Split-phase anti-countercurrent control method and system for three-phase inverter

Abstract

The invention discloses a split-phase anti-countercurrent control method and system for a three-phase inverter. The method comprises the following steps: acquiring output power, load power and grid-connected power of each phase of the three-phase inverter in real time; for each phase, calculating the difference between the load power and the output power, if the difference is less than or equal to 0, judging that the phase has countercurrent, and performing corresponding split-phase control; and if the difference is greater than 0, judging that the phase has a countercurrent trend, and carrying out corresponding split-phase control.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a phase-by-phase anti-reverse current control method and system for three-phase inverters. Background Technology

[0002] The problems of low voltage, heavy overload, and three-phase imbalance in power distribution systems are becoming increasingly serious. In the case of three-phase imbalance, the problem of local reverse current is prominent, which is one of the core pain points of existing energy storage technologies. The root cause is that the control logic has not broken through the limitation of "total three-phase power" and cannot adapt to the load imbalance conditions that are common in actual power grids.

[0003] Traditional solutions only monitor the total three-phase power or the total current at the grid connection point. When the load on one phase suddenly decreases while the loads on other phases remain normal, even if the total three-phase power does not exceed the limit, the lighter-loaded single phase may still experience reverse power transmission. For example, if the load on phase A drops from 30kW to 10kW, while the inverter's phase A output remains at 20kW, the total power may still be in a balanced state, but phase A has experienced 10kW of reverse current, causing a local voltage rise in the grid or triggering protection devices.

[0004] Some solutions upgrade to a three-phase four-wire system by introducing a neutral wire to cope with imbalance. However, due to the limitation of the bus capacitor capacity in the initial design, the capacitor cannot effectively absorb the extra current when the load is severely unbalanced, resulting in DC bus voltage fluctuations and even affecting the stable operation of the inverter. In essence, the core requirement of independent phase regulation has not been solved.

[0005] Traditional energy storage solutions can usually only meet the power dispatch control of three-phase total active and reactive power, and cannot control each phase separately, thus failing to effectively solve single-phase heavy overload and reverse current problems.

[0006] Traditional power quality equipment can only compensate for reactive power, failing to address active power issues. Furthermore, energy storage and power quality equipment cannot coordinate their control, leading to overcompensation and undercompensation problems. Therefore, a technology is needed that can control each phase separately and resolve issues such as reverse current and three-phase imbalance. Summary of the Invention

[0007] Purpose of the invention: To address the limitations of existing methods in phase-by-phase control and their inability to effectively resolve issues such as single-phase overload and reverse current, this invention proposes a phase-by-phase anti-reverse current control method and system for three-phase inverters. Focusing on the grid-connected control subfield of three-phase inverters, this invention provides precise phase-by-phase control for the anti-reverse current function of three-phase inverters in new energy power generation systems (such as photovoltaics and energy storage).

[0008] Technical solution: A phase-by-phase anti-reverse current control method for a three-phase inverter, comprising:

[0009] Real-time acquisition of output power, load power, and grid-connected power of each phase of the three-phase inverter;

[0010] For each phase, calculate the difference between the load power and the output power. If the difference is less than or equal to 0, it is determined that there is reverse current in that phase, and corresponding phase control is performed. If the difference is greater than 0, it is determined that there is a reverse current trend in that phase, and corresponding phase control is performed.

[0011] Furthermore, for the phase control where the difference is less than or equal to 0, the following are included:

[0012] Determine whether the difference between the absolute value of the grid-connected power and the set power is less than the set threshold. If it is less, reduce the output power of that phase until the absolute value of the grid-connected power equals the set power. If it is not less, cut off the output of that phase.

[0013] Furthermore, for the phase control where the difference is greater than 0, the following are included:

[0014] Determine whether the rate of change of the difference between the load power and the output power exceeds a threshold within a set time period. If the rate of change exceeds the threshold, it is determined that there is a reverse current trend in that phase, and the output power of that phase is reduced at a set rate.

[0015] Furthermore, the change threshold is 0.5 kW / ms.

[0016] Furthermore, the set rate is 80% of the rate of change of the difference between the load power and the output power within a set time period.

[0017] This invention proposes a phase-by-phase anti-reverse current control system for a three-phase inverter, comprising:

[0018] The calculation module is configured to: acquire the output power of each phase of the three-phase inverter, the load power, and the grid-connected power in real time;

[0019] The phase-separation control module is configured to: for each phase, calculate the difference between the load power and the output power; if the difference is less than or equal to 0, determine that there is reverse current in that phase and perform corresponding phase-separation control; if the difference is greater than 0, determine that there is a reverse current trend in that phase and perform corresponding phase-separation control.

[0020] Furthermore, in the phase-splitting control module, the phase-splitting control for the difference being less than or equal to 0 includes:

[0021] Determine whether the difference between the absolute value of the grid-connected power and the set power is less than the set threshold. If it is less, reduce the output power of that phase until the absolute value of the grid-connected power equals the set power. If it is not less, cut off the output of that phase.

[0022] Furthermore, in the phase-splitting control module, the phase-splitting control for the difference being greater than 0 includes:

[0023] Determine whether the rate of change of the difference between the load power and the output power exceeds a threshold within a set time period. If the rate of change exceeds the threshold, it is determined that there is a reverse current trend in that phase, and the output power of that phase is reduced at a set rate.

[0024] Furthermore, the change threshold is 0.5 kW / ms.

[0025] Furthermore, the set rate is 80% of the rate of change of the difference between the load power and the output power within a set time period. Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] (1) This invention breaks through the limitations of traditional total power control. By independently monitoring and adjusting each phase, a separate phase independent control system is established to realize the independent acquisition and calculation of voltage, current and power of each phase. It can accurately identify the reverse current state of a single phase or multiple phases. For the three-phase load difference (such as 30kW for phase A, 40kW for phase B and 20kW for phase C), the output power of each phase inverter can be adjusted differently to ensure that the phase with lighter load does not have reverse power transmission. It completely solves the problem of three-phase total power balance but single-phase reverse current. It is suitable for typical unbalanced load scenarios such as industrial and commercial and civil use, and ensures that there is no local reverse power transmission in each phase.

[0027] (2) By using the reverse flow trend prediction mechanism, the present invention moves the control node from "already reversed" to "will reverse", which shortens the response time by more than 50% compared with the traditional solution and avoids short-term reverse flow exceeding the standard;

[0028] (3) The graded adjustment strategy of the present invention reduces frequent power fluctuations and controls the oscillation amplitude within ±1% of the rated power, which is far better than the ±5% of the traditional solution, ensuring the stability of local load power supply. Attached Figure Description

[0029] Figure 1 This is a flowchart of a phase-by-phase anti-reverse flow control method for a three-phase inverter proposed in this invention. Detailed Implementation

[0030] The technical solution of the present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0031] Example 1:

[0032] This invention proposes a phase-by-phase anti-reverse current control method for three-phase inverters, such as... Figure 1 As shown, the main steps include:

[0033] Step 1: Simultaneously collect the output current, output voltage, load power, and grid-connected power of each phase at the inverter's output terminal, load terminal, and grid connection point;

[0034] Step 2: Filter the collected output current, output voltage, load power, and grid-connected power for each phase to remove interference signals and calibrate the grid voltage phase to ensure data accuracy. Calculate the output power based on the output current and output voltage.

[0035] Step 3: For each phase, calculate the difference between the load power and the output power. If the difference is ≤0, it is determined that there is reverse current in that phase, and corresponding phase control is performed. If the difference is greater than 0, it is determined that there is a reverse current trend in that phase, and corresponding phase control is performed.

[0036] In this embodiment of the invention, the phase control when the difference is less than or equal to 0 includes:

[0037] Determine whether the difference between the absolute value of the grid-connected power and the set power is less than the set threshold. If it is less, reduce the output power of that phase until the absolute value of the grid-connected power equals the set power. If it is not less, cut off the output of that phase.

[0038] In other words, if there is reverse current and the risk is high (the difference between the absolute value of the grid-connected power and the set power is greater than the set threshold): immediately cut off the output of that phase; if there is reverse current but the risk is low (the difference between the absolute value of the grid-connected power and the set power is less than the set threshold): reduce the load power of that phase proportionally to eliminate the reverse current.

[0039] In this embodiment of the invention, the phase control when the difference is greater than 0 includes: determining whether the rate of change of the difference between the load power and the output power exceeds a change threshold within a set time period, and reducing the output power of that phase at a set rate only when the change threshold is exceeded.

[0040] In other words, when there is a reverse flow trend, the load power should be reduced slowly to block the reverse flow in advance.

[0041] This invention, through phase-by-phase independent monitoring and adjustment, establishes a phase-by-phase independent control system to achieve independent acquisition and calculation of voltage, current, and power for each phase. It accurately identifies the reverse current state of a single or multiple phases. For three-phase load differences (e.g., 30kW for phase A, 40kW for phase B, and 20kW for phase C), the output power of each phase inverter can be adjusted differently to ensure that the phase with a lighter load does not experience reverse power transmission, thus completely solving the problem of balanced total three-phase power but single-phase reverse current.

[0042] Example 2:

[0043] This invention proposes a phase-by-phase anti-reverse current control method for three-phase inverters, which mainly includes the following steps:

[0044] At the inverter's output, load, and grid connection points, the output current, output voltage, load current, and grid-connected power of each phase are collected every 52µs. After filtering, these data are transmitted to the main control unit.

[0045] The main control unit calculates the difference between the load power of each phase and the output power in real time to determine whether there is reverse flow or reverse flow trend.

[0046] If the difference between the load power and the output power of phase B is less than or equal to 0, it is determined that phase B has reverse current. When the absolute value of the grid-connected power is much greater than the set power, it is determined to be high risk. At this time, the main control unit immediately cuts off the output of phase B. If the absolute value of the grid-connected power is close to the set power, it is determined to be low risk. Then, the output power of phase B is reduced proportionally until the difference between it and the set power is a small positive value (such as 50W) to eliminate reverse current.

[0047] Assuming that the difference between the load power and the output power of phase C is greater than 0, but the difference between the load power and the output power of phase C decreases rapidly (slope < -0.5kW / ms), it is determined that phase C has a reverse current trend. At this time, the main control unit slowly reduces the load power of phase C (at a rate of 80% of the slope) to block the reverse current in advance.

Claims

1. A split-phase anti- reverse flow control method for a three-phase inverter, characterized by: The method comprises: real-time acquisition of output power of each phase of a three-phase inverter, load power and grid-connected power; for each phase, calculating a difference between the load power and the output power, and if the difference is less than or equal to 0, determining that reverse current exists in the phase and performing corresponding phase-by-phase control; if the difference is greater than 0, determining that reverse current trend exists in the phase and performing corresponding phase-by-phase control.

2. The split-phase anti- freewheeling control method for a three-phase inverter according to claim 1, wherein: For the phase-by-phase control with the difference less than or equal to 0, the method comprises: judging whether a difference between an absolute value of the grid-connected power and a set power is less than a set threshold, and if yes, reducing the output power of the phase until the absolute value of the grid-connected power is equal to the set power, and if no, cutting off the output of the phase.

3. The split-phase anti-inrush control method for a three-phase inverter of claim 1, wherein: For the phase-by-phase control with the difference greater than 0, the method comprises: judging whether a change rate of the difference between the load power and the output power exceeds a change threshold within a set time period, and only when the change rate exceeds the change threshold, determining that reverse current trend exists in the phase and reducing the output power of the phase at a set rate.

4. The split-phase anti-inrush control method for a three-phase inverter of claim 3, wherein: The change threshold is 0.5 kW / ms.

5. The split-phase anti-inrush control method for a three-phase inverter of claim 3, wherein: The set rate is 80% of the change rate of the difference between the load power and the output power within the set time period.

6. A split-phase anti- reverse flow control system for a three-phase inverter, characterized by: The method comprises: a calculation module configured to acquire output power of each phase of a three-phase inverter, load power and grid-connected power in real time; a phase-by-phase control module configured to, for each phase, calculate a difference between the load power and the output power, and if the difference is less than or equal to 0, determine that reverse current exists in the phase and perform corresponding phase-by-phase control; if the difference is greater than 0, determine that reverse current trend exists in the phase and perform corresponding phase-by-phase control.

7. A split-phase anti- reverse flow control system for a three-phase inverter as claimed in claim 6, wherein: In the phase-by-phase control module, for the phase-by-phase control with the difference less than or equal to 0, the method comprises: judging whether a difference between an absolute value of the grid-connected power and a set power is less than a set threshold, and if yes, reducing the output power of the phase until the absolute value of the grid-connected power is equal to the set power, and if no, cutting off the output of the phase.

8. A split-phase anti- reverse flow control system for a three-phase inverter as claimed in claim 6, wherein: In the phase-by-phase control module, for the phase-by-phase control with the difference greater than 0, the method comprises: judging whether a change rate of the difference between the load power and the output power exceeds a change threshold within a set time period, and only when the change rate exceeds the change threshold, determining that reverse current trend exists in the phase and reducing the output power of the phase at a set rate.

9. A split-phase anti- reverse flow control system for a three-phase inverter as claimed in claim 8, wherein: The change threshold is 0.5 kW / ms.

10. The split-phase anti- reverse flow control method for a three-phase inverter according to claim 8, wherein: The set rate is 80% of the change rate of the difference between the load power and the output power within the set time period.

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