Auxiliary power supply device for inverter, inverter and starting method thereof

Abstract

The present invention discloses an auxiliary power supply device for an inverter. The inverter includes multiple power modules connected in parallel. The auxiliary power supply device comprises: multiple soft-start circuits, each coupled to the DC terminal of a corresponding power module; multiple distributed auxiliary power supplies, each having an input coupled to the DC terminal of a corresponding power module; and a centralized auxiliary power supply, having an input coupled to the AC side of the inverter and an output coupled to the DC side of the inverter. By providing a centralized auxiliary power supply, the present invention replaces the AC-side auxiliary power supplies in all power modules and eliminates the AC-side soft-start circuits in all power modules, thereby improving system cost, volume, loss, and electromagnetic compatibility.

Description

Technical Field

[0001] The present invention relates to the field of inverters, and in particular to an auxiliary power supply device for an inverter, an inverter and a starting method thereof. Background Art

[0002] Energy storage inverter systems, consisting of a bidirectional energy storage inverter and an energy storage medium (such as a power battery), can make microgrids more intelligent and stable. As a core component of future microgrids, energy storage inverter systems can greatly benefit users.

[0003] like Figure 1 As shown, the energy storage inverter operates in grid-connected mode, with its AC side coupled to the grid via an AC panel, and its DC side coupled to the battery via a DC panel, allowing energy to flow in both directions. The position and structure of the AC and DC panels can be adjusted based on actual conditions, and the AC and DC panels can also be removed. In grid-connected mode, the energy storage inverter can be used in conjunction with new energy equipment to smooth the intermittent output of renewable energy, improving power quality and grid reliability. For peak power consumption scenarios, the energy storage inverter performs load balancing and peak-to-valley shifting to reduce grid investment and electricity costs. Furthermore, the energy storage inverter can also perform reactive power control and grid frequency regulation to improve grid quality.

[0004] like Figure 2 As shown, the energy storage inverter operates in standalone mode, with its AC side coupled to local loads via an AC panel and its DC side coupled to the battery via a DC panel. The AC panel's location and structure can be customized based on actual needs, and it can also be removed. The energy storage inverter converts battery energy into AC power, which is then transmitted to the AC side to power critical local loads.

[0005] like Figure 3 As shown, the energy storage inverter operates in DC voltage source mode. Its AC side is coupled to the grid via an AC panel, and its DC side is coupled to at least one DC converter via a DC panel, allowing for bidirectional energy flow. The DC converter can be a PV adapter, a DC charger, or something similar. The location and structure of the AC panel can be customized based on actual needs, and both the AC and DC panels can be removed. The energy storage inverter operates in DC voltage source mode, acting as a rectifier to provide a DC voltage source, delivering energy to the load on the DC side.

[0006] As a core component in microgrids, bidirectional energy storage inverters have increasingly higher power requirements from users, and different applications require different power levels. Generally speaking, energy storage inverters include multiple power modules connected in parallel to increase the power level. Figure 4 FIG. 1 shows a circuit diagram of a power module in an existing inverter. Figure 4 As shown, in order to satisfy Figures 1 to 3 In the three modes shown, the power module is internally equipped with an AC isolated auxiliary power supply 3 and a DC isolated auxiliary power supply 4; an AC start-up circuit 1 corresponding to the AC isolated auxiliary power supply 3, and a DC start-up circuit 2 corresponding to the DC isolated auxiliary power supply 4. The AC start-up circuit 1 includes an AC main switch and an AC soft-start circuit, while the DC start-up circuit 2 includes a DC main switch and a DC soft-start circuit. The primary side of the AC isolated auxiliary power supply 3 is coupled to the AC side of the power module, while the primary side of the DC isolated auxiliary power supply 4 is coupled to the DC side of the power module. The secondary sides of the AC isolated auxiliary power supply 3 and DC isolated auxiliary power supply 4 are connected in parallel to power auxiliary circuits within the module, such as the control board and relays. The grid-connected mode imposes safety regulations on grid-connected inverters: the DC and AC sides of the inverter must be essentially isolated from each other in the event of a single failure. The auxiliary power supplies within the power module, which draw power from the AC and DC sides, must also meet these requirements. Therefore, both auxiliary power supplies on the DC and AC sides are high-voltage isolated power supplies, converting the high-voltage input to a low-voltage output. However, high-voltage isolated power supplies are bulky and complex in circuitry.

[0007] The power module is equipped with two high-voltage isolated auxiliary power supplies, so that the power module can be started from the AC side or the DC side. That is, the DC side and the AC side of the bidirectional energy storage inverter are equipped with auxiliary power supplies, so that the inverter system can be started from the DC side or the AC side, while meeting Figures 1 to 3 Please refer to the three working modes shown in Figure 1 and Figure 4 In grid-connected mode, the AC terminals (R, S, T) of the power module are coupled to the grid, and the DC terminals (DC+, DC-) are coupled to the battery. The grid supplies power to the AC isolated auxiliary power supply 3 inside the power module. By closing the AC soft-start loop, the power module can be started from the AC terminal; or the battery supplies power to the DC isolated auxiliary power supply 4 inside the power module. By closing the DC soft-start loop, the power module can be started from the DC terminal. Please refer to Figure 2 and Figure 4 In standalone mode, the AC terminals (R, S, T) of the power module are coupled to the load, and the DC terminals (DC+, DC-) are coupled to the battery. The battery supplies power to the DC isolated auxiliary power supply 4 inside the power module, closing the DC soft start loop to start the power module from the DC terminal. Please also refer to Figure 3 and Figure 4 In the DC voltage source mode, the AC terminals (R, S, T) of the power module are coupled to the grid, and the DC terminals (DC+, DC-) are coupled to the DC converter. The grid supplies power to the AC isolated auxiliary power supply 3 inside the power module. By closing the AC soft start loop, the power module can be started from the AC terminal.

[0008] Existing solutions can meet the requirements of grid-connected, independent, DC voltage source modes, and basic insulation between the DC port and the AC grid. However, two high-voltage isolated auxiliary power supplies and two soft-start circuits are configured inside the power module, increasing the overall cost and complexity of the inverter system. Furthermore, as high-power inverter systems tend to be higher in voltage, selecting AC relays that meet basic insulation requirements in the AC start-up circuit is difficult and costly. As power levels increase, the above-mentioned defects become more prominent. For example, an inverter system consisting of 10 power modules in parallel requires at least 10 AC isolated auxiliary power supplies 3, 10 DC isolated auxiliary power supplies 4, 10 sets of AC start-up circuits (including soft-start circuits), and 10 sets of DC start-up circuits (including soft-start circuits). The two high-voltage isolated power supplies and two soft-start circuits within the power module significantly limit the optimization of the inverter in terms of cost, volume, and loss, weakening the product's competitiveness.

[0009] Therefore, it is very necessary to find an auxiliary power supply device for an inverter, an inverter and a starting method thereof that are low-cost, small in size and can simultaneously meet multiple working modes. Summary of the Invention

[0010] In view of this, one object of the present invention is to provide an auxiliary power supply device for an inverter, which realizes a starting power supply in a DC voltage source mode through a centralized auxiliary power supply, thereby significantly improving the cost, volume, loss, electromagnetic compatibility performance, etc. of the entire system.

[0011] In order to achieve the above object, the present invention provides an auxiliary power supply device for an inverter, wherein the inverter includes a plurality of power modules connected in parallel, and the auxiliary power supply device includes:

[0012] A plurality of soft start loops, each of which is coupled between the DC terminal of a corresponding power module and the conversion circuit;

[0013] A plurality of distributed auxiliary power supplies, each having an input terminal coupled between a DC terminal of a corresponding power module and a soft start circuit; and

[0014] A centralized auxiliary power supply has an input end coupled to the AC side of the inverter and an output end coupled to the DC side of the inverter.

[0015] The present invention also provides an inverter, comprising:

[0016] A plurality of power modules, wherein the AC ends of the plurality of power modules are coupled in parallel to form an AC side of the inverter, and the DC ends of the plurality of power modules are coupled in parallel to form a DC side of the inverter;

[0017] The inverter further includes a centralized auxiliary power supply, the input end of which is coupled to the AC side of the inverter, and the output end of which is coupled to the DC side of the inverter;

[0018] Wherein, each of the power modules includes:

[0019] a soft start circuit coupled to the DC terminal of the power module; and

[0020] A distributed auxiliary power supply has an input terminal coupled between the soft-start loop and the DC terminal of the power module.

[0021] The present invention also provides a method for starting an inverter. The inverter includes: n power modules connected in parallel; and a centralized auxiliary power supply having an input coupled to the AC side of the inverter and an output coupled to the DC side of the inverter. Each power module includes: a soft start circuit coupled to the DC side of the power module; and a distributed auxiliary power supply having an input coupled between the soft start circuit and the DC side of the power module.

[0022] The method comprises the following steps:

[0023] Establishing the DC side voltage of the inverter to supply power to the distributed auxiliary power supply;

[0024] Closing the soft start loops of the n power modules to establish the AC side voltage of the n power modules;

[0025] Close the AC-side main switches of the n power modules.

[0026] The present invention replaces the AC-side auxiliary power supply in all power modules with a centralized auxiliary power supply, eliminating the AC-side soft-start circuit in all power modules. This reduces cost and size within the power modules (PMs). The centralized auxiliary power supply, comprised of an AC relay and a DC bridge, eliminates high-frequency switching components, resulting in high reliability and improved electromagnetic compatibility. Furthermore, it reduces auxiliary power supply losses and remains disconnected during normal operation. Consequently, the overall system significantly improves cost, size, losses, and electromagnetic compatibility.

[0027] The above description will be described in detail below with reference to implementation examples, and a further explanation of the technical solution of the present invention will be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To make the above and other objects, features, advantages and embodiments of the present invention more apparent, the accompanying drawings are described as follows:

[0029] Figure 1 A circuit diagram of an energy storage inverter operating in a grid-connected mode in the prior art;

[0030] Figure 2 A circuit diagram of an energy storage inverter operating in an independent mode in the prior art;

[0031] Figure 3 A circuit diagram of an energy storage inverter operating in a DC voltage source mode in the prior art;

[0032] Figure 4 A schematic diagram showing the internal structure of a power module of an energy storage inverter in the prior art is shown;

[0033] Figure 5 A circuit diagram of an energy storage inverter in a grid-connected operation mode according to a preferred embodiment of the present invention is shown;

[0034] Figure 6 A schematic diagram showing the internal structure of a power module of an energy storage inverter according to a preferred embodiment of the present invention is shown;

[0035] Figure 7 A circuit diagram of an energy storage inverter in an independent operation mode according to a preferred embodiment of the present invention is shown;

[0036] Figure 8 A circuit diagram of an energy storage inverter in a DC voltage source mode according to a preferred embodiment of the present invention is shown;

[0037] Figure 9 A flow chart of a method for starting an energy storage inverter in a DC voltage source mode according to a preferred embodiment of the present invention is shown. DETAILED DESCRIPTION

[0038] For a more detailed and complete description of the present invention, reference is made to the accompanying drawings and the various embodiments described below. Like numbers in the drawings represent like or similar components. Well-known components and steps are not described in the embodiments to avoid unnecessary limitations on the present invention. Furthermore, to simplify the drawings, some well-known and commonly used structures and elements are depicted in simplified schematic form.

[0039] The present invention provides an auxiliary power supply device for an inverter, which may be an energy storage inverter, such as a bidirectional energy storage inverter that realizes bidirectional energy flow. The inverter includes multiple power modules and an auxiliary power supply device, and the multiple power modules are connected in parallel. Based on the functions to be implemented, the auxiliary power supply device includes an auxiliary circuit and an auxiliary power supply, wherein the auxiliary power supply supplies power to the controllers, relays, drivers, etc. within the multiple power modules. The auxiliary circuit corresponds to the soft start circuit within the power module, which is controlled by the controller within the power module to realize the soft start of the power module.

[0040] Specifically, the auxiliary power supply device includes: multiple soft-start circuits, each coupled between the DC terminal of a corresponding power module and a conversion circuit; multiple distributed auxiliary power supplies, each with its input coupled between the DC terminal of a corresponding power module and the soft-start circuit; and a centralized auxiliary power supply, with its input coupled to the AC side of the inverter and its output coupled to the DC side of the inverter. The inverter and its auxiliary power supply device of this embodiment will be described below with reference to specific embodiments and accompanying drawings.

[0041] Example 1

[0042] Figure 5 FIG1 shows a circuit diagram of an energy storage inverter (hereinafter referred to as inverter) according to an embodiment of the present invention. Figure 5 As shown, an energy storage inverter (hereinafter referred to as the inverter) 100 includes multiple power modules PM1, PM2, PM3, etc. connected in parallel. The AC terminals of the multiple power modules are coupled in parallel to form the AC side of the inverter 100, and the DC terminals of the multiple power modules are coupled in parallel to form the DC side of the inverter. Optionally, the AC bus includes multiple sets of AC terminals, with the three-phase AC terminals of each power module correspondingly connected to a set of three-phase AC terminals on the AC bus; the DC bus includes multiple sets of DC terminals, with the DC terminals of each power module correspondingly connected to a set of DC terminals on the DC bus. The AC side is coupled to the grid 7 via an AC switch, and the DC side is coupled to the energy storage element, namely the battery 8, via a DC fuse and a DC switch. The inverter 100 operates in a grid-connected mode to enable the grid to charge the battery or the battery to discharge the battery to the grid. The AC switch, circuit breaker, DC switch, and DC fuse serve as power distribution protection devices.

[0043] The inverter 100 includes a system auxiliary power supply 5, which is coupled to the AC switch and the AC side of the inverter via a circuit breaker. The system auxiliary power supply 5 supplies power to the inverter's control devices, such as the system controller. In grid-connected or standalone modes, the system controller enables the startup of the battery (or other energy storage medium). The system auxiliary power supply 5 includes an uninterruptible power supply (UPS) and a power supply unit (PSU), wherein the PSU's input is coupled to the grid and the UPS, and the PSU's output is coupled to the control device. When the AC switch and circuit breaker remain closed, the grid provides input power to the PSU, which converts the grid voltage into low-voltage DC power to power the control device. When the grid fails or the device goes offline, the AC switch and circuit breaker are disconnected, and the UPS provides input power to the PSU to continue powering the control device.

[0044] The inverter 100 also includes a centralized auxiliary power supply 6, whose input end is coupled to the AC side of the inverter 100, and whose output end is coupled to the DC side of the inverter 100. Optionally, the DC bus further includes a set of DC terminals electrically connected to the output end of the centralized auxiliary power supply 6. Generally speaking, the capacity of the centralized auxiliary power supply is much smaller than the capacity of the power module. Preferably, a wire can be used to realize the electrical connection between the output end of the centralized auxiliary power supply 6 and the DC terminal in the DC bus; but other connection structures can also be used without limitation. The input end of the centralized auxiliary power supply 6 is coupled to the AC switch and the AC side of the inverter through a circuit breaker; the output end of the centralized auxiliary power supply 6 is coupled to the DC fuse and the DC side of the inverter in sequence.

[0045] The following takes the power module PM1 as an example to further describe its internal structure. Figure 6 As shown, a starting circuit 2 and a distributed auxiliary power supply 4 are provided inside the power module. The conversion circuit of the power module PM1 includes a bidirectional inverter bridge and a DC bus, wherein the DC bus includes a positive DC bus, a negative DC bus, and a bus capacitor. The positive DC bus is coupled to the positive DC terminal DC+, the negative DC bus is coupled to the negative DC terminal DC-, the bus capacitors Cd1 and Cd2 are connected in series, and the common connection point corresponds to the DC bus midpoint BUSN. The starting circuit 2 is coupled between the DC terminal (DC+, DC-) of the power module PM1 and the conversion circuit. Furthermore, the starting circuit 2 is coupled in series between the DC terminal (DC+, DC-) and the conversion circuit. The starting circuit 2 includes a DC main switch and a soft start circuit, both coupled between the DC terminal (DC+, DC-) and the conversion circuit. The DC main switches include two sets, and the soft-start circuits include two sets. One set of DC main switches is connected in parallel with one set of soft-start circuits. The parallel start circuits are coupled in series between the DC terminal (DC+) and the conversion circuit. The other set of DC main switches is connected in parallel with the other set of soft-start circuits. The parallel start circuits are coupled in series between the DC terminal (DC-) and the conversion circuit. The DC main switches can be relays, typically called DC main relays, and can be selected based on the capacity of the power module. Their rated current is generally 200A-400A. The soft-start circuit is a DC soft-start circuit, consisting of a switch and a resistor connected in series. The switch can be a relay, typically called a DC preload relay, with a rated current generally of 20A-50A, to slowly build up the DC bus voltage. The input of the distributed auxiliary power supply 4 is coupled between the start circuit 2 and the DC terminal of the power module PM1, and the input of the distributed auxiliary power supply 4 is connected in parallel with the DC terminal of the power module PM1. The output of the distributed auxiliary power supply 4 is coupled to the internal load to supply power to the internal load. The internal load includes a controller board, a relay, a Hall sensor or a driver, etc. In this embodiment, an EMI filter is further provided at the DC end of the power module PM1.

[0046] It is understandable that the starting circuit 2 is specifically a DC starting circuit, and the distributed auxiliary power supply 4 is specifically a DC isolated auxiliary power supply. Figure 6 As shown, the AC side of power module PM1 does not require an AC isolated auxiliary power supply. The corresponding AC starting circuit only includes the AC main switch, eliminating the need for an AC soft-start circuit. The AC main switch can be a high-capacity contactor or relay. In power module PM1, L1-L3 are AC filter inductors, Cfa / Cfb / Cfc are AC filter capacitors, the bidirectional inverter bridge is the main topology of the conversion circuit, and the internal load is the auxiliary power supply. The structures of the remaining power modules PM2, PM3, etc. are identical to those of power module PM1.

[0047] Please refer to Figure 5 and Figure 6 Multiple DC soft-start circuits, multiple distributed auxiliary power supplies 4, and a centralized auxiliary power supply 6 serve as auxiliary power supplies for the inverter, ensuring reliable startup and stable operation of multiple power modules. The output of the centralized auxiliary power supply 6 is essentially coupled to the DC terminals of the multiple power modules. For example, the output of the centralized auxiliary power supply 6 is electrically connected to the DC busbar on the DC side of the inverter 100 via a wire. The DC+ and DC- terminals of the multiple power modules are electrically connected to the DC busbar on the DC side of the inverter 100 via a busbar, achieving a parallel connection.

[0048] Compared to the prior art, the power module PM of the present invention eliminates the need for an AC soft-start circuit and an AC isolated auxiliary power supply. This means the auxiliary circuit only requires a DC soft-start circuit, and the auxiliary power supply only requires a DC auxiliary power supply. If the inverter includes n power modules PM1, PM2, PM3, ... PMn connected in parallel, the auxiliary power supply device of the present invention will correspondingly include n DC soft-start circuits, n distributed auxiliary power supplies 4, and one centralized auxiliary power supply 6, for a total of 2n+1 necessary structures. The auxiliary power supply device in the original inverter requires at least n AC soft-start circuits, n AC isolated auxiliary power supplies, n DC soft-start circuits, and n DC isolated auxiliary power supplies, for a total of at least 4n necessary structures. Clearly, the volume, structure, and cost of the inverter system of the present invention have been significantly improved. As the power level increases, the optimized auxiliary power supply structure of the modules connected in parallel proposed by the present invention becomes even more advantageous.

[0049] like Figure 5As shown, the centralized auxiliary power supply 6 includes: a switching circuit, a first end of which is coupled to the AC side of the inverter; and a rectifier circuit, a first end of which is coupled to the second end of the switching circuit, and a second end of which is coupled to the DC side of the inverter. The switching circuit also includes a control device whose control end is coupled to the inverter 100, so that the switching circuit is controlled by the control device. The control device is, for example, a system controller. Preferably, the switching circuit includes a relay. Further, the switching circuit includes a first AC relay RL1 and a second AC relay RL2 connected in series, and the setting of the two relays can achieve redundant isolation. The control end of the first AC relay RL1 and the control end of the second AC relay RL2 are both coupled to the control device. The rectifier circuit includes a three-phase rectifier bridge 61.

[0050] The auxiliary power supply device may also include a backup centralized auxiliary power supply to form a redundant arrangement with the centralized auxiliary power supply 6. The backup centralized auxiliary power supply may have the same structure as the centralized auxiliary power supply 6. The main structure of the centralized auxiliary power supply is a small relay and a rectifier bridge, which is low-cost and simple in structure.

[0051] Please refer to Figure 5 and Figure 6 , the inverter 100 operates in grid-connected mode, with its AC side coupled to the grid 7 and its DC side coupled to the battery 8, enabling bidirectional energy flow. Since there are only DC isolated auxiliary power supplies and DC soft start circuits inside the power module, the power module can only be started from the DC end. The battery 8 supplies power to the distributed auxiliary power supply 4 inside each power module, which converts the input power provided by the battery 8 into low-voltage DC power (for example, 12V, 5V, etc.) to power the internal load. The power module ID is allocated to determine the power module to be started. The DC soft start circuit inside the power module is closed, and the battery 8 charges the bus capacitors Cd1 and Cd2 in each power module to provide the energy required for the power module to start. The bidirectional inverter bridge converts the electrical energy of the bus capacitor into AC energy to charge the AC side capacitors Cfa, Cfb and Cfc, and closes the AC main switch to complete the power module startup. All power modules are started in sequence, and the inverter completes the startup.

[0052] When the DC side of the inverter is coupled to the energy storage element, the centralized auxiliary power supply 6 is not working, that is, the switch circuit remains open. The energy storage element can be any energy storage medium, such as a battery, a super capacitor, etc.

[0053] Example 2

[0054] Figure 7 The following figure shows a circuit diagram of an energy storage inverter according to another embodiment of the present invention. The difference between Example 2 and Example 1 is that inverter 100 operates in standalone mode, with its AC side coupled to the load, and the battery powering the load. For other details, please refer to the description of Example 1 and will not be repeated here.

[0055] Example 3

[0056] Figure 8 FIG2 shows a circuit diagram of an energy storage inverter according to another embodiment of the present invention. Embodiment 3 differs from Embodiment 1 in that inverter 100 operates in a DC voltage source mode, with its DC side coupled to an energy-consuming element, such as a DC load. The DC load may be, but is not limited to, a DC converter, such as a buck converter, a boost converter, a buck-boost converter, a buck+boost converter, a flyback converter, a forward converter, a Cuk converter, a charge pump, or other types of converters.

[0057] Because there are only DC isolated auxiliary power supplies and DC soft start circuits inside the power module, the power module can only be started from the DC end. In this embodiment, there is no energy source on the DC side of the inverter 100, and the DC energy required for starting the power module is provided by a centralized auxiliary power supply. When the inverter is started, the centralized auxiliary power supply 6 is enabled to supply power to the distributed auxiliary power supply 4 of each power module. The distributed auxiliary power supply 4 converts the input power provided by the centralized auxiliary power supply 6 into low-voltage DC power (for example, 12V, 5V, etc.) to power the internal load. The system controller or the host computer determines the power module to be started first (for example, the i-th power module, i=1,2,3...), and sets the i-th power module as the main power module. At this time, the soft start circuit inside the i-th power module is closed. Taking the startup of the first power module, PM1, as an example, after the soft-start circuit within power module PM1 closes, the output power of the centralized auxiliary power supply 6 charges the bus capacitors Cd1 and Cd2 of power module PM1. The bidirectional inverter bridge converts the power from the bus capacitors into AC power to charge the AC-side capacitors Cfa, Cfb, and Cfc. The AC main switch is closed, completing the startup of power module PM1 and shutting down the centralized auxiliary power supply 6. The activated power module PM1 then performs PWM rectification on the grid input power to output a DC voltage, thereby establishing a DC voltage on the DC side of the inverter. This DC voltage charges the DC bus capacitors of the remaining power modules, PM2, PM3, and so on, providing startup energy for the remaining power modules. All power modules are then started sequentially, completing the inverter startup.

[0058] Generally speaking, the power provided by the centralized auxiliary power supply 6 is less than the starting energy required by multiple power modules. The centralized auxiliary power supply 6 only provides the starting power of some power modules and the power required by multiple distributed auxiliary power supplies. In this embodiment, taking 10 power modules as an example, the centralized auxiliary power supply 6 provides the open-loop no-load operating energy of one power module (such as PM1) and the energy of the distributed auxiliary power supplies in the 10 power modules. In this way, the volume and cost of the centralized auxiliary power supply 6 are optimized. For example, for a power module of about 100KW, the rated power of its distributed auxiliary power supply is about 100W, and the starting power or open-loop power required by the power module is about 2KW. Then, the rated power of the centralized auxiliary power supply 6 is set to about 3KW. The centralized auxiliary power supply 6 mainly includes a three-phase rectifier bridge, a relay and a heat sink. The three-phase rectifier bridge is mainly composed of diode devices and has low cost; the capacity of the relay is small (for example, less than 3KW in this embodiment) and the cost is relatively low. The cost of a centralized auxiliary power supply is approximately one-fifth of that of n AC-side distributed auxiliary power supplies and n AC-side soft-start circuits; the volume and structural complexity are also greatly reduced; and the centralized auxiliary power supply does not require high-frequency switching, has high reliability, and excellent EMC performance. Therefore, the solution of the present invention is far superior to the existing solution of n AC-side isolated auxiliary power supplies and n AC-side soft-start circuits inside n power modules. In addition, the three-phase rectifier bridge in the centralized auxiliary power supply is composed of diodes, which are easy to select and simple to control. Its structure and design are also superior to those of AC isolated auxiliary power supplies and AC soft-start circuits. The auxiliary circuit power supply device proposed in the present invention optimizes the auxiliary circuit of the inverter and is particularly suitable for architectures with multiple power modules connected in parallel.

[0059] In this embodiment, the inverter operates in a DC voltage source mode, converting the input AC power into DC power to power subsequent DC loads. When the inverter is started, the switch circuit of the centralized auxiliary power supply 6 is closed, and the uncontrolled rectifier circuit converts the AC input of the inverter into a first DC voltage and inputs it to the DC side of the inverter, powering multiple distributed auxiliary power supplies 4 and providing startup power for at least one power module. After at least one power module is started, the switch circuit is disconnected, and the centralized auxiliary power supply 6 stops working. The started power module converts the AC input of the inverter into a second DC voltage (for example, 750 to 1000V) and inputs it to the DC side of the inverter, powering multiple distributed auxiliary power supplies 4 and providing startup power for the remaining power modules. Among them, the power capacity of the centralized auxiliary power supply is much smaller than the power capacity of the power module, and has a smaller structure, lower cost, and simpler structure.

[0060] In grid-connected mode, when the battery is over-discharged, the DC side battery cannot be discharged when the inverter starts, and the DC voltage cannot be established. A centralized auxiliary power supply is required to provide DC voltage to complete the startup of the power module. Please refer to the description in Example 3 for details.

[0061] According to a preferred embodiment of the present invention, the inverter includes n power modules PM1, PM2, PM3, ..., PMn connected in parallel. The auxiliary power supply device comprises n soft-start circuits, n distributed auxiliary power supplies 4, and one centralized auxiliary power supply 6. Preferably, the auxiliary power supply device comprises n soft-start circuits, n distributed auxiliary power supplies 4, and two centralized auxiliary power supplies 6, which are connected in parallel to form a redundant structure.

[0062] According to another preferred embodiment of the present invention, Figure 8 As shown, the DC side of the inverter is coupled to an energy-consuming element. When the inverter is started, the centralized auxiliary power supply 6 supplies power to the multiple distributed auxiliary power supplies 4. Figure 5 As shown, the DC side of the inverter is coupled to an energy storage element, which supplies power to the multiple distributed auxiliary power sources 4.

[0063] According to another preferred embodiment of the present invention, when the DC side of the inverter is coupled to an energy storage element, the switch circuit remains disconnected; when the DC side of the inverter is coupled to an energy consumption element and the inverter is started, the switch circuit is closed, and the rectifier circuit 61 converts the AC side voltage of the inverter into a DC voltage to power the multiple distributed auxiliary power supplies 4.

[0064] like Figure 9 As shown, a method for starting an inverter is also provided, wherein the inverter includes: n power modules, which are connected in parallel; and a centralized auxiliary power supply 6, whose input end is coupled to the AC side of the inverter, and whose output end is coupled to the DC side of the inverter; wherein each of the power modules includes: a starting circuit, which is coupled in series to the DC end of the power module; and a distributed auxiliary power supply 4, whose input end is coupled between the starting circuit and the DC end of the power module, and the starting circuit includes a main switch and a soft start circuit connected in parallel.

[0065] The method comprises the following steps:

[0066] Establishing the DC side voltage of the inverter to supply power to the distributed auxiliary power supply 4;

[0067] Closing the soft start loops of the n power modules to establish the AC terminal voltages of the n power modules;

[0068] Close the AC end main switches of the n power modules.

[0069] According to another preferred embodiment of the present invention, establishing the DC side voltage of the inverter includes: determining whether the inverter operates in a DC voltage source mode; if so, establishing the DC side voltage of the inverter through the centralized auxiliary power supply 6.

[0070] According to another preferred embodiment of the present invention, when the inverter operates in a DC voltage source mode, the centralized auxiliary power supply 6 converts the AC input of the inverter into a first DC voltage and inputs the first DC voltage to the DC side of the inverter to supply power to the distributed auxiliary power supplies 4 of the n power modules;

[0071] Determine a power module to be started first, for example, the i-th power module, close the soft start circuit of the i-th power module, control the first DC voltage to charge the DC capacitor of the i-th power module, and the i-th power module converts the DC capacitor voltage into an AC voltage to charge the AC capacitor of the i-th power module;

[0072] The AC end main switch of the i-th power module is closed to complete the soft start of the i-th power module, and the centralized auxiliary power supply 6 stops working;

[0073] The i-th power module converts the AC input of the inverter into a second DC voltage and inputs the second DC voltage into the DC side of the inverter to provide energy required for starting the remaining n-1 power modules.

[0074] It is understandable that the i-th power module can be set to any one of the n power modules, such as the 1st power module, the 5th power module, and so on.

[0075] According to another preferred embodiment of the present invention, taking the power module PM1 as an example, the inverter startup method may specifically include the following steps:

[0076] i. First, the system auxiliary power supply 5 works, and then the system controller starts working, receiving a DC voltage source operating mode instruction;

[0077] ii. The system controller controls the first relay RL1 and the second relay RL2 to close (the two relays can achieve redundant isolation), and the rectifier bridge 61 outputs a first DC voltage to the DC port of the power modules PM1 to PMn, and the distributed auxiliary power supply 4 of all power modules starts working; thereafter, the ID is assigned between the power modules, and the power module PM1 to be started first is determined, and the DC soft start circuit of the power module PM1 is controlled to be closed. PM1 detects whether the voltage of the DC port is within a predetermined range, that is, PM1 detects whether the voltage of the DC port is an uncontrolled rectifier voltage;

[0078] iii. The soft start circuit inside PM1 works and charges the DC bus capacitor;

[0079] iv. PM1 phase-locks the grid voltage to obtain the angle value θ of the grid voltage on the AC side of the inverter;

[0080] v.PM1 starts the bidirectional inverter bridge in an open loop, converting the first DC voltage into an AC voltage to charge the AC CAP (Cfa / Cfb / Cfc);

[0081] vi. PM1 closes the main circuit AC relay, and PM1 completes startup; the PWM signal of the bidirectional inverter is blocked; the first relay RL1 and the second relay RL2 are disconnected, and the rectifier bridge 61 stops running;

[0082] vii. PM1 starts the DC voltage source mode and outputs a PWM signal to the bidirectional inverter bridge to control the switching operation of the bidirectional inverter. It rectifies the grid voltage into a second DC voltage and outputs it to the DC ports of power modules PM1 to PMn, establishing a DC voltage at all DC ports of PM1 to PMn.

[0083] According to another preferred embodiment of the present invention, after PM1 starts the DC voltage source mode, PM2 to PMn are started. Taking PM2 as an example, the process includes the following steps:

[0084] i. The soft start circuit inside PM2 closes and charges the DC bus capacitor;

[0085] ii. PM2 phase-locks the grid voltage to obtain the angle value θ of the AC side grid voltage;

[0086] iii. PM2 starts the bidirectional inverter bridge in an open loop, converting the second DC voltage into an AC voltage to charge the AC CAP (Cfa / Cfb / Cfc);

[0087] iv. PM2 closes the main circuit AC relay, and PM2 switches from open-loop inverter mode to DC voltage source mode.

[0088] The startup process for power modules PM3-PMn is similar to that for power module PM2 and is not detailed here. The first DC voltage is the uncontrolled rectifier voltage, and the second DC voltage is the output voltage of the power module. For a 220V grid, the first DC voltage is the peak line voltage of the uncontrolled rectifier voltage, typically ranging from 350-450V to mitigate the effects of grid fluctuations. The second DC voltage ranges from 750-1000V.

[0089] The present invention replaces the AC-side auxiliary power supply in all power modules by providing a centralized auxiliary power supply, while eliminating the AC-side soft-start circuit in all power modules. The auxiliary circuit in the power module only includes a DC auxiliary power supply and a DC soft-start circuit, which reduces the cost and volume of the power module. In addition, the inverter of the present invention can meet the requirements of grid-connected mode, independent mode, and DC voltage source mode, as well as basic insulation between the DC port and the AC power grid. In the present invention, the centralized auxiliary power supply is composed of relays and rectifier bridges, without high-frequency switching devices, with high reliability and better electromagnetic compatibility. At the same time, the auxiliary power supply loss is reduced. The centralized auxiliary power supply is always in a disconnected state when the inverter is working normally, which reduces the loss. Therefore, the cost, volume, loss, electromagnetic compatibility, etc. of the entire system are significantly improved.

[0090] Although the present invention has been disclosed above in terms of embodiments, this is not intended to limit the present invention. Anyone skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the appended claims.

Claims

1. An auxiliary power supply device for an inverter, wherein the inverter comprises a plurality of power modules connected in parallel, characterized in that: The auxiliary power supply device includes: A plurality of soft start circuits, each of the soft start circuits being coupled between the DC terminal of a corresponding power module and the conversion circuit; A plurality of distributed auxiliary power supplies, each having an input terminal coupled between a DC terminal of a corresponding power module and a soft start circuit; and A centralized auxiliary power supply has an input end coupled to the AC side of the inverter and an output end coupled to the DC side of the inverter.

2. The auxiliary power supply device for an inverter according to claim 1, characterized in that: A soft start loop and a distributed auxiliary power supply are provided inside each power module.

3. The auxiliary power supply device for an inverter according to claim 1, characterized in that: The centralized auxiliary power supply includes: a switch circuit, a first end of which is coupled to the AC side of the inverter; and The rectifier circuit has a first end coupled to the second end of the switch circuit and a second end coupled to the DC side of the inverter.

4. The auxiliary power supply device for an inverter according to claim 3, characterized in that: The switch circuit further includes a control terminal coupled to the control device of the inverter, so that the switch circuit is controlled by the control device.

5. The auxiliary power supply device for an inverter according to any one of claims 1 to 4, characterized in that: The auxiliary power supply device also includes a backup centralized auxiliary power supply to form a redundant configuration with the centralized auxiliary power supply.

6. The auxiliary power supply device for an inverter according to claim 3, characterized in that: The switching circuit includes a first AC relay and a second AC relay connected in series, and the rectifying circuit includes a three-phase rectifier bridge.

7. The auxiliary power supply device for an inverter according to any one of claims 1 to 4, characterized in that: The DC side of the inverter is coupled to an energy storage element, and the energy storage element supplies power to the multiple distributed auxiliary power sources.

8. The auxiliary power supply device for an inverter according to any one of claims 1 to 4, characterized in that: The DC side of the inverter is coupled to an energy-consuming element. When the inverter is started, the centralized auxiliary power supply supplies power to the multiple distributed auxiliary power supplies.

9. The auxiliary power supply device for an inverter according to claim 3, characterized in that: The DC side of the inverter is coupled to an energy storage element, and the switching circuit remains disconnected; or the DC side of the inverter is coupled to an energy consumption element. When the inverter is started, the switching circuit is closed, and the rectifier circuit converts the AC input of the inverter into a DC voltage and inputs it to the DC side of the inverter to power the multiple distributed auxiliary power supplies.

10. The auxiliary power supply device for an inverter according to claim 1 or 2, characterized in that: The inverter includes n power modules connected in parallel, and the auxiliary power supply device is composed of n soft start loops, n distributed auxiliary power supplies and one centralized auxiliary power supply.

11. An inverter comprising a plurality of power modules, wherein the AC ends of the plurality of power modules are coupled in parallel to form an AC side of the inverter, and the DC ends of the plurality of power modules are coupled in parallel to form a DC side of the inverter; characterized in that: The inverter further includes a centralized auxiliary power supply, the input end of which is coupled to the AC side of the inverter, and the output end of which is coupled to the DC side of the inverter; Wherein, each of the power modules comprises: a soft start circuit coupled to the DC terminal of the power module; and A distributed auxiliary power supply has an input terminal coupled between the soft start loop and the DC terminal of the power module.

12. The inverter according to claim 11, characterized in that The centralized auxiliary power supply includes: a switch circuit, a first end of which is coupled to the AC side of the inverter; and The rectifier circuit has a first end coupled to the second end of the switch circuit and a second end coupled to the DC side of the inverter.

13. The inverter according to claim 12, characterized in that: The switch circuit further includes a control terminal coupled to the control device of the inverter, so that the switch circuit is controlled by the control device.

14. The inverter according to claim 12, characterized in that The switching circuit includes a first AC relay and a second AC relay connected in series, and the rectifying circuit includes a three-phase rectifier bridge.

15. The inverter according to any one of claims 12 to 14, characterized in that: The DC side of the inverter is coupled to an energy-consuming element. When the inverter is started, the centralized auxiliary power supply supplies power to the multiple distributed auxiliary power supplies. Alternatively, the DC side of the inverter is coupled to an energy storage element. The energy storage element supplies power to the multiple distributed auxiliary power supplies.

16. The inverter according to claim 12, characterized in that: The DC side of the inverter is coupled to an energy storage element, and the switching circuit remains disconnected; or the DC side of the inverter is coupled to an energy consumption element, and when the inverter is started, the switching circuit is closed, and the rectifier circuit converts the AC side voltage of the inverter into a DC voltage to power the multiple distributed auxiliary power supplies.

17. A method for starting an inverter, characterized in that: The inverter includes: n power modules connected in parallel; and a centralized auxiliary power supply, whose input is coupled to the AC side of the inverter and whose output is coupled to the DC side of the inverter; wherein each power module includes: a soft start circuit coupled to the DC side of the power module; and a distributed auxiliary power supply, whose input is coupled between the soft start circuit and the DC side of the power module; The method comprises the following steps: Establishing a DC side voltage of the inverter to supply power to the distributed auxiliary power supply; Closing the soft start loops of the n power modules to establish an AC side voltage of the n power modules; Close the AC-side main switches of the n power modules.

18. The method for starting an inverter according to claim 17, wherein: The establishing of the DC side voltage of the inverter includes: determining whether the inverter operates in a DC voltage source mode; if so, establishing the DC side voltage of the inverter through the centralized auxiliary power supply.

19. The method for starting an inverter according to claim 18, wherein: When the inverter operates in a DC voltage source mode, the centralized auxiliary power supply converts the AC input of the inverter into a first DC voltage and inputs the first DC voltage to the DC side of the inverter to supply power to the distributed auxiliary power supplies of the n power modules; Closing the soft start circuit of the i-th power module, controlling the first DC voltage to charge the DC capacitor of the i-th power module, and the i-th power module converting the DC capacitor voltage into an AC voltage to charge the AC capacitor of the i-th power module; Closing the AC side main switch of the i-th power module to complete the soft start of the i-th power module, and stopping the centralized auxiliary power supply; The i-th power module converts the AC input of the inverter into a second DC voltage and inputs the second DC voltage to the DC side of the inverter to provide energy required for starting the remaining n-1 power modules.

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