Wide-input converter topological structure and control method thereof

Abstract

The invention relates to a wide-input converter topological structure and a control method thereof, and the structure comprises a DC side structure which is used for connecting a DC power grid, a DC power supply or a DC load; the AC side structure is used for connecting an AC power grid, an AC power supply or an AC load. According to the invention, the residual energy stored by the super capacitor can be fully utilized, the distribution and storage demand is reduced, and the energy storage support time is prolonged. Renewable energy can be ensured to continuously generate power under the condition of low input of new energy such as wind and light, and the utilization rate of the new energy is improved. The wide-input converter can adopt a network following or network construction control method, when the network construction control method is adopted, the voltage and frequency of the power grid can be supported, and the stability of the new energy access power grid system is improved. The method can be widely applied to the technical field of converter control.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and in particular to a wide-input converter topology structure and a control method thereof. Background Art

[0002] In recent years, the new energy industry has been given equal importance to both land and sea, and the wind power and solar power generation industries have been promoted on a large scale. Various new energy projects such as smart photovoltaics, offshore wind power, wind-solar complementarity, biomass power generation, temperature difference power generation, and wave power generation have been launched one after another. With the continuous development of the new energy industry and the continuous increase in the proportion of new energy, the traditional power system has developed into a new power system with the "double high" characteristics of a high proportion of new energy and a high proportion of power electronic equipment. In order to ensure the stable operation of the new power system, grid-type converters and energy storage systems have become necessary equipment to ensure the transient and steady-state balance and power balance under the access of a high proportion of new energy and a high proportion of power electronic equipment to the power grid system.

[0003] Inverter equipment has been widely used in the fields of wind power generation, photovoltaic power generation, energy storage systems, etc. In the wind power grid-connected system, wind energy is converted into AC power through wind turbines, and AC power is converted into DC power through rectifiers. The DC power obtained is further inverted into AC power that meets the grid connection conditions through grid-connected converters and connected to the grid system. In the photovoltaic grid-connected system, light energy generates DC power through photovoltaic panels. The DC power obtained is usually controlled by MPPT (Maximum power point tracking) to invert the maximum DC power generated by the photovoltaic voltage panel into AC power through grid-connected converters and connected to the grid system. In the energy storage system, the energy storage power supply provides DC power, and inverter equipment is also required to invert DC power into AC power and connect it to the AC grid. In new energy fields such as wind power, photovoltaics, energy storage, biomass power generation, temperature difference power generation, wave power generation, etc., the electric energy generated by renewable energy through conversion equipment is only in two forms: AC and DC. In the process of grid connection, these two forms of electric energy are usually converted into DC electric energy first, and then inverted by the grid-connected converter equipment to obtain AC electric energy to supply power to the AC grid. Therefore, in the above new energy fields, the converter is an important equipment for electric energy conversion and grid connection.

[0004] The typical three-phase converter topology is as follows: Figure 1 The traditional three-phase full-bridge structure shown in FIG. 1 can realize the conversion function of DC power to three-phase AC power. In a typical three-phase converter topology, each bridge arm has two controllable switching devices, capacitors, and C 1. One side is the DC side of the converter, the inductor L 1. L 2. LThe 3 side is the AC side of the converter. By performing PWM (Pulse-Width Modulation) control on the six switching devices in the three bridge arms, the DC side electric energy can be inverted into the AC side electric energy. The typical PWM control methods of the switching devices are SPWM (Sinusoidal Pulse Width Modulation) control and SVPWM (Space Vector Pulse Width Modulation) control. The closed-loop control of this typical three-phase converter can adopt a grid-following control method or a grid-forming control method. When the grid-following control method is adopted, the converter presents a current source characteristic, and the converter transmits electric energy to the grid based on the power current value; when the grid-forming control method is adopted, the converter presents a voltage source characteristic, and the converter provides voltage frequency support to the grid based on the voltage frequency value and transmits electric energy.

[0005] In the above typical three-phase converter under SPWM control mode, the maximum voltage utilization rate is about 0.866, that is, the three-phase AC side line voltage and the DC side voltage meet the following voltage conversion ratio range:

[0006] in, M 0SPWM is the voltage conversion ratio of a typical three-phase converter.

[0007] In the above typical three-phase converter under SVPWM control mode, the maximum voltage utilization rate is 1, that is, the three-phase AC side line voltage and the DC side voltage meet the following voltage conversion ratio range:

[0008] in, M 0SVPWM is the voltage conversion ratio of a typical three-phase converter.

[0009] Due to the limitation of voltage conversion ratio, under the premise of certain grid voltage, when the voltage on the DC side of the converter is lower than a certain value, the converter will not work properly. Therefore, in the case of new energy grid connection, when the power generation of renewable energy such as wind power and solar power or the output voltage of energy storage is lower than a certain value, the new energy grid connection system will stop generating power. However, wind and solar resources are highly volatile, and energy storage systems with supercapacitors as the medium also have a large output voltage range due to their state of charge. This will result in a large amount of wind and solar abandonment resource waste in the case of using typical converter equipment. Energy storage grid connection systems represented by supercapacitors will lead to a significant increase in the demand for energy storage capacity.

[0010] To solve the above problems, a typical optimization solution is to add a boost converter link in the front stage of the typical three-phase converter to adapt to the wide range of DC side voltage input. The typical three-phase converter topology with the front stage boost converter is as follows: Figure 2 As shown. The latter stage of this topology still uses a typical three-phase converter topology, and the former stage uses a Boost converter for DC boost conversion, thereby reducing the DC voltage required on the DC side of the converter, and realizing the effective use of renewable energy under low wind and solar input conditions and supercapacitor energy storage systems under low charge conditions. The switch device of the former stage Boost converter adopts PWM control, and its typical closed-loop control is a voltage and current dual closed-loop control method.

[0011] In the above typical three-phase converter with a pre-stage Boost converter, under the SPWM control mode, the three-phase AC side line voltage and the DC side voltage meet the following voltage conversion ratio range:

[0012] in, M 1SPWM The voltage conversion ratio of a typical three-phase converter with a front-stage Boost converter is introduced.

[0013] In the above typical three-phase converter with a front-stage Boost converter, the maximum voltage utilization rate is 1 under the SVPWM control mode, that is, the three-phase AC side line voltage and the DC side voltage meet the following voltage conversion ratio range:

[0014] in, M 1SVPWM The voltage conversion ratio of a typical three-phase converter with a front-stage Boost converter is introduced.

[0015] However, affected by parasitic parameters, the boost capability of the pre-boost converter is limited, and under extreme duty cycle conditions, the efficiency and transient response performance of the pre-boost converter will drop significantly. Therefore, the duty cycle of the pre-boost converter switch S1 is usually limited to 0.8-0.9, and the typical boost ratio of the pre-boost converter does not exceed 6-8 times. Therefore, constructing a converter topology with a wider input range and its control method is an effective way to improve the utilization rate of new energy, reduce the demand for supercapacitor energy storage, reduce the investment cost of new energy grid connection, and increase the power generation of new energy. Summary of the invention

[0016] In view of the above problems, the purpose of the present invention is to provide a wide-input converter and a control method thereof. The wide-input converter has a wide input characteristic, which can make full use of the surplus energy stored in the supercapacitor, and at the same time ensure that renewable energy continues to generate electricity under low wind and solar power input conditions, thereby improving the utilization rate of new energy.

[0017] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a wide input converter topology structure, comprising: a DC side structure for connecting to a DC grid, a DC power supply or a DC load; an AC side structure for connecting to an AC grid, an AC power supply or an AC load; The DC side structure adopts a three-phase bridge arm structure, which includes a first bridge arm, a second bridge arm and a third bridge arm, the first bridge arm is provided with a first switch device and a second switch device; the second bridge arm is provided with a third switch device and a first capacitor; the third bridge arm is provided with a second capacitor and a third capacitor; Also includes a first inductor, a second inductor and a fourth switching device; The first ends of the first inductor and the second inductor are connected in parallel and connected to the positive electrode of a DC grid, a DC power supply or a DC load; the first end of the first switching device is connected to the second end of the second switching device and then connected to the second end of the second inductor; the first end of the first capacitor is connected in parallel to the first end of the second switching device and then connected to the second end of the fourth switching device; the second end of the first capacitor is connected to the first end of the third switching device and then connected to the second end of the first inductor; the first end of the fourth switching device is connected to the first end of the second capacitor; the second end of the second capacitor is connected to the first end of the third capacitor; the second end of the first switching device, the second end of the third switching device, and the second end of the third capacitor are connected and then connected to the negative electrode of a DC grid, a DC power supply or a DC load.

[0018] Further, the AC side structure adopts a three-phase bridge arm structure, which includes a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; the fourth bridge arm is provided with a fifth switch device and a sixth switch device; the fifth bridge arm is provided with a seventh switch device and an eighth switch device; the sixth bridge arm is provided with a ninth switch device and a tenth switch device; The AC side structure also includes a third inductor, a fourth inductor and a fifth inductor; The first end of the fifth switch device is connected to the second end of the sixth switch device and then connected to the first end of the fifth inductor; the first end of the seventh switch device is connected to the second end of the eighth switch device and then connected to the first end of the fourth inductor; the first end of the ninth switch device is connected to the second end of the tenth switch device and then connected to the first end of the third inductor; The first end of the sixth switch device, the first end of the eighth switch device, and the first end of the tenth switch device are connected to the first end of the fourth switch device and the first end of the second capacitor; The second end of the fifth switch device, the second end of the seventh switch device, and the second end of the ninth switch device are connected, and then connected to the second end of the first switch device, the second end of the third switch device, and the second end of the third capacitor; The second end of the fifth inductor is connected to phase a of an AC power grid, an AC power source or an AC load; The second end of the fourth inductor is connected to the b phase of the AC power grid, AC power supply or AC load; The second end of the third inductor is connected to the C phase of the AC power grid, the AC power source or the AC load.

[0019] Furthermore, the first end of the first to third capacitors is the positive electrode of the capacitor, and the second end is the negative electrode of the capacitor.

[0020] Furthermore, the first to tenth switch devices are also connected to respective drive circuits via third terminals, respectively.

[0021] In a second aspect, the present invention provides a method for controlling a DC side structure of a wide input converter, comprising the following steps: According to actual needs, the closed-loop control strategy of the DC side structure is determined to be a voltage-current dual-loop control strategy; at the same time, the DC side switch control mode is selected as a PWM control mode; According to the grid connection requirements, the closed-loop control strategy of the AC side structure is determined to be a grid-following control strategy or a grid-building control strategy; at the same time, according to the voltage conversion ratio requirements of the converter, the AC side switch control mode is determined to be an SPWM control mode or an SVPWM control mode; Based on a determined closed-loop control strategy and a control method of the switch device, each switch device in the wide input converter topology is controlled.

[0022] Furthermore, in the PWM control mode, the duty ratio of the control signals of the first switch device and the third switch device is D , the control signal of the third switching device lags the control signal of the first switching device by 180°; The second switch device and the fourth switch device are respectively complementary to the control signals of the first switch device and the third switch device, and the duty ratios of the second switch device and the fourth switch device are both 1- D , the control signal of the fourth switching device lags the control signal of the second switching device by 180°.

[0023] Furthermore, the control signal duty ratios of the first switching device and the third switching device are DThe range of is greater than 0.5 and less than the limit duty cycle; wherein the value range of the limit duty cycle is between 0.8 and 0.9.

[0024] Furthermore, in the voltage-current dual-loop closed-loop control strategy adopted by the DC side structure, the current sampling of the current loop is the DC side current, and the voltage sampling of the voltage loop is the sum of the voltages of the second capacitor and the third capacitor.

[0025] Furthermore, in the closed-loop control strategy adopted by the AC side structure, the current sampling of the current loop is the current of the third to fifth inductors, and the voltage sampling of the voltage loop is the three-phase voltage of the AC side a, b, and c.

[0026] Furthermore, the voltage conversion ratio range of the switch device in the AC side structure under the SPWM control mode is:

[0027] in, M SPWM It is the ratio of the AC side power supply or load line voltage to the DC side load or voltage of the wide input converter under SPWM control mode; The voltage conversion ratio range under SVPWM control is:

[0028] in, M SVPWM It is the ratio of the AC side power supply or load line voltage to the DC side load or voltage of the wide input converter under SVPWM control mode.

[0029] The present invention adopts the above technical solution, which has the following advantages: 1. The wide-input grid-connected converter proposed in the present invention has a wide-input characteristic, which can make full use of the surplus energy of supercapacitor energy storage, reduce the storage demand, and extend the energy storage support time.

[0030] 2. The present invention can ensure that renewable energy continues to generate electricity under low wind and solar power input conditions, thereby improving the utilization rate of new energy.

[0031] 3. The wide input converter proposed in the present invention can adopt a grid-following or grid-building control method. When the grid-building control method is adopted, it can support the grid voltage and frequency and improve the stability of the new energy access grid system.

[0032] Therefore, the present invention can be widely applied in the field of converter control technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings: Figure 1 It is a typical three-phase converter topology; Figure 2 It is a typical three-phase converter topology structure with a front-stage Boost converter introduced; Figure 3 A wide input converter topology structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of overall control of a wide input converter provided in an embodiment of the present invention; Figure 5 It is a PWM control signal of a DC-side switch device of a wide input converter provided in an embodiment of the present invention; Figure 6 The active and reactive power changes on the grid side provided in the embodiment of the present invention; Figure 7 The system frequency change provided in the embodiment of the present invention; Figure 8 is the AC side output voltage of the wide input converter provided in an embodiment of the present invention; Fig. 9 The instantaneous value of the three-phase voltage on the grid side provided in the embodiment of the present invention; Fig.10 The dq axis current of the wide input converter provided in the embodiment of the present invention; Fig.11 The instantaneous value of the three-phase current on the grid side provided in the embodiment of the present invention; Fig.12 is the grid line voltage amplitude of a typical three-phase converter solution provided in an embodiment of the present invention; Fig.13 is the phase voltage of a typical three-phase converter solution provided in an embodiment of the present invention; Fig.14 is the frequency of a typical three-phase converter solution provided in an embodiment of the present invention; Fig.15 The grid current of a typical three-phase converter solution provided in an embodiment of the present invention; Fig.16 The energy storage output of a typical three-phase converter solution provided in an embodiment of the present invention; Fig.17 The energy storage capacity of 8640MWs provided in the embodiment of the present invention is the voltage amplitude of the power grid line in a typical three-phase converter solution; Fig.18The energy storage capacity of 8640MWs provided in the embodiment of the present invention is the phase voltage of a typical three-phase converter solution; Fig.19 The energy storage capacity of 8640MWs provided in the embodiment of the present invention is at a typical three-phase converter solution frequency; Fig. 20 The energy storage capacity of 8640MWs provided in the embodiment of the present invention is the grid current in a typical three-phase converter solution; Fig.21 The energy storage capacity of 8640MWs provided in the embodiment of the present invention is the energy storage output of a typical three-phase converter solution; Fig. 22 The voltage amplitude of the power grid line of a typical three-phase converter solution introducing a front-stage Boost converter provided in an embodiment of the present invention; Fig.23 The phase voltage of a typical three-phase converter solution with a front-stage Boost converter provided in an embodiment of the present invention; Fig.24 The frequency of a typical three-phase converter solution with a front-stage Boost converter provided in an embodiment of the present invention; Fig.25 The grid current of a typical three-phase converter scheme introducing a front-stage Boost converter provided in an embodiment of the present invention; Fig.26 The energy storage output of a typical three-phase converter solution with a front-stage Boost converter provided in an embodiment of the present invention; Fig. 27 The grid line voltage amplitude of the three-phase converter solution with a typical introduction of a front-stage Boost converter in the energy storage capacity of 2430MWs provided in the embodiment of the present invention; Fig.28 The phase voltage of the three-phase converter scheme with a typical introduction of a front-stage Boost converter in an energy storage capacity of 2430MWs provided in an embodiment of the present invention; Fig.29 The energy storage capacity of 2430MWs provided in the embodiment of the present invention is at a typical three-phase converter scheme frequency with a front-stage Boost converter introduced; Fig.30 The grid current of the three-phase converter scheme with a typical introduction of a front-stage Boost converter in an energy storage capacity of 2430MWs provided in an embodiment of the present invention; Fig.31 The energy storage capacity of 2430MWs provided in the embodiment of the present invention is the energy storage output of a three-phase converter solution in which a front-stage Boost converter is typically introduced; Fig.32 The grid line voltage amplitude of the wide input converter solution provided in the embodiment of the present invention; Fig.33 The phase voltage of the wide input converter solution provided in the embodiment of the present invention; Fig.34 The frequency of the wide input converter solution provided in the embodiment of the present invention; Fig.35 The grid current of the wide input converter solution provided in the embodiment of the present invention; Fig.36 This is the energy storage output of the wide input converter solution provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] In some embodiments of the present invention, a wide input converter topology is provided, which includes: a DC side structure and an AC side structure, wherein the DC side structure is used to connect a DC grid, a DC power supply or a DC load; and the AC side structure is used to connect an AC grid, an AC power supply or an AC load. The wide input converter provided by the present invention has a wide input characteristic, which can make full use of the surplus energy of supercapacitor energy storage, reduce the storage demand, and extend the energy storage support time. Renewable energy can continue to generate electricity under low wind and solar energy input conditions, thereby improving the utilization rate of new energy. The proposed wide input converter can adopt a grid-following or grid-building control method. When the grid-building control method is adopted, it can support the grid voltage and frequency, and improve the stability of the new energy access grid system.

[0037] Correspondingly, in some other embodiments of the present invention, a control method for a wide input converter topology structure is provided.

[0038] Example 1 like Figure 3As shown, the present invention provides a wide input converter topology structure, which includes: a DC side structure for connecting a DC grid, a DC power supply or a DC load; and an AC side structure for connecting an AC grid, an AC power supply or an AC load.

[0039] Furthermore, the DC side structure adopts a three-phase bridge arm structure, which includes a first bridge arm, a second bridge arm and a third bridge arm, the first bridge arm is provided with a first switch device S1 and a second switch device S2; the second bridge arm is provided with a third switch device S3 and a first capacitor C 1; A second capacitor is provided on the third bridge arm C 2 and the third capacitor C 3.

[0040] Furthermore, the DC side structure also includes a first inductor L 1. Second inductor L 2. The fourth switch device S4. The first inductor L 1 and the second inductor L The first end of the first switch device S1 is connected in parallel with the second end of the second switch device S2 and then connected to the positive electrode of the second inductor. L 2 is connected to the second end; the first capacitor C The first end of the first capacitor 1 and the first end of the second switch device S2 are connected in parallel to the second end of the fourth switch device S4; C The second end of 1 is connected to the first end of the third switch device S3 and then to the first inductor L 1; the first end of the fourth switch device S4 is connected to the second capacitor C 2 is connected to the first end; the second capacitor C The second terminal of 2 and the third capacitor C 3; the second end of the first switch device S1, the second end of the third switch device S3, and the third capacitor C The second end of 3 is connected to the negative pole of the DC grid, the DC power supply or the DC load.

[0041] Furthermore, the first to third capacitors C 1~ C The first end of 3 is the positive electrode of the capacitor, and the first to third capacitors C 1~ C The second end of 3 is the negative electrode of the capacitor.

[0042] Furthermore, the AC side structure adopts a three-phase bridge arm structure, which includes a fourth bridge arm, a fifth bridge arm and a sixth bridge arm. The fourth bridge arm is provided with a fifth switch device S5 and a sixth switch device S6; the fifth bridge arm is provided with a seventh switch device S7 and an eighth switch device S8; the sixth bridge arm is provided with a ninth switch device S9 and a tenth switch device S10 .

[0043] Furthermore, the AC side structure also includes: a third inductor L 3. The fourth inductor L 4. Fifth Inductor L 5. The first end of the fifth switch device S5 is connected to the second end of the sixth switch device S6 and then connected to the fifth inductor L 5; the first end of the seventh switch device S7 and the second end of the eighth switch device S8 are connected to the fourth inductor L The first end of the ninth switch device S9 is connected to the first end of the tenth switch device S 10 The second end of the third inductor is connected to L 3; the first end of the sixth switch device S6, the first end of the eighth switch device S8, the tenth switch device S 10 The first end of the fourth switch device S4 is connected to the first end of the second capacitor C 2; the second end of the fifth switch device S5, the second end of the seventh switch device S7, and the second end of the ninth switch device S9 are connected to the second end of the first switch device S1, the second end of the third switch device S3, and the third capacitor C The second end of 3 is connected to the fifth inductor L The second end of 5 is connected to the a phase of the AC grid, AC power supply or AC load; the fourth inductor L The second end of 4 is connected to the b phase of the AC grid, AC power supply or AC load; the third inductor L The second end of 3 is connected to the c phase of the AC grid, AC power supply or AC load.

[0044] Furthermore, the first to tenth switching devices S1 to S 10 They are also connected to respective driving circuits via the third terminals.

[0045] Furthermore, the first to tenth switching devices S1 to S 10 An N-channel field effect transistor MOSFET or an insulated gate transistor IGBT is used; when the first to tenth switching devices use an N-channel field effect transistor MOSFET, the first end of the first to tenth switching devices is the drain of the MOSFET, the second end is the source of the MOSFET, and the third end is the gate of the MOSFET; when the first to tenth switching devices are insulated gate transistors IGBT, the first end of the switching device is the collector of the IGBT, the second end is the emitter of the IGBT, and the third end is the gate of the IGBT.

[0046] Furthermore, in this embodiment, the wide input converter topology can realize bidirectional flow of energy. The second switch device S2 and the fourth switch device S4 can also be replaced with diode devices with the same direction as the parasitic diodes of the corresponding switch devices. In this case, the wide input converter can realize single-phase flow of energy, and the flow direction is from the DC side to the AC side of the converter; the first switch device S1 and the third switch device S3 can also be replaced with diode devices with the same direction as the parasitic diodes of the corresponding switch devices. In this case, the wide input converter can realize single-phase flow of energy, and the flow direction is from the AC side to the DC side of the converter.

[0047] Example 2 like Figure 4 As shown, based on the wide input converter topology structure provided in Example 1, this embodiment provides a control method for the wide input converter topology structure, which includes the following steps: According to actual needs, the DC side closed-loop control strategy is selected as the voltage and current dual-loop control strategy; at the same time, the DC side switch control mode is selected as the PWM control mode; According to the grid connection requirements, the AC side closed-loop control strategy is selected as the grid-following control strategy or the grid-building control strategy; at the same time, according to the converter voltage conversion ratio requirements, the AC side switch control mode is selected as the SPWM control mode or the SVPWM control mode; Based on a determined closed-loop control strategy and a control method of the switch device, each switch device in the wide input converter topology is controlled.

[0048] Furthermore, in this embodiment, the PWM control signal of the DC side switch device of the wide input converter is as follows: Figure 5 shown.

[0049] Furthermore, the duty ratio of the control signals of the first switching device S1 and the third switching device S3 is D , the control signal of the third switch device S3 lags the control signal of the first switch device S1 by 180°; the control signals of the second switch device S2 and the fourth switch device S4 are complementary to the control signals of the first switch device S1 and the third switch device S3, respectively, and the duty ratios of the second switch device S2 and the fourth switch device S4 are both 1− D , the control signal of the fourth switching device S4 lags behind the control signal of the second switching device S2 by 180°.

[0050] Furthermore, the duty ratio of the control signal of the first switching device S1 and the third switching device S3 is D The range of is greater than 0.5 and less than the limit duty cycle; according to practical experience, the limit duty cycle usually ranges from 0.8 to 0.9.

[0051] Furthermore, in the DC side voltage and current dual-loop closed-loop control strategy, the current sampling of the current loop is the DC side current, and the voltage sampling of the voltage loop is the sum of the voltages of the second capacitor C2 and the third capacitor C3.

[0052] Furthermore, in the AC side closed-loop control strategy, the current loop current sampling is the third to fifth inductor L 3~ L 5, and the voltage sampling of the voltage loop is the three-phase voltage of a, b, and c on the AC side; when the closed-loop control on the AC side is the grid-building control strategy, the wide-input converter presents a voltage source characteristic, which can provide AC voltage and frequency support for the AC grid or AC load; when the closed-loop control on the AC side is the grid-following control strategy, the wide-input converter presents a current source characteristic, which can provide active and reactive power for the AC grid.

[0053] Furthermore, since the three-phase bridge arm on the AC side is the same as a typical three-phase full-bridge circuit, its control method can directly adopt the existing three-phase full-bridge SPWM control or SVPWM control, which is not elaborated in the present invention.

[0054] Furthermore, the voltage conversion ratio range of the AC side switch device under the SPWM control mode is:

[0055] in, M SPWM It is the ratio of the AC side power supply or load line voltage to the DC side load or voltage of the wide input converter under SPWM control mode.

[0056] Furthermore, the voltage conversion ratio range of the AC side switch device under the SVPWM control mode is:

[0057] in, M SVPWM It is the ratio of the AC side power supply or load line voltage to the DC side load or voltage of the wide input converter under SVPWM control mode.

[0058] It can be seen that compared with Figure 1 The typical three-phase converter topology shown in Figure 2 The typical three-phase converter topology structure with the front-stage Boost converter is shown in FIG. Figure 3 The wide input converter topology shown has a larger converter voltage conversion ratio range when the AC side switch device adopts the same control method. Under the operating condition of a certain AC side voltage, the DC side of the wide input converter described in this example can allow a lower voltage input. Therefore, the wide input converter described in this example has a wider voltage input range.

[0059] Example 3 In this embodiment, a wide-input converter topology, an SPWM switch control strategy, and a grid-forming closed-loop control strategy are adopted, and a supercapacitor energy storage grid-connected scenario is used. By comparing with a typical three-phase converter and a typical converter with a front-stage Boost converter under the same SPWM switch control strategy and grid-forming closed-loop control strategy, the superiority of the wide-input converter topology proposed in the present invention is illustrated.

[0060] In the typical implementation of the supercapacitor energy storage grid-connected system, the DC side input voltage is 60kV, the total capacity of the supercapacitor is 1800MWs, and the energy storage support time is 6s. The energy storage support capacity under different converter topology schemes is compared by using a short-time simulation method to simulate the long-term energy storage support characteristics. The converter inductance is 2mH, the switch device on-resistance is 0.05Ω, and the freewheeling diode on-resistance is 0.01Ω. The grid-side line voltage is 170kV, the phase voltage is 100kV, the line impedance is 0.001Ω, and the converter three-phase filter capacitor is 8uF. The equivalent three-phase resistance of the power grid is set to 100Ω, and the inductance is set to 0.01H. It is assumed that the grid load increases suddenly after 5s, and the load power increase is equivalent to a resistive-inductive load with a parallel resistance of 100Ω and an inductance of 0.01H.

[0061] In the typical implementation of the supercapacitor energy storage grid-connected system, the proposed wide input converter is under the SPWM switch control mode and the grid closed-loop control mode, and the grid side active and reactive power changes are as follows: Figure 6 As shown. At 5s, the grid load suddenly increases from 150MW to about 300MW. From the simulation results, it can be seen that before 5s, the active load of the grid was 150MW, and it suddenly increased to 300MW at 5s. After the load power suddenly changed, the grid can still maintain stable operation. It can be seen that the proposed wide input converter has the ability to support the grid under the grid control method. The system frequency changes as shown in Figure 7 As shown. 5s ago, the system frequency was maintained at a given value of 50Hz. After the grid load suddenly changed at 5s, the frequency dropped to 49.88Hz. The proposed wide input converter can achieve the active-frequency droop control characteristics under the droop control mode. The AC side output phase voltage electromotive force amplitude, grid line voltage amplitude, and grid line voltage effective value of the wide input converter are shown in Figure 8 As shown. It can be seen that the proposed wide input converter can independently construct the output electromotive force through supercapacitor energy storage under the grid control mode, and reach the given value of 100kV. The line voltage amplitude on the grid side is about 170kV, and the effective value of the line voltage on the grid side is about 122kV. At 5s, the grid load suddenly increased to 300MW, and the output phase voltage electromotive force amplitude of the converter can still be stabilized at 100kV, realizing the zero-static error tracking of the voltage loop. The instantaneous value of the three-phase voltage on the grid side is shown in Fig. 9As shown in Figure 1, the three-phase voltage on the grid side is a sine wave with an amplitude of 100 kV and a phase difference of 120°. The dq axis current of the proposed wide input grid converter is as follows: Fig.10 As shown in the figure. When the grid load is 150MW, the d-axis current is stable at about 1kA. At 5s, the grid load suddenly increases to 300MW, and the converter dq-axis current stabilizes at a new equilibrium point after a very short transient process. At this time, the d-axis current is stable at about 2kA, achieving decoupling of the current loop and zero-static tracking. The instantaneous value of the three-phase current on the grid side is shown in the figure. Fig.11 As shown in the figure, the three-phase current on the grid side is a sine wave with an amplitude of about 1kA when the load is 150MW, and it is a sine wave with an amplitude of about 2kA when the load suddenly changes to 300MW in 5s. In terms of amplitude, the current can follow the change of load and remain stable. In terms of current waveform and phase, the three-phase current on the grid side can still remain a sine wave with a phase difference of 120°.

[0062] The above simulation results demonstrate the effectiveness of the proposed wide input converter under the SPWM switch control and grid-forming closed-loop control strategy in the typical case. Furthermore, under this typical control mode, the proposed wide input converter is compared with the typical three-phase converter and the typical three-phase converter with the introduction of the front-stage Boost converter in the supercapacitor energy storage system. The beneficial effect of the typical case is explained.

[0063] In the supercapacitor energy storage grid-connected system, a typical three-phase converter topology is adopted, and the grid line voltage amplitude, phase voltage, frequency, current and energy storage output are as follows: Fig.12 , Fig.13 , Fig.14 , Fig.15 , Fig.16 As shown. After all generators stop outputting at the 8th second, the supercapacitor energy storage support time is about 1.5s, and the grid voltage and current drop after 9.5s. Based on the comparison standard of energy storage support from the 8th second to the 14th second, the total capacity of supercapacitors using a typical three-phase converter topology must reach 8640MWs to enable the grid system to achieve the support time. At this capacity, the grid line voltage amplitude, phase voltage, frequency, current and energy storage output are as follows: Fig.17 , Fig.18 , Fig.19 , Fig. 20 , Fig.21 shown.

[0064] In a typical three-phase converter topology with a front-stage Boost converter, the grid line voltage amplitude, phase voltage, frequency, current and energy storage output are as follows: Fig. 22 , Fig.23 , Fig.24 , Fig.25 , Fig.26As shown. After all generators stop outputting at the 8th second, the supercapacitor supports for about 4.5 seconds, and the grid voltage and current drop after 12.5 seconds. Based on the comparison standard of energy storage supporting from the 8th second to the 14th second, the total capacity of supercapacitors in a typical three-phase converter topology structure with a front-stage Boost converter must reach 2430WMs to enable the grid system to achieve the support time. At this capacity, the grid line voltage amplitude, phase voltage, frequency, current and energy storage output are as follows: Fig. 27 , Fig.28 , Fig.29 , Fig.30 , Fig.31 shown.

[0065] When the proposed wide input converter topology is adopted, the grid line voltage amplitude, phase voltage, frequency, current and energy storage output are as follows: Fig.32 , Fig.33 , Fig.34 , Fig.35 , Fig.36 After all generators stop outputting power at the 8th second, the supercapacitor energy storage supports power for about 6 seconds, and the grid voltage and current drop after the 14th second.

[0066] In summary, under the assumed working conditions of the above typical cases, the simulation conclusions show that in terms of supercapacitor energy storage support time, the typical three-phase converter scheme with the introduction of a pre-stage Boost converter is 200% higher than the typical three-phase converter scheme, and the proposed wide input converter scheme is 300% higher than the typical three-phase converter scheme and 33% higher than the typical three-phase converter scheme with the introduction of a pre-stage Boost converter; in terms of energy storage capacity demand, the typical three-phase converter scheme with the introduction of a pre-stage Boost converter is 72% lower than the typical three-phase converter scheme, and the proposed wide input converter scheme is 79% lower than the typical three-phase converter scheme and 26% lower than the typical three-phase converter scheme with the introduction of a pre-stage Boost converter.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A wide input converter topology structure, comprising: The DC side structure is used to connect a DC grid, a DC power supply or a DC load; the AC side structure is used to connect an AC grid, an AC power supply or an AC load; and is characterized in that: The DC side structure adopts a three-phase bridge arm structure, which includes a first bridge arm, a second bridge arm and a third bridge arm, the first bridge arm is provided with a first switch device and a second switch device; the second bridge arm is provided with a third switch device and a first capacitor; the third bridge arm is provided with a second capacitor and a third capacitor; Also includes a first inductor, a second inductor and a fourth switching device; The first ends of the first inductor and the second inductor are connected in parallel and connected to the positive electrode of a DC grid, a DC power supply or a DC load; the first end of the first switching device is connected to the second end of the second switching device and then connected to the second end of the second inductor; the first end of the first capacitor is connected in parallel to the first end of the second switching device and then connected to the second end of the fourth switching device; the second end of the first capacitor is connected to the first end of the third switching device and then connected to the second end of the first inductor; the first end of the fourth switching device is connected to the first end of the second capacitor; the second end of the second capacitor is connected to the first end of the third capacitor; the second end of the first switching device, the second end of the third switching device, and the second end of the third capacitor are connected and then connected to the negative electrode of a DC grid, a DC power supply or a DC load.

2. A wide input converter topology structure as claimed in claim 1, characterized in that: The AC side structure adopts a three-phase bridge arm structure, which includes a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; the fourth bridge arm is provided with a fifth switch device and a sixth switch device; the fifth bridge arm is provided with a seventh switch device and an eighth switch device; the sixth bridge arm is provided with a ninth switch device and a tenth switch device; The AC side structure also includes a third inductor, a fourth inductor and a fifth inductor; The first end of the fifth switch device is connected to the second end of the sixth switch device and then connected to the first end of the fifth inductor; the first end of the seventh switch device is connected to the second end of the eighth switch device and then connected to the first end of the fourth inductor; the first end of the ninth switch device is connected to the second end of the tenth switch device and then connected to the first end of the third inductor; The first end of the sixth switch device, the first end of the eighth switch device, and the first end of the tenth switch device are connected to the first end of the fourth switch device and the first end of the second capacitor; The second end of the fifth switch device, the second end of the seventh switch device, and the second end of the ninth switch device are connected, and then connected to the second end of the first switch device, the second end of the third switch device, and the second end of the third capacitor; The second end of the fifth inductor is connected to phase a of an AC power grid, an AC power source or an AC load; The second end of the fourth inductor is connected to the b phase of the AC power grid, AC power supply or AC load; The second end of the third inductor is connected to the C phase of the AC power grid, the AC power source or the AC load.

3. The DC side structure of a wide input converter according to claim 2, characterized in that: The first end of the first to third capacitors is the positive electrode of the capacitor, and the second end is the negative electrode of the capacitor.

4. The DC side structure of a wide input converter according to claim 2, characterized in that: The first to tenth switch devices are also connected to respective drive circuits via third terminals, respectively.

5. A control method for the DC side structure of a wide input converter according to any one of claims 1 to 4, characterized in that: The following steps are involved: According to actual needs, the closed-loop control strategy of the DC side structure is determined to be a voltage-current dual-loop control strategy; at the same time, the DC side switch control mode is selected as a PWM control mode; According to the grid connection requirements, the closed-loop control strategy of the AC side structure is determined to be a grid-following control strategy or a grid-building control strategy; at the same time, according to the voltage conversion ratio requirements of the converter, the AC side switch control mode is determined to be an SPWM control mode or an SVPWM control mode; Based on a determined closed-loop control strategy and a control method of the switch device, each switch device in the wide input converter topology is controlled.

6. A control method for a DC side structure of a wide input converter as claimed in claim 5, characterized in that: In the PWM control mode, the duty ratio of the control signals of the first switch device and the third switch device is D , the control signal of the third switching device lags the control signal of the first switching device by 180°; The second switch device and the fourth switch device are respectively complementary to the control signals of the first switch device and the third switch device, and the duty ratios of the second switch device and the fourth switch device are both 1- D , the control signal of the fourth switching device lags the control signal of the second switching device by 180°.

7. A control method for a DC side structure of a wide input converter as claimed in claim 6, characterized in that: The duty ratio of the control signals of the first switching device and the third switching device D The range of is greater than 0.5 and less than the limit duty cycle; wherein the value range of the limit duty cycle is between 0.8 and 0.

9.

8. The control method of the DC side structure of a wide input converter according to claim 5, characterized in that: In the voltage-current dual-loop closed-loop control strategy adopted by the DC side structure, the current sampling of the current loop is the DC side current, and the voltage sampling of the voltage loop is the sum of the voltages of the second capacitor and the third capacitor.

9. A control method for a DC side structure of a wide input converter as claimed in claim 5, characterized in that: In the closed-loop control strategy adopted by the AC side structure, the current sampling of the current loop is the current of the third to fifth inductors, and the voltage sampling of the voltage loop is the three-phase voltage of the AC side a, b, c.

10. The method for controlling the DC side structure of a wide input converter according to claim 5, characterized in that: The voltage conversion ratio range of the switching device of the AC side structure under the SPWM control mode is: in, M SPWM It is the ratio of the AC side power supply or load line voltage to the DC side load or voltage of the wide input converter under SPWM control mode; The voltage conversion ratio range under SVPWM control is: in, M SVPWM It is the ratio of the AC side power supply or load line voltage to the DC side load or voltage of the wide input converter under SVPWM control mode.

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