Deepakraj M. Divan

Performance characterization of a high-power dual active bridge DC-to-DC converter

The analysis, control, and performance of a high-power, high-power-density DC/DC power converter that is based on the single-phase dual active bridge topology is described. For high-output voltages, on the order of kilovolts, a cascaded output structure is considered. The impact of snubber capacitance and magnetizing inductance on the soft switching region and various control strategies are discussed. Computer simulation results of a current mode controller are presented. Since the leakage inductance of the transformer is the main energy transfer element, special transformer design techniques are utilized to carefully control this parameter. The layout for a completed prototype 50 kW, 50 kHz unit operating with an input voltage of 1600 VDC is presented. Some experimental results are also presented.<<ETX>>

Zero-switching-loss inverters for high-power applications

The development of zero switching loss inverters has attracted much interest for industrial applications. Two topologies for realizing zero switching losses in high-power converters are proposed. The actively clamped resonant DC link inverter uses the concept of a lossless active clamp to restrict voltage stresses to only 1.3-1.5 supply voltage. For applications demanding substantially better spectral performance, the resonant pole inverter (RPI), also called the quasi-resonant current mode inverter, is proposed as a viable topology. Using only six devices rated at supply voltage, this circuit transfers the resonant components to the AC side of each phase and thus requires additional inductor and capacitor (LC) components. On the other hand, the RPI is capable of true pulsewidth modulation (PWM) operation at high frequency as opposed to discrete pulse modulation operation found in resonant DC link invertors. >

Acoustic noise reduction in sinusoidal PWM drives using a randomly modulated carrier

Acoustic noise in an inverter-driven AC electric machine can be reduced by avoiding the concentration of harmonic energy in distinct tones. One method to spread out the harmonic spectrum without the use of programmed PWM (pulse-width modulation) is to cause the switching pattern to be random. It is proposed that the switching pattern can be randomized by modulating the triangle carrier in sinusoidal PWM (pulse-width modulation) with bandlimited white noise. All the advantages of sinusoidal PWM are preserved with this technique. These include real-time control, linear operation, good transient response, and a constant average switching frequency. By controlling the bandwidth and RMS value of the pink noise modulation, it is shown that the instantaneous variation in switching frequency as well as the bandwidth of the energy spectrum in the machine can be specified within predetermined limits. Experimental results show the absence of acoustic noise concentrated at specific tones which is present with conventional sinusoidal modulation. >

Design considerations for charge equalization of an electric vehicle battery system

Charge equalization for series-connected battery strings has important ramifications on battery life. It enhances the uniformity of the battery cells and, hence, improves the life of the battery as a whole. A new charge equalization technique for a series string of battery cells has been recently proposed by the authors. The basic technique utilizes a simple isolated DC-to-DC power converter with a capacitive output filter along with a multiwinding transformer. The possibility of integrating the trickle charge function with the charge equalization function is potentially very attractive, as it can lead to an efficient and low-cost implementation.

Comparison of multilevel inverters for static VAr compensation

Inverter-based static VAr compensators (SVCs) can benefit from the use of a multilevel invertor structure which allows the elimination of the step-up transformer. The inherent high quality of the multistep waveform allows operation without PWM, thus high switching losses are avoided. This paper discusses the issues affecting the application of multilevel invertor structures as reactive power compensators and compares the device MVA and reactive component MVA requirements of two topologies that have been presented in prior literature. The modulation strategy strongly affects the voltage balancing in the DC bus capacitors as well as their ripple current rating and capacitance value.<<ETX>>

Angle controlled current regulated rectifiers for AC/AC converters

Rectifier control schemes for use in AC-DC-AC voltage-sourced resonant link converters with controlled rectifiers are discussed. Resonant link converters require the use of discrete pulse modulation. Control of the AC-to-DC converter by means of averaging methods or duty-cycle control is not inherent with this type of modulation. However, it is shown that the voltage-sourced rectifier cannot be operated solely on the basis of instantaneous quantities. A bang-bang control scheme is developed which independently controls the angle and the magnitude of the AC line current vector. The magnitude of the current is controlled using a linear combination of the link voltage error and the current magnitude error. The current reference is derived by the use of load torque estimation. In addition, the current vector that satisfies the sliding-mode criteria and results in the lowest voltage ripple is chosen to further minimize the size of the link capacitor. >

Control strategies for direct torque control using discrete pulse modulation

A scheme for direct torque control of AC machines using discrete pulse modulated inverters, such as the resonant DC link inverter, is presented. A unique feature of the control method presented is that only one current sensor in the DC link is required. Excellent control of torque, stator flux and motor current waveshapes is obtained without affecting the high dynamic performance associated with the direct self-control of machines. A control that does not use the zero voltage vector is defined, and an observer is proposed for estimation of the motor current using only one current sensor in the DC link. A direct bang-bang (sliding mode) torque controller is then derived on the basis of this current observer. Experimental verification of simulation results on a resonant DC link inverter drive with a switching frequency of 27 kHz is included. The inverter switching scheme is implemented using a real-time Motorola DSP56000 digital signal processor-based controller.<<ETX>>

Synchronous frame based controller implementation for a hybrid series active filter system

This paper proposes a synchronous reference frame based controller for a hybrid series active filter system. A hybrid series active filter system has been designed, built and installed at Beverly Pump Station in New England Electric utility for 765 kVA adjustable speed drive load to meet IEEE 519 recommended harmonic standards. The series active filter is rated 35 kVA-4% of the load kVA, and is controlled by a synchronous reference frame based controller to act as a harmonic isolator between the supply and load. This paper discusses the basic synchronous reference frame controller structure and addresses its operation under nonunity controller loop gain conditions. Design trade-offs and implementation issues of the synchronous reference frame controller are discussed. Operation of the hybrid series active filter system under off-tuned passive filter conditions and its impact on the performance of the synchronous reference frame based controller is experimentally evaluated. Effectiveness of the series active filter to provide harmonic damping and the use of simpler and low cost power factor correction capacitors as passive filters, is demonstrated by laboratory experimental results. Field installation and laboratory experimental results demonstrate the practical viability of the synchronous reference frame based controller for hybrid series active filter to provide harmonic isolation of nonlinear loads and to comply with IEEE 519 recommended harmonic standards.

Flux-based active filter controller

This paper presents a synchronous frame flux-based control method for a parallel active filter application. The flux-based controller directly implements the inverter switchings in the synchronous reference frame by a hysteresis rule-based carrier-less pulse-width modulation (PWM) strategy to achieve high current bandwidth. This paper addresses the issues and impact on parallel active filtering requirements for utility interface of commonly used harmonic front-ends. The synchronous frame flux-based controller provides additional insights for harmonic current compensation requirements. Simulation results provide the validation of the flux-based active filter controller to meet IEEE Standard 519 recommended harmonic standards for large rated nonlinear loads under balanced and unbalanced supply conditions.

Contactless power delivery system for mining applications

The ability to transfer large amounts of electrical power (up to 1 MW) to a moving load has traditionally used means that are unreliable, inefficient, and potentially unsafe. These include sliding or rolling metal contacts, sliding carbon brushes, and trailing cables. More recently, flat inductively coupled coils have been used to help mitigate these problems. Except for the inductively coupled coils, these techniques have not been developed with the capabilities of power electronics in mind. This paper presents the first conceptual description of a power delivery system design unifying power electronics and a coaxial-winding transformer for devices that require a contactless connection and/or relative motion while delivering large amounts of power. The transformers unique characteristics and how they might be used to advantage in combination with power electronics are emphasized. Potential applications are flexible power distribution, material handling, electric vehicle boost, and battery opportunity recharge. Test results of a small scale prototype are presented and verify these initial concepts.