Bus soft start method of energy storage inverter

Abstract

The application discloses a bus soft start method of an energy storage inverter, and comprises the following steps: setting a first BUS voltage threshold and a second BUS voltage threshold, opening a first-stage soft start switch, performing first-stage soft start BUS bus voltage boosting of an AC end through the first-stage soft start switch and an uncontrolled rectifier bridge circuit, closing the first-stage soft start switch when the voltage is greater than the first BUS voltage threshold, opening a second-stage soft start switch, performing second-stage soft start BUS bus voltage boosting of the AC end through the second-stage soft start switch and a Heric power circuit, and closing the first-stage soft start switch and the second-stage soft start switch when the voltage is greater than the second BUS voltage threshold. The application realizes the phased boosting requirement of the BUS bus through the uncontrolled rectifier bridge circuit and the Heric power circuit, does not need to introduce power devices, reduces the hardware cost and space requirement, and meets the soft start control execution requirement. The BUS soft start execution control is smooth and safe, can maintain the stable operation of the low-voltage energy storage inverter, and guarantees the product operation stability and reliability.

Description

Technical Field

[0001] This invention relates to a bus soft-start method for an energy storage inverter, belonging to the technical field of bus start-up methods for low-voltage energy storage inverters. Background Technology

[0002] Low-voltage energy storage inverters consist of photovoltaic panels, batteries, and energy storage inverters. They are used to convert direct current to alternating current and can simultaneously charge and discharge the battery.

[0003] The low-voltage energy storage inverter adopts a dual active bridge (DAB) DC-DC converter topology. When the DC voltage gain is close to 1, it facilitates the controller's implementation of control strategies, enabling soft switching, reducing the resonant current amplitude, decreasing the equipment's return power, and lowering switching losses. To meet the DC voltage gain requirements, the standard bus voltage will vary under different operating conditions, but it will always be higher than the peak value of the mains voltage.

[0004] Low-voltage energy storage inverters face various operating conditions during operation. One such condition is when the inverter is operating under grid connection but there is no photovoltaic output, making it impossible to establish bus voltage and preventing the inverter from starting. To address this, a bus hard-start module design is typically used, which undoubtedly increases cost and requires unnecessary space. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art and to propose a bus soft-start method for energy storage inverters, which addresses the problems of high cost and unfavorable space layout of traditional bus hard start.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A bus soft-start method for an energy storage inverter is disclosed, based on a dual active bridge converter circuit. The dual active bridge converter circuit includes a BUS bus and an AC (mains) terminal and a PV (photovoltaic) terminal connected to the BUS bus. A bus capacitor and a Heric power loop are connected in parallel on the BUS bus.

[0008] An uncontrolled rectifier bridge circuit is connected in parallel on the BUS bus. A first-order soft-start switch is provided between the uncontrolled rectifier bridge circuit and the AC terminal of the mains power supply. A second-order soft-start switch is provided between the Heric power circuit and the AC terminal of the mains power supply.

[0009] The bus soft-start method includes the following steps:

[0010] S1 threshold setting: Set a first BUS voltage threshold and a second BUS voltage threshold, wherein the second BUS voltage threshold is greater than the first BUS voltage threshold;

[0011] S2 soft start trigger performs status detection on the photovoltaic (PV) terminal and is triggered when the photovoltaic (PV) terminal is connected to the grid and has no output.

[0012] S3 first-stage soft start: When the first-stage soft start switch is turned on, the AC power supply is boosted to the BUS bus through the first-stage soft start switch and the uncontrolled rectifier bridge circuit, and the BUS bus voltage is monitored in real time.

[0013] S4 Second Stage Soft Start: When the detected BUS bus voltage is greater than the first BUS voltage threshold, the first stage soft start switch is closed and the second stage soft start switch is opened. The AC power terminal boosts the second stage soft start BUS bus voltage through the second stage soft start switch and Heric power circuit, and detects the BUS bus voltage in real time.

[0014] After the S5 soft start is completed, when the detected BUS bus voltage is greater than the second BUS voltage threshold, both the first-stage soft start switch and the second-stage soft start switch are turned off.

[0015] Preferably, in step S3, a first-stage soft-start BUS bus voltage boost time limit is set.

[0016] If the detected BUS bus voltage is greater than the second BUS voltage threshold within the first-stage soft-start BUS bus voltage boost time limit, proceed directly to step S5.

[0017] If the voltage of an undetected detection bus exceeds the first bus voltage threshold within the first-stage soft-start bus voltage boost time limit, a soft-start anomaly is triggered.

[0018] Preferably, in step S4, a second-stage soft-start BUS bus voltage boost time limit is set.

[0019] If the voltage of an undetected detection bus exceeds the second bus voltage threshold within the second-stage soft-start bus voltage boost time limit, a soft-start anomaly is triggered.

[0020] Preferably, in step S4, the second-stage soft start switch has an on-delay, and after the second-stage soft start switch is turned on after the delay, the first-stage soft start switch is turned off.

[0021] Preferably, the uncontrolled rectifier bridge circuit includes diodes D1, D2, D3, and D4.

[0022] The negative terminal of the BUS bus is connected to the positive terminal of the BUS bus via diodes D2 and D1 in a forward direction, and the other terminal is connected to the positive terminal of the BUS bus via diodes D4 and D3 in a forward direction.

[0023] The first-stage soft-start switch includes resistors R1 and R2, relay switch RLY1, and relay switch RLY2.

[0024] The L terminal of the AC power supply is connected to the connection line of diodes D3 and D4 via resistor R1 and relay switch RLY1, and the N terminal of the AC power supply is connected to the connection line of diodes D1 and D2 via resistor R2 and relay switch RLY2.

[0025] The beneficial effects of this invention are mainly reflected in:

[0026] 1. The phased boosting requirement of the BUS bus is achieved through an uncontrolled rectifier bridge circuit and Heric power circuit, without the need to introduce power devices, which reduces hardware costs and space requirements, and meets the soft start control execution requirements.

[0027] 2. The busbar soft start control is smooth and safe, and can maintain the stable operation of the low-voltage energy storage inverter, thus ensuring the stability and reliability of the product operation. Attached Figure Description

[0028] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0029] Figure 1 This is a flowchart illustrating a bus soft-start method for an energy storage inverter according to the present invention.

[0030] Figure 2 This is a schematic diagram of the soft-start execution process of a bus soft-start method for an energy storage inverter according to the present invention.

[0031] Figure 3 This is a circuit diagram of the dual active bridge converter circuit in the bus soft-start method of an energy storage inverter according to the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other.

[0034] This invention provides a bus soft-start method for an energy storage inverter, such as... Figure 3 As shown, based on a dual active bridge converter circuit, the dual active bridge converter circuit includes a BUS bus and AC and PV terminals connected to the BUS bus. A bus capacitor C1 and a Heric power circuit are connected in parallel on the BUS bus. The Heric power circuit is as follows... Figure 3 As shown, it is composed of IGBT1, IGBT2, IGBT3, IGBT4, IGBT5, and IGBT6, and their connection relationship and principle are existing technologies, which will not be described in detail here.

[0035] In this case, if Figure 1 As shown, an uncontrolled rectifier bridge circuit is connected in parallel on the BUS bus. A first-stage soft-start switch is provided between the uncontrolled rectifier bridge circuit and the AC terminal of the mains power, and a second-stage soft-start switch is provided between the Heric power circuit and the AC terminal of the mains power.

[0036] More specifically, refer to Figure 1 As shown, the uncontrolled rectifier bridge circuit includes diodes D1, D2, D3, and D4. One path of the negative terminal of the BUS bus passes through diodes D2 and D1 and is connected to the positive terminal of the BUS bus, while the other path passes through diodes D4 and D3 and is connected to the positive terminal of the bus. The first-stage soft-start switch includes resistors R1 and R2, relay switch RLY1, and relay switch RLY2. The L terminal of the AC power supply is connected to the connection between diodes D3 and D4 through resistor R1 and relay switch RLY1, and the N terminal of the AC power supply is connected to the connection between diodes D1 and D2 through resistor R2 and relay switch RLY2.

[0037] The second-stage soft start switch includes relay switch RLY3 and relay switch RLY4. The L terminal of the AC power supply is connected to the insulated gate bipolar transistor IGBT5 through relay switch RLY3, and the N terminal of the AC power supply is connected to the insulated gate bipolar transistor IGBT6 through relay switch RLY4.

[0038] like Figures 1 to 3 As shown, the bus soft start method includes the following steps:

[0039] Threshold setting: Set a first BUS voltage threshold and a second BUS voltage threshold, wherein the second BUS voltage threshold is greater than the first BUS voltage threshold.

[0040] Soft start triggering is used to detect the status of the photovoltaic (PV) terminal. It is triggered when the photovoltaic (PV) terminal is connected to the grid and has no output.

[0041] First-stage soft start: When the first-stage soft start switch is turned on, the AC power supply is boosted through the first-stage soft start switch and the uncontrolled rectifier bridge circuit to boost the voltage of the BUS bus in the first stage, and the BUS bus voltage is monitored in real time.

[0042] The second-stage soft start is initiated when the detected BUS bus voltage exceeds the first BUS voltage threshold. The first-stage soft start switch is closed, and the second-stage soft start switch is opened. The AC power supply is boosted through the second-stage soft start switch and Heric power circuit, and the BUS bus voltage is monitored in real time.

[0043] After the soft start is complete, when the detected BUS bus voltage is greater than the second BUS voltage threshold, both the first-stage soft start switch and the second-stage soft start switch will be closed.

[0044] Detailed implementation process and principle explanation:

[0045] The standard bus voltage of low-voltage energy storage inverters is generally higher than the peak value of the mains power. The traditional method is to directly boost the voltage of the BUS bus by introducing power devices, which is costly and takes up a lot of space.

[0046] In this case, the introduction of an uncontrolled rectifier bridge circuit and the Heric power circuit in the existing technology are used to achieve phased voltage boosting of the BUS bus, which can meet the requirements of boost soft start without the need for additional power devices.

[0047] Specifically, the low-voltage energy storage inverter itself has a management controller, which can realize signal acquisition and control of the dual active bridge converter circuit. The management controller will not be limited or described in detail here.

[0048] Before performing the soft start operation, the soft start command is first triggered, which is done by detecting the status of the photovoltaic (PV) terminal. The command is triggered when the PV terminal is connected to the grid and has no output.

[0049] When the soft start is triggered, the first stage of soft start is performed. At this time, the first stage soft start switch is turned on, that is, the relay switch RLY1 and the relay switch RLY2 are turned on. The mains power is charged to the bus capacitor C1 through the uncontrolled rectifier bridge circuit through the resistor R1 and the resistor R2. At this time, the bus voltage continues to rise.

[0050] During the continuous rise of the bus voltage, real-time BUS bus voltage detection is performed. When the detected BUS bus voltage is greater than the first BUS voltage threshold, the second-stage soft start is triggered. When the second-stage soft start is started, relay switches RLY1 and RLY2 are turned off, and relay switches RLY3 and RLY4 are turned on. At this time, the Heric power circuit is working, and the BUS bus voltage continues to rise.

[0051] When the detected BUS bus voltage is greater than the second BUS voltage threshold, the soft start is completed. At this time, relay switches RLY1, RLY2, RLY3, and RLY4 are all in the closed state.

[0052] The first BUS voltage threshold and the second BUS voltage threshold are explained. The second BUS voltage threshold is generally the bus reference voltage, which is the pull-up setting of traditional power devices. The first BUS voltage threshold is set with reference to the mains peak voltage. When setting, the first BUS voltage threshold is the difference between the mains peak voltage and a fixed value, that is, the first BUS voltage threshold is less than the mains peak voltage.

[0053] In one specific embodiment, such as Figure 2 As shown, in the first-stage soft boot step, the first-stage soft boot BUS bus voltage boost time limit is set.

[0054] If the detected BUS bus voltage is greater than the second BUS voltage threshold within the first-stage soft-start BUS bus voltage boost time limit, the soft-start process is completed directly.

[0055] If the voltage of an undetected detection bus exceeds the first bus voltage threshold within the first-stage soft-start bus voltage boost time limit, a soft-start anomaly is triggered.

[0056] Specifically, under normal circumstances, the bus voltage will continuously rise during the charging process of the bus capacitor through the uncontrolled rectifier bridge circuit. However, when there is component damage or load-side fault, there may be a situation where the voltage cannot be boosted. Therefore, online fault feedback is adopted, and the first-stage soft-start bus voltage boosting time limit is set. This time limit is generally 60 seconds, but it can be extended or shortened accordingly. It is only necessary to set a time monitoring that can realize feedback.

[0057] When performing specific operations, the system has a time stamp, that is, when the first-stage soft start switch is powered on, the corresponding control operation is performed when the target or time limit is reached.

[0058] In one specific embodiment, such as Figure 2 As shown, in the second-stage soft start, a time limit for boosting the BUS bus voltage is set. If, within this time limit, the undetected BUS bus voltage exceeds the second BUS voltage threshold, a soft start anomaly is triggered. In other words, if the BUS bus voltage fails to rise sufficiently during the Heric power circuit's power-on process, an anomaly is triggered.

[0059] In one specific embodiment, such as Figure 2 Therefore, the second-stage soft start switch has an on-delay time, and after the second-stage soft start switch is turned on after the delay, the first-stage soft start switch is turned off.

[0060] To elaborate, a typical system has a mains power soft start trigger time stamp, a first-stage soft start end time stamp, a second-stage soft start start time stamp, a second-stage soft start switch delay time stamp, and a second-stage soft start end time stamp. The corresponding control and execution are performed through the time stamps and timing of each stage, thereby meeting the execution requirements of the soft start method.

[0061] As described above, the phased voltage boost requirement of the BUS bus is achieved through an uncontrolled rectifier bridge circuit and the Heric power circuit, eliminating the need for power devices, thus reducing hardware costs and space requirements while meeting the soft-start control execution requirements. The bus soft-start execution control is smooth and safe, maintaining the stable operation of the low-voltage energy storage inverter, thereby ensuring product operational stability and reliability.

[0062] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0063] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A bus soft-start method for an energy storage inverter, based on a dual active bridge converter circuit, wherein the dual active bridge converter circuit includes a BUS bus and an AC terminal and a PV terminal connected to the BUS bus, and a bus capacitor and a Heric power circuit are connected in parallel on the BUS bus, characterized in that, An uncontrolled rectifier bridge circuit is connected in parallel on the BUS bus. A first-order soft-start switch is provided between the uncontrolled rectifier bridge circuit and the AC terminal of the mains power supply. A second-order soft-start switch is provided between the Heric power circuit and the AC terminal of the mains power supply. The bus soft-start method includes the following steps: S1 threshold setting: Set a first BUS voltage threshold and a second BUS voltage threshold, wherein the second BUS voltage threshold is greater than the first BUS voltage threshold; S2 soft start trigger performs status detection on the photovoltaic (PV) terminal and is triggered when the photovoltaic (PV) terminal is connected to the grid and has no output. S3 first-stage soft start: When the first-stage soft start switch is turned on, the AC power supply is boosted to the BUS bus through the first-stage soft start switch and the uncontrolled rectifier bridge circuit, and the BUS bus voltage is monitored in real time. S4 Second Stage Soft Start: When the detected BUS bus voltage is greater than the first BUS voltage threshold, the first stage soft start switch is closed and the second stage soft start switch is opened. The AC power terminal boosts the second stage soft start BUS bus voltage through the second stage soft start switch and Heric power circuit, and detects the BUS bus voltage in real time. After the S5 soft start is completed, when the detected BUS bus voltage is greater than the second BUS voltage threshold, both the first-stage soft start switch and the second-stage soft start switch are closed. The first BUS voltage threshold is the difference between the mains peak voltage and a fixed value, and the first BUS voltage threshold is less than the mains peak voltage. The second BUS voltage threshold is the bus reference voltage.

2. The bus soft-start method for an energy storage inverter according to claim 1, characterized in that: In step S3, the first-stage soft-start BUS bus voltage boost time limit is set. If the detected BUS bus voltage is greater than the second BUS voltage threshold within the first-stage soft-start BUS bus voltage boost time limit, proceed directly to step S5. If the voltage of an undetected detection bus exceeds the first bus voltage threshold within the first-stage soft-start bus voltage boost time limit, a soft-start anomaly is triggered.

3. The bus soft-start method for an energy storage inverter according to claim 1, characterized in that: In step S4, the second-stage soft-start BUS bus voltage boost time limit is set. If the voltage of an undetected detection bus exceeds the second bus voltage threshold within the second-stage soft-start bus voltage boost time limit, a soft-start anomaly is triggered.

4. The bus soft-start method for an energy storage inverter according to claim 3, characterized in that: In step S4, the second-stage soft start switch has an on-delay time. After the second-stage soft start switch is turned on after the delay, the first-stage soft start switch is turned off.

5. The bus soft-start method for an energy storage inverter according to claim 1, characterized in that: The uncontrolled rectifier bridge circuit includes diodes D1, D2, D3, and D4. The negative terminal of the BUS bus is connected to the positive terminal of the BUS bus via diodes D2 and D1 in a forward direction, and the other terminal is connected to the positive terminal of the BUS bus via diodes D4 and D3 in a forward direction. The first-stage soft-start switch includes resistors R1 and R2, relay switch RLY1, and relay switch RLY2. The L terminal of the AC power supply is connected to the connection line of diodes D3 and D4 via resistor R1 and relay switch RLY1, and the N terminal of the AC power supply is connected to the connection line of diodes D1 and D2 via resistor R2 and relay switch RLY2.

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