Systems and methods for reducing the magnitude of harmonics produced by a power inverter
View Patent ↗Systems and methods are provided for operating a pulse width modulation (PWM) circuit in a direct current (DC) to alternating current (AC) power inverter to reduce the magnitude of harmonics. The PWM circuit operates using a reference signal having an irregular period. In one implementation the irregular periodicity includes a sequence of periods uniformly distributed about a target period.
1. A direct current (DC) to alternating current (AC) pulse width modulation (PWM) power inverter including a set of switches and a control logic operating said set of switches based on a control signal and a reference signal, the improvement comprising:
said control signal comprising a sine wave having a frequency equal to the desired output of said power inverter; and
said reference signal comprising a triangular wave, said wave having irregular periodicity,
wherein,
said irregular periodicity comprises a sequence of a predetermined number (n) of juxtaposed different periods, said sequence exhibiting a uniform probability distribution with mean at a target period (T target ),
said n different periods differ from one another by a multiple of a fixed time value (Δt), and
an upper bound period (T upper ) and a lower bound period (T lower ) of the n different periods satisfy the following respective equations:
T lower =T target −( n×Δt )/2
and
T upper =T lower +( n×Δt ).
2. The power inverter of claim 1 wherein said power inverter comprises a single-phase power inverter.
3. The power inverter of claim 1 wherein said power inverter comprises a three-phase power inverter.
4. The power inverter of claim 1 wherein said control signal is generated by said control logic.
5. The power inverter of claim 1 wherein said reference signal is generated by said control logic.
6. A method for having a control logic perform pulse width modulation comprising:
using a control signal having regular periodicity; and
using a reference signal having irregular periodicity,
operating said pulse width modulation in a power inverter based upon said control signal and said reference signal, wherein,
said irregular periodicity comprises a sequence of a predetermined number (n) of juxtaposed different periods, said sequence exhibiting a uniform probability distribution with mean at a target period (T target ),
said n different periods differ from one another by a multiple of a fixed time value (Δt), and
an upper bound period (T upper ) and a lower bound period (T lower ) of the n different periods satisfy the following respective equations:
T lower =T target −( n ×Δt )/2
and
T upper =T lower +( n ×Δt ).
7. The method of claim 6 wherein said control signal comprises a sinusoidal waveform.
8. The method of claim 6 wherein said control signal is generated by said control logic.
9. The method of claim 6 wherein said reference signal comprises a triangular waveform.
10. The method of claim 6 wherein said reference signal is generated by said control logic.
11. The method of claim 6 wherein said power inverter comprises a single-phase power inverter.
12. The method of claim 6 wherein said power inverter comprises a three-phase power inverter.