Soft start method and system of energy storage system shared by multiple medium-voltage AC ports

Abstract

The invention discloses a soft start method and system for a multi-medium-voltage alternating-current port shared energy storage system, and belongs to the technical field of flexible interconnection power distribution technologies. The method specifically comprises the following steps: carrying out uncontrolled rectification charging on a CHB and a PFCM of the multi-medium-voltage AC port shared energy storage system, and charging the sum of the capacitor voltage of the PFCM and the capacitor voltage of the CHB to a first threshold value; the bypass pre-charging circuit is used for continuously charging to a second threshold value; performing closed-loop control, and increasing the CHB capacitor voltage to a rated value by adjusting a DAB phase shift ratio and CHB charging and discharging current; and performing feeder power flow active control and SOC balance control, and when the power of the three feeders is smaller than a set feeder steady-state threshold, the SOC is balanced and the CHB capacitor voltage is maintained at a rated value, judging that the start of the multi-medium-voltage AC port shared energy storage system is completed, thereby realizing soft start of the multi-medium-voltage AC port shared energy storage system. According to the invention, the safety, stability and reliability of the soft start process are improved.

Description

Technical Field

[0001] This invention belongs to the field of flexible interconnected power distribution technology, and more specifically, relates to a soft-start method and system for a multi-medium voltage AC port shared energy storage system. Background Technology

[0002] Driven by the "dual carbon" goal, the widespread integration of new power sources such as distributed wind and solar power generation and electric vehicle charging piles poses a challenge to the traditional operation mode of the power distribution network.

[0003] Scholars have proposed a novel chain-type battery energy storage power conversion multi-AC-port cascaded H-bridge energy storage system (MACP-CHB-ESS). This system is based on the existing single-AC-port CHB-ESS structure and incorporates flexible interconnect technology. By adding low-power half-bridge modules, the MCP-CHB-ESS has multiple medium-voltage AC ports. However, for the MCP-CHB-ESS, smooth startup control is a critical prerequisite for ensuring the normal operation of the system in engineering applications. Inappropriate startup methods may cause severe voltage and current surges, or even trigger system oscillations, thereby affecting the safe and stable operation of the AC system. Therefore, there is an urgent need to develop a soft-start method based on the MCP-CHB-ESS. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a soft-start method and system for a multi-medium-voltage AC port shared energy storage system. It utilizes a parallel architecture of dual HBSMs (Half-Bridge Sub-Modules) with FBSM (full bridge sub-module) control, combined with CHB (cascaded H-bridge) cascade control, DAB (Dual Active Bridge) phase-shift soft-start energy management, and IGBT (Insulated Gate Bipolar Transistor) in the PFCM (power flow control module) for dynamic voltage regulation and compensation of feeder power. Through a two-stage pre-charging process from a first threshold to a second threshold, precise DAB boost, and coordinated control of the feeder and SOC (State of Charge), the system achieves power efficiency between ports, suppresses inrush current, and improves the safety of starting the multi-medium-voltage AC port shared energy storage system.

[0005] The present invention adopts the following technical solution.

[0006] The first aspect of the present invention provides a soft-start method for a multi-medium-voltage AC port shared energy storage system, comprising:

[0007] Uncontrolled rectification charging is performed on CHB and PFCM of the multi-medium voltage AC port shared energy storage system to charge the sum of the PFCM capacitor voltage and CHB capacitor voltage to a first threshold, thereby obtaining the capacitor voltage sum that reaches the first threshold.

[0008] Based on the capacitor voltage that reaches the first threshold, the pre-charge circuit is bypassed, and charging continues until the capacitor voltage reaches the second threshold, thus obtaining the capacitor voltage that reaches the second threshold.

[0009] Closed-loop control is performed on the capacitor voltage that reaches the second threshold. By adjusting the DAB shift ratio and the CHB charging and discharging current, the CHB capacitor voltage is raised to the rated value, thus obtaining the CHB capacitor voltage that reaches the rated value.

[0010] The CHB capacitor voltage reaches the rated value and is used for active feeder power flow control and SOC equalization control. When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, it is determined that the multi-medium voltage AC port shared energy storage system has been started, realizing the soft start of the multi-medium voltage AC port shared energy storage system.

[0011] Preferably, the uncontrolled rectified charging of the CHB and PFCM of the multi-medium voltage AC port shared energy storage system, charging the sum of the PFCM capacitor voltage and the CHB capacitor voltage to a first threshold, to obtain the capacitor voltage sum reaching the first threshold, specifically includes:

[0012] Set all IGBT drive signals in PFCM and FBSM to low level and lock them out, while using an independent mains power supply for PFCM and TBS.

[0013] Close the circuit breaker at the output of the multi-medium voltage AC port shared energy storage system and disconnect the main circuit contactor switch. Through the feeder circuit containing the pre-charge resistor, perform uncontrolled rectified charging of the capacitors in CHB and PFCM until the PFCM capacitor voltage V... PFCMa With CHB capacitor voltage V pa The sum of these values ​​reaches the first threshold, thus obtaining the sum of the capacitor voltages that reach the first threshold.

[0014] Preferably, the disconnection of the main circuit contactor switch, through a feeder circuit containing a pre-charging resistor, performs uncontrolled rectified charging of the capacitors of CHB and PFCM until the PFCM capacitor voltage V... PFCMa With CHB capacitor voltage V pa The sum reaches the first threshold, specifically including:

[0015] When the main circuit contactor switch is open, the pre-charging circuit is connected, and the capacitor is charged through the resistor. At this time, the AC voltage of the mains is distributed according to the impedance of the diode rectifier bridge, the pre-charging resistor and the internal resistance of the capacitor, resulting in the voltage drop of the diode and the voltage division of the pre-charging resistor and the internal resistance of the capacitor.

[0016] Obtain the effective value of the input AC voltage, calculate the peak voltage after rectification, subtract the voltage drop of the diode and the voltage division of the pre-charge resistor and the internal resistance of the capacitor, and set the first threshold based on the rated voltage of the capacitor.

[0017] The capacitors of PFCM and CHB are charged until the sum of the voltages of the PFCM and CHB capacitors reaches a first threshold.

[0018] Preferably, when the internal resistance of the capacitor is divided, the capacitor voltage distribution satisfies the KVL principle and does not exceed the rated withstand voltage of the IGBT and the capacitor.

[0019] Preferably, the step of bypassing the pre-charge circuit based on the capacitor voltage reaching the first threshold and continuing to charge until the capacitor voltage reaches the second threshold, to obtain the capacitor voltage reaching the second threshold, specifically includes:

[0020] Close the main circuit contactor switch, bypass the pre-charging resistor, and perform uncontrolled rectified charging. According to the impedance distribution of each diode, bypass pre-charging resistor, and capacitor internal resistance, the voltage drop is distributed. On the AC side of the power grid, the capacitors of CHB and PFCM are charged sequentially through the closed main circuit contactor switch, the filter inductor, and then through the diode rectifier bridge. The charging stops when the sum of the PFCM capacitor voltage and the CHB capacitor voltage is charged from the first threshold to the second threshold, thus obtaining the capacitor voltage sum that reaches the second threshold.

[0021] Preferably, the closed-loop control of the capacitor voltage reaching the second threshold, by adjusting the DAB shift ratio and the CHB charging / discharging current to raise the CHB capacitor voltage to the rated value, specifically includes:

[0022] Reset the PI controller within the DAB control loop;

[0023] The DAB control loop is engaged to adjust the shift ratio to inject battery energy, thereby raising the CHB capacitor voltage to near the system's rated voltage.

[0024] Activate CHB charge / discharge control to smoothly transition the CHB capacitor voltage to the system's rated voltage;

[0025] When the CHB capacitor voltage reaches the rated value, the charging is considered complete, and the CHB capacitor voltage reaches the rated value.

[0026] Preferably, the DAB control loop, which adjusts the shift ratio to inject battery energy and raises the CHB capacitor voltage to near the system rated voltage, specifically includes:

[0027] The CHB capacitor voltage reference value is set to the system rated voltage. The shift ratio is adjusted by the DAB control loop to inject battery energy into the DC side of CHB, thus obtaining the CHB capacitor voltage.

[0028] The difference between the CHB capacitor voltage detection value and the system rated voltage drives the IGBT switch of the DAB control loop to raise the CHB capacitor voltage to close to the system rated voltage.

[0029] Preferably, the step of implementing CHB charge / discharge control to smoothly transition the CHB capacitor voltage to the system rated voltage specifically includes:

[0030] The d-axis current reference value is limited, and the total DC voltage reference value of the CHB control voltage outer loop jumps to the rated value.

[0031] The q-axis current ramp start-up, the reference value of the q-axis current in the inner loop of the CHB control current increases from 0 to the reference value of the initial operating condition according to the preset slope;

[0032] The dq axis coordinated control uses a PI controller to track the d-axis and q-axis current reference values, driving the IGBT of the FBSM to adjust the charging and discharging current until the CHB capacitor voltage stabilizes.

[0033] Preferably, the process of performing active feeder power flow control and SOC balancing control on the CHB capacitor voltage that has reached the rated value is defined as follows: when the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC balancing range, and the CHB capacitor voltage remains at the rated value, the multi-medium voltage AC port shared energy storage system is determined to have started successfully. Specifically, this includes:

[0034] Reset the PI controller of the feeder power flow control loop, unlock the IGBT of the half-bridge submodule of the PFCM, and enable it to operate normally according to the control signal;

[0035] Set the q-axis current reference value and d-axis current reference value of each feeder current as the d / q-axis target command value for controlling the feeder current;

[0036] The system obtains the feedback of feeder current and grid voltage, calculates the error between the feeder current and the target command value of the d / q axis of the control feeder current, and calculates the feeder power error in combination with the grid voltage. The system then dynamically adjusts the IGBT switching state of the PFCM and the IGBT duty cycle of the CHB through the PI controller until the feeder power error is less than the feeder steady-state threshold.

[0037] Monitor the SOC of each battery cell in each FBSM, and adjust the charge and discharge duty cycle of the IGBT in the FBSM until the SOC difference of each battery cell converges to the set SOC balance range.

[0038] When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, the multi-medium voltage AC port shared energy storage system is considered to have completed startup.

[0039] A second aspect of the present invention provides a soft-start system for a multi-medium-voltage AC port shared energy storage system, comprising the soft-start method for a multi-medium-voltage AC port shared energy storage system described in the first aspect, including:

[0040] An uncontrolled rectifier charging module is used to perform uncontrolled rectifier charging on the CHB and PFCM of a multi-medium voltage AC port shared energy storage system, charging the sum of the PFCM capacitor voltage and the CHB capacitor voltage to a first threshold, thereby obtaining the capacitor voltage sum that reaches the first threshold.

[0041] The bypass pre-charge circuit charging module is used to bypass the pre-charge circuit and continue charging until the capacitor voltage reaches a second threshold, based on the capacitor voltage reaching a first threshold, to obtain the capacitor voltage reaching the second threshold.

[0042] The closed-loop charging module is used to perform closed-loop control on the capacitor voltage that reaches the second threshold. By adjusting the DAB shift ratio and the CHB charging and discharging current, the CHB capacitor voltage is raised to the rated value, thus obtaining the CHB capacitor voltage that reaches the rated value.

[0043] The output module is used to perform active feeder power flow control and SOC equalization control on the CHB capacitor voltage that has reached the rated value. When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, it is determined that the multi-medium voltage AC port shared energy storage system has been started, thus realizing the soft start of the multi-medium voltage AC port shared energy storage system.

[0044] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0045] This invention effectively suppresses surge current and avoids damage to capacitors and IGBTs due to overcurrent by combining two-stage pre-charging with uncontrolled rectification. The graded charging, which sequentially charges to the first threshold, the second threshold, and the rated value, ensures that the voltage change rate is always lower than the device's safety limit, thereby improving the safety, reliability, and stability of the soft-start process.

[0046] Precise energy injection via DAB and battery capacity adjustment through phase shifting raise the CHB capacitor voltage to the rated value, reducing switching losses;

[0047] By combining the error between the feeder active current on the d-axis and the feeder reactive current on the q-axis and the target command value, the active power and reactive power error can be dynamically adjusted by regulating the IGBT of the PFCM, thereby achieving dynamic active power and reactive power compensation and improving the power supply quality and reliability of the power grid.

[0048] By reusing the PFCM's IGBT to achieve uncontrolled rectified charging, a dedicated pre-charging circuit is eliminated. The DAB reuses the battery interface converter, eliminating the need for an additional DC-DC module and reducing the hardware cost of the soft-start process. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the process of a shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram showing the topological details of a shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention.

[0051] Figure 3 This is a schematic diagram of the topology of a shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the capacitor voltage waveform in a CHB-ESS shared energy storage system with multiple medium-voltage AC ports provided according to an embodiment of the present invention;

[0053] Figure 5 This is a schematic diagram of the DC bus voltage of a shared energy storage system PFCM with multiple medium-voltage AC ports provided according to an embodiment of the present invention;

[0054] Figure 6 This is a schematic diagram of the current waveform of the feeder 1 connected to the shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention;

[0055] Figure 7 This is a schematic diagram of the current waveform of the feeder 2 connected to the shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention;

[0056] Figure 8 This is a schematic diagram of the current waveform of the feeder 3 connected to the shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention;

[0057] Figure 9 This is a schematic diagram of the power flow of the feeder connected to a shared energy storage system with multiple medium-voltage AC ports provided in accordance with an embodiment of the present invention. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0059] like Figure 1 , Figure 2 and Figure 3 As shown, Embodiment 1 of the present invention provides a soft-start method for a multi-medium-voltage AC port shared energy storage system, comprising the following steps:

[0060] Step 1: Perform uncontrolled rectification charging on CHB and PFCM of the multi-medium voltage AC port shared energy storage system, and charge the sum of the PFCM capacitor voltage and CHB capacitor voltage to a first threshold to obtain the capacitor voltage sum that reaches the first threshold.

[0061] In a preferred but non-limiting embodiment of the present invention, step 1 specifically includes:

[0062] Step 1.1: Since the initial voltage of the capacitor is zero, set all IGBT drive signals in PFCM and FBSM to low level and lock them out. At the same time, provide independent mains power to PFCM and TBS.

[0063] Step 1.2: Close the MACP-CHB-ESS output circuit breaker and open the main circuit contactor switch. Through the feeder circuit containing the pre-charging resistor, perform uncontrolled rectified charging of the capacitors of CHB and PFCM. The pre-charging resistor is located after the circuit breaker and connected to the filter inductor. The pre-charging resistor is connected in parallel with the bypass switch. The main circuit contactor switch includes SW1, SW2, and SW3.

[0064] Step 1.3: During the charging process, the AC voltage from the mains slowly charges the capacitor through the diode rectifier bridge until the PFCM capacitor voltage V... PFCMa With CHB capacitor voltage V pa The sum of these values ​​reaches the first threshold, thus obtaining the sum of the capacitor voltages that reach the first threshold.

[0065] The first threshold is determined by the diode voltage drop, the pre-charge resistor, the capacitor internal resistance, and the device withstand voltage. At this point, the capacitor voltage distribution satisfies the KVL principle and does not exceed the rated withstand voltage of the IGBT and the capacitor.

[0066] More preferably, step 1.3 includes:

[0067] Step 1.3.1: According to the KVL principle, when the main circuit contactor switch is open, the pre-charging circuit containing the resistor is connected, and the capacitor is slowly charged through the resistor. At this time, the AC voltage of the mains is distributed according to the impedance of the diode rectifier bridge, the pre-charging resistor and the internal resistance of the capacitor, and the voltage drop of the diode and the voltage division of the pre-charging resistor and the internal resistance of the capacitor are obtained. At this time, the capacitor voltage distribution satisfies the KVL principle and does not exceed the rated withstand voltage of the IGBT and the capacitor.

[0068] Step 1.3.2: Determine the effective value of the input AC voltage, calculate the peak voltage after rectification, subtract the voltage drop of the diode obtained in Step 1.3.1 and the voltage division caused by the pre-charging resistor and the internal resistance of the capacitor, and set the first threshold voltage based on the rated voltage of the capacitor, charging to the PFCM capacitor voltage V. PFCMa With CHB capacitor voltage V pa The sum of these values ​​reaches the first threshold, which represents the voltage of the first stage of the pre-charge non-empty rectification phase.

[0069] Step 2: Based on the capacitor voltage that reached the first threshold in Step 1, bypass the pre-charge circuit and continue charging until the capacitor voltage reaches the second threshold, thus obtaining the capacitor voltage that reaches the second threshold.

[0070] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes:

[0071] Close the main circuit contactor switch, bypass the pre-charge resistor, and perform uncontrolled rectified charging. All switching transistors are locked to 0. The principle is the same as in step 1. Based on the KVL principle, the pre-charge resistor is bypassed. The voltage drop is distributed according to the impedance distribution of each diode, the bypass pre-charge resistor, and the internal resistance of the capacitor. On the AC side of the mains, the capacitors of CHB and PFCM are charged sequentially through the closed main circuit contactor switch, the filter inductor, and then through the diode rectifier bridge. The voltage V of the PFCM capacitor is increased. PFCMa With CHB capacitor voltage V pa The sum of the voltages is charged from the first threshold to the second threshold and then charging stops, resulting in the sum of the capacitor voltages that reach the second threshold.

[0072] At this point, the capacitor voltage is close to the system's rated operating voltage, providing a stable starting point for subsequent controllable charging, which includes, but is not limited to, unlocking the IGBT and initiating closed-loop control.

[0073] The pre-charge resistor is connected in parallel with switches SW1-SW3 to protect sensitive components in the circuit from high-current surges by limiting current and controlling the rate of voltage rise. These sensitive components include, but are not limited to, capacitors and switching devices. When the DC bus capacitor is initially charged, it is essentially in a short-circuit state. If the current is not limited, the power supply will directly charge the capacitor, resulting in an extremely high instantaneous current that could damage the rectifier diodes, capacitors, or the power supply itself.

[0074] Step 3: Perform closed-loop control on the capacitor voltage that reaches the second threshold in Step 2. By adjusting the DAB shift ratio and CHB charging and discharging current in CHB-ESS, the CHB capacitor voltage is raised to the rated value and stably put into system operation.

[0075] In a preferred but non-limiting embodiment of the present invention, step 3 specifically includes:

[0076] Step 3.1: Reset the PI controller within the DAB control loop.

[0077] The integral term of the PI controller continuously accumulates error signals. If there is a large initial error during system startup, mode switching, or fault recovery, the integral term may quickly accumulate to the limit value, leading to integral saturation. This can cause the control output to exceed the reasonable range, resulting in overvoltage, overcurrent, or oscillation. Resetting the integral term of the PI controller will bring the integrator to zero, thus avoiding integral saturation caused by sudden error changes in the initial stage. The core purpose is to eliminate the interference of historical error accumulation on the current control and ensure the stability and reliability of the system during critical stages such as startup, switching, and fault recovery.

[0078] Step 3.2: Engage the DAB control loop, adjust the shift ratio to inject battery energy, and rapidly increase the CHB capacitor voltage to near the system's rated voltage.

[0079] More preferably, step 3.2 includes:

[0080] The CHB capacitor voltage reference value is set to the system rated voltage. The DAB control loop injects battery energy into the DC side of CHB by adjusting the shift ratio, thus obtaining the CHB capacitor voltage.

[0081] The difference between the CHB capacitor voltage detection value and the system rated voltage drives the IGBT switch of the DAB control loop to quickly raise the CHB capacitor voltage to close to the system rated voltage.

[0082] Step 3.3: Activate CHB charge / discharge control to smoothly transition the CHB capacitor voltage to the system's rated voltage and smoothly switch to steady-state operation.

[0083] More preferably, step 3.3 includes:

[0084] Step 3.3.1, d-axis current reference value limiting: The total DC voltage reference value of the CHB control voltage outer loop jumps to the rated value to limit the amplitude of the d-axis current reference value and prevent overcurrent.

[0085] Step 3.3.2, q-axis current ramp start, the reference value of the q-axis current in the inner loop of CHB control current increases from 0 to the reference value of the initial working condition according to the preset slope;

[0086] Step 3.3.3: dq-axis coordinated control. The CHB control current inner loop tracks the d-axis and q-axis current reference values ​​through a PI controller, driving the FBSM's IGBT to adjust the charging and discharging current and maintain capacitor voltage stability. Step 3.4: When the CHB capacitor voltage reaches its rated value, charging is considered complete. At this point, the CHB capacitor voltage stabilizes at its rated value, the main circuit contactor remains closed, and the system switches to normal operating mode. As one of the prominent substantive features of this invention, by setting up an energy storage system and using a control method of CHB charging and discharging control with d-axis current reference value limiting, q-axis current ramp start, and dq-axis coordinated control, reactive power compensation is achieved, improving the safety and stability of the AC system.

[0087] Step 4: Perform active power flow control and SOC equalization control on the capacitor voltage that has reached the rated value in Step 3 until the power of the three feeders stably tracks the reference value, the SOC equalization meets the standard, and the capacitor voltage is maintained at the rated value, thereby realizing the soft start of the multi-medium voltage AC port shared energy storage system.

[0088] In a preferred but non-limiting embodiment of the present invention, step 4 specifically includes:

[0089] Step 4.1: Reset the PI controller of the feeder power flow control loop and unlock the IGBT of the half-bridge submodule of the PFCM so that it can operate normally according to the control signal;

[0090] Step 4.2: Set the q-axis current reference value and d-axis current reference value of each feeder current as the d / q-axis target command value for controlling the feeder current;

[0091] Step 4.3: Obtain the feedback of feeder current and grid voltage, solve for the error between the feeder current and the target command value of the d / q axis of the control feeder current in Step 4.2, solve for the feeder power error in combination with the grid voltage, and dynamically adjust the IGBT switching state of PFCM and the IGBT duty cycle of CHB through the PI controller until the feeder power error is less than the feeder steady-state threshold.

[0092] Step 4.4: Monitor the SOC of each battery cell in each FBSM, and adjust the charge and discharge duty cycle of the IGBT in the FBSM until the SOC difference of each battery cell converges to the set SOC balance range to achieve SOC balance.

[0093] Step 4.5: When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the capacitor voltage is maintained at the rated value, the system enters steady state, and the MACP-CHB-ESS system is determined to have started successfully.

[0094] Embodiment 2 of the present invention provides a soft-start system for a multi-medium-voltage AC port shared energy storage system, which implements the soft-start method for a multi-medium-voltage AC port shared energy storage system described in Embodiment 1, including:

[0095] An uncontrolled rectifier charging module is used to perform uncontrolled rectifier charging on the CHB and PFCM of a multi-medium voltage AC port shared energy storage system, charging the sum of the PFCM capacitor voltage and the CHB capacitor voltage to a first threshold, thereby obtaining the capacitor voltage sum that reaches the first threshold.

[0096] The bypass pre-charge circuit charging module is used to bypass the pre-charge circuit and continue charging until the capacitor voltage reaches a second threshold, based on the capacitor voltage reaching a first threshold, to obtain the capacitor voltage reaching the second threshold.

[0097] The closed-loop charging module is used to perform closed-loop control on the capacitor voltage that reaches the second threshold. By adjusting the DAB shift ratio and the CHB charging and discharging current, the CHB capacitor voltage is raised to the rated value, thus obtaining the CHB capacitor voltage that reaches the rated value.

[0098] The output module is used to perform active feeder power flow control and SOC equalization control on the CHB capacitor voltage that has reached the rated value. When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, it is determined that the multi-medium voltage AC port shared energy storage system has been started, thus realizing the soft start of the multi-medium voltage AC port shared energy storage system.

[0099] MACP-CHB-ESS expands ports by integrating cascaded full-bridge submodules into the medium-voltage AC ports. Each FBSM consists of two parallel half-bridge submodules, one of which is directly connected to the feeder, while the other is connected to the next submodule of the CHB-ESS.

[0100] By connecting an additional HBSM in parallel with the DC side of the FBSM, the number of medium-voltage AC ports is expanded, thus constructing a MACP-CHB-ESS system with multiple AC ports.

[0101] In MACP-CHB-ESS, the main loop consisting of FBSM and the newly added HBSM is defined as the power flow control module. The HBSM connected to the feeder is responsible for regulating the power flow between feeders and controlling the charging and discharging process of the energy storage system. This part is called the power flow regulation half-bridge.

[0102] The HBSM connected to the CHB-ESS is used to maintain the DC bus voltage stability of the PFCM and ensure the internal energy balance of the system; this part is called the balancing half-bridge. Embodiment 3 of the present invention provides a MACP-CHB-ESS, connected to three feeders, with feeder 1 designated as the balancing feeder. During startup, uncontrolled rectification charging is first performed on the CHB and PFCM until the module's capacitor voltage reaches a stable value. Subsequently, interconnect module voltage control is activated, and the DAB control loop within the CHB-ESS charges the capacitor voltages of the CHB and PFCM to the commanded value. Finally, after the capacitor voltage stabilizes, power flow control is activated, completing the soft-start process of the MACP-CHB-ESS.

[0103] The application of the above structure and method will be further explained below with specific simulation examples; in conjunction with the above embodiments, the system is simulated and verified using MATLAB / Simulink software, and the simulation parameters are shown in Table 1.

[0104] Table 1 Simulation Parameters

[0105]

[0106] Figure 4 and Figure 5 These are the CHB submodule capacitor voltage waveforms and the PFCM capacitor voltage waveforms during the soft start process of MACP-CHB-ESS, respectively. Figures 6 to 8 The waveforms of the current in each feeder during the soft start process are shown. Figure 9 The waveforms show the active and reactive power of each feeder during the soft start process.

[0107] Simulation results show that the proposed MACP-CHB-ESS soft-start scheme can achieve smooth device startup, and the capacitor voltage waveforms of the CHB-ESS and PFCM sub-modules exhibit a smooth and stable trend throughout the charging process, ultimately reaching the rated value. The proposed soft-start scheme, with its step-by-step unlocking control and PI controller reset, significantly reduces the inrush current, effectively minimizing the impact on the power grid during startup, thus verifying the effectiveness of the proposed soft-start scheme.

[0108] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0109] This invention effectively suppresses surge current and avoids damage to capacitors and IGBTs due to overcurrent by combining two-stage pre-charging with uncontrolled rectification. The graded charging, which sequentially charges to the first threshold, the second threshold, and the rated value, ensures that the voltage change rate is always lower than the device's safety limit, thereby improving the safety, reliability, and stability of the soft-start process.

[0110] Precise energy injection via DAB and battery capacity adjustment through phase shifting raise the CHB capacitor voltage to the rated value, reducing switching losses;

[0111] By combining the error between the feeder active current on the d-axis and the feeder reactive current on the q-axis and the target command value, the active power and reactive power error can be dynamically adjusted by regulating the IGBT of the PFCM, thereby achieving dynamic active power and reactive power compensation and improving the power supply quality and reliability of the power grid.

[0112] By reusing the PFCM's IGBT to achieve uncontrolled rectified charging, a dedicated pre-charging circuit is eliminated. The DAB reuses the battery interface converter, eliminating the need for an additional DC-DC module and reducing the hardware cost of the soft-start process.

[0113] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A soft-start method for a multi-medium-voltage AC port shared energy storage system, characterized in that: Uncontrolled rectification charging is performed on CHB and PFCM of the multi-medium voltage AC port shared energy storage system to charge the sum of the PFCM capacitor voltage and CHB capacitor voltage to a first threshold, thereby obtaining the capacitor voltage sum that reaches the first threshold. Based on the capacitor voltage that reaches the first threshold, the pre-charge circuit is bypassed, and charging continues until the capacitor voltage reaches the second threshold, thus obtaining the capacitor voltage that reaches the second threshold. Closed-loop control is performed on the capacitor voltage that reaches the second threshold. By adjusting the DAB shift ratio and the CHB charging and discharging current, the CHB capacitor voltage is raised to the rated value, thus obtaining the CHB capacitor voltage that reaches the rated value. The CHB capacitor voltage reaches the rated value and is used for active feeder power flow control and SOC equalization control. When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, it is determined that the multi-medium voltage AC port shared energy storage system has been started, realizing the soft start of the multi-medium voltage AC port shared energy storage system.

2. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 1, characterized in that: The uncontrolled rectification charging of the CHB and PFCM of the multi-medium voltage AC port shared energy storage system, charging the sum of the PFCM capacitor voltage and the CHB capacitor voltage to a first threshold, and obtaining the capacitor voltage sum reaching the first threshold, specifically includes: Set all IGBT drive signals in PFCM and FBSM to low level and lock them out, while using an independent mains power supply for PFCM and TBS. Close the circuit breaker at the output of the multi-medium voltage AC port shared energy storage system and disconnect the main circuit contactor switch. Through the feeder circuit containing the pre-charge resistor, perform uncontrolled rectified charging of the capacitors in CHB and PFCM until the PFCM capacitor voltage V... PFCMa With CHB capacitor voltage V pa The sum of these values ​​reaches the first threshold, thus obtaining the sum of the capacitor voltages that reach the first threshold.

3. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 2, characterized in that: The disconnecting main circuit contactor switch, through a feeder circuit containing a pre-charge resistor, performs uncontrolled rectified charging of the capacitors of CHB and PFCM until the PFCM capacitor voltage V... PFCMa With CHB capacitor voltage V pa The sum reaches the first threshold, specifically including: When the main circuit contactor switch is open, the pre-charging circuit is connected, and the capacitor is charged through the resistor. At this time, the AC voltage of the mains is distributed according to the impedance of the diode rectifier bridge, the pre-charging resistor and the internal resistance of the capacitor, resulting in the voltage drop of the diode and the voltage division of the pre-charging resistor and the internal resistance of the capacitor. Obtain the effective value of the input AC voltage, calculate the peak voltage after rectification, subtract the voltage drop of the diode and the voltage division of the pre-charge resistor and the internal resistance of the capacitor, and set the first threshold based on the rated voltage of the capacitor. The capacitors of PFCM and CHB are charged until the sum of the voltages of the PFCM and CHB capacitors reaches a first threshold.

4. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 3, characterized in that: When the internal resistance of the capacitor is divided, the capacitor voltage distribution satisfies the KVL principle and does not exceed the rated withstand voltage of the IGBT and the capacitor.

5. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 1, characterized in that: The process involves bypassing the pre-charge circuit based on the capacitor voltage reaching a first threshold, and continuing to charge until the capacitor voltage reaches a second threshold, thereby obtaining the capacitor voltage reaching the second threshold. Specifically, this includes: Close the main circuit contactor switch, bypass the pre-charging resistor, and perform uncontrolled rectified charging. According to the impedance distribution of each diode, bypass pre-charging resistor, and capacitor internal resistance, the voltage drop is distributed. On the AC side of the power grid, the capacitors of CHB and PFCM are charged sequentially through the closed main circuit contactor switch, the filter inductor, and then through the diode rectifier bridge. The charging stops when the sum of the PFCM capacitor voltage and the CHB capacitor voltage is charged from the first threshold to the second threshold, thus obtaining the capacitor voltage sum that reaches the second threshold.

6. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 1, characterized in that: The closed-loop control of the capacitor voltage reaching the second threshold, which involves adjusting the DAB shift ratio and the CHB charging / discharging current to raise the CHB capacitor voltage to the rated value, specifically includes: Reset the PI controller within the DAB control loop; The DAB control loop is engaged to adjust the shift ratio to inject battery energy, thereby raising the CHB capacitor voltage to near the system's rated voltage. Activate CHB charge / discharge control to smoothly transition the CHB capacitor voltage to the system's rated voltage; When the CHB capacitor voltage reaches the rated value, the charging is considered complete, and the CHB capacitor voltage reaches the rated value.

7. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 6, characterized in that: The DAB control loop, which adjusts the shift ratio to inject battery energy, raises the CHB capacitor voltage to near the system's rated voltage, specifically includes: The CHB capacitor voltage reference value is set to the system rated voltage. The shift ratio is adjusted by the DAB control loop to inject battery energy into the DC side of CHB, thus obtaining the CHB capacitor voltage. The difference between the CHB capacitor voltage detection value and the system rated voltage drives the IGBT switch of the DAB control loop to raise the CHB capacitor voltage to close to the system rated voltage.

8. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 6, characterized in that: The implementation of CHB charge / discharge control, which smoothly transitions the CHB capacitor voltage to the system's rated voltage, specifically includes: The d-axis current reference value is limited, and the total DC voltage reference value of the CHB control voltage outer loop jumps to the rated value. The q-axis current ramp start-up, the reference value of the q-axis current in the inner loop of the CHB control current increases from 0 to the reference value of the initial operating condition according to the preset slope; The dq axis coordinated control uses a PI controller to track the d-axis and q-axis current reference values, driving the IGBT of the FBSM to adjust the charging and discharging current until the CHB capacitor voltage stabilizes.

9. The soft-start method for a multi-medium voltage AC port shared energy storage system according to claim 1, characterized in that: The process involves actively controlling the power flow and maintaining SOC balance of the CHB capacitor voltage to its rated value. When the power of the three feeders is less than the set steady-state threshold, the SOC difference is within the set SOC balance range, and the CHB capacitor voltage remains at its rated value, the multi-medium voltage AC port shared energy storage system is considered to have completed startup. Specifically, this includes: Reset the PI controller of the feeder power flow control loop, unlock the IGBT of the half-bridge submodule of the PFCM, and enable it to operate normally according to the control signal; Set the q-axis current reference value and d-axis current reference value of each feeder current as the d / q-axis target command value for controlling the feeder current; The system obtains the feedback of feeder current and grid voltage, calculates the error between the feeder current and the target command value of the d / q axis of the control feeder current, and calculates the feeder power error in combination with the grid voltage. The system then dynamically adjusts the IGBT switching state of the PFCM and the IGBT duty cycle of the CHB through the PI controller until the feeder power error is less than the feeder steady-state threshold. Monitor the SOC of each battery cell in each FBSM, and adjust the charge and discharge duty cycle of the IGBT in the FBSM until the SOC difference of each battery cell converges to the set SOC balance range. When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, the multi-medium voltage AC port shared energy storage system is considered to have completed startup.

10. A soft-start system for a multi-medium-voltage AC port shared energy storage system, comprising the soft-start method for a multi-medium-voltage AC port shared energy storage system as described in any one of claims 1-9, characterized in that: An uncontrolled rectifier charging module is used to perform uncontrolled rectifier charging on the CHB and PFCM of a multi-medium voltage AC port shared energy storage system, charging the sum of the PFCM capacitor voltage and the CHB capacitor voltage to a first threshold, thereby obtaining the capacitor voltage sum that reaches the first threshold. The bypass pre-charge circuit charging module is used to bypass the pre-charge circuit and continue charging until the capacitor voltage reaches a second threshold, based on the capacitor voltage reaching a first threshold, to obtain the capacitor voltage reaching the second threshold. The closed-loop charging module is used to perform closed-loop control on the capacitor voltage that reaches the second threshold. By adjusting the DAB shift ratio and the CHB charging and discharging current, the CHB capacitor voltage is raised to the rated value, thus obtaining the CHB capacitor voltage that reaches the rated value. The output module is used to perform active feeder power flow control and SOC equalization control on the CHB capacitor voltage that has reached the rated value. When the power of the three feeders is less than the set feeder steady-state threshold, the SOC difference is within the set SOC equalization range, and the CHB capacitor voltage remains at the rated value, it is determined that the multi-medium voltage AC port shared energy storage system has been started, thus realizing the soft start of the multi-medium voltage AC port shared energy storage system.

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