Inverters Flashcards
What does an inverter do?
changes DC electricity into AC
Whether part of a grid-direct or battery-based system, an inverter changes DC into AC electricity. Some (but not all) battery-based inverters also include a battery charger, which takes AC from the grid or a generator and converts it to DC to charge the batteries.
In order to meet _______________ requirements, if utility power shuts down, a grid-direct inverter must also shutdown
anti-islanding
During a utility outage or maintenance, an “island” can be created by a power source supplying electricity to a portion of the grid that is thought to be de-energized. There have been incidents where workers have been electrocuted by backup generators improperly connected to a customer’s AC service panel. To ensure that a grid-direct PV system does not create an “island,” UL and IEEE standards require the inverter to shut down immediately in the event of the loss of grid power. These inverters may be called ‘anti-islanding’ inverters
Select the two most important parameters when choosing a specific grid-direct inverter
AC output voltage;
Inverter power rating in watts
First, the AC output voltage must match the grid voltage at the installation location. Second, the inverter power rating must be able to process the DC power from the connected module or array, otherwise there will be wasted power. If the connected module or array ‘overloads’ the specified inverter, either a second inverter can be installed, or a larger power inverter should be used.
What is the likely outcome of this? Array Vmp less than inverter minimum input voltage: _____
Inverter operates at lower than optimal power or may not operate at all
If the maximum power voltage (Vmp) of the array is less than the minimum inverter input voltage, the system will operate at lower than optimal power (off of the maximum power point) and, if the voltage is so low that it is completely out of the inverters DC operating voltage window, it will not operate at all. In a particularly bad design, the inverter also may shut down when the array temperature is high on hot summer days.
If the open circuit voltage (Voc) of the array exceeds the maximum inverter DC input voltage, the inverter may be damaged and/or the warranty voided. Most inverters record the maximum input voltage, so the manufacturer will know if excess voltage damaged the inverter, which isn’t covered under warranty
What is the likely outcome of this? Array Voc greater than inverter maximum input voltage: _____
inverter damage and/or voided warranty
If the maximum power voltage (Vmp) of the array is less than the minimum inverter input voltage, the system will operate at lower than optimal power (off of the maximum power point) and, if the voltage is so low that it is completely out of the inverters DC operating voltage window, it will not operate at all. In a particularly bad design, the inverter also may shut down when the array temperature is high on hot summer days.
If the open circuit voltage (Voc) of the array exceeds the maximum inverter DC input voltage, the inverter may be damaged and/or the warranty voided. Most inverters record the maximum input voltage, so the manufacturer will know if excess voltage damaged the inverter, which isn’t covered under warranty
To operate the connected PV array at the “knee” of its I-V curve, grid-direct inverters use _______________________
maximum power point tracking
Grid-direct inverters monitor the actual array operating characteristics so that the most power is produced continually. Maximum power occurs at the “knee” of the I-V curve of a module or array, where the product of Vmp and Imp equals the maximum power the module or array is capable of producing (under the specific environmental conditions it is experiencing). The maximum power point is the point with the highest possible wattage output (power) of any point on the I-V curve