Application of Power Electronics Chapter 10 Application of Power Electronics

Application of Power Electronics 10.1 DC motor drivers ( thyristor-DC motor system ) 10.2 Frequency converters and AC drivers 10.3 Uninterruptible Power Supply ( UPS ) 10.4 Switching Power Supply 10.5 Power factor correction (PFC) 10.6 Application in utility power system 10.7 Other applications

10.1 DC motor drivers ( Thyristor-DC motor system ) 10.1.1 Rectifier mode of operation 10.1.2 Inverter mode of operation 10.1.3 Reversible DC motor drive system (four-quadrant operation)

10.1.1 Rectifier mode of operation Waveforms and equations (10-1) where (for 3-phase half-wave) Waveforms of 3-phase half-wave rectifier with DC motor load

Speed-torque (mechanic) characteristic when load current is continuous (10-2) For 3-phase half-wave (10-3) (10-4) For 3-phase bridge For 3-phase half-wave (10-5)

Speed-torque (mechanic) characteristic when load current is discontinuous EMF at no load (taking 3-phase half-wave as example) For a  60º For a > 60º For 3-phase half-wave

(a1< a2 < a3  60º, a5 > a4 > 60º) Speed-torque (mechanic) characteristic when load current is discontinuous For different a The point of EMF at no load is raised up. The droop rate becomes steer. (softer than the continuous mode) For 3-phase half-wave (a1< a2 < a3  60º, a5 > a4 > 60º)

10.1.2 Inverter mode of operation Equations are just the same as in the rectifier mode of operation except that Ud, EM and n become negative. E.g., in 3-phase half-wave Or in another form (10-3) (10-4) Speed-torque characteristic of a DC motor fed by a thyristor rectifier circuit ) cos ( å + - = R I U E d M b (10-11) e C n - = 1 å + R I U d b cos (10-12)

10.1.3 Reversible DC motor drive system (4-quadrant operation) Back-to-back connection of two 3-phase bridge circuits

4-quadrant speed-torque characteristic of Reversible DC motor drive system

10.2 Frequency converters and AC drivers Composite converter: Combination of two or more converters in cascaded connection Indirect AC to AC converters (AC-DC-AC converters) Composite converters Indirect DC to DC converters (Isolated DC to DC converters)

Indirect AC to AC converters (AC-DC-AC converters) Classifications According to type of the DC links: AC-DC-AC converters Voltage-source type Current-source type According to whether output voltage and frequency is variable: AC-DC-AC converters Variable voltage variable frequency (VVVF) (AC-DC-AC frequency converters) Constant voltage constant frequency (CVCF) In narrow sense, frequency converter only refers to VVVF AC-DC-AC converter.

10.2.1 Configurations of AC-DC-AC converters Configurations with one-direction power flow Voltage-source type Current-source type

Configuration with regenerative energy dissipating circuit Braking transistor and braking resistor

Configurations with regenerative power feedback through inversion-mode thyristor rectifier circuit Voltage-source type Current-source type

Configurations realizing bi-directional power flow through double-sided PWM converters Voltage-source type Current-source type 16

10.2.2 Major Applications of AC-DC-AC frequency converters (VVVF converters) Adjustable speed AC motor drives Advantages of AC motors over DC motors Energy saving on AC motors High-performance AC motor drives Control of AC motors driven by AC-DC-AC frequency converters (VVVF converters) Constant voltage frequency ratio control Slip frequency control Vector control Direct torque control

10.3 Uninterruptible power supplies (UPS) Basic configuration of UPS Major Applications of CVCF converters

UPS with back-up energy source

UPS with back-up energy source and bypass lines

10.4 Switching Power Supply Linear power supply Line frequency AC input Rectifier Filter Series Pass Regulator Transformer DC Regulated DC output Line frequency Isolation Switching power supply Regulated DC output Line frequency AC input Inverter Filter Transformer DC High frequency AC Rectifier AC High frequency Isolation Indirect DC to DC converter

Point of load regulation (POL) Specifically means a particular switching power supply for a large size IC chip, such as a CUP or a memory chip. Synchronous Buck Synchronous Boost

A typical application of switching power supply Power system for telecommunication equipment

Control of switching power supply Voltage mode control Current mode control Peak current mode control Average current mode control

Voltage mode control

Current mode control

Peak current mode control

Average current mode control

10.5 Power Factor Correction (PFC) Operation principle of typical PFC circuit Single-phase boost PFC 3-phases single-switch boost PFC Single stage PFC

Single-phase boost PFC

3-phases single-switch boost PFC

Single stage PFC ( ) A typical converter

10.6 Application in utility power system High voltage DC transmission (HVDC) Reactive power compensation Harmonics suppression Power quality control, FACTS and custom power

High voltage DC transmission (HVDC)

Reactive power compensation Thyristor switched capacitor (TSC) Thyristor controlled reactor (TCR) Static var generator (SVG)

Thyristor switched capacitor (TSC) U

TSC waveforms when the capacitor is switched in/out VT 1 2 The voltage across the thyristor must be nearly zero when switching in the capacitor, and the current of the thyristor must be zero when switching out the capacitor.

TSC with the electronic switch realized by a thyristor and an anti-parallel diode The capacitor voltage will be always charged up to the peak of source voltage. The response to switching-out command could be a little slower (maximum delay is one line-cycle).

Thyristor-controlled reactor (TCR) To control the effective current flowing through the reactor by controlling delay angle, therefore control the reactive power absorbed by the reactor. u a i b c n

Static var generator (SVG) Also called static compensator (STATCOM) VSC based SVG CSC based SVG

Operation principle of SVG

Harmonic suppression Two solutions Power factor correction Circuit configuration of an Active power factor (APF) Two solutions Power factor correction Harmonic compensation

Operation principle of APF

Power quality control Power quality problems Power quality controllers Current harmonics APF Reactive power SVC or SVG Dynamic voltage restorer (DVR) Voltage sag Universal power quality controller (UPQC) Voltage flicker

Flexible AC Transmission System (FACTS) FACTS is actually a general term of application if power electronic to the utility electric power transmission system - for higher controllability and larger transmission capacity. Typical FACTA devices SVC SVG Thyristor Switched Series Capacitor (TSSC) Thyristor Controlled Series Compensator (TCSC) Static Synchronous Series Compensator (SSSC) Unified Power Flow Controller (UPFC)

Custom Power Custom power is a general term of application of power electronics to the utility electric power distribution system for better quality and higher reliability of the power supplying to different customers. Typical Custom Power devices SVC or SVG (D-STATCOM) DVR APF Solid State Transfer Switch (SSTS)

10.7 Other applications Lighting Power supply for different lamps Power supply for gas discharge lamps is specifically called ballast. Welding Typical configuration of an electronic ballast Typical configuration of a welding power supply