Balancing system for a three-phase grid

Abstract

Method (100) for balancing an undervoltage three-phase electrical grid, the method comprising, for each phase: obtaining (110) voltage values and average voltage values; calculating (120) balance coefficients based on the voltage values and the average voltage values; calculating (130) an overvoltage unbalance threshold and an undervoltage unbalance threshold based on the balance coefficients; identifying (140) at least one overvoltage phase if the balance coefficients in said phase are above the overvoltage unbalance threshold; identifying (150) at least one undervoltage phase if the balance coefficients in said phase are below the undervoltage unbalance threshold; injecting power to the at least one undervoltage phase and absorbing power from the at least one overvoltage phase.

Description

[0001] BALANCING SYSTEM

[0002] DESCRIPTION

[0003] Object of the invention

[0004] The present invention relates to a method and system for balancing a low-voltage three-phase electrical network.

[0005] The system for balancing a low-voltage three-phase electrical network falls within the electrical and industrial distribution sector.

[0006] The system for balancing a three-phase electrical network has been specifically designed for use in three-phase low-voltage networks with neutral, which exhibit load imbalance between phases, with an unequal load between phases.

[0007] Background of the invention

[0008] The imbalance of electrical networks occurs when loads are unevenly distributed among the phases of the electrical network, either when there is distributed generation in a network and at some points current is injected into one of the phases of the network.

[0009] Due to the imbalance, voltage imbalance problems can occur, causing some phases to have a higher voltage than nominal, and other phases to have a lower voltage than nominal.

[0010] Furthermore, unbalanced networks are often very inefficient due to wiring losses. This is because, when an imbalance exists, some phases carry more current than others, and due to the resistivity of the wiring, this current difference causes an increase in resistive losses that are proportional to the square of the current. Currently, there are different systems on the market for balancing electrical networks, such as the use of zigzag transformers. However, the zigzag transformer-based system is entirely passive and cannot be controlled. It also has a large reactive power component that reduces the network's efficiency.

[0011] EP2672603A1 describes procedures relating to other ways of balancing an electrical network such as shifting loads between phases to balance the network. This methodology has disadvantages, such as the need for a large number of devices, synchronization difficulties between switching devices, and micro-cuts during switching.

[0012] Therefore, there is a demand for a balancing system that addresses the shortcomings of the state of the art, especially with the growing number of users injecting power into the electrical grid using different generation technologies, coupled with new consumption profiles with higher energy requirements, such as electric vehicle chargers, which are also in an expansion phase.

[0013] The present invention satisfies this need in the new electrical scenario.

[0014] Description of the invention

[0015] By using the phase balancing procedure according to the present invention, the current between the different phases is equalized. This is achieved by constantly monitoring the voltage at an undetermined point in the network. Due to the network impedance, a difference in current between the phases will cause a voltage difference between them, i.e., an imbalance.

[0016] Thus, in a first aspect, the present invention relates to a method for balancing a three-phase low-voltage electrical network. The method comprises, for each phase, obtaining voltage and average voltage values, calculating balancing coefficients based on the voltage and average voltage values, calculating an overvoltage imbalance threshold and an undervoltage imbalance threshold based on the balancing coefficients, identifying at least one phase with excess voltage if the balancing coefficients in that phase are above the overvoltage imbalance threshold, and absorbing power from the at least one phase with excess voltage.

[0017] Identify at least one phase with low voltage if the balancing coefficients in that phase are below the low voltage imbalance threshold and inject the absorbed power in phase to the at least one phase with low voltage; or inject the absorbed power with a phase shift of [-0.8 to 0.8] to the at least one phase with low voltage.

[0018] Alternatively, the method also allows the absorbed power to be dissipated through one or more loads.

[0019] Reactive power is generated at the time of injection. To generate reactive power, the current must be injected at a phase angle.

[0020] Reactive power differs from active power primarily in its phase shift angle. Reactive power is power that circulates but is not utilized. The balancing system works, in the first instance, by generating active power flows, but it can also generate "less efficient" power flows by injecting reactive power. This expands the balancing capacity range because, in addition to the power transferred between phases, it can also utilize the loss or improvement in efficiency in at least one of the phases to raise or lower the voltage level in the low-voltage network phases. Regarding the phase shift range, this can be expressed as a power factor from -0.8 to +0.8.

[0021] In a first example, the power injected into at least one phase with low voltage is obtained from the power absorbed from the at least one phase with excess voltage.

[0022] In another example, obtaining voltage values ​​and average voltage values ​​involves monitoring voltage values ​​in real time with a sampling frequency of at least one hertz. In another example, absorbing power from the overvolted phase involves calculating an injection power through iterative calculation to reduce the voltage of that phase to the average voltage values.

[0023] In another example, injecting power into the low-voltage phase involves calculating an injection power by means of iterative calculation to raise the voltage of that phase to the average voltage values.

[0024] In another example, identifying a phase with excess voltage if the balancing coefficients in that phase are above the overvoltage imbalance threshold involves generating an automatic alert.

[0025] In another example, identifying a phase with low voltage if the balancing coefficients in that phase are below the low voltage imbalance threshold involves generating an automatic alert.

[0026] A second aspect of the invention relates to a balancing system for a low-voltage three-phase electrical network. The balancing system comprises a control system that stores instructions for executing the method according to the first aspect of the invention.

[0027] The balancing system comprises at least one switching matrix configured to switch one or more overvoltage phases to one or more undervoltage phases to absorb power from the overvoltage phases and inject power into the undervoltage phases.

[0028] The balancing system comprises AC / DC converters configured to absorb power from the phase with excess voltage and the system comprises DC / AC converters to inject power into the phase with low voltage.

[0029] The balancing system also includes a phase selector configured to select one of the system's power supply phases. The balancing system according to the present invention, for balancing a low-voltage three-phase electrical network, allows:

[0030] Remote control: The balancing system allows remote selection of the phase(s) for power absorption, the phase(s) for power injection, and the power to be transferred or switched between phases. The balancing system also allows remote configuration of the overvoltage and undervoltage imbalance thresholds based on the balancing coefficients.

[0031] Real-time monitoring: The balancing system allows evaluation and reporting of the network imbalance status in real time via MQTT (Message Queuing Telemetry Transport).

[0032] Active and reactive power control: The balancing system allows the system to be configured to perform active and reactive power compensation.

[0033] In the preferred embodiment, to perform the balancing, the balancing system can enter "voltage mode," which balances the system taking into account the mains voltage. This mode balances the voltages of the three phases of a three-phase network. Balancing can be carried out without measuring the mains current, although the system allows for its measurement and recording using current sensors.

[0034] To complement the description set forth in this document and to aid in a better understanding of the characteristics of the balancing procedure and system according to the present invention, schematics are included as an integral part of said description, where, for illustrative and non-limiting purposes, the following has been represented:

[0035] Figure 1 shows a first example of a method for balancing a low-voltage three-phase electrical network.

[0036] Figure 2 shows a schematic of a balancing system for a low-voltage three-phase electrical network. Figure 3 shows a second example of a method for balancing a low-voltage three-phase electrical network.

[0037] Figure 4 shows the effect of the balancing system on a low-voltage three-phase electrical network.

[0038] Figure 5 shows the effect of the balancing system being on and off in a low-voltage three-phase electrical network.

[0039] Detailed realization of the invention

[0040] Figure 1 shows a method (100) for balancing a low-voltage three-phase electrical network, the method (100) comprises, for each phase:

[0041] In process (110) of Figure 1, method (100) involves obtaining voltage values ​​and average voltage values. A continuous monitoring process is implemented that captures and analyzes voltage measurements on the electrical network.

[0042] In one example, the voltage is shown with a sampling frequency of one hertz. This allows for obtaining a precise, real-time picture of the three-phase network's behavior.

[0043] To obtain a reference for the normal state of the electrical network, the average of the phase voltages that do not fall below a defined nominal voltage threshold (around 10% of the nominal network voltage) is calculated. This information is used as a benchmark to assess voltage imbalances between phases.

[0044] In process (120), the balancing coefficients are calculated based on the voltage values ​​and the average values. These coefficients are calculated as the voltage of each of the phases divided by the average voltage calculated in process (110).

[0045] In process (130), an overvoltage imbalance threshold and an undervoltage imbalance threshold are calculated based on the balancing coefficients.

[0046] The procedure programmably defines overvoltage imbalance thresholds and undervoltage imbalance thresholds.

[0047] In process (140), based on the imbalance coefficients and predefined thresholds, the system determines a phase with excess voltage if the balance coefficients in that phase(s) are above the overvoltage imbalance threshold. Power must be absorbed from this phase(s). In process (140), method (100) is configured to absorb power from the phase(s) with excess voltage.

[0048] In process (150), based on the imbalance coefficients and predefined thresholds, the system identifies phase(s) with low voltage if the balance coefficients in those phase(s) are below the low-voltage imbalance threshold. In process (150), method (100) is configured to inject power into the phase(s) with low voltage. The injection of absorbed power can be in phase or with a phase shift of [-0.8 to 0.8] power factor. Reactive power is generated at the time of power injection. To generate reactive power, current must be injected with a certain phase shift angle. Reactive power produces a voltage drop in at least one phase, resulting in a virtual movement of the neutral, which implies a voltage rise in the other phase(s).

[0049] Alternatively, the method also allows the absorbed power to be dissipated through one or more loads.

[0050] Alternatively, method (100) is configured to dissipate the power absorbed or extracted by loads / consumption, so that there is no effect of raising the voltage by injecting current, but there is an effect of lowering the voltage in phase with excess voltage producing the technical effect of balancing.

[0051] Figure 2 shows a balancing system (1000) of a low-voltage three-phase electrical network according to the present invention, wherein the balancing system (1000) comprises a control system (1100) that stores instructions for the execution of methods for balancing a low-voltage three-phase electrical network.

[0052] The control system (1100) comprises a microcontroller (1155) and a computer (1150).

[0053] The control system (1100) is configured to execute the algorithm that enables the balancing of three-phase networks. The control system (1100) is configured to perform the acquisition of voltage (Y), current (X), frequency, voltage / current phase shift, voltage / voltage phase shift, as well as active and reactive power, and analytical functions.

[0054] The control system (1100) is configured to send / receive data to a server / cloud (1800) to monitor the grid imbalance status, grid voltages, current, frequencies, diagnostic system, and equipment operating log, as well as to manually adjust equipment settings or power transfer on the grid. This data can be received / sent in real time by an operator (1700).

[0055] The control system (1100) is configured to perform OTA updates.

[0056] The balancing system (1000) further comprises two switching matrices (1200) configured to switch one or more overvoltage phases to one or more undervoltage phases to absorb power from the overvoltage phases and inject power into the undervoltage phases.

[0057] The control system (1100) is responsible for activating digital outputs for switching the relays.

[0058] The balancing system (1000) has two switching matrices (1200). Each switching matrix (1200) allows you to connect the input of the balancing system (1000) to any of the three phases, and its output to any of the three phases. Each switching matrix (1200) consists of six relays. This module receives the switching signal from the control system (1100) and performs the switching to select the absorption and injection phases. Furthermore, this module includes a safety system that prevents the accidental activation of two absorption or injection relays within the same switching matrix (1200), which would cause a short circuit.

[0059] For energy transfer, the balancing system (1000) has the possibility of performing all possible logical combinations:

[0060] The balancing system (1000) also includes AC / DC converters (1300) configured to absorb power from the phase with excess voltage. These AC / DC converters (1300) convert alternating current (AC) to direct current (DC), and their power supply comes from the phase(s) selected as "absorption" in the switching matrix (1200).

[0061] The balancing system (1000) also includes DC / AC converters (1400) to inject power into the low-voltage phase(s). In a possible implementation, this module consists of an inverter that converts the DC voltage to AC voltage and injects it into the grid. The inverter is controlled and monitored by the control system (1100).

[0062] The balancing system (1000) also includes an internal temperature monitoring and control system. The balancing system (1000) also includes a phase selector (1500) configured to select one of the system's power supply phases. The control system (1100) and the ventilation system are powered by single-phase power. If the control system (1100) and the ventilation system are randomly connected between one of the phases and neutral, the balancing system (1000) would cease to function if one of these phases fails. The phase selector (1500) solves this problem, as in the event of a failure of one or two of the three phases, the phase selector (1500) will automatically switch phases and select the phase that is not faulty.This system switches instantly (without restart or loss of functionality) to the available phase, so unless all three phases are in a failure situation, the control (1100) and temperature monitoring and control system will continue to function.

[0063] Figure 3 shows an embodiment of a second method (200) for balancing a low-voltage three-phase electrical network, which can be carried out by the balancing system (1000). The method (200) comprises:

[0064] Phase selection

[0065] In process (210), the balancing system (1000) continuously monitors the phase voltages of the low-voltage network. Method (200) performs a constant monitoring process that captures and analyzes voltage measurements in the electrical network at a frequency of one hertz. This allows for obtaining an accurate, real-time picture of the behavior of the low-voltage electrical network.

[0066] In process (220), the balancing system (1000) detects voltage drops in any of the phases. The balancing system (1000) compares the voltage and current measurements of each phase with predefined ranges. If values ​​outside these limits are detected, the balancing system (1000) determines that the phase in question has experienced a voltage drop. This early detection of voltage drops in the phases is beneficial for taking timely action and minimizing the impact on the operation of the electrical system. If the balancing system (1000) detects a voltage drop in any of the phases, an automatic alert is generated.

[0067] In process (230), the balancing system (1000) performs the average calculation: To obtain a reference for the normal state of the electrical network, the balancing system (1000) calculates the average of the voltages of the phases that are not experiencing a voltage drop. This information is used as a point of comparison to evaluate voltage imbalances between phases.

[0068] In decision (240), the method branches into two paths depending on whether the balancing system (1000) is operational or on standby. If the balancing system (1000) is on standby, method (200) proceeds to process (260). If the balancing system (1000) is operational, method (200) proceeds to process (250).

[0069] In process (260), the balancing system (1000) performs the calculation of the unbalance coefficients. These coefficients are calculated as phase voltage divided by the average voltage calculated in the previous step.

[0070] In decision (262), the balancing system (1000) identifies whether there is an imbalance. If there is an imbalance, method (200) proceeds to process (264). In process (264), the balancing system (1000) is started, i.e., standby mode is removed, and in process (266) the balancing system (1000) performs a phase selection:

[0071] Overvoltage and undervoltage imbalance thresholds are programmably defined. Based on the imbalance coefficients and predefined thresholds, the balancing system (1000) determines:

[0072] Phases with excess voltage: Phases with imbalance coefficients exceeding the overvoltage imbalance threshold. Of these phases, the balancing system (1000) is configured to absorb power.

[0073] Low-voltage phases: Phases with imbalance coefficients below the low-voltage imbalance threshold. Of these phases, the balancing system (1000) is configured to inject power.

[0074] In process (268), the balancing system (1000) controls the switching system using the switching matrices (1200). The balancing system (1000) sends the command to the switching matrices (1200) to switch, enabling the system to absorb and inject power into the phases. In process (270), the balancing system (1000) performs the startup and low-voltage grid connection of the power system: The balancing system (1000) continuously monitors the power system and waits until it is fully connected to the grid and ready for operation.

[0075] In process (250), if the balancing system (1000) is operational, the balancing system (1000) selects the control mode. The balancing system (1000) can either bring the phase with overvoltages to the medium voltage or the phase with undervoltages to the medium voltage. The balancing system (1000) selects the mode that is most favorable in terms of overall performance.

[0076] In process (252), the balancing system (1000) carries out the selection of the injection power. Once the control mode has been selected, the injection power is calculated iteratively using a Pl control. The objective of the Pl control is to select the optimal power to "bring" the phase with overvoltages to the average voltage, or the phase with low voltage to the average voltage, depending on the control mode in which the balancing system (1000) is operating.

[0077] The balancing system (1000) is constantly evaluating the power setting. In decision (254), it is checked whether the power setting is below a certain value. If the power setting is below a certain value, the algorithm resets, and the system enters standby mode in process (256). If the algorithm does not reset, the system continues in process (210) monitoring the voltage.

[0078] Figure 4 shows how the balancing system (1000) has acted dynamically to keep the three voltages as similar as possible.

[0079] The graph (2000) shows the three voltages (A, B, C) of each of the phases at one-second intervals.

[0080] Graph (3000) indicates which low-voltage phases (A, B) are being injected with current to increase the voltage of the corresponding phase. Finally, graph (4000) shows which high-voltage phases (A, C) are being drawn from current, resulting in a voltage decrease in those phases.

[0081] The effectiveness of the balancing system (1000) in regulating voltage may depend on the line impedance and the power to be injected, since the maximum power that the inverter can transfer from one line to another is the nominal power of the equipment.

[0082] In Figure 5, you can compare the network voltages when the balancing system (1000) is active and when it is off.

[0083] Between 03:34 and 21:33, the power part of the balancing system (1000) was deactivated, leaving it only in monitoring mode.

[0084] It can be clearly observed that when the balancing system (1000) was operating, the system was balanced. However, when the power section of the balancer was switched off, the voltage difference reached more than 30V.

[0085] In graph (5000), it can be seen that phase (B) has a low voltage value, while phases (A, C) have a value above the average voltage.

[0086] In graph (5000), the system selects that phase (B) will be the injection phase, and that phases (A, C) will be the absorption phases.

[0087] Therefore, a first switching matrix (1200) selects phase (A) as absorption and phase (B) as injection phase, and a second switching matrix (1200) selects phase (C) as absorption phase and phase (B) as injection phase.

Claims

CLAIMS 1. Method (100) for balancing a low-voltage three-phase electrical network, the method comprising, for each phase: Obtain (110) voltage values ​​and average voltage values; Calculate (120) balancing coefficients based on voltage values ​​and average voltage values; Calculate (130) an overvoltage imbalance threshold and an undervoltage imbalance threshold based on the balancing coefficients; Identify (140) at least one overvoltage phase if the balancing coefficients in that phase are above the overvoltage imbalance threshold; and absorb power from the at least overvoltage phase; Identify (150) at least one undervoltage phase if the balancing coefficients in that phase are below the undervoltage imbalance threshold; and inject the absorbed power in phase into the at least one undervoltage phase or inject the absorbed power with a phase shift of [-0.8 to 0.8] into the at least one undervoltage phase; or dissipate the absorbed power through one or more loads.

2. The method (100) according to claim 1, wherein the power injected into the at least one low-voltage phase is obtained from the power absorbed from the at least one high-voltage phase.

3. The method (100) according to claim 1 or 2, wherein obtaining voltage values ​​and average voltage values ​​comprises monitoring voltage values ​​in real time with a sampling frequency of at least one hertz.

4. The method (100) according to claims 1 to 3, wherein absorbing power from the phase with excess voltage comprises calculating an injection power by means of iterative calculation to lower the voltage of said phase to average values.

5. The method (100) according to claims 1 to 4, wherein injecting power into the low-voltage phase comprises calculating an injection power by means of iterative calculation to raise the voltage of said phase to average values.

6. The method (100) according to claims 1 to 5 above, wherein identifying a phase with excess voltage if the balancing coefficients in said phase are above the overvoltage imbalance threshold comprises generating an automatic alert.

7. The method (100) according to claims 1 to 5, wherein identifying a phase with low voltage if the balancing coefficients in said phase are below the low voltage imbalance threshold comprises generating an automatic alert.

8. Balancing system (1000) of a low-voltage three-phase electrical network, where the system comprises: A control system (1100) that stores instructions for the execution of the method according to claims 1 to 7; at least one switching matrix (1200) configured to switch one or more overvoltage phases to one or more undervoltage phases to absorb power from the overvoltage phases and inject power into the undervoltage phases; AC / DC converters (1300) configured to absorb power from one or more phases with excess voltage; and DC / AC converters (1400) to inject power into one or more phases with low voltage.

9. The balancing system (1000) according to claim 8, further comprising a ventilation system.

10. Balancing system (1000) according to claim 8 or 9, further comprising a phase selector (1500) configured to select a system feed phase.

11. Balancing system (1000) according to claims 8 to 10, wherein the control system (1100) further comprises a microcontroller (1155) and a computer (1150).

12. Balancing system (1000) according to claims 8 to 11, further comprising means for electrical protections (1600).

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