1.6. MODulation Subsystem

The Modulation Subsystem adjusts the output voltage or current according to the voltage measured on the external analog input, MOD Pin 25 of JS1, named VMOD. This signal has an allowed input range 0-10V. Modulation requires the power supply to be configured for Keypad (TS Series and MT Series D Version front panels) or Remote mode. Rotary control mode or external program control mode cannot be used with these commands.

Modulation allows a set point adjustment of voltage or current by another input. The modulation signals can be derived from an external device, such as a thermistor, or from the sampling of the output current or voltage. When used with software containing advanced numerical methods, feeding the output voltage or current to adjust the set point current or voltage allows user defined output profiles. The system, incorporating this feature, introduces another negative feedback path with gain controlled by a user programmed attenuator.

Modulation can be introduced into the control loop either adding a variable to the set point or by multiplying a variable with the set point. Additive functions are useful for introducing series and parallel impedances and multiplier functions are useful for adjusting voltages or currents sources. Table 1.2 describes the four options: control input 1 and 2 for voltage and current control and control type 0 and 1 for multiplier and additive functions.

1.6.1. MODulation:TYPE:SELect

This command is composed of two comma separated, modulation parameters. The first parameter, control input, defines whether the modulation table adjusts output voltage or output current. When the control input is set to 1, VMOD selects the modulation table to adjust output voltage. When control input is set to 2, VMOD selects the modulation table to adjust output current. Setting the control input to the default value of 0, disables the modulation function. Information on programming the lookup table is provided in Table 1.2 .

The second command parameter, control type, defines the expression for modulating output voltage or current. With type set to 0, table data points are used in a multiplying expression. With type set to 1, table data points are used in an addition expression.

The choice of using type 0 or type 1 modulation depends on the application. Only one set point can be modulated at any given time. The query command returns two comma separated parameters, the control input followed by the control type.

Table 1.2 Modulation Subsystem parameters control input
Control Input	Control Type 1	Control Type 2
0 (Default)	Disabled	Disabled
1	V_o = G_v[V_ref x Mod(VMOD)]	V_o = G_v[V_ref + Mod(VMOD)]
2	I_o = G_v[I_ref x Mod(VMOD)]	I_o = G_v[I_ref + Mod(VMOD)]

Notes:

V_o is the adjusted output voltage as a function of the modulation operator
I_o is the adjusted output current as a function of the modulation operator
V_ref is input voltage set point reference
I_ref is input current set point reference
VMOD is the input modulation set point reference
G_v is the system gain as defined by the full scale output voltage, V_fs , divided by the maximum input voltage set point reference, V_ref,max
G_i is the system gain as defined by the full scale output current, I_fs , divided by the maximum input current set point reference, I_ref,max

Mod(VMOD), modulation, can be an expression, constant, or other numerical operator. A user friendly method chosen by Magna-Power Electronics is a table based algorithm using piecewise linear approximation. This numerical method allows linear or non-linear modulation to be introduced simply by defining the constants in a table.

Command Syntax:: MODulation:TYPE:SELect <NR1>[,<NR1>]
Examples:: MOD:TYPE:SEL 1,0, MOD:TYPE:SEL 2,1, MODulation:TYPE:SELect 0
Query Syntax:: MODulation:TYPE:SELect?
Return Param:: <NR1>, <NR1>

1.6.2. MODulation:TABLe

This command programs the user defined modulation table described in MODulation:TYPE:SELect. The feature allows the user to program non-linear output voltage and current profiles to fit their application needs, such as source emulation or output adjustments with respect to an external sensor. Modulation functionality may be used either by issuing SCPI commands as detailed in this section or by entering the values into a table from the RIS Panel software.

The lookup table contains 4 columns and up to 50 rows; it stores an output profile as a function of the analog input voltage applied to terminal 25 of JS1, VMOD. As shown in Table 1.3, the first column stores the table row and the second column sets an analog input VMOD. The third column stores the Mod value associated with VMOD for that table row.

The fourth column of the lookup table, Loc, defines whether the table is stored in an active or temporary location. Certain applications may need to transition between different tables while the power supply is still running. For example, emulation of solar panel’s voltage/current characteristics requires continuous external data acquisition along with quick and smooth table loading . The modulation subsystem provides two storage locations, Loc 0 or 1, to help improve table loading performance. With Loc set to 0, data will be stored to the Active Table, the table which is actively applied to the modulation function. With Loc set to 1, data will be stored to the Cache Table, the table intended to be accessed in the next in the profile. During the power on cycle, modulation tables stored in EEPROM are copied into volatile RAM.

Modulation linearly interpolates between data points to form a piecewise-linear curve. Each column has to have data in an acceptable range. All tables less than 50 rows must be terminated with a VMOD value of 9999. Mod values at and past a row with VMOD of 9999 does not affect modulation.

Table 1.3 Modulation table parameters
Description	Column 1: Row	Column 2: VMOD	Column 3: Mod	Column 4: Loc
Acceptable Range	1 to 50	0.0 to 10.0	-1000.0 to 1000.0	0 to 1

While the table will store any value within the acceptable range, the power supply is limited by its output voltage and current specifications. For example, when using type 1 modulation, MOD:TYPE:SEL 1,1, a user can store a Mod value of -1000, but the power supply will only output a voltage down to 0 V. From row 1 to 50, VMOD has to be in ascending order.

Modulation points are read with two comma separated parameters, formatted as: Row, Loc. The query will return four parameters, formatted in the same way as the save table command above.

Command Syntax:: MOD:TABL <NR1>(<NRF>,<NRF>,<NR1>)
Examples:: MOD:TABL 12(0.13, 1.6, 1), MODulation:TABLe 20(2.0, 15.002, 0), MOD:TABL 13(1.5, -1.29, 0), MOD:TABL 14(9999, 0, 1)
Query Syntax:: MOD:TABL? <NR1>,<NR1>
Return Param:: <NR1>(<NRF>,<NRF>,<NR1>)

1.6.3. MODulation:SAVE

This command copies the Active Table in RAM to a non-volatile, EEPROM memory. The Active Table, which is stored in RAM, loses its data on power down cycles. This command allows this data to be recovered at the power on cycle.

Command Syntax:: MOD:SAVE, MODulation:TABLe:SAVE
Examples:: MOD:SAVE

1.6.4. MODulation:TABLe:LOAD

This command copies all data stored in the Cache Table to the Active Table. The command provides two optional parameters for initiating the activate set points for voltage and current. The command lets users quickly load tables and simultaneous change the power supply’s output operating point.

Command Syntax:: MOD:TABL:LOAD [<NRF>, <NRF>]
Examples:: MOD:TABL:LOAD, MODulation:TABLe:LOAD, MODulation:TABL:LOAD 93.4, 30.3