sect-6

Section 6: Static Switch Operation & Control

Chapter 1 - Static Switch Principles

1.1 Introduction .............................................................................................. 6-1

1.2 Static switch construction ......................................................................... 6-2

1.3 Static switch control system ..................................................................... 6-41.3.1 Control system overview ............................................................. 6-41.3.3 Control power supplies ................................................................ 6-7

Chapter 2 - Static Switch Driver Board (4542043 Z)

2.1 Chapter overview ..................................................................................... 6-9

2.2 General description ................................................................................... 6-92.2.1 Circuit board functions ................................................................ 6-92.2.2 Input/Output connections ............................................................. 6-92.2.3 Block Diagram ........................................................................... 6-10

2.3 Detailed circuit description .................................................................... 6-112.3.1 Introduction ................................................................................ 6-11

2.4 Summary information ............................................................................. 6-15

Chapter 3 - Static Switch Driver Board (4542041 X)

3.1 Chapter overview .......................................................................................17

3.2 General description .....................................................................................173.2.1 Circuit board functions ..................................................................173.2.2 Input/Output connections ...............................................................173.2.3 Block Diagram ...............................................................................18

3.3 Detailed circuit description ........................................................................193.3.1 Introduction ....................................................................................19

3.4 Summary information .................................................................................23S-6.FM5 - Issue 2 Dated 21/08/97 i

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service Manualii S-6.FM5 - Issue 2 Dated 21/08/97

Section 6:

Chapter 1 - Static Switch Principles

1.1 Introduction

The static switch assembly is responsible for controlling the transfer of criticalload power between the bypass mains supply and the inverter output supply.

Figure 6-1: Static switch power block

In order to perform this function, the static switch assembly contains two 3-phaseswitching circuits; one is connected between the UPS output switch and thebypass mains supply, and the other between the UPS output switch and the invert-er supply (See Figure 6-1). For reasons of clarity, these are referred to in thismanual as the bypass-side and inverter-side static switches respectively.

Bypass-side static switch

The bypass-side static switch comprises a pair of inverse-parallel-configuredSCRs connected in series with each bypass mains supply line (See Figure 6-2).

Figure 6-2: Bypass-side static switch

BypassMains

Supply

InverterOutputSupply

UPS LogicBoard

CriticalLoadSupply

Static Switch

Inverter-Side

Static Switch

Bypass-Side

Static SwitchDriverBoard

Static Switch Assembly

Static Switch Driver Board

BypassMains

Supply

ToCriticalLoad

U

V

Ws6-c1.fm5 - Issue 2 Dated 21/08/97 6-1

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 1 - Static Switch PrinciplesWhen the static switch control logic decides to connect the load to the bypassmains supply it signals the Static Switch Driver Board to trigger all six SCRs si-multaneously; thus allowing passage of the bypass supply a.c. mains through tothe critical load i.e. all six SCRs receive a gate drive signal for the whole timethat the bypass-side is required to be turned on.

Inverter-side static switch

The term static switch might be considered a misnomer when describing theinverter-side circuit; as in a standard 7200 module this normally comprises astraightforward three-phase circuit breaker connected in series with the inverteroutput. If necessary, provision has been made to allow this contactor to be re-placed with a solid state circuit (as used in the bypass-side static switch) as theproduct is developed.

The contactor is controlled by the Static Switch Driver Board.

1.2 Static switch construction

The static switch power components and the rectifier power components are as-sembled on the same heatsink , as illustrated below.

Figure 6-3: Static switch assembly wiring details

45

420

43

Z6-2 s6-c1.fm5 - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 1 - Static Switch PrinciplesFigure 6-4: Static switch construction

ST

AT

IC B

YP

AS

S M

AIN

S F

EE

DR

EC

TIF

IER

3-P

h M

AIN

S F

EE

D

Bypass SCRsConnections to snubber boards

and gate drivers

Snubber boardGate Driver (trigger) board

RECTIFIER OUTPUT

45

42

04

3Zs6-c1.fm5 - Issue 2 Dated 21/08/97 6-3

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 1 - Static Switch PrinciplesFigure 6-5: System control overview

1.3 Static switch control system

1.3.1 Control system overview

Figure 6-6 illustrates the basic static switch control circuit.

The decision making logic which determines whether to close the bypass-sideor inverter-side static switch is contained on the UPS Logic Board under soft-ware control (see chart 7-12 on page 7-183) and provides the Static SwitchDriver Board with independent load on bypass and load on inverter com-mand signals. The Static Switch Driver Board processes these signals and pro-vides suitable outputs to control the bypass-side SCRs and inverter-sidecontactor.

U-PhaseMains

U-PhaseInverter

Load

Transfer Logic

ON ON

PCB Logic Boards

Mains-side switch enable

a) Bypass voltage OK (10%)

b) No bypass frequency error

c) No Open-circuit bypass SCR

d) Bypass Disable Switch ena-bled i.e. not in inhibit position.

e) Permission to close static bypass gained from Parallel Logic Board (in 1+1 system only)

Transfer Control

Transfer Mains-to-Inverter

a) Sync OK (Inv/Mains 9 with respect to each other

b) Inverter voltage OK (10%)

c) Parallel condition satisfactory (1+1 system only)

(a) + (b) + (c) = OK to transfer

Transfer Inverter-to-Mains

a) Critical bus volts fail (10%)

b) Sync OK = No breakSync not OK = 1 cycle break

Transfer Lockout

a) More than 8 transfer attempt in 1 minute = load locked on bypass

Inverter-side switch enable

a) Inverter voltage OK (10%)

b) No inverter frequency error

c) No Overload timeout150% (1 min)125% (10 min)110% (1 Hr)101% (9 Hrs)

d) Inverter Disable Switch ena-bled i.e. not in inhibit position.

e) Permission to close output contactor gained from Parallel Logic Board (in 1+1 system only)6-4 s6-c1.fm5 - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 1 - Static Switch PrinciplesFigure 6-6: Static switch control system

1.3.1.1 Analogue control signals

Inverter voltage sense

The 3-phase inverter voltage is sensed at a point between the output transformerand inverter-side static switch (contactor), and should therefore be at the nominalUPS output voltage whenever the inverter is operating. The three independentline-to-neutral sense signals are attenuated to 1% on the High Voltage InterfaceBoard and then passed to the UPS Logic Board where they are converted to a dig-ital form and monitored by the boards microprocessor system.

Note: these same signals also pass straight through the UPS Logic Board to theInverter Logic Board where they serve as the output voltage feedback signals.

Bypass mains voltage sense

The 3-phase bypass mains voltage is sensed at a point between the bypass supplyisolator and the bypass-side static switch, and should therefore be at the nominalmains voltage whenever the bypass switch is closed. The three independent line-to-neutral sense signals are attenuated to 1% on the High Voltage Interface Boardand then passed to the UPS Logic Board where they are converted to a digitalform and monitored by the boards microprocessor system.


OutputTfrmr

3 Phase Power

Inverter

DC Bus Pos

DC Bus Neg Cri

tica

l Lo

ad

BypassSupply

Inverter-sideContactor (K1)

Operator Logic Board

Operator Control Panel

BypassMains

Supply

Bypass-sideStatic Switch

UPS LogicBoard

High VoltageInterface Board

Byp

ass

vo

ltag

e

sen

se

Inve

rte

r vo

ltag

e s

en

se

Inve

rte

r cu

rre

nt

sen

se

Output voltage sense

Output current sense

K1

Au

xilia

ry s

en

ses6-c1.fm5 - Issue 2 Dated 21/08/97 6-5

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 1 - Static Switch PrinciplesOutput (critical load) voltage sense

The 3-phase UPS output voltage is sensed immediately ahead of the output isola-tor (on the hot side of the output contactor K1) and therefore accurately representsthe voltage offered to the critical load. The three independent line-to-neutral sensesignals are attenuated to 1% on the High Voltage Interface Board and then passedto the UPS Logic Board where they are converted to a digital form and monitoredby the boards microprocessor system.

Output (critical load) current sense

The output current is sensed by three individual current transformers (CTs) locat-ed immediately ahead of the output isolator (on the hot side of the output currenttransformers) and therefore monitors the critical load current. These current sensesignals are calibrated by jumpers fitted to the High Voltage Interface Board andthen passed to the UPS Logic Board where they are summed and converted to adigital form and monitored by the boards microprocessor system.

1.3.1.2 Digital control signals

UPS Logic Board

Various digital signals affecting the static switch operation are passed betweenthe UPS Logic Board and the other boards connect to it. These can broadly be cat-egorised as:

static switch status and alarm data generated on the UPS Logic Board andpassed to the Operator Control Panel via the Operator Logic Board alsoto the Alarms Interface Board (for remote indication) where fitted.

transfer control logic signals passed to the Static Switch Driver Board. metering data generated on the UPS Logic Board and passed to the Opera-

tor Control Panel. control data entered at the Operator Control Panel which is stored by the

UPS Logic Board e.g. manual load transfer selection. external control options e.g. emergency shutdown, on-generator sync-

inhibit, isolator status.


In addition to the transfer control signals obtained from the UPS Logic Board, theStatic Switch Driver Board also receives a status signal from auxiliary contacts ofthe inverter-side contactor to detect its operational status.

1.3.2 Transfer control philosophy

Under normal circumstances the UPS Logic Board will request the Static SwitchDriver Board to connect the load to the inverter supply i.e. bypass-side openand inverter-side closed.

This situation will be maintained unless an inverter fault renders it incapable ofproviding the required load supply parameters (e.g. low battery voltage, inverterover/under voltage, inverter overload shutdown) or it is manually selected OFF(from Operator Control Panel or UPS Logic Board inverter enable switch) etc.Note: if the cause of the transfer clears when the load is on-bypass the load willautomatically transfer back to the inverter-side after a brief period to allow the in-verter control time to re-establish itself. For example, a fault on an inverter phasemay cause an erroneous overload to be detected, or the output volts to dip belowthe undervoltage threshold, and initiate a load transfer to bypass. However, once6-6 s6-c1.fm5 - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 1 - Static Switch Principlesthe load is removed from the inverter its output will return to normal and requestthe load to be returned to the inverter.

This type of fault could cause the load to tick-tock between the inverter and by-pass; and to overcome this problem the transfer control logic permanently trans-fers the load to bypass if more than 8 transfers occur within 60 seconds.

Bypass-to-inverter transfer mechanism

When the load is transferred from bypass to inverter the signal to close the in-verter-side contactor is applied 150ms before the bypass-side SCR drive sig-nals are removed. This is to allow time for the contactor to close before the bypassSCRs are turned OFF. In practice the contactor should close well within 50ms.;consequently, there will be an overlap period where both sides of the staticswitch are closed simultaneously, and the inverter and bypass voltages are effec-tively connected in parallel. Once the contactor is closed an auxiliary contact sig-nals the bypass SCRs to open immediately. This type of transfer is referred to asa closed transfer as the load is transferred without a supply break.

Note: if the contactor does not close, as indicated by the auxiliary contact, theUPS Logic Board will re-establish the load-on-bypass command before the150ms time-out period, keeping the load on bypass.

Before the transfer control logic will allow a closed transfer from bypass to invert-er it must verify that the inverter voltage is synchronised to the bypass supply. Ifthis condition is not met then the transfer action is prohibited. Also, as this is acontrolled transfer (i.e. not initiated by a fault condition) the inverter voltageregulation circuit is momentarily increased to matched the bypass voltage whilethe transfer takes place once the load is on-inverter the inverter reverts to itsnominal voltage. This is to limit any volts difference across the inverter-sidecontactor while it is being closed, and so prolong contactor life.

Inverter-to-bypass transfer mechanism

A load transfer from inverter to bypass can be initiated by manual selection (con-trolled transfer) or by a fault condition (uncontrolled); however the results aresimilar in that a closed transfer, as described above, will take place providingthe two supplies are synchronised. That is, the bypass-side SCRs are requestedto turn ON before the inverter-side contactor is de-energised, thus effecting ano-break transfer.

If the inverter is not synchronised to the bypass supply when the load transfer isrequested then the inverter-side contactor is opened before the bypass-sideSCRs are turned ON and the load will experience a slight power-break of up to 1cycle. This type of transfer is referred to as an open transfer, and protects theload from out-of-phase voltage differences which could put twice the phase volt-age potential on the critical load busbar.

1.3.3 Control power supplies

All circuit boards concerned with the static switch control function are poweredfrom either the AC-DC Power Supply Board or the DC-DC Power Supply Boardand are active when either supply is live.s6-c1.fm5 - Issue 2 Dated 21/08/97 6-7

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 1 - Static Switch Principles6-8 s6-c1.fm5 - Issue 2 Dated 21/08/97

Section 6:

Chapter 2 - Static Switch Driver Board (4542043 Z)

2.1 Chapter overview

This chapter contains a circuit description of the Static Switch Driver Board cur-rently used across the whole 7200 Series UPS model range, and should be read inconjunction with circuit diagram SE-4542043-Z (1 page).

Part N SE-4542043-Z is a direct replacement for Part N SE-4542041-X whichmay be fitted to units manufactured prior to February 1997. Although there areonly minor differences between the two boards a full explanation of the StaticSwitch Driver Board Part N SE-4542041-X can be found in Section 19 Chapter3.

2.2 General description

2.2.1 Circuit board functions

This board is responsible for providing the bypass-side static switch SCRs withtheir gate drive signals when the UPS Logic Board requests Load-on-bypass, andfor energising the inverter-side contactor when it requests Load-on-inverter. Inso doing, the board contains interlocking controls to prevent simultaneous opera-tion of both circuits: thereby controlling the load transfer characteristics.

It also provides the necessary galvanic signal isolation between the low-voltageenvironment of the control electronics and the high-voltage environment sur-rounding the bypass SCR devices and inverter-side contactor.

2.2.2 Input/Output connections

The Static Switch Driver Board has eleven connectors, all of which are describedbelow:

X1 to X6 Output gate drive signals to static switch SCRs X7 Not used X8 DC supply for the inverter-side contactor X9 Switched energising supply for the inverter-side contactor X10 inverter-side contactor auxiliary contacts (used for contactor sta-

tus monitoring) X13 Ribbon cable to the UPS Logic Board: carrying control logic sig-

nals and power supplies etc.

WARNING TAKE EXTREME CARE WHEN WORKING ON THIS BOARD IN SITU.

The inverter-side contactor energising supply at connectors X8 and X9 is ob-tained from the DC Busbar and is at a potentially dangerous DC voltage wheneverthe rectifier is operating or the UPS battery circuit breaker is closed. Similarly, mains a.c. voltage is present on the SCR drive connectors at all timeswhen the load is on inverter or bypass.s6-c2.fm5 - Issue 2 Dated 21/08/97 6-9

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 2 - Static Switch Driver Board (4542043 Z)2.2.3 Block Diagram

The following illustration shows the Static Switch Driver Board at its most basicfunctional block diagram level the function of each of the blocks shown is de-scribed in the following text.

Figure 6-7: Static Switch Driver Board basic block diagram

Transfer interlock logic

The transfer interlock logic is at the heart of the boards operation. It determineswhether the inverter-side contactor is closed or the static bypass SCRs areturned on; and in so doing, it controls the load transfer operation between the in-verter and bypass supplies.

There are three inputs to this static logic block. The load-on-inverter and load-on-bypass signals are produced on the UPS Logic Board and are the primary loadtransfer request inputs. The interlocking function also employs a signal derivedfrom auxiliary contacts of the inverter-side contactor which confirms the con-tactors status.

Contactor switching logic

The contactor switching logic block contains a solid-state switching circuitwhich is controlled by the transfer interlock logic and connects the DC busbar(battery) voltage through to the inverter-side contactors closing coil.

Mixer gate

The mixer gate combines the load-on-bypass command signal from the transferinterlock logic with a 30kHz modulating signal to provide the output driver cir-cuit with a modulated drive waveform. This type of drive signal is used to mini-

InverterContactor

DC Bus

Contactor

Load-on-inverter

Load-on-bypass

StaticSwitchSCRGates

Volts

OutputDriverCircuit

ModulatorOscillator

SupplyMonitor

MixerGate

ContactorSwitching

Logic

con

tro

lsw

itch

TransferInterlock

Logic

Auxiliary

PowerSupply

Control Power+12V+5VSupply

+12V

12V6-10 s6-c2.fm5 - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 2 - Static Switch Driver Board (4542043 Z)mise the size of the transformers in the output driver circuit, which are necessaryto provide signal isolation.

Note that the mixer gate output is inhibited by the supply monitor circuit if itdetects a low control power supply voltage: this also provides a reset pulse oninitial power-up.

Modulation oscillator

This is a free running oscillator of approximately 30kHz which provides a modu-lating signal to the mixer gate as described immediately above.

Output driver circuit

This circuit contains three pairs of power drivers which are all driven by the mod-ulated signal from the mixer gate. Each pair of drivers is connected in a push-pull configuration across the output transformers primary windings to provideadequate drive power.

Supply monitor

The supply monitor senses the voltage on the +12V control power rail andserves two functions: first, it provides reset signal to the mixer gate to prevent itturning on the static switch SCRs during power-up, until the supply rail has hadchance to stabilise. Second, it inhibits the mixer gate if it detects that the +12Vrail falls below 8V.

Power Supply

12V power rails are connected to this board from the UPS Logic Board via X13pins 1-12. These are connected to a voltage regulator circuit which provides a sta-bilised +5V rail which is required by the boards electronic devices.

2.3 Detailed circuit description

2.3.1 Introduction

This description, which refers to the circuit blocks shown in Figure 6-7, shouldbe read in conjunction with diagram SE-4542043-Z.

inverter-side contactor control

The inverter-side contactor is energised by the high DC voltage present on theDC busbar. The full bus voltage is applied to X8 pins 1-3 and the coil is connectedto X9 pins 1-3. Note that the positive supply is directly connected via pins 3 andthe contactor is controlled by switching the bus negative supply to X9 pin 1.

The contactor is energised by a logic high [INV-L> signal applied to X13 pin 15from the UPS Logic Board. This signal turns on V32 which, via opto-isolatorV41, then turns on V31 and thus connects the contactor coil negative side to thenegative DC busbar supply at X8-1. The contactor should close within 50ms.

Note: the supply to V31 gate is obtained from the positive DC bus (battery) volt-age present at X8 pins 3 via V41, R23 and R24; however it is limited to 13V byzener V21. V12 and V13 are flywheel diodes to protect V41 and V31.

When the contactor closes, its auxiliary contacts short out X10 pins 1-2 whichthen pulls D5-8 to a logic low and informs the transfer interlock logic of thecontactors status. The contactor should take between 60-100ms to open.s6-c2.fm5 - Issue 2 Dated 21/08/97 6-11

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 2 - Static Switch Driver Board (4542043 Z)Static switch SCR control

The bypass-side SCRs are controlled by the transfer interlock logic circuitoutput at D5 pin 12 (best monitored at X11: 0-3 which should be made). Whenthis point goes high it drives N2 pin 7 high which then takes D2 pin 2 and 3high, which triggers the SCRs, vi the driver FETs V2 and V11.

D2 is annotated mixer gate in the block diagram (See Figure 6-7) and turns onthe static switch SCRs when its outputs (D2 pins 6 & 9) are high. The input to D2pin 2 and 3 is connected to the output of N3, which is a power supply monitor,and goes low to inhibit the SCR drive signal in the event of a power failure (andduring initial power-up). The input to D2 pin 1 and 5 is a 30kHz square wavesignal provided by D1, which is a free running oscillator: thus, provided there isno problem with the power rails, when the output from N2 pin 7 goes high it en-ables D2 to pass the 30kHz modulating signal through to the output driver gatesof V2 and V11.

Note: V2 and V11 are supplied from the -12V rail to provide suitable outputswitching levels to the isolating pulse transformers driving the power SCRs.


The 30kHz output from the mixer gate (D2 pins 6 & 9) are connected to thegates of V2 & V11, which are the output line driver devices. Taking V2 as an ex-ample: when the 30kHz drive signal to D2 pin 6 is high FET V2 turns on. Thisconnects the -12V through to T1, T3 and T5 primaries with the +12V rail. Whenthe 30kHz drive signal is low D2 outputs go to a high impedance state; thus the12V output at V2 is switched on and off at a 30kHz rate.

As can be seen on the circuit diagram, V2 and V11 output is connected to theSCRs gate drive connectors via pulse transformers T1 to T6 which provide thenecessary signal isolation. Suppression capacitors C34 and C35 protect the driverFETs from the transformers reactive currents.


Figure 6-8: Transfer interlock logic

As explained in the previous paragraphs, the transfer interlock logic controls thesignal which initiates the static switch SCR driver circuit i.e. the output fromD5-12 turns on the static switch when high and vice versa.

[MNS-L>1 = Load

onBypass

[INV-L>1 = Load

onInverter

ContactorAux Fdbk

1 = ContactorOpen

1 = Turn onbypass SCRs

1 = CloseOutput Contactor

8

910

D6

12

1311

D6

5

64

D6

9 8

D5

V10

C6330n

R28

470k

R48

470k

1 2

D5

5 6

U5

11 10

U5

1

23

D6

13 12

D5

3 4

D56-12 s6-c2.fm5 - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 2 - Static Switch Driver Board (4542043 Z)This circuit is controlled by three inputs shown in the diagram above. These are:

[INV-L> which goes high when the UPS Logic Board is requesting load-on-inverter (i.e. contactor closed).

[MNS-L> which goes high when the UPS Logic Board is requesting load-on-bypass (i.e. static switch SCRs turned on).

Auxiliary contacts from the inverter-side contactor which is logic lowwhen the contactor is closed and vice versa.

The [INV-L> and [MNS-L> signals are mutually exclusive i.e. the control systemon the UPS Logic Board prevents it from requesting both conditions simultane-ously. The following paragraphs described the circuit action when the load istransferred between one power source and the other.

Load transfer from bypass to inverter - When the UPS Logic Board re-quires a load transfer to inverter it simultaneously drives the [MNS-L> low andthe [INV-L> high.

1. Prior to the transfer, the load is on the bypass supply, which means that D6pin 10 is low (turning on the bypass SCRs).

2. The low [MNS-L> signal is inverted to a high at D5 pin 4 which takes D6pin 1 high.

3. The same high [MNS-L> signal is also inverted to a low at D5-2, howeverR28/C6 applies a 150ms time delay on this signal before it reaches D6 pin 12.This is to hold on the bypass SCRs until the inverter-side contactor has hadtime to close (contactor should close within 50ms).

4. After 150ms D6 pins 1 & 2 will both be high and this will drive D6 pin 3low which drives D6 pin 10 high and D5 pin 12 low turning off thebypass SCRs.

5. The high [INV-L> signal:

a) is inverted twice, at D5-6 and D5-10, and applies a high at D6 pin 5. However this has no immediate effect on the circuit.

b) turns on V32, which switches on the inverter-side contactor energising supply (see earlier output contactor control earlier in this section).

6. When the inverter-side contactor closes it applies a low to D5-9 which isinverted to a high at D5-8 and D6 pin 6.

7. With D6 pins 5 and 6 now both high, the output at D6 pin 4 goes lowwhich drives D6 pin 10 high and D6 pin 11 low, which then turns off thebypass SCRs. That is, if the inverter-side contactor has closed it will openthe bypass SCRs immediately and doesnt wait 150ms.

Note 1: the above description shows that when transferring normally from by-pass to inverter the bypass SCRs are held on until the inverter-side contactoris closed (auxiliary contacts closed), therefore the load is transferred without asupply break i.e. closed transfer.

Note 2: Once the UPS Logic Board software decides to transfer to inverter, thebypass SCRs are held on for a 150ms period. The contactor, if OK, should closewithin 50ms. If this is the case, as indicated by the contactor auxiliary contacts,the bypass SCRs are opened immediately. If this is NOT the case then the UPSs6-c2.fm5 - Issue 2 Dated 21/08/97 6-13

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 2 - Static Switch Driver Board (4542043 Z)Logic Board software will re-establish the load on bypass command and removethe load on inverter request to close the inverter-side contactor.

Note 3: The load on inverter request is given 5 seconds to achieve its objective,otherwise the micro will annunciate an alarm (#41) [Output: No Voltage] on theOperator Control Panel and will not attempt further transfers.

Load transfer from inverter to bypass - When the UPS Logic Board re-quires a load transfer to bypass it simultaneously drives the [MNS-L> high andthe [INV-L> low.

1. Prior to the transfer, the load is on the inverter supply, which means that D5pin 12 is low (turning off the bypass SCRs).

2. The high [MNS-L> signal is:

a) inverted to a low at D5 pin 4 which takes D6 pin 1 low.

b) inverted to a high at D5 pin 2 which takes D6 pin 2 low. Note: that in this instance there is no delay on the signal reaching D6 pin 2 as the time delay is bypassed by V10.

3. A logic low at either of D6 pins 1 or 2 will drive D6 pin 8 high; howeverthis has no immediate effect on the circuit (step 4a below).

4. The low [INV-L> signal:

a) is inverted twice, at D5-6 and D5-10, and applies a low at D6 pin 5 which results in a high at D6 pin 9.

b) turns off V32, which switches off the inverter-side contactor energising supply (see output contactor control earlier in this section).

5. With logic highs at D6 pin 8 (step 3) and pin 9 (step 4a), the output from D8pin 10 now switches low and D5 pin 12 high which is the state necessaryto turn on the bypass SCRs.

6. When the inverter-side contactor opens it applies a high to D5-9 which isinverted to a low at D5-8 and D6 pin 6 which then holds D6 pin 9 high andreinforces (overrides) the effect of the [INV-L> signal on D6 pin 5.

Note: the above description shows that when transferring normally from invert-er to bypass the bypass SCRs are turned on immediately the [INV-L> signal re-quests the inverter-side contactor to open, therefore the load is transferredwithout a supply break i.e. closed transfer. The contactor should open within 60-100ms.

Power supplies

The devices on this board require various operating voltages. The main 12Vsupply rails are provided by the UPS Logic Board and connected via X13 pins 1to 12. +12V and 0V are then connected to a simple three-terminal regulator whichprovides a +5V supply rail, as shown.

Note that D1 and D2 are both 5V operating devices but are fed from the -12V and0V power rails. This is to shift their output signal levels to that required to switchthe output drivers (V2 and V11).6-14 s6-c2.fm5 - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 2 - Static Switch Driver Board (4542043 Z)Power supply monitor

N3 monitors the +12V rail and -12V rail and its output pin 5 goes low if the+12V falls below approximately 6.8V or the -12 falls below approximately-10.6V. This inhibits the mixer gate D2 and the output line driver devices andso prevents the bypass SCRs from being turned on. Power supply failure couldcause intermittent SCR triggering and, in the worst case, present a half-wave loadsupply. The power supply monitor avoids such occurrences.

2.4 Summary information

Table 6-1: Static Switch Driver Board configuration jumpers

JumperLink

Position

Function

X11

0 - 1open Enable load on inverter command (Standard)

closed Disable load on inverter command

0 - 2open Enable load on bypass command(Standard)

closed Disable load on bypass command

0 - 3open Disables bypass fire command

closed Enable bypass fire command (Standard)

0 - 4 N/A Not used

0 - 5

open Test static switch temperature monitor

closedInhibit static switch temperature monitor

(standard)s6-c2.fm5 - Issue 2 Dated 21/08/97 6-15

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 2 - Static Switch Driver Board (4542043 Z)6-16 s6-c2.fm5 - Issue 2 Dated 21/08/97

Section 19:

Chapter 3 - Static Switch Driver Board (4542041 X)

3.1 Chapter overview

This chapter contains a circuit description of the Static Switch Driver Board4542041X which was used across the whole 7200 Series UPS model range priorto February 97, when it was superseded by Part No. 4542043Z (see Chapter 2).This chapter should be read in conjunction with circuit diagram SE-4542041-X(1 page).

3.2 General description

3.2.1 Circuit board functions

This board is responsible for providing the bypass-side static switch SCRs withtheir gate drive signals when the UPS Logic Board requests Load-on-bypass, andfor energising the inverter-side contactor when it requests Load-on-inverter. Inso doing, the board contains interlocking controls to prevent simultaneous opera-tion of both circuits: thereby controlling the load transfer characteristics.

It also provides the necessary galvanic signal isolation between the low-voltageenvironment of the control electronics and the high-voltage environment sur-rounding the bypass SCR devices and inverter-side contactor.

3.2.2 Input/Output connections

The Static Switch Driver Board has eleven connectors, all of which are describedbelow:

X1 to X6 Output gate drive signals to static switch SCRs X7 Not used X8 DC supply for the inverter-side contactor X9 Switched energising supply for the inverter-side contactor X10 inverter-side contactor auxiliary contacts (used for contactor sta-

tus monitoring) X13 Ribbon cable to the UPS Logic Board: carrying control logic sig-

nals and power supplies etc.

WARNING TAKE EXTREME CARE WHEN WORKING ON THIS BOARD IN SITU.

The inverter-side contactor energising supply at connectors X8 and X9 is ob-tained from the DC Busbar and is at a potentially dangerous DC voltage wheneverthe rectifier is operating or the UPS battery circuit breaker is closed. Similarly, mains a.c. voltage is present on the SCR drive connectors at all timeswhen the load is on inverter or bypass.s6-c2OLD.fm - Issue 2 Dated 21/08/97 19-285

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 3 - Static Switch Driver Board (4542041 X)3.2.3 Block Diagram

The following illustration shows the Static Switch Driver Board at its most basicfunctional block diagram level the function of each of the blocks shown is de-scribed in the following text.

Figure 19-9: Static Switch Driver Board basic block diagram


The transfer interlock logic is at the heart of the boards operation. It determineswhether the inverter-side contactor is closed or the static bypass SCRs areturned on; and in so doing, it controls the load transfer operation between the in-verter and bypass supplies.

There are three inputs to this static logic block. The load-on-inverter and load-on-bypass signals are produced on the UPS Logic Board and are the primary loadtransfer request inputs. The interlocking function also employs a signal derivedfrom auxiliary contacts of the inverter-side contactor which confirms the con-tactors status.

Contactor switching logic

The contactor switching logic block contains a solid-state switching circuitwhich is controlled by the transfer interlock logic and connects the DC busbar(battery) voltage through to the inverter-side contactors closing coil.

Mixer gate

The mixer gate combines the load-on-bypass command signal from the transferinterlock logic with a 30kHz modulating signal to provide the output driver cir-cuit with a modulated drive waveform. This type of drive signal is used to mini-

InverterContactor

DC Bus

Contactor

Load-on-inverter

Load-on-bypass

StaticSwitchSCRGates

Volts

OutputDriverCircuit

ModulatorOscillator

SupplyMonitor

MixerGate

ContactorSwitching

Logic

con

tro

lsw

itch

TransferInterlock

Logic

Auxiliary

PowerSupply

Control Power12V+5V-7VSupply19-286 s6-c2OLD.fm - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 3 - Static Switch Driver Board (4542041 X)mise the size of the transformers in the output driver circuit, which are necessaryto provide signal isolation.

Note that the mixer gate output is inhibited by the supply monitor circuit if itdetects a low control power supply voltage: this also provides a reset pulse oninitial power-up.

Modulation oscillator

This is a free running oscillator of approximately 30kHz which provides a modu-lating signal to the mixer gate as described immediately above.


This circuit contains three pairs of power drivers which are all driven by the mod-ulated signal from the mixer gate. Each pair of drivers is connected in a push-pull configuration across the output transformers primary windings to provideadequate drive power.

Supply monitor

The supply monitor senses the voltage on the +12V control power rail andserves two functions: first, it provides reset signal to the mixer gate to prevent itturning on the static switch SCRs during power-up, until the supply rail has hadchance to stabilise. Second, it inhibits the mixer gate if it detects that the +12Vrail falls below 8V.

Power Supply

12V power rails are connected to this board from the UPS Logic Board via X13pins 1-12. These are connected to two voltage regulator circuits which providestabilised +5 and -7V supply rails which are required by several of the boards de-vices.

3.3 Detailed circuit description

3.3.1 Introduction

This description, which refers to the circuit blocks shown in Figure 19-9, shouldbe read in conjunction with diagram SE-4542041-X.

inverter-side contactor control

The inverter-side contactor is energised by the high DC voltage present on theDC busbar. The full bus voltage is applied to X8 pins 1-3 and the coil is connectedto X9 pins 1-3. Note that the positive supply is directly connected via pins 3 andthe contactor is controlled by switching the bus negative supply to X9 pin 1.

The contactor is energised by a logic high [INV-L> signal applied to X13 pin 15from the UPS Logic Board. This signal turns on V32 which, via opto-isolatorV41, then turns on V31 and thus connects the contactor coil negative side to thenegative DC busbar supply at X8-1. The contactor should close within 50ms.

Note: the supply to V31 gate is obtained from the positive DC bus (battery) volt-age present at X8 pins 3 via V41, R23 and R24; however it is limited to 13V byzener V21. V12 and V13 are flywheel diodes to protect V41 and V31.

When the contactor closes, its auxiliary contacts short out X10 pins 1-2 whichthen pulls D5-8 to a logic low and informs the transfer interlock logic of thecontactors status. The contactor should take between 60-100ms to open.s6-c2OLD.fm - Issue 2 Dated 21/08/97 19-287

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 3 - Static Switch Driver Board (4542041 X)Static switch SCR control

The bypass-side SCRs are controlled by the transfer interlock logic circuitoutput at D6 pin 11 (best monitored at X12-3 which should be made). When thispoint goes high it drives N3 pin 7 high which then takes D2 pin 4 and D3/D4pins 7 and 16 high, which triggers the SCRs.

D2 is annotated mixer gate in the block diagram (See Figure 19-9) and turns onthe static switch SCRs when its output (D2 pin 6) is high. The input to D2 pin 3is connected to the output of N4, which is a power supply monitor, and goes lowto inhibit the SCR drive signal in the event of a power failure (and during initialpower-up). The input to D2 pin 5 is a 30kHz square wave signal provided by D1,which is a free running oscillator: thus, provided there is no problem with thepower rails, when the output from N3 pin 7 goes high it enables D2 to pass the30kHz modulating signal through to the output driver gates of D3 and D4.

Note: D1 and D2 are supplied from the -7V and -12V power rails to shift theiroutput switching levels to that required for driving the output line drivers D3/D4.


The 30kHz output from the mixer gate (D2-8) is connected to the gates of Q3/Q4, which are the output line driver devices. Taking D4a as an example: when the30kHz drive signal to D4-1 is high the two drivers within D4a turn on. This con-nects the -12V at D4-2 through to D4-3 and +12V (from N3 output) at D4-7through to D4-6. When the 30kHz drive signal is low D4 outputs go to a highimpedance state; thus the 12V outputs at D4 pins 3 and 6 are switched on andoff at a 30kHz rate.

As can be seen on the circuit diagram, D4 outputs are connected to the SCRs gatedrive connectors via pulse transformers T1 and T2 which provide the necessarysignal isolation. V3 to V4 are flywheel diodes and protect the driver devices fromthe transformers reactive currents.


Figure 19-10: Transfer interlock logic

8

910

D6

12

1311

D6

1

23

D6

5

64

D65 6

D5

11 10

D5

1 2

D5

3 4

D5

9 8

D5

R29

470k

V10

C6330n

[MNS-L>1 = Load

onBypass

[INV-L>1 = Load

onInverter

ContactorAux Fdbk

1 = ContactorOpen

1 = Turn onbypass SCRs

1 = CloseOutput Contactor19-288 s6-c2OLD.fm - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 3 - Static Switch Driver Board (4542041 X)As explained in the previous paragraphs, the transfer interlock logic controls thesignal which initiates the static switch SCR driver circuit i.e. the output fromD6-11 turns on the static switch when high and vice versa.

This circuit is controlled by three inputs shown in the diagram above. These are:

[INV-L> which goes high when the UPS Logic Board is requesting load-on-inverter (i.e. contactor closed).

[MNS-L> which goes high when the UPS Logic Board is requesting load-on-bypass (i.e. static switch SCRs turned on).

Auxiliary contacts from the inverter-side contactor which is logic lowwhen the contactor is closed and vice versa.

The [INV-L> and [MNS-L> signals are mutually exclusive i.e. the control systemon the UPS Logic Board prevents it from requesting both conditions simultane-ously. The following paragraphs described the circuit action when the load istransferred between one power source and the other.

Load transfer from bypass to inverter - When the UPS Logic Board re-quires a load transfer to inverter it simultaneously drives the [MNS-L> low andthe [INV-L> high.

1. Prior to the transfer, the load is on the bypass supply, which means that D6pin 11 is high (turning on the bypass SCRs).

2. The low [MNS-L> signal is inverted to a high at D5 pin 2 which takes D6pin 1 high.

3. The low [MNS-L> signal is also inverted to a high at D5-4, however R29/C6 applies a 150ms time delay on this signal before it reaches D6 pin 2. Thisis to hold on the bypass SCRs until the inverter-side contactor has had timeto close (contactor should close within 50ms).

4. After 150ms D6 pins 1 & 2 will both be high and this will drive D6 pin 3low which drives D6 pin 10 high and D6 pin 11 low turning off thebypass SCRs.

5. The high [INV-L> signal:

a) is inverted twice, at D5-6 and D5-10, and applies a high at D6 pin 5. However this has no immediate effect on the circuit.

b) turns on V32, which switches on the inverter-side contactor energising supply (see earlier output contactor control earlier in this section).

6. When the inverter-side contactor closes it applies a low to D5-9 which isinverted to a high at D5-8 and D6 pin 6.

7. With D6 pins 5 and 6 now both high, the output at D6 pin 4 goes lowwhich drives D6 pin 10 high and D6 pin 11 low, which then turns off thebypass SCRs. That is, if the inverter-side contactor has closed it will openthe bypass SCRs immediately and doesnt wait 150ms.

Note 1: the above description shows that when transferring normally from by-pass to inverter the bypass SCRs are held on until the inverter-side contactoris closed (auxiliary contacts closed), therefore the load is transferred without asupply break i.e. closed transfer.s6-c2OLD.fm - Issue 2 Dated 21/08/97 19-289

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 3 - Static Switch Driver Board (4542041 X)Note 2: Once the UPS Logic Board software decides to transfer to inverter, thebypass SCRs are held on for a 150ms period. The contactor, if OK, should closewithin 50ms. If this is the case, as indicated by the contactor auxiliary contacts,the bypass SCRs are opened immediately. If this is NOT the case then the UPSLogic Board software will re-establish the load on bypass command and removethe load on inverter request to close the inverter-side contactor.

Note 3: The load on inverter request is given 5 seconds to achieve its objective,otherwise the micro will annunciate an alarm (#41) [Inverter: No Voltage] on theOperator Control Panel and will not attempt further transfers.

Load transfer from inverter to bypass - When the UPS Logic Board re-quires a load transfer to bypass it simultaneously drives the [MNS-L> high andthe [INV-L> low.

1. Prior to the transfer, the load is on the inverter supply, which means that D6pin 11 is low (turning off the bypass SCRs).

2. The high [MNS-L> signal is:

a) inverted to a low at D5 pin 2 which takes D6 pin 1 low.

b) inverted to a low at D5-4 which takes D6 pin 2 low. Note: that in this instance there is no delay on the signal reaching D6 pin 2 as the time delay is bypassed by V10.

3. A logic low at either of D6 pins 1 or 2 will drive D6 pin 8 high; howeverthis has no immediate effect on the circuit (step 4a below).

4. The low [INV-L> signal:

a) is inverted twice, at D5-6 and D5-10, and applies a low at D6 pin 5 which results in a high at D6 pin 9.

b) turns off V32, which switches off the inverter-side contactor energising supply (see earlier output contactor control earlier in this section).

5. With logic highs at D6 pin 8 (step 3) and pin 9 (step 4a), the output from D8pin 10 now switches low and D6 pin 11 high which is the state necessaryto turn on the bypass SCRs.

6. When the inverter-side contactor opens it applies a high to D5-9 which isinverted to a low at D5-8 and D6 pin 6 which then hold D6 pin 9 high andreinforces (overrides) the effect of the [INV-L> signal on D6 pin 5.

Note: the above description shows that when transferring normally from invert-er to bypass the bypass SCRs are turned on immediately the [INV-L> signal re-quests the inverter-side contactor to open, therefore the load is transferredwithout a supply break i.e. closed transfer. The contactor should open within 60-100ms.

Power supplies

The devices on this board require various operating voltages. The main 12Vsupply rails are provided by the UPS Logic Board and connected via X13 pins 1to 12. These are then connected to two simple three-terminal regulators whichprovide +5V and -7V supply rails, as shown.

Note that D1 and D2 are both 5V operating devices but are fed from the -12V and-7V power rails. This is to shift their output signal levels to that required to switch19-290 s6-c2OLD.fm - Issue 2 Dated 21/08/97

7200 Series UPS Service Manual SECTION 6 - Static Switch Operation & ControlCHAPTER 3 - Static Switch Driver Board (4542041 X)the output drivers (D3 and D4). The -7V rail also offsets the output from N3 tothe mixer gate input.

Power supply monitor

N4 monitors the +12V rail and -12V rail and its output pin 6 goes low if the+12V falls below approximately 6.8V or the -12 falls below approximately-10.6V. This inhibits the mixer gate and the output line driver devices (via V11)and so prevents the bypass SCRs from being turned on. Power supply failurecould cause intermittent SCR triggering and, in the worst case, present a half-wave load supply. The power supply monitor avoids such occurrences.


Table 19-2: Static Switch Driver Board configuration jumpers

JumperLink

Position Function

X11 1 - 2 Inhibit static switch temperature monitor

2 - 3 Enable static switch temperature monitor (Standard)

X12

0 - 1 OPEN Enable load on inverter command (Standard)

0 - 1 CLOSED Disable load on inverter command

0 - 2 OPEN Enable load on bypass command(Standard)

0 - 2 CLOSED Disable load on bypass command

0 - 3 OPEN Disables bypass fire command

0 - 3 CLOSED Enable bypass fire command (Standard)s6-c2OLD.fm - Issue 2 Dated 21/08/97 19-291

SECTION 6 - Static Switch Operation & Control 7200 Series UPS Service ManualCHAPTER 3 - Static Switch Driver Board (4542041 X)19-292 s6-c2OLD.fm - Issue 2 Dated 21/08/97

Section 6: Static Switch Operation & ControlChapter 1 - Static Switch Principles1.1 Introduction1.2 Static switch construction1.3 Static switch control system1.3.1 Control system overview1.3.2 Transfer control philosophy1.3.3 Control power supplies

Chapter 2 - Static Switch Driver Board (4542043 Z)2.1 Chapter overview2.2 General description2.2.1 Circuit board functions2.2.2 Input/Output connections2.2.3 Block Diagram

2.3 Detailed circuit description2.3.1 Introduction


Chapter 3 - Static Switch Driver Board (4542041 X)3.1 Chapter overview3.2 General description3.2.1 Circuit board functions3.2.2 Input/Output connections3.2.3 Block Diagram

3.3 Detailed circuit description3.3.1 Introduction


sect-6

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