Patent Description:
The power technology is developed starting from direct current (DC). In <NUM>, Edison Electric Light Company established the first DC power station in London. In the same year, Nikola Tesla invented the world's first alternating current (AC) generator. From <NUM> to <NUM>, Hungarians K. Zipernowsky, O. Blathy and M. Deri proposed the core-type transformer technology and shell-type transformer technology. In April <NUM>, American A. Kennelly proposed that if the alternating current is a sine wave, the concept of "impedance" can be introduced to calculate the AC circuit based on the Ohm's law. Compared to DC whose voltage is difficult to be boosted and bucked, the voltage of AC can be easily changed using transformers, so that AC power transmission and AC power grid have developed rapidly, thereby forming a pattern of generating AC-transmitting AC-distributing AC.

With the extension of transmission distance and the increase of transmission power and the transmission voltage, various defects of AC power transmission technology in practical applications have been revealed. After weighing the economic benefits and operating characteristics of AC power transmission and DC power transmission, the DC transmission technology was reused.

In the <NUM>, a DC power transmission technology based on AC power generation and AC power distribution is invented. In the DC power transmission technology, the AC power at a transmission terminal is firstly rectified into DC power, which is sent to a receiving terminal via DC transmission wires; the DC power is inverted to AC power, and sent to a receiving terminal of the AC power grid. Since the boost and buck of the voltage can only be completed by AC transformers, the DC power transmission technology based on the above-mentioned structure is adopted. In <NUM>, the concept of a grid-controlled mercury arc valve capable of rectification and inverter was born, and the grid-controlled mercury arc valves were successfully developed more than ten years later. In <NUM>, the grid-controlled mercury arc valves were applied to DC power transmission, resulting in the establishment of a landmark DC power transmission system connecting the Swedish mainland and Gotland with submarine cables.

The development of the DC power transmission technology is marked by rectification and inversion. After <NUM>, silicon controlled rectifiers (SCRs) replaced the grid-controlled mercury arc valves, which occupied the dominant position of DC power transmission for more than <NUM> years, resulting in substantial increases in transmission distance, transmission power and transmission voltage, thereby greatly increasing the number of DC power transmission systems. In the <NUM>, flexible DC transmission technology was born, which is a new type of power transmission technology based on Voltage Source Converter (VSC), self-shutdown device and pulse width modulation (PWM) technology. Later, IEEE officially named the flexible DC transmission technology as Voltage Source Converter based High Voltage Direct Current (VSC-HVDC).

The VSC-HVDC power transmission technology has made great progress so far, which shows many advantages over the DC power transmission technology based on silicon controlled rectifiers and the AC power transmission technology. For example, the power transmission is more stable; the allowable working voltage of the cable insulation for DC is two times higher than that for AC; besides, the DC power transmission control system has advantages of fast response, accurate adjustment, easy operation and multi-objective control. Under the condition that the wire cross-sectional areas are the same and the available powers delivered are equal, a power loss of DC power transmission wires is about <NUM>/<NUM> of that of AC power transmission wires, and a transmission efficiency of the DC power transmission wires is twice or more than that of the AC power transmission wires. However, due to the large investment of the DC transmission converter station, the construction cost of the DC power transmission wires is extremely expensive. Therefore, it is crucial to promote the development of the VSC-HVDC transmission technology.

With the development of high power electronic components and control technologies thereof, the power electronic transformer (PET)-DC transformer, which realizes voltage conversion and energy transfer through power electronic conversion technology, has received more and more attention. This kind of DC transformer was proposed at the end of the last century, and its working principle is to achieve a voltage conversion from one DC voltage to another DC voltage or more DC voltages through high-frequency chopping, transformation, isolation, and high-frequency rectification. The PET-DC transformer has advantages of almost <NUM>% equivalent duty ratio, simple structure, lower energy consumption than that of a power frequency transformer, and high power density through increasing switching frequency.

However, since the so-called "DC transformer" still needs to be realized by the AC transformers during the transformation, a DC-to-AC chopping link and an AC-to-DC rectifying link are still needed in the DC transformer. Therefore, the so-called "DC transformer" and the existing DC transformers have the same essence.

The proportion of renewable energy generation, especially photovoltaic power generation, is rising, so that the situation of transmission technology and engineering will undergo major changes. With photovoltaic power generation accounting for <NUM>%, <NUM>%, <NUM>%, and more than <NUM>% of the total power generation, an era of "generating DC-transmitting DC-distributing DC" is coming. Therefore, the full DC transformer power transmission technology will be a preferred choice to become a basic framework of the global energy Internet in the future.

An application <CIT> discloses a battery module having utility not only for off-peak power storage but also as a component of D. (step-down or step-up) transformers. transformer can function as the principal component of a D. line terminal and enables that terminal to be disconnected from the line without disrupting the rest of the system. The invention also utilizes a plurality of rechargeable batteries for both power storage and voltage scaling, in a D. distribution system.

In order to solve the technical problems in DC to AC and AC to DC conversions during power transmission, the present disclosure provides a full DC boost-buck power transmission system.

The present disclosure provides a full DC boost-buck power transmission system, comprising:.

In an arrangement, after the transmission of the DC power is completed, the series subunits in the at least one buck station are configured as a DC power supply to supply power to a power grid with a voltage lower than a voltage of the series subunits in the at least one buck station.

In an arrangement, the at least one boost station comprises a plurality of boost substations connected in series; the plurality of boost substations are respectively installed at different locations; the DC power supply consists of a plurality of DC power supplies which are different from each other in type and are configured to charge the first battery packs of each of the boost substations.

In an arrangement, the boost station is adjacent to the DC power supply and is able to output voltage; the buck station is established in a center of a user group and is able to provide an access voltage; and a plurality of backup power supply inlets and a plurality of power supply outlets are further provided to access boost stations and buck stations.

The invention is as disclosed in claims. Any described arrangements not covered by claims are for information purposes only.

Specifically, the full DC boost-buck power transmission system is constructed as follows.

(<NUM>) The boost station is configured to boost voltage in the full DC boost-buck power transmission system, where the boost station comprises a first battery pack unit, which is composed of the charging series stack including a certain number of battery packs, and hardware and software serving the charging series stack.

The charging series stack is composed of a certain number of battery packs with the same model, the same nominal voltage, and the same rated capacity, where the number of the battery packs is determined by the voltage of the power grid and the specifications of the battery packs. All battery packs are connected in parallel and accept charging from the DC power supply on the primary side. the DC power supply may be any kind of a photovoltaic power plant, a fuel cell power plant, a wind power generator that directly outputs DC, a DC power supply rectified by AC power outputted from hydropower stations, a DC power supply rectified by AC power outputted from thermal power stations, a DC hydropower station and a thermal power station. After the charging for the battery packs in the boost station is completed, the battery packs are connected in series to become a high voltage power supply. After connecting to the power grid to supply power, the first battery pack unit enters a process of discharge and performs remote power transmission to the buck station. After the discharging is completed, the first battery pack unit is disconnected from the high-voltage cable, and the battery packs in the first battery pack unit are changed to be connected in parallel again, so as to accept low-voltage charging from the DC power supply on the primary side. The above-mentioned process can be repeated cyclically to realize the function of the full DC buck-boost power transmission system.

In order to achieve the above-mentioned functions, the hardware of the boost station should include a fixing mechanism and device for installing the battery packs, cables, interfaces, switches, transfer switches, power diodes, ground wires, and hardware for detecting and managing the battery packs. The cables, the interfaces, the switches, the transfer switches, the power diodes, the ground wires, and the hardware for detecting and managing the battery pack are configured for functions of the series connection, parallel connection and series-parallel interchange function of the battery packs. Based on the hardware of the boost station, the battery packs in the boost station can accept charging and connect to high voltage for remote power transmission after being installed properly. Besides, the battery packs can be replaced or updated as needed.

The nominal voltage and optimal charging current of the battery packs in the charging series stack should be determined by the output voltage and output current of the above-mentioned DC power supply, and further determined by the grid voltage, where the specific relationship is as follows.

The charging condition:
the output voltage of the primary DC power supply is Vc; the nominal voltage of the battery pack is Vb≈Vc/<NUM>; the optimal charging current Ib and the number n of the battery packs should preferably match the output current Ic of the primary DC power supply, that is <MAT>.

Power transmission condition:
the nominal voltage of the power grid is Vw; the nominal voltage of the battery packs is Vb, if the charging series stack formed by all the battery packs are connected to the power grid for power supply, the transmission condition should satisfy the following relationship: <MAT>.

Therefore, the number of the battery packs are determined as follows: <MAT>.

(<NUM>) The buck station is configured to buck voltage in the full DC boost-buck power transmission system, where the buck station comprises a second battery pack unit, which is composed of the series stack to be charged including a certain number of battery packs, and hardware and software serving the charging series stack.

The series stack to be charged is composed of a certain number of the battery packs with the same charging and discharging characteristics and the same optimal charging current, where the number of the battery packs is determined by the grid voltage, the load demand, and the specifications of the battery pack. In the second battery pack unit, all the battery packs are connected in series and connected to the power grid through the high-voltage cable for charging. After the charging for the battery packs in the buck station is completed, all the battery packs are disconnected from the high-voltage power grid, and form a plurality of new DC power supply to supply power to the loads (electrical appliances) and electricity consumers, or connected in parallel to be a power supply with low voltage and high current to supply power to the loads, or connected in series to form a DC power supply with different voltages to supply power to the loads, microgrids, distributed power grid and local power grid. After the discharge of each of the battery packs in the buck station is completed, all the battery packs are disconnected from the load and the load grid, and are changed to be connected in series again, and connected to the power grid through the high-voltage cable for charging. The buck station operates repeatedly in this way according to the above-mentioned process.

The hardware of the buck station includes a fixing mechanism and device for installing the battery packs, cables, interfaces, switches, transfer switches, power diodes and ground wires. The cables, the interfaces, switches, transfer switches, power diodes and ground wires are provided for series connection, parallel connection and series-parallel interchange of the battery packs, separating and combining the charged battery packs, and connecting the charged battery packs to the power grid, loads and the ground wire. Based on the hardware of the buck station, the battery packs in the buck station can be charged and connected to the loads so as to supply power to the users after installed properly. Besides, the battery packs can be replaced or updated as needed.

A nominal voltage, a rated capacity of the battery pack string of the series stack to be charged and the optimal charging current are determined by the following conditions.

The selection of each of the battery packs in the series stack to be charged is not restricted by the specification of the battery packs in the charging series stack. The optimal charging current of all battery packs must be the same, while their nominal voltages and rated capacities can be different, but the nominal value and number of voltage, current intensity of the battery pack string to be charged are determined by the type and number of loads.

The actual total voltage Vbc of the charged battery string is as follows: <MAT> where Vw is an actual output voltage of the power grid transmitting through the high-voltage power grid.

According to requirements of the loads, the series stack to be charged can be constructed to form a series stack, a parallel combination and a battery pack unit.

<FIG>, <FIG>, <FIG> and <FIG> show a circuit of the full DC buck-boost power transmission system composed of a boost station and a buck station in different working states.

As show in <FIG>, in the circuit of the full DC buck-boost power transmission system, the DC power supply charges the first battery pack unit, where each of the battery packs in the second battery pack unit is neither connected to the power grid nor to the load. A first part of the battery packs in the second battery pack unit is connected in series to form the series subunit to supply power to the load; a second part of the battery packs in the second battery pack unit is connected in parallel to be the parallel subunit to supply power to the load; and a third part of the battery packs in the second battery pack unit form the single battery pack unit to independently supply power to the load.

As shown in <FIG>, the first battery pack unit is connected to the power grid through the high-voltage power grid to charge the second battery pack unit, and the second battery pack unit is connected to the power grid through the high-voltage cable to be charged.

As shown in <FIG>, the first series stack in the first battery pack unit is divided into three first series sub-stacks, where each of the series sub-stack has the same number of battery packs, and the series sub-stacks are alternately connected to the high-voltage power grid to charge the second battery pack unit.

As shown in <FIG>, the battery packs in the first battery pack unit are connected in parallel and charged by the DC power supply again. Besides, the second series stack in the second battery pack unit is separated into three power supplies, including a series subunit with a plurality of battery packs connected in series, a parallel subunit with a plurality of battery packs connected in parallel, and a single battery pack subunit. The series subunit, the parallel subunit and the single battery pack subunit are respectively connected to their load interfaces to supply power to their loads.

(<NUM>) In the full DC buck-boost transmission system, battery packs can be connected in series in remote locations to meet the voltage requirements and connected to the DC power grid to become a DC power source. In other words, several low-voltage boost stations can be connected in series to form a total high-voltage boost station. The former is called a boost substation and the latter is called a boost station. Each of the boost substations has its own primary power supply for charging. These primary power supplies can be in different locations, and they can also be power supplies of different nature. The number of battery packs in the boost station is determined by the grid voltage and the nominal voltage of the battery packs. <FIG> and <FIG> show a diagram of the structure and status of the boost station.

(<NUM>) Some components and accessories are provided in the ordinary battery packs to adapt to the application in the present disclosure. According to whether the devices are installed or not, and the method of installation, the battery packs can be divided into A-type battery pack, B-type battery pack and C-type battery pack, in which:
As shown in <FIG>, the A-type battery pack is an ordinary battery pack without any additional components or accessories. However, in actual appliances, a single-pole single-throw switch is provided at the positive electrode of the boost station, and a single-pole double-throw switch is provided at the negative electrode of the buck station.

As shown in <FIG>, in the B-type battery pack, a diode is provided at a positive electrode of the ordinary battery pack to allow current to flow into the battery pack and prevent current from flowing out of the battery pack. There is a single-pole double-throw switch provided between the diode and the positive electrode. When the positive electrode of the battery pack is connected to the diode through the switch, the battery can be charged; when the switch is connected to the load, the battery packs supply power to the load. In addition, a single-pole single-throw switch is provided at the positive electrode of the buck station and a single-pole double-throw switch is provided at the negative electrode of the buck station.

As shown in <FIG>, in the C-type battery pack, a diode is provided at a negative electrode of the ordinary battery pack to allow current to flow out of the battery pack and prevent current from flowing into the battery pack. There is a single-pole double-throw switch provided between the diode and the negative electrode. When the negative electrode of the battery pack is connected to the diode through the switch, the battery can be charged; when the switch is connected to the load, the battery packs supply power to the load. In addition, a single-pole double-throw switch is provided at the positive electrode of the buck station and a single-pole single-throw switch is provided at the negative electrode of the buck station.

(<NUM>) <FIG> shows a circuit in which the first battery pack unit in the boost station adopting the A-type battery packs is connected to the power grid through the high-voltage cable for power supplying; as shown in <FIG>, the states switches are changed, so that each of the battery packs in the first battery pack unit is connected in parallel, where the positive electrode of the battery packs is connected to the DC power supply, and the negative electrode of the battery packs is connected to the ground wire, so as to be charged from the first battery pack unit.

(<NUM>) After the charging on the buck station is completed, the second battery pack unit in the buck station adopting the A-type battery packs forms subunits with three typical connection modes, including a single battery pack subunit, a parallel subunit (parallel combination of the battery packs) and a series subunit (battery packs connected in series), where the specific circuit diagram and implementation process are given as below.

(<NUM>) As shown in <FIG>, in the buck station, each of the A-type battery packs in the second battery pack unit is connected in series to form the second series stack for charging. The battery packs are connected to the high-voltage interface, and the diode is turned on, so that all the battery packs are charged, where the diode is provided for preventing the battery packs in the second battery pack from sending power to the high-voltage power grid.

As shown in <FIG>, after the charging in the second battery pack unit is completed, the states of the switches in each of the battery packs are changed, so that each of the battery packs become a single battery pack subunit and is used as a load power supply respectively.

(<NUM>) As shown in <FIG>, after the charging on the buck side is completed, a part of the battery packs is connected in parallel to form a parallel subunit to become a power supply for the loads.

(<NUM>) <FIG> shows a circuit according to an arrangement of the present disclosure, in which the second battery pack unit in the buck station adopting the A-type battery packs for charging on the buck side. As shown in <FIG>, after the charging on the buck side is completed, a part of the battery packs in the second battery pack unit is connected in series to form a series subunit, where each of the battery packs is connected in series to become a series subunit.

(<NUM>) As shown in <FIG>, after the charging on the buck side is completed, a part of the battery packs in the second battery pack unit is connected in series to form a series subunit, and a part of the battery packs are connected in parallel to become a parallel subunit, and then the series subunit and parallel subunit are configured to supply power to the corresponding loads.

(<NUM>) After the charging on the buck station is completed, the second battery pack unit in the buck station adopting the B-type ordinary battery packs forms subunits with three typical connection modes, including a single battery pack subunit, a parallel subunit and a series subunit, where the specific circuit diagram and implementation process are given as below.

(<NUM>) As shown in <FIG>, the second battery pack unit in the buck station adopting the B-type battery pack is charging on the buck side. The switch <NUM> is connected to the high-voltage interface.

As shown in <FIG>, after the charging on the buck side is completed, the switch K83 is turned off. By changing the state of the switches in the positive electrode and the negative electrode of each of the battery packs, each of the B-type battery packs can independently supply their own loads.

(<NUM>) As shown in <FIG>, after the charging of the B-type battery on the buck side is completed, a part of the battery packs in the second battery pack unit is connected in parallel to form the parallel subunit, where each of the battery packs in the parallel subunit is provided with a bypass cable. When each of the battery packs in the second battery pack unit is charging on the buck side, the bypass cables are left floating.

As shown in <FIG>, after the charging of the battery packs in the second battery pack unit is completed, the positive electrode of each of the battery packs is connected to the bypass cable, and the other end of each of the battery packs is connected to the ground wire, so that the battery packs are connected in parallel to supply power.

(<NUM>) As shown in <FIG>, the second series stack formed by the B-type battery packs in the second battery pack unit is charging on the buck side, where the circuit in <FIG> is the same as that in <FIG>, and the bypass cable of the first battery pack in the series stack can be omitted.

As shown in <FIG>, after the charging on the buck side is completed, the battery packs in the second battery pack unit are connected in series to form a series subunit to supply power to the loads.

(<NUM>) As shown in <FIG>, after the charging on the buck side is completed, a part of the B-type battery packs in the second battery pack unit are connected in series to form a series subunit, and a part of the B-type battery packs are connected in parallel to become a parallel subunit, and then the series subunit and parallel subunit are configured to supply power to the corresponding loads.

(<NUM>) After the charging on the buck station is completed, the second battery pack unit in the buck station adopting the C-type ordinary battery packs forms subunits with three typical connection modes, including a single battery pack subunit, a parallel subunit and a series subunit, where the specific circuit diagram and implementation process are given as below.

(<NUM>) As shown in <FIG>, the second battery pack unit in the buck station adopting the C-type battery pack is charging on the buck side.

As shown in <FIG>, after the charging on the buck side is completed, the states of the switches in the positive electrode and the negative electrode of each of the battery packs are changed, each of the C-type battery packs can independently supply their own loads.

(<NUM>) As shown in <FIG>, after the charging of the C-type battery on the buck side is completed, a part of the battery packs in the second battery pack unit is connected in parallel to form the parallel subunit.

(<NUM>) As shown in <FIG>, the second series stack formed by the C-type battery packs in the second battery pack unit is charging on the buck side, where a bypass cable is provided at the negative electrode of each of the battery packs.

(<NUM>) As shown in <FIG>, after the charging on the buck side is completed, a part of the C-type battery packs in the second battery pack unit are connected in series to form a series subunit, and a part of the C-type battery packs are connected in parallel to become a parallel subunit, and then the series subunit and parallel subunit are configured to supply power to the corresponding loads.

(<NUM>) As shown in Figs. <NUM>-<NUM> and <FIG>, regardless of whether the above-mentioned second battery pack unit adopts the A-type battery pack, the B-type battery pack or the C-type battery pack, after the charging on the buck side is completed, the battery packs in the second battery pack unit can be moved away from the installation positions to supply power to the loads, or supply power to the loads without being moved away from the installation positions.

(<NUM>) As shown in <FIG>, the full DC buck-boost power transmission system provided in the present disclosure is actually an open full DC buck-boost power station and transmission grid, which has the following characteristics.

(<NUM>) In order to ensure that the DC power supply on the primary side continuously supplies power to the open full DC high voltage transmission and distribution power grid, the boost station should provide with two or more sets of the first battery pack unit for receiving the power input from the DC power supply on the primary side in turn. Similarly, in order to ensure that the buck station continuously supplies power to the loads, two or more sets of the second battery pack units should be provided.

It should be noted that, if the DC power supply on the primary side generates power intermittently or randomly, different measurement should be implemented according to the charging condition of the first battery pack unit:.

In the present disclosure, the battery packs are adopted as the main component and the conversion of the connection mode is applied, so that the battery packs form a parallel connection for low-voltage charging, and then the battery packs are changed to be connected in series to obtain a high-voltage power to supply power to the second battery pack unit. After the charging for the battery packs in the second battery pack unit is completed, the second battery pack unit is divided into a plurality of single battery pack subunits, a plurality of parallel subunits and a plurality of series subunits to supply power to their corresponding loads. After the DC power supply of the second battery pack unit is completed, the connection modes of the first and the second battery pack units are respectively restored, and then the system is performed repeatedly in the above-mentioned way, thereby achieving storage, boost, power transmission, buck and supply of the DC power. Since there is no AC-DC conversion in the process, the system provided in the present disclosure is called the full DC buck-boost transmission system.

The present disclosure will be further described in detail below with reference to the accompanying drawings and embodiments.

The full DC high voltage transmission and distribution power grid provided in the present disclosure has the following basic working principles:.

The output voltage of the DC power supply in the primary side is Vc; each of the battery packs of the first battery pack unit in the boost station has the same specification, that is, each of the battery packs has the same nominal voltage, the same rated capacity and the same optimal charging current. A matching relationship between a nominal voltage Vb and the actual voltage Vc is: <MAT>.

The optimal charging current of each of the battery packs is Ib; the number of the battery packs in the first battery pack is n; Ib and Ic should preferably satisfy the following relationship: <MAT>.

If the nominal voltage of the power grid is Vw, and all the battery packs form a first series stack and connected to the power grid for power transmission, the transmission condition should satisfy the following relationship: <MAT> then <MAT>.

The series subunits with higher voltage should be placed at a high-voltage terminal closer to the power grid.

Described below are preferred embodiments in practical application, which may be not the best design for the actual case.

In the arrangement, the DC power supply on the primary side adopts an isolated photovoltaic power plant, where the isolated photovoltaic power plant has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A.

In the boost station, the battery packs in the first battery pack unit are A-type battery packs with the same specification, where the nominal voltage of each of the battery packs ≈<NUM> V/<NUM>=<NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the number of the battery packs is <NUM>. Therefore, the sum of the optimal charging current of the first battery pack unit is equal to <NUM> A. According to <FIG> and its description, each of the A-type battery packs in the first battery pack unit is connected in parallel, so that the DC power supply on the primary side charges the first battery pack unit at full capacity. After the charging on the boost side is completed, the connection mode of each of the A-type battery packs in the first battery pack unit is changed to a series connection with reference to <FIG> to form a first series stack, so that the first series stack connects to the power grid via the diode to transmit electricity power, where the transmission voltage is <NUM>×<NUM> V=<NUM> kV, and the transmission current is <NUM> A.

In the buck station, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV. Therefore, the total number of the battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit can be configured as follows.

The accompanying drawings and descriptions of the connection modes of the battery packs are as follows:.

In the boost station, the battery packs in the first battery pack unit is A-type battery packs with the same specification, where the nominal voltage of each of the battery packs is ≈<NUM> V/<NUM>=<NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the number of the battery packs is <NUM>. Therefore, the sum of the optimal charging current of the first battery pack unit is equal to <NUM> A. After the charging on the boost side is completed, the connection mode of each of the A-type battery packs in the first battery pack unit is changed to a series connection, so that the first series stack connects to the power grid via the diode to transmit electricity power, where the transmission voltage is <NUM>×<NUM> V=<NUM> kV, and the transmission current is <NUM> A.

There are four buck stations <NUM>, including a buck station 140a, a buck station 140b, a buck station 140c and a buck station 140d, where the composition of the four buck stations is as follows.

In the buck station, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV. Therefore, the total number of battery packs is <NUM>. 33kV/<NUM> kV=<NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit a can be configured as follows.

In the buck station b, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV. Therefore, the total number of the battery packs is <NUM> kV/<NUM> kV=<NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit a can be configured as follows.

In the buck station c, the second battery pack unit b is divided into two types of subunits, where the battery packs in each type of subunits can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. In the first specification subunit, the nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; the total number of battery packs is <NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. In the second specification subunit, the nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; the total number of battery packs is <NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. The first specification subunit and the second specification subunit are connected in series, and thus the total nominal voltage of the second battery pack unit b is <NUM> kV+<NUM> kV=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the connection mode of the buck station a. the second battery pack unit can be configured as follows.

The first specification subunit can be configured as follows.

The second specification subunit includes <NUM> single battery pack subunits, in which the nominal voltage of each of the single battery pack subunits is 300V; and each of the battery pack subunits is used as a charging pile for electric vehicles.

In the buck station d, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV. Therefore, the total number of battery packs is <NUM> kV/<NUM> kV=<NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. After the power supply is completed, the second battery pack unit are connected according to user loads, so that each of the battery packs is used as a charging pile for nearby electric vehicles.

In the buck station, the working current of the buck station a is <NUM> A; the working current of the buck station b is <NUM> A; the working current of the buck station c is <NUM> A; and the working current of the buck station d is <NUM> A; and thus, the total working current of the four buck stations connected in parallel is: <NUM> A+<NUM> A+<NUM> A+<NUM> A=<NUM> A.

In the arrangement, the DC power supply on the primary side includes a first DC power supply 110a, a second DC power supply 11b and a third DC power supply 110c, where the first DC power supply 110a is a photovoltaic power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A; the second DC power supply 110b is a photovoltaic power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A; and the third DC power supply <NUM> is a DC power supply rectified from a hydropower station or a DC power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A.

In the boost station, the battery packs in the first battery pack unit are A-type battery packs with the same specification, where the nominal voltage of each of the battery packs is <NUM> V, the optimal charging current of each of the battery packs is <NUM> A. The boost substation matched with the DC power supply a has <NUM> battery packs; the boost substation matched with the DC power supply b has <NUM> battery packs; and the boost substation matched with the DC power supply c has <NUM> battery packs. After the three boost substations are charged by their corresponding DC power sources on the primary side, the battery packs in each of the boost substations are changed to be connected in series, and the voltage of each of boost substation is <NUM> kV, <NUM> kV and <NUM> kV, respectively. And then each of the boost substation is connected in series at different places, and is connected to the power grid through the diode for power transmission, where the total voltage is <NUM> KV, and the transmission current is 250A.

There are three buck stations, including a first buck substation <NUM>-<NUM>, a second buck substation <NUM>-<NUM> and a third buck substation <NUM>-<NUM>, where their compositions are as follows.

In the first buck substation <NUM>-<NUM>, the battery packs in the first battery pack unit are A-type battery packs with the same specification, where the nominal voltage of each of the battery packs is <NUM> V, the optimal charging current of each of the battery packs is <NUM> A, and the total optimal charging voltage is <NUM> kV/<NUM>=<NUM> kV; the total number of battery packs is <NUM> kV/<NUM> kV≈<NUM>, and the total nominal voltage is <NUM>×120V=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the first buck substation <NUM>-<NUM> is changed according to the user loads and the type of the battery pack. The first buck substation <NUM>-<NUM> can be configured as follows.

In the second substation <NUM>-<NUM>, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV. The total number of the battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. After the charging on the buck station is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user load and the type of the corresponding battery pack, and the composition is constructed as follows.

In the third substation <NUM>-<NUM>, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV; the total number of the battery packs is <NUM> kV/<NUM> kV≈ <NUM>; and their total nominal voltage is <NUM>×<NUM> V=<NUM> kV. After the charging on the buck station is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user load and the type of the corresponding battery pack, and the composition is as follows.

<NUM> single battery pack subunits, where a voltage of each of single battery pack subunits is <NUM>. 3kV, and each of the single battery pack subunits is used as a charging pile for nearby electric vehicles.

In the buck station, the working current of the first buck substation <NUM>-<NUM> is <NUM> A; the working current of the second buck substation <NUM>-<NUM> is <NUM> A; and the working current of the third buck substation <NUM>-<NUM> is <NUM> A. Therefore, the total working current of three buck substations connected in parallel is: <NUM> A+<NUM> A+<NUM> A =<NUM> A.

In the arrangement, the full DC buck-boost power transmission system is the same as that in the above-mentioned arrangements, and the DC power supply on the primary side includes a first DC power supply <NUM>-1A, a second DC power supply <NUM>-1B, a third DC power supply <NUM>-1C and a fourth DC power supply <NUM>-1D, where the first DC power supply <NUM>-1A is a photovoltaic power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A; the second DC power supply <NUM>-1B is a photovoltaic power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A; the third DC power supply <NUM>-1C is a DC power supply rectified from a hydropower station or a DC power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A; and the fourth DC power supply <NUM>-1D is a photovoltaic power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A.

There are two boost stations in the arrangement, including the first boost station <NUM>-<NUM> and the second boost station <NUM>-<NUM>. The first boost station <NUM>-<NUM> has three boost substations at different places connected in series, including a first boost substation <NUM>-1A, a second boost substation <NUM>-1B, and a third boost substation <NUM>-1C. The battery packs in the first boost substation and the second boost substation are A-type battery packs with the same specification, where the nominal voltage of each of the battery packs is <NUM> V, the optimal charging current of each of the battery packs is <NUM> A. The first boost substation <NUM>-1A matched with the first DC power supply <NUM>-1A has <NUM> battery packs; and the second boost substation <NUM>-1B matched with the second DC power supply <NUM>-1B has <NUM> battery packs. The battery packs in the third boost substation <NUM>-1C are A-type battery packs with the same specification, where the nominal voltage of each of the battery packs =<NUM>/<NUM>=<NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the number of the battery packs is <NUM>. After the three boost substations are respectively charged by their corresponding DC power supplies on the primary side, the battery packs in the boost station are changed to be connected in series, where the voltage of the boost substations respectively are <NUM>×<NUM> V=<NUM> kV, <NUM>×<NUM> V=<NUM> kV and <NUM> ×<NUM> V=<NUM> kV. Each of the boost substations is connected in series at different places, and is connected to the power grid through the diode for power transmission, the total voltage is <NUM> kV, and the current is <NUM> A. The battery packs in the second boost station <NUM>-<NUM> are A-type battery pack with the same specification, where the nominal voltage of each of the battery packs is <NUM> V, and the optimal charging current of each of the battery packs is <NUM> A. The second boost substation <NUM>-1A matched with the fourth DC power supply <NUM>-<NUM> has <NUM> battery packs. After the first battery pack unit in the second boost substation <NUM>-<NUM> is charged by the corresponding DC power supply on the primary side, the battery packs are changed to be connected in series, and connected to the power grid through the diode for power transmission, where the voltage is <NUM>×<NUM> V=<NUM> kV, and the current is <NUM> A.

There are four buck stations, including a first buck substation <NUM>-<NUM>, a second buck substation <NUM>-<NUM>, a third buck substation <NUM>-<NUM>, where their compositions are as follows.

In the first buck substation <NUM>-<NUM>, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV; therefore, the total number of battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> V=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit can be configured as follows.

In the second buck substation <NUM>-<NUM>, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV; therefore, the total number of battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> V=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit can be configured as follows.

In the third buck substation <NUM>-<NUM>, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV; therefore, the total number of battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> V=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit can be configured as follows.

In the fourth buck substation <NUM>-<NUM>, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV; therefore, the total number of battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> V=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the battery packs in the second battery pack unit is changed according to the user loads and the type of the battery pack. the second battery pack unit can be configured as follows.

In the arrangement, the full DC buck-boost power transmission system is the same as that in the above-mentioned arrangements, and the DC power supply on the primary side is a photovoltaic power station, which has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A.

There are two boost stations in the arrangement, including a high voltage boost station 120A and a high current boost station 120B. The high voltage boost substation 120A adopts the A-type battery packs, where the nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is 200A; and the number of the battery packs is <NUM>. The high current boost substation 120B adopts the A-type battery packs, where the nominal voltage of each of the battery packs is <NUM> V; the optimal charging current of each of the battery packs is <NUM> A; and the number of the battery packs is <NUM>. If the sum of the optimal charging current after the two boost stations are connected in parallel is equal to <NUM> A, the power supplies on the primary side can respectively charge the battery packs at full capacity. After the charging is completed, when the DC power supply on the primary side is matched with the high voltage boost station 120A, all battery packs are changed to form three first series stacks, where each of the first series stacks includes <NUM> battery packs; each of the first series stack is connected to the power grid through the diode for power transmission, where the voltage is <NUM>×<NUM> V=<NUM> kV, and the current is <NUM> A. when the DC power supply on the primary side is matched with the high current boost station 120B, all <NUM> battery packs are connected in series after being charged, and connected to the power grid through the diode for power transmission, where the voltage is <NUM>×<NUM> V=<NUM> kV, and the current is <NUM> A.

In the buck station, all battery packs in the second battery pack unit share the same specification, which can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V; the optimal charging current each of the battery packs is <NUM> A, which is slightly less than the current delivered by the high voltage boost station, and slightly less than one-third of the current delivered by the high current boost station. The optimal total charging voltage is <NUM> kV/<NUM>=<NUM> kV; the total number of battery packs is <NUM> kV/<NUM> kV≈<NUM>, and their total nominal voltage is <NUM>×<NUM> kV=<NUM> kV. After the charging on the buck side is completed, the connection mode of each of the A-type battery packs is changed according to the user loads and the type of the battery pack. The second battery pack unit can be configured as follows.

The above-mentioned full DC buck-boost power transmission system is applied to an isolated photovoltaic power station to continuously supply power to electrical loads. The two boost stations 120A and 120B are equivalent for the same buck station.

In the arrangement, the DC power supply on the primary side is a photovoltaic power station or a wind turbine generator.

When the DC power supply is a photovoltaic power station, the DC power supply has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A.

In the buck station, the battery packs in the second battery pack unit can be any one of A-type battery packs, B-type battery packs, and C-type battery packs. The nominal voltage of each of the battery packs is <NUM> V. The battery packs in the second battery pack unit are constructed according to the optimal charging current as follows.

There are <NUM> series subunits consisting of <NUM> battery packs with the optimal charging current of 9A, where the total nominal voltage of each of the series subunit is <NUM> V. All the <NUM> series subunits are connected in parallel for charging.

After the charging on the buck side is completed, the buck station is disconnected from the photovoltaic power station, and the <NUM> series subunits are separated from each other. Therefore, the battery packs in each of the series subunits are separated from each other, and are connected in parallel, so that each of the series subunits is divided into <NUM> single battery pack subunits, and each of the single battery pack subunits independently supplies power to a user, where the total number of the users is <NUM>×<NUM>=<NUM>; the total current is <NUM>×<NUM> A=<NUM> A; and the distance of the users from the buck station is less than <NUM>.

When the DC power supply is a wind turbine generator with a DC output without inverter, the DC power supply has a power of <NUM> MW, an output voltage of <NUM> V, and an output current of <NUM> A.

The nominal voltage of each of the series subunits is <NUM> V, and all the series subunits are connected in parallel for charging.

After the charging on the buck side is completed, each of the series subunits is disconnected from the wind turbine generator; the battery packs in each of the series subunits are also disconnected from each other, so that each of battery packs independently supplies power to a user, where the distance of the users from the buck station is less than <NUM>; a total number of users is <NUM> × (<NUM> + <NUM> + <NUM>) = <NUM>; and the total current is <NUM> × <NUM> A + <NUM> × <NUM> A + <NUM> × 12A=2064A.

In the arrangement, illustrated is an open full DC buck-boost transmission and transformation power grid, where the composition and the operation state of the power grid will be described as follows.

As shown in <FIG>, GYDW is a high-voltage power grid, where there are three boost stations and two buck stations connected to the high-voltage power grid.

CDCLD1is composed of A-type ordinary type battery packs, where the fully charged battery packs in the drawing are filled with gray to distinguish; the CDCLD1 is connected to the high-voltage power grid through the diode to supply power. ZLJK1 is a DC interface <NUM> provided for the first series stack <NUM>-<NUM>.

CDCLD2 is composed of the A-type battery pack, where the fully charged battery packs in the drawing are filled with gray to distinguish; the CDCLD2 is connected to the high-voltage power grid through the diode to supply power; the second series stack <NUM> in the first battery pack unit is composed of a plurality of series sub-stacks, including CDCLD2a, CDCLD2b, and CDCLD2c, where the series sub-stacks may not be arranged in the same place, and there is a certain distance from each other. ZLJK2a is a DC interface 2a provided for the CDCLD2a; ZLJK2b is a DC interface 2b provided for the CDCLD2b; and ZLJK2c is a DC interface 2c, provided for the CDCLD2c.

CDCLD3 is composed of A-type battery packs, where the fully charged battery packs in the drawing are filled with gray to distinguish; the CDCLD2 is connected to the high-voltage power grid through the diode to supply power. ZLJK3 is a DC interface <NUM>, provided for the third series stack <NUM> in the first battery pack unit.

The diode is provided for preventing current flowing into the charging series stacks.

BCDXDCZ1 is a first series stack <NUM> to be charged, consisting of B-type or C-type battery packs. The battery packs without fill color in the drawing are being charged. After the BCDXDCZ1 is fully charged, the connection mode of the battery packs can be changed to form a single battery pack subunit, a parallel subunit and a series subunit. FZJK1a, FZJK1b and FZJK1c are respectively a load interface provided for the parallel combination of the battery packs to be charged or the series stack of the battery packs to be charged.

BCDXDCZ2 is a second series stack <NUM> to be charged, consisting of B-type or C-type battery packs. The battery packs without fill color in the drawing are being charged. FZJK1a, FZJK1b and FZJK1c are respectively a load interface provided for the parallel combination of the battery packs to be charged or the series stack of the battery packs to be charged.

YLJK: a reserved interface, configured to connect the other subunit of the second battery group unit that meets the technical indicators in the future to the power grid. Therefore, an open power grid is provided for connecting to other power grids in remote regions.

<FIG> schematically show the circuit of the full DC high voltage transmission and distribution power grid in another working state according to the arrangement of the present disclosure.

The third series stack <NUM> is disconnected from the high-voltage power grid and connected to the ZLJK3 for charging on the boost side.

After the charging on the buck side is completed and the second series stack to be charged <NUM> is disconnected from the power grid, the second series stack to be charged <NUM> forms a parallel subunit and a series subunit, so that the subunits are connected to their corresponding loads to supply power; FZJK2a: a load interface 2a, connected to the series subunit; FZJK2b: a load interface 2b, connected to the parallel subunit; and FZJK2c: a load interface 2c, connected to the single battery pack subunit.

Each of the charging series stacks in the first battery pack unit and each of the series stacks to be charged the second battery pack unit have two working states of being charged and charging, but the periods of their working state are different. Therefore, there are many combinations of working conditions of the entire power grid, and the combinations of working conditions are constantly changing. There are about dozens of connection modes, where only two connection modes are listed out in the above-mentioned arrangements. In actual use, the switching of the working conditions of each of the boost stations and each of the buck station should be controlled by a power grid management center. The smart grid technologies including hardware and software for overall management, control, adjustment, and detection are not elaborated herein.

The industrial applicability of various types of power transmission systems of the present disclosure are introduced when explaining the full DC buck-boost power transmission system in the above-mentioned arrangements.

In order to implement the full DC buck-boost power transmission system of the present disclosure, the power grid is provided with the following characteristics: a battery pack in the first battery pack unit for boosting is disconnected from the power grid when charging on the boost side, and they are connected to the power grid only when they charge the battery packs in the second battery pack unit on the buck side. The battery packs in the second battery pack unit for bucking is connected to the power grid only when they need to be charged, and they are disconnected from the power grid when supplying power to the loads. Therefore, if the power grid fails, the power station can continue to work, where the battery packs in the first battery pack unit can continue to be charged, and the battery packs in the second battery pack unit can continue to supply power to the loads. Therefore, the DC power supply system has the advantages of safe, easy to handle power grid accidents, and simple and reliable control and management system.

The present disclosure tightly combines power generation, energy storage and power supply, and has strong resistance to fluctuations in the power generation terminal and the user terminal.

The present disclosure can obtain high-quality DC power and eliminate various types of AC harmonics.

Claim 1:
A full DC boost-buck power transmission system, comprising:
at least one boost station;
at least one buck station;
a power grid management center;
a DC power supply; and
a cable (<NUM>) provided for connecting the at least one boost station to the at least one buck station;
characterized in that the at least one boost station comprises a plurality of first battery packs, and the first battery packs are connected in parallel for storage of DC power from the DC power supply;
when the storage of the first battery packs is completed, the first battery packs are disconnected from the DC power supply and are connected in series to perform the boost operation, and then connected to the cable (<NUM>) to supply the DC power to the at least one buck station; and after transmission of the DC power is completed, the first battery packs are disconnected from the cable (<NUM>) and connected in parallel, and then connected to the DC power supply for the storage of the DC power;
the at least one buck station comprises a plurality of second battery packs, and the second battery packs are connected in series for transmission of DC power from the boost station to the buck station;
when the transmission of the DC power is completed, the second battery packs of the at least one buck station are configured to form a plurality of single battery pack subunits, a plurality of series subunits and a plurality of parallel subunits, so that the different kinds of the subunits are independently connected to their corresponding loads for transmission of the DC power from the subunits to their corresponding loads; after the supply of DC power from the subunits to their corresponding loads is completed, the second battery packs in the at least one buck station are disconnected from the loads and connected in series, and then connected to the cable (<NUM>) for transmission of DC power from the boost station; and
the power grid management center is configured to switch connection modes of the battery packs (XDCZ00) in the at least one boost station and the at least one buck station between series connection and parallel connection and to switch connection and disconnection of at least one booster station with the cable (<NUM>) as well as to switch connection and disconnection of at least one buck station with the cable (<NUM>), to achieve storage, boost, transmission, buck and supply of DC power.