Medium-voltage modular electric energy router and control method thereof

Abstract

The invention relates to the technical field of electric energy routers, in particular to a medium-voltage modularized electric energy router, which takes a modularized multi-level converter as a basic topology, the modularized multi-level converter adopts a three-phase six-bridge-arm structure, and supports medium-voltage alternating-current and direct-current micro-grid application through cascade boosting of low-voltage sub-modules. The sub-module in each bridge arm comprises a power module, a DAB converter and a hybrid energy storage module which are connected in parallel, and the hybrid energy storage module comprises a super capacitor and a storage battery pack, so that challenges of high-rate frequent charging and discharging on an energy storage battery can be handled, the working reliability of the electric energy router is further improved, and the electric energy quality of the system is improved; the problem that when an electric energy router in a conventional power distribution network is applied to an alternating-current and direct-current micro-grid, the electric energy quality is prone to decline is solved.

Description

Technical Field

[0001] The present application relates to the technical field of power routers, and in particular to a medium voltage modular power router and a control method thereof. Background Art

[0002] Independent microgrids can use local renewable energy to solve the problem of electricity shortage in remote areas, which is of great significance to improving the quality of life of people in remote areas. At present, most independent microgrids adopt AC / DC hybrid networking, which combines the advantages of AC microgrids and DC microgrids and is the mainstream development direction of independent microgrids in the future. However, with the continuous expansion of the scale of AC / DC hybrid independent microgrids, traditional AC / DC interface converters are gradually unable to meet the development requirements of diversified power supply methods, multi-directional energy flow, and intelligent energy management.

[0003] To address this problem, the existing patent application with publication number CN116404648A proposes a solution for applying a power router to an AC / DC hybrid independent microgrid, and specifically discloses an AC / DC hybrid microgrid, including a DC bus module, a low-voltage AC bus module and a power router; the low-voltage AC bus module is used to maintain the voltage and frequency balance of the low-voltage AC bus module through the power router and the high-voltage AC grid in grid-connected mode or island mode; the DC bus module is used to perform voltage self-control in grid-connected mode or island mode, and to smooth the power shortage when switching from grid-connected mode to island mode.

[0004] As a new type of multifunctional power distribution equipment, the power router can connect the DC bus module, the low-voltage AC bus module and the external high-voltage AC grid to achieve flexible interconnection between AC and DC subgrids. However, under harsh working conditions, the power routers widely used in conventional distribution networks may encounter challenges such as short-term input power shortage, output voltage drop or interruption, which in turn affects the power quality of the system. Summary of the invention

[0005] Based on this, it is necessary to provide a medium voltage modular power router and a control method thereof to address the problem that power quality is easily degraded when the power router in the conventional distribution network is applied to the AC / DC microgrid.

[0006] In a first aspect, the present application provides a medium-voltage modular power router, which is based on a modular multilevel converter topology. The modular multilevel converter adopts a three-phase six-bridge arm structure. The sub-module of each bridge arm includes a power module, a DAB converter and a hybrid energy storage module connected in parallel. The hybrid energy storage module includes a supercapacitor and a battery pack.

[0007] Furthermore, the hybrid energy storage module includes a supercapacitor, a first switch tube, a second switch tube, an inductor and a battery pack. The supercapacitor is connected in parallel to the output end of the DAB converter, the first end of the supercapacitor is connected to the first end of the first switch tube, the first end of the second switch tube and the first end of the inductor are both connected to the second end of the first switch tube, the second end of the inductor is connected to the first end of the battery pack, and the second end of the battery pack and the second end of the second switch tube are both connected to the second end of the supercapacitor.

[0008] Furthermore, each bridge arm includes a full-bridge power sub-module and N-1 half-bridge power sub-modules.

[0009] Furthermore, a fault isolation switch is provided on the DC side of the modular multi-level converter.

[0010] Furthermore, the DAB converter adopts double phase shift control.

[0011] Furthermore, the transmission power and current stress of the DAB converter are respectively:

[0012]

[0013] Where P is the transmission power of the DAB converter, I st is the current stress of the DAB converter, n is the high-frequency transformer ratio, V1 is the input voltage of the DAB converter, V2 is the output voltage of the DAB converter, f s is the switching frequency of the DAB converter, L is the sum of the auxiliary inductance and the leakage inductance; D1 is the intra-bridge shift phase ratio, D2 is the inter-bridge shift phase ratio, k is the voltage transfer ratio and k=V1 / nV2.

[0014] Furthermore, the switch tubes in the power module, the DAB converter and the hybrid energy storage module are all IGBTs.

[0015] Furthermore, the IGBT is a reverse conducting IGBT.

[0016] In a second aspect, the present application provides a control method for a medium voltage modular power router. The method comprises:

[0017] Step S102, obtaining the DC subnet voltage, AC subnet frequency and the remaining power of the hybrid energy storage module;

[0018] Step S104, obtaining a target operating mode of the power router according to the DC subnet voltage, the AC subnet frequency, the remaining power of the hybrid energy storage module and the current operating mode of the power router;

[0019] Step S106, switching the working mode of the power router to the target working mode; wherein the target working mode is one of a suspension operation mode, an AC charging mode, a DC charging mode, a hybrid charging mode, an AC discharge mode, a DC discharge mode and a hybrid discharge mode.

[0020] Furthermore, the method further comprises:

[0021] Step S108, obtaining the working status of each submodule in the medium voltage modular power router;

[0022] Step S110: If it is detected that the working state of the submodule is faulty, the fault isolation switch corresponding to the submodule is closed.

[0023] The above-mentioned medium-voltage modular power router is based on the modular multi-level converter topology. The modular multi-level converter adopts a three-phase six-bridge-arm structure. Through the cascade boost of each low-voltage sub-module, it supports the application of medium-voltage AC / DC microgrids. At the same time, the sub-modules in each bridge arm include a power module, a DAB converter and a hybrid energy storage module connected in parallel, and the hybrid energy storage module includes a supercapacitor and a battery pack, which can cope with the challenge of high-rate frequent charging and discharging to the energy storage battery, thereby further improving the working reliability of the power router and improving the power quality of the system. In addition, the control method of the above-mentioned medium-voltage modular power router obtains the target working mode of the power router according to the DC subnet voltage, the AC subnet frequency, the remaining power of the hybrid energy storage module and the current working mode of the power router, and switches the working mode of the power router to the target working mode, which can significantly improve the operating efficiency and flexibility of the power router. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a medium voltage modular power router in one embodiment;

[0025] Figure 2 A topology diagram of a modular multi-level converter in one embodiment;

[0026] Figure 3 A schematic diagram of the structure of a full-bridge power module and a half-bridge power module in one embodiment;

[0027] Figure 4 is a circuit topology diagram of a DAB converter in one embodiment;

[0028] Figure 5 A DPS phase shift modulation waveform diagram in one embodiment;

[0029] Figure 6 A schematic diagram of the structure of a hybrid energy storage module in one embodiment;

[0030] Figure 7 A schematic flow chart of a control method for a medium voltage modular power router in one embodiment;

[0031] Figure 8 A schematic diagram of seven working modes of a medium voltage modular power router in one embodiment;

[0032] Fig. 9 The figure is a schematic diagram of the working mode switching process of a medium voltage modular power router in one embodiment. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0034] Example 1

[0035] like Figure 1 As shown, this embodiment provides a medium voltage modular power router, which is based on a modular multilevel converter (MMC) topology. The MMC adopts a three-phase six-bridge arm structure, that is, it includes three phases A, B, and C. Each phase contains two bridge arms with symmetrical upper and lower structures. Each bridge arm includes N series-connected submodules (Submodule, SM) and bridge arm inductors. The positive pole of the DC subnet is connected to the full-bridge power module of the upper bridge arm of each phase of the MMC, and the negative pole is connected to the full-bridge power module of the lower bridge arm of each phase of the MMC. The three phases of the AC subnet are respectively connected to the bridge arm inductors in the three-phase bridge arms of the MMC. Each submodule includes a power module, a DAB converter, and a hybrid energy storage module connected in parallel.

[0036] The power module adopts a mixed mode of full-bridge power module + half-bridge power module, and the sub-module adopting the full-bridge power module is called the full-bridge power sub-module (FB SM), and the sub-module adopting the half-bridge power module is called the half-bridge power sub-module (HB SM). Figure 2 As shown, each bridge arm includes a full-bridge power submodule and n half-bridge power submodules (HB SM i , i=1,2,...n,n=N-1). When a circuit fails, the full-bridge power module can effectively use its internal capacitor to absorb the fault current, ensure that the system has no oscillation, and provide higher flexibility and freedom for DC grid fault ride-through control.

[0037] Further, Figure 3The specific structures of the half-bridge power module and the full-bridge power module are shown. The half-bridge power module consists of two switch tubes (Q1 and Q2), two anti-parallel diodes (M1 and M2) and a DC capacitor (C1). Each half-bridge power module can output two voltages (levels), namely "0" level and "1" level. The full-bridge submodule consists of four switch tubes (Q3, Q4, Q5 and Q6), four anti-parallel diodes (M3, M4, M5 and M6) and a DC capacitor (C2). Each full-bridge power module can output three voltages (levels), namely "-1" level, "0" level and "1" level.

[0038] The input side of each submodule is provided with a fault isolation switch S, which is a normally open switch. When the fault isolation switch is closed, the submodule connected to the fault isolation switch is bypassed and does not participate in the work. When the fault isolation switch is disconnected, the submodule connected to the fault isolation switch operates normally. Therefore, when a submodule fails, the faulty submodule can be isolated by controlling the fault isolation switch connected to the submodule to close, so as to improve the working reliability of the power router.

[0039] Taking the upper bridge arm of phase A as an example, a fault isolation switch S1 is provided on the input side of the full-bridge power submodule, and the fault isolation switch S1 includes four terminals, the first terminal and the second terminal are both connected to the positive pole of the DC subnet, the third terminal is connected to the second end of the switch tube Q3 in the full-bridge power submodule, and the fourth terminal is connected to the half-bridge power submodule FB SM1. When the first terminal of the fault isolation switch S1 is connected to the third terminal, the full-bridge power submodule is turned on, and when the second terminal of the fault isolation switch S1 is connected to the fourth terminal, the full-bridge power submodule is disconnected.

[0040] The input side of the half-bridge power submodule FB SM1 is provided with a fault isolation switch S2, which includes four terminals. The first terminal and the second terminal are both connected to the second end of the switch tube Q4 in the full-bridge power submodule, the third terminal is connected to the second end of the switch tube Q1 in the half-bridge power submodule FB SM1, and the fourth terminal is connected to the second end of the switch tube Q1 in the half-bridge power submodule FB SM2. When the first terminal of the fault isolation switch S2 is connected to the third terminal, the half-bridge power submodule FB SM1 is turned on, and when the second terminal of the fault isolation switch S2 is connected to the fourth terminal, the half-bridge power submodule FB SM1 is turned off. Similarly, the half-bridge power submodule HB SM i A fault isolation switch S is provided on the input side of i (i=3,...n), fault isolation switch S i It includes four terminals, the first terminal and the second terminal are connected to the half-bridge power submodule HB SM i-1 The second terminal of the middle switch tube Q2 and the third terminal are connected to HB SMi The second terminal of the middle switch tube Q1 and the fourth terminal are connected to HB SM i+1 The second end of the switch tube Q1 in the middle. In particular, for the last fault isolation switch Sn, its fourth end is connected to the bridge arm inductor. Therefore, the conductivity of each submodule can be flexibly controlled by the fault isolation switch of each submodule, thereby improving the reliability and flexibility of the entire system. It can be understood that the connection method of the fault isolation switches in other bridge arms of phase A, as well as phases B and C is the same as the connection method of the fault isolation switch in the upper bridge arm of phase A.

[0041] This embodiment uses a DAB converter as an intermediate stage to achieve bidirectional power transmission between the AC / DC microgrid and the built-in hybrid energy storage module of the power router, and to achieve electrical isolation. Figure 4 The specific structure of the DAB converter is shown, including two full-bridge circuits, two capacitors (C3 and C4), an inductor and a high-frequency transformer T. The two full-bridge circuits serve as power conversion circuits on the input side (primary side) and the output side (secondary side), respectively. The high-frequency transformer provides the required current isolation and voltage matching between the two voltage levels, and the inductor serves as an instantaneous energy storage device. The input side full-bridge circuit is composed of switch devices S1-S4, which are alternately turned on and off to achieve bidirectional energy transmission. Among them, the driving signals of S1 and S4 are the same, the driving signals of S2 and S3 are the same, and the driving signals of S1 and S2 are opposite. The output side full-bridge circuit is composed of switch devices Q7-Q10, and its structure is similar to the input side full-bridge circuit. The driving signals of Q7 and Q10 are the same, the driving signals of Q8 and Q9 are the same, and the driving signals of Q7 and Q8 are opposite.

[0042] The working principle of the DAB converter is mainly based on phase shift control. By changing the phase difference (i.e., phase shift angle) between the full-bridge circuit on the input side and the full-bridge circuit on the output side, bidirectional flow of energy can be achieved. The modulation technology of the DAB converter mainly includes single phase shift (SPS), extended phase shift (EPS), double phase shift (DPS), etc. The DAB converter in this embodiment adopts double phase shift control, which can reduce the reflux power and improve the transmission efficiency of the system. Combined with Figure 4 The DAB converter circuit topology shown in the figure is Figure 5 The DPS phase shift modulation waveform of the DAB converter shown in FIG. 1 can obtain the transmission power of the DAB converter as shown in equation (1) and the current stress of the DAB converter as shown in equation (2):

[0043]

[0044] Figure 4 In the figure, D1 is the bridge displacement ratio, D2 is the bridge displacement ratio, T hs is half switching period, vH1 Represents the output voltage waveform of the primary H-bridge, v H2 Represents the secondary side H-bridge output voltage waveform, v H1 and v H2 All are three-level waveforms, v L It represents the voltage waveform across the inductor L in the DAB converter, i L represents the current waveform of the inductor L in the DAB converter, S1, S2, S3 and S4 represent the drive signals of the switches in the primary H-bridge, Q1, Q2, Q3 and Q4 represent the switches Q7, Q8, Q9 and Q10 in the primary H-bridge, respectively. 10 In formula (1), P is the transmission power of the DAB converter, n is the high-frequency transformer ratio, V1 is the input voltage of the DAB converter, that is, the output voltage of the full-bridge power module or the half-bridge power module, V2 is the output voltage of the DAB converter, that is, the input voltage of the hybrid energy storage module, and f s is the switching frequency of the DAB converter, L is the inductance of the DAB converter, specifically the sum of the auxiliary inductance and the leakage inductance, I st is the current stress of the DAB converter, k is the voltage transfer ratio, k=V1 / nV2.

[0045] The hybrid energy storage module (HESS) consists of a lithium battery module, a bidirectional Buck-Boost circuit and a supercapacitor. Figure 6 The specific structure of the hybrid energy storage module is shown, including a super capacitor C, a switch tube S5, a switch tube S6, an inductor L and a battery pack Bat. The super capacitor is connected in parallel to the output end of the DAB converter, the first end of the super capacitor is connected to the first end of the switch tube S5, the first end of the switch tube S6 and the first end of the inductor are both connected to the second end of the switch tube S5, the second end of the inductor is connected to the first end of the battery pack, and the second end of the battery pack and the second end of the switch tube S6 are both connected to the second end of the super capacitor. Preferably, the switch tube S5 and the switch tube S6 are both reverse conducting IGBTs, and the reverse conducting IGBT integrates an IGBT and a freewheeling diode (FWD), and the freewheeling diode is connected in reverse parallel with the IGBT. This structure enables the IGBT to be turned on even under reverse voltage, thereby improving the efficiency and reliability of the circuit.

[0046] The bidirectional Buck-Boost circuit can realize the bidirectional flow of energy. In Buck mode, when the input voltage is higher than the output voltage, energy flows from the input end to the output end, realizing energy conversion and output power provision, and the battery pack is charged at this time; in Boost mode, when the input voltage is lower than the output voltage, energy flows from the output end to the input end, realizing energy feedback and input power compensation, and the battery pack is discharged at this time. The lithium battery in the battery pack has the characteristics of high energy density, and the supercapacitor has the characteristics of high power and fast charging and discharging. The hybrid energy storage module composed of the two has the advantages of high energy density, high power density, and long cycle life, and can quickly respond to frequent and large power fluctuations in the microgrid, thereby improving the performance of the power router.

[0047] The medium voltage modular power router in this embodiment is based on the modular multilevel converter topology. The modular multilevel converter adopts a three-phase six-bridge-arm structure. Through the cascade boost of each low-voltage sub-module, it supports medium voltage AC / DC microgrid applications. At the same time, the sub-modules in each bridge arm include a power module, a DAB converter and a hybrid energy storage module connected in parallel, and the hybrid energy storage module includes a supercapacitor and a battery pack, which can cope with the challenge of frequent charging and discharging at a high rate to the energy storage battery, thereby further improving the working reliability of the power router and improving the power quality of the system.

[0048] Example 2

[0049] Based on the medium voltage modular power router proposed in Example 1, Figure 7 As shown, this embodiment provides a control method for a medium voltage modular power router, and takes the method applied to a terminal as an example. It can be understood that the method can also be applied to a server, and can also be applied to a system including a terminal and a server, and is implemented through the interaction between the terminal and the server. In this embodiment, the method includes the following steps:

[0050] Step S102, obtaining the DC subgrid voltage (U), the AC subgrid frequency (f) and the remaining capacity (SOC) of the hybrid energy storage module.

[0051] Among them, the remaining power of the hybrid energy storage module is the remaining power SOC of the battery group in the hybrid energy storage module, SOCmin≤SOC≤SOCmax, SOCmax represents the upper limit of the battery SOC, SOCmin represents the lower limit of the battery SOC, SOCopt represents a certain SOC value obtained by the optimization algorithm, and the SOCopt values ​​obtained under different optimization algorithms are different.

[0052] Step S104, obtaining a target working mode of the power router according to the DC subnet voltage, the AC subnet frequency, the remaining power of the hybrid energy storage module and the current working mode of the power router.

[0053] Based on the characteristics of the system energy conversion process, this embodiment defines Figure 8 The seven working modes of the power router are shown:

[0054] a) Suspended operation mode: The hybrid energy storage module neither charges nor discharges, and electric energy flows bidirectionally between the AC subgrid and the DC subgrid through the MMC, which is equivalent to the traditional hybrid microgrid interconnection interface converter.

[0055] b) AC charging mode: The AC subgrid supplies power to the DC subgrid and the hybrid energy storage module at the same time. Under the action of the MMC, the AC power reaches the power modules of each submodule through the bridge arm inductor. The capacitors in the power modules are continuously charged and discharged, and the power modules output a specific voltage, so that the bridge arm outputs a fixed bridge arm voltage and approaches the DC subgrid voltage, achieving the purpose of controlling AC and DC currents. At the same time, the DAB converter transmits electrical energy to the hybrid energy storage module, and the supercapacitor charges quickly, actively bearing the impact of short-term, high-power loads. After passing through the bidirectional Buck-Boost circuit, the electrical energy is finally stored in the battery pack.

[0056] c) DC charging mode: The DC subgrid supplies power to the AC subgrid and the hybrid energy storage module at the same time. Under the action of the MMC, the DC power outputs a stepped bridge arm voltage from the submodule bridge arm and approaches the AC subgrid voltage. The electric energy is transmitted to the supercapacitor through the DAB converter to charge the supercapacitor. With its high power density and fast charging and discharging characteristics, the supercapacitor can respond quickly and store a large amount of electric energy. Subsequently, this electric energy is stored in the battery pack through the bidirectional Buck-Boost circuit.

[0057] d) Hybrid charging mode: The hybrid energy storage module is charged by both the AC subnet and the DC subnet. Similarly, combining the DC charging mode and the AC charging mode, it can be seen that the electric energy is transmitted by the DAB converter, charged by the supercapacitor, and stored in the battery pack after the bidirectional Buck-Boost circuit.

[0058] e) AC discharge mode: The AC subgrid discharges to the DC subgrid and the hybrid energy storage module at the same time. In this mode, the AC subgrid has a large demand for power, and the DC subgrid provides power to the AC subgrid, while the power router compensates part of the power. In this mode, the supercapacitor responds quickly to discharge, and after the power is transmitted through the DAB converter, the MMC outputs a stepped bridge arm voltage that approaches the AC subgrid voltage, supplying power to the AC subgrid. The battery pack replenishes power to the supercapacitor through a bidirectional Buck-Boost circuit to maintain the supercapacitor voltage.

[0059] f) DC discharge mode: The DC subgrid discharges to the AC subgrid and the hybrid energy storage module at the same time. The AC subgrid provides power to the DC subgrid. In order to maintain the power stability of the DC subgrid, the power router will also compensate the DC subgrid with additional power. In this mode, the supercapacitor, with its fast response characteristics, quickly discharges, and the power enters the MMC after being efficiently transmitted by the DAB converter. Under the precise control of the MMC, a stable DC voltage is output to ensure that the DC subgrid can obtain a continuous and reliable power supply. At the same time, in order to maintain the continuous discharge capability of the supercapacitor, the battery pack will provide it with necessary power supplement.

[0060] g) Hybrid discharge mode: The hybrid energy storage module discharges to the AC subgrid and the DC subgrid at the same time. Similarly, combining the AC discharge mode and the DC discharge mode, it can be seen that the electric energy is first transmitted through the DAB converter, and then output through the bridge arm of the MMC to compensate and balance the power demand of the AC subgrid and the DC subgrid. In this process, the battery pack, as the main energy source, provides a continuous supply of electric energy to the supercapacitor. With its high power output characteristics, the supercapacitor quickly responds to and meets the instantaneous power demand of the power grid, realizing an efficient energy management strategy of "on-demand and on-demand". Such a design not only improves the flexibility and stability of the entire power system, but also ensures a continuous and reliable supply of electric energy.

[0061] Step S106, switching the working mode of the power router to the target working mode.

[0062] Exemplarily, the working mode of the power router may be switched according to the method shown in Table 1. Specifically, the working mode of the power router may be switched by controlling the on and off states of each switch tube in the power router.

[0063] After the power router is initialized, it enters the floating operation mode. After the power router enters the floating operation mode, when U is normal, f is too high, and SOC < SOCmax, or when U is too low, f is too high, and SOCopt < SOC < SOCmax, the power router is switched from the floating operation mode to the AC charging mode. When U is too high, f is normal, and SOC = SOCmax, or when U is too high, f is too low, and SOCopt < SOC < SOCmax, the power router is switched from the floating operation mode to the DC charging mode. When U is too high, f is too high, and SOC < SOCmax, the power router is switched from the floating operation mode to the hybrid charging mode. When U is too low, f is too low, and SOC > SOCmin, the power router is switched from the floating operation mode to the hybrid discharging mode. When U is normal, f is too low, and SOC > SOCmin, or when U is too high, f is too low, and SOCmin < SOC < SOCopt, the power router is switched from the floating operation mode to the AC discharging mode. When U is too low, f is normal, and SOC > SOCmin, or when U is too low, f is too high, and SOCmin < SOC < SOCopt, the power router is switched from the floating operation mode to the DC discharging mode.

[0064] After the power router enters the AC charging mode, when U is too low, f is normal, and SOC > SOCmin, the power router is switched from the AC charging mode to the DC discharging mode. When U is normal, f is too high, and SOC = SOCmax, or when U is normal, f is normal, the power router is switched from the AC charging mode to the floating operation mode.

[0065] After the power router enters the DC charging mode, when U is normal, f is too low, and SOC > SOCmin, the power router is switched from the DC charging mode to the AC discharging mode. When U is too high, f is normal, and SOC = SOCmax, or when U is normal, f is normal, the power router is switched from the DC charging mode to the floating operation mode.

[0066] After the power router enters the AC discharging mode, when U is too high, f is normal, and SOC < SOCmax, the power router is switched from the AC discharging mode to the DC charging mode. When U is normal, f is too low, and SOC = SOCmin, or when U is normal, f is normal, the power router is switched from the AC discharging mode to the floating operation mode.

[0067] After the power router enters the DC discharging mode, when U is normal, f is too high, and SOC < SOCmax, the power router is switched from the DC discharging mode to the AC charging mode. When U is too low, f is normal, and SOC = SOCmin, or when U is normal, f is normal, the power router is switched from the DC discharging mode to the floating operation mode.

[0068] After the power router enters the hybrid charging mode, when U is too high, f is normal, and SOC<SOCmax, the power router switches from the hybrid charging mode to the DC charging mode; when U is normal, f is too high, and SOC<SOCmax, the power router switches from the hybrid charging mode to the AC charging mode; when U is too high, f is too high, and SOC=SOCmax, or U is too high, f is normal, and SOC=SOCmax, or U is normal, f is too high, and SOC=SOCmax, the power router switches from the hybrid charging mode to the suspension operation mode.

[0069] After the power router enters the hybrid discharge mode, when U is normal, f is too low, and SOC>SOCmin, the power router switches from the hybrid discharge mode to the AC discharge mode; when U is too low, f is normal, and SOC>SOCmin, the power router switches from the hybrid discharge mode to the DC discharge mode; when U is too low, f is too low, and SOC=SOCmin, or U is too low, f is normal, and SOC=SOCmin, or U is normal, f is too low, and SOC=SOCmin, the power router switches from the hybrid discharge mode to the suspension operation mode.

[0070] Table 1

[0071]

[0072]

[0073] In order to more intuitively display the conversion between various working modes, Fig. 9 The working mode switching flow chart of the medium voltage modular power router is shown. It can be understood that the "too high", "too low" and "normal" mentioned above are all judged based on preset thresholds, and these preset thresholds can be flexibly set by technicians in this field according to actual needs.

[0074] Furthermore, when a fault isolation switch is provided on the DC side of the modular multilevel converter in the medium voltage modular power router, the method of this embodiment further comprises the following steps:

[0075] Step S108, obtaining the working status of each submodule in the medium voltage modular power router.

[0076] The working state of the submodule includes normal operation and fault. Specifically, it can be determined whether the current working state of the submodule is normal or faulty according to the output voltage, output current, etc. of each submodule.

[0077] Step S110: If it is detected that the working state of the submodule is faulty, the fault isolation switch corresponding to the submodule is closed.

[0078] For example, if an abnormal voltage, excessive current, or excessive temperature is detected in a submodule, the fault isolation switch corresponding to the submodule is closed to bypass the submodule, thereby being able to quickly respond and isolate the faulty submodule in the medium-voltage modular power router, reducing the impact of the fault on the entire power system.

[0079] The control method of the medium voltage modular power router of this embodiment obtains the target working mode of the power router according to the DC subnet voltage, the AC subnet frequency, the remaining power of the hybrid energy storage module and the current working mode of the power router, and switches the working mode of the power router to the target working mode, which can significantly improve the operating efficiency and flexibility of the power router. In addition, the power router can improve the transmission quality of power and further ensure the stability of power by performing additional compensation for power.

[0080] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A medium voltage modular power router, characterized in that: The medium voltage modular power router is based on a modular multilevel converter topology. The modular multilevel converter adopts a three-phase six-bridge arm structure. The submodule of each bridge arm includes a power module, a DAB converter and a hybrid energy storage module connected in parallel. The hybrid energy storage module includes a supercapacitor and a battery pack.

2. The medium voltage modular power router according to claim 1, characterized in that: The hybrid energy storage module includes a supercapacitor, a first switch tube, a second switch tube, an inductor and a battery pack. The supercapacitor is connected in parallel to the output end of the DAB converter, the first end of the supercapacitor is connected to the first end of the first switch tube, the first end of the second switch tube and the first end of the inductor are both connected to the second end of the first switch tube, the second end of the inductor is connected to the first end of the battery pack, and the second end of the battery pack and the second end of the second switch tube are both connected to the second end of the supercapacitor.

3. The medium voltage modular power router according to claim 1, characterized in that: Each bridge arm includes a full-bridge power sub-module and N-1 half-bridge power sub-modules.

4. The medium voltage modular power router according to claim 1, characterized in that: A fault isolation switch is provided on the DC side of the modular multi-level converter.

5. The medium voltage modular power router according to claim 1, characterized in that: The DAB converter adopts double phase shift control.

6. The medium voltage modular power router according to claim 5, characterized in that: The transmission power and current stress of the DAB converter are: Where P is the transmission power of the DAB converter, I st is the current stress of the DAB converter, n is the high-frequency transformer ratio, V1 is the input voltage of the DAB converter, V2 is the output voltage of the DAB converter, f s is the switching frequency of the DAB converter, L is the sum of the auxiliary inductance and the leakage inductance; D1 is the intra-bridge shift phase ratio, D2 is the inter-bridge shift phase ratio, k is the voltage transfer ratio and k=V1 / nV2.

7. The medium voltage modular power router according to claim 1, characterized in that: The switch tubes in the power module, the DAB converter and the hybrid energy storage module are all IGBTs.

8. The medium voltage modular power router according to claim 7, characterized in that: The IGBT is a reverse conducting IGBT.

9. A control method for a medium voltage modular power router, characterized in that: The method comprises: Step S102, obtaining the DC subnet voltage, AC subnet frequency and the remaining power of the hybrid energy storage module; Step S104, obtaining a target operating mode of the power router according to the DC subnet voltage, the AC subnet frequency, the remaining power of the hybrid energy storage module and the current operating mode of the power router; Step S106, switching the working mode of the power router to the target working mode; wherein the target working mode is one of a suspension operation mode, an AC charging mode, a DC charging mode, a hybrid charging mode, an AC discharge mode, a DC discharge mode and a hybrid discharge mode.

10. The control method of the medium voltage modular power router according to claim 9, characterized in that: The method further comprises: Step S108, obtaining the working status of each submodule in the medium voltage modular power router; Step S110: If it is detected that the working state of the submodule is faulty, the fault isolation switch corresponding to the submodule is closed.

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