Power converter circuitry for photovoltaic devices

Abstract

Power converter circuitry includes a direct current (DC) input comprising a first DC input node and a second DC input node, an alternating current (AC) output comprising a first AC output node coupled to the first DC input node and a second AC output node, a first boost switch coupled between the second DC input node and a boost intermediate node, a second boost switch coupled between the boost intermediate node and a common node, a boost inductor coupled between the boost intermediate node and the first DC input node, a link capacitor coupled between the second DC input node and the common node, a first half-bridge switch coupled between the second DC input node and a half-bridge intermediate node, a second half-bridge switch coupled between the half-bridge intermediate node and the common node, and a half-bridge inductor coupled between the half-bridge intermediate node and the second AC output node.

Claims

1. Power converter circuitry comprising: a direct current (DC) input; an alternating current (AC) output coupled to the DC input; a boost converter comprising a first boost switch and a second boost switch coupled between the DC input and a boost converter output and configured to receive a DC input signal from a DC device coupled to the DC input and provide a boosted DC signal at the boost converter output; a link capacitor coupled across the DC input and the boost converter output, wherein the link capacitor is sized to provide a capacitance configured to cause the power converter circuitry to operate at a power factor between 0.7 and 1; and a half-bridge converter coupled between the boost converter output and the AC output and configured to receive the boosted DC signal and provide an AC output signal at the AC output.

2. The power converter circuitry of claim 1 further comprising control circuitry coupled to the boost converter and the half-bridge converter and configured to: maintain a power drawn from the DC device coupled to the DC input at a substantially constant value; and provide the AC output signal at the AC output.

3. The power converter circuitry of claim 2 wherein the control circuitry is further configured to track a maximum power point of an output of the DC device.

4. The power converter circuitry of claim 3 wherein the control circuitry is further configured to maximize a power conversion efficiency of the power converter circuitry.

5. The power converter circuitry of claim 4 wherein the control circuitry is further configured to control the state of one or more switches in the half-bridge converter based on a voltage at the output of the DC device, a current at the output of the DC device, and a voltage at the AC output.

6. The power converter circuitry of claim 1 further comprising: an additional AC output; and an additional half-bridge converter coupled between the boost converter output and the additional AC output and configured to receive the boosted DC signal and provide an additional AC output signal at the additional AC output.

7. The power converter circuitry of claim 6 further comprising control circuitry coupled to the boost converter, the half-bridge converter, and the additional half-bridge converter and configured to: maintain a power drawn from the DC device coupled to the DC input at a substantially constant value; and provide the AC output signal at the AC output.

8. The power converter circuitry of claim 7 wherein the control circuitry is further configured to track a maximum power point of an output of the DC device.

9. The power converter circuitry of claim 8 wherein the control circuitry is further configured to maximize a power conversion efficiency of the power converter circuitry.

10. The power converter circuitry of claim 9 wherein the control circuitry is further configured to control a state of one or more switches in the half-bridge converter and the additional half-bridge converter based on a voltage at the output of the DC device, a current at the output of the DC device, and a voltage at the AC output.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

(2) FIG. 1 is a functional schematic illustrating conventional power converter circuitry.

(3) FIG. 2 is a functional schematic illustrating power converter circuitry according to one embodiment of the present disclosure.

(4) FIGS. 3A-3C are a series of graphs illustrating the operation of power converter circuitry according to one embodiment of the present disclosure.

(5) FIGS. 4A-4D are a series of graphs illustrating the operation of power converter circuitry according to one embodiment of the present disclosure.

(6) FIG. 5 is a functional schematic illustrating power converter circuitry according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

(7) The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

(8) It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

(9) It will be understood that when an element such as a layer, region, or substrate is referred to as being on or extending onto another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly on or extending directly onto another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being over or extending over another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly over or extending directly over another element, there are no intervening elements present. It will also be understood that when an element is referred to as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being directly connected or directly coupled to another element, there are no intervening elements present.

(10) Relative terms such as below or above or upper or lower or horizontal or vertical may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

(11) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms a, an, and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes, and/or including when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

(12) Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(13) FIG. 2 shows power converter circuitry 18 according to one embodiment of the present disclosure. The power converter circuitry 18 includes a direct current (DC) input comprising a first DC input node DC.sub.IN1 and a second DC input node DC.sub.IN2, an alternating current (AC) output comprising a first AC output node AC.sub.OUT1 and a second AC output node AC.sub.OUT2, a link capacitor C.sub.LINK, a boost converter, and a half-bridge converter. The first AC output node AC.sub.OUT1 is coupled to the first DC input node DC.sub.IN1. The boost converter includes a first boost switching element Q.sub.B1 coupled between the second DC input node DC.sub.IN2 and a boost intermediate node B.sub.IM, a second boost switching element Q.sub.B2 coupled between the boost intermediate node B.sub.IM and a common node COMM, and a boost inductor L.sub.B coupled between the boost intermediate node B.sub.IM and the first DC input node DC.sub.IN1. The link capacitor C.sub.LINK is coupled between the second DC input node DC.sub.IN2 and the common node COMM. The half-bridge converter includes a first half-bridge switching element Q.sub.HB1 coupled between the second DC input node DC.sub.IN2 and a half-bridge intermediate node HB.sub.IM, a second half-bridge switching element Q.sub.HB2 coupled between the half-bridge intermediate node HB.sub.IM and the common node COMM, and a half-bridge inductor L.sub.HB coupled between the half-bridge intermediate node HB.sub.IM and the second AC output node AC.sub.OUT2. For purposes of illustration, a photovoltaic panel 20 is coupled in parallel with an input capacitor C.sub.IN between the first DC input node DC.sub.IN1 and the second DC input node DC.sub.2, and the AC output is connected to an AC electrical grid 22 such that the first AC output node AC.sub.OUT1 is coupled to a neutral connection of the AC electrical grid 22. In some embodiments, an optional additional link capacitor C.sub.LINK2 is coupled between the first DC input node DC.sub.IN1 and the common node COMM.

(14) Power converter control circuitry 24 is coupled to each one of the first boost switching element Q.sub.B1, the second boost switching element Q.sub.B2, the first half-bridge switching element Q.sub.HB1, and the second half-bridge switching element Q.sub.HB2 and configured to provide switching control signals to each one of the switching elements in order to control the state thereof. As shown in FIG. 2, each one of the first boost switching element Q.sub.B1, the second boost switching element Q.sub.B2, the first half-bridge switching element Q.sub.HB1, and the second half-bridge switching element Q.sub.HB2 may be transistor devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) including a gate contact (G), a drain contact (D), and a source contact (S). Specifically, the first boost switching element Q.sub.B1, the second boost switching element Q.sub.B2, the first half-bridge switching element Q.sub.HB1, and the second half-bridge switching element Q.sub.HB2 may be silicon carbide MOSFETs that provide high blocking capability and low on-state resistance. Those skilled in the art will appreciate that any suitable switching element may be used for each one of the first boost switching element Q.sub.B1, the second boost switching element Q.sub.B2, the first half-bridge switching element Q.sub.HB1, and the second half-bridge switching element Q.sub.HB2 without departing from the principles herein.

(15) The power converter control circuitry 24 may be configured to operate the first boost switching element Q.sub.B1 and the second boost switching element Q.sub.B2 such that a power drawn from the photovoltaic panel 20 remains substantially constant while charging the link capacitor C.sub.LINK. Specifically, the power converter control circuitry 24 may operate the first boost switching element Q.sub.B1 and the second boost switching element Q.sub.B2 such that a maximum power point of an output of the photovoltaic panel 20 is tracked. The power converter control circuitry 24 may operate the first half-bridge switching element Q.sub.HB1 and the second half-bridge switching element Q.sub.HB2 to provide an AC output signal to the AC electrical grid 22. The input capacitor C.sub.IN is provided to filter ripple at the switching frequency of the switching elements and is thus designed based on the maximum allowable high-frequency voltage ripple. The input capacitor C.sub.IN is not designed to store energy for power pulsation due to the connected AC electrical grid 14, since this is accomplished by the link capacitor C.sub.LINK as discussed in detail below.

(16) The boost converter effectively boosts a DC input voltage V.sub.IN provided by the photovoltaic panel 20 at the DC output to provide a link voltage V.sub.LINK across the link capacitor C.sub.LINK. This boosted link voltage V.sub.LINK together with the input voltage V.sub.IN from the photovoltaic panel 20 is then converted by the half-bridge converter into an AC grid voltage V.sub.G, which is provided at the AC output. The power drawn (V.sub.IN, I.sub.IN) from the photovoltaic panel 20 remains relatively constant in order to maximize the energy harvest and efficiency thereof. In one embodiment, the input voltage V.sub.IN from the photovoltaic panel 20 may be maintained at 400 V with minimal ripple. The pulsating power required by the half-bridge converter to deliver the grid voltage V.sub.G is provided by the link capacitor C.sub.LINK, which stores energy when the instantaneous grid power is less than the power drawn from the photovoltaic panel 20 and releases stored energy when the instantaneous grid power is higher than the power drawn from the photovoltaic panel 20. The voltage swing in the link voltage V.sub.LINK is designed to be significantly larger than in conventional converters to reduce the size of link capacitor C.sub.LINK. Details of the relationship between the input voltage V.sub.IN, the link voltage V.sub.LINK, and the grid voltage V.sub.G are illustrated in FIG. 3A. Further, FIGS. 3A through 3C show an AC grid current I.sub.G provided from the half-bridge converter to the AC output. As illustrated, a phase of the grid current I.sub.G may change in relation to the grid voltage V.sub.G such that a power factor of the power converter circuitry 18 changes. The timing of switching control signals provided by the power converter control circuitry 24 to the switching elements in the power converter circuitry 18 may change in response to changes in the power factor in order to properly deliver the grid voltage V.sub.G and the grid current I.sub.G. The link capacitor C.sub.LINK must be designed to adequately supply power to maintain the grid voltage V.sub.G and the grid current I.sub.G at the desired values in both leading and lagging power factor situations. Accordingly, the capacitance of the link capacitor C.sub.LINK must be chosen based on the worst case scenario, which is the leading power factor shown in FIG. 3C. In various embodiments, the link capacitor C.sub.LINK may be designed such that the power converter circuitry 18 is capable of operating at power factors between 0.7 and 1, leading or lagging. For an output power of 2 kW, the power converter circuitry 18 may provide a 120 Hz ripple component in the input voltage V.sub.IN attributable to the power pulsation of the AC electrical grid 14 around 4.2 V peak-to-peak, which is around 1.05% of a 400 V input voltage, as may be typical for the photovoltaic panel 12, which may provide efficiency as high as 95.7% and a total harmonic distortion of 2.1%.

(17) The boost inductor L.sub.B and the half-bridge inductor L.sub.HB may be designed through loss and volume optimization in order to meet total harmonic distortion requirements. The objective in the design of the boost inductor L.sub.B and the half-bridge inductor L.sub.HB is to minimize volume and losses, which include conduction losses, switching loss, and inductor copper and core losses. When a power output of the power converter circuitry 18 is greater than 2 kW, the link capacitor C.sub.LINK may have a capacitance of 30 F with a maximum voltage of 1100 V, the input capacitor may have a capacitance of 5 F with a maximum voltage of 500 V, the boost inductor L.sub.B may have an inductance of 230 H, the half-bridge inductor L.sub.HB may have an inductance of 230 H, and a switching frequency of the power converter circuitry 18 may be 75 kHz. In one embodiment, the boost inductor L.sub.B and the half-bridge inductor L.sub.HB are implemented on a common magnetic structure as coupled inductors.

(18) FIGS. 4A through 4D illustrate the basic premise of operation of the power converter circuitry 18. These figures show switching control signals provided to the first boost switching element Q.sub.B1 and the second boost switching element Q.sub.B2, which are provided in an alternating fashion such that when the first boost switching element Q.sub.B1 is closed, the second boost switching element Q.sub.B2 is open, and vice versa. Similarly, switching control signals provided to the first half-bridge switching element Q.sub.HB1 and the second half-bridge switching element Q.sub.HB2 are provided in an alternating fashion such that when the first half-bridge switching element Q.sub.HB1 is closed, the second half-bridge switching element Q.sub.HB2 is open, and vice versa. The duty cycles of the switching signals are changed by the power converter control circuitry 24 in order to move from a first point P1 in the grid voltage V.sub.G, which is a negative peak, to a second point P2, which is a neutral point, and a third point P3, which is a positive peak. The intermediate duty cycles of the switching control signals can be extrapolated from those shown. Those skilled in the art will appreciate that the switching control signals may change in order to provide a desired power factor as discussed above.

(19) The power converter control circuitry 24 may measure voltages and/or currents from various points in the power converter circuitry 18 (e.g., the input voltage V.sub.IN, an input current I.sub.IN, the link voltage V.sub.LINK, the grid voltage V.sub.G, the grid current I.sub.G, or the voltage and/or current at any other point) and adjust the switching control signal provided to the first boost switching element Q.sub.B1, the second boost switching element Q.sub.B2, the first half-bridge switching element Q.sub.HB1, and the second half-bridge switching element Q.sub.HB2 accordingly. In one embodiment, the power converter control circuitry 24 uses maximum power point tracking to provide the switching control signals to the first boost switching element Q.sub.B1 and the second boost switching element Q.sub.B2 in order to maximize power extraction from the photovoltaic panel 20, the details of which will be appreciated by those skilled in the art. The power converter control circuitry 24 may further use a proportional-integral control along with a sinusoidal reference signal generated by a phase-locked loop in order to provide the switching control signals to the first half-bridge switching element Q.sub.HB1 and the second half-bridge switching element Q.sub.HB2 and thus provide a desired AC output signal to the AC electrical grid 22.

(20) The topology of the power converter circuitry 18 provides several benefits. First, because the first DC input node DC.sub.IN1 and the first AC output node AC.sub.OUT1 are coupled together and the first AC output node AC.sub.OUT1 is coupled to a neutral connection of the AC electrical grid 22, at least one of the terminals of the photovoltaic panel 20 is effectively grounded. Grounding at least one of the terminals of the photovoltaic panel 20 effectively nullifies any parasitic capacitance that may be present between a chassis on which the photovoltaic panel 20 is provided (which is generally grounded as mandated by code) and the photovoltaic panel 20 itself. Accordingly, the performance of the power converter circuitry 18 may be significantly improved.

(21) Second, the topology of the power converter circuitry 18 significantly reduces the required size (i.e., volume) of the link capacitor C.sub.LINK when compared to conventional approaches. This in turn allows for the use of a capacitor that is not electrolytic. For example, the link capacitor C.sub.LINK may be a film capacitor or the like due to the relatively small capacitance required thereof. In some embodiments, the capacitance of the link capacitor C.sub.LINK is less than 50.0 F with a maximum voltage of 1100 V for a power output of the power converter circuitry 18 greater than 2 kW. In various embodiments, the capacitance of the link capacitor C.sub.LINK may be less than 40 F, and even less than 35 F. In one embodiment, a power module based on the topology discussed herein measures 139 mm by 122 mm, with a separate control board measuring 70 mm by 68 mm. The boost inductor L.sub.B and the half-bridge inductor L.sub.HB may be ferrite core planar inductor cores assembled with Litz wire for maximum efficiency and measure 58 mm by 38 mm.

(22) When compared to the power converter circuitry 10 discussed above with respect to FIG. 1, the location of the link capacitor C.sub.LINK is moved. Accordingly, rather than providing a buck-boost converter and a half-bridge converter, the power converter circuitry 18 discussed herein provides a boost converter and a half-bridge converter. These changes in topology and the corresponding changes in the operation of the power converter circuitry 18 as a result thereof allow the size of the link capacitor C.sub.LINK to be further reduced when compared to the approach discussed above. Specifically, volume reductions of up to 15% for the link capacitor C.sub.LINK may be achieved when using the power converter circuitry 18 discussed herein due to the increased voltage placed across the link capacitor C.sub.LINK in this topology. Additionally, the new position of the link capacitor C.sub.LINK changes the current provided through the boost inductor L.sub.B. Specifically, the boost inductor L.sub.B in the power converter circuitry 18 may experience up to a 5% reduction in RMS current when compared to the buck-boost inductor L.sub.BB shown in the power converter circuitry 10 discussed above with respect to FIG. 1. This may result in reduced copper losses and thus increased efficiency of the power converter circuitry 18. Furthermore, the new position of C.sub.LINK reduces the high frequency RMS current in the input capacitor C.sub.IN by about 80% when compared to the power converter circuitry 10 discussed above with respect to FIG. 1.

(23) While FIG. 2 shows power converter circuitry 18 for a single-phase AC electrical grid, the principles of the present disclosure may also be applied to a multi-phase AC system. FIG. 5 thus shows power converter circuitry 26 for a split-phase AC electrical grid according to one embodiment of the present disclosure. The power converter circuitry 26 shown in FIG. 5 is substantially similar to that shown in FIG. 2 and includes the DC input, the AC output, the link capacitor C.sub.LINK, the boost converter, and the half-bridge converter as described above. Further, the power converter circuitry 26 includes an additional AC output comprising a third AC output node AC.sub.OUT3 and a fourth AC output node AC.sub.OUT4 and an additional half-bridge converter. The third AC output node AC.sub.OUT3 is coupled to the first DC input node DC.sub.IN1. The additional half-bridge converter includes a third half-bridge switching element Q.sub.HB3 coupled between the second DC input node DC.sub.IN2 and a second half-bridge intermediate node HB.sub.IM2, a fourth half-bridge switching element Q.sub.HB4 coupled between the second half-bridge intermediate node HB.sub.IM2 and the common node COMM, and a second half-bridge inductor L.sub.HB2 coupled between the second half-bridge intermediate node HB.sub.IM22 and the fourth AC output node AC.sub.OUT4. For context, a photovoltaic panel 28 is coupled between the first DC input node DC.sub.IN1 and the second DC input node DC.sub.IN2, a first phase of an AC electrical grid 30A is coupled to the AC output, and a second phase of the AC electrical grid 30B is coupled to the additional AC output.

(24) The power converter circuitry 26 shown in FIG. 5 operates in substantially the same manner as that discussed above, and thus enjoys the same benefits. However, the benefits discussed above may be even more significant in the case of the split-phase topology. In particular, both a peak current through the boost inductor L.sub.B and an RMS current through the boost inductor L.sub.B may be significantly reduced (e.g., by 41% and 18%, respectively, when compared to the power converter circuitry 10 discussed above with respect to FIG. 1) such that the efficiency of the power converter circuitry 26 is significantly increased. In one embodiment, the first half-bridge inductor L.sub.HB1 and the second half-bridge inductor L.sub.HB2 are implemented on a common magnetic structure as coupled inductors.

(25) Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.