For a sensorless predictive current controlled boost dc-dc converter, its small-signal model that contains a number of parasitic parameters, is derived in this paper. This model indicates that the type of system becomes type 0 even with the correction of voltage loop proportional-integral controller, leading to the existence of output voltage steady-state error. Then a self-correction differential current observer (SDCO) is proposed to eliminate this steady-state error and gain high transient response speed. The self-correction part of the SDCO makes the system become type 1 to achieve no steady-state error for output voltage, whereas the differential part can guarantee that the intermediate calculation results do not overflow. By carrying out a series of simulation verifications, further investigation proves that the proposed algorithm has good robustness. Finally, the effectiveness of the proposed algorithm is verified by experimental results.

Sensorless Predictive Current Controlled DC–DC Converter With a Self-Correction Differential Current Observer

Constant frequency average current mode (ACM) control is a widely used control scheme for converters requiring precise current control. However, its transient response is relatively slow, while the switching loss and driving loss significantly diminish the light load efficiency. To solve these issues, the I2 control ACM is proposed. By combining the fast direct current feedback and integral feedback, the I2 control achieves both wide bandwidth and accurate current control. As a particular embodiment of this concept, by adopting constant on-time modulation, constant on-time I2 control needs no artificial ramp, and has a fast dynamic response. Moreover, due to the decrease of the switching frequency, constant on-time I2 control improves the efficiency in discontinuous conduction mode. The concept of I2 control can be extended to other modulations. A small-signal model using the describing-function-based equivalent circuit model is proposed. The model is accurate up to 1/2 switching frequency. Based on the model, the design guidelines are discussed. The proposed control is verified with simulation and hardware measurement results.

$I^{2}$ Average Current Mode Control for Switching Converters

This part of the paper takes a new look at the stability of the fundamental periodic behavior and the associated subharmonic oscillation boundary in dc–dc switching regulators with fixed-frequency pulse width modulation. After revisiting different approaches applied to a unified reduced-order model of switching regulators, the work presents a novel way of obtaining such a boundary without any simplification nor order reduction. A new simple closed-form condition is then obtained using the new approach, which is valid for different strategies with both trailing edge and leading edge modulation schemes. The critical condition is obtained from the steady-state response using an asymptotic approach without resorting to frequency-domain Fourier analysis or using the monodromy or the Jacobian matrix of the discrete-time model. Unlike the method based on the Fourier series expansion, the proposed method does not require the use of any transform and, most importantly, can be applied to bilinear switching regulators. As a byproduct of the proposed method, a singularity problem that is encountered in steady state, when the system involves integrators in the feedback loop, is addressed and a solution is developed to achieve a closed-form expression in the presence of such integrating feedback loops.

A New Approach for Accurate Prediction of Subharmonic Oscillation in Switching Regulators—Part I: Mathematical Derivations

A unified observer for robust sensorless control of DC–DC converters

This work presents a novel mixed-signal control scheme for a boost power factor correction (PFC) rectifier. The digital controller modulates the inductor peak current to produce a low-distortion ac line current in discontinuous conduction mode (DCM) and continuous conduction mode (CCM), without the need for average current sensing. A lookup table (LUT) optimizes efficiency at low input currents, by allowing operation at 125–500-kHz DCM based on calculated thresholds. At high input currents, the converter operates at 1-MHz CCM for reduced inductor footprint. An analog off-time generator with a digital frequency locked loop facilitates CCM operation, eliminating the need for slope compensation in the current loop and reduces frequency variations. The LUT is programmed with an adaptive output voltage of 250/450 V for low/high mains line voltage (85–265 Vrms) to optimize efficiency over a broad range of conditions. The 150-W PFC prototype operates up to 1 MHz with a peak efficiency of 95% and a total harmonic distortion of 5%.

A Multimode 1-MHz PFC Front End With Digital Peak Current Modulation

This paper proposes a small-signal model for average current mode control based on an equivalent circuit. The model uses a three-terminal equivalent circuit model based on a linearized describing function method to include the feedback effect of the sideband frequency components of the inductor current. The model extends the results obtained in peak current mode control to average current mode control. The proposed small-signal model is accurate up to half switching frequency, predicting the subharmonic instability. The proposed model is verified using SIMPLIS simulation and hardware experiments, which show good agreement with the measurement results. Based on the proposed model, new feedback design guidelines are presented. The proposed design guidelines are compared with several conventional, widely used design criteria. By designing the external ramp following the proposed design guidelines, the quality factor of the double poles at half of the switching frequency in the control-to-output transfer function can be precisely controlled. This helps the feedback loop design to achieve wide control bandwidth and proper damping.

Yingyi

Papers

Analysis and Design of Average Current Mode Control Using a Describing-Function-Based Equivalent Circuit Model