Hysteresis Comparator Research Articles

Robust DPC-SVM control strategy for shunt active power filter based on H∞ regulators

This paper proposes an improved direct power control (DPC) strategy for shunt active power filter (SAPF). The conventional DPC control suffers from variable switching frequency and high-power ripples due to hysteresis comparators used. In order to overcome the drawbacks and to ensure a fast response, a perfect reference tracking with required dynamic behavior and low power ripple level, a direct power control combined with space vector modulation DPC-SVM is proposed. An H∞ regulator is considered for the closed loop active and reactive power. The effectiveness of the proposed DPC-SVM control based on H∞ regulator is examined by simulation and experimental validation using Matlab/Simulink software with a real-time interface based on dSPACE 1104 under different loading conditions.

An Improved Sensorless DTC Technique for Two/Three-Level Inverter Fed Asynchronous Motor

The Direct Torque Control (DTC) technique was designed to provide high performance for a three-phase asynchronous motor’s behavior by accurately controlling the flux and torque of the latter. However, this conventional DTC generates strong ripples at the level of flux and torque and a variation of the switching frequency since it uses hysteresis comparators, for this reason, the sine-triangle pulse width modulation (SPWM) has been proposed to improve it. The use of Integral Proportional Regulators (PI) allows the generation of the voltage direct and quadrature components that serve as inputs for the SPWM. The technique thus presented provides a fixed switching frequency and lower undulations at the torque and the stator flux. The objective of this work is to apply the improved DTC technique for the control of a cage asynchronous motor that will be powered by two inverters of different topologies; the first is the two-level and the second is the three-level of Neutral point clamped NPC structure. In addition, the control strategy uses a speed estimator that allows the elimination of the mechanical sensor, which greatly increases the reliability of the system. To evaluate the performance and efficiency of the proposed method, a simulation using the MATLAB / SIMULINK software and a fair comparison between the results of the two inverters will be made.

Comparative study of ANN DTC and conventional DTC controlled PMSM motor

In this paper an Artificial Neural Network (ANN) algorithm is presented in order to solve the problems associated with the conventional DTC approach. In order to improve the performances of the DTC controlled PMSM and to reject the disturbances, an ANN algorithm is used. This intelligent artificial technique is used to select the optimal voltage vector. In order to reduce the torque and flux ripples, the hysteresis comparators and the switching table have been substituted by the ANN technique. Simulation using Matlab/Simulink environment and experimental results around the Dspace-1104, are presented to test the performances of this approach. Simulation and experimental results show the high performances of the ANN-DTC compared to the conventional DTC; in particular the reduction of the ripples in torque and flux.

Fast and accurate technique for comparator offset voltage simulation

A universal simulation technique for determining comparator offset voltage is proposed. The proposed technique uses a modified successive approximation algorithm to determine the offset voltage in short simulation time while preserving accuracy and precision. The comparator's input waveform is selectively reset to provide a quasi-monotonic stimulus to the comparator; thus, comparator's hysteresis can be identified and accurately determined. The technique is implemented in a parameterized Verilog-A model and can be applied to any type of comparator. Monte Carlo simulation of StrongArm dynamic comparator implemented in 180 nm CMOS technology shows that the proposed technique achieves 45 × speed-up in simulation time compared to the standard linear search, while achieving similar accuracy.

Fixed-frequency implementation of sliding-mode controllers for photovoltaic systems

Traditional implementation of sliding-mode controllers, based on hysteresis comparators, exhibits variable switching frequency. Such a condition makes it difficult to select the semiconductor devices, design the passive elements of dc/dc converters, and design the sensing filters usually adopted for removing the switching noise from currents and voltages. Those problems are always present in photovoltaic systems based on variable-frequency sliding-mode controllers. Therefore, this paper proposes an implementation methodology for sliding-mode controllers providing constant switching frequency, which is aimed for grid-connected photovoltaic applications. The proposed solution does not compromise the power production of the PV system, hence it provides the same PV power in comparison with the classical variable-frequency implementation. Finally, the performance and correct operation of the fixed-frequency implementation are demonstrated using both simulation and experimental results.

Analysis, Design, and Implementation of Accurate ZVS Angle Control for EV Battery Charging in Wireless High-Power Transfer

To acquire high efficiency and reduce electromagnetic interference in wireless high-power charging for electric vehicles (EVs), it is of great importance to realize accurate zero voltage switching angle (ZVSA) control of the inverter. However, the traditional zero-crossing detection cannot be applied in high power because of considerable noise and poor accuracy in wide power range applications. In this paper, to suppress the noise in high power, a current hysteresis comparator is adopted, and an enhanced phase detection methodology is proposed to measure the phase of resonant current by using a reference signal produced by a processor. Meanwhile, to improve the accuracy of ZVSA, a uniform time delay compensation method (UTDCM) by considering the whole time delays synthetically is proposed, and a uniform time delay equation can be obtained to guarantee the high accuracy of phase detection, especially in the wide power range. Finally, a novel control strategy with the ZVSA loop based on UTDCM is proposed for battery charging in wireless high-power transfer system. A 500-W wireless power transfer prototype is built to verify the accuracy of ZVSA based on UTDCM and the system efficiency can achieve 94.17% with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> = 0.22.

A Novel Switching Tables of Twelve Sectors DTC for Induction Machine Drive Using Artificial Neural Networks

The direct torque control (DTC) is one of the actively researched control schemes of induction machines (IMs), which is based on the decoupled control of stator flux and electromagnetic torque. The traditional twelve sectors DTC control scheme of IM drive using hysteresis comparators and switching table has considerable electromagnetic torque ripple, stator flux ripple and harmonic distortion of voltage/current for IM drive. In order to ensure a robust twelve sectors DTC control scheme and minimize the harmonic distortion of stator current, a novel switching tables of twelve sectors DTC control scheme with the application of the artificial intelligence technique (artificial neural networks (ANNs)). The electromagnetic torque, stator flux and harmonic distortion of stator current are determined and compared with the traditional twelve sectors DTC control scheme. The simulation of the proposed switching tables were carried out in Matlab/Simulink software. A comparative study of the proposed switching tables is also presented to illustrate the merits of each of the switching table on the performance of the twelve sectors DTC control scheme.

Comparison between Modified MPC and DTC Control Method for Permanent Magnet Synchronous Motor

Direct torque control (DTC) and model predictive control (MPC) are widely used in the control of permanent magnet synchronous motor (PMSM). However, DTC for PMSM can cause large torque ripples and flux ripples, high harmonic distortion of the stator current, and high acoustic noises. Compared to DTC, MPC considers all possible switching states which can reduce the ripples of torque and flux. MPC with one-step delay compensation for PMSM and DTC with one-step delay compensation and two hysteresis comparators for PMSM have been proposed to solve some drawbacks of these two controllers. This paper makes a detailed comparison between these two improved control methods through Simulink and hardware experiments results to analyse the four indicators-torque ripple, flux ripple, transient time and THD of inverter current.

A Direct Power Control of the Doubly Fed Induction Generator Based on the Three-Level NSVPWM Technique

The paper proposes a direct power control (DPC) scheme for the doubly fed induction generator (DFIG) for variable speed wind-power generation. The machine is connected as a generator. Its rotor is fed by a three-level NPC inverter. We propose to control the DFIG with a technique based on the DPC control performances. A combination of a three-level neural space vector pulse width modulation (3L-NSVPWM) strategy and reactive and active power controllers is made to replace hysteresis comparators used in the traditional DPC drive resulting in a fixed switching frequency of the power converter. The performances obtained by using this control technique are shown under Matlab/Simulink software

Low-Complexity Model Predictive Torque Control Method Without Weighting Factor for Five-Phase PMSM Based on Hysteresis Comparators

An improved model predictive torque control (MPTC) method without weighting factors is proposed for five-phase permanent magnet synchronous machine (PMSM) drives, which aims to reduce heavy computation complexity, and the low-order current harmonics existing in harmonic subspace in the traditional finite-control-set (FCS) MPTC. In the proposed MPTC scheme, a modified control set consisting of virtual voltage vectors has been defined and adopted with two hysteresis comparators. Duty ratio optimization is also introduced to reduce torque ripples and eliminate weighting factors in the predefined cost function. In addition, a digital delay compensation solution of the proposed MPTC scheme is adopted to improve the control precision. Finally, a series of hardware-in-loop real-time simulation and experimental tests is achieved to compare the performances of the proposed and traditional FCS-MPTC schemes. Simulation and experimental results have verified the effectiveness of the proposed MPTC scheme.

High-Efficiency PFM Boost Converter With an Accurate Zero Current Detector

In this brief, an integrated pulse-frequency modulation boost converter with an accurate zero current detector (ZCD) is presented. The proposed ZCD is used to improve the power efficiency of the boost converter and comprises two hysteresis comparators, the transistors ${M} _{{Z1}}$ – ${M} _{{Z3}}$ , and a set–reset latch to eliminate the reverse current of the high-side switch in the energy release period. This ZCD can also avoid early or delayed detection and ensure stable operation in the discontinuous conduction mode. Furthermore, a new comparator incorporating an appropriate logic gate is developed to eliminate a constant current during the energy storage period. The proposed boost converter was designed and fabricated using the standard TSMC 0.18- $ {\mu }\text{m}$ 1P6M CMOS technology with a chip area of 0.43 mm2. The experimental results revealed that the maximum power efficiency of 88.39% is achieved at a load current of 50 mA, and the light-load efficiency is enhanced by the proposed ZCD. Furthermore, power efficiency of the boost converter with the proposed ZCD is 28.29% higher than that of the existing ZCD design at a load current of 1 mA.

Dynamic performance improvement of single‐phase PWM converters with power hysteresis control scheme

This study presents a direct power control (DPC) scheme with pulse width modulation module and two hysteresis comparators, for the application in single-phase PWM converters to overcome the drawbacks of conventional proportion-integration-based DPC (PI-based DPC), including poor dynamic performance and complexity of tuning PI parameters. According to the outputs of inner-loop power hysteresis controllers, the proposed DPC scheme divides d-q reference frame into four sectors. In each sector, the dynamic power components are estimated to be equivalent as the outputs of PI controllers in PI-based DPC. The proposed DPC scheme provides a new solution of non-linear hysteresis control to achieve fast dynamic performance with constant switching frequency. Additionally, due to inductance parameter mismatch, the effect on powers is analysed in detail, and an inductance parameter on-line estimation method is present and discussed. A comprehensive comparison of conventional table-based DPC, PI-based DPC and the proposed DPC methods has been conducted in this study, including steady-state performance with respect to different factors, and dynamic response under different extreme conditions. The experimental results have verified the effectiveness of the proposed DPC scheme.

A novel switching boost inverter applied to photovoltaic power generation system

SummaryThis paper presents a new topology of the input current continuous switch boost inverter (ICCSBI) and a perturbation observation with hysteresis comparator method. Because the traditional inverter needs to join the dead time to avoid short circuit, the dead time will cause distortion of the output current. And the traditional inverter is not suitable for photovoltaic power generation because it is a buck converter. The ICCSBI structure improves the booster circuit, which refers to the Z‐source inverter. It can get higher voltage than traditional inverter. Meanwhile, the ICCSBI not only retains the advantages of the Z‐source inverter but also reduces the number of passive components. In addition, the hysteresis band comparator is added to the perturbation observation method to make the system better robustness at the maximum power point of the photovoltaic system. In the photovoltaic system, to ensure the output current stable, the current control method is added to the ICCSBI. Finial, the experimental results are presented to demonstrate the new topology and control method.

Study on the losing control problem of direct torque control in permanent magnet synchronous motor drive

In direct torque controlled permanent magnet synchronous motor drives, when the rotor speed or the load torque changes, the effect of a certain voltage vector on the torque also changes. In heavy-load or high-speed operating conditions, the torque may lose control. This paper presents an intensive investigation into this issue. With the help of relevant derivative curves, the primary cause for the losing control problem is analysed. Further study reveals that the effect of a certain voltage vector on the load angle is no relevant for the load conditions. Based on this property, by replacing the torque hysteresis comparator with a load angle hysteresis comparator, a modified direct torque control called the load-angle-feedback direct torque control is proposed and the original superiorities of the direct torque control are well preserved. Comparison between the direct torque control and the proposed method shows that the load capacity and speed operation range may be obviously extended by utilizing the proposed method.

A self-powered piezoelectric energy harvesting interface circuit with efficiency-enhanced P-SSHI rectifier * * Project supported by the National Natural Science Foundation of China (Nos. 61574103, U1709218) and the Key Research and Development Program of Shaanxi Province (No. 2017ZDXM-GY-006).

The key to self-powered technique is initiative to harvest energy from the surrounding environment. Harvesting energy from an ambient vibration source utilizing piezoelectrics emerged as a popular method. Efficient interface circuits become the main limitations of existing energy harvesting techniques. In this paper, an interface circuit for piezoelectric energy harvesting is presented. An active full bridge rectifier is adopted to improve the power efficiency by reducing the conduction loss on the rectifying path. A parallel synchronized switch harvesting on inductor (P-SSHI) technique is used to improve the power extraction capability from piezoelectric harvester, thereby trying to reach the theoretical maximum output power. An intermittent power management unit (IPMU) and an output capacitor-less low drop regulator (LDO) are also introduced. Active diodes (AD) instead of traditional passive ones are used to reduce the voltage loss over the rectifier, which results in a good power efficiency. The IPMU with hysteresis comparator ensures the interface circuit has a large transient output power by limiting the output voltage ranges from 2.2 to 2 V. The design is fabricated in a SMIC 0.18 μm CMOS technology. Simulation results show that the flipping efficiency of the P-SSHI circuit is over 80% with an off-chip inductor value of 820 μH. The output power the proposed rectifier can obtain is 44.4 μW, which is 6.7× improvement compared to the maximum output power of a traditional rectifier. Both the active diodes and the P-SSHI help to improve the output power of the proposed rectifier. LDO outputs a voltage of 1.8 V with the maximum 90% power efficiency. The proposed P-SSHI rectifier interface circuit can be self-powered without the need for additional power supply.

Fixed Switching Period Discrete-Time Sliding Mode Current Control of a PMSM

A fixed switching period sliding mode control (SMC) for permanent-magnet synchronous machines (PMSMs) is presented. The aim of this paper is to design an SMC that improves the traditional PI-based field-oriented control transient response, as well as to reduce the switching frequency variations of the direct torque control. Such SMC requires a decoupling method of the control actions, which also brings constant switching functions slopes. These constant slopes allow to calculate the required hysteresis band value to control the switching frequency. The digital implementation degrades the performance of the hysteresis comparator, and as a consequence, the previously calculated band becomes inaccurate to regulate the switching frequency. In order to recover the analogue hysteresis band comparator performance, a predictive algorithm is proposed. Finally, a set of experimental results with constant switching frequency during a torque reversal and speed control tests are provided.

Flux-Angle-Difference Feedback Control for the Brushless Doubly Fed Machine

In direct torque control (DTC) of the brushless doubly fed machine (BDFM) system, the inverter switching voltage vectors cannot always meet the control requirements, and the torque will lose control. For the losing control problem, this paper presents a solution of indirectly controlling torque by controlling the angle difference between the power motor (PM) stator flux and the control motor (CM) stator flux (called as the flux-angle-difference). Firstly, based on the CM static coordinate system BDFM model, the derivative equations of CM stator flux amplitude, the torque, and the flux-angle-difference are deduced. The losing control problem of BDFM’s DTC is studied by utilizing the CM stator flux amplitude and the torque derivatives. From the flux-angle-difference derivative, it is found that the phase angles of the flux-angle-difference derivative curves remain unchanged. Based on this property, by replacing the torque hysteresis comparator of conventional DTC with a flux-angle-difference hysteresis comparator, a modified control strategy called flux-angle-difference feedback control (FADFC) is proposed to solve the losing control problem. Finally, the validity and the good dynamic characteristic of the FADFC strategy are verified by simulation results.

Full-order observer for direct torque control of induction motor based on constant V/F control technique

This paper presents another control method for the three-phase induction motor that is direct torque control based on constant voltage per frequency control technique. This method uses the magnitude of stator flux and torque errors to generate the stator voltage and phase angle references for controlling the induction motor by using constant voltage per frequency control method. Instead of hysteresis comparators and optimum switching table, the PI controllers and space vector modulation technique are used to reduce torque and stator-flux ripples and achieve constant switching frequency. Moreover, the coordinate transformations are not required. To implement this control method, a full-order observer is used to estimate stator flux and overcome the problems from drift and saturation in using pure integrator. The feedback gains are designed by simple manner to improve the convergence of stator flux estimation, especially in low speed range. Furthermore, the necessary conditions to maintain the stability for feedback gain design are introduced. The simulation and experimental results show accurate and stable operation of the introduced estimator and good dynamic response of the proposed control method.

Study on a switching‐pattern hysteresis current control method based on zero voltage vector used in three‐phase PWM converter

The conventional hysteresis current control (C-HCC) method has a fast transient response and good robust performance. However, due to interphases dependency among the three-phase currents, several shortcomings, for example, a high-switching frequency and large cycle current oscillation will arise inevitably when C-HCC is applied in a three-phase pulse width modulation (PWM) voltage-source converter (VSC). First, this study gives a review on the space vector-based HCC (SV-HCC) which is researched to overcome the shortcomings of C-HCC. The SV-HCC can avoid the most shortcomings of C-HCC. However, SV-HCC has more hysteresis comparator and the adjustment process of hysteresis band (HB) is fussy. In addition, the switching numbers of the three-phase bridge-legs are unbalanced. Then, a switching pattern (SP)-based HCC method is presented in this study which refers to the concept of zero voltage vector in space vector PWM (SVPWM). The presented method set an HB which depends on the system parameters. In the presented method, zero-vector SP will be selected when the three-phase current errors are all within the given HB, and conversely, the specified switching logic will be selected when the current error exceeds the HB. Finally, the effectiveness and superiority of the presented method are verified by simulation and experiment tests.

A new type of single-phase five-level inverter

At present, Neutral Point Clamped (NPC) multilevel inverter is widely applied in new energy field. However, it has some disadvantages including low utilization rate of direct current (DC) voltage source and the unbalance of neutral potential. Therefore, a new single-phase five level inverter is proposed in this paper. It has two stage structure, the former stage is equivalent to three level DC/DC converter, and the back stage uses H bridge to realize inverter. Compared with the original central clamp type inverter, the new five level inverter can improve the utilization of DC voltage, and realize the neutral point potential balance with hysteresis comparator.