What is subharmonic oscillation?

What is subharmonic oscillation?

Sub-harmonic oscillation is normally characterized by observing alternating wide and narrow pulses at the switch node. For peak current mode control, sub-harmonic oscillation occurs with a duty cycle greater than 50%.

What causes subharmonic oscillation?

The source of subharmonic oscillations is the simultaneous conditions of fixed frequency and fixed peak amplitude of inductor current as shown in part a of the accompanying figure. On each succeeding cycle the current perturbation is multiplied by S2/S1. If S2/S1 is greater than 1, the system is unstable.

What is current mode control?

Current-mode control addresses the slow response of voltage-mode control because the inductor current rises with a slope determined by the difference between the input and output voltages and hence responds immediately to line- or load-voltage changes.

What is peak current mode control?

The method is called Peak Current Mode Control, also known as Current Programmed Mode Control. One input is a sensed current, that current could be switch current or inductor current. The other input is called the control input, the value of which sets the peak value of the current, when a controller is operating.

Why slope compensation is required?

In order to avoid sub-harmonic oscillation, slope compensation is essential for peak-current mode when duty cycle is above 50%. Even though the duty cycle is below 50%, it is desirable to add a slope compensation to decrease the influence of noise.

What means current mode?

n the ratio of the electric current flowing at a particular point in a conductor to the cross-sectional area of the conductor taken perpendicular to the current flow at that point.

What is current mode boost converter?

The boost converter with current-mode control can operate successfully with just a Type II compensator and has four main characteristics. These are: a single pole at low frequency determined by the output capacitor & load resistor, an ESR zero and an RHP zero which moves with operating conditions.

What does peak current mean?

The peak current is the maximum amount of current which output is capable of sourcing for brief periods of time. When a power supply or an electrical device is first turned on, high initial current flows into the load, starting at zero and rising until it reaches a peak value, known as the peak current.

What happens to current in a buck converter?

The conceptual model of the buck converter is best understood in terms of the relation between current and voltage of the inductor. The decreasing current will produce a voltage drop across the inductor (opposite to the drop at on-state), and now the inductor becomes a current source.

What is ramp compensation?

Note that the control voltage is no longer flat as in conventional voltage-mode control, but has a negative sawtooth superimposed on it as seen in Figures 12.23 and 12.24. This is called “slope compensation” or “ramp compensation,” and it represents a possible solution to subharmonic instability.

What is voltage control mode?

Voltage mode control represents the most basic method, in which only the output voltage is returned through a feedback loop. The differential voltage, which is obtained to compare the output voltage with the reference voltage by an error amp, is compared with triangular waves by a PWM generator.