Energy Storage Solution

An Energy Storage Solution consists of one or more Energy Storage Modules.

An Energy Storage Module (ESM) is similar to a Capacitor Module in that it stores energy in a capacitor bank. The important differences are:

An ESM will generally have a lot more capacitance (20mF or more) than a typical Capacitor Module, and therefore can store a lot more energy
Has its own power transistors to control energy flow to and from the DC Bus
Operates under its own voltage range, separate from the shared DC Bus of the servo system
Can also add Expansion Modules (EM) storage capcitors to further increase energy storage
Other forms of energy storage include Double Layer Capacitors (DLC) and batteries

ESM Types

Energy Storage
1. Similar to a capacitor module, stores braking energy, that can be used later in the cycle
2. Add EMs for additional energy storage
3. Multiple EMs are connected in parrallel
Supply Power
1. Provides backup power when mains supply is not available
2. Add EMs for additional energy storage
3. Multiple EMs are connected in parrallel
Energy Storage and Supply
1. Performs both functions of energy storage and backup power
2. The amount of energy storage reserved for backup power is configurable
3. Add EMs for additional energy storage
4. Multiple EMs are connected in parrallel
Storage Manager
1. Performs both functions of energy storage and backup power
2. The amount of energy storage reserved for backup power is configurable
3. Supports various extended energy storage modules including EMs, DLCs, batteries
4. Multiple DLCs are connected in series

Control Types

There are two Control Types - Threshold Voltages and Droop Control. The control type depends on the selected ESM's ControlTyp setting in the database.

Threshold Voltages

The ESM engages when U_DC reachs either the lower or upper threshold voltages.

ESM_V1
- The upper bus voltage threshold when the ESM starts to store braking energy by feeding current into its capacitors (sink current, I_S)
- The sink current, I_S, is the needed current to maintain U_DC = ESM_V1, up to I_Smax
ESM_V0
- The lower bus voltage threshold when the ESM starts to supply power to the bus (source current, I_Q). when the loss of Mains supply power
- The source current, I_Q, is the needed current to maintain U_DC = ESM_V0, up to I_Qmax

Note: In the chart below, U₀ = ESM_V0 and U₁ = ESM_V1

The control characteristics for supply devices define the relationship between U_DC and I_DC. Voltage U_DC is the voltage at the terminals of the device. The current vector system applies, i.e., current I_DC is positive when the current flows into the device from the DC grid (sink mode) and negative when it flows out of the device (source mode).

In the control characteristic, the DC-current equals 0 in these voltage ranges:

U_DC ≤ U_min
U_Q1 ≤ U_DC ≤ U_S1
U_DC ≥ U_max

Symbol	Description	Units	Range
I_Q2	Maximum current in source mode	A	I_Q2≤ I_Q1
I_Q1	Current of a constant value in source mode	A	I_Q1≤ 0
I_S1	Current of a constant value in sink mode	A	I_S1≥ 0
I_S2	Maximum current in sink mode	A	I_S1≤ I_S2

U_min	Minimum voltage	V	U_min< U_max
U_Q2	Minimum voltage of current I_Q1	V	U_min < U_Q2 ≤ U_Q1
U_Q1	Minimum voltage of current 0	V	U_Q2 < U_Q1 ≤ U_S1
U_S1	Start voltage of slope G_S1	V	U_Q1 < U_S1 ≤ U_S2
U_S2	Start voltage of slope G_S2	V	U_S1 < U_S2 ≤ U_max
U_max	Maximum voltage	V	U_min< U_max

G_Q2	Slope of curve up to U_Q2	A/V	G_Q2>0
G_Q1	Slope of curve up to U_Q1	A/V	G_Q1>0
G_S1	Slope of curve starting at U_S1	A/V	G_S1>0
G_S2	Slope of curve starting at U_S2	A/V	G_S2>0

Voltage Levels

For proper ESM operation, set the voltage levels per the following:

Voltage Levels: ESM

ESM_V0 < Vz0 < ESM_V1 <= Vz1

Voltage Levels: ESM + Supply Peak Power Optimization (Vt0 & Vt1)

ESM_V0 < Vz0 < Vt0 < Vt1 < ESM_V1 <= Vz1

UI and Inputs

ESM graphics are shown without and with an expansion module.

Clicking on the ESS on the Main form displays the details as shown below. The selection of an Energy Storage Solution includes one or more ESMs with zero ore more EMs. The example shown is 01x DEK module (20mF) with 02x EM2.0A2020 Expansion Modules (40mF each) for a total 100mF. The DEK is a combined Energy Storage and Supply module, where in this case, 70% of its storage capacity is reserved for backup power.

The following inputs can be set on the Main form or during selection in the ESM database.

Type: Energy Storage
- ESM_V1 is the bus voltage when the ESM starts to store braking energy
Type: Energy Supply
- ESM_V0 is the bus voltage when the ESM starts to supply backup power to the bus when loss of Mains supply power
- Time of Power Loss is the time in the cycle when Mains supply power is lost
- Power Loss Duration is the duration for no Mains supply power. It can be set on the Main form, or in the Power vs Time chart by clicking on the button
- Both the Time of Power Loss and Power Loss Duration can be set on the Main form, or in the Power vs Time chart by clicking on the power profiles button
Type: Energy Storage and Supply
- Storage used for Backup Power is the amount energy storage reserved for backup supply power

Formula

Energy Storage

The formula to calculate energy storage is:

Symbol	Description	Units
E	Storable energy	J
C	Capacitance	F
V₀	Minimum voltage (typically 200V for Energy Storage, 0V for Backup Supply)	V
V₁	Maximum voltage (typically 450V)	V

ESM I2t

The ESM I2t model is applied to Energy Storage Modules (ESMs)

Symbol	Description	Units
I	Application current at sample [n]	A
I_N	Rated continuous current	A
I_Max	Rated maximum current	A
t_max	Duration at rated max current	s
I2t_n-1	I2t value at previous sample [n-1]	%

Double Layer Capacitors (DLCs)

DLCs can be connected in series or parallel. Consider the solution 01x DSM4.0-60-xx-xx 04x DLC-2-10-90. The Model name uses the following nomenclature: 1 DSM, connected to 4 parallel banks of DLCs. Each bank contains 2 DLCs in series. Each DLC has 10F capacity and a maximum voltage of 90V. Overall there are 8 storage modules with 20F in total and a maximum voltage of 2 x 90V = 180V