Method and system for treating battery current fluctuation of mobile emergency energy storage vehicle under unbalanced working condition

Abstract

The invention relates to the technical field of power electronic conversion, in particular to a method and a system for managing current fluctuation of a battery of a mobile emergency energy storage vehicle under an unbalanced working condition. And power fluctuation and frequency doubling current are generated by the mobile emergency energy storage vehicle under a three-phase imbalance working condition due to lack of main network support. By inhibiting the current fluctuation of the battery of the emergency energy storage vehicle, the service life of the battery is prolonged, and the stability of emergency power supply is ensured. According to the method and system for treating the current fluctuation of the battery of the mobile emergency energy storage vehicle under the unbalanced working condition, the method is mainly applied to an energy storage system of the mobile emergency energy storage vehicle, the safety and reliability of the whole energy storage system are improved by restraining the current fluctuation of the battery of the mobile emergency energy storage vehicle under the unbalanced working condition, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic conversion, and particularly to a method and system for controlling the current fluctuation of the battery of a mobile emergency energy storage vehicle under unbalanced operating conditions. Background Art

[0002] Under the background of the complex power grid structure and frequent occurrence of sudden faults, in island operation areas, due to the lack of continuous and stable power support from the main power grid, the ability to regulate voltage and frequency is weak, resulting in an increasing demand for stable and reliable emergency power supplies. Therefore, the emergency power supply must have the ability of rapid response to provide reliable power supply for loads at critical moments.

[0003] When the load is three-phase unbalanced, it can be decomposed into positive-sequence component, negative-sequence component, and zero-sequence component. For the three-phase three-wire connection mode, since there is no zero-sequence current path, the influence of the zero-sequence component is not considered. In the d-q coordinate system, the positive-sequence component and negative-sequence component of the three-phase unbalanced voltage will be coupled with each other, generating a second-harmonic component:

[0004]

[0005] In the formula, E dq represents the complex vector of the electromotive force in the d-q coordinate system, represents the complex vector of the positive-sequence electromotive force in the d-q coordinate system, represents the complex vector of the negative-sequence electromotive force in the d-q coordinate system, and ω represents the angular frequency of the grid electromotive force;

[0006] In the actual island operation situation, the distribution network often presents a three-phase unbalanced operating condition. Under the condition of a three-phase unbalanced load, due to the current fluctuation of the energy storage system, it has an impact on the battery life and system stability. Therefore, controlling the current fluctuation of the energy storage system under unbalanced operating conditions to improve the safety and reliability of the battery system has become an important research direction for the optimization of the current power system.

[0007] Facing island operation and sudden power supply demands, as a flexible mobile energy storage system, the mobile emergency energy storage vehicle can quickly access the island operation area or the power grid with serious three-phase unbalanced problems. By multiplexing the motor windings and converters to integrate the motor and charging system for dynamic regulation, it controls the current fluctuation of the battery of the mobile emergency energy storage vehicle, improves the safety and reliability of the entire energy storage system, and extends the service life of the battery, enabling it to have the ability of rapid response in case of emergency. Summary of the Invention

[0008] The object of the present invention is to propose a method for controlling the current fluctuation of the battery of a mobile emergency energy storage vehicle under unbalanced operating conditions, so as to solve the problems of power fluctuation and double-frequency current generated by the mobile emergency energy storage vehicle under three-phase unbalanced conditions in the island operation area due to the lack of main grid support. The invention prolongs the service life of the battery and ensures the stability of emergency power supply by suppressing the current fluctuation of the battery of the emergency energy storage vehicle.

[0009] To achieve the above object, the present invention provides the following technical solution: A method for controlling the current fluctuation of the battery of a mobile emergency energy storage vehicle under unbalanced conditions, comprising the following steps:

[0010] S1: Detection and connection: Use the monitoring system of the emergency energy storage vehicle to detect the three-phase voltage or current of the power grid in real time, identify the unbalanced situation and determine the degree of unbalance; Connect the unbalanced power grid or load to the AC port, connect the DC source to the front-stage winding circuit, and perform a fast discharge operation through the split-phase open-winding motor.

[0011] S2: Energy distribution and regulation: Only provide the positive-sequence electromotive force vector in the d-q coordinate system at the DC port, and the double-frequency component generated by the negative-sequence electromotive force vector is absorbed by the discharge resistor; Use a centralized controller to manage the energy flow of each port, completely share the sampling and control data of the front-stage circuit and the three-phase unbalanced control circuit in the controller, and couple the control variables of the three-phase unbalanced control circuit to the front-stage control loop through mathematical formulas.

[0012] S3: Power regulation control: When the emergency energy storage vehicle is connected to an unbalanced load or power grid, the monitoring system detects the three-phase unbalanced voltage. Only the positive-sequence component is given at the DC end, the negative-sequence component of the d-axis is given as 0, and the voltage component of the q-axis is given as 0. Compare with the given value to obtain an error signal, use a PI controller to adjust the error signal, generate a reference value of the current, use the reference value of the current as the input, and perform SVPWM modulation through the control of the current loop and the inverse Park transformation; The negative-sequence component is given at the right port, and the voltage component of the q-axis is given as 0. Repeat the above adjustment, generate the reference value, control and modulation process to achieve power regulation and suppress the double-frequency fluctuation at the DC port.

[0013] Preferably, the emergency energy storage vehicle adopts a new type of two-port electric drive reconfiguration vehicle-mounted converter, and the new type of two-port electric drive reconfiguration vehicle-mounted converter includes a DC port, an AC port, a front-stage winding, an open-winding split-phase motor, and a three-phase unbalanced control circuit; The DC input voltage of the DC port is U DC , and is provided with a filter capacitor C DC ; The front-stage winding adopts a three-phase full-bridge structure and is composed of six power switch bridge arms. The midpoints of each bridge arm are A, B, and C respectively. The positive and negative poles of the DC input voltage are respectively connected to both ends of the bridge arm in the front-stage winding circuit; The AC port includes three AC power supplies AC A, AC B , AC C , each phase is connected to a filter capacitor C A , C B , C C Each phase is connected to a circuit breaker S1, S2, S3, and is led out through a phase splitting point; the open winding split-phase motor adopts a multiplexed motor winding L A1 , L A2 , L B1 , L B2 , L C1 , L C2 The three-phase unbalanced control circuit adopts a three-phase full-bridge structure, which consists of six power switch bridge arms, the midpoints of each bridge arm are A', B', C', and the DC capacitor C DC' It is connected to the upper and lower ends of the bridge arm, with a discharge resistor R on the right, and four circuit breakers S4, S5, S6, and S7 connected to both ends of the resistor. The control circuit works in drive mode or DC-AC electric drive reconstruction mode.

[0014] Preferably, the multiplexed motor windings and device circuits form a DC-AC two-port converter, integrating the open-winding split-phase motor with the electric drive reconstruction technology, and realizing flexible adjustment of the motor drive or the two-port power supply through a set of controllers; the left DC port utilizes the fast discharge capability of the energy storage system to dynamically adjust the power output to meet the load demand; the three-phase unbalanced management circuit is connected to a DC compensation capacitor and a discharge resistor, the DC capacitor is used to stabilize the DC voltage of the management circuit and provide energy buffering, and the discharge resistor is used to absorb the double frequency fluctuation of the DC port power, release the residual charge of the capacitor, and limit the discharge rate of the capacitor.

[0015] Preferably, the multiplexed motor windings and device circuits are combined to form a DC-AC two-port converter, and dual SVPWM modulation is performed by synthesizing an AC voltage through 64 voltage vectors.

[0016] Preferably, after the mobile emergency energy storage vehicle arrives at the scene, the unnecessary energy supply is first cut off by the circuit breaker, and then the required DC power supply or load is connected to the corresponding port. After the connection is completed, the circuit breaker contacts are closed, and then the two-port electric drive reconstruction vehicle converter is started; during the operation of the converter, the circuit breaker remains in a non-working state.

[0017] Preferably, the method also includes real-time monitoring of parameters of each port of the system, including DC port current, DC port voltage, AC port current and three-phase imbalance control circuit current; when the three-phase imbalance of the load changes, the system stability is evaluated based on the monitoring data, and the stable operation of the system is maintained by adjusting the control strategy.

[0018] Preferably, during the process of suppressing the second - harmonic fluctuation of the DC - port power, the parameters of the PI controller are adaptively adjusted; according to the magnitude of the unbalance degree, the system response speed, and the current fluctuation condition, the proportional coefficient and the integral coefficient of the PI controller are dynamically changed to optimize the control effect.

[0019] A system for controlling the battery current fluctuation of a mobile emergency energy - storage vehicle under unbalanced working conditions, comprising:

[0020] A monitoring module: used for real - time detecting the three - phase voltage or current of the power grid, identifying the unbalance situation and determining the unbalance degree;

[0021] A control module: adopting a centralized controller to manage the energy flow of each port, sharing the sampling and control data of the pre - stage circuit and the three - phase unbalance control circuit, and coupling the control variables of the three - phase unbalance control circuit to the pre - stage control loop; according to the detected unbalanced voltage, controlling the power output of the DC port and the right - hand port to suppress the second - harmonic fluctuation of the DC port;

[0022] A circuit module: including a novel two - port electric - drive reconfigured vehicle - mounted converter, the novel two - port electric - drive reconfigured vehicle - mounted converter having a DC port, an AC port, a pre - stage winding, an open - winding split - phase motor, and a three - phase unbalance control circuit, realizing the functions of electric - energy conversion, distribution, and unbalance control.

[0023] Preferably, the monitoring module is further used for real - time monitoring the battery state of the mobile emergency energy - storage vehicle, including the battery power and the battery temperature; when the battery power is lower than the set threshold or the battery temperature exceeds the normal range, an alarm signal is sent, and the control strategy is adjusted to protect the battery.

[0024] Preferably, the control module also has a fault - diagnosis function. When faults occur in components such as power - switching devices, filter capacitors, and circuit breakers in the circuit module, the fault location is quickly located, the faulty circuit is cut off, a standby circuit is started, or corresponding protection measures are taken to ensure the safe operation of the system.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. The method and system for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced conditions can accurately identify and process the double-frequency components generated under three-phase unbalanced conditions through specific control strategies and the design of a new two-port electric drive reconfigured vehicle-mounted converter. During actual operation, when the emergency energy storage vehicle is connected to an unbalanced load or power grid, the monitoring system detects the three-phase unbalanced voltage in real time. The control strategy makes the DC port only provide the positive-sequence electromotive force vector, and guides the double-frequency components generated by the negative-sequence electromotive force vector to the discharge resistor for absorption. This energy distribution method avoids the direct impact of double-frequency fluctuations on the battery, greatly reducing the fluctuation amplitude of the battery current. Compared with traditional systems, the battery operates in a more stable current environment, significantly reducing the damage to the internal structure of the battery caused by current fluctuations, thus significantly extending the service life of the battery.

[0027] 2. The method and system for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced conditions. The stable current output reduces the internal resistance loss of the battery, thereby reducing the heat generation phenomenon during the operation of the battery. Overheating is one of the important factors affecting the battery performance and life. Excessive temperature will accelerate the internal chemical reactions of the battery, resulting in battery capacity attenuation and increased internal resistance. The present invention effectively reduces the heat loss of the battery by suppressing current fluctuations, enabling the battery to operate in a more suitable temperature environment, further ensuring the performance and stability of the battery.

[0028] 3. The method and system for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced conditions. In the island operation area or under the three-phase unbalanced conditions of the power grid caused by sudden faults, the system of the present invention can respond quickly. The new two-port electric drive reconfigured vehicle-mounted converter of the mobile emergency energy storage vehicle can connect the AC port to the unbalanced power grid or load in a short time, and at the same time, the DC source quickly discharges through the split-phase open-winding motor to provide stable power support for the load. This fast response ability ensures that in an emergency, the system can supply power to critical loads in a timely manner, ensuring the normal operation of important equipment and enhancing the emergency power supply ability of the entire power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a conventional connection diagram of the motor in the drive mode of the present invention;

[0031] Figure 2 It is a structural diagram of the new two-port electric drive reconfigured vehicle-mounted converter of the present invention;

[0032] Figure 3 Macro schematic diagram of the novel two-port electric drive reconfigured vehicle-mounted converter of the present invention;

[0033] Figure 4 Operation flow chart of the mobile emergency energy storage vehicle of the present invention arriving at the scene;

[0034] Figure 5 Schematic diagram of energy flow for unbalance governance of the present invention;

[0035] Figure 6 Control block diagram for suppressing power double-frequency fluctuation of the present invention;

[0036] Figure 7 DC port current waveform diagram of the present invention with load unbalance degree added;

[0037] Figure 8 DC port voltage waveform diagram of the present invention with load unbalance degree added;

[0038] Figure 9 Unbalanced load voltage waveform diagram of the present invention with load unbalance degree added;

[0039] Figure 10 AC port current waveform diagram of the present invention with load unbalance degree added;

[0040] Figure 11 Current waveform of the three-phase unbalance governance circuit of the present invention with load unbalance degree added;

[0041] Figure 12 DC port current waveform diagram of the present invention with load unbalance degree reduced;

[0042] Figure 13 DC port voltage waveform diagram of the present invention with load unbalance degree reduced;

[0043] Figure 14 Unbalanced load voltage waveform diagram of the present invention with load unbalance degree reduced;

[0044] Figure 15 AC port current waveform diagram of the present invention with load unbalance degree reduced;

[0045] Figure 16 Current waveform of the three-phase unbalance governance circuit of the present invention with load unbalance degree reduced. Detailed implementation manner

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] Please refer to Figures 1-16 , the present invention provides a technical solution:

[0048] A method for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions, comprising the following steps:

[0049] S1: Detection and connection: Use the monitoring system of the emergency energy storage vehicle to continuously detect the three-phase voltage or current of the power grid, identify the unbalanced situation and determine the degree of unbalance; Connect the unbalanced power grid or load to the AC port, connect the DC source to the primary winding circuit, and perform a rapid discharge operation through a split-phase open-winding motor.

[0050] S2: Energy distribution and regulation: Only provide the positive-sequence electromotive force vector in the d-q coordinate system at the DC port, and the double-frequency component generated by the negative-sequence electromotive force vector is absorbed by the discharge resistor; Use a centralized controller to manage the energy flow of each port, completely share the sampling and control data of the primary circuit and the three-phase unbalance control circuit in the controller, and couple the control variables of the three-phase unbalance control circuit to the primary control loop through a mathematical formula.

[0051] S3: Power regulation control: When the emergency energy storage vehicle is connected to an unbalanced load or power grid, the monitoring system detects the three-phase unbalanced voltage. Only the positive-sequence component is given at the DC end, the negative-sequence component of the d-axis is set to 0, and the voltage component of the q-axis is set to 0. Compare with the given value to obtain an error signal, use a PI controller to adjust the error signal, generate a reference value of the current, use the reference value of the current as the input, and perform SVPWM modulation through the control of the current loop and the inverse Park transformation; The negative-sequence component is given at the right port, the voltage component of the q-axis is set to 0, and the above adjustment, reference value generation, control and modulation processes are repeated to achieve power regulation and suppress the double-frequency fluctuation at the DC port.

[0052] In the AC-DC conversion mode, the multiplexed motor winding and the device circuit are combined to form a DC-AC two-port converter, and the AC voltage is synthesized through 64 voltage vectors for dual SVPWM modulation.

[0053] After the mobile emergency energy storage vehicle arrives at the scene, it first cuts off the unnecessary energy supply through the circuit breaker, and then connects the required DC power supply or load to the corresponding port. After the connection is completed, the circuit breaker contacts are closed, and then the two-port electric drive reconstruction vehicle converter is started; during the operation of the converter, the circuit breaker remains in a non-working state.

[0054] The method also includes real-time monitoring of system port parameters, including DC port current, DC port voltage, AC port current and three-phase imbalance management circuit current; when the three-phase imbalance of the load changes, the system stability is evaluated based on the monitoring data, and the stable operation of the system is maintained by adjusting the control strategy.

[0055] A system for controlling battery current fluctuations of a mobile emergency energy storage vehicle under unbalanced working conditions, comprising:

[0056] Monitoring module: used to detect the three-phase voltage or current of the power grid in real time, identify imbalance and determine the degree of imbalance;

[0057] Control module: A centralized controller is used to manage the energy flow of each port, share the sampling and control data of the front-stage circuit and the three-phase unbalanced control circuit, and couple the control variables of the three-phase unbalanced control circuit to the front-stage control loop; according to the detected unbalanced voltage, the power output of the DC terminal and the right-hand port is controlled to suppress the double frequency fluctuation of the DC port;

[0058] Circuit module: including a new two-port electric drive reconstruction vehicle-mounted converter, which has a DC port, an AC port, a front-stage winding, an open-winding split-phase motor and a three-phase unbalanced control circuit to realize the conversion, distribution and unbalanced control functions of electric energy.

[0059] The monitoring module is also used to monitor the battery status of the mobile emergency energy storage vehicle in real time, including battery power and battery temperature; when the battery power is lower than a set threshold or the battery temperature is out of a normal range, an alarm signal is sent and the control strategy is adjusted to protect the battery.

[0060] The control module also has a fault diagnosis function. When a fault is detected in a power switch device, filter capacitor, circuit breaker or other component in the circuit module, the fault position is quickly located, the fault circuit is cut off, the backup circuit is started or corresponding protective measures are taken to ensure the safe operation of the system.

[0061] In the process of suppressing the double frequency fluctuation of the DC port power, the parameters of the PI controller are adaptively adjusted; according to the size of the imbalance, the system response speed and the current fluctuation, the proportional coefficient and the integral coefficient of the PI controller are dynamically changed to optimize the control effect.

[0062] General connection of the motor in drive modeFigure 1 As shown, U DC represents the input voltage of the left DC port, and C DC represents a capacitor. When the load changes suddenly, the capacitor can supply power briefly to prevent the voltage from dropping suddenly; it is connected to the motor through a switching tube. Since there is a split-phase point in the open-winding motor, it can be connected to the AC power grid; on the right side, it is connected to the DC output port through a switching tube, and C DC' represents a capacitor, which can make the output voltage more stable, and U DC' represents the output voltage of the right DC port;

[0063] The new two-port electric drive reconfigurable vehicle-mounted converter is as Figure 2 shown. This device includes a DC port, where U DC represents the DC input voltage, and C DC represents a filter capacitor for smoothing the output voltage; the front-stage winding adopts a three-phase full-bridge structure, which consists of six power switch bridge arms. Each bridge arm has a corresponding power electronic power switch. The power electronic power switch devices are S A1 , S B1 , S C1 , S A2 , S B2 , S C2 . The power electronic switch devices S A1 , S A2 form the S A bridge arm, the power electronic switch devices S B1 , S B2 form the S B bridge arm, the power electronic switch devices S C1 , S C2 form the S C bridge arm, respectively forming the midpoints A, B, and C of the bridge arms. The positive and negative poles of the DC input voltage are respectively connected to both ends of the S A bridge arm in the front-stage winding circuit. The AC port includes three AC power supplies, which are AC A , AC B , AC C . Each phase is connected with a filter capacitor, which are C A , C B , C C . Each phase is connected with a circuit breaker, which are S1, S2, and S3, to automatically cut off the current when a circuit fault occurs, thus protecting the safety of electrical equipment and circuits. The AC port is led out through a split-phase point, which can adapt to three-phase power supplies or loads without the need for inductors or equipment; the open-winding split-phase motor adopts a multiplexed motor winding, including L A1 , L A2 , L B1 , L B2 , L C1 , L C2, realizing flexible adjustment of the three-port power supply; the right side adopts a three-phase unbalanced control circuit, which adopts a three-phase full-bridge structure and consists of six power switch bridge arms. Each bridge arm has a corresponding power electronic power switch. The power electronic power switch devices are S A'1 , S B'1 , S C'1 , S A'2 , S B'2 , S C'2 , power electronic switching device S A'1 , S A'2 Composition A' Bridge arm, power electronic switching device S B'1 , S B'2 Composition B' Bridge arm, power electronic switching device S C'1 , S C'2 Composition C' The bridge arms form the midpoints A', B', and C' of the bridge arms respectively, and the DC capacitor C DC' Connected to S C The upper and lower ends of the bridge arm; a discharge resistor R is connected on the right side to absorb the double frequency fluctuation of the DC port power. Four circuit breakers S4, S5, S6, and S7 are connected to both ends of the resistor respectively. The control circuit works in drive mode or DC-AC electric drive reconstruction mode.

[0064] In the DC-AC operation mode, the multiplexed motor windings and equipment circuits form a DC-AC two-port converter, integrating the open-winding split-phase motor with the electric drive reconstruction technology. A set of controllers is used to achieve flexible adjustment of the motor drive or the two-port power supply. Without the need for additional power components, the problem of double frequency fluctuation of the energy storage system can be effectively solved, providing higher power output during emergency operations and improving the response speed and stability of the emergency power supply. The left DC port can dynamically adjust the power output to meet the load demand through the rapid discharge capability of the energy storage system. The three-phase unbalance management circuit is connected to the DC compensation capacitor and the discharge resistor. The DC capacitor is mainly used to stabilize the DC voltage of the management circuit, provide sufficient energy buffering to provide unbalance management capabilities, and improve the stability of the system and the safety of the energy storage system. The discharge resistor ensures that when the system stops running, the residual charge on the capacitor can be safely released to prevent the voltage from being retained for a long time, accelerate the voltage decay, and provide a certain damping effect for the control of the capacitor voltage to limit the discharge rate of the capacitor.

[0065] In the AC-DC conversion mode, the multiplexed motor windings and device circuits are combined to form a DC-AC two-port converter. In this mode, dual SVPWM modulation can be performed by synthesizing AC voltage through 64 voltage vectors.

[0066] The macroscopic diagram of the new two-port electric drive reconstruction vehicle converter is shown in Figure 3shown.

[0067] In isolated operation areas or when serious three-phase imbalance occurs in the power grid, the emergency energy storage vehicle detects the three-phase voltage or current of the power grid in real time through the monitoring system, identifies the imbalance, and determines the degree of imbalance through data analysis. At this time, the unbalanced power grid or load is connected through the AC port. The energy storage vehicle responds quickly to the demand, and the DC source is connected to the front-stage winding circuit to perform rapid discharge operations through the split-phase open-winding motor to ensure subsequent stable operation; the three-phase imbalance control circuit is connected to the discharge resistor through the circuit breaker. When three-phase imbalance occurs, the discharge resistor absorbs the double frequency fluctuation caused by the DC source to solve the three-phase imbalance problem.

[0068] The operation flow chart of the mobile emergency energy storage vehicle arriving at the scene is as follows: Figure 4 shown.

[0069] In driving mode, the motor rotation is powered by the on-board energy storage system. When the emergency energy storage vehicle arrives at the scene, it first cuts off the unnecessary energy supply through the circuit breaker, then connects the required DC power supply or load to the required port, and starts the converter after all connections are completed.

[0070] After the mobile emergency energy storage vehicle arrives at the scene, the contacts of the circuit breaker must be closed before the two-port electric drive reconstruction on-board converter can be started. Similarly, during the operation of the converter, the circuit breaker is not allowed to work to ensure the safety and reliability of the system.

[0071] The following introduces the control strategy of three-phase unbalance:

[0072] The energy flow diagram of imbalance management is as follows Figure 5 shown.

[0073] The AC port is connected to an island operation area or a severely unbalanced power grid. When the new two-port electric drive reconstruction on-board converter is running, it is known from the background that the negative sequence electromotive force vector will generate double frequency fluctuations on the AC source or load side. Therefore, for the suppression of three-phase imbalance, only the positive sequence electromotive force vector in the dq coordinate system is provided at the DC port. The double frequency component generated by the negative sequence electromotive force vector will be absorbed by the discharge resistor, thereby ensuring the stability and safety of emergency power support provided by the DC end. The device uses a centralized controller to manage the energy flow of each port. The sampling and control data of the front-stage circuit and the three-phase unbalance control circuit are fully shared in the controller. The control variables of the three-phase unbalance control circuit can be coupled to the front-stage control loop through mathematical formulas without communication.

[0074] The control block diagram for suppressing power double frequency fluctuation is as follows Figure 6 shown.

[0075] When the emergency energy storage vehicle is connected to an unbalanced load or power grid, its monitoring system detects the three-phase unbalanced voltage in real time. The voltage vector according to the background technology is composed of a positive sequence component and a negative sequence component with a frequency doubling in the dq coordinate system. When there is no conversion device between the right-side discharge resistor and the AC port, the power supply at this time is supplied by the DC end. Therefore, in order to suppress the power double frequency fluctuation at the DC end, at this time, the DC end only needs to give the positive sequence component, and the double frequency component caused by the negative sequence is given by the right-side discharge resistor, and the negative sequence component of the d-axis is given to 0. Since the d-axis is usually aligned with the grid voltage vector and represents the active component, and the q-axis is orthogonal to the d-axis and represents the reactive component, in the control strategy, the voltage component of the q-axis is given as 0, and the error signal is obtained by comparing it with the given value. The error signal is then adjusted using a PI controller to generate a reference value for the current, which is used as input for SVPWM modulation through the control of the current loop and the inverse Pike transform. Similarly, for the right-hand port, only the negative-sequence component needs to be given, and the voltage component of the q-axis is given as 0, and the error signal is obtained by comparing it with the given value. The error signal is then adjusted using a PI controller to generate a reference value for the current, which is used as input for SVPWM modulation through the control of the current loop and the inverse Pike transform to achieve power regulation, that is, to suppress the double frequency fluctuation of the DC port.

[0076] The DC port current waveform with load imbalance is as follows: Figure 7 shown.

[0077] The DC port voltage waveform with load imbalance is as follows: Figure 8 shown.

[0078] The unbalanced load voltage waveform with load imbalance is as follows Figure 9 shown.

[0079] The current waveform of the AC port with unbalanced load is as follows: Figure 10 shown.

[0080] The current waveform of the three-phase unbalanced control circuit with load imbalance is as follows: Figure 11 shown.

[0081] After applying a step signal to increase the load imbalance at 0.6 seconds, that is, when the new two-port electric drive reconstruction vehicle converter is connected to an unbalanced load, the unbalanced load produces a double frequency fluctuation on the DC port, and the current of the AC port also fluctuates significantly, causing the DC port current pulsation characteristics to increase significantly. At the same time, the DC voltage is also affected by the double frequency fluctuation and becomes temporarily unstable. Due to the sudden change characteristics of the step signal, although the unbalanced load voltage experiences a short disturbance, it quickly returns to a balanced state. When the three-phase imbalance of the load causes the double frequency fluctuation of the system, the double frequency component of the power generated by the DC port begins to be absorbed by the discharge resistor, causing a significant change in the current waveform, indicating that the double frequency fluctuation of the DC port originally caused by the increase in imbalance is quickly suppressed.

[0082] The DC port current waveform with reduced load imbalance is as follows: Figure 12 shown.

[0083] The DC port voltage waveform with reduced load imbalance is as follows: Figure 13 shown.

[0084] The unbalanced load voltage waveform with reduced load imbalance is as follows Figure 14 shown.

[0085] The current waveform of the AC port with reduced load imbalance is as follows: Figure 15 shown.

[0086] The current waveform of the three-phase unbalance control circuit for reducing load imbalance is as follows: Figure 16 shown.

[0087] After applying a step signal to reduce the load imbalance at 0.9 seconds, the three-phase load that was originally in an unbalanced state turned into a balanced state. As a result, the pulsation of the DC side current and voltage was significantly reduced and restored to a balanced state; the unbalanced load voltage quickly returned to the original balanced level after a short disturbance. At the same time, the current waveform of the AC port and the current waveform of the three-phase unbalanced control circuit also synchronously returned to the previous stable state.

[0088] Through comparative analysis of increasing load imbalance and reducing load imbalance, in general, the new two-port electric drive reconstruction vehicle converter successfully eliminates the double frequency interference caused by load imbalance, effectively restores the parameters of each port of the system to a stable operating state quickly, and fully demonstrates the excellent performance of the converter in dynamic adjustment and compensation.

[0089] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0090] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the current fluctuation of the battery of a mobile emergency energy storage vehicle under unbalanced operating conditions, characterized in that, It includes the following steps: S1: Detection and connection: Use the monitoring system of the emergency energy storage vehicle to detect the three-phase voltage or current of the power grid in real time, identify the unbalance situation and determine the degree of unbalance; Connect the AC port to the unbalanced power grid or load, connect the DC source to the primary winding circuit, and perform a rapid discharge operation through the split-phase open-winding motor; S2: Energy distribution and regulation: Only provide the positive-sequence electromotive force vector in the d-q coordinate system at the DC port, and the double-frequency component generated by the negative-sequence electromotive force vector is absorbed by the discharge resistor; Adopt a centralized controller to manage the energy flow of each port, completely share the sampling and control data of the primary circuit and the three-phase unbalance treatment circuit in the controller, and couple the control variables of the three-phase unbalance treatment circuit to the primary control loop through mathematical formulas; S3: Power regulation control: When the emergency energy storage vehicle is connected to an unbalanced load or power grid, the monitoring system detects the three-phase unbalanced voltage. Only the positive-sequence component is given at the DC end, the negative-sequence component of the d-axis is set to 0, and the voltage component of the q-axis is set to 0. Compare with the given value to obtain an error signal, use a PI controller to adjust the error signal, generate a reference value of the current, take the reference value of the current as the input, and perform SVPWM modulation through the control of the current loop and the inverse Park transformation; The negative-sequence component is given at the right port, the voltage component of the q-axis is set to 0, and repeat the above adjustment, reference value generation, control, and modulation processes to achieve power regulation and suppress the double-frequency fluctuation at the DC port.

2. A method for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced operating conditions according to claim 1, characterized in that: The emergency energy storage vehicle adopts a new two-port electric drive reconstruction vehicle-mounted converter, which includes a DC port, an AC port, a front winding, an open-winding split-phase motor and a three-phase unbalanced control circuit; the DC input voltage of the DC port is U DC , with filter capacitor C DC The front winding adopts a three-phase full-bridge structure, which consists of six power switch bridge arms, the midpoints of each bridge arm are A, B, and C, and the positive and negative poles of the DC input voltage are respectively connected to the two ends of the bridge arm in the front winding circuit; the AC port contains three AC power supplies AC A , AC B , AC C , each phase is connected to a filter capacitor C A , C B , C C Each phase is connected to a circuit breaker S1, S2, S3, and is led out through a phase splitting point; the open winding split-phase motor adopts a multiplexed motor winding L A1 , L A2 , L B1 , L B2 , L C1 , L C2 The three-phase unbalanced control circuit adopts a three-phase full-bridge structure, which consists of six power switch bridge arms, the midpoints of each bridge arm are A', B', C', and the DC capacitor C DC' It is connected to the upper and lower ends of the bridge arm, with a discharge resistor R on the right, and four circuit breakers S4, S5, S6, and S7 connected to both ends of the resistor. The control circuit works in drive mode or DC-AC electric drive reconstruction mode.

3. A method and system for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions according to claim 1, characterized in that: In the DC-AC operation mode, the multiplexed motor winding and the device circuit form a DC-AC two-port converter, integrating the open-winding split-phase motor and the electric drive reconstruction technology, and realizing flexible adjustment of the motor drive or the two-port power supply through a set of controllers; The left DC port utilizes the fast discharge ability of the energy storage system to dynamically adjust the power output to meet the load demand; The three-phase unbalance treatment circuit is connected to the DC compensation capacitor and the discharge resistor. The DC capacitor is used to stabilize the DC voltage of the treatment circuit and provide energy buffering. The discharge resistor is used to absorb the double-frequency fluctuation of the power at the DC port, release the residual charge of the capacitor, and limit the discharge rate of the capacitor.

4. A method for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions according to claim 1, characterized in that: In the AC-DC conversion mode, the multiplexed motor winding and the device circuit are combined to form a DC-AC two-port converter, and double SVPWM modulation is performed by synthesizing the AC voltage through 64 voltage vectors.

5. A method for controlling the current fluctuation of the battery of a mobile emergency energy storage vehicle under unbalanced operating conditions according to claim 1, characterized in that: After the mobile emergency energy storage vehicle arrives at the site, first cut off the unnecessary energy supply through the circuit breaker, then connect the required DC power supply or load to the corresponding port. After the connection is completed, close the circuit breaker contact, and then start the two-port electric drive reconstruction vehicle-mounted converter; During the operation of the converter, the circuit breaker remains in a non-operating state.

6. A method for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions according to claim 1, characterized in that: The method also includes real-time monitoring of the parameters of each port of the system, including the DC port current, DC port voltage, AC port current, and the current of the three-phase unbalance treatment circuit; When the three-phase unbalance degree of the load changes, evaluate the system stability according to the monitoring data, and maintain the stable operation of the system by adjusting the control strategy.

7. A method for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions according to claim 1, characterized in that: During the process of suppressing the second - harmonic fluctuation of the DC - port power, the parameters of the PI controller are adaptively adjusted; according to the magnitude of the unbalance degree, the system response speed, and the current fluctuation condition, the proportional coefficient and the integral coefficient of the PI controller are dynamically changed to optimize the control effect.

8. A system for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions according to any one of claims 1-7, characterized in that, It includes: Monitoring module: used to detect the three - phase voltage or current of the power grid in real - time, identify the unbalance situation and determine the degree of unbalance; Control module: adopts a centralized controller to manage the energy flow of each port, share the sampling and control data of the pre - stage circuit and the three - phase unbalance treatment circuit, and couple the control variables of the three - phase unbalance treatment circuit to the pre - stage control loop; according to the detected unbalanced voltage, control the power output of the DC port and the right - hand port, and suppress the second - harmonic fluctuation of the DC port; Circuit module: includes a new type of two - port electric - drive reconfigurable vehicle - mounted converter, and the new type of two - port electric - drive reconfigurable vehicle - mounted converter has a DC port, an AC port, a pre - stage winding, an open - winding split - phase motor, and a three - phase unbalance treatment circuit, realizing the functions of electric - energy conversion, distribution, and unbalance treatment.

9. A system for controlling the current fluctuation of the battery of a mobile emergency energy storage vehicle under unbalanced working conditions according to claim 8, characterized in that: The monitoring module is also used to monitor the battery state of the mobile emergency energy - storage vehicle in real - time, including the battery power and the battery temperature; when the battery power is lower than the set threshold or the battery temperature exceeds the normal range, an alarm signal is sent, and the control strategy is adjusted to protect the battery.

10. A system for controlling the battery current fluctuation of a mobile emergency energy storage vehicle under unbalanced working conditions according to claim 8, characterized in that: The control module also has a fault - diagnosis function. When a fault occurs in components such as the power - switch device, filter capacitor, and circuit breaker in the circuit module, the fault location is quickly located, the faulty circuit is cut off, the standby circuit is started, or corresponding protection measures are taken to ensure the safe operation of the system.

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