ST AN2316 Application note

AN2316

Application Note

Improved ST7LITE05 AC Chopper Driver Solution

Introduction

This application note presents an AC motor or load circuital solution improvement of efficiency over the one discussed in a previously published application note, AN1255.

Above all, this solution does not have limits on where it may be applied, embracing all types of AC asynchronous monophase motor applications (e.g. refrigerators, hydraulic pumps, fans, and lamps).

Due to the increasing electric pollution of the environment, European standards impose restrictions on Electromagnetic Compatibility (EMC). The proliferation of non-linear loads and the consequential increase in harmonics pollution in power distribution lines have induced various technical committees to establish maximum limits on the harmonic content produced by all industrial and domestic devices. Manufacturers of these devices are required to conform to this new standard and develop products which function with new operational characteristics.

The most common method used to vary the AC monophase motor voltage is a TRIACbased phase angle partialization technique. Although this is a simple, low-cost solution that has been used for several years, it is problematic because of the excessive harmonic distortion which reduces the efficiency of the entire system. These systems typically include a complex inverter drive which is quite expensive, and, while they can solve the load’s harmonic content problems, they do not address those same problems in the electric lines.

March 2006

Rev 1

1/24

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Contents	AN2316 - Application Note

Contents

1	STEVAL-IHM006V1 Circuit Description . . . . . . . . . . . . . . . . . . . . . . . . .		. 4
2	EMC Precompliance Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . .		10
	2.1	Electrical Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	2.2	EMC Double-Filter Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
3	Safety and Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		13

3.1 STEVAL-IHM006V1 Board Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Environmental Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.3 Mandatory Checks Before Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4 Start-up Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4	ST7FLITE05 Software Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		16
	4.1	Peripheral Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	4.2	Firmware Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
	4.3	Development Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19

5	Library Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		22
	5.1	Software downloads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
	5.2	File Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
6	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		23

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AN2316 - Application Note	List of Figures

List of Figures

Figure 1. Two-Switch Drive Motor Schematic (ST patented) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 2. Basic Working Principal Illustration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 3. System Waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 4. EMC Measurement Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 5. EMC Double-Filter Stage Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 6. 20kHz Switching Frequency EMC Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 7. 35kHz Switching Frequency EMC Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 8. STEVAL-IHM006V1 Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 9. ST7FLITE05 Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 10. Softec STVD7 v3.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 11. ST7 Visual Programmer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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STEVAL-IHM006V1 Circuit Description		AN2316 - Application Note

1	STEVAL-IHM006V1 Circuit Description
	This ST-patented solution uses a working switch mode to solve third harmonic problems.
	The base circuit can be viewed as a mains voltage double-chopper without any preliminary
	AC/DC conversion type (see Figure 1 on page 6).
Note:	The AC chopper STEVAL-IHM006V1 provides customers with a demo that regulates the
	voltage in AC motors or loads of up to 300W. This allows the user to demonstrate smooth,
	silent, and efficient regulation with respect to TRIAC solutions.
	The double-chopper is a device which energizes the load beginning from any level of the
	sinusoidal voltage wave and demagnetizes the load with a freewheeling current system,
	thereby obtaining voltage and current regulation of the load.
	Starting from a perfect sinusoidal-shaped mains curve, the regulated current is also
	sinusoidal for all the power levels that the user desires to transfer to the load. By neglecting
	the electronic device losses, the circuit incoming power S is equal to the outgoing power:
	Equation 1
	S = VAC(RMS) IAC(RMS) = VLOAD(RMS) ILOAD(RMS)
	where,
	VAC(RMS) = Root Mean Squared (RMS) Mains Voltage,
	IAC(RMS) = RMS Input Current,
	VLOAD(RMS) = RMS Load Voltage, and
	ILOAD(RMS) = RMS Output Current.
	The IAC(RMS) and ILOAD(RMS) currents are related as follows:
	Equation 2
	ILOAD(RMS)	VAC(RMS)
	------I--A----C-----(--R-------MS--------)-----	= -----------------------------------------
		VLOAD(RM S)

The circuit operates as a converter, particularly as an AC/AC converter or transformer. It has no limitation in terms of load impedance since it works with both, inductive and ohmic loads, with notable angles between the current and the voltage.

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AN2316 - Application Note	STEVAL-IHM006V1 Circuit Description

The circuit is based on the following parts (see Figure 1):

●IGBT Z1

Together with diodes D1, D2, D5, and D6, it performs current freewheeling (only for inductive load).

●IGBT Z2

Together with diodes D3, D4, D7, and D8, it is the main switch through which the load is energized.

●Pulse Transformer T1

It allows the signal derived from the PWM generator to be transferred to the Z1 gate. This component electrically insulates the input from the output’s entry signal and phase inversion.

●PWM generator

This is provided by the ST7Lite05 microcontroller.

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6/24

DriveSwitch-Two .1 Figure

STEVAL

+15V

OUT 1

S 1

NOT ASSEMBLED

470-1/4W

DescriptionCircuit IHM006V1-

Line filter

5 A

MAINS

320VAC

220K 1/2W

STTH306

C16

C17

250V14L

PHASE

100nF x 2

phase

100nF x 2

1µF 250VAC

RV1

250V10L

RV2

STGP7NB60HD

RV3

2 STGP7NB60HD

PHASE

5.6-1/4W

STTH306

ASYNCHRONOUS

+5V

MOTOR

L78L05A/TO92

1N4148

2 GND

R15

D16 1N4148

Motor

1.2k

0.1µF

47µF-25V

NOT ASSEMBLED

pulse transformer

0.1µF-100V

Q5 3

T1 7

Schematic

R14 R

1 BC557

VCONTROL

NOT ASSEMBLED C18

270K

D10

0.1µF-100V

100pF

18V

NOT ASSEMBLED

RS-196-375

PHASE

D11

STTH108

NTC22

C10

(ST

t°

10µF 25V

BC547

D12

C15

patented)

AN2316

CLKIN/AIN4/PB4

STTH108

+5V

C25

VSS

PA0/LTIC

100nF

PA1

D13

+5V

VDD

PA2/ATPWM0

RESET

PA3

+15V

AIN0

SS/AIN0/PB0

22K

PA4

12K 1/4W

SCK/AIN1/PB1

R10

VDD

+15V

PA5/ICCDATA

C12

VIPer12A DIP

L1 1mH

MISO/AIN2/PB2

D14

D15

0.1µF

MOSI/AIN3/PB3

0.1µF

PA6/MCO/ICCCLK

PA7

470K

2.2K

STTH108

18V

J10

ST7LITE09

R11 15

C13

C14

0.1µF

CON6_0

R12 10K

1µF-450V

Application

AI12268

10µF 25V

BC547

R13 0

JP1

BC557

+5V

RESET

CON10A

Note

AN2316 - Application Note									STEVAL-IHM006V1 Circuit Description

	In order to avoid short-circuiting the mains through switches Z1 and Z2, they must work in a
	complementary manner. When Z1 is ON, Z2 must be OFF and vice-versa.
	For example, if the line voltage at J1 is positive with respect to J2, and the PWM signal goes
	from high-to-low, Z2 switches ON with a delay inserted by its own gate capacitance and by
	resistor R3 so the load is energized. In the meantime, Z1 switches OFF instantaneously.
Note:	In this condition, if the current is positive (i.e. it goes into J1 and comes out from J2), it will
	flow through D4, Z2, D7, and the load. Conversely, if the current is negative, it will be going
	out from J1 and closing through the load, D3, Z2, and D8.
	As is the case with the current, when the PWM goes from low-to-high, Z2 is turned OFF
	instantaneously, while Z1 is switched ON with a delay. This enables a freewheeling current
	to flow through Z1.
	Given these relationships, if “δ” is the duty cycle (see Figure 2 on page 8), the load voltage
	is may be expressed as:
	Equation 3
	VLOAD( t) =				δ VAC( t) =				δ VMAX sin ( ω t)
	where,
	VLOAD = Load voltage,
	VAC = Mains voltage, and
	VMAX = Maximum sinusoidal voltage.
	The load current may be expressed as:
	Equation 4
	I		( t) =	1	I		( t) =	1	I		sin (ω t + ϕ )
	I	LOAD	( t) =	--	I	AC	( t) =	--	I	M AX	sin (ω t + ϕ )
		LOAD		δ		AC		δ		M AX

where,

ILOAD = Load current,

IAC = Input current,

IMAX = Maximum current value, and

ϕ = the angle between the current and voltage.

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STEVAL-IHM006V1 Circuit Description		AN2316 - Application Note

	The relationships expressed in Equation 3 and Equation 4, and Figure 2 show that it is
	possible to control power fed to the load by changing the PWM signal duty cycle.
Note:	The load is assumed to be inductive so the high frequency harmonics are filtered in the
	current waveform (see Figure 3 on page 9 for system waveform details).

Figure 2. Basic Working Principal Illustration

Bi-directional PWM Chopping

Vline

Load Current

duty cycle

Duty Cycle Increase

AI12267

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+ 16 hidden pages

ST AN2316 Application note

STEVAL-IHM006V1 Circuit Description

Figure 2. Basic Working Principal Illustration