An electric vehicle charging station system with a shared DC bus

Abstract

The present invention discloses an electric vehicle charging station system with a common DC bus, belonging to the field of electric vehicle charging equipment. The system includes a DC bus, an AC module, a plurality of charging modules and a plurality of switching modules. The DC bus includes at least two groups of DC buses: a first voltage DC bus and a second voltage DC bus; the AC module includes an AC power supply, a connection unit and an alternating unit, and the alternating unit includes two groups of cascaded three-phase H-bridge converters, and the DC side can generate a first voltage and a second voltage, which are respectively connected to the first voltage DC bus and the second voltage DC bus. The charging module and the switching module are connected correspondingly, and the charging module selects to connect different DC buses according to different electric vehicle charging requirements, and doubles the charging power of the corresponding electric vehicle by switching the switch to different switching positions, thereby accelerating the charging speed. The system has low cost, high reliability, convenient access to photovoltaic and energy storage equipment, and flexible charging and high fault tolerance.

Description

Technical Field

[0001] The invention relates to the field of electric vehicle charging equipment, in particular to an electric vehicle charging station system with a common direct current bus. Background Art

[0002] With the rapid development of electric vehicles, the charging voltage, current and speed of electric vehicles are constantly improving. Public charging stations must not only adapt to the charging rate requirements of different electric vehicles, but also need to connect to photovoltaics and energy storage as much as possible to provide low-carbon new energy electricity.

[0003] The input end of a charging station in the prior art is directly connected to a 10kV AC power supply, and the corresponding DC bus is generated through the output end of the power electronic transformer of the previous stage, and then connected to the DC / DC charging pile to charge the electric vehicle. It has the characteristics of easy access to new energy, easy maintenance, and bidirectional energy flow. However, the power electronic transformer used in this type of charging station system requires a large number of power electronic converter modules to undergo multi-stage power conversion, and the insulation withstand voltage design of the power electronic converter module needs to be considered according to the 10kV voltage level, resulting in high cost, large size, low energy conversion efficiency, and difficult reliability of the charging station. In addition, each DC / DC charging pile in this solution corresponds to an electric vehicle, and its charging capacity is fixed, and it cannot be flexibly configured according to the charging needs of the vehicle.

[0004] There is also a charging station that uses the input ports of multiple charger modules in series to form an MMC converter. Each MMC bridge arm is connected in series by several charger modules. The upper and lower bridge arms of the same phase have two inductors in series to suppress circulating current. The AC input end of the MMC converter is directly connected to the 10kV AC bus of the power grid. The DC output end of the MMC is a high-voltage DC bus that can be connected to a high-voltage DC load. The charger module of this solution is directly connected to the 10kV AC power grid, and its insulation withstand voltage level is required to be high. Multiple charger modules in each bridge arm need to be connected in series, so if a charger module fails, the charger modules of the same phase bridge arm or even the charger module group of the same phase will be affected. At the same time, the 10kV high voltage of the DC output end of the charging station is not conducive to the access of new energy such as energy storage and photovoltaics. Therefore, this solution leads to high cost, large size, and difficult reliability of the charging station, which is not convenient for the access of new energy. Summary of the invention

[0005] In order to overcome the technical problems in the prior art such as high insulation voltage level of the converter resulting in high cost and large size, low reliability of multiple converter modules in series, inconvenience in connecting to photovoltaics and energy storage, and in meeting various charging needs of electric vehicles, this patent proposes an electric vehicle charging station system with a common DC bus.

[0006] In order to achieve the above-mentioned object, the technical solution adopted by the present invention is: an electric vehicle charging station system with a common DC bus, characterized in that: the DC bus includes at least two groups of DC buses: a first voltage DC bus and a second voltage DC bus; the AC module includes an AC power supply, a connection unit and an alternating unit; one side of the connection unit is connected to the AC power supply, and the other side is connected to the alternating unit; the alternating unit includes two groups of cascaded three-phase H-bridge converters, the AC side of each group of the three-phase H-bridge converters is connected to the connection unit, the DC side voltage of each group of the three-phase H-bridge converters forms the first voltage, and the two groups of the three The DC sides of the three-phase H-bridge converters are cascaded to form the second voltage, and the DC sides of the cascaded three-phase H-bridge converters are connected to the first voltage DC bus and the second voltage DC bus; the charging module includes two DC / DC charging converters, and according to the charging power requirements of different electric vehicles, the input end of the DC / DC charging converter is selected to be connected to the first voltage DC bus or the second voltage DC bus; the switching module includes two switching switches, whose inputs are correspondingly connected to the outputs of the two DC / DC charging converters of the charging module, and whose outputs are connected to the electric vehicle charging interface.

[0007] Furthermore, the switching switch is a double-pole double-throw mechanical switch or a switch composed of power electronic devices. The two outputs of the switching switch are respectively connected to two corresponding charging interfaces. The output of the DC / DC charging converter is connected to different charging interfaces through different switching positions of the switching switch, so that the two DC / DC charging converters in the charging module can charge the electric vehicle with the same charging interface in parallel through the switching switch, or can charge the electric vehicles with two charging interfaces independently through the switching switch.

[0008] Furthermore, the connection unit includes a switch circuit breaker and an industrial frequency isolation transformer; one side of the switch circuit breaker is connected to the AC power supply, and the other side is connected to the high voltage side of the industrial frequency isolation transformer; the low voltage side of the industrial frequency isolation transformer is connected to the AC side of the cascaded three-phase H-bridge converter.

[0009] Furthermore, the industrial frequency isolation transformer is a three-phase three-column type, the high-voltage side winding is connected in a triangle or a star connection, and is connected to the medium-voltage AC power supply through the switch circuit breaker; the low-voltage side includes two groups of independent three-phase windings, the two groups of three-phase windings have the same voltage and phase, the three windings of the three-phase windings are independent of each other and are not connected, and are respectively connected to the AC side of the three-phase H-bridge converter.

[0010] Furthermore, the AC power supply is a three-phase 10KV or 35KV AC power supply.

[0011] Furthermore, the first voltage is 750V, and the second voltage is 1500V.

[0012] Furthermore, the three-phase H-bridge converter adopts a single-stage frequency-doubled PWM modulation mode, the carrier frequencies of the PWM modulation of the two groups of three-phase H-bridge converters are the same, and the phase difference is 180 degrees. The AC output filter adopts an LCL or L-type filter circuit for filtering, and the leakage inductance of the power frequency isolation transformer can be used as the grid-side inductance of the LCL filter or the inductance of the L-type filter in the three-phase H-bridge inverter.

[0013] Furthermore, the electric vehicle charging station system also includes a DC module, and an output side of the DC module is connected to the first voltage DC bus or the second voltage DC bus.

[0014] Furthermore, the DC module includes a photovoltaic panel and a photovoltaic inverter. The photovoltaic inverter is a DC / DC inverter, the input side of which is connected to the photovoltaic panel, and the output side is connected to the DC bus, so as to realize a unidirectional flow of energy from the photovoltaic panel to the DC bus.

[0015] Furthermore, the electric vehicle charging station system also includes an energy storage module, which includes an energy storage battery and an energy storage inverter. The energy storage inverter is an isolated DC / DC inverter, one side of which is connected to the first voltage DC bus or the second voltage DC bus, and the other side is connected to the energy storage battery. The energy flow direction is bidirectional, and the energy of the DC module and the AC module is stored during low-peak electricity consumption, and discharged during peak electricity consumption to provide energy for the electric vehicle.

[0016] The present invention can achieve the following beneficial effects:

[0017] Low system cost and high reliability: The present invention adopts a power frequency transformer for high and low voltage isolation, which has the characteristics of mature technology, high reliability and low cost. At the same time, the AC-DC converter of the present invention adopts a main circuit topology of two groups of three-phase H-bridge converters in cascade. The H-bridge main circuit is a two-level circuit. Each bridge arm has only two power electronic switching devices connected in series. The topology structure is simple, the control is simple, and the converter reliability is high.

[0018] Small grid-connected harmonic pollution: The AC-DC converter adopts a three-phase H-bridge converter and a unipolar PWM modulation method. The AC side output equivalent switching frequency is twice the actual switching frequency of the device. At the same time, the AC output filter adopts an LCL filter, which can effectively reduce the harmonic pollution to the AC power grid.

[0019] Meeting the charging requirements of electric vehicles with different powers: The two three-phase H-bridge converters in the system are cascaded on the DC side and can output three DC buses, namely, the positive bus, the negative bus and the zero bus. The rated voltage between the positive bus and the zero bus is 750V, the rated voltage between the zero bus and the negative bus is 750V, and the rated voltage between the positive bus and the negative bus is 1500V. According to the charging power requirements of different electric vehicles, their charging converters can be connected to buses with different voltages. When the charging voltage and power are low, a 750V DC voltage bus can be connected. When the charging voltage and power are high, a 1500V DC voltage bus can be connected.

[0020] Convenient access to photovoltaic and energy storage equipment to improve energy conversion efficiency: The three-phase H-bridge inverter in this system can output low DC bus voltages of 750V and 1500V, which is convenient for access to photovoltaic inverters and energy storage inverters, and improves energy conversion efficiency.

[0021] Improved flexibility and fault tolerance of electric vehicle charging: The output of each charging converter is connected to a double-pole double-throw switch, each switch has two outputs, and each output corresponds to a charging interface of an electric vehicle. Two adjacent charging converters form a charging module. The two charging converters of the same charging module can be connected to two independent charging interfaces through a switch, or they can be connected to the same charging interface in parallel through a switch. When two charging converters charge an electric vehicle through the same charging interface, the charging power of the corresponding electric vehicle can be doubled, speeding up the charging speed. When one charging converter in the charging module stops working, the other charging converter can be connected to the corresponding charging interface through a switch to charge the corresponding electric vehicle, thereby increasing the online rate of the charging port. Therefore, the addition of the switch and module greatly improves the flexibility and fault tolerance of electric vehicle charging, and reduces the impact of the failure of a part of the charging converter in the system on the charging of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an overall block diagram of a charging station system for an electric vehicle charging station system with a common DC bus according to the present invention.

[0023] Figure 2 The present invention is a structural diagram of a three-phase H-bridge converter of an electric vehicle charging station system with a common DC bus.

[0024] Figure 3 The present invention discloses a DC / DC converter topology diagram for a charging module of an electric vehicle charging station system with a common DC bus.

[0025] Among them: 1. AC power supply, 2. switch circuit breaker, 3. power frequency isolation transformer, 4. alternating unit, 5. DC bus, 6. charging module, 7. switching module, 8. photovoltaic inverter, 9. energy storage inverter. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0027] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] like Figure 1 As shown, the present invention provides an electric vehicle charging station system with a common DC bus, including: a medium-voltage AC power supply, a switch circuit breaker, an industrial frequency isolation transformer, an alternating unit composed of two groups of cascaded three-phase H-bridge converters connected to the low-voltage side of the transformer, a DC ±750V bus, a photovoltaic converter and an energy storage converter connected to the DC bus at the input end, and the output ends of the two converters are respectively connected to photovoltaic panels and energy storage units, and there are multiple charging modules connected to the DC bus, a switching module composed of multiple switching switches connected to the output end of the charging module, and an electric vehicle. The DC / DC charging converter topology in the charging module is an isolated DAB topology structure, which can achieve bidirectional energy flow. The access of photovoltaic, energy storage equipment and DC charging piles is achieved through a three-phase H-bridge converter, and flexible charging of electric vehicles is achieved at the same time, with high fault tolerance and high reliability.

[0029] The specific implementation method is that the medium voltage AC voltage side is the grid power supply line, which is connected to the high voltage side of the isolation power frequency transformer through a switch circuit breaker. The transformer is a three-phase three-column type, and its high voltage side adopts a triangle connection or a star connection, and the low voltage side adopts two groups of three-phase independent windings; two groups of three-phase H-bridge converters are cascaded, and the AC input end of each phase is respectively connected to the low voltage side winding of the transformer, and the output end of the two groups of three-phase H-bridge converters leads to a DC bus to form a ±750V DC bus. Each charging module contains two groups of DC / DC charging converters. Each charging module corresponds to a switching module, and the charging converter charges the electric vehicle through the corresponding switching switch. Figure 1 As shown in the figure, the input terminals of the charging converters A1 and A2 are respectively connected to DC+, DC0 and DC0, DC- to access the 750V DC bus, and the output terminals of the charging converters A1 and A2 are respectively connected to the switching switches A1 and A2, and the electric vehicles A1 and A2 are charged by closing and opening the switches.

[0030] The switching switch is a double-pole double-throw switch or a power electronic switch. When the two double-pole double-throw switches of the switching switches A1 and A2 are connected to the upper contacts, the charging converter A1 and the charging converter A2 charge the electric vehicle A1 at the same time, which can greatly improve the charging speed of the electric vehicle and meet the user's demand for charging speed. When the switching switch A1 is connected to the upper contact, the switching switch A2 is connected to the lower contact, and the charging converter A1 and the charging converter A2 charge the electric vehicle A1 and the electric vehicle A2 respectively, which can meet the needs of multiple users for charging at the same time. When one of the charging converters of the charging module fails, the other charging converter can replace the failed converter to charge the corresponding electric vehicle. If the charging converter A1 is damaged, the charging converter A2 can be connected to the upper contact to charge the electric vehicle A1, ensuring that the electric vehicle A1 is charged normally and reliably. In addition, when the charging voltage and power required by the electric vehicle are relatively large, the input terminals of the charging converters B1 and B2 can be connected to DC+ and DC- to access a 1500V DC voltage, and then the high-power electric vehicles B1 and B2 can be charged by switching switches B1 and B2.

[0031] The medium voltage AC power is stepped down by a transformer and then converted into DC power by two sets of cascaded H-bridge converters. The inverter circuit uses a three-phase H-bridge. The three-phase H-bridge structure is as follows: Figure 2 As shown. L1, L3, L5 are the leakage inductance of the transformer, which serves as the grid-side inductance of the inverter LCL filter. L2, L4, L6 are the inverter-side filter inductors. C1, C3, C4 are AC filter capacitors. C2 is a DC filter capacitor. Q1~Q12 are all power electronic switching devices, which can be IGBT / diode modules and MOSFETs based on silicon materials, or switching devices based on silicon carbide or gallium nitride. D1~D12 are the anti-parallel diodes of Q1~Q12 respectively.

[0032] The DC / DC converter in the invention adopts an isolated DAB topology structure. The DAB topology structure is as follows: Figure 3 As shown. The circuit topology consists of a high-frequency transformer T, an inductor Lr, an input capacitor Cin, an output capacitor Cout, a full-bridge H1 and a full-bridge H2. The transformer ratio is N:1, and the specific value of N can be adjusted according to load requirements. S1 to S8 in the full-bridge H1 and the full-bridge H2 are all power electronic switching devices, which can be IGBT / diode modules and MOSFETs based on silicon materials, or switching devices based on silicon carbide or gallium nitride; D1 to D8 are anti-parallel diodes of S1 to S8 respectively.

[0033] The photovoltaic converter is a DC / DC converter, one side of which is connected to a DC 750V or 1500V bus, and the other side is connected to a photovoltaic panel. The energy flow direction is unidirectional, from the photovoltaic cell to the DC bus, and the photovoltaic panel can be controlled to operate at the maximum power tracking point. The energy storage converter is an isolated DC / DC converter, one side of which is connected to a DC 750V or DC 1500V bus, and the other side is an energy storage unit (which can be a lithium battery or other battery energy storage unit). The energy flow direction is bidirectional, and can flow from the 750V or 1500V bus to the energy storage unit, or from the energy storage unit to the 750V or 1500V bus. The energy in the distributed energy and the energy storage device can realize the local consumption of energy in the charging station proposed by the present invention. The energy in the distributed energy (photovoltaic) and the energy storage device provides electric energy to the electric vehicle through the photovoltaic converter and the energy storage converter, the DC bus converter and other converters, respectively, to realize the local consumption of energy.

[0034] 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 preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An electric vehicle charging station system with a common DC bus, characterized in that: Including DC bus, AC module, multiple charging modules and multiple switching modules; The DC bus includes at least two groups of DC buses: a first voltage DC bus and a second voltage DC bus; The AC module includes an AC power supply, a connection unit and an alternating unit; one side of the connection unit is connected to the AC power supply, and the other side is connected to the alternating unit; the alternating unit includes two groups of cascaded three-phase H-bridge converters, the AC side of each group of the three-phase H-bridge converters is connected to the connection unit, the DC side voltage of each group of the three-phase H-bridge converters forms the first voltage, the DC sides of the two groups of the three-phase H-bridge converters are cascaded to form the second voltage, and the DC side of the cascaded three-phase H-bridge converters is connected to the first voltage DC bus and the second voltage DC bus; The connection unit includes a switch circuit breaker and an industrial frequency isolation transformer; one side of the switch circuit breaker is connected to the AC power supply, and the other side is connected to the high voltage side of the industrial frequency isolation transformer; the low voltage side of the industrial frequency isolation transformer is connected to the AC side of the cascaded three-phase H-bridge converter; The three-phase H-bridge converter adopts a single-stage frequency-multiplied PWM modulation mode, the carrier frequencies of the PWM modulation of the two groups of three-phase H-bridge converters are the same, and the phase difference is 180 degrees, and the AC output filter adopts an LCL type or L type filter circuit for filtering, and the leakage inductance of the power frequency isolation transformer is used as the grid-side inductance of the LCL filter or the inductance of the L type filter in the three-phase H-bridge converter; The charging module includes two DC / DC charging converters. According to the charging power requirements of different electric vehicles, the input end of the DC / DC charging converter is selectively connected to the first voltage DC bus or the second voltage DC bus; The switching module includes two switching switches, whose inputs are connected to the outputs of the two DC / DC charging converters of the charging module, and whose outputs are connected to the electric vehicle charging interface; The switching switch is a double-pole double-throw mechanical switch or a switch composed of power electronic devices. The two outputs of the switching switch are respectively connected to two corresponding charging interfaces. The output of the DC / DC charging converter is connected to different charging interfaces through different switching positions of the switching switch, so that the two DC / DC charging converters in the charging module can charge the electric vehicle of the same charging interface in parallel through the switching switch, or charge the electric vehicles of two charging interfaces independently through the switching switch; The electric vehicle charging station system further includes a DC module, and an output side of the DC module is connected to the first voltage DC bus or the second voltage DC bus; The electric vehicle charging station system also includes an energy storage module, which includes an energy storage battery and an energy storage converter. The energy storage converter is an isolated DC / DC converter, one side of which is connected to the first voltage DC bus or the second voltage DC bus, and the other side is connected to the energy storage battery. The energy flow direction is bidirectional, and the energy of the DC module and the AC module is stored during low-peak electricity consumption, and is discharged during peak electricity consumption to provide energy for the electric vehicle.

2. The electric vehicle charging station system with a common DC bus according to claim 1 is characterized in that: The industrial frequency isolation transformer is a three-phase three-column type, the high-voltage side winding adopts a triangle connection or a star connection, and is connected to the AC power supply through the switch circuit breaker; the low-voltage side includes two groups of independent three-phase windings, the voltage and phase of the two groups of three-phase windings are the same, the three windings of the three-phase windings are independent of each other and are not connected, and are respectively connected to the AC side of the three-phase H-bridge converter.

3. The electric vehicle charging station system with a common DC bus according to claim 1, characterized in that: The AC power supply is a three-phase 10KV or 35KV AC power supply.

4. The electric vehicle charging station system with a common DC bus according to claim 1, characterized in that: The first voltage is 750V, and the second voltage is 1500V.

5. The electric vehicle charging station system with a common DC bus according to claim 1, characterized in that: The DC module includes a photovoltaic panel and a photovoltaic converter. The photovoltaic converter is a DC / DC converter, the input side of which is connected to the photovoltaic panel, and the output side is connected to the DC bus, so as to realize a unidirectional flow of energy from the photovoltaic panel to the DC bus.

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