Stability optimization method based on virtual resistor and nonunity voltage feedback loop for cascaded DC-DC converters
Abstract:
This project proposes a stability optimization method based on virtual resistor and non-unity
voltage feedback loop for cascaded DC-DC converters. Oscillating phenomenon or instability
would occur occasionally with two or more closed-loop DC-DC converters in series. Virtual
resistor and non-unity voltage feedback are to modify the feedback loop instead of only a direct
voltage feedback to improve stability and get rid of oscillating behavior. Based on the stability
analysis of DC-DC converters with distributed parameters, several cases have been derived.
After that, relative to different cases, two modified methods based on virtual resistor and nonunity voltage feedback loop are proposed to stabilize the overall system.
Existing method:
Many renewable energy generators, battery charging systems and some other electrical devices
are comprised of two or more converters as well. However, sometimes the closed-loop controlled
trailing converter would act as constant power load and behave as negative impedance in smallsignal analysis. Thus, the stability of the overall system would be deteriorated and oscillating
phenomenon occurs in such system with several cascaded converters. Hence, stability analysis
and optimization is a cause of concern for cascaded converters. In order to achieve power
decoupling and remove the interaction between the front-end converter and the trailing
converter, the conventional solution is to add a large capacitor as a buffer on the dc bus.
Proposed method:
In this paper, stability of DC-DC converter with equivalent series resistors (ESRs) and negative
load is analyzed. It has been found that several cases would occur depending on the ESR values.
According to different cases, modified feedback method based on virtual resistor and extra
proportional voltage loop is presented. Virtual resistor is implemented by adding proportional
Further Details Contact: A Vinay 9030333433, 08772261612
Email: takeoffstudentprojects@gmail.com | www.takeoffprojects.com
feedback of inductor current into the control loop which is mainly used in grid-connected
inverters with LCL filter.
Block diagram:
Block diagram of cascaded DC power systems.
Advantages:

High voltage levels can be obtained

Lower 𝑑𝑡 leading to lower elctromagnetic interference (EMI)

Lower switching losses

Lower harmonic distortion with increasing number of DC voltage levels
𝑑𝑣
Applications:
 The high-voltage supplies for cathode ray tubes
 Switched mode power supplies, including DC to DC converters.
 Speed controllers for DC motors
 Class D Electronic amplifiers
 Switched capacitor filters
 Variable-frequency drive
Further Details Contact: A Vinay 9030333433, 08772261612
Email: takeoffstudentprojects@gmail.com | www.takeoffprojects.com