A Photovoltaic and Negative-Sequence Cooperative Compensation Control Method for Electrified Railways

Abstract

The present invention discloses a coordinated compensation control method for photovoltaic and negative sequence of electrified railways, specifically: collecting electrical quantities at the point of common coupling, the grid-connected reverse point of the photovoltaic power station, and the grid-connected point of the traction substation, and calculating the voltage unbalance degree through sequence component decomposition; establishing an analytical model of the negative sequence component for "weak grid - traction substation - photovoltaic power station"; calculating the negative sequence current emission capacity of the photovoltaic power station based on the grid connection guidelines of the photovoltaic power station and with the safety operation boundary of the photovoltaic power station as a constraint; calculating the reference current command of the negative sequence compensation amount for the traction substation and the photovoltaic power station branch according to the analytical model with the national standard limit value at the point of common coupling as a constraint. The present invention can achieve full-range compensation of the negative sequence voltage at the point of common coupling, not only utilize the negative sequence active support ability of new energy, but also reduce the negative sequence compensation capacity of the STATCOM device in the traction substation, saving investment costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of power quality governance, and particularly relates to a coordinated compensation control method for negative sequence of photovoltaic and electrified railway. Background Art

[0002] Driven by the "dual carbon" goal, the proportion of new energy installed capacity in the power grid and the capacity of unbalanced loads such as electrified railways have both increased. The dynamic changes at the source end and load end have made power quality problems mainly characterized by negative sequence increasingly prominent, triggering problems such as disconnection of new energy power stations and distributed photovoltaics, tripping of user motors, and torsional vibration of generator shaft systems many times, seriously affecting the safety and stability of the power grid and the normal production and living electricity consumption of users. To address the negative sequence problem, on the one hand, STATCOM devices are usually used for compensation in electrified railway traction substations. On the other hand, large-scale photovoltaic power stations can also provide necessary auxiliary support services when meeting the power generation requirements. However, due to the intermittent, random, and volatile output of photovoltaic power stations, most of the grid-connected inverters are not operating at full load. Therefore, how to achieve coordinated compensation of negative sequence between electrified railways and photovoltaic power stations has become an urgent problem to be solved. Summary of the Invention

[0003] The present invention provides a coordinated compensation control method for negative sequence of photovoltaic and electrified railway. By controlling the negative sequence current commands of the STATCOM device in the traction substation and the grid-connected inverter of the photovoltaic power station, enabling them to jointly undertake the task of negative sequence governance, it is of great significance for improving the power quality of the power grid and increasing the equipment utilization rate.

[0004] A coordinated compensation control method for negative sequence of photovoltaic and electrified railway according to the present invention includes the following steps:

[0005] Step 1: Collect electrical quantities at the point of common coupling, the grid-connected point of the photovoltaic power station, and the grid-connected point of the traction substation, and calculate the unbalance degree of the electrical quantities through sequence component decomposition.

[0006] Step 2: Establish an analytical model of negative sequence components for "traction substation - photovoltaic power station".

[0007] Step 3: Based on the grid connection guidelines of the photovoltaic power station, with the safe operation boundary of the photovoltaic power station as a constraint, calculate the negative sequence current emission capacity of the photovoltaic power station.

[0008] Step 4: With the national standard limit at the point of common coupling as a constraint, according to the analytical model in Step 2, calculate the reference current commands of the negative sequence compensation amounts for the branches of the traction substation and the photovoltaic power station.

[0009] Further, in Step 1, the output voltage of the connected photovoltaic power station is converted into three-phase alternating current by the grid-connected inverter. The positive and negative sequence components of the electrical quantities in the three-phase coordinate system are:

[0010]

[0011]

[0012] Where: X represents the voltage or current component, and a is the complex operator are the positive-sequence component and the negative-sequence component respectively, represent the voltage and current components of phases A, B, and C respectively.

[0013] Furthermore, the unbalance degrees of the electrical quantities in step 1 include the voltage unbalance degree VUF and the current unbalance degree CUF:

[0014]

[0015] Where: and are respectively and in the complex expression form.

[0016] Furthermore, the negative-sequence component analysis model of "traction substation - PV power station" in step 2 is:

[0017]

[0018] Where: ε PCC is the three-phase voltage unbalance degree at the point of common coupling, CUF PCC is the current unbalance degree at the point of common coupling, VUF TSS is the high-voltage unbalance degree at the incoming line side of the traction substation, CUF PV is the current unbalance degree at the outlet of the grid-connected inverter, is the positive-sequence impedance of the traction substation, is the negative-sequence equivalent impedance of the PV power station, is the positive and negative-sequence impedance of the transmission line from the point of common coupling to the traction substation, is the negative-sequence impedance of the transmission line from the point of common coupling to the PV power station.

[0019] Furthermore, the negative-sequence current emission capacity in step 3 is calculated as:

[0020]

[0021] Where: are respectively the negative-sequence current commands of the PV power station and the STATCOM compensation device of the traction substation, represents the remaining capacity of the unit.

[0022] Furthermore, the reference current command of the negative-sequence compensation amount in step 4 is:

[0023]

[0024] Wherein: is the compensation current required for the common connection point, is the positive-sequence current of the traction substation, and k1 is Among them, is the negative-sequence impedance on the STATCOM side, is the positive-sequence impedance on the traction substation side, is the positive-sequence current on the STATCOM side, represents the real-time unbalance degree, is the negative-sequence current of the traction substation;

[0025]

[0026] Wherein: the response coefficient k p is a constant, is the national standard limit, and ε PCC is the voltage unbalance degree of the common connection point measured in real time.

[0027] The beneficial technical effects of the present invention are:

[0028] The present invention can achieve full-range compensation of the negative-sequence voltage at the common connection point, utilizes the negative-sequence active support ability of new energy, reduces the negative-sequence compensation capacity of the STATCOM device in the traction substation, makes full use of the remaining capacity of the grid-connected inverter equipment in the photovoltaic power station, saves the investment cost of the compensation device, improves the power quality of the power grid, and improves the equipment utilization rate. Description of the Drawings

[0029] Figure 1 is the flow chart of the negative-sequence coordinated compensation control method for photovoltaic and electrified railway of the present invention. Specific Embodiments

[0030] The present invention will be further described in detail below with reference to the drawings and specific implementation methods.

[0031] In a specific embodiment of the present invention, the flow chart is as[[ID=S0]] Figure 1 shown and includes the following steps:

[0032] [[ID=S4]]Step 1: Collect the voltage and current at the common connection point, the outlet of the grid-connected inverter of the photovoltaic power station, and the outlet of the traction power supply system, and calculate the unbalance degree of each electrical quantity through sequence component decomposition:

[0033] The positive and negative sequence components of the electrical quantity in the three-phase coordinate system are:

[0034]

[0035]

[0036] Where: X represents the voltage or current component, are the positive sequence component and the negative sequence component respectively, and a is the complex operator are the positive sequence component and the negative sequence component respectively, respectively represent the voltage and current components of phases A, B, and C.

[0037] The unbalance degree includes the voltage unbalance degree VUF and the current unbalance degree CUF:

[0038]

[0039] Where: and are respectively and in the complex expression form.

[0040] Step 2: Establish a negative sequence component analysis model of "traction substation - photovoltaic power station".

[0041]

[0042] Where: ε PCC is the three-phase voltage unbalance degree at the point of common coupling, CUF PCC is the current unbalance degree at the point of common coupling, VUF TSS is the high voltage unbalance degree at the incoming line side of the traction substation, CUF PV is the current unbalance degree at the outlet of the grid-connected inverter, is the positive sequence impedance of the traction substation, is the negative sequence equivalent impedance of the photovoltaic power station, is the positive and negative sequence impedance of the transmission line from the point of common coupling to the traction substation, is the negative sequence impedance of the transmission line from the point of common coupling to the photovoltaic power station.

[0043] Step 3: Based on the grid connection guidelines of the photovoltaic power station, calculate the negative sequence current emission capacity of the photovoltaic power station with the safe operation boundary of the photovoltaic power station as the constraint.

[0044]

[0045] Where: are the negative sequence current commands of the compensation devices STATCOM of the photovoltaic power station and the traction substation respectively, represents the remaining capacity of the unit.

[0046] Step 4: With the national standard limit value at the point of common coupling as the constraint, calculate the reference current commands of the negative sequence compensation amounts of the traction substation and the photovoltaic power station branches according to the analysis model in Step 2.

[0047]

[0048] In the formula: is the compensation current required for the common connection point, is the positive-sequence current of the traction substation, and k1 is where is the negative-sequence impedance on the STATCOM side, is the positive-sequence impedance on the traction substation side, is the positive-sequence current on the STATCOM side, represents the real-time unbalance degree, is the negative-sequence current of the traction substation;

[0049]

[0050] In the formula: The response coefficient k p is a constant, is the national standard limit, and ε PCC is the voltage unbalance degree of the common connection point measured in real time.

Claims

1. A photovoltaic and electrified railway negative sequence collaborative compensation control method, characterized in that, Including the following steps: Step 1: Collect the electrical quantities of the common connection point, the grid-connected inverter point of the photovoltaic power station, and the grid-connected point of the traction substation, and calculate the unbalance degree of the electrical quantities through sequence component decomposition. The unbalance degree of the electrical quantities includes the voltage unbalance factor VUF and the current unbalance factor CUF: In the formula, and are respectively and in complex number representation forms; Step 2: Establish a negative sequence component analysis model of "traction substation - photovoltaic power station". The negative sequence component analysis model of "traction substation - photovoltaic power station" is: Where: ε PCC is the three-phase voltage unbalance degree of the common connection point, CUF PCC is the current unbalance degree of the common connection point, VUF TSS is the high voltage unbalance degree at the incoming line side of the traction substation, CUF PV is the current unbalance degree at the outlet of the grid-connected inverter, is the positive sequence impedance of the traction substation, is the negative sequence equivalent impedance of the PV power station, are the positive and negative sequence impedances of the transmission line from the common connection point to the traction substation, is the negative sequence impedance of the transmission line from the common connection point to the PV power station; Step 3: Based on the grid connection guidelines of the photovoltaic power station, with the safe operation boundary of the photovoltaic power station as the constraint, calculate the negative sequence current emission capacity of the photovoltaic power station. The negative sequence current emission capacity is: Where: are the negative sequence current commands of the STATCOM of the PV power station and the traction substation compensation device respectively, represents the remaining capacity of the unit; Step 4: With the national standard limit value at the common connection point as the constraint, according to the analysis model in Step 2, calculate the reference current command of the negative sequence compensation amount for the traction substation and the photovoltaic power station branch.

2. The method for photovoltaic and electrified railway negative sequence collaborative compensation control according to claim 1, characterized in that, In Step 1, the output voltage of the connected photovoltaic power station is converted into three-phase alternating current through a grid-connected inverter.

3. The photovoltaic and electrified railway negative sequence coordinated compensation control method according to claim 1 is characterized in that: The reference current command value of the negative sequence compensation amount in Step 4 is: Wherein: is the compensation current required for the common connection point, is the positive sequence current of the traction substation, and k1 is wherein, is the negative sequence impedance on the STATCOM side, is the positive sequence impedance on the traction substation side, is the positive sequence current on the STATCOM side, represents the real-time unbalance degree, is the negative sequence current of the traction substation; Where: response coefficient k p is a constant, is the national standard limit, ε PCC It is the voltage imbalance degree of the common connection point measured in real time.

Images