Abstract: A battery pack includes a plurality of electrochemical cells and a control circuit. The battery pack provides power to a tool in the form of a pulse width modulated waveform. The plurality of electrochemical cells provide a total output voltage. The control circuit is coupled to the plurality of electrochemical cells and receives a trigger signal from the tool. In response to the trigger signal, the control circuit determines whether a pulse width of the pulse width modulated waveform requires adjustment. Additionally, the control circuit can be configured to receive an indication of the total output voltage. In this case, the control circuit determines whether the pulse width of the pulse width modulated wavefrom requires adjustment based on the level of the total output voltage.

Abstract: The introduction of new high power devices like integrated gate commutated thyristors (IGCTs) and high voltage insulated gate bipolar transistors (IGBTs) accelerates the broad use of pulse width modulation (PWM) voltage source converters in industrial and traction applications. This paper summarizes the state-of-the-art of power semiconductors. The characteristics of IGCTs and high voltage IGBTs are described in detail. Both the design and loss simulations of a two level 1.14 MVA voltage source inverter and a 6 MVA three-level neutral point clamped voltage source converter with active front end enable a detailed comparison of both power semiconductors for high power PWM converters. The design and the characteristics of a commercially available IGCT neutral point clamped PWM voltage source converter for medium voltage drives are discussed. Recent developments and trends of traction converters at DC mains and AC mains are summarized.

Abstract: This paper deals with an implementation of a new control algorithm for a three-phase shunt active filter to regulate load terminal voltage, eliminate harmonics, correct supply power-factor, and balance the nonlinear unbalanced loads. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a DC bus capacitor is used as an active filter (AF). The control algorithm of the AF uses two closed loop PI controllers. The DC bus voltage of the AF and three-phase supply voltages are used as feedback signals in the PI controllers. The control algorithm of the AF provides three-phase reference supply currents. A carrier wave pulse width modulation (PWM) current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBTs of the AF. Test results are presented and discussed to demonstrate the voltage regulation, harmonic elimination, power-factor correction and load balancing capabilities of the AF system.

Abstract: In this paper, a fast voltage control strategy of three-phase AC/DC pulsewidth modulation (PWM) converters applying a feedback linearization technique is proposed. First, incorporating the power balance of the input and output sides in system modeling, a nonlinear model of the PWM converter is derived with state variables such as AC input currents and DC output voltage. Then, by input-output feedback linearization, the system is linearized and a state feedback control law is obtained by pole placement. With this control scheme, output voltage responses become faster than those in a conventional cascade control structure. For robust control to parameter variations, integrators are added to the exact feedback control law. Since the fast voltage control is feasible for load changes, it is shown that the DC electrolytic capacitor size can be reduced. In addition, the capacitor current is analyzed for size reduction of the capacitor. As is usual with PWM converters, the input current is regulated to be sinusoidal and the source power factor can be controlled at unity. The experimental results are provided to verify the validity of the proposed control algorithm for a 1.5 kVA insulated gate bipolar transistor PWM converter system.

Abstract: Orthogonal frequency-division multiplexing (OFDM) baseband signals may be modeled by complex Gaussian processes with Rayleigh envelope distribution and uniform phase distribution, if the number of carriers is sufficiently large. The output correlation function of instantaneous nonlinear amplifiers and the signal-to-distortion ratio can be derived and expressed in an easy way. As a consequence, the output spectrum and the bit-error rate (BER) performance of OFDM systems in nonlinear additive white Gaussian noise channels are predictable both for uncompensated amplitude modulation/amplitude modulation (AM/AM) and amplitude modulation/pulse modulation (AM/PM) distortions and for ideal predistortion. The aim of this work is to obtain the analytical expressions for the output correlation function of a nonlinear device and for the BER performance. The results in closed-form solutions are derived for AM/AM and AM/PM curves approximated by Bessel series expansion and for the ideal predistortion case.

Abstract: A high-performance contactless electrical energy transmission (CEET) technique which employs the inductive energy transmission principle is described. The proposed technique enables the implementation of high-efficiency, high-power-density, fully-regulated CEET systems suitable for applications with a wide input range and a wide load range. The CEET system in this invention consists of an input-side variable-frequency inverter and an output-side regulated rectifier. A high efficiency of the system is achieved by recovering the energy stored in the leakage inductances of the transformer by incorporating them in the operation of the circuit, and by employing high-frequency-inverter and controlled-rectifier topologies that allow a controlled bi-directional power flow through the transformer. A feed forward, variable-switching-frequency control of the inverter is used to maintain a substantially constant power transfer through the transformer when the input voltage changes. A local PWM control is used for the output-side rectifier to achieve a tight regulation of the output in the presence of load variations.

Abstract: This paper introduces a new family of PWM DC-DC nonisolated converters. The new converters are generated using three-state commutation cells, comprising two active switches, two diodes and coupled inductors. The main advantages over the classical converters are low conduction and commutation losses, and low input and output current ripple. Due to these features, the new converters are suitable for low voltage and high current applications. Theoretical analysis and experimentation results are presented.

Abstract: In this paper, the relationship between common-mode voltage and switching states in a neutral-point-clamped (NPC) inverter is clarified, and a new pulsewidth-modulation (PWM) strategy for reducing the common-mode voltage in an NPC inverter-fed AC motor drives is proposed. Among a total of 27 switching states in the NPC inverter, the proposed PWM uses only 19 switching states that generate common-mode voltage of which the magnitude is the same or less than one-sixth of DC-bus voltage. Moreover, the proposed PWM strategy satisfied the constraint that the output voltage vector should be changed by only one switching action. Not requiring extra hardware, the NPC inverter with the proposed PWM results in a remarkable reduction in peak-to-peak of common-mode voltage, compared to a two-level inverter and an NPC inverter controlled by conventional PWM. The proposed PWM strategy can be easily implemented in software without degradation of control performance in AC motor drives.

Abstract: Frequency modulation (FM) and random switching methods have been used for reducing conducted electromagnetic interference (EMI) in power converters. Limited theoretical studies and comparisons of these schemes, however, are available. In this paper, a detailed analysis and the spectral characteristics of a random carrier-frequency (RCF) technique for suppressing conducted EMI in an offline switched-mode power supply are presented. The analysis provides a theoretical platform for studying the characteristics of this random switching scheme. The level of randomness is defined for the RCF scheme and varied in the converter example so that the effects on the power spectra can be demonstrated. Theoretical predictions of the spectral characteristics of this scheme are confirmed with measurements. The RCF scheme has been compared with the standard constant-frequency pulsewidth modulation (PWM) scheme and the FM scheme. Comparisons of their spectral performance show that the RCF scheme has better conducted EMI suppression than the FM and standard PWM schemes.

Abstract: This paper proposes a new family of random modulation techniques for three-phase power converters which operate with a fixed switching frequency. The techniques are based on adjusting the duration of the zero-vectors or adjusting the three pulse positions in a switching period. Three methods are selected for experimental tests because they preserve the fixed switching frequency known from standard PWM techniques. The new methods are also compared with random switching frequency modulation and with fixed switching frequency modulation. Voltage, current and acoustic noise spectra are used for comparison and it is concluded that two of the techniques are especially useful at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in some applications.

Abstract: Analytical solutions of pulse width modulation (PWM) strategies for multilevel neutral point clamped (NPC) and cascaded inverters are presented. These solutions show that the alternative phase opposition disposition (APOD) PWM strategy for NPC inverters produces the same spectral components as the phase shifted carrier PWM (PSCPWM) strategy for cascaded inverters, when the carrier frequencies are adjusted to achieve the same number of total switch transitions for each inverter over one fundamental cycle. From this understanding, a method is proposed to apply the harmonically superior phase disposition (PD) PWM strategy for NPC inverters to cascaded inverters, to achieve improved harmonic performance for the modulation of cascaded inverters. Both theoretical and experimental results confirming this understanding are presented.

Abstract: A multi-phase power supply utilizes a current sensor including a sensor inductor winding connected in parallel with a filter inductor winding at the output of each phase for sensing the phase currents and balancing the current by adjusting the duty cycle of each phase through feedback control. In addition, in a multi-module power supply configuration, current between power supply modules is balanced through use of the same current sensor and current sharing technique. Each phase of the power supply includes at least one input power source and a current sensor. The sensor inductor winding and the filter inductor winding have the same number of turns and are wound about a magnetic core also present at each phase. A differential amplifier at each phase senses and amplifies any voltage difference between the outputs of the sensor inductor winding and the corresponding filter inductor winding. A current-sharing bus is formed between each of the phases, carrying the summed and averaged outputs from all the differential amplifiers. A feedback correction circuit at each phase utilizes the voltage on the current-sharing bus as a reference to control a pulse width modulator in adjusting the duty cycle of the corresponding phase, thereby balancing the load current among the phases. In a multi-module, multi-phase power supply, the current-sharing bus and a voltage-sharing bus are extended between each module and the phases of each module to achieve the same current balancing between all phases and modules.

Abstract: This paper investigates the acoustic noise radiated from two nominally identical induction motors when fed from sinusoidal, and asymmetric regular sampling subharmonic and space-vector pulsewidth modulation (PWM) converters. The theory for analyzing the noise spectrum is developed further to account for the interaction between the motor and the drive. It is shown that manufacturing tolerances can result in significant differences in the noise level emitted from nominally identical motors, and that mechanical resonances can result in extremely high noise emissions. Such resonances can be induced by stator and rotor slot air-gap field harmonics due to the fundamental component of current, and by the interaction between the airgap field harmonics produced by the fundamental and the PWM harmonic currents. The significance of the effect of PWM strategy on the noise is closely related to the mechanical resonance with vibration mode order zero, while the PWM strategy will be critical only if the dominant cause of the emitted noise is the interaction of the fundamental air-gap field and PWM harmonics.

Abstract: For balancing battery cells connected in a series string, a simple and high performance battery balancing system is proposed. In this system, a technique of DC to DC converter with PWM control is used for balancing all cell voltages completely. The switching surge and noise are made small by soft switching with inductor commutation. This system is suitable for electric vehicles, hand-held personal computers, UPS etc.

Abstract: The electrical characteristics of an isolated induction-generator-based system are improved through the association with a voltage-source pulsewidth modulation (PWM) inverter The electronic converter allows the achievement of a better system behavior in many aspects: voltage regulation, frequency stabilization, and reactive power compensation The system operation strategy consists of maintaining constant synchronous frequency at the induction generator via an association with a PWM inverter The system power balance and the generator voltage regulation may be accomplished by two different means: through the rotor speed regulation, or by sending part of the energy stored in the inverter DC side to the grid through a single-phase line, in case the rotor speed is not regulated and a single-phase grid connection is available The obtained results demonstrated the system is stable, robust, and an effective source of regulated three-phase voltages

Abstract: The always-increasing switching frequency of modern solid-state power switches, together with the application of multi-converter topologies, make it possible to use pulse width modulation (PWM) in high power applications of STATCOMs (static synchronous compensators). This paper investigates the control system for a PWM-based STATCOM. First of all, a discrete-time model of the STATCOM is derived to take into account the discrete-time implementation of the controller. Secondly, the control algorithm is detailed. It ensures decoupled control of the real and reactive power exchanged between the power converter and the electric-energy system. This is necessary to control the DC capacitor voltage during transients of the exchanged reactive power. Finally, the control of the capacitor voltage is explained in detail. The controller is tailored to keep the capacitor voltage almost constant in spite of the fast control of the reactive power. This helps to reduce the capacitor size significantly. The main contributions are illustrated using a 15 kVA laboratory prototype.

Abstract: In this paper, an analysis of common mode voltage or "neutral lift" in the new emerging voltage source inverter type medium voltage adjustable speed drive (MV-ASD) systems is presented. Both cascaded multilevel (CML) inverter and 3-level NPC inverter topologies are analyzed. An equivalent circuit model to determine the common mode voltage stress is presented. Analysis and simulation results are discussed and worst case common mode voltage excursion is computed for an example 800 hp, 4160 V MV-ASD. It is shown that certain system components are excessively stressed and in the MV-ASD system these data are particularly useful in specifying system components and for proper design of the system. Possible effects of common mode voltage and its dv/dt on medium voltage motor bearings are discussed. A new multilevel PWM strategy is introduced which results in zero common-mode voltage. Simulation results are shown to illustrate the effectiveness of these schemes. Finally, experimental results from a 800 hp, 4160 V, MV-ASD system are presented.

Abstract: In this paper two different control strategies for a PWM rectifier without line voltage sensors are compared. The direct power control (DPC) which has no need for line voltage measurements is compared to the conventional voltage oriented control (VOC) strategy in rotating coordinates with a novel line voltage estimator. The steady-state performance of both strategies is compared with regards to voltage unbalance and pre-distorted grid. Furthermore, the use of discontinuous modulation is motivated in the classical control strategy and is analyzed along with the novel line voltage estimator. It is shown that the VOC strategy with line voltage estimator exhibits several advantages compared to DPC. Some simulations and experimental results verifying the comparison are presented.

Abstract: This paper proposes a control method for three-phase voltage-source PWM rectifiers using only a single current sensor in the DC-link. A PWM modulation strategy for reconstructing three phase currents from the DC-link current is given. When 3/spl phi/ input currents cannot be reconstructed, a method for modifying the switching state of the PWM rectifier and a method for the predictive state observer is proposed. Compensation of the 2 sampling delays is also included, and this method is combined with all of the experiments. Performance differences between the two methods in a typical voltage source PWM rectifier are investigated experimentally.

Abstract: A comparative investigation on the use of random modulation schemes for DC/DC power converters is presented. The modulation schemes under consideration include randomized pulse position modulation, randomized pulsewidth modulation (PWM) and randomized carrier-frequency modulation with fixed and variable duty cycle. The paper emphasizes the suitability and applicability of each scheme in DC/DC power converters. Issues addressed include the effectiveness of randomness level on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes, and the low-frequency power spectral density (PSD) of each scheme. The validity of the analyses is confirmed experimentally by using a DC/DC buck converter operating in the continuous conduction mode. The PSD of the output under each scheme is presented and compared.

Abstract: This paper presents a new control strategy to improve the performance of the PWM boost type rectifier when operating under an unbalanced supply. An analytical solution for harmonic elimination under unbalanced input voltages is obtained resulting in a smooth (constant) power flow from AC to DC side in spite of the unbalanced voltage condition. Based on the analysis of the open loop configuration, a closed loop control solution is proposed. Simulation results show excellent response and stable operation of the new rectifier control algorithm. A laboratory prototype has been designed to verify the discussions and analyses done in this paper. Theoretical and experimental results show excellent agreement. Elimination of the possibility of low order AC and DC side harmonics due to unbalance is expected to materially affect the cost of DC link capacitor and AC side filter. The proposed method will be particularly useful in applications where the large second harmonic at the DC link may have a severe impact on system stability of multiply connected converters on a common link.

Abstract: This paper describes design and implementation of a digital controller for an experimental low-power converter in a battery-powered system with power management. Multiple operating modes are used to maintain high efficiency over wide ranges of input voltages and loads. A current estimation technique to perform load-dependent mode switching is proposed and tested. A digital PID regulator design example is described, with emphasis on practical limitations imposed by the fixed-point arithmetic and the delay due to sampling and processing.

Abstract: This paper introduces a true zero-current and zero-voltage transition (ZCZVT) commutation cell for DC-DC pulsewidth modulation (PWM) converters operating with an input voltage less than half the output voltage. It provides zero-current switching (ZCS) and zero-voltage switching (ZVS) simultaneously, at both turn on and turn off of the main switch and ZVS for the main diode. The proposed soft-switching technique is suitable for both minority and majority carrier semiconductor devices and can be implemented in several DC-DC PWM converters. The ZCZVT commutation cell is placed out of the power path, and, therefore, there are no voltage stresses on power semiconductor devices. The commutation cell consists of a few auxiliary devices, rated at low power, and it is only activated during the main switch commutations. The ZCZVT commutation cell, applied to a boost converter, has been analyzed theoretically and verified experimentally. A 1 kW boost converter operating at 40 kHz with an efficiency of 97.9% demonstrates the feasibility of the proposed commutation cell.

Abstract: Three-phase current-type pulse width modulation (PWM) rectifiers are becoming increasingly popular as the front-end converter unit in power electronic systems due to tighter electromagnetic compatibility (EMC) regulations. In this paper the control of the current source PWM rectifier in the synchronously rotating reference frame is discussed. A control system is presented in which the active and reactive power are independently controlled with real and imaginary axis components of the supply current vector. A new damping method for supply current oscillations is introduced. The method operates in an open-loop manner and is very suitable for microcontroller implementation since the calculation power demand is low. Furthermore, it is shown that in the synchronously rotating coordinates, where the sinusoidal variables appear as DC quantities, the compensation of the reactive power drawn by the supply filter can be done very easily. The proposed control methods are realized using a single-chip Motorola MC68HC916Y1 microcontroller. The experimental tests show excellent performance in both steady state and transient conditions.

Abstract: In this paper, a novel control scheme of three-phase PWM rectifiers eliminating the AC voltage and current sensors is proposed. Both the phase angle and the magnitude of the source voltage are estimated by controlling the deviation between the rectifier current and its model current to be zero. The phase currents can be reconstructed from switching states of the PWM rectifier and the measured DC link currents. To eliminate the calculation time delay effect of the microprocessor, a predictive state observer is employed. The proposed control scheme reduces the system cost and improves its reliability. The feasibility of the proposed AC sensorless technique for PWM rectifiers has been verified through experiments using a high performance DSP chip.

Abstract: A Class D amplifier comprises a pulse width modulator and an output stage. In this paper we analyze the power dissipation mechanisms and derive the overall power efficiency of the output stage realized using the finger and waffle layouts. We compare the relative merits of these layouts; we propose two design methodologies to determine the aspect ratios of the transistors in the output stage for optimum power efficiency (optimum for a given fabrication process, supply voltage and load resistance): (1) optimization to a single modulation index point and (2) optimization to a range of modulation indexes. For the design of an output stage with optimum power efficiency (and small IC area), we recommend optimization to a range of modulation indexes and a layout realized by the waffle structure. The theoretical analysis and derivations are verified on the basis of computer simulations and measurements on fabricated prototype ICs.

Abstract: This paper proposes a transformer-assisted pulsewidth modulation (PWM) zero-voltage switching pole inverter. As the auxiliary-resonant-commutated pole inverter (ARCPI), the proposal guarantees zero-voltage switching of the main switch and zero-current switching of the auxiliary switch, with a small power auxiliary circuit and full PWM capability. In particular, problems outstanding with the ARCPI such as control complexity, auxiliary switch protection, and center-tap potential variation, etc., are solved in the proposal. The commutation process is discussed step by step in the paper. A detailed analysis for the auxiliary circuit with regard to commutation duration/duty-cycle limitation, auxiliary switch peak current/RMS current, resonant capacitor RMS current, as well as pole output voltage loss are presented afterwards. A design methodology for the auxiliary circuit is recommended based on the analysis. The proposal is experimentally verified with a 4.25 kW half-bridge inverter prototype.

Abstract: Power electronic converters, when tightly regulated, have constant power sink characteristics at their inputs. This is a destabilizing effect, which is known as negative impedance instability, for the DC/DC converters feeding these loads in a multi-converter power electronic system. In this paper, necessary and sufficient conditions of stability for PWM DC/DC converters with constant power and conventional constant voltage loads are expressed. A nonlinear robust stabilizing controller based on feedback linearization techniques is proposed. Furthermore, the stability of the proposed controller for the Buck converter using the second theorem of Lyapunov is verified.

Abstract: A PWM current source frequency converter is an alternative to control variable speed AC-drives instead of commonly used voltage source frequency converters. Space vector control techniques are widely adopted for high performance drives while the control system is most conveniently implemented by microprocessors, microcontrollers and DSPs. Space vector pulse width modulation is also an appropriate technique for the phase current modulation of a current source converter (CSC). Either "5-switch" or "4-switch" space vector modulation can be used, the latter being perhaps more popular. Different modulation strategies can be developed by selecting an appropriate vector sequence for the switching cycle. Therefore this paper discusses the significance of the vector sequence on the IGBT switching voltages in order to reduce switching losses of the CSC bridge. An optimal vector modulation strategy, which minimizes the switching losses of the CSC bridge, is developed and analyzed in detail. Finally, the results are verified by PSpice(R) simulations.