An ac soft start circuit for an energy storage converter

Abstract

The utility model discloses an alternating current soft start circuit for energy storage converter, including parallel's N phase full bridge power circuit and DC support capacitor, N phase full bridge power circuit is by N group symmetry's bridge arm, and each group bridge arm upper and lower bridge arm is at least configured two power switch devices, and every power switch device all has one body diode reverse parallel, the utility model discloses the design structure is reasonable through parallel's N phase full bridge power circuit and DC support capacitor, and every bridge arm of N phase full bridge power circuit all is at least by two power switch devices reverse parallel one body diode composition, realizes the switching of uncontrolled rectification pre -charge, controllable rectification fine charge and controllable normal rectification or inverter after parallel operation, realizes the " no impact " of current almost zero, and the regulation of active and reactive, solves traditional at the start, has increased the current -limiting resistance, short -circuit contactor and its drive circuit not only improves cost and size, and easily leads to resistance burnout, the problem of poor reliability.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, specifically to an AC soft-start circuit for an energy storage converter. Background Technology

[0002] During the initial startup phase of a power storage converter (PCS), a significant instantaneous voltage difference exists between the DC-side support capacitor and the battery. Directly closing the grid-connected contactor would generate a surge current of up to several thousand amperes. This could not only cause contactor contact erosion and welding, endangering the safety of main power devices (such as IGBTs), and causing excessive instantaneous energy and overvoltage damage to the capacitor, but also cause a sudden drop in grid voltage, posing a serious threat to grid stability and the lifespan of the equipment itself. To address this core issue, soft-start technology has emerged.

[0003] Existing soft-start methods typically employ a current-limiting resistor connected in series in the DC support capacitor charging circuit. During the initial startup phase, the capacitor is pre-charged through the current-limiting resistor. Once the capacitor voltage approaches the peak grid voltage, the current-limiting resistor is short-circuited via a relay or contactor, completing grid connection. However, this method has significant drawbacks: firstly, it increases system cost and size by adding a current-limiting resistor, a short-circuit contactor, and its drive circuit; secondly, if the short-circuit contactor sticks or fails to close properly, it can lead to resistor burnout or system failure to start, resulting in poor reliability. Utility Model Content

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide an AC soft-start circuit for energy storage converters.

[0005] To achieve the above objectives, this utility model provides the following technical solution: An AC soft-start circuit for an energy storage converter includes an N-phase full-bridge power circuit and a DC support capacitor connected in parallel. The N-phase full-bridge power circuit is located on the AC side and connected to the AC power grid. The two ends of the DC support capacitor are connected to a battery interface. The N-phase full-bridge power circuit consists of N symmetrical bridge arms. Each bridge arm has at least two power switching devices in both the upper and lower arms, and each power switching device is connected in anti-parallel to a body diode. In the N sets of symmetrical bridge arms, the midpoint of each set of bridge arms is connected to the corresponding N phase lines of the AC power grid, forming an electrical path on the N-phase AC side.

[0006] Furthermore, the power switching device is an IGBT switching device.

[0007] Furthermore, filter inductors are installed on the electrical path of the N-phase AC side to limit the charging current.

[0008] Furthermore, a first switching switch is installed on each of the electrical paths on the N-phase AC side. The first switching switch is located between the filter inductor and the AC power grid and is used to select different filter branches.

[0009] Furthermore, a second switching switch is connected to the connection line between the DC support capacitor and the positive terminal of the battery interface to control the on / off state of the DC bus.

[0010] Compared with existing technologies, this AC soft-start circuit for energy storage converters has the following advantages: This invention utilizes a parallel N-phase full-bridge power circuit and a DC support capacitor. The N-phase full-bridge power circuit consists of N symmetrical bridge arms, with each bridge arm containing at least two power switching devices connected in anti-parallel to a single diode. During operation, it enables switching between uncontrolled rectifier pre-charging, controlled rectifier fine charging, and controlled normal rectification or inversion after grid connection. This achieves near-zero current "impact-free" operation and regulation of active and reactive power. It solves the problems of traditional methods that require the addition of current-limiting resistors, short-circuit contactors, and their drive circuits during startup, which not only increases cost and size but also easily leads to resistor burnout and poor reliability. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the soft-start circuit of the energy storage converter of this utility model; Figure 2 This is a flowchart of the soft-start circuit based on the present invention.

[0012] In the diagram: 1. DC support capacitor; 2. IGBT switching device; 3. Body diode; 4. Filter inductor; 5. First switching switch; 6. Second switching switch. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0014] like Figure 1-2As shown, this utility model provides a technical solution: an AC soft-start circuit for an energy storage converter, including an N-phase full-bridge power circuit and a DC support capacitor 1 connected in parallel. The N-phase full-bridge power circuit is located on the AC side and connected to the AC power grid. The two ends of the DC support capacitor 1 are connected to the battery interface. The N-phase full-bridge power circuit consists of N sets of symmetrical bridge arms. Each set of bridge arms has at least two power switching devices configured on the upper and lower bridge arms, and each power switching device is connected in anti-parallel to a body diode 3. In the N sets of symmetrical bridge arms, the midpoint of each set of bridge arms is connected to the corresponding N phase lines of the AC power grid to form an electrical path on the N-phase AC side. The power switching devices are IGBT switching devices 2. Filter inductors 4 are provided on the electrical path on the N-phase AC side to limit the charging current. First switching switches 5 are provided on the electrical path on the N-phase AC side. The first switching switches 5 are located between the filter inductors 4 and the AC power grid to select different filter branches. A second switching switch 6 is also connected on the connection line between the DC support capacitor 1 and the positive terminal of the battery interface to control the on / off state of the DC bus.

[0015] In use, the N-phase full-bridge power circuit is a three-phase full-bridge power module. There are three first switching switches 5, which are located on the electrical path between the three-phase full-bridge power circuit and the AC power grid. After the first switching switch 5 is connected to the corresponding filter inductor 4, it is connected to the midpoint of the three-phase full-bridge power circuit. The three bridge arms of the three-phase full-bridge power circuit have a first power module, a second power module, a third power module, and a fourth power module on both sides of the midpoint, respectively. The first power module and the second power module are connected in series, and the third power module and the fourth power module are connected in series. At the same time, each power module is composed of an IGBT switching device 2 and a body diode 3 connected in anti-parallel, forming three bridge arms. The three bridge arms are connected in parallel, with the upper end connected to the positive terminal of the DC side and the lower end connected to the negative terminal of the DC side, and connected in parallel with the DC support capacitor 1.

[0016] The soft-start process of the AC soft-start circuit for energy storage converters based on this utility model is as follows: Step 1: System self-check and initialization: The control system is powered on, completes hardware self-test, checks the frequency, phase and amplitude information of the grid voltage, detects DC voltage, and after confirming that there are no faults, it enters the soft start process.

[0017] The second step is uncontrolled rectification pre-charging: The IGBT switching device 2 in the three-phase full-bridge power module is kept off. At this time, the anti-parallel diodes of the three-phase full-bridge form a three-phase uncontrolled rectifier bridge. The grid voltage charges the DC-side support capacitor through the filter inductor 4 and the off power device body diode 3. During this stage, the charging current is limited to a safe range due to the current limiting effect of the inductor. The DC-side voltage Udc gradually rises.

[0018] The third step is to determine if pre-charging is complete: The DC-side voltage Udc is monitored in real time and compared with the peak grid line voltage Upk. When the condition |Udc-Upk|≤ΔU is met (where ΔU is a set voltage tolerance threshold), the pre-charging stage is determined to be complete. At this time, the DC-side voltage is close to the peak grid voltage and the voltage difference is very small.

[0019] Fourth, after pre-charging is complete, the control system switches from uncontrolled rectification mode to controlled rectification mode: First, a grid voltage-oriented vector control strategy is employed, with a phase-locked loop (PLL) precisely tracking the phase and frequency of the grid voltage. Second, the control objective is to ensure that the DC-side voltage Udc accurately tracks the peak value of the grid line voltage (or slightly exceeds the peak value by a safety margin). Then, by adjusting the d-axis current reference value (active current component), the active power absorbed from the grid is controlled, thereby finely regulating the DC-side voltage to achieve complete synchronization with the grid voltage and bring the difference to near zero. Finally, in this stage, the AC-side current is controlled near zero or to a very small value, achieving "zero current" or "micro-current" synchronization.

[0020] Step 5: Close the grid-connected contactor: When the DC side voltage Udc stably tracks the peak voltage of the grid and the AC side current is less than the set safety threshold, a closing command is issued to attract the grid connection contactor. Since the voltage across the capacitor is equal in amplitude and phase to the grid voltage at the moment of closing, and the current is almost zero, no inrush current will be generated, thus achieving "impact-free" grid connection.

[0021] Step 6: Switch to normal operating mode: After the grid-connected contactor is reliably closed, the control system switches the operating mode from the controllable rectification mode to the normal grid-connected inverter or rectification mode, and adjusts the active and reactive power according to the actual field application requirements. At the same time, by utilizing the IGBT's own topology, there is no need to add an external rectifier bridge, which expands the application scenarios. It also eliminates the need for external current-limiting resistors and short-circuit contactors, effectively reducing system cost, size and failure points, and significantly improving reliability.

Claims

1. An AC soft-start circuit for an energy storage converter, characterized in that: It includes an N-phase full-bridge power circuit connected in parallel and a DC support capacitor (1). The N-phase full-bridge power circuit is located on the AC side and connected to the AC power grid. The two ends of the DC support capacitor (1) are connected to the battery interface. The N-phase full-bridge power circuit consists of N sets of symmetrical bridge arms. Each set of bridge arms has at least two power switching devices in the upper and lower bridge arms, and each power switching device is connected in anti-parallel to a body diode (3). In the N sets of symmetrical bridge arms, the midpoint of each set of bridge arms is connected to the corresponding N phase lines of the AC power grid, forming an electrical path on the N-phase AC side.

2. The AC soft-start circuit for an energy storage converter according to claim 1, characterized in that: The power switching device is an IGBT switching device (2).

3. The AC soft-start circuit for an energy storage converter according to claim 1, characterized in that: Each of the N-phase AC side electrical paths is equipped with a filter inductor (4) to limit the charging current.

4. The AC soft-start circuit for an energy storage converter according to claim 3, characterized in that: Each of the N-phase AC side electrical paths is equipped with a first switching switch (5), which is located between the filter inductor (4) and the AC power grid, and is used to select different filter branches.

5. The AC soft-start circuit for an energy storage converter according to claim 1, characterized in that: A second switching switch (6) is also connected on the connection line between the DC support capacitor (1) and the positive terminal of the battery interface, which is used to control the on / off state of the DC bus.

Images