The main features are:

2.2.1 Power Circuit
2.2.2 Control, Protection and Interface
2.2.3 Mechanical Arrangement
2.2.4 Cooling System

(Ref. SLA-650-01-01 to SLA-658-01-01)

The drawings used to describe the power supplies are shown in the power circuit schematics of SLA-650-01-01 to SLA-658-01-01. The power circuit is discussed under:

• Input Section
• Converter Section
• Output Section

Input Section

• This section contains the circuit breaker (CB1) with input current protection, contactor (CR1), EMI filter, diode bridge (BR1) and dc bus filters (LF and CF1). The input power cables are connected to the power inlet at the rear of the power supplies and then to the circuit breaker located at the front of the units.
• The EMI filter that keeps the input line conducting emission to within FCC Class A limits is placed between the circuit breakers and the contactor.
• The main input isolation is the contactor CR1. The bypass lines with fuses F1 to F3 and resistors R1 to R3 provide a soft charging of the dc bus filter.
• The line-to-line voltage is routed from the output of the EMI filter to the control transformer (TRC) for control logic supplies.
• The dc bus section starts with a three phase air cooled diode bridge module. The LF reactor inductance and the dc bus electrolytic capacitors (CF1) constitute the dc filter with low roll-off frequency 90 to 130Hz to reduce the 360Hz ripple.
• The discharging resistors (RCF) are connected across the dc bus capacitor bank to discharge the capacitors in the off state.
• The dc bus electrolytic capacitors are separated from the input to the IGBT power converter stage by a high frequency choke (LHF) in order to keep their ac current components low.
• The semiconductor grade fuse (FDC) protects the input in case of an IGBT failure.
• The input, output and control sections are isolated from the converter section by metal shielding, to reduce EMI noise.
• One small 120V fan (34CFM) provides cooling to the input, output and control sections for the 10kW and 15kW units.

Converter Section

• The full bridge converter consists of 2 dual IGBT switches, a high frequency step down transformer and secondary ultra fast diodes in a push pull rectifier configuration. All the components are air cooled. There is one low ESR, high RMS current capacitor (CHF1) connected directly to the input of the IGBT switch power module. This provides the low impedance necessary for high current pulses at this stage.
• The main components of this power module (full-bridge converter) are dual IGBT power transistors. These have been selected to operate well within their safe operating area (SOA). In order to protect them from voltage overshoot during the off transition period, a RDC snubber network with very fast diodes and high current pulse capacitors is installed directly on the IGBTs. The converter frequency is approximately 20kHz which is high enough to avoid any audible noise without appreciably increasing the switching losses.
• Two ball bearing fans (100CFM/fan) provide the forced air cooling for the converter module, the IGBT snubber diodes, the HF power transformer (TR1) and the output dc choke (LO1).
• The HF power transformer has a centre tap two winding secondary in order to reduce the number of output rectifier diodes output losses to a minimum.
• The current sensed on the transformer primary side via a current transformer with a 1000A/1A ratio is used in an inner current loop to ensure the symmetry of the transformer current pulses and to limit it in case of any secondary overcurrent situation.

Output Section

• The output of the secondary ultra-fast rectifier stage produces a square voltage waveform of a variable duty cycle and fixed 40kHz frequency.
• The output current is sensed by a LEM current sensor. This signal is used for output current monitoring and current sharing in the case of parallel operation.
• One set of output voltage sensing resistors connected directly to the output diode section is used in an inner voltage loop to ensure a fast response on any line/load change.
• The other set of output voltage sensing resistors is connected to the final power supply output. This signal is used for output voltage monitoring and precise voltage regulation.
• The free wheeling diodes protect the output from reverse voltage and provides a load current path when the power supply is turned off.
• The switching harmonics are filtered out via an LC output filter (LO1, CO1, CO2 and RC).
• The next filter stage (LO2, COUT and busbar sandwiches) located in the EMI isolated section, filters out the very high frequency components.
• The ground resistor (RG) located in the output section, connected between the negative output bus and chassis ground, provides the ground monitoring signal. The provision for a positive bus ground resistor connection is also made.

(Refer to Drawing No. SLA-650-05-01 to SLA-658-05-01)

The following printed circuit boards are designed to meet the regulation, control, protection and interface requirements described in the specifications:

Switch Regulation and Control Board (SWRCB)		IP-30422, Rev. 2.1
Dual IGBT Board (DGDB)		IP-30452
Transformer Bias Board (TBB)		IP-30451. Rev. 0.1

Switch Regulation and Control Board (SWRCB)

This board has the following sections:

• Logic Power Supply Section
• Output Driver Section
• Control Logic Section
• Regulation Section
• Monitoring and Protection Section

Logic Power Supply Section

• On board mounted electronic supply section uses an external control transformer 240/120V:36VCT to provide ±15V, +24V voltages to the SWRCB electronics.
• The 480V line fed units use an intermediate 480/120V step transformer and the 208V line fed units do not.

Output Driver Section

• The output driver section provides the driving pulses for the IGBT gate pulse transformers located on the DGDB boards next to the IGBT switches.

Control Logic Section

The control logic section includes:

• Start/Stop/Reset Logic: receives remote On/Off/Reset commands via input opto-couplers. Enable/disable the outputs to contactor and IGBTs. The off command automatically reset all the faults.
• Protection Logic: inhibits the regulators and IGBT gatings and trip the input contactor upon faults. All the faults are latched until the Reset or Off command are received.
• Status and Fault Annunciation: local displays are on the front panel LEDs. Remote signals are sent to a DB25 connector (J1).

Regulation Section

The regulation section consists of the circuitries for the following functions:

• Output Current Limiting
• Output Voltage Regulation (PI Controller)
• Inner Voltage Loop Regulation (P controller)
• Transformer Primary Current Regulation
• Triangular Wave Generator
• Pulse Width Modulation

This section performs the output voltage regulation and current limiting for the power supply.

• In stand-alone CV mode (Constant Voltage) operation, the output voltage is closed-loop regulated by a PI regulator based on the output voltage sensing and the remote program voltage. The output of this regulator is the reference signal for the inner voltage regulator.
• The output current limiter is in an 'OR' connection with the output voltage loop. It takes over the output regulation when the current limiter is set lower than the output voltage demand.
• The inner voltage regulation is employed to improve the system dynamic response. Its input is the rectifier secondary voltage. Its output is the reference of the inner most regulation stage of the transformer primary current regulation.
• The primary current regulator regulates the transformer primary current to insure proper line regulation as well as to reduce the 360Hz voltage ripple at the power supply output. Its output signal sets the level for pulse width modulation.
• The pulse width of the gating signals to the IGBTs is determined by the 20kHz ±3kHz triangular wave and the primary current regulator output level. The gating signals are taken from this board to the IGBT driver boards (DGDB) mounted directly on the IGBT modules.
• The primary current limiter circuitry is used to restrict the pulse width in case of excessive transformer primary current. This limiter clamps the pulse width to zero before the Start or in case of pulse inhibit status. When released, the limiter output level is gradually increased in order to avoid any excessive current due to a possible output short circuit.

Monitoring and Protection

• The output voltage and current is monitored by the two front panel three (3) digit (red LED) meters.
• The status and protection LEDs are located at the front panel display (see paragraph 2.1.9).
• The protection includes:
  • Primary Overcurrent (POC)
  • Output Overcurrent (OC)
  • Output Overload (OL)
  • Heatsink/Transformer Overtemperature and Charging Resistors Overload (OT)
  • Electronic Supply Fault (ELSPY)

(Ref. Dwg. No. SLA-650-03-01 to SLA-658-03-01 and SLA-650-03-02 to SLA-658-03-02)

The mechanical arrangement of the power supplies is based upon a NEMA 1 chassis construction, sized to fit standard 19" rack mounting. The power conversion section is separated by a metal shield from the input/output/control section for maximum EMI reduction. The power input/output connections are at the rear of the cabinet. The air openings at the front of the cabinet provide sufficient air intake. Dimensions of the power chassis are 5.25"H x 19"W x 22"D for 5kW units and 8.75H x 19"W x 22"D for 10kW and 15kW units.

The layout of the front/rear panel as well as the internal arrangement of the power supplies are as shown in drawings SLA-650-03-01 to SLA658-03-01 and SLA-650-03-02 to SLA-658-03-02.

The unit semiconductors are all placed on one air cooled heatsink and provide a compact power module design.

The power supply utilizes forced air for IGBTs, fast diodes and diode bridge heatsink assembly, as well as for magnetic components. The two fans, 100CFM mounted directly on the front of the heatsinks insure sufficient cooling for the semiconductors. For 10kW and 15kW units, another fan provides the necessary cooling to other magnetic components, snubber resistors, electrolytic and capacitors. The air intake opening is located at the front of the chassis. The magnetics are designed to require minimum air flow to stay within temperature specifications.

The main design features meet the Customer specification no. PS-340-250-01-RO.

(Ref. Dwg. No. SLA-650-03-01 to SLA-658-03-01 and SLA-650-003-02 to SLA-658-03-02)

The mechanical design of the power supplies are based on the customer's specifications and good shielding/layout practices. The cabinet is divided into 2 sections.

• Input/Output/Control Section
• Power Conversion Section

Both sections are described in Section 2.2.1 and 2.2.3. The power supplies are housed in two different chassis sizes; 5kW units are 5.25"H x 19"W x 22"D; and the 10kW and 15kW units are 8.75"H x 19"W x 22"D. All the customer interconnections, both input/output power and control/monitoring are located at the rear of the power supply. The mechanical design ensures that the power supply will survive the random vibration tests.

The basic electrical design considerations include:

• Electrical input/output/ground isolation as specified in the Customer Specification, Section 2.3.
• EMI input power lines conducted emission limits as per FCC rules, Part 15, Class A.
• Derating of the components according to the Customer's Specification, Section 6.0.
• Provision for the power supplies parallel operation with other power supplies of the same rating.
• Input power factor and power supply efficiency according to the Customer Specification Section 2.2.
• Reliable operation under abnormal input voltage and in case of loss of input phase as per Customer Specification, Sections 2.1.7 and 2.1.8).
• Power supply protection which surpasses the Customer Specification Sections 2.2.12 and 3.3.
• The bus bars used are sized such that their temperature rise is kept less than 10°c under worst operating conditions.
• The cables used are Tefzel and Teflon. These insulated conductors do not contains any asbestos, halogens or PVC and are fire retardant. The temperature rating of the cable is 120°C minimum.

The worst case component ratings are established to meet the specifications of the power supplies. The design margins are based on Inverpower experience and the requirements of the specifications.

The recommended spare parts listing is also given.