How Big Inverter Improves Profitability of PV Power Plants

The yield of photovoltaic power plants has historically been a topic of concern to various power investors and power generation companies. There are many factors that affect the profitability of photovoltaic power plants, including initial investment costs, later-stage operation and maintenance costs, and power generation. Considered from the inverter side, the main factors affecting the yield are the installation and maintenance of the inverter, the initial construction investment, power generation, and reliability.

In recent years, various inverter manufacturers have introduced a number of more advanced photovoltaic grid-connected inverters through continuous R&D and innovation to meet the high yield requirements of customers. TC500KH is the latest generation of inverter products of TBEA. After a comprehensive upgrade of hardware, software and structure, the maximum conversion efficiency is as high as 98.7%, European efficiency is as high as 98.4%, and MPPT tracking efficiency reaches 99.5% (Dynamic, respectively). ) and 99.9% (static), power density reached 277W/kg, with strong market competitiveness.


TC500KH renderings

First, how does TC500KH achieve 98.7% conversion efficiency?

The factors affecting the conversion efficiency of the inverter are mainly composed of hardware factors and software factors. The hardware factors are mainly composed of power device loss, filter reactance loss and heat dissipation fan loss. The software factors are mainly affected by the modulation algorithm.

(1) How to reduce power device loss?

The power device converts the DC output from the PV array into an important part of the AC power. It is the core of the inverter. The loss of this part accounts for the largest proportion of the total inverter losses. Reducing this part of the losses will make the entire inverter Conversion efficiency has been greatly improved.

a. Adopt latest generation NPT IGBT

The NPT type IGBT is a single-crystal non-through power semiconductor device. Compared with the conventional PT type IGBT device, this device has the advantages of small switching loss and good high temperature characteristics. The following figure shows the turn-off waveforms of the PT-type IGBT and the NPT-type IGBT. It can be clearly seen that the switching loss of the NPT-type IGBT is much smaller than that of the PT-type IGBT.


PT IGBT Turn-Off Waveform NPT IGBT Turn-Off Waveform

b. SVPWM modulation algorithm with minimum switching loss

The minimum switching loss SVPWM algorithm means that each phase switch does not operate at 120 degrees within one cycle, the total effective switching times is reduced by 1/3, and the power device does not operate in the positive and negative peak areas of the current, which reduces the full load loss of the inverter by 1400 W. Effectively reduce power device losses.


Traditional SVPWM Modulation Strategy Minimum Switching Loss SVPWM Modulation Strategy

(2) How to reduce the loss of the filter reactor?

The filter reactor has the function of converting the square wave output from the power device into a sine wave, which is an important link for ensuring the power quality of the inverter output. TC500KH grid-connected inverter adopts LCL filter design and has better high-frequency attenuation characteristics. Compared with the L-type filter, the total inductance is smaller. Compared with the LC-type filter, the three-phase grid-connected system has better filtering effect and higher power quality.

The loss of the filter reactor is mainly composed of iron loss, copper loss and stray loss. The iron loss is related to the quality and quantity of the silicon steel sheet; the copper loss is related to the winding process of the winding and the passing current; the stray loss is related to the leakage inductance. Reducing iron loss has a significant effect on reducing reactor losses and improving inverter efficiency. So the conjugate reactor designed by magnetic integration technology was successfully applied in the inverter. The reactor is a conjugate design of two inductors, which can cancel part of the magnetic circuit in the iron yoke and reduce the amount of silicon steel. ,Reduce reactor iron loss, improve reactor efficiency.


Conjugate reactor design

Before and after reactor optimization:

The magnetic circuit can be seen from the figure that the magnetic path of the yoke 1 and the iron yoke 3 cancel each other in the conjugated iron yoke 2, and the loss of the iron yoke 2 will be small, and the overall efficiency can be improved. The magnetic circuits of the iron yoke 2 and the iron yoke 3 are independent of each other, and the magnetic circuits cannot cancel each other to generate the iron yoke loss, which affects the efficiency.

(3) How to reduce the loss of cooling fan

The heat dissipating fan is responsible for the function of ventilating and dissipating the internal heat-generating components of the inverter, and is an important part of ensuring the stable operation of the inverter. The loss of the heat dissipating fan is also a non-negligible part of the total loss of the inverter.

In order to reduce the loss of heat dissipation fans, we must start with the selection of fans. Choosing a cooling fan with low power consumption and brand name is one of the most effective methods to reduce the loss. Fans can also cause problems that cannot be ignored - the amount of exhaust air is reduced. In order to achieve the optimized heat dissipation function with the least loss of the fan, the components' structure and air duct must be properly designed. After a series of optimized designs, the low-power cooling fan with intelligent speed control function is applied to the inverter, its power consumption is only 450W, and the loss is reduced by 44% compared to the constant speed fan, and the heat dissipation is reduced. The power consumption of the system ensures the reliability of the heat dissipation of the inverter.

Second, how does TC500KH have extremely high reliability?

(1) Reliable heat dissipation design

The TC500KH adopts the heat dissipation mode of the front air inlet and the rear high air outlet. According to the temperature class of each component, the TC500KH is rationally laid out. It utilizes fluid inertia and negative pressure buoyancy to perform scientific shunting of cold air, making all power devices The temperature has reached a strict derating standard, and the heat dissipation efficiency has been greatly improved to ensure long-term stable operation of the equipment.

Through the thermal simulation at an ambient temperature of 50°C and an altitude of 3000m, it can be clearly seen that the superiority of the TC500KH heat-dissipating system design does not exceed 100°C for the IGBT of the core device (the maximum allowable core temperature for the IGBT is 175°C).


Inverter speed field Inverter temperature field

(2) Reliable protection design

a. Cabinet surface protection design

The protection design of the external cabinet is mainly based on the selection and surface treatment of the shell material. The TC500KH grid-connected inverter housing is assembled from high-quality hot-dip galvanized sheet. The surface of the cabinet is electrostatic powder coating and treated with common cold-rolled steel sheet. Compared with anti-corrosion performance, the strength is better, and it can effectively resist the invasion of sand.

b. Protection design of the air inlet of the cabinet

As the most direct protection device of the inverter, the air filter plays an important role in the protective effect of the cabinet. The TC500KH grid-connected inverter is equipped with a double-layered air filter at the air inlet to effectively prevent dust from entering the cabinet and protect internal components from dust.


Inside the air intake outside the inlet

c. Protection design of cabinet gaps

The gap treatment of the cabinet is very important for the protection performance of the whole machine. Under normal circumstances, the gap mainly occurs at the door panel. In order to ensure the airtightness of the internal air duct, the TC500KH grid-connected inverter adopts a closed design at the rear and both sides of the cabinet to prevent dust from entering the cabinet from the door panel gap. In addition, the edge of the outer frame of the cabinet is flanged and the inside edge of the door is equipped with a sealed foam. When the door is closed, the foam fits the flange and the dust cannot enter through the gap in the door.


Sealing foam location

d. Protective design of the control section

The inverter control section is mainly composed of PCBA. This part is less tolerant to dust and requires more rigorous protection. First, the TC500KH grid-connected inverter provides peripheral protection by encapsulating the control part in the module. Secondly, the circuit board is subjected to two anti-coating processes twice to protect the circuit board from dust. The three anti-paints have good resistance to high and low temperature performance. After curing, they form a transparent protective film with superior insulation, moisture, leakage, shock, dust, corrosion, aging, and corona resistance.


Three anti-paint coating effect chart

(3) Reliable high altitude design

The impact of altitude on electrical equipment is mainly reflected in three aspects: 1 low temperature, poor working conditions of electronic devices; 2 low air pressure, electrical insulation is affected; 3 thin air, poor heat dissipation conditions. In order to ensure that the inverter can operate reliably at high altitudes, the impact of these three aspects on the inverter should be fully considered in the design.

Low temperature: The ambient temperature in high altitude areas is low, and the temperature in some areas is even lower than -40°C, which seriously affects the reliability of the operation of electronic devices. The TC500KH grid-connected inverter can quickly increase the internal temperature of the cabinet to a reasonable range by configuring the heater inside the inverter to ensure that the inverter can operate reliably at low temperatures.

Low air pressure: Low air pressure will cause the breakdown voltage of the electrical clearance to decrease, affect the insulation of the electrical equipment, and increase the possibility of breakdown at high voltage. The TC500KH grid-tied inverter is designed strictly in accordance with the high-altitude standard and the electrical clearance is designed to be 1.5 times higher than the standard altitude.


Clearance correction factor table

The air is thin: In the thin air, the density of the air is reduced, resulting in poor thermal conditions of the inverter. The TC500KH grid-connected inverter fully considers the influence of altitude in the design, and through multiple thermal simulations and experimental comparisons, reasonably optimizes the layout of the heating device in the air duct; in addition, the optimal selection and design of the radiator and the cooling fan are performed. The inverter can still operate at full power when it meets an altitude of 3000m and an ambient temperature of 50°C.

Third, how can TC500KH reduce investment in power plant construction?

TC500KH as a high power density inverter, the whole size of only 1500mm × 2150mm × 850mm (width × height × depth), occupying a small space, can effectively reduce the inverter room area, reduce the inverter room construction Investment is of great significance in reducing the initial construction cost of the power station.

Fourth, how to reduce the cost of operation and maintenance of TC500KH?

The design of TC500KH grid-connected inverter fully considers the influence of power station maintenance on the on-site power generation, and thus reasonably optimizes the structural layout of the inverter. By packaging heat dissipation fans, control systems, and three-phase IGBTs into a single module, after the fault location, the operation and maintenance personnel can pull out and replace the faulty module. The replacement time of a single module does not exceed 20 minutes, reducing the impact of equipment failure on the power generation. To the lowest.


Pre-modular maintenance

V. Summary

As one of the core power generation equipments of photovoltaic power plants, inverters play a crucial role in improving the overall profitability of power plants. Adopting grid-connected inverters with high efficiency, high reliability, high power density, and good maintainability can provide users with higher yields, lower construction investment, and lower maintenance costs for photovoltaic power plants. The high yields escort.

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