NB/T 32004-2018Technical specification of PV grid-connected inverter (English PDF)

3.1 Photovoltaic grid-connected inverter

A device that converts the direct current output from the photovoltaic array into alternating current and feeds it into the power grid.

Note 1. Inverters mentioned in this standard all refer to photovoltaic grid-connected inverters.

Note 2. The technical requirements and test methods specified in this standard are not applicable to inverters in AC components.

3.2 Preparatory photovoltaic inverter

Box-type or box-type combined photovoltaic grid-connected inverter devices including inverters, power transformers, high and low voltage switchgear and control equipment, including containerized type. The typical AC rated voltage level at high-voltage side is between 3.6 kV and 40.5 kV.

3.3 Photovoltaic array simulator

A power source that simulates the static and dynamic current and voltage characteristics of a photovoltaic array.

3.4 Inverter a.c. output terminal

The connection point for the external output power on the AC side of the inverter.

3.5 Isolated inverter

An inverter with electrical isolation between the AC output circuit and the photovoltaic DC input circuit.

Note: This kind of electrical isolation can be realized inside the inverter, or it can be realized by a combination of external independent dedicated isolation transformers on the AC side as required during use.

4.1 Classification by the number of output phases on the AC side

According to the number of output phases on the AC side, it can be divided into.

- Single-phase inverter;

- Three-phase inverter.

4.2 Classification by installation environment

According to the installation environment, it can be divided into.

- Indoor Type I (with temperature adjustment device);

- Indoor type II (without temperature adjustment device);

- Outdoor type.

4.3 Classification by electrical isolation

According to the electrical isolation, it can be divided into.

- Isolated type;

- Non-isolated type.

4.4 Classification by access voltage level

According to the access voltage level, it can be divided into.

- A type inverter.

Refers to photovoltaic inverters used in photovoltaic power stations that are connected to the grid through voltage levels of 35 kV and above, or connected to the public grid through voltage levels of 10 kV and above;

- Type B inverter.

Refers to photovoltaic inverters used in photovoltaic power generation systems that are connected to the grid through a voltage level of 380 V and connected to the user side of the grid through a voltage level of 10 kV and below, including inverters used in residential environments and directly connected to residential low-voltage power supply network facilities.

Note: In the electromagnetic compatibility test of the inverter connected to the grid via an independent power transformer, the type A limit is adopted.

4.5 Classification by other factors

Other types not listed above but declared by the manufacturer.

5.1 Temperature

The ambient air temperature range of the indoor inverter. indoor type I. 0 °C ~ +40 °C; indoor type II. -20 °C ~ +40 °C.

The ambient air temperature range of the outdoor inverter. -25 °C ~ +60 °C.

5.2 Humidity

Indoor relative humidity range. Indoor type I. 5% ~ 85% without condensation; Indoor type II. 5% ~ 95% without condensation. Outdoor relative humidity range. 4% ~ 100%, with condensation.

5.3 Altitude

The altitude of the installation site does not exceed 2000 m. When the altitude of the inverter installation site is greater than 2000 m, it shall consider the decrease of electrical dielectric strength.

5.4 Shock and vibration

The inverter may be subject to shock and vibration during production, transportation, installation, operation, maintenance. Reasonable precautions are required to avoid damage. The method specified in 11.6.4 shall be used for verification.

5.5 Transport and installation

For inverters above 50kg, it must indicate the center of gravity of the inverter on the package to facilitate transportation and handling. If the transportation and installation conditions of the inverter are different from those specified in Chapter 5, the manufacturer and user shall reach a special agreement.

5.6 Enclosure protection

Outdoor inverters must meet the minimum IP54 requirements; indoor inverters must meet the minimum IP20 requirements.

5.7 UV exposure

The polymer material of the outdoor inverter enclosure shall have sufficient resistance to material aging caused by ultraviolet (UV) radiation; it needs to be evaluated for resistance to ultraviolet radiation or provide a third-party qualified test report. After the UV radiation test, the sample shall show no obvious signs of deterioration, including cracks or breaks. If the degradation of the component does not affect the protection it provides, the requirements of this clause can be ignored.

6.1 Temperature limit

The temperature of the materials and components used in the equipment must not exceed the limits specified in Table 1 to Table 3. In general, if the inverter's related components or their surface temperature does not change more than 1 °C/h, it is considered that the inverter has reached a thermally stable state.

Under full power conditions, the temperature rise test lasts for up to 7 hours (simulating one day's sun exposure), except that if a longer test can prove that it will produce greater danger.

6.2 Electric shock protection requirements

6.2.1 Direct contact protection requirements

6.2.1.1 General requirements

a) To prevent people from directly contacting live parts that cause harm to people, the measures to prevent direct contact shall be achieved through one or more of the measures specified in 6.2.1.2 or 6.2.1.3.

b) Open components and devices do not need to take protective measures against direct contact, but their operating instructions must clearly require the necessary protective measures to be provided after the installation of the final product is completed.

c) Inverters scheduled to be installed in enclosed electrical operation areas do not need to take protective measures against direct contact. If maintenance personnel need to energize it during installation or maintenance, the protective measures shall meet the requirements of 6.2.1.2.3.

6.2.1.2 Enclosure and barrier protection

6.2.1.2.1 General requirements

Provide a protective enclosure and safety barrier; its parts shall not be disassembled without tools. Polymer materials that meet these requirements shall meet the requirements of 6.1 and 6.5 at the same time. When the inverter is used outdoors, the polymer enclosure of the inverter must meet the requirements of 5.7 when exposed to sunlight.

6.2.1.2.2 Requirements for protection against contact

a) After passing the enclosure and safety protection, the distance between people and live parts must meet the following requirements.

1) The voltage of live parts is less than or equal to the specified safe voltage - It is accessible;

2) The voltage of live parts is greater than the specified safe voltage - It is not accessible, meanwhile there must be sufficient electrical clearance between the live parts.

Note: The safety voltage limit is specified in accordance with the requirements of the standard GB/T 3805.

b) The inverter adopts enclosure or shielding protection; it shall be inspected according to the method of 11.2.2.1, to prevent the dangerous live parts from being touched.

6.2.1.2.3 Maintenance personnel contact area

When the enclosure needs to be opened during installation or maintenance, meanwhile the inverter needs to be energized, protection against contact shall be provided for live parts with a voltage greater than the specified safe voltage that may be unintentionally touched during the maintenance process. The protection requirements shall be inspected according to the method of 11.2.2.1.

6.2.1.3 Insulation protection of live parts

Insulation shall be determined according to the impulse voltage, temporary overvoltage or working voltage of the inverter; the most severe condition shall be selected according to the requirements of 6.2.3. Without the use of tools, the insulation protection shall not be removed.

6.2.2 Requirements for indirect contact protection

6.2.2.1 General requirements

a) In the case where the insulation between the contactable conductor and the live parts of the inverter fails, in order to prevent contact with the current that has the risk of electric shock, protection of indirect contact is required. There are generally 2 ways of indirect contact protection. Protective class I. Basic insulation and protective grounding; Protective class II. Double insulation or reinforced insulation.

b) If the indirect contact protection depends on the installation method, the installation manual shall clearly indicate the relevant hazards and specify the installation method in detail.

c) Circuits that use insulation for indirect protection shall meet the requirements of 6.2.3.

d) For the part whose voltage is less than the specified safe voltage [see a)

1) in 6.2.1.2.2], this kind of circuit does not have the risk of electric shock.

6.2.2.2 Protective connection and grounding

The inverter shall provide a reliable protective connection and protective grounding, to ensure the electrical connection between accessible conductive parts and with the external grounding conductor. Figure 1 shows an example of the inverter and its related protective connections and grounding. Description.

7.1 Automatic ON/OFF

The inverter shall be able to realize the corresponding automatic ON/OFF operations according to the voltage input conditions, or failures and post-failure recovery.

7.2 Communication function

The inverter shall be equipped with a local communication interface; the communication interface shall have fixation measures, to ensure the validity of its connection. The electromagnetic compatibility of the communication port shall meet the requirements of 8.4; meanwhile it shall be easy to form a network.

Communication can choose RS485, optical cable, PLC power carrier, Ethernet, wireless and other methods for communication. The communication content shall include inverter operation status, fault alarm and other related information.

The photovoltaic power station's power control system can communicate the active power control, reactive power control and other control requirements to the inverter; the communication protocol should match the communication protocol of the photovoltaic power station.

8.1 Electrical parameters

8.1.1 Input requirements

When the inverter is working within the normal input working voltage range, the Sudden change of residual current The longest time the inverter is disconnected from grid measured continuous maximum input current or power shall not exceed 110% of the nominal maximum input value; the measured inverter working voltage range shall not exceed the value declared by the manufacturer plus the voltage control accuracy declared by the manufacturer.

8.1.2 Output requirements

When the inverter is working within the normal input and output operating voltage range, the continuous output current of the inverter shall not exceed 110% of the nominal maximum continuous output current. At this time, the over-current protection device and the over-temperature protection device shall not act.

When the inverter is working within the normal input and output working voltage range, it can continuously output the nominal rated power, meanwhile it shall not exceed 110% of the nominal rated output power. At this time, the over-current protection and over-temperature protection devices shall not operate.

8.2 Efficiency requirements

For the inverter, the efficiency of its energy conversion is determined by dynamic MPPT efficiency, static MPPT efficiency and conversion efficiency.

The maximum conversion efficiency etamax and the average weighted total efficiency etat,c of the inverter shall not be lower than the requirements in Table 15. It is required that the dynamic MPPT efficiency calculated by the test shall not be less than 90%. Among them, the average weighted total efficiency is the average weighted efficiency of static MPPT efficiency and conversion efficiency under different voltages calculated according to the efficiency weighting coefficients of typical solar resource areas in China.

The conversion efficiency includes all auxiliary power and control power losses.

For inverters with external independent dedicated isolation transformers, they may be assessed according to the conversion efficiency limits of non-isolated inverters without transformers; they can also be assessed according to the conversion efficiency limits of isolated inverters with isolation transformers. The loss includes loss of the isolation transformer. The conversion efficiency limit of the preparatory photovoltaic grid-connected inverter device can refer to the limit of the isolated inverter, which needs to include the loss of the isolation transformer.

9.1 Over/under voltage protection

9.1.1 Overvoltage protection at DC input side

When the input voltage on the DC side is higher than the maximum value of the DC array access voltage allowed by the inverter, the inverter must not start and a warning signal will be issued at the same time. After the DC side voltage is restored to the allowable working range of the inverter, the inverter shall be able to start normally.

9.1.2 Over/under voltage protection at AC output side

For Class B inverters, when the grid-connected point's voltage exceeds the voltage range as specified in Table 1 of GB/T 29319-2012, see Table 32; it shall stop transmitting power to the grid lines within a corresponding period of time. This requirement applies to any phases in a multi-phase system.

Note: The manufacturer can declare the upper limit of normal working voltage between 110%UN and 135%UN and indicate it in the manual.

9.2 Over/under frequency protection

For Class B inverters, when the grid-connected point frequency exceeds the operating range of 47.5Hz ~ 50.2Hz, it shall stop supplying power to the grid within 0.2s. When the grid frequency is lower than 49.5 Hz, or higher than 50.2 Hz, the inverters that are out of service must not be connected to the grid at this time. The inverter shall be able to restart operation when the grid frequency is restored to the allowed grid frequency.

For Class A inverters, the frequency protection configuration shall meet the requirements of 8.3.6.

9.3 Incorrect phase sequence or polarity

9.3.1 Polarity misconnection

The inverter can automatically protect when the DC input or AC output polarity of the inverter is incorrectly connected. When the polarity and phase sequence are correctly connected, the inverter shall be able to work normally.

9.3.2 AC phase loss protection

When the AC output phase of the inverter is missing, the inverter will automatically protect and stop working. The inverter shall be able to operate normally after correct connection.

9.4 DC input overload protection

9.4.1 If the inverter's input terminal does not have the power limiting function, protection is required when the inverter's input power exceeds 1.1 times the nominal maximum DC input power.

9.4.2 If the inverter's input terminal has a power limiting function, when the output power of the photovoltaic array exceeds the maximum DC input power allowed by the inverter, the inverter shall automatically limit the current and work at the maximum AC output power allowed.

9.5 Output short circuit protection

When the inverter is turned on or running, if a short circuit on the output side is detected, the inverter shall be able to automatically protect. It is required that there is no electric shock hazard in the accessible conductive parts, meanwhile the parts with electric hazard and mechanical hazard shall not be touched. If the recorded short-circuit current exceeds the maximum rated current of the circuit, the measured maximum short-circuit current must be written in the installation manual.

9.6 Reverse discharge protection

When the DC side voltage of the inverter is lower than the allowable working range or is in the shutdown state, there shall be no reverse current flowing out of the inverter DC side. […]