Time-varying Current Observer with Parameter Estimation for Multiphase Low-Voltage High-Current Voltage Regulator Modules Jia Luo, Nattorn Pongratananukul, Jaber A. Abu-Qahouq, Issa Batarseh School of Electrical Engineering & Computer Science University of Central Florida, Orlando, FL 32816
[email protected] A time-varying current observer with load resistance estimation is designed in this paper to estimate the instant load current and individual inductor currents in multiphase VRMs to achieve current sharing. The adaptive control method is applied to estimate the load changes and simplifies the time-varying system into a nonlinear time invariant system.
Abstract- Current sharing in interleaved converters is an essential issue for low-voltage, high-current Voltage Regulator Modules (VRMs). The most common method is to sense the average voltage across low-side switches to obtain phase currents. In this paper, an instantaneous current sensing method is presented to observe instant load current and phase currents for multiphase buck converter. Since the load value is time varying, an adaptive control method is applied to estimate load changing. The proposed current observer can also be used for other topologies requiring current sensing. A digital observer is designed and implemented using a DSP controller.
Another challenge of the switching power supply modeling is its nonlinear characteristic due to the switch mode shift [3]. It causes the observer to be nonlinear. In this paper, a decoupling technique is designed to simplify this problem.
Keyword- Current observer, parameter estimation, current sharing, VRM
Next section presents the state apace model for the power stage. The adaptive observer with load resistance estimation is given in section III. The simulation and experiment results are presented in section IV and V respectively. The conclusion is given in section VI.
I. INTRODUCTION Voltage Regulator Modules (VRMs) for powering microprocessors and telecom systems require very low supply voltage while drawing high current. Current sharing is very important in multiphase VRMs to achieve low current stress and high efficiency. Therefore, different kinds of current sensing methods are developed to meet different control requirements.
II. STATE SPACE MODEL FOR POWER STAGE The power stage model of a 4-phase buck converter is shown in Figure 1. The challenge for modeling switching mode converters is that they have many different operating modes. For example, a PWM controlled 4-phase buck converter shown in Figure 1 has 5 operating modes when the duty ratio is 0≤D
