Emerging Hybrid and Electric Vehicles and Their Impact on Energy and Emissions

Philip T. Krein - Professor and Director, Grainger Center for Electric Machinery and Electromechanics, UIUC Department of Electrical and Computer Engineering. Hybrid and electric automobiles have a long history, but are practical today because of advances in power electronics and control technologies. Hybrid designs were originally seen as a temporary approach leading toward fully electric cars, but now have demonstrated special merits. These types of cars greatly enhance fuel efficiency while reducing environmental impact. In this talk, fundamental characteristics of electric transportation are examined. What are the energy storage needs, the power needs, the control requirements, and the reliability concerns? The major types of present and near-term hybrid cars will be introduced, with emphasis on tradeoffs for low emissions, high fuel economy, control flexibility, and practicality. Hybrid cars today can be designed to cut major pollutants by 90% and give fuel economy double or more compared to conventional cars. Next-generation hybrids will blur distinctions with electric cars. They will recharge largely from the electricity grid, with a degree of flexibility that will alter electric utilities in fundamental ways. Electric cars continue to improve, and may be an important factor in automotive markets over the next decade

Discrete-Time Ripple Correlation Control for Maximum Power Point Tracking

Ripple correlation control (RCC) is a high-performance real-time optimization technique that has been applied to photovoltaic maximum power point tracking. This paper extends the previous analog technique to the digital domain. The proposed digital implementation is less expensive, more flexible, and more robust. with a few simplifications, the RCC method is reduced to a sampling problem; that is, if the appropriate variables are sampled at the correct times, the discrete-time RCC (DRCC) algorithm can quickly find the optimal operating point. First, the general DRCC method is derived and stability is proven. Then, DRCC is applied to the photovoltaic maximum power point tracking problem. Experimental results verify tracking accuracy greater than 98% with an update rate greater than 1 kHz

A Current-Sensorless Digital Controller for Active Power Factor Correction Control Based on Kalman Filters

For low-power AC-DC converters, power factor correction (PFC) can be accomplished simply with certain converters operating in discontinuous conduction mode (DCM). At higher power levels, DCM results in higher losses, so most PFC converters use current feedback to actively track the correct current waveshape. This work presents a way to provide PFC control without the current sensor, by replacing the sensor with a Kalman filter, which is essentially a stochastic observer. Experimental results verify its high power factor and low total harmonic distortion (THD)

Digital Ripple Correlation Control for Photovoltaic Applications

Ripple correlation control (RCC) is a fast, robust online optimization technique. RCC is particularly suited for switching power converters, where the inherent ripple provides information about the system operating point. The present work examines a digital formulation that has reduced power consumption and greater robustness. A maximum power point tracker for a photovoltaic panel demonstrates greater than 99% tracking accuracy and fast convergence

Analysis and Design of Switched Capacitor Converters

Switched capacitor converters have become more common in recent years. Crucial to understanding the maximum power throughput and efficiency is a model of the converter\u27s equivalent resistance. A new form for equivalent resistance is derived and discussed in a design context. Quasi-resonant operation is also explored and compared to non-resonant operation. Several capacitor technologies are evaluated and compared

Singular Perturbation Theory for DC-DC Converters and Application to PFC Converters

Many control schemes for dc-dc converters begin with the assertion that inductor currents are fast states and capacitor voltages are slow states. This assertion must be true for power factor correction (PFC) converters to allow independent control of current and voltage. In the present work, singular perturbation theory is applied to boost converters to provide rigorous justification of the time scale separation. Krylov-Bogoliubov-Mitropolsky (KBM) averaging is used to include switching ripple effects. A relationship between inductance, capacitance, load resistance, and loss resistances derives from an analysis of an approximate model. Similar results hold for buck and buck-boost converters. An experimental boost converter and a simulated PFC boost support the derived requirement

Series-Parallel Approaches and Clamp Methods for Extreme Dynamic Response with Advanced Digital Loads

The series-input parallel-output dc-dc converter combination provides inherent sharing among the converters. With conventional controls, however, this sharing is unstable. Recent literature work proposes complicated feedback loops to correct the problem, at the cost of dynamic performance. This paper shows that a simple sensorless current mode control stabilizes sharing with fast dynamics suitable for advanced digital loads. With this control in place, a super-matched current sharing control emerges. Sharing occurs through transients, limited only by the energy limits of the converters. The control approach has considerable promise for high-performance voltage regulator modules. For even faster response, clamping techniques are proposed

Control Technique for Series Input-Parallel Output Converter Topologies

A series input-parallel output DC-DC converter topology inherently provides output current sharing among the phases, provided the input voltages are forced to share. With conventional output voltage feedback controls, input voltage sharing is unstable. Recent literature work proposes complicated feedback loops to provide stable voltage sharing, at the expense of dynamic performance. In the current work, a simple controller based on the sensorless current mode approach (SCM) stabilizes voltage sharing without compromising system performance. The SCM controllers reject source disturbances, and allow the output voltage to be tightly regulated by additional feedback control. With SCM control in place, a #super-matched# current sharing control emerges. Sharing occurs through transients, evolving naturally according to the power circuit parameters. The control approach has considerable promise for high-performance voltage regulator modules, and for other applications requiring high conversion ratios. Experimental results confirm the control operation. A sample four-phase converter has demonstrated good disturbance rejection, static sharing, and dynamic sharing

A Stabilizing, High-Performance Controller for Input Series-Output Parallel Converters

A form of sensorless current mode (SCM) control stabilizes sharing in multiphase input-series-output-parallel (ISOP) dc-dc converter topologies. Previously, ISOP converters have been proposed to reduce the voltage and current ratings of switching devices. Since the inputs are all connected in series, each phase need only be rated for a fraction of the total input voltage. Voltage and current sharing are key - if there is any phase-to-phase imbalance, the system benefits are substantially reduced. In the present work, a simple SCM controller is shown to guarantee stable sharing. Each phase acts independently on the same output reference and desired input voltage. The algorithm and the physics of the circuit lead to balanced input voltages and output currents, even during transients. The ISOP topology is a special case of an interleaved multiphase system. A reduced-order small-signal model is presented. The model is composed of two factors, a single-phase equivalent and a multidelay comb filter. The model fits a measured transfer function well and can be used in feedback design. Experimental results for a five-phase converter demonstrate fast response to a load step, line disturbance rejection, accurate static and dynamic sharing, and high efficiency

Increased Performance of Battery Packs by Active Equalization

Battery packs for most applications are series strings of electrochemical cells. Due to manufacturing variations, temperature differences, and aging, the individual cells perform differently. When a complete pack is charged and discharged as a single two-terminal circuit element, some cells are chronically overcharged, undercharged, or overdischarged, all of which act to reduce cell life. The performance and life of the complete pack is limited by the weakest cell. Many methods have been proposed and explored to mitigate this problem. In the present work, a switched-capacitor converter is shown to be a simple and effective method to maintain equal cell or monoblock charge conditions. Design criteria are discussed