Optical storage grid-connected source end direct power control method for railway traction power supply system

Abstract

The invention belongs to the technical field of alternating-current electrified railway traction power supply, and particularly relates to an optical storage grid-connected source end direct power control method for a railway traction power supply system. A voltage transformer PTa connected to a traction bus a is used for collecting traction bus voltage, a bus current transformer CTa is used for collecting bus current, and a grid-connected current transformer CTc is used for collecting grid-connected current; then, power supply power and grid-connected power are calculated, and the power supply power is traction bus power; calculating a grid-connected power instruction, performing closed-loop control on a grid-connected converter, and finally generating a control instruction required by the railway traction power supply optical storage grid-connected equipment; wherein the control system compares the grid-connected power at the current moment with the grid-connected power at the previous moment, and adjusts the step length of the grid-connected power. According to the method, only the source end current at the traction bus is collected to calculate the source end power, photovoltaic electric energy grid connection at the traction substation is achieved by directly controlling the source end power, and the problem that the voltage unbalance degree is increased due to the fact that residual electricity is reversely sent to a public power grid can be solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of AC electrified railway traction power supply, and particularly relates to a method for directly controlling power of a grid-connected source end of a railway traction power supply system. BACKGROUND

[0002] Electrified railways play a crucial role in economic and social development. At present, there are many researches and explorations on the application of new energy power generation technology in the field of rail transit. Distributed photovoltaic and energy storage are in the demonstration application stage in the electrified railway traction power supply system. The distributed photovoltaic and energy storage systems reported in the public are connected to the traction network side of the electrified railway traction power supply system, and the output power of the photovoltaic and energy storage system is adjusted in real time according to the traction load information. Here, the traction load information refers to the load power of the multiple feeders of the traction substation of the electrified railway traction power supply system.

[0003] In the prior art, patent No. CN211351725U discloses an electrified railway traction power supply system based on a multi-source access structure; the paper "Day-ahead energy optimization and dispatching strategy of electrified railway'source-grid-train-storage' collaborative energy supply system" proposes a system scheme for the application of new energy in the electrified railway traction power supply system, but does not involve the power control of the grid-connected end. Patent CN110729909A proposes a device-level control method, but does not involve the calculation method of the output power reference value. Therefore, if the traditional self-generation and self-use, and surplus power grid-connected operation mode is adopted, the above-mentioned method is easy to cause the increase of voltage unbalance degree of the grid side, because the railway traction power supply system belongs to single-phase power supply.

[0004] Patents CN111313465A, CN111262245A, CN110190628A, CN113492733A, and the papers "Real-time energy management and control strategy of electrified railway station based on 'rules + optimization'", and "Low-frequency stability research on emergency power supply scheme of photovoltaic and energy storage access traction power supply system" all disclose or propose different forms of new energy control methods applied in the electrified railway traction substation, which all need to obtain the traction load data of the traction substation in order to calculate the output power of the new energy. In addition, in order to realize real-time control, the traction load power is calculated through the voltage of the traction bus and the current of the feeder, as shown in Figure 1 , where CT is the feeder current transformer. In addition, the railway traction power supply system generally has multiple feeder current transformers, as shown in Figure 2 , so the load current acquisition and calculation are complex.

[0005] In the aspect of photovoltaic and energy storage grid-connected control of the railway traction power supply system, real-time control is mainly based on traction load data. The existing technology mainly has the following shortcomings: 1. Most of the reported new energy power generation technologies applied to railway traction power supply systems adopt a self-consumption and surplus power grid connection operation mode. However, the new energy power generation systems connected to the railway traction power supply system are all single-phase grid-connected systems. The surplus photovoltaic power fed back to the public grid is manifested as single-phase power, which will cause a large negative sequence current and thus worsen the voltage imbalance of the public grid.

[0006] 2. Currently, most control methods for renewable energy power generation systems applied in railway traction substations require obtaining traction load data from the traction substation to calculate the renewable energy output power. Generally, railway traction power supply systems have multiple feeders, requiring the collection of load currents from all feeders to calculate load power. Therefore, the large number of feeder current samples increases hardware complexity. Calculating the currents and power of multiple feeders also increases software computational complexity. Furthermore, the number of feeders varies between different traction substations, making standardized design difficult.

[0007] Therefore, the present invention provides a method for direct power control at the source end of a photovoltaic-storage grid-connected power supply system for railway traction power supply. Summary of the Invention

[0008] The purpose of this invention is to provide a direct power control method for the source end of a photovoltaic-storage grid-connected railway traction power supply system. This method eliminates the need to collect multiple feeder currents and calculate load power; it only requires collecting the source end current at the traction bus, i.e., the traction bus current, to calculate the source end power, thus reducing the number of samples. Furthermore, by directly controlling the source end power, the photovoltaic power at the traction substation can be grid-connected and absorbed, avoiding the backflow of surplus power into the public grid and preventing increased voltage imbalance. This method helps promote the application of new energy sources in the railway sector, facilitates the integration of new energy sources with rail transit, and improves the green development level of electrified railways.

[0009] The specific technical solution adopted by this invention is as follows: A direct power control method for the source end of a railway traction power supply system with photovoltaic and energy storage grid connection involves: acquiring the traction bus voltage via a voltage transformer PTa connected to the traction bus a; acquiring the bus current via a bus current transformer CTa; and acquiring the grid-connected current via a grid-connected current transformer CTc. Then, the power supply and grid-connected power are calculated; the power supply power is the traction bus power. The grid-connected power command is then calculated, and closed-loop control of the grid-connected converter is performed. Finally, the control commands required for the railway traction power supply system with photovoltaic and energy storage grid connection are generated. The control system compares the grid-connected power at the current moment with that at the previous moment and adjusts the grid-connected power step size accordingly. The power of the grid-connected converter is directly controlled by the magnitude of the power supply, so that the power supply is close to 0. This means that when there is a traction load, the photovoltaic power is fed into the traction grid for consumption, and when there is a traction load, the regenerative braking energy is stored in the energy storage system. The source end direct power control method comprises the following steps: Step 1: calculating the current power source power P by the voltage and current information collected by the bus voltage transformer PTa, the bus current transformer CTa and the grid-connected current transformer CTc s (k-1) and the grid-connected power P c (k-1), both of which are recorded as the power at the previous moment, the previous moment being represented by (k-1); Step 2: determining whether to adjust the grid-connected power step according to the value of the adjustment grid-connected power step state State_TZ; here, State_TZ=1 indicates that the grid-connected power step needs to be adjusted, and State_TZ=0 indicates that the grid-connected power step does not need to be adjusted; If the grid-connected power step does not need to be adjusted, a fixed grid-connected power step Δp is obtained; if the grid-connected power step needs to be adjusted, an adjusted grid-connected power step-m×Δp is obtained; here, m is a positive number less than 1: Step 3: calculating the grid-connected power instruction; if the power source power at the previous moment is greater than 0, i.e. P s (k-1)>0, the grid-connected power instruction value P× c (k) at the current moment is the sum of the grid-connected power instruction value P× c (k-1) at the previous moment and the adjustment grid-connected power step Δp; if the power source power at the previous moment is not greater than 0, i.e. P s (k-1)≤0, the grid-connected power instruction value P× c (k) at the current moment is the grid-connected power instruction value P× c (k-1) at the previous moment minus the adjustment grid-connected power step Δp; the obtained grid-connected power instruction value P× c (k) at the current moment is used for closed-loop control of the grid-connected converter; Step 4: determining whether to adjust the grid-connected power step according to the current power source power change; when the power source power at the previous moment is greater than 0, i.e. P s (k-1)>0, if the current power source power does not increase, i.e. P s (k)≤P s (k-1), the grid-connected power step is not adjusted, and the state State_TZ is set to 0; otherwise, the grid-connected power step is adjusted, and the state State_TZ is set to 1; when the power source power at the previous moment is not greater than 0, i.e. P s (k-1)≤0, if the current power source power does not decrease, i.e. P s (k)≥P s(k-1), then the grid-connected power step is not adjusted, the state State_TZ is set to 0; otherwise, the grid-connected power step is adjusted, and the state State_TZ is set to 1; wherein, when the grid-connected power step is adjusted, the photovoltaic converter operates in an MPPT state or a power limiting state; Step 5: judging whether to stop, if stopping, ending running, if not stopping, returning to start again.

[0010] The technical effects achieved by the application are as follows: The application does not need to collect feeder current and calculate traction load power. The number of feeders of a traction substation is not completely the same, and the traditional method needs to calculate the traction load power according to all feeder currents and bus voltage. The one kind of railway traction power supply system light storage grid-connected source end direct power control method of the application only needs to collect bus voltage, bus current and grid-connected current of the traction substation, effectively reduces the number of current collection, helps to simplify the hardware sampling circuit, reduce the software calculation amount, and also helps to standardize the sampling circuit and software.

[0011] The application realizes source following load, and avoids that the photovoltaic residual electricity on-grid deteriorates voltage unbalance degree. The one kind of railway traction power supply system light storage grid-connected source end direct power control method of the application directly controls the power of the grid-connected converter according to the size of the power supply power, so that the power supply power is close to 0, realizes source following load, can avoid that the photovoltaic residual electricity is fed back to the public power grid, and does not aggravate the voltage unbalance degree of the power grid side. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 CN113492733A traction load collection schematic diagram in the prior art is shown in Figure 1; Figure 2 The traction power supply system feeder current transformer (CTa-CTan, CTb1-CTbn) schematic diagram is shown in Figure 2; Figure 3 The main circuit structure schematic diagram of the new energy conversion device of the application is shown in Figure 3; Figure 4 The main circuit structure schematic diagram of the railway traction power supply system light storage grid-connected equipment of the application is shown in Figure 4; Figure 5 The source end direct power control flow chart of the application is shown in Figure 5. DETAILED DESCRIPTION

[0013] In order to make the purpose and advantages of the application more clear and explicit, the application is specifically described below in combination with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the application, and does not strictly limit the specific protection scope requested by the application.

[0014] As Figure 2As shown, generally traction substation in low voltage side has two traction bus, two traction bus each has multiple feeder. In order to simplify the description, the following with traction substation of a single traction bus connected to the railway traction power supply system of photovoltaic storage grid connected equipment for example to explain. In the following, traction bus is recorded as traction bus a, refers to the traction bus.

[0015] As shown in Figure 3 , generally traction substation incoming line is public power grid three phase power supply, through the traction transformer TT three phase power supply to voltage as 27.5kV single phase power supply connection to traction bus a, traction transformer TT and traction bus a between the bus current transformer CTa. Traction bus a connection multiple feeder, each feeder set a current transformer, such as Figure 3 In the CTa to CTn.

[0016] Railway traction power supply system of photovoltaic storage grid connected equipment generally connected to the traction bus a, for detecting grid current generally set grid current transformer CTc. Railway traction power supply system of photovoltaic storage grid connected equipment main circuit structure can have many kinds, such as Figure 4 As shown in two typical structure, respectively for direct current bus coupling interconnection and alternating current bus coupling interconnection photovoltaic power generation and energy storage system circuit structure.

[0017] As shown in Figure 5 , a railway traction power supply system of photovoltaic storage grid connected source end direct power control method, through the voltage transformer PTa connected to the traction bus a traction bus voltage acquisition, through the bus current transformer CTa acquisition bus current, through the grid current transformer CTc acquisition grid current; Then, calculate the power, grid power, and then calculate the grid power instruction, grid connected inverter closed loop control, finally generate the control instruction required by the railway traction power supply photovoltaic storage grid connected equipment; Wherein, the control system compares the grid power at the current time and the last time, adjust the grid power step; According to the size of the power directly control grid connected inverter power, so that the power is close to 0, that is, in the traction load with traction state to realize the photovoltaic power energy to traction net energy consumption, in the traction load with regenerative braking state to the regenerative braking energy storage to energy storage system; The source end direct power control method includes the following steps: Step 1: through the bus voltage transformer PTa, bus current transformer CTa, grid current transformer CTc acquisition voltage, current information calculation of the current power P s (k-1) and grid power P c (k-1), all recorded as the previous time power, the previous time by (k-1) represents; Step 2: According to the value of the grid-connected power step adjustment state State_TZ, it is determined whether to adjust the grid-connected power step; here, State_TZ=1 indicates that the grid-connected power step needs to be adjusted, and State_TZ=0 indicates that the grid-connected power step does not need to be adjusted. If the grid-connected power step does not need to be adjusted, a fixed grid-connected power step Δp is obtained; if the grid-connected power step needs to be adjusted, an adjusted grid-connected power step -m×Δp is obtained; here, m is a positive number less than 1: Step 3: Calculate the grid-connected power instruction; if the power supply power at the previous moment is greater than 0, i.e. P s (k-1)>0, then the grid-connected power instruction value P× c (k) at the current moment is the sum of the grid-connected power instruction value P× c (k-1) at the previous moment and the adjusted grid-connected power step Δp; if the power supply power at the previous moment is not greater than 0, i.e. P s (k-1)≤0, then the grid-connected power instruction value P× c (k) at the current moment is the grid-connected power instruction value P× c (k-1) at the previous moment minus the adjusted grid-connected power step Δp; the closed-loop control of the grid-connected converter is performed according to the obtained grid-connected power instruction value P× c (k) at the current moment. Step 4: Determine whether to adjust the grid-connected power step according to the change of the power supply power at the current moment; when the power supply power at the previous moment is greater than 0, i.e. P s (k-1)>0, if the current power supply power does not increase, i.e. P s (k)≤P s (k-1), the grid-connected power step is not adjusted, and the state State_TZ is set to 0; otherwise, the grid-connected power step is adjusted, and the state State_TZ is set to 1; when the power supply power at the previous moment is not greater than 0, i.e. P s (k-1)≤0, if the current power supply power does not decrease, i.e. P s (k)≥P s (k-1), the grid-connected power step is not adjusted, and the state State_TZ is set to 0; otherwise, the grid-connected power step is adjusted, and the state State_TZ is set to 1; wherein, when the grid-connected power step is adjusted, the photovoltaic converter operates in an MPPT state or a power limiting state according to the output power demand, MPPT is “Maximum Power Point Tracking”, which is a commonly used term in the industry. The power limiting state is a running state of the photovoltaic converter, which means that the photovoltaic does not run at the maximum power, but runs at a certain state smaller than the maximum power according to the external instruction.

[0018] Step 5: judging whether to stop or not, if yes, ending the operation, if no, returning to start again.

[0019] The working principle of the present application is that the source end is controlled in the present application. The traction load power is not calculated by collecting the multi-way feeder current, and only the voltage and current at the traction bus are collected to calculate the source end power, and the grid-connected converter power is directly controlled according to the size of the power source power.

[0020] The direct power control is used in the present application. The grid-connected converter power is directly controlled according to the size of the power source power, so that the power source power is close to 0, that is, the photovoltaic electric energy can be fed to the traction network to be consumed when the traction load is in the traction state, and the regenerative braking energy can be stored in the energy storage system when the traction load is in the regenerative braking state.

[0021] The variable power step is used in the present application. The direct power control with variable power step is used, that is, the power step is adjusted according to the change of the power source power. When the power source power changes towards 0, the power step is maintained unchanged. When the power source power changes beyond 0 in the undesired direction, the power step is adjusted to a smaller negative value.

[0022] In the present application, the feeder current collection and the calculation of the traction load power are not needed. The number of feeders of the traction substation is not completely the same, and the traditional method needs to calculate the traction load power according to all feeder currents and bus voltage. The direct power control method of the railway traction power supply system photovoltaic storage grid-connected source end in the present application only needs to collect the bus voltage, bus current and grid-connected current of the traction substation, so that the number of current collection is effectively reduced, which is helpful to simplify the hardware sampling circuit, reduce the software calculation amount, and also helpful to the standardization of the sampling circuit and software.

[0023] In the present application, the source follows the load, and the voltage imbalance degree is avoided due to the feedback of the photovoltaic residual electricity to the public power grid. The direct power control method of the railway traction power supply system photovoltaic storage grid-connected source end in the present application directly controls the grid-connected converter power according to the size of the power source power, so that the power source power is close to 0, the source follows the load, and the feedback of the photovoltaic residual electricity to the public power grid can be avoided, so that the voltage imbalance degree of the power grid side is not aggravated.

[0024] The above is only the preferred embodiment of the present application, and it should be pointed out that, for ordinary skilled persons in the art, some improvements and refinements can be made without departing from the principle of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application. The structures, devices and operation methods not specifically described and explained in the present application are implemented according to the conventional means in the art, unless otherwise specified and limited.

Claims

1. A method for direct power control at the source end of a photovoltaic-storage grid-connected railway traction power supply system, characterized in that: The system collects the traction bus voltage via voltage transformer PTa connected to traction bus a, the bus current via bus current transformer CTa, and the grid-connected current via grid-connected current transformer CTc. Then, it calculates the power supply and grid-connected power, with the power supply power being the traction bus power. Next, it calculates the grid-connected power command, performs closed-loop control of the grid-connected converter, and finally generates the control commands required for the railway traction power supply photovoltaic-storage grid-connected equipment. The control system compares the current grid-connected power with the previous time and adjusts the grid-connected power step size accordingly. The power of the grid-connected converter is directly controlled by the magnitude of the power supply, so that the power supply is close to 0. This means that when there is a traction load, the photovoltaic power is fed into the traction grid for consumption, and when there is a traction load, the regenerative braking energy is stored in the energy storage system.

2. The method for direct power control at the source end of a photovoltaic-storage grid-connected railway traction power supply system according to claim 1, characterized in that: The source-side direct power control method includes the following steps: Step 1: Calculate the current power P using the voltage and current information collected by the bus voltage transformer PTa, bus current transformer CTa, and grid-connected current transformer CTc. s (k-1) and grid-connected power P c (k-1) represents the power at the previous moment, which is represented by (k-1).

3. The method for direct power control at the source end of a photovoltaic-storage grid-connected railway traction power supply system according to claim 2, characterized in that: The source-side direct power control method further includes the following steps: Step 2: Determine whether to adjust the grid-connected power step size based on the value of State_TZ. Here, State_TZ=1 indicates that the grid-connected power step size needs to be adjusted, and State_TZ=0 indicates that the grid-connected power step size does not need to be adjusted. If no adjustment of the grid-connected power step size is required, a fixed grid-connected power step size Δp is obtained; if the grid-connected power step size needs to be adjusted, the adjusted grid-connected power step size -m×Δp is obtained; here, m is a positive number less than 1.

4. The method for direct power control at the source end of a photovoltaic-storage grid-connected railway traction power supply system according to claim 3, characterized in that: The source-side direct power control method further includes the following steps: Step 3: Calculate the grid-connected power command; if the power supply power was greater than 0 at the previous moment, i.e., P... s If (k-1)>0, then the current grid-connected power command value P× c (k) represents the grid-connected power command value P× at the previous moment. c (k-1) is the sum of the power step size Δp adjusted to the grid connection; if the power supply power in the previous moment was not greater than 0, i.e., P s If (k-1)≤0, then the current grid-connected power command value P× c (k) represents the grid-connected power command value P× at the previous moment. c (k-1) Subtract the adjustment step size Δp for grid-connected power; based on the current grid-connected power command value P× c (k) Perform closed-loop control of the grid-connected converter.

5. The method for direct power control at the source end of a photovoltaic-storage grid-connected railway traction power supply system according to claim 4, characterized in that: The source-side direct power control method further includes the following steps: Step 4: Determine whether to adjust the grid-connected power step size based on the current power supply change; when the power supply was greater than 0 in the previous moment, i.e., P... s If (k-1)>0, and the current power supply does not increase, i.e., P s (k)≤P s If (k-1), then the grid-connected power step size is not adjusted, and the state State_TZ is set to 0; otherwise, the grid-connected power step size is adjusted, and the state State_TZ is set to 1; when the power supply power in the previous moment is not greater than 0, i.e., P s (k-1)≤0, if the current power supply does not decrease, i.e., P s (k)≥P s If (k-1), then the grid-connected power step size is not adjusted and the state is set to State_TZ=0; otherwise, the grid-connected power step size is adjusted and the state is set to State_TZ=1. When adjusting the grid-connected power step size, the photovoltaic converter operates in MPPT state or power limiting state.

6. The method for direct power control at the source end of a photovoltaic-storage grid-connected railway traction power supply system according to claim 5, characterized in that: The source-side direct power control method further includes the following steps: Step 5: Determine if a shutdown is required. If a shutdown is required, end the operation; otherwise, return and start over.

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