Soft-start Method Research Articles

A soft-start scheme based on mismatch of OPA for DC-DC converters

Aiming at output voltage overshoot during start-up period, a soft-start scheme for dc-dc converters with the features of a small on-chip capacitor is adopted in this article. The proposed soft-start method utilizes the mismatch characteristics of operational amplifiers (OPAs) to generate a small current for charging the capacitor, thereby reducing the capacitor size. The experimental results reveal that the proposed soft-start scheme is implemented in 0.18 μm BCD process and occupies an area size of 0.018 mm2. The proposed soft-start period of 500μs is achieved with an on-chip capacitor of 10.8 pF. Besides, the peak efficiency of the dc-dc converter that employing proposed soft-start scheme can reach 94.86 % and the deviation of the output voltage is within ±2.25 %.

A Soft Start Method for Doubly Fed Induction Machines Based on Synchronization with the Power System at Standstill Conditions

Due to their exceptional operational versatility, doubly fed induction machines (DFIM) are widely employed in power systems comprising variable renewable energy-based electrical generation sources, such as wind farms and pumped-storage hydropower plants. However, their starting and grid synchronization methods require numerous maneuvers or additional components, making the process challenging. In this paper, a soft start method for DFIM, inspired by the traditional synchronization method of synchronous machines, is proposed. This method involves matching the frequencies, voltages, and phase angles on both sides of the main circuit breaker, by adjusting the excitation through the controlled power converter at standstill conditions. Once synchronization is achieved, the frequency is gradually reduced to the rated operational levels. This straightforward starting method effectively suppresses large inrush currents and voltage sags. The proposed method has been validated through computer simulations and experimental tests, yielding satisfactory results.

Analysis of a Doubly-Fed Induction Motor for Soft Start Operation based on Stator Flux Vector Control

This paper aims at analysis of an operation of a doubly-fed induction motor (DFIM). The paper mainly focuses on the soft start method for the DFIM using the conventional topology that is normally used in the case of a doubly-induction generator (DFIG). Likewise, the details about reactive power control is also discussed. With the proposed method, the DFIM can start from zero to any speed by controlling the machine-side converter (MSC). The computer simulation is performed to a 5 kW wound rotor induction motor using PLECS software. The simulation results validate that the DFIM can operate from the rest to any speed while operating only under the conventional topology.

Research on Fixed-Slope On-Chip Soft-Start Method Applied to Buck DC–DC Converter

A fixed-slope soft-start method applicable to Buck converters for on-chip integration is proposed to address the issue of varying power stresses (device voltage, current stress) during start-up with different output voltages. The main mechanism involves combining feedback coefficient sampling with a fixed-slope reference voltage to achieve a slow rise in the reference voltage by equating the soft-start charging current to a pulse current through the on-chip integration of a small capacitor. This allows for fixed-slope start-ups for different set output voltages. Spike elimination techniques are employed to address charging current spikes caused by pulse periods, enhancing precise control over the soft-start time. By replacing the traditional resistor divider network with a capacitive divider network in the soft-start method, DC power consumption is minimized. Upon completion of the soft start, a smooth transition to a steady-state operation occurs, with the automatic shutdown of the soft-start module reducing static power consumption. A specific circuit design and layout verification based on 0.18 μm high-voltage BCD technology demonstrates that the proposed method maintains a fixed-slope start-up of approximately 5 mV/μs within the chip’s output range of 0.9 V to 4 V, with a slope control accuracy of up to 98%. The soft-start circuit effectively eliminates surge currents generated during start-up under full load conditions of 3 A and no-load conditions of 0 A, reducing the overall surge current by 44% and enabling a stable voltage rise and the smooth transition to a steady-state operation.

Predictive power control strategy without grid voltage sensors of the Vienna rectifier

AbstractThis paper proposes a predictive power control strategy for the three‐phase, six‐switch Vienna rectifier without grid voltage sensors to reduce the hardware cost and complexity of a high‐power PWM rectifier system. Firstly, an algorithm for calculating the AC‐side voltage in the αβ coordinate system is derived according to the operating principle of the Vienna rectifier, and a voltage observer is constructed by combining a second‐order low‐pass filter to estimate the grid voltage. Secondly, a soft start method is designed to solve the problem that the rectifier is prone to inrush current when it is started. Furthermore, the control method of grid voltage sensorless is combined with predictive power control with good dynamic characteristics and simple parameter settings to form the control strategy proposed in this paper. Finally, simulation analysis and experimental verification are carried out on the proposed control strategy. Simulation and experimental results show that the grid voltage estimation has high accuracy, a good surge current suppression effect, unit power factor operation, low input current harmonic content, and good dynamic and steady‐state performance. Therefore, the correctness and effectiveness of the strategy proposed in this paper are verified.

Research on a soft-start method for LCC-LCC compensated bidirectional wireless power transfer system

The increased popularity of electric vehicles and the pursuit of user convenience makes bidirectional wireless power transfer (BWPT) an attractive technology for charging batteries. To improve the transmission efficiency of BWPT and limit the external radiated magnetic field, it is necessary to ensure the zero-voltage switching (ZVS) operation of the converter on the transmitter-side and limit the transient start-up current of the inverter when the system is working. To solve this problem, this paper proposes a soft-start modulation strategy based on an H-bridge inverter on the transmitter-side. First, the circular characteristics of dual LCC compensation topology are analysed based on an equivalent circuit. Secondly, according to the characteristics of the input impedance angle and current of the transmitter-side, a soft-start control method combining frequency and phase shift control is proposed. Finally, the feasibility of the proposed soft-start modulation strategy is verified on a prototype.

Novel soft-start method for three-phase voltage source rectifier based on virtual resistor control

Novel soft-start method for three-phase voltage source rectifier based on virtual resistor control

Hybrid Control-Based Closed-Loop Soft Start-Up Method for LLC Resonant Converters

LLC resonant converters are prone to generating a large inrush current during the start-up process, which will cause damage to the resonant elements and threaten the safe operation of the circuit. In this study, we investigate the soft-start method to suppress the inrush current of an LLC resonant converter. Based on the traditional frequency-decreasing method, we integrate PWM control to broaden the output voltage gain range during the start-up. Additionally, to ensure the smooth establishment of the output voltage, the controller performs the closed-loop control of the duty cycle and frequency in sequence based on the rate of output voltage rise. A prototype experiment based on STM32F334C8T6 is established to experimentally validate the presented soft start-up method. The experiment results indicate that the soft start-up method improves the start-up performance, reduces the maximum inrush current by 47.5% compared with that of the frequency-decreasing method, and builds up the output voltage quickly. The start-up process is smooth, which improves the reliability of the LLC resonant converter.

Large-capacity AC superimposed DC power supply for the degradation evaluation of DC-link capacitors

The DC-link capacitor, whose operating voltage is a periodic irregular waveform, is a key device in the converter. A large-capacity DC/AC superimposed experimental power supply above 100 kVA is an important piece of equipment that must be used in the aging research of DC-link capacitors. The irregular periodic operating voltage of the DC support capacitor is equivalent in the form of DC voltage superimposed with multiple harmonics based on the Fast Fourier transform analysis. The power supply is mainly divided into four parts: an AC module, a DC module, a protection module, and an isolation component. The composited harmonics are output by the IGBT (Insulated Gate Bipolar Transistor) inverter of the AC module. The soft start method is applied to the AC module in order to ensure the long-term reliable operation of the power supply. The kV-level high-voltage is output by four inverter units connected in series. The amplitude and phase control of harmonic decomposition is adopted, and the inverter is controlled by Sinusoidal Pulse Width Modulation. The output voltage of the power supply is close to the operating voltage of the capacitor. Based on the designed power supply, the degradation experiment was carried out. The temperature rise and aging characteristics of DC-link capacitors under different AC/DC ratios were studied.

Implementasi Soft Starting Abb Pstx 570 Motor Tiga Phasa Mesin Hammermill di PT.Central Proteina Prima,Tbk

In industry, electric motors play an important role as energy for motion in equipment in the production process. During the starting process, it can draw currents up to 5 to 7 times the nominal current when working normally. So that it can have a bad effect on the electric motor and the surrounding electrical equipment. The method that uses the ABB PSTTX 570 Soft Starting is through the method of starting an electric motor using a thyristor circuit. The soft start method is suitable for cars that are quite powerful. The purpose of the soft start method is to obtain a smaller starting current, to reduce the impact of large peak currents during the starting process and to achieve a constant rated speed. In this method, the current in the motor flows slowly during starting until it reaches the rated value within a certain period of time certain. Soft starting measurable display when motor voltage is 34%, moor current is 7.3 A active power is 0.14 kW when motor voltage is 70% motor current is 1782.5 A with active 371.09 kW and when motor voltage is 100% up motor 111.6 A with an active power of 23.65 kW. In terms of size, the advantage of the soft starter is that it is simpler than the inverter starting equipment.

Research on digital soft start method of boost DC-DC switching power supply

Due to the progress of science and technology and the rapid development of the economy, human performance requirements for electronic products are getting higher and higher. Therefore, it is necessary to study a Boost-type DC-DC converter with high conversion efficiency, miniaturization, strong stability, and fast start speed. Currently, there are many ways to solve the DC-DC switching power supply problem. By analyzing the switching power supply, an efficient digital soft start method for boosting DC-DC switching power supply. This method adopts programmable digital technology. By precharging the output capacitor with the multiplexed substrate switching circuit, the output current rises steadily, and the soft start effect of the switching power supply is achieved. Based on the 0.18um BCD process, the test shows that when the input voltage is 3.7 V, the output voltage is 4.6 V, and the duty ratio is 20%, the soft start time is 210 us when the PVT changes and the steady rise of the output voltage does not produce the surge current phenomenon. Through theoretical analysis and experimental verification, the proposed method has the obvious advantages of simple structure, strong stability, low power consumption, and fast starting speed.

An optimized soft‐start procedure of dual active bridge converter for charging current suppression

As a typical topology of solid-state transformer, dual active bridge converter (DABC) is widely used for voltage levels conversion due to its advantage in bidirectional power transfer and galvanic isolation. In the start-up process, an overcurrent will occur when the converter charges the output capacitor. To address this problem, special soft-start procedures are used to protect switches from the inrush current. The soft-start framework used in this paper adds an inner-phase-shift in the closed loop control. Compared to the conventional step-to-step soft-start methods, it simplifies the transition process from the open loop to the closed loop control. However, higher current stress appears in the soft-start process. So, based on the framework, an optimized soft-start procedure with simple implementation, including the phase transformation and the inverse-trigonometric inner-phase-shift, is proposed to improve the voltage tracking performance and reduce the charging current further. The simulation and experimental results confirm the effectiveness of the proposed soft-start procedure on the output voltage control and charging current suppression.

A novel soft-start method for SVG based on D-axis orientation

In this paper, a novel method for shock-free soft-start is proposed. The novel method can realize the aim of no-overshoot and inrush of current during the entire soft-start process, thus the start process is safe, stable, and reliable. When the uncontrolled rectification stage ends, a sinusoidal signal synchronized with the grid voltage is generated through dq coordinate transformation and D-axis orientation, then the signal is transmitted to the three-phase inverter bridge. The AC voltage output of the inverter bridge is superimposed on both ends of the soft-start resistor along with the grid. The open-loop control method is adopted to gradually reduce the modulation ratio of the sinusoidal PWM wave until the capacitor voltage on the DC side reaches the rated voltage value, then the soft-start resistor is removed, which means the shock-free soft-start process is completed. Experimental results prove the effectiveness and feasibility of the control strategy proposed in this paper.

Research of Motor Soft Start by High Voltage Motor Drive Inverter

The over-current phenomenon of direct starting of high voltage and high power motor is serious bad for the safety of motor. We are usually using motor soft start method when we need to start a motor. There are some motor soft start methods, they can somehow reduce the starting over-current, but they are still having some defects except motor drive inverter. Motor drive inverter can not only realize the purpose of energy saving, but also is an ideal soft start device. We can see a lot of papers about control method research of motor drive inverter, but no paper research on motor soft start by motor drive inverter [1]. This paper focuses on research of motor soft start by motor drive inverter. The optimal frequency range of soft start is obtained through theoretical analysis. The simulation results verify the correctness and feasibility of the theoretical analysis.

Blackstart from HVDC‐connected offshore wind: Hard versus soft energization

In recent years, renewable energy sources have been integrated on a large scale in power systems all around the world to address the environmental sustainability concerns. With conventional thermal generators being phased out, large offshore wind power plants present a viable alternative to provide blackstart services for power system restoration. In this paper, by means of simulations, grid-forming wind turbines are shown to successfully energize the offshore transformer and the HVDC export link in a controlled manner, to ultimately supply the onshore grid. Two methods for energizing the offshore network have been compared:the prevalent hard-switching approach and the more complex soft-start method. Additionally, control has been implemented to mitigate the significant transients in the export link associated with pre-charging of the onshore converter. It is shown that soft-start can provide faster energization with smaller transients compared to hard-switching. Moreover, the sensitivity analyses performedin this study illustrate the impact of pre-insertion resistor design and voltage ramp-up rates on transients during hard-switching and soft-start, respectively. The results presented in the paper also show that a separate controlled pre-charging stage of the onshore converter from its DC terminals is essential for the safe energization and operation of the export link.The manuscript has been accepted for publication in IET Renewable Power Generation.

Coupled autotransformer and magnetic‐control soft‐start method for super‐large‐capacity high‐voltage motors

The large current generated by a direct start of the super-large-capacity high-voltage induction motor would have a huge impact on the power grid as well as the motor itself. Traditional soft starters have the shortcomings of discontinuous adjustment, voltage sags, sudden torque mutation, secondary current impact and high cost. To resolve this issue, the authors propose a novel coupled autotransformer and magnetic-control (CATMC) soft-start method. The structure of the new CATMC soft starter combines the functions of the autotransformer and magnetic control reactor via an innovative electric and magnetic circuit design. In this study, the authors analyse the magnetic circuit structure and working principles of the CATMC soft starter. Then, to validate its principle and performance, the authors conduct a simulation study using ANSYS software and design and test an 18 MW/10 kV CATMC soft starter prototype. The simulation results demonstrate that the CATMC soft starter effectively avoids secondary current impact and constrains the motor starting current to <2.5 times the rated current. The public connection point bus voltage also meets the voltage sag requirement of the IEEE standard and reduces the impact on the power grid.

A novel soft start method of super large capacity high voltage motor

The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself. The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained. Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high, the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed. The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced, and specific examples are analyzed and compared. It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one. Finally, the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.

A High Speed On-Chip Soft-Start Technique With High Start-Up Stability for Current-Mode DC-DC Converter

In high efficiency and high-frequency applications, the soft-start methods for DC-DC converter with fast output voltage settling speed have attracted widespread attention. A novel soft-start circuit with controllable start-up time, high start-up speed, high stability, and no off-chip capacitor for a current mode DC-DC is proposed in this paper. The proposed soft-start circuit introduces a current-limiting feedback technique so that the inductor current during soft-start is controllable. The stability of the soft-start technique is verified theoretically in this paper. A Boost converter using this novel soft-start technique is fabricated in 0.35 μm BCD process. The soft-start time of the Boost converter is only 380 μs at the conditions of 45 V output voltage, 20 μF load capacitance, and 500 mA load current.

Maximum power extraction under different vector-control schemes and grid-synchronization strategy of a wind-driven Brushless Doubly-Fed Reluctance Generator

This paper proposes an advanced strategy to synchronize the wind-driven Brushless Doubly-Fed Reluctance Generator (BDFRG) to the grid-side terminals. The proposed strategy depends mainly upon determining the electrical angle of the grid voltage, θv and using the same transformation matrix of both the power winding and grid sides to ensure that the generated power-winding voltage has the same phase-sequence of the grid-side voltage. On the other hand, the paper proposes a vector-control (power-winding flux orientation) technique for maximum wind-power extraction under two schemes summarized as; unity power-factor operation and minimum converter-current. Moreover, a soft-starting method is suggested to avoid the employed converter over-current. The first control scheme is achieved by adjusting the command power-winding reactive power at zero for a unity power-factor operation. However, the second scheme depends on setting the command d-axis control-winding current at zero to maximize the ratio of the generator electromagnetic-torque per the converter current. This enables the system to get a certain command torque under minimum converter current. A sample of the obtained simulation and experimental results is presented to check the effectiveness of the proposed control strategies.

Asynchronous operation characteristics and soft‐starting method for the brushless doubly‐fed motor

The brushless doubly-fed motor (BDFM) is versatile and can perform under several modes of operation. Other than the commonly used doubly-fed mode, BDFM can also operate in an asynchronous mode wherein the control winding of the motor is short circuited. The proposed study first analysed the mechanical characteristics of BDFM operation under this mode, whereby it was noted that there exist two induction torque components corresponding to different pole pairs within the motor. The motor, therefore, behaved as a conventional induction machine. Based on the above analysis and by introducing the concept of equivalent resistance of the machine-side inverter, an asynchronous soft-starting method for BDFM is proposed herein. By switching one side of the inverter bridge arms to the off state and adjusting the duty cycle on the other side, a controllable equivalent resistance is obtained and inserted into the control winding of BDFM. Consequently, the starting characteristic of BDFM can be improved to achieve soft start-up of the motor. Finally, experiments were conducted on a 30 kW BDFM prototype, of which, the results verify the accuracy of the torque analysis and improved performance of the proposed soft-starting method.