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Modern systems‐on‐chip use multiple current references to guarantee appropriate circuit biasing according to the required performance and power consumption. New reference topologies have emerged due to the necessity of ultra‐low‐power systems. Still, in the micro‐Ampere domain, the most common architectures are preferred in industry‐based applications, due to their reliability and accuracy. Motivated by the limited documentation and data associated with current references for SoCs, this work presents key observations in the design decisions, based on error contributions from the inherent elements of a reliable voltage‐to‐current reference architecture. Monte Carlo simulations show results for a 5 μA current reference, with inaccuracies at ±3σ of ±4% and ±1.3%, without and with trimming, respectively. Furthermore, two current references were fabricated using a 0.18 μm CMOS standard technology, in two different SoCs. Measurement results across voltage and temperature variations showed results for 50 μA ± 0.24% and 5 μA ± 0.8% current references without trimming. [ABSTRACT FROM AUTHOR]

This paper presents a study of control strategies for 5-phase permanent magnet synchronous motors (PMSMs) supplied by a five-leg voltage source inverter. Based on the vectorial decomposition of the multi-phase machine, fictitious machines, magnetically decoupled, allow a more adequate control. In this paper, our study focuses on the vector control of a multi-phase machine using a linear proportional-integral-derivative (PID) current regulator in the cases of sinusoidal and trapezoidal back-electromotive force (EMF) waveforms. In order to determine currents’ references, two strategies are adopted. First one aims to minimize copper losses under constant torque, while the second one targets to increase torque for a given copper losses. These techniques are tested under a variable speed control strategy based on a proportional-integral (PI) regulator and experimentally validated.

This study proposes several easy-to-implement control strategies when seven-phase axial flux brushless DC machines with trapezoidal back electromotive forces operate in normal and faulty modes by taking into account constraints on voltage and current. The constraints are related to the converter and machine design in terms of maximum values of current and voltage. The considered faults are cases in which one or two phases of the machine are open-circuited. Numerical computations based on analytical formulations are applied to obtain torque-speed characteristics, including the flux-weakening operation. The methods determine current references to ensure the torque optimisations while currents and voltages are within their limits. The usefulness of the methods is verified by numerical results.

In the context of future permanent magnet synchronous machines (PMSMs) with a high number of phases (>7) in integrated drives, this study proposes several control strategies when multiphase PMSMs with non‐sinusoidal back electromotive forces (back‐EMFs) operate in healthy and open‐circuit faults. In all operation modes, the considered constraint on current is related to the maximum root mean square current allowable in one phase of the machine. The constraint on voltage limits the maximum peak value of the phase voltage determined by the DC‐bus voltage of the converter. When one or two phases are open‐circuited, to maximise torque and respect the constraints, new current references obtained by several proposed methods in rotating and natural frames are imposed to the machine. Owing to the non‐sinusoidal waveform of back‐EMFs and the considered constraints, numerical computations based on analytical formulations are required to obtain maximal torque‐speed characteristics, including the flux‐weakening operation. The usefulness of the proposed strategies is verified by numerical and experimental results. [ABSTRACT FROM AUTHOR]

Under the low‐voltage ride‐through (LVRT) of the doubly fed induction generator, extra efforts are required for the model predictive control (MPC)‐based direct stator/rotor current controls (DSCC/DRCC) against the stator flux oscillation. Constant stator/rotor currents are maintained at the cost of rotor/stator current oscillations, respectively, due to stator flux oscillation. Necessity to incorporate the stator flux transient in the MPC‐based DSCC/DRCC under the LVRT is analysed based on tracking effects of the current references. To quantify LVRT effect with the MPC‐based DSCC/DRCC, analytical expressions of the stator current, rotor current and rotor voltage are proposed, whose accuracy is validated based on comparison with the time‐domain simulations. On the basis of analytical study, advantages and disadvantages of the DSCC/DRCC are analysed considering impacts of the current oscillations on the security of the rotor‐side converter. With the DRCC, rotor voltage increase is suppressed with damping to the stator flux oscillation and rotor current constraint is satisfied without decreasing stator output power; thus, the LVRT effect is desirable compared with the DSCC. The MPC‐based DSCC/DRCC is extended to LVRT under the asymmetrical fault to realise effective control to both the positive and negative sequence stator/rotor currents. [ABSTRACT FROM AUTHOR]

This paper presents a study of control strategies for 5-phase permanent magnet synchronous motors (PMSMs) supplied by a five-leg voltage source inverter. Based on the vectorial decomposition of the multi-phase machine, fictitious machines, magnetically decoupled, allow a more adequate control. In this paper, our study focuses on the vector control of a multi-phase machine using a linear proportional-integral-derivative (PID) current regulator in the cases of sinusoidal and trapezoidal back-electromotive force (EMF) waveforms. In order to determine currents' references, two strategies are adopted. First one aims to minimize copper losses under constant torque, while the second one targets to increase torque for a given copper losses. These techniques are tested under a variable speed control strategy based on a proportional-integral (PI) regulator and experimentally validated. [ABSTRACT FROM AUTHOR]

This study proposes several easy-to-implement control strategies when seven-phase axial flux brushless DC machines with trapezoidal back electromotive forces operate in normal and faulty modes by taking into account constraints on voltage and current. The constraints are related to the converter and machine design in terms of maximum values of current and voltage. The considered faults are cases in which one or two phases of the machine are open-circuited. Numerical computations based on analytical formulations are applied to obtain torque-speed characteristics, including the flux-weakening operation. The methods determine current references to ensure the torque optimisations while currents and voltages are within their limits. The usefulness of the methods is verified by numerical results. [ABSTRACT FROM AUTHOR]

During the grid disturbances, particularly voltage sags, if the grid-connected converter’s (GCC’s) power references are kept at the pre-fault level, the excessive currents would flow. This could force the inverter disconnection, which is in conflict with the grid codes and the tendency to keep the GCC system connected to the grid as long as possible. Keeping the system connected for a prolonged periods of time offers a possibility of a more effective grid support, better exploitation of available energy resources and generally more reliable power supply. The aim of this paper is to address the utilization of active and reactive power production capacities during unbalanced voltage sags with respect to the current limits. First proposed algorithm gives the grid operator the opportunity to choose whether active or reactive power production is prioritized during voltage disturbance, with the curtailment done only to the extent that the current limits are not surpassed. Second approach allows for the power factor to stay the same before and during the sag. Selected hardware-in-the-loop experiments are presented to validate the developed theoretical background and implemented algorithm. [ABSTRACT FROM AUTHOR]

Low‐voltage ride‐thorough capability is among the challenges in the operation of medium‐ and large‐scale grid‐connected photovoltaic power plants (PVPPs). In addition, reactive power injection during voltage sags is required by power system operators in order to enhance the voltage of the point of common coupling. The performance of medium‐ and large‐scale grid‐connected PVPPs during these events is studied. An algorithm for the calculation of current references, in the dq‐frame, during voltage sags is introduced, which considers the inverter current limitation, grid code requirements and the amount of extracted power from photovoltaic strings. The proposed algorithm uses the full current capacity of the inverter in injecting active or reactive powers to the grid during voltage sags, which leads in a better grid voltage enhancement. The performance of proposed control strategies is investigated on a 150‐kVA PVPP connected to the 12.47‐kV medium‐voltage test‐case system simulation model during different fault conditions. An experimental setup of the 3.3‐kVA grid‐connected three‐level neutral‐point‐clamped inverter with a dc/dc converter illustrates and validates the performance of the controller in injecting required active/reactive power and supporting the network voltage. [ABSTRACT FROM AUTHOR]

A new Temperature compensated Ring Oscillator is presented. This CMOS ring oscillator consists of five current starved stage which is fed by a voltage and a current reference. In this paper a new method based on previous works has been proposed, in which required Temperature characteristic is imposed to the oscillator. The oscillation frequency of the proposed oscillator is 14.5 MHz and the simulation results in CMOS 0.18μm technology with a 1.8- V power supply showed that the temperature coefficient is 31.1 ppm/°C in the Temperature range of -15 ºC to 65 ºC. The total power consumption of circuit is 587 μW. [ABSTRACT FROM AUTHOR]

This paper proposes a predictive control method with zero-sequence voltage injection to efficiently reduce the switching losses of three-phase voltage source inverters (VSIs). In the proposed predictive control method, three-phase future voltage references modified by a zero-sequence voltage injection are generated to clamp one of the three legs with the largest load current. Furthermore, the future zero-sequence voltage, which is produced online with the future voltage and current references in every sampling period, optimally adjusts the clamping duration on each leg, depending on the load angle. In addition, the proposed method selects the zero vector on the basis of the polarity of the future zero-sequence voltage to reduce the switching losses. Using a predefined cost function, the proposed predictive control scheme chooses one optimal voltage state closest to the future voltage references modified by the zero-sequence voltage injection. Therefore, the proposed predictive control method can perform load current control and minimize the switching losses of the VSI under any load condition regardless of the load angle. [ABSTRACT FROM AUTHOR]

In this paper, a low-complexity dual-voltage-loop digital control architecture is presented for voltage regulators (VRs), delivering power to processors. The proposed digital control architecture uses low speed and less complex digital-to-analog converters instead of high-speed analog-to-digital converters, thus significantly reducing the system complexity and cost. In this control architecture, there are two voltage loops, and the voltage reference is dynamically generated to selectively track one of them, as compared to other control methods where the output voltage tracks the voltage reference. Moreover, a straightforward control law is used, which does not require any compensator, making the proposed digital architecture simple and easy to implement. The dual-voltage-loop architecture breaks dependence between the system transient response and the system control bandwidth. One voltage loop is designed for the stable system operation, and the other is dedicated for the load transient response. Thus, the digital controller can be designed in such a way that the VR operates at a relatively low switching frequency to reduce power losses, and at the same time, it is also able to provide fast transient response. The proposed small signal model reveals that the inner current loop is analog and the voltage loop is digital. The proposed controller thus can benefit from both: having valuable features of digital control but without limitations such as limit cycle, which is eliminated by the inherent dithering characteristic. Theoretical, simulation and experimental results prove the effective operation and excellent dynamic performance of the low-complexity digital controller, thus making it a valuable candidate for a high-volume, low-cost digital controller for processors' VRs. [ABSTRACT FROM AUTHOR]

The paper suggests an energy management control strategy of wayside Li-ion capacitor (LiC) based energy storage for light railway vehicles (LRV). The installation of wayside supercapacitor (SC) storage devices, as widely recognized, allows the recovery of the braking energy for increasing the system efficiency as well as a better pantograph voltage profile. A new type of SC, LiC, interfaced with dc-interleaved converter has been presented. This technology has an energy density comparable to batteries and power density much higher than the batteries. The authors propose a control strategy based on the maximum kinetic energy recovery throughout braking operations of the running vehicles. The stored energy comes back to the vehicles during the accelerations. The strategy stays on the knowledge of the state of charge of LiC device and the actual vehicle speeds. In particular, the control algorithm evaluates, in real time, the actual value of LiC voltage and current references on the basis of the vehicles inertial forces and acceleration estimations, taking into account the power losses of the system. Experimental tests made on electromechanical simulator, equipped with a 136-V, 30.5-F LiC module, fully confirm the validity of the suggested control. Finally, experimental characterization of LiC module has been achieved. [ABSTRACT FROM AUTHOR]

This paper suggests a novel energy management control algorithm for metro trains based on speed measurement and acceleration estimation. The aim of the control is to recover in a supercapacitor (SC) storage device the maximum energy regenerated during train electrical braking and to limit the contact line peak current. The energy management control is integrated with the motor drive control, since discharge and charge of SC are connected to motoring and braking operations of the train. The algorithm is based on two nested loops on voltage and current of SC. The voltage and current references are calculated on the basis of the estimation of the train inertial force and acceleration, taking into account the power losses of the system. A simplified mathematical model of the whole electrical drive has been developed and the main features of the control strategy have been presented. Numerical simulations show the efficacy of suggested control and the energy saving obtained for metro trains. Experimental tests made on an electromechanical simulator fully confirm theoretical results. [ABSTRACT FROM AUTHOR]

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