Power electronics conditioning system with half-winding generator setup

A power generation system (100) including an inverter (140) structured to convert a direct current (DC) power output from an external source (110) to an alternating current (AC) power. The inverter includes at least one phase for converting the DC power to a corresponding phase of AC power. The system also includes an alternator (124) of a generator set (120). The alternator includes at least one phase, each comprising a first winding section and a second winding section coupled in series between a point of common coupling and an output terminal of the phase. A phase of the inverter is connected in parallel with the first winding section of the alternator. The inverter is configured to provide reactive power compensation, power factor correction or acts as an active filter to provide harmoincs damping and the system can be used to buffer and handle grids transients.

TECHNICAL FIELD

The present disclosure generally relates to power generation systems.

BACKGROUND

Autonomous alternating current (AC) micro-grids have been widely used in power generation and distribution systems. An autonomous AC micro-grid often includes a generator set (also referred to as “genset”), which may have an engine powered by fuel. The engine may be operatively coupled to an alternator, and the alternator may be configured to generate electrical energy for providing power to the autonomous AC micro-grid.

A hybrid power generation system may include one or more supplemental power sources for providing power to an autonomous AC micro-grid. A supplemental power source may relate to an alternative energy system, which may include a renewable energy source (e.g., solar energy, wind energy) or an energy storage device (e.g., battery pack, ultra-capacitor). In order to supply power to load, a renewable energy source and/or an energy storage device can be coupled to an autonomous AC micro-grid through a direct current (DC) to alternating current (AC) inverter. There is a challenge of achieving the desirable operation for the hybrid power generation system.

SUMMARY

In one aspect, the inventive concepts disclosed herein are directed to a power generation system comprising an inverter and a generator set. The inverter is configured to convert a direct current (DC) power from an external power source to an alternating current (AC) power. The inverter includes at least one phase for converting the DC power to a corresponding phase of AC power. The generator set includes an alternator. The alternator includes at least one phase, wherein each phase of the alternator comprises a first winding section and a second winding section coupled in series between a point of common coupling and an output terminal of the phase. Each phase of the inverter corresponds to one phase of the alternator and is connected in parallel with the first winding section of the corresponding phase of the alternator.

In some embodiments, the inverter includes three phases and the alternator includes three phases. In some embodiments, at least one phase of the inverter includes an LC filter circuit, and the LC filter circuit and the first winding section of the corresponding phase of the alternator are configured to form an LCL filter circuit.

In some embodiments, the generator set is configured to supply power to a load via a PCC (power command control) network, and the power generation system further includes a controller configured to operate the generator set and the inverter according to one of a first mode, a second mode, and a third mode. The first mode corresponds to the generator set providing power the load, the second mode corresponds to the external power source providing power the load through the inverter and the third mode corresponds to a hybrid load sharing mode.

In some embodiments, the hybrid load sharing mode relates to a period of high power demand of the load, wherein the external power source and the generator set are configured to provide power to the load. In some embodiments, the hybrid load sharing mode relates to a low energy level of the external power source, wherein the external power source is configured to supply reactive power to the load and the generator set is configured to decrease a supply of reactive power to the load.

In some embodiments, the power generation system further includes an AC micro-grid configured to connect to a grid network. The AC micro-grid includes the generator set, wherein the external power source is coupled to the AC micro-grid through the inverter. In some embodiments, the AC micro-grid corresponds to a recreational vehicle.

In some embodiments, the external power source corresponds to an energy storage device. In some embodiments, the external power source corresponds to a renewable energy device.

In a further aspect, the inventive concepts disclosed herein are directed to a power generation system comprising an external power source, an inverter, an AC micro-grid, and a load. The inverter is configured to convert a direct current (DC) power from an external power source to an alternating current (AC) power. The inverter includes at least one phase for converting the DC power to a corresponding phase of AC power. The AC micro-grid is configured for connection to a grid via a power command control (PCC) network. The AC micro-grid includes a generator set, and the generator set includes an alternator. The alternator includes at least one phase, wherein each phase of the alternator comprises a first winding section and a second winding section coupled in series between a point of common coupling and an output terminal of the phase. Each phase of the inverter corresponds to one phase of the alternator and is connected in parallel with the first winding section of the corresponding phase of the alternator. The load is configured for connection to the grid network via the PCC network, and to receive AC power from at least one of the generator set and the external power source.

In some embodiments, the inverter includes three phases and the alternator includes three phases. In some embodiments, at least one phase of the inverter includes an LC filter circuit, and the LC filter circuit and the first winding section of the corresponding phase of the alternator are configured to form an LCL filter circuit.

In some embodiments, the power generation system further includes a controller configured to operate the generator set and the inverter according to one of a first mode, a second mode, and a third mode. The first mode corresponds to the generator set providing power the load, the second mode corresponds to the external power source providing power the load through the inverter, and the third mode corresponds to a hybrid load sharing mode. In some embodiments, the hybrid load sharing mode relates to a period of high power demand of the load, wherein the external power source and the generator set are configured to provide power to the load. In some embodiments, the hybrid load sharing mode relates to a low energy level of the external power source, wherein the external power source is configured to supply reactive power to the load and the generator set is configured to decrease a supply of reactive power to the load.

In some embodiments, the external power source corresponds to an energy storage device. In some embodiments, the external power source corresponds to a renewable energy device. In some embodiments, the external power source is coupled to the AC micro-grid through the inverter. In some embodiments, the AC micro-grid corresponds to a recreational vehicle.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, any alternations and further modifications in the illustrated embodiments, and any further applications of the principles of the disclosure as illustrated therein as would normally occur to one skilled in the art to which the disclosure relates are contemplated herein.

Referring to the Figures generally, various embodiments disclosed herein relate to a hybrid power generation system including a generator set (genset) operating in conjunction with an external power source. The genset can power an autonomous alternating current (AC) micro-grid that supplies power to distributed loads. The genset may include, for example, a wound-field synchronous alternator driven by diesel engine. The alternator includes at least one phase of AC power. Each phase of the alternator includes a first winding section and a second winding section coupled in series between a point of common coupling and an output terminal of the phase.

In some embodiments, the external power source may include, for example, a renewable energy source (e.g., solar energy, wind energy) or an energy storage device (e.g., battery, ultra-capacitor). The external power source is coupled to the AC-grid through an inverter structured to convert DC power output from the external power source into AC power. The inverter has at least one phase, and each phase can convert the DC power into a corresponding phase of AC power. A phase of the inverter is connected in parallel with the first winding section of a corresponding phase of the alternator. In some embodiments, each phase of the inverter includes an LC filter consisting of an inductor and a capacitor. The LC filter of the inverter and the first winding section of the corresponding phase of the alternator can form an LCL filter for filtering the harmonics of the inverter, thereby achieving improved operation of the hybrid power generation system.

In some embodiments, the system disclosed herein can be used to buffer and handle grid transients, for example to facilitate meeting grid codes and low voltage ride through (LVRT) requirements. In some implementations, the system may include an inverter configured to provide a load to absorb excess power in response to an LVRT event, to provide power for sudden load transients, to provide power factor correction of genset output, to provide harmonics damping, to provide genset output/control stabilization, to buffer mechanical shock to genset, etc. The inverter can lower spinning reserve requirements by quickly absorbing load transients, reducing the need for oversizing a genset to handle transients and/or running at inefficient operation settings. This may increase efficiency and lower emissions by use of a smaller genset, etc. The system can enable gradual load take-up/response by the genset, which may provide various benefits such as saving fuel, avoiding excess emissions, reducing noise and/or human perception of the load change, providing an easier control problem via allowing a slower response, less mechanical stress on engine, etc.

In some embodiments, the inverter may be coupled to a battery or capacitor bank, and the inverter can perform in-phase balance correction of the alternator by loading low utilized phases (to charge) or by boosting overloaded phase output (to lower alternator damage curve or lengthen time alternator can spend in overload by unloading the most heavily loaded phase and balancing the transient output). In some embodiments, the inverter can also be actively operated to counter/filter unwanted harmonics in the genset output. In some embodiments, the inverter would be operating through the coupling ratio of the genset output to the number of center tap turns, and control of the inverter voltage output (or input if bi-directional) may be adjusted accordingly.

Referring now toFIG. 1, a schematic diagram of a hybrid power generation system100is shown according to an example embodiment. The hybrid power generation system100includes an AC micro-grid (e.g., the autonomous AC micro-grid)112connected to a grid network150via a power command control (PCC) network. The hybrid power generation system100also includes an external source110coupled to the AC micro-grid112through an inverter140. The AC micro-grid112can supply power to distributed loads (e.g., the load160) via the PCC network. The load160may include various types of electric equipment, such as one or more air conditioners, lighting, kitchen appliance, entertainment devices, and/or other different devices. Power demand of the load160may vary over time. For example, power demand of the load160may be light when most electric devices are turned off, or may be high when most electric devices are turned on. Another genset170can also be connected to the grid network150as a power source. It should be understood that although one load160and one other genset170are shown in the illustrated example, there may be multiple loads and gensets coupled to the grid network150.

In some embodiments, the AC micro-grid112may be implemented on vehicles (e.g., RV's), stationary facilities, industrial work machines, and so on. The AC micro-grid112can be powered by a genset120and supplemented by power supplied from the external source110. In the illustrated embodiment, the genset120includes an engine122as a prime mover and an alternator124as an electric machine coupled to and driven by the engine122. The engine122may include an internal combustion engine or any other suitable prime mover that consumes fuel (e.g., gasoline, diesel fuel, natural gas, etc.) during operation and provides a mechanical energy (e.g., a rotational torque) to drive the alternator124through, for example, a crankshaft.

The alternator124is operatively coupled to the engine122and may be powered by the engine122to generate electric power for running, for example, the load160. The alternator124may include an induction machine, a switched reluctance machine, or any other suitable electric motor or generator capable of generating electrical output in response to mechanical input, or mechanical output in response to electrical input. In some embodiments, the alternator124may be a starter/alternator, integrating the functions of a starter motor and an alternator used in the engine122. In some embodiments, alternator124is a wound-field synchronous generator (WFSG) driven by a diesel engine. The genset120may operate at a fixed speed to produce electricity at a grid frequency. In some embodiments, the rated rotational speed of the engine122and the alternator124is 1500 rpm for 50 Hz grid applications, or 1800 (or 1200) rpm for 60 Hz grid applications.

The controller114is communicably coupled to the genset120, the inverter140, and/or any other component or device of the AC micro-grid112. In some embodiments, the controller114is communicably coupled to one or more of the external power sources110. Communication between and among the components may be via any number of wired or wireless connections. For example, a wired connection may include a serial cable, a fiber optic cable, a CATS cable, or any other form of wired connection. In comparison, a wireless connection may include the Internet, Wi-Fi, cellular, radio, etc. In one embodiment, a CAN bus provides the exchange of signals, information, and/or data. The CAN bus includes any number of wired and wireless connections.

The controller114may be implemented as a general-purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a digital signal processor (DSP), a group of processing components, or other suitable electronic processing components. In some embodiments, the controller114may include one or more memory device (e.g., NVRAM, RAM, ROM, Flash Memory, hard disc storage, etc.) that stores data and/or computer code for facilitating the various processes executed by the controller114. The one or more memory devices may be or include tangible, non-transient volatile memory or non-volatile memory, database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described herein. In some embodiments, the controller114may be integrated as part of the genset120(e.g., an engine controller). In other embodiments, the controller114may be a standalone device.

The external power source110may include a renewable energy source116, such as a solar energy source and/or a wind energy source. The external power source110may include an energy storage device118, such as a battery pack and/or an ultra-capacitor. Any number of renewable energy sources116and/or energy storage devices118may be provided in various embodiments. In some embodiments, the external power source110is configured to provide a DC power output.

The external power source110is coupled to the AC micro-grid112through the inverter140(also called power electronics conditioning system) for supplementing the power supply of the genset120. The inverter140may include one or more phases. In the illustrated embodiment, the inverter140has three phases, each corresponding to a phase of the alternator124. Structural details of the inverter140are described below with reference toFIG. 3. It is noted that the inverter140in various embodiments can be a single direction output inverter, a bi-directional inverter, or an output inverter paired with a passive rectifier to allow bi-directional operation.

Referring toFIG. 2, the genset120is shown in greater detail. The genset120is shown to include an engine122and an alternator124. In some embodiments, the alternator124includes a rotor (not shown in the present Figure) and a stator202. Other alternator components are omitted in the Figure for the ease of explaining. The rotor may be a permanent magnet or field coils structured to generate a magnetic field. The stator202may include windings wound on iron cores (i.e., the armature windings). Although three-phase windings L1, L2, and L3are shown inFIG. 2for illustration, it should be understood that the stator202may include windings of any suitable phases and constructed of any suitable material. In some embodiments, the rotor may be surrounded by the armature windings L1, L2, and L3of the stator202. The engine122can drive the rotor to rotate, thereby generating a moving magnetic field around the stator202and inducing a voltage difference between two ends of each winding of the stator202.

As shown inFIG. 2, the three phases of windings L1, L2, and L3are in a wye (“Y”) connection (also called a “star” connection), in which one terminal of each winding is connected to a common coupling point (also known as common neutral) N while the other terminal (e.g., A, B, C) of the winding is connected to the PCC network for outputting a voltage. In some embodiments, there is a 120-degree difference in phase between any two phases. That is, the voltage on the first winding L1is 120-degree ahead of (or behind) the voltage on the second winding L2, the voltage on the second winding L2is 120-degree ahead of (or behind) the voltage on the third winding L3, and the voltage on the third winding L3is 120-degree ahead of (or behind) the voltage on the first winding L1. Each winding includes a first winding section and a second winding section coupled in series between the point of common coupling N and the output terminal of the phase. For example, the first winding L1includes a first winding section204and a second winding section206coupled in series between the common coupling point N and the output terminal A, the second winding L2includes a first winding section208and a second winding section210coupled in series between N and the output terminal B, and the third winding L3includes a first winding section212and a second winding section214coupled in series between N and the output terminal C.

The hybrid power generation system100can be configured to supply power to the load160in various operation modes, such as the genset only operation mode, the hybrid load sharing operation mode, and the external power source only operation mode. In some embodiments, the controller114is configured to facilitate supplying power to the load160, for example by configuring operation of the genset120, the inverter140, and/or any other component of the hybrid power generation system100.

In the genset only operation mode, the external power source110may be at an OFF state and/or disconnected from the AC micro-grid112, as a result of, for example, insufficient energy level available from the external power source110. The genset120alone in the AC micro-grid112supplies power to the load160. When power demand of the load160is changing, the engine122is kept running at a fixed speed. For example, the engine122may run at 1500 rpm for 50 Hz grid applications. The engine122may run at 1800 (or 1200) rpm for 60 Hz grid applications. An automatic voltage regulator (AVR, not shown in the present Figures) of the alternator124regulates the magnitude of AV voltages on the three phases L1, L2, and L3to keep the voltages within predefined limits. The genset120delivers active power Pgand reactive power Qgto the load160. In some embodiments, the total system output active power Ptis equal to active power Pg, and output reactive power Qtis equal to the reactive power Qg.

The hybrid load sharing operation mode may be associated with the external power source110having sufficient energy level over a period of time, such as to allow the external power source110to supplement power supply of the genset120when the power demand of the load160is high. It should be understood that the hybrid load sharing operation mode may also be associated with the energy level of the external power source110being low, but the primary function of the external power source110would be supplying reactive power Qito reduce reactive power Qgdrawn from the genset120. Both the genset120and the external power source110(through the inverter140) are delivering active and reactive power to an AC bus of the AC micro-grid112. As a result, the total system output active power Ptdemanded by the load160is shared between the genset120and the external power source110(through the inverter140), according to the following equations:
Pt=kPPg+(1−kP)Pi,

wherein kPis a ratio factor for active power sharing, and Piis the active power delivered by the external power source110through the inverter140. Similarly, the total system output reactive power Qtdemanded by load160is:
Qt=kQQg+(1—kQ)Qi,

wherein kQis a ratio factor for reactive power sharing, and Qiis the active power delivered by the external power source110through the inverter140.

The external power source only operation mode may be associated with sufficient energy level available from the external power source110, and/or light power demand of the load160. The genset120can be disconnected from the AC micro-grid112, leaving the external power source110alone to supply power to the load160(through the inverter140). Both total system output active power Ptand total system output reactive Qtare delivered only by the external power source110through the inverter140.

In some embodiments, a period of high power demand and/or low power demand may be determined by comparison to one or more threshold values. In some embodiments, a period of high power demand may be determined when a voltage level and/or voltage change of the grid network150exceeds a threshold value. For example, a period of high power demand may be determined when a measured voltage exceeds a particular voltage value and/or when a voltage change exceeds a predetermined percentage value. A period of low power demand may be similarly determined (e.g., when a measured voltage is less than a particular voltage value). A period of high and/or low power demand may be determined using any suitable manner.

In some embodiments in which the external power source110includes an energy storage device (e.g., the energy storage device118), the energy storage device may be configured to provide power to supplement the power generated by the genset120(e.g., in periods of high demand) and store excess power generated by the genset120(e.g., in periods of low demand).

In some embodiments, one or more of the operation modes of the hybrid power generation system100can be additionally or alternatively configured to buffer and handle grid transients, for example to facilitate meeting grid codes and low voltage ride through (LVRT) requirements. In some implementations, the system100may include an inverter (e.g., the inverter140) configured to provide a load to absorb excess power in response to an LVRT event, to provide power for sudden load transients, to provide power factor correction of the genset output, to provide harmonics damping, to provide output/control stabilization of the genset120, to buffer mechanical shock to the genset120, etc. The inverter can lower spinning reserve requirements by quickly absorbing load transients, reducing the need for oversizing a genset to handle transients and/or running at inefficient operation settings. The system100can be configured to enable gradual load take-up/response by the genset120, which may provide various benefits such as saving fuel, avoiding excess emissions, reducing noise and/or human perception of the load160change, providing an easier control problem via allowing a slower response, less mechanical stress on the engine122, etc.

In some embodiments, the inverter may be coupled to a battery or capacitor bank (e.g., of the external source110), and the inverter can perform in-phase balance correction of the alternator124by loading low utilized phases (to charge) or by boosting overloaded phase output (to lower alternator damage curve or lengthen time the alternator124can spend in overload by unloading the most heavily loaded phase and balancing the transient output). In some embodiments, the inverter can also be actively operated to counter/filter unwanted harmonics in the genset output. In some embodiments, the inverter would be operating through the coupling ratio of the genset output to the number of center tap turns, and control of the inverter voltage output (or input if bi-directional) may be adjusted accordingly.

Referring toFIG. 3, a schematic diagram300shows one phase of an inverter310in connection with a corresponding phase (L1) of an alternator320. In some embodiments, the inverter310and the alternator320correspond to the inverter140and the alternator124, respectively. It should be understood that although only one phase is shown inFIG. 3, the inverter310may include any suitable number of phases, each phase being connected to a corresponding phase of the alternator320.

As shown, a phase of the inverter310includes two DC buses302and304, which can be connected to the external power source110and receive the DC power output from the external power source110. Power electronics312in the inverter310can convert the DC power received from the DC buses302and304to AC voltage of appropriate magnitude, frequency, and phase and output the AC voltage on the AC buses306and308. In some embodiments, the power electronics312can synchronize the magnitude, frequency, and/or phase of the AC voltage to the voltage of the AC micro-grid112. In some embodiments, each phase of the inverter310includes a half bridge consisting of two switch elements connected in series between the DC buses302and304. The switch elements can be, for example, metal oxide semiconductor field effect transistor (MOSFET) switches, insulated gate bipolar transistor (IGBT) switches, gated thyristors, silicon controller rectifiers (SCR), as well as a variety of other devices.

In some embodiments, the ON/OFF state of each switch element may be controlled by, for example, a pulse width modulation (PWM) controller (not illustrated in the present Figure). In particular, the PWM controller may generate sequential pulses to selectively and individually drive each gate of the switch elements, causing the switch element to switch between an ON and OFF state, in order to generate an AC voltage (e.g., sine-wave voltage).

In some embodiments in which the alternator320has three phases with 120-degree difference between any two phases. Each phase of the inverter310may be controlled to generate the AC voltage of corresponding phase angle, to synchronize with the corresponding phase of the alternator320. It should be understood that the PWM controller may be configured and implemented as software (e.g., firmware), hardware, or combination thereof. It should also be understood that each phase of the inverter310may have a separate PWM controller or a single controller may be configured to control more than one phase of the inverter310independently.

In some embodiments, at least one phase of the inverter310includes an LC filter comprising of an inductor314and a capacitor316. The inductor314and the capacitor316may be configured for filtering harmonics from the AC voltage output by the power electronics312. The harmonics may be caused by the switching of the power electronics312and may damage sensitive equipment or the connected load, such as in applications above several kilowatts. Any suitable inductor314may be provided with any suitable inductance rating, and any suitable capacitor316may be provided with any suitable capacitance rating. In some embodiments, a rating of each of the inductor314and the capacitor316are selected according to desired filter characteristics as described herein. In some embodiments, the inductor314and the capacitor316may be omitted.

The inductor314and the capacitor316are coupled in series between the AC buses306and308. When connected to the corresponding phase L1of the alternator320, the capacitor316is coupled in parallel with the first winding section322, and the capacitor316is coupled in series with the second winding section324as shown inFIG. 3. The AC bus306may be coupled to the common coupling point N of the alternator320.

InFIG. 3, the inductor314, the capacitor316, and the first winding section322form an LCL filter for filtering the AC voltage output to the PCC network. The LCL filter may have various advantages over an LC filter formed by the inductor314and the capacitor316. For example, the LCL filter can produce better attenuation of power electronics switching harmonics than the LC filter. The LCL filter may have lower grid current distortion and reactive power production relative to the LC filter. The LCL filter can use a relatively low switching frequency for a given harmonic attenuation. It is noted that in some embodiments, the inductor314may be omitted from the inverter310, and an LCL filter may be formed by directly connecting the inverter output (AC buses306and308) with the windings324and322of the alternator320.

References herein to the positions of elements (e.g., “middle,” “above,” “below,” etc.) are merely used to describe the position of various elements in the drawings. It should be noted that the position of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

Similarly, while operations may be depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all operations be performed, to achieve desirable results. Moreover, the separation of various aspects of the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described methods can generally be integrated in a single application or integrated across multiple applications.