Inverter output voltage synthesis using novel dead time compensation

A dead-time compensation method in vector-controlled pulse width modulator (PWM) voltage source inverters (VSIs) is proposed. The method is based on a feedforward approach that produces compensating signals obtained from the I/sub d/-I/sub q/ current and inverter output angular frequency references in the rotating reference (d-q) frame. It provides excellent inverter output voltage distortion correction for both fundamental and harmonic components. The correction is not affected by the magnitude of the inverter output voltage or current distortions. Since this dead-time compensation method allows current loop calculations in the d-q frame at a slower sampling rate, with a conventional microprocessor than calculations in the stationary reference frame, a fully digital. vector-controlled speed regulator with just a component current control loop is realized for PWM VSIs. Simulations and test results obtained for the compensation method are also described. >

For an inverter drive induction motor control system, a typical problem encountered is the nonlinear voltage gain caused by the non ideal characteristics of the power inverter. The switch dead time will introduce waveform distortion and fundamental voltage drop to the system. If not compensated, such distortions will introduce harmonic components which will cause additional loss in the induction machine. Therefore, the impact of harmonics caused by switching dead time are essential to induction motor drive design, especially when the motor is running at low speed. In this paper, a dead time compensation method is proposed. By adding a 6th order resonant controller to the existing current loop PI controller, the negative sequence 5th order and positive sequence 7th order current harmonics caused by the dead time are eliminated. The overall control scheme is implemented in synchronous rotating d-q reference frame. The controller resonant frequency is 6 times to the synchronous frequency, which is calculated with mechanical speed and slip. Experiment results of steady state and dynamic response studies are presented to validate the effectiveness of the proposed method.

Single-photon avalanche diode (SPAD)-based light detection and ranging (LiDAR) introduces significant pileup errors at high echo photon flux due to the SPAD's dead time. To expand the application of single-photon LiDAR in the field of remote sensing, autonomous driving, etc., it is crucial to perform rapid and accurate ranging within an echo photon flux of a wide dynamic range. Emerging SPAD array detectors combined with specific photon detection modes attempt to strike a balance between photon detection efficiency and hardware resources, necessitating the development of appropriate dead time compensation methods. Therefore, we experimentally investigated a synchronous single-photon ranging LiDAR operating in a mode where up to two photons are detected per laser cycle, and proposed dead time compensation methods based on forward modeling of the photon detection process. The results show that, using a wide laser pulse of 3.5 ns, the compensated ranging error is less than 4.2 cm, while the uncompensated ranging error is as max as 17.96 cm. Our method provides a reference for dead time compensation in single-photon LiDAR that requires comprehensive consideration of detection efficiency and hardware resources.

Stand-alone inverter supplies constant voltage to loads. However, when a three-phase stand-alone inverter supplies unbalanced load, the generated output voltages also become unbalanced. The nonlinear characteristics of inverter dead time cause a more serious distortion in the output voltage. With unbalanced load, voltage distortion caused by dead time differs from voltage distortion under balanced load. Phase voltages in the stationary reference frame include unbalanced odd harmonics and then, d-q axis voltages in the synchronous reference frame have even harmonics with different magnitude, which are mitigated by the proposed multiple resonant controller. This study analyzes the voltage distortion caused by unbalanced load and dead time, and proposes a novel dead time compensation method. The proposed control method is tested on a 10-kW stand-alone inverter system, and shows that total harmonic distortion (THD) is reduced to 1.5% from 4.3%.

This article presents an enhanced space vector pulse width modulation (SVPWM) strategy based on vector space decomposition (VSD) for the dual three-phase machines fed by two dc-source voltage source inverters (VSIs). Compared with existing methods that only account for balanced dc-link voltages, the proposed method considers unbalanced dc-link voltages in both the α-β and z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> planes. Two categories of medium voltage vectors are first defined in this article. An enhanced 12-sector SVPWM strategy that toggles two categories of medium voltage vectors in each fixed 30° sector is proposed. Moreover, the performance of the proposed method, including the modulation depth, the range of the dc-link voltage ratio, and the toggling point of the medium vector is analyzed. The proposed method can reduce the computational burden of the complicated sector classifications and it easily chooses suitable vectors to track the reference voltage with changes in the dc-link voltage ratio. The experimental results of the proposed SVPWM techniques are verified in a dual three-phase permanent magnet synchronous machine (PMSM) fed by two dc-source VSIs.

In order to effectively avoid the shoot-through issue of the semiconductor device (such as the power metal-oxide-semiconductor field-effect transistor (MOSFET)) adopted in the phase leg of the motor drives, a dead-time zone should be inserted. However, the nonlinearity caused by the dead-time effect will bring about voltage/current distortion, as well as high-order harmonics, which largely degrades the performance of motor drives, especially in low-speed operations with slight loads. In this paper, a dead-time compensation method is proposed to suppress such side effects caused by dead-time zones and improve the performance of motor drives. Compared with other existing methods, the proposed method is mainly focused on the switching characteristics of the power MOSFET, which is directly relative to the compensation time in each pulse-width modulation (PWM) period. Firstly, a detailed derivation process is elaborated to reveal the relationship between compensation time and the switching performance of the MOSFET. Meanwhile, the switching process of the MOSFET is also well analyzed, which summarizes the variations in the switching time of the MOSFET with a varied load current. Then, the multipulse test (MPT) is carried out to obtain accurate values of the switching time with the varied load current in a wide range (0–80 A) and form a 2D lookup table. As a result, the compensation method can easily be realized by combining the lookup table and linear interpolation based on the phase current of the motor dynamically. Finally, the effectiveness of the proposed method is verified based on a 12 V permanent magnet synchronous machine (PMSM) drive system. According to the relative experiment results, it can be clearly observed that the time-domain waveform distortion, high-order harmonics, and total harmonic distortion (THD) value are reduced significantly with the proposed dynamic compensation method.

The optimal PWM method is widely in high power drive systems for its capability of achieving low output distortion at low switching frequency. However, the PWM dead-time inserted into PWM pulses for avoiding “shoot through” of inverter bridge arms will introduce modulation errors between ideal optimal PWM patterns and actual outputs. This problem is extremely severe in high power drives for the large dead time, and will cause large distortion of the optimal PWM output waveforms. This paper took the selective harmonic PWM (SHEPWM) as an example. First, the basic principles of SHEPWM and dead-time effects were presented. By analyzing the polarity of three level inverter output currents and switching behaviors of the inverter, a dead-time compensation method based on on-line switching angle adjustment for the optimal PWM method is proposed. Finally, the experimental results were given for verifying the effectiveness of the proposed scheme.

This paper analyzed a dead-time effect and zero-current clamping phenomenon in FOC control strategy, and then proposed corresponding compensation measures. The Field Oriented Control (FOC) strategy of brushless motor is improved according to this Dead-time Compensation measure. On the basis of the existing FOC control theory, a dead-time hysteresis loop is added near the current zero-crossing point to prevent current fluctuation and zero-point clamping from causing errors. The dead-time compensation is carried out in each PWM cycle according to the principle that the actual volt-second area is equal. Finally, the feasibility of the method was verified by experiments, the results showed that the compensation method effectively improves the current waveform and improves the stability of the motor operation, and it proved to be of good use value.

The dead-time effect in a three-phase voltage source inverter can result in voltage losses, current waveforms distortion and torque pulsation. In order to improve the current waveforms and decrease the torque pulsation, this paper analyzes the influence of dead-time on output voltage in detail, and proposes a dead-time compensation method of SVPWM, which through changing the traditional 180 degree turn-on mode into 120 degrees plus 180 degrees turn-on mode, thanks to the alternate use of the two strategies, the influence of dead time can be reduced to zero. The implementation is simple since only program needs to be modified comparing to traditional SVPWM technique, and by simulation and experiments results the correctness and feasibility of the algorithm are also be verified.

This paper proposes a new dead time compensation method for a PWM inverter. Recently, PWM inverters are widely used for industrial applications, such as ac motor drives, distributed grid-connected systems and a static synchronous compensator (STATCOM). The nonlinear characteristics of the switch and the dead time cause a current distortion and a deterioration of the power quality. The dominant harmonics is the 5th and 7th harmonics in the stationary reference frame, and the 6th harmonics in the synchronously rotating frame. In this paper, a resonant controller which compensates the 6th harmonics in the synchronously rotating frame is proposed. This method does not require any off-line experimental measurements, additional hardware and complicated mathematical calculations. Furthermore it is easy to implement and does not cause any stability problem.

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.

This work proposes an anti-windup structure for the ltered Smith predictor (FSP) which belongs to a class of dead-time compensators (DTCs). The proposed FSP structure does not use any extra tuning parameter due to the anti-windup characteristic. In addition stability analysis is presented based on describing function method to show robustness properties of the controller. Simulation results are used to compare the obtained solution with other anti-windup DTCs and a constrained model-based predictive controller (MPC). Experimental results on a neonatal intensive care unit are presented in order to shown the usefulness of the proposed controller.

SVPWM Performance of PMSM Variable Speed and Impact of Diagnosis Sensors Faults

Aiming at deficiencies of output voltage distortion and circulating current generation caused by dead-time effect in the modulation process, a simple and feasible dead time compensation strategy is presented. Firstly, the influence of dead-time effect on the output voltage of bridge is analysed, and a dead time compensation strategy is added between the modulation signal and dead time procession. According to the current direction of the bridge, the rising edge or falling edge of the driving signal is selectively delayed to compensate for dead-time effect. Secondly, an Optimized Triple Phase-shift (OTPS) modulation strategy is adopted with minimizing leakage inductor current Root-Mean-Square (RMS) control, which minimizes current stress, achieves soft-switching operation, avoids phase-shift errors caused by Dead-Time Effect, and optimizes control performance of DC-DC converters. Finally, simulated and experimental results are added to verify the correctness and effectiveness of the proposed method.

A new method for reducing the harmonics involved in the output voltages of a double-connected inverter is proposed. By adding four auxiliary switching devices and an interphase transformer with a secondary winding to the conventional 12-step inverter, output voltages of the proposed circuit can produce almost the same waveforms as a conventional 36-step inverter. In this paper, circuit performances and output voltage waveforms are discussed, and optimum parameters are derived. The effects on harmonic reductions are then clarified by theoretical and experimental results, and the ratings of system components are investigated. >