FIELD OF THE INVENTION:
The present invention relates to control of power conversion apparatus, and more
particularly, to switching power converter apparatus and methods of operation thereof.
BACKGROUND ART:
Switching power converters are used to convert a direct current (DC) voltage into a
different, stable DC voltage with high efficiency. They are often used in electronics, such as
mobile phones, computer equipments, automobile etc. Switching power converter circuits
often include one or more switching elements, such as metal-oxide semiconductor FETs
(MOSFETs), that selectively couple a DC power source to an inductor, such that the inductor
is periodically charged and discharged to produce a DC output voltage. They also
alternatively couple and decouple a voltage source to a load. An output filter, such as one
comprising an inductor and a capacitor, removes high frequency switching noise to produce
the desired average output voltage.
Very common switching converters are the boost converter, buck converter, buck/boost
converter and fly-back converter. To achieve a larger bandwidth, an additional freewheeling
switch is sometimes incorporated across the inductor in comparison to their conventional
counterparts. These modified topologies are basically the tri-state, due to presence of an
additional mode, version of their conventional circuit configurations.
A controller controls the switching components to maintain a substantially average output
voltage over the load. A combination of feedback and feed-forward loops provides inputs to
the controller. There is only one feedback loop, which generally senses a level of an output
voltage across the load and desired reference voltage, in feedback, to the controller. Feed-
forward loops generally sense an input voltage, a current through the load, the reference
voltage, in forward paths to the controller. The controller typically adjusts the duty ratio
(i.e., the portion of time that the output is switched high relative to the switching period) of
the switching components in order to control the average voltage output by the output
filter.
Over the last decade, several control methods, applied on such kind of dc-dc converter
topologies, have been reported [1] K. Viswanathan, R. Oruganti and D. Srinivasan, "A Novel
Tri-State Boost Converter With Fast Dynamics", IEEE Transactions on Power Electronics,
Vol. 17, No. 5, pp.677-683, Sept 2002; [2] K. Viswanathan, R. Oruganti and D. Srinivasan,
"Dual-Mode Control of Tri-State Boost Converter for Improved Performance", IEEE
- 2 -

Transactions on Power Electronics, Vol. 20, No. 4, pp.790-797, July 2005;[3] D. Ma, W. H.
Ki and C. Y. Tsui, "A Pseudo-CCM/DCM SIMO Switching Converter With Freewheel
Switching", IEEE Journal of Solid-State Circuits, Vol. 38, No. 6, June 2003;[4] D. Ma and W.
H. Ki, "Fast-Transient PCCM Switching Converter With Freewheel Switching Control" IEEE
Transactions on Circuits and Systems-II: Express Briefs, Vol. 54, No. 9, September
2007;[5] M. Veerachary, "Signal flow graph modelling of multi-state boost DC-DC
converters", IEE Proc.-Electr. Power Appl., Vol. 151, No. 5, September 2004;[6] S. Kapat,
A. Patra and S. Banerjee, "A Novel Current Controlled Tri-State Boost Converter with
Superior Dynamic Performance", ISCAS, Proceeding of IEEE, May, 2008.
Most of the above techniques consider a method combined of a voltage controller and a
current controller. Moreover, the control signal of the current controller comprises the input
voltage, reference voltage and average load current related by multiplication and division. It
makes them complicated and costly. A current controller has been considered in [6], where
the overall closed loop control is based on the current control comprising of one feed-back
loop consisting of both the output voltage and the reference voltage and another feed-
forward loop connected to the reference voltage. Though, transient performance is
significantly improved, efficiency degrades with decreasing load.
US 7170267 relates to a system and method control an output voltage across a load using
current mode control to control current through an output filter connected to the load. The
output voltage across the load is compared with a reference voltage to generate a reference
current signal indicative of a desired average current through the load. A control signal is
generated to indicate when an output current is greater than the desired output current.
The output filter is alternately coupled to a first supply rail and to a second supply rail in
response to the control signal to generate an average current through the load.
US 6744647 is directed to a power converter apparatus includes an input port and an output
port. First and second inductors are coupled to the output port. A first switching circuit is
coupled to the input port and the first inductor. The first switching circuit is operative to
repetitively perform a cycle including a first state in which the first switching circuit couples
the first inductor to the input port such that energy is transferred from the input port to the
first inductor, a second state in which the first switching circuit short circuits the first
inductor, and a third state in which the first switching circuit decouples the first inductor
such that energy is transferred from the first inductor to the output port. A second switching
circuit is coupled to the input port and the second inductor and implements a similar cycle.
The second switching circuit may operate such that the first and second states of the second

switching circuit substantially coincide with the third state of the first switching circuit.
Related methods are also described.
OBJECTS OF THE INVENTION:
It is thus the basic object of the present invention to provide for a more simple and effective
controller for a dc-dc converter with a freewheeling of the inductor current.
Another object of the invention is directed to a control system for a dc-dc converter which
would be adapted to encompass a wide range of the input voltage and the load current
without going into instability.
A further object of the present invention is directed to a fast response energy efficient
current control methodology for a Dc-Dc Converter with freewheeling switch which would be
adapted for any converter with freewheeling switch.
Another object of the invention is directed to the provision of a current control
methodology/systems involving the same for variety of end uses and applications which
would with two reference currents (Iref+ and Iref-) for a dc-dc converter with a
freewheeling switch result in a large closed loop bandwidth.
A further object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses wherein Iref+ could be
obtained from a feedback loop comprising the output voltage and the reference voltage
along with a compensator to improve the voltage regulation and dynamic response.
A further object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses wherein the Iref- with a
manually adjustable voltage and its implementation would be adapted to adjust the
freewheeling interval and improve the dynamic performance compared to voltage mode
method.
Yet further object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses wherein the Iref- with
reference voltage feed-forward and its implementation would provide an opportunity for an
adjustable voltage regulation with tri-state operation and improves the regulation
characteristics.

Another object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses wherein Iref- with input
voltage feed-forward and its implementation would enlarge the range of input voltage with
tri-state operation and improves the line regulation as well as audio susceptibility.
A further object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses wherein the Iref- with load
current feed-forward and its implementation would enlarge the range of the load current
with tri-state operation and improves the load regulation.
Yet another object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses which would favour
efficient and selective switching during transient and steady state to enhance the efficiency.
Another object of the invention is directed to the provision of a current control
methodology/system involving the same for variety of end uses wherein the switching of the
pair of switches would be selectively controlled whereby MOSFETs Slwould be adapted to
be controlled throughout, but S2 will be deactivated using a transient detection circuit and
the activation of of S2 will be governed by the transient detection circuit along with the
current control technique mentioned earlier.
Yet another object of the present invention is directed to an efficient transient detection
technique adapted to detect the time instant when a transient occurs, and it also detects
the settling time instant .
A further object of the invention is directed to provision of a stabilizing ramp signal will be
adapted to be switched in or added to the circuit when the transient detection circuit
determines the steady state operation.
NATURE OF THE INVENTION:
The proposed current controlled method /system is based on inductor current and two
current references, namely Iref+ and Iref-. At the start of the clock period, MOSFETs SI
turns on and S2 turns off. Inductor current rises and continues to rise until it reaches Iref+
when SI turns off. Then the inductor current starts falling until it reaches Iref- when S2
turns on. Inductor current then remains almost same till the arrival of the next clock pulse.

Iref+ is obtained from the feedback loop comprising the output voltage and the reference
voltage along with a controller, either PI controller or lag-lead controller. Iref- is obtained
from multiple feed-forward paths connected to the input voltage, Vin, the sensed average
load current, Is2, the reference voltage, Vref and a manually adjustable voltage source.
The above disclosed nature of the invention is further illustrated hereunder in relation to the
following non-limiting exemplary illustrations as per the following accompanying figures:
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Fig. 1: is a block diagram illustrating the art of the prior methodology to control a tri-
state boost converter;
Fig. 2: is a block diagram illustrating the present invention of a current control
methodology;
Fig. 3: illustrates the switching waveforms comprising the inductor current as well as
two reference currents relating to the present invention;
Fig. 4: is a block diagram illustrating the feedback and feed-forward mechanism to
generate Iref+ and Iref-;
Fig. 5: illustrates the simulation result regarding the improvement in reference voltage
transient response achieved by way of the present invention;
Fig. 6: illustrates the confirmation of the above simulation result using test result;
Fig. 7: illustrates the simulation result regarding the improvement in load transient
response achieved by way of the present invention; and
Fig. 8: illustrates the confirmation of the above simulation results using test result.
DETAILED DESCRIPTION OF THE ACCOMPANYING FIGURES:
Reference is first invited to accompanying figure 1 which illustrates a prior methodology to
control a tri-state boost converter presently used in the art. As shown in the figure , pi
followed by Drl indicates the gate signal of the switch SI. pi is generated using Voltage
Mode Control method, which has the drawbacks --- limited closed loop bandwidth due to the

slow voltage dynamics, loop-gain varies with the input voltage, poor line regulation, and
poor stability margin.
p2 followed by Dr2 indicates the gate signal of switch S2. p2 is generated from a reference
current, Idc, which is obtained through multiplication as well as division using Vin, Vref and
lout. This makes difficulty in implementation in analog domain. It can not assure the stability
in fast time scale.
Reference is now invited to accompanying figure 2 which is an illustrative embodiment by
way of a block diagram the current control methodology according to the present invention.
As shown in the figure, in Fig. 2, pi followed Drl indicates the gate signal of switch SI. pi
is generated from current loop comprising Iin and Iref+, where Iref+ is obtained from a
voltage loop comprising Vo and Vref. This maintains a tight regulation in the output voltage,
also improves the transient behavior. p2 followed by Dr2 indicates the gate signal of the
switch S2. p2 is obtained from a current loop comprising Iin and Iref-. Iref- is generated
from a feed-forward loop comprising Vref, Vin, lout, and an adjustable voltage. It improves
the efficiency of the converter at operating conditions, regulation, and transient response. It
also enhances the operating region of the circuit without compromising the stability.
Importantly, in accordance with the basic aspect of the invention under the the above
disclosed control methodology the same involves a current control method with two
reference currents (Iref+ and Iref-) for a dc-dc converter with a freewheeling switch results
in a large closed loop bandwidth. Iref+ is obtained from a feedback loop comprising the
output voltage and the reference voltage along with a compensator to improve the voltage
regulation and dynamic response. Iref- with a manually adjustable voltage and its
implementation provides a scope to adjust the freewheeling interval and improves the
dynamic performance compared to voltage mode method.Iref- with reference voltage feed-
forward and its implementation provides an opportunity for an adjustable voltage regulation
with tri-state operation and improves the regulation characteristics. Iref- with input voltage
feed-forward and its implementation enlarges the range of input voltage with tri-state
operation and improves the line regulation as well as audio susceptibility. Iref- with load
current feed-forward and its implementation enlarges the range of the load current with tri-
state operation and improves the load regulation.
In accordance with another aspect of the invention the same is directed to efficient use of
the switch S2, where S2 will be activated during transient and deactivated at steady state to
enhance the efficiency. Advantageously, while switch SI will be controlled throughout, but

S2 will be deactivated using a transient detection circuit. The operation of S2 will come into
picture only when there is a transient. It will be detected, S2 starts operating till the
response settles, which will be detected. Therefore the activeness of S2 will be governed by
the transient detection circuit along with the current control technique mentioned earlier.
According to yet another aspect of the invention the same is directed to an efficient
transient detection technique. This will detect the time instant when a transient occurs, and
it also detects the settling time instant. It is done using the current lout and a high pass
filter with a proper bandwidth.
Yet further aspect of the invention would provide for the incorporation of a ramp signal
during steady state to stabilize the operation of the circuit when S2 is being deactivated.
Stabilizing ramp signal will be switched in or added to the circuit when the transient
detection circuit determines the steady state operation.
Figure 3 shows the switching waveform relating to the proposed current control
methodology explained in relation to figure 2 above.
In Fig. 3, the basic concept of the current control system is presented. The control action
depends on the inductor current, Iin, and two reference currents to generate the gate
signals of the switches.
Figure 4 is an illustration inside the current control method/system. As shown in the
figure, the generation of two reference currents Iref- and Iref+, is presented using a block
diagram. The controller may be a proportional, proportional + integral. -
The above current control methodology can be applied to any circuit specifications. By way
of example, it was tested for the following specifications:
L=275uH, C=540uF, Vref=25V, Vin = 15V, Iout=[0.5A, 1A].
The simulation result for the transient response due to a step change in reference voltage
from 25V to 26V and back for an 15V input obtained are illustrated in accompanying figure
5.
The test result for the transient response due to step change in reference voltage from 25V
to 26V for an input voltage of 15V of the proposed current control are shown in figure 6.

Also, simulation result for the transient response due to a step change load current from 1A
to 0.5A and back for an 15V input are illustrated by way of figure 7.
Finally figure demonstrates the test result for the transient response due to step change in
load current from 1A to 0.5A for an input voltage of 15V of the proposed control.
It is thus possible by way of the above disclosed current control method and systems
involving the same to provide for a controller for a dc-dc converter with a freewheeling of
the inductor current. Advantageously, the invention encompasses a wide range of the
input voltage and the load current without going into instability. Importantly also, the
invention is directed to favour meeting the required generalized control methodology which
is applicable for any converter with freewheeling switch.
The above disclosed nature of the fast response energy efficient current control
methodology for a Dc-Dc converter with freewheeling switches and systems involving' the
same present invention are thus directed to favour the following:
a. Bandwidth increase to l/5th of the switching frequency for dc-dc converters with right
half plane zero and l/3th of the switching frequency for other converters.
b. Retaining the improved efficiency of classical operation (i.e., without S2)
c. Load and line regulations are significantly improved.
d. Load transient response is improved by about 20 times compared to current mode
controlled classical dc-dc converters.
e. Improved supply transient response using classical current mode control, is retained.
f. It can be applied to power supply circuit requiring DC-DC conversion.

Dated this 17th day of October, 2008 Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)