Wiring problems of the common DC bus of the frequency converter

The diodes in the diagram are a group of rectifier diodes.

It is part of the frequency converter. As a DC bus feedback system, it is possible to connect in this way. Since the system absorbs less energy from the grid, it is generally possible to connect only one.

Also, the rectifier is not depicted in the diagram.

If the rectifier input is not directly connected to the power grid, but is output by the transformer, then it belongs to the 12-pulse rectification.

12-pulse rectification, on the one hand, can reduce the harmonics of the power grid.

On the other hand, it can make the DC bus voltage more stable. Fuse.

Load leads to the inverter.

between lines.

The fuse can be used with a fast fuse. At the time of power-on of the inverter, it is known that because the capacitor voltage is zero, the short-term charging current will be too large and the capacitance will be damaged, so it is necessary to design a pre-charging circuit, which is composed of an IGBT (electronic switch) and a current-limiting resistor (also known as a charging resistor).

The main purpose of braking resistor is to dissipate the energy generated during braking, and if the braking time is not high, it can theoretically not be added. However, generally the inverter will be equipped with a braking resistor.

Depending on your problem compensation, it is recommended that you do not do this, and it is best to replace the rectifier bridge with a PWM rectifier module at the front end, so that the energy can flow on both sides. Collinear is achieved in this way.

This diode represents the rectifier circuit inside the inverter, inside the inverter. If you are using the public DC bus power supply mode, there is only one rectifier module, and the other inverters can be directly connected to the DC bus. No braking resistor is required.

This is a common DC bus system consisting of three frequency converters.

Summary. Dear, no, first of all, the parallel connection of the DC bus needs to ensure that the voltage of the two buses is equal, and the DC voltage of the two inverters with different power inputs may be different, which will lead to the instability of the DC voltage and affect the normal operation of the inverter. Secondly, if the output current of the two inverters is inconsistent, it will also lead to uneven current distribution after the DC bus is connected in parallel, which will have a negative impact on the entire system.

Therefore, in order to ensure the safety, reliability and operational stability of the system, it is recommended to use multiple inverters only under the same power input, or use a **controller that shares the DC bus to manage multiple inverters.

Dear, no, first of all, the parallel connection of the DC bus needs to ensure that the voltage of the two buses is equal, and the DC voltage of the two inverters with different power inputs may be different, which will lead to the instability of the DC voltage, which will affect the normal operation of the inverter. Secondly, if the output current of the two inverters is inconsistent, it will also lead to uneven current distribution after the DC bus is connected in parallel, which will have a negative impact on the whole system. Therefore, in order to ensure the safety, reliability and operational stability of the system, it is recommended to use multiple inverters only under the same power input, or use a **controller that shares the DC bus to manage multiple inverters.

What are the consequences if it is used.

DC voltage instability: There may be differences in the DC voltage of two inverters input from different power supplies, if their DC buses are forcibly connected in parallel, then the two DC power supplies will affect each other, resulting in unstable DC voltage, and then affect the normal operation of the inverter. Uneven current distribution:

If the output current of the two inverters is inconsistent, it will also lead to uneven current distribution after the DC bus is connected in parallel, which will have a negative impact on the whole system, such as affecting the stability and life of the equipment. Easy to cause electrical faults: due to the potential difference between the inverters with different power inputs, it is easy to cause electrical faults when the DC bus is connected in parallel, such as short circuit, overcurrent and other problems, which will threaten the safety of the equipment.

It is related to the output voltage U, the load power factor COS and the efficiency of the inverter.

Suppose the output is three-phase, load balanced, the DC bus voltage is UDC, and the current is IDC.

Then, udc*idc* = 3u*i*cos.

idc=（√3u*cosφ/udc*η)i。

The UDC can be considered constant, and if the load efficiency is high, it can be considered constant for myopia, but if there is a load such as a motor, the COS will also change when the U changes. Or if you don't change, when the load increases, i changes, and cos will also change.

Therefore, it cannot be simply considered that the relationship is proportional.

3*UAC*IAC*COS * =UDC*IDCIDC= 3*UAC*IAC*COS * UDCUAC is the input line voltage, IAC is the input line current, COS is the input power factor, which is the rectification efficiency, UDC is the DC bus voltage, and IDC is the DC bus current.

The input power factor of the inverter is higher, the DC bus power factor is 1, the rectification efficiency of the inverter is higher, close to 1, and the DC bus voltage UDC Therefore, it can be roughly considered.

idc≈√3*。Considering the power factor and efficiency, the IDC will be a little larger.

AC becomes DC and then AC out.

1. The system has the highest power efficiency;

2. The feedback energy of the motor can be utilized;

3. Instantaneous power failure will not jump out of shutdown.

4. The power factor is high, up to more than 95%;

5. The harmonics of the power grid are low;

6. It can reduce the speed sharply;

7. Frequent starting operation is allowed;

8. The motor power does not need to be the same.

It's a pity that Green Bojie can not engage in the inverter industry.

Alternating - Straight - Orthogonal;

This is the principle of the inverter, the three-phase 380V (220V) 50Hz alternating current through the rectifier bridge rectification into pulsating direct current, through the electrolytic capacitor filtering into smooth direct current, the control board to IPM that is, the intelligent power module, not only the power switching device and the drive circuit are integrated. Moreover, it has built-in fault detection circuits such as overvoltage, overcurrent and overheating, and can send the detection signal to the control of the CPU >, IGBT "inverter bipolar transistor with insulated gate" or module, and then turn the smooth direct current into three-phase alternating current with variable frequency.

As mentioned by the brothers above, the DC bus voltage is high, and because it needs to be converted when converting DC to AC, it will limit the current resistance in order to prevent the diode from burning out before passing through the inverter module'.Therefore, the switching frequency and output frequency are low.

If a fixed voltage of alternating current is required, then the DC bus voltage is high, and the switching frequency and output frequency are low.

Because the output is a DC pulse wave, it becomes a sine wave after the integration circuit.

However, the DC bus voltage is basically fixed.

There is no direct relationship between the DC bus voltage and the switching frequency and output frequency.

And these concepts are not the same thing at all.

Most of today's frequency converters adopt AC-DC-AC mode.

That is, the alternating current is rectified to DC first, and then the DC is inverted to AC.

The DC link is called the bus, and the DC voltage is called the bus voltage.