CN101645603A - Negative sequence management method of energy injection type balance electric system - Google Patents

Abstract

The invention discloses a negative sequence management method of an energy injection type balance electric system. The method comprises the following steps: detecting imbalance of three phases of a power grid side and asymmetry of all phases of a load side in real time; selecting converter with lighter loads for phase at the power grid side for rectification according to the imbalance of three phases of the power grid side; connecting direct current output by the converter at the power grid side to the converter connected with heavy load phase by a common direct-current bus; and carrying out inverse output on loads by the converter connected with heavy loads. The method solves the problem of negative sequence management of asymmetric loads of the electric system.

Description

An Energy Injection Balanced Power System Negative Sequence Treatment Method

technical field

The invention relates to a negative-sequence control method of an electric power system, in particular to an energy-injection balanced negative-sequence control method of the electric power system.

Background technique

According to electrotechnical principles, any asymmetrical load can be decomposed into three sets of symmetrical components: positive sequence, negative sequence and zero sequence by the method of symmetrical components. The most typical asymmetrical loads are electric railway traction systems, electric arc furnaces in the metallurgical industry, etc.

The main hazards caused by factors such as unbalanced three-phase voltage or current: (1) The operation of the rotating motor in an asymmetric state will cause additional loss and heat generation in the rotor, which will cause the overall or local temperature of the motor to rise. In addition, the reverse magnetic field will generate additional torque. It will vibrate the motor. For generators, a series of higher harmonics are also formed in the stator. (2) It causes various protections with negative sequence components as starting components to malfunction, which directly threatens the operation of the power grid. (3) Unbalanced voltage causes non-characteristic harmonics in silicon rectifier equipment. (4) For generators and transformers, when the three-phase load is unbalanced, if the maximum phase current is controlled to be the rated value, the other two phases cannot be fully loaded, so the utilization rate of the equipment will decrease. On the contrary, if the rated capacity is to be maintained, the It will cause an overload of one phase with a large load, and there will also be unbalanced magnetic circuit, which will cause waveform distortion and increase the additional loss of equipment.

Contents of the invention

In order to solve the problems of negative-sequence voltage and current generated by asymmetrical loads in the power system, the present invention proposes an energy-injection balanced power system negative-sequence control method. Selectively absorb unbalanced energy from phases with lighter loads, and selectively inject energy into phases with heavier loads through the AC-DC-AC conversion link, so as to realize the basic balance of three-phase loads on the grid side.

The technical solution adopted by the present invention to solve the above technical problems is: real-time detection of the unbalance degree of the three phases on the grid side and the asymmetry of each phase on the load side, and select the phase with a lighter load on the grid side according to the unbalance degree of the three phases on the grid side A converter is used for rectification, and the output DC of the grid-side converter is connected to the converter connected to the heavy-load phase through the public DC bus, and the converter connected to the heavy-load performs inversion output to the load.

An energy injection balanced power system negative sequence control method, comprising the following steps: real-time detection of the asymmetry of each phase on the load side and the unbalance of the three phases on the grid side, and selecting a phase with a lighter load on the load side according to the asymmetry Use a converter for rectification. The rectified output of the converter is connected to the grid side converter corresponding to the heavy load phase through the common DC bus, and the grid side converter is inverted and output to the grid side corresponding to the heavy load phase.

An energy-injected balanced power system negative-sequence control method, comprising the following steps: real-time detection of the asymmetry of each phase on the load side, selecting a phase with a lighter load according to the asymmetry for rectification with a converter, and the phase of the converter The output DC is connected to the converter of the heavy-load phase through the DC bus, and is output by the commutation of the heavy-load phase.

The technical effect of the present invention is that: the present invention selectively draws unbalanced energy from phases with lighter loads, and selectively injects energy into phases with heavier loads through the AC-DC-AC conversion link, thereby realizing three-phase loads on the grid side The basic balance of the system solves the imbalance problem of the power system in a real sense.

The present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

FIG. 1 is a topological structure diagram of Embodiment 1 of the present invention. In the figure, 1. is the grid-side transformer, 2 is the grid-side converter group, 3 is the load-side converter group, and 4 is the DC capacitor.

FIG. 2 is a topological structure diagram of Embodiment 2 of the present invention. In the figure, 1 is the load-side converter group, and 2 is the DC capacitor.

Fig. 3 is a flow chart of the present invention.

Detailed ways

Referring to FIG. 1, FIG. 1 is a topology diagram of Embodiment 1 of the present invention. The energy balance device shown in Figure 1 is connected in parallel in the main circuit during normal operation. The input of the grid-side converter group is connected to the grid-side step-down transformer or directly connected to the grid-side three-phase system, and the commutation output is connected to the load by the common DC bus. side converter group to realize the injection of excess asymmetric energy on the grid side to the heavier phase on the load side; Basically balanced, the structure can realize bi-directional transmission of energy. The working method of the first topology diagram is as follows: Real-time detection of the unbalance of the three phases on the grid side and the asymmetry of each phase on the load side, and select the phase with a lighter load on the grid side for rectification according to the control strategy. The amount of energy that the converter can draw from the grid side can be flexibly controlled, and its output DC is connected to the single-phase converter group on the load side through the common DC bus. Finally, the phase corresponding to the heavy load is selected according to the control strategy through the single-phase converter connected to the phase. The converter performs inverting output to the load, and injects the unbalanced energy of the grid side into the heavy load phase of the asymmetrical load, so as to realize the basic balance of the three phases of the grid side. The second working method of the first topology diagram is: real-time detection of the asymmetry of each phase on the load side and the unbalance of the three phases on the grid side, and select the phase with a lighter load on the load side via the single-phase connected to it according to the control strategy Phase converter rectification, the rectification output is connected to the grid-side converter through the common DC bus, and finally selects the phase corresponding to the heavy load on the grid side according to the control strategy, and carries out power transmission to the phase of the grid side through the connected converter arm. Inverter output, by absorbing the unbalanced energy on the load side and injecting it into the heavy load phase on the unbalanced grid side, so as to achieve the basic balance of the three phases on the grid side.

Referring to FIG. 2, FIG. 2 is a topology diagram of Embodiment 2 of the present invention. The energy balance device shown in Figure 2 is connected in parallel with the three-phase load when it is working normally. The asymmetry of the traction load on both sides is detected in real time, and the unbalanced energy is selectively extracted from the phase with the lighter load according to the control strategy. In the DC-AC conversion link, energy is selectively injected into the phases with heavier loads, so as to realize the basic balance of the three-phase loads on the secondary side of the main transformer. The working mechanism of the second topology is: detect the asymmetry of each phase on the load side in real time, select the phase with a lighter load for rectification according to the control strategy, the amount of energy absorbed by the converter can be flexibly controlled, and its output DC is connected through the DC bus to other phases of single-phase converter groups, and finally select the phase corresponding to the heavy load according to the control strategy to carry out inversion output to the phase through the single-phase converter connected to the phase, and inject the energy of the light load phase into the heavy load phase. Load phase, so as to realize the basic balance of each phase on the load side.

Referring to Fig. 3, Fig. 3 is a flowchart of the present invention. The process is: real-time detection of the unbalance degree of the three-phase current, according to the design of the controller control strategy, determine the direction of the power flow, that is, decide which phase to draw the unbalanced power, and at the same time inject energy into which phase; while determining the direction of the power flow According to the control algorithm, the corresponding current command is obtained, and the trigger pulse is sent to the corresponding working converter according to the current command, and the converter is driven to work through the driving circuit.

Claims (3)

1. A negative-sequence treatment method of an energy-injected balanced power system, comprising the steps of: detecting in real time the degree of unbalance of the three phases on the grid side and the degree of asymmetry of each phase on the load side, and selecting according to the degree of unbalance of the three phases on the grid side The phase with lighter load on the grid side is rectified by a converter, and the output DC of the grid side converter is connected to the converter connected to the heavy load phase through the common DC bus, and the converter connected to the heavy load is reversed to the load. change output. 2. An energy injection balanced power system negative sequence control method, comprising the following steps: real-time detection of the asymmetry of each phase on the load side and the unbalance of the three phases on the grid side, and selecting a lighter load on the load side according to the asymmetry The phase is rectified by a converter, and the rectified output of the converter is connected to the grid side converter corresponding to the heavy load phase through the common DC bus, and the grid side converter is inverted and output to the grid side corresponding to the heavy load phase. 3. An energy-injected balanced power system negative sequence control method, comprising the following steps: real-time detection of the asymmetry of each phase on the load side, and selecting a phase with a lighter load according to the asymmetry for rectification and commutation The output DC of the inverter is connected to the converter of the heavy load phase through the DC bus, and is output by the converter of the heavy load phase.

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