Cooperative control method of multiple direct current charging pile systems

Abstract

The application provides a kind of collaborative control method of multiple direct current charging pile systems, by comparing whether the direct current side voltage of the i th charging pile system is equal to the direct current bus rated voltage, if not equal, then establish the virtual inertia control strategy suitable for direct current charging pile system;Get the virtual inertia control of adaptive parameter optimization, and as a primary control;The relative voltage deviation between the direct current side voltage of each charging pile and the inertia center voltage is obtained;Adopt inertia center collaborative control to carry out secondary control to virtual parameter;Using backstepping method to reconstruct current inner loop, output PWM signal, realize the collaborative operation control of multiple direct current charging piles;The method can optimize the collaborative control effect of multiple charging pile systems, can effectively stabilize the output voltage of direct current charging pile when load is switched, can provide sufficient inertia and damping support for direct current system, effectively improve dynamic performance and voltage disturbance rejection capability, so as to fully guarantee the stability of charging process.

Description

Technical Field

[0001] This invention relates to a collaborative control method for a multi-DC charging pile system, belonging to the field of DC power distribution network control. Background Technology

[0002] As electric vehicle sales increase year by year, DC charging piles and fast charging technology, which serve as a bridge between the power grid and electric vehicles, are also developing rapidly.

[0003] Ensuring effective control of charging station systems to provide safe, efficient, and stable charging services for vehicle owners is a key measure for the steady development of the electric vehicle industry. Therefore, improving the control performance of charging station systems is gradually becoming a hot topic in the electric vehicle field.

[0004] Current research on the control of DC charging piles mostly focuses on traditional control methods, including droop control, master-slave control, and voltage-current dual closed-loop control. However, under traditional control methods, power electronic devices have the characteristic of small inertia. When the load side changes are complex, the system under traditional control methods has obvious deficiencies in dynamic performance and voltage disturbance rejection capability.

[0005] In addition, most DC charging piles are currently designed to support one or more electric vehicles. In this model, the safety of the charging process largely depends on the stable operation of a single charging pile. Furthermore, as the charging equipment ages, the line resistance will directly affect the stability of the DC voltage.

[0006] The above-mentioned issues should be considered and resolved in the collaborative control process of multiple DC charging pile systems. Summary of the Invention

[0007] The purpose of this invention is to provide a collaborative control method for a multi-DC charging pile system to address the problem that the dynamic performance and voltage disturbance rejection capability are significantly insufficient when the load side changes in the existing technology, and need to be improved.

[0008] The technical solution of this invention is:

[0009] A collaborative control method for a multi-DC charging pile system includes the following steps:

[0010] S1. Compare the DC-side voltage of the i-th charging pile system among multiple DC charging pile systems. With DC bus rated voltage Check if they are equal. If they are not equal, proceed to the next step S2; if they are equal, end the process.

[0011] S2. Establish a virtual inertial control strategy suitable for DC charging pile systems;

[0012] S3. Analyze the virtual parameters, including virtual inertia and virtual damping coefficient, in the virtual inertial control strategy established in step S2. Based on voltage fluctuations, obtain the virtual inertial control with adaptive parameter optimization, and use it as the primary control.

[0013] S4. Introduce an inertial center voltage to make an overall response to the voltage deviation of the DC charging pile system caused by load changes. Based on the inertial center voltage, obtain the relative voltage deviation between the DC side voltage of each charging pile and the inertial center voltage.

[0014] S5. Based on the relative voltage deviation obtained in step S4, the virtual parameters are controlled in a secondary manner using inertial center collaborative control. The virtual inertial control after the virtual parameters are controlled in a secondary manner is used as the voltage outer loop to adjust the input power of each charging pile to stabilize the DC side voltage.

[0015] S6. Based on virtual inertial control as the voltage outer loop, the current inner loop is reconstructed using the reverse calculation method to output PWM signals and realize the coordinated operation control of multiple DC charging piles.

[0016] Furthermore, in step S1, a virtual inertial control strategy suitable for the DC charging pile system is established, specifically as follows:

[0017] S21. Add a virtual capacitor to the DC charging pile system. In the i-th charging pile system, the relationship between the input and output currents on both sides of the virtual capacitor is expressed as follows:

[0018] ,

[0019] in, Input current to the virtual capacitor; For system output current; This represents the virtual capacitance value of the i-th charging pile system, which is also the virtual inertia value of the i-th charging pile system. The voltage value output by the virtual inertial control; t is time;

[0020] S22. The input current of the virtual capacitor is equivalent to the difference between the rated current and the damping current, resulting in the control strategy for the i-th charging pile system:

[0021] ,

[0022] in, This is a reference value for the current flowing from the system to the DC side. For the system output current, This is a virtual capacitance value. This is the virtual damping coefficient. DC side voltage This is the voltage value output by the virtual inertial control.

[0023] S23. Introducing voltage-current droop control, the final virtual inertial control expression is:

[0024] ,

[0025] in, The droop coefficient is... This is the rated voltage of the DC bus.

[0026] Furthermore, in step S3, the virtual inertial control with adaptive parameter optimization is obtained as follows:

[0027]

[0028] in, These are the initial virtual parameters of the i-th charging pile system; Let be the voltage change rate of the i-th charging pile system; These are the positive adjustment parameters.

[0029] Further, in step S4, based on the inertial center voltage, the relative voltage deviation between the DC side voltage of each charging pile and the inertial center voltage is obtained, specifically,

[0030] S41, Inertial center voltage u c for:

[0031]

[0032] Among them, C v.i Let u represent the virtual inertia value of the i-th charging pile system. i C represents the DC-side voltage of the i-th charging pile system. t This represents the inertia value of the charging pile system, which is numerically equal to the sum of the virtual inertia values ​​of each charging pile system.

[0033] S42. Calculate the relative voltage deviation between the DC side voltage and the inertial center voltage of each charging pile:

[0034]

[0035] Among them, u i U represents the DC-side voltage of the i-th charging pile system. c This represents the voltage at the center of inertia.

[0036] Furthermore, in step S5, based on the relative voltage deviation obtained in step S4, inertial center cooperative control is used to perform secondary control on the virtual parameters. The virtual inertial control after secondary control of the virtual parameters is used as the voltage outer loop to adjust the input power of each charging pile. Specifically,

[0037] S51. Based on the relative voltage deviation obtained in step S4, the virtual parameters are controlled secondaryly using inertial center cooperative control:

[0038] ,

[0039] Among them, C v.i This represents the virtual capacitance value of the i-th charging pile system. This is the virtual damping coefficient. , These are the initial virtual parameters of the i-th charging pile system. Let be the voltage change rate of the i-th charging pile system. These are the positive adjustment parameters, u i This represents the DC-side voltage of the i-th charging pile system. This is the rated voltage of the DC bus. and It is a positive adjustment parameter; Relative voltage deviation The rate of change;

[0040] S52. The method of adjusting the input power of each charging pile by using virtual inertial control after secondary control of virtual parameters as the voltage outer loop is to add an additional input current on the basis of virtual inertial control. Additional input current Calculated as system output current As part of this, the virtual inertial control expression is:

[0041] ,

[0042] in, The droop coefficient is... This is the rated voltage of the DC bus. DC side voltage For the system output current, This is a virtual capacitance value. This is the virtual damping coefficient. This is the voltage value output by the virtual inertial control.

[0043] Furthermore, in step S52, an additional input current is added. The expression is:

[0044] ,

[0045] in, , and For the proportional, derivative, and integral positive control parameters of the i-th system; This represents the rate of change of relative voltage deviation. This is the integral value of the relative voltage deviation.

[0046] Furthermore, in step S6, the inner current loop is reconstructed using a reverse calculation method, specifically as follows:

[0047] S61. The current inner loop based on PI control is represented in the dq coordinate system as:

[0048] ,

[0049] in, , For the line inductance and resistance between the transformer and the converter, , Let represent the components of the AC side voltage along the d and q axes. For the AC side frequency, u i This represents the DC-side voltage of the i-th charging pile system. , For the switching signal, the components of the AC side current along the d and q axes in the rotating coordinate system. , The rate of change is expressed as:

[0050] ;

[0051] S62. To achieve voltage tracking control in the charging pile system, based on back-calculation control, the error is defined, and a Lyapunov positive definite function expression is constructed. According to the Lyapunov asymptotic stability theorem, the reconstructed current loop switching signal in the i-th system is designed. , .

[0052] Further, in step S62, the error is defined, and the Lyapunov positive definite function expression is constructed, specifically as follows:

[0053] S621, Define errors e1 and e2:

[0054] ,

[0055] in, , Let represent the components of the alternating current along the d and q axes of the rotating coordinate system. The inner loop reference current is obtained from virtual inertial control; The value is zero;

[0056] S622. Construct the Lyapunov positive definite function expression:

[0057] ,

[0058] ,

[0059] Where e1 and e2 are errors, , For the constructed Lyapunov function;

[0060] S623. Based on Lyapunov's asymptotic stability theorem, design the reconstructed current loop switching signal for the i-th system. , for:

[0061] ,

[0062] Among them, u i This represents the DC-side voltage of the i-th charging pile system. , For the line inductance and resistance between the transformer and the converter; Let represent the components of the alternating current along the d and q axes in the rotating coordinate system; , These are the components of the AC side voltage along the d and q axes; For AC side frequency; d1 and d2 are the inner loop reference currents obtained from virtual inertial control; d1 and d2 are constants greater than zero.

[0063] The beneficial effects of this invention are:

[0064] I. This collaborative control method for a multi-DC charging pile system, based on virtual inertial control, employs inertial center collaborative control as a secondary control mechanism. This optimizes the collaborative control effect of the multi-charging pile system, effectively enhances the consistency of voltage response across all systems, and enables the multi-charging pile system to quickly recover stability during load switching. This method effectively stabilizes the DC charging pile output voltage during load switching, while providing sufficient inertia and damping support for the DC system, effectively improving dynamic performance and voltage disturbance rejection capability, thereby fully ensuring the stability of the charging process.

[0065] Second, the collaborative control method of this multi-DC charging pile system takes into account the line resistance loss on the common DC bus. When multiple charging piles are running collaboratively, it can effectively reduce the impact of line loss on the voltage of the common bus. Moreover, after disconnecting a charging pile, the remaining system can still run collaboratively. Experimental simulation has verified that the method of this invention has higher advantages and safety in "interconnected multi-charging". Attached Figure Description

[0066] Figure 1 This is a flowchart illustrating the collaborative control method of a multi-DC charging pile system according to an embodiment of the present invention.

[0067] Figure 2This is a schematic diagram illustrating the dynamic response between the virtual capacitor and the DC-side voltage in the embodiment;

[0068] Figure 3 This is a schematic diagram of the dynamic response between the virtual damping and the DC-side voltage in the embodiment;

[0069] Figure 4 This is a schematic diagram of the voltage oscillation curve of the DC charging pile system under disturbance in the embodiment;

[0070] Figure 5 This is a schematic diagram of the single-cycle oscillation curve of the relative voltage deviation in the embodiment;

[0071] Figure 6 This is an explanatory block diagram of inertial center cooperative control based on virtual inertial control in the embodiment;

[0072] Figure 7 This is a schematic diagram illustrating the changes in the output voltage of the three charging piles in the embodiment;

[0073] Figure 8 This is a schematic diagram illustrating the change in the common bus voltage in the embodiment;

[0074] Figure 9 This is a schematic diagram illustrating the changes in the output power of the three charging piles in the embodiment. Detailed Implementation

[0075] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0076] Example

[0077] A collaborative control method for a multi-DC charging pile system, such as Figure 1 This includes the following steps:

[0078] S1. Compare the DC-side voltage of the i-th charging pile system among multiple DC charging pile systems. With DC bus rated voltage Check if they are equal. If they are not equal, proceed to the next step S2; if they are equal, end the process.

[0079] S2. Establish a virtual inertial control strategy suitable for DC charging pile systems;

[0080] In step S2, based on the virtual synchronous machine model in the AC system and analogous to the key parameters in the AC-DC microgrid, a virtual inertial control strategy suitable for the DC charging pile system is established. This strategy builds upon the virtual synchronous machine model of the traditional AC system. In a traditional synchronous machine, when the frequency changes abruptly, the kinetic energy stored in the rotor provides inertial support to maintain frequency stability. The inertia of a DC system is mainly manifested in its ability to maintain DC-side voltage stability. Similar to the AC system, when the DC-side voltage changes abruptly, the DC system can rely on the energy stored in the parallel capacitor on the DC side to provide inertia. Therefore, by analogy with the VSM technology's method of simulating the rotor motion equation, a virtual capacitor is added to the DC system. To increase inertia. When the system is disturbed, the ability of the system to resist DC-side voltage fluctuations is improved through the charging and discharging of capacitors. Taking a single system as an example, the relationship between the input and output currents on both sides of the virtual capacitor can be expressed as follows:

[0081] (1)

[0082] in, Input current to the virtual capacitor; For system output current; This represents the virtual capacitance value of the i-th charging pile system, which is also the virtual inertia value of the i-th charging pile system. This is the voltage value output by the virtual inertial control. For time;

[0083] Meanwhile, to enable virtual inertial control to possess damping characteristics similar to VSM technology, the input current of the virtual capacitor is equivalent to the difference between the rated current and the damping current. This allows the damping coefficient to suppress large voltage fluctuations on the DC side when voltage fluctuations occur in the DC system, and the output current to be adjusted appropriately according to the degree of fluctuation to maintain DC voltage stability. From this, the preliminary expression for virtual inertial control can be obtained:

[0084] (2)

[0085] in, This is a reference value for the current flowing from the system to the DC side; For damping current; This is the virtual damping coefficient; DC side voltage This represents the capacitance value of the virtual capacitor.

[0086] Based on the inertial and damping characteristics of a DC system, voltage-current droop control is introduced. Utilizing the droop characteristic, voltage fluctuations can be further reduced, improving the effectiveness of virtual inertial control. The final virtual inertial control expression is obtained as follows:

[0087] (3)

[0088] in, This is the rated voltage of the DC bus. DC side voltage This is the voltage value output by the virtual inertial control. The droop coefficient is... For the system output current, This is the virtual damping coefficient.

[0089] S3. Analyze the virtual parameters, including virtual inertia and virtual damping coefficient, in the virtual inertial control strategy established in step S2. Based on voltage fluctuations, obtain the virtual inertial control with adaptive parameter optimization, and use it as the primary control.

[0090] In step S3, for the virtual capacitor For the i-th system, we can obtain from equation (3):

[0091] (4)

[0092] in, This is the voltage value output by the virtual inertial control. DC side voltage The droop coefficient is... This is the rated voltage of the DC bus. For the system output current, This is the virtual damping coefficient.

[0093] The inertia of a DC system largely depends on the charging and discharging characteristics of the parallel capacitor on the DC side, whose capacitance value is a constant. However, under virtual inertia control, the virtual capacitance value is a virtual quantity. When the value of is constant, the virtual capacitance value is inversely proportional to the rate of change of DC side voltage. Therefore, the virtual capacitance value can be changed to improve the DC side voltage change curve, which confirms the possibility of adaptive control of virtual capacitance from a mechanistic perspective.

[0094] The relationship between virtual capacitance and DC-side voltage, such as Figure 2 It can be seen that when the system is disturbed at t=4s, the larger the virtual capacitance, the smaller the DC side voltage overshoot and the smaller the voltage change rate, but the longer the system stabilization time.

[0095] Regarding virtual damping, for the i-th system, we can obtain from equation (3):

[0096] (5)

[0097] in, DC side voltage This is the voltage value output by the virtual inertial control. The droop coefficient is... This is the rated voltage of the DC bus. For the system output current, This is the capacitance value of the virtual capacitor. This is the virtual damping coefficient.

[0098] Similarly, virtual damping is a virtual quantity, when When the value of the virtual resistance is constant, it is inversely proportional to the deviation of the DC-side voltage. Therefore, the virtual damping value can be changed to enhance the system's ability to suppress DC-side voltage. The relationship between virtual damping and DC-side voltage is as follows: Figure 3 It can be seen that when the system experiences a disturbance at t=4s, the system with larger virtual damping exhibits smaller DC-side voltage overshoot and a shorter settling time. The simulation results confirm the relationship between virtual damping and the DC-side voltage fluctuation amplitude.

[0099] The DC-side voltage fluctuation curve during load switching of the charging pile system is as follows: Figure 4 Since the voltage deviates from the rated value, it is necessary to adjust the virtual parameter values ​​in a timely manner at the corresponding stages to help the system stabilize the DC side voltage as soon as possible. Based on the above analysis, the adjustment of virtual parameters in different voltage oscillation ranges is designed as shown in Table 1. In Table 1, DC side voltage With DC bus rated voltage The deviation value; This represents the rate of change of the common bus voltage.

[0100] Table 1 shows the virtual parameters designed for different ranges of voltage oscillation.

[0101]

[0102] Based on the analysis of the relationship between the above virtual parameters and voltage changes, taking the first... Taking a single system as an example, the virtual inertial control equation for adaptive parameter optimization is expressed as:

[0103] (6)

[0104] in, The droop coefficient is... This is the rated voltage of the DC bus. DC side voltage This is the voltage value output by the virtual inertial control. For the system output current, This is the capacitance value of the virtual capacitor. This is the virtual damping coefficient. The first Initial virtual parameters of a charging pile system; For the first Voltage variation rate of each charging pile system; These are the positive adjustment parameters.

[0105] S4. Introduce an inertial center voltage to make an overall response to the voltage deviation of the DC charging pile system caused by load changes. Based on the inertial center voltage, obtain the relative voltage deviation between the DC side voltage of each charging pile and the inertial center voltage.

[0106] In step S4, based on the inertial center voltage, the relative voltage deviation between the DC side voltage and the inertial center voltage of each charging pile is obtained, specifically as follows:

[0107] S41, Inertial center voltage u c for:

[0108] (7)

[0109] Among them, C v.i Let u represent the virtual inertia value of the i-th charging pile system. i C represents the DC-side voltage of the i-th charging pile system. t This represents the inertia value of the charging pile system, which is numerically equal to the sum of the virtual inertia values ​​of each charging pile system.

[0110] S42. Calculate the relative voltage deviation between the DC side voltage and the inertial center voltage of each charging pile:

[0111] (8)

[0112] Among them, u i U represents the DC-side voltage of the i-th charging pile system. c This represents the voltage at the center of inertia.

[0113] S5. Based on the relative voltage deviation obtained in step S4, the virtual parameters are controlled in a secondary manner using inertial center collaborative control. The virtual inertial control after the secondary control of the virtual parameters is used as the voltage outer loop to adjust the input power of each charging pile to stabilize the DC side voltage and achieve consistency of DC side voltage response when the load is switched on and off.

[0114] S51. Based on the relative voltage deviation obtained in step S4, the virtual parameters are controlled secondaryly using inertial center cooperative control:

[0115] (9),

[0116] Among them, C v.i This represents the virtual capacitance value of the i-th charging pile system. This is the virtual damping coefficient. , These are the initial virtual parameters of the i-th charging pile system. Let be the voltage change rate of the i-th charging pile system. These are the positive adjustment parameters, u i This represents the DC-side voltage of the i-th charging pile system. This is the rated voltage of the DC bus. and It is a positive adjustment parameter; Relative voltage deviation The rate of change;

[0117] In step S51, such as Figure 5 , No. Relative voltage deviation of each charging pile system The single-cycle oscillation curve has four intervals: In interval ①, the relative voltage deviation A positive value and a positive rate of change indicate that the system's electrical energy is greater than the system average and it is absorbing more electrical energy from other systems. Therefore, to prevent this system from drifting away from other systems, its input electrical energy should be reduced. Simultaneously, to make its output voltage approach the maximum voltage more quickly... Within this range, virtual capacitance and virtual damping should be added. Within range ②, the relative voltage deviation... A positive value but a negative rate of change indicates that although the electrical energy of this system is greater than the system average, it is releasing electrical energy to other systems. Compared to interval ①, interval ② can slightly reduce the reduction in input electrical energy, while reducing the virtual capacitance and increasing the virtual damping to ensure that the system does not experience large fluctuations. Similarly, the relative voltage deviations in intervals ③ and ④... If the value is negative, the input electrical energy should be increased in this stage. Compared with interval ③, the input electrical energy value in interval ④ should be lower. The changes in virtual parameters in intervals ③ and ④ can be compared with those in intervals ① and ②. It is worth noting that in order for each system to operate stably, it is necessary to set upper and lower bounds for the virtual parameter values. Thus, the final expression of the virtual parameters in the virtual inertial control equation of formula (9) can be obtained.

[0118] S52. The method of adjusting the input power of each charging pile by using virtual inertial control after secondary control of virtual parameters as the voltage outer loop is to add an additional input current on the basis of virtual inertial control. Additional input current Calculated as system output current As part of this, the virtual inertial control expression is:

[0119] (10)

[0120] in, The droop coefficient is... This is the rated voltage of the DC bus. DC side voltage For the system output current, This is a virtual capacitance value. This is the virtual damping coefficient. This is the voltage value output by the virtual inertial control.

[0121] In step S52, an additional input current is applied. The expression is:

[0122] (11)

[0123] in, , and For the proportional, derivative, and integral positive control parameters of the i-th system; This represents the rate of change of relative voltage deviation. This is the integral value of the relative voltage deviation.

[0124] In step S52, the inertial center control method needs to adjust the input electrical energy of the system to suppress voltage fluctuations and reduce interference. The oscillation occurs. Therefore, an additional input current needs to be added to the original control method. This is used to change the input current in virtual inertial control. An additional input current is added to the virtual inertial control expression. This allows the voltage to be higher or lower than the voltage at the center of inertia. The system should promptly reduce or increase the input current. This is to optimize the dynamic response capability of the overall system's coordinated control.

[0125] S6. Based on virtual inertial control as the voltage outer loop, the current inner loop is reconstructed using the reverse calculation method to output PWM signals and realize the coordinated operation control of multiple DC charging piles.

[0126] S61. The current inner loop based on PI control is represented in the dq coordinate system as:

[0127] (12)

[0128] in, For the line inductance and resistance between the transformer and the converter, Let represent the components of the AC side voltage along the d and q axes. For the AC side frequency, u i This represents the DC-side voltage of the i-th charging pile system. This is a switching signal. The components of the AC current along the d and q axes of the rotating coordinate system are included. , The rate of change can be expressed as:

[0129] (13)

[0130] S62. To achieve voltage tracking control of the charging pile system, the error is defined according to the classic back-calculation control steps. , :

[0131] (14)

[0132] in, Let represent the components of the alternating current along the d and q axes of the rotating coordinate system. The inner loop reference current is obtained from virtual inertial control; The value is zero.

[0133] Construct the Lyapunov positive definite function expression:

[0134] (15)

[0135] According to Lyapunov's asymptotic stability theorem, for equation (15) to be stable, it should be that... Therefore, after differentiating equation (15) Differentiating equation (14) yields And substitute equation (13) into And then bring people We can obtain:

[0136] (16)

[0137] Where d1 is a constant greater than zero; is the derivative value of the Lyapunov function; For error; For error The derivative value.

[0138] At this time, if you want Switching signals can be designed. :

[0139] (17)

[0140] Among them, u i This represents the DC-side voltage of the i-th charging pile system. For the line inductance and resistance between the transformer and the converter; Let represent the components of the alternating current along the d and q axes in the rotating coordinate system; This represents the d-axis component of the AC side voltage. For AC side frequency; The inner loop reference current is obtained from virtual inertial control; d1 and d2 are constants greater than zero.

[0141] Substitute equation (17) into equation (16). The expression at this point is: Since d1 is a constant greater than zero, therefore Always less than 0, positive definite function Monotonically decreasing. According to Lyapunov's asymptotic stability theorem, the designed switching signal... Can make Maintain a stable state.

[0142] Similarly, construct the Lyapunov function. :

[0143] (18)

[0144] According to Lyapunov's asymptotic stability theorem, for equation (18) to be stable, it should be that... Differentiate equation (18) Differentiating equation (14) yields And substitute equation (13) into And then bring people We can obtain:

[0145] (19)

[0146] Where d2 is a constant greater than zero; is the derivative value of the Lyapunov function; For error; For error The derivative value.

[0147] Similarly, to ensure the function Stable, constructing switching signals :

[0148] (20)

[0149] Among them, u i This represents the DC-side voltage of the i-th charging pile system. For the line inductance and resistance between the transformer and the converter; Let represent the components of the alternating current along the d and q axes in the rotating coordinate system; This represents the q-axis component of the AC side voltage. d2 is the AC side frequency; d2 is a constant greater than zero.

[0150] Substituting equation (20) into equation (19), we get The expression is: Since d2 is a positive definite Lyapunov function, it is a positive definite Lyapunov function. Monotonically decreasing. According to Lyapunov's asymptotic stability theorem, at this point... Maintain a stable state.

[0151] In step S6, based on the virtual inertial control as the voltage outer loop, the current inner loop is reconstructed using a back-reasoning method, and a PWM signal is output to further improve the control effect. By using the proposed virtual inertial control method as the voltage outer loop and improving the current inner loop to achieve voltage-current dual-loop control, the control effect is improved. From the above steps S1-S6, the block diagram of the inertial center cooperative control based on virtual inertial control is as follows: Figure 6 As shown, Figure 6 In this context, 1 / s is the integration module; Limiter is the limiting module.

[0152] This collaborative control method for multiple DC charging pile systems can effectively stabilize the output voltage of DC charging piles during load switching, while providing sufficient inertia and damping support for the DC system, effectively improving dynamic performance and voltage disturbance rejection capability, thereby fully ensuring the stability of the charging process. Based on virtual inertial control, this invention employs inertial center collaborative control as a secondary control method, which optimizes the collaborative control effect of the multiple charging pile system, effectively enhancing the consistency of voltage response across systems, and enabling the multiple charging pile system to quickly recover stability during load switching.

[0153] This collaborative control method for multiple DC charging pile systems takes into account the line resistance loss on the common DC bus. When multiple charging piles are running collaboratively, it can effectively reduce the impact of line loss on the voltage of the common bus. Furthermore, after disconnecting one charging pile, the remaining system can still operate collaboratively. Experimental simulations have verified that the method of this invention has higher advantages and safety in "interconnected multi-charging".

[0154] This collaborative control method for multiple DC charging pile systems can establish virtual inertial control suitable for DC systems. The DC charging pile system will also possess the external characteristics of a synchronous machine, providing inertial and damping support. This transforms electric vehicles from traditional passive loads into special loads that can actively participate in charging pile regulation, quickly smoothing DC-side voltage fluctuations during load switching. This method proposes a "many-to-many" charging mode with interconnected charging piles, collaboratively controlling multiple charging piles to charge multiple electric vehicles. In interconnected mode, it effectively reduces the impact of load switching and line resistance on DC-side voltage and can promptly disconnect a charging pile in case of a fault, fully ensuring the safety and efficiency of the charging pile system.

[0155] This collaborative control method for multiple DC charging pile systems, after establishing a model of coordinated operation of multiple DC charging piles, first draws an analogy between key parameters in AC and DC systems, improving the virtual synchronous machine model in the AC system into a virtual inertial control method suitable for the DC system. Based on this, the key virtual parameters are adaptively adjusted and optimized as primary control. Then, an inertial center collaborative control strategy is adopted as secondary control to adjust the input power of each charging pile system and further adjust the virtual parameters, thereby ensuring the consistency of voltage response of each system under different parameters. Finally, the current inner loop is reconstructed using a back-calculation method, compensating for the weak dynamic performance of traditional PI control, thus achieving collaborative operation control of multiple DC charging piles.

[0156] This collaborative control method for multiple DC charging pile systems can significantly reduce the impact of electric vehicle load switching and line resistance on the common bus voltage of the charging piles. When a charging pile fails, it can be disconnected in time, and the voltage of the remaining charging piles can be reduced by a small disturbance and quickly restored to stability, thus fully ensuring the safety and efficiency of the multi-charging pile system.

[0157] The experimental simulation analysis of the collaborative control method of this multi-DC charging pile system in the embodiment is as follows:

[0158] This paper focuses on the collaborative control of a multi-charging pile system. Using Matlab / Simulink, simulation analysis is performed on multiple DC charging pile systems. The rated voltage of the DC charging piles in the system is 750V, with a maximum output power of 375kW, and the electric vehicle load power is 187kW. Considering three DC charging piles and two electric vehicle loads, and assuming different line resistances between each charging pile and the DC bus, with the virtual capacitance and virtual resistance of the three charging piles decreasing sequentially, simulation analysis is conducted for the switching of electric vehicle loads during system operation, as well as for the scenario where a charging pile fails and is disconnected to ensure overall system stability. The effectiveness of the proposed control strategy is verified based on the resulting changes in the charging pile output voltage and load voltage.

[0159] The simulation conditions are set as follows: First, three charging piles operate collaboratively. At t=4s and t=5s, the multi-charging pile system connects and disconnects the load, and then disconnects the third charging pile at t=6s. Next, two charging piles operate collaboratively. At t=8s and t=9s, the system connects and disconnects the load, and then disconnects the second charging pile at t=10s. Finally, the first charging pile operates independently. At t=12s and t=13s, the system connects and disconnects the load. In the simulation, before t=4s, the charging pile system has already connected an electric vehicle load, and at t=4s, it begins to connect another electric vehicle load. The simulation results are as follows. Figure 7 , Figure 8 , Figure 9 As shown.

[0160] Depend on Figure 7 It can be seen that during the period t=4~6s, the three charging piles operate collaboratively. A second vehicle load is connected at t=4s and disconnected at t=5s. At this time, the output voltages of all three charging piles experience disturbances. Because the virtual capacitance and virtual damping of the three charging piles decrease sequentially, the first charging pile has better control, with its output voltage u1 changing the least. The output voltage u2 of the second charging pile changes moderately, and the output voltage u3 of the third charging pile changes the most. Due to the line resistance, after connecting the second electric vehicle load at t=4s, the voltage across the line resistance increases slightly, and the common bus voltage drops by approximately 2V. Figure 8 As shown. Furthermore, due to differences in the length and aging of the charging lines, the line resistance varies among different charging stations, resulting in different power outputs. For example... Figure 9 As shown, during the period from t=4 to 6s, the output power P1, P2, and P3 of the three charging piles to the load are inversely proportional to the magnitude of their line resistance.

[0161] like Figure 7 and Figure 8 At t=6s, the third charging station malfunctioned and was subsequently disconnected. The output voltages u1 and u2 of the remaining two charging stations experienced minor disturbances but quickly stabilized. The common bus voltage U... dc The voltage drops by approximately 1V, and the power required by the load is provided jointly by the two charging piles. At t=8s and t=9s, the second vehicle load is connected and disconnected. Compared to the coordinated operation of the three charging piles, the output voltages u1 and u2 of the first and second charging piles experience increased disturbances, and the power output of both charging piles varies more significantly. When a new load is connected, the common bus voltage U... dc The voltage drops by approximately 3V. At t=10s, the second charging station is disconnected, leaving only the first charging station operating in the entire system. At this time, the output voltage u1 of the first charging station remains stable after a small disturbance and can provide the required power to the load. However, the common bus voltage U... dc The voltage dropped by approximately 2V. At t=12s and t=13s, the vehicle load was connected and disconnected, by... Figure 7 , Figure 8 , Figure 9 Simulation results show that, compared with the coordinated operation of multiple charging pile systems, the single charging pile system experiences greater output voltage fluctuations and increased power output variations when load changes occur. Furthermore, the voltage on the common bus will drop by approximately 5V after a new load is added.

[0162] Simulation results show that, compared with the traditional single-pile-multiple-charger method, the interconnected multi-charger system exhibits better control performance when dealing with vehicle load switching. Voltage fluctuations at each charging pile are smaller, avoiding significant power output variations and extending their lifespan to some extent. Most importantly, the multi-charger system effectively reduces the impact of line resistance on the common bus voltage, ensuring efficient charging and thus verifying the superior performance of the proposed control strategy. Furthermore, when one charging pile fails and is disconnected, the remaining charging piles can still operate safely, further validating the safety of the proposed control strategy.

[0163] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A collaborative control method for a multi-DC charging pile system, characterized in that: Includes the following steps, S1. Compare the DC-side voltage u of the i-th charging pile system in a multi-DC charging pile system. i With DC bus rated voltage u n Check if they are equal. If they are not equal, proceed to the next step S2; if they are equal, end the process. S2. Establish a virtual inertial control strategy suitable for DC charging pile systems; S3. Analyze the virtual parameters, including virtual inertia and virtual damping coefficient, in the virtual inertial control strategy established in step S2. Based on voltage fluctuations, obtain the virtual inertial control with adaptive parameter optimization, and use it as the primary control. S4. Introduce an inertial center voltage to make an overall response to the voltage deviation of the DC charging pile system caused by load changes. Based on the inertial center voltage, obtain the relative voltage deviation between the DC side voltage of each charging pile and the inertial center voltage. In step S4, based on the inertial center voltage, the relative voltage deviation between the DC side voltage and the inertial center voltage of each charging pile is obtained, specifically as follows: S41, Inertial center voltage u c for: ， Among them, C v.i u represents the virtual capacitance value of the i-th charging pile system. i C represents the DC-side voltage of the i-th charging pile system. t This represents the inertia value of the charging pile system, which is numerically equal to the sum of the virtual inertia values ​​of each charging pile system. S42. Calculate the relative voltage deviation between the DC side voltage and the inertial center voltage of each charging pile: ， Among them, u i U represents the DC-side voltage of the i-th charging pile system. c Indicates the voltage at the center of inertia; S5. Based on the relative voltage deviation obtained in step S4, the virtual parameters are controlled in a secondary manner using inertial center collaborative control. The virtual inertial control after the virtual parameters are controlled in a secondary manner is used as the voltage outer loop to adjust the input power of each charging pile to stabilize the DC side voltage. S6. Based on virtual inertial control as the voltage outer loop, the current inner loop is reconstructed using the reverse calculation method to output PWM signals and realize the coordinated operation control of multiple DC charging piles.

2. The collaborative control method for a multi-DC charging pile system as described in claim 1, characterized in that: In step S1, a virtual inertial control strategy suitable for DC charging pile systems is established, specifically as follows: S21. Add a virtual capacitor to the DC charging pile system. In the i-th charging pile system, the relationship between the input and output currents on both sides of the virtual capacitor is expressed as follows: ， in, Input current to the virtual capacitor; For system output current; This represents the virtual capacitance value of the i-th charging pile system, which is also the virtual inertia value of the i-th charging pile system. The voltage value output by the virtual inertial control; t is time; S22. The input current of the virtual capacitor is equivalent to the difference between the rated current and the damping current, resulting in the control strategy for the i-th charging pile system: ， in, This is a reference value for the current flowing from the system to the DC side. For the system output current, This is a virtual capacitance value. This is the virtual damping coefficient. DC side voltage This is the voltage value output by the virtual inertial control. S23. Introducing voltage-current droop control, the final virtual inertial control expression is: ， in, The droop coefficient is... This is the rated voltage of the DC bus.

3. The collaborative control method for a multi-DC charging pile system as described in claim 2, characterized in that: In step S3, the virtual inertial control with adaptive parameter optimization is obtained as follows: ， in, , These are the initial virtual parameters of the i-th charging pile system; Let be the voltage change rate of the i-th charging pile system; These are the positive adjustment parameters.

4. The collaborative control method for a multi-DC charging pile system as described in any one of claims 1-3, characterized in that: In step S5, based on the relative voltage deviation obtained in step S4, inertial center cooperative control is used to perform secondary control on the virtual parameters. The virtual inertial control resulting from this secondary control is used as the voltage outer loop to adjust the input power of each charging pile. Specifically, S51. Based on the relative voltage deviation obtained in step S4, the virtual parameters are controlled secondaryly using inertial center cooperative control: ， Among them, C v.i This represents the virtual capacitance value of the i-th charging pile system. This is the virtual damping coefficient. , These are the initial virtual parameters of the i-th charging pile system. Let be the voltage change rate of the i-th charging pile system. These are the positive adjustment parameters, u i This represents the DC-side voltage of the i-th charging pile system. This is the rated voltage of the DC bus. and It is a positive adjustment parameter; Relative voltage deviation The rate of change; S52. The method of adjusting the input power of each charging pile by using virtual inertial control after secondary control of virtual parameters as the voltage outer loop is to add an additional input current on the basis of virtual inertial control. Additional input current Calculated as system output current As part of this, the virtual inertial control expression is: ， in, The droop coefficient is... This is the rated voltage of the DC bus. DC side voltage For the system output current, This is a virtual capacitance value. This is the virtual damping coefficient. This is the voltage value output by the virtual inertial control.

5. The collaborative control method for a multi-DC charging pile system as described in claim 4, characterized in that: In step S52, an additional input current is applied. The expression is: ， in, , and For the proportional, derivative, and integral positive control parameters of the i-th system; This represents the rate of change of relative voltage deviation. This is the integral value of the relative voltage deviation.

6. The collaborative control method for a multi-DC charging pile system as described in any one of claims 1-3, characterized in that: In step S6, the inner current loop is reconstructed using a reverse calculation method, specifically as follows: S61. The current inner loop based on PI control is represented in the dq coordinate system as: ， in, , For the line inductance and resistance between the transformer and the converter, , Let represent the components of the AC side voltage along the d and q axes. For the AC side frequency, u i This represents the DC-side voltage of the i-th charging pile system. , For the switching signal, the components of the AC side current along the d and q axes in the rotating coordinate system. , The rate of change is expressed as: ； S62. To achieve voltage tracking control in the charging pile system, based on back-calculation control, the error is defined, and a Lyapunov positive definite function expression is constructed. According to the Lyapunov asymptotic stability theorem, the reconstructed current loop switching signal in the i-th system is designed. , .

7. The collaborative control method for a multi-DC charging pile system as described in claim 6, characterized in that: In step S62, the error is defined, and the Lyapunov positive definite function expression is constructed, specifically as follows: S621, Define errors e1 and e2: ， in, , Let represent the components of the alternating current along the d and q axes of the rotating coordinate system. The inner loop reference current is obtained from virtual inertial control; The value is zero; S622. Construct the Lyapunov positive definite function expression: ， ， Where e1 and e2 are errors, , For the constructed Lyapunov function; S623. Based on Lyapunov's asymptotic stability theorem, design the reconstructed current loop switching signal for the i-th system. for: ， Among them, u i This represents the DC-side voltage of the i-th charging pile system. For the line inductance and resistance between the transformer and the converter; Let represent the components of the alternating current along the d and q axes in the rotating coordinate system; , These are the components of the AC side voltage along the d and q axes; For AC side frequency; d1 and d2 are the inner loop reference currents obtained from virtual inertial control; d1 and d2 are constants greater than zero.

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