# Ward Leonard control

Ward Leonard control

Ward Leonard Control, also known as the Ward Leonard Drive System, was a widely used DC motor speed control system introduced by Harry Ward Leonard in 1891. In early 1900s, the control system of Ward Leonard was adopted by the U.S Navy and also used in passenger lift of large mines. It also provided a solution to moving sidewalk at the Paris Exposition of 1900, which many others had failed to operate properly.Fact|date=November 2007 Until the 1980s, when the Ward Leonard control system started to be replaced by other systems, primarily thyristor controllers, it was widely used for elevators because of it offered smooth speed control and consistent torque. Many Ward Leonard control systems and variations on them remain in use. [cite conference | first = A.B. | last = Kulkarni | authorlink = | coauthors = | title = Energy consumption analysis for geared elevator modernization: upgrade from DC Ward Leonard system to AC vector controlled drive | booktitle = Conference Record of the 2000 IEEE Industry Applications Conference | pages = vol.4, pp.2066-2070 | publisher = Institute of Electrical and Electronics Engineers | date= Oct 2000 | location = | url = | doi = | id = | accessdate = ]

Basic concept

A Ward Leonard drive is a high-power amplifier in the multi-kilowatt range, built from rotating electrical machinery. A Ward Leonard drive unit consists of a motor and generator with shafts coupled together. The motor, which turns at a constant speed, may be AC or DC powered. The generator is a DC generator, with field windings and armature windings. The input to the amplifier is applied to the field windings, and the output comes from the armature windings. The amplifier output is usually connected to a second motor, which moves the load, such as an elevator. With this arrangement, small changes in current applied to the input, and thus the generator field, result in large changes in the output, allowing smooth speed control.

A more technical description

The speed of motor is controlled by varying the voltage fed from the generator, Vgf, which varies the output voltage of the generator. The varied output voltage will change the voltage of the motor, since they are connected directly through the armature. Consequently changing the Vgf will control the speed of the motor. The picture of the right shows the Ward Leonard control system, with the Vgf feeding the generator and Vmf feeding the motor. [cite journal | first = A.K. | last = Datta | authorlink = | coauthors = | title = Computerless optimal control of Ward Leonard drive system | booktitle = International Journal of Systems Science | pages = vol.4, pp.671–678 | publisher = | date= 1973| location = | url = | doi = | id = | accessdate = ]

Mathematical approach

Among many ways of defining the characteristic of a system, obtaining a transfer characteristic is one of the most commonly used methods. Below are the steps to obtain the transfer function, eq 4.

Before going into the equations, first conventions should be set up, which will follow the convention Datta used. The first subscripts 'g' and 'm' each represents generator and motor. The superscripts 'f', 'r',and 'a', correspond to field, rotor, and armature.

Wi = plant state vertorK = gaint = time constantJ = polar moment of inertiaD = angular viscous frictionG = rotational inductance constants = laplace operator

eq 1: The generator field equation Vgf = RgfIgf + LgfIgf

eq 2: The equation of electrical equilibrium in the armature circuit -GgfaIgfWgr + (Rga + Rma) Ia + (Lga + Lma) Ia + GmfaImfWmr = 0

eq 3: Motor torque equation -TL = JmWmr+DmWmr

With total impedance, Lga + Lma, neglected, the transfer function can be obtained by solving eq 3 TL = 0.

eq 4: Transfer function: $frac\left\{W_m^r\left(S\right)\right\}\left\{V_g^f\left(S\right)\right\} = cfrac\left\{K_BK_v/D_m\right\}\left\{\left(t_g^fs+1\right)left \left[t_ms+cfrac\left\{K_m\right\}\left\{D_m\right\} ight\right] \right\}$ [cite journal | first = A.K. | last = Datta | authorlink = | coauthors = | title = Computerless optimal control of Ward Leonard drive system | booktitle = International Journal of Systems Science | pages = vol.4, pp. 671&ndash;678 | publisher = | date= 1973| location = | url = | doi = | id = | accessdate = ]

with the constants defined as below.

: $K_B = frac\left\{G_m^faV_m^f\right\}\left\{R_m^f\left(R_g^a+R_m^a\right)\right\}$

: $K_v = frac\left\{G_g^faW_g^r\right\}\left\{R_g^f\right\}$

: $t_m = frac\left\{J_m\right\}\left\{D_m\right\}$

: $t_g^f = frac\left\{L_g^f\right\}\left\{R_g^f\right\}$

: $K_m = D_m+K_B^2\left(R_g^a + R_m^a\right)$

ee also

* Amplidyne
* Brushed DC electric motor
* Electric motor
* Electronic speed control
* Harry Ward Leonard
* Motor controller
* Motor-generator

References

;Citations

;General references
*cite web | last = Leonard | first = H. Ward | title = Descendants Of William Ward of Sudbury Born Abt 1603, and Other Related Families| work = | publisher = rootsweb.com | date = 2006 | url = http://worldconnect.genealogy.rootsweb.com/cgi-bin/igm.cgi?op=GET&db=rckline-wards&id=I14813 | accessdate = 2006-08-08
*cite journal | last = The Editors | first = | authorlink = | coauthors = | title = Technology for Electrical Components | journal = Power Transmission Design | volume = | issue = | pages = 25–27 | publisher = | date= Nov 1989 | url = | doi = | id = | accessdate =
*cite journal | last = Gottlieb | first = I.M. | authorlink = | coauthors = | title = Electric Motors & Control Techniques 2nd Edition | journal = | volume = | issue = | pages = | publisher = TAB Books | date= 1994 | url = | doi = | id = | accessdate =
*cite book | url = http://books.google.com/books?id=8mQewRR_3q4C&pg=RA1-PA20&lpg=RA1-PA20&dq=%22ward+leonard%22+drive&source=web&ots=TcpJmCH4mV&sig=VasW_IFD1-M-oFNZwt2wNxQSSes#PRA1-PA20,M1
pages = 20–21 | title = Practical Variable Speed Drives and Power Electronics | author = Malcolm Barnes | year = 2003 | isbn = 978-0750658089

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• Harry Ward Leonard — Infobox Scientist name = Harry Ward Leonard box width = image width = 229px caption = Harry Ward Leonard birth date = February 8, 1861 birth place = Cincinnati, Ohio, U.S.A death date = February 18, 1915 death place = New York, U.S.A residence =… …   Wikipedia

• Harry Ward Leonard — (* 8. Februar 1861 in Cincinnati, Ohio; † 18. Februar 1915 in New York) war ein US amerikanischer Elektroingenieur und Erfinder. Seine 30 jährige Karriere spannte sich vom späten 19. bis in das frühe 20. Jahrhundert. Er wurde mit seiner …   Deutsch Wikipedia

• Leonard Braithwaite — Leonard Austin Braithwaite (born October 23, 1923) is a lawyer and politician in Ontario, Canada. He served in the Legislative Assembly of Ontario from 1963 to 1975, as a member of the Liberal Party. He was the first Black Canadian to be elected… …   Wikipedia

• Ward Churchill — Infobox Celebrity name = Ward Churchill imagesize = 200px caption = Ward Churchill speaking at the Bay Area Anarchist Book Fair, May 2005. birth date = birth date and age|mf=yes|1947|10|2 birth place = Elmwood, Illinois, United States death date …   Wikipedia

• WARD, Frederick William (1847-1934) — journalist was born in New Zealand on 5 April 1847. He was the fourth son of the Rev. Robert Ward, a Primitive Methodist clergyman, and was educated for the same ministry. He came to Australia in his early twenties and was associated with the Rev …   Dictionary of Australian Biography

• Direct torque control — (DTC) is one method used in variable frequency drives to control the torque (and thus finally the speed) of three phase AC electric motors. This involves calculating an estimate of the motor s magnetic flux and torque based on the measured… …   Wikipedia

• Harry W. Leonard — Harry Ward Leonard (* 8. Februar 1861 in Cincinnati; † 18. Februar 1915 in New York) war ein US amerikanischer Elektroingenieur und Erfinder. Seine 30 jährige Karriere spannte sich vom späten 19. bis in das frühe 20. Jahrhundert. Er wurde mit… …   Deutsch Wikipedia

• Brushed DC electric motor — A brushed DC motor is an internally commutated electric motor designed to be run from a direct current power source. Contents 1 Simple two pole DC motor 2 The commutating plane 2.1 Compensation for stator field distortion …   Wikipedia

• Booster (electric power) — A Booster was a motor generator (MG) set used for voltage regulation in direct current (DC) electrical power circuits. The development of alternating current and solid state devices has rendered it obsolete. Boosters were made in various… …   Wikipedia

• Electric motor — For other kinds of motors, see motor (disambiguation). For a railroad electric engine, see electric locomotive. Various electric motors. A 9 volt PP3 transistor battery is in the center foreground for size comparison. An electric motor converts… …   Wikipedia