Multi-port electric vehicle fast charging system and control method thereof

Abstract

The application belongs to the technical field of electric vehicle charging, and specifically discloses a multi-port electric vehicle fast charging system and a control method thereof. In view of the problem that the existing two-stage solid-state transformer charging system is difficult to realize sub-module voltage balance, high power factor and full load range operation at low cost, the system adopts the structure of cascaded H-bridge rectification stage, multi-active bridge isolation stage and flexible power switching matrix, realizes rectification stage capacitor voltage balance through dq decoupling control strategy, and realizes accurate power distribution of the isolation stage in combination with phase shift control and power decoupling algorithm. The control method dynamically adjusts the power output of the isolation stage and the on-off of the relays in the flexible power switching matrix according to the electric vehicle access sequence, and ensures the balance of the voltages of the H-bridge capacitors. The application supports 100% unbalanced load operation without additional reactive compensation or balanced winding, has the advantages of high power factor, compact structure and low cost, and can realize simultaneous fast charging of multiple electric vehicles.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle (EV) technology, and in particular to a multi-port fast charging system for electric vehicles based on a two-stage SST (solid-state transformer) and its control method. Background Technology

[0002] The typical architecture of existing SST-based multiport electric vehicle fast charging systems is a three-stage structure, consisting of a rectifier stage, an isolation stage, and an electric vehicle charger converter. To reduce the number of power conversion stages in SST-based multiport electric vehicle fast charging systems, a two-stage structure is proposed, comprising a rectifier stage and an isolation stage that also functions as an electric vehicle charger converter. This eliminates the need for a dedicated electric vehicle charger converter, thereby reducing system size and cost.

[0003] However, multi-port electric vehicle fast charging systems based on two-stage SST need to address the problem of unbalanced capacitor voltage in the sub-modules of the rectifier stage converter. Furthermore, existing multi-port electric vehicle fast charging systems based on two-stage SST employ reactive current injection strategies or add power balancing windings to operate under 100% unbalanced load conditions, which increases the system's size, cost, and losses. Summary of the Invention

[0004] This invention provides a multi-port electric vehicle fast charging system and its control method, which solves the technical problem that the existing multi-port electric vehicle fast charging system based on two-stage SST cannot simultaneously achieve voltage balance of sub-module capacitors in the rectifier stage converter, high power factor, and full-range operation under different load conditions at a low cost.

[0005] To address the above technical problems, this invention first provides a multi-port electric vehicle fast charging system, including a rectifier stage, an isolation stage, and a flexible power switching matrix; the rectifier stage includes... A series of H-bridges; the isolation level adopts Multiple active bridge converters, each Each H-bridge is connected to a multi-active bridge converter. One input terminal, one active bridge converter Each output terminal is connected to a flexible power switching matrix. The flexible power switching matrix has one input terminal; Each input terminal is connected to the isolation level. Each output terminal; the flexible power switching matrix is ​​equipped with... One output terminal, used for connection A car.

[0006] Preferably, the active power of each H-bridge is controlled to meet the following requirements: ,in Indicates the first The active power of the H-bridge This represents the DC component of the H-bridge capacitor voltage. It is the amplitude of the grid current. It is the input inductance on the grid side. This is the angular frequency of the grid voltage.

[0007] Preferably, a voltage balance control strategy based on dq decoupling control is adopted. The output voltage of each H-bridge is a DC voltage reference value, specifically including:

[0008] By sampling the voltage of each H-bridge capacitor to And compared with DC voltage reference value respectively For comparison, a PI controller is used to generate the d-axis compensation component. to ;

[0009] Compensation components to Duty cycle with d-axis After superposition, the d-axis duty cycle of each H-bridge is generated. to ;

[0010] Will to q-axis duty cycle Phase with grid voltage The final d-axis duty cycle of each H-bridge is obtained by inverse dq / am transformation. to ;

[0011] Phase-shifted sinusoidal pulse width modulation technology is used to transform the duty cycle signal. to Convert to the PWM drive signal required for H-bridge to .

[0012] Preferably, the d-axis duty cycle and q-axis duty cycle Generate through the following steps:

[0013] Calculate the average value of all H-bridge capacitor voltages and subtract it from twice the power frequency ripple in the total DC voltage of the H-bridge calculated using the voltage ripple calculation method. Then, compare this result with the DC voltage reference value. The input voltage regulator uses a PI controller to obtain the d-axis current reference value. ;

[0014] grid-side current Generating virtual current with a 90° lag , to the actual current Virtual current Phase with grid voltage The d-axis and q-axis current components are obtained through am / dq transformation. and ;

[0015] d-axis current reference value d-axis current component The input is a d-axis current regulator using a PI controller, and its output is related to the introduced q-axis current. The decoupling components are subtracted to obtain the d-axis duty cycle signal. ;

[0016] q-axis current reference value q-axis current component The input uses a PI controller for the q-axis current regulator, and its output is related to the introduced d-axis current. The decoupled components are added together to obtain the q-axis duty cycle signal. .

[0017] Preferably, during the charging process, a phase-shifting control strategy and a power decoupling algorithm are used to control the power of the input and output ports of the isolation stage, so that each primary side port of the isolation stage provides the same power, the output power of each secondary side port gradually approaches its respective output power reference value, and each secondary side port has constant voltage and constant current characteristics.

[0018] Preferably, the specific process of controlling the input and output port power of the isolation stage using a phase-shift control strategy and a power decoupling algorithm is as follows:

[0019] The sampled DC voltage output value and the reference DC voltage value of the secondary side port are input to a voltage regulator using a PI controller to obtain the reference DC current value of the secondary side port.

[0020] The secondary-side port output DC current sample value is multiplied by the secondary-side port DC voltage reference value to obtain the secondary-side port output power feedforward;

[0021] The sampled DC current value and the reference DC current value at the secondary side port are input to a current regulator using a PI controller. The current regulator outputs a power regulation value, which is then added to the power feedforward value to obtain the output power reference value.

[0022] The output power reference value is input to the power decoupling control algorithm module. The power decoupling algorithm is used to determine the phase shift angle, and the phase shift angle is transmitted to the isolation stage to control the power of the input and output ports of the isolation stage.

[0023] Preferably, the flexible power switching matrix uses multiple relays to... One input terminal is connected to One output terminal.

[0024] Preferably, the multi-active bridge converter adopts a primary-side... One winding, secondary side Multi-winding transformer with one winding. , .

[0025] Preferably, the H-bridge in the rectifier stage is replaced with a diode-clamped three-level full bridge or an active-clamped three-level full bridge, and the H-bridge in the multi-active bridge converter is replaced with a two-level half bridge, a diode-clamped three-level half bridge, or an active-clamped three-level half bridge.

[0026] The present invention also provides a control method for the aforementioned multi-port electric vehicle fast charging system, the key feature of which is that the control method includes the following steps:

[0027] S1. Obtain the number of electric vehicles that need to be charged. and their respective requested charging power to ;

[0028] S2. When the first electric vehicle connects, the charging power is adjusted according to the request of the first electric vehicle. The output power of each rectifier H-bridge and each output port of the isolation stage is determined with the goal of ensuring that the power of each rectifier H-bridge is equal.

[0029] S3. By controlling the drive signals of the rectifier stage and the isolation stage, the output power of the isolation stage output port used for the next electric vehicle is gradually reduced from the current value to zero, while the output power of other isolation stage output ports connected to the currently charging electric vehicle is increased, so as to keep the total charging power of the currently charging electric vehicle unchanged.

[0030] S4. When the output power of the isolation stage output port used for the next electric vehicle drops to zero, disconnect it from the current electric vehicle, and then adjust its output voltage to match the battery voltage of the next electric vehicle; after matching, close the relay and connect the next electric vehicle.

[0031] S5. By controlling the drive signals of the rectifier stage and the isolation stage, with the goal of satisfying the requested charging power of each connected electric vehicle and ensuring that the power of each rectifier stage H-bridge is equal, control all working ports of the isolation stage to output new power values.

[0032] S6. Repeat steps S3 to S5 until all electric vehicles are connected and charged with their requested charging power.

[0033] This invention provides a multi-port electric vehicle fast charging system and its control method. The system adopts a structure of cascaded H-bridge rectifier stages, multiple active bridge isolation stages, and a flexible power switching matrix. A dq decoupling control strategy is used to achieve voltage balance in the rectifier stage capacitors, and phase-shift control and a power decoupling algorithm are combined to precisely allocate power to the isolation stages. The control method dynamically adjusts the power output and relay on / off states according to the electric vehicle connection sequence to ensure power balance across all H-bridges. The technical effects achieved by this invention are as follows:

[0034] 1) High integration and low cost: It eliminates the need for a dedicated electric vehicle charging converter, simplifies the structure, and reduces the system size and cost;

[0035] 2) Superior operating performance: The innovative control strategy ensures that the capacitor voltage of the rectifier stage submodule remains balanced even under 100% unbalanced load conditions, and the grid side always maintains a high power factor.

[0036] 3) Strong flexibility and scalability: The flexible power switching matrix and dynamic control method enable the system to simultaneously fast charge multiple electric vehicles with different battery voltages and power requests, achieving true flexible power allocation and full-range operation capability.

[0037] This invention supports 100% unbalanced load operation without the need for additional reactive power compensation or balancing windings. It has the advantages of high power factor, compact structure and low cost, and can enable multiple electric vehicles to be charged simultaneously and quickly. Attached Figure Description

[0038] Figure 1 This is a circuit diagram of a multi-port electric vehicle fast charging system;

[0039] Figure 2 This is the average equivalent circuit model diagram of the rectifier stage;

[0040] Figure 3 This is a schematic diagram based on a single-phase dq decoupling control strategy;

[0041] Figure 4 This is a schematic diagram of a voltage balance control strategy based on single-phase dq decoupling control.

[0042] Figure 5 This is a voltage vector diagram of the rectifier stage;

[0043] Figure 6 This is a circuit diagram of the isolation stage of a MAB converter with a multi-winding transformer;

[0044] Figure 7 It is a polygonal equivalent circuit diagram of a multi-winding transformer;

[0045] Figure 8This is a typical square wave AC voltage and current waveform diagram of a MAB converter using SPS control;

[0046] Figure 9 This is a schematic diagram of a power decoupling algorithm with a PI controller;

[0047] Figure 10 This is a flowchart of the control method for a multi-port electric vehicle fast charging system;

[0048] Figure 11 This is a diagram illustrating the power distribution process when the first electric vehicle connects to the charging system.

[0049] Figure 12 This is a diagram illustrating the power distribution process when the second electric vehicle connects to the charging system. Figure 12 (a) is the circuit diagram for the first step of connecting the second car. Figure 12 (b) is the circuit diagram for the second step of connecting the second car;

[0050] Figure 13 This is a diagram illustrating the power distribution process when the third electric vehicle connects to the charging system. Figure 13 (a) is the circuit diagram for the first step of connecting the third car. Figure 13 (b) is the circuit diagram for the second step of connecting the third car;

[0051] Figure 14 This is a diagram illustrating the power distribution process when the fourth electric vehicle connects to the charging system. Figure 14 (a) is the circuit diagram for the first step of connecting the fourth car. Figure 14 (b) is the circuit diagram for the second step of connecting the fourth car;

[0052] Figure 15 It shows the current and voltage waveforms of the isolation stage and the battery. Figure 15 (a) represents the output current of isolation stage output ports #1, #2, #3, and #4. ), Figure 15 (b) shows the output current of isolation stage output ports #5, #6, #7, and #8. ), Figure 15 (c) represents the output voltages of isolation stage output ports #1, #2, #3, and #4. ) and battery voltage ( ), Figure 15 (d) represents the output voltage of isolation stage output ports #5, #6, #7, and #8. ) and battery voltage ( ), Figure 15 (e) represents the battery charging current. );

[0053] Figure 16 It shows the current and voltage waveforms of the rectifier stage. Figure 16 In the middle (a), the AC current input to the rectifier stage is represented. Figure 16 In the middle (b), the AC voltage of the power grid is represented. Figure 16 In the diagram, (c) represents the output voltage of the cascaded H-bridge. Figure 16 In the middle (d), the capacitor voltage of the H-bridge is represented;

[0054] Figure 17 This is a structural diagram of a three-level full-bridge submodule. Figure 17 (a) shows the structure of the diode-clamped three-level full-bridge submodule. Figure 17 (b) shows the active clamped three-level full-bridge submodule structure;

[0055] Figure 18 This is a diagram of a two-level half-bridge circuit.

[0056] Figure 19 This is a diagram of a three-level half-bridge circuit. Figure 19 Figure (a) shows the structure of a diode-clamped three-level half-bridge circuit. Figure 19 (b) is a schematic diagram of an active clamped three-level half-bridge circuit. Detailed Implementation

[0057] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0058] This invention provides a multi-port fast charging system for electric vehicles based on a two-stage SST, the circuit structure of which is as follows: Figure 1 As shown, it includes a rectifier stage, an isolation stage, and a flexible power switching matrix. The rectifier stage employs a CHB (Cascaded H-Bridge) converter, which includes... A series of H-bridges. The isolation level uses... Multiple active bridge (MAB) converters, each Each H-bridge is connected to one MAB converter. One input terminal, one MAB converter Each output terminal is connected to a flexible power switching matrix. Then the flexible power switching matrix has input terminals, so it has a total of One input terminal. The flexible power switching matrix has... One output terminal, used for connection A vehicle. The flexible power switching matrix is ​​equipped with... A series of relays arranged in an array to Flexible power switching matrices can be used via relays. to Will The output of the MAB converter Connected to electric vehicles Therefore, flexible power allocation can be achieved through appropriate control strategies. Various switching structures can be used as flexible power switching matrices. This paper employs, for example... Figure 1 The full matrix structure shown is not only flexible in power distribution but also easier to understand. Since the flexible power switch matrix does not regulate the voltage and current of the charging ports, the isolation stage also functions as an electric vehicle charging converter.

[0059] Ignoring the resistance of the grid-side circuit, the average equivalent circuit model of the rectifier stage can be derived, such as... Figure 2 As shown. Figure 2 middle, and These represent the grid-side voltage and current, respectively. For input inductance, to for The tracking coefficient of each H-bridge (mainly determined by the parameter mismatch between the gate drive circuit and the power device). to Generated for closed-loop control Duty cycle of each H-bridge, to express The capacitor voltage of the H-bridge to for The capacitance values ​​of the H-bridges, to for The equivalent load of each H-bridge.

[0060] According to Kirchhoff's laws, the following set of differential equations describing the operating characteristics of the rectifier stage can be derived:

[0061] (1)

[0062] To achieve precise control of the rectifier stage active power and submodule DC voltage, this paper adopts a strategy based on single-phase dq decoupling control, the control principle of which is as follows: Figure 3 As shown. Simultaneously, a voltage ripple calculation method is employed to eliminate the double power frequency ripple in the total DC voltage of the H-bridge. Figure 3 middle, This represents the reference value for the H-bridge DC voltage. This represents the average voltage across the H-bridge capacitors. The angular frequency of the grid voltage. This represents the grid voltage amplitude. The system uses a PI controller as the voltage regulator, tracking the DC voltage reference value by controlling the average voltage of all H-bridge capacitors. Its output generates a d-axis current reference value. q-axis current reference value Typically provided by the higher-level dispatch center, its value determines the amount of reactive power injected into the grid. The system uses a phase-locked loop (PLL) to obtain the grid voltage phase. At the same time, by controlling the grid-side current Lag Generating virtual current Finally, the actual current is converted through am / dq transformation. With virtual current The transformation into d-axis and q-axis current components is shown below:

[0063] (2)

[0064] The system employs two PI controllers as the d-axis current regulator and the q-axis current regulator, respectively. These two controllers ensure that the d-axis and q-axis currents can track their respective reference values. This is achieved by introducing... The decoupling component enables decoupling control between the d-axis and q-axis currents, and the controller ultimately generates the d-axis and q-axis duty cycle signals. and .

[0065] Voltage balance control strategies based on single-phase dq decoupling control, such as... Figure 4 As shown. Figure 4 In the process, the H-bridge capacitor voltage is sampled. to And compared with DC voltage reference value respectively For comparison, a PI controller is used to generate the d-axis compensation component. to Compensation components are compared with the d-axis duty cycle. After superposition, the d-axis duty cycle of each H-bridge is generated. to .Will to , and The final d-axis duty cycle of each H-bridge is obtained through the inverse dq / am transform (i.e., the inverse of the am / dq transform). to Finally, phase-shifted sinusoidal pulse width modulation (SPWM) technology is used to adjust the duty cycle signal. to Convert to the PWM drive signal required for H-bridge to .

[0066] Despite adopting such Figure 4 The voltage balance control strategy shown is applicable, but it should be noted that the power imbalance range between the H-bridges still has limitations. Under the assumption that the rectifier stage input power factor is 1, Figure 5 The voltage vector relationship of the rectifier stage is shown. Based on Kirchhoff's laws, the following system of equations can be derived:

[0067] (3)

[0068] (4)

[0069] in, The phasor represents the output voltage of each H-bridge. For the phasor of the grid voltage, It is the phasor of the grid-side current. to This represents the final d-axis duty cycle for each H-bridge. to This represents the final q-axis duty cycle for each H-bridge.

[0070] Substituting equation (4) into equation (3), we can obtain the following equation:

[0071] (5)

[0072] according to Figure 4 , and Since they are in phase, their phase is zero, therefore the following equation can be derived:

[0073] (6)

[0074] in, and These are the amplitudes of the grid voltage and current.

[0075] No. The active power of the H-bridge and reactive power It can be calculated as follows:

[0076] (7)

[0077] According to equation (7), the first The active power of the H-bridge It can be calculated as follows:

[0078] (8)

[0079] At the same time, the total input active power Obtained from the following formula:

[0080] (9)

[0081] Therefore, the magnitude of the grid current can be calculated as follows:

[0082] (10)

[0083] Substituting equation (10) into equation (8), the duty cycle is... for:

[0084] (11)

[0085] Assumption If the reactive power is uniformly distributed in the H-bridge without overmodulation, the following equation can be obtained:

[0086] (12)

[0087] (13)

[0088] Substituting equation (12) into equation (13), the power The following constraints must be met:

[0089] (14)

[0090] To achieve capacitor voltage balance among the H-bridges in a cascaded H-bridge converter, the active power of each H-bridge must meet the constraint range given in equation (14). If this range is exceeded, the capacitor voltage balance will not be maintained due to excessive power imbalance between H-bridges, resulting in the rectifier stage failing to operate normally.

[0091] The isolation stage uses a MAB converter with a multi-winding transformer, and its circuit diagram is as follows. Figure 6 As shown. In Figure 6 In the middle, order , It is the input DC voltage of the primary-side converter. It is the output DC voltage of the secondary-side converter. It is direct current, and the turns ratio of the four-winding transformer is... , It is an equivalent leakage sensation. Winding current of a multi-winding transformer.

[0092] The polygonal equivalent circuit of a multi-winding transformer is as follows: Figure 7 As shown. Figure 7 middle, and respectively converted to port To port The square wave AC voltage and the equivalent winding current, Represents any two ports and The equivalent branch current between any two ports. and Equivalent branch inductance between The derivation formula is as follows:

[0093] (15)

[0094] Among them, the branch inductance equivalent to the primary side of the transformer It is given by the following formula:

[0095] (16)

[0096] Single-phase shift (SPS) control is the most commonly used control strategy in MAB converters, and this paper also adopts this strategy. Typical square-wave AC voltage and current waveforms of a MAB converter using SPS control are shown below. Figure 8 As shown. In Figure 8 middle, It is the switching cycle. It is the first The, the The phase shift angle of the MAB converter. Therefore, the transmission power between any two ports. It can be represented as:

[0097] (17)

[0098] in, It is the switching frequency. It is the first , The input / output DC voltage of a MAB converter can be calculated as follows:

[0099] (18)

[0100] Ignoring power losses in the MAB converter, the total power of all ports is zero. (Settings) The total output power of each port is... Represented as:

[0101] (19)

[0102] As can be seen from equation (19), the total output power of each port is The function means that the output power of each port can be directly determined by... control.

[0103] Since the proposed MAB converter in the two-stage SST-based multi-port fast charging system for electric vehicles is also used as an electric vehicle charging converter, the output power of any port in the MAB converter should be decoupled. Simultaneously, to achieve capacitor voltage balance in the CHB converter, the primary-side port (i.e., Figure 6 ports in ~port Ideally, this will provide the same power, and preferably there will be no power transfer between the primary-side ports. Therefore, let .because , And the output power of each port is Therefore, according to equation (19), the following function is obtained:

[0104] (20)

[0105] Here, the Newton-Raphson iteration method is used to achieve power decoupling, and its iteration function is calculated as follows:

[0106] . (twenty one)

[0107] in It is the Jacobian matrix. It consists of power partial derivatives and is given by the following equation:

[0108] . (twenty two)

[0109] Substituting equations (20) and (22) into equation (21), we can obtain The iterative function is:

[0110] . (twenty three)

[0111] in, Indicates the current iteration number, where This represents the output power reference value generated by the closed-loop controller.

[0112] According to equation (23), the new phase shift angle By using data from previous iterations The phase shift angle is used to obtain the output power. Therefore, the output power of all ports in the MAB converter gradually approaches the output power reference value.

[0113] In the proposed two-stage SST-based multi-port fast charging system for electric vehicles, the MAB converter is also used as the electric vehicle charging converter. Therefore, the secondary port of the MAB converter (i.e. Figure 6Ports #(g+1) to #m in the circuit should possess constant voltage (CV) and constant current (CC) characteristics. Therefore, a power decoupling control with a PI controller is proposed, such as... Figure 9 As shown. In Figure 9 In this context, the PI controller is used as a voltage and current regulator. This is the reference value for the DC voltage at the secondary side port. It is the reference value of the DC current at the secondary side port generated by the voltage regulator. It is the sampled value of the DC voltage output from the secondary side port. It is the sampled value of the DC current output from the secondary side port. This is the output power reference value. A feedforward term is used. To improve the dynamic performance of decoupling control. Finally, the power decoupling algorithm given in equation (23) is used to determine the phase shift angle. (in The specific calculation process is as follows:

[0114] Sampled DC voltage output from the secondary side port Reference value of DC voltage at the secondary side port The input voltage regulator uses a PI controller to obtain the reference value of the DC current at the secondary port. ;

[0115] Sampled DC current output from the secondary side port Reference value of DC voltage at the secondary side port Multiply to obtain the secondary-side port output power feedforward;

[0116] Sampled DC current output from the secondary side port Reference value of DC current at the secondary side port The input is a current regulator using a PI controller. The output of the current regulator is a power regulation value, which is added to the power feedforward value to obtain the output power reference value. ;

[0117] Power reference value The input is fed into the power decoupling control algorithm module, and the power decoupling algorithm given in equation (23) is used to determine the phase shift angle. (in ).

[0118] To illustrate the working principle of the proposed multi-port fast charging system for electric vehicles based on a two-stage SST, the parameters listed in Table 1 are used in the following analysis. The peak phase voltage of the AC grid is 8164V, which is the peak phase voltage of a 10kV distribution AC grid. The system has a rated power of 480kW and can provide four 120kW charging ports. The rectifier stage has 8 H-bridges, the isolation stage has 4 MAB converters, and the MAB uses a 2-input, 2-output four-winding transformer. The number of electric vehicle charging ports is 4. For the rectifier stage, the rated capacitor voltage of the H-bridge is 1200V, and the power devices in the H-bridge are 1700-V SiC MOSFETs or IGBTs. These 1700V SiC MOSFETs / IGBTs have a switching frequency of 5kHz. The capacitance of the H-bridge is 6.7mF. The rectifier stage uses a 16mH input AC inductor. For the MAB converter, the rated DC voltages of the primary-side H-bridge and the secondary-side H-bridge are 1200V and 800V, respectively. Therefore, the power devices in the primary-side H-bridge and the secondary-side H-bridge are 1700-V SiC MOSFETs and 1200-V SiC MOSFETs, respectively. The transformer turns ratio is selected as... Its equivalent leakage inductance is 25uH. A 100uF DC blocking capacitor is used in the simulation, connected in series with the transformer winding. The switching frequency of the MAB converter is 20kHz. The output capacitor of the MAB converter has a capacitance of 500uF, followed by an additional output LC filter. This additional output LC filter is used to further reduce current ripple in the battery charging current. The inductance and capacitance of the additional output LC filter are 2uH and 50uF, respectively. In the simulation, the state of charge (SOC) of the lithium-ion battery is set to 50%, 25%, 10%, and 5%.

[0119] Table 1: Main Simulation Parameters

[0120]

[0121] For the proposed two-stage SST-based multi-port fast charging system for electric vehicles, capacitor voltage balance in the H-bridge of the CHB converter is crucial. Although based on Figure 4 The voltage balance control of the single-phase dq decoupling controller shown is applied to the rectifier stage, but the active power of each rectifier stage H-bridge should be within the constraint range given in equation (14). Otherwise, due to the excessive unbalanced power between the rectifier stage H-bridges, the rectifier stage will not function properly. Therefore, this embodiment of the invention also provides a control method for a multi-port electric vehicle fast charging system, which utilizes a MAB converter and a flexible power switching matrix for dynamic power allocation, such as... Figure 10 As shown, the control method specifically includes the following steps:

[0122] S1. Obtain the number of electric vehicles that need to be charged. and their respective requested charging power to ;

[0123] S2. When the first electric vehicle connects, the charging power is adjusted according to the request of the first electric vehicle. The output power of each rectifier H-bridge and each output port of the isolation stage is determined with the goal of ensuring that the power of each rectifier H-bridge is equal.

[0124] S3. By controlling the drive signals of the rectifier stage and the isolation stage, the output power of the isolation stage output port used for the next electric vehicle is gradually reduced from the current value to zero, while the output power of other isolation stage output ports connected to the currently charging electric vehicle is increased, so as to keep the total charging power of the currently charging electric vehicle unchanged.

[0125] S4. When the output power of the isolation stage output port used for the next electric vehicle drops to zero, disconnect it from the current electric vehicle, and then adjust its output voltage to match the battery voltage of the next electric vehicle; after matching, close the relay and connect the next electric vehicle.

[0126] S5. By controlling the drive signals of the rectifier stage and the isolation stage, with the goal of satisfying the requested charging power of each connected electric vehicle and ensuring that the power of each rectifier stage H-bridge is equal, control all working ports of the isolation stage to output new power values.

[0127] S6. Repeat steps S3 to S5 until all electric vehicles are connected and charged with their requested charging power.

[0128] To more clearly illustrate the proposed dynamic power allocation strategy, this paper presents a case study in which a two-stage SST-based multi-port electric vehicle fast charging system is sequentially connected to four electric vehicles. The charging power of these four electric vehicles is set at 120kW.

[0129] When the first electric car ( When connected to the proposed two-stage SST-based multi-port electric vehicle fast charging system, all relays in the first column of the flexible power switching matrix will close, such as... Figure 11 As shown. To charge the first electric vehicle with a total power of 120kW, the output power of each rectifier stage H-bridge is... This is also equivalent to the output port of each MAB converter. The output power of each rectifier stage H-bridge is the same, so the active power of each rectifier stage H-bridge is kept within the constraint range specified by equation (14). Therefore, the capacitor voltage balance of the H-bridge in the CHB converter is guaranteed. The MAB converter is controlled to output 15kW at each output port, and this power is directly delivered to the first electric vehicle through a flexible power switching matrix.

[0130] Due to the second electric vehicle ( The battery voltage of the second electric vehicle is usually different from that of the first electric vehicle, so a two-step method is used to connect the second electric vehicle, such as... Figure 12 As shown, Figure 12 (a) is the circuit diagram for the first step of connecting the second car. Figure 12 (b) shows the circuit diagram for the second step of connecting the second car. In the first step, power decoupling control is adopted. The output power of the isolation stage output ports #1, #3, #5 and #7 gradually increases to 30kW, while the output power of the isolation stage output ports #2, #4, #6 and #8 gradually decreases to zero. Therefore, the total charging power of the first electric vehicle is guaranteed to be 120kW. Since the total charging power of the first electric vehicle remains at 120kW, the output power of each rectifier stage H-bridge remains the same, equal to 15kW, and equation (14) is still satisfied. Then, the four relays connecting ports #2, #4, #6 and #8 in the first column of the flexible power switching matrix are disconnected, and the output voltages of the isolation stage output ports #2, #4, #6 and #8 are gradually controlled to match the battery voltage of the second electric vehicle. Once the output voltages of the isolation stage output ports #2, #4, #6 and #8 are close to the battery voltage of the second electric vehicle, the four relays connecting ports #2, #4, #6 and #8 in the second column of the flexible power switching matrix will close, as shown in the diagram. Figure 12 As shown in (a). In the second step, the total charging power of the first and second electric vehicles is 240kW, therefore the output power of each rectifier stage H-bridge is... This is also equivalent to the output port of each MAB converter. The output power of each H-bridge remains the same, so the active power of each H-bridge is still within the constraints given by equation (14), and the capacitor voltage balance of the H-bridge can be guaranteed. Then, the MAB converter is controlled to output 30kW at each output port, and the output power of each rectifier stage H-bridge is also increased to 30kW, such as Figure 12 As shown in (b), this power is directly delivered to the first and second electric vehicles via a flexible power switching matrix. Therefore, the charging power of the second electric vehicle is also 120kW.

[0131] To accommodate a third electric vehicle ( The two-step method is still used, such as... Figure 13As shown, Figure 13 (a) is the circuit diagram for the first step of connecting the third car. Figure 13 Figure (b) shows the circuit diagram for the second step of connecting the third vehicle. In the first step, power decoupling control is used to gradually increase the output power of rectifier stage output ports #4 and #5 to 60kW, while gradually decreasing the output power of isolation stage output ports #3 and #6 to zero. This ensures that the total charging power of the first and second electric vehicles is 240kW. Since the total charging power of the first and second electric vehicles remains at 240kW, the output power of each rectifier stage H-bridge remains at 30kW, and equation (14) is still satisfied. Next, the five relays in the first and second columns of the flexible power switching matrix are disconnected, gradually controlling the output voltage of isolation stage output ports #3 and #6 to match the battery voltage of the third electric vehicle. Once the output voltage of isolation stage output ports #3 and #6 approaches the battery voltage of the third electric vehicle, the two relays in the third column of the flexible power switching matrix are closed, as shown in Figure 1. Figure 13 As shown in (a). In the second step, the total charging power of the first, second, and third electric vehicles is 360kW. Therefore, the output power of each H-bridge in the rectifier stage is... The output power of isolation stage output ports #3 and #6 must be 60kW, while the output power of the remaining ports is 30kW or 45kW. The output power of each rectifier stage H-bridge remains unchanged, so its active power is still within the constraints specified in equation (14), and the capacitor voltage balance of the H-bridge is maintained. Finally, the MAB converter is controlled to output 30kW, 45kW, or 60kW at the output ports, and the output power of the rectifier stage H-bridge is also increased to 45kW, as shown below. Figure 13 As shown in (b), this power is directly supplied to the first, second, and third electric vehicles via a flexible power switching matrix. Therefore, the charging power of the third electric vehicle is also 120kW.

[0132] To accommodate a fourth electric vehicle ( The two-step approach will still be used, such as... Figure 14 As shown, Figure 14 (a) is the circuit diagram for the first step of connecting the fourth car. Figure 14(b) is the circuit diagram for the second step of connecting the fourth vehicle. In the first step, power decoupling control is used to gradually increase the output power of rectifier stage output ports #1 and #8 to 90kW, while the output power of isolation stage output ports #2 and #7 is gradually reduced to zero. At the same time, the output power of isolation stage output ports #3, #6 and #4, #5 are set to 60kW and 30kW respectively. Therefore, the total charging power of the first, second and third electric vehicles is guaranteed to be 360kW. Since the total charging power of the first, second and third electric vehicles remains at 360kW, the output power of the rectifier stage H-bridge is 45kW, and equation (14) is still satisfied. Next, the six relays in the first, second and third columns of the flexible power switching matrix are disconnected, and the output voltage of isolation stage output ports #2 and #7 is gradually adjusted to match the battery voltage of the fourth electric vehicle. Once the output voltage of isolation stage output ports #2 and #7 is close to the battery voltage of the fourth electric vehicle, the two relays in the fourth column of the flexible power switching matrix will close, as shown in Figure 1. Figure 14 As shown in (a). In the second step, the total charging power of the first, second, third, and fourth electric vehicles is 480kW. Therefore, the output power of each rectifier stage H-bridge is... The output power of each MAB converter output port is also calculated to be 60kW. The output power of each rectifier stage H-bridge is equal, ensuring that the active power of each rectifier stage H-bridge remains within the constraint range specified in equation (14), thereby maintaining the capacitor voltage balance of the rectifier stage H-bridge. Subsequently, the MAB converter is controlled to output 60kW at each output port, and the output power of each rectifier stage H-bridge is also increased to 60kW, such as Figure 14 As shown in (b), this power is directly delivered to the first, second, third, and fourth electric vehicles via a flexible power switching matrix. Therefore, the charging power of the fourth electric vehicle is also 120kW.

[0133] like Figures 11 to 14 As shown, by adopting the proposed dynamic power allocation strategy, the active power of each rectifier stage H-bridge is always within the constraint range specified by equation (14), successfully maintaining the capacitor voltage balance of the rectifier stage H-bridge. In addition, the system can operate under 100% unbalanced load conditions (i.e., when some charging ports output power of 0, other charging ports can output full power).

[0134] To verify the effectiveness of the proposed topology and control method, a simulation model was built in MATLAB / Simulink. The main parameters of the simulation model are shown in Table 1. The simulation results are as follows: Figure 15 and Figure 16 As shown. Figure 15 The current and voltage waveforms of each output port of the system isolation stage and the battery are displayed. Figure 15(a) represents the output current of isolation stage output ports #1, #2, #3, and #4. ), Figure 15 (b) shows the output current of isolation stage output ports #5, #6, #7, and #8. ), Figure 15 (c) represents the output voltages of isolation stage output ports #1, #2, #3, and #4. ) and battery voltage ( ), Figure 15 (d) represents the output voltage of isolation stage output ports #5, #6, #7, and #8. ) and battery voltage ( ), Figure 15 (e) represents the battery charging current. Based on the working principle of the multi-port electric vehicle fast charging system based on the two-stage SST proposed above, the simulation results are explained at several time intervals.

[0135] In time Previously, all outputs of the MAB converter were connected in parallel and connected to the battery of the first electric vehicle, such as Figure 11 As shown. To charge the first electric vehicle with a total power of 120kW, the output power of each MAB converter output port is 15kW. The SOC of the first electric vehicle's battery is set to 50%, and its open-circuit (OC) voltage is 781.98V, therefore the output current of the MAB converter is set to 19.18A. Simultaneously, constant current (CC) mode is used to charge the battery of the first electric vehicle. Figure 15 In the middle, time Simulated output current to The simulated total charging current is 19.17A. The voltage is 153.50A. (Simulated battery voltage) The voltage is approximately 790.26V, higher than the battery's over-the-top (OC) voltage. This is because a voltage drop occurs across the battery's internal resistance. Therefore, the simulated charging power of the first electric vehicle is approximately 121.30kW.

[0136] In time At that time, the second electric vehicle was ready to connect to the proposed two-stage SST-based multi-port electric vehicle fast charging system. Since the second electric vehicle's battery SOC was set to 25%, its OC voltage was 772.39V, lower than that of the first electric vehicle. Therefore, a system was adopted as described above... Figure 12 The two-step method is shown. In time... At that time, by using power decoupling control, the output current It gradually increased to 38.36A, while the output current... It gradually decreases to zero. Therefore, the simulated total charging current of the first electric vehicle... The current remains at 153.50A, meaning the power supplied to the first electric vehicle remains at 120kW. At time t=0.39s, the four relays in the first column of the flexible power switching matrix disconnect. At that time, control the output voltage To match the battery voltage of the second electric vehicle. In time At that time, the four relays in the second column close, and the second car is connected to the proposed two-stage SST-based multi-port electric vehicle fast charging system, but the charging current is zero. At that time, the output current Set to 38.84A and use CC mode to charge the battery of the second electric vehicle. Figure 15 In time At that time, the simulated output current The simulated total charging current is 38.90A. The voltage is 155.60A. (Simulated battery voltage) The voltage is 780.55V. Due to the voltage drop across the battery's internal resistance, the battery voltage during charging is higher than the battery's open-circuit voltage. Therefore, the simulated charging power of the second electric vehicle is approximately 121.45kW.

[0137] In time At that time, the third electric vehicle was ready to connect to the proposed two-stage SST-based multi-port electric vehicle fast charging system. Since the third electric vehicle's battery SOC was set to 15%, its OC voltage was 761.26V, lower than that of the second electric vehicle. Therefore, as... Figure 13 As shown, the two-step method is still used. In time... At that time, by using power decoupling control, the output current and The output current gradually increased to 77.68A and 76.73A, while... and It gradually decreases to zero. Therefore, the simulated total charging current of the first and second electric vehicles... and Maintaining between 153.50A and 155.60A means that the power delivered to the first and second electric vehicles remains at 120kW. (At time...) At that time, five relays in the first and second columns of the flexible power switching matrix disconnect. At that time, control the output voltage and To match the battery voltage of the third electric vehicle. In time At time t=0.80s, the two relays in the third column close, and the third electric vehicle is connected to the proposed multi-port electric vehicle fast charging system based on a two-stage SST, but the charging current is zero. At time t=0.80s, the output current... and Set to 78.82A and use CC mode to charge the battery of the third electric vehicle. Figure 15 middle, Simulated output current and The simulated total charging current is 78.88A. The voltage is 157.75A. (Simulated battery voltage) The voltage is approximately 769.55V. Due to the voltage drop across the battery's internal resistance, the battery voltage during charging will be higher than the battery's open-circuit voltage. Therefore, the simulated charging power of the third electric vehicle is approximately 121.40kW.

[0138] In time At that time, the fourth electric vehicle was ready to connect to the proposed two-stage SST-based multi-port electric vehicle fast charging system. Since the fourth electric vehicle's battery SOC was set to 5%, its OC voltage was 723.64V, lower than that of the third electric vehicle. Therefore, a system was adopted as described above. Figure 14 The two-step method is shown. In time... At that time, by using power decoupling control, the output current and The output current gradually increased to 115.09A and 116.52A, while... and It gradually decreases to zero. Therefore, the simulated total charging current of the first, second, and third electric vehicles... The current ratings remain at 153.50A, 155.60A, and 157.75A respectively, meaning that the power delivered to the first, second, and third electric vehicles remains at 120kW. (Time) At that time, six relays in the first, second, and third columns of the flexible power switching matrix disconnect. When adjusting the output voltage and To match the battery voltage of the fourth electric vehicle. (In time) At that time, two relays in the fourth column close, and the fourth electric vehicle connects to the proposed two-stage SST multi-port electric vehicle fast charging system, but the charging current is zero. At that time, the output current and Set to 82.91A, CC mode was activated to charge the battery of the fourth electric vehicle. Figure 15 In the middle, time Simulated output current and The simulated total charging current is 83.20A. The voltage is 166.50A. (Simulated battery voltage) The voltage is approximately 732.37V, which is higher than the battery's over-charge (OC) voltage due to the voltage drop across the battery's internal resistance. Therefore, the simulated charging power of the fourth electric vehicle is approximately 121.94kW.

[0139] In time Subsequently, the proposed multi-port electric vehicle fast charging system based on a two-stage SST provided a total power of 480kW for four electric vehicles.

[0140] Figure 16 The current and voltage waveforms of the rectifier stage are shown. Figure 16 In the middle (a), the AC current input to the rectifier stage is represented. Figure 16 In the middle (b), the AC voltage of the power grid is represented. Figure 16 In the diagram, (c) represents the output voltage of the cascaded H-bridge. Figure 16 In the diagram, (d) represents the capacitor voltage of the rectifier stage H-bridge. Figure 16 Figures (a) and (b) show the simulated input AC current and simulated grid AC voltage of the rectifier stage. The input AC current gradually increases with increasing charging power. arrive During the time interval, the first electric vehicle connects to the proposed two-stage SST-based multi-port electric vehicle fast charging system with a charging power of 120kW. The simulated input AC current of the rectifier stage is 21.97A RMS, and the AC grid voltage is 8164V (peak). Simultaneously, the input AC current is in phase with the grid AC voltage, achieving unity power factor. During the time interval... At that time, a second electric vehicle was connected to the system, increasing the charging power to 240kW, and the simulated input AC current rose to 43.15A RMS. At that time, connecting a third electric vehicle increased the charging power to 360kW, and the simulated input AC current increased to 63.84A RMS. When a fourth electric vehicle is connected, the charging power increases to 480kW, and the simulated input AC current reaches 84.87A RMS. The output of the CHB converter is as follows: Figure 16 As shown in (c), this is a multi-level stepped wave. The capacitor voltage of the H-bridge in the CHB converter is as follows: Figure 16 As shown in (d). From Figure 16 It can be seen that the capacitor voltage of the H-bridge in the CHB converter remains balanced, and the fluctuation of the capacitor voltage is... Within this range, the effectiveness of the voltage balance control method proposed in this paper is verified.

[0141] from Figure 15 and Figure 16 It can be seen that by using the proposed dynamic power allocation strategy, the proposed multi-port electric vehicle fast charging system based on two-stage SST can operate under 100% unbalanced load conditions.

[0142] Simulation results verify that the system can provide 120kW charging power to four electric vehicles simultaneously at a rated power of 480kW, and that the capacitor voltage fluctuation of each rectifier stage H-bridge is small, indicating that the system operates stably and reliably.

[0143] It should be noted that, Figure 17 This is a structural diagram of a three-level full-bridge submodule. Figure 17 (a) shows the structure of the diode-clamped three-level full-bridge submodule. Figure 17 (b) shows the active clamped three-level full-bridge submodule structure; Figure 18 This is a diagram of a two-level half-bridge circuit. Figure 19 This is a diagram of a three-level half-bridge circuit. Figure 19 Figure (a) shows the structure of a diode-clamped three-level half-bridge circuit. Figure 19 Figure (b) shows the structure of an active clamped three-level half-bridge circuit. The H-bridge in the rectifier stage of this invention can be replaced with... Figure 17 The diode-clamped three-level full-bridge or actively clamped three-level full-bridge shown can be replaced with the H-bridge in the multi-active bridge converter. Figure 18 and Figure 19 The two-level half-bridge, three-level diode clamped half-bridge, or three-level active clamped half-bridge shown are examples.

[0144] When the H-bridge in the rectifier stage is replaced with a diode-clamped three-level full-bridge or an active-clamped three-level full-bridge, the constraint of equation (14) still applies; when the H-bridge in the multi-active bridge converter is replaced with a two-level half-bridge, a three-level diode-clamped half-bridge, or a three-level active-clamped half-bridge, the constraints of equations (17) to (19) still apply. The value needs to be corrected to the first , The input / output DC voltage of the half-bridge circuit is half of the DC input / output DC voltage, and other theoretical derivations and conclusions still apply.

[0145] In summary, the multi-port electric vehicle fast charging system and its control method provided by the embodiments of the present invention support 100% unbalanced load operation without the need for additional reactive power compensation or balancing windings. It has the advantages of high power factor, compact structure and low cost, and can realize the simultaneous fast charging of multiple electric vehicles.

[0146] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-port electric vehicle fast charging system, characterized in that: It includes a rectifier stage, an isolation stage, and a flexible power switching matrix; the rectifier stage includes... A series of H-bridges; the isolation level adopts Multiple active bridge converters, each Each H-bridge is connected to a multi-active bridge converter. One input terminal, one active bridge converter Each output terminal is connected to a flexible power switching matrix. The flexible power switching matrix has one input terminal; Each input terminal is connected to the isolation level. Each output terminal; the flexible power switching matrix is ​​equipped with... One output terminal, used for connection Electric vehicles; Controlling the active power of each H-bridge to meet the requirements ,in Indicates the first The active power of the H-bridge This represents the DC component of the H-bridge capacitor voltage. These are the amplitudes of the grid voltage and current, respectively. It is the input inductance on the grid side. The angular frequency of the grid voltage; During the charging process, a phase-shifting control strategy and a power decoupling algorithm are used to control the power of the input and output ports of the isolation stage, so that each primary side port of the isolation stage provides the same power, the output power of each secondary side port gradually approaches its respective output power reference value, and each secondary side port has constant voltage and constant current characteristics.

2. The multi-port electric vehicle fast charging system according to claim 1, characterized in that: A voltage balance control strategy based on dq decoupling control is adopted for control. The output voltage of each H-bridge is a DC voltage reference value, specifically including: By sampling the voltage of each H-bridge capacitor to And compared with the DC voltage reference value respectively For comparison, a PI controller is used to generate the d-axis compensation component. to ; Compensation components to Duty cycle with d-axis After superposition, the d-axis duty cycle of each H-bridge is generated. to ; Will to q-axis duty cycle Phase with grid voltage The final d-axis duty cycle of each H-bridge is obtained by inverse dq / am transformation. to ; Phase-shifted sinusoidal pulse width modulation technology is used to transform the duty cycle signal. to Convert to the PWM drive signal required for H-bridge to .

3. The multi-port electric vehicle fast charging system according to claim 2, characterized in that, d-axis duty cycle and q-axis duty cycle Generate through the following steps: Calculate the average value of all H-bridge capacitor voltages and subtract it from twice the power frequency ripple in the total DC voltage of the H-bridge calculated using the voltage ripple calculation method. Then, compare this result with the DC voltage reference value. The input voltage regulator uses a PI controller to obtain the d-axis current reference value. ; grid-side current Generating virtual current with a 90° lag , to the actual current Virtual current Phase with grid voltage The d-axis and q-axis current components are obtained through am / dq transformation. and ; d-axis current reference value d-axis current component The input is a d-axis current regulator using a PI controller, and its output is related to the introduced q-axis current. The decoupling components are subtracted to obtain the d-axis duty cycle signal. ; q-axis current reference value q-axis current component The input uses a PI controller for the q-axis current regulator, and its output is related to the introduced d-axis current. The decoupled components are added together to obtain the q-axis duty cycle signal. .

4. The multi-port electric vehicle fast charging system according to claim 1, characterized in that, The specific process of controlling the input and output port power of the isolation stage using a phase-shift control strategy and a power decoupling algorithm is as follows: The sampled DC voltage output value and the reference DC voltage value of the secondary side port are input to a voltage regulator using a PI controller to obtain the reference DC current value of the secondary side port. The secondary-side port output DC current sample value is multiplied by the secondary-side port DC voltage reference value to obtain the secondary-side port output power feedforward; The sampled DC current value and the reference DC current value at the secondary side port are input to a current regulator using a PI controller. The current regulator outputs a power regulation value, which is then added to the power feedforward value to obtain the output power reference value. The output power reference value is input to the power decoupling control algorithm module. The power decoupling algorithm is used to determine the phase shift angle, and the phase shift angle is transmitted to the isolation stage to control the power of the input and output ports of the isolation stage.

5. The multi-port electric vehicle fast charging system according to any one of claims 1 to 3, characterized in that: The flexible power switching matrix uses multiple relays to... One input terminal is connected to One output terminal.

6. The multi-port electric vehicle fast charging system according to claim 5, characterized in that: The multi-active bridge converter adopts primary-side... One winding, secondary side Multi-winding transformer with one winding. , .

7. The multi-port electric vehicle fast charging system according to claim 6, characterized in that, The H-bridge in the rectifier stage is replaced with a diode-clamped three-level full bridge or an active-clamped three-level full bridge, and the H-bridge in the multi-active bridge converter is replaced with a two-level half bridge, a diode-clamped three-level half bridge, or an active-clamped three-level half bridge.

8. A control method applied to the multi-port electric vehicle fast charging system of claim 7, characterized in that, The control method includes the following steps: S1. Obtain the number of electric vehicles that need to be charged. and their respective requested charging power to ; S2. When the first electric vehicle connects, the charging power is adjusted according to the request of the first electric vehicle. The output power of each rectifier H-bridge and each output port of the isolation stage is determined with the goal of ensuring that the power of each rectifier H-bridge is equal. S3. By controlling the drive signals of the rectifier stage and the isolation stage, the output power of the isolation stage output port used for the next electric vehicle is gradually reduced from the current value to zero, while the output power of other isolation stage output ports connected to the currently charging electric vehicle is increased, so as to keep the total charging power of the currently charging electric vehicle unchanged. S4. When the output power of the isolation stage output port used for the next electric vehicle drops to zero, disconnect it from the current electric vehicle, and then adjust its output voltage to match the battery voltage of the next electric vehicle; after matching, close the relay and connect the next electric vehicle. S5. By controlling the drive signals of the rectifier stage and the isolation stage, with the goal of satisfying the requested charging power of each connected electric vehicle and ensuring that the power of each rectifier stage H-bridge is equal, control all working ports of the isolation stage to output new power values. S6. Repeat steps S3 to S5 until all electric vehicles are connected and charged with their requested charging power.

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