CN102638039B - Three-phase chain-type static synchronous compensator - Google Patents

Abstract

The invention relates to a three-phase chain-type static synchronous compensator, which belongs to the technical fields of flexible AC power transmission and distribution systems and power electronics. Its structure is as follows: multiple groups of H-bridge inverter units are connected in series to form a first chain structure, the first filter inductors are connected in series at both ends of the first chain structure, and three groups of the same first filter inductors are connected in series. The chain structure is connected in a delta way to form a three-phase chain static synchronous compensator in delta connection; multiple groups of H-bridge inverter units are connected in series to form a second chain structure, and the three-phase chain static in delta connection Each of the three outlets of the synchronous compensator is connected in series with a second chain structure, and each outlet of the second chain structure is connected to the grid through a second filter inductor and a circuit breaker in turn. The static synchronous compensator of the present invention has the ability to compensate reactive power and negative sequence current at the same time, and has lower requirements on the withstand voltage of the device. The H-bridge inverter unit adopted is a modular structure, which is convenient for production, simple in structure, and low in cost. low.

Description

A three-phase chain static synchronous compensator

technical field

The invention relates to a three-phase chain static synchronous compensator, which belongs to the technical fields of flexible AC power transmission and distribution systems and power electronics.

Background technique

In the fields of power system, steelmaking, metallurgy, wind power generation, electrified railway, etc., reactive power compensation and unbalance compensation are getting more and more attention from relevant departments. Excessive reactive power will increase the loss and voltage drop of the line, and frequent reactive power fluctuations will also seriously affect the quality of the bus voltage, ranging from reducing the electrical life of the surrounding electrical equipment, to severely affecting the surrounding generators and electrical equipment due to If the voltage is unqualified and the protection operates, it will lead to accidents such as power outages and factory failures. Therefore, the power sector has set strict standards for the assessment of power factor, usually requiring the power factor of the power consumption site to reach 0.9 or above, otherwise it will be fined, in some power consumption sites with frequent fluctuations in reactive power, such as electrification Railways and steel mills are often required to use dynamic reactive power compensation devices with fast response capabilities for governance. In recent years, the accidents of generator and load tripping caused by excessive negative-sequence voltage unbalance at public connection points have been frequently reported, and the power sector has also paid more and more attention to the assessment of negative-sequence voltage unbalance at public connection points. Power Quality-Three-phase Voltage Unbalance (GB/T15543-2008) requires that each user connected to the public connection point cause the allowable value of the voltage negative sequence unbalance at this point to be generally 1.3%, and shall not exceed 2.6% for a short time. Power users whose voltage unbalance degree exceeds the standard must use compensation equipment to compensate the unbalance degree within the acceptable range.

In most places where electricity is used, such as electrified railways, steel mills, metallurgy, etc., the problems of substandard power factor and excessive negative sequence unbalance often exist at the same time, and they need to be treated at the same time. In recent years, due to the rapid development of flexible AC power transmission and distribution technology, the three-phase chained static synchronous compensator (hereinafter referred to as STATCOM) based on the H-bridge inverter unit structure has been widely used in power distribution systems for reactive power and negative sequence dynamic compensation. Traditional chained STATCOM mainly has two topological structures, that is, delta connection and star connection, as shown in Figure 1 and Figure 2. The star-connected STATCOM has the characteristics of simple structure and low cost, and can be used for dynamic reactive power compensation in power distribution systems, but when the star-connected chained STATCOM is used for negative sequence compensation, the current and voltage of the three phases are equal There are differences, and the control is very difficult. At present, the chained STATCOM of the star connection method does not have the ability to compensate for negative sequence; the STATCOM of the delta connection method each phase links to withstand the line voltage of the system, because the line voltage of the system is basically three-phase Symmetrical, when used to compensate the negative sequence, only need to control the STATCOM to generate the corresponding asymmetric current to better compensate the negative sequence current of the power distribution system, so the delta-connected chained STATCOM has the ability to simultaneously compensate reactive power and Negative sequence capability. At present, there are many cases where delta-connected chained STATCOMs are used in industrial sites to compensate reactive power and negative sequence at the same time. However, each phase of delta-connected chained STATCOMs bears The line voltage of the system, compared with the star-connected chained STATCOM under the same voltage level and capacity, requires a higher withstand voltage level of each insulated gate bipolar transistor (hereinafter referred to as IGBT) device, or must be connected in series. H-bridge unit to achieve the same withstand voltage level, so that the delta-connected chained STATCOM cost is much higher than the star-connected chained STATCOM.

Contents of the invention

The purpose of the present invention is to propose a three-phase chain synchronous static compensator to make up for the shortcomings of the star connection method and the delta connection method. Good ability to compensate negative sequence, thereby reducing the cost of equipment.

The three-phase chain-type static synchronous compensator proposed by the present invention has a structure as follows: multiple groups of H-bridge inverter units are connected in series to form a first chain-type structure, and a first filter is connected in series at both ends of the first chain-type structure. Inductor, three sets of the same first chain structure with filter inductors in series are connected in a delta way to form a three-phase chain static synchronous compensator with delta connection; multiple sets of H-bridge inverter units are connected in series to form the first Two-chain structure, each of the three outlets of the delta-connected three-phase chain static synchronous compensator is connected in series with a second chain structure, and the outlet of each second chain structure passes through the second filter inductance and A circuit breaker is connected to the grid.

The three-phase chained static synchronous compensator proposed by the present invention has the advantage that compared with the existing star-connected chained STATCOM, the three-phase chained static synchronous compensator of the present invention has a delta-connected part , so the static synchronous compensator of the present invention has better ability to compensate negative sequence compared with the STATCOM of existing star connection; The chain-type static synchronous compensator is connected to the power grid after connecting several groups of H-bridge unit structures in series at the outlet of each terminal of the delta-connected chain-type STATCOM, so IGBTs with relatively low withstand voltage levels can be used. Therefore, the three-phase chain-type static synchronous compensator of the present invention has the ability to compensate reactive power and negative sequence current at the same time, and has lower requirements on the withstand voltage of the device. The H-bridge inverter unit adopted is a modular structure, which is convenient Production, simple structure and low cost.

Description of drawings

Fig. 1 is a structural schematic diagram of an existing star-connected three-phase chain static synchronous compensator.

Fig. 2 is a structural diagram of an existing delta-connected three-phase chain static synchronous compensator.

Fig. 3 is a schematic diagram of the structure of the three-phase chain static synchronous compensator proposed by the present invention.

Fig. 4 is a structural schematic diagram of an H-bridge unit inverter in a three-phase chain static synchronous compensator.

Detailed ways

The three-phase chain-type static synchronous compensator proposed by the present invention has a structure as shown in Figure 3, which is: multiple groups of H-bridge inverter units are connected in series to form a first chain structure, and at both ends of the first chain structure Each of the first filter inductors is connected in series, and three sets of the same first chain structure with filter inductors are connected in a delta manner to form a three-phase chain static synchronous compensator with a delta connection; multiple sets of H bridges are inverted Connector units are connected in series to form a second chain structure, and a second chain structure is connected in series at each of the three outlets of the three-phase chain static synchronous compensator in the delta connection method, and the outlets of each second chain structure are in turn It is connected to the grid through a second filter inductor and a circuit breaker.

In the three-phase chain-type static synchronous compensator of the present invention, the number h of H-bridge modules connected in series in each phase inside the delta connection and the number j of H-bridge modules connected in series in each phase outside the triangle connection can be based on the grid voltage level and the negative sequence compensation capability And flexible settings.

As shown in Figure 3, the three-phase chain-type static synchronous compensator of the present invention is formed by cascading basic H-bridge inverter units. First, h H-bridge inverter units are connected in series to form a first chain structure, And a filter inductor L ₁ is connected in series at both ends of the chain structure, and three groups of the same chain structure with filter inductors are connected in a delta way to form a three-phase chain static synchronous compensator with a delta connection method. Its three outlets lead to terminals x, y, and z respectively, and a second chain structure composed of j H-bridge inverter units is connected in series at each terminal, and each second chain structure passes through the first chain structure in turn. The second filter inductor L ₂ and the circuit breaker Q are connected to the three-phase power system. The values of h and j can be flexibly set according to the voltage level and the compensation ability for negative sequence. Looking at the three-phase chain-type static synchronous compensator proposed by the present invention from the side of the power grid, it is similar to the chain-type STATCOM of the star connection method, but the neutral point is expanded to a chain-type STATCOM connected in an angular shape; looking at the power grid from the side of the device, It is similar to the chained STATCOM of the delta connection method, except that a chain structure formed by connecting multiple H-bridge inverter units in series is connected in series at the outlet of each phase.

In the three-phase chain-type static synchronous compensator proposed by the present invention, the structure of the H-bridge inverter unit includes two bridge arms, wherein each bridge arm is composed of two upper and lower insulated gate bipolar transistors (IGBT) and It is composed of diodes connected in reverse parallel with two upper and lower insulated gate bipolar transistors, and a capacitor and a discharge resistor are connected in parallel on the DC side, and a terminal is drawn from the midpoint of each bridge arm. As shown in Figure 4, the H-bridge inverter unit includes two bridge arms, of which the left bridge arm is composed of two upper and lower IGBTs (S1 and S2) and diodes D1 and D2 connected in antiparallel to S1 and S2 respectively, and the right bridge arm The arm consists of two upper and lower IGBTs (S3 and S4) and diodes D3 and D4 connected in antiparallel to S3 and S4 respectively. And a capacitor C and a discharge resistor R are connected in parallel on the DC side, the midpoint of the left bridge arm leads to terminal a, and the midpoint of the right bridge arm leads to terminal b. The working principle of the H-bridge inverter unit is as follows: Assume that the voltage on the DC side is E after the H-bridge capacitor is charged. When IGBT1 is turned on and IGBT2 is turned off, the voltage of terminal a relative to the negative electrode of the capacitor is E; when IGBT1 is turned off and IGBT2 is turned on, the voltage of terminal a relative to the negative electrode of the capacitor is 0; when IGBT3 is turned on, IGBT4 is turned off , the voltage of terminal b relative to the negative pole of the capacitor is E, when IGBT3 is turned off and IGBT4 is turned on, the voltage of terminal b relative to the negative pole of the capacitor is 0. Therefore, the voltage difference between terminals a and b can have three levels in total, namely +E, -E, and 0.

Claims (1)

1. A three-phase chain-type static synchronous compensator is characterized in that the structure of the static synchronous compensator is: multiple groups of H-bridge inverter units are connected in series to form the first chain structure, and in the first chain structure A first filter inductance is connected in series at both ends, and three sets of the same first chain structure with the first filter inductance are connected in a delta manner to form a three-phase chain static synchronous compensator in a delta connection; The H-bridge inverter units are connected in series to form a second chain structure, and each of the three outlets of the delta-connected three-phase chain static synchronous compensator is connected in series with a second chain structure, and each second chain structure The outlet of the structure is connected to the grid through a second filter inductor and a circuit breaker in turn.

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