Literature review of Average Current Mode Control of Switching Power Supplies

        According to author Saini & et.al, (2016) it is conducted that; the ACMC for the Buck DC-Dc Converter is used for the reduction of the Voltage control Ripple control the different application like the LED lighting, correctors for the power factors and the battery charger, and eliminate the above problem the ACMC is preferred for this solution. In the two-loop converters of dc-dc, this is also a significant and well solution. The inherent benefits include; more resistance to noise, the invisibility of logic or digital circuits, and there are no requirements when it comes to slope compensation. At a point for achieving the best proportional gain, the amplifier of current error was crafted (N.Vishwanathan & V.Ramanarayanan, 2002). That point is where the inductor current's down-slope and saw-tooth voltage's upslope implemented to the modulator of pulse-width are equal to each other. But a higher ripple of inductor current was reached with this high gain; a proportional amplified component of the ripple was contained in the control voltage which can intersect the waveform of sawtooth voltage more than only once over every period of switching. Due to it, an instability in switching was created posing a restriction on both the sensed current at peak and duty cycle. Because of an error amplifier, a pole of high frequency deletes the component of switching frequency in the current that is sensed. This pole guarantees only the optimal condition of a slope, but when it comes to specific and clear sensing of current, nothing is contributed by it. This FYP paper or project proposes a technique for overcoming the above limitations which regulate and tracks the DC or actual average current in converter's every branch (Saini & et al., 2016).

For CMC of SMPS, the comparison and analysis of the model are explained according to the author Kotecha, (2010), In this case, the ACMC method is a different application of the CMC method. Instead of controlling the peak current, the controlled one is an average current of an inductor. The RC network is compensating, and the external ramp compensates the average flow of ramp dynamically. When control schemes which are conventional are concerned, a set program is followed by the peak current of an inductor which offers compensation that is fixed or absolute. As, the best source of flow, PWM converter of dc-dc behaves and provides  benefits as compared to other control schemes. At a 50 percent duty ratio, this projector model exhibits sustained oscillations. For improving the power-factor, this model is efficient in boost converters because the input current illustrates the current of an inductor in a unique topology. After the utilization of analysis of discrete time, a small-signal model was crafted like past procedures. The further compensation of the average current is sensed by a network of RC circuit ( Kotecha, 2010).

According to the author Ramya he has compared the peak and average current mode control of bridgeless fly back rectifier that has been improved through the help of bidirectional switch. The outer loop regarding the voltage feedback is employed by control schemes for maintaining voltage of output as an inner loop and a constant. For obtaining a regulated and constant voltage at the output by changing input voltage and this can be done through average and peak current mode control of fly back rectifier. This can be done through closed loop control scheme. Through this control scheme it can be seen that the current through the inductor is extremely high and this increase many issues in the circuit.

These serious issues include peak to average current errors, a need for slope compensation and poor noise. The voltages at the reference have been increased through multiplying the output voltage error and the rectified input voltage. Through the use of this control method technique there is better load regulation and also line voltage with the help of inner loop of current and compared with the voltage mode control. For getting improved and high power fly back rectifier with low losses a quite improved fly back rectified can be made. In that bridgeless control there is only one switch that is attached with a common gate drive, diode and also there is another winding at the secondary side of the rectifier. The positive point is that the weight of the rectifier is not affected with these additional components.

This kind of rectifier can be used as the adaptor. In this paper there is discussion on some designs of average current mode control with its software simulations and also with hardware results. The output rating of this rectifier was noted as 12 Volts and 1.5 Ampere current. In this paper different control topologies has been simulated but in the end the most suitable topology is the control method for fly back because this topology was involved in sensing the input voltage and then according to that it regulate the output voltage (Chandranadhan & Renjini.G, 2015).

In this paper the author chen has given a new digital technique for charge the battery and achieve a constant voltage and current at the output and there is no requirement of any feedback control. The main idea for achieving constant current at the output and this can be achieved through limiting the duty cycle of these chargers. As the voltages of battery have been increased to the present voltage level through the use of constant current mode then after this the control mode shift its self towards the constant voltage mode. This type of digital controlled chargers is used for charging the battery of UPS. In this paper there are different controls methods are proposed through the help of software. Also in this paper there are some experimental results has been showed that will demonstrate the effectiveness of this design and its implementation (Chen & Lai, 2012).

In this paper the author David has given the idea about the universal input single stage, high power factor power supply for high brightness LEDs that was based on integrated buck fly back converter. The high brightness LEDs have become a very important researched because these LEDs are used in many applications. In this paper, the streetlight has been implemented with the implementation of the integrated buck fly back converter that has been developed in the past. In this application the use of converter is just basically for giving proper power factor correction from the output of the AC source. The LM3524 IC is used for the control loop.

 This IC has been implemented for checking the feasibility of the converter in dimming mode.   In the first step the load of the LED is liberalized means constant voltages are applied at the output. Then for calculating the proper IBFC topology the load of the LED has been moulded properly according to that and then after this in the second step this converter has been designed and then tested in the lab. And for the fixed frequency and constant current control at the output the converter has been moulded according to that. In this paper there are some simulation results of this controller and then these simulation results has been tested by the experimental results (Gacio, Alonso, Calleja, García, & Rico-Secade, 2011).

In this paper the author has discussed the fast switching control topology that will be used for series parallel tuned LCL. In this paper the author has proposed this idea for inductive power transfer system. In this topology there is use of an idea of traditional controlled rectifiers and these rectifiers are involved in giving regulated output voltage at the output through the rectifier. This topology has the ability to provide continuous power regulation as well as the smooth power transitions between the two main states of the switch and these are on and off state. Due to this condition the rectifier controller was involved in giving proper output voltage through the rectifier. Then after this in this paper there is steady stated analysis of this topology has been presented and this has been implemented through the real and reactive power.

In this paper there are some SPICE simulations of this topology. Then after this these all results are verified with the help of hardware simulations by setting the power at 1.5 kW and dc voltages are at 300 volts. The hardware results show the efficiency of dc output pickup controller at 95% and that has been recorded at full load and when this is operated at one third of the rated power so still its efficiency is above than 85%. In this paper there is complete design of LCL pickup controller has been proposed. This kind of rectifier can be used as the adaptor. In this paper there is discussion on some designs of average current mode control with its software simulations and also with hardware results.

This controller was involved in providing a continuous power control at the output from no load to a full load. There are two modes for the proposed controller in the paper. A specified steady state AC analysis with their unique characteristics has been presented in this paper of these two modes (Huang, Boys, & Covic, 2013).

In this paper the author Ying Qiu has discussed about the digital average current mode control of the digital average current mode control of PWM DC-DC converters without use of current sensors. In this paper there is use of digital average mode control technique for the pulse width modulation. And for the fixed frequency and constant current control at the output the converter has been molded according to that. The controller was designed to control and estimate the current of the inductor in the DC-DC converters and this can be done through the help of first order discrete time low pass filter. The main aim of this paper is the design of this first order low pass filter so that this controller is able to calculate average current of the inductor after every switching cycle means that as the positive cycle come these controllers calculate the current through the controller.

In this paper there is technique that will investigate the inductor current from the DC-DC converter by just setting the value of the duty cycle so that this method estimate the average current through the inductor and then after this remove all types of errors from the estimated inductor current and the calculated inductor current from the circuit. For this control technique an algorithm has been designed and this was based on two loop control structure that was involved in giving accurate and regulated voltages at the output of the converter and this can be achieved with the help of just basic converters that are known as the buck-boost, buck and boost converters. In this article there is discussion about these controllers design and their simulations on the MATLAB. Then after this there are some experimental results of this controller that has been seen through hardware simulations (Ying Qiu & Chen, 2010).

According to the authors Leon he has given the sliding mode control scheme that was based for boost converters and this technology is used for high voltage and low power applications. In this paper there is complete design and its analysis of the high voltage boost converter that was operating between the two phases. The first phase is continuous conduction mode and the other one is the discontinuous conduction mode. The converter is operated with the help of 12 volt battery from the car and there is 1200 volts at the output of the DC-DC boost converter with the gain of 100.

In this design of boost converter for switching there is use of hysteretic comparator. And through the use of this comparator it decreases the risk of modular saturation and also helps the converter to operate in both modes. The sliding mode technique is used in this converter for stabilizing the dynamic behavior of the switching regulator of the boost converter and also for the stability of the system. Through the use of silicon carbide devices the performance of the converter can be investigated for power switch realization. There are also some applications of this design that include efficient lighting system that is based on LED (Leon-Masich, Valderrama-Blavi, Bosque-Moncusí, & Maixé-Altés, 2015).

In this paper the author Jian Li has proposed a new modelling approach as well as the equivalent circuit representation for the current mode control has been designed. For improving the efficiency of the light load systems on time current mode control has been used, through the use of this technology there is reduction in the switching frequency can be seen for minimizing switching loss. In this paper there is proper design for the constant on time control of the current mode control. There are some past models for constant on time control but these models are unable to give ideal response.

 In this paper there is new model for the constant on time control. In this paper through the help of proposed model the fundamental difference and the constant frequency and peak current mode control has been analyzed in proper way with simulation. The propose modelling method that has been proposed in this paper can be extended to other current mode controls like V² controls. In this paper there is complete simulation and experimental has been presented for this proposed model of constant on time current mode control (Li & Lee, 2010).

According to the author Miguel he has proposed a design for average inductor current sensor that can be used for digitally controlled switched mode control for the power supplies. For the two signals that are the current and voltages there is a need of analogue to digital conversion for the digital controlled switched power mode supplies.

Through the use of window analogue to digital converter the complexity of the voltage analogue to digital converter can be easily reduced. But on the other side for current analogue to digital conversion there is need of high range of resolution required for wide range of signals this phenomenon increased the complexity during the power conversion. In this paper there is a design of simple feedback sensor and this sensor is capable of average the high current through the inductor. This can be done through the help of two analogue comparators as well as the low pass filter. Through the use of this approach there are very low external components and also very low use of digital hardware resources. In this paper proper experimental result with the help of simulations has been presented. This can be done by giving 12 voltages at the input and achieve 19 volts at the output of the converter. The main application of this sensor is in the digitally controlled 400 watt and 400 volts boost converter (Rodr´ıguez, Lopez, Azcondo, Sebastian, & Maksimovic, 2012).

Control Scheme of Average Current Mode Control of Switching Power Supplies

Voltage Mode Control Scheme of Average Current Mode Control of Switching Power Supplies

For this scheme the circuit diagram shown in the figure below. Its single voltage feedback path is the major advantage of this circuit wherein by comparing the waveform the duty ratio is controlled that is obtained from the resulting error voltage through the operational amplifier along with the ramp that is fixed. To design and analyze owing it to the single loop so this circuit topology is easy. In voltage mode control the modulation is stable due to the high ramp amplitude. Due to low impedance at the output cross-regulation is better compared to current-mode control. Moreover, there are the following disadvantages of this technique and because of their disadvantages this could not be used in certain application these are given below;

1.      As compared to the current-mode control voltage-mode control has the slow response due to any change by the change in output voltage in input voltage or else load resistance would be first required to be sensed. In the input voltage as well as load resistance the voltage feedback loop will then correct any changes.

2.      In the feedback loop the RC-circuit at the output adds an extra pole. Moreover, through the controller a zero would be required.

3.      With the change in line voltage the open loop gains of the circuit changes. 

Figure: boost converter voltage mode control

Current Mode Control Scheme of Average Current Mode Control of Switching Power Supplies

In most power supply topologies the disadvantages of the voltage-mode control are important as well as by this scheme most of these were effectively alleviated. For designing the control circuits current mode control schemes become popular as compared to other scheme of control. As in the figure you can see the circuit diagram for the current-mode control. Multi loop scheme is used in this current mode control scheme. The peak value of the inductor current controls by the inner loop, output voltage is controlled by the outer voltage loop. This is quite complicated modelling than the voltage-mode control also requires modelling of sampled data. Short circuit protection is provided by these schemes as well as in PWM converters over current protection. The response of this scheme is fast as well as wide band. There is also some limitation of this scheme which we discussed here;

1.      In this method with two current loops the circuit analysis becomes difficult.

2.      At the duty ratio 0.5 the control loop has inherent instability. The following things that made more complication while analyzing such as higher duty cycles, slope compensation,

3.      It produces noise in the loop when the ripple produces due to the small amount of current.

4.      Since the control loop is forcing a current drive load regulation is significantly affected.

It is clear from the above disadvantages although this scheme alleviates the restriction through the voltage-mode control, for the operation of PWM converters it is still not the optimum mode of control. In reality, in the power control technology indicates the recent development.

Figure: dc-dc buck converter operating under current mode control scheme.

Because of the new controller that help to control the flows of voltage mode control. By providing feed-forward voltage this controller significantly enhance the design of voltage-mode control to the changes in the input voltage as well as resulting in smaller parasitics by using BicMOS. The voltage feed-forward could be achieved if the compensating ramp is made proportional to the input voltage. Without providing the voltage feed-back the control modulation is accomplished. Moreover, this eliminated the problem of slow response. In high frequency capabilities these design changes result as well as for RC-circuit higher bandwidth at the output. In voltage mode several problems of the earlier topologies have been improved in the controller. 

 Peak CMC problem of Average Current Mode Control of Switching Power Supplies

There are various problems in the peak Current mode control; like

·         Poor noise immunity

·         Current error peak to average

·         The necessity of Slope Compensation

·         Topology problem

Figure 5: Buck Converter with ACMC in the inner loop

The circuit which is shown as above is the ACMC for the buck-buck converters to reduce the ripple voltage of control. A buck converter includes of the inductor L, a filter capacitor C, a switch S, a diode D_o, as well as a load resistor RL. Above figure present the duty cycles D, and the switching frequency. The output voltage and supply voltage are VA and VI respectively. For sensing the inductor current, Rs or the resistance is put within the inductor branch. Across Rs for determining the potential difference, a different amplifier of unit gain is used. Meanwhile, its VRs or sensed voltage is its output. To a low-pass filter's input, VRs voltage is delivered while the filter is designed for eliminating the ripple component of the switching frequency. Considering the equality between VRI, the reference voltage, and VPI, the filter's output voltage, an amplifier which is non-inverting that is used with a  finite gain. Vel or control voltage at the controller’s output is compared with V_saw, the saw tooth signal which produces D, the necessary duty cycle. (Saini & et.al, 2016)

References of Average Current Mode Control of Switching Power Supplies

Kotecha, R. M. (2010). Analysis and Comparison of Popular Models forCurrent-Mode Control of Switch Mode Power Supplies. INDIA: Wright State University.

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=.

Chandranadhan, R., & Renjini.G. (2015). Comparison Between Peak and Average current. IEEE International Conference on Technological Advancements in Power & Energy.

Chen, B.-Y., & Lai, Y.-S. (2012). New Digital-Controlled Technique for Battery. IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, 59(3).

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.

Gacio, D., Alonso, J. M., Calleja, A. J., García, J., & Rico-Secade, M. (2011). A Universal-Input Single-Stage High-Power-Factor Power Supply for HB-LEDs Based on Integrated Buck–Flyback Converter. Manuel Rico-Secade, 58(2), IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS.

Huang, C.-Y., Boys, J. T., & Covic, G. A. (2013). LCL Pickup Circulating Current Controller. IEEE TRANSACTIONS ON POWER ELECTRONICS, 28(4).

Leon-Masich, A., Valderrama-Blavi, H., Bosque-Moncusí, J., & Maixé-Altés, J. (2015). Sliding- Mode Control- Based Boost. IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS .

Li, J., & Lee, F. C. (2010). New Modeling Approach and Equivalent Circuit. IEEE TRANSACTIONS ON POWER ELECTRONICS, 25.

N.Vishwanathan, & V.Ramanarayanan, D. (2002). Average Current Mode Control of High Voltage DC Power Supply for Pulsed Load Application. IEEE.

Rodr´ıguez, M., Lopez, V. M., Azcondo, F. J., Sebastian, J., & Maksimovic, D. (2012). Average Inductor Current Sensor for Digitally Controlled Switched-Mode Power Supplies. IEEE TRANSACTIONS ON POWER ELECTRONICS, 27(8).

Saini, D., & et.al. (2016). Average Current-Mode Control of Buck DC-DC Converter With Reduced Control Voltage Ripple. IEEE, 3070-3075.

Ying Qiu, H. L., & Chen, X. (2010). Digital Average Current-Mode Control of PWM DC–DC Converters Without Current Sensors. IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, 57(5).