Valley Current Mode Research Articles

Chaos control of Superbuck converter based on resonant parametric perturbation method

As a current control method, valley current mode (VCM) control is widely applied in DC-DC converters due to its absence of dead time restrictions and excellent transient response performance. This paper constructs a discrete iterative model of the VCM-controlled Superbuck converter. The bifurcation diagram is employed to analyze the impact of the reference current variation on the converter, and further validation is conducted through phase portraits and Poincaré sections. By introducing the resonant parametric perturbation method, a small perturbation signal is applied to the reference current to achieve chaos control. Simulation results demonstrate that this method effectively suppresses the chaotic behaviour of the Superbuck converter with the variation of reference current, significantly improving the performance and output ripple of the converter.

고효율 및 슬림형 전압 평형 3-레벨 벅 컨버터

The 3-level buck converter features half the switch voltage stress of the conventional synchronous buck converter. The operating frequency of the output inductor is also twice the switching frequency. The slope of the inductor current can be reduced as well due to the flying capacitor voltage, which can greatly reduce the size of the output inductor. Therefore, the 3-level buck converter can achieve high efficiency and high power density. The flying capacitor voltage must be half the input voltage to achieve the abovementioned strength. Most conventional control schemes for the voltage balance of the flying capacitor adopt a peak or valley current mode control method using real-time current sensing. Therefore, the control algorithm is complicated, and high performance and expensive digital controller is required. This study proposes an independent two-loop voltage mode control scheme that can guarantee the flying capacitor voltage to be half of the input voltage. The proposed control scheme can be simply implemented without current detection and does not require complicated control algorithms. Thus, simple and low-cost micro controller can be used. Experimental results from a rated prototype of 500 W are provided to verify the performance of the proposed control scheme.

Digital Predictive Current-Mode Control of Three-Level Flying Capacitor Buck Converters

This article investigates the use of digital predictive current-mode control (DPCMC) in dc-dc three-level flying capacitor (3LFC) buck converters. In particular, stability and flying capacitor (FC) balancing properties of predictive peak, average, and valley current-mode controllers are studied when operated in single- and multisampled modes. A variant of the multisampled DPCMC obtained through a fast-update of the duty cycle command is also disclosed and analyzed. Results indicate that single-sampled DPCMC is always stable, and that fast-update approaches can strongly improve the converter dynamic response. Multisampled controllers are also shown to be inherently more robust than single-sampled ones against timing mismatches in the control signals, resulting in a smaller FC voltage imbalance. The analysis is validated in simulation and experimentally on a 500 kHz, 12-1.5 V, 500 mA 3LFC buck case study.

A high performance adaptive on-time controlled valley-current-mode DC–DC buck converter

This paper presents an AOT-controlled (adaptive-on-time, AOT) valley-current-mode buck converter for portable application. The buck converter with synchronous rectifier not only uses valley-current-mode control but also possesses hybrid-mode control functions at the same time. Due to the presence of the zero-current detection circuit, the converter can switch freely between the two operating modes without the need for an external mode selection circuit, which further reduces the design difficulty and chip area. The converter for the application of high power efficiency and wide current range is used to generate the voltage of 0.6–3.0 V with a battery source of 3.3–5.0 V, while the load current range is 0.05–2 A. The circuit can work in continuous conduction mode with constant frequency in high load current range. In addition, a stable output voltage can be obtained with small voltage ripple. In pace with the load current decreases to a critical value, the converter transforms into the discontinuous conduction mode smoothly. As the switching period increases, the switching loss decreases, which can significantly improve the conversion efficiency. The proposed AOT controlled valley current mode buck converter is integrated with standard 0.18 μm process and the simulation results show that the converter provides well-loaded regulations with power efficiency over 95%. When the circuit switches between the two conduction modes drastically, the response time can be controlled within 30 μs. The undershoot voltage is controlled within 25 mV under a large current hopping range.

Decentralized Quasi-Fixed-Frequency Control of Multiphase Interleaved Hybrid Dickson Converters for Fault-Tolerant Automotive Applications

Emerging autonomous-driving systems necessitate a fault-tolerant power management system to ensure continuous power delivery to the safety processor and sensor loads, while the forthcoming 48-V bus system requires power conversion at high and wide-ranging input voltages. To address the challenges in future automotive applications, this article demonstrates a modular multiphase system with N+1 redundancy as the preregulator converter in a two-stage cascaded power conversion system. Each phase is implemented based on the 4-to-1 hybrid Dickson topology, which enables efficient high-ratio voltage conversion. This article proposes a new decentralized quasi-fixed-frequency control scheme based on the valley current mode and on-time control. In contrast to existing methods, the proposed scheme: 1) enables decentralized interleaving of the multiphase system using distributed phase-locked-loop-based synchronization in the event of a failure in any phase, which is advantageous in terms of modularity and scalability; 2) incorporates droop voltage control to achieve balanced current sharing and voltage regulation in a multiphase system; and 3) offers self-balancing of the flying-capacitor voltages, which eliminates the need for any additional control circuitry. The performance of the proposed scheme is verified using a 36-W four-phase experimental prototype.

Novel sliding valley current mode pulse train control for switching DC-DC converter

ABSTRACTMulti valley current mode pulse train (MVC-PT) control technology can completely eliminate the low-frequency oscillation phenomenon of DC-DC switching converters operated in continuous conduction mode (CCM). However, this method needs to increase the number of preset value to broaden the output power range, which will increase the complexity and cost of the controller, and reduce the robustness of the system. Meanwhile, the output voltage ripple is uncontrollable and varied with the changes of the load. In this paper, a novel sliding valley current mode PT (SVC-PT) control technique is proposed to solve the above-mentioned problem. The SVC-PT operating principle and the deficiency of MVC-PT method are analysed in details. The approximate discrete-time models of SVC-PT and MVC-PT controlled switching DC-DC converters are constructed and compared. The comparison results verify that the proposed control method can thoroughly lessen the restriction of the controller on the output power range. Moreover, the control circuit is simplified and the output voltage ripple can be controlled. Finally, the simulation and experimental results are present to prove the feasibility and scientific of SVC-PT control technology.

Universal Compensation Ramp Auto-Tuning Technique for Current Mode Controls of Switching Converters

The conventional slope compensations for current mode controls do not take all the parameters’ changes into account, so the variations on small-signal transfer functions limit the voltage loop bandwidth (BW). In order to optimize the dynamic performance of current-mode control, this letter proposes a universal auto-tuning technique for external ramp slope based on the sensed slope of current feedback signal. The tuning mechanism keeps the quality factor of the double poles unchanged over the duty cycle variation, inductor tolerance, sensing element variation, and topology change, thus a consistent wide BW control is achieved without the limitation from the corner cases. Simple digital and analog implementations are proposed to realize the auto-tuning concept. This method is applicable to digital and analog current-mode controllers with peak current mode, valley current mode, and average current mode operations. The effectiveness of the proposed method is verified by simulation and experimental results.

Parameter-Insensitive Mixed-Signal Hysteresis-Band Current Control for Point-of-Load Converters With Fixed Frequency and Robust Stability

The inductor current ripple under hysteresis current control is sensitive to system as well as controller parameters, which often deviates from the desired band. Thus, a phase-locked-loop (PLL) is employed to regulate the switching frequency over the operating range. Digital platform drastically simplifies this using an all-digital PLL (ADPLL) and offers the controller-tuning flexibility for improved performance. However, the use of uniform voltage-sampling often leads to multilimit cycle instability. This paper proposes a mixed-signal hysteretic current controller (MSHCC) with the digital voltage-loop and the analog current-loop. A digital-to-analog converter is sufficient to generate time-multiplexed current references. This achieves robust stability and parameter-insensitive current ripple by sampling the error-voltage at the rising edge of the high-side gate signal. Stability analysis is carried out using discrete-time models. The proposed MSHCC can be configured to either of the peak, average, or valley current-mode techniques along with the flexibility to adjust the switching frequency using an ADPLL for real-time energy-optimization. The proposed scheme is implemented using an FPGA device and tested on a buck converter prototype. The MSHCC scheme can be extended to a multiphase buck converter.

Asymmetric Instability Conditions for Peak and Valley Current Programmed Converters at Light Loading

Three types of bifurcations (instabilities) in the DC-DC converter under valley current mode control (VCMC) are analyzed, which is an extension of a recent paper on the peak current mode control (PCMC). The three bifurcations are border-collision, period-doubling, and saddle-node bifurcations. The corresponding critical (instability) conditions are derived. The derived conditions divide the parameter space into different operating modes. Contrary to the general belief that the critical conditions for VCMC and PCMC are symmetric with respect to the duty cycle D=1/2, most critical conditions are actually asymmetric. The dynamics symmetry is converter, bifurcation, loading, and parameter dependent, verified by bifurcation diagrams and time-domain simulations. The VCMC boost converter has rich dynamics and it is extensively analyzed.

Valley current mode pulse train control technique for switching DC–DC converters

To eliminate the low-frequency oscillation phenomenon in pulse train controlled switching DC–DC converters operating in continuous conduction mode (CCM), a valley current mode pulse train control technique is proposed. The experimental results show that by using the proposed control technique, the low-frequency oscillation in the pulse train (PT) controlled CCM switching DC–DC converter can be eliminated, while the great robustness and excellent transient performance of the traditional PT control technique can be retained.

Valley current mode pulse train control switching converter and its energy model analysis

Pulse train (PT) control technique is a novel discrete control technique for switching converter operating in discontinuous conduction mode (DCM). When the inductive energy storage is not zero, the low-frequency oscillation phenomenon may occur in PT controlled switching converters operating in continuous conduction mode (CCM). The low-frequency oscillation phenomenon will seriously affect the steady and transient performances of switching converters. In order to solve this problem, valley current mode pulse train (VCM-PT) control technique, which extends the application range from DCM to CCM, is proposed in this paper. The energy model of VCM-PT controlled switching converter is derived and compared with the energy model of PT controlled switching converter. Result indicates that the VCM-PT controlled CCM switching converter has the same energy transfer mode as the traditional PT controlled DCM switching converter and can eliminate fundamentally the low-frequency oscillation phenomenon.

Symmetrical dynamical characteristic of peak and valley current-mode controlled single-phase H-bridge inverter

Complex dynamical phenomenon was studied in the single phase H-bridge inverter which was controlled by either a peak current or a valley current. The state functions and the discrete iterative map equations were established to analyze the dynamical phenomenon in the single phase H-bridge inverter. The dynamical characteristics of the single phase H-bridge inverter, such as time domain waveform diagram, bifurcation diagram, and folding map, were obtained by using the numerical calculation when the circuit parameters varied in specific range. Moreover, the simulation results were obtained by using the OrCAD-PSpice software to validate the numerical calculation. Both the numerical calculation and the circuit simulation show that the symmetrical dynamical phenomenon occurs in the single phase H-bridge inverter controlled by the peak current or the valley current.

SYMMETRICAL DYNAMICS OF CURRENT-MODE CONTROLLED SWITCHING DC-DC CONVERTERS

Peak Current-Mode (PCM) and Valley Current-Mode (VCM) controlled switching dc-dc converters have symmetrical dynamical behaviors within a wide circuit parameter variation range. To investigate the symmetrical dynamical behaviors between PCM and VCM controlled switching dc-dc converters, the iterative map models and inductor current borderlines that exist in the bifurcation diagrams of both PCM and VCM controlled buck, boost, and buck-boost converters are established. The research results of bifurcation behaviors indicate that the bifurcation diagrams of PCM and VCM controlled switching dc-dc converters have symmetrical dynamical behaviors corresponding to a symmetrical point (SP). The simulation results show that time-domain waveforms of PCM and VCM controlled switching dc-dc converters working in periodic orbits have symmetrical axis and SP, and the SP also exists in corresponding phase portraits. Experimental results are given to verify the analysis and simulation results in this paper.

Practical application of valley current mode control in a flyback converter with a large duty cycle

This study proposes the application of valley current mode (VCM) control in a flyback dc–dc converter with a large duty cycle. The use of VCM control eliminates the need of slope compensation in operation under a duty cycle greater than 50%. For operation with duty cycle near the boundary value (50%), a relatively small compensation ramp is required comparing with that of the conventional peak current mode (PCM) control. Moreover, the noise sensitivity issue of PCM control is also addressed by the change of the current sensing position in VCM and hence the immunity against the current spike. The VCM-controlled flyback converter achieves consistent steady-state and transient-response performances as its PCM-controlled counterpart. Stability analyses of inner current loop and overall closed-loop system are presented. Experiments are also conducted to evaluate the effectiveness of VCM control in controlling the flyback dc–dc converter.

Current Mode Control for Boost Converters With Constant Power Loads

This paper describes how current mode control provides active damping for boost converters with constant power loads. Small-signal control-to-output transfer functions are derived for peak or valley current mode controlled boost converter with a downstream regulated converter modeled as constant power load. Furthermore, it is shown how load current feedforward presents an effective way to improve power load transient responses. Modeling and design approaches are validated by test circuit simulations, demonstrating stable operations using current mode control under constant power loads, and improved power step load transient responses based on load current feedforward.

Fast-Scale and Slow-Scale Subharmonic Oscillation of Valley Current-Mode Controlled Buck Converter

A valley current-mode (VCM) controlled buck converter with current source load (CSI) has complex phenomena of fast-scale and slow-scale subharmonic oscillations. The piecewise smooth switching model of the VCM controlled buck converter with CSI is established. It is found that attractive regions of fast-scale and slow-scale subharmonic oscillations exist in the bifurcation diagram, and two tori exist in the corresponding Poincaré mapping. The research results by time-domain simulation indicate that U-type subharmonic oscillation (SO) constituted by SO and frequency-reduced subharmonic oscillation (FSO) exists in inductor current, and sine-type SO constituted by fast scale and low scale exists in output voltage respectively. Experimental results are given to verify the analysis and simulation results.

Symmetrical dynamics of peak current-mode and valley current-mode controlled switching dc–dc converters with ramp compensation

The discrete iterative map models of peak current-mode (PCM) and valley current-mode (VCM) controlled buck converters, boost converters, and buck–boost converters with ramp compensation are established and their dynamical behaviours are investigated by using the operation region, parameter space map, bifurcation diagram, and Lyapunov exponent spectrum. The research results indicate that ramp compensation extends the stable operation range of the PCM controlled switching dc-dc converter to D > 0.5 and that of the VCM controlled switching dc–dc converter to D < 0.5. Compared with PCM controlled switching dc–dc converters with ramp compensation, VCM controlled switching dc–dc converters with ramp compensation exhibit interesting symmetrical dynamics. Experimental results are given to verify the analysis results in this paper.

Analysis of symmetrical dynamic phenomenon of peak and valley current-mode controlled switching DC-DC converters

Peak current and valley current controlled switching DC-DC converters show symmetrical dynamic phenomenon within a wide circuit parameter range. The unified discrete iterative map model of peak current and valley current controlled buck, boost, and buck-boost converters is established, and the unified piecewise smooth iterative map and their corresponding characteristic equations are also derived. The forward and inverse bifurcation diagrams and Lyapunov exponent spectrums with duty ratio as parameter are obtained by numerical simulation. The research results indicate that the bifurcation diagrams and Lyapunov exponent of peak and valley current-mode controlled switching converters show symmetrical dynamic phenomenon corresponding to a symmetrical point or a symmetrical axis. The numerical simulation results are verified by the time-domain simulation, which further indicates that with the duty ratio varying, the peak and valley current-mode controlled switching converter reveals a symmetrical dynamic phenomenon, or a symmetrical dynamic phenomenon accompanying an asymmetrical dynamic phenomenon, or an asymmetrical dynamic phenomenon.

A Digital Current-Mode Control Technique for DC–DC Converters

The objective of this paper is to propose a simple digital current mode control technique for dc-dc converters. In the proposed current-mode control method, the inductor current is sampled only once in a switching period. A compensating ramp is used in the modulator to determine the switching instant. The slope of the compensating ramp is determined analytically from the steady-state stability condition. The proposed digital current-mode control is not predictive, therefore the trajectory of the inductor current during the switching period is not estimated in this method, and as a result the computational burden on the digital controller is significantly reduced. It therefore effectively increases the maximum switching frequency of the converter when a particular digital signal processor is used to implement the control algorithm. It is shown that the proposed digital method is versatile enough to implement any one of the average, peak, and valley current mode controls by adjustment of the sampling instant of the inductor current with respect to the turn-on instant of the switch. The proposed digital current-mode control algorithm is tested on a 12-V input and 1.5-V, 7-A output buck converter switched at 100kHz and experimental results are presented