Power conversion device superimposing a tertiary harmonic wave
View Patent ↗A power conversion device includes a three-phase voltage inverter, a two-phase/three-phase converter, a tertiary harmonic wave generator, an adder, a PWM controller, and a tertiary harmonic wave amplitude determining unit. The tertiary harmonic wave generator generates a sinusoidal tertiary harmonic wave signal synchronized with three-phase voltage command signals and having a frequency which is three times as high as that of the three-phase voltage command signal. Further, the tertiary harmonic wave generator includes a tertiary harmonic wave amplitude determining unit for determining the amplitude of the tertiary harmonic wave signal at which the power loss of a three-phase voltage inverter is minimized, based on a voltage amplitude command value responding to two-phase voltage command signals and an output power factor command value responding to an output request to a power system.
1. A power conversion device comprising:
a three-phase voltage inverter that includes a circuit having three legs connected in parallel, each of the legs including two arms connected in series and each of the arms including a switching element and a freewheeling diode connected to each other in antiparallel, and that converts a DC voltage from a DC power supply into a three-phase AC voltage and outputs the three-phase AC voltage to a power system;
a two-phase/three-phase converter for converting a two-phase voltage command signal into a sinusoidal three-phase voltage command signal;
a tertiary harmonic wave generator for generating a sinusoidal tertiary harmonic wave signal synchronized with the sinusoidal three-phase voltage command signal and having a frequency which is three times as high as that of the sinusoidal three-phase voltage command signal;
an adder for outputting a three-phase modulated wave signal in which the sinusoidal tertiary harmonic wave signal is superimposed on the sinusoidal three-phase voltage command signal; and
a PWM controller for generating a gate signal for driving each of the switching elements by comparing the three-phase modulated wave signal with a triangular wave carrier signal, wherein the tertiary harmonic wave generator includes a tertiary harmonic wave amplitude determining unit for determining an amplitude of the sinusoidal tertiary harmonic wave signal at which a power loss of the three-phase voltage inverter is minimized, based on a voltage amplitude command value responding to the two-phase voltage command signal and an output power factor command value responding to an output request to the power system,
wherein the two-phase voltage command signal includes a d-axis voltage command signal and a q-axis voltage command signal, and the voltage amplitude command value is a square root of a sum of a square value of the d-axis voltage command signal and a square value of the q-axis voltage command signal.
2. The power conversion device according to claim 1 , wherein the tertiary harmonic wave amplitude determining unit determines the amplitude of the sinusoidal tertiary harmonic wave signal corresponding to a combination of the voltage amplitude command value and the output power factor command value from a table for defining a relationship of the voltage amplitude command value, the output power factor command value, and the amplitude of the sinusoidal tertiary harmonic wave signal at which the power loss of the three-phase voltage inverter is minimized.
3. The power conversion device according to claim 1 , wherein the tertiary harmonic wave amplitude determining unit determines the amplitude of the sinusoidal tertiary harmonic wave signal based on a function having the voltage amplitude command value and the output power factor command value.