On-grid distributed photovoltaic power redistribution optimization method

Abstract

The present invention relates to an on-grid distributed photovoltaic power redistribution optimization method. Facilities, such as lines, transformers, and switches, which access an auxiliary power system are arranged; an automatic control device is mounted; parameters such as a target power issued by a power grid, an expected power value of each photovoltaic power generation area, the bus voltage and current of the auxiliary power system, the state and current of a conventional generator set grid-connected main switch, and the rotating speed of a turbine are collected; the operation state of a conventional generator set and the voltage quality of an auxiliary power bus are monitored; an expected power-generation power of each distributed photovoltaic power generation area for on-grid power generation is compared with the target power issued by the power grid; and by means of an optimized power distribution algorithm, an optimal power generation area is selected to be merged into the auxiliary power bus. Therefore, resources of a photovoltaic power station are fully utilized while a power grid connection protocol is reserved; additionally, frequent switch operation of operators is effectively replaced, thereby achieving automatic switching; and safe and reliable operation of an auxiliary power system during photovoltaic merging is guaranteed by means of locking logic of merging conditions.

Description

A method for optimizing online distributed photovoltaic power redistribution TECHNICAL FIELD

[0001] The present application relates to a method for optimizing online distributed photovoltaic power redistribution. BACKGROUND

[0002] In recent years, the installation capacity of distributed photovoltaic power stations has developed rapidly due to their small pollution, outstanding environmental protection benefits, and low site requirements. Photovoltaic power generation output presents the characteristics of "large in summer and autumn, small in winter and spring, and no light in late peak". With the increase of installed capacity, the intra-day and inter-day volatility is significantly enhanced. In addition, due to the limitation of the flexibility of the power system operation, when the power supply exceeds the load demand, photovoltaic power consumption may be limited. In many places in China, distributed photovoltaic power has been limited. Moreover, the online electricity price has a downward trend.

[0003] Traditional power plants, such as thermal power plants and hydropower stations, have installed distributed photovoltaic power stations in the open space, roof, and idle area outside the plant. In the early stage, due to new energy price subsidies, the economic benefits of photovoltaic power generation after online are relatively considerable. However, under the background of light abandonment and power limitation, the installed capacity cannot be fully online during the period when the photovoltaic power generation efficiency is the highest, and most of the photovoltaic resources are idle and wasted. Therefore, it is necessary to study the improvement of the utilization efficiency and economic value of distributed photovoltaic power stations. Traditional power plants, such as thermal power plants and hydropower stations, have a centralized load center, i.e., a plant power system. Generally, the power generated by the generator is supplied to the plant power load through a high-voltage transformer in the plant. If the excess power of the online photovoltaic power can be supplied to the plant power load, the full utilization of photovoltaic resources can be realized, and the consumption of plant power can be saved. The traditional generator can output more power to the grid, and the economic benefits are obvious. To realize the online distributed photovoltaic power and the flexible access to the plant power system, there are mainly problems: (1) how to directly access the plant power system from the online distributed photovoltaic power; (2) how to distribute the online power and the plant power to realize the optimization of power; (3) how to control the impact on the plant power system when accessing the plant power system to prevent the influence on the safe and stable operation of the traditional generator; and (4) how to reduce the operation of the operator to realize the automatic switching of the distributed photovoltaic power generation. Therefore, improvement and innovation are imperative.

[0004] SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide a method for optimizing online distributed photovoltaic power redistribution, which can access the plant power system under the premise of online distributed photovoltaic power, realize the full utilization of photovoltaic resources, create good economic benefits, and ensure the safe and stable operation of the plant power system.

[0006] In order to achieve the above object, the technical scheme of the present application is:

[0007] An online distributed photovoltaic power redistribution optimization method, comprising the following steps:

[0008] Step one: arranging line facilities connected to the plant power system

[0009] A section of busbar is introduced in the plant power system standby interval as a photovoltaic access busbar (plant power busbar);

[0010] A cable line is connected to the above busbar at the low port of the grid-connected switch on the high-voltage side of the distributed photovoltaic power generation area booster, and corresponding switch equipment is added, and the switches are G1, G2, G3……Gi respectively; if the voltage on the high-voltage side of the distributed photovoltaic power generation booster is inconsistent with the voltage level of the plant power system busbar, a transformer device needs to be added;

[0011] Step two: installing a control device

[0012] The device is installed in the control room of the distributed photovoltaic system in a group screen mode;

[0013] The device has two network communication interfaces, one of which is connected to the DCS system of the traditional generator set, and the other is connected to the AGC control system of the distributed photovoltaic power station;

[0014] The device has an input quantity interface;

[0015] The device has an output quantity interface;

[0016] The device has a voltage and current analog quantity interface;

[0017] Step three: the control device collects data

[0018] The target power issued by the power grid, the expected maximum power value of each photovoltaic power generation area, the grid-connected switch state, the plant power side switch state, the plant system busbar voltage and current, the traditional generator set grid-connected main switch state and current, and the steam turbine speed are collected by the control device respectively;

[0019] The control device is a prior art and can meet the above functions, such as a PLC controller;

[0020] Step four: access plant power control logic

[0021] (1) Traditional generator set operation state judgment

[0022] Grid-connected state: the traditional generator set grid-connected main switch is in the closed position, and the current is greater than 10% of the rated value;

[0023] Plant power busbar quality requirements:

[0024] a) Bus voltage harmonic content is less than 4%;

[0025] b) Bus voltage amplitude is within ± 6% of the rated voltage;

[0026] c) Current rate of change is less than the maximum load start-up current rate of change;

[0027] In grid-connected state, and the auxiliary power bus meets the above quality requirements, allowing the distributed photovoltaic into the auxiliary power system;

[0028] Shutdown state: the grid-connected main switch of the traditional generator set is in the split position, and the turbine speed is less than or equal to the turning gear speed;

[0029] In the shutdown state, and the auxiliary power bus meets the above quality requirements, allowing the distributed photovoltaic into the auxiliary power system;

[0030] Start-stop state: the grid-connected main switch of the traditional generator set is in the split position, and the turbine speed is greater than the turning gear speed and less than the rated speed, and the distributed photovoltaic is prohibited from entering the auxiliary power system;

[0031] Other state: the distributed photovoltaic is prohibited from entering the auxiliary power system;

[0032] (2) Photovoltaic power generation area selection logic for entering the auxiliary power system

[0033] The expected power of each photovoltaic area is PF1, PF2, PF3, … PFn;

[0034] The target power issued by the grid is Pm, and the auxiliary power bus load power is Pg;

[0035] The sum of the expected power of any two photovoltaic power generation areas is:

[0036] PH2 = Pfi + Pfj, i = 1, 2, 3 … n-1, j = 2, 3, 4 … n

[0037] The sum of the expected power of any three photovoltaic power generation areas is:

[0038] PH3 = PFi + PFj + PFk, i = 1, 2, 3 … n-2, j = 2, 3, 4 … n-1, k = 3, 4 … n

[0039] By analogy, the sum of the expected power of all photovoltaic power generation areas is obtained:

[0040] PHA = ∑Pi, i = 1, 2, 3 … n

[0041] (1) When Pm < Pi, where Pi = min(PF1, PF2, PF3, … PFn), send a closing command and close the grid-side switch Wi of the i-th photovoltaic power generation area, and send an opening command to disconnect the remaining grid-side switches;

[0042] When (PHA-Pi) < plant power Pg, send the closing command, close all the plant side switches except the Gi switch, and all the photovoltaic areas except the i th photovoltaic area are connected to the power side of the power plant;

[0043] When (PHA-Pi) > plant power Pg, sort the expected power of the remaining distributed photovoltaic power generation areas except the i th photovoltaic area, and then subtract the minimum power from (PHA-Pi) until it is less than the plant power, at which time the corresponding photovoltaic area grid side switch is turned off and the plant power side switch is closed;

[0044] (2) When Pi < Pm < Pj, where Pi = max(PF1, PF2, PF3, … PFn) and Pj = min(PH2), send the closing command, close the grid side switches of the two power corresponding power generation areas of PH2, and send the opening command, open the remaining grid side switches;

[0045] For example, min(PH2) is composed of PFm and PFn, close the Wm and Wn switches, and open the remaining grid side switches;

[0046] When (PHA-Pj) < plant power Pg, send the closing command, close all the plant side switches except the m th and n th switches, and all the photovoltaic areas except the m th and n th photovoltaic power generation areas are connected to the power side of the power plant;

[0047] When (PHA-Pj) > plant power Pg, sort the expected power of the remaining distributed photovoltaic power generation areas except the m th and n th photovoltaic areas, and then subtract the minimum power from (PHA-Pj) until it is less than the plant power, at which time the corresponding photovoltaic area grid side switch is turned off and the plant power side switch is closed;

[0048] (3) When max{PH(n-1)} < Pm < PHN, where PH(n-1) is the sum of the expected power of any (n-1) photovoltaic areas, send the closing command, close all the photovoltaic power generation area grid side switches W, and send the opening command, open all the plant power side switches G.

[0049] The method of the present application proposes an online distributed photovoltaic power redistribution optimization method, by arranging the line, transformer, switch and other facilities connected to the plant power system, installing an automatic control device, collecting the target power issued by the power grid, the expected power value of each photovoltaic power generation area, the plant bus voltage, current, the state of the grid-connected main switch of the traditional generator set, current, turbine speed and other parameters, monitoring the operation state of the traditional generator set and the plant bus voltage quality, comparing the expected power generation of the online distributed photovoltaic power generation area with the target power issued by the power grid, selecting the optimal power generation area to be connected to the plant power bus through the optimized power distribution algorithm, realizing the full utilization of the photovoltaic power station resources under the premise of reserving the grid-connected protocol, effectively replacing the frequent operation of the switch by the operator, realizing automatic switching, and ensuring the safe and reliable operation of the plant power system through the blocking logic of the connection condition. BRIEF DESCRIPTION OF DRAWINGS

[0050] Fig. 1 is a schematic diagram of the online photovoltaic area connected to the plant power system according to the present application.

[0051] Fig. 2 is a schematic diagram of the online photovoltaic area connected to the plant power system according to the application example. DETAILED DESCRIPTION

[0052] The specific implementation of the present application is further described in detail in combination with the embodiments.

[0053] EMBODIMENT

[0054] Original system composition:

[0055] The rated voltage of the plant bus is 10kV, and the load power is 15MW;

[0056] The rated voltage of the online bus is 10kV, and the online distributed photovoltaic power station is composed of three areas, the first power generation area has a capacity of 2MW, the second has a capacity of 2.5MW, and the third has a capacity of 1MW;

[0057] Step one: arranging the line facilities connected to the plant power system

[0058] A section of bus switch Z is connected to the plant power system standby interval;

[0059] A cable line is connected to the Z bus between the high-voltage side of the photovoltaic 1 area transformer and the grid-connected switch W1 on the T side, and a switch G1 is added;

[0060] A cable line is connected to the Z bus between the high-voltage side of the photovoltaic 2 area transformer and the grid-connected switch W2 on the T side, and a switch G2 is added;

[0061] A cable line is connected to the Z bus between the high-voltage side of the photovoltaic 3 area transformer and the grid-connected switch W3 on the T side, and a switch G3 is added;

[0062] Because the voltage level of the plant bus and the voltage level of the photovoltaic on-grid bus are both 10 kV, it is unnecessary to increase a step-up or step-down transformer;

[0063] Step two: install the control device

[0064] The device is located in the control room of the distributed photovoltaic system and is installed in a group screen manner.

[0065] The device uses a PLC controller and has two Ethernet communication interfaces, one of which is connected to the DCS system of the traditional generator set, and the other is connected to the AGC control system of the distributed photovoltaic power station.

[0066] The device has 10 input quantity interfaces.

[0067] The device has 10 output quantity interfaces.

[0068] The device has 3 sets of three-phase voltage and 3 sets of three-phase current analog quantity interfaces.

[0069] Step three: the control device collects data

[0070] The data collected by the control device includes:

[0071] 1. Through Ethernet communication with the photovoltaic AGC control platform, the target power issued by the power grid and the expected maximum power value of the three photovoltaic power generation areas are obtained.

[0072] 2. Through Ethernet communication with the DCS platform of the traditional generator set, the on-off state of the traditional generator set grid-connected main switch and the turbine speed are obtained.

[0073] 3. Through the input quantity, the on-off state of the grid-connected side switches W1, W2, and W3, the on-off state of the plant power side switches G1, G2, and G3, and the on-off state of the traditional generator set grid-connected main switch are accessed.

[0074] 4. Through the analog quantity, the three-phase voltage and current Ia, Ib, and Ic of the plant system bus voltage Ua, Ub, and Uc are accessed.

[0075] 5. Through the output quantity, the closing and opening of the six switches W1, W2, W3, G1, G2, and G3 are controlled.

[0076] Step four: access the plant power control logic

[0077] 1. Traditional unit grid-connected state judgment

[0078] Grid-connected state: the traditional generator set grid-connected main switch is in the on position, and the current is greater than 10% of the rated value.

[0079] Stop state: the main switch of the traditional generator set is in the split position, and the turbine speed is less than or equal to the speed of 4 revolutions per minute;

[0080] Start-stop state: the main switch of the traditional generator set is in the split position, and the turbine speed is greater than the speed of 4 revolutions per minute and less than the rated speed of 3000 revolutions per minute; the distributed photovoltaic power is prohibited to be connected to the power system, and the G1, G2 and G3 switches are disconnected;

[0081] Other state: the distributed photovoltaic power is prohibited to be connected to the power system, and the G1, G2 and G3 switches are disconnected;

[0082] 2. Quality state judgment of the power bus

[0083] (1) The harmonic content of the bus voltage is less than 4%;

[0084] (2) The amplitude of the bus voltage is within ±6% of the rated voltage, i.e. between 9.4kV and 10.6kV;

[0085] (3) The current change rate is less than the current change rate when the maximum load is started, in this example, the maximum load is the induced draft fan with a capacity of 8MW and a rated voltage of 10kV, and the current change rate when the induced draft fan is started is 3260A / s;

[0086] In the grid-connected state or the stop state, and when the quality of the power bus meets the requirements, the distributed photovoltaic power is allowed to be connected to the power system.

[0087] 3. Selection logic of the photovoltaic power generation area connected to the power system

[0088] The distributed photovoltaic power station in this embodiment has three photovoltaic power generation areas, the first area has a capacity of 2MW, the second area has a capacity of 2.5MW, and the third area has a capacity of 1MW, with a total capacity of 5.5MW;

[0089] The simultaneous generation capacity of the first area and the second area is 4.5MW;

[0090] The simultaneous generation capacity of the second area and the third area is 3.5MW;

[0091] The simultaneous generation capacity of the first area and the third area is 3MW;

[0092] (1) If the target power value issued by the grid dispatching is 5MW, which is greater than the simultaneous generation capacity of the first area and the second area of 4.5MW and less than the total capacity of 5.5MW, then all the three photovoltaic power generation areas should be connected to the grid side, the disconnecting command is sent to disconnect the G1, G2 and G3, and the closing command is sent to close the W1, W2 and W3.

[0093] (2) If the target power value issued by the grid dispatch is 4.3MW, which is greater than the simultaneous generation capacity of 3.5MW of 2nd and 3rd areas, and less than the simultaneous generation capacity of 4.5MW of 1st and 2nd areas, then 1st and 2nd areas should be connected to the grid side, 3rd area is connected to the plant power system, send the opening command, disconnect G1, G2, W3, send the closing command, close W1, W2, G3;

[0094] (3) If the target power value issued by the grid dispatch is 0.9MW, which is less than the minimum power value of 1MW of 3 areas, 3rd area is connected to the grid side, 1st and 2nd areas should be connected to the plant power side; send the opening command, disconnect W1, W2, G3, send the closing command, close G1, G2, W3.

[0095] Finally, the roof photovoltaic of 5.5MW in the plant area of this embodiment, according to the load limit condition, the capacity of 2.5MW of 2nd area meets the demand of grid dispatch in normal condition, if 1st and 3rd areas do not generate power on the grid, they are in idle state, it is expected that the less power generation is more than 12,000kWh per day, according to 18 sunny effective power generation days per month, the less power generation is more than 216,000kWh, according to the grid protocol photovoltaic power generation price of 0.378 yuan, the monthly loss is more than 81,600 yuan, and the annual loss is more than 979,000 yuan. If 1st and 3rd areas are connected to the plant power system to supply the plant power load, the monthly consumption of the thermal power generating unit plant load is reduced by 216,000kWh, the power generation unit can generate 216,000kWh more on the grid, according to the grid power generation price of 0.41 yuan of the province where this embodiment is located, the annual income is 1.06 million yuan.

Claims

1. A method for online distributed photovoltaic power redistribution optimization, characterized in that, The method comprises the following steps: Step 1: arranging line facilities of the access power system A section of busbar is led out from the standby interval of the power system as a photovoltaic access busbar; A cable line is connected to the above busbar at the high-voltage side of the step-up transformer of each distributed photovoltaic power generation area and the lower port of the grid-connected switch, and corresponding switch equipment is added; Step 2: installing a control device The device is installed in the control room of the distributed photovoltaic system in a group screen manner; The device has two network communication interfaces, one of which is connected with the DCS system of the traditional generator set, and the other of which is connected with the AGC control system of the distributed photovoltaic power station; The device has an input quantity interface; The device has an output quantity interface; The device has a voltage and current analog quantity interface; Step 3: data acquisition by the control device The target power issued by the power grid, the expected maximum power value of each photovoltaic power generation area, the grid-side switch state, the power system busbar voltage and current, the grid-side main switch state and current of the traditional generator set, and the steam turbine speed are acquired by the control device; Step 4: access power control logic (1) traditional generator set operation state judgment Grid-connected state: the grid-connected main switch of the traditional generator set is in the closed position, and the current is greater than 10% of the rated value; Power system busbar quality requirements: a) the harmonic content of the busbar voltage is less than 4%; b) the amplitude of the busbar voltage is within ±6% of the rated voltage; c) the current change rate is less than the current change rate at the maximum load start; When the grid-connected state and the power system busbar meet the above quality requirements, the distributed photovoltaic power is allowed to be connected to the power system; Shutdown state: the grid-connected main switch of the traditional generator set is in the open position, and the steam turbine speed is less than or equal to the turning gear speed; When the shutdown state and the power system busbar meet the above quality requirements, the distributed photovoltaic power is allowed to be connected to the power system; Start-stop state: the grid-connected main switch of the traditional generator set is in the open position, and the steam turbine speed is greater than the turning gear speed but less than the rated speed, so the distributed photovoltaic power is prohibited from being connected to the power system; Other states: the distributed photovoltaic power is prohibited from being connected to the power system; (2) selection logic of photovoltaic power generation areas connected to the power system The expected power of each photovoltaic area is PF1, PF2, PF3, …, PFn; The target power issued by the power grid is Pm, and the power system busbar load power is Pg; The sum of the expected powers of any two photovoltaic power generation areas is PH2=Pfi+Pfj, i=1, 2, 3 … n-1, j=2, 3, 4 … n The sum of the expected powers of any three photovoltaic power generation areas is PH3=PFi+PFj+PFk, i=1, 2, 3 … n-2, j=2, 3, 4 … n-1, k=3, 4 … n By analogy, the sum of the expected powers of all photovoltaic power generation areas is PHA=∑Pi, i=1, 2, 3 … n (1) when Pm ​ ​ ​ When (PHA-Pi) < plant power Pg, send the closing command, close all the plant side switches except the Gi switch, and all the photovoltaic areas except the i th photovoltaic area are connected to the power side of the power plant; When (PHA-Pi) > plant power Pg, sort the expected power of the remaining distributed photovoltaic areas except the i th photovoltaic area, and then subtract the minimum power from (PHA-Pi) until it is less than the plant power, at which time the corresponding photovoltaic area grid side switch is turned off and the plant power side switch is closed; (2) When Pi < Pm < Pj, where Pi = max(PF1, PF2, PF3, …, PFn) and Pj = min(PH2), send the closing command, close the grid side switch of the two power corresponding power generation areas of PH2, and send the opening command, open the remaining grid side switches; When (PHA-Pj) < plant power Pg, send the closing command, close all the plant side switches except the m th and n th switches, and all the photovoltaic areas except the m th and n th photovoltaic areas are connected to the power side of the power plant; When (PHA-Pj) > plant power Pg, sort the expected power of the remaining distributed photovoltaic areas except the m th and n th photovoltaic areas, and then subtract the minimum power from (PHA-Pj) until it is less than the plant power, at which time the corresponding photovoltaic area grid side switch is turned off and the plant power side switch is closed; (3) When max{PH(n-1)} < Pm < PHN, where PH(n-1) is the sum of the expected power of any (n-1) photovoltaic areas, send the closing command, close all the photovoltaic power area grid side switches W, and send the opening command, open all the plant power side switches G.

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