Alternating Current–Direct Current
The AC–DC converter power systems are electrical devices that transform AC into DC voltage and current for compensating the requirements of given loads like motors and appliances. The current is simultaneously delivered in a regulated manner without affecting the output even under the variations in the input power and all connected devices [
When the sine wave is measured on both sides of the zero volt, the highest value has to be equal to the amplitude. If there is a DC element besides zero volts, the output waveform is symmetrical at about this point rather than zero [
If the frequency of a signal is 50 Hz, the period has to be 20 ms (1/50) because the input signal follows a sinusoidal function. The waveform V1 (t) in
The angle α1 is the converter triggering voltage point. The converter has to turn on above this point at any condition. After the angle α2, the converter has to be switched off.
If we take the difference between α1 and α2, we will get the conduction angle for the converter. The
The converter output capacitors provide load current for a few milliseconds even if the input power is unavailable, which is referred as converter’s holding current. The suggested technique employs a load current prediction network, which creates the load current condition for the following cycle prior to the holding current time. As a result, the load state is forecast and the converter acts against the load current variation if necessary. The frequency of this operation is equivalent to the switching frequency of the converter because the power unit supply output ripple frequency matches the switching frequency of the converter. If the load is constant, the waveform has a continuous repeated shape. When the load current suddenly changes, the current gets fluctuated.
Load prediction and output sense circuits are merged into a single circuit. There is no need for an additional output sense circuit if it already exists in the converter. The converter switching operation and Pulse Width Modulation (PWM) control circuits differ but these circuits have to operate in accordance to variations in input voltage and load current. This circuit is implemented using software logic or hardwired logic circuits [
There is a current ramp during the increment time of load current, which has to be determined by the control circuit and control action has to be taken place.
The load current ripple sense is linked to a current detecting circuit, which generates two output signals like D(t) and C(t), among which C(t) acts as the clock signal for the proceeding section. It is a clock frequency that is synchronous to the converter switching signal. Its zero crossing is defined by the average ripple current value. D(t) is a logic signal that increases as the out loading current increases and decreases as the out loading current decreases. To make a decision on load current change, at least three consecutive D(t) signals have to be observed. The load prediction control logic is clearly depicted in
If the prediction logic signal is getting consecutive high signals, then there is an increase in load current requirement. If the prediction logic signal receives successive high and low signals, the load current remains unchanged. If it is getting low signal sequence, then there is a decrease in load current. C(t) is the clock signal in
Switched-Mode Power Supplies (SMPS) are used to control the input voltage. When building a power supply, the designer considers a high output voltage as an important characteristic because ripple in the design is an important factor [
It is derived from the sensing resistor, which is connected in series with the load. This signal is routed to the ripple current detection circuit as depicted in
When the voltage source is slightly lesser than the reference value, the op-output amp returns to its minus saturation level, which allows it to function as a threshold detector. When the input voltage is lesser than the input reference voltage, the op-amp voltage comparator is a circuit that is dependent on both the input voltage and the input reference voltage [
The connection of the D(t) signal to the source of the D Flip Flop is shown in
Whenever an input signal comes, the operational amplifier provides an output at the cathode terminal of the diode. The use of operational amplifier is not relevant if the input signal always has higher values. The diode forward biases and it keeps the capacitor charge constant without discharging it back to the operational amplifier. The capacitor needs a slow discharging path, which is not shown in this circuit for the next entry voltage from the input signal.
The value of electronic simulation results depends on how well it predicts physical reality and how quickly it produces results. A mismatch between the simulator and the actual performance sends a product into expensive repetitive debugging cycles [
The input voltage sensing circuit is connected parallel to the AC–DC converter. It works as a supervisory circuit, which controls the AC–DC operation according to the available input supply from the AC source.
The simulated waveforms of the input voltage monitoring circuit are shown in
The triggering angle is computed using
The designed triggering point is placed at 30° from the incoming sine wave impulses. The input waveform is not switching continuously to the output. Triggering occurs at 30° and ends at 150°. In each half cycle of the full wave rectified outputs, it conducts just 120° out of 180°. As a result, the conduction voltage gets increased to 200 V in each cycle.
The output of the load sense circuit is a square wave. If no current is necessary, the output is a high and low pulsing signal. If additional load current is required, the output constantly remains high.
V3 is the signal from the current sense circuit and Out1 is the logic used to determine the load current condition. R38 resistor is used to limit the current to the base of the Q9 transistor and R47 resistor is used to pull up the base of the Q9 to high. In ensures that the Q9 PNP transistor is always turned off if no signal is received from the V3 source. The R45 resistor is used to limit the current flowing through the Q9 transistor and to control the current flowing through the base of the Q12 transistor. The Q12 transistor controls the discharge of the C15 capacitor. When Q12 is turned on, it short circuits the C15 capacitor to ground and allows this capacitor to discharge to ground. R36 resistor is used to limit the discharge current to ground. If R36 value is too low, the capacitor’s life is reduced.
C15 capacitor has a direct path of charging to ground via R37 resistor. When the Q12 transistor is turned off, the capacitor charges to the VCC level. In this circuit, the D12 Zener diode also plays an important role in determining the turn ON time of the out signal. R44 resistor is used to control the self-discharge of the C15 capacitor. When the base junction of Q10 transistor receives enough current to turn on, it turns on Q11 transistor. When there is a pulsating signal from the V3 source, the R41 resistor is used to pull down the Q10 base to ground potential, which ensures that the transistor is turned off. The Zener diode D15 is used here to adjust the Q10 transistor’s base triggering voltage point [
The voltage increase across a capacitor is expressed as,
The load prediction circuit is a frequency detection circuit, which provides a high signal when the input frequency is lower than the set value.
The open condition of the switch indicates that the input signal is active. The Zener diode starts conducting only when the voltage across C1 exceeds VZ. As a result, this section is also ignored in this calculation. Across the C1 capacitor, the Thevenin is equivalent.
Thevenin equivalent across the C1 capacitor when the switch is turned off yields this equivalent circuit. When the switch is turned off, the equivalent circuit is shown as in
The resistance of R2 >> R1, so
When VZ > VC1, the output is triggered.
If there is any pulse coming more than tH pulse width, the output gets increased. The load current sense output is always in pulse mode with the same frequency as the converter switching frequency. Hence, the output is always in the OFF state.
When the Switch SW is in ON state, the resistor R3 is in parallel with C1 and R2 as illustrated in
The maximum voltage come across C1 is VCC. The C1 discharge equation is expressed as,
The resistance of R2 >> R3
The value of tL indicates the maximum time required in the output to transition from a high to a low state. As a thump rule, the tL value has to be less than one-tenth of the tH value. It allows a faster transition from high to low in the output.
The transistor Q10 triggers the output whereas the Zener diode triggers the base. If the required current is not available, the system gets failed at a slightly higher voltage level.
The LT3798 is an isolated fly back controller that requires no opto-coupler of output voltage feedback for a single output power supply. By continuously regulating the input current using the LT3798 controller, the system achieves a power factor (PF) better than 0.97. The diode current in a flyback converter has a triangular waveform structure with a peak of the maximum secondary winding and a base of the flyback period. The output winding current, Nx, is the primary coil current whereas NPS is the primary to secondary coil ratio [
During flyback time, the base current is half the secondary coil peak current and zero for the rest of the cycle. The formula is expressed as,
The FB pin voltage division resistors are used to set the output voltage. From the schematic design, the resistors R6 and R5 create a resistor divider [
Consider R5 as a known value and then apply
The supplied voltage to the flyback converter is 230 V AC, which has a maximum voltage of 400 V waveform in a single ended measurement.
The designed output voltage is 24 V and the output voltage waveform is represented as V(n008). When the output voltage reaches a steady state, it becomes more stable. Constant power supply ripple is typically measured at twice the normal line frequency. The proposed method has little higher ripple voltage compared to the existing method.
The proposed method needs few additional monitoring circuits to decide the converter turn ON and OFF conditions.
Voltage across R48 resistor is linked to the input of an electrical energy follower circuit, which gives an output equivalent to the ripple current through the load. An op amp-based comparator as opposed to an op amp compares two inputs and delivers the result of the evaluation
The input power signal is represented by the V(N003, N006) waveform and the flyback gate pulses are represented by the V(n20) signal. V(n008) represents the output voltage values. The primary functions of a power supply are to convert an input voltage to a designed output voltage as represented in
The primary application for this proposed solution is Brushless DC (BLDC) based ceiling fans. A BLDC motor is an electronically commutated motor that is powered by a DC electric power supply. Current
The converter operates in the suggested approach whenever the voltage level exceeds the specified intended value, which in this case is 200 V. As a result, the converter only activates when the voltage level is more than 200 V.
Power tools are used in a variety of household applications like gridding, fastener driving, drilling, gardening tools, cutting and polishing. Electric motors are commonly used in power tools. Machine tools seem to be either battery-powered or electrically operated (corded or cordless). The input power gives the DC or AC engines in wired power tools. Battery-powered tools employ DC motors to run on battery power [
Permanent magnet engines are classified into two types as BLDC motors and Permanent Magnet Synchronous Motors (PMSMs) based on the Back-EMF (BEMF). Both BLDC and PMSM motors use permanent magnets on the rotor but have different BEMF patterns and flux distribution patterns. The BEMF variation in the stator of a BLDC motor is trapezoidal whereas the BEMF variation in the stator of a PMSM motor is sinusoidal. A good and efficient control technique has to be used to get high performance [
SL# | Parameters | Existing method | Proposed method |
---|---|---|---|
1 | Output voltage | Stable | Stable |
2 | Input capacitance | 100 uF | 0.47 uF |
3 | Startup time | Less | Higher |
4 | Inrush current | Higher | Lower |
5 | Output regulation | Higher | Lower |
6 | Conduction time | Higher | Lower |
The output voltage of a converter has to be stable to the designed voltage because it is a basic requirement for all switch mode converters. The output of switch mode converters has ripples and the quality of the converter is defined by the amount of ripples in the output. The proposed converter is applicable for fixed and constant load applications. The application voltage is not critical in this case and a wider input voltage tolerance range is also acceptable for this type of application. Even if the proposed concept has little variation in the output voltage as in
Designing a converter for applications that require a low output noise level results in a delayed startup due to an excessive output inrush current. Output inrush current is caused by improper design and its effect on output filters, soft start time, switching frequency or output capacitance. Industrial applications that draw current from a 4–20-mA current loop or energy harvesting has to store the required energy at the input capacitance before turning on the converter [
Though the converter output voltage has little ripples, it meets the specific application, which is planned to implement this method.
AC–DC converters are used in power electronics equipment such as commercial, medical, military, and telecommunications applications. The use of high value and high voltage rated DC link capacitors reduces the power density of the converter and limits the product reliability. This paper introduced a novel approach to this problem and examined its viability. There is a feasibility to reduce DC link capacitance value for AC–DC converters to reduce the input ripple current. Simulations are done for each section and its results are analyzed to get more clarity before preparing an actual proto. Control logic circuit requires further analysis and needs to be prototyped for testing. There are some disadvantages such as low regulation, more ripple voltage, etc. but there are some specific applications where this parameter is not so important. The recommendation is to look for and implement this type of application. There are numerous future applications for this paper. For example, it is possible to use this method in the aerospace industry and specific commercial products.