Direct-current bus pre-charging circuit of energy storage converter based on digital control and control method of direct-current bus pre-charging circuit

Abstract

The invention discloses an energy storage converter direct-current bus pre-charging circuit based on digital control and a control method, and relates to the technical field of energy storage converter control, and the energy storage converter direct-current bus pre-charging circuit comprises a main power loop, a controller, a current detection unit and a voltage detection unit; wherein the main power loop comprises a direct current side bus, a direct current bus capacitor and at least one IGBT (Insulated Gate Bipolar Translator) module; the current detection unit and the voltage detection unit are arranged on the main power loop; the controller is respectively connected with the current detection unit, the voltage detection unit and the at least one IGBT module; the current detection unit is used for collecting a bus current value of the main power loop; the voltage detection unit is used for monitoring the bus voltage value of the main power loop in real time; and the controller is used for driving the at least one IGBT module to pre-charge the direct-current bus capacitor by sending a PWM signal to the at least one IGBT module. The technical problems of high system cost and poor flexibility in the prior art are relieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage converter control, in particular to a DC bus pre-charging circuit and control method of an energy storage converter based on digital control. BACKGROUND

[0002] In an energy storage converter, pre-charging of the DC bus capacitor is a key step to prevent surge current damage to power devices during power-on. The traditional scheme usually uses a "relay + slow-start resistor" pre-charging circuit, however, this scheme has many defects: 1. Mechanical life limitation: Frequent operation of the relay contacts can cause aging, and in the case of frequent charge and discharge (such as frequency modulation energy storage), its life will be significantly shortened. This not only increases the cost of equipment maintenance, but also may cause system failure, affecting the stable operation of the energy storage system.

[0003] 2. Energy loss: The pre-charging resistor continuously generates heat during operation, causing energy waste and reducing system efficiency. In high-power scenarios, additional cooling devices need to be designed to ensure normal operation of the equipment, further increasing system cost and complexity.

[0004] 3. Poor flexibility: The pre-charging time of the traditional pre-charging circuit is fixed and cannot be adaptively adjusted according to the residual voltage of the bus capacitor or the battery voltage, making it difficult to meet the pre-charging needs of different working conditions.

[0005] 4. Large volume: The relay and resistor occupy a large space, which is not conducive to improving the power density of the energy storage system and limiting the miniaturization and integration development of the equipment. SUMMARY

[0006] The purpose of the present application is to solve at least one of the above technical problems by providing a DC bus pre-charging circuit and control method of an energy storage converter based on digital control.

[0007] In a first aspect, an embodiment of the present application provides a DC bus pre-charging circuit of an energy storage converter based on digital control, comprising: a main power circuit, a controller, a current detection unit and a voltage detection unit; wherein the main power circuit comprises a DC side bus connected with an energy storage unit, a DC bus capacitor and at least one IGBT module; the current detection unit and the voltage detection unit are arranged on the main power circuit; the controller is connected with the current detection unit, the voltage detection unit and the at least one IGBT module respectively; the current detection unit is used to collect the bus current value of the main power circuit; the voltage detection unit is used to monitor the bus voltage value of the main power circuit in real time; and the controller is used to drive the at least one IGBT module to pre-charge the DC bus capacitor by sending a PWM signal to the at least one IGBT module.

[0008] Optionally, the IGBT module comprises a three-phase ANPC topology.

[0009] Optionally, a fuse is further arranged in series on the main power circuit.

[0010] Optionally, the current detection unit comprises a current sensor arranged in series between the energy storage unit and the DC side bus.

[0011] Optionally, the voltage detection unit comprises a voltage division network composed of two voltage division resistors.

[0012] Optionally, the controller comprises a controller based on a digital signal processor and a field programmable gate array architecture.

[0013] In a second aspect, the embodiments of the present application further provide a control method of a DC bus pre-charging circuit of a digital control-based energy storage converter, comprising: detecting a bus voltage value of the main power circuit in real time; determining whether an absolute value of a difference between the bus voltage value and an output voltage of an energy storage unit is greater than a preset threshold value; if yes, sending a PWM signal to the at least one IGBT module based on the controller to drive the at least one IGBT module to pre-charge the DC bus capacitor.

[0014] Optionally, during the pre-charging of the DC bus capacitor, the method further comprises: calculating a deviation value between the bus voltage value and a target voltage value in real time; based on the deviation value, dynamically adjusting a duty cycle of the PWM signal by using a PID algorithm to control a charging current slope.

[0015] Optionally, the method further comprises: when the bus voltage value reaches the target voltage value, stopping the pre-charging of the DC bus capacitor.

[0016] Optionally, during the pre-charging of the DC bus capacitor, the method further comprises: obtaining a rising edge slope of a charging current during the pre-charging of the DC bus capacitor; if the rising edge slope of the charging current is lower than a preset slope threshold value, determining that the DC bus capacitor has a health problem.

[0017] The present application provides a digital control-based energy storage converter DC bus pre-charging circuit and control method, which realizes flexible charging of a DC bus capacitor through digital control technology, has fault diagnosis capability, has advantages such as no mechanical wear, low energy loss, compact size, etc., effectively improves the reliability and energy efficiency of the energy storage converter, and solves the technical problems of high system cost and poor flexibility in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A schematic diagram of a digitally controlled energy storage converter DC bus pre-charge circuit provided in an embodiment of the present invention; Figure 2 A flowchart illustrating a control method for a digitally controlled pre-charge circuit of a DC bus in an energy storage converter, provided as an embodiment of the present invention.

[0020] In the diagram: 1. Controller, 2. Current detection unit, 3. Voltage detection unit, 4. DC bus, 5. DC bus capacitor, 6. IGBT module, 7. Fuse. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Figure 1 This is a schematic diagram of a digitally controlled DC bus pre-charge circuit for an energy storage converter according to an embodiment of the present invention. Figure 1 As shown, it includes: a main power circuit, a controller 1, a current detection unit 2, and a voltage detection unit 3; wherein, the main power circuit includes a DC-side bus 4 connected to the energy storage unit, a DC bus capacitor 5, and at least one IGBT module 6; the current detection unit 2 and the voltage detection unit 3 are both located on the main power circuit; the controller 1 is connected to the current detection unit 2, the voltage detection unit 3, and at least one IGBT module 6 respectively.

[0023] Specifically, the current detection unit 2 is used to collect the bus current value of the main power circuit; Voltage detection unit 3 is used to monitor the bus voltage value of the main power circuit in real time; The controller 1 is used to drive at least one IGBT module 6 to precharge the DC bus capacitor 5 by sending a PWM signal to at least one IGBT module 6.

[0024] Specifically, IGBT module 6 is an Insulated Gate Bipolar Transistor (IGBT) module, which is a composite fully controllable voltage-driven power semiconductor device composed of BJT (Bipolar Junction Transistor) and MOS (Insulated Gate Field Effect Transistor), combining the advantages of high input impedance of MOSFET and low on-state voltage drop of GTR.

[0025] Preferably, the IGBT module 6 includes a three-phase ANPC topology.

[0026] The IGBT module with pre-charging circuit directly reused by the main power circuit provided in this embodiment of the invention reduces hardware costs, shrinks system size, and increases power density.

[0027] Specifically, such as Figure 1 As shown, the energy storage unit is a battery pack (its positive and negative terminals are respectively...) Figure 1 The Bat+ and Bat- symbols (marked in the diagram) provide power to the system. The DC bus capacitor 5 is used to stabilize the bus voltage, and the IGBT module 6 is responsible for the conversion and transmission of electrical energy.

[0028] Preferably, such as Figure 1 As shown, a fuse 7 is also connected in series in the main power circuit. When an abnormal overcurrent occurs in the circuit, the fuse 7 can quickly cut off the circuit and protect the IGBT module 6 and other critical components.

[0029] Preferably, the current detection unit 2 includes a current sensor connected in series between the energy storage unit and the DC side bus 4.

[0030] Preferably, such as Figure 1 As shown, the voltage detection unit 3 includes a voltage divider network consisting of two voltage divider resistors.

[0031] Preferably, controller 1 includes a controller based on a digital signal processor (DSP) and field programmable gate array (FPGA) architecture.

[0032] Specifically, controller 1 outputs a PWM (Pulse Width Modulation) signal to the IGBT module 6 drive circuit based on the collected bus current and bus voltage values, thereby controlling the IGBT module 6 to turn on and off.

[0033] Figure 2 This is a flowchart illustrating a control method for a digitally controlled pre-charge circuit of a DC bus in an energy storage converter, according to an embodiment of the present invention. Figure 2 As shown, the method specifically includes the following steps: Step S202: Real-time detection of the bus voltage value of the main power circuit.

[0034] Step S204: Determine whether the absolute value of the difference between the bus voltage and the output voltage of the energy storage unit is greater than a preset threshold.

[0035] Step S206: If yes, then the controller sends a PWM signal to at least one IGBT module to drive at least one IGBT module to precharge the DC bus capacitor.

[0036] Specifically, the control method provided in this embodiment of the invention includes a pre-charge start condition and a pulse injection stage. The pre-charge start condition includes: detecting the output voltage (Vbat) of the energy storage unit (e.g., a battery) and the bus voltage (Vbus). When |Vbat - Vbus| > a preset threshold (e.g., 50V), the pre-charge process is triggered. This condition ensures that pre-charging occurs when there is a large difference between the bus voltage and the battery voltage, avoiding excessive current surges.

[0037] The pulse injection phase includes: during the positive half-cycle, to... Figure 1 The bridge arm Q1 sends a PWM signal with a duty cycle of 1%-5%, while Q2 remains off. At this time, the current path is: Bat+ → Q1 → BUSN. During the negative half-cycle, a PWM signal with a duty cycle of 1%-5% is sent to bridge arm Q2, while Q1 remains off. At this time, the current path is: BUSN → Q2 → Bat-. By adjusting the PWM duty cycle to control the charging current slope (e.g., limiting dI / dt < 10A / ms), inrush current is effectively prevented.

[0038] Specifically, during the pre-charging process of the DC bus capacitor, the method provided in this embodiment of the invention further includes closed-loop regulation, specifically including: Calculate the deviation between the bus voltage value and the target voltage value in real time; for example, the target voltage value is Vbat × 95%. Based on the deviation value, a PID algorithm is used to dynamically adjust the duty cycle of the PWM signal to control the charging current slope. Specifically, the smaller the deviation value, the closer it is to the target voltage value, so the duty cycle of the PWM signal is reduced to decrease the charging current slope.

[0039] Specifically, when the bus voltage reaches the target voltage, the pre-charging of the DC bus capacitor stops. At this time, if the main contactor is present, it is closed; otherwise, it directly enters the normal operation mode.

[0040] Preferably, the method provided in this embodiment of the invention further includes fault diagnosis during the pre-charging process of the DC bus capacitor, specifically including: Obtain the rising slope of the charging current during the pre-charging process of the DC bus capacitor; If the rising slope of the charging current is lower than the preset slope threshold, it is determined that there is a health problem with the DC bus capacitor.

[0041] Among the health issues identified is capacitor aging. Specifically, the equivalent series resistance of an aging capacitor increases, and monitoring the current slope can help detect these health problems in a timely manner.

[0042] Preferably, the method provided in this embodiment of the invention further includes health monitoring of the IGBT module: determining whether the IGBT has defects by measuring the voltage spike amplitude when the PWM is turned off. Abnormal voltage spike amplitude may indicate problems such as overheating or poor soldering of the IGBT.

[0043] In an optional embodiment provided by this invention, the following adjustments are made to the 500kW energy storage converter: 1) Circuit Structure Adjustment: Due to the increased power level, higher power specifications are required for components such as IGBT modules and DC bus capacitors in the main power circuit to meet the requirements of high current and high voltage operation. Simultaneously, the range and accuracy of the current sensor and voltage detection circuit also need to be adjusted accordingly to ensure accurate signal acquisition.

[0044] 2) Control Parameter Optimization: Based on the characteristics of the 500kW energy storage converter, adjust the frequency and duty cycle range of the PWM signal. During the pulse injection phase, appropriately reduce the initial duty cycle, such as setting it to 0.5%-3%, to better control the high-current charging process. In closed-loop regulation, optimize the PID parameters to improve the control response speed and stability.

[0045] 3) Fault Diagnosis Adjustment: The fault diagnosis thresholds are redefined to suit the operating characteristics of capacitors and IGBTs in high-power scenarios. For example, for capacitor ESR detection, the threshold for current rise slope is adjusted based on the characteristics of high-power capacitors; for IGBT health monitoring, the judgment criteria for voltage spike amplitude are optimized considering the voltage and current stress during high-power operation.

[0046] In another optional embodiment provided by the present invention, a five-phase full-bridge topology is adopted, specifically including: 1) Circuit Structure Changes: The main power circuit adopts a five-phase full-bridge topology, which increases the number of bridge arms compared to the three-phase full-bridge topology. In the pre-charge control circuit, the IGBTs of the five-phase bridge arms need to be appropriately selected and controlled. The layout and connection methods of the current sensor and voltage detection circuit also need to be adjusted according to the new topology.

[0047] 2) Control Strategy Adjustment: During the pulse injection phase, a suitable combination of five-phase bridge arms is selected for pre-charging, such as selecting two adjacent bridge arms for alternating charging to achieve a more uniform voltage rise. During closed-loop regulation, the target value of the bus voltage is recalculated based on the voltage characteristics of the five-phase topology, and the parameters of the PID algorithm are adjusted to ensure control effectiveness.

[0048] 3) Fault Diagnosis Extension: Due to changes in topology, the fault characteristics of capacitors and IGBTs will differ. Fault diagnosis requires analyzing the current and voltage variation patterns in the five-phase circuit to establish a new fault diagnosis model. For example, analyzing the differences in current across different bridge arms can help determine if an IGBT is faulty, and the health status of capacitors can be assessed based on the balance of the five-phase bus voltages.

[0049] As described above, the embodiments of the present invention provide a digitally controlled DC bus pre-charging circuit and control method for an energy storage converter, which has the following technical advantages compared with the prior art: (1) By abandoning the traditional pre-charge relays and resistors, the main circuit IGBTs (such as the upper and lower arms of the three-phase ANPC topology) are directly reused, which reduces hardware costs, shrinks system size, and increases power density.

[0050] (2) A fast-acting fuse is connected in series between the DC bus and the IGBT as a backup protection. When an abnormal overcurrent occurs in the circuit, the fast-acting fuse can quickly cut off the circuit and protect the IGBT and other key components.

[0051] (3) Add a high-precision current sensor and bus voltage detection circuit to monitor the current and voltage signals during the pre-charging process in real time, and provide accurate data support for control and fault diagnosis.

[0052] (4) Pulse injection precharge: A specific IGBT is driven by a PWM signal with an extremely low duty cycle, and its body diode is used for freewheeling to gradually raise the bus voltage. This method can effectively control the charging current and avoid the impact of surge current on the device.

[0053] (5) Closed-loop regulation: Based on the difference between the bus voltage and the target value, the PWM frequency and duty cycle are dynamically adjusted to achieve precise control of the charging process and ensure that the bus voltage reaches the target value stably.

[0054] (6) Fault diagnosis: By analyzing the pre-charge current waveform, the equivalent series resistance (ESR) of the capacitor and the health status information of the IGBT are obtained. Potential faults can be detected in time, improving the reliability and stability of the system.

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A digitally controlled DC bus pre-charge circuit for an energy storage converter, characterized in that, include: The system comprises a main power circuit, a controller, a current detection unit, and a voltage detection unit; wherein, the main power circuit includes a DC-side bus connected to the energy storage unit, a DC bus capacitor, and at least one IGBT module; the current detection unit and the voltage detection unit are both disposed on the main power circuit; the controller is connected to the current detection unit, the voltage detection unit, and the at least one IGBT module respectively; The current detection unit is used to collect the bus current value of the main power circuit; The voltage detection unit is used to monitor the bus voltage value of the main power circuit in real time. The controller is configured to drive the at least one IGBT module to precharge the DC bus capacitor by sending a PWM signal to the at least one IGBT module.

2. The DC bus pre-charge circuit of the energy storage converter based on digital control according to claim 1, characterized in that: The IGBT module includes a three-phase ANPC topology.

3. The DC bus pre-charge circuit of the energy storage converter based on digital control according to claim 1, characterized in that: A fuse is also connected in series in the main power circuit.

4. The DC bus pre-charge circuit of the energy storage converter based on digital control according to claim 1, characterized in that: The current detection unit includes a current sensor connected in series between the energy storage unit and the DC side bus.

5. The DC bus pre-charge circuit of the energy storage converter based on digital control according to claim 1, characterized in that: The voltage detection unit includes a voltage divider network consisting of two voltage divider resistors.

6. The DC bus pre-charge circuit of the energy storage converter based on digital control according to claim 1, characterized in that: The controller includes a controller based on a digital signal processor and a field-programmable gate array architecture.

7. A control method for the DC bus pre-charge circuit of an energy storage converter based on digital control as described in any one of claims 1-6, characterized in that: include: Real-time detection of the bus voltage value of the main power circuit; Determine whether the absolute value of the difference between the bus voltage value and the output voltage of the energy storage unit is greater than a preset threshold; If so, the controller sends a PWM signal to the at least one IGBT module to drive the at least one IGBT module to precharge the DC bus capacitor.

8. The method according to claim 7, characterized in that: During the pre-charging process of the DC bus capacitor, the method further includes: Calculate the deviation between the bus voltage value and the target voltage value in real time; Based on the deviation value, a PID algorithm is used to dynamically adjust the duty cycle of the PWM signal in order to control the charging current slope.

9. The method according to claim 7, characterized in that: The method further includes: stopping the pre-charging of the DC bus capacitor when the bus voltage value reaches the target voltage value.

10. The method according to claim 7, characterized in that: During the pre-charging process of the DC bus capacitor, the method further includes: Obtain the rising slope of the charging current during the pre-charging process of the DC bus capacitor; If the rising slope of the charging current is lower than a preset slope threshold, then the DC bus capacitor is determined to have a health problem.

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