Driver for electrochromic glass unit
A method for controlling an electrochromic device is provided. The method includes applying a constant supply current to the electrochromic device and determining an amount of charge transferred to the electrochromic device, as a function of time and current supplied to the electrochromic device. The method includes ceasing the applying the constant supply current, responsive to a sense voltage reaching a sense voltage limit and applying one of a variable voltage or a variable current to the electrochromic device to maintain the sense voltage at the sense voltage limit, responsive to the sense voltage reaching the sense voltage limit. The method includes terminating the applying the variable voltage or the variable current to the electrochromic device, responsive to the determined amount of charge reaching a target amount of charge.
1. A method for controlling an electrochromic device, comprising:
determining an amount of charge transferred to the electrochromic device, as a function of time and current supplied to the electrochromic device;
applying one of a variable voltage or a variable current to the electrochromic device to maintain a sense voltage, measured at one or more sense voltage terminals of the electrochromic device, at a sense voltage limit, responsive to the sense voltage reaching the sense voltage limit, wherein the one or more sense voltage terminals are distinct from voltage source bus bars of the electrochromic device;
terminating the applying the variable voltage or the variable current to the electrochromic device, responsive to the determined amount of charge reaching a target amount of charge;
reversing a polarity of a reversible constant current supply, wherein the reversible constant current supply applies a constant supply current with the reversed polarity to the electrochromic device;
reversing a polarity of a reversible variable voltage supply, wherein the reversible variable voltage supply applies the variable voltage with the reversed polarity to the electrochromic device, and wherein the sense voltage limit is zero volts; and
delaying the terminating for a predetermined amount of time during which the sense voltage is held at zero volts.
2. The method of claim 1 , wherein terminating occurs after reaching a desired transmissivity of the electrochromic device equating to the target amount of charge.
3. The method of claim 1 , further comprising:
measuring the sense voltage of the electrochromic device; and
measuring a current supplied to the electrochromic device, wherein determining the amount of charge is based on summing digital values of the current over a span of time.
4. The method of claim 1 , wherein determining the amount of charge transferred to the electrochromic device comprises:
integrating, over time, a current supplied to the electrochromic device.
5. The method of claim 1 , wherein once the amount of charge transferred equals the target amount of charge to be transferred the driver starts voltage process comprising measuring voltage at the one or more sense voltage terminals.
6. The method of claim 1 , wherein the sense voltage is held at zero volts to rezero the driver as to the state of charge of the electrochromic device.
7. The method of claim 1 , wherein determining the amount of charge transferred to the electrochromic device further comprises:
applying analog to digital conversion to a current supplied to the electrochromic device, to produce a digital value of the current supplied to the electrochromic device; and
adding values from a time series of the digital value of the current supplied to the electrochromic device.
8. The method of claim 1 , wherein:
the variable voltage or the variable current is supplied to the voltage source bus bars of the electrochromic device; and
the sense voltage is measured from the one or more sense voltage terminals of the electrochromic device located elsewhere on the electrochromic device than the voltage source bus bars.
9. The method of claim 1 wherein the sense voltage is measured from an edge of the electrochromic device.
10. The method of claim 1 , further comprising:
monitoring the sense voltage; and
applying one of a charge or a discharge to the electrochromic device, responsive to a deviation of the sense voltage, after a predetermined relaxation time, by more than a predetermined relaxation amount of voltage.
11. The method of claim 1 wherein if a state of charge does not match the target amount of charge a sequestration process is initiated.
12. The method of claim 1 , wherein a sequestration process is initiated every time a fully bleached state is met.