Photovoltaic and wind power generation access system and method for reducing negative sequence current of traction network

Abstract

The present invention discloses a photovoltaic and wind power generation access system and method for reducing negative sequence current of traction network. The system is as follows: the voltage of three-phase power grid is converted into α and β two-phase voltage through a balanced traction transformer, and the DC busbars of photovoltaic power generation and wind power generation are respectively connected to the α and β two-phase power supply arms through two sets of single-phase converters to realize grid connection; the method is as follows: the detection module detects the α and β two-phase traction load power current and calculates the difference of traction load power current; the traction network side current and the traction load power current difference are compared, and the grid connection current fed back to the α and β two-phase power supply arms is calculated. The present invention solves the problem of maximizing the use of new energy technology while reducing the impact of negative sequence current of traction network, and overall improves the comprehensive power supply quality level and comprehensive benefits of traction power supply system.

Description

Technical Field

[0001] The present invention belongs to the high-speed railway transportation industry, and in particular relates to a photovoltaic and wind power generation access system and method for reducing negative sequence current of a traction network. Background Art

[0002] The traction power supply system is the only power supply source for high-speed railway electric locomotives. Its power supply quality level will affect the safe and reliable operation of locomotives on the one hand, and will also affect the three-phase power supply system on the other hand. At present, the main power quality problem of high-speed railways lies in the imbalance of the three-phase power supply system caused by single-phase high-power traction loads, that is, the negative sequence current problem.

[0003] Photovoltaic power generation and wind power generation are green and environmentally friendly new energy power generation technologies and are widely used around the world. Traditional research on photovoltaic power generation and wind power generation grid connection focuses on three-phase power systems. The traction power supply system is also a very large network with the extension of railway lines, including areas with sufficient sunshine and wind power. If photovoltaic energy can be introduced into the traction power supply system, it will have a significant effect on improving the green and environmental protection level of the traction power supply system.

[0004] Traditional photovoltaic and wind power grid connection is mainly for three-phase power systems and household single-phase systems. Directly applying this method to traction power supply systems will ignore the particularity of the traction power supply system structure. Summary of the invention

[0005] In view of the above problems, under the premise of making maximum use of new energy technologies, the present invention provides a photovoltaic and wind power generation access system and method for reducing the negative sequence current of the traction network.

[0006] The photovoltaic power generation and wind power generation access system for reducing the negative sequence current of the traction network of the present invention is specifically: the three-phase grid voltage is converted into α and β two-phase voltages through a balanced traction transformer. Photovoltaic power generation and wind power generation adopt a centralized access mode, and the DC busbars of photovoltaic power generation and wind power generation are connected to the α and β two-phase power supply arms respectively through two groups of single-phase converters to achieve grid connection, and the two groups of single-phase converters have the same installation capacity.

[0007] Another detection module detects the magnitude of the α and β phase traction load power current and transmits it to the controller. The controller reasonably distributes the current fed into the power supply arm by each group of converters according to the load current difference.

[0008] A photovoltaic power generation and wind power generation access method for reducing negative sequence current of a traction network of the present invention uses the above system, and the specific steps are as follows:

[0009] Step 1: Assume that the current of photovoltaic power generation and wind power generation connected to the traction grid is equivalent to I = I c1+I c2 , I c1 ,I c2 The detection module detects the magnitudes of the α and β phase traction load power currents I1 and I2, and the difference in traction load power current is equivalent to ΔI L =|I1-I2|.

[0010] Step 2: Compare the difference between the traction grid current and the traction load power current, and calculate the grid-connected current fed back to the α and β phase power supply arms.

[0011] When I≤|ΔI L |, the photovoltaic and wind power generation capacities compensate for the insufficient negative sequence. At this time, the photovoltaic and wind power generation currents are fully fed into the heavy-load power supply arm to reduce the negative sequence. At this time, the negative sequence current I - =|I1-I2-I|.

[0012] When I>|ΔI L |, indicating that the photovoltaic and wind power generation capacities are sufficient to compensate for the negative sequence. At this time, the photovoltaic and wind power generation currents are fed into the two power supply arms at the same time, which not only compensates for the current difference to balance the traction load power, but also balances the excess current to make the synthetic negative sequence 0. At this time, the two sets of converter feed currents are

[0013]

[0014] When both power supply arms are in no-load condition, the output currents of the two converters are equal. The resultant negative sequence is also 0.

[0015] The beneficial technical effects of the present invention are:

[0016] The present invention solves the problem of maximizing the use of new energy technologies while reducing the impact of negative sequence current in the traction network, thereby improving the overall power supply quality level and comprehensive benefits of the traction power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural diagram of the photovoltaic power generation and wind power generation connected to the traction power supply system of the present invention.

[0018] Figure 2 This is a schematic diagram of the current detection and control method for connecting photovoltaic power generation and wind power generation to a traction power supply system according to the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] A photovoltaic power generation and wind power generation access system for reducing negative sequence current of a traction network according to the present invention is as follows Figure 1As shown, specifically: the three-phase grid voltage is transformed into α and β two-phase voltages through a balanced traction transformer, and the DC busbars of photovoltaic power generation and wind power generation are connected to the α and β two-phase power supply arms respectively through two sets of single-phase converters to achieve grid connection, and the two sets of single-phase converters have the same installation capacity.

[0021] Another detection module detects the magnitude of the α and β phase traction load power current and transmits it to the controller. The controller reasonably distributes the current fed into the power supply arm by each group of converters according to the load current difference.

[0022] At the same time, a step-up transformer T is arranged between the single-phase converter and the two-phase power supply arm to play the role of isolation and voltage boosting.

[0023] A photovoltaic power generation and wind power generation access method for reducing negative sequence current of a traction network according to the present invention is as follows Figure 2 As shown, the specific steps are:

[0024] Step 1: Assume that the current of photovoltaic power generation and wind power generation connected to the traction grid is equivalent to I = I c1 +I c2 The detection module detects the magnitude of the α and β phase traction load power currents I1 and I2. The difference in traction load power current is equivalent to ΔI L =|I1-I2|.

[0025] Step 2: Compare the difference between the traction grid current and the traction load power current, and calculate the grid-connected current fed back to the α and β phase power supply arms.

[0026] When I≤|ΔI L |, the photovoltaic and wind power generation capacities compensate for the insufficient negative sequence. At this time, the photovoltaic and wind power generation currents are fully fed into the heavy-load power supply arm to reduce the negative sequence. At this time, the negative sequence current I - =|I1-I2-I|.

[0027] When I>|ΔI L |, indicating that the photovoltaic and wind power generation capacities are sufficient to compensate for the negative sequence. At this time, the photovoltaic and wind power generation currents are fed into the two power supply arms at the same time, which not only compensates for the current difference to balance the traction load power, but also balances the excess current to make the synthetic negative sequence 0. At this time, the two sets of converter feed currents are

[0028]

[0029] When both power supply arms are in no-load condition, the output currents of the two converters are equal. The resultant negative sequence is also 0.

[0030] Example:

[0031] Take the case where the load only contains active current, the load current of one phase is 500A, the load current of the other phase is 200A, and the photovoltaic output equivalent current is 100A. When photovoltaic power is not connected, the synthetic negative sequence current is 300A; if photovoltaic power is only connected to the light-load phase, the synthetic current is 400A; if photovoltaic power is only connected to the heavy-load phase, the synthetic current is 200A. It shows that the photovoltaic current fed into different power supply phases will have a significant impact on the synthetic negative sequence of the system, and the use of the method of the present invention will help reduce the level of negative sequence current in the traction network.

Claims

1. A photovoltaic power generation and wind power generation access system for reducing negative sequence current of a traction network, characterized in that: In the system, the three-phase grid voltage is converted into α and β two-phase voltages through a balanced traction transformer. The DC busbars of photovoltaic power generation and wind power generation are connected to the α and β two-phase power supply arms through two sets of single-phase converters to achieve grid connection. The two sets of single-phase converters have the same installation capacity. The detection module detects the magnitude of the α and β two-phase traction load power current and transmits it to the controller. The controller reasonably distributes the current fed into the power supply arm by each set of single-phase converters according to the load current difference. The specific control steps of the system are as follows: Step 1: Assume that the current of photovoltaic power generation and wind power generation connected to the traction grid is equivalent to I = I c1 +I c2 , I c1 ,I c2 The detection module detects the α and β phase traction load power currents i1(t) and i2(t), and calculates the current magnitudes I1 and I2. The traction load power current difference is equivalent to ΔI L =|I1-I2|; Step 2: Compare the difference between the traction grid current and the traction load power current, and calculate the grid-connected current fed back to the α and β phase power supply arms; When I≤|ΔI L |, the photovoltaic and wind power generation capacities compensate for the insufficient negative sequence. At this time, the photovoltaic and wind power generation currents are fully fed into the heavy-load power supply arm to reduce the negative sequence. At this time, the negative sequence current I - =|I1-I2-I|; When I>|ΔI L |, indicating that the photovoltaic power generation and wind power generation capacity are sufficient to compensate for the negative sequence. At this time, the photovoltaic power generation and wind power generation currents are fed into the two-phase power supply arms at the same time, which not only compensates for the current difference to balance the traction load power, but also balances the excess current to make the synthetic negative sequence 0. At this time, the two groups of single-phase converters feed currents are: When both phase power supply arms are in no-load condition, the output currents of the two groups of single-phase converters are equal. The resultant negative sequence is also 0.

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