g is the synchronous angular velocity, R _f is the stator resistance, L _fd and L _fq are the stator dq axis inductance , ψ _f is the rotor flux linkage.

As shown in Figure 8, the energy storage device adopts voltage rise constant frequency control. P _ref and P are the active power reference command and actual active power output of the energy storage device respectively; L ₁ and C ₁ are the AC side inductance and capacitance; u _pd , u _pq are respectively the dq-axis components of the three-phase voltage u _pa , u _pb , and u _pc on the output side of the converter in the energy storage device shown in Figure 4, which are obtained by dq transformation, u _pdref and u _{pqref are the d-axis and u pqref} respectively. The q-axis voltage reference command is set to a constant value; i _pd and i _pq are respectively the three-phase current i _pa , i pb and i pc of the three-phase current i pa, i _pb and i _pc on the output side of the converter in the energy storage device shown in Figure 4, which are converted by dq. axis component. In the voltage rise constant frequency control mode, the converter in the energy storage device adopts double closed-loop control under the dq axis. The outer loop of the double closed-loop control adopts voltage PI control. The voltage rise refers to the introduction of active power PI into the voltage outer loop of the d-axis. Control, the PI control of active power compares the active power output P of the energy storage system with P _ref . The difference result u _pf after passing through the PI controller is used as the feedback of the voltage outer loop. The voltage outer loop separates u on the dq axis. Compare _pd with u _pdref and u _pq with u _pqref . The difference between u _pdref and u _pd on the voltage outer ring of the d-axis minus u _pf and passed through the PI controller is subtracted from the cross-coupling term ωC ₁ u _pq . The d-axis current command value i _pdref , the difference between u _pqref and u _pq on the q-axis voltage outer ring is added to the cross-coupling term ωC ₁ u _pd after passing through the PI controller, and the q-axis current command value i _pqref is obtained. Active power The addition of the power adjustment link makes the voltage PI control's adjustment of the converter output voltage affected by the droop characteristics of power transmission. The medium voltage AC subgrid voltage changes with the system power flow under the voltage PI control. Setting P _ref to 0 makes the energy storage system The active power output of is maintained at 0; in the inner loop current PI control, the difference between i _pdref and i _pd on the d-axis current inner loop is added to the cross-coupling term ωL ₁ i _pq after passing through the PI controller to obtain the d-axis Modulation voltage command value u _d , the difference between i _pqref and i _pq on the q-axis current inner loop is subtracted from the cross-coupling term ωL ₁ i _pd after passing through the PI controller to obtain the q-axis modulation voltage command value u _q ; u _q and u _d are then subjected to dq transformation to obtain the modulated wave signals u _a , u _b and u _c controlled by SVPWM; constant frequency means that the output voltage frequency f of the converter in the energy storage device is directly set to a constant value, and the synchronous rotation angle (dq transformation angle) only changes with time t, and ω is the angular velocity.

As shown in Figure 9, in the constant input DC voltage + constant output current control mode of the DC/DC hydrogen production power supply, the inverter in the DC/DC hydrogen production power supply adopts double closed-loop control, and the outer loop of the double closed-loop control adopts voltage PI control. To stabilize the capacitor voltage at the DC input terminal, the voltage outer loop compares the capacitor voltage value U ₁ at the DC input terminal with the constant voltage reference value U _ref , and the difference is passed through the PI controller to output the DC current command value I _1ref , double closed-loop control The inner loop uses current PI control to stabilize the output current of the DC/DC hydrogen production power supply. The current inner loop collects the output DC current I ₁ and I _1ref of the DC/DC hydrogen production power supply for comparison, and the difference is passed through the PI controller as SVPWM control signal.

In the above embodiments, each embodiment is described with its own emphasis. For parts that are not detailed or documented in a certain embodiment, please refer to the relevant descriptions of other embodiments.

The above-described embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still implement the above-mentioned implementations. The technical solutions described in the examples are modified, or some of the technical features are equivalently replaced; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions in the embodiments of this application, and should be included in within the protection scope of this application.

Claims (7)

1. A large-capacity off-grid wind-solar complementary hydrogen production DC microgrid, which is characterized by: including m medium voltage AC subnets, medium voltage DC distribution boards, k DC/DC hydrogen production power sources, r DC/AC inverters Transformer power supply and low-voltage AC network power supply; each medium-voltage AC subnetwork is connected to the medium-voltage DC distribution board through the corresponding transformer rectifier device, and the input ends of the k DC/DC hydrogen production power supplies are respectively connected to the corresponding medium-voltage DC distribution board. The circuit breaker _Bk is connected to the medium-voltage DC distribution board, the output end of each DC/DC hydrogen production power supply is connected to an electrolyzer, and the input ends of the r DC/AC inverter power supplies pass through the corresponding medium-voltage DC circuit breaker. B _k is connected to the medium-voltage DC distribution board, and the output end of each DC/AC inverter power supply supplies power to the low-voltage AC network;

   Each medium-voltage AC subnetwork includes new energy stations, energy storage devices and medium-voltage AC distribution boards. New energy stations and energy storage devices are connected to the medium-voltage AC distribution board through AC circuit breakers _Sk ; medium-voltage AC An AC circuit breaker _Sk is connected between the distribution board and the transformer rectifier device, and a medium-voltage DC circuit breaker B _k is connected between the transformer rectifier device and the medium-voltage DC distribution board; the low-voltage AC network includes a low-voltage AC distribution board and several electrical loads, the output end of each DC/AC inverter power supply is connected to the low-voltage AC distribution board through the AC circuit breaker _Sk , and the low-voltage AC distribution board is connected to the backup power supply through the AC circuit breaker _Sk ;

   The new energy station is a photovoltaic power station or a wind power station composed of several wind turbines. The solar photovoltaic array in the photovoltaic power station is boosted by a DC/AC inverter and transformer and then connected to the medium voltage AC distribution board. The direct output voltage of the stator of the fed wind turbine is boosted by a transformer and then connected to the medium voltage AC distribution board or the permanent magnet direct drive wind turbine in the wind turbine. The output voltage of the back-to-back full power converter is boosted by a transformer and then connected to the medium voltage. AC distribution board;

   The control method of the large-capacity off-grid wind-solar complementary hydrogen production DC microgrid:

   The hydrogen production system adjusts the output of the photovoltaic power station or wind turbine to the system according to the dispatching instructions;

   The bidirectional energy storage converter in the energy storage device adopts voltage rising constant frequency control to keep the system frequency of the medium voltage AC subnet unchanged and the active power output of the energy storage device to be 0;

   Transformer rectifier device converts AC into DC;

   Under constant input DC voltage control, the DC/DC hydrogen production power supply compares the DC input terminal capacitor voltage with a constant voltage reference value. After PI control, the DC input terminal capacitor voltage is maintained stable. Under constant output current control, the DC/DC hydrogen production power supply The hydrogen power supply adjusts the output current according to the change of the capacitor voltage at the DC input end. Through the adjustment of the output DC current, the system load is automatically adjusted as the new energy output changes;

   Among them, in the voltage rise constant frequency control mode, the converter in the energy storage device adopts double closed loop control under the dq axis. The outer loop of the double closed loop control adopts voltage PI control. The voltage rise refers to the introduction of active power into the voltage outer loop of the d axis. PI control; constant frequency means that the output voltage frequency f of the converter in the energy storage device is directly set to a constant value, and the synchronous rotation angle only changes with time t.
2. The large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to claim 1, characterized in that: the voltage transformation and rectification device includes a rectifier transformer and a rectifier, and the rectifier transformer adopts two primary sides that are phase-shifted by +7.5° and -7.5° 12-pulse rectifier transformer. The rectifier uses four sets of full-wave uncontrolled rectifier bridges.
3. The large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to claim 1, characterized in that: the energy storage device consists of a bidirectional energy storage converter, a battery system and a transformer, and the bidirectional energy storage converter adopts a belt The three-phase two-level voltage source type SVPWM converter structure of AC side inductance and capacitance, the DC side of the bidirectional energy storage converter is connected to the battery system, and the on-off control of IGBT devices S _D1 -S _D6 is realized. The electric energy converted from DC to AC is boosted by the transformer and connected to the medium voltage AC distribution board through the AC circuit breaker.
4. The large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to claim 1, characterized in that: the DC/DC hydrogen production power supply includes a single-phase diode clamped three-level inverter, a transformer and a single-phase bridge. type rectifier; the DC/AC inverter power supply includes a DC/AC inverter and a transformer. The DC/AC inverter consists of three single-phase diode clamped three-level inverters and three single-phase transformers. composition.
5. The large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to claim 1, characterized in that: the DC/AC inverter in the photovoltaic power station, the rotor side converter of the doubly-fed wind turbine of the wind turbine unit, or The machine-side converter of the permanent magnet direct-drive wind turbine adopts PI control of active and reactive power in the constant power control mode; in the constant power control of the DC/AC inverter in the photovoltaic power station, P _s and Q _s respectively are the active power output and reactive power output of the photovoltaic power station, P _sref and Q _sref are the active power scheduling instructions and reactive power scheduling instructions of the given photovoltaic power station; the maximum power output of the current photovoltaic power station is calculated by maximum power point tracking control Capacity P _smax , as the maximum limit of P _sref , set P _sref less than P _smax , set the reactive power command Q _sref to 0, so that the reactive power output of the photovoltaic power station remains at 0; P _s and P _sref , Q _s and The difference of Q _sref is passed through the PI controller as the d-axis current reference command i _sdref and q-axis current reference command i _sqref of the DC/AC inverter in the photovoltaic power station. i _sd and i _sq are respectively the DC/AC inverter. The components of the output current of the inverter on the d-axis and q-axis, the differences between i _sd and i _sdref , i _sq and i _sqref are respectively passed through the PI controller, and then the output voltage of the DC/AC inverter on the d axis is added to each. The feedforward term u _sd and the output voltage feedforward term u _sq of the q-axis, the output voltages u _sdref and u _sqref are the dq-axis modulated voltage signals of the DC/AC inverter;

   In the constant power control of the doubly-fed wind turbine rotor side converter in the wind turbine, P _w and Q _w are the active power output and reactive power output of the wind turbine respectively, and P _wref and Q _wref are given Active power dispatching instructions and reactive power dispatching instructions; the maximum power output capability P _wmax of the current wind turbine is calculated by maximum power point tracking control. As the maximum limit of P _wref , set P _wref less than P _wmax , and the reactive power instruction Q _wref is set to 0, so that the reactive power output of the wind turbine remains at 0; the output results i _wdref and i _wqref of the differences between P _w and P _wref , Q _w and Q _wref respectively after passing through the PI controller are respectively the rotor side converter current The d-axis current reference command and q-axis current reference command of the rotor side converter. The components of the output current of the rotor side converter in the dq axis are i _wd and _{i wq} respectively. The differences between i wd and i _wdref , i _wq and i _wqref are calculated by After the PI controller, the output results are subtracted and added to ω _s [-L _m U _s /(ω _e L _s ) + σL _r i _wd ] and ω _s σL _r i _wd respectively, and the rotor side converter is obtained in dq The active modulated voltage signal u _wdref and the reactive modulated voltage signal u _wqref on the shaft, where ω _s and ω _e are the slip angular velocity and synchronous angular velocity respectively, L _s is the dq-axis stator self-inductance, and L _r is the dq-axis rotor self-inductance , L _m is the mutual inductance of the equivalent winding of the dq-axis stator and rotor, σ is the magnetic leakage coefficient of the generator, and U _s is the stator voltage;

   In the constant power control of the machine-side converter of the permanent magnet direct-drive wind turbine in the wind turbine, P _g and Q _g are the active power output and reactive power output of the wind turbine respectively, and P _gref and Q _gref are respectively Given active power scheduling instructions and reactive power scheduling instructions; calculate the maximum power output capability P _gmax of the current wind turbine through maximum power point tracking control, as the maximum limit of P _gref , set P _gref less than P _gmax , reactive power The power command Q _gref is set to 0, so that the reactive power output of the wind turbine remains at 0; the difference between Q _g and Q _gref , P _g and P _gref respectively passes through the PI controller, and the output results i _gdref and i _gqref are respectively the machine The d-axis current reference command and q-axis current reference command of the side converter, the components of the output current of the machine-side converter in the d-axis and q-axis are i _gd and i _gq respectively, i _gd and i _gdref , i _gq and After the difference of i _gqref passes through the PI controller, the output results are subtracted and added to (ω _g L _fq i _gq -R _f i _gd ) and (R _f i _gq +ω _g L _fd i _gd +ω _g ψ _f ), obtain the d-axis and q-axis modulated voltage signals u _gdref and u _gqref of the machine-side converter, where ω _g is the synchronous angular velocity, R _f is the stator resistance, L _fd and L _fq are the stator dq axis inductance, and ψ _f is Rotor flux linkage.
6. The large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to claim 1, characterized in that: in the voltage rise constant frequency control mode of the energy storage device, the converter in the energy storage device adopts dq-axis double closed-loop control , the outer loop of the double closed-loop control adopts voltage PI control. The voltage rise refers to the introduction of active power PI control into the voltage outer loop of the d-axis. The PI control of active power compares the active power output P of the energy storage system with P _ref . The result u _pf of the difference after passing through the PI controller is used as the feedback of the voltage outer loop. The voltage outer loop compares u _pd with u _pdref and u _pq with u _pqref on the dq axis respectively. On the voltage outer loop of the d axis, u _pdref and After subtracting u _pf from the difference of u _pd and passing through the PI controller, it is subtracted from the cross coupling term ωC ₁ u _pq to obtain the d-axis current command value i _pdref , and the difference between u _pqref and u _pq on the q-axis voltage outer ring. After passing through the PI controller, the q-axis current command value i _pqref is obtained after adding the cross-coupling term ωC ₁ u _pd . The addition of the active power adjustment link makes the voltage PI control's adjustment of the converter output voltage affected by the droop characteristics of power transmission. Influence, under voltage PI control, the voltage of the medium-voltage AC subgrid changes with the system power flow. Setting P _ref to 0 keeps the active power output of the energy storage system at 0; in the inner loop current PI control, the current inner loop of the d-axis After the difference between i _pdref and i _pd passes through the PI controller, it is added to the cross coupling term ωL ₁ i _pq to obtain the d-axis modulation voltage command value u _d . The difference between i _pqref and i _pq on the q-axis current inner loop is After the PI controller, the q-axis modulation voltage command value u _q is obtained by subtracting the cross-coupling term ωL ₁ i _pd ; u _q and u _d are then transformed by dq to obtain the modulated wave signals u _a , u _b and u _c controlled by SVPWM; Constant frequency means that the output voltage frequency f of the converter in the energy storage device is directly set to a constant value, and the synchronous rotation angle only changes with time t;

   Among them, P _ref and P are the active power reference command and actual active power output of the energy storage device respectively; L ₁ and C ₁ are the AC side inductance and capacitance; u _pd and u _pq are the output side of the converter in the energy storage device respectively. The dq-axis components of the three-phase voltage u _pa , u _pb , u _pc obtained by dq transformation, u _pdref and u _pqref are the d-axis and q-axis voltage reference commands respectively, which are set to constant values; i _pd and i _pq are storage respectively. The dq axis component obtained by dq transformation of the three-phase current i _pa , i _pb , and i _pc on the output side of the converter in the energy device; ω is the angular velocity.
7. The large-capacity off-grid wind-solar complementary hydrogen production DC microgrid according to claim 1, characterized in that: in the constant input DC voltage + constant output current control mode of the DC/DC hydrogen production power supply, the DC/DC hydrogen production power supply The mid-inverter adopts double closed-loop control. The outer loop of the double-closed loop control adopts voltage PI control to stabilize the capacitor voltage at the DC input end. The voltage outer loop compares the capacitor voltage value U ₁ at the DC input end with the constant voltage reference value U _ref . The difference outputs the DC current command value I _1ref after passing through the PI controller. The inner loop of the double closed-loop control uses current PI control to stabilize the output current of the DC/DC hydrogen production power supply. The current inner loop collects the output of the DC/DC hydrogen production power supply. The DC current I ₁ is compared with I _1ref , and the difference is used as the control signal of SVPWM after passing through the PI controller.

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