3 The Converter Unit
3.1 Introduction
The Converter Unit contains the power electronics of the eSite Modular system, i.e. the rectifiers and the solar converters. The Converter Unit is sealed and tamper-proof, preventing users from opening the unit and unintentionally damaging it. This also protects the user from contact with high-temperature components and dangerous voltage levels.
eSite Modular can use AC power from grid and/or genset and DC solar power to support the customer load.
The Converter Unit is available in three different versions:
RSE
Rectifier capacity: 10.5 kW (3 x 3500 W) Solar Converter: 6.6 kW (3 x 2200 W)
RE
Rectifier capacity: 10.5 kW (3 x 3500 W)
SE
Solar Converter: 13.2 kW (6 x 2200 W)
Warning
Do not open the Converter Unit. Opening the Converter Unit can result in serious injury. The Converter Unit does not contain any user serviceable parts.
Caution
In case of severe failure or performance deviations, the Converter Unit must be returned to eSite Power Systems along with a replacement report. A Return Material Authorization (RMA) number is provided from eSite Power Systems. The RMA number must be clearly labelled on the returning box to eSite Power Systems for the warranty issue to be processed.
3.2 Rectifiers
The RE and RSE Converter Units converts input AC supply via 3 AC/DC rectifiers into -48V DC. The rectifiers provide a maximum of 3.5 kW per unit, for a total of 10.5 kW. The input from the AC source(s) is continuously monitored on all phases to ensure that the most efficient AC source is used. Switching between the connected AC sources is automatic.
3.2.1 Silicon Controlled Rectifier (SCR)
The eSite patented Silicon Controlled Rectifier (SCR) functionality is designed to improve the performance of the system compared to a traditional Automatic Transfer Switch (ATS). Both an ATS and SCR allows for switching between two AC sources, but while the ATS is based on mechanical switching, the SCR uses power semiconductors.
The advantages of SCR include
No moving parts that are sensitive to dust and wear.
Unlimited number of cycles.
Automatic control of the AC input with adaptable thresholds remotely through eSite Tools.
Overvoltage protection. Input with overvoltage condition is immediately disconnected to protect the rectifier and the system from wiring faults.
No separate voltage supply is required for SCR to operate.
No manual bypass switch is required. SCR is incorporated into the Converter Unit and the power lines run separately.
Individual control of each AC phase. One SCR per rectifier.
3.2.2 Electrical protection
eSite Modular is equipped with extensive high voltage protection. It withstands electrical hazards such as lightning-induced voltage spikes, malfunctioning gensets or poor grid stability. This is not only prevented from causing damage, but all incoming surge energy is converted into useful energy. The protection is automatic with no need for a manual reset.
Figure 3.1. illustrates electrical surges from the grid and/or genset(s) divided into different areas.
Surge pulses usually caused by lightning. Gas discharge tubes are used in the input AC stages together with varistors and capacitors to dampen the pulse to a manageable level.
Combination of surge pulses from lightning and voltage spikes from the grid due to inductive switching, poor grid stability, and long transmission lines. The spikes can also derive from gensets with malfunctioning Automatic Voltage Control (AVR). Carefully selected components in the SCR absorbs these pulses without breaking the affected components.
Long lasting voltage increases from the grid and gensets. Increases can be caused by incorrect wiring resulting in 400 V AC instead of 240 V AC. SCR disconnects the voltage source. The voltage is constantly monitored and when in the allowed range, the voltage source is automatically reconnected.
Figure 3.2 shows surge areas in which the rectifiers in the eSite Modular system are protected. The rectifiers are protected from disturbances located in all three areas (A, B, and C).
The only regulatory demand for rectifiers is to be protected from electrical surges in area A. With additional Surge Protection Device (SPD) area B can also be protected but region C remains unprotected.
3.2.3 Rectifier efficiency and derating
The current limit is 19 A for each rectifier, due to that the power output will be reduced at lower AC voltages. Figure 3.3 shows the power derating vs input voltage below 45 °C.
The peak rectifier efficiency is at 95 %. The overall power system peak performance is at 94 %. Figure 3.4 shows the rectifier efficiency measured in watt per rectifier.
3.3 Solar converters
In the RSE and SE Converter Units, DC power from the solar panels is converted via internal solar converters into -48V DC. Each converter provides a maximum of 2.2 kW and is designed as a non-isolated step down DC/DC converter that is protected against ground faults, reversed polarity, and over voltages.
The performance of each converter is optimized with a dedicated Maximum Power Point Tracker (MPPT) algorithm that continuously maximizes power output from the panels. The solar converters are tightly integrated with the rectifiers and the battery charge strategies to optimize the use of solar power.
3.4 Convection cooling
The eSite Modular Converter Unit is cooled using passive convection cooling (see figure 3.5). The solution is constructed to perform adequate cooling without any fans, filters, or moving parts.
All electronics are sufficiently cooled.
No system power is needed for cooling.
Minimized maintenance and no moving parts that require repairs.
Completely silent.
3.5 Technical specifications
Mounting
Frame support on cabinet
Height x Width x Depth (mm)
995 x 541 x 234 (mm)
Weight (kg)
RSE: 65 kg, RE: 60 kg
Type
Dual single-phase inputs to each rectifier, controlled via solid-state transfer switch, no moving parts
Nominal
230 - 250 VAC
Range
85 - 300 VAC
Frequency
45 - 65 Hz
Input Current
3 x 19 A
Power Factor
>0,99
THD
< 5% at 230 VAC, 100 % load
Input Voltage Derating
Linear derating for each phase starting at 190 VAC, down to 1500 W@85 VAC
Protection
Varistor transient protection of all phases towards neutral Varistor and GDT transient protection towards protective earth Solid state transfer switch for long duration over voltages
Operational Range
-42 to -58 VDC
Rectifier Capacity
3500 W
Total Output Power (RE/RSE models)
10500 W
Current
195 A @ 54 VDC
Max Current
235 A
Output Power Derating by Ambient Temperature, Continuous Operation (230 VAC)
Continuous power at 45 ⁰C: 9750 W Continuous power at 50 ⁰C: 8500 W
Output Power Derating by Ambient Temperature, Cyclic Operation (230 VAC). Full power is available again after a cooling period of ~45 minutes.
Full power at 45 ⁰C for 65 minutes, then derating to 9750 W Full power at 50 ⁰C for 40 minutes, then derating to 8500 W
Rectifier Peak Efficiency
95 % (including solid state transfer switch)
DC Power System Efficiency
94 % (including all MCB:s, cooling power and DC distribution)
Nominal Input Voltage
125 VDC
Permitted Input Voltage Range
50 - 150 VDC
Power Conversion Capacity
2200 W (RSE/SE)
Maximum Input Current
20 ADC
Power Conversion Peak Efficiency
> 96,5 %
Nominal Temperature
-20 to +45 °C
Operating Temperature
-20 to +50 °C
Storage Temperature
-40 to +70 °C
Relative Humidity
0 to 99 %
Cooling
Passive Convection Cooling
IP Code
IP65 Conversion part, IP54 Connection part
EMC
ETSI EN 300 386 V1.6.1
Safety
EC/EN 60950-1, EC/EN 60950-22 IEC EN IEC 62368-1:2014
Environmental Standards
ETSI 300 019-1-2 Class 2.3 Public transportation ETSI 300 019-1-4 Class 4.2H Stationary use at non-weather protected locations – extremely warm dry CE and RoHS compliant
MTBF
>350 000 h (@T ambient 25 °C) according to Siemens SN29500
Isolation
3.0 kVAC mains – Earth 1.5 kVAC mains – Sec 707 VDC mains – Earth
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