DC Charging Pile and Charging Station for Electric Vehicles

Abstract

The present invention discloses a DC charging pile and a charging station for electric vehicles. The DC charging pile for electric vehicles includes: an AC / DC rectification module, which includes a rectified DC side and a rectified AC side; a DC / AC inversion module, which includes an inverted DC side and an inverted AC side; an inversion module control unit, configured to generate an inversion control instruction according to the acquired current signal and voltage signal on the AC distribution network side, a preset harmonic distortion rate, and a power factor when the AC / DC rectification module charges the electric vehicle; the DC / AC inversion module is further configured to respond to the inversion control instruction, obtain electric energy from the AC / DC rectification module and invert it into an AC waveform corresponding to the inversion control instruction, so that the current waveform fed into the AC distribution network side by the DC charging pile meets the preset harmonic distortion rate and power factor. The DC charging pile for electric vehicles improves the power quality of the power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric vehicle charging, and particularly relates to a DC charger and a charging station for electric vehicles. Background Art

[0002] In recent years, the electric vehicle industry in China has developed rapidly, and the state, local governments and enterprises are vigorously promoting the construction of electric vehicle charging facilities such as charging piles and charging stations. Currently, electric vehicle charging piles are mainly divided into two types: AC charging piles and DC charging piles. Among them, the power of AC charging piles is relatively small, generally not exceeding 10 kW; the power of DC charging piles is generally relatively large, generally greater than 60 kW. DC charging piles can reduce the charging time and are more favored by electric vehicle owners.

[0003] However, when a DC charging pile is operating, it will bring some negative impacts on the power quality of the power grid. For example, the total harmonic distortion rate of the current waveform even reaches about 7% - 10%, exceeding the regulations of relevant standards. In addition, waveform distortion will not only affect the power supply quality of the power grid, but may also cause damage to other electrical equipment in the power grid. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a DC charger and a charging station for electric vehicles to improve and enhance the power quality of the power grid connected to electric vehicle charging facilities.

[0005] In a first aspect, the present invention provides a DC charger for electric vehicles, comprising:

[0006] an AC / DC rectification module, which includes a rectified DC side and a rectified AC side. The rectified AC side is used to connect to an AC distribution network to obtain electric energy from the AC distribution network; the rectified DC side is used to connect to an electric vehicle to charge the electric vehicle.

[0007] a DC / AC inversion module, which includes an inverted DC side and an inverted AC side. The inverted DC side obtains electric energy from the rectified DC side; the inverted AC side is used to connect to the AC distribution network.

[0008] an inversion module control unit, which is used to generate an inversion control instruction according to the acquired current signal and voltage signal on the AC distribution network side, a preset harmonic distortion rate and power factor when the AC / DC rectification module charges the electric vehicle.

[0009] The DC / AC inversion module is further used to respond to the inversion control instruction, obtain electric energy from the AC / DC rectification module and invert it into an AC waveform corresponding to the inversion control instruction, so that the current waveform fed into the AC distribution network side by the DC charger meets the preset harmonic distortion rate and power factor.

[0010] Furthermore, the electric vehicle DC charging pile further comprises:

[0011] Current signal acquisition module;

[0012] The current signal acquisition module is used to acquire the current signal i on the AC power distribution network side;

[0013] Correspondingly, the inverter module control unit is used to obtain a fundamental signal i through a low-pass filter. f ; and take i and i f The difference between the harmonic components i in the current signal i is obtained. h ; and h Multiply by the harmonic compensation coefficient ɑ to get the harmonic compensation instruction i h * ; and the harmonic compensation instruction i h * The inverter control command is input to the DC / AC inverter module.

[0014] Furthermore, the electric vehicle DC charging pile further comprises:

[0015] Voltage signal acquisition module, current signal acquisition module;

[0016] The voltage signal acquisition module is used to acquire the voltage signal u on the AC distribution network side;

[0017] The current signal acquisition module is used to acquire the current signal i on the AC power distribution network side;

[0018] Correspondingly, the inverter module control unit is used to obtain a voltage phase value through a phase-locked loop from the voltage signal u; and obtain a reactive current i in the current signal i according to the voltage phase value and the current signal i. re ; The reactive current i re Multiply by the reactive power compensation coefficient β to get the reactive power compensation instruction i re * ; and the reactive power compensation instruction i re * The inverter control command is input to the DC / AC inverter module.

[0019] Furthermore, the electric vehicle DC charging pile further comprises:

[0020] Voltage signal acquisition module, current signal acquisition module;

[0021] The voltage signal acquisition module is used to acquire the voltage signal u on the AC distribution network side;

[0022] The current signal acquisition module is used to acquire the current signal i on the AC power distribution network side;

[0023] Accordingly, the inverter module control unit is configured to obtain a voltage phase value from the voltage signal u through a phase-locked loop; obtain a reactive current i in the current signal i based on the voltage phase value and the current signal i re ; multiply the reactive current i re by a reactive power compensation coefficient β to obtain a reactive power compensation command i re * ; and

[0024] obtain a fundamental wave signal i from the current signal i through a low-pass filter f ; and take the difference between i and i f to obtain a harmonic component i in the current signal i h ; multiply i h by a harmonic compensation coefficient ɑ to obtain a harmonic compensation command i h * ; and

[0025] sum the reactive power compensation command i re * and the harmonic compensation command i h * to obtain the inverter control command; and input the inverter control command into the DC / AC inverter module.

[0026] Furthermore, the DC charging pile for electric vehicles further includes:

[0027] a rectifier module control unit, which is configured to generate a rectifier control command according to the obtained current signal and voltage signal on the AC distribution network side and the charging demand and battery state information recorded in the charging request when a charging request of the electric vehicle is obtained;

[0028] the AC / DC rectifier module, which is configured to obtain electric energy from the AC distribution network and rectify it into a DC current waveform adapted to the electric vehicle in response to the rectifier control command, and charge the electric vehicle; and

[0029] feed the AC waveform generated during rectification into the AC distribution network side.

[0030] Furthermore, for the DC charging pile for electric vehicles, the DC / AC inverter module includes an embedded control unit and a power unit;

[0031] the embedded control unit generates a given input command according to the obtained inverter control command and the actual output feedback by the power unit, and sends it to the power unit;

[0032] the power unit generates an actual output, i.e., an AC waveform corresponding to the inverter control command, in response to the given input command.

[0033] Further, for the DC charging pile of the electric vehicle, the preset power factor is a positive value and is not less than 0.95 (or a value closer to 1.0);

[0034] The preset harmonic distortion rate is not greater than 1%.

[0035] Further, for the DC charging pile of the electric vehicle, the value range of the harmonic compensation coefficient is (-1, 0);

[0036] When the harmonic compensation coefficient ɑ is 0, the inverter control instruction is zero, and the DC / AC inverter module does not suppress the harmonic current component generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0037] When the harmonic compensation coefficient ɑ is a value greater than -1 and less than 0, the inverter control instruction is not zero, and the AC waveform corresponding to the inverter control instruction output by the DC / AC inverter module compensates for the harmonic current component generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0038] Further, for the DC charging pile of the electric vehicle, the value range of the reactive power compensation coefficient is (-2, 0);

[0039] When the reactive power compensation coefficient β is 0, the inverter control instruction is zero, and the DC / AC inverter module does not perform reactive power compensation on the reactive current generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0040] When the reactive power compensation coefficient β is a value greater than -2 and less than 0, the inverter control instruction is not zero, and the AC waveform corresponding to the inverter control instruction output by the DC / AC inverter module compensates for the reactive power generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0041] In a second aspect, the present invention provides an electric vehicle charging station, comprising:

[0042] A plurality of DC charging piles as described in claim 1;

[0043] Each DC charging pile is respectively connected to the AC distribution network;

[0044] Each DC charging pile charges the electric vehicle independently;

[0045] When charging the electric vehicle, the current harmonic component fed by any DC charging pile into the AC distribution network satisfies the preset distortion rate; and

[0046] The reactive current fed by any DC charging pile into the AC distribution network satisfies the preset power factor.

[0047] The DC charging pile and charging station for electric vehicles provided by the present invention are provided with a DC / AC inverter module, an AC / DC rectifier module, and an inverter module control unit. The inverter module control unit generates an inverter control instruction according to the current signal and voltage signal on the AC distribution network side obtained in real time and the preset harmonic distortion rate and power factor. The DC / AC inverter module responds to the inverter control instruction, obtains DC electric energy from the AC / DC rectifier module, and inversely converts it into an AC waveform corresponding to the inverter control instruction, so that the AC waveform fed into the AC distribution network side by the entire DC charging pile meets the preset harmonic distortion rate and power factor, thereby improving and enhancing the power quality of the power grid connected to the electric vehicle charging facilities, making it meet the relevant national and industrial standards, and promoting the development of the electric vehicle charging facilities industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The exemplary embodiments of the present invention can be more completely understood by referring to the following drawings:

[0049] Figure 1 Schematic diagram of the composition of the DC charging pile for electric vehicles according to the preferred embodiment of the present invention;

[0050] Figure 2 Schematic diagram of the control of the DC / AC inverter module and the inverter module control unit of the DC charging pile for electric vehicles according to the preferred embodiment of the present invention;

[0051] Figure 3 Schematic diagram of the composition of the charging station according to the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] Now, the exemplary embodiments of the present invention will be introduced with reference to the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not limitations on the present invention. In the drawings, the same unit / element is denoted by the same reference numeral.

[0053] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. In addition, it can be understood that the terms defined in the commonly used dictionary should be understood as having a meaning consistent with the context of their related fields, and should not be understood as idealized or overly formal meanings.

[0054] Electric vehicle, abbreviated as EV for Electric Vehicle.

[0055] Battery management system, abbreviated as BMS for short.

[0056] Specifically, the distortion rate is used to characterize the degree of waveform distortion and is an index for measuring the power quality. To prevent the harm of harmonics in the power system, the harmonic management standard requires that the voltage distortion rate and harmonic content at the connection point do not exceed the specified limits.

[0057] DC charging piles need to rectify alternating current into direct current, and the load they carry (i.e., the DC battery) is a non-linear load, which will have a negative impact on the power quality of the AC distribution network. According to existing actual operation experience, it is mainly manifested in the following two aspects:

[0058] 1) Excessive harmonics. Since the AC / DC rectification is used to convert the mains alternating current into direct current for charging the electric vehicle's battery, current and harmonic voltage harmonics will be generated on the AC distribution network side. After adopting the PWM rectification technology, theoretically, the current harmonics generated in the AC / DC rectification process are very small (e.g., about 1%). However, during actual operation, the total distortion rate of the current waveform of some DC charging piles on the AC distribution network side can reach about 7% - 10%.

[0059] 2) Reactive power problem. Actual operation shows that the power factor of the DC charging pile is negative, that is, it presents capacitive reactive power to the outside (i.e., the AC distribution network). Therefore, the DC charging pile needs to absorb reactive power.

[0060] Aiming at the problems of excessive current harmonics fed into the AC distribution network by the current electric vehicle DC charging piles and ineffective reactive power compensation and other power quality problems, the present invention proposes an electric vehicle DC charging pile and charging station with the function of improving power quality.

[0061] Field operation shows that the harmonic voltage on the grid side connected to the DC charging pile is basically generated by harmonic current. As long as the harmonic current can be filtered out, the voltage waveform will be greatly improved accordingly.

[0062] Specifically, a smaller-capacity inverter module is set up, and the AC current generated by it is used to compensate for the current harmonics and reactive current (i.e., reactive power) generated by a larger-capacity rectifier module when charging the battery. Specifically, by servo-controlling in real time the AC current output by the smaller-capacity inverter module, the harmonic current generated by the rectifier module when the charging pile charges the battery is suppressed, and the capacitive reactive current generated by the rectifier module when the charging pile charges the battery is absorbed, thereby improving the problems of excessive harmonics and capacitive reactive power of the DC charging pile, so that the harmonic level (corresponding to the harmonic distortion rate) and reactive power (corresponding to the power factor) fed by the DC charging pile into the AC distribution network meet the requirements of relevant national standards.

[0063] Such as Figure 1As shown, the DC charging pile for electric vehicles in this embodiment includes:

[0064] An AC / DC rectification module, which includes a rectified DC side and a rectified AC side. The rectified AC side is used to connect to the AC distribution network to obtain electrical energy from the AC distribution network; the rectified DC side is used to connect to the electric vehicle to charge the electric vehicle.

[0065] A DC / AC inversion module, which includes an inverted DC side and an inverted AC side. The inverted DC side obtains electrical energy from the rectified DC side; the inverted AC side is used to connect to the AC distribution network.

[0066] An inversion module control unit, which is used to generate an inversion control command according to the acquired current signal and voltage signal on the AC distribution network side, the preset harmonic distortion rate, and power factor when the AC / DC rectification module charges the electric vehicle.

[0067] The DC / AC inversion module is also used to respond to the inversion control command, obtain electrical energy from the AC / DC rectification module and invert it into an AC waveform corresponding to the inversion control command, so that the current waveform fed into the AC distribution network side by the DC charging pile meets the preset harmonic distortion rate and power factor.

[0068] In the DC charging pile for electric vehicles in this embodiment, the DC side of the DC / AC inversion module is connected to DC electrical energy, and its AC side feeds AC current into the AC distribution network. The inversion module control unit generates an inversion control command, which is also the given input of the DC / AC inversion module, that is, the expected AC waveform output by the DC / AC inversion module. In response to this inversion control command, the DC / AC inversion module controls the inversion power unit through the embedded control unit in a closed loop and outputs this AC waveform.

[0069] Specifically, the inversion module control unit respectively determines the current harmonic component and the reactive current according to the acquired voltage waveform and current waveform; and constructs the given input to the DC / AC inversion module, that is, the AC waveform, according to the current harmonic component and the reactive current.

[0070] During specific implementation, in order to independently control the total distortion rate of the current waveform and the reactive current, the DC charging pile for electric vehicles in this embodiment further includes:

[0071] A current signal acquisition module;

[0072] The current signal acquisition module is used to acquire the current signal i on the AC distribution network side;

[0073] Correspondingly, the inversion module control unit is used to obtain the fundamental wave signal i by passing the current signal i through a low-pass filter f ; and take the difference between i and i f to obtain the harmonic component i in the current signal ih ; and multiplying i h by the harmonic compensation coefficient ɑ to obtain a harmonic compensation command i h * ; and using the harmonic compensation command i h * as an inverter control command and inputting it into the DC / AC inverter module.

[0074] Specifically, when implemented, to independently control the total harmonic distortion rate of the current waveform and the reactive current, the DC charging pile for electric vehicles in this embodiment further includes:

[0075] a voltage signal acquisition module and a current signal acquisition module;

[0076] The voltage signal acquisition module is used to acquire the voltage signal u on the AC distribution network side;

[0077] The current signal acquisition module is used to acquire the current signal i on the AC distribution network side;

[0078] Correspondingly, the inverter module control unit is used to obtain a voltage phase value by passing the voltage signal u through a phase-locked loop; according to the voltage phase value and the current signal i, obtain the reactive current i in the current signal i re ; multiplying the reactive current i re by the reactive compensation coefficient β to obtain a reactive compensation command i re * ; and using the reactive compensation command i re * as an inverter control command and inputting it into the DC / AC inverter module.

[0079] Specifically, when implemented, the DC charging pile for electric vehicles in this embodiment further includes:

[0080] a voltage signal acquisition module and a current signal acquisition module;

[0081] The voltage signal acquisition module is used to acquire the voltage signal u on the AC distribution network side;

[0082] The current signal acquisition module is used to acquire the current signal i on the AC distribution network side;

[0083] Correspondingly, the inverter module control unit is used to obtain a voltage phase value by passing the voltage signal u through a phase-locked loop; according to the voltage phase value and the current signal i, obtain the reactive current i in the current signal i re ; multiplying the reactive current i re by the reactive compensation coefficient β to obtain a reactive compensation command i re * ; and

[0084] obtaining a fundamental wave signal i by passing the current signal i through a low-pass filter f ; and taking i and if The difference is taken to obtain the harmonic component i in the current signal i h ; and i h is multiplied by the harmonic compensation coefficient ɑ to obtain the harmonic compensation command i h * ; and

[0085] The reactive power compensation command i re * and the harmonic compensation command i h * are summed to obtain the inverter control command; and the inverter control command is input to the DC / AC inverter module.

[0086] In specific implementation, the DC fast charger for electric vehicles in this embodiment further includes:

[0087] A rectifier module control unit, which is used to generate a rectification control command according to the acquired current signal and voltage signal on the AC distribution network side and the charging demand and battery state information recorded in the charging request when the charging request of the electric vehicle is obtained;

[0088] An AC / DC rectifier module, which is used to respond to the rectification control command, obtain electric energy from the AC distribution network and rectify it into a DC current waveform suitable for the electric vehicle, and charge the electric vehicle; and

[0089] Feed the AC waveform generated incidentally during rectification into the AC distribution network side.

[0090] It should be understood that the rectifier module control unit is also the Figure 1 main controller in

[0091] In specific implementation, the DC / AC inverter module of the DC fast charger for electric vehicles in this embodiment includes an embedded control unit and a power unit;

[0092] The embedded control unit generates a given input command according to the acquired inverter control command and the actual output fed back by the power unit, and sends it to the power unit;

[0093] The power unit responds to the given input command to generate an actual output, that is, the AC waveform corresponding to the inverter control command.

[0094] In specific implementation, the preset power factor of the DC fast charger for electric vehicles in this embodiment is a positive value and not less than 0.95 (or a value closer to 1.0);

[0095] The preset total harmonic distortion rate is not greater than 1%.

[0096] In specific implementation, the value range of the harmonic compensation coefficient of the DC fast charger for electric vehicles in this embodiment is (-1, 0);

[0097] When the harmonic compensation coefficient ɑ is 0, the inverter control command is zero, and the DC / AC inverter module does not suppress the harmonic current component generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0098] When the harmonic compensation coefficient ɑ is a value greater than -1 and less than 0, the inverter control command is not zero, and the AC waveform corresponding to the inverter control command output by the DC / AC inverter module compensates for the harmonic current component generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0099] In specific implementation, for the DC charging pile of the electric vehicle in this embodiment, the value range of the reactive power compensation coefficient is (-2, 0).

[0100] When the reactive power compensation coefficient β is 0, the inverter control command is zero, and the DC / AC inverter module does not perform reactive power compensation on the reactive current generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0101] When the reactive power compensation coefficient β is a value greater than -2 and less than 0, the inverter control command is not zero, and the AC waveform corresponding to the inverter control command output by the DC / AC inverter module compensates for the reactive power generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0102] In specific implementation, the control unit of the inverter module in this embodiment determines the current harmonic component and the reactive current respectively according to the acquired voltage waveform and current waveform; and constructs the given input, that is, the AC waveform, input to the DC / AC inverter module according to the current harmonic component and the reactive current.

[0103] In specific implementation, the control unit of the inverter module in this embodiment determines the harmonic compensation coefficient ɑ and the reactive power compensation coefficient β respectively according to the preset total harmonic distortion rate of the current waveform and the preset power factor (such as, 1.0 or 0.98) (that is, the control target); multiplies the current harmonic component by the harmonic compensation coefficient ɑ, multiplies the reactive current by the reactive power compensation coefficient β, and sums these two products to obtain the given input, that is, the AC waveform, input to the DC / AC inverter module.

[0104] Specifically, the compensation coefficient is determined when setting the control target; both the harmonic compensation coefficient ɑ and the reactive power compensation coefficient β are dimensionless numbers.

[0105] Specifically, the harmonic compensation coefficient is set to compensate for the harmonic current components generated by the rectifier module of the DC charging pile and fed into the AC distribution network. Its value range is (-1, 0), where the negative sign indicates "phase inversion". When the harmonic compensation coefficient is 0, it means that the DC / AC inverter module does not need to output to suppress the harmonic current components generated by the rectifier module of the DC charging pile when charging the battery; at this time, all the harmonic current components generated by the rectifier module of the DC charging pile are fed into the AC distribution network. When the harmonic compensation coefficient is -1, it means that the DC / AC inverter module outputs a servo-controlled AC waveform to compensate for the harmonic current components generated by the rectifier module of the charging pile when charging the battery, so that the total harmonic current components fed into the AC distribution network by the DC charging pile as a whole are 0; when the harmonic compensation coefficient is a value greater than -1 and less than 0, the DC / AC inverter module outputs an AC waveform corresponding to the inverter control command and feeds it into the AC distribution network to compensate for the harmonic current components generated by the rectifier module of the DC charging pile and fed into the AC distribution network.

[0106] Specifically, the reactive power compensation coefficient is set to compensate for the reactive power generated when the DC charging pile charges the battery. Its value range is (-2, 0), where the negative sign indicates "phase inversion". When the reactive power compensation coefficient is 0, it means that the DC / AC inverter module does not need to output servo-control to achieve reactive power compensation; at this time, all the capacitive reactive power generated when the charging pile charges the battery is fed into the AC distribution network. When the reactive power compensation coefficient is -1, it means that the DC / AC inverter module outputs a servo-controlled AC waveform (i.e., the inverted reactive current) to compensate for the capacitive reactive power generated when the DC charging pile charges the battery, so that the DC charging pile appears as a resistor externally. Considering that there are certain control errors in the control system, in order to ensure that the capacitive reactive power generated by the DC charging pile when charging the battery is fully compensated by the DC / AC inverter module, a certain margin is usually taken, such as taking the reactive power compensation coefficient as -2. In this way, the inductive reactive power generated by the DC / AC inverter module in real-time servo-control is greater than the capacitive reactive power of the charging pile, so that the DC charging pile appears as a resistive-inductive externally. When the reactive power compensation coefficient is a value greater than -2 and less than 0, the inverter control command is not zero, and the DC / AC inverter module outputs an AC waveform corresponding to the inverter control command to compensate for the reactive power generated by the AC / DC rectifier module of the DC charging pile when charging the battery.

[0107] Specifically, according to the actual control needs, combined with the above value rules of the harmonic compensation coefficient ɑ and the reactive power compensation coefficient β, the total harmonic distortion rate of the current waveform and the reactive current can be controlled independently.

[0108] Specifically, according to the acquired voltage waveform and current waveform, the fundamental current and harmonic current are separated, and the current harmonic components are determined; according to the acquired voltage waveform, the voltage phase is separated, and the reactive current is determined based on the voltage phase and the current waveform.

[0109] The overall control schematic block diagram of the inverter module control unit and the DC / AC inverter module is as Figure 2 shown, where u is the voltage signal on the AC distribution network side acquired by the voltage signal acquisition module, and i is the current signal on the AC distribution network side acquired by the current signal acquisition module.

[0110] In specific implementation, the voltage signal acquisition module of this embodiment is a voltage transformer arranged on the AC distribution network side; the current signal acquisition module is a current transformer arranged on the AC distribution network side.

[0111] As Figure 2 shown, in the inverter module control unit, the current signal i passes through a low-pass filter (Low Pass Filter, abbreviated as LPF) to obtain the fundamental signal i f ; take the difference between i and i f to obtain the harmonic component i h in the current signal i. After multiplying i h by the harmonic compensation coefficient ɑ, the harmonic compensation command i h * of the DC / AC inverter module is obtained.

[0112] In the inverter module control unit, the voltage signal u passes through a phase-locked loop (Phase Locked Loop, PLL) to obtain the voltage phase value; according to its phase value, combined with the current signal i, the reactive current i re in i can be obtained. After multiplying the reactive current i re by the reactive compensation coefficient β, the reactive compensation command i re * of the DC / AC inverter module is obtained. Summing i h * and i re * yields the inverter control command input to the DC / AC inverter module, that is, the AC waveform i * . Denote the actual output current of the DC / AC inverter module as i2.

[0113] In specific implementation, the DC / AC inverter module of this embodiment is embedded with a proportional-integral (Proportional-Integral, abbreviated as PI) control unit. When the DC / AC inverter module adopts PI control, at time t, the output of the proportional-integral control unit is:

[0114]

[0115] where \(e(t)=u(t)-x(t)\); (2)

[0116] Equation (1) is PI regulation in the continuous domain; where

[0117] \(y(t)\) is the output of the proportional-integral control unit, which is also the given input of the power unit of the DC / AC inverter module; \(x(t)\) is the actual output of the power unit of the DC / AC inverter module, that is Figure 2 \(i_2\) in; \(u(t)\) is the inverter control command input to the DC / AC inverter module, that is Figure 2 \(i\) in * .

[0118] When implementing the proportional-integral control unit of the DC / AC inverter module using digital control technology, Equation (1) is discretized to obtain:[[]]

[0119]

[0120] In Equation (3), \(Y(n)\) is the given input at time \(n\), and \(X(n - 1)\) is the actual output at time \((n - 1)\).

[0121] Equation (3) is a position-type PI regulator. Since its integral operation requires accumulating a large number of errors, it is not suitable for direct use in digital control. It needs to be transformed into the form of a recursive PI regulator. The transformation method is as follows:[[]]

[0122] Following Equation (3) and substituting \((n - 1)\) for \(n\), we get:[[]]

[0123]

[0124] Denote the difference between the given input (i.e., the command signal) and the actual output (i.e., the feedback signal) as \(e\), then we have:[[]]

[0125] \(e(j)=Y(j)-X(j)\); (5)

[0126] Subtract Equation (4) from Equation (3) and substitute Equation (5) to obtain:[[]]

[0127] \(Y(n)=Y(n - 1)+K\) P \(\cdot[e(n - 1)-e(n - 2)]+K\) I \(\cdot e(n - 1)\); (6)

[0128] Equation (6) is the mathematical representation of the recursive PI regulator. Compared with the position-type PI regulator, the recursive PI regulator requires fewer variables for operation, which is beneficial for digital programming.[[]]

[0129] It should be understood that the proportional-integral control embedded in the above DC / AC inverter module is only taken as a specific example. The DC / AC inverter module can also embed other control methods disclosed in the prior art, such as hysteresis control, adaptive control, neural network control, etc., which will not be elaborated here.

[0130] In specific implementation, the DC / AC inverter module of this embodiment responds to the inverter control instruction, outputs an AC waveform on its AC side, and feeds it into the AC distribution network side, so that the power factor of the charging pile on the AC distribution network side is a preset power factor, and the current waveform fed into the AC distribution network is not greater than the preset total current waveform distortion rate.

[0131] Specifically, the preset power factor is a positive value and not less than 0.95 (or a value closer to 1.0); the total distortion rate of the preset current waveform is not greater than 1%.

[0132] In specific implementation, in terms of hardware, a DC / AC inverter module is added to an existing DC charging pile, and a voltage transformer and a current transformer are arranged on the AC distribution network side; in terms of software, an inverter module control unit is added and set on the original main controller unit.

[0133] It should be understood that Figure 1 is a schematic diagram of the principle. In specific implementation, the charging pile and the electric vehicle are connected by a multi-core cable with a multi-core connector arranged at its end, and each core of the multi-core cable is used to transmit communication signals and power signals.

[0134] Specifically, the AC power supply is directly connected to the mains AC distribution network, which can be a single-phase 220V power supply or a three-phase 380V power supply.

[0135] The main controller (i.e., the charging controller) determines the current charging demand and battery state of the EV based on the communication information with the battery management system (Battery Management System, abbreviated as BMS) of the EV, and at the same time controls the AC / DC rectifier module to output DC power to charge the power battery according to the limitations of many factors such as the temperature rise of the charging pile itself and the power and current of the AC distribution network.

[0136] Preferably, the AC / DC rectifier module adopts PWM rectification instead of phase-controlled rectification.

[0137] Particularly, since the geometric size of the DC charging pile is generally large, while the geometric sizes of the DC / AC inverter module and the inverter module control unit are usually small, the inverter module and the inverter module control unit can be encapsulated in the DC charging pile together, so as to form an electric vehicle DC charging pile with the function of improving power quality.

[0138] The capacity of the DC / AC inverter module is not greater than 10% of the capacity of the AC / DC rectifier module.

[0139] Preferably, the capacity of the DC fast charger for electric vehicles is 60 kW.

[0140] The DC fast charger for electric vehicles has the following characteristics:

[0141] 1. Significantly reduce the current harmonic value fed by the charger into the AC distribution network to meet the national standard.

[0142] 2. Be able to controllably adjust the power factor of the charger on the AC distribution network side with a preset power factor, so that the DC fast charger as a whole does not present a capacitive nature.

[0143] 3. The capacity and size of the set AC / DC inverter module are both small; by integrating the AC / DC inverter module and the inverter module control unit inside the charger, a DC fast charger for electric vehicles with the function of improving power quality can be formed.

[0144] As Figure 3 shown, the charging station of this embodiment includes a plurality of the above-mentioned DC fast chargers for electric vehicles; each DC fast charger is respectively connected to the AC distribution network; each DC fast charger independently charges an electric vehicle; when charging the battery of an electric vehicle, the current harmonic component fed by any DC fast charger into the AC distribution network meets the preset distortion rate, and the reactive current fed by any DC fast charger into the AC distribution network meets the preset power factor.

[0145] Specifically, the current DC fast chargers have two modes: single-pile single-gun and single-pile double-gun. For a single-pile single-gun charger, there is only one charging gun for one pile and can only charge one electric vehicle at the same time; while for a single-pile double-gun charger, there are two charging guns for one pile and can charge two electric vehicles at the same time.

[0146] Different from the prior art in which a common power quality improvement device is centrally set for a charging station with multiple chargers, in the charging station of this embodiment, each DC fast charger independently improves the power quality fed into the AC distribution network, thereby ensuring that the power quality of the whole station meets the relevant standards. Each charger in the charging station of this embodiment is independently controlled, with flexible control, less energy consumption, and energy conservation and environmental protection.

[0147] Different from the prior art in which a 30% reactive power compensation capacity needs to be reserved for a charging station with multiple chargers, in the charging station of this embodiment, no additional reactive power compensation capacity needs to be set, reducing the procurement cost and operation and maintenance cost. Any DC fast charger in the charging station of this embodiment can flexibly control the power factor fed into the AC distribution network, improving the control flexibility.

[0148] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0149] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0150] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0151] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0152] The present invention has been described above by referring to a few embodiments. However, as is well known to those skilled in the art, as defined by the appended patent claims, other embodiments equivalent to those disclosed above of the present invention equally fall within the scope of the present invention.

[0153] Generally, all terms used in the claims are construed according to their ordinary meaning in the technical field, unless otherwise expressly defined therein. All references to "a / the [device, component, etc.]" are to be construed openly as being at least one instance of the device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless expressly stated.

Claims

1. An electric vehicle DC charging pile, characterized in that, Comprising: An AC / DC rectification module, which includes a rectified DC side and a rectified AC side. The rectified AC side is used to connect to the AC distribution network to obtain electric energy from the AC distribution network; The rectified DC side is used to connect to an electric vehicle to charge the electric vehicle; A rectification module control unit, which is used to generate a rectification control instruction according to the obtained current signal and voltage signal on the AC distribution network side, and the charging demand and battery state information recorded in the charging request when a charging request of the electric vehicle is obtained; The AC / DC rectification module is further used to, in response to the rectification control instruction, obtain electric energy from the AC distribution network, rectify it into a DC current waveform adapted to the electric vehicle, and charge the electric vehicle; and feed the AC waveform generated incidentally during rectification into the AC distribution network side; The AC / DC rectification module and the electric vehicle as a whole present a capacitive characteristic to the AC distribution network; A DC / AC inversion module, which includes an inverted DC side and an inverted AC side. The inverted DC side obtains electric energy from the rectified DC side; the inverted AC side is used to connect to the AC distribution network; An inversion module control unit, which is used to generate an inversion control instruction according to the obtained current signal and voltage signal on the AC distribution network side, a preset harmonic distortion rate, and a power factor when the AC / DC rectification module charges the electric vehicle; the preset power factor is a positive value and not less than 0.95; the preset harmonic distortion rate is not greater than 1%; The DC / AC inversion module is further used to, in response to the inversion control instruction, obtain electric energy from the AC / DC rectification module and invert it into an AC waveform corresponding to the inversion control instruction, so that the current waveform fed into the AC distribution network side by the DC charging pile meets the preset harmonic distortion rate and power factor, and the DC charging pile as a whole does not present a capacitive characteristic to the AC distribution network; The capacity of the DC / AC inversion module is not greater than 10% of the capacity of the AC / DC rectification module; The AC / DC inversion module and the inversion module control unit are integrated inside the charging pile to form an electric vehicle DC charging pile with a function of improving power quality.

2. The electric vehicle DC charging pile according to claim 1, characterized in that, Further comprising: A current signal acquisition module; the current signal acquisition module is used to acquire the current signal i on the AC distribution network side; Accordingly, the inverter module control unit is used to obtain a fundamental wave signal i from the current signal i through a low-pass filter f ; and take the difference between i and i f to obtain a harmonic component i in the current signal i h ; and multiply i h by a harmonic compensation coefficient ɑ to obtain a harmonic compensation command i h * ; and use the harmonic compensation command i h * as the inverter control command and input it into the DC / AC inverter module.

3. The electric vehicle DC charging pile according to claim 1, characterized in that, Further comprising: A voltage signal acquisition module and a current signal acquisition module; The voltage signal acquisition module is used to acquire the voltage signal u on the AC distribution network side; The current signal acquisition module is used to acquire the current signal i on the AC distribution network side; Accordingly, the inverter module control unit is configured to obtain a voltage phase value from the voltage signal u through a phase-locked loop; obtain a reactive current i in the current signal i based on the voltage phase value and the current signal i re ; multiply the reactive current i re by a reactive power compensation coefficient β to obtain a reactive power compensation command i re * ; and use the reactive power compensation command i re * as the inverter control command and input it to the DC / AC inverter module.

4. The electric vehicle DC charging pile according to claim 1, characterized in that, Further comprising: A voltage signal acquisition module and a current signal acquisition module; The voltage signal acquisition module is used to acquire the voltage signal u on the AC distribution network side; The current signal acquisition module is used to acquire the current signal i on the AC distribution network side; Accordingly, the inverter module control unit is configured to obtain a voltage phase value from the voltage signal u through a phase-locked loop; obtain a reactive current i in the current signal i according to the voltage phase value and the current signal i re ; multiply the reactive current i re by a reactive power compensation coefficient β to obtain a reactive power compensation command i re * ; and The current signal i is passed through a low-pass filter to obtain a fundamental wave signal i f ; and the difference between i and i f is taken to obtain the harmonic component i h in the current signal i; and i h is multiplied by a harmonic compensation coefficient ɑ to obtain a harmonic compensation command i h * ; And The reactive power compensation command i re * and the harmonic compensation command i h * are summed to obtain the inverter control command; and the inverter control command is input to the DC / AC inverter module.

5. The electric vehicle DC charging pile according to any one of claims 2, 3, and 4, characterized in that, The DC / AC inversion module includes an embedded control unit and a power unit; The embedded control unit generates a given input instruction according to the obtained inversion control instruction and the actual output feedback by the power unit, and sends it to the power unit; The power unit generates an actual output, i.e., an AC waveform corresponding to the inverter control instruction, in response to the given input instruction.

6. The electric vehicle DC charging pile according to claim 2, characterized in that, The value range of the harmonic compensation coefficient ɑ is (-1, 0); When the harmonic compensation coefficient ɑ is 0, the inverter control instruction is zero, and the DC / AC inverter module does not suppress the harmonic current components generated by the AC / DC rectifier module of the DC charging pile when charging the electric vehicle. When the harmonic compensation coefficient ɑ is a value greater than -1 and less than 0, the inverter control instruction is not zero, and the AC waveform corresponding to the inverter control instruction output by the DC / AC inverter module compensates for the harmonic current components generated by the AC / DC rectifier module of the DC charging pile when charging the electric vehicle.

7. The DC charging pile for electric vehicles according to claim 3, characterized in that, The value range of the reactive power compensation coefficient β is (-2, 0); When the reactive power compensation coefficient β is 0, the inverter control instruction is zero, and the DC / AC inverter module does not compensate for the reactive current generated by the AC / DC rectifier module of the DC charging pile when charging the electric vehicle. When the reactive power compensation coefficient β is a value greater than -2 and less than 0, the inverter control instruction is not zero, and the AC waveform corresponding to the inverter control instruction output by the DC / AC inverter module compensates for the reactive power generated by the AC / DC rectifier module of the DC charging pile when charging the electric vehicle.

8. An electric vehicle charging station, characterized in that, Including: A plurality of DC charging piles as described in claim 1; Each DC charging pile is respectively connected to the AC distribution network; Each DC charging pile charges the electric vehicle independently; When charging the electric vehicle, the current harmonic components fed by any DC charging pile into the AC distribution network meet a preset distortion rate; and The reactive current fed by any DC charging pile into the AC distribution network meets a preset power factor; The charging station does not need to reserve 30% of the reactive power compensation capacity.

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