The present disclosure relates, generally, to power converters for converting direct current (DC) power to alternating current (AC) power and, more particularly, to devices, systems, and methods for tracking a maximum power point of a DC power source to increase the overall energy extracted from the DC power source.
Power inverters convert a DC power to an AC power. For example, some power inverters are configured to convert the DC power to an AC power suitable for supplying energy to an AC grid and, in some cases, an AC load that may or may not be coupled to the AC grid. One particular application for such power inverters is the conversion of DC power generated by an alternative energy source, such as photovoltaic cells (“PV cells” or “solar cells”), fuel cells, DC wind turbine, DC water turbine, and other DC power sources, to a single-phase AC power for delivery to the AC grid at the grid frequency.
In photovoltaic applications, the power delivered by each photovoltaic cell may vary in magnitude over time due to temporal variations in operating conditions including changes in sunlight intensity, angle of incidence of sunlight, ambient temperature and other factors. As such, photovoltaic cells have an operating point at which the values of the current and voltage of the cell result in an ideal or “maximum” power output. This “maximum power point” (“MPP”) is a function of environmental variables, including light intensity and temperature. Inverters for photovoltaic systems may include some form of maximum power point tracking (“MPPT”) as a mechanism of identifying and tracking the maximum power point (“MPP”) and adjusting the inverter to exploit the full power capacity of the cell at the MPP.
Additionally, in a typical photovoltaic power system, an inverter may be associated with one or more solar cell panels. For example, some systems include strings of solar cell panels that deliver a relatively high, combined voltage (e.g., nominal 450 V) to a single, large inverter. Alternatively, in other systems such as a distributed photovoltaic power system, an inverter may be associated with each solar cell panel. In such systems, the solar cell panels are typically small, relatively low voltage (e.g., 25 V). The inverter may be placed in close proximity to the associated solar cell panel to increase the conversion efficiency of the overall system.
According to one aspect, a method for an inverter configured to convert a direct current (DC) received from a DC power source to an alternating current (AC) may include executing a maximum power point tracking algorithm to extract a substantially maximum power from the DC power source. Additionally, the method may include monitoring an output power of the DC power source while executing the maximum power point tracking algorithm and, in response to the output power of the DC power source being less than a first output power, adjusting a command signal to modify a power point of the DC source until the output power of the DC power source is above a second reference output power greater than the first reference output power.
In some embodiments, adjusting the command signal may include adjusting the command signal by multiple discrete, predetermined amounts. Additionally, in some embodiments, the command signal may be adjusted in response to the output power of the DC power source being less than the first reference output power for a first period of time. For example, the first period of time may be equal to about 10 seconds.
In some embodiments, the method may include returning to execution of the maximum power point algorithm without adjusting the command signal in response to the output power of the DC power source increasing above the second reference output power during the first period of time. Additionally, in some embodiments, the method may include, in response to the output power of the DC power source being less than the first output power, storing (i) a command signal value of the command signal and (ii) an output power value of the DC power source prior to adjusting the command signal. In such embodiments, adjusting the command signal may include adjusting the command signal until the output power of the DC power source is above the stored output power value by a reference power amount. The method may also include returning to the execution of the maximum power point algorithm using the adjusted command signal in response to the output power of the DC power source exceeding the stored output power value by the reference power amount. In some embodiments, returning to execution of the maximum power point algorithm may include returning to the execution of the maximum power point algorithm for a second time period and the method may further include monitoring the output power of the DC power source during the second time period. Additionally, the method may include performing one of (i) returning to the execution of the maximum power point algorithm using the adjusted command signal in response to the output power exceeding the second reference output power during the second time period, or readjusting the command signal to response to expiration of the second time period. In some embodiments, the second time period may be equal to about 600 seconds.
In some embodiments, the method may also include comparing the adjusted command signal to a command signal reference and returning the command signal back to the stored command signal value in response to the adjusted command signal being less than the command signal reference. In such embodiments, returning the command signal back to the stored command signal value may include adjusting the command signal by a discrete predetermined amount until the command signal substantially equals the stored command signal value.
Additionally, in some embodiments, the method may include adjusting the command signal in a first direction, comparing the adjusted command signal to a command signal reference, and adjusting the command signal in a second direction opposite the first direction in response to the adjusted command signal having a predetermined relationship with the command signal reference. Further, in some embodiments, the command signal may be embodied as a voltage command signal and adjusting the command signal may include decrementing the voltage command signal by a discrete voltage amount. Alternatively, in some embodiments, the command signal may be embodied as a current command signal and adjusting the command signal may include incrementing the current command signal by a discrete current amount.
According to another aspect, an inverter for converting direct current (DC) power from a DC power source to alternating current (AC) power may include an inverter controller configured to execute a maximum power point tracking algorithm to extract a substantially maximum power from the DC power source, the maximum power point tracking algorithm to adjust a power point of the DC power source of the inverter based on a command signal. The inverter controller may also be configured to monitor an output power of the DC power source while executing the maximum power point tracking algorithm and, in response to the output power of the DC power source being less than a first output power for a first period of time, store a command signal value of the command signal, store a power output value of the output power of the DC power source, adjust the command signal until the output power of the DC power source is above the stored power output value by a reference power amount, and return to the execution of the maximum power point algorithm using the adjusted command signal in response to the DC power source exceeding the stored power output value by the reference power amount.
In some embodiments, the inverter controller may be further configured to compare the adjusted command signal to a command signal reference and return the command signal back to the stored command signal value in response to the adjusted command signal having a predetermined relationship with the command signal reference. In such embodiments, to return the command signal back to the stored command signal value may include to adjust the command signal by a discrete predetermined amount until the command signal substantially equals the stored command signal value.
Additionally, in some embodiments, to return to execution of the maximum power point algorithm may include to return to the execution of the maximum power point algorithm for a second time period. In such embodiments, the inverter controller may be further configured to monitor the output power of the DC power source during the second time period and perform one of: return to the execution of the maximum power point algorithm using the adjusted command signal in response to the output power exceeding the second reference output power during the second time period, or (ii) readjust the command signal to response to expiration of the second time period.
In some embodiments, the inverter controller may be further configured to return to execution of the maximum power point algorithm without adjusting the command signal in response to the output power of the DC power source increasing above the second reference output power during the first period of time. Additionally, in some embodiments, the inverter controller may be configured to adjust the command signal in a first direction, compare the adjusted command signal to a command signal reference, and adjust the command signal in a second direction opposite the first direction in response to the adjusted command signal having a predetermined relationship with the command signal reference.
Further, in some embodiments, the command signal may be embodied as a voltage command signal and the inverter controller may be configured to adjust the command signal by decrementing the voltage command signal by a discrete voltage amount. Alternatively, the command signal may be embodied as a current command signal and the inverter controller may be configured to adjust the command signal by incrementing the current command signal by a discrete current amount.
According to a further aspect, an apparatus may include a solar panel and an inverter coupled to the solar panel. The solar panel may include a plurality of solar cells configured to generate a direct current (DC) power output in response to receiving an amount of sunlight. The inverter may include a converter circuit to convert the DC power output to the AC power output, a converter control circuit to control an input converter of the converter circuit based on a voltage command signal, a maximum power point tracking (MPPT) circuit, and a memory. The memory may have stored therein a plurality of instructions, which when executed by the MPPT circuit, result in the MPPT circuit executing a maximum power point tracking algorithm to generate the voltage command signal to the input converter to cause the input converter to adjust a power point of the plurality of solar cells to extract a substantially maximum power from the solar panel, monitoring the DC power output of the solar panel while executing the maximum power point tracking algorithm, and, in response to the DC output power of the solar panel being less than a first output power, adjusting the voltage command signal until the DC output power of the solar panel is above a second reference output power greater than the first reference output power.
In some embodiments, adjusting the voltage command signal may include adjusting the voltage command signal in response to the DC output power of the solar panel being less than the first reference output power for a first period of time. Additionally, in some embodiments, the plurality of instructions may further result in the MPPT circuit returning to execution of the maximum power point algorithm without adjusting the voltage command signal in response to the DC output power of the solar panel increasing above the second reference output power during the first period of time.
Additionally, the plurality of instructions may result in the MPPT circuit, in response to the DC output power of the solar panel being less than the first output power, storing a voltage command signal value of the voltage command signal and an output power value of the solar panel prior to adjusting the command signal. In such embodiments, adjusting the voltage command signal may include adjusting the voltage command signal until the DC output power of the solar panel is above the stored output power value by a reference power amount. Additionally, the plurality of instructions may further result in the MPPT circuit returning to the execution of the maximum power point algorithm using the adjusted voltage command signal in response to the DC output power of the solar panel exceeding the stored output power value by the reference power amount.
In some embodiments, returning to execution of the maximum power point algorithm may include returning to the execution of the maximum power point algorithm for a second time period. In such embodiments, the plurality of instructions further result in the MPPT circuit monitoring the DC output power of the solar panel during the second time period and performing one of returning to the execution of the maximum power point algorithm using the adjusted voltage command signal in response to the DC output power exceeding the second reference output power during the second time period, or readjusting the voltage command signal to response to expiration of the second time period. Additionally or alternatively, in some embodiments, the plurality of instructions further result in the MPPT circuit comparing the adjusted voltage command signal to a voltage command signal reference and returning the voltage command signal back to the stored voltage command signal value in response to the adjusted voltage command signal being less than the voltage command signal reference.
While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Some embodiments of the disclosure, or portions thereof, may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the disclosure may also be implemented as instructions stored on a tangible, machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; and others.
Referring now to
For example, as shown in
As discussed above, the inverter 206 is used to convert a DC power input to an AC power output. An illustrative system 200 utilizing the inverter 206 is illustrated in
The inverter 206 is electrically connected to the DC source 204 and configured to convert a DC waveform generated by the DC source 204 to an AC waveform suitable for delivery to the AC grid 202 and, in some embodiments, loads coupled to the AC grid 202. The AC grid 202 may be embodied as, for example, a utility power grid that supplies utility AC power to residential and commercial users. Such utility power grids may be characterized as having a generally sinusoidal bipolar voltage at a fixed grid frequency (e.g., f=ω/2π=50 Hz or 60 Hz).
As discussed above, in some embodiments, the DC source 204 may be embodied as one or more photovoltaic cells. In such embodiments, the DC source 204 and the inverter 206 may be associated with each other so as to embody an AC photovoltaic module (ACPV) 300 as illustrated in
Referring now to
Additionally, in some embodiments, the inverter 206 may include communication circuitry 412. The communication circuitry 412 may be communicatively coupled to the inverter controller 410 or may be incorporated therein in some embodiments. The inverter controller 410 may utilize the communication circuitry 412 to communicate with remote devices, such as remote controllers or servers. In one particular embodiment, the communication circuitry 412 is embodied as a power line communication circuit configured to communicate with remote devices over an AC power line, such as the AC power line interconnects coupled to the output of the output converter 404. However, in other embodiments, other communication technologies and/or protocols may be used. For example, in some embodiments, the communication circuitry 412 may be embodied as a wireless or wired communication circuit configured to communicate with remote devices utilizing one or more wireless or wired communication technologies and/or protocols such as Wi-Fi™, Zigbee®, ModBus®, WiMAX, Wireless USB, Bluetooth®, TCP/IP, USB, CAN-bus, HomePNA™, and/or other wired or wireless communication technology and/or protocol.
In use, the input converter 400 of the inverter 206 is configured for electrically coupling the DC source 204 to receive a DC waveform therefrom. The input converter 400 converts the DC waveform to a bus waveform, which in the illustrative embodiment is a DC waveform but may be an AC waveform in other embodiments. Similarly, the output converter 404 is configured to be electrically coupled to the AC grid 202 and convert the bus waveform (i.e., either a DC waveform or an AC waveform) to the output AC waveform at the grid frequency for delivery to the AC grid 202.
As discussed above, the inverter controller 410 is electrically coupled to the input converter 400 and configured to control the operation of the input converter 400 to convert the input DC waveform from the DC source 204 to a bus waveform (e.g., a DC bus waveform) at the power bus 402. To do so, the inverter controller 410 may provide a plurality of switching and/or control signals to various circuits of the input converter 400. Additionally, as discussed below, the inverter controller 410 controls the operation of the input converter 400 based on a global maximum power point tracking (“MPPT”) method.
Illustratively, the inverter controller 410 is also electrically coupled to the output converter 404 and configured to control the operation of the output converter 404 to convert the bus waveform to the output AC waveform suitable for delivery to the AC grid 202. In the illustrative embodiment as discussed in more detail below, the inverter controller 410 is configured to use a pulse width modulation (“PWM”) algorithm to control the output converter 404 such that the output AC waveform is pulse width modulated. To do so, the inverter controller 410 may provide a plurality of switching and/or control signals to various circuits of the output converter 404.
Referring now to
Referring now to
The processing circuit 602 may be embodied as any type of processing circuitry capable of performing the functions described herein. For example, the processing circuit 602 may be embodied as one or digital signal processors, microprocessors, microcontrollers, or the like. Such processors may have one or more processing cores. Similarly, the memory 604 may be embodied as one or more memory device or data storage locations including, for example, dynamic random access memory devices (DRAM), synchronous dynamic random access memory devices (SDRAM), double-data rate synchronous dynamic random access memory device (DDR SDRAM), flash memory devices, and/or other volatile memory devices. Additionally, although only a single memory 604 is illustrated in
The processing circuitry 602 includes a plurality of control modules, which may be embodied as firmware/software programs (e.g., stored in the memory 604), discrete hardware circuitry, and/or a combination of hardware and software. In the illustrative embodiment, the processing circuitry 602 includes an MPPT control module 610 and an input converter control module 612. Of course, it should be appreciated that additional or other modules, functionality, and features may be included in the processing circuitry 604 depending on the particular implementation. For example, in embodiments wherein the inverter controller 410 also controls the output converter 404, the processing circuitry 604 includes an output converter control module.
The MPPT control module 610 provides global maximum power point tracking of the DC power source 204. To do so, the MPPT control module 610 is configured to sense, receive, or otherwise calculate the input power, PIN, supplied by the DC power source 204. The MPPT control module 610 may be configured to directly sense the input power, PIN, or to derive the input power, PIN, based on other signals such as the voltage, VS, or current, IS, of the DC power supply 204. Additionally, it should be appreciated that in other embodiments, the MPPT control module 610 may receive additional input signals.
The MPPT control module 610 executes a global maximum power point tracking method as discussed in more detail below in regard to
As discussed above, the input converter control module 612 controls the operation of the input converter 400. To do so, the input converter control module 612 generates a plurality of switch control signals, qx, to control a plurality of switches of the input converter 400. In the illustrative embodiment, the input converter control module 612 utilizes a pulse width modulation (PWM) control module 614 to generate the control signals, qX, based on a plurality of inputs including the voltage command signal, VS*, and a feedback signal of the input voltage of the DC power source 204, VS. As a function of the control signal, qX, the power point of the DC power source 204 is modified, which in turn adjusts or modifies the input power, PIN, generated by the DC power source 204. The input converter control module 612 may also perform various safety and/or quality verification checks on the input converter 400 such as ensuring that the input voltage to the input converter 400 and the voltage of the power bus 402 are within predetermined ranges.
As discussed above, the MPPT control module 610 is configured to execute a global maximum power point tracking method in which the MPPT control module 640 performs a power curve search for the global maximum power point based on particular criteria. One illustrative embodiment of a global maximum power point tracking method 700 that may be executed be the MPPT control module 610 is shown in
While executing the main MPPT control method in block 702, the MPPT control module 610 monitors the DC input power, PIN, supplied by the DC power source 204 in block 704. As discussed above, the DC input power, PIN, may be sensed, calculated, or otherwise derived by the MPPT control module 610. While the input power, PIN, remains above a lower reference threshold power level, the method 700 loops back to block 702 in which the MPPT control module 610 continues to execute the main MPPT control method. However, if the input power, PIN, drops below the lower reference threshold power level, the MPPT control module 610 determines that a shading event has occurred, and the method 700 advances to block 706 in which the MPPT control module 610 searches for a new global maximum power point. It should be appreciated that in some embodiments, the method 700 may incorporate a form of hysteresis to ensure that the shading event is not transitory or otherwise temporary (e.g., quick overshadowing of a portion of the solar cells of the DC photovoltaic module 302). For example, as discussed in more detail below in regard to method 800, a wait period may be used to ensure that the DC input power, PIN, remains below the lower reference threshold power level for a reference period of time.
As discussed above, the MPPT control module 610 searches for a new global maximum power point in block 706. To do so, the command signal is adjusted in block 708 by a reference amount. As discussed above, the command signal may be a voltage command signal, a current command signal, an impedance command signal, a duty cycle command signal, or the like. Depending on the type of command signal and/or other criteria, the command signal may be incremented or decremented in block 708. For example, in embodiments in which the command signal is embodied as a reference voltage command signal, the command signal is decremented in block 708 by the reference amount.
In block 710, the MPPT control module 610 determines whether the command signal has reached a reference command signal threshold level. The command signal threshold level is selected to ensure that the command signal is not decremented or incremented to a value too small or too large for the inverter 206. As such, the reference command signal may be an upper and/or lower threshold level. If the command signal has not reached the command signal threshold level, the method 700 advances to block 712 in which the MPPT control module 610 monitors the DC input power, PIN, of the DC source 204 to determine whether it has increased to a level greater than a reference input power level. In some embodiments, the reference input power level may be based on, a function of, or substantially equal to a previous power level (e.g., the input power level, PIN, just prior to execution of block 706), the lower threshold power level of block 704, a predefined input power level, and/or the like. Again, an amount of hysteresis may be incorporated into the reference input power level to ensure the MPPT control module 610 does not continually jump into and out of the search for a new global maximum power point. For example, in some embodiments, the reference input power level is defined as a predetermined reference amount greater than the DC input power level, PIN, just prior to execution of block 706 (i.e., the previous input power level prior to searching for a new global maximum power point).
If the DC input power, PIN, is not greater than the reference input power level, the method 700 loops back to block 708 in which the command variable is adjusted further as discussed above. However, if the MPPT control module 610 determines that the DC input power, PIN, has increased to a level greater than the reference input power, the method 700 advances to block 714 in which the MPPT control module 610 returns to the main MPPT control method of block 702 using the newly adjusted command signal. In this way, a new global maximum power point is determined by adjusting the command signal until the DC input power level, PIN, is greater than the reference input power level. It should be appreciated that the reference input power level may be selected to ensure that a global maximum power point is found rather than a local maximum power point (i.e., a power point in which the DC input power level is greater than the previous input power level but less than the input power level at the global maximum power point).
Referring back to block 710, if the MPPT control module 610 determines that the command signal has reached the reference threshold level, the method 700 advances to block 716 in some embodiments. In such embodiments, the MPPT control module 610 determines whether global searching should continue in the opposite direction in block 716. That is, the MPPT control module 610 may be configured to initially search the power curve in one direction and subsequently search the power curve in the opposite direction if no global maximum power point is found. For example, the MPPT control module 610 may be configured to initially decrement the command signal until the command signal reaches a reference lower threshold value (or until a new global maximum power point is found) and subsequently increment the command signal until the command signal reaches a reference upper threshold value (or until a new global maximum power point is found).
If the MPPT control module 610 determines that global searching should continue in the opposite direction in block 716, the method 700 loops back to block 708 in which the command signal is adjusted in the opposite direction. However, if the MPPT control module 610 determines that no additional global searching is to be performed, the method 700 advances to block 718 in which the command signal is returned to the amount of the previous command signal prior to execution of block 706 (i.e., the command variable amount prior to searching for a new global maximum power point). In some embodiments, the command signal is adjusted or stepped to the previous command variable gradually.
Accordingly, the MPPT control module 610 executes the method 700 to perform a standard MPPT control method until the DC power input, PIN, from the DC power source 204 drops below a threshold level. In response, the MPPT control module 610 is configured to search for a new global maximum power point by adjusting the command signal until the DC power input, PIN, reaches or surpasses a reference input power level, which is selected to ensure a global maximum power point has found. As discussed above, the power curve may be searched in an incrementing direction, a decrementing direction, or in both directions depending on the type of command signal used, the particular implementation, and/or other criteria.
Referring now to
The method beings with block 802 in which the main MPPT control method is executed. To do so, as discussed above, the MPPT control module 610 may use any known MPPT method to monitor the power output of the DC power source 204 (e.g., a PV module) and generate a command signal based on an MPPT algorithm (see, e.g., U.S. Patent Publication No. 2008/0183338, entitled “Ripple Correlation Control Based on Limited Sampling” by Jonathan W. Kimball et al.). While executing the main MPPT control method in block 802, the MPPT control module 610 monitors the DC power input, PIN, supplied by the DC source 204 to the inverter 206 in block 702. As discussed above, the DC input power, PIN, may be sensed, calculated, or otherwise derived by the MPPT control module 610. If the power input, PIN, is determined to be less than a lower reference threshold level, PLOW, the method 800 advances to block 806 in which a first wait state is established. In on illustrative embodiment, the lower reference threshold level, PLOW, is selected to be 50 W, but may be set to other values in other embodiments.
During the wait state of block 806, the MPPT control module 610 waits for a period of time, T1, to ensure that the decreased power input, PIN, from the DC source 204 is not temporary (e.g., a quick overshadowing or covering of a portion of the solar cells of the DC photovoltaic module 302). In one illustrative embodiment, the predetermined period of time, T1, is set to about 10 seconds, but may be longer or shorter in other embodiments.
During the first wait state of block 806, the MPPT control module 612 also monitors the DC power input, PIN. If the power input, PIN, is determined to have increased above a upper reference threshold level, PHIGH, in block 808, the method 800 loops back to block 802 in which the main MPPT control method is continued. In this way, the MPPT control module 610 includes an amount of hysteresis to ensure the shading event is not transitory or otherwise temporary. In one illustrative embodiment, the upper reference threshold level, PHIGH, is selected to be 120 W.
If, however, the first wait state of block 806 expires prior to the DC power input, PIN, increasing above the upper reference threshold level, PHIGH, the MPPT control module 610 determines that a long-term shading event has occurred and searches for a new global maximum power point. For example, as shown in
Referring back to
After the present command voltage signal, V*PREV, and the present input power, PPREV, have been stored in block 810, the MPPT control module 610 searches for a new global maximum power point in block 812. To do so, the command voltage signal is decremented by a reference amount, VSTEP, in block 814. The value of the reference voltage step, VSTEP, may be selected such that the input power, PIN, does not abruptly change. For example, in one illustrative embodiment, VSTEP is equal to about 0.1 V, but may be equal to other amounts in other embodiments.
After the command voltage signal, V*, has been decremented, the MPPT control module 610 determines whether the command voltage variable, V*, is less than or equal to a reference minimum threshold voltage, VMIN, in block 816. As discussed above in regard to the method 700 of
If the DC input power, PIN, is not greater than the reference amount above the previous input power (PPREV+PLIM), the method 800 loops back to block 814 in which the voltage command signal is decremented again. If, however, the input power, PIN, is greater than the reference amount above the previous input power (PPREV+PLIM), the method 800 advances to block 820 in which the MPPT control module 610 returns to executing the main MPPT control method using the new voltage command signal. Additionally, in block 822, a second wait state is established. During the second wait state of block 822, the MPPT control module 610 waits a period of time, T2, and monitors the DC power input, PIN. If the power input, PIN, is determined to have further increased above the reference upper threshold level, PHIGH, in block 824, the method 800 exits the global maximum power point search block 812 and loops back to block 802 in which the main MPPT control method is continued using the new command voltage signal. However, if the power input, PIN, is determined to be less than the predetermined upper threshold level, PHIGH, the method 800 loops back to block 822 in which the second wait state is continued.
If the second wait state of block 722 expires prior to the power input, PIN, increasing above the predetermined upper threshold level, PHIGH, the method 800 loops back to block 814 wherein the voltage command signal, V*, is decremented again. In this way, the main MPPT control method is executed with the new command variable, which is greater than the reference amount above the previous input power (PPREV+PLIM), for a period of time until (i) the input power, PIN, increases again above the predetermined upper threshold level, PHIGH, or (ii) the second wait state expires. Upon expiration of the second wait state, the method 800 advances to block 814 wherein the global maximum power point search is continued. In the illustrative embodiment, the period of time, T2, of the second wait state is selected such that T2>T1. For example, in one illustrative embodiment, T2 is equal to about 600 seconds.
Referring now back to block 816, if the MPPT control module 610 determines that the command voltage signal, V*, is less than or equal to a reference minimum threshold voltage, VMIN, the method 800 advances to block 826 in which the command voltage signal, V*, is returned to the previous command voltage level, V*PREV. To do so, the command voltage signal, V*, is incremented by the predetermined amount, VSTEP, in block 828. After the command voltage, V*, has been incremented in block 828, the MPPT control module 610 determines whether the command voltage signal, V*, is greater than or equal the previous command voltage signal, V*PREV, in block 830. If not, the method 800 loops back to block 826 and 828 in which the command voltage signal, V*, is further incremented. However, if the command voltage signal, V*, is determined to be greater than or equal the previous command voltage command signal, V*PREV, in block 830, the method 800 loops hack to block 802 in which the main MPPT control method is continued using the previous voltage command signal.
In this way, the MPPT control module 610 executes the method 800 to perform a search for a new global maximum power point during events in which the output power from the DC source 204 falls below a predetermined threshold for a predetermined amount of time. That is, rather than continuously performing the power curve search of the method 800, the search is performed only during conditions of shading or overcast in which the power output of the inverter 206 is substantially less than its rated power. Accordingly, the search for a new global maximum power point is executed during conditions when it is beneficial.
There is a plurality of advantages of the present disclosure arising from the various features of the apparatuses, circuits, and methods described herein. It will be noted that alternative embodiments of the apparatuses, circuits, and methods of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the apparatuses, circuits, and methods that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims.
The present application is a continuation application of commonly-owned and co-pending U.S. application Ser. No. 15/273,235, entitled Device And Method For Global Maximum Power Point Tracking, filed on Sep. 22, 2016, which application is a continuation application of U.S. application Ser. No. 14/552,131, entitled “Device and Method for Global Maximum Power Point Tracking,” which was filed on Nov. 24, 2014, and which is a continuation application of U.S. application Ser. No. 13/324,027, entitled “Device and Method for Global Maximum Power Point Tracking,” which was filed on Dec. 13, 2011, and which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 61/506,602, entitled “DEVICE AND METHOD FOR GLOBAL MAXIMUM POWER POINT TRACKING,” which was filed on Jul. 11, 2011, the entirety of each of which is hereby incorporated by reference.
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