Pulse Frequency Modulation - PFM
Various PWM schemes are possible. Only one is shown here. By varying the pulse width of the amplitude of the sine wave can be changed.
Variable voltage can be generated through the use of fixed pulse width, but instead (by different pulse amplitude (pulse amplitude modulation - PAM) or pulse rate Pulse Frequency Modulation - PFM).
The DC output from Chopper and PWM circuits is known to be plagued by high harmonic content. Most DC motors, but can tolerate a pulsed DC supply, since the inductance of the motor itself and the mechanical inertia of the rotor to help smooth out the fluctuations in the supply voltage. Since there is no current when the switching device is switched off, the technique is relatively lossless. Cogging can occur if the chopper frequency is too low.
The voltage regulator can be manually activated in an open-loop system, but for the continuous voltage control, the inverter must be included in a feedback loop in a closed-loop system. The control system monitors the actual output voltage and provides a control signal, which is an analog or a digital representation of the error signal to correct the pulse width modulator of any discrepancies. If voltage is control for controlling the speed of the error signal is a tachometer generator to the engine output shaft will be used derived.
Electronic voltage regulation is also an essential part of many generator applications. In automotive systems, generator or alternator with variable speed, which depends directly driven by the engine speed. It has its full voltage at the output of the lowest speed to give, but the tension is when the engine speed increases will be retained. Generators used in 12 volt systems usually have built in voltage regulation. In HEV applications a chopper regulator at the output of the generator used to keep the voltage on the DC-link within narrow limits in order to damage the battery. If the battery is fully charged, the battery management system itself separates it from the supply to prevent overcharging.

Linear Voltage Regulator:

For low power applications, a series or linear is often used. It is less efficient than a switching regulator, because the fluctuations in the supply voltage must be addressed, and the resulting power dissipated from the drop-volt transistor series but offers a pure DC. Series regulators are not suitable for high power applications such as electric traction in which the efficiency in mind.
Thyristor Voltage Control When powered by AC, s are used thyristors (SCR) in series with the load to a variable voltage to the blocking of the passage of current to the load for the first part of the cycle on and off the river by a signal to the gate creating the SCR. A single SCR affects only one polarity of the waveform. To change the positive and negative current will require two SCRs connected in parallel and in opposite polarity or a triac (bidirectional SCR). By varying the delay (phase angle) before the power is turned on can, the average current, and thus the average voltage seen by the load, be varied, as shown below.
This is the same principle as with dimmer switch.
Gate Turn Off Thyristor (GTO) can be used to turn power switching it on and that more control over the duration of the current through the device.
Current Control In many applications, the motor current the motor can supply through the inductor in the circuit was, and it is often desirable to control the current directly, rather than the voltage, or to obtain faster and more accurate control of the current and hence the torque. In this case, a shunt resistor or a current transformer is used to the current monitor. The difference between the actual and target currents in a high-gain feedback loop used to provide the necessary current regulation.
Current control is particularly important for induction motors in order to protect the motor against excessive start current. A current feedback signal is used to the firing angle of the thyristors in the rectifier or inverter circuits for limiting the current change in its reference value.

Converters:

This is a generic term for circuits that could provide AC or DC outputs from either AC (mains frequency) or DC (battery) supply lines. These include power bridges for the elimination of supply and AC supply inverters for generating an AC waveform from a battery.
Buck and Boost Converters Buck and Boost converters, DC / DC converters, the equivalent of AC DC transformers.
Buck Converter:

The buck converter is used to reduce the DC voltage. The chopper above is an example of a step-down DC converter.
Boost Converter The boost converter is used to increase voltage.
The route can Step up or step down the input voltage by varying the duty cycle of the switch transistor.
The transistor switch turns off the power supply voltage on the LC circuit on and off. When the transistor is to recharge the inductor and the diode cuts the capacitor. When the transistor switches, the inductor discharges through the diode, through the capacitor can charge up. Note that the polarity of the output voltage is the reverse of the input voltage. With a low load when the transistor is switched off for more than 50% of the time, the voltage that appears at the output is lower than the supply and the circuit acts like a step down transformer. With a high load when the transistor is switched on more than it is off, the tension builds on the capacitor and the output voltage of the supply voltage. Voltage control by varying the duty cycle is thus made available.