Patent Description:
Renewable energy sources include solar energy, wind power, tidal wave energy and the like. A solar power conversion system may include a plurality of solar panels connected in series or in parallel. The output of the solar panels may generate a variable dc voltage depending on a variety of factors such as time of day, location and sun tracking ability. Since the majority of applications are designed to run on <NUM> volts ac power, solar inverter systems are employed to convert the variable dc voltage of the solar panels to a <NUM> volts ac power source.

In accordance with the topology difference, solar inverter systems may be divided into four categories, namely micro solar inverter systems, string solar inverter systems, central solar inverter systems and solar inverter systems having power optimizers. A micro solar inverter is an inverter designed to operate with a single solar panel. The micro solar inverter converts the direct current output from the single solar panel into alternating current. A string solar inverter is an inverter designed to operate with a plurality of solar panels connected in series. The string solar inverter converts the direct current output from the plurality of solar panels into alternating current.

In a central solar inverter system, a combiner box is employed to bring the outputs of a plurality of solar panels/strings together and consolidate the incoming power into one main power source. The center solar inverter converts the direct current from the main power source into alternating current. In a solar inverter system having power optimizers, each solar panel is connected to the inverter through a power optimizer. The power optimizer may be implemented as a four-switch buck-boost converter. The four-switch buck-boost converter is used to increase the energy output from the solar panel by tracking the maximum power point of the solar panel. <CIT> discloses that a photovoltaic device includes at least one photovoltaic cell and a DC/DC converter electrically coupled to the at least one photovoltaic cell. <CIT> provides a method for providing a maximum power point tracking process for an energy generating device.

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present disclosure which provide a control method for achieving a high efficiency operation of a solar system having a plurality of power optimizers.

Aspects of the invention are set out in accordance with the appended claims. Embodiments not falling in the scope of the claims are provided for illustrative purposes.

An advantage of an embodiment of the present disclosure is a solar power system providing higher efficiency power conversion.

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present disclosure.

The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to preferred embodiments in a specific context, namely a control method for improving the performance of a solar power system having a plurality of power optimizers. The disclosure may also be applied, however, to a variety of power systems. Hereinafter, various embodiments will be explained in detail with reference to the accompanying drawings.

<FIG> illustrates a block diagram of a solar power system in accordance with various embodiments of the present disclosure. The solar power system <NUM> comprises a plurality of power modules <NUM>, <NUM> and <NUM>, an inverter <NUM>, a plurality of local controllers <NUM>, <NUM> and <NUM>, and a central controller <NUM>. In some embodiments, the power modules <NUM>, <NUM> and <NUM> are connected in series to build a higher voltage fed into the inverter <NUM> as shown in <FIG>. The inverter <NUM> converts the direct current from the plurality of power modules into alternating current fed into a load and/or a power grid <NUM>.

In some embodiments, each power module (e.g., power module <NUM>) comprises a solar panel and a power optimizer. A local controller (e.g., local controller <NUM>) is electrically coupled to a corresponding power module (e.g., power module <NUM>). The local controller is employed to control the operation of the power module. The detailed operation principles of the local controllers will be described below with respect to <FIG>.

As shown in <FIG>, a first power module <NUM> comprises a first solar panel <NUM> and a first power optimizer <NUM>. Likewise, a second power module <NUM> comprises a second solar panel <NUM> and a second power optimizer <NUM>. A third power module <NUM> comprises a third solar panel <NUM> and a third power optimizer <NUM>.

The power modules <NUM>, <NUM> and <NUM> of the solar power system <NUM> are connected in series. As shown in <FIG>, a first terminal <NUM> of the first power module <NUM> is connected to a positive input terminal of the inverter <NUM>. A second terminal <NUM> of the first power module <NUM> is connected to a first terminal <NUM> of the second power module <NUM>. As shown in <FIG>, there may be a plurality of power modules connected in series and between the second power module <NUM> and the third power module <NUM> as indicated by the dashed line <NUM>. As such, the second terminal <NUM> of the second power module <NUM> is connected to the first terminal <NUM> of the third power module <NUM> through the plurality of power modules (not shown) as indicated by the dashed line <NUM>. A second terminal of the third power module <NUM> is connected to the negative input terminal of the inverter <NUM>.

The outputs of the power modules <NUM>, <NUM>, <NUM> and the plurality of power modules between <NUM> and <NUM> are connected in series to build a higher voltage fed into the inverter <NUM>. As shown in <FIG>, the series connected power modules function as a direct current power source and the inverter <NUM> converts the energy from the direct current power source into alternating current. The structure of the power modules (e.g., power module <NUM>) will be described below with respect to <FIG>.

The inverter <NUM> is employed to invert a dc waveform received from the output of the plurality of power modules <NUM>, <NUM> and <NUM> to an ac waveform. In some embodiments, the inverter <NUM> may comprise a plurality of switching elements such as insulated gate bipolar transistor (IGBT) devices. Alternatively, each inverter unit may include other types of controllable devices such as metal oxide semiconductor field effect transistor (MOSFET) devices, bipolar junction transistor (BJT) devices, super junction transistor (SJT) devices, bipolar transistors and/or the like.

The central controller <NUM> is employed to control the operation of the inverter <NUM>. More particularly, the central controller <NUM> receives various operation parameters from the power modules as well as the inverter <NUM>. Based upon the various operation parameters, the central controller <NUM> generates a variety of control signals to control the operation parameters of the inverter <NUM> such as the input voltage Vbus of the inverter <NUM>, the output current of the inverter <NUM> and/or the like.

It should be noted that <FIG> illustrates a central controller and a plurality of local controllers. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the central controller <NUM> and the plurality of local controllers <NUM>, <NUM> and <NUM> in <FIG> may be replaced by a single controller. Furthermore, a person skilled in the art would understand there may be various communication channels between the central controller <NUM> and the plurality of local controllers <NUM>, <NUM> and <NUM>.

It should further be noted the system configuration shown in <FIG> is merely an exemplary system and is not meant to limit the current embodiments. A person skilled in the art would understand that other necessary elements/components, such as input filters, output filters and/or the like, may alternatively be added into the solar power system <NUM> depending on different applications and design needs.

<FIG> illustrates a block diagram of a first implementation of the power modules shown in <FIG> in accordance with various embodiments of the present disclosure. In some embodiments, the power modules <NUM>, <NUM> and <NUM> shown in <FIG> may be of a similar structure. For simplicity, only the block diagram of the first power module <NUM> is illustrated in detail in <FIG>.

The first power module <NUM> includes the first solar panel <NUM>, the first power optimizer <NUM> and a first capacitor <NUM>. The first power module <NUM> further comprises a first input/output terminal <NUM> and a second input/output terminal <NUM>. As shown in <FIG>, the first capacitor <NUM> and the first solar panel <NUM> are connected in series and between the first input/output terminal <NUM> and the second input/output terminal <NUM>. More particularly, the capacitor <NUM> is connected to a positive terminal of the first solar panel <NUM>.

The first power optimizer <NUM> has three input/output terminals. As shown in <FIG>, a first input/output terminal <NUM> is connected to the first input/output terminal <NUM> of the first power module <NUM>. A second input/output terminal <NUM> is connected to a common node of the first capacitor <NUM> and the first solar panel <NUM>. A third input/output terminal <NUM> is connected to the second input/output terminal <NUM> of the first power module <NUM>. The detailed schematic diagram of the first power optimizer <NUM> will be described below with respect to <FIG>.

One advantageous feature of having the first capacitor <NUM> and the first solar panel <NUM> connected in series is the voltage stresses across the output capacitor (e.g., the first capacitor <NUM>) of the first power optimizer <NUM> have been reduced, thereby improving the reliability of the solar power system.

<FIG> illustrates a block diagram of a second implementation of the power modules shown in <FIG> in accordance with various embodiments of the present disclosure. The first power module <NUM> includes the first solar panel <NUM>, the first power optimizer <NUM> and the first capacitor <NUM>.

As shown in <FIG>, the first solar panel <NUM> and the first capacitor <NUM> are connected in series and between the first input/output terminal <NUM> and the second input/output terminal <NUM>. More particularly, the capacitor <NUM> is connected to a negative terminal of the first solar panel <NUM>. The first power optimizer <NUM> has three input/output terminals. As shown in <FIG>, the first input/output terminal <NUM> is connected to the first input/output terminal <NUM> of the first power module <NUM>. A second input/output terminal <NUM> is connected to a common node of the first capacitor <NUM> and the first solar panel <NUM>. A third input/output terminal <NUM> is connected to the second input/output terminal <NUM> of the first power module <NUM>. The detailed schematic diagram of the first power optimizer <NUM> will be described below with respect to <FIG>.

<FIG> illustrates a schematic diagram of the first power optimizer shown in <FIG> in accordance with various embodiments of the present disclosure. In some embodiments, the first power optimizer <NUM> is implemented as a four-switch buck-boost converter. Throughout the description, the first power optimizer <NUM> is alternatively referred to as the buck-boost converter <NUM>.

The buck-boost converter <NUM> comprises a first high-side switch <NUM>, a first low-side switch <NUM>, a second high-side switch <NUM>, a second low-side switch <NUM> and an inductor <NUM>. Throughout the description, the first high-side switch <NUM> is alternatively referred to as the first high-side switch S1. The first low-side switch <NUM> is alternatively referred to as the first low-side switch S2. The second high-side switch <NUM> is alternatively referred to as the second high-side switch S4. The second low-side switch <NUM> is alternatively referred to as the second low-side switch S3. The inductor <NUM> is alternatively referred to as the inductor L1.

The first high-side switch S1 and the first low-side switch S2 are connected in series between the second input/output terminal <NUM> and the third input/output terminal <NUM> of the buck-boost converter <NUM>. The second high-side switch S4 and the second low-side switch S3 are connected in series between the first input/output terminal <NUM> and the second input/output terminal <NUM>. The inductor L1 is coupled between the common node of the first high-side switch S1 and the first low-side switch S2, and the common node of the second high-side switch S4 and the second low-side switch S3.

The buck-boost converter <NUM> may further comprise a controller <NUM>. As shown in <FIG>, the controller <NUM> may detect the output voltage Vo of the first solar panel <NUM> and the current flowing through the solar panel <NUM>, and generate a plurality of gate drive signals for driving switches S1, S2, S3 and S4 accordingly. The controller <NUM> may be a PWM controller. Alternatively, the controller <NUM> may be implemented as a digital controller such as a microcontroller, a digital signal processor and/or the like.

It should be noted that while the example throughout the description is based upon a buck-boost converter and a controller configured to generate gate drive signal for the buck-boost converter (e.g., buck-boost converter shown in <FIG>), the buck-boost converter <NUM> as well as the controller <NUM> shown in <FIG> may have many variations, alternatives, and modifications. For example, the controller <NUM> may detect other necessary signals such as the operation temperature and the solar radiation of the first solar panel <NUM>.

Furthermore, there may be one dedicated driver or multiple dedicated drivers coupled between the controller <NUM> and the switches S1, S2, S3 and S4. In sum, the buck-boost converter <NUM> and the controller <NUM> illustrated herein is limited solely for the purpose of clearly illustrating the inventive aspects of the various embodiments. The present disclosure is not limited to any particular power topology.

The buck-boost converter <NUM> may be divided into two portions, namely a buck converter portion and a boost converter portion. The buck converter portion may comprise the first high-side switch S1 and the first low-side switch S2. The buck converter portion and the inductor L1 may function as a step-down converter when the second high-side switch S4 is always on and the second low-side switch S3 is always off. Under such a configuration, the buck-boost converter <NUM> operates in a buck mode.

The boost converter portion of the buck-boost converter <NUM> may comprise the second high-side switch S4 and second low-side switch S3. The boost converter portion and the inductor L1 may function as a step-up converter when the first high-side switch S1 is always on and the first low-side switch S2 is always off. Under such a configuration, the buck-boost converter <NUM> operates in a boost mode. Furthermore, the buck-boost converter <NUM> operates in a pass-through mode when the high-side switches S1 and S4 are always on, and the low-side switches S2 and S3 are always off.

The switches (e.g., the first high-side switch S1) shown in <FIG> may be implemented as n-type metal oxide semiconductor (NMOS) transistors. Alternatively, the switches may be implemented as other suitable controllable devices such as metal oxide semiconductor field effect transistor (MOSFET) devices, bipolar junction transistor (BJT) devices, super junction transistor (SJT) devices, insulated gate bipolar transistor (IGBT) devices, gallium nitride (GaN) based power devices and/or the like.

It should further be noted that while <FIG> illustrates four switches S1, S2, S3, and S4, various embodiments of the present disclosure may include other variations, modifications and alternatives. For example, the first low-side switch S2 may be replaced by a freewheeling diode and/or the like. The second high-side switch S4 may be replaced by a rectifier diode and/or the like.

Based upon different application needs, the buck-boost converter <NUM> may be configured to operate in three different operating modes, namely the buck mode, the boost mode and the pass-through mode. The detailed operating principles of these three modes will be described below with respect to <FIG>.

<FIG> illustrates a schematic diagram of the first power optimizer shown in <FIG> in accordance with various embodiments of the present disclosure. The structure and the operating principles of the first power optimizer <NUM> shown in <FIG> are similar to the structure and the operating principles of the first power optimizer <NUM> shown in <FIG>, and hence are not discussed herein again to avoid repetition.

<FIG> illustrates a power-voltage characteristic curve and a current-voltage curve of a solar panel in accordance with various embodiments of the present application. The horizontal axis of <FIG> represents the output voltage of a solar panel. There may be two vertical axes. The first vertical axis Y1 represents the current flowing through the solar panel. The second vertical axis Y2 represents the power generated from the solar panel.

A first curve <NUM> shows the current flowing through the solar panel versus the output voltage of the solar panel. The current of the solar panel is in a range from about zero to a short circuit current Isc. The voltage of the solar panel is in a range from about zero to an open circuit voltage Voc.

The solar panel may produce its maximum current Isc when there is a short circuit in the solar panel. As shown in <FIG>, when the solar panel is shorted, the output voltage of the solar panel is approximately equal to zero. Conversely, the maximum voltage Voc of the solar panel occurs when there is an open circuit occurred (e.g., the solar panel is disconnected from any circuit). Under the open circuit condition, the current flowing through the solar panel is approximately equal to zero.

A second curve <NUM> shows the power generated by the solar panel versus the output voltage of the solar panel. The power available from the solar panel is the product of the current flowing though the solar panel and the output voltage of the solar panel. As shown in <FIG>, at the short circuit and the open circuit conditions, the power of the solar panel is about zero. The maximum available power Pmax of the solar panel is at a point on the knee of the curve <NUM> as shown in <FIG>. The voltage and current at this maximum power point are designated as Ump and Imp, respectively as shown in <FIG>.

The second curve <NUM> may be divided into two portions, namely a first portion <NUM> and a second portion <NUM>. As shown in <FIG>, the first portion <NUM> is a line sloping upward from about zero to the maximum power Pmax. The second portion <NUM> is a line sloping downward from the maximum power Pmax to about zero.

The maximum power Pmax of the solar panel can be obtained through a trial and error process. For example, the output voltage and the current flowing through the solar panel are measured during a plurality of predetermined testing intervals. In each testing interval, the power of the solar panel is calculated based upon the measured voltage and current values. If the power in a new testing interval is approximately equal to the power in a previous testing interval, the voltage of the solar panel is maintained unchanged. Otherwise, depending on the operating point of the solar panel, the output voltage of the solar panel may be adjusted accordingly. For example, when the solar panel operates at the first portion <NUM> of the curve <NUM>, both the power and the voltage are increased or decreased at the same time. The output voltage of the solar panel is increased by a predetermined value. As a result, the power of the solar panel approaches close to the maximum available power under a particular amount of solar radiation.

On the other hand, when the solar panel operates at the second portion <NUM> of the curve <NUM>, the power and the voltage go to opposite directions. For example, the power is increased, but the voltage is decreased. Alternatively, the power is decreased, but the voltage is increased. In order to approach close to the maximum available power, the voltage of the solar panel is decreased by a predetermined value. Through the trial and error process, under a particular amount of solar radiation, the maximum power point or Pmax of the solar panel can be tracked.

<FIG> illustrate a flow chart of a method <NUM> for controlling the solar power system <NUM> shown in <FIG> in accordance with various embodiments of the present application. This flow chart shown in <FIG> is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, various steps as illustrated in <FIG> may be added, removed, replaced, rearranged and repeated.

<FIG> illustrates a first portion of the method <NUM> in accordance with various embodiments of the present application. <FIG> illustrates a second portion of the method <NUM> in accordance with various embodiments of the present application.

Referring back to <FIG>, the solar power system <NUM> may include n power modules connected in series between two input terminals of the inverter <NUM>. Each power module comprises a solar panel, a capacitor and a power optimizer. In some embodiments, the power optimizer is implemented as a four-switch buck-boost converter. The structure of the power modules has been discussed above with respect to <FIG>, and hence is not discussed again to avoid repetition.

The solar power system <NUM> may further comprise a plurality of local controllers and at least a central controller. Each local controller is employed to control the operation of a corresponding power module. The central controller is employed to control the operation of the inverter.

The method <NUM> starts at step <NUM> where the local controllers and the central controller of the solar power system reset a plurality of registers. For example, various operation parameters measured previously and saved in the register units of the local controllers and the central controller are reset before the local controllers and the central controller proceed further.

At step <NUM>, the local controllers configure their respective solar panels to operate at their maximum output power Pmax (e.g., P1max, P2max,. , Pnmax) through a suitable control mechanism such as a trial and error process discussed about with respect to <FIG>. The local controllers detect or measure the power flows of the power modules. It should be noted the measured power flow is the maximum output power of each power module. Also at step <NUM>, the local controllers detect or measure the maximum power point tracking (MPPT) currents of the solar panels. The MPPT currents of the solar panels are Imp1, Imp2,. The MPPT current (e.g., Imp) of a solar panel has been discussed above with respect to <FIG>, and hence is not discussed again to avoid repetition.

At step <NUM>, a mode transition range is obtained. In particular, the midpoint Io_typ of the mode transition range is a current flowing through the plurality of power modules. In some embodiments, the current Io_typ is approximately equal to a sum of the maximum power flows (P1max, P2max,. , Pnmax) of the plurality of power solar panels divided by an input voltage of the inverter. The input voltage of the inverter is regulated by the central controller. In some embodiments, the input voltage of the inverter is proportional to a reference in the central controller. The reference is a predetermined value, which may vary depending on different applications and design needs.

In some embodiments, the lower limit Io_min of the mode transition range is about <NUM>% of the midpoint. The upper limit Io_max of the mode transition range is about <NUM>% of the midpoint. It is appreciated that the values of the upper limit and the lower limit are merely examples, and may be changed to different values depending on different applications and design needs.

At step <NUM>, the local controllers determine whether the MPPT currents of the solar panels fall into the mode transition range. At step <NUM>, if none of the MPPT currents of the solar panels fall into the mode transition range, the method <NUM> proceeds to step <NUM> where the respective power optimizers stay at the existing modes (e.g., buck mode or boost mode) to achieve their own maximum available power. Additionally, the central controller regulates the input voltage of the inverter equal to the sum of the maximum power flows (P1max, P2max,. , Pnmax) of the plurality of solar panels divided by the current Io_typ.

Also at step <NUM>, if at least one MPPT current falls into the mode transition range, the method <NUM> proceeds to step <NUM>. At step <NUM>, if only one MPPT current falls into the mode transition range, the method <NUM> proceeds to step <NUM>. Otherwise, the method <NUM> proceeds to step <NUM>.

At step <NUM>, for the power modules having their MPPT currents in the mode transition range, the local controllers configure the associated power optimizers to operate in the pass-through mode. Furthermore, at step <NUM>, the central controller regulates the input voltage of the inverter equal to the sum of the maximum power flows (P1max, P2max,. , Pnmax) of the plurality of solar panels divided by the current Io_typ.

At step <NUM>, for the power module having the MPPT current in the mode transition range, the corresponding local controller configure the associated power optimizer to operate in the pass-through mode. Furthermore, at step <NUM>, the central controller regulates the input voltage of the inverter equal to the sum of the maximum power flows (P1max, P2max,. , Pnmax) of the plurality of solar panels divided by the MPPT current of the power module.

After the method <NUM> finishes the mode transitions at steps <NUM> or <NUM>, the method <NUM> proceeds to step <NUM> where after a suitable delay, the method <NUM> return to step <NUM>.

<FIG> illustrate a mode transition control scheme in accordance with various embodiments of the present application. This control scheme shown in <FIG> is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

According to the flow chart shown in <FIG>, the power optimizers may operate in three modes, namely the buck mode, the boost mode and the pass-through mode. Before a mode transition process, a power optimizer operates in a buck mode <NUM>. A local controller associated with the power optimizer may configure the power optimizer to leave the buck mode and enter the pass-through mode as indicated by arrow <NUM> if a duty cycle of the buck portion of the power optimizer is greater than a predetermined value D1. In some embodiments, the predetermined value D1 is about <NUM>%. In the pass-through mode <NUM>, the power optimizer is labelled as a power optimizer entering the pass-through mode from the buck mode. If this power optimizer leaves the pass-through mode, it has to enter the boost mode <NUM> as indicated by arrow <NUM>. In addition, the power optimizer cannot enter the boost mode <NUM> immediately. There is a predetermined delay T2. In some embodiments, the predetermined delay T2 is in a range from about one second to about three seconds.

Similarly, before a mode transition process, a power optimizer may operate in the boost mode <NUM>. The local controller may configure the power optimizer to leave the boost mode <NUM> and enter the pass-through mode <NUM> as indicated by arrow <NUM> if a duty cycle of the boost portion of the power optimizer is less than a predetermined value D2. In some embodiments, the predetermined value D2 is about <NUM>%. In the pass-through mode <NUM>, the power optimizer is labelled as a power optimizer entering the pass-through mode from the boost mode. If this power optimizer leaves the pass-through mode, it has to enter the buck mode <NUM> as indicated by arrow <NUM>. In addition, the power optimizer cannot enter the buck mode <NUM> immediately. There is a predetermined delay T1. In some embodiments, the predetermined delay T1 is in a range from about one second to about three seconds.

<FIG> illustrates a block diagram of another solar power system in accordance with various embodiments of the present disclosure. The solar power system <NUM> is similar to the solar power system <NUM> shown in <FIG> except that each solar panel (e.g., the first solar panel <NUM>) and its corresponding power optimizer (e.g., the first power optimizer <NUM>) are connected in cascade. The output capacitors C1, C2 and C3 are placed at the outputs of their respective power optimizers.

Claim 1:
A method for controlling a solar power system, wherein the solar power system comprises a plurality of power optimizers(<NUM>,<NUM>,<NUM>) and a plurality of local controllers(<NUM>, <NUM>, <NUM>), the plurality of power optimizers are configured to be connected to a plurality of solar panels(<NUM>,<NUM>,<NUM>) to form a plurality of power modules(<NUM>,<NUM>,<NUM>) connected in series between two input terminals(<NUM>, <NUM>) of an inverter(<NUM>); the plurality of local controllers coupled to their respective power modules;
the method comprising:
obtaining a maximum power flow of each solar panel based upon operation parameters of the plurality of the solar panels; and
configuring a first power optimizer(<NUM>) of the plurality of power optimizers, based upon a maximum power point tracking, MPPT, current of a first solar panel(<NUM>) of the plurality of solar panels, to switch between a buck mode and a pass-through mode or between a boost mode and the pass-through mode, if the MPPT current of the first solar panel is within a mode transition range, wherein:
the mode transition range includes an upper limit(Io_max), a lower limit(Io_min) and a midpoint, and the midpoint(Io_typ) of the mode transition range is a current flowing through the plurality of power modules, and wherein the current is approximately equal to a sum of the maximum power flows of the plurality of solar panels divided by an input voltage of the inverter.