Novel power distribution architecture used in power distribution system

Abstract

A power distribution system includes phase and neutral lines, an AC power source, a first AC-passing DC blocker, a first DC power source, and a first AC-blocking DC-passing device. The AC power supply is electrically connected between the phase line and the neutral line. A first AC-through-DC blocker is electrically connected between an AC power source and a neutral line and includes a series LC filter having a capacitor and an inductor connected in series, where the AC power source and the AC-through-DC blocker form an AC path. The first DC power supply is electrically connected between the phase line and the neutral line. The first alternating current blocking direct current passing device is electrically connected between the first direct current power source and the neutral line and comprises a parallel LC filter, the parallel LC filter is provided with a capacitor and an inductor which are connected in parallel, and the first direct current power source and the first alternating current blocking direct current passing device form a direct current path; and the AC path and the DC path are mutually independent paths between the phase line and the neutral line.

Description

Technical Field

[0001] The present invention generally relates to the field of power distribution, and more particularly to a novel power distribution architecture for use in a power distribution system to achieve simultaneous distribution of alternating current and direct current in a power distribution network. Background Art

[0002] With the increasing use of renewable energy sources (RES) in low-voltage distribution networks, there has recently been a discussion about whether AC should be used in low-voltage distribution lines. This is because most renewable energy sources are more compatible with DC than AC. For example, photovoltaic panels are usually connected to the AC grid through a DC / DC converter and then to an inverter; wind turbines are connected to the AC network through a rectifier and then to an inverter. In the distribution system, due to the use of AC, the power generated by solar panels and wind turbines must undergo additional DC / AC conversion. In addition, AC distribution systems require AC / DC conversion to meet the needs of DC loads. DC loads in distribution systems are also gradually increasing. One of the reasons is the development of electric vehicles, which require DC to complete battery charging.

[0003] There are three main types of distribution systems used so far. The first is an AC distribution system: AC is used for distribution lines; DC generated by renewable energy sources (RES) is converted to AC by inverters, and rectifiers convert AC to DC for use by DC loads. The second is a DC distribution system: DC is used for distribution lines; AC from the main grid is converted to DC by rectifiers for use in the low-voltage network, and inverters are used to convert DC to AC for use by AC loads. The third is a hybrid AC / DC distribution system: two distribution networks are usually built; one for AC components and the other for DC components, such as renewable energy sources and DC loads.

[0004] In this regard, AC distribution system is the main type widely used in the world, while DC and hybrid AC / DC distribution systems are still in the experimental stage and are not widely popularized. Each type has its advantages and disadvantages. The advantage of the first type is that no inverter is required to convert DC in the distribution line to AC for use by AC loads. However, it requires an inverter to convert DC generated by renewable energy into AC to inject it into the distribution line, and a rectifier is required to convert AC in the distribution line to DC for use by DC loads. The advantage of the second type is that no inverter is required to convert DC generated by renewable energy into AC, and the DC in the distribution line can be compatible with DC loads. However, in the second method, an inverter will be required to convert DC in the distribution line into AC for use by AC loads. The advantage of the third type is that AC / DC conversion is minimized. However, it is incompatible with the existing distribution network because the existing distribution network has only one distribution network, and this type requires two independent distribution networks to work. If the third type of distribution network is adopted, an additional distribution network will need to be built, which will bring expensive costs.

[0005] Based on the above, in order to overcome the shortcomings of the above three methods, the solutions currently needed include: eliminating the need for inverters to convert DC power generated by renewable energy into AC power; eliminating the need for power electronic equipment on the load side to perform AC / DC or DC / AC conversion; reducing the number of AC / DC or DC / AC conversions as much as possible; and avoiding the construction of two independent distribution networks for AC and DC equipment.

[0006] Furthermore, transmitting AC and DC simultaneously in the distribution line and extracting power for AC and DC devices respectively would be a solution to achieve the above goals. In the current technology, this can be achieved by a three-phase zigzag transformer. The zigzag transformer can act as an AC-DC coupling and decoupling device. The AC device is connected to the windings of the transformer, while the DC device is connected to the neutral point of the transformer. However, the main disadvantages of the zigzag transformer are that it is only applicable to three-phase systems and is designed to extract AC and DC at the same location at the same time, which means that when only AC or DC is extracted from the distribution line, the equipment utilization rate is wasted. Therefore, a new distribution system architecture is needed that can distribute AC and DC simultaneously in the distribution line, and the AC and DC devices used can operate independently. Summary of the invention

[0007] In the technical solution of the present invention, a new power distribution architecture is proposed, which distributes the AC and DC in the power distribution system to AC loads and DC loads respectively. Controlling the AC and DC power can flow simultaneously in the distribution line. The proposed technical solution can extract the superposition state of AC and DC in the distribution line, so that the AC equipment and DC equipment can work independently, that is, controlling the AC current to flow into the AC equipment and the DC current to flow into the DC equipment. By controlling the DC voltage source powered by renewable energy (RES), the DC power is directly injected into the distribution line, so that the proposed distribution control scheme does not need to use power electronic equipment on the load side to convert between AC and DC (such as DC / AC conversion). After simulation verification, the proposed scheme can realize the control of AC and DC to flow simultaneously in the distribution line, and at the same time, the AC and DC in the distribution line current flow into the AC equipment and DC equipment respectively.

[0008] The present invention provides a power distribution system, characterized in that it includes a phase line and a neutral line, an AC power supply, a first AC through-DC blocker, a first DC power supply and a first AC blocking DC through-device. The AC power supply is electrically connected between the phase line and the neutral line. The first AC through-DC blocker is electrically connected between the AC power supply and the neutral line, and includes a series LC filter, which has a capacitor and an inductor connected in series, wherein the AC power supply and the AC through-DC blocker form an AC path. The first DC power supply is electrically connected between the phase line and the neutral line. The first AC blocking DC through-device is electrically connected between the first DC power supply and the neutral line, and includes a parallel LC filter, which has a capacitor and an inductor connected in parallel, wherein the first DC power supply and the first AC blocking DC through-device form a DC path, and the AC path and the DC path are mutually independent paths between the phase line and the neutral line.

[0009] In some embodiments, the capacitor and the inductor of the parallel LC filter of the first AC blocking DC pass-through device have a series resistance and Where, if the series resistance and If L is known, then select L according to the formula " and C " , which are the inductance value of the inductor and the capacitance value of the capacitor of the parallel LC filter respectively, and if the series resistance and If L is unknown, then another formula can be used to select " and C " .

[0010] In some embodiments, the inductors of the series LC filter and the parallel LC filter are both variable inductors, and when the series LC filter or the parallel LC filter consumes reactive power, the corresponding inductor reduces its inductance value through its variable inductor.

[0011] In some embodiments, the parallel LC filter also has a first variable resistor and a second variable resistor, and the capacitor and the inductor of the parallel LC filter are each connected in series with the first variable resistor and the second variable resistor, respectively, so that the resonant frequency of the parallel LC filter is adjustable.

[0012] In some embodiments, the power distribution system also includes: a second DC power supply, electrically connected between the phase line and the neutral line, and including a renewable energy source and a DC / DC converter, so that the DC power supply can be powered by the renewable energy source and provide DC power via the DC / DC converter; and a second AC blocking DC pass-through, electrically connected between the second DC power supply and the neutral line, and including a parallel LC filter having a capacitor and an inductor connected in parallel.

[0013] In some embodiments, the power distribution system is characterized in that it also includes: an AC load, electrically connected between the phase line and the neutral line; a second AC through-DC blocker, electrically connected between the AC load and the neutral line, and including a series LC filter, which has a capacitor and an inductor connected in series, wherein the AC load and the second AC through-DC blocker form an AC load path; a DC load, electrically connected between the phase line and the neutral line; and a second AC blocking DC through-DC device, electrically connected between the DC load and the neutral line, and including a parallel LC filter, which has a capacitor and an inductor connected in parallel, wherein the DC load and the second AC blocking DC through-DC device form a DC load path, and the AC load path and the DC load path are independent of each other.

[0014] In some embodiments, the number of the series LC filters of the first alternating current passing through the DC block is multiple, and the multiple series LC filters are connected in parallel to each other.

[0015] In some embodiments, the series LC filter is a fixed resonant frequency series LC filter or a tunable resonant frequency LC filter, and the resonant frequencies of the series LC filter are different.

[0016] In some embodiments, the number of the parallel LC filters of the first AC blocking DC pass-through device is multiple, and the multiple parallel LC filters are connected in series with each other.

[0017] In some embodiments, the parallel LC filter is a fixed resonant frequency parallel LC filter or a tunable resonant frequency LC filter, and the resonant frequencies of the filters are different.

[0018] With the above configuration, the advantages of the proposed power distribution control scheme include:

[0019] The defects of using load-side power electronic equipment for AC / DC conversion in an AC distribution system and using DC / AC conversion in a DC distribution system are eliminated; in the proposed technical solution, AC loads and DC loads can directly receive AC and DC from distribution lines.

[0020] The defects of the inverter using RES for DC / AC conversion in the AC power distribution system are eliminated; in the proposed technical solution, DC power can be directly injected into the distribution line.

[0021] Conversion between AC and DC is minimized through a single network; on the other hand, a hybrid AC / DC distribution system requires two separate distribution networks to work.

[0022] Giving distribution line currents zero crossover current is a practical technical effect that enhances the operation of fuses and circuit breakers.

[0023] Compared with AC distribution system, using DC as the power transmission medium in the distribution line to distribute DC to DC loads, rather than using AC as the transmission medium to distribute AC to rectifiers and then to DC loads, will reduce the skin effect on the distribution line. Using DC as one of the transmission media can increase the effective cross-sectional area of ​​the distribution line. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and / or other aspects and advantages of the present invention will become apparent and more easily understood by referring to the description of the embodiments in conjunction with the following drawings, in which:

[0025] Figure 1 It is a current schematic diagram of the distribution line in the proposed technical solution;

[0026] Figure 2 A configuration diagram of an AC / DC separation device, a transformer, a converter, and a load according to some embodiments of the present invention;

[0027] Figure 3 A configuration diagram of a fixed resonant frequency LC filter according to some embodiments of the present invention is shown;

[0028] Figure 4 A configuration diagram of a solid-state transformer in a power distribution architecture according to some embodiments of the present invention is shown;

[0029] Figure 5 A schematic diagram of using a fixed resonant frequency LC filter and considering the series resistance of an inductor and a capacitor according to some embodiments of the present invention is shown;

[0030] Figure 6 A configuration diagram of an LC filter with adjustable resonant frequency is shown according to some embodiments of the present invention;

[0031] Figure 7 A configuration diagram of a parallel LC filter with adjustable resonant frequency is shown according to some embodiments of the present invention;

[0032] Figure 8 According to some embodiments of the present invention, a configuration diagram of a combination of an AC passing through a DC blocker and a series inductor and capacitor of an AC device is presented;

[0033] Fig. 9 According to some embodiments of the present invention, a configuration diagram of a single capacitor for AC passing through a DC blocker is presented;

[0034] Fig.10 A configuration diagram of a cascaded sub-AC through-DC blocker and a sub-AC blocking DC through-DC blocker is presented according to some embodiments of the present invention;

[0035] Fig.11 An example diagram of a single-phase distribution network using cooperative transformers using the proposed control scheme is presented;

[0036] Fig.12 Present a schematic diagram of the DC power supply control principle with the output voltage as the control variable;

[0037] Fig.13 An example diagram of introducing a power distribution configuration in a three-phase balanced system according to some embodiments of the present invention is shown;

[0038] Fig.14 An example diagram of introducing a power distribution configuration in a three-phase unbalanced system according to some embodiments of the present invention is shown;

[0039] Fig.15 A schematic diagram of a 4-bus single-phase test system constructed by simulation according to some embodiments of the present invention is shown;

[0040] Fig.16 , Fig.17 , Fig.18 , Fig.19 , Fig. 20 , Fig.21 , Fig. 22According to some embodiments of the present invention, a diagram showing the output power, current and voltage of a simulated DC power supply and a DC load voltage diagram is shown;

[0041] Fig.23 , Fig.24 , Fig.25 According to some embodiments of the present invention, a distribution line current diagram of different line segments simulated by simulation is shown;

[0042] Fig.26 , Fig. 27 , Fig.28 A diagram of AC power and AC load voltages of a simulated AC source (ie, the secondary terminals of a transformer) is shown according to some embodiments of the present invention. DETAILED DESCRIPTION

[0043] In the following description, a new power distribution architecture for use in a power distribution system is described as a preferred example. Modifications, including additions and / or substitutions, may be made to those skilled in the art without departing from the scope and spirit of the invention. Specific details may be omitted to avoid obscuring the invention; however, this disclosure is written to enable those skilled in the art to implement the teachings of the invention without undue experimentation.

[0044] In view of the above problems, the present disclosure proposes a new distribution architecture in a distribution system, which controls AC equipment and DC equipment to simultaneously inject AC and DC into the distribution line, and allows the superposition state of AC and DC to form the distribution line current in the proposed technical solution. Figure 1 The current diagram of the distribution line in the proposed technical solution is an exemplary result of a superposition state. The AC and DC power can be extracted from the superposition state in the distribution line by the proposed AC and DC separation device, so that the AC and DC can pass through the AC and DC devices respectively.

[0045] In the disclosure, it will be assumed that the power source connected to the main grid is: (1) a transformer and a bidirectional AC / DC converter; or (2) a solid-state transformer. The DC / DC converter interface voltage source powered by the RES is controlled to operate according to the maximum power point tracking (MPPT) curve. The power imbalance between the RES DC generation and the DC load is compensated by controlling the bidirectional AC / DC converter and the solid-state transformer connected to the main grid. On the load side, the proposed AC / DC separation device extracts AC and DC from the distribution line current, thereby providing AC and DC to the AC and DC loads, respectively.

[0046] For ease of understanding, the following description includes, in order: (1) an AC / DC separation device; (2) explanation of the control principle of the proposed solution; (3) configuration of the proposed solution in a three-phase power grid; (4) advantages of the proposed solution; and (5) demonstration of the operation of the proposed technical solution.

[0047] The proposed (1) AC / DC separation device will be described below.

[0048] In some embodiments, the AC-DC separation device includes an "AC-through-DC blocker" and an "AC-blocking-DC passer". The AC-through-DC blocker is used to block DC power and allow AC power in the distribution line to pass through. The AC-blocking-DC passer is used to block AC power in the distribution line and allow DC power in the distribution line to pass through. The AC-through-DC blocker can be installed by being connected in series with an AC device. The AC-blocking-DC passer can be installed by being connected in series with a DC device. In this way, AC power and DC power can flow and separate in the distribution line at the same time so that the AC device and the DC device can work independently.

[0049] In some embodiments, the configuration of the AC / DC separation device, the transformer, the converter and the load is as follows: Figure 2 As shown. The low voltage side of the transformer is modeled as an AC voltage source; meanwhile, the DC side of the bidirectional AC / DC converter is modeled as a DC voltage source. For the adopted device, the AC passes through a DC blocker, which is installed in series with an AC component, such as an AC power source or an AC load; and the AC blocker DC pass-through is installed in series with a DC component, such as a DC power source or a DC load. In this configuration, in the current of the distribution line, AC and DC can flow simultaneously, but only AC passes through the AC device and DC passes through the DC device. The converter is modeled as a voltage source with an output resistance Rs. For this, Rs may be different for different devices. When the DC power generated by the RES exceeds the DC power demand of the DC load, the inverter in the bidirectional AC / DC converter is activated and converts the excess DC power into AC power and feeds the AC power back to the main grid. On the other hand, when the DC power generated by the RES is not enough to meet the DC power demand of the DC load, the rectifier in the bidirectional AC / DC converter is activated, thereby converting the AC power in the main grid into DC power and feeding the DC power to the DC load.

[0050] Here, it is assumed that each AC device is installed with an AC through DC blocker in series, and each DC device is also installed with an AC blocking DC pass-through in series. Provided below are different configurations of AC through DC blocks and AC blocking DC pass-throughs in various embodiments. In some embodiments, even in the same power distribution system, different configurations of AC through DC blocks and AC blocking DC pass-throughs can be used for different AC and DC devices.

[0051] (A) Fixed resonant frequency LC filter

[0052] Figure 3 Fixed resonant frequency LC filters according to some embodiments of the present invention are shown, wherein the left side is a series LC filter 100A, and the right side is a parallel LC filter 100B. Figure 3 The series LC filter 100A and the parallel LC filter 100B shown are used to extract the AC and DC currents from the power distribution line. The impedance of the series LC filter 100A is The impedance of the parallel LC filter 100B is Its resonant frequency is and And they can be expressed as:

[0053] Where f is the frequency of the AC power passing through the LC filter. The impedance of the filter and is a function of the frequency of the alternating current.

[0054] In the power system, the frequency of AC power is strictly controlled near its nominal frequency, such as 50Hz or 60Hz. ) , C ) , L " , C " The choice should make the resonant frequency of the LC filter and Equal to (or close to) the nominal frequency of the power grid, thereby being able to separate the AC and DC currents in the distribution line currents. and The closer it is to the nominal frequency of the grid, the better its AC and DC separation performance.

[0055] The series LC filter 100A is a DC blocker with a capacitance of C ) The capacitor blocks direct current and also acts as an alternating current at its resonant frequency. The zero impedance path is Similarly, the parallel LC filter 100B can act as a DC current passing through the inductor L " zero impedance path, which blocks the resonant frequency The alternating current is is infinite for alternating current, that is The series LC filter 100A and the parallel LC filter 100B can be used in power systems to block the high-order harmonics of AC power. In the present disclosure, a new technical means is adopted to separate AC power and DC power in the distribution line to avoid superposition and influence.

[0056] In small power grids with low system inertia, the AC frequency varies greatly. When the resonant frequency of the above LC filter is not close to the AC frequency in the distribution system, its AC and DC separation performance will deteriorate. To address this problem, the subsequent description proposes an LC filter with adjustable resonant frequency to cope with the situation of small power grids.

[0057] Figure 4 A configuration diagram of a solid-state transformer 110 in a power distribution architecture according to some embodiments of the present invention is shown. The solid-state transformer 110 can solve the problem of frequency variation of AC power, and has many application scenarios in the power distribution system. One of the significant advantages of the solid-state transformer 110 is that the output AC frequency on the low-voltage side can be fixed to a nominal value through the inverter 112, that is, its AC output frequency can be different from the AC frequency of the power grid. On the other hand, the output AC frequency of the transformer must be equal to the AC frequency of the power grid, which may deviate greatly from the nominal value. The above-mentioned LC filter and the solid-state transformer 110 can cooperate with each other. Figure 4 The configuration shown is that the solid-state transformer 110 is used in the power distribution system. In this case, the inverter 112 in the solid-state transformer 110 can fix the AC frequency in the power distribution system to the nominal frequency. Through this configuration, the AC frequency can be closely matched with the resonant frequency of the LC filter, wherein the LC filter includes an AC-through DC blocker 114 and an AC-blocking DC-through device 116, thereby well separating AC and DC.

[0058] Figure 5 A schematic diagram of using a fixed resonant frequency LC filter and considering the series resistance of an inductor and a capacitor according to some embodiments of the present invention is shown, wherein the left side is a series LC filter 120A and the right side is a parallel LC filter 120B. In some practices, there is a small series resistance in the inductor and the capacitor. Figure 5 It is shown that when these small series resistances are taken into account, a more precise statement Figure 3 Schematic diagram of the LC filter in FIG. In this case, the resonant frequencies of the series LC filter 120A and the parallel LC filter 120B are and It can be expressed as:

[0059] The expression of remains the same as that of formula (3), while The expression of takes a new form. Even if and Equal to (or close to) the nominal grid frequency, L ) , C ) , l " 、c " The selection rules are the same as before. If the series resistor R C" and r #" If L is known, then L can be selected according to formula (6) " and C " If the series resistor and If L is unknown, then L can be selected according to formula (4) " and C " .

[0060] (B) Tunable resonant frequency LC filter

[0061] The aforementioned Figure 3 and Figure 5 When the resonant frequency of the fixed resonant frequency LC filter shown deviates from the AC frequency, the separation performance of AC and DC will deteriorate. Figure 6 1 shows an adjustable resonant frequency LC filter according to some embodiments of the present invention, wherein the left side is a series LC filter 130A, and the right side is a parallel LC filter 130B. In order to make the resonant frequency of the LC filter adjustable so that it can follow the time-varying AC frequency in the power distribution system with a transformer, in some embodiments, a solution proposed is to use a variable inductor in the LC filter, such as Figure 6 shown. Figure 6 The resonant frequency of the series LC filter 130A and the parallel LC filter 130B in FIG. 1 is and It can be expressed as:

[0062] The series LC filter 130A and the parallel LC filter 130B can measure the AC frequency in the power distribution system through a phase-locked loop and change the L accordingly. * and L + ,make and Another method to make the oscillation frequency track the AC frequency is to measure the reactive power consumption of the LC filter to control the L * and L + When the resonant frequency of the LC filter is equal to the AC frequency, no reactive power is consumed or injected. Therefore, when the LC filter consumes reactive power, it means that the inductance of the LC filter is too strong and L should be reduced. * and L+ , so that and Can track AC frequency and vice versa.

[0063] Figure 7 The following are some embodiments of the present invention according to which a parallel LC filter with adjustable resonant frequency can be used. Figure 7 As shown, in some embodiments, another method of controlling the resonant frequency of the parallel LC filter 140 is to install a variable resistor in series with the capacitor and the inductor. The resonant frequency of the parallel LC filter 140 can be expressed as:

[0064] Control variable resistor r ,) and R ," The resistance value can make Follow the AC frequency. Although the variable resistor can be connected in series with the inductor, it is not the best solution because the DC current will flow through it, which will cause power loss. If the variable resistor is not connected in series with the inductor, that is, R ," = 0, only R is used ,) Still available is adjustable and can be driven according to formula (9) To follow the AC frequency.

[0065] Figure 6 and Figure 7 The configuration in the figure is only an example of making the resonant frequency of the LC filter adjustable, and is not intended to limit the present invention. In practice, there are many other possible configurations, such as replacing the capacitor with a variable capacitor. The principle here is to control the resonant frequency of the series LC filter and the parallel LC filter to follow the AC frequency. The discussion here ignores the effect of the small series resistance of the inductor and capacitor on the expression of the resonant frequency of the LC filter. It should be noted that the principle here is to make its resonant frequency follow the AC frequency.

[0066] (C) Cooperation between AC equipment and AC through DC blocker

[0067] Figure 8 In some embodiments according to the present invention, a combination of an AC-through-DC blocker 150 and a series inductor and capacitor of an AC device 152 is considered. When the series inductor and capacitor of the AC device 152 are known, the AC-through-DC blocker 150 can be constructed by combining the series inductor and capacitor of the AC device 152. The structure is as follows: Figure 8 As shown. The design principle of AC passing through DC blocker is to select L - and C - , causing resonance between the capacitor and inductor in the AC device 152 and the AC passing through the DC blocker 150.

[0068] Here, it is considered that the AC device 152 may be an AC load, which is composed of only one resistor R .C0％123％ and an inductor L .C0％123％ If the AC load is an inductive load and has no capacitor, a capacitor C can be designed. - The AC formed by the DC block 150 makes L .C0％123％ and C - Resonance occurs between them. When AC passes through the DC blocker, the inductor l .C0％123％ The series inductor and capacitor c - The resonant frequency of the series capacitor can be expressed as:

[0069] According to the above design principles, you can choose c - To make As close to the nominal grid frequency as possible. In some embodiments, the inductor and capacitor in the AC-DC blocker 150 are not necessarily installed at the same time. In some embodiments, the inductor is l - The inductor and capacitor are c - The capacitor can be replaced by a variable inductor and a variable capacitor as described above, so that the resonant frequency between the inductor and the capacitor in the AC device and the AC passing through the inductor and the capacitor in the DC blocker is consistent with the grid frequency.

[0070] (D) Single capacitor AC through DC blocker

[0071] Fig. 9 According to some embodiments of the present invention, a single capacitor is considered to be used for the AC-through DC blocker 160. A single capacitor can be used for the AC-through DC blocker 160 (ie, it is a single capacitor filter), and its structure is as follows Fig. 9 As shown. The capacitor can essentially block the passage of direct current. In order to provide a lower AC impedance to the capacitor, in some embodiments, the capacitor C4 can be set as large as possible to make the AC impedance across the capacitor as low as possible.

[0072] (E) Cascaded sub-AC through DC blocker and sub-AC blocking DC through device

[0073] Fig.10In some embodiments of the present invention, a cascaded sub-AC through-DC blocker 172A and a sub-AC blocking DC pass-through 172B are shown. The configuration of the AC through-DC blocker 170A and the AC blocking DC pass-through 170B can be further expanded to use a sub-AC through-DC blocker 172A and a sub-AC blocking DC pass-through 172B. These sub-AC through-DC blockers 172A and sub-AC blocking DC pass-throughs 172B can be cascaded together to enhance the AC and DC separation performance of the AC through-DC blocker 170A and the AC blocking DC pass-through 170B, and the structure thereof is as follows: Fig.10 As shown. The AC can be connected in parallel by the DC block 170A ) The AC blocking DC pass-through device 170B can be composed of N sub-AC blocks 172A, and the AC blocking DC pass-through device 170B can be composed of N sub-AC blocks 172A and N sub-AC blocks 172B. " The AC blocking DC pass-through device 172B is composed of a plurality of AC blocks.

[0074] In addition to the aforementioned single capacitor configuration sub-AC-through-DC blocker, the resonant frequencies of the other mentioned sub-AC-through-DC blockers and sub-AC-blocking-DC passers can be set to different values ​​to meet the requirements of AC and DC separation at different AC frequencies. For example, assuming that the nominal frequency in a small power grid with a small system inertia is 50Hz, and the frequency varies between 49.5Hz and 50.5Hz, an AC-through-DC blocker composed of three sub-AC-through-DC blockers can be constructed, which is formed by three fixed resonant frequency series LC filters connected in parallel; and an AC-blocking-DC passer composed of three sub-AC-blocking-DC passers can be constructed, which is formed by three fixed resonant frequency parallel LC filters connected in series.

[0075] In some embodiments, the resonant frequencies of the three fixed resonant frequency series LC filters (or using adjustable resonant frequency LC filters) in the three sub-AC / DC blockers can be set to 49.75 Hz, 50 Hz, and 50.25 Hz, respectively, thereby providing a low impedance path for AC power between 49.5 Hz and 50.5 Hz to provide AC power through the AC / DC blocker.

[0076] In some embodiments, the resonant frequencies of the three fixed resonant frequency parallel LC filters (or LC filters with adjustable resonant frequency) in the three sub-AC blocking DC pass-through devices can be set to 49.75 Hz, 50 Hz, and 50.25 Hz, respectively, thereby establishing a high impedance path for AC current between 49.5 Hz and 50.5 Hz to prevent AC current from passing through the AC blocking DC pass-through device.

[0077] The following is a description of the control principle of the proposed solution in (2):

[0078] Fig.11 An example diagram of a single-phase distribution network using cooperative transformers using the proposed control scheme is presented. Fig.12 A schematic diagram of the DC power supply control principle with the output voltage as the control variable is shown. In this example, the scenario assumes that the DC power generated by RES and provided to the DC power supply 182 is insufficient to meet the DC power demand of the DC load. Therefore, the rectifier will be activated, wherein the bidirectional AC / DC converter acts as the DC power supply 180, which provides DC power to the load.

[0079] exist Fig.11 In the proposed scheme, AC and DC power flow in the phase and neutral lines at the same time and are separated at the AC devices and DC devices, respectively. Therefore, the distribution network in the proposed scheme can be interpreted as two independent circuits, one is an AC circuit with an AC component, and the other is a DC circuit with a DC component, which share the same phase and neutral lines.

[0080] The independent performance of the AC circuit and the DC circuit promotes the independent design of the control method of the AC component and the DC component without considering the coupling effect of each other. In the proposed technical solution, a PI controller can be applied to control the voltage output of the bidirectional AC / DC converter powered by the main grid to adjust the DC load voltage without knowing the AC load voltage and the AC load voltage of the RES powered converter to drive its power output to follow the MPPT curve. Fig.12 The control principle of these converters is shown. Here, the rectifier is activated when the bidirectional AC / DC converter injects active power; otherwise, the inverter is activated. The turns ratio in the AC transformer can also be controlled like the DC source to regulate the AC load voltage. The proposed control scheme is compatible with existing control methods for both AC and DC distribution systems. Fig.12 The control scheme shown is only one of the possible control methods and is not intended to limit the present invention. When a grid-connected solid-state transformer is used, the inverter and bidirectional DC-DC converter in the solid-state transformer can be controlled to adjust the AC load voltage and the DC load voltage respectively.

[0081] The following is a description of the configuration of the solution proposed in (3) in a three-phase power grid, which focuses on introducing the configuration of the power distribution architecture of the present invention into the three-phase power grid.

[0082] Fig.13An example diagram of introducing a power distribution configuration in a three-phase balanced system according to some embodiments of the present invention is shown. Here, a three-phase transformer can supply power to a three-phase AC power source. For ease of understanding, it is assumed that a three-phase AC power source and a three-phase AC load can be connected in a Y shape (star connection). In some embodiments, a similar configuration can also be performed using a delta connection. A three-phase system can be analyzed using the same logic as a single-phase system. When the three-phase load is completely balanced and there are no AC harmonics, there is no flow of AC power on the neutral line; otherwise, AC power will flow between the AC power source and the AC load through the neutral line. The DC power from the DC power source is divided into three equal DC currents for parallel transmission in the three-phase line and the neutral line.

[0083] The three-phase system includes an A-phase distribution line, a B-phase distribution line, and a C-phase distribution line. The A-phase distribution line, the B-phase distribution line, and the C-phase distribution line can be connected to an AC through a DC blocker, and then connected to a neutral line via a grid-connected AC power source and a converter. The A-phase distribution line, the B-phase distribution line, and the C-phase distribution line can be connected to an AC load, each AC load is connected in series with an AC through a DC blocker, and then connected to the neutral line. The A-phase distribution line, the B-phase distribution line, and the C-phase distribution line can be connected to an AC blocking DC pass-through device, and then connected to a resistor, wherein the resistor is connected to a DC power supply, which is a DC power supply powered by RES.

[0084] Fig.14 An example diagram of introducing a power distribution configuration in a three-phase unbalanced system according to some embodiments of the present invention is shown. Fig.14 As shown, the proposed technical solution has significant potential advantages when working under three-phase unbalanced conditions. One major advantage is that different DC power sources providing DC power at three different voltage levels can be connected to the three-phase (A phase, B phase and C phase) distribution line. In this scenario, the proposed technical solution can provide DC power at three different voltage levels to meet the needs of different DC loads.

[0085] The following is a description of the technical advantages of the power distribution architecture proposed in (4).

[0086] The main advantage of the proposed power distribution technology is that it reduces the conversion between AC and DC at the load side and does not require the conversion of DC generated by RES into AC, so that RES can directly inject DC into the distribution line. The advantages described herein include providing zero-crossing current and reducing skin effect in the distribution line by operating the protection device.

[0087] (A) Zero-crossing current in distribution line current:

[0088] Since the distribution line current is composed of AC and DC, as long as the DC component amplitude is not greater than the AC component amplitude in the distribution line, the distribution line current will be equal to zero at a certain moment. Figure 1 An example of distribution line current has been shown. Figure 1 In a circuit, DC can shift AC up or down, depending on the direction of flow of AC and DC. If AC and DC flow in the same direction, the distribution line current is formed by the upward-moving AC, offset by the DC, and vice versa. Zero current crossings facilitate the operation of fuses and circuit breakers because it allows arcs to be extinguished easily.

[0089] On the other hand, in a DC distribution system, the DC current never reaches zero. Even if the fuses and circuit breakers operate, arcs may still exist between the terminals; this will require additional procedures to extinguish the arcs.

[0090] (B) Skin effect in current distribution lines:

[0091] The skin effect is a phenomenon in which alternating current flows on the surface of a distribution line rather than throughout the entire distribution line. The proposed technical solution can reduce the alternating current in the distribution line, thereby reducing the skin effect. In the proposed technical solution, the DC load is powered by the DC component in the distribution line current. On the other hand, in an AC distribution system, the power used by the DC load is distributed using AC. It is then converted into DC using a rectifier at the DC load. Under the same AC load and DC load, the proposed technical solution can result in less AC current on the distribution line than in the AC distribution network. Since there is no skin effect, DC can be better utilized in the distribution line than AC. In this technical solution, DC is used as the distribution medium in the distribution line, and DC is distributed to the DC load, thereby better utilizing the cross-sectional area of ​​the distribution line.

[0092] The following is a description of the operation of the technical solution proposed in (5).

[0093] Fig.15 A schematic diagram of a 4-bus single-phase test system constructed by simulation according to some embodiments of the present invention is shown. Fig.15 As shown in Figure 1, a 4-bus single-phase test system is built in MATLAB / Simulink to demonstrate the operation of the proposed technical solution; the parameters set can be shown in Table 1, and the Figure 3 LC filter model in . Table 1: Test system parameters

[0094] In this simulation stage, it is assumed that the DC power supply 192 is powered by RES and needs to follow its MPPT by controlling its voltage output, setting it to 5000W before 20 seconds and to 7000W after 20 seconds. The DC power supply 190 needs to adjust the DC voltage at the DC load to 150V by controlling its DC voltage output. The AC source can be modeled as the secondary terminals of an ideal single-phase transformer, and the ratio in the transformer is controlled to provide an AC source of 250V and 50Hz at the secondary terminals. It is also assumed that the nominal AC voltage amplitude in the distribution system is 220V. In order to provide an AC voltage amplitude of approximately 220V to the AC load, an amplitude of 250V is set on the transformer to compensate for the voltage drop on the distribution line. In this simulation stage, it is assumed that the turns ratio in the transformer is fixed, because the simulation period is short (30 seconds) and the transformer cannot be switched frequently. The DC power from RES is not enough to meet the needs of the DC load, so the rectifier will be activated, as shown in Figure 2. Fig.15 In some embodiments, when the AC frequency in the power distribution system varies greatly, it can be used Figure 6 The LC filter in the circuit is designed so that its resonant frequency can track the AC frequency.

[0095] Two simulations were performed. The first simulation was for an ideal situation, and the second simulation took into account the switching effect of the power converter. In the first simulation, the DC power supplies 190 and 192 were modeled as controllable ideal DC voltage sources. In the second simulation, the DC power supply 190 was modeled as the output of a rectifier powered by a three-phase voltage source simulating the main power grid, and the DC power supply 192 was modeled as the output of a boost converter powered by a voltage source powered by RES. In the two simulations, the control gain of the DC power supply was different. In the simulation, the voltage of the DC power supply was regarded as a control variable. In the second simulation, the trigger angle of the rectifier and the duty cycle of the boost converter can be controlled. In the two simulations, the PI controller was used to control the control variable of the DC power supply 190, and to adjust the DC load voltage and the control variable of the DC power supply 192 to adjust its active power output, thereby tracking the MPPT curve. The simulation results of the two simulations are very similar, so there will be some overlap in the figures provided below.

[0096] Simulation (A): DC power supply and DC load

[0097] Fig.16 , Fig.17 , Fig.18 , Fig.19 , Fig. 20 , Fig.21 , Fig. 22According to some embodiments of the present invention, the output power, current and voltage of a simulated DC power supply and the DC load voltage are shown. After the MPPT curve of the DC power supply is increased from 5000W to 7000W within 20 seconds, the active power output of the DC power supply 192 increases from 5000W to 7000W, while the active power output of the DC power supply 190 decreases. It is estimated that the increase in the active power output of the DC power supply 192 will cause the DC load voltage on the bus 2 to increase. To restore the DC load voltage to 150V, the DC power supply 190 must reduce its active power output. In addition, it can be observed that the DC power supply 192 can track the MPPT curve.

[0098] Simulation (B): Distribution line current

[0099] Fig.23 , Fig.24 , Fig.25 The power distribution line currents of different line segments simulated according to some embodiments of the present invention are shown. In the line between bus 1 and bus 2, the AC and DC flow directions are the same, that is, the AC power source and the DC power source provide AC and DC power from bus 1 to the loads at bus 2 and bus 4. Therefore, the line current consists of upward moving AC, such as Fig.23 As shown. For this, the zero crossing of the distribution line current occurs after 20 seconds. In the line between bus 2 and bus 3, the flow directions of AC and DC are opposite, that is, AC flows from bus 2 to bus 3 and provides AC to the AC load at bus 4, while DC power supply 192 provides DC from bus 3 to the DC load at bus 2. Therefore, the line current consists of AC moving downward, as shown in Fig.24 As shown. Bus 4 has only AC loads. Therefore, no DC flows in line 34. Fig.25 The line current I *+ Basically it's communication.

[0100] Simulation (C): AC power supply and AC load

[0101] Fig.26 , Fig. 27 , Fig.28 According to some embodiments of the present invention, the AC power and AC load voltage of the simulated AC power source (i.e., the secondary terminal of the transformer) are shown. It can be seen that for the AC voltage, the voltage of the AC load 194 is higher than the voltage of the AC load 196 because the voltage drop of the AC load 194 is smaller. The AC load voltage is regulated near the nominal voltage of 220V. The increase in the MPPT curve of the DC power source 192 at 20 seconds does not affect the AC load voltage, demonstrating the independence of the AC and DC circuits.

[0102] As for the above simulation results, it shows that in the proposed scheme, the AC circuit works independently of the DC circuit.

[0103] In summary, the present invention proposes a new power distribution architecture for simultaneously distributing AC and DC power in a distribution network. The use of power electronic equipment in AC / DC or DC / AC conversion is reduced. In addition, DC power is allowed to be distributed with zero crossing current, which is beneficial to the protection scheme in the distribution system. Moreover, the effective cross-sectional area of ​​the distribution line is increased by distributing the power required by the DC load in the form of DC, that is, the skin effect on the distribution line is reduced.

[0104] Although several embodiments of the present invention have been described, it will be appreciated by those skilled in the art that changes may be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

[0105] The embodiments disclosed herein may be implemented using computing devices, computer processors, or electronic circuits, including but not limited to application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and other programmable logic devices configured or programmed according to the teachings of the present disclosure. Based on the teachings of the present disclosure, a person skilled in the art of software or electronics may easily prepare computer instructions or software codes that run in a general or special computing device, computer processor, or programmable logic device.

[0106] All or part of the embodiments may be implemented in one or more general purpose or computing devices, including server computers, personal computers, laptop computers, mobile computing devices such as smart phones and tablet computers.

[0107] The embodiments include computer storage media storing computer instructions or software codes that can be used to program a computer or microprocessor to perform any of the processes of the present invention. The storage media can include, but are not limited to, floppy disks, optical disks, Blu-ray disks, DVDs, CD-ROMs and magneto-optical disks, ROMs, RAMs, flash memory devices, or any type of medium or device suitable for storing instructions, codes, and / or data.

[0108] Various embodiments of the present invention may also be implemented in a distributed computing environment and / or a cloud computing environment, wherein one or more processing devices interconnected by a communication network execute all or part of the machine instructions in a distributed manner, and the communication network includes an intranet, a wide area network (WAN), a local area network (LAN), the Internet, and other forms of data transmission media.

[0109] The above description of the present invention is for illustration and description purposes only. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations will be apparent to those skilled in the art.

[0110] The described embodiments are presented in order to best explain the principles of the invention and the practical application, thereby enabling others skilled in the art to understand various embodiments and with the various modifications as are suited to the particular use contemplated.

Claims

1. A power distribution system, characterized in that: include: Phase and neutral wires; an AC power source electrically connected between the phase line and the neutral line; a first AC through-DC blocker electrically connected between the AC power source and the neutral line and comprising a series LC filter having a capacitor and an inductor connected in series, wherein the AC power source and the AC through-DC blocker form an AC path; A first DC power supply electrically connected between the phase line and the neutral line; and The first AC blocking DC pass-through is electrically connected between the first DC power supply and the neutral line, and includes a parallel LC filter having a capacitor and an inductor connected in parallel, wherein the first DC power supply and the first AC blocking DC pass-through form a DC path, and the AC path and the DC path are mutually independent paths between the phase line and the neutral line.

2. The power distribution system according to claim 1, characterized in that: The capacitor and the inductor of the parallel LC filter of the first AC blocking DC pass-through device respectively have series resistances and And the resonant frequency of the parallel LC filter It is expressed as: Where, if the series resistance and is known, then according to formula (B) select L " and C " , which are the inductance value of the inductor and the capacitance value of the capacitor of the parallel LC filter respectively, and if the series resistance and If L is unknown, then select the L according to formula (A) " and C " .

3. The power distribution system according to claim 1, characterized in that: The inductors of the series LC filter and the parallel LC filter are both variable inductors, and when the series LC filter or the parallel LC filter consumes reactive power, the corresponding inductor reduces its inductance value through its variable inductor.

4. The power distribution system according to claim 1, characterized in that: The parallel LC filter also has a first variable resistor and a second variable resistor, and the capacitor and the inductor of the parallel LC filter are respectively connected in series with the first variable resistor and the second variable resistor, so that the resonant frequency of the parallel LC filter is adjustable.

5. The power distribution system according to claim 1, characterized in that: Also includes: a second DC power source electrically connected between the phase line and the neutral line and comprising a renewable energy source and a DC / DC converter, so that the DC power source can be powered by the renewable energy source and provide DC power via the DC / DC converter; as well as The second AC blocking DC pass-through device is electrically connected between the second DC power source and the neutral line and includes a parallel LC filter having a capacitor and an inductor connected in parallel.

6. The power distribution system according to claim 1, characterized in that: Also includes: an AC load, electrically connected between the phase line and the neutral line; A second AC through-DC blocker is electrically connected between the AC load and the neutral line and includes a series LC filter having a capacitor and an inductor connected in series, wherein the AC load and the second AC through-DC blocker form an AC load path; a DC load electrically connected between the phase line and the neutral line; and The second AC blocking DC pass-through is electrically connected between the DC load and the neutral line and includes a parallel LC filter having a capacitor and an inductor connected in parallel, wherein the DC load and the second AC blocking DC pass-through form a DC load path, and the AC load path and the DC load path are independent of each other.

7. The power distribution system according to claim 1, characterized in that: The number of the series LC filters of the first alternating current passing through the DC blocker is plural, and the plural series LC filters are connected in parallel with each other.

8. The power distribution system according to claim 7, characterized in that: The series LC filter is a fixed resonant frequency series LC filter or an adjustable resonant frequency LC filter, and the resonant frequencies of the series LC filter are different.

9. The power distribution system according to claim 1, characterized in that: The number of the parallel LC filters of the first AC blocking DC pass-through device is multiple, and the multiple parallel LC filters are connected in series.

10. The power distribution system according to claim 9, characterized in that: The parallel LC filter is a fixed resonance frequency parallel LC filter or an adjustable resonance frequency LC filter, and the resonance frequencies of the filters are different.

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