System and method for burner ignition using sensorless constant mass flow draft inducers

1. A motor controller for a burner system including a draft inducer fan configured to draw air through an airflow path through the burner system, and a vacuum switch, said motor controller comprising:

an inverter configured to supply current to a motor configured to rotate the draft inducer fan; and

a processor communicatively coupled to said inverter, wherein said processor is configured to:

receive a draft inducer control signal from a system controller;

determine a first mass flow rate based on a target mass flow rate to be generated by the draft inducer, wherein the first mass flow rate is greater than the target mass flow rate;

compute a starting speed based on the first mass flow rate using a mass flow curve;

instruct, in response to the draft inducer control signal, said inverter to supply a first current during a first period to said motor to rotate the draft inducer fan at the computed starting speed to produce a first mass flow through the burner system, the first mass flow having the first mass flow rate; and

instruct said inverter to supply a second current, during a second period starting at an expiration of the first period, to said motor to rotate the draft inducer fan to produce a second mass flow through the burner system, the second mass flow having the target mass flow rate for normal operation of the burner.

2. The motor controller of claim 1 , wherein the processor is configured to determine the first mass flow rate by multiplying the target mass flow rate by a factor of at least 1.2.

3. The motor controller of claim 1 , wherein the mass flow curve is expressed as either a formula or a lookup table stored in a memory.

4. The motor controller of claim 1 , wherein the processor is further configured to determine the second mass flow based on the target mass flow rate using a mass flow curve.

5. The motor controller of claim 4 , wherein the mass flow curve is expressed as either a formula or a lookup table stored in a memory.

6. The motor controller of claim 1 , wherein the first period has a duration of at least 30 seconds.

7. A method of operating a motor for a draft inducer in a burner system, the motor coupled to a draft inducer fan configured to move air though an airflow path of the burner system, said method comprising:

receiving, by a motor controller configured to supply current to the motor, a draft inducer control signal from a system controller;

determine, by the motor controller, a first mass flow rate based on a target mass flow rate to be generated by the draft inducer, wherein the first mass flow rate is greater than the target mass flow rate;

calculating, by the motor controller, a starting speed based on the first mass flow rate using a mass flow curve;

supplying, in response to the draft inducer control signal, a first current, during a first period, to the motor to rotate the draft inducer fan at the calculated starting speed to produce a first mass flow through the burner system, the first mass flow having the first mass flow rate; and

supplying a second current, during a second period starting at an expiration of the first period, to the motor to rotate the draft inducer fan to produce a second mass flow through the burner system, the second airflow having a target mass flow rate for normal operation of the burner.

8. The method of claim 7 , further comprising determining, by the motor controller, the first mass flow rate by multiplying the target mass flow rate by a factor of at least 1.2.

9. The method of claim 7 , wherein the mass flow curve is expressed as one of a formula and a lookup table stored in memory.

10. The method of claim 7 , further comprising calculating, by the motor controller, a second speed corresponding to the second mass flow based on the target mass flow rate using a mass flow curve.

11. The method of claim 10 , wherein the mass flow curve is expressed as at least one of a formula and a lookup table stored in memory.

12. The method claim 7 , wherein the first period has a length of at least 30 seconds.

13. A burner system comprising:

a burner;

a heat exchanger;

a collection manifold;

a motor coupled to and configured to turn a draft inducer fan configured to draw an airflow through an airflow path from said collection manifold and across said burner and through said heat exchanger;

a vacuum switch configured to actuate when a mass flow rate through the airflow path is sufficient to produce a vacuum above a vacuum threshold, thereby enabling operation of said burner; and

a motor controller coupled to said motor and configured to:

receive a draft inducer control signal from a system controller;

determine a first mass flow rate based on a target mass flow rate to be generated by the draft inducer, wherein the first mass flow rate is greater than the target mass flow rate; and

calculate a starting speed based on the first mass flow rate using a mass flow curve;

operate said motor, during a first period, to rotate said draft inducer fan at the calculated starting speed to produce a first mass flow through the airflow path, the first mass flow having the first mass flow rate; and

operate said motor, during a second period starting at an expiration of the first period, to rotate said draft inducer fan to produce a second mass flow through the airflow path, the second mass flow having the target mass flow rate for normal operation of the burner.

14. The burner system of claim 13 , wherein the motor controller is further configured to determine the first mass flow rate by multiplying the target airflow rate by a factor of at least 1.2.

15. The burner system of claim 13 , wherein the mass flow curve is expressed as one of a formula and a lookup table stored in a memory.

16. The burner system of claim 13 , wherein the motor controller is further configured to calculate a second speed based on the target mass flow rate using a mass flow curve.

17. The burner system of claim 16 , wherein the mass flow curve is expressed as at least one of a formula and a lookup table stored in a memory.