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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
inrush current the transient current drawn by an electrical apparatus when it is suddenly connected to a power source. The inrush current may be larger in magnitude than the steady-state fullload current. The transient response is short in time and the electrical equipment generally supports the inrush current, provided it does not happen frequently. For a single transient, the thermal limit of the equipment is not reached, but if it is switched on and switched off several times within a short period, the temperature can rise very quickly. In case of transformers, the inrush current is not sinusoidal even if the voltage is due to the hysteresis of the ferromagnetic core. insertion loss (1) worst-case loss of the device across the stated frequency range. The loss due to the insertion of the unit in series with a signal path. (2) transmission loss of an RF or microwave component or system, typically measured in decibels. insolation incident solar radiation.
Power Supplies and PSRR
Published in Douglas Self, Audio Power Amplifier Design, 2013
Inrush current is most conveniently measured with purpose built-instruments such as the Voltech power analyser range. A cheaper method is to use a current transformer (typically of the ‘giant-clothes-peg’ type clamped around one of the primary connections, and connected to a digital oscilloscope; this is naturally only cheaper if you already have a digital oscilloscope. It is characteristic of inrush current that its peak value varies widely from one switch-on to the next, as it depends crucially on the point of the mains cycle at which the transformer is connected. If you’re unlucky, the transformer core briefly saturates and a big peak current is drawn by the primary. For this reason, repeated tests — possibly up to fifty — have to be done before you are confident you have experienced the worst case. This often has to be spread out over some time to avoid over-taxing inrush suppression components.
Introduction
Published in J. R. Coaton, A. M. Marsden, Lamps and Lighting, 2012
An incandescent filament lamp has a cold resistance which is only about 8 per cent of its hot operating resistance. The maximum inrush current occurs when the lamp is switched on at the AC voltage peak and this may have a peak value of about 20 times the normal rms current. The time taken for the current to drop to a steady value depends on the thermal time constant of the filament and varies from a few milliseconds to several seconds. In discharge lamp circuits using parallel power factor correction, a large momentary inrush current flows after switch-on until the capacitor is charged. Again, the maximum circuit current occurs when the capacitor is switched on at AC voltage peak, its value depending on the resistance and inductance in the circuit and the supply impedance. For example, a 5 µF capacitor switched on to a 230 V AC supply will take a peak current of between 50 and 100 A for about 25 µs. In switch-start fluorescent lamp circuits using choke or choke-capacitor ballasts the maximum ballast inrush current occurs when the starter contacts close at zero voltage. The inrush current lasts for about 10 ms and has a value of up to six times the normal. Some discharge lamps may act as partial rectifiers for a few cycles during starting, during which time a current of two or three times the normal will be drawn from the mains supply.
Novel Soft-Start Technique for Grid Integration of LCL-filtered Inverters
Published in IETE Journal of Research, 2022
The start-up inrush current can be mitigated by passive or active methods. In passive method [29], series resistors are added between the inverter and the grid at the instant of grid connection. Once the inverter has built up its voltage, it is connected to the grid with high series resistance. The additional resistors are cut-off from the circuit after a small time from the instant of connection. In another method, a dedicated soft-start control pulse circuitry [30] is used to provide pulses to the inverter during start-up. The soft-start pulses have constant duty cycle and a frequency higher than that of the normal control pulses. The actual control pulses are activated after start-up. A soft-start method for the inverter feeding a load is presented in [31]. It employs inverter pulses whose pulse-width increases gradually from cycle by cycle. An active method based on injecting reverse DC component current [32] is used to mitigate the inrush current. The starting transient current consists of different frequency components both periodic and aperiodic. The method proposes to inject a reverse voltage with same shape as that of the aperiodic component current. A voltage prediction control strategy is used in [33] during the instant of connection, by properly predicting the voltage magnitude and angle required for unity power factor operation. During the process of start-up, another current feedforward control is employed which senses DC link voltage and acts to restore the system to nominal operating point for any changes in DC link voltage. A start-up method for LCL-filtered three-phase GCI is presented in [34]. The inverter pulses are blocked initially and the grid connection switch is closed so that the grid current flows through grid side filter inductor and the capacitor. Based on setting a threshold to this capacitor current, the inverter pulses are active with a time delay.
Five-Level Switched Capacitor Inverter for Photovoltaic Applications
Published in IETE Technical Review, 2022
Ashutosh Kumar Singh, Rajib Kumar Mandal, Ravi Raushan, Ravi Anand
The proposed inverter is operating in six valid operating modes to generate five levels in the output voltage as presented in Figure 2. Mode 1: Under this mode, the inverter will have zero output voltage and the switching status is presented in Figure 2(a). Charging of capacitor happens in this mode, and a strong inrush current may be drawn if the capacitor voltage is zero. The power electronics switching devices T5, T6, T7, and T8 are OFF, whereas remaining switching devices T1, T2, T3, and T4 are ON. The capacitor is getting charged from the input dc source and its steady-state voltage may reach up to the voltage magnitude of the DC source.Mode 2: It is noticed from Figure 2(b) that the DC source voltage (Vdc) is being applied across the load under this mode of inverter operation. The T1, T2, T4, and T6 switches are ON and other power electronics switches are in OFF state. The capacitor inside inverter is also charging from the input DC source voltage.Mode 3: As in Figure 2(c), the voltage produced by the inverter may become identical to double the magnitude of the input DC source (2Vdc). The switches T4, T6, and T7 are ON, while the other switches are OFF in this mode.Mode 4: As in Figure 2(d), the inverter generates zero voltage at the output while the capacitor connected to the input DC source through T1 and T2 switches is getting charged. Only T1, T2, T5 and T6 switches are ON while other switches are OFF.Mode 5: As in Figure 2(e), the output voltage generated by the inverter under this mode is having negative polarity and the magnitude is same as the DC source voltage (Vdc). The T1, T2, T3, and T5 switches are ON, while T4, T6, T7, and T8 switches remain OFF. The capacitor under this mode is getting charged from the DC voltage source. The steady-state voltage of the capacitor may reach up to the voltage magnitude of DC source.Mode 6: As in Figure 2(f), the inverter produces output voltage of negative polarity and its magnitude can become twice the input DC source voltage (2Vdc). The T3, T5 and T8 switches are ON, while the others are OFF.