Petar J. Grbovic

Master/Slave Control of Input-Series- and Output-Parallel-Connected Converters: Concept for Low-Cost High-Voltage Auxiliary Power Supplies

This paper deals with low-cost high input voltage auxiliary power supplies. The objective of the paper is to give an overview of the existing solutions, and then present a new, efficient, and cost-effective solution. The proposed solution is based on input-series- and output-parallel (ISOP)-connected converters topology and simple decoupled master/slave control strategy. The main output voltage is controlled by the master converter, while the input voltages and output currents are controlled and balanced by the slave converter. The ISOP topology has two important advantages, namely the use of two series-connected rated for lower voltage converters gives a significant reduction of the switch-mode power supply overall cost and size, and loss free balancing of the voltages of the input serially connected filter capacitors. The proposed solution is theoretically analyzed and experimentally verified on a laboratory setup. The experimental results are presented and discussed.

An IGBT Gate Driver for Feed-Forward Control of Turn-on Losses and Reverse Recovery Current

This paper addresses the problem of turn on performances of an insulated gate bipolar transistor (IGBT) that works in hard switching conditions. The IGBT turn on dynamics with an inductive load is described, and corresponding IGBT turn on losses and reverse recovery current of the associated freewheeling diode are analysed. A new IGBT gate driver based on feed-forward control of the gate emitter voltage is presented in the paper. In contrast to the widely used conventional gate drivers, which have no capability for switching dynamics optimisation, the proposed gate driver provides robust and simple control and optimization of the reverse recovery current and turn on losses. The collector current slope and reverse recovery current are controlled by means of the gate emitter voltage control in feed-forward manner. In addition the collector emitter voltage slope is controlled during the voltage falling phase by means of inherent increase of the gate current. Therefore, the collector emitter voltage tail and the total turn on losses are significantly reduced. The proposed gate driver was experimentally verified and compared to a conventional gate driver, and the results are presented and discussed in the paper.

The Ultracapacitor-Based Controlled Electric Drives With Braking and Ride-Through Capability: Overview and Analysis

Two issues are still a great challenge in design and application of advanced controlled electric drives: 1) recovery of the braking energy and 2) ride-through capability of the drive system. Apart from ordinary solutions, such as back-to-back and matrix converters, the ordinary drive converter equipped with an energy storage element is used in specific applications such as traction and lift drives. This approach came into focus recently with rapid development of electrochemical double-layer capacitors, so-called ultracapacitors. The ultracapacitor is an electrochemical capacitor having energy density much greater than that of standard electrolytic capacitors. Additionally, the ultracapacitor power density is much higher than that of the existing electrochemical batteries. In this paper, a regenerative controlled electric drive having extended ride-through capability is discussed. The basic principle has been extensively analyzed, including a detailed analysis of all operational modes. A bidirectional three-level dc-dc converter has been considered as the interface power converter. The ultracapacitor design guideline is given. A control algorithm that allows control of the dc bus voltage and the ultracapacitor voltage and current has been presented and briefly analyzed. The regenerative controlled drive system has been tested, and the results are presented and discussed.

Modeling and Control of the Ultracapacitor-Based Regenerative Controlled Electric Drives

Two issues are still a great challenge in the design and application of advanced controlled electric drives, namely, recovery of the braking energy and ride-through capability of the drive system. Apart from the ordinary solutions, such as back-to-back and matrix converters, an approach based on the ordinary diode front-end-drive converter equipped with an energy-storage element is used in some applications, such as traction and lift drives. This approach has come into focus recently with the rapid development of electrochemical double layer capacitors, so-called ultracapacitors. To achieve system flexibility and better efficiency, the ultracapacitor is connected to the drive via a dc-dc converter. The converter is controlled in such a way as to fulfill the control objectives: the control of the dc-bus voltage, the ultracapacitor state of charge, and peak-power filtering. In this paper, we have discussed the modeling and control aspects of the regenerative controlled electric drive using the ultracapacitor as energy-storage and emergency power-supply device. The presented model and control scheme have been verified by simulation and a set of experiments on a 5.5-kW prototype. The results are presented and discussed in this paper.

A Novel Three-Phase Diode Boost Rectifier Using Hybrid Half-DC-Bus-Voltage Rated Boost Converter

A novel three-phase diode boost rectifier is proposed in this paper. The core of the proposed topology is a power conversion device [the loss-free transformer (LFT)] with two terminals; one input and one output. The input is parallel-connected with the dc bus capacitor, while the output is connected between the rectifier plus rail and the dc bus plus rail. The LFT is controlled in such a way to control the rectifier current and boost the dc bus voltage. In contrast to the ordinary boost rectifiers, the switches of the new boost rectifier are rated on a fraction of the dc bus voltage and a fraction of the input current. It makes this topology very compact and efficient. Power rating, size, and losses depend strongly on the ratio of the dc bus voltage to rectifier voltage (boosting factor). For example, if the boosting factor is low, below 1.5, the power converter efficiency could be 98-99%. The proposed boost rectifier has been analyzed and experimentally verified on a 5.5-kW prototype. The results are presented and discussed.

The Ultracapacitor-Based Regenerative Controlled Electric Drives With Power-Smoothing Capability

Modern controlled electric drive applications, such as lifts, port rubber tyred gantry cranes, and tooling machines, are characterized by high ratio of the peak to average power. Moreover, such applications have a need for braking at rated power. In ordinary drives, the braking energy, which represents 30%-40% of the consumed energy, is dissipated on a brake resistor. Apart from this “energetic” issue, the mains interruption, the input current quality, and the mains peak power are additional issues to be addressed. A novel ultracapacitor-based controlled regenerative electric drive with peak power-smoothing function is presented in this paper. The ultracapacitor with an interconnection dc-dc converter is used to store and recover the braking energy. In addition, the dc-dc converter controls and smooths the rectifier input power. In comparison to state-of-the-art solutions, the new solution has better performance regarding size, cost, and efficiency. The presented solution is theoretically analyzed and experimentally verified. The results are presented and discussed.

A Three-Terminal Ultracapacitor-Based Energy Storage and PFC Device for Regenerative Controlled Electric Drives

Most of modern controlled electric drive applications, such as lifts, cranes, and tooling machines, are characterized by a high ratio of the peak to average power. In addition, such applications have high demand for braking at the full rated power. In ordinary drives, the braking energy, which represents 30%-50% of the consumed energy, is dissipated on a brake resistor. Apart from this “energetic” issue, power supply interruption and the input current quality are two additional issues to be solved. A novel regenerative controlled electric drive based on an ultracapacitor as energy storage is presented in this paper. The ultracapacitor with an interface dc-dc converter is used to store and recover the braking energy. In addition, the dc-dc converter controls the rectifier current and reduces the drive input current total-harmonic-distortion factor down to 30%. Moreover, the dc bus voltage is boosted and controlled to be constant and ripple free regardless of the load and the mains voltage variation. In comparison to state-of-the-art solutions, the new solution has better performance regarding size, cost, and efficiency. The presented solution is theoretically analyzed and experimentally verified. The results are presented and discussed.

Loss-Free Balancing Circuit for Series Connection of Electrolytic Capacitors Using an Auxiliary Switch-Mode Power Supply

Most of todays power converters such as three-phase variable-speed drives, uninterruptible power systems, welding converters, and telecom and server power supplies are based on voltage-source converters equipped with bulky DC-link electrolytic capacitors. To be able to handle full DC bus voltage, the DC bus capacitor is arranged as series-connected electrolytic capacitors rated at lower voltage. An electrolytic capacitor, however, is not an ideal capacitor. It has significant leakage current that strongly depends on the capacitor temperature, voltage, and ageing conditions. To compensate large dispersion of the leakage current and ensure acceptable sharing of the total DC bus voltage among the series-connected capacitors, a passive balancing circuit is often used. Drawbacks of the ordinary passive balancing circuit, such as size, significant losses, and standby consumption are discussed in this paper. An active loss-free balancing circuit, which utilizes an auxiliary switch-mode power supply (SMPS) to equalize the capacitor voltages, is proposed. The capacitors midpoint (MP) is connected to the SMPS via two devices; namely a current injection device and a compensation device. The current injection device injects current into the capacitors MP, while the compensation device sinks the difference between the capacitor leakage currents and the injected current. As a result, the capacitor voltages are controlled and maintained in the desired ratio. The proposed balancing technique is theoretically analyzed and experimentally verified on a laboratory setup. The results are presented and discussed.

Efficiency optimization of a single-phase boost DC-DC converter for electric vehicle applications

One of the main problems in autonomous electric vehicles is the energy storage, because a high autonomy and high power condition demand large mass, big volume and high cost of the storage unit. Consequently, in order to avoid power losses and to downsize the storage unit and the electric systems, the electric power train in the vehicle must be as efficient as possible. This paper proposes a methodology to optimize the efficiency of a DC-DC converter that interface the storage unit with the motors drive. In this way, with the purpose of increasing the efficiency, this methodology combines three techniques: 1) The use of low-loss components such as Si CoolMos, GaN and SiC diodes and Mosfets, and Multilayer Ceramic Capacitors, 2) a complete power loss analysis as a function of the switching frequency and a calculation method of core losses based on the approximation of Fourier Series, and 3) the Area Product Analysis of magnetic components. With this methodology, it is possible to achieve high efficiency and high power density, which is suitable for automotive applications. The methodology has been verified with a set of tests on a 1kW prototype. As a result of the proposed methodology, a power efficiency of 99% was experimentally obtained.

Five-Level Unidirectional T-Rectifier for High-Speed Gen-Set Applications

Multilevel power electronic topologies are being proposed in the recent technical literature for use in power generating units, especially when the reduction in the power filter overall dimensions and the lowering of current and voltage waveform ripple and total harmonic distortion are considered of primary importance. This is the case of high-speed gen-set units, where recent design techniques on high rotational speed permanent-magnet synchronous generators (PMSGs) have significantly reduced the inductance even for industrial voltage rated applications. This paper deals with a five-level unidirectional T-rectifier (5L T-RECT); the proposed topology is theoretically investigated, and simulation results and losses analysis are achieved with reference to an insulated-gate bipolar transistor (IGBT) phase-leg module which has been manufactured on purpose and tested.