A source voltage-clamped resonant link inverter for a PMSM using apredictive current control technique

A simple source voltage-clamped resonant link (SVCRL) inverter is proposed to clamp the DC-link voltage to the input source voltage and reduce the current rating of a resonant inductor. The current control of a permanent magnet synchronous motor (PMSM) employing a predictive current control technique (PCCT) for the SVCRL, inverter is also investigated to overcome the disadvantage of the current-regulated delta modulation (CRDM) control technique. By employing the PCCT based on the discrete model of a PMSM and estimation of back electromotive force (EMF), the minimized current ripple with a small number of switchings can be obtained. Finally, the comparative computer simulation and experimental results are given to show the usefulness of the proposed technique     

A simple and robust digital current control technique of a PMsynchronous motor using time delay control approach

A simple and robust digital current control technique of a permanent magnet (PM) synchronous motor using a time delay control approach is presented. Among the various current control schemes for a voltage source inverter-fed PM synchronous motor drive, the predictive control is known to give a superior performance. This control technique, however, requires the full knowledge of machine parameters and operating conditions, and gives an unsatisfactory response under the parameter mismatch between the motor and controller. To overcome such a limitation, the disturbances caused by the parameter variations are estimated by using a time delay control approach and used for the computation of the reference voltages by a simple feedforward control. Thus, the steady-state control performance can be significantly improved in an extremely simple manner, while retaining the good characteristics of the predictive control such as the good transient response and stable inverter operation. The proposed control scheme is implemented on a PM synchronous motor using the software of DSP TMS320C30 and the effectiveness is verified through the comparative simulations and experiments     

Discrete time modeling and control of the voltage source converterfor improved disturbance rejection

A new voltage source converter control approach is presented, based on multivariable z-domain control techniques. Using time-averaging theory in the synchronous reference frame, a linear time-varying model of the converter is developed. The new model may be directly employed as an efficient simulation tool and used as a basis for developing discrete time inverter controls. Application of digital control techniques results in current step tracking in one switching period, with zero overshoot. While DC load fluctuations are rapidly compensated through nonlinear feedforward, AC system voltage disturbances are rejected through a positive and negative sequence bias estimation scheme. As a result, the converter may operate at its current limit under even severe AC voltage unbalance and only a balanced AC current will flow, thus ensuring full protection of the semiconductor devices in all three converter legs. Experimental results validate both the time-varying simulation model as well as the proposed control design     

Design of a position sensor for torque ripple minimization of a voltage source inverter fed self-synchronous machine

A study on the torque ripple minimization of a voltage source inverter fed selfsynchronous machine is presented. This study is based on a design of a position sensor which allows us to suppress undesirable voltage harmonics and hence to minimize electromagnetic torque ripple. We use the optimized pulse width modulation (PWM) method as a basis for the design of this position sensor. Thus, the obtained inverter control circuit is a very simple design and there is no need for a microprocessor or for specialized PWM integrated circuits for its implementation. The obtained simulation results are compared with practical results for a self-controlled synchronous machine, using the classical control method and the proposed method.     

Adaptive high bandwidth current control for induction machines

For high performance induction machine control, the technique of indirect rotor flux oriented vector control is commonly utilized. The torque performance of this technique is significantly affected by the performance of the current control loops. In this paper a new adaptive high bandwidth current controller for induction machines is presented. The technique is derived and validated through simulation and experimental results. The new architecture is shown to achieve a dead-beat response, with a rise time of one sample period and no overshoot, when the inverter voltage limit is not exceeded. When the voltage limit is exceeded the current response is achieved in a minimum time with no overshoot. It is shown that the new control technique achieves similar dynamic response to the conventional dead-beat control scheme while eliminating parameter sensitivity issues. It is demonstrated that the new algorithm offers higher bandwidth than the commonly used synchronous frame proportional plus integral control technique while maintaining good steady state performance.     

Performance evaluation of an FPGA controlled soft switched inverter

A field programmable gate array (FPGA) based controller is proposed for a dc link series resonant inverter. The basic operation of the zero current switching inverter is briefly described. A strategy of decoupling the control of the dc link current from the load current is identified and referred as decoupled current control (DCC). The use of gate-controlled devices like metal-oxide-semiconductor field-effect transistor/insulated gate bipolar transistor/MOS-controlled thyristor permits a higher resonance frequency at the link of the inverter. The increased frequency enables the application of pulse density modulation technique with a bang-bang controller to synthesise and control the wave-shapes of current and voltage of the inverter. The DCC strategy eliminates the conventional analogue controller. A digital sequence controller has been designed using the state machine technique for the reliable operation of the inverter. The digital design is implemented on a single chip FPGA. To verify the proposed control strategy and the FPGA controller, a prototype has been built and tested. The test results show that a sinusoidal inverter output voltage is maintained with total harmonic distortion less than 5% and a regulation of about 1% from no-load to full-load, including non-linear and transient loads. The performance of the inverter with the FPGA controller is promising and attractive for uninterrupted power supply applications.     

Control of Single-Phase-to-Three-Phase AC/DC/AC PWM Converters for Induction Motor Drives

This paper proposes a novel control scheme of single-phase-to-three-phase pulsewidth-modulation (PWM) converters for low-power three-phase induction motor drives, where a single-phase half-bridge PWM rectifier and a two-leg inverter are used. With this converter topology, the number of switching devices is reduced to six from ten in the case of full-bridge rectifier and three-leg inverter systems. In addition, the source voltage sensor is eliminated with a state observer, which controls the deviation between the model current and the system current to be zero. A simple scalar voltage modulation method is used for a two-leg inverter, and a new technique to eliminate the effect of the dc-link voltage ripple on the inverter output current is proposed. Although the converter topology itself is of lower cost than the conventional one, it retains the same functions such as sinusoidal input current, unity power factor, dc-link voltage control, bidirectional power flow, and variable-voltage and variable-frequency output voltage. The experimental results for the V/f control of 3-hp induction motor drives controlled by a digital signal processor TMS320C31 chip have verified the effectiveness of the proposed scheme     

A new quasi-resonant DC-link PWM inverter using single switch for soft switching

This paper presents a new quasi-resonant DC-link (QRDCL) inverter. Only one switching device is used to create zero voltage instants under all load conditions. The maximum voltage across the inverter devices is maintained at around (1.01-1.1) times the input source voltage. The circuit has the flexibility of selecting switching instants of the resonant link in synchronism with any PWM technique. Control technique does not require the help of inverter switches to create the zero voltage instants in the DC-link, and voltage and current sensors are eliminated from the control circuit. In this paper, the principle of operation and detailed analysis of the proposed QRDCL inverter are presented and design considerations for achieving soft switching are obtained. Detailed PSPICE simulation studies are carried out to study the feasibility of the proposed topology under various load conditions. The experimental results of the proposed QRDCL PWM inverter feeding a three phase induction motor are given.     

An accurate approach of nonlinearity compensation for VSI inverter output voltage

An accurate nonlinearity compensation technique for voltage source inverter (VSI) inverters is presented in this paper. Because of the nonlinearity introduced by the dead time, turn-on/off delay, snubber circuit and voltage drop across power devices, the output voltage of VSI inverters is distorted seriously in the low output voltage region. This distortion influences the output torque of IM motors for constant V/f drives. The nonlinearity of the inverter also causes 5th and 7th harmonic distortion in the line current when the distributed energy system operates in the grid-connected mode, i.e., when the distributed energy system is parallel to a large power system through the VSI inverter. Therefore, the exact compensation of this nonlinearity in the VSI inverter over the entire range of output voltage is desirable. In this paper, the nonlinearity of VSI inverter output voltage and the harmonic distortion in the line current are analyzed based on an open-loop system and a L-R load. By minimizing the harmonic component of the current in a d-axis and q-axis synchronous rotating reference frame, the exact compensation factor was obtained. Simulations and experimental results in the low frequency and low output voltage region are presented.     

Interfacing Renewable Energy Sources to the Utility Grid Using a Three-Level Inverter

This paper presents a novel approach for the connection of renewable energy sources to the utility grid. Due to the increasing power capability of the available generation systems, a three-level three-phase neutral-point-clamped voltage-source inverter is selected as the heart of the interfacing system. A multivariable control law is used for the regulator because of the intrinsic multivariable structure of the system. A current source (playing the role of a generic renewable energy source) is connected to the grid using a three-level inverter in order to verify the good performance of the proposed approach. Large- and small-signal d-q state-space averaged models of the system are obtained and used to calculate the multivariable controller based on the linear quadratic regulator technique. This controller simultaneously regulates the dc-link voltage (to operate at the maximum power point of the renewable energy source), the mains power factor (the power is delivered to the grid at unity power factor), and the dc-link neutral-point voltage balance. With the model and regulator presented, a specific switching strategy to control the dc-link neutral-point voltage is not required. The proposed controller can be used for any application, since its nature makes possible the control of any system variable. The good performance of the presented interfacing solution in both steady-state and transient operation is verified through simulation and experimentation using a 1-kW neutral-point-clamped voltage-source-inverter prototype, where a PC-embedded digital signal processor board is used for the controller implementation     

A hysteresis current control for single-phase multilevel voltage source inverters: PLD implementation

In most high-performance applications of voltage source pulse-width modulation inverters, current control is an essential part of the overall control system. In this paper, a hysteresis current control technique for a single-phase five-level inverter with flying-capacitor topology is proposed. Logic controls and a programmable logic device are suitable for handling a large number of switches and implementation of state transitions. This method also considers how to improve unbalanced voltages of capacitors using voltage vectors in order to minimize switching losses. The simulation and experimental results describe and verify the current control technique for the inverter.     

A novel current initialization scheme for parallel resonant dc link inverter

In this paper a novel current initialization scheme is proposed for a parallel resonant dc link inverter. The method of current initialization is based on the state transition analysis of the system as a boundary-value problem. It is shown that, for a given load current, it is possible to force the dc link voltage to go to zero at a prescribed time by properly choosing the initial dc link current. This technique makes it possible to operate the resonant dc link inverter without any zero-crossing failure, which is the most important issue for satisfactory operation of such an inverter. The proposed current initialization technique is validated through digital computer simulation studies and practical implementation results.     

Dual-inverter control strategy for high-speed operation of EV induction motors

An integrated starter/alternator (ISA) is normally designed to have high pole structure (10-14 poles) for high starting torque. However, its back electromotive force (EMF) at the peak revolutions per minute should be less than its battery voltage for the power flow control. For example, the back-EMF of a 12-pole ISA should be 42 V at 6000 r/min. These types of conflicting requirements lead to a nonclassical motor design that has extremely large field-weakening range (8:1/spl sim/10:1). In this paper, we are considering the use of an induction machine instead of a permanent synchronous machine. As an idea for solving the voltage limit problem, two inverters are utilized with an objective of sharing the required voltage. The secondary inverter only takes care of the reactive voltage component that grows very fast in high-speed operation. Therefore, an extra voltage source is not required for the secondary inverter. Only a capacitor bank suffices for the secondary inverter.     

Tri-State Current Source Inverter WithImproved Dynamic Performance

Traditional dc–ac current source inverter (CSI) has a right-half-plane (RHP) zero in its control-to-output transfer function. This RHP zero causes the inverter output to fall before rising when a step increase in command reference is required (commonly known as non-minimum-phase effect). To achieve a better dynamic response, this paper proposes the design of a tri-state CSI using only an additional semiconductor switch for introducing unique freewheeling states to the traditional six active and three null states of a CSI. With the freewheeling states inserted appropriately within the inverter state sequence, the inductive boosting and discharging intervals can be decoupled, allowing the RHP zero to be eliminated with only minor circuit modifications (high level control schemes like predictive and multiloop voltage/current control remain unchanged). The designed inverter can be controlled using an appropriately formulated digital pulsewidth modulation algorithm, which can conveniently be implemented using a digital signal processor with an on-chip carrier-based modulator and an external digital programmable logic device. The resulting inverter is tested by simulation and experimentally using a laboratory prototype for demonstrating its improved dynamic performance with no commutation difficulties introduced.      

SVPWM电压源逆变器供电异步电动机的动态仿真

建立了三相异步电动机在d-q坐标系下的动态数学模型,并介绍了控制异步电动机运行的两种控制技术:正弦波脉宽调制(SPWM)技术和空间电压矢量脉宽调制(SVPWM)技术。在Matlab/Simulink环境下,分别建立SPWM和SVPWM电压源型逆变器供电的三相异步电动机的动态仿真模型,比较分析了在这两种控制方式下的仿真结果。结果表明,较之SPWM控制方式,SVPWM的异步电动机变频调速系统启动快,转矩脉动小,定子电流谐波小,具有较好的动态性能和稳态性能。     

High-bandwidth current control for torque-ripple compensation in PMsynchronous machines

Active compensation of torque harmonics in high-performance synchronous permanent magnet (PM) motor drives requires high-bandwidth current control. It is demonstrated that proportional integral (PI) current control exhibits performance limits, even when feedforward compensation of the rotor induced voltage and the stator inductance drop is used. High bandwidth requirements are satisfied using a digital deadbeat current controller. Sampling time delays are eliminated to the extent possible by means of a current predictor. The current controller and the predictor refer to a model of the parasitic effects of the PM synchronous machine that is acquired and adapted to parameter changes in real time. Stator current distortions due to deviations from the sinusoidal flux linkage distribution are thus eliminated. The control system facilitates compensation of high-frequency torque ripple of the machine     

An improved deadbeat control for UPS using disturbance observers

A digital control technique for the inverter stage of uninterruptible power supplies is proposed, which is based on a predictive regulator on both output voltage and inductor current. Its aim is to achieve a deadbeat dynamic response for the controlled variables (output voltage and inverter current). Besides the linear state feedback which allocates system poles at the origin so as to achieve deadbeat response for all state variables, the use of a disturbance observer for the estimation of the load current and of any other source of errors (such as dead-times, parameter, and model mismatches) is investigated. The proposed solution is able to guarantee a fast dynamic response and also a precise compensation of any source of unpredictable disturbance. Moreover, with a proper design of observer parameters, it is possible to reduce control sensitivity to model uncertainties, parameter mismatches, and noise on sensed variables, which usually characterizes existing deadbeat control techniques. Finally, the control algorithm is quite simple and requires only the measurements of the output voltage and inductor current. Experimental results on a single-phase 2 kVA prototype show the effectiveness of the proposed approach.     

Three-phase power quality compensator under the unbalanced sources and nonlinear loads

A three-phase voltage-source inverter for a power quality compensator under the unbalanced mains and nonlinear loads is proposed to provide balanced three-phase source current and improve input power factor. The proposed converter is based on the conventional three-phase voltage-source inverter with three additional ac power switches to achieve three-level pulsewidth modulation. The voltage stress of three ac power switches is clamped to half the dc-link voltage. The balanced reference mains currents are estimated using the dc-bus voltage and load currents. A proportional-integral voltage controller is used in the outer loop to compensate the switching losses of the voltage-source inverter. To perform the integrated power quality compensation, a hysteresis current control scheme is adopted to track the balanced line current command in phase with mains voltage. Three voltage levels are generated on the ac terminal of the proposed inverter. Computer simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.     

基于状态空间的PWH逆变器的PI数字双环控制方法研究

本文分析了正弦波PWM逆变器的实际应用情况和数字控制的特点,在建立了逆变器及其控制系统的状态空间模型基础之上,采用了一种带输出电流前馈的PI数字双环控制方案（电感电流内环输出电压外环）,并对控制系统直接离散化后利用极点配置的方法设计了控制系统参数,最后给出了在各种实验条件下的仿真波形。仿真结果表明,该方案设计简单可行,井能很好地达到逆变电源的各项性能指标要求。     

On-line compensation of dead-time and inverter nonlinearity with disturbance voltage observer

This paper discusses and analyses a simple on-line compensation scheme for dead-time and inverter nonlinearity in the pulse width modulated (PWM) voltage source inverter (VSI). Dead-time effect and voltage drop in switching devices cause nonlinearity between reference and output voltage. In a conventional three-phase six-switch inverter, this nonideal condition adds extraneous harmonics that badly disturb voltage characteristics. In its turn, voltage disturbance causes distortion of the current waveform and degrades performance. In this paper, an on-line dead-time compensation method based on inverse dynamics control is proposed, and it is much simpler than conventional full/reduced order observation methods adopted in dead-time compensation. Disturbance voltages are observed on-line with no additional circuitry or off-line measurements. The observed disturbance voltages are fed back to the voltage reference for compensation. Stability problem of the proposed observer arisen from inverter delay and parameter mismatch was analysed. The proposed method is applied to a surface-mounted permanent-magnet synchronous motor (SPMSM) drive. The effectiveness of the proposed scheme is validated by the experimental results.