PRINCIPLE THEORY OF SINGLE PHASE FEEDING POWER …

PRINCIPLE THEORY OF SINGLE PHASE FEEDING POWER CONDITIONER

FOR AC TRACTION

Tetsuo UZUKA, Yoshifumi MOCHINAGA,

Shin-ichi HASE

Railway Technical Research Institute

Hikari-cho 2-8-38, Kokubunji city, Tokyo, Japan

Tel: +81.425,73.7334 Fax: +81.425.73.7388

e-mail: [email protected]

Summary

Most of Japanese AC electrified trains such as JR group's Shinkansen use a 3-phase to 2-phase transformation system. In some cases, a 3-phase to single phase feeding system would be better than the 3-phase to 2-phase system. For example, a directional feeding system is not fit for the depot that needs single phase. Different phase directional feeding system has another problem that trains have to run across different phase circuits at every substation (and sometimes at every sectioning post.) The 3-phase to single phase feeding system can avoid this problem and it supports parallel feeding easily.

We are trying to apply a new type of 3-phase to single phase transformation feeding system called "SFC: single phase feeding power conditioner." A scalene Scott-connected transformer and a pair of self-commutated inverters constitute the basic configuration of SFC. Proper transformation ratio between Main-phase and Teaser should be even in SFC under the latest traction loads. Inverters are connected to both phases of secondary side of transformer.

SFC feeds trains from a slant phase (from Teaser to Main-phase, thus a feeding voltage phase is 45 degrees lag from teaser) of the secondary side of the scalene Scott-connected transformer. Primary side of the transformer is connected to the power grid.

A pair of self-commutated inverters is controlled by PWM method so that they can handle active power and reactive power. Inverters compensate reactive power of each secondary side respectively to regulate a 3-phase voltage fluctuation. Further, inverters connected back-to-back in DC side can accommodate an active power in the Main-phase and Teaser of secondary side of transformer each other, so that 3-phase side active power would balance. Thus SFC can feed any type of single phase feeding loads, without unbalance of 3-phase side.

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Rated capacity of SFC (transformer and two inverters) should be approximately equal to all loads of feeding circuit, if 3-phase side voltage fluctuation should be zero. Actually, desirable capacity depends on relative rate of power source capacitor to traction load and demands of 3-phase side.

We have proved a principle theory of SFC using 200V-scale mini-model and variety types of imitation loads, such as resistor (self-commutated car), thyristor phase controlled car. According to the result of this test, SFC can feed any type of traction load and can suppress 3-phase voltage unbalance.

Keywords AC electrification, substation, power electronics, single phase feeding power conditioner

1 Introduction

The power of AC feeding electric railways such as JR groups' Shinkansen, should be received from a powerful and high-tension source. At the railway substation of main lines, the feeding transformer transfers three-phase electric power to a pair of single-phase feeding circuits in Japan.

But in some cases, a 3-phase to single phase feeding system would be better than a 3-phase to 2-phase system. For example,

In different phase feeding of directional system, trains have to run across different phase circuits at every substation (and sometimes at every sectioning post.)

In single phase feeding system, trains can easily use energy from regenerative braking.

Directional feeding system is not fit for the depot that needs single phase.

We are trying to apply a new type of 3-phase to single phase transformation feeding system called "SFC: single phase feeding power conditioner." A scalene Scott-connected transformer and a pair of self-commutated inverters constitute a basic configuration of SFC.

SFC feeds trains from a slant phase (from Teaser to Main-phase) of the secondary side of the scalene Scott-connected transformer. A pair of self-commutated inverters is controlled by PWM method so that they can handle active power and reactive power. Inverters compensate reactive power of each secondary side respectively to regulate a 3-phase voltage fluctuation. Further, inverters connected back-to-back in DC side can mutually accommodate an active power in the Main-phase and Teaser of secondary side of transformer, so that 3-phase side active power would balance.

This paper gives an outline of the SFC, the theoretical studies of compensation using an SFC and reports on successful results using small models of all traction systems.


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2 Single phase feeding from 3 phase power grid

2.1 Scalene Scott-connected transformer

Fig. 1(a) shows an example of a 3-phase grid and (normal) Scott-connected trans-former and feeding circuits. Fig. 1(b) shows a scalene Scott-connected transformer that feeds traction loads from slant phase(from Teaser to Main-phase).

Scott connect

J transfornie

Teaser

U W Main-phase Power Grid

EMU

V Scalene Scott connected transformer

Scott angle i

u w ,SlPower Gr ph FC

Fig. 1 Scott and Scale Scott connected transformer

Both normal Scott-connected transformer and scalene type are designed such that both secondary sides, Main-phase and Teaser, have same loads and their power factors are equal. A Scott angle (slant phase to Teaser) would express a transformation ratio between Main-phase and Teaser. A proper Scott angle for traction loads is shown below. 1]

4 2

Where p: Scott angle from slant phase to teaser,: power factor angle of load

Thus a proper Scott angle is it/4 (45 degree, lag from teaser) under latest PWM controlled traction loads whose power factor angle is 0.

V Scalerie Scott Teaser

connected transformer' SIant,':i L* iv

PIP se Main p se

U w Power Grid

INV Capacitor

Fig. 2 SFC(Single phase Feeding power Conditioner)

. ,. ,. ...


(a)3-phase side

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2.2 Basic composition of SFC

SFC is made of a pair of self-commutated inverters, which connect both phases of secondary side of feeding transformer, coupled with DC side capacitor. Fig. 2 shows basic configuration of SFC.

At first, to control reactive power, inverters operate independently both at Main-phase side and Teaser. Next, inverters' power delivery control circuit compares active powers of Main-phase load and Teaser load, and delivers active power from bigger load circuit to smaller one via DC capacitor. Then SFC can keep balance of active power between Main-phase circuit and Teaser. In scalene Scott-connected transformer, single phase train load would be regarded as lead load in Main phase, and lag load in Teaser.

All of control circuits that control active power passing, DC voltage fluctuation, reactive power compensation issue orders to their respective objects. And current control circuit integrates these orders and decides the current object of inverters. PWIvI control circuit drives GTO thyristors of the inverters for the current object.

2.3 Principle method to compensate

2.3.1 Principle method to compensate

Set a traction load in a slant phase feeding circuit of SFC(Scott angle is it/4, see Fig. 3), where 0: load's power factor angle, P. active power, Q. reactive power, I. load current, V: feeding voltage(slant phase).

v/ I VT

PO M r. VM QW QM

(h) PWM converter car (c) Thyristor phase control car Fig. 3 Philosophy of compensation

In this situation, 3-phase current unbalance ratio, expressed by positive phase sequence current I. and negative phase sequence current I, derived from the following equation, is equal to 100%. In Japan, voltage unbalance ratio, which is defined as a ratio of 3-phase negative phase sequence voltage to positive phase sequence voltage is stipulated to be held below 3% under average load of 2 hours continuous on AC electrified line.

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'2

3-phase voltage fluctuations AV, AV are calculated by the following equations, where P : short circuit capacity of power source, W: load power.

AVuv 2W 7 6 7 8

= ----sin(---t - —)x sin(— it - —)

P. 12 2 12 2

2W 7C U t U —sin(—

- —) x sin P5 12 2 12 2

AVwu 2W 6 t 0

= —sin(— - -) x sin(— -

P5 42 42

W = = VI

Then secondary side active and reactive power PMIPT QM 'QT would as follows.

JT = v cos x I Cos - o 05V1(cos0 +sinO)

4

7C JT

PT =Vsin 4 '

xIcos( A

+e )

=0.5V1(c0s0— sin O)

JT Q,1,, = Vcos - x Isin(_O) = O.5V/(sine — cos O)

3T JT Vsin - x /sin( + 0) 0.5V1(cos0 + sin O)

When SFC has sufficient capacity of inverters to compensate, SFC compensate voltage fluctuations as follows. To reduce 3-phase voltage fluctuation, SFC minimizes reactive

power of Main-phase and Teaser (QM' QT). SFC always provides active power of

Main-phase and Teaser (EM, T) to balance 3-phase power. Active power P provided

from Main-phase Pm to Teaser PT is an average of both side powers, expressed by

next equation.

PC=(PM-PT)/2

In this way the rated capacity of SEC (transformer and two inverters) is expressed

as follows. It should he approximately equal to all loads of feeding circuit, if 3-phase

side voltage fluctuation should be equal to zero. Actually, desirable capacity depends on relative rate of power source capacitor to traction load and demands 3-phase side. Fig. 4 shows a relationship between traction load angle and rated capacity of SEC.

For PWM controlled car(e = 0), rated capacity of SFC is equal to the load, and for

thyristor controlled car(8 = I6), it would be 1.04W.

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C P~Q =0.5WJl~2sin 2 O_2sin 0 cos O

C1 [=0.5W1+ 2sin 2 0 + 2sin 0cosB

C=C M +Cl

1.5

UVI -

C

-180 150 120 -90 60 30 0 30 60 90 120 150 180 .,. . -0.5 Loadangle(deg)

Fig. 4 Rated capacity of SFC and traction load power factor angle

2.3.2 For PWM controlled car

Fig. 3(a) shows a compensating case of PWM controlled car running. Load's power factor angle is 0, then SFC minimizes reactive power of Main-phase and Teasc.r(QM, Q). SFC doesn't have to handle active power to balance 3-phase power. Rated capacity of SFC required for complete compensation is 1.0W: just equal to the load capacity W.

2.3.3 For thyristor phase controlled car

Fig. 3(b) shows a case of Thyristor phase controlled car(0 = 7T/6). In this case, SFC compensates reactive power of Main-phase and Teaser(QM, QT). first. Then, SFC would accommodate active power P provided from Main-phase P. to Teaser PT,

since PM>PT. Therefore, rated capacity of SFC required for complete compensation is 1.04W: approximately equal to the load capacity W.

3 Test equipment and result

3.1 Outline

We made a small model of SFC to estimate our principle theory. The model system consists of a pair of self-commutated inverters, a scalene Scott-connected transformer, line inductors, an auto transformer, and a single-phase dummy load for a slant phase feeding circuit. One model simulates the PWM-controlled cars, and the other simulates thyristor phase controlled cars.

.: ,.. .................................•

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Inverter

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The output voltage of single inverter is 220V, and its capacity is 1OkVA, respectively. We use 1S-1P BiMOS power transistors to switch with switching frequency 7kHz. It can simulate the real scale model using GTO thyristors with 3-pulse, 8 level series coupled.

R Slant phase Load

AT

t

EEE

phase

Scalene Main ont~o connectedP

rrTr

Transformer Circuit Reactor scot

Fig. 5 SFC Test circuit

Fig. 5 shows an SFC model configuration. With this circuit, we could examine basic active power delivery of Main-phase and Teaser, compensation of reactive power. To adjust slant phase voltage about 200V, we set auto transformer to Slant phase using a dummy load.

3.2 Compensate for PWM converter car

A result of SEC compensation, with condition of slant phase resistor load(dummy load of PWM converter cars running), is expressed in Fig. 6 Where 3-phase side current is in order I > IV >

I, and unbalanced without compensation (a). Especially, lw is

very small. Currents of scalene Scott-connected transformer secondary side I, and I are nearly equal since inverters didn't work.

25 U lu

20 ...lw

15 —-0--- liii --_-

• A it - .-- -- --S.

0 ---- - -

0 5 10 15 20 Load current(A)

25 IkI

15

ti 10 A It

U

0 5 Load cent(A) 15 20

(a) Without compensation (h) With compensation

Fig. 6 3-phase current with resistor load

TRA -- - - -

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When inverters work, 3-phase current is approximately balanced by suitable reactive power compensation (b). I and I are nearly equal also, but smaller than case (a).

3.3 Compensate for thyristor phase control car

Fig. 7 shows 3-phase side current provided for thyristor phase control. In this case, currents are unbalanced more terribly than resistor load. I and It are nearly equal

After SFC operation, currents of 3-phase side are controlled to keep balance. I and it are nearly equal but smaller than case (a).

25 • lu _.

IV .tt2()

: —15

It


25 • Lu £ Iv

15 • 1w IM

10


(a) Without compensation (b) With compensation Fig. 7 3-phase current with thyristor load

Voltage unbalance ratio and voltage drop ratio(UV phase) for resistor and thyristor are illustrated in Fig. 8. As a result of compensation, both the unbalance ratio and the voltage fluctuation ratio dropped to a half. Unbalance between load and inverters supposedly causes this insufficient result.

10 -• fliyristor load without SFC - • Thyristor load with SFC

S . - - Resistor load without SFC > Resistor loid with SFC

-

0 5 10 1.5 20 Load current()

10 4 -Thyristor load without SFC -W--- Thvristor load with SFC

A - - Resistor l6611l )( Resisttot load with SFC


(a) Voltage unbalance (b) Voltage drop(IJV phase)

Hg. 8 3-phase voltage unbalance ratio and fluctuation

.,- rgsssss


ith SVC

vC

60

•— 40

20

0

-10

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4 Conclusions

We proposed an SFC that can feed various types of single phase AC traction loads without 3-phase side voltage fluctuation and unbalance, using inverters to compensate reactive power and accommodate active power. We made a small model of SFC and proved principle compensating theory.

SFC is now under construction and will start commercial running in October 1997 at Hokuriku Shinkansen Nagano depot substation, for Nagano Olympic 1998.

1 00

A

- 20 0 20 40 6D so 100

R()

Fig.10 Load zone in R-X plane of trains

BIBLIOGRAPHY

Tetsuo UZUKA(33). was born in Miyagi Prefecture, Japan. on July 7, 1964. He received the B.S. and M.S. degrees in instrumentation engineering from Keio University, Yokohama, Japan in 1987 and 1989, respectively. In 1989, he joined Railway Technical Research Institute, Tokyo, Japan. He has been engaged in research and development of AC feeding electric railway system. He is a member of the Institute of Electrical Engineers of Japan.

Yoshifumi MOCHINAGA(50), was born in Saga Prefecture, Japan. on November 29, 1946. He received the B.S. and Ph.D. degrees in electrical engineering from Science University


k"xNaRK-616

of Tokyo, Tokyo, Japan in 1980 and 1994, respectively. In 1967, he joined Japanese National Railways. He has been engaged in research and development of AC feeding electric railway system at Railway Technical Research Institute, Japan. He is a member of the Institute of Electrical Engineers of Japan.

Shin-ichi HASE(42), was born in Hokkaido, Japan, on June 8, 1955. He received the B.S. degrees in electrical engineering from Muroran Institute of Technology, Hokkaido, Japan in 1978. In 1978, he joined Japanese National Railways. He has been engaged in research and development of AC and DC feeding electric railway system at Railway Technical Research Institute, Japan. He is a member of the Institute of Electrical Engineers of Japan.

Reference

Mochinaga, Hamada, Arai: "Development of Static Unbalanced Power Compensator with Scalene Scott-Connected Transformer for AC Traction System", Trans. TEE of Japan, Vol. 110-D, No. 1, pp. 41-50,1990


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PRINCIPLE THEORY OF SINGLE PHASE FEEDING POWER …