**1. The influence of the energy storage system connected to the power grid on the operating voltage of the system**In order to analyze the influence of the energy storage technology on the system operating voltage after the energy storage technology is connected to the system, the node voltages before and after the energy storage system are connected to the system are calculated as follows.

**1) Calculation of node operating voltage before installing energy storage device**The system wiring diagram is shown in Figure 1.

The equivalent circuit of the system is shown in Figure 2, where R and X are the resistance and equivalent reactance of a phase, respectively, and U and 1 represent the phase voltage and phase current.

The voltage drop of a network element refers to the vector difference between the voltages at the first and last points of the element, which can be seen from the equivalent circuit （2）

Taking the phasor U_{2} as the reference axis, if I and cosφ are known, the phasor diagram can be made as shown in Figure 3a.

AB in the figure is the voltage drop phasor (R+jX)I. The voltage drop component is decomposed into two components AD and DB in the same direction and perpendicular to the voltage phasor U_{2}, and the absolute value of these two components is

Then the voltage drop of the network element can be expressed as

Where ΔU and δU_{2}—the longitudinal and transverse components of the voltage drop.

Using power instead of current, the above equation can be rewritten as

The voltage at the head of the element is

Where δ——phase difference of the voltage phasor at the end of the element.

If the voltage phasor U_{1} is used as the reference axis, and the current I and cosφ_{1} are known, the voltage drop phasor can also be decomposed into two components in the same direction and perpendicular to U_{1}, as shown in Figure 3b, then

If you substitute power, you can get

The voltage at the end of the element is

2) Calculation of node operating voltage after installing energy storage device

When the energy storage device is installed on the load side, the system network is shown in Figure 4.

The equivalent circuit diagram of the system after installing the energy storage device is shown in Figure 5, where R and X are the resistance and equivalent reactance of a phase, respectively, and U and I represent the phase voltage and phase current.

Comparing Figure 2 and Figure 5, it can be seen that formula (4) will be changed to the following formula:

Comparing Equation (4) and Equation (12), it can be found that after installing the energy storage system on the load side, the voltage drop on network components such as lines and transformers can be effectively reduced.

**2. Influence of the energy storage system connected to the power grid on the system network loss**The power loss of the network element includes the power loss when the current passes through the resistance and the equivalent reactance of the element and the loss when the voltage is applied to the equivalent admittance to ground of the element. Considering the low voltage level of the energy storage system connected to the power grid, the loss on the parallel admittance can be ignored.

1) Calculation of network loss before installing energy storage device

The network elements mainly refer to the transmission line and the transformer. Assuming that the system transmits the power of S=P+jQ to the network, the power loss generated by the current in the resistance and reactance of the line is

2) Calculation of network loss after adding energy storage device

When the energy storage system is installed on the load side, after the energy storage system transmits the power of S’=p’+jQ’ to the system, the power loss generated by the current on the resistance and reactance of the line is:

The relevant parameter units of each formula are: impedance is Ω, admittance is S, voltage is kV, and power is MVA.

Comparing Equation (13) and Equation (15), it can be concluded that AS’ is less than As, and it can be obtained that the network loss can be reduced after the energy storage device is installed on the load side.