CN104821576B - Direct current traction power supply system based on buck type direct current-direct current converter - Google Patents

Abstract

The present invention discloses a DC traction power supply system based on a step-down DC converter and a control method thereof. A set of rectifiers consisting of a traction transformer TT _i‑1 and a rectifier unit U _i‑1 is added to each substation; a step-down DC converter BUCK is set between two substations. The step-down DC converter BUCK is controlled by voltage and current tracking to achieve the functions of voltage reduction and power output, and to compensate for the load power and the voltage at the end of the contact network, thereby solving the problem of severe voltage drop in the contact network and insufficient load power during the peak operation period, and providing technical guarantee for increasing the distance between the power supply arm and the traction substation.

Description

DC Traction Power Supply System Based on Step-Down Direct-to-Direct Converter

technical field

The invention belongs to the field of transportation, and in particular relates to a novel DC traction power supply system based on a step-down direct-to-direct converter.

Background technique

The DC traction power supply system refers to the DC traction power supply system obtained from the rectified AC power supply of the public grid, and is mostly used for power supply in urban rail transit such as subways and light rails. The DC traction power supply system consists of a traction substation and catenary. Usually, the traction substation is composed of two independent (medium voltage) AC power sources and two 12-pulse traction rectifier units paralleling to form an equivalent 24-pulse wave. The traction rectifier unit is composed of traction transformers, diode rectifiers and accessories, and the traction network is composed of catenary (or contact rail) and steel rails.

During the peak hours of operation, the current of the traction network increases, and the pressure loss of the catenary is serious. The system is very likely to be unable to provide the power required by the traction load, which has a serious impact on the reliable operation of the system. In addition, the two traction systems of the DC traction power supply system The distance between substations is generally 2-4km. Due to the impact of the catenary voltage drop, the power supply distance cannot be extended, resulting in a huge investment in the construction of traction substations. Obviously, increasing the power supply distance and ensuring load power are important measures to improve the technical performance and economic performance of the DC traction power supply system.

In order to solve the problem of catenary voltage drop and load dynamics, the present invention sets up a step-down direct-to-direct converter between the two traction substations. Through the control method of voltage and current tracking, the converter can not only ensure the catenary The level of power supply can also provide power for the traction load, which solves the problem of serious voltage drop in the catenary and insufficient load power, thus providing a technical guarantee for increasing the distance between substations.

Contents of the invention

The technical problem of the present invention is to provide a DC traction power supply system and its control method based on step-down direct-to-direct converters to solve the problems of severe catenary voltage drop and insufficient load power, and to provide a solution for increasing the distance between substations Technical Guarantee.

The present invention solves its technical problem, and the adopted technical scheme is:

A DC traction power supply system based on step-down DC-DC converters, consisting of a traction network composed of multiple traction substations SS, contact lines C and running rails R, each traction substation SS has a traction transformer TT _i The rectification device composed of rectifier unit U _i , the DC side of rectifier unit U _i is directly connected to the running rail R through the contact line C, and its feature is that a set of traction transformer TT _i-1 and rectifier unit U i is added in each substation The rectification device composed of _i-1 , the additional rectification device is also connected between the AC power supply and the traction network, and the negative pole of the additional rectification unit U _i-1 is connected in series with the positive pole of the original 24-pulse (12-pulse) rectification unit U _i ; Between the two substations, a step-down direct-to-direct converter BUCK is set, and the positive pole of the step-down direct-to-direct converter BUCK power supply is connected in series with the positive pole of the additional rectifier cabinet U _i-1 and the additional rectifier cabinet of the adjacent substation Between U _i+2 , i is a non-zero natural even number; the positive and negative poles of the load of the step-down direct-to-direct converter BUCK are respectively connected to the contact line C and the running rail R between the two substations.

With the device and method of the present invention, the problems of severe catenary voltage drop and insufficient load power can be solved by the additional rectifier unit _U1 and step-down straight-to-straight converter BUCK, and the distance between the power supply arm and the traction substation can be increased , is an innovation and an important measure to improve the technical performance and economic performance of the DC traction power supply system.

The most important thing is: adopt the voltage and current tracking control method to control the step-down converter BUCK, so that it can compensate the load power and the terminal voltage of the catenary, thus solving the problem of severe catenary voltage drop and load dynamics during the peak period of operation. Insufficient problems, thus providing a technical guarantee for increasing the distance between the power supply arm and the traction substation.

Description of drawings

Figure 1 is a structural diagram of a substation in a traditional DC traction power supply system.

Fig. 2 is a structural diagram of a novel DC traction power supply system based on a step-down direct-to-direct converter provided by the present invention.

Fig. 3 is a control schematic diagram of the step-down direct-to-direct converter provided by the present invention.

Detailed ways

The device and method of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Figure 1 is a structural diagram of a substation in a traditional DC traction power supply system, and Figure 2 is a structural diagram of a new DC traction power supply system based on a step-down direct-to-direct converter BUCK. As shown in Figure 1, the DC sides of the two substations are directly connected to the running rail R through the contact line C.

For ease of description, two substations SS ₁ and SS ₂ are taken as examples below, and i is taken as 2 at this time without loss of generality.

The embodiment of the present invention is shown in Figure 2. A step-down direct-to-direct converter BUCK is installed between the two traction substations SS ₁ and SS _2. The positive pole of the power supply of the step-down direct-to-direct converter BUCK is connected to the additional rectifier unit U ₁ The positive pole of the step-down direct-to-direct converter BUCK is connected in series with the contact line C, and the negative pole of the load of the step-down direct-to-direct converter BUCK is connected to the running rail R. The negative pole of the additional rectifier unit U ₁ is connected in series with the positive pole of the original 24-pulse ( ₁₂ -pulse) rectifier unit U _{2 .} The positive pole of the power supply of the DC-DC converter BUCK is connected in series with the positive pole of the additional rectifier cabinet _U1 , and the positive and negative poles of the load of the step-down DC-DC converter BUCK are respectively connected to the contact line C and the running rail R in the middle of the two substations.

Its control method is shown in Figure 3, the control schematic diagram of the step-down direct-to-direct converter, through the voltage and current tracking control method to control the step-down direct-to-direct converter BUCK, so as to realize the power output and ensure the power supply voltage function.

The specific steps are: Mode 1: The given value I _che ^* of the load current is compared with the feedback value I _che of the load current, and the output is sent to the PWM generator through PI regulation. Mode 2: The given value V _Buck ^* of the output voltage of the step-down direct-to-direct converter BUCK is compared with the feedback value V _Buck of the output voltage of the step-down direct-to-direct converter BUCK, and the output is sent to the PWM generator through PI adjustment. Mode 3: Combining the first two modes, the method of outer loop voltage and inner loop current is adopted to ensure the current output tracking command when the voltage is stable. According to the work requirements, the output signals of the two PWM generators can be flexibly switched and selected, and then the output signal Pulse is sent to the switch K of the step-down direct-to-direct converter BUCK circuit to control its opening and closing.

The control method in Figure 3 can be used to control the step-down direct-to-direct converter BUCK to realize the power output and ensure the power supply voltage, thereby solving the problem of serious voltage drop in catenary and insufficient load power, and increasing the power supply and traction substation. distance.

The structural scheme, control method, basic principle and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments. What the above-mentioned embodiments and description describe are only the present invention The structural scheme, control method and basic principle of the present invention, without departing from the spirit and scope of the present invention, the present invention will also have various changes and improvements, and these changes and improvements all fall within the scope of the claimed invention. The protection scope of the invention is defined by the appended claims and their equivalents.

Claims (1)

1. A DC traction power supply system based on step-down direct-to-direct converters, composed of a traction network composed of multiple traction substations SS, contact lines C and running rails R, each traction substation SS has a traction transformer The rectification device composed of TTi and rectifier unit Ui, the DC side of the rectifier unit Ui is directly connected to the running rail R through the contact line C, and its characteristic is that a set of traction transformer TT _i-1 and rectifier unit _Ui The rectification device composed of _-1 , the additional rectification device is also connected between the AC power supply and the traction network, and the negative pole of the additional rectification unit U _i-1 is connected in series with the positive pole of the original rectification unit U _i ; between the two substations A step-down direct-to-direct converter BUCK, the positive pole of the buck power supply of the step-down direct-to-direct converter is connected in series between the positive pole of the additional rectifier cabinet U _i-1 and the additional rectifier cabinet U _i+2 of the adjacent substation, i is Non-zero natural even number; the positive and negative poles of the load of the step-down direct-to-direct converter BUCK are respectively connected to the contact line C and the running rail R in the middle of the two substations.