A us off-grid inverter

Abstract

The utility model provides a kind of UL off-grid inverter, belong to inverter technical field, it includes, DC / DC step-up and step-down circuit, for completing battery step-up and step-down, voltage equalizing circuit, for ensuring that two-phase voltage amplitude of inverter is symmetrical, output zero line is taken to DC bus midpoint, two-phase three-level inverter circuit, for output specified AC voltage, by DC / DC step-up and step-down circuit and voltage equalizing circuit cooperation, make DC input first through high-frequency isolation step-up and step-down, positive and negative bus keep symmetry, common-mode noise is greatly reduced, electromagnetic compatibility is better, two-phase inverter bridge and LC filter combination after output voltage harmonic is extremely low, power quality meets UL off-grid requirement, L1 and L2 end with same neutral point N as reference, can software setting zero degree cophasal parallel output 120V large current, or 180 ° split-phase output 240V, hardware does not need additional transformer or switch, volume weight reduces, cost drops accordingly.

Description

Technical Field

[0001] This utility model belongs to the field of inverter technology, specifically relating to an American standard off-grid inverter. Background Technology

[0002] In off-grid scenarios such as residential energy storage and RVs, the US standard single-phase three-wire (L1-L2-N) inverter requires the inverter to simultaneously provide both 120Vac and 240Vac voltage levels to meet the needs of different household loads. Traditional US standard off-grid inverters typically use a fixed 120Vac single-phase two-wire output. When users need to drive European standard or industrial equipment with 220Vac to 240Vac, an additional three-tapped power frequency step-up transformer must be connected in series at the back end of the inverter. While this approach can increase the voltage level, it brings the following significant drawbacks: reduced efficiency (copper and iron losses of the transformer itself reduce the overall conversion efficiency by 5% to 8%), increased size and weight (the power frequency transformer is bulky, which is not conducive to portable or vehicle applications), increased cost (the additional transformer and its associated heat dissipation and mounting structure increase the overall cost by approximately 20% to 30%), complex wiring (users need to manually switch transformer taps according to the load type, which is inconvenient and prone to misconnection), no redundancy, transformer failure results in complete unit failure, long maintenance cycles, and poor system reliability. Utility Model Content

[0003] The purpose of this invention is to provide an American standard off-grid inverter, which aims to solve the problems raised in the background art.

[0004] A US standard off-grid inverter includes,

[0005] DC / DC step-up / step-down circuit, used to complete the battery step-up / step-down conversion;

[0006] The voltage equalization circuit is used to ensure that the voltage amplitudes of the two phases of the inverter are symmetrical, and the output neutral line is taken from the midpoint of the bus.

[0007] A two-phase three-level inverter circuit is used to output a specified AC voltage;

[0008] The DC / DC step-up / step-down circuit and the voltage equalization circuit are electrically connected, and the voltage equalization circuit is electrically connected to the two-phase three-level inverter circuit.

[0009] Furthermore, the DC / DC step-up / step-down circuit includes power switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8, a capacitor C1, and a transformer T1. Power switches Q1, Q2, Q3, and Q4 form a first H-bridge, and power switches Q5, Q6, Q7, and Q8 form a second H-bridge. Two ends of the first H-bridge are electrically connected to the two ends of the transformer T1. One output terminal of the transformer T1 is electrically connected to one end of the capacitor C1. The remaining output terminal of the transformer T1 is electrically connected to one end of the second H-bridge, and the other end of the capacitor C1 is electrically connected to the second H-bridge.

[0010] Furthermore, the voltage equalization circuit includes power switch Q9, power switch Q10, inductor L1, capacitor C2, and capacitor C3. One end of power switch Q9 and power switch Q1 are electrically connected to the two ends of the second H-bridge, and the remaining end of power switch Q9 and power switch Q1 is electrically connected to one end of inductor L1. The other end of inductor L1 is electrically connected to the parallel connection of one end of capacitor C2 and capacitor C3.

[0011] Furthermore, the two-phase three-level inverter circuit includes power switches Q11, Q12, Q13, Q14, Q15, Q16, Q17, and Q18, inductors L2 and L3, and capacitors C4 and C5. Power switches Q11, Q12, Q13, and Q14 form a third H-bridge, and power switches Q15, Q16, Q17, and Q18 form a freewheeling bridge. The third H-bridge has two ends electrically connected to the two ends of the freewheeling bridge arm. One end of the freewheeling bridge arm is electrically connected to one end of inductor L1. The two ends of the freewheeling bridge arm are respectively electrically connected to one end of inductor L2 and inductor L3. The other end of inductor L2 is electrically connected to one end of capacitor C4. The other end of inductor L3 is electrically connected to one end of capacitor C5. The other ends of capacitors C4 and C5 are connected in parallel. The parallel connection of capacitors C4 and C5 is electrically connected to one end of the freewheeling bridge arm. The two ends of the third H-bridge are respectively electrically connected to one end of capacitors C2 and C3.

[0012] Furthermore, one end of the inductor L2 is designated as the L1 terminal, one end of the inductor L3 is designated as the L2 terminal, and the parallel connection of the capacitors C4 and C5 is designated as the N terminal.

[0013] Furthermore, in the two-phase three-level inverter circuit, the L1 terminal to the N terminal is 120Vac, and the L2 terminal to the N terminal is 120Vac. The phase relationship between the L1 terminal and the L2 terminal is set. When it is set to 0 degrees, the L1 terminal and the L2 terminal can be connected in parallel for output, and the inverter outputs a US standard single-phase 120Vac voltage. When it is set to 180 degrees, the L1 terminal and the L2 terminal output in split phase, that is, the L1 terminal to the L2 terminal is 240Vac.

[0014] Compared with the prior art, the beneficial effects of this utility model are:

[0015] This ASME standard off-grid inverter utilizes a DC / DC step-up / step-down circuit and a voltage equalization circuit to ensure that the DC input is first isolated at high frequency and then precisely divided, maintaining symmetry between the positive and negative buses, significantly reducing common-mode noise, and improving electromagnetic compatibility. The two-phase inverter bridge combined with an LC filter results in extremely low output voltage harmonics, meeting ASME standard off-grid power quality requirements. With L1 and L2 terminals referencing the same neutral point N, it can be software-configured to output a 120V high-current parallel connection at zero degrees of in-phase operation, or a 240V output at 180° reverse phase splitting. No additional transformer or switch is required in the hardware. The reduced weight leads to lower costs. The midpoint of the filter capacitor serves as the neutral line, performing both filtering and bus voltage equalization. Component reuse is high, power density is increased, and the full-bridge DC / DC circuit with a high-frequency transformer enables bidirectional lossless energy flow between the battery and the bus. The switching between grid-connected charging and off-grid discharging is rapid, and it is compatible with multiple battery voltage platforms. In the event of a fault in any bridge arm, the remaining portion can still operate at half power. The modular structure facilitates maintenance and expansion, making it suitable for off-grid scenarios such as RVs and outdoor energy storage, extending battery life and improving system reliability and flexibility. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0017] Figure 1 This is the overall circuit diagram of this utility model;

[0018] Figure 2 This is a schematic diagram of the present invention when the phase difference between L1 and L2 is set to 0°.

[0019] Figure 3 This is a schematic diagram of the present invention when the phase difference between L1 and L2 is set to 180°.

[0020] In the diagram: 1. DC / DC step-up / step-down circuit; 2. Voltage equalization circuit; 3. Two-phase three-level inverter circuit. Detailed Implementation

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

[0022] In the description of this utility model, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0024] Please see Figure 1-3 The technical solution provided in this embodiment is as follows:

[0025] A US standard off-grid inverter includes,

[0026] DC / DC step-up / step-down circuit 1 is used to complete the battery step-up / step-down conversion;

[0027] Voltage equalization circuit 2 is used to ensure the symmetrical amplitude of the two-phase inverter voltages, and the output neutral line is taken from the midpoint of the bus.

[0028] Two-phase three-level inverter circuit 3 is used to output a specified AC voltage;

[0029] The DC / DC step-up / step-down circuit 1 is electrically connected to the voltage equalization circuit 2, and the voltage equalization circuit 2 is electrically connected to the two-phase three-level inverter circuit 3.

[0030] In a specific embodiment of this invention, the DC / DC step-up / step-down circuit 1 and the voltage equalization circuit 2 work together to achieve efficient and stable voltage division of the input DC voltage, ensuring symmetrical amplitude of the positive and negative bus voltages, thereby effectively suppressing common-mode interference and improving system electromagnetic compatibility. Simultaneously, the two-phase three-level inverter circuit 3 adopts a combination of a dual H-bridge structure and an LC filter circuit, significantly reducing output voltage harmonic distortion and meeting the stringent power quality requirements of US standards for off-grid inverters. Furthermore, by flexibly setting the phase relationship between L1 and L2, this inverter can seamlessly switch between single-phase 120Vac parallel output and 240Vac split-phase output modes, compatible with the diverse load requirements of US standard single-phase three-wire residential systems, without the need for additional transformers or switching switches, simplifying system design and reducing costs. In off-grid applications (such as RVs and outdoor energy storage systems), this inverter can efficiently utilize battery pack energy. The DC / DC step-up / step-down circuit 1 supports bidirectional energy flow for grid-connected charging and off-grid discharging, extending battery life. Its modular design also facilitates later maintenance and expansion.

[0031] Specifically, the DC / DC step-up / step-down circuit 1 includes power switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8, capacitor C1, and transformer T1. Power switches Q1, Q2, Q3, and Q4 form a first H-bridge, and power switches Q5, Q6, Q7, and Q8 form a second H-bridge. Two ends of the first H-bridge are electrically connected to the two ends of transformer T1. One output terminal of transformer T1 is electrically connected to one end of capacitor C1. The remaining output terminal of transformer T1 is electrically connected to one end of the second H-bridge, and the other end of capacitor C1 is electrically connected to the second H-bridge.

[0032] In a specific embodiment of this invention, high-efficiency bidirectional energy flow is achieved using a full-bridge synchronous (Q1-Q8) + high-frequency transformer T1, enabling lossless bidirectional energy transfer between the battery side and the bus side. The efficiency is ≥96%, the charge / discharge switching time is <10ms, and it offers wide input voltage adaptability. By adjusting the transformer turns ratio and duty cycle, it is compatible with 36V~64V (lead-acid) or 40V~58V (lithium-ion) battery packs, eliminating the need for an external DC-DC boost module. For electrical isolation and protection, the high-frequency transformer T1 provides ≥3kV isolation withstand voltage, blocking ground fault current. The power switching bridge Q1-Q8 features reverse-parallel MOSFET power switches, naturally preventing reverse current flow and eliminating the need for additional reverse-current protection MOSFETs.

[0033] Specifically, the voltage equalization circuit 2 includes power switch Q9, power switch Q10, inductor L1, capacitor C2 and capacitor C3. One end of power switch Q9 and power switch Q1 are electrically connected to the two ends of the second H bridge, respectively. The remaining end of power switch Q9 and power switch Q1 is electrically connected to one end of inductor L1, and the other end of inductor L1 is electrically connected to the parallel terminal of one end of capacitor C2 and capacitor C3.

[0034] In a specific embodiment of this utility model, the symmetrical bus is automatically balanced. Q9, Q10 and inductor L1 form a Buck-Boost voltage equalization branch, which detects the bus midpoint voltage deviation in real time and dynamically compensates ≤±1%, ensuring symmetrical inverter bridge arm voltage, stable neutral line potential, reducing DC component, suppressing DC bias caused by power device parameter discrepancies or load asymmetry, avoiding transformer / inductor saturation, extending the life of magnetic components, and having a simple structure. The voltage equalization function is completed with only two power switching transistors, one inductor and two capacitors. Compared with the traditional dual-Buck voltage equalization scheme, the number of components is reduced by 50% and the power density is increased.

[0035] Specifically, the two-phase three-level inverter circuit 3 includes power switches Q11, Q12, Q13, Q14, Q15, Q16, Q17, and Q18, inductors L2 and L3, and capacitors C4 and C5. Power switches Q11, Q12, Q13, and Q14 form the third H-bridge, while power switches Q15, Q16, Q17, and Q18... The three H-bridges are connected to the two ends of the freewheeling bridge arm. One end of the freewheeling bridge arm is connected to one end of inductor L1. The two ends of the freewheeling bridge arm are connected to one end of inductor L2 and inductor L3, respectively. The other end of inductor L2 is connected to one end of capacitor C4. The other end of inductor L3 is connected to one end of capacitor C5. The other ends of capacitors C4 and C5 are connected in parallel. The parallel connection of capacitors C4 and C5 is connected to one end of the freewheeling bridge arm. The two ends of the three H-bridges are connected to one end of capacitors C2 and C3, respectively.

[0036] In a specific embodiment of this utility model, dual-mode flexible output is provided: 120Vac / 30A (single-phase high current) in 0° parallel mode and 240Vac / 15A (split-phase power supply) in 180° split-phase mode, with one-button switching, compatible with all types of US standard household sockets. Low THD and high voltage regulation accuracy are achieved through a three-level H-bridge + LC filter (L2-L3 / C4-C5) reducing THD to <3% and load regulation rate ≤±1%, meeting UL1741 and IEEE1547 requirements for harmonics and voltage regulation in off-grid inverters. Modular redundant design allows for separate arrangement of the H-bridge and filter, enabling independent replacement; in the event of a fault in any bridge arm, the remaining bridge arms can still operate at half power, improving system availability.

[0037] Specifically, one end of inductor L2 is designated as L1, one end of inductor L3 is designated as L2, and the parallel connection of capacitors C4 and C5 is designated as N.

[0038] In a specific embodiment of this utility model, the midpoint of the filter capacitor is directly used as the N line, eliminating the need for a power frequency isolation transformer or neutral line reactor. This reduces weight and cost, and avoids the additional voltage drop and loss caused by the neutral line reactor.

[0039] Dual 120V symmetrical output, compatible with 120 / 240V US standard systems. L1-N and L2-N are each 120V, with phase separation of 0° (120V / high current) or 180° (L1-L2=240V). One set of hardware can cover all US standard household socket requirements without the need for an external switching switch. Shortest common-mode circuit, excellent EMI performance. The N terminal is directly connected to the midpoint of the DC bus, forming the shortest common-mode return path, reducing common-mode voltage dv / dt. Combined with LC filtering, conducted EMI can be attenuated by more than 10dB, making it easier to pass FCC Part 15B. Filtering and voltage equalization: the structure reuses capacitors C4 and C5, which serve as both inverter bridge output filter capacitors and voltage divider capacitors in voltage equalization circuit 2, achieving "one capacitor for two purposes," reducing component count and increasing power density by approximately 15%.

[0040] Specifically, in the two-phase three-level inverter circuit 3, the L1 terminal to the N terminal is 120Vac, and the L2 terminal to the N terminal is 120Vac. The phase relationship between the L1 terminal and the L2 terminal is set. When it is set to 0 degrees, the L1 terminal and the L2 terminal can be connected in parallel for output, and the inverter outputs a US standard single-phase 120Vac voltage. When it is set to 180 degrees, the L1 terminal and the L2 terminal output in split phase, that is, the L1 terminal to the L2 terminal is 240Vac.

[0041] In a specific embodiment of this utility model, the same power circuit can seamlessly switch between 120Vac parallel connection and 240Vac phase splitting under software control, without the need for external relays or transformer reconfiguration, reducing the number of components and size by 15%–20%.

[0042] Working principle:

[0043] Step 1: DC Input and Bidirectional Energy Conversion

[0044] The battery pack DC power (36–64V lead-acid or 40–58V lithium battery) input DC / DC buck-boost circuit.

[0045] An isolated dual full-bridge circuit (Q1-Q8 + transformer T1) uses a high-frequency transformer (1:10 ratio) to boost the voltage, generating a high-voltage DC bus (e.g., a ±200V symmetrical bus). Synchronization technology achieves a conversion efficiency of ≥96% and a charge / discharge mode switching time of <10ms.

[0046] Energy can flow in both directions: when off-grid, it discharges to power the load; when on-grid, it charges the battery in reverse.

[0047] Step 2: Voltage Equalization Control of Positive and Negative Busbars

[0048] The high-voltage DC bus enters the voltage equalization circuit.

[0049] The Buck-Boost voltage equalization branch (Q9-Q10 + inductor L1) detects the bus midpoint voltage deviation in real time and dynamically adjusts the charge distribution of capacitors C2 and C3 to control the voltage imbalance within ≤±1%.

[0050] The bus midpoint is directly used as the output neutral line (N terminal), eliminating the need for an additional neutral line reactor and reducing losses.

[0051] Step 3: Dual-mode inverter output

[0052] After equalization, the DC power is input to the two-phase three-level inverter circuit, and H-bridge inversion is performed by the third H-bridge and the freewheeling bridge arms (Q11-Q18).

[0053] Phase setting determines the output mode:

[0054] 0° Parallel mode: L1 and L2 are in phase, and the parallel output is a single-phase 120Vac (e.g., 30A high current), which is suitable for American standard sockets.

[0055] 180° split-phase mode: L1 and L2 are out of phase, output 240Vac(L1-L2)+120Vac(L1 / L2-N), compatible with US standard three-wire electrical appliances (such as dryers).

[0056] The LC filter (L2-L3 / C4-C5) suppresses the output voltage harmonic distortion (THD) to <3% and the load regulation rate to ≤±1%.

[0057] Step 4: Flexible Switching and Compatibility

[0058] Users set the phase difference (0° or 180°) via the display screen, and the software controls the inverter bridge drive signal to achieve seamless switching of output modes without the need for external transformers or mechanical switches.

[0059] Filter capacitors C4 and C5 are reused as voltage equalization and voltage divider capacitors, reducing the number of components and increasing power density by 15%.

[0060] Step 5: Fault Redundancy and Protection

[0061] Modular design: If any inverter arm fails, the remaining arms can operate at half power.

[0062] Safety isolation: The high-frequency transformer provides ≥3kV electrical isolation to block grounding faults; the power switch bridge naturally prevents reverse current injection.

[0063] Finally, it should be noted that the above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A US standard off-grid inverter, characterized in that, include, DC / DC step-up / step-down circuit (1) is used to complete the battery step-up / step-down conversion; The voltage equalization circuit (2) is used to ensure that the voltage amplitude of the two phases of the inverter is symmetrical, and the output neutral line is taken to the midpoint of the bus. A two-phase three-level inverter circuit (3) is used to output a specified AC voltage; The DC / DC step-up / step-down circuit (1) is electrically connected to the voltage equalization circuit (2), and the voltage equalization circuit (2) is electrically connected to the two-phase three-level inverter circuit (3).

2. The American standard off-grid inverter according to claim 1, characterized in that, The DC / DC step-up / step-down circuit (1) includes power switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, capacitor C1, and transformer T1. Power switches Q1, Q2, Q3, and Q4 form a first H-bridge, and power switches Q5, Q6, Q7, and Q8 form a second H-bridge. Two ends of the first H-bridge are electrically connected to the two ends of transformer T1. One output terminal of transformer T1 is electrically connected to one end of capacitor C1. The remaining output terminal of transformer T1 is electrically connected to one end of the second H-bridge, and the other end of capacitor C1 is electrically connected to the second H-bridge.

3. The American standard off-grid inverter according to claim 2, characterized in that, The voltage equalization circuit (2) includes a power switch Q9, a power switch Q10, an inductor L1, a capacitor C2, and a capacitor C3. One end of the power switch Q9 and the power switch Q1 are electrically connected to the two ends of the second H-bridge, and the remaining end of the power switch Q9 and the power switch Q1 is electrically connected to one end of the inductor L1. The other end of the inductor L1 is electrically connected to one end of the parallel connection of the capacitors C2 and C3.

4. The American standard off-grid inverter according to claim 3, characterized in that, The two-phase three-level inverter circuit (3) includes power switches Q11, Q12, Q13, Q14, Q15, Q16, Q17, and Q18, inductors L2 and L3, and capacitors C4 and C5. Power switches Q11, Q12, Q13, and Q14 form a third H-bridge, and power switches Q15, Q16, Q17, and Q18 form a freewheeling bridge arm. The two ends of the third H-bridge are electrically connected to the two ends of the freewheeling bridge arm. One end of the freewheeling bridge arm is electrically connected to one end of inductor L1. The two ends of the freewheeling bridge arm are respectively electrically connected to one end of inductor L2 and inductor L3. The other end of inductor L2 is electrically connected to one end of capacitor C4. The other end of inductor L3 is electrically connected to one end of capacitor C5. The other ends of capacitors C4 and C5 are connected in parallel. The parallel connection of capacitors C4 and C5 is electrically connected to one end of the freewheeling bridge arm. The two ends of the third H-bridge are respectively electrically connected to one end of capacitors C2 and C3.

5. A Delta off-grid inverter as claimed in claim 4, wherein, One end of the inductor L2 is designated as L1, one end of the inductor L3 is designated as L2, and the parallel connection of the capacitors C4 and C5 is designated as N.

6. A Delta off-grid inverter as claimed in claim 5, wherein, The L1 terminal of the two-phase three-level inverter circuit (3) is 120Vac to the N terminal, and the L2 terminal is 120Vac to the N terminal. The phase relationship between the L1 terminal and the L2 terminal is set. When it is set to 0 degrees, the L1 terminal and the L2 terminal can be connected in parallel for output, and the inverter outputs a US standard single-phase 120Vac voltage. When it is set to 180 degrees, the L1 terminal and the L2 terminal are split phase output, that is, the L1 terminal is 240Vac to the L2 terminal.

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