Frequency Pulse Width Modulation Research Articles

Development of a Hardware-in-the-loop Simulator for Spacecraft Attitude Control Using Thrusters

In this study, a Hardware-In-the-Loop (HIL) simulator using thrusters is developed to validate the spacecraft attitude system. To control the attitude of the simulator, eight cold gas thrusters are aligned with roll, pitch and yaw axis. Also linear actuators are applied to the HIL simulator for automatic mass balancing to compensate the center of mass offset from the center of rotation. The HIL simulator consists of an embedded computer (Onboard PC) for simulator system control, a wireless adapter for wireless network, a rate gyro sensor to measure 3-axis attitude of the simulator, an inclinometer to measure horizontal attitude, and a battery set to supply power for the simulator independently. For the performance test of the HIL simulator, a bang-bang controller and Pulse-Width Pulse-Frequency (PWPF) modulator are evaluated successfully. The maneuver of 68 deg. in yaw axis is tested for the comparison of the both controllers. The settling time of the bang -bang controller is faster than that of the PWPF modulator by six seconds in the experiment. The required fuel of the PWPF modulator is used as much as 51% of bang-bang controller in the experiment. Overall, the HIL simulator is appropriately developed to validate the control algorithms using thrusters.

A single stage three-level full bridge resonant AC/DC converter

This article presents a new three-level full bridge resonant single stage AC/DC converter. The converter is operated with a variable frequency pulse width modulation controller (PWM). A PWM is used to provide the required input current shaping as well as regulating the DC-bus voltage, whereas variable frequency control is used to tightly regulate the output voltage. Zero voltage switching (ZVS) is achieved for all switches. The proposed topology can operate with either continuous or discontinuous input current while maintaining high power factor. Owing to ZVS operation, reduced component stresses and low circulating currents the proposed converter has high conversion efficiency making it suitable for higher power operations compared to existing single stage AC/DC topologies as well as operating with universal input voltage. Operation, analysis and performance of the converter will be presented in this article.

PWM Inverters Using Split-Wound Coupled Inductors

The number of output-voltage levels available in pulsewidth-modulated (PWM) voltage-source inverters can be increased by inserting a split-wound coupled inductor between the upper and lower switches in each inverter leg. Interleaved PWM control of both inverter-leg switches produces three-level PWM voltage waveforms at the center tap of the coupled inductor winding, representing the inverter-leg output terminal, with a PWM frequency twice the switching frequency. The winding leakage inductance is in series with the output terminal, with the main magnetizing inductance filtering the instantaneous PWM-cycle voltage differences between the upper and lower switches. Since PWM dead-time signal delays can be removed, higher device switching frequencies and higher fundamental output voltages are made possible. The proposed inverter topologies produce five-level PWM voltage waveforms between two inverter-leg terminals with a PWM frequency up to four times higher than the inverter switching frequency. This is achieved with half the number of switches used in alternative schemes. This paper uses simulated and experimental results to illustrate the operation of the proposed inverter structures.

Optimal On‐Off Attitude Control for the Brazilian Multimission Platform Satellite

This work deals with the analysis and design of a reaction thruster attitude control for the Brazilian Multimission platform satellite. The three‐axis attitude control systems are activated in pulse mode. Consequently, a modulation of the torque command is compelling in order to avoid high nonlinear control action. This work considers the Pulse‐Width Pulse‐Frequency (PWPF) modulator which is composed of a Schmidt trigger, a first‐order filter, and a feedback loop. PWPF modulator holds several advantages over classical bang‐bang controllers such as close to linear operation, high accuracy, and reduced propellant consumption. The Linear Gaussian Quadratic (LQG) technique is used to synthesize the control law during stabilization mode and the modulator is used to modulate the continuous control signal to discrete one. Numerical simulations are used to analyze the performance of the attitude control. The LQG/PWPF approach achieves good stabilization‐mode requirements as disturbances rejection and regulation performance.

Variable structure attitude manoeuvre control and active vibration damping of three-axis-stabilized flexible spacecraft

This paper presents a dual-stage control system design method for the three-axis-rotational manoeuvre and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as the sensor and actuator. In this design approach, the attitude control system and vibration suppression were designed separately using a lower-order model. The design of the attitude controller was based on the variable structure control (VSC) theory, leading to a discontinuous control law. This controller accomplishes asymptotic attitude maneouvring in the closed-loop system and is insensitive to the interaction of elastic modes and uncertainty in the system. The advantage of this dual-stage approach is that once the desired orientation is attained under the VSC law, only the elastic motion is governed by the decoupled linear second-order systems describing elastic dynamics. To this end, modal velocity feedback and optimal positive position feedback control methods are presented and compared for actively damping the elastic oscillations using piezoelectric materials as an additional sensor and actuator bonded on the surface of the flexible appendages. In addition, a special configuration of actuators for three-axis attitude control is also investigated: the pitch attitude controlled by a momentum wheel and the roll/yaw control achieved by on-off thrusters, which is modulated by the pulse width-pulse frequency modulation technique to construct a proper control torque history. Numerical simulations are performed to show that the rotational manoeuvre and vibration suppression are accomplished in spite of the presence of disturbance torque and parameter uncertainty.

Development of an Attitude Guidance and Control System for the Thunderstar Suborbital Spacecraft

This paper outlines a method of developing a quaternion attitude guidance and control system for a rigid body suborbital spacecraft using cold gas thrusters over a short-duration mission. It has been specifically developed for integration aboard the Thunderstar spacecraft of Starchaser Industries, a three-man capsule designed for space tourism. The system described consists of three principal components: an autoflight computer that generates incidence and roll rate demands from analysis of the predicted flight path trajectory, a quaternion controller that produces a demand torque, and a pulse-width pulse-frequency modulator that determines the necessary thruster fire signals. The spacecraft attitude and flight path dynamics are defined within the upper to middle Earth atmosphere together with the cold gas thruster dynamics. The effect of disturbances on spacecraft attitude has been investigated and the most significant found to be due to crew motion and aerodynamics. The system concept has been evaluated through modelling in SIMULINK and has been found to meet the requirements laid out for a typical Thunderstar mission.

A Low-Cost High-Efficiency CCFL Inverter With New Capacitive Sensing and Control

A new low-cost and efficient cold cathode fluorescent lamp (CCFL) inverter for liquid crystal display (LCD) application is suggested in this paper. The topology of the inverter is derived from modified class E-type resonant electronic ballasts and has a dc-like input current. In addition, a new sensing circuit for lamp current and transformer voltage is proposed. A simple RC-network measures the voltage of a ballasting capacitor in series with the lamp instead of the lamp current itself while the lamp is floated. Utilizing the printed circuit board capacitors for the sensing capacitors and integrating small-valued sensing resistors into a control integrated circuit make the inverter very simple, efficient, and cost-effective. The new sensing circuit can solve many problems that arise when a terminal of the lamp is grounded to sense the lamp current. The control circuits for the prototype experiments are also described in detail. The frequency control scheme with a fixed off-time and a varying on-time was chosen to maintain the operation of zero-voltage switching in the entire dimming range and to reduce the complexity of the control circuits. The control circuits have an analog dimming function using a current control loop, a low frequency pulsewidth modulation dimming, open-lamp protection and voltage regulation, and soft-on/off functions

USE OF RECURRENCE PLOT ANALYSIS FOR DETECTING CHAOS AND NOISE IN NONLINEAR SWITCHING CIRCUITS

DC–DC converters controlled by naturally sampled, constant frequency pulse width modulation give rise to a wide range of bifurcation and chaos depending on the change in the system parameter values. Knowledge of transitions from regular to chaotic behavior is essential to understand the underlying dynamics of nonlinear switching circuits. While linear approaches are often insufficient to describe such processes, there are nonlinear methods available but requires long time observations. To overcome these difficulties, a newly developed pattern recognition method of nonlinear dynamics called Recurrence plot analysis method is proposed to detect transitions between periodic and chaotic states. The recurrence plot is a two-dimensional representation technique that brings out distance correlations in a time series and make it instantly apparent whether a system is periodic or chaotic. In this paper, the proposed method is applied to a nonlinear switching Buck converter, Boost converter, and Buck–Boost converters to analyze their period doubling route to chaos behavior and to distinguish chaos from noisy behavior. This may lead to a better understanding of the nonlinear switching systems, that may allow us to design stable, chaotic free switching circuits.

A novel converter topology for multiple individually regulated outputs

Power supply voltages in digital systems have reduced considerably in recent years, and often digital components requiring different voltages are present on the same board. This has increased the demand for multiple output power distribution systems with tight individual load voltage regulation. This paper presents a power distribution system having a central power supply that acts as a controlled current source whose output is connected to individual loads on a time shared basis. All the magnetics are concentrated in the converter acting as the current source. The current source can be realized by a current controlled buck, buck-boost, or single-ended primary inductance converter (SEPIC). First, a comparative analysis of buck, buck-boost, and SEPIC based implementation of the current source is carried out. Next, a buck-based current source implementation with constant frequency pulse-width modulation control for the output voltages is described. Detailed component and control design, simulations, and experimental results for a 100-W prototype are presented.

Comparative study of switching controls in vibration and acoustic noise reductions for switched reluctance motor

A comparative study of vibration and acoustic noise reductions via electronic switching controls for switched reluctance motor (SRM) is presented. First, studies concerning the acoustic noise and vibration sources, their effects and the existing mitigation approaches are given. Then five switching control approaches, which belong to the magnetic and electronic remedies, are proposed and applied to the established SRM drive to comparatively evaluate their effectiveness and limitations. These approaches include random frequency pulse width modulation with harmonic spectrum shaping, turn-on and turn-off angles advanced shift with fixed dwell angle, randomising turn-off angle, current-tail profiling without and with advancing commutation shift. The theoretical basis, implementation and performance evaluation of each approach are presented in detail. Comparative evaluation shows that the hybrid approach combining the current-tail profiling and the commutation advancing can yield the best compromise performance in vibration reduction, acoustic noise reduction and improved energy conversion efficiency.

High-frequency pulse width modulation implementation using FPGA and CPLD ICs

Pulse width modulation (PWM) has been widely used in power converter control. Most high power level converters operate at switching frequencies up to 500 kHz, while operating frequencies in excess of 1 MHz at high power levels can be achieved using the planar transformer technology. The contribution of this paper is the development of a high-frequency PWM generator architecture for power converter control using FPGA and CPLD ICs. The resulting PWM frequency depends on the target FPGA or CPLD device speed grade and the duty cycle resolution requirements. The post-layout timing simulation results are presented, showing that PWM frequencies up to 3.985 MHz can be produced with a duty cycle resolution of 1.56%. Additionally, experimental results are also presented for low cost functional verification of the proposed architecture.

New Cascaded Control System for Current-Source Rectifiers

A control method for current-source rectifiers (CSRs), which realizes substantially sinusoidal line currents, unity displacement power factor, and a dc-link current control with excellent dynamic properties is presented. CSRs are usually operated by pulsewidth-modulation (PWM) or space-vector-modulation techniques. However, due to the mains LC filter resonant circuits when using these modulation methods the system stability has to be investigated, resulting in restrictions on the minimum PWM frequency and the minimum size of the LC filter. Furthermore most known dc-link current control loops use dc-link inductors of considerable size. This limits the dynamic performance and, therefore, reduces the attainable efficiency of CSRs. To overcome these problems, a new cascaded dc-link current control system for CSRs is presented. Its inner capacitor voltage controller is based on a time-discrete modulation method, which realizes a fundamentally stable control of the mains LC filter resonant circuits, avoiding the mentioned restrictions. The system controlled by the superimposed dc-link current controller is linearized by a new approach, allowing excellent dynamic performance and, therefore, a comparatively small dc-link inductor to be used. The paper includes guidelines on how to design the mains filter components and the dc-link inductor. The feasibility of the presented cascaded controller is confirmed by measurements taken on a 60-kVA model current-source converter and different loads.

A Resonant MOSFET Gate Driver With Efficient Energy Recovery

High frequency pulse-width modulation (PWM) converters generally suffer from excessive gate drive loss. This paper presents a resonant gate drive circuit that features efficient energy recovery at both charging and discharging transitions. Following a brief introduction of metal oxide semiconductor field effect transistor (MOSFET) gate drive loss, this paper discusses the gate drive requirements for high frequency PWM applications and common shortcomings of existing resonant gate drive techniques. To overcome the apparent disparity, a new resonant MOSFET gate drive circuit is then presented. The new circuit produces low gate drive loss, fast switching speed, clamped gate voltages, immunity to false trigger and has no limitation on the duty cycle. Experimental results further verify its functionality.

Control of shape memory alloy actuator using pulse width modulation

Shape memory alloys (SMA), in particular nickel–titanium alloy (or nitinol), have been usedas actuators in some astronautic, aeronautic and industrial applications. The future will seemore SMA application if less energy is required for actuation. This paper presents thedesign and experimental results of control of an SMA actuator using pulse widthmodulation (PWM) to reduce the energy consumption by the SMA actuator.A SMA wire test stand is used in this research. Open-loop testing of the SMAwire actuator is conducted to study the effect of the PWM parameters. Based ontest results and parameter analysis of the pulse width (PW) modulator, a PWmodulator is designed to modulate a proportional plus derivative (PD) controller.Experiments demonstrate that control of the SMA actuator using PWM effectively savesactuation energy while maintaining the same control accuracy as compared tocontinuous PD control. PWM also demonstrates robustness to external disturbances.A comparison with a pulse width pulse frequency modulator is also presented.

Control of Shape Memory Alloy Actuators Using Pulse-Width Pulse-Frequency (PWPF) Modulation

This paper presents the design and experimental results of control of a Shape Memory Alloy (SMA) actuator using Pulse-Width Pulse-Frequency (PWPF) modulation to reduce the energy consumption of the SMA actuator. An SMA wire test stand is used in this research. Based on results of open-loop testing of the SMA wire actuator and parameter analysis of the PWPF modulator, a PWPF modulator is designed to modulate a Proportional plus Derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PWPF modulation effectively save actuation energy while maintaining same control accuracy as compared to continuous PD control.

A new pulse modulation adaptive controller (PMAC) applied to HVAC systems

The paper proposes a new switching control law (pulse modulation adaptive controller, PMAC) that implements pulse-width–pulse-frequency modulation. Pulse durations are determined to maintain the amplitude of variation in the controlled variable at or below a user-defined level. In addition to providing quantifiable control performance, PMAC can reduce component wear by issuing fewer switches than conventional control schemes. The control law is developed around a first-order system characterization but incorporates an adaptive loop, which allows application to a wide range of non-first-order and also time-variant systems. Test results are presented from applying PMAC to both simulated and real HVAC systems.

Half-bridge inverter using 4H-SiC gate turn-off thyristors

This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm/sup 2/) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V//spl mu/s in these devices.

Fixed-frequency space-vector-modulation control for three-phase four-leg active power filters

The paper presents a three-dimensional space-vector-modulation scheme for three-phase four-wire active power filters. The focus is on the implementation of a fixed frequency pulse width modulation (PWM) scheme with a minimum number of switch commutations per period and maximum DC bus voltage utilisation. For three-wire applications, space vector modulation is known to provide better utilisation of the DC voltage compared to a sinusoidal PWM approach. This concept is extended to four-wire applications by employing a four-leg active power filter. The largest symmetrical region in which the active filter's voltage space vector may reside is identified. Restricting the voltage space vector to this region avoids over-modulation and thereby prevents the production of low order harmonics. A digital controller is employed to provide deadbeat current control. The combination of the digital controller and the modulation scheme gives the four-leg active power filter the capability to independently track reference current waveforms in the three phases within one switching period. The four-leg active power filter may be used for harmonic compensation, reactive power compensation, load balancing, and neutral current compensation. Experimental results obtained from a 5 kVA laboratory active power filter validate the proposed modulation scheme as well as the control design.

Vibration suppression of flexible spacecraft during attitude control

This paper presents a new approach to vibration reduction of flexible spacecraft during attitude control by using pulse width pulse frequency (PWPF) modulator for thruster firing and smart materials for active vibration suppression. The experiment was conducted on the Naval Postgraduate School (NPS)'s flexible spacecraft simulator (FSS), which consists of a central rigid body and an L-shape flexible appendage. A pair of on–off thrusters are used to re-orient the FSS. To actively suppress vibrations introduced to the flexible appendage, embedded piezoelectric ceramic patches are used as both sensors and actuators to detect and counter react to the induced vibration. For active vibration suppression using the piezoelectric ceramic patches, positive position feedback (PPF) control targeting at the first two flexible modes of the FSS system is used. Experimental results demonstrate the effectiveness of the control strategy of PWPF modulation for attitude control and PPF for active vibration suppression.

Spacecraft Vibration Reduction Using Pulse-Width Pulse-Frequency Modulated Input Shaper

Minimizing vibrations of a flexible spacecraft actuated by on-off thrusters is a challenging task. This paper presents the first study of Pulse-Width PulseFrequency (PWPF) modulated thruster control using command input shaping. Input shaping is a technique which uses shaped command to ensure zero residual vibration of a flexible structure. PWPF modulation is a control method which provides pseudo-linear operation for an on-off thruster. The proposed method takes full advantage of the pseudo-linear property of a PWPF modulator and integrates it with a command shaper to minimize the vibration of a flexible spacecraft induced by on-off thruster firing. Compared to other methods, this new approach has numerous advantages: 1) effectiveness in vibration suppression, 2) dependence only on modal frequency and damping, 3) robustness to variations in modal frequency and damping, 4) easy computation and 5) simple implementation. Numerical simulations performed on an eight-mode model of the Flexible Spacecraft Simulator (FSS) in the Spacecraft Research and Design Center (SRDC) at US Naval Postgraduate School (NPS) demonstrate the efficacy and robustness of the method.