Patent Application
20250105660
This disclosure relates to transfer switches.
Several recent developments have brought direct current (DC) power systems back into competition with alternating current (AC) power systems. DC power systems have inherent advantages such as less power loss during transmission and no energy wasted on reactive components. However, DC power systems have been limited in power distribution applications because of limitations, such as difficulties in stepping up or stepping down voltages and difficulties in designing switching/protecting gears. Developments in power electronics have made both DC voltage transforming and DC protection/switching possible at high voltage levels. As a result, many concepts plan to use DC power for industrial and residential applications. In these applications, DC power may be provided by different sources, such as batteries, solar panels, electric vehicles, sub-division level DC power from utilities, etc. To provide proper safety and functions, many applications allow only one power source at any given time. Therefore, transfer switches are needed to make selections between DC sources. If both AC power and DC power are used as power sources, transfer switches are also needed to select between the AC and DC power sources. Also, in some applications, such as DC electric vehicle charging and discharging, bidirectional DC current needs to be provided. Transfer switches may provide solutions to allow control of current direction.
By way of introduction, the preferred embodiments described below include systems and methods for semiconductor-based solutions for transfer switches with DC legs.
In an embodiment, a transfer switch is provided that operates between a first power source and a second power source, the transfer switch comprising: a semiconductor-based DC circuit breaker connected to the first power source and a load, the semiconductor-based DC circuit breaker including a DC circuit breaker handle that opens and closes the semiconductor-based DC circuit breaker; a second circuit breaker connected to the second power source and the load, the second circuit breaker including a circuit breaker handle that opens and closes the second circuit breaker; and an actuator configured to operate a DC circuit breaker mechanical arm and a second circuit breaker mechanical arm that interact with the DC circuit breaker handle and the circuit breaker handle for the second circuit breaker, respectively, such that the semiconductor-based DC circuit breaker and the second circuit breaker are mechanically interlocked, wherein the mechanical interlocking of the semiconductor-based DC circuit breaker and the second circuit breaker is configured, such that only one circuit breaker of the semiconductor-based DC circuit breaker and the second circuit breaker is closed at any time.
In an embodiment, a transfer switch is provided for bi-directional DC current flow, the transfer switch comprising: a first semiconductor-based DC circuit breaker configured to allow power flow from an input power source to an output power load, the first semiconductor-based DC circuit breaker including a first handle configured to open and close the first semiconductor-based DC circuit breaker; a second semiconductor-based DC circuit breaker configured to allow power flow from the output power load to the input power source, the second semiconductor-based DC circuit breaker including a second handle configured to open and close the second semiconductor-based DC circuit breaker; and an actuator configured to operate mechanical arms that interact with the first handle and the second handle such that the first semiconductor-based DC circuit breaker and the second semiconductor-based DC circuit breaker are mechanically interlocked, the mechanical interlocking of the first semiconductor-based DC circuit breaker and the second semiconductor-based DC circuit breaker being configured such that only one semiconductor-based DC circuit breaker of the first semiconductor-based DC circuit breaker and the second semiconductor-based DC circuit breaker is closed at any time.
In an embodiment, a method is provided for switching between a first power source and a DC power source using a transfer switch, the transfer switch comprising a semiconductor-based DC circuit breaker connected to the DC power source, a second circuit breaker connected to the second power source, and an actuator connected to a DC circuit breaker mechanical arm and a second circuit breaker mechanical arm, the second circuit breaker mechanical arm and the DC circuit breaker mechanical arm being configured to interact with a circuit breaker handle for the second circuit breaker and a DC circuit breaker handle, respectively, such that the second circuit breaker and the semiconductor-based DC circuit breaker are mechanically interlocked, the mechanical interlocking between the second circuit breaker and the semiconductor-based DC circuit breaker being configured such that only one circuit breaker of the second circuit breaker and the semiconductor-based DC circuit breaker is closed at any time, the method comprising: providing the transfer switch with the second circuit breaker closed and the semiconductor-based DC circuit breaker open; opening the second circuit breaker, opening the second circuit breaker comprising rotating the actuator in a first rotational direction, such that: the second circuit breaker mechanical arm moves the circuit breaker handle of the second circuit breaker from an ON position to past an OFF overcenter position; and the DC circuit breaker mechanical arm moves the DC circuit breaker handle of the semiconductor-based DC circuit breaker below an ON overcenter position, which leaves open the semiconductor-based DC circuit breaker; and closing the semiconductor-based DC circuit breaker comprising further rotating the actuator in the first rotational direction, such that the DC circuit breaker mechanical arm moves the DC circuit breaker handle to an ON position.
Any one or more of the aspects described above may be used alone or in combination. These and other aspects, features and advantages will become apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings. The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments and may be later claimed independently or in combination.
To facilitate an understanding of embodiments, principles, and features of the present invention, they are explained hereinafter with reference to implementation in illustrative embodiments. In particular, they are described in the context of a transfer switch with at least one solid-state DC circuit breaker. Embodiments of the present invention, however, are not limited to use in the described devices or methods.
The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present invention.
These and other embodiments of the transfer switch and the solid-state DC circuit breaker according to the present disclosure are described below with reference to
The embodiments described herein provide systems and methods for a semiconductor-based DC transfer switch 100. The semiconductor-based DC transfer switch 100 uses two individual circuit breakers that are mechanically interlocked in such a way that only one of the two circuit breakers can be closed at any time. One advantage of using circuit breakers in a transfer switch is that circuit breakers provide the functions of both circuit protection and power disconnection, and hence reduce the number of components and the complexity of the system. An actuator 130, such as a motor, operates mechanical arms 114, 124 that interact with the handles of the circuit breakers 110, 120. The actuator 130 may be operated both manually and automatically. At least one of the circuit breakers is a semiconductor-based DC circuit breaker.
Traditional DC mechanical circuit breakers occupy more space and require stronger operators when system voltage is high. As a result, using DC mechanical circuit breakers in a transfer switch provides that the transfer switch is inherently larger in size and requires more power to operate. In addition, DC mechanical circuit breakers are more difficult to pair with AC circuit breakers, as the AC circuit breakers are normally smaller in size. Semiconductor-based DC circuit breakers improve the switching reliabilities and reduce the size at the same voltage rating, which in turn provide smaller and more flexible designs for the transfer switches. In addition, to fully realize the advantage of DC power, high DC voltages are used. Traditional mechanical switches become complicated with bare minimum reliability when DC voltage is above 250V. For general purpose DC protection with voltage higher than 600V, mechanical switches start to face feasibility issues. For these high voltage DC switching or protection, semiconductor-based switches are more suitable.
The system includes two power sources (e.g., the AC power source 101 and the DC power source 103). In an embodiment, the AC power source 101 and the DC power source 103 may be, for example, utility power and power from a backup system such as a generator or battery or from a renewable power source such as solar or wind, respectively. In another embodiment, the two power sources are both DC power sources.
For residential uses, houses have seen an increased demand for electricity, especially with the growing popularity of electric vehicles. The increased demand may result in a possible shortage of electricity if relying on utilities alone. Further, under uncontrollable circumstances, such as extreme weather conditions, utility power may be disrupted. To ensure that basic essential functions of a home, such as air conditioners, cook tops, refrigerators and so on, are still available under such conditions, backup power systems have also become increasingly popular. Many utility companies now accept locally generated energy to be sold back to the grid, to save cost to the homeowner. As a result, more houses are equipped with additional energy sources than just utility power. Common energy sources as of today are backup generators, renewable sources such as solar systems, battery systems, electric vehicles, other renewable power sources, and/or alternative sources such as wind power and hydropower that may be less popular. These different power sources may be installed into a single home with many different combinations, together with the already available utilities. However, only one source can be used at a certain time to power the house. An energy management system is needed to switch between these power sources and to allow flexible configurations based on the needs of a customer. Similar issues may exist for commercial or industrial electrical systems.
A transfer switch as described herein is used to switch between the two power sources, for example, the AC power source 101 and the DC power source 103. Alternate current (AC) power is typically used in a majority of electrical systems as a form of supply. However, many electronic devices and end systems, such as electric vehicles, home appliances, and data centers use direct current (DC) power, for example high voltage DC power. For high voltage DC power, the DC power source 103 may be a high voltage power source with a voltage equal to or greater than 250V, in particular greater than 600V. The embodiments described below include systems with two power sources. If additional power sources are used, two or more of the described systems may be used as modules to manage the electrical system as described in
The load 150 may be any electrical circuit including, for example, one or more appliances, lighting fixtures, a battery, an electric vehicle, and/or other electrical equipment.
The system includes two circuit breakers, including at least semiconductor-based DC circuit breakers for the one or more legs that use DC power. In
The semiconductor-based DC circuit breaker 120 is a solid-state circuit breaker. Solid state circuit breakers use power electronics as switching components instead of contacts as in traditional thermal-magnetic circuit breakers, and the switching process is arc free. Solid state circuit breakers may be used in both AC and DC systems. However, solid state circuit breakers normally have an air gap in series with power electronic components for isolation purposes. For solid state circuit breakers designed for AC systems, air gaps may be used as fail-safe mechanisms when power electronics fail in shorted conditions. In such a situation, the arc can simply interrupt AC power with the help of natural zero crossing. In DC systems, however, simple air gaps may not be used because of a possibility of its own failure on interruption. In a first embodiment, the transfer switch includes a first semiconductor-based (solid-state) DC circuit breaker 200 with redundant power electronics that reduces or eliminates DC arcs in air gaps under a single component failure mode analysis.
TVS semiconductor diodes are monolithic devices fabricated using standard semiconductor techniques. TVS semiconductor diodes include very fast response time, low clamping voltage, and high reliability. MOV devices are ceramic masses composed of metal-oxide grains. The boundary between grains forms a region with non-linear current and voltage performance, which behaves as a diode. The diodes arrange themselves in a random multitude of parallel and series combinations.
The first MOSFET module 220 and the second MOSFET module 230 function as each other's redundancy. The first protection device 240 and the second protection device 245 also function as each other's redundancy.
Referring back to the solid-state DC circuit breaker 200 of
In an embodiment, a power denial feature may be included in the circuit 400, as shown in
While the solid-state DC circuit breaker 200 may be used in the transfer switch of
The power electronics section 540 includes main power electronics modules, such as the power electronic module 550 that includes one or more MOSFETs or Thyristors, and a first overvoltage protection device 545. The first overvoltage protection device 545 is used to protect the main power electronics modules during the overvoltage after fast interruptions. The power electronic module 550 may be a single component or multiple components connected in parallel. The first overvoltage protection device 545 may be connected in parallel to the power electronic module 550, as shown in
The air gap section 510 is in series to the power electronics section 540 and is configured to perform fail-safe interruption and to provide isolation. The air gap section 510 includes an isolation switch 525 that is connected in series to a fail-safe interruption combination. The fail-safe interruption combination has a mechanical switch 515 connected in parallel to a solid-state component 530, and a second overvoltage protection device 520 such as a MOV or a TVS. The second overvoltage protection device 520 may be a single components or multiple components connected in parallel. Both the mechanical switch 515 and the isolation switch 525 may be triggered to turn off by the sensing and control circuit 280 through actuators, such as solenoids and electromagnets. The mechanical switch 515 and the isolation switch 525 are configured in such a way that the mechanical switch 515 is always open before the isolation switch 525.
The fail-safe operation sequence is as following: under conditions with component failures, such as when the power electronic module 550 is shorted, the sensing and control circuit 280 detects a fault condition or receives turn-off signals and sends a turn-off signal to the power electronic module 550. However, the power electronic module 550 is not able to interrupt, and load current is still present, as shown in
For the second method, a voltage monitoring is added across the mechanical switch 515, and the voltage across the mechanical switch 515 is used to determine if the solid-state component 530 is turned on. When the mechanical switch 515 is opened by the actuator, an arc is drawn, and a voltage jump in the order of 10-20V is seen across the mechanical switch 515. The higher voltage level may be used as the trigger to turn on the solid-state component 530, and hence commute the current from the mechanical switch 515 to the solid-state component 530, as shown in
When the circuit breaker 500 is in normal condition, the operating sequence above may still be implemented. The difference is that the power electronic module 550 interrupts the current at the beginning of the sequence, and the air gap section 510 opens without load current. To reclose the circuit, the isolation switch 525 and the mechanical switch 515 are first closed in no particular order. Then, the sensing and control circuit 280 perform a self-test and turns on the power electronic module 550 if the self-test is successful. In case of a failure, such as a shorted power electronic module 550, the self-test is unsuccessful, and the operation sequence for the air gap section 510 as described above is performed to interrupt current again. In case of another failure, such as a shorted solid-state component 530, the power electronic module 550 does not turn on and no-load current is available.
Alternative semiconductor-based (solid-state) DC circuit breakers may be used. The semiconductor-based DC circuit breaker(s) 120 and the AC circuit breaker 110 are each provided with a handle 112, 122 that is configured to turn ON or OFF the respective circuit breaker 110, 120.
Referring back to
In operation,
The above operating sequence also applies if the two sources are both DC power sources and two semiconductor-based DC circuit breakers 120 are used. The load 150 may be fed by either DC source based on the position of the actuator 130, as shown in
In an embodiment, applications may require bidirectional DC power flow. For example, in electric vehicle charging applications, utility power can be converted to high voltage DC and applies fast charging to the vehicle. At the same time, the vehicle can also send high voltage DC power back to utilities for savings by an owner on an energy bill. In such applications, only one direction of power flow at any given time, and the proposed transfer switch can provide a solution as in
The embodiments described above include two power sources 101, 103 (of in the case of
The advantage of using the semiconductor-based transfer switch modules in
It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend on only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.
While the present invention has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.
