Basic knowledge and selection reference of AC variable frequency power supply

　　1. Application

　　The variable frequency power supply is mainly used for power grid simulation. It can simulate the power grids of various countries in the world to power the product and test the relevant parameters by other test instruments .

　　II. Indicators

　　The basic indicator of variable frequency power supply is that the voltage and frequency can be adjusted under a certain capacity. The typical parameters are as follows:

　　Capacity: 500VA or more

　　Voltage: 0~300V, 600V, step 0.1V

　　Voltage stability: ≤±1%

　　Voltage measurement accuracy: ≤±2%

　　Frequency: 45～65～500Hz

　　Frequency stability: ≤±0.1%

　　Waveform distortion: ≤±2%

　　Rated current: P/V (220V, 110V)

　　Current measurement accuracy: ≤±2%

　　Key indicators: capacity, waveform distortion, rated current, frequency range

　　3. Model Selection

　　1. Determine the load characteristics: ① resistive load; ② inductive load; ③ capacitive load; ④ rectifier load; ⑤ mixed load.

　　2. Determine the output mode: single-phase, three-phase

　　3. Determine the power supply capacity: Since different load characteristics will result in different inrush currents when the load starts, the power supply selection must take into account the impact of the inrush current, otherwise the power supply will not be able to output normally.

　　(1) Resistive load: Power supply capacity = 1.1 × load rated power

　　(2) Resistive-inductive or resistive-capacitive load: Power supply capacity = 1.1 × load apparent power

　　(3) Motor load: When the motor load is started directly, the starting impact current is about 5 to 7 times the rated current, and the starting time is generally within 2 seconds. The 2-second overload capacity of the general power supply is 2 times. If it exceeds this range, the power supply will be overloaded. Therefore, considering the starting capacity, the power supply capacity of the motor load that is directly started should be 3 times the motor power, otherwise soft starting measures should be taken.

　　(4) Rectifier load: Its input circuit contains rectifier diodes (or thyristors) and filter capacitors. If there is no soft start device in the input circuit, the load can be regarded as a short circuit at the moment the input switch is closed, which will generate a large impact current and cause power supply overcurrent protection. If large starting impact currents occur frequently, it will also have an adverse effect on the load circuit. Therefore, the user's rectifier load input circuit should adopt soft start measures to limit the starting current.

　　Since the rectified load current is a pulse current, the current crest factor can reach 3 to 3.5 times, so it has a certain impact on the power supply output voltage waveform and long-term operating output. The degree of impact is determined by the load current crest factor. Usually, when the load current crest factor is >2, the power supply capacity is selected according to the following formula:

　　Load current crest factor

　　Power capacity = ------------------ × load apparent power

　　2 If the rectifier load is mixed with other loads that have higher requirements on voltage waveform, the power supply margin should be increased on the basis of the above.

(5) For mixed loads ,　　please select according to the proportion of different loads.　　

　　NF(Japanese): Recommended: ☆☆☆☆☆

　　Recommended direction: high-quality product selection

　　Recommended series: EPO AC variable frequency power supply (frequency range: DC ~ 500Hz)

　　Recommended reason: ① High current: 2kVA current is 10A/20A

　　②Shock resistance: can withstand 4 times shock for 3 seconds

　　③High precision: 0.5 stability

　　Ouyuan: Recommended: ☆☆☆☆

　　Recommended direction: High performance product selection

　　Recommended series: APG AC variable frequency power supply (frequency range: DC ~ 500Hz)

　　Recommended reasons: ① Large capacity, small size crystal type/high frequency standard power supply

　　②Low distortion interference, input/output completely isolated

　　③Super strong crest factor ratio can reach 3.5:1

　　Aino: Recommended: ☆☆☆☆

　　Recommended direction: cost-effective choice

　　Recommended series: 97 series AC variable frequency power supply (frequency range: 45～400Hz)

　　Recommended reason: ①The product is reliable

　　②3 times impact resistance

　　③ Reasonable price

　　Epps: Recommended: ☆☆☆☆

　　Recommended direction: cost-effective choice

　　Recommended series: AFC series AC variable frequency power supply (frequency range: 45 ~ 400Hz)

　　Recommended reason: ①The product is reliable

　　② Output programmable, gradual output

　　③ Reasonable price

　　5. Notes:

　　(1) Due to the fierce competition in power supply products, manufacturers are gradually reducing product costs, especially in terms of rated current. Please choose a product with a larger rated current than the commonly used voltage, which has a wider range of applications. That is: commonly used 200V/500VA

　　If the rated current is calculated based on 220V: 500/220=2.3A

　　The rated current calculated according to the maximum output voltage is smaller: 500/300=1.6A

　　(2) In addition to comparing basic indicators, for products with mixed production loads, since output parameters need to be adjusted frequently, it would be more convenient to use if there were multiple sets of memory modes.