Pulse width modulation type audio amplifier having variable average switching frequency

Pulse width modulation (PWM) techniques involving different switching sequences are used in space vector-based PWM generation for reducing line current ripple in induction motor drives. This study proposes a hybrid PWM technique employing five switching sequences. The proposed technique is a combination of continuous PWM, discontinuous PWM (DPWM) and advanced bus clamping PWM methods. Performance of the proposed PWM technique is evaluated and compared with those of the existing techniques on a constant volts per hertz induction motor drive. In terms of total harmonic distortion in the line current, the proposed method is shown to be superior to both conventional space vector PWM (CSVPWM) and DPWM over a fundamental frequency range of 32–50 Hz at a given average switching frequency. The reduction in harmonic distortion is about 42% over CSVPWM at the rated speed of the drive.

A method of deriving the switching instants of different space vectors in the direct torque control of induction motor drives using pulse width modulated voltage source inverters is described in this paper. The switching instants of different space vectors are determined to reduce torque ripple compared to the commonly used space vector concept based on the sinusoidal pulse width modulation technique. The time durations of two adjacent voltage space vectors and the corresponding zero voltage space vectors are determined in this method depending on maximum and average switching frequency, allowable for the switching devices in the three-phase inverter. The sampling rate of the impressed reference voltage vector (in other words the switching frequency of the carrier wave) is varied to keep the torque ripple within the specified limit, determined by maximum allowable switching frequency. This paper also deals with the optimum switching pattern to reduce the average switching frequency of the switching devices. A simulation program is developed in order to verify the validity of the theory.

This paper presents the application of the Finite Control Set - Model Predictive Control (FCS-MPC), or simply MPC, for grid current control for three rectifier topologies based on dual converters. Two of the topologies have a reduced number of controlled switches, replacing some of the Insulated Gate Bipolar Transistors (IBGTs) by diodes. Despite these topologies have been discussed in the literature, they always employ Proportional-Integral (PI) controllers and pulsewidth modulation (PWM) strategies. This paper will show that the MPC method is able to provide sinusoidal currents with low harmonic content. Simulations are performed in order to compare MPC and PWM performances and an experimental result is provided for one of studied configurations. It is shown that for the same average switching frequency, MPC provides currents with harmonic content somewhat higher than PWM. On the other hand, transient response to reference changes is much faster and smoother when MPC is applied.

Advanced bus-clamping pulse width modulation (ABCPWM) techniques have been shown to outperform continuous and discontinuous (i.e. bus-clamping) pulse width modulation methods in terms of line current distortion, pulsating torque (in case of motor drives) and inverter switching loss at a given average switching frequency under certain operating conditions. These ABCPWM methods clamp a phase to a dc rail (as in discontinuous modulation) and switch another phase at twice the nominal switching frequency (unlike discontinuous modulation). The `double-switching' of the three phases in different intervals makes the implementation of such modulation schemes challenging. Further, the microcontrollers and digital signal processors available for power electronic applications are oriented towards implementation of continuous and discontinuous modulation schemes. This paper discusses the implementation of ABCPWM schemes on such processors. The features of the on-chip pulse-generation module in the digital signal processor are effectively utilized so as to avoid external hardware and to reduce the number of interrupts.

A multiaverage random switching frequency space vector pulsewidth modulation (MARSF-SVPWM) strategy is proposed in this article, in order to further disperse the high-order harmonics concentrated at the switching frequency and its integer multiplies in the output voltage of the inverter. The proposed strategy divides the fundamental period equally, with different stages corresponding to different average switching frequencies and spread-spectrum ranges, in contrast with the conventional random switching frequency space vector pulsewidth modulation (RSF-SVPWM), under the premise of maintaining the same overall average switching frequency and spread-spectrum range. The simulation and experimental results demonstrate that, even in the case of a narrow spread-spectrum range, the proposed MARSF-SVPWM strategy can obtain a better effect of high-order harmonic dispersion.

Despite the intensive research work on the application of model predictive control (MPC) for multi-phase machines, there are many challenges still to be handled such as high circulating currents, variable switching frequency, and high computation burden. This paper proposes a simple, yet efficient predictive current control (PCC) for six-phase induction motor (IM) that reduces considerably circulating current, computation cost, and switching frequency. In the proposed method, a group of four candidate voltage vectors (VVs) is formed in each control sample. Unlike similar methods reported in literature, these candidate vectors are generated based on a simple lookup table and the previous optimal VV. The lookup table is designed such that it allows only one commutation in each control sample. The performance of the proposed method is assessed experimentally using a one kW asymmetrical six-phase induction motor (A6PIM). Different performance indices are investigated to compare the proposed method against two different PCC methods in literature at different operating conditions. The experimental results confirm that about 50% reduction in average switching frequency and 15% in current total harmonic distortion at different speed ranges are observed with the proposed method compared to the conventional one.

Rotor eddy current loss reduction, which may largely depend on the pulse-width modulation (PWM) strategies, is a key issue for high-speed permanent magnet synchronous motors (PMSM). In this paper, five PWM strategies are applied to a surface-mounted PMSM, respectively, and the rotor eddy current losses are investigated with FEM. Influence of the PWM strategies and their average switching frequency on the rotor eddy current loss is figured out, so that conclusions of reducing rotor eddy current loss in the high-speed PMSMs can be drawn.

The LCL filter is often the bulkiest component in grid-tied converters, which is designed to satisfy the grid harmonic standards such as IEEE519. To reduce the filter requirement, application of the spread spectrum modulation (SSM) to LCL filter design is investigated in this paper. Filter design methodology for SSM is presented and a comparative analysis between the conventional pulse-width modulation (PWM) and SSM is carried out focusing on their impact on the filter design. It is shown that under the same average switching frequency, LCL filter parameters required for SSM can be substantially reduced compared to the conventional PWM.

Power converters with semiconductors switching only at predefined, equidistant instants — known as "discrete-time switching", "synchronized switching" or "clocked commutation" — show considerably different current control behavior compared to pulse-width modulated (PWM) converters with linear current con trollers. This paper presents and explains some of the effects of discrete-time-switching on output current waveforms, especially when using a predictive switching state selection algorithm. Typical characteristics of generated switching state patterns are presented. A single-phase and a three-phase inverter controlled by a predictive discrete-time modulation strategy are considered. Analytical, experimental and simulation results show that average switching frequency and error current RMS are well defined, in spite of the inherent randomness of the control scheme.

Simulators have been used to evaluate drivers' reactions to various transportation products. Most research, however, has concentrated on their technical performance. This paper considers driver's motion perception on a vehicle simulator through the analysis of human sensibility ergonomics. A sensibility ergonomic method is proposed in order to improve the reliability of vehicle simulators. A simulator in a passenger vehicle consists of three main modules such as vehicle dynamics, virtual environment, and motion representation modules. To evaluate drivers' feedback, human perceptions are categorized into a set verbal expressions collected and investigated to find the most appropriate ones for translation and angular accelerations of the simulator. The cut-off frequency of the washout filter in the representation module is selected as one sensibility factor. Sensibility experiments were carried out to find a correlation between the expressions and the cut-off frequency of the filter. This study suggests a methodology to obtain an ergonomic database that can be applied to the sensibility evaluation of dynamic simulators.

This paper presents a controller-hardware-in-the-loop simulation (C-HILS) framework for validating models, evaluating control performance, and assessing the thermal lifetime of a tens-of-kilowatt inverter. The real inverter and the C-HILS platform were operated in parallel, and accuracy was quantified using phase-current root mean square error, voltage spectral analysis, and total harmonic distortion (THD). Across a wide range of SVPWM and DPWM cases, deviations remained within 2–5%, confirming close agreement between experiment and simulation. Using the validated C-HILS system, sampling frequency and output power were swept while comparing current tracking, THD, average switching frequency, semiconductor losses, and efficiency. SVPWM achieved lower THD, whereas DPWM reduced average switching frequency and switching losses, improving efficiency. C-HILS waveforms were then applied to a Foster thermal network to reconstruct the junction–temperature trajectory; Tj(t), and ΔTj and Tj,min were mapped to lifetime using the Bayerer model. For a representative cyclic mission, ΔTj decreased from approximately 25.6 °C with SVPWM to about 17.5 °C with DPWM, increasing the estimated lifetime from approximately 1.36 years to 9.14 years. These results demonstrate that the proposed C-HILS framework provides a unified pre-prototype tool for model verification, control strategy comparison, and quantitative thermal reliability assessment of shipboard propulsion inverters.

A multistep model predictive current control strategy for reducing the switching frequency of inverters is proposed to address the challenges of low energy efficiency of small power induction motors. Based on the discrete mathematical model of the motor drive system, the strategy extends the current trajectory corresponding to each allowable switching sequence employing iterative prediction with quadratic interpolation, and uses average switching frequency within the predicted range as a cost function. In order to acquire the ideal switching vector in real-time, the cost function conducts online rolling optimization. Compared to model predictive direct current control, this method can reduce the average switching frequency of the two-level inverter while enhancing current harmonic performance. The simulation results verify the efficiency of the proposed method.

Finite-state predictive torque control (FS-PTC) is computationally expensive, since it uses all voltage vectors (VVs) available from a power converter for prediction and actuation. The computational burden is rapidly increased with the number of VVs and objectives to be controlled. Moreover, designing a cost function with more than two control objectives is a complex task. This paper proposes a simplified algorithm based on a new direct torque control (DTC) switching table to reduce the number of VVs to be predicted and objectives to be controlled. The new switching table also assists to reduce average switching frequency and its variation range. As a result, the cost function is simplified by not requiring to include the frequency term. Experimental results show that the average execution time and the average switching frequency for the proposed algorithm are greatly reduced without affecting the torque and flux performances achieved in the conventional FS-PTC.

An improved model predictive direct power control (MPDPC) for three-phase grid-connected converters is proposed. In the proposed method, two voltage vectors are applied during a control period and their duty cycles are determined by a fuzzy logic-based modulator. The inputs to the modulator are the active and reactive power errors and the output is the duty cycle of the first (main) voltage vector. The fuzzy rules are developed based on expert knowledge and the fact that small/large power errors can be compensated by applying the main voltage vector for a small/large portion of the switching period. The candidate voltage vector pairs are examined on a control Lyapunov function and the pair that satisfy the closed-loop stability criteria are selected. The voltage vector pairs are then applied following a proposed switching pattern through which reduced average switching frequency is achieved. Comparative simulation and hardware-in-the-loop studies between the proposed method and a most recently introduced duty cycle-based MPDPC confirm that in addition to lower average switching frequency, better quality currents and active and reactive powers can be achieved under the proposed MPDPC.

This work proposes a three-phase AC-DC-AC converter suitable for operation as unified power quality conditioner (UPQC). The proposed converter is composed of a six-leg three-phase cell connected with H-bridge floating cells at the grid side. This configuration makes three-legs of the six-leg cell shared between load and grid. The six-leg cell is naturally able to cope with all load unbalance, such that no current unbalance is transmitted from load to grid. Additionally, the H-bridges provide multilevel features to the converter grid side, reducing harmonic distortion. Two operations of the proposed converter are analysed: DC-link voltage ratio of 3:1 and 2:1. Converter model, space vector pulse width modulation (SVPWM) and control strategy are presented. The proposed converter is compared with conventional solutions considering harmonic distortion, semiconductor losses, average switching frequency, number and reverse blocking voltage of semiconductor devices. Experimental results are presented for validation.