Background of Average Current Mode Control of Switching Power Supplies

The FYP is “Average Current Mode Control of Switching Power Supplies” which is further dived in two parts;

·         Current Mode Control (CMC)

·         Voltage Mode Control (VMC)

Now the implementation of the CMC is in SPS (Switching power supplies), that's since the inductor current control peak. CMC is often raising the few problems like the immunity of noise, compensation of slope, errors in peak to average current. Now by using the ACMC eliminate these problems, and also used for the currents control of the inductor. (Dixon, 1999)

There are two loops in the CMC which is shown in the below figure 1;

Figure 3: Peak CMC circuit an waveform

By the comparing upslope of the inductor current, the peak method for the functions of the inductor current, where an outer loop sets the current program level. When an instantaneous current reached the desired level, comparator turns the power switch off. Ramp current is tiny which is compared at the programming level when V_INis low. Into the Control circuit, the friction of the volt coupled is caused, by turn off immediately; the operating mode by the greater ripple obtained the result of the sub harmonic. For the successful operation, the circuit layout and the bypassing are critically important (Chunxiao & Lclunun, 1999).

SPS is hidden by the inner current loop that simplifies a control loop of an external voltage and enhances the performance of the power supply in various methods, involving the improved dynamics. To control the average inductor current of the state space is the purpose of the inner. If the ripple current of the inductor is small, then the control of inductor current peak is equivalent for the current power of the average inductor. Using the Buck topology in the SPS where the inductor is used as an output.

ACMC in Power Electronic Converter

The ACMC is the two loop technique, (inner, outer, and the voltage) in power electronics. There are many applications which are used in the higher switching, frequency, as well as the lower power segment at the changing frequency. The main features of the ACMC is compared by the current mode control , where the ACMC is used as the high gain by the wide bandwidth as a CEA current error Amplifier for the average force of the current by the converter, in the inductor current as demand is the reference current of the small error. The Advantage of the ACMC is include for the large noise margin , where the additional requirements for the slope compensations , is easy for the current limit of the implementation , and the excellent voltage as well as the regulation of current , in continuous and discontinuous modes of inductors. ( Purton & et.al, 2002)

Principle of Operation of Average Current Mode Control of Switching Power Supplies

The implementation of the ACMC for the analog amplifiers is used as the error amplifier plus utilize the wide band sensing of the inductor current where it include the DC and AC components. Below figure presents the basic buck converter by the synchronous rectification. The waveform of voltage is representing by the inductor current which is connected by the input of the CEA through the large gain of the DC as well as low frequencies for the average force , where the inductor current is follow the reference that is connected with other input. ( Purton & et.al, 2002)

Figure 4: Schematic of Buck converter with ACMC

Analog versus Digital Control
Analog Control of Average Current of Switching Power Supplies

There are few advantages of the analog control;

·         Relative simplicity

·         Lower cost ;wider bandwidth ;small delay among effect and cause

·         Amplitude and time of finer resolution

Now some are a disadvantage which is including;

·         Fixed relatively

·         Simple functionality

·         Noise is susceptibility

·         Drift and ageing

·         Large number of components  

Digital Control of Average Current Mode Control of Switching Power Supplies

The advantages are listed below

·         Programmability

·         Nonlinear control; adaptive

·         Possibility of self-calibration and diagnosis

Now some are a disadvantage which is including;

·         The software development is tedious

·         Time consuming

·         Expensive

·         Microcomputer suffers from noise

·         Sampling and quantization

References of Average Current Mode Control of Switching Power Supplies

Purton, K., & et.al. (2002). AVERAGE CURRENT MODE CONTROL IN POWER ELECTRONIC CONVERTERS – ANALOG. http://chamilo1.grenet.fr/ujf/courses/PGEL4107/document/Datasheet_UC3842/K-D-Purton.pdf?cidReq=PGEL4107&id_session=0&gidReq=0&origin=.

Chunxiao, S., & Lclunun, B. (1999). Modeling of Average Current Mode Control In PWM DC/DC Converters. IEEE.

Dixon, L. (1999). Average Current Mode Control of Switching Power Supplies. Unitrode APPLICATION NOTE.