Multi-modal maximum power point tracking optimization solar photovoltaic system
A multi-modal maximum power point tracking optimization solar photovoltaic system is provided. A maximum power point tracking optimizer is connected to and powered by at least one solar cell. The maximum power point tracking optimizer configured to operate: in a pass-through mode when said at least one solar cell voltage is greater than a pass-through threshold and greater than a ratio of the open-circuit voltage of said at least one solar cell, said pass-through mode flowing current through a pass-through circuit; in an optimizing mode when said at least one solar cell voltage is greater than an optimizing threshold and less than a ratio of the open-circuit voltage of said at least one solar cell, said optimizing mode modulating current flow using a DC-to-DC switching circuit to direct the voltage of said at least solar cell towards said ratio of the open-circuit voltage; in an active bypass mode when said at least one solar cell voltage is less than an active bypass threshold, said active bypass mode flowing current through an active bypass circuit.
1 . A multi-modal maximum-power-point-tracking (MPPT) integrated circuit for optimization of power of a string of interconnected solar cells, comprising:
a sample and hold circuit having open-circuit voltage sampling pulses for periodic measurements of open-circuit voltage (V OC ) of said string of interconnected solar cells at a specified frequency and pulse duration;
a device for measuring the open-circuit voltage of said string of interconnected solar cells and calculating a multiplier of said open-circuit voltage as the maximum-power-point set-point;
a high-side field-effect transistor switch (high-side FET switch);
a low-side field-effect transistor switch (low-side FET switch);
a switching circuit operating at a specified frequency and with an adjustable switching duty cycle;
a multi-modal control algorithm providing shutdown mode when said integrated circuit is turned off, a pass-through mode having a pass-through power efficiency, an optimizing mode having an optimizing power efficiency, and an active bypass mode to increase photovoltaic power from string of interconnected solar cells;
an under-voltage lockout (UVLO) circuit to monitor the voltage of said string of interconnected solar cells, to enable said active bypass mode, and to protect said MPPT integrated circuit during power up and power down;
wherein said high-side FET switch is connected to a first FET driver capable of either turning it on or off;
wherein said low-side FET switch is connected to a second FET driver capable of either turning it on or off; and
wherein said MPPT integrated circuit operates in said active bypass mode of operation when the voltage of said string of interconnected solar cells falls below a UVLO threshold voltage setting while being sufficiently large to avoid said shutdown mode of operation, by turning on said low-side FET switch and turning off said high-side FET switch.
2 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said multi-modal control algorithm further includes a rectifier bypass mode of operation.
3 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 2 , wherein said rectifier bypass mode of operation is configured for use with a Schottky barrier rectifier coupled across output positive and output negative electrical leads of said integrated circuit.
4 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said optimization of power comprises an electronic circuit voltage regulator for regulating the operating voltage of said string of interconnected solar cells.
5 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said specified voltage sampling duration is in the range of less than 100 micro-seconds up to 10 milli-seconds.
6 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said high-side field-effect transistor and said low-side field-effect transistor are n-channel field-effect transistors (NMOS transistors).
7 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said optimizing mode of operation is a switching mode of operation with said high-side field-effect transistor being on with said adjustable switching duty cycle being greater than 0 and less than 100% of the time between said open-circuit voltage sampling pulses.
8 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said multi-modal power optimization control algorithm utilizes a transition voltage value obtained by multiplying said open-circuit voltage by a pre-determined constant factor.
9 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 8 , wherein said pre-determined constant factor is a number between 0.65 and 0.90.
10 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 9 , wherein said multiplier is a pre-determined constant factor between 0.75 and 0.80.
11 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said device comprises an 8-bit analog-to-digital converter (ADC) configured to digitize said open-circuit voltage (VOC) and an 8-bit digital-to-analog converter (DAC) configured to generate a control signal corresponding to said maximum-power-point set-point.
12 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein, in said optimizing mode of operation, said adjustable switching duty cycle is adjusted to regulate an operating voltage of said string of interconnected solar cells toward said maximum-power-point set-point.
13 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said maximum-power-point set-point is based on a most-recent measured open-circuit voltage (VOC) obtained during a prior open-circuit voltage sampling pulse and is maintained until a subsequent open-circuit voltage sampling pulse updates said maximum-power-point set-point.
14 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said integrated circuit package comprises a BOOST lead configured to be coupled to an external boost capacitor for driving said high-side FET switch.
15 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , further comprising a soft-landing circuit configured to ramp said adjustable switching duty cycle during a transition from said shutdown mode of operation to said optimizing mode of operation and/or said pass-through mode of operation.
16 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein, in said pass-through mode of operation, said high-side FET switch is maintained substantially on between said periodic open-circuit voltage sampling pulses and said low-side FET switch is maintained off.
17 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said high-side FET switch has an on-state drain-to-source resistance less than 25 milliohms and said low-side FET switch has an on-state drain-to-source resistance less than 60 milliohms.
18 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said periodic measurements occur at a repetition period in a range of 2 seconds to 20 seconds.
19 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said specified frequency of said switching circuit is in a range of 300 kHz to 700 kHz.
20 . The multi-modal maximum-power-point-tracking (MPPT) integrated circuit of claim 1 , wherein said integrated circuit is packaged in a low-profile package having a thickness of less than 1 mm and having an exposed metallic pad for heat sinking.