A large DC-gain highly efficient hybrid switched-capacitor-boost converter for renewable energy systems

Traditionally, switched-capacitor (SC) converters have suffered from high transient currents, which limit both the efficiency and power density of such converters. Soft-charging operation can be employed to eliminate the current transients and greatly improve the power density of SC converters. In this approach, a second-stage magnetic converter is cascaded with the SC stage to act as a controlled current load. Another approach is to use resonant SC converters with zero-current switching. This paper shows that resonant and soft-charging operations of SC converters are closely related, and a technique will be proposed, which achieves either operation by adding a single inductor to existing SC topologies. In addition, since most preexisting resonant or soft-charging SC converters were devised in an ad-hoc manner, this paper formulates an analytical method that can determine whether an existing conventional SC converter topology is compatible with the proposed approach. A number of common SC topologies are analyzed, including Dickson, series-parallel, ladder, Fibonacci, and doubler configurations. Through comparison to simulated results, as well as experimental work, the proposed method is validated and a family of high-performance SC converters is obtained.

Switched Capacitor (SC) DC-DC converters are transformer and inductor less DC-DC converters that are used to step up, step down or invert a supply voltage where the power requirements are usually less than 5W. The outputs of the currently available SC converters are referenced with respect to the input supply ground. Though SC converters are ideally suited for many low power miniaturized industrial applications due to their small size, lack of ground isolation in SC converters prevents their use in low power applications that require ground isolation due to ground noise sensitivity of the load. The work presented in this paper introduces the concept of ground isolation in a buck SC converter without the use of isolation transformers like conventional DC-DC converters. Switched capacitors driven by opto-isolated drives are employed to transfer power from the source to the load. The introduction of ground isolation in SC converters significantly widens its scope of application in industry. A state space averaged (SSA) model of the SC converter is developed to study its dynamic and steady state characteristics. The validity of the SSA model is verified with measurements on the hardware model.

Switched capacitor (SC) dc–dc converters are showing great potential for new applications such as data centres, electric vehicles, and power transmission. Many SC topologies have been synthesized on an ad-hoc basis, although new computer methods are being introduced to formalize this process. This article presents a general synthesis technique that can be incorporated into a computer algorithm to assist with the development of new SC circuits. The technique is based on interleaving SC converter circuits, where two unipolar converters are connected in parallel, and each leg is driven by separate, complementary gate signals. By applying this method to the traditional Ladder SC converter, a topology termed a simplified interleaved ladder (SIL) converter, is synthesized and tested using a hardware prototype. The resonant implementation of the SIL converter has desirable features for MV/LV applications when compared with other existing SC circuits.

A ground-isolated switched capacitor (SC) dc-dc converter-based current equalization scheme for partially shaded photovoltaic (PV) strings of a grid-connected system is presented. SC converters are compact, light, and have very high efficiency even for a wide variation in load under certain operating conditions. These features make them ideal for integration with the PV module for current equalization. The factors affecting the maximum output power that the SC converter can deliver, the limiting value of the maximum output power, and efficiency issues of the SC converter are studied. These studies are required to optimize the design of the equalizing SC converter and to maximize its efficiency. A novel algorithm that utilizes the results of the aforementioned analysis to maximize the net power available due to the SC converter-based current equalization scheme for grid-connected applications is proposed. Experimental results showing the advantages of current equalization with SC converters as compared to that with conventional dc-dc converters are presented.

This paper describes switched-capacitor (SC) inductor and Frequency Dependent Negative Resistor (FDNR) which use second generation current conveyor (CC II). In general CC II's used in SC circuits are not always used as CC II and there are phase periods in which CC II behaves as much simpler active device like unity gain buffer (UGB). In this paper, CC II's in SC circuits always behave as CC II to make full use of CC II. Then an SC inductor in which effects of parasitic capacitors can be reduced is proposed. And SC FDNR which uses CC II to get a simple circuit structure is also proposed. Both circuits are controlled by simple two-phase control clock. The spreads of capacitor values are 1. The sum of capacitor values of SC FDNR is 4. This value is the smallest reported value in SC FDNR circuits. Simulation results by SWITCAP and experimental results by discrete components are shown.

The switched capacitor (SC) circuit has been applied to analog signal processing, but few reports have been made on the application to power circuit. Recently, a report has been made on the dc‐dc converter using the SC circuit, but the circuit still has a number of problems, e.g., the loss due to the switching element or equivalent resistance of the SC circuit, the output ripple and the noise.From such a viewpoint, this paper presents first the theoretical and experimental investigations on the energy loss, energy transmission efficiency and output power of the dc‐dc converter using the basic SC circuit. Based on that result, dc‐dc converters are considered using a series‐parallel switching SC circuit with more than one capacitor. It is seen as a result that the loss due to the equivalent resistance is inevitable, even if ideal switching elements or capacitors are used in those SC circuits.As a means to cope with this problem, the dc‐dc converter using a new SC circuit is proposed, where the zero‐voltage switching mechanism is employed using a high‐frequency supply and the peak‐detector circuit. It is shown theoretically that the loss due to the equivalent resistance is not produced in principle in the proposed SC circuit. A result of experiment is shown with a drastic improvement.

The switched-capacitor (SC) converters are gaining popularity in some practical use. Its resonant counterpart, with a small inductor as current shaper in the architecture, has the advantage of smoother charging current, smaller voltage and current variation ratio and so on. This paper presents a generic and thorough analysis of the efficiency mechanism of the resonant switched-capacitor converter (RSCC). It decomposes any RSCC into three basic sub-circuits of SRLC circuit, CRLC circuit and SRLC² circuit, which are analyzed and compared with corresponding sub-circuits of SCC, respectively. Then the overall efficiency of a RSCC could be derived. Furthermore, a new calculation method of output impedance is developed in another perspective to reveal the high efficiency mechanism of RSCC. On this basis, the high efficiency operation condition for RSCC could be obtained. Finally, a resonant bridge modular switched-capacitor converter (RBMSCC) is proposed and built for example of extended implementation of RSCC to achieve high efficiency operation. Some useful comments for designing resonant switched-capacitor converters are suggested.

A new switched-capacitor(SC) DC-DC converter is presented. This converter consists of n ring-shaped capacitors connected by switches. The converter has the following features as compared with conventional SC converters: (1) since only one capacitor is charged at one time, the inrush current and the input current ripple are small; (2) the converter has a smaller number of switches; (3) all floating switches form totem-pole connections with grounded switches, thus driving them is easy; and (4) since the generation of the magnetic field is few, together with some signal processing circuits, it is possible to be implemented in one chip IC form such as a system-on-chip.

A new circuit is proposed for a steep step-up of the line voltage. It integrates a switched-capacitor (SC) circuit within a boost converter. An SC circuit can achieve any voltage ratio, allowing for a boost of the input voltage to high values. It is unregulated to allow for a very high efficiency. The boost stage has a regulation purpose. It can operate at a relatively low duty cycle, thus avoiding diode-reverse recovery problems. The new circuit is not a cascade interconnection of the two power stages; their operation is integrated. The simplicity and robustness of the solution, the possibility of getting higher voltage ratios than cascading boost converters, without using transformers with all their problems, and the good overall efficiency are the benefits of the proposed converter.

In this paper, a novel nonisolated interleaved high step-up DC-DC converter is proposed based on the coupled inductor and voltage multiplier cell (VMC) methods. Due to the interleaved structure, its input current ripple is low. The low input current ripple and also high power efficiency make the proposed converter suitable for renewable energy applications like photovoltaic (PV) and fuel cell (FC) power generation systems. The windings of the coupled inductors are combined with VMCs to further increase the output voltage with a low power switch’s duty cycle. This combination also leads to obtaining a flexible voltage gain that can be adjusted by coupled inductors’ turns ratio and power switches’ duty cycle. The voltage peaks over semiconductors are much lower than the output voltage. Therefore, low-rated semiconductors can be used for the implementation of the proposed converter, which can reduce the cost and volume. Generally, high voltage gain, low voltage, current stress of power switches, low input current ripple, high efficiency, common ground between the input and output ports, and a low number of elements are the main benefits of the suggested structure. The operation principle, steady-state analysis, and comparison with other converters are presented to show the advantages of the suggested converter. Also, a prototype is built, and the experimental results are presented to prove the theoretical analysis. This prototype is implemented with 200 W rated power, 25 V∼400 V voltage conversion, and 50 kHz switching frequency. Additionally, the efficiency is measured at 95.3% at the rated power.

Efficient analysis techniques for complex switched-capacitor (SC) converters are essential design tools for the development of practical SC converters. Techniques that use state-space equations based on conventional circuit analysis methods have proven effective in modeling the practical performance of SC converters. Iterative methods of design based on these analysis techniques require the formulation of many Kirchhoff voltage and current equations, which is time consuming if derived manually. Here, an algorithm is introduced to automate the creating of the matrices required for state-space-based modeling of SC converters. The state equations are generated algorithmically, given a standard node incidence matrix generated from a user-defined netlist. The algorithm enables a designer to quickly iterate SC converter design solutions based on their predicted performance. The resulting models are compared against manually generated models, simulations, and experimental results.

Switched capacitor (SC) dc–dc converters, which have traditionally been used for on-chip power supplies, are now being considered for medium to high-power applications. This paper presents a method for automatically synthesizing SC converters as well as deriving the expressions for their charge-multipliers. Charge multipliers can be used to calculate important design characteristics such as converter output voltage regulation, efficiency, and component current ratings, which can then be used to appraise different topologies. However, whilst a full appraisal of converters also requires component voltage ratings, this work is the first step in developing an automatic software tool that will employ a search-based algorithm to generate optimum SC topologies for a given application. The method is based on the proposition that all SC converters can be synthesized from a so-called “basic cell”. The automatic derivation and solution of the charge transfer equations for a traditional Fibonacci SC converter is presented as an example of the proposed method, which is validated against existing analytic equations as well as a detailed Spice simulation. The automatic calculation of the charge-multipliers for two other well-known SC converters is also demonstrated, including a new, arbitrarily generated circuit, which again is validated against detailed spice simulations.

A power management unit (PMU) with battery extender and output load regulation is presented using 0.18$\mu$m CMOS technology. For designing few sub-circuits of the PMU, subthreshold region of MOSFET is utilized, which significantly contributes to achieve low power operation. The proposed PMU consists of a voltage regulator, a voltage monitor, a battery backup module and two DC-DC Switched Capacitor (SC) Converters. The regulator output voltage V OUT is regulated at 0.95 V and 0.968 V at input voltages of 0.98 V and 1.33 V respectively. To ensure continuous operation at the load circuit, a battery extender module is implemented in case of unavailability of EH source. The power consumption of the PMU at input voltages of 0.98 V and 1.33 V is 46nW and 1.567 $\mu$W respectively. Near threshold operation is ensured at the load side by further regulating the voltage at the output to 0.67 V and 0.5 V using 3:2 and 2:1 SC Converters respectively. The current consumption of the 3:2 and 2:1 SC Converters is 748 nA and 751 nA respectively. The proposed PMU can deliver output current up to 1 mA at 1.33 V of input voltage and is suitable for numerous applications where low power operation is essential as it consumes a small amount of power.

In recent years, there has been an ever-increasing interest in monolithic power supplies. Integrating the power supply with the application has many direct benefits, including a reduction of the bill of materials and reduced size. Even more substantial are the potential efficiency gains due to reduced power delivery network losses and voltage margins, especially in a world dominated by energy limited devices where this translates directly into improved battery life. However, to warrant a migration to integrated power supplies, it is crucial that these gains do not get eclipsed by the decreased efficiency of the power converter caused by the reduced quality of integrated passives. Switched-Capacitor (SC) converters have become more and more popular because, contrary to inductive converters, they only use transistors and capacitors, both of which are native to CMOS technologies and scale well into deep-submicron nodes. The maximal efficiency of an SC converter depends on two factors [1]: a topological parameter whose optimal value depends on the Voltage Conversion Ratio (VCR), and a, the relative size of the parasitic, so-called Bottom-Plate (BP), capacitance to the flying capacitance. The further the VCR is removed from 1/1 and the larger a, the lower the efficiency that is obtained. With a typically around 1.5% for MOM- and MIM-, and 7% for MOS capacitors, an SC converter could theoretically achieve an efficiency of 89% and 79% respectively for a 1/2 conversion [1]. Due to additional losses (control, leakage, etc.), this efficiency ceiling is lower, but its existence is still confirmed by previous work. The highest reported monolithic SC converter efficiencies in baseline CMOS are 87% [2], although at a more favorable VCR of 4/5, and 85% [3], both using MIM capacitors. Higher efficiencies have been demonstrated using high-density Deep-Trench (90%) [4] or Ferro-Electric (91% in 1/2) [5] capacitors, which have reportedly up to 25 times smaller α. However, these capacitors are not part of baseline CMOS and thus require additional masks and costs.

Hybrid and resonant switched-capacitor (SC) converters have the potential to achieve higher power densities than conventional dc-dc converters. This work presents an interleaved, 20 V to 120 V, resonant SC converter which could be used in applications that benefit from high power density and efficiency. The resonant topology of this SC converter enables a compact and efficient design that minimizes losses. We use a new split-phase control scheme that incorporates precisely timed additional transition states to increase the converter efficiency. A two-phase interleaved design increases the output power and simultaneously decreases the output ripple through harmonic cancellation. In addition to experimental evaluation of a 95.7% efficient, GaN-based prototype of this interleaved converter, an analysis of current sharing between interleaved phases is performed.