Ich Ngo Tracking Number: 173143 Paper Number: 2009-4613

7th International Energy Conversion Engineering Conference 2 - 5 August 2009, Denver, Colorado

AIAA 2009-4613

Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Evolution of Solar Array Shunt Regulators for Boeing Satellites

Ich D. Ngo The Boeing Company, Space and Intelligence Systems

P.O. Box 92919 MC W-S25-C564

Los Angeles, Ca 90009 USA

Ich.d.ngo@boeing.com

ABSTRACT

In the last 30 years, the power capability of Boeing satellites went from 1kW (spinner satellites) to 20kW. These satellites use solar power as primary power source and solar array regulator is required to provide a tightly regulated power bus. Many different topologies of solar array regulators were used for different Boeing satellite design. This paper addresses the features and trade considerations of each type of solar array shunt regulator for increasingly complex and high power satellites. 1. INTRODUCTION

For satellites that use a power system architecture employing a fully regulated power bus, a solar array regulator is required in sunlight operating mode. Boeing satellites use solar array shunt regulator to maintain bus regulation in sunlight mode. A solar array Shunt Regulator is a voltage regulator that regulates the power bus by shunting excess solar array current in response to the changes in payload demand. Boeing has used different shunt regulator topologies for different satellite product lines

1) Boeing 376 satellite product line (1kW to 2kW power level) uses a linear shunt regulator for 30V bus regulation

2) Boeing 601 satellite product line (2kW to 4kW power level) uses a switching shunt regulator for 50V bus regulation.

3) Boeing 601HP satellite product line (4kW to 8kW power level) uses a boost shunt regulator for 50V bus regulation

4) Boeing 702 satellite product line (10kW to 20kW power level) also uses the same boost shunt topology with design enhancement for 100V bus regulation.

2. BOEING 376 LINEAR SHUNT REGULATOR

The Boeing 376 satellites are low power spinning satellites, typical spacecraft power level is between 1kW to 2kW. Linear shunt regulators are used for bus voltage regulation in sunlight mode. The design has four linear shunt regulators in a unit and the regulators

are connected to four solar circuit groups as shown in Figure 1. Each regulator is connected to the tapped input of a solar circuit group (1/3 of the total solar circuit). The bus voltage is sensed and current is shunted from the tapped input of a solar circuit by its associated linear shunt regulator when the bus voltage exceeds a predetermined threshold. The linear shunt regulator, when active, decreases the lower 1/3 solar circuit voltage linearly and thus decreases the solar circuit current supplying to the power bus.

Figure 1 Boeing 376 Linear Shunt Regulator

Figure 2 Linear Shunt Regulator Block Diagram

Each linear shunt regulator is individually fused and can be disabled separately through a switch in series with each tap switch as shown in figure 2. Hence, no current will be shunted as a result any of the linear shunt regulator failing short.

Spacecraft Bus

U

U

U

U

L

L

L

LLinear Shunt Regulator

Tap A

Tap B

Tap C

Tap D

J2

J1Bus

CMD / TM

CMD / TM

CMD / TM

CMD / TM

Regulator Interface to Solar Panel

V panel

V bus

Upper panel(Untapped)

Lower panel

(Tapped)

Control Circuit

Spacecraft loads

BusI upper

I lowerI upper + I lower

I upper

Limiter

Module disable switchV panel

V bus

Upper panel(Untapped)

Lower panel

(Tapped)

Control Circuit

Spacecraft loads

BusI upper

I lowerI upper + I lower

I upper

Limiter

Module disable switch

V bus

Upper panel(Untapped)

Lower panel

(Tapped)

Control Circuit

Spacecraft loads

BusI upper

I lowerI upper + I lower

I upper

Limiter

Module disable switch

Figure 3 Bus Voltage Limiter Set Point Profile

Each linear shunt regulator has a slightly different set-point so current shunting is sequential. As the load current increase, the shunt regulator will start untapped the current from tap D to tap A as shown in Figure 3.

Figure 4 Linear Shunt Regulator Unit

The benefit of using linear shunt regulator is low Electrical Magnetic Interference (EMI) noise. However, these linear regulators generate significant heat; each regulator can dissipate up to 55W in the current design. Therefore, for higher power satellites, linear shunt regulator power dissipation is too high and thermal design would be very challenging.

3. BOEING 601 SWITCHING SHUNT REGULATOR

The Boeing 601 satellites are 3-axis or body-stabilized spacecraft, power level is between 2kW to 4 kW. There are two solar wings per spacecraft and each solar wing is regulated by a switching shunt regulator unit. Each switching shunt regulator unit consists of multiple modules regulating the bus power. Each module voltage set point is staggered by 0.5V, sequentially shunting excessive solar array current. Each module can totally pass or totally shunt solar array current and one module partially passes the solar array current to meet the power demand of the spacecraft.

A module partially passes solar array current to the power bus by switching the associated solar circuit group between ground and power bus voltage, (or hard switching the solar array circuits) thus produces very high switching noise. However the switching devices

are either saturated or open, so power dissipation is much lower than that of the linear shunt regulator.

Figure 5 shows the unit block diagram of the switching shunt regulator. Array inputs are divided into a small group of strings that tied to individual Field Effect Transistor (FET) switch to ground and switch to bus through the bus diode. Having smaller group of solar array strings to each FET help to reduce the EMI current switching on the unit. Each FET is switching in sequential so that not all four FETs are switching at the same time to further reduce the EMI noise from high switching current. Each module also has a series connected relay at the return path to allow disabling of the module. Hence, there will be no current shunted due to any of the switching shunt regulator failing short.

Figure 5 Boeing 601 Switching Shunt Regulator

The switching shunt regulator regulates the spacecraft bus at one of the four equally spaced voltage set points ranging from 51.2V to 52.7V during sunlight operation. Figure 6 shows the bus voltage changes as the load current increase.

Figure 6 Bus voltage regulations versus the load current

The Boeing 601 switching shunt regulator unit acts as the solar panel yoke cross member as shown in figure 7.

Figure 7 Switching Shunt Regulator Unit 4. BOEING 601HP BOOST SHUNT

REGULATOR

The Boeing 601HP satellites are also 3-axis satellites, power level between 4kW to 8kW. Two boost shunt regulator units per spacecraft are used.

Each regulator unit consists of multiple power modules or boost shunt regulator module. Each boost shunt regulator module can either totally pass solar array current or totally shunt the array current. One of the boost shunt regulator module would act like a conventional boost DC-DC converter, whereas the input voltage (solar array circuit) is lower than the output voltage (power bus).

Figure 8 is the block diagram of the Boeing 601HP Boost Shunt Regulator Unit. Unlike the Boeing 601 switching shunt regulator which is hard switching the array, where the array input voltage goes from zero to the bus voltage on every switching cycle, the Boeing 601HP Boost Shunt Regulator switches the array input through the boost inductor. Array input voltage stays at a dc level lower than the output voltage with a small ac ripple sitting on the top of the dc level. This soft switching scheme allows the regulator to switch at a higher current level and produce low switching noise. There are 8 array strings per boost shunt regulator module. All the array string isolation diodes are housed inside the module. Each module also has a series connected relay at the return path to allow disabling of the module in case of any FET switch failing short that can permanently shunt the array current to ground. The power bus is regulated by sequentially shunting excess solar array current based on each boost shunt regulator’s (or module’s) own local set point. Each power module voltage has slightly different local bus set point. An error amplifier in the master module forces the power module to regulate the bus to a single set point. Figure 9 shows the main error amplifier control scheme. Figure 10 shows the single bus regulation set point control diagram.

Figure 8 Boeing 601HP Boost Shunt Regulator

Figure 9 Main error amplifier control scheme

Figure 10 Single Bus Set Point Control Diagram

The Boeing 601HP Boost Shunt Regulator unit also acts as the solar panel yoke cross member as shown in figure 11.

s/a diode

Power module

Vcontrolfrom mastermodule

relay driver

aux supplygate driver

pwm circuit

local erroramplifier

s/c loadx 8

x 7

Ishuntedsense res.

Total s/a currentsense resistor

Solar arraypowercircuitsgroup

Coupled-inductor boost topologys/a diode

Power module

Vcontrolfrom mastermodule

relay driver

aux supplygate driver

pwm circuit

local erroramplifier

s/c loadx 8

x 7

Ishuntedsense res.

Total s/a currentsense resistor

Solar arraypowercircuitsgroup

Coupled-inductor boost topology

55.25 V

54.95 V

54.65 V

54.35 V

54.05 V

53.75 V

53.45 V

8.1 V

6.2 V

0 A

120 A

PWR MOD. setpointVcontrol

S/C loads

Active 52.9 V

55.25 V

54.95 V

54.65 V

54.35 V

54.05 V

53.75 V

53.45 V

8.1 V

6.2 V

8.1 V

6.2 V

0 A

120 A

0 A

120 A

Shunting

Unshunting

PWR MOD. setpointVcontrol

S/C loads

Active 52.9 V

Figure 11 Boeing 601HP Boost Shunt Regulation Unit

Two significant improvements were made in the Boeing 601HP satellite product line: 1) Low EMI noise 2) Tightly regulated bus

5. BOEING 702 BOOST SHUNT REGULAOR

The Boeing 702 satellites use the same boost shunt regulator topology from Boeing 601HP. Instead of mounting the units on the yoke of the solar wing, the boost shunt regulators are integrated with the battery charger, battery discharge controller and a low voltage controller to form a unit Integrated Power Controller (IPC) unit inside the spacecraft. Figure 12 shows the IPC unit block diagram.

There are two IPCs per spacecraft. Multiple boost shunt regulators are housed in each IPC. Bus voltage was raised to 100V for high power capability.

Figure 13 shows the portion of boost shunt regulator block diagram in the IPC unit. The array isolation diodes are not part of the IPC. They are located on the array panel. There is a FET switch in series with each boost shunt regulator module at the array input and a bypass diode from the array input to the bus output. Any failure in the boost shunt regulator module can be removed by disabling the series FET switch and the array power will flow to the bus through the bypass diode.

The Boeing 702 boost shunt regulators use the same bus regulation scheme used in the Boeing 601HP. The power bus is regulated by sequentially shunting excess solar array current based on each boost shunt regulator’s (or module’s) own local set point. Each power module voltage has slightly different local bus set point. An error amplifier in the master module forces the power module to regulate the bus to a single set point. Figure 9 shows the main error amplifier control scheme. Figure 14 shows the single bus regulation set point control diagram.

Figure 12 Boeing 702 Integrated Power Controller

Figure 13 Boeing 702 Boost Shunt Regulator Block Diagram

Figure 14 Boeing 702 Single Bus Set Point Control Diagram

LVC

CIRCUIT 1

LVCCIRCUIT 2

LVC MODULE

BCC MODULE

CHARGE CONTROL

CHARGE CONTROL

SOLAR ARRAY

x7 100BU

30BU

SWD

+

UMBIL

CHG IN

BATTERYDSCH

CONTROL

S/A CONTROL

BVC MODULE 7

DSCH CONTROL

S/A CONTROL

BVC MODULE 1

Boost Shunt Regulator

102.4 V

102.1 V

101.9 V

101.6 V

101.3 V

101 V

100.9 V

-1 V 0 A

120 A

Unshunting

PWR MOD. setpointVcontrol

S/C loads

Active 100 V

-6 V

0 A

120 A

0 A

120 A

Shunting

PWR MOD. setpointVcontrol

S/C loads

Active

102.4 V

102.1 V

101.9 V

101.6 V

101.3 V

101 V

100.9 V

-1 V 0 A

120 A

Unshunting

PWR MOD. setpointVcontrol

S/C loads

Active 100 V

-6 V

0 A

120 A

0 A

120 A

Shunting

PWR MOD. setpointVcontrol

S/C loads

Active

The Boeing 702 Integrated Power Controller unit outline is shown figure 15.

Figure 15 Boeing 702 Integrated Power Controller Unit

Several improvements were made for the 702 product line: 1) Modular approach allows power scalability 2) Single bus regulation set point for sunlight and eclipse operation modes 3) Combining all power processing functions into one unit significantly increase the specific power 4) Solid state switch is used in place of mechanical relay to increase the reliability of enabling/disabling modules 6. SPECIFIC POWER COMPARISON

Table 6.1 Specific power comparison summary on all Boeing Satellites Solar Array Shunt Regulators 7. SUMMARY

Four generations of Boeing solar array regulators were discussed. Improvements including bus regulation, EMI performance, thermal dissipations and specific power were made in the newer generations of solar array regulators. These improvements positioned Boeing for more efficient high power satellites

References: 1. Boeing Satellite Systems information:

http://www.boeing.com/satellite 2. W. Krummann and H. Ayvazian, “The Hughes

601HP Spacecraft Power Subsystem,” Proceedings of the 33rd Intersociety Engineering Conference for Energy Conversion, August 1998

3. Robert Hill, “The Boeing 702 Spacecraft Power

Subsystem,” Proceedings of the 36rd Intersociety Engineering Conference for Energy Conversion, August 2001

4. Ashley, C., “Full Shunt Boost Switching Voltage

Limiter for Solar Panel Array,” U.S. Patent No. 5,504,418, April 1996.

200W/unit

190W/unit

52W/unit

55W/unit

Max. Power Dissipation

666W/KgEstimate ~ 30Kg

20KWCompact, soft switching, low noise,

low dissipation

702

251W/Kg2 x regulators = 31.8Kg

8KWSoft switching,lower switching

noise, low dissipation

601HP

190W/Kg2 x regulators = 21Kg

4KWHard switching solar array circuits,

high switching noise, low dissipation

601

245W/Kg5 x regulators = 8.16Kg

2KWLinearly shunting solar array circuits,

low EMI, high dissipation

376

Specific powerTotal weightPower Capabilitie

s

FeaturesBoeing Satellite

Product lines

200W/unit

190W/unit

52W/unit

55W/unit

Max. Power Dissipation

666W/KgEstimate ~ 30Kg

20KWCompact, soft switching, low noise,

low dissipation

702

251W/Kg2 x regulators = 31.8Kg

8KWSoft switching,lower switching

noise, low dissipation

601HP

190W/Kg2 x regulators = 21Kg

4KWHard switching solar array circuits,

high switching noise, low dissipation

601

245W/Kg5 x regulators = 8.16Kg

2KWLinearly shunting solar array circuits,

low EMI, high dissipation

376

Specific powerTotal weightPower Capabilitie

s

FeaturesBoeing Satellite

Product lines