KR-102962837-B1 - Single-phase independent control device for three-phase voltage stabilization and neutral current reduction

KR102962837B1KR 102962837 B1KR102962837 B1KR 102962837B1KR-102962837-B1

Abstract

The power quality improvement device of the present invention may include a plurality of single-phase inverter units independently provided corresponding to each phase of a three-phase distribution line, a plurality of independent transformer units each connecting the output of each single-phase inverter unit in series to the three-phase distribution line, and a control unit that individually controls each single-phase inverter unit based on a signal from a detection unit that detects the voltage or current of the three-phase distribution line. The control unit may independently perform voltage control to resolve inter-phase voltage imbalance by controlling the magnitude of the output voltage of each phase, or current control to reduce the neutral point current of the three-phase distribution line by controlling the current phase of each phase.

Inventors

우병국
서봉교
김복년
임다니엘지섭

Assignees

주식회사 크로커스

Dates

Publication Date: 20260512
Application Date: 20250801

Claims (12)

A plurality of single-phase inverter units independently provided corresponding to each phase of the three-phase distribution line; A plurality of independent transformer units that inject a compensation voltage by connecting the output of each single-phase inverter unit in series to the three-phase distribution line, respectively; and A control unit that individually controls each single-phase inverter unit based on a signal from a sensing unit that detects the voltage and current of the above three-phase distribution line; comprising, The above control unit is, The single-phase inverter unit is controlled to generate only the compensation voltage corresponding to the difference between the reference voltage of the three-phase distribution line and the output voltage detected by the detection unit, and A voltage control function that resolves inter-phase voltage imbalance by controlling the magnitude of the above compensation voltage, and A power quality improvement device that independently performs a current control function to reduce neutral point current by minimizing the vector sum of three-phase currents through controlling the current phase of each phase by adjusting the reactive power injected through the above compensation voltage.
In Article 1, A rectifier that receives AC power from the above-mentioned three-phase distribution line and converts it into DC power, and It includes a DC link unit that receives the DC power from the above rectifier unit and supplies it to the plurality of inverter units, The above DC link section is, It smooths the ripple component included in the DC power transmitted from the above rectifier to form a stable DC voltage, and A power quality improvement device characterized by temporarily storing and buffering regenerative energy generated from a load connected to the above three-phase power distribution line.
In Article 1, The above control unit is, Synchronization unit for measuring the frequency and phase of a three-phase distribution line; A calculation unit that calculates a voltage error or neutral point current based on voltage and current information detected from the above-mentioned detection unit; and A power quality improvement device comprising: a PWM generation unit that generates a PWM signal to be transmitted to each inverter unit based on the calculation result of the above calculation unit.
In Article 1, When the load connected to the above three-phase distribution line is unbalanced and the output voltage of each phase forms an unbalanced voltage vector, The above control unit is, A power quality improvement device that individually controls each inverter unit based on the unbalanced voltage vector detected through the above-mentioned sensing unit to compensate for the output voltage of each phase to form a balanced voltage vector having the same magnitude and a phase difference of 120 degrees.
In Article 1, The above control unit is, A power quality improvement device characterized by individually adjusting the reactive power injected into each phase and thereby changing the current phase of each phase to compensate so that the sum of the unbalanced three-phase current vectors becomes zero, thereby reducing the neutral point current.
In Article 1, If the load connected to the above three-phase distribution line is unbalanced, The above control unit is, Voltage imbalance is resolved by individually controlling each inverter unit so that the output voltage of each phase forms a balanced voltage vector having the same magnitude and a phase difference of 120 degrees, and A power quality improvement device that reduces neutral point current by adjusting the current phase of each phase so that the vector sum of the three-phase currents is minimized.
In Article 1, It includes a filter section provided between the output terminal of each inverter section and the input terminal of each independent transformer section, and The above filter unit is, An inductor connected in series to the output terminal of the above-mentioned inverter unit, and It includes a capacitor connected in parallel between the output terminal of the above inductor and ground, and A power quality improvement device that reduces high-frequency components caused by PWM switching included in the output of the above-mentioned inverter section.
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In Article 1, It includes a DC link section for supplying stable DC power in common to multiple inverter sections, and A power quality improvement device that achieves inter-phase energy balance by controlling an inverter unit corresponding to the second phase to supply power to a load on the second phase of the three-phase distribution line using the energy stored in the DC link unit when regenerative power is generated in the first phase of the three-phase distribution line and energy flows into the DC link unit.
In Article 2, The current control of the above control unit is, It is performed through phase control of the AC input stage in the above rectifier, or This is performed by injecting reactive power for each phase in the above inverter section, and The above control unit is a power quality improvement device that selects or combines one of the rectifier unit control and the inverter unit control according to system operating conditions.
In Article 1, The current control function of the above-mentioned control unit is performed by adjusting the reactive power injected into each phase, and The above control unit, in order to optimally calculate the above reactive power, A first control loop that performs real-time short-term optimization including Model Predictive Control (MPC), and A power quality improvement device using a hybrid control algorithm including a second control loop that performs periodic global optimization including PSO (Particle Swarm Optimization).
In Article 1, The current control of the above control unit is performed by adjusting the reactive power injected into each phase, and The above control unit, in order to optimally calculate the above reactive power, The unbalanced state of the measured voltage and current is analyzed using a linear matrix model to perform first-order compensation that compensates for most of the neutral point current, and A power quality improvement device that sequentially performs secondary compensation using Quadratic Programming (QP) to minimize the neutral point current remaining after the above primary compensation.

Description

Single-phase independent control device for three-phase voltage stabilization and neutral current reduction The present invention relates to a single-phase independent control device that significantly improves the stability of the power system and power quality by independently performing a voltage control function that resolves inter-phase voltage imbalance by individually controlling the voltage of each phase to address load imbalance problems occurring in a three-phase power distribution system, and a current control function that reduces neutral point current by actively controlling the current phase of each phase. Generally, power systems use a three-phase alternating current system to efficiently transmit large amounts of power generated at power plants. The three-phase power is stepped down to the operating voltage through a grid transformer and then supplied to each consumer through three-phase distribution lines. In an ideal three-phase distribution system, the voltage vectors of the R, S, and T phases each have the same magnitude and maintain a phase difference of 120 degrees from each other, forming a perfect equilibrium state. In this equilibrium state, the vector sum of the three phase currents at the neutral point of the Y-connected system transformer is zero, so no current flows through the neutral line, allowing the system to operate stably. However, as illustrated in FIG. 1, in most cases, the types and capacities of the loads (130) connected to each phase at the end of the actual power distribution system are not uniform, and the condition in which the load amount of each phase is different is called load imbalance. This load imbalance causes the amount of current flowing through the distribution lines of each phase to be different, and also causes the voltage drop due to line impedance to be different for each phase. As a result, inter-phase voltage imbalance inevitably occurs, in which the magnitude of the final voltage reaching each load is different. Therefore, there is an urgent need for the development of technology for a new type of three-phase power quality improvement device that can effectively respond to the load imbalance problem that frequently occurs in modern power grids and fundamentally solve the voltage imbalance and neutral point current problems resulting therefrom. Figure 1 is a conceptual diagram of a problem situation in which inter-phase voltage imbalance and neutral point current occur due to load imbalance in a conventional three-phase distribution system. Figure 2 is a circuit diagram showing the configuration of a three-phase interlocking power quality improvement device according to the prior art. Figure 3 is a graph showing the problem that output voltage imbalance is not resolved when an unbalanced load is applied to the conventional device of Figure 2. FIG. 4 is an explanatory diagram schematically showing the overall structure of a single-phase independent control system according to the present invention. FIG. 5 is a detailed circuit diagram showing the specific configuration of a single-phase independent control type three-phase power quality improvement device according to the present invention. Figure 6 is a graph showing that the output voltage is perfectly balanced when an unbalanced load is applied to the device of the present invention of Figure 5. Figure 7 is a data graph demonstrating voltage stabilization performance by comparing the input voltage and stabilized output voltage of the device of the present invention in an actual rapidly changing load environment. FIG. 8 is an explanatory diagram of the solution to the inter-phase voltage imbalance problem by comparing the unbalanced voltage vector state before the application of the voltage control function of the present invention and the voltage vector restored to a perfectly balanced state after application. FIG. 9 is an explanatory diagram of the solution to the neutral point current problem by comparing the unbalanced current vector state before the application of the current control function of the present invention with the state after application in which the phase is compensated and the vector sum becomes zero. The power quality improvement device (200) of the present invention is described according to FIGS. 1 to 9. In FIGS. 1 to 3, a conventional three-phase interlocking CVR device is described, and in FIGS. 4 to 8, a three-phase power quality improvement device (200) capable of reducing neutral point current through single-phase independent control according to the present invention is described. In FIG. 1, in the basic configuration of a three-phase power distribution system, a transformer (110) can receive high-voltage three-phase power from the outside and convert it into a low voltage that can be used by consumers to supply power to the area. The three-phase power line (120) may be a thick main line that serves as a main passage for transmitting power from the transformer (110) to