How to connect single-phase motor with WECON inverter?

1. Basic principles

As shown in Figure 1, the starting winding (also called auxiliary winding) is connected in series with a capacitor to achieve a vertical phase with the running winding.

The alternating magnetic field realizes the purpose of motor winding rotation.

In general:

A． The capacitance value of the starting capacitor > the capacitance value of the running capacitor, some motors do not have a starting capacitor;

Starting capacitor = 1950×I/U/cosθ, where cosθ is the power factor and generally takes about 0.75;

B． The centrifugal switch is generally in the off state when it is thrown off at 75%~80% of the rated frequency;

C． The running winding resistance is smaller than the starting winding;

2. Identify the main and auxiliary windings

As shown in Figure 1 above, remove all the capacitors first, and at least 1/2/3 of the points that can be measured (points 1 and 4 are short-circuit points, so only look at point 1), and measure the resistance between the two points respectively: R12 /R13 /R23, sort it.

In the above figure, the three from large to small must be: R23> R13> R12, the subscript of the largest item does not appear as the common terminal, the main winding with the same maximum and minimum items, and the remaining end is the auxiliary winding. For some motors, the common ends can be separated, so it is enough to measure the coil resistance, the main winding with small resistance, and the auxiliary winding with large resistance.

3. Driven with capacitor

Note 1: Any type of inverter driving single-phase motor can only use VF mode;

Note 2: The turn ratio parameter of the driving mode with capacitance does not work, and the voltage value at both ends of the main and auxiliary windings cannot be adjusted through the parameters;

4. Driven without capacitor

5. Example

Test equipment: 1.5kw single-phase motor, 1.5kw inverter

Motor winding: 16mH@10kHz, auxiliary winding: 16mH@10kHz

Start capacitor: 150uF 450VAC, running capacitor: 30uF 450VAC

Step1. Winding identification

As shown in Figure 2 below, R_red-red = 2.9Ω, R_black-black = 4.9Ω, R_green-green = 0.3Ω, so it is judged that red is the main winding, black is the auxiliary winding, and green is the centrifugal switch.

Step2. Wiring

5. Problem and Solution

A. Large current in low frequency band after startup

The large current in the low frequency band is because the motor is not started and rotates, and the large slip results in small internal resistance and large current. The solution can be as follows: use different VF curves such as square curves to reduce the voltage in the low frequency band; appropriately increase the starting capacitor to make the difference in the intersection angle of the two-phase windings as close to 90° as possible, thereby increasing the starting torque and reducing the slip.

B. Large current in middle frequency band after startup

In the mid-frequency band, the instantaneous centrifugal switch action will cause current jitter, so it is necessary to reduce the voltage through the multi-point VF curve during this period, so as to control the current reduction.

C. Heating

Adjusting the turns ratio(F2.13) changes the voltage value of the main and auxiliary windings, and reducing the current of the auxiliary winding can reduce the heat generation.