CN111987732A - Electric energy exchanger and method suitable for flexible interconnection of feeder lines of power distribution network - Google Patents
Electric energy exchanger and method suitable for flexible interconnection of feeder lines of power distribution network Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E70/00—Other energy conversion or management systems reducing GHG emissions
- Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin
Abstract
In the scheme, two PSR converters are respectively connected with a feeder line and are commonly connected with a direct current bus, and the PSR converters are used for controlling the output power of electric energy exchange between the two feeder lines; one end of the Boost converter is connected with the photovoltaic unit, and the other end of the Boost converter is connected with the direct current bus and used for carrying out maximum power tracking on the photovoltaic unit; one end of the DAB converter is connected with the storage battery, and the other end of the DAB converter is connected with the direct current bus and used for controlling the storage battery to store electric energy in the direct current bus. The alternating current-direct current converter can realize active regulation and control of output power when electric energy is exchanged for a feeder line of a power distribution network, so that the load of the feeder line is balanced; according to the scheme, the DAB converter and the Boost converter can be used for penetrating and connecting intermittent distributed power sources such as a photovoltaic unit and the like into a power supply system, so that uninterrupted power supply for important loads can be realized while the load balance regulation of a feeder line is realized.
Description
Technical Field
The invention relates to the field of power distribution network flexible interconnection, in particular to an electric energy exchanger and a method suitable for power distribution network feeder line flexible interconnection.
Background
With the proposal of energy internet strategy and the acceleration of construction pace of intelligent power grids, especially intelligent power distribution networks in China, a new generation energy system with high-efficiency fusion of multiple energy sources taking the power grids as a core puts higher requirements on flexibility, controllability and strong elasticity of the power distribution networks. Under the wide application background of a large amount of access of multiple types of distributed power supplies such as distribution network photovoltaic, wind-powered electricity generation and the novel load that uses electric automobile as the representative, the power variety continuously increases, and load characteristic is diversified day by day, and these new changes have brought a great deal of influence for distribution network safety and stability operation, if: the power flow direction is increasingly complex, the load fluctuation is aggravated, the electric energy quality problems such as voltage out-of-limit and the like are increasingly prominent, the power supply reliability is reduced, and the relay protection is mistakenly operated and refused to operate. Distribution network feeder flexible interconnection is regarded as the important mode of solving these problems, and current distribution network mainly adopts closed loop design, open loop operation mode, and distribution network feeder interconnection still adopts traditional contact switch, and this kind of mechanical switch action number of times is low, the speed is slow, the regulation and control ability is weak, can't satisfy distribution network flexible interconnection and intelligent power distribution network construction requirement, becomes the main bottleneck that restricts distribution network operation level and further promote, shows in following several aspects specifically: (1) weak control ability: the power on the present distribution network tie line is decided by the system trend, and traditional interconnection switch is through just closing when only certain feeder trouble or maintenance to guarantee to the uninterrupted power supply of important load, do not possess the initiative regulation and control ability to the interconnection power, it is many to heavily transship the main circuit of change moreover, and the load changes the power supply ability low, is difficult to reach predetermined contact target. (2) High permeability access is difficult: because the distribution network structure mode adopting the traditional interconnection switch is usually radial or the feeder line is weak in interconnection, when a large amount of intermittent distributed power supplies are accessed at high permeability, a large amount of distributed power supplies, micro-grids and flexible loads are difficult to accept.
Disclosure of Invention
The invention provides an electric energy exchanger and an electric energy method suitable for flexible interconnection of power distribution network feeders, and aims to solve the problems that an energy system in the prior art cannot control output power of a power supply feeder and cannot be connected to a distributed power supply, a micro-grid and a flexible load.
The technical scheme provided by the invention is as follows:
an electrical energy exchanger suitable for flexible interconnection of distribution network feeders, comprising: two PSR converters, a Boost converter and a DAB converter;
the two PSR converters are respectively connected with a feeder line, are commonly connected with a direct current bus and are used for controlling the output power of electric energy exchange between the two feeder lines;
one end of the Boost converter is connected with the photovoltaic unit, and the other end of the Boost converter is connected with the direct current bus and used for carrying out maximum power tracking on the photovoltaic unit;
one end of the DAB converter is connected with the storage battery, and the other end of the DAB converter is connected with the direct current bus and used for controlling the storage battery to store electric energy in the direct current bus.
Preferably, the PSR converter includes:
a microcontroller and a bridge arm unit;
the microcontroller is connected with the bridge arm unit and is used for controlling the on-off of the bridge arm unit;
the bridge arm units are connected in parallel to the direct current bus, connected with the feeders and used for controlling the output power of the electric energy exchange among the feeders.
Preferably, the electric energy exchanger further comprises: an LC filter;
the LC filter is connected in series between the bridge arm unit and the feeder line.
Preferably, the power exchanger further comprises: a Buck converter;
and the Buck converter is connected in parallel between the DAB converter and the storage battery and is used for carrying out direct-current chopping.
An electric energy exchange method based on the electric energy exchanger is characterized by comprising the following steps:
by a virtual synchronous machine control method, the PSR converter controls the electric energy of the two feeders to be transferred through a direct current bus;
controlling the storage battery to store electric energy in a direct current bus through the DAB converter;
and controlling a photovoltaic unit to supply power to the direct current bus through the Boost converter to compensate electric energy.
Preferably, the controlling, by the virtual synchronous machine control method, the PSR converter controls the electric energy of the two feeders to be transferred via the dc bus, including:
according to the load power and the rated capacity in the feeder line, the microcontroller determines a power output value for transferring electric energy from the direct current bus to the feeder line;
and according to the power output value, the microcontroller controls the on-off of the bridge arm unit through a virtual synchronous machine control method, and the electric energy in the heavy-load feeder line is transferred to the light-load feeder line through the direct current bus.
Preferably, the controlling the bridge arm unit by the microcontroller through the virtual synchronous machine control method includes:
according to the voltage and the current of the feeder line at the output side of the LC filter, the microcontroller controls the virtual synchronizer to make a given value of grid-connected voltage;
and based on the given grid-connected voltage value, the microcontroller controls the on-off of the bridge arm unit.
Preferably, the setting of the grid-connected voltage given value by the microcontroller through virtual synchronous machine control according to the feeder line voltage and current at the output side of the LC filter includes:
constructing a virtual synchronous controller model on the output side of the LC filter, and acquiring the rated angular frequency, the virtual angular frequency, the output voltage effective value and the rated voltage effective value of the virtual synchronous controller;
calculating to obtain active power and reactive power based on the voltage and the current of the feeder line, and obtaining mechanical torque and electromagnetic torque based on the active power and the reactive power;
formulating a phase angle set value based on the mechanical torque, the electromagnetic torque, the rated angular frequency and the virtual angular frequency;
formulating a voltage given value based on the reactive power and the reactive power preset value, the output voltage effective value and the rated voltage effective value;
And formulating a grid-connected voltage given value according to the feeder line voltage, the phase angle given value and the voltage given value.
Preferably, the formulating a grid-connected voltage given value based on the feeder line voltage and current at the output side of the LC filter by virtual synchronous machine control includes:
preferably, the formulating a phase angle set value based on the mechanical torque, the electromagnetic torque, the rated angular frequency and the virtual angular frequency includes:
subtracting the mechanical torque from the electromagnetic torque to obtain a first difference value;
the rated angular frequency and the virtual angular frequency are subjected to difference to obtain a second difference value;
obtaining an updated virtual angular frequency through active-frequency droop control based on the first difference and the second difference;
and integrating to obtain a phase angle given value based on the updated virtual angular frequency.
Preferably, the formulating a voltage given value based on the reactive power and the reactive power preset value, the output voltage effective value and the rated voltage effective value comprises:
subtracting the reactive power from a preset reactive power value to obtain a third difference value;
subtracting the output voltage effective value from the rated voltage effective value to obtain a fourth difference value;
and obtaining a voltage given value through reactive-voltage droop control based on the third difference and the fourth difference.
Preferably, the formulating a grid-connected voltage given value according to the feeder line voltage, the phase angle given value and the voltage given value comprises:
multiplying the given value of the phase angle by the given value of the voltage to obtain an instantaneous value of the given value of the voltage;
the feeder line voltage is differed from the instantaneous value, and the difference is integrated according to the inductive reactance value of the LC filter to obtain a given value of the internal current;
and obtaining a grid-connected voltage set value through PR control according to the grid-connected current set value.
Preferably, the controlling the storage battery to store the electric energy in the direct current bus through the DAB converter includes:
setting a minimum charge threshold and a maximum charge threshold of the storage battery through a DAB converter;
if the charge quantity of the storage battery is smaller than the minimum threshold value, charging, otherwise, controlling the storage battery to be in a floating charge state;
when the power of the feeder line is lost, if the charge capacity of the storage battery is smaller than a minimum threshold value, controlling the storage battery to be in a floating charge state; otherwise, controlling the storage battery to discharge.
Preferably, the controlling, by the Boost converter, the photovoltaic unit to supply power to the dc bus for power compensation includes:
based on maximum power tracking control, the Boost converter acquires a voltage reference value of the photovoltaic unit;
And making a difference between the voltage reference value and the actual voltage value, and controlling the photovoltaic unit to keep the maximum output power through PI regulation.
Compared with the prior art, the invention has the beneficial effects that:
the technical scheme provided by the invention comprises the following steps: two PSR converters, a Boost converter and a DAB converter; the two PSR converters are respectively connected with a feeder line, are commonly connected with a direct current bus and are used for controlling the output power of electric energy exchange between the two feeder lines; one end of the Boost converter is connected with the photovoltaic unit, and the other end of the Boost converter is connected with the direct current bus and used for carrying out maximum power tracking on the photovoltaic unit; one end of the DAB converter is connected with the storage battery, and the other end of the DAB converter is connected with the direct current bus and used for controlling the storage battery to store electric energy in the direct current bus. The alternating current-direct current converter can realize active regulation and control of output power when electric energy is exchanged for a feeder line of a power distribution network, so that the load of the feeder line is balanced; according to the scheme, the DAB converter and the Boost converter can be used for penetrating and connecting intermittent distributed power sources such as a photovoltaic unit and the like into a power supply system, so that uninterrupted power supply for important loads can be realized while the load balance regulation of a feeder line is realized.
In the scheme, the converter only comprises two AC/DC converters, a Boost converter and a DAB converter, and is topologically connected to a DC bus, so that the converter is simple in structure and low in investment cost.
Drawings
Fig. 1 is a structural diagram of an electric energy exchanger suitable for feeder line flexible interconnection of a distribution network according to the present invention;
FIG. 2 is a power exchanger topology connection diagram of the present invention;
FIG. 3 is a block diagram of a virtual synchronous motor control for the AC/DC converter of the present invention;
FIG. 4 is a control block diagram of the Boost converter of the present invention;
fig. 5 is a control block diagram of the DAB converter of the present invention.
Detailed Description
For a better understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawings and examples.
The first embodiment is as follows:
the patent proposes a four-port electrical energy exchanger and a control method thereof. The four-port electric energy exchanger is characterized by mainly comprising two alternating current ports and two direct current ports. The structure diagram of the electric energy exchanger is shown in fig. 1, the topological connection diagram is shown in fig. 2, wherein two alternating current ports are both voltage type bidirectional converters and are connected to a power distribution network through an LC filter and a transformer, a direct current port 1 is connected to a photovoltaic unit through a Boost converter, a direct current port 2 is connected to an energy storage unit through a bidirectional active bridge converter, and the four ports are connected through a common direct current bus. The control method of the four-port electric energy exchanger comprises virtual synchronous machine control of an alternating current port voltage type bidirectional converter, maximum power tracking control of a direct current port 1Boost converter and single phase-shifting control of a direct current port 2 bidirectional active bridge converter. The specific control process is as follows:
(1) And controlling a virtual synchronous machine of the alternating current port voltage type bidirectional converter.
Since the control methods of the converters of the ac ports 1 and 2 are the same, the ac port 1 will be described as an example as shown in fig. 3.
1) Detecting three-phase voltage Uabc and current iabc at the output side of the LC filter, obtaining U0dq and i0dq through abc/dq conversion, and obtaining active power Pe and reactive power Qe after performing power calculation by applying an instantaneous reactive power theory;
2) dividing an active power instruction Pref and a reactive power instruction Qref which need to be obtained by a power grid rated angular frequency omegan respectively to obtain a mechanical torque Tm and an electromagnetic torque Te;
3) respectively subtracting the product of the electromagnetic torque Te, the difference value (omega n-omega) between the rated angular frequency omega n and the virtual angular frequency omega and the active-frequency droop coefficient Dp from the mechanical torque Tm, dividing the obtained result by the rotational inertia J, integrating to obtain the virtual angular frequency omega, and integrating omega to obtain the phase angle given value theta;
4) adding the difference (Qref-Qe) of the reactive power instruction Qref and the reactive power Qe to the product of the difference (U0-Un) of the output voltage effective value U0 and the rated voltage effective value Un and a reactive-voltage droop coefficient Dq, and multiplying the obtained result by a voltage regulation coefficient K and an integral factor s to obtain a voltage given value E;
5) Multiplying the voltage given value E and the phase angle given value theta to obtain an instantaneous value E of the voltage given value;
6) and dividing the difference between the instantaneous value e of the voltage given value and the three-phase voltage Uabc by the inductance L, integrating the obtained result to obtain a grid-connected current given value iref, obtaining an output grid-connected voltage given value eref through a PR controller, and performing sinusoidal PWM modulation to obtain a switching signal of a switching tube of the converter at the alternating current port 1.
(2) And (3) maximum power tracking control of the direct current port 1 converter.
The direct current port 1 of the electric energy exchanger is connected with the photovoltaic unit through a Boost converter, in order to realize the maximum consumption of distributed Power supplies such as photovoltaic, when illumination or temperature changes, the photovoltaic needs to be kept to have the maximum output Power all the time, therefore, the direct current port converter of the electric energy exchanger adopts Maximum Power Point Tracking (MPPT) control. As shown in fig. 4, the reference value U × pv of the photovoltaic voltage is obtained through the MPPT, and is different from the actual photovoltaic voltage Upv, and a control signal is obtained through the PI link, thereby completing the maximum power tracking of the photovoltaic output power.
(3) Single phase shift control of the dc port 2 bi-directional active bridge converter.
In order to prevent the overcharge and overdischarge of the storage battery and to prevent frequent charging and discharging, a state of charge SOC of a residual capacity is introduced, a charging and discharging threshold value [ SOCmin, SOCmax ] of the storage battery SOCbat is set, the SOCmin is 20%, the SOCmax is 80%, and the following rules are set:
1) When the system has critical power redundancy, if the SOCbat is < SOCmin, the storage battery is charged; and if the SOCbat is larger than or equal to the SOCmin, the storage battery enters a floating charge state.
2) When the system has critical power shortage, if SOCbat is less than or equal to SOCmin, the storage battery enters a floating charge state, and meanwhile, the system performs load shedding operation according to the load grade and the importance degree; if SOCbat is greater than SOCmin, the storage battery is discharged to make up for the power shortage.
The bus voltage Udc is compared with a reference voltage
Comparing, and obtaining DAB conversion through PI control linkPhase shift control signal of device
As shown in fig. 5, when the battery SOCbat is not in the charge/discharge threshold interval, the battery protection unit operates in a float state to protect the battery performance.
Example two:
the embodiment provides an electric energy exchanger suitable for flexible interconnection of feeder lines of a distribution network, and the structure diagram of the electric energy exchanger, as shown in fig. 1, includes: two PSR converters, a Boost converter and a DAB converter;
the two PSR converters are respectively connected with a feeder line, are commonly connected with a direct current bus and are used for controlling the output power of electric energy exchange between the two feeder lines;
one end of the Boost converter is connected with the photovoltaic unit, and the other end of the Boost converter is connected with the direct current bus and used for carrying out maximum power tracking on the photovoltaic unit;
One end of the DAB converter is connected with the storage battery, and the other end of the DAB converter is connected with the direct current bus and used for controlling the storage battery to store electric energy in the direct current bus.
The PSR converter comprises:
a microcontroller and a bridge arm unit;
the microcontroller is connected with the bridge arm unit and is used for controlling the on-off of the bridge arm unit;
the bridge arm units are connected in parallel to the direct current bus, connected with the feeders and used for controlling the output power of the electric energy exchange among the feeders.
The electrical energy exchanger further comprises: an LC filter;
the LC filter is connected in series between the bridge arm unit and the feeder line.
The electrical energy exchanger further comprises: a Buck converter;
and the Buck converter is connected in parallel between the DAB converter and the storage battery and is used for carrying out direct-current chopping.
Example three:
the embodiment provides a power exchange method based on a power exchanger, which comprises the following steps:
by a virtual synchronous machine control method, the PSR converter controls the electric energy of the two feeders to be transferred through a direct current bus;
controlling the storage battery to store electric energy in a direct current bus through the DAB converter;
and controlling a photovoltaic unit to supply power to the direct current bus through the Boost converter to compensate electric energy.
The method for controlling the PSR converter to control the electric energy of the two feeders to be transferred through the direct current bus by the virtual synchronous machine control method comprises the following steps:
according to the load power and the rated capacity in the feeder line, the microcontroller determines a power output value for transferring electric energy from the direct current bus to the feeder line;
and according to the power output value, the microcontroller controls the on-off of the bridge arm unit through a virtual synchronous machine control method, and the electric energy in the heavy-load feeder line is transferred to the light-load feeder line through the direct current bus.
The method for controlling the bridge arm unit through the virtual synchronizer and the microcontroller control the on-off of the bridge arm unit comprises the following steps:
according to the voltage and the current of the feeder line at the output side of the LC filter, the microcontroller controls the virtual synchronizer to make a given value of grid-connected voltage;
and based on the given grid-connected voltage value, the microcontroller controls the on-off of the bridge arm unit.
According to the feeder line voltage and the current of the output side of the LC filter, the microcontroller controls the given value of the grid-connected voltage through a virtual synchronous machine, and the method comprises the following steps:
constructing a virtual synchronous controller model on the output side of the LC filter, and acquiring the rated angular frequency, the virtual angular frequency, the output voltage effective value and the rated voltage effective value of the virtual synchronous controller;
Calculating to obtain active power and reactive power based on the voltage and the current of the feeder line, and obtaining mechanical torque and electromagnetic torque based on the active power and the reactive power;
formulating a phase angle set value based on the mechanical torque, the electromagnetic torque, the rated angular frequency and the virtual angular frequency;
formulating a voltage given value based on the reactive power and the reactive power preset value, the output voltage effective value and the rated voltage effective value;
and formulating a grid-connected voltage given value according to the feeder line voltage, the phase angle given value and the voltage given value.
The method is characterized in that a given value of grid-connected voltage is formulated by controlling a virtual synchronous machine based on the voltage and the current of a feeder line at the output side of an LC filter, and comprises the following steps:
formulating a phase angle set value based on the mechanical torque, the electromagnetic torque, the rated angular frequency and the virtual angular frequency, comprising:
subtracting the mechanical torque from the electromagnetic torque to obtain a first difference value;
the rated angular frequency and the virtual angular frequency are subjected to difference to obtain a second difference value;
obtaining an updated virtual angular frequency through active-frequency droop control based on the first difference and the second difference;
and integrating to obtain a phase angle given value based on the updated virtual angular frequency.
The voltage given value is formulated based on the reactive power and the reactive power preset value, the output voltage effective value and the rated voltage effective value, and the voltage given value comprises the following steps:
subtracting the reactive power from a preset reactive power value to obtain a third difference value;
subtracting the output voltage effective value from the rated voltage effective value to obtain a fourth difference value;
and obtaining a voltage given value through reactive-voltage droop control based on the third difference and the fourth difference.
The method for formulating the grid-connected voltage set value according to the feeder line voltage, the phase angle set value and the voltage set value comprises the following steps:
multiplying the given value of the phase angle by the given value of the voltage to obtain an instantaneous value of the given value of the voltage;
the feeder line voltage is differed from the instantaneous value, and the difference is integrated according to the inductive reactance value of the LC filter to obtain a given value of the internal current;
and obtaining a grid-connected voltage set value through PR control according to the grid-connected current set value.
Through the DAB converter, control the electric energy in the storage battery storage direct current bus, include:
setting a minimum charge threshold and a maximum charge threshold of the storage battery through a DAB converter;
if the charge quantity of the storage battery is smaller than the minimum threshold value, charging, otherwise, controlling the storage battery to be in a floating charge state;
When the power of the feeder line is lost, if the charge capacity of the storage battery is smaller than a minimum threshold value, controlling the storage battery to be in a floating charge state; otherwise, controlling the storage battery to discharge.
Through the Boost converter, control photovoltaic unit is to direct current bus power supply carries out the electric energy compensation, includes:
based on maximum power tracking control, the Boost converter acquires a voltage reference value of the photovoltaic unit;
and making a difference between the voltage reference value and the actual voltage value, and controlling the photovoltaic unit to keep the maximum output power through PI regulation.
Example four:
the embodiment provides a multi-port coordination control strategy of the power exchanger, and when the power exchanger is in different operation modes, the coordination control strategy is different, so that the operation mode division is required. When the two feeders supply power normally, namely the distribution network runs normally, the two alternating current ports of the electric energy exchanger are connected to the grid; when both feeder lines are in fault or only one feeder line is in normal power supply, namely, the power distribution network is in fault/maintenance state, both alternating current ports of the electric energy exchanger are off-grid or only one alternating current port is in grid-connection, and due to the fact that the power distribution network is in different operation states and the load states of the transformer are different at different moments, in order to achieve load balance of the feeder lines, avoid heavy load of a main transformer and distributed energy consumption, and keep safe and stable economic operation of the power distribution network, the electric energy exchanger is divided into 9 operation modes according to the operation states of the power distribution network and the load conditions of the transformer.
| Mode(s) | |
AC Port 2 | T1 State | |
| Mode | ||||
| 1 | Grid connection | Grid connection | Is normal | Is normal |
| Mode 2 | Grid connection | Grid connection | Is normal | Heavy load |
| Mode 3 | Grid connection | Grid connection | Heavy load | Is normal |
| Mode 4 | Grid connection | Grid connection | Heavy load | Heavy load |
| Mode 5 | Grid connection | Off-grid | Is normal | Out of service |
| Mode 6 | Grid connection | Off-grid | Heavy load | Out of service |
| Mode 7 | Off-grid | Grid connection | Out of service | Is normal |
| Mode 8 | Off-grid | Grid connection | Out of service | Heavy load |
| Mode 9 | Off-grid | Off-grid | Out of service | Out of service |
For convenience of presentation, define Pac1、Pac2The feeder power, P, of the distribution network 1, 2, respectivelyVSG1、PVSG2AC ports 1, 2 Power, P, respectivelypvFor photovoltaic output, Pac-load1、Pac-load2The power of the AC load of the 1 and 2 feeder lines of the power distribution network, STRated capacity of T1, T2, Pdc-loadIs the DC load power of DC port 2. Pnet1、Pnet2、Pnet3The critical redundant power of the system is respectively when the two ends are connected in a grid mode, the single end is connected in a grid mode and the two ends are disconnected in a grid mode. The specific expression is as follows:
in each port, AC ports 1, 2 and DC port 2 allow energy to flow in both directions, and the power flowing into the distribution network is defined to be positive, the power flowing out of the AC port is defined to be positive, and the battery is charged to be positive.
Mode 1: AC ports 1 and 2 of the PSR are connected to the grid, the photovoltaic works in the MPPT state, T1 and T2 are normally loaded, and load balance is achieved among feeders through power exchange.
(1) Mode 1-1: the system has critical power redundancy, and the storage battery is charged. At this time, the output power reference values of the AC ports 1, 2 are:
(2) modes 1 to 2: the system has critical power redundancy, and the storage battery works in a floating charging state. At this time, the output power reference values of the AC ports 1, 2 are:
(3) modes 1 to 3: the system has critical power shortage, the storage battery reaches the discharge limit and is in a floating charge state, and load shedding operation is carried out according to load grades. At this time, the output power reference values of the AC ports 1, 2 are:
(4) modes 1 to 4: the system has a critical power deficit and the battery discharges. At this time, the output power reference values of the AC ports 1, 2 are:
mode 2: the AC ports 1 and 2 of the PSR are connected to the grid, the photovoltaic works in an MPPT state, the T1 is loaded normally, the T2 is overloaded, the PSR transfers the T2 partial load by coordinating energy interaction among the ports, the T2 is enabled to quit the heavy load and keep the normal state, and the loads of the two feeders are balanced.
(1) Mode 2-1: the system has critical power redundancy, and the storage battery is charged. At this time, the output power reference values of the AC ports 1, 2 are:
(2) mode 2-2: the PSR system has critical power redundancy, and the storage battery works in a floating charge state. At this time, the output power reference values of the AC ports 1, 2 are:
(3) modes 2 to 3: the system has critical power shortage, the storage battery reaches the discharge limit and is in a floating charge state, and load shedding operation is carried out according to load grades. The output power reference values of AC ports 1, 2 at this time are:
(4) Modes 2 to 4: the PSR system has a critical power deficit and the battery is discharged. At this time, the output power reference values of the AC ports 1, 2 are:
mode 3: the AC ports 1 and 2 of the PSR are connected to the grid, the T1 is heavily loaded, and the T2 is normally loaded. Similar to the case of mode 2, no further description is provided herein.
Mode 4: AC ports 1 and 2 of the PSR are connected to the grid, the photovoltaic works in an MPPT mode, both T1 and T2 carry heavy loads, the PSR transfers partial loads of T1 and T2 through energy interaction between the ports, so that both T1 and T2 leave the heavy loads and keep a normal state, and the loads of the two feeders are balanced.
(1) Mode 4-1: the system has critical power redundancy and the storage battery is charged. At this time, the output power reference values of the AC ports 1, 2 are:
(2) mode 4-2: the system has critical power redundancy, and the storage battery works in a floating charging state. At this time, the output power reference values of the AC ports 1, 2 are:
(3) mode 4-3: the PSR system has critical power shortage, the storage battery reaches the discharge limit and is in a floating charge state, and load shedding operation is carried out according to load grades. At this time, the output power reference values of the AC ports 1, 2 are:
(4) mode 4-4: the PSR system has a critical power deficit and the battery is discharged. At this time, the output power reference values of the AC ports 1, 2 are:
mode 5: the AC port 1 of the PSR is connected with the grid, the AC port 2 is disconnected from the grid due to the fault or maintenance of the power distribution network 2, the photovoltaic works in the MPPT mode, T1 is normal, T2 is stopped, the PSR realizes the uninterrupted power supply of the T2 load by coordinating the energy interaction among the ports to transfer the T2 load, and the power distribution network power supply reliability is improved.
(1) Mode 5-1: the system has critical power redundancy, and the storage battery is charged. At this time, the output power reference values of the AC ports 1, 2 are:
(2) mode 5-2: the system has critical power redundancy, and the storage battery works in a floating charging state. At this time, the output power reference values of the AC ports 1, 2 are:
(3) mode 5-3: the system has critical power shortage, the storage battery is in a floating charge state because the storage battery reaches the discharge electrode limit, and load shedding operation is carried out according to the load grades. At this time, the output power reference values of the AC ports 1, 2 are:
(4) mode 5-4: the system has a critical power deficit and the battery discharges. At this time, the output power reference values of the AC ports 1, 2 are:
mode 6: the method comprises the steps that an AC port 1 of a PSR is connected with a grid, an AC port 2 is disconnected from the grid due to faults or maintenance of a power distribution network 2, a photovoltaic works in an MPPT mode, a T1 heavy load is carried out, a T2 is stopped, and the PSR transfers a T1 partial load and a T2 load through energy interaction among all the ports in a coordinated mode, so that the T1 is withdrawn from the heavy load and is kept in a normal state, and uninterrupted power supply is carried out on the T2 load.
(1) Mode 6-1: the system has critical power redundancy, and the storage battery is charged. At this time, the output power reference values of the AC ports 1, 2 are:
(2) mode 6-2: the system has critical power redundancy, and the storage battery works in a floating charging state. At this time, the output power reference values of the AC ports 1, 2 are:
(3) Mode 6-3: the system has critical power shortage, the storage battery is in a floating charge state because the storage battery reaches the discharge electrode limit, and load shedding operation is carried out according to the load grades. At this time, the output power reference values of the AC ports 1, 2 are:
(4) mode 6-4: the PSR system has critical power shortage, the storage battery discharges, and the photovoltaic works in an MPPT mode. At this time, the output power reference values of the AC ports 1, 2 are:
mode 7: the AC port 1 of the PSR is disconnected from the power distribution network 1 due to fault or maintenance, the AC port 2 is connected to the power grid, the T1 is shut down, the T2 is normal, and the PSR keeps uninterrupted power supply to the T1 load by coordinating energy interaction among the ports to transfer the T1 load. Similar to the case of mode 5, no further description is provided herein.
Mode 8: the PSR is characterized in that an AC port 1 of the PSR is disconnected from the power distribution network 1 due to fault or maintenance, an AC port 2 is connected to the power grid, T1 is shut down, a T2 heavy load is carried out, the PSR transfers the T1 load and the T2 partial load through energy interaction among all ports in a coordinated mode, and the T2 is enabled to quit the heavy load and keep a normal state and supply power to the T1 load uninterruptedly. Similar to the case of mode 6, it will not be described in detail here.
Mode 9: the AC ports 1 and 2 of the PSR are out of the grid due to the fact that the power distribution grids 1 and 2 are in fault at the same time, the photovoltaic works in an MPPT mode, T1 and T2 are stopped, and the PSR keeps uninterrupted power supply to T1 and T2 loads by coordinating energy interaction among the ports to transfer the T1 and T2 loads.
(1) Mode 9-1: the system has critical power redundancy, and the storage battery is charged. At this time, the output power reference values of the AC ports 1, 2 are:
(2) mode 9-2: the system has critical power redundancy, and the storage battery works in a floating charging state. At this time, the output power reference values of the AC ports 1, 2 are:
(3) mode 9-3: the system has critical power shortage, the storage battery reaches the discharge limit and is in a floating charge state, and load shedding operation is carried out according to load grades. At this time, the output power reference values of the AC ports 1, 2 are:
(4) mode 9-4: the system has a critical power deficit and the battery discharges. At this time, the output power reference values of the AC ports 1, 2 are:
when the electric energy exchanger is in different operation modes, the coordination control strategies are different, and the active power commands obtained by the two alternating current port converters are also different.
Compared with the prior art, the two alternating current ports of the electric energy exchanger in the scheme are respectively connected with a 10kV power distribution network through a 10/0.4kV transformer, the voltage of the alternating current ports is 380V, the electric energy exchanger works in a low-voltage state, the topological structure is simple, and the investment cost is saved; in the aspect of functions, the feeder load can be balanced, the main transformer heavy load is avoided, distributed energy sources are consumed, uninterrupted power supply to the important load is achieved, and the operation safety and stability of the power distribution network are improved.
It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.
Claims (14)
1. An electrical energy exchanger suitable for flexible interconnection of distribution network feeders, comprising: two PSR converters, a Boost converter and a DAB converter;
The two PSR converters are respectively connected with a feeder line, are commonly connected with a direct current bus and are used for controlling the output power of electric energy exchange between the two feeder lines;
one end of the Boost converter is connected with the photovoltaic unit, and the other end of the Boost converter is connected with the direct current bus and used for carrying out maximum power tracking on the photovoltaic unit;
one end of the DAB converter is connected with the storage battery, and the other end of the DAB converter is connected with the direct current bus and used for controlling the storage battery to store electric energy in the direct current bus.
2. An electrical energy exchanger as in claim 1 wherein the PSR converter comprises:
a microcontroller and a bridge arm unit;
the microcontroller is connected with the bridge arm unit and is used for controlling the on-off of the bridge arm unit;
the bridge arm units are connected in parallel to the direct current bus, connected with the feeders and used for controlling the output power of the electric energy exchange among the feeders.
3. The electrical energy exchanger of claim 2, further comprising: an LC filter;
the LC filter is connected in series between the bridge arm unit and the feeder line.
4. The electrical energy exchanger of claim 1, further comprising: a Buck converter;
And the Buck converter is connected in parallel between the DAB converter and the storage battery and is used for carrying out direct-current chopping.
5. An electric energy exchange method based on the electric energy exchanger of any one of claims 1 to 4, comprising:
by a virtual synchronous machine control method, the PSR converter controls the electric energy of the two feeders to be transferred through a direct current bus;
controlling the storage battery to store electric energy in a direct current bus through the DAB converter;
and controlling a photovoltaic unit to supply power to the direct current bus through the Boost converter to compensate electric energy.
6. The method of claim 5, wherein the controlling the PSR converter to transfer the power of the two feeders via the dc bus by the virtual synchronous machine control method comprises:
according to the load power and the rated capacity in the feeder line, the microcontroller determines a power output value for transferring electric energy from the direct current bus to the feeder line;
and according to the power output value, the microcontroller controls the on-off of the bridge arm unit through a virtual synchronous machine control method, and the electric energy in the heavy-load feeder line is transferred to the light-load feeder line through the direct current bus.
7. The method of claim 6, wherein the controlling the switching of the bridge arm units by the microcontroller through a virtual synchronous machine control method comprises:
According to the voltage and the current of the feeder line at the output side of the LC filter, the microcontroller controls the virtual synchronizer to make a given value of grid-connected voltage;
and based on the given grid-connected voltage value, the microcontroller controls the on-off of the bridge arm unit.
8. The method of claim 7, wherein said microcontroller formulates a grid-tie voltage setpoint by virtual synchronous machine control based on the feeder voltage and current at the output of said LC filter, comprising:
constructing a virtual synchronous controller model on the output side of the LC filter, and acquiring the rated angular frequency, the virtual angular frequency, the output voltage effective value and the rated voltage effective value of the virtual synchronous controller;
calculating to obtain active power and reactive power based on the voltage and the current of the feeder line, and obtaining mechanical torque and electromagnetic torque based on the active power and the reactive power;
formulating a phase angle set value based on the mechanical torque, the electromagnetic torque, the rated angular frequency and the virtual angular frequency;
formulating a voltage given value based on the reactive power and the reactive power preset value, the output voltage effective value and the rated voltage effective value;
and formulating a grid-connected voltage given value according to the feeder line voltage, the phase angle given value and the voltage given value.
9. The method of claim 8, wherein the grid-tied voltage setpoint is established by virtual synchronous machine control based on the feeder voltage and current at the output of the LC filter.
10. The method of claim 9, wherein formulating a phase angle setpoint based on the mechanical torque, electromagnetic torque, nominal angular frequency, and virtual angular frequency comprises:
subtracting the mechanical torque from the electromagnetic torque to obtain a first difference value;
the rated angular frequency and the virtual angular frequency are subjected to difference to obtain a second difference value;
obtaining an updated virtual angular frequency through active-frequency droop control based on the first difference and the second difference;
and integrating to obtain a phase angle given value based on the updated virtual angular frequency.
11. The method of claim 9, wherein formulating a voltage setpoint based on the reactive power and reactive power preset values, output voltage effective values and rated voltage effective values comprises:
subtracting the reactive power from a preset reactive power value to obtain a third difference value;
subtracting the output voltage effective value from the rated voltage effective value to obtain a fourth difference value;
And obtaining a voltage given value through reactive-voltage droop control based on the third difference and the fourth difference.
12. The method of claim 9, wherein said formulating a grid-tied voltage setpoint based on said feeder voltage, phase angle setpoint, and voltage setpoint comprises:
multiplying the given value of the phase angle by the given value of the voltage to obtain an instantaneous value of the given value of the voltage;
the feeder line voltage is differed from the instantaneous value, and the difference is integrated according to the inductive reactance value of the LC filter to obtain a given value of the internal current;
and obtaining a grid-connected voltage set value through PR control according to the grid-connected current set value.
13. The method of claim 5, wherein said controlling the battery to store electrical energy in the dc bus via the DAB converter comprises:
setting a minimum charge threshold and a maximum charge threshold of the storage battery through a DAB converter;
if the charge quantity of the storage battery is smaller than the minimum threshold value, charging, otherwise, controlling the storage battery to be in a floating charge state;
when the power of the feeder line is lost, if the charge capacity of the storage battery is smaller than a minimum threshold value, controlling the storage battery to be in a floating charge state; otherwise, controlling the storage battery to discharge.
14. The method of claim 5, wherein the controlling, by the Boost converter, a photovoltaic unit to supply power to the DC bus for power compensation comprises:
based on maximum power tracking control, the Boost converter acquires a voltage reference value of the photovoltaic unit;
and making a difference between the voltage reference value and the actual voltage value, and controlling the photovoltaic unit to keep the maximum output power through PI regulation.
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