PMS for the USV

The PMS of the USV open
The PMS of the USV closed
The PMS installed in the avionic bay of the USV

In the frame of a contract with CIRA (Centro Italiano Ricerche Aerospaziali) TSD enterely designed, developed and manufactured the Power Management System (PMS) for the Unmanned Space Vehicle (USV)  that has flown on february 2007.

The main tasks of the PMS are hereinafter listed:

to activate /deactivate the USV electrical loads
to allow the battery charging by means of  the signals coming from the Battery Charger
to send to the Battery Charger the HK data related to the battery during the charging phase
to decode activation /deactivation commands via the MIL-STD1553B I/F
to acquire all the Electrical Power System HK data and transmit them to the DHOB1 via  MIL-STD1553B I/F

The PMS functions are performed by means of four modules:

Battery Interface Management A (BIMA) for the primary battery management
Battery Interface Management B (BIMB) for the secondary battery management
Power Control Unit (PCU) for the power management and communication
Power Distribution Module A, B and C (PDMA, PDMB and PDMC) for the power control & distribution to the USV electronic subsystems and a backplane that implements also the routing of the power lines in addition to the routing of the analog and digital signals.

An internal power bus, providing, +28V, +5[VDC] power lines, is envisaged to supply all the PMS electronic modules. The communication between the modules takes place on a redundant internal RS485 bus, thus allowing future easy upgrading of the PMS. The use of FPGA device as communication and control device allows achieving high integration of the logic functions thus reducing the number of the electronic components.

USV PMS Main Specifications
 • MIL-STD 1553 bus I/F for command reception and housekeeping data transmission  • Power and Data I/Fs to two Batteries  • Two internal independent power buses distributing each 1.2 [KW] @ 30[Vdc]  • redundant output power lines with overload and short circuit protection
Total output power
 • 2.4[kW] @ 30[Vdc]
Current rating
 • up to 10[A] each power line
H/K Acquisition rate
1 Hz
Battery monitoring I/F SMBus
Power consumption

22 [W]

Dimensions 292 x 247 x 220 [mm]
16 [Kg]



Power Control Unit

The Power Control Unit represents the core of the PMS. Its main tasks are:

to receive, via MIL-STD1553B I/F, the  commands from the DHOB
to check that every received command is in the foreseen PMS command list and is compatible with PMS status
to manage the distribution of power to the specific USV electrical loads
to receive the command acknowledge from the PDM boards via RS485 serial bus
to acquire the voltage, current and temperature of the dc/dc converters located on the modules
to acquire the temperature of the cabinet, side wall and back-plane
to collect all the PMS HK data and send them to the DHOB via the MIL-STD1553B I/F

The PCU has two redundant DC/DC converters that deliver power to all the PMS electronic boards via the PMS internal power bus; the unit is based on the following functional blocks:

MIL-STD1553B Communication Engine (MCE) that acts as remote terminal
Field Programmable Gate Array (FPGA)
ATMEL 80C32 micro-controller
E2PROM in which the alarm thresholds are stored
RS485 interface for the data transmission/reception over the PMS1 serial bus
An analogue section that consists of the A/D converter and the signal conditioning circuits.

Power Distribution Modules

Three PDM modules are envisaged for the PMS named PDMA, PDMB and PDMC. Each PDM module distributes the power coming from the two PMS power buses to all the USV subsystems. Each PDM module is based on three main functional blocks:
PMS RS485 Serial Bus I/F for the communication with the PCU
Data acquisition for the monitoring of the PMS output power lines (Main & Redundant)
Redundant Solid state power controller array for the connection of USV loads to the PMS internal power buses (Primary power bus & Secondary power bus)

Each Power Controller is based on a solid-state relay. Each PDM module may be equipped with up to 16 power controllers, in particular:

8 Power controllers with maximum current of 1.5A (a 25% derating is already considered w.r.t. the value specified by the manufacturer)
8 Power controllers with maximum current of 7.5A (a 25% derating is already considered w.r.t. the value specified by the manufacturer)

Each USV subsystem is supplied by two Power Controllers (Main & Redundant). The mission critical subsystems are powered by two Power Controllers located on two different PDMs: in this manner, in case of a fault on the former PDM, the subsystem can be supplied by the latter one.

Battery Interface Modules

The main tasks of the BIM modules are hereinafter reported:

to connect the battery strings to the internal power bus
to acquire battery strings current and voltage via SMBus
to acquire the temperature of each battery string via SMBus
to acquire battery pressure
to acquire the charging relays status
to acquire bi-stable relays status
to acquire the current and voltage of the power bus
to provide an interface circuitry for the Battery chargers located in the Battery Charger


The main functional blocks of a BIM module are:

  Battery Charger I/F
  Battery activation devices consisting of two 50[A] hi-rel bi-stable relay SMBUS I/F
  RS485 I/F and data acquisition controller hosted in a FPGA
  Data Acquisition  based on 12 bit A/D converter for battery pressure acquisition, for power bus current monitoring

The activation of  the batteries is performed by using Hi-rel redundant bi-stable relays. Their activation is controlled by an equipment (EGCE Battery Charger functionality) external to the PMS. This solution is typically adopted in applications requiring high reliability to avoid to have the activation of the PMS batteries under the S/W control. In this case, in fact, a failure of the S/W could produce a undesired deactivation of the battery with  a catastrophic impact on the mission. The bi-stable relay is the only switching device that is able to hold the activation status even if the activation signal is removed. This feature allows to perform, on Ground, an irreversible activation.

The battery charger is located outside the PMS. It is a functional module of the EGCE equipment. The PMS is only equipped with a interface circuit with the charger hosted  in the EGCE. This interface is located in the PMS BIM modules.