__________ method is an internal method for controlling the inverter output voltage.

Question

Examoogle · Accepted Answer

Pulse width modulation

Explanation: Pulse Width Modulation (PWM) is an internal control technique where the inverter's switching states are adjusted to control the output voltage magnitude and frequency. By varying the width of the output pulses, the average output voltage can be regulated without needing external components.

Working Principle: In PWM, the power semiconductor switches (IGBTs/MOSFETs) are turned on and off multiple times within a single half-cycle. By changing the duty cycle (the ratio of pulse width to pulse period), the fundamental component of the output voltage is controlled. This eliminates the need for bulky external voltage regulation circuitry.

Key Formulas: $V_{rms} = V_s \sqrt{\frac{D}{T}}$ — RMS output voltage of a PWM inverter; $V_{avg} = V_s \cdot D$ — Average DC component

Key Points: PWM allows for simultaneous control of output voltage and frequency.; It significantly reduces lower-order harmonics, improving power quality.; Internal control means no external auxiliary components like choppers or tapped transformers are required.; The switching frequency of PWM is generally much higher than the fundamental output frequency.

Advantages: Reduced harmonic distortion; Simplified power circuit; High efficiency due to switching control

Disadvantages: Higher switching losses in devices; Requires complex control circuitry (microcontrollers/DSP)

Applications: Variable Frequency Drives (VFDs); Uninterruptible Power Supplies (UPS); Renewable energy grid-tie inverters

Additional Info: External methods for voltage control include using an AC voltage regulator or a DC-DC chopper before the inverter.. Option B (Chopper) is an external method usually placed between the DC source and the inverter bridge.

Answer: D is correct — Pulse Width Modulation (PWM) is an internal control technique used to vary the output voltage by modulating the duration of the conducting state of the inverter switches.

Exam Tip: Always distinguish between 'Internal Control' (performed by switching within the inverter) and 'External Control' (performed by modifying input DC or output AC via external components).

Related Questions

Discussion (0)