Methods and apparatuses for controlling output voltages of inverters driving of electric motors

An apparatus for controlling an output voltage of an inverter driving an electric motor, the apparatus comprising:

• a low pass filter (LPF) configured to remove harmonic components of an output current, which is output to the electric motor, to obtain a fundamental component of the output current;
• a current total harmonic distortion (THD) calculation unit configured to calculate a current THD by using the fundamental component of the output current;
• a modulation method determination unit configured to compare the current THD with a reference current THD and configured to determine a pulse width modulation (PWM) method to be changed from a first modulation method for reducing the harmonic components of the output current to a second modulation method for reducing a switching frequency of the inverter if the current THD is less than the reference current THD, the PWM method modulating a pulse width of a control pulse signal for controlling the output voltage of the inverter;
• and
• a control pulse signal generation unit configured to generate the control pulse signal based on the determined PWM method.

A system for driving an electric motor, the system comprising:

• a current detector configured to detect an output current which is output to the electric motor;
• a control apparatus configured to determine a pulse width modulation (PWM) method for modulating a pulse width of a control pulse signal based on a current total harmonic distortion (THD) of the output current and configured to generate the control pulse signal based on the determined PWM method;
• and
• an inverter configured to convert an input power supply into an output voltage based on the control pulse signal and configured to supply the output voltage to the electric motor;
• wherein the control apparatus comprises:
• a low pass filter (LPF) configured to remove harmonic components of the output current to obtain a fundamental component of the output current;
• a current THD calculation unit configured to calculate the current THD by using the fundamental component of the output current;
• a modulation method determination unit configured to compare the current THD with a reference current THD and determines the PWM method to be changed from a space vector pulse width modulation (SVPWM) technique to a discontinuous pulse width modulation (DPWM) technique;
• and
• a control pulse signal generation unit configured to generate the control pulse signal based on the determined PWM method.